F&S International Edition 2015

D 11665 F

International Edition

2015

International Edition

U-RANGE 2000 8 nm – 40 μm

WĂƌƟ ĐůĞ ƐŝnjĞ ĂŶĚ ƉĂƌƟ ĐůĞ ƋƵĂŶƟ ƚLJ ĚĞƚĞƌŵŝŶĂƟ ŽŶ ŽĨ ŝŶŚĂůĂďůĞ ĂĞƌŽƐŽůƐ

for Filtration and Separation Technologies

Highlights 2014

Dear Readers,

In Germany and the neighbouring countries, the magazine F&S has been quite an institution for the past 28 years – after all, it is the only German-speaking trade journal exclusively dedicated to filtration and separation technology but also to the treatment of disperse substance systems.

Our readers and advertisers especially value F&S because of the high quality of the published articles and essays that were often trendsetting and also describe today’s valid standards.

For the fifteenth time, we have now had a small part of our broad editorial spectrum translated into English. These are contributions that were published in the year 2014.

By doing so, we want to provide the contents of our magazine to process engineers in non-German-speaking countries as well.

As we said, this is only a small selection of our articles. With a complete translation of all the articles that were published in the year 2014, you would now hold a thick book of about 450 pages in your hands.

We would like to wish you a lot of reading pleasure and would be pleased to receive your feedback.

If you would like to find out more about the German F&S, please do not hesitate to contact us at the address listed below (also see imprint: page 60).

With best regards

Eckhard von der Lühe Publisher

VDL-Verlag GmbH Heinrich-Heine-Straße 5 D - 63322 Rödermark Phone: + 49 (0) 60 74 / 92 08 80 Fax:

+ 49 (0) 60 74 / 9 33 34

E-mail: vdl-verlag@t-online.de Internet: www.fs-journal.de

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No. 15/2015

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U-RANGE 2000 8 nm to 40 μm

WĂƌƟĐůĞ ƐŝnjĞ ĂŶĚ ƉĂƌƟĐůĞ ƋƵĂŶƟƚLJ ĚĞƚĞƌŵŝŶĂƟŽŶ ŽĨ ŝŶŚĂůĂďůĞ ĂĞƌŽƐŽůƐ ƵƐŝŶŐ ƚŚĞ ĚĞǀŝĐĞ ĐŽŵďŝŶĂƟŽŶ hͲ^DW^ ͬ &ŝĚĂƐΠ ϮϬϬ Žƌ WƌŽŵŽΠ hͲZ E' ϮϬϬϬ ŵĞĂƐƵƌĞŵĞŶƚ ƌĞƐƵůƚƐ ĂƌĞ Ă ĐŽŵďŝŶĂƟŽŶ of the results from the U-SMPS and the Fidas® or Promo® and can be completely displayed and analyzed on a touch screen. Up to 8 measurements can be compared here. dŚĞ ĞǀĂůƵĂƟŽŶ ƐŽŌǁĂƌĞ ĂůůŽǁƐ ǀĂƌŝŽƵƐ ĨŽƌŵƐ ŽĨ ĚĂƚĂ ĞǀĂůƵĂƟŽŶ ;ĞdžƚĞŶƐŝǀĞ ƐƚĂƟƐƟĐƐ ĂŶĚ ĂǀĞƌĂŐŝŶŐͿ ĂŶĚ ĞdžƉŽƌƚ ĐĂƉĂďŝůŝƟĞƐ͘

W Highlights 2014

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In-situ Efficiency Measurement for HEPA-Filters C. Schweinheim Electrostatic precipitation of different flue gas components from small wood-fired furnaces M. Kaul, E. Schmidt

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dŚĞ hͲZ E' ϮϬϬϬ ŝƐ ŽƉĞƌĂƚĞĚ ƵƐŝŶŐ Ă ŐƌĂƉŚŝĐĂů ƵƐĞƌ interface on the U-SMPS control unit touch screen. The &ŝĚĂƐΠ ĂŶĚ WƌŽŵŽΠ ŵĞĂƐƵƌĞŵĞŶƚ ƟŵĞƐ ĂƌĞ ĂƵƚŽŵĂƟĐĂůůLJ ĂĚĂƉƚĞĚ ƚŽ ƚŚĞ hͲ^DW^ ƐĐĂŶ ƟŵĞƐ͘

Particle measuring technology and filter testing according to the latest state of the art H. Lyko 14

dŚĞ ǀŽůƚĂŐĞ ŝŶ ƚŚĞ D ĐůĂƐƐŝĮĞƌ ŝƐ ǀĂƌŝĞĚ ĐŽŶƟŶƵŽƵƐůLJ͕ ƌĞƐƵůƟŶŐ ŝŶ ŚŝŐŚĞƌ ĐŽƵŶƚ ƐƚĂƟƐƟĐƐ ƉĞƌ ƐŝnjĞ ĐŚĂŶŶĞů͘ /Ŷ ĂĚĚŝƟŽŶ͕ ƚŚŝƐ ĞŶĂďůĞƐ Ă ƐŝnjĞ ƌĞƐŽůƵƟŽŶ ŽĨ ƵƉ ƚŽ ϲϰ ƐŝnjĞ ĐŚĂŶŶĞůƐ ƉĞƌ ĚĞĐĂĚĞ͘ dŚĞ ŝŶƚĞŐƌĂƚĞĚ ĚĂƚĂ ůŽŐŐĞƌ ĂůůŽǁƐ ůŝŶĞĂƌ ĂŶĚ ůŽŐĂƌŝƚŚŵŝĐ ĚŝƐƉůĂLJ ŽĨ ƚŚĞ ŵĞĂƐƵƌĞĚ ǀĂůƵĞƐ ŽŶ the device itself.

Numerical simulation of flow and particle precipitation in filtration fabrics D. Hund , K. Schmidt, S. Ripperger

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Flotation-filtration-process with ceramic membranes for water treatment J. Ludwig, M. Beery, L. León, S. Ripperger

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Separation processes on ships and offshore installations S. Ripperger

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Ceramic hollow fibre membrane technology for the treatment of oil-field produced water M. Ebrahimi, St. Kerker, S. Daume, F. Ehlen, I. Unger, St. Schütz, P. Czermak

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Water management in the paper industry with and without membranes H. Lyko

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Technical solutions and innovations for wastewater treatment and sewage sludge treatment A report on the IFAT 2014 H. Lyko

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100 years of activated sludge processes H. Lyko

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Extra-large modules for membrane reactors M. Lyko

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Washing of suspensions by means of dynamic disk filters D. Goldnik, S. Ripperger

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Viscose speciality fibres for filtration applications Ph. Wimmer

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Recovery of beer from surplus yeast System comparison of the separation technology used W.-D. Herberg

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The U-RANGE 2000 is typically operated as a standĂůŽŶĞ ĚĞǀŝĐĞ͕ ďƵƚ ĐĂŶ ĂůƐŽ ďĞ ĐŽŶŶĞĐƚĞĚ ƚŽ Ă ĐŽŵƉƵƚĞƌ Žƌ ŶĞƚǁŽƌŬ ƵƐŝŶŐ ǀĂƌŝŽƵƐ ŝŶƚĞƌĨĂĐĞƐ ;h^ ͕ > E͕ t> E͕ Z^ͲϮϯϮͬϰϴϱͿ͘ dŚĞ &ŝĚĂƐΠ ϮϬϬ ŝƐ Ă dms ZŚĞŝŶůĂŶĚ ĐĞƌƟĮĞĚ ĮŶĞ ĚƵƐƚ ŵĞĂƐƵƌĞŵĞŶƚ ƐLJƐƚĞŵ for ambient air quality measureŵĞŶƚƐ ĨŽƌ ƌĞŐƵůĂƚŽƌLJ ƉƵƌƉŽƐĞƐ͘ /Ŷ ĂĚĚŝƟŽŶ ƚŽ ƚŚĞ ŵĞĂƐƵƌĞŵĞŶƚ ŽĨ ƚŚĞ ƉĂƌƟĐůĞ ƐŝnjĞ ĚŝƐƚƌŝďƵƟŽŶ ŝŶ ƚŚĞ ƐŝnjĞ ƌĂŶŐĞ ŽĨ ϯϬϬ Ŷŵ ƚŽ ϰϬђŵ͕ ŝƚ ĐŽŶƟŶƵŽƵƐůLJ ĂŶĚ ƐŝŵƵůƚĂŶĞŽƵƐůLJ ĚĞƚĞƌŵŝŶĞƐ ƚŚĞ ĨŽůůŽǁŝŶŐ WDͲĨƌĂĐƟŽŶƐ͗ WD1 ͕ WDϮ͘ϱ ͕ WDϰ ͕ PM10 ͕ ĂŶĚ d^W ;WDtotͿ͘ dŚĞ &ŝĚĂƐΠ ϮϬϬ ŝƐ ĂůƐŽ ĞƋƵŝƉƉĞĚ ǁŝƚŚ Ă ĮůƚĞƌ ŚŽůĚĞƌ ĨŽƌ ƚŚĞ ŝŶƐĞƌƟŽŶ ŽĨ ĂŶ ĂďƐŽůƵƚĞ ĮůƚĞƌ ;ϰϳ Žƌ ϱϬ ŵŵ ŝŶ ĚŝĂŵĞƚĞƌͿ͘ dŚŝƐ ĞŶĂďůĞƐ Ă ƐƵďƐĞƋƵĞŶƚ ĐŚĞŵŝĐĂů ĂŶĂůLJƐŝƐ ŽĨ ƚŚĞ ĐŽŵƉŽƐŝƟŽŶ ŽĨ ĂŶ ĂĞƌŽƐŽů͕ ĨŽƌ ĞdžĂŵƉůĞ͘ dŚĞ hͲZ E' ϮϬϬϬ ŵĂLJ ďĞ ƵƐĞĚ ĨŽƌ ŝŶĨĞƌƌŝŶŐ ƉĂƌƟĐůĞ ƉƌŽƉĞƌƟĞƐ͘ dŚĞ ĚĞǀŝĐĞƐ͚ ĂĐĐƵƌĂƚĞ ƐŝnjĞ ĚĞƚĞƌŵŝŶĂƟŽŶ ĂŶĚ ƌĞůŝĂďůĞ ƉĞƌĨŽƌŵĂŶĐĞ ĂƌĞ ĞdžƚƌĞŵĞůLJ ŝŵƉŽƌƚĂŶƚ ŝŶ ĂƉƉůŝĐĂƟŽŶƐ͘ ůů ĐŽŵƉŽŶĞŶƚƐ ĂƌĞ ƌĞƋƵŝƌĞĚ ƚŽ ƉĂƐƐ ƐƚƌŝĐƚ ƋƵĂůŝƚLJ ĂƐƐƵƌĂŶĐĞ ƚĞƐƟŶŐ Ăƚ WĂůĂƐΠ ǁŚĞƌĞ ƚŚĞLJ ĂƌĞ ĂƐƐĞŵďůĞĚ ŝŶͲ house.

Palas GmbH Greschbachstr. 3b ϳϲϮϮϵ <ĂƌůƐƌƵŚĞ͕ 'ĞƌŵĂŶLJ WŚŽŶĞ͗ нϰϵ ϳϮϭ ϵϲϮϭϯͲϬ &Ădž͗ нϰϵ ϳϮϭ ϵϲϮϭϯͲϯϯ ͲDĂŝů͗ ŵĂŝůΛƉĂůĂƐ͘ĚĞ /ŶƚĞƌŶĞƚ͗ ǁǁǁ͘ƉĂůĂƐ͘ĚĞ

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Contents

F & S International Edition

No. 15/2015

Contents Highlights 2014

W Separation processes on ships and offshore installations

Adhesives for the manufacture of filter media for vehicle component assembly M. Dressler

81

New standards for surface purity, energy efficiency and nanoparticles under discussion A Report on Cleanzone 2014

82

Future importance of natural product-process technology for chemical production S. Ripperger

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Imprint

W Technical solutions and innovations for wastewater treatment and sewage sludge treatment

60

ACHEMA Hall 5.1 Stand B 20

www.paco-online.com www.heta.com

P A C O Group of Companies The Beauty of Perfection Beauty is not always visible to the eye of the beholder. For instance, if a technical process within a vessel runs absolutely smoothly because all constituent components and operations contribute toward a total process of the highest possible quality, this is beauty in perfection.

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Highlights 2014

In-situ Efficiency Measurement for HEPA-Filters C. Schweinheim* HEPA filter housings are mandatory in bio-safety laboratories class BSL3 (exhaust air) and BSL4 (supply and exhaust air). HEPA filter elements have to meet requirements of EN 1822 after manufacturing process. But additionally operators of bio-safety laboratories are asking the question more often whether the installed HEPA filter elements are still meeting the quality requirements after delivery and installation as well as later during operation. It would be ideal if the operator would have a compact measuring equipment available to check both efficiency ratio and integrity of the HEPA filter elements without de-installation.

1. Abstract European standard EN 1822 “High Efficiency Air Filters (EPA, HEPA and ULPA)” and cleanroom standard ISO 14 644-3 “Metrology & Test Methods” are the base thinking about development, design, manufacturing and operation of a measuring equipment for HEPA filter elements as installed in a safe change HEPA filter housing. Both standards are describing the feeding and uniform distribution of test aerosol into the filter housing, and the number and size of the test particles. Further the standards concentrate on upstream raw air measurement resp. particle count, leakage tests and downstream scanning procedures in order to calculate the efficiency ratio of the filter element.

EN 1822 describes also the setup of the test rack for test aerosol feeding and scanning. Although it is impossible to copy that exactly for an in-situ measurement in an installed HEPA filter housing, the principles of EN 1822 have been complied with when designing a compact measurement device. The final setup of the measurement device, including aerosol generator, mixing box, optical particle counters, dilution stages, control, is described in detail.

Most important is the validation process of the measuring system in combination with the relevant filter housing. The parameters for aerosol feeding and uniform aerosol distribution are a result of the validation process and will allow the exact equal setting and result without opening of the filter housing or de-installation of the HEPA filter element later during operation. Both is mandatory in bio-safety laboratories, not only in regard of safety aspects. Cost – effectiveness and also time – saving procedures are important for the operators of such laboratories.

Although the responsibility for the safety and the procedures in a bio-safety laboratory can’t be transferred to a third party, a third party expertise on the in-situ efficiency measurement process is an additional advantage. The paper describes the single steps of such a third party expertise shortly.

Finally the other periodic qualifications/procedures of a HEPA filter element installed in a HEPA filter housing for bio-safety laboratories will be highlighted, such as leakage tests for the filter element gasket seat, the disinfection of the filter element and filter housing and the safe change procedure.

try and region as well as the users and authorities requirements different standards may apply: a. American BMBL (Biosafety in Microbiological and Biomedical Laboratories) of Centers of Disease Control and Prevention (CDC) & National Institutes of Health (NIH), 5th Edition 2007. b. Canadian Biosafety Standards and Guidelines, 1st Edition, 2013. c. European standards EN 12 128 Laboratories for Research, Development and Analysis, EN 1620 Large scale manufacturing and production processes and EN 1822 HEPA and ULPA filters.

Besides that a lot of local rules and guidelines have to be taken into consideration.

For bio-safety level BSL3 filtration of exhaust air by means of H14 HEPA filters is mandatory while for bio-safety level BSL4 filtration of supply air and double filtration of exhaust air is the requirement. According to the a. m. standards the filter housings have to provide following features at least: 1. HEPA filters have to undergo a leakage and seating inspection after installation.

2. It must be possible to inspect HEPA filters as installed. This applies also for series-installed HEPA filters which have to be inspected individually. Inspection includes measurement of separation efficiency as well as determination of possible leaks.

3. A fumigation of the filter housing and the HEPA filters with formalin or hydrogen peroxide must be possible.

4. It must be possible to exchange HEPA filters with low contamination.

HEPA filter housings for biosafety laboratories fulfill all these requirements.

2. HEPA filter housings in bio-safety laboratories HEPA filter housings (Fig. 1) have to be used in bio-safety laboratories class 3 and 4 (BSL3 – BSL4) according to international standards for both supply and exhaust air. Depending on the coun* Claus Schweinheim Head of Business Unit Krantz, Caverion Deutschland GmbH, Uersfeld 24, 52072 Aachen, Germany Fig. 1: HEPA filter housing for bio-safety laboratory

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Highlights 2014

3. EN 1822 and ISO 14 644-3 Inspection of installed HEPA filters may be based on two different standards, EN 1822 and ISO 14 644-3. While the European standard EN 1822 deals with inspection of HEPA filters after manufacturing by means of particle measurement, ISO standard 14 644-3 deals with test procedures of cleanrooms and clean areas. Different procedures are described in this standard relating leak tests and particle measurement. Regarding the tests ISO 14 644-3 requires: 1. Artificial generated polydisperse or atmospheric aerosol, median diameter between 0.1 μm and 0.5 μm 2. The detection limit of the optical particle counter (OPC) should be the same as the median aerosol diameter or even lower 3. If the OPC provides more than one channel between detection limit and 0.5 μ, a channel should be used where the highest number of particles will be shown downstream 4. The aerosol concentration should be high enough upstream, use of a dilution system could be necessary 5. If the aerosol concentration is not stable, particle counting should be done upstream and downstream at the same time 6. Aerosol concentration and uniform distribution has to be checked 7. Scanning of filter element downstream and comparison of particle counts with upstream particle concentration

Fig. 2: In-situ test setup

On the contrary EN 1822 determines the procedure of HEPA filter tests in more detail. Although it applies for HEPA filter testing after production normally, it makes sense to follow its procedures as far as possible for in-situ efficiency measurement and leak testing, too.

4. Description of the validation process Testing according EN 1822 has to be done with test aerosols at MPPS size, which is most penetrating particle size. This depends on the air velocity through the filter element, but can be

determined between 0.15 μm and 0,2 μm.

DEHS (=Di-2-Ethylhexyl-Sebacat) – test aerosol complies with this requirement and delivers a particle concentration of >108 particles/cm3. This allows a reliable calculation even at high separation ratio (filter class H14 = separation ratio > 99,995%).

The biggest challenge in complying with EN 1822 during in-situ efficiency measurement in a filter housing is the uniform distribution of aerosol. The standard allows a deviation of not more than 10% from the average aerosol concentration at 9 representative points of the filter sur-

Fig. 3: Aerosol dispersion setup

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Fig. 4: Aerosol dispersal measuring points

Fig. 5: Efficiency measurement setup

Fig. 6: Efficiency measurement sequence

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Fig. 7: Third-party certificate

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Highlights 2014

face. In a test set-up of a production environment aerosols can be fed upstream in a distance of tenfold diameter of the duct system which allows a good mixture of aerosol and airflow. In a filter housing, especially for the second HEPA filter stage, there are 450mm only for uniform distribution of aerosols. The solution and invention is a pre-mixing box where test aerosol and addition air are mixed and then fed together with high pressure by means of a special distribution device into the filter housing and the airflow in front of the filter element.

With this arrangement and setup the uniform aerosol distribution according EN 1822 could be demonstrated also in the limited space of a HEPA filter housing.

The efficiency measurement setup is arranged accordingly (Fig. 2 to Fig. 6). Aerosol feeding is done as described before. Particle counting is done both upstream and downstream at the same time in order to eliminate deviations and problems by volatile feeding of aerosols.

The efficiency measurement is done fully automatically by the Krantz in-situ efficiency measurement system. The system, which consists of two trolleys, will be connected with the aerosol feeding device, the upstream and downstream measuring ports and the scanner of the filter housing. Filter housing and HEPA filter element data will be transferred to the systems via read-in of QR – codes. Afterwards the process is fully automatic according the following sequence.

The result of the efficiency measurement process can be displayed and printed as a test report according EN 1822, as a graph or can be send to a BMS systems for documentation.

Evidence of validation was done by testing the uniform distribution, the efficiency of an unloaded filter element, the efficiency of a loaded filter element and a leak test of a damaged filter element three times each.

Frankfurt am Main · 15 – 19 June 2015

5. Third-party approval An expert report of the validation process and the efficiency measurement process (Fig. 7) was made by TÜV SÜD Industrie Service GmbH. The expertise consists of the following details.

1. Review of the relevant HEPA filter class H14 regarding the requirements of EN 1822-4 and EN 1822-5.

2. Inspection of test setup.

3. Function test of the particle filter housing and the a. m. scan procedure at manufacturer plant, based on EN 1822-4 and EN 1822-5, too.

4. Inspection of functional tests of the particle filter housing according the determinations of EN 1822-4 (leakage test) and EN 1822-5 (efficiency measurement).

5. Documentation of results (qualification report).

6. Audit of work environment.

7. A certificate is issued as evidence of the procedure.

6. Periodic qualification of the HEPA filter Based on the requirements of the standards for bio-safety laboratories as mentioned above in chapter 1, other periodic qualifications of the HEPA filter have to be done besides the efficiency measurement and the leak testing of the filter element.

1. HEPA filters have to undergo a seating inspection after installation.

To check the tight seat of a HEPA filter element, a leak test device (Fig. 8) can be connected to the filter seat test groove from outside the filter housing. The tightness will be measured according the constant pressure method, which allows a quick and easy read off of the leakage airflow.

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Highlights 2014

2. A fumigation of the filter housing and the HEPA filters with formalin or hydrogen peroxide must be possible.

Filter housings and HEPA filters must be decontaminated periodically. This is done by means of disinfection with either formalin or hydrogen peroxide. Disregarding the disinfection media the procedure of disinfection must be validated by means of bio-indicators. The disinfection parameters like duration and concentration have to be developed for each single design of filter housing. It is essential for the positive result of the process that a so-called “octopus” is used to bring disinfection media to each connection of the filter housing (with its hoses and pipes behind) and also to “dead” areas e.g. of the filter element clamping device (Fig. 9).

Furthermore the filter elements and the gaskets have to be resistant against the disinfection media to avoid changing the filter elements after each disinfection cycle.

3. It must be possible to exchange HEPA filters under conditions of low contamination.

Changing filter elements requires a bag-in / bag-out (BIBO) procedure using plastic bags and heat seal devises to avoid any contamination. This is a required method also if the filter housing was decontaminated previously and it will ensure additional safety both to personnel and environment. Different methods of sealing and cutting the changing bags are available including sealing documentation.

Fig. 8: Leak test device

Fig. 9: Disinfection setup

Fig. 10: Sealing and cutting during safe change with HSD classic device

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Fig. 11: Sealing and cutting during safe change with HSD hightec device

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Highlights 2014

Electrostatic precipitation of different flue gas components from small wood-fired furnaces M. Kaul, E. Schmidt* 1. Introduction The particulate components of flue gases from small wood-fired furnaces clearly differ in concentration and contents.

On the one hand the kind and moisture content of the used fuel are decisive.

On the other hand, different operating parameters in the furnace chamber play a role which can influence the conversion of the fuel. With an incomplete combustion, caused by irregular mixing of fuel and atmospheric oxygen or by lacking air supply, primarily uncombusted carbon compounds appear in the form of soot.

Low temperature zones in the combustion chamber, caused through evaporation of water bound in the fuel, favour the development of polycyclic aromatic hydrocarbons (PAK) in tars. With good combustion conditions, the fuel can be converted stoichiometrically, so that low volatile ash components and newly formed salts will primarily appear. Hence, we essentially distinguish between soot, salts, and tars in the particulate emissions /1, 2/.

Studies by the Institute of Particle Technology (IPT) of the University of Wuppertal dealt with the question of * Dipl.-Ing. Matthias Kaul, Prof. Dr.-Ing. habil. Eberhard Schmidt University of Wuppertal Institute of Particle Technology Rainer-Gruenter-Straße, Gebäude FF 42119 Wuppertal Tel.: +49 202 439 1524, Fax: +49 202 439 3957 E-mail: kaul@uni-wuppertal.de

whether the different composition of the flue gas ingredients affects the electrostatic precipitation during the flue gas purification. For this purpose, a pilot plant was developed which provides an insight into the precipitation behaviour of individual particulate flue gas components with the help of different particle generators and a customary electrostatic precipitator for small solid-fuel furnaces

by Kutzner+Weber. Soot was examined in the form of graphite particles. Salt particles were generated from a sodium chloride solution. Di-ethylhexyl sebacate (DEHS) that, with its permittivity, constitutes a representative substitute for tars containing PAK. Through the consideration of the pure components, interaction of the substances among each other, which can also influence the precipitation, was excluded.

The study results can give indications of a sensible linkage of furnace-control and electrostatic precipitator design and control and thus make contributions to the emission reduction for domestic heating with wood.

2. Pilot plant The pilot plant used (Fig. 1) is three metres long and consists of single wall furnace tube segments made of stainless steel with a diameter of 180 mm. The modular design allows the use of the different flue gas components through simple conversion. At the aerosol inlet, the respective particle generator is installed which, with the help of filtered compressed air, disperses the material to be examined into the plant. A “Defined Nano Particle Generator” DNP 2000 by Palas is used

Fig. 1: Experimental set-up (l = 3 m, d=180 mm) with TSI atomiser and Grimm SMPS system

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Tab. 1: Modal and median values of particle size distribution, overall precipitation efficiencies by number and specific values of the examined aerosols

Fig. 3: Number density distribution and fractional precipitation efficiency of soot, calculated from mobility equivalent diameters

Fig. 2: “Zumikron” electrostatic precipitator by Kutzner + Weber; spray electrode tungsten wire (l=200 mm, d=0.25 mm)

for the generation of graphite particles, an atomiser system 3076

by TSI for the presentation of salts, as well as a Sinclair-La MerGenerator, which produces a DEHS aerosol by condensation of salt cores. After a one metre long inlet zone, the aerosol stream passes the electrostatic precipitator “Zumikron” (Fig. 2). Particles are charged here electrically and are precipitated in the area of the active electrical field, or else are precipitated during the further course of the pilot plant on the inside of the grounded furnace tube. After another one and a half metres, the sampling is done for the particle size analysers by means of isokinetic extraction. For graphite and salt, a “Scanning Mobility Particle Sizer” System (SMPS) by Grimm is used. For DEHS, an optical particle sizer 1.109, also

by Grimm, is used, since an interference of the sensitive internal electrode of the SMPS through the liquid-dispersed DEHS cannot be excluded. Finally, the aerosol velocity is monitored in front of the outlet with a Testo hot ball-anemometer. With an average gas velocity of 0.4 m/s, there is a volume flow of 0.61 m3/min and turbulent flow at a pipe Reynolds number of 4550.

3. Measurement of the precipitation efficiencies For assessment of the efficiency of the electrostatic precipitator, the precipitation efficiency to be achieved with the different test particles must be determined. For this purpose, the particle concentration is measured with separator switched off (craw) and with separator switched on (cclean). From the results, the number-related distribution densities q0(x) in the raw gas and in the clean gas, as well as the fractional precipitation efficiency, can be determined.

The median and modal values, as well as the calculated number-related overall precipitation efficiencies, can be found and accumulated for all examined substances in table 1.

Beginning with graphite, the distribution densities of both operating modes, with the resultant fractional precipitation efficiency, are plotted in figure 3. In addition, the number-related overall concentrations are shown here for raw gas and clean gas.

It can be seen that the particle size distribution shifts from the fine range in the direction of the coarser range through the use of the electrostatic precipitator. This behaviour is reflected in the development of the fraction precipitation efficiency. At the beginning of the measuring range at 11 nm the precipitation efficiency starts at 99 % steadily decreasing until it reaches its valley value at a particle size of 45 nm and a precipitation of 35 %, before rising again. At the upper end of the effective range of the “Differential

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Fig. 4: Number density distribution and fractional precipitation efficiency of NaCl, calculated from mobility equivalent diameters

Mobility Analyser“ (DMA) of the SMPS-system used for graphite (1083 nm), the precipitation efficiency already is 68 % again. On average, the achieved precipitation efficiency for soot amounts to 79.8 %. The median shifts from 24.7 nm to 38.9 nm and the modal value from 35.9 nm to 45.1 nm.

With NaCl, used as a substitute for salts contained in the flue gases, the results shown in figure 4 look similar. On account of a different DMA, the measuring range already begins at 5.5 nm, but ends at 350 nm. Here too, a clear shift in the particle size distribution into the coarse range is evident, wherein the distribution also becomes slightly wider and therefore more level at the same time. The fraction precipitation efficiency describes this fact with an initially very low course at 11 %, followed by a sharp increase beginning with 9.5 nm, which reaches its peak of 80 % precipitation at 20 nm. In the further course, the precipitation decreases steadily up to the end of the measuring range with 350 nm to 40 %.

The average achieved precipitation efficiency amounts to 62.7 %.

The median shifts from 35.6 nm in the raw gas to 42.7 nm in the clean gas. The modal value is raised from 55.4 nm to 65.8 nm.

The particle size distribution of the DEHS ranges in a higher size range than the other two featured aerosols. As can be seen in Figure 5, the particles generated through the Sinclair-La Mergenerator range between 265 nm and 675 nm. The fraction precipitation efficiency is subject to slight fluctuations of about 33.2 % on average only in the observed size range, which manifests itself with nearly identical distribution densities in the raw gas and clean gas. The specific median and modal values are consistent in both operating modes.

4. Evaluation and discussion For the validation and interpretation of the test results obtained, it is recommended to do a comparison with theoretically determined precipitation efficiencies. For this purpose, the pilot plant is assumed to be an electrostatic precipitator tube. Two particle char-

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Tab. 2: Specific values for pilot plant

Fig. 5: Number distribution density and fractional precipitation efficiency of DEHS calculated from scattered light equivalent diameters

ging models are distinguished according to the size of the particles to be charged. The diffusion charging comes into play for small particles up to a size of approx. 0.5 μm. The fraction precipitation efficiency for thus charged particles is calculated according to (1) with q as particle charge, Ea as electric field strength in the precipitation zone, lSE as discharge electrode length, μ as dynamic gas viscosity and xp as particle diameter. The Cunningham factor (Cu) accounts non continuum effects for drag calculation of small particles, which is not to be neglected with particles under 10 μm.

The factor is calculated according to

(2) with λm as mean free path length of gas molecules and with the constants A1 ... A3.

For particles from approx. 0.5 μm upwards, the charging of the particles can be estimated via the model of the field charging. Here too, the Cunningham factor affects particle sizes under 10 μm. The precipitation efficiency can be calculated via equation 3, (3), wherein E1 describes the electric field strength in the charging zone and ε0 the absolute dielectric constant of the vacuum. A variable of the particle conductivity is integrated through (4) with the substance-specific permittivity εr /3, 4, 5, 6/. The underlying values for the calculation are in tables 1 and 2.

It is remarkable that the variable p as the only substance-specific parameter is used exclusively with the calculation of the field charging, but not with the diffusion charging. Thus, in the comparisons of the experimentally determined precipitation efficiencies shown in figure 6, with the theoretically calculated ones, one can distinguish between the substances with the particle sizes relevant for the field charging only. The calculated precipitation efficiency in the area of the diffusion charging is not substance-specific.

It can be seen that the measurement values based on the tests qualitatively reflect the theoretically determined precipitation efficiencies very well. The measurement values lie very close together F & S International Edition

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Fig. 6: Experimentally determined precipitation efficiencies (calculated from different equivalent diameters) and precipitation efficiencies calculated with the help of diffusion / field charging models

in the overlapping measuring ranges of the diffusion charging, something that can be proven theoretically. The precipitation minimum typical for electrostatic precipitators, between 0.1 and 1 μm, can easily be located. The remarkably bad precipitation of NaCl particles of less than 15 nm is presumably due to the low residence time in the area of the discharge electrode. 0.5 s is not sufficient for reliable charging of the particles in the low nanoscale range /3,8/.

5. Conclusion The electrostatic precipitation of particulate flue gas components is to be looked at as being regardless of their material composition in the relevant nanoscale range. This fact is understandable theoretically and has now been proven practically. Depending on the installation situation of the electrostatic precipitator, the ingredients may still be of some relevance. In particular, particles of the magnitude discussed here tend to agglomerate shortly after their formation, so that a shift of the particle size distribution into the micrometer range becomes likely. The theoretical evaluation carried out in this work suggests that there are material based differences to be expected for the processes and particle size ranges evaluated here. The diverse composition of the flue gas components, depending on the situation in the combustion chamber, can be counteracted with a sensible connection between the furnaceand the precipitator-control.

Acknowledgements We owe thanks to the ELSTATIK Foundation Günter & Sylvia Lüttgens for their kind support.

Literature: /1/ T. Nussbaumer and P. Hasler: Bildung und Eigenschaften von Aerosolen aus Holzfeuerungen, Holz als Roh- und Werkstoff, Springer publishing company, Heidelberg (1999) /2/ J. Kelz, T. Brunner and I. Obernberger, Emissionsfaktoren und chemische Charakterisierung von Feinstaubemissionen moderner und alter Biomasse-Kleinfeuerungen über typische Tageslastverläufe, Environmental Science Europe, Springer publishing company, Heidelberg (2012) /3/ H. J. White, Entstaubung industrieller Gase mit Elektrofiltern, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig (1969) /4/ H. J. Lowe and D. H. Lucas, The Physics of Electrostatic Precipitation, British Journal of Applied Physics, Vol. 4 Suppl. 2 P40, IOPScience (1953) /5/ S. K. Friedlander, Smoke, Dust and Haze, Fundamentals of Aerosol Dynamics, Oxford University Press, New York (2000) /6/ M. Stieß, Mechanische Verfahrenstechnik - Partikeltechnologie 1, Springer Verlag, Heidelberg (2009) /7/ Dielectric Constants of Common Materials http://www.rafoeg.de/20,Dokumentenarchiv/ 20,Daten/dielectric_chart.pdf [accessed on 13.03.14] /8/ M. Kaul and E. Schmidt, Experimental Investigations into Electrostatic Precipitators with high flow-velocities, Filtech, 13-15 October 2009, Wiesbaden (II-768 – II-772)

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Highlights 2014

Particle measuring technology and filter testing according to the latest state of the art H. Lyko* The comparability and reproducibility of measured results that are obtained with particle counters, operational settings and outer boundary conditions affecting these, and practical experiences with the application in industry and the environment formed a big topic of this year’s Aerosol Technology Seminar in Karlsruhe, to which Palas GmbH was able to welcome a total of 55 participants. The second big subject area on which there are always new questions is the testing of filters and separators. Here current developments in testing equipment, the use of aerosol technology for the development of new separation processes and filter testing for different industrial application cases were considered.

Overcoming the separation gap through drop condensation At the University of Technology of Kaiserlautern, Prof. Siegfried Ripperger and employee Felix Haller are examining the drop condensation for nanoparticles, with the aim of overcoming the so-called separation gap of filters (see also/1/). Particles in the critical size range between 100 nm and 1000 nm should be enlarged through heterogeneous condensation before being filtered. The essential components of the test facility for this are a nanoparticle generator, two membrane contactors for the saturation or supersaturation of the air, a nanoparticle counter before the contactor path and an optical particle counter behind it (see Fig. 1).

Behind the condensation stage, there is an element for drop separation, for example a knitted fabric (see Fig. 2). For different source aerosols (NaCl, DEHS), the degree of supersaturation is determined, where preferably all germs of the raw aerosol are activated. The degree of activation and the generated average drop diameter as a function of the supersaturation are entered into a database for different types of particles. The experiments are accompanied by the modelling of the heat and mass transfer within the tubular membranes of the contactors. The drop separation is measured and also simulated for different knitted fabrics. For supersaturation, there are also other technical solutions besides the contactor path, packed columns among others. The studies in Kaiserslautern are embedded into a BMWI project, for which research is also going on at the Institute of Technical Thermodynamic and Refrigeration (Prof. Schaber) of KIT, and also with BASF, in order to develop an overall process that is competitive in terms of energy and economics. *Dr.-Ing. Hildegard Lyko Dortmund, E-mail mylko@t-online.de

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Influence of charge on the electrometer measurements The classification of ultrafine particles with a Scanning Mobility Particle Sizer (SMPS) is the standard method for deter-

mining the particle size distribution in the nanometer range. An essential component of this method is the generation of a defined charge state of the aerosol.

Currently, the standard widely accepted is

Fig. 1: Diagram of the test facility for enlarging of nanoparticles by means of heterogeneous condensation in which the supersaturation of the air is achieved with the aid of membrane contactors (Image: Chair of Particle Process Engineering, Technical University of Kaiserslautern)

Fig. 2: Drop separator by Rhodius GmbH, with which enlarged particles are precipitated from air streams through droplet condensation (Image: Chair of Particle Process Engineering, Technical University of Kaiserslautern)

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the charging of the aerosol by means of radioactive radiation from an 85Kr source. Because the use of a radioactive source is subject to statutory requirements relating to installation and operation of such devices, and these make transporting the device from one measurement location to another very expensive, soft X-rays are being examined as an alternative. However, with this one receives systematically different results in the measured particle size distribution, something that again is due to the different charge distributions generated by both charger models. At the University of Paderborn, in cooperation with the University of Leipzig (Prof.

Wiedensohler), there are studies on how the charger model and other influencing factors of the experimental set-up affect the charge distribution. Prof. Hans-Joachim Schmid, University of Paderborn, showed results from the parallel operation of both charger models. The charge distribution generated through the soft X-ray examination radiation is thus corrected with the help of the comparative values, so that the average relative deviation of the particle concentrations in the size range between 20 and 400 nm becomes minimal. After this correction, only minor unsystematic variations remain, partly through other influences.

Mara Pfeffinger also dealt with the comparison of different particle charging systems for nanoparticle measurement in a Bachelor thesis that was supervised by the Institute for Mechanical Process Engineering and Machines of KIT in cooperation with Palas GmbH. For this purpose, three alternatives, an 85Kr charger with 370 MBq radiation intensity (current standard), an 85Kr charger with 57 MBq, and also an X-ray emitter, were operated in parallel on an electrometer in order to determine, with the help of the obtained particle size distribution, the influence of the volume flow of the particle concentration and the particle material on the neutralisation by the respective emitter. Among other things, it was found that the X-ray emitter can neutralise / charge higher volume flows than the krypton source with low performance. In addition, the influence of the charger is greater with particle materials that bear charges from the outset. This difference could be observed with the comparison of graphite particles and DEHS aerosols.

Essential disadvantages of the X-ray source are its price (it is substantially more expensive than a Kr emitter) and its service life of about 5,000 h in total. Because of this, it is unsuitable for continuous measurements for a long period.

1100 particle standard (mono-disperse particles of 1 μm diameter). As Dr. Maximilian Weiß of Palas elaborated, the field meter is exposed to different influences that can affect its measuring accuracy. Thus, the temperature at the installation site influences the amplification factors of the photomultiplier and electronic amplifier, contamination by ambient dust becomes particularly noticeable on the optics and also the intensity of the source of light can decrease in the course of its service life. With a new instrument for online monitoring of the correct amplifications, with the help of the measured quantity size distributions, onsite maintenance appointments can be reduced. The patented development was explained with the help of a typical calibrating curve of the aerosol spectrometer. Caused through the transition from Raleigh to Mie scattering, the calibrating curve (plot of the scattered light intensity in relation to the particle diameter) gets flatter in a specific particle size range, resulting in a signal accumulation in the corresponding raw data channels. This effect becomes visible through a marginal secondary maximum in the course of the measured particle size distribution. Since this is a physical effect that depends exclusively on the source of light, it does not need to be calibrated. Thus one can conclude from this part of the distribution curve, whether the light scattering and/or its detection are still functioning perfectly.

With a decrease in the optical amplification, this maximum moves to a lower raw data channel (i.e. to a lower particle diameter). An automatic readjustment of the optical amplification is not allowed in certified devices, but the operator receives a status message and thus may carry out maintenance. The monitoring system should be tested in a future measuring campaign together with TÜV Rheinland.

Fine dust measurement in ambient air The FIDAS Fine dust measurement system by Palas has meanwhile successfully undergone the “Suitability test for continuous parallel emission measurement of the PM10 and the PM2.5 fractions in the suspended particulate matter in stationary applications” (see announcement of 1st April 2014 in the Federal Gazette). Karsten Pletscher of TÜV Rheinland, which is an executing test institute, summarised the test measures, of which the practical part alone took about 1.5 years. The entire test report for this is reviewable on the Internet under www.qal1.de. In addition to the testing of two structurally identical FIDAS systems in the laboratory and in field tests, the method also included manufacturer’s certification according to ISO 9001, as well as testing to verify the fundamental suitability of the Quality Management System (QMS) for the compliant production of a measuring device according to DIN EN 15267 – 2 /2/. Planned as the next steps are the corresponding certification in Great Britain, the approval of the FIDAS 200 Indoor variation, the qualification of further evaluation algorithms other than those named in the announcement and the Proof of conformity with CENTS 16450 /3/.

The operation of the FIDAS as a field meter also assumes maintenance at defined time intervals, and among other things, regular testing of the sensitivity of the particle sensor with the CalDust

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Fig. 3: Arrangement of particle counters and reference devices for calibration, permanent set-up at the World Calibration Center for Aerosol Physics (WCCAP) in Leipzig

Calibration of particle counters In the EU FP7 ACTRIS project (Aerosols, Clouds, and Trace gases Research Infrastructure Network, see www.actris.net), the three existing European infrastructures to better understand the ambient air quality EUSAAR (see www.eusaar.net), CLOUDNET (see www. cloudnet.org) and a program to measure trace gases are integrated in a common framework. Within the scope of the FP6 EUSAAR project (European Supersites for Atmospheric Aerosol Research), a network of 20 European measuring stations for long term monitoring of the air quality was established in the period from 2006 to 2011 and CLOUDNET (see www. cloud-net.org) pursued the production of vertical profiles of cloud and aerosol properties. A working package of ACTRIS includes the improvement and standardisation of the in-situ recording of aerosol properties and the introduction of standardised and comparable measurement and evaluation procedures. This project part is headed by Prof. Alfred Wiedensohler of the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig. In his

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lecture, he addressed the requirements for the calibration of particle counters. Since there is no counting standard, a reference concentration must be determined with an independent electrical measurement. The following steps are required as a calibration sequence: - Calibration of an aerosol electrometer against a femto-A source at a metrology institution - Calibration of a reference particle counter against the reference electrometer - Calibration of individual particle counters.

The equipment necessary for this is implemented in a permanent test set-up at the World Calibration Center for Aerosol Physics (WCCAP) in Leipzig (see Fig. 3).

The approach was shown with the help of different commercial condensation core counters. The overall configuration of an SMPS contains a differential mobility analyser in which the particles are classified according to their mobility (size), as well as a subsequent condensation core counter (CPC). The CPC has a size-dependent counting efficiency, and in addition corrections must be carried out for particle losses internally and in the sam-

pling line. With the DMA, the penetration efficiency for particles below 100 nm is dependent on size. The geometry of the DMA and also the sheath air volume flow determine the detectable size range of a DMA and the sheath air volume flow also influences the exact size determination.

In different workshops within the scope of the above-mentioned EU projects, a large number of SMPS devices were compared with each other, with the aim of not exceeding a measurement uncertainty of 10% for the long term aerosol measurement in the ambient air. An overview of the numerous measurements and the recommendations derived from them are described in /4/.

Besides the fact that there is no counting standard, the insecurity still exists with aerosol electrometers that a portion of the particles is multiply charged and is therefore also counted several times as a particle during data conversion. The probability of multiple charging rises with the particle size and is compensated by a correction algorithm. Another possibility for the elimination of multiply charged particles is the series connection of two DMA. However, the ideal for the

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calibration is a monodisperse aerosol where no multiple charges appear. This was illustrated by Felix Lüönd of the Federal Institute of Metrology (METAS) in Switzerland. He described the production of such calibrating aerosols through heterogeneous condensation on particle germs. Silver particles were produced through vapour deposition of silver on nanoparticles generated with a spark generator (from Au, Cu, C, W) in a three-zone furnace (cf. /5/). However, uncharged particles are produced in the evaporation furnace, which are then charged in a DMA, in which case the fraction of the homogeneously nucleated and multiply charged particles is then rejected. Another heterogeneous condensation method, in which the charge of the primary particles is maintained, is the condensation of highly molecular, semi-volatile hydrocarbons (here Tetracontan, C40) on NaCl particles. This method leads to monodisperse aerosols of an average particle size around100 nm.

Dependence of the scattered light measurement methods from the light source

Characterisation of an impactor with an aerosol spectrometer In addition to the particle size distribution, knowledge of the chemical composition is necessary for the evaluation of the health effects of fine dust. This information is not provided by an aerosol spectrometer, but with the help of an impactor, particles can be classified not only according to their size, but they can also be collected on suitable substrates and can afterwards be analysed.

In the cooperation project Helmholtz Virtual Institute of Complex Molecular Systems in Environmental Health (HICE), which is headed by the Helmholtz Centre in Munich and the University of Rostock, there is intense concentration on reactive organic compounds in environmental aerosols, namely in the gaseous phase as well as in particle form, and also on the influence of the increasing combustion of biomass and biofuels on the existing health risk.

Erwin Karg of the Helmholtz Centre described the Ultra-III project by pursuing this issue through selective samplings of the fractions PM0.1 PM2.5 and PM10 in a typical medium-sized German city (Augsburg). In order to be able to produce a reliable correlation between size fraction (corr. to an impactor stage) and the chemicals involved, these are characterised with the help of particle counters. It was found that, on account of its high resolution, the

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Different aerosol spectrometers use different sources of light, and so it stands to reason to systematically examine the influence of the wavelength of light on the scattering behaviour of particles and measured size distributions. Katja Schiz, KIT, did this with the help of the white light aerosol spectrometer welas (light wavelengths 370 - 770 nm), the fine dust measuring device FIDAS operated with the help of a polychromatic light source with narrow-band spectrum (LED 400 - 520 nm) and a laser-based sensor, in which only one light wavelength (660 nm) is used.

Droplet aerosols with 0.2 to 8 μm particle diameter were used as testing aerosols in each case. Differences were shown between the welas and Fidas systems, with larger particle diameters from about 3.7 μm, in that Fidas tends to display larger particle diameters.

With both devices, the standard deviation increases with rising particle diameter. Calibrating curves were recorded for all three light sources. While in welas and Fidas fundamentally similar profiles were measured and respectively a clear link was measured between scattered light intensity and particle diameters, the calibrating curve of the laser sensor showed ambiguities, i.e. different particle sizes were seen in the same scattered light intensity. These ambiguities appeared in the particle size range between 2 and 5 μm, from which it was concluded that this measuring arrangement is of limited use in the Mie range.

Highlights 2014

Table 1: Comparison of energy classes for the filter class F7 according to the current state of classification in the original version (2012), the currently applicable applicable version at the time of the seminar (2014) and the planned 2015 version (for ratification in the CC FIL main committee).

welas white light aerosol spectrometer is very suitable for characterising an impactor stage, if one resorts to particles with a known refraction index.

Overlapping of different measuring ranges The U-Range measurement system of Palas, which was explained by Jürgen Spielvogel, integrates an electrometer with a condensation nuclei counter and an aerosol spectrometer, and can measure particle sizes of 8 nm up to 40 μm as a whole. However, the two measuring methods detect physically very different sizes, namely the diameter in the lower size range equivalent to electric mobility and a scattered light diameter in the upper range.

The overlapping range of the two measuring methods comprises the particle sizes of about 180 nm to 1400 nm. From the analysis of both measured physical quantities, conclusions on particle properties can be drawn. The difference between measured mobility diameters and optical diameters is corrected (i.e. the curves of the size distribution coincide in the overlapping range) through a form factor, which results from the refraction index of the considered particle material.

Health hazards by printer and copier emissions Through their emissions, laser printers and photocopiers have the reputation of having a detrimental impact on the well-being and health of people who are in the same room with such devices daily or for long periods of time. Existing toxicological studies brought no clear findings. In a study funded by the German Social Accident Insurance doctors of the University Hospital Munich examined test persons, which were exposed voluntarily to the printer emissions in a specially created exposure chamber. Among a total of 52 test persons, there were 23 healthy people, 15 affected persons according to their own information supplied, and 14 so-called mild asthmatics. The technical part of the study i.e. the selection of the printers, the design and instrumentation of the exposure chamber including the

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quantitative and qualitative modelling of the particle emissions, the operation of the printer and the entire control and measuring technology monitoring were task of the Federal Insitute for Materials Research and Testing (Bundesanstalt für Materialprüfung BAM). Dr. Stefan Seeger, who had already reported about printer emissions in past seminars, described the approach and the results of this study. Printer models were selected in each case that had distinguished themselves in preceding measurements through especially high or especially low emission values. During the operation of the high-emitting devices, a plateau concentration was achieved of about 100.000 particles per cm3, this is a value that does not occur in practice over a longer period with normal printer usage. The test persons were exposed in each case for 75 min. to a virtually continuous printer operation, still followed by a fifteen minute subsided phase. The stay in the chamber, the medical examinations before and after the exposure, including psychomotor tests before and after the printer operation took about 5 - 6 hours per test person.

The essential result of the examinations was that, though a subjective discomfort was expressed, however, no evidence was found that laser printers caused measurable damage to health. However, it is still recommended to operate laser printers in separate rooms. The final report of the study /6/ is available at www.dguv.de.

Basic research on particle separation from humid air As has been reported several times, the pressure loss of a dust filter, depending on the type of particles to be separated, can be considerably altered by varying the humidity particularly for hygroscopic particles. The mechanism of action decisive for this, in particular in view of the morphology of the particles and the particle contacts on single fibres are an object of the studies by Dr. Qian Zhang, which he is conducting at the University of Wuppertal. In the experimental part of the work, differently hygroscopic particles are precipitated on individually clamped

fibres. For this purpose, a mini module for single fibre restraint was developed, which can be inserted into a filter test apparatus.

The particles precipitated on the fibres are examined by means of ESEM (environmental scanning electron microscopy) and X-ray spectroscopy. Beside the description of the change of the morphology of the particles precipitated on the fibres, a model should be developed for the quantitative description of the detected mechanisms of action.

New energy efficiency classes for air filters In April 2011, the Eurovent- energy label for air filters was introduced and positively accepted by many manufacturers, as Thorsten Stoffel of GEA Air Treatment GmbH explained. Following a complaint to the European Commission, it was found that Eurovent may not use the original label with its division into 7 classes (A – G) and the colours green through red at all because this label is subject to EC copyright and applies only to regulated products such as refrigerators and washing machines. In the initial change, which had to be done very at short notice, a new label was launched in 2013 with the five classes A through D. Through the reduction of the number of classes, there was a broadening of the classes, i.e. of the respective value ranges for the energy consumptions according to which a filter of a specific performance class is classified into the energy efficiency classes. As evidenced with an examination of the thus certified filters, this classification contradicts the legal requirements for European energy classification. Accordingly, the energy consumptions of all certified filters of one performance class must be subject to a normal distribution i.e. the maximum is approximately in the middle range of values, whilst the number with especially good i.e. low consumption decreases, just as it does with especially high consumption. However, in the reality of the still existing 5-class classification, too many filters still belong to the energy class A. If one then still includes the confidence interval that results when testing through the usage of ASHRAE- test dust and some other test parameters, a differentiation becomes even more difficult. Thus, for example, with the filter class F7, up to 5 -62 % of all 242 tested filters could be assigned to the efficiency class A. To allow a better differentiability and to meet the European standards, the classification was changed again, namely by the fact that the energy value ranges of the classes B and C are now valid for the new classes C and D, the initial value of the worst class E

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Filter testing in laboratory and practice For testing of cleanable filter media, a vertical raw gas duct is specified as a reference system in ISO 11057 of 2011 /7/, while the testing according to VDI 3926 describes a horizontal raw gas duct.

According to ISO 11057, horizontal raw gas ducts continue to be permitted when they meet certain criteria of equivalence. With the test bench MMTC 3000, Palas offers a test bench with one vertical and one horizontal raw gas duct each and equivalent, moveable pure gas section. In a cooperation project together with the Saxon Textile Research Institute (STFI) the dust feed was optimised, a correlation was carried out between the modes of operation with vertical and horizontal raw gas duct and the influence of the crossflow suction and the filter shape was examined. Martin Schmidt, Palas, described the construction of the test bench and its peculiarities. These are a dust feed unit with weighing for the verification of the raw gas concentration, a truncated raw gas duct compared to ISO 11057 with homogeneous dust distribution, a filter medium holder with fixture device for easy removal of the test specimen and an optical on-line emission measurement with representative sampling and the aerosol spectrometer PROMO. As dust dispens-

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was reduced accordingly and the upper classes once were reduced on the one hand and were extended by the new efficiency class A+ on the other hand (s. Table 1 exemplarily for filters of the class 7).

This new classification applied from 2015. For how long cannot yet be foreseen, because, with the expected launch of a new test standard ISO 16890 for 2016, according to which the separation efficiencies of the fractions PM10, PM2,5 and PM1 are determined with a different test dust, different filter classes and energy values also arise.

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Highlights 2014

ers, a belt feeder with weighing unit was used on the vertical raw gas duct and on the horizontal duct, a brush generator was used. Pural NF was used as a test dust. In both cases, the required dust concentration on the filter could be set with a deviation from the mean value of less than 3%. The equivalence of both test set-ups exists if the parameters residual pressure loss, average cycle time, embedded dust mass and pure gas concentration do not deviate from each other by more than 10%. This could be proven and, with the dosing consistency in the dust feed, this system turned out better than ISO 11057 dictates.

The measurements for the equivalence of both test set-ups were carried out on the STFI which also had the task to develop and to qualify a filter medium as a reference medium according to ISO 11057 (s. Table 2). As Marian Hierhammer, STFI, demonstrated, the material samples considered exhibited a wide spread of the characteristic surface mass and air permeability. These led to differences in the determined filter characteristic values.

Although the requirements of the standard were proven, it was pointed out that a comparability of the test results of different test benches is possible only with perfectly matched test processes.

Ralf Heidenreich of the Institute of Air Handling and Refrigeration (ILK) in Dresden addressed different filtration tasks in the industry in which the purified air is also recirculated to the workplace.

For a complete performance testing of filtering separators, a test rig is used in which filter elements of different designs ( tubes, bags, cartridges or plates) can be operated with compressed air regeneration and their pressure, energy and separation behaviour can be determined. Using various sample measurements it was shown that, for example, the fractional separation efficiencies to be measured of a filter can decisively depend on the test aerosol used, which is why the measurement with actual aerosols resulting in the work process is important. The timing and the pressure difference for the filter regeneration are optimised in view of the energy consumption and the pure gas concentration that is to be observed. Typical industrial processes with nanoparticle emissions are, for example, laser cutting processes and welding processes. Examples were shown with number concentrations of particles of about 80 nm, which were in the order of magnitude of up to about 1 million particles /cm3. The retention of the filtering separator used was approximately 99.9947%. In the filter testing of industrial vacuums, the penetration degree is specified, which is also determined from

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the measured particle numbers before and after the test specimen and must not exceed a maximum value applying for the respective dust class.

For the testing of compressed air filters, there is a test bench on which the measurement of the separation efficiency under system pressure (up to 7 bar) is determined. Martin Schmitz and Sven Schütz of Palas presented the system DFP 3000, in which not only the test section including the aerosol sensor is designed pressure resistant, but also the provision of the aerosol against this excess pressure takes place. For this purpose, the system AGF 3000 with two-fluid nozzle and the Laskin nebuliser PLG 3000 can be used as droplet generators, in addition, a brush generator is available for the dosage of test dust up to 3 bar. The pressure adaptation of the sampling volume flow is done automatically.

The bottom measurement limit of the aerosol spectrometer in the DFP 3000 is 0.2 μm, and this measurement limit also exists in the big compressed air filter test bench that is operated at the Institut für Umwelt- und Energietechnik (IUTA) in Duisburg (cf. /8/). If one wants to detect the size fractions below 0.2 μm, one is dependent on the prior depressurisation of the sample volume. How different depressurisation devices like a nozzle with and without pressure reducer or a micrometering valve affect measured particle size distributions, was specifically investigated

by Dr. Wolfgang Mölter-Siemens at the IUTA. The application of the quantity size distributions for the different depressurisation systems in comparison to particle measurement without depressurisation showed, in any case, a clear however different reduction of the particle numbers.

Among the rest, these are caused through evaporation of droplets through the depressurisation itself, however, also through particle losses in the flow cross sections of the depressurisation devices. From these results, the requirement followed to carry out a careful error evaluation during the compressed air filter testing with particle measurement at ambient pressure and to incorporate the transmission function of the devices immediately in the technical documentation.

Dispersing of nanoparticles Rodrigo Renato Retamal Martin is investigating at the University of Dresden, whether and how dispersing of nanoparticles by means of ultrasound is suitable as SOP (standard operating procedure) for the preparation of the characterisation of nanoparticles. Although this paper

has a unique feature insofar that, here, suspensions and not aerosols are being considered, the task definition in view of the particle measurement is similar to that of aerosol generators: the particles to be examined must be dispersed in such a way that the particle size distribution can be unambiguously and reproducibly measured afterwards. This means, for optical measuring methods for suspensions, that no particles sediment or no impurities are entered into the sample through the dispersing method. Here, it was shown that, with increasing energy input through the sonotrode (i.e. increasing duration of the dispersing) into the sample (pyrogenic silicic acid in water), the proportion in coarse particles increases, which is apparently entered through abrasion on the sonotrode. The formation of agglomerates from the primary particles is also possible. Accordingly, a defined end point of the dispersion, expressed as energy per volume, which is introduced through the sonotrode, is impossible to find. On top of that, coarse particles must be removed through filtration before the measurement.

Literature: /1/ Niklas, J.; Ripperger, S.: Untersuchungen zur heterogenden Kondensation von Wasserdampf in Membrankontaktoren; Chemie Ingenieur Technik 2011, 83, No.8, p. 1219 – 1228 /2/ EN 15267-2:2009: Air quality – Certification of automated measuring systems – Part 2: Initial assessment of the AMS manufacturer’s quality management system and post certification surveillance for the manufacturing process /3/ CEN/TS 16450:2013: Ambient air - Automated measuring systems for the measurement of the concentration of particulate matter (PM10; PM2.5) /4/ Wiedensohler, A. et al.: Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions; Atmospheric Measurement Techniques 5, 2012, S. 657 – 685 /5/ Zihlmann, S.; Lüönd, F.; Spiegel, J.K.: Seeded growth of monodisperse and spherical silver nanoparticles; Journal of Aerosol Science 75, 2014, p. 81-93 /6/ Seeger, S.; Langner, J.; Nowak, D.; Jörres, R.A.; Karrasch, S.; Ehret, M.; Herbig, B.; Schierl, R.: Untersuchung möglicher gesundheitlicher Gefährdungen durch Drucker- und Kopierer-Emissionen (DGUV, code number FP 294), Final report of the project partners, May 2014, see www.dguv.de /7/ ISO 11057:2011; Air quality -- Test method for filtration characterization of cleanable filter media /8/ Mölter-Siemens, W.; Lauber, G.; Kerßenboom, A.; Lindermann, J.; Finger, H.; Haep, S.: Abscheidung feinster Tropfen mit mehrschichtigen faserförmigen Filtermedien, dargestellt am Beispiel der Druckluftfiltration; F&S Filtrieren und Separieren 25, 2011, No.3 p. 150 - 156

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Numerical simulation of flow and particle precipitation in filtration fabrics D. Hund , K. Schmidt, S. Ripperger* 1. Introduction When using fabrics for cake filtration, the separated solid matter is deposited on the inflow area of the filter medium. Until the formation of the filter cake, a decisive significance is attached to the filter medium. In the early stage of the filtration process, it substantially influences the particle retention, the cake structure and the filtrate stream. During the further course of the filtration process, the filter cake takes over the particle precipitation and the filter medium takes over the support function for the cake.

Moreover, the influence of the filter cake on the filtrate stream becomes dominant in the process. At the end of the cake filtration, the interaction of the filter medium with the filter cake influences the cake discharge. The requirements arising thereby for a fabric are partly contrary, so that the selection of a filter medium constitutes an optimisation problem, where the requirements of the operation and the features of filter media must be considered in a well-balanced manner.

Through different arrangements of the crossing points of the warp and weft threads, fabrics are produced in different binding modes. Plain weave is easiest, where a weft thread is guided alternately above and below a warp thread. Other binding modes result from corresponding variations in the offset of the bond points, so that patterns are created that repeat at certain intervals.

With the yarns, a distinction is made between monofilament, multifilament and staple fibre yarns. A multifilament yarn consists of a huge number of fibres (filaments) that are usually twisted, swirled or curled together. The fibre crosssections are predominantly round, but can nevertheless also have other crosssection forms. A monofilament is a thread that consists of one filament. If multifilament threads are processed into fabrics then, in addition to the fabric pores, the pore spaces in the filaments, between the individual fibres, are still to be considered due to the bonding.

Therefore, the pore structure of a raw fabric and hence also the filtration properties are determined by warp and weft thread types (monofilament, multifilament) warp and weft thread densities and the kind of weave.

To improve the filtration properties of fabrics further, there are so-called refining methods. Through thermal treatments, shrinkage and fixing of the structure can be achieved. A frequently used method is calendaring, in which the fabric is passed through heated rollers. Through the high temperature and the high pressure, threads are flattened, multifilament threads are compressed, the fabric pores are constricted and, if necessary, also evened out and the surface is smoothed. Through different physical-chemical modifications of the surfaces, the electrostatic properties and also the wetting and adsorption properties of the fibres can be purposefully influenced. With all these measures, the particle precipitation and the removal of filter cake can be influenced. The * Dipl.-Ing. David Hund, Dr.-Ing. Kilian Schmidt, Prof. Dr.-Ing. Siegfried Ripperger Department of Mechanical Process Engineering Technische Universität Kaiserslautern Gottlieb-Daimler-Str. 67663 Kaiserslautern Tel.: 0631-205-2121 www.uni-kl.de/MVT

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Fig. 1: Monofilament fabric (left) and multifilament fabric (centred) in plain weave and multifilament and monofilament fabric made from a satin weave (right)

variation possibilities in the production and modification of fabrics permit an extensive adaptation to the respective requirements.

Monofilament fabrics have relatively smooth surfaces, from which the cake can be removed more easily than with multifilament fabrics. Multifilament fabrics, as well as multilayered fabrics, favour a depth filtration and hence also the separation of fine particles. In Fig. 1, a monofilament and multifilament fabric in plain weave and a combined monofilament and multifilament fabric in satin weave are respectively illustrated.

Multilayer fabrics are designed and selected such that the lowest layer with regard to the inflow side is decisive for the force transmission (e.g. in belt filters) and/or for the drainage effect at the filtrate outlet, while the first layer significantly determines the filtration. Fabrics of synthetic fibrous materials are primarily used for filtration, like polypropylene (PP), polyester (PES), polyamides (PA), polyacrylonitrile (PAN), polyetheretherketone (PEEK) or polytetrafluoroethylene (PTFE).

Pore Size Characteristics Permeability and Bubble Point

Extended measuring range: submicrone pores from 150 nm measurable

Especially suitable for nonwoven and meltblown materials

Pore Size Meter PSM 165 Topas GmbH Oskar-Röder-Str. 12 D-01237 Dresden

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E-Mail office@topas-gmbh.de Internet www.topas-gmbh.de

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Highlights 2014

the first term according to the DARCY equation. In this case, the value Kl is also called the permeability and the reciprocal value is also called the resistance.

Surface and wetting behaviour

Fig. 2: Cluster formation within a fleece

With corresponding fine pores, filter media with a hydrophobic surface are permeated only above the wetting pressure.

In the other case, air can only permeate a fabric completely moistened with liquid above the bubble point pressure.

2. Typical filtration properties

Particle retention

For the characterisation of fabrics, among other things, directly measurable properties are determined, such as for example the surface mass (g/m2), the fabric thickness and the thread density. Then the pore volume can be determined from that. In addition, the air permeability at a specific pressure difference, the ultimate tensile strength and maximum expansion and, in relation to filtration, usually also the filter medium resistance to a liquid, the bubble point pressure for determining the maximum pore size and the particle separation curve are determined. Often filtration tests are also carried out with the suspension to be filtered.

Permeability to fluid media The dependence of the pressure drop – can be determined of the flow velocity, w, with the following equation: Therein, ρ is the density of the fluid and η is the dynamic viscosity. The constants K1 and Kt are dependent on the fabric structure and are adapted to experimental results. The first term considers the viscous (laminar) throughflow and the second term is important in the occurrence of turbulence. Often one is located in the transition area, so that, e.g. with the throughflow of air, a turbulent proportion must be expected and in the case of a liquid, the throughflow can be described only with

With cake filtration, the retention of particles in the filter medium is essentially based on the following mechanisms: - the sieve effect, - achievement of a stable layer within the fabric structure, - bridge formation and - adhesion to the interior surface.

If a particle is bigger than the pore dimensions, it is separated. If all particles of the suspension are bigger than the biggest pore of the filter medium, a 100% retention is achieved. For cake filtration, this case is usually not desired, because the filtrate stream is limited through the correspondingly high resistance of the filter medium. Due to their spatial expansion, some particles are guided to the inner surface of the filter medium while permeating the filter medium and can then be precipitated due to adhesive forces.

This effect is summerised with the concept interception. In German this effect is also treated under the concept “Sperreffekt”. It therefore not only involves precipitation due to the sieve effect, but also the effects where e.g. a fibre of the filter medium is blocking the path of the particle.

A particle is also precipitated if e.g. it comes in contact with several fibres of a fabric at the same time and takes on a stable position. Then one can observe that further particles collect at such places and form so-called clusters. A particle achieves

Fig. 3: left: Plan view of the generated and the actual fabric; centred: sectional images of the warp thread; right: sectional image of the weft thread.

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a stable position when it has contact with the fibre structure or already precipitated particles at three different places. In Fig. 2, such a situation is illustrated on a fleece.

On account of bridge formation (pore blocking), suspended particles are separated that have a size clearly below the dimensions of the pores of the filter medium. In certain conditions, the particles are obstructed during passage through a pore, so that they collect in the surroundings of the pore and bridge it. Only afterwards a filter filter cake can build up. Up to the formation of bridges, particles can pass the pores so that a cloudy filtrate occurs during this period of time (turbidity shock breakthrough). Bridge formation occurs in most cases of a cake-forming filtration, since the pores of the selected filter medium are mostly bigger than the particles of the suspension.

There are some empirical approaches for predicting bridge formation that Schnitzer /1/ has summarized. Accordingly, the particle concentration and the particle size in relation to the pore dimensions, the flow rate and hence also the pressure difference, the particle size distribution and the interaction between the particles of the suspension and between the particles and the filter medium, determine whether bridge formation occurs or not. An accumulation of particles will be favoured if there are electrostatic bonding interactions between the filter medium and the particles.

Bonding mechanisms matter with cake filtration, in particular to the formation of bridges and clusters. In this, the Vander-Waals force and also the electrostatic interaction are of significance.

3. Numerical calculation of the throughflow of fabrics The often used models for the description of the throughflow of multifilament fabrics are based on strongly simplified (idealised) geometrical structures.

Some were introduced and discussed by Schnitzer and Ripperger /2/. For the case of multifilament fabrics, the underlying structures usually deviate strongly from the reality. To clearly improve the calculation and prediction of the flow and particle precipitation in fabrics, programs have been developed during recent years for the numerical simulation of the flow and particle precipitation in fabrics and other porous substances.

3.1 Generation of the fabric structure The starting point of the numerical simulation is the truest possible three-dimensional generation of the geometrical struc-

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Permeability B/m²

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Coarsen Real woven fabric

Voxel length /μm

Fig. 4: left: Influence of the voxel size on the permeability; right: Pore with low and high resolution

ture of the fabric. Hereinafter, the program DNSlab is introduced, which was developed for this at the Chair of Particle Process Engineering, University of Kaiserslautern.

With the DNSlab structural generator, the structural generation is done on the basis of virtual 3D fabric models. The structure is generated so that its structural parameters, such as for example porosity, weight per unit area and chord length distribution, correspond to the actual structure. The structural generation process ensures the compliance of these parameters within certain limits.

In order to produce realistic 3D fabric models, the relevant parameters (thread width, thread spacing, fabric thickness, etc.) were calculated for the results presented here from reflected light microscopy images, SEM images, as well as cross-sectional images and the textile technology testing results. A visual comparison of the actual fabric and the 3D model in Fig. 3 shows good conformity.

However, in the area of contact of the warp and weft threads, overlapping of the threads was assumed, simplified in order to better replicate the simulation of the actual fabric.

In addition, by means of the developed software there is the possibility to provide and illustrate microstructures on the basis of three-dimensional image data, such as for example micro-computer tomography (μ CT), and to use them directly as a model for the numerical simulation.

resistance. The description of the particle motion considers particle fluid friction, particle inertia and the influence of Brownian molecular motion. Here, the particles can also collide with the collector elements (e.g. fibres or precipitated particles). For the following

WOVEN STRUCTURES FOR INDUSTRIAL APPLICATIONS

3.2 Discretisation of the flow chamber Discretisation for the numerical calculation is based on a voxel structure with DNSlab, i.e. the permeated space within the filter medium is structured through a uniform computational grid consisting of cubic cells (voxels). From this, the flow chamber is filled in the filter medium. This generated structure is the basis of the flow simulation based thereon. The voxel size is orientated on the dimensions of the pores at the crossing points of the warp and weft threads. For the calculation of the flow, these pores should be resolved at least with 10 voxels. For the examined fabric, this corresponds to a voxel size of approx. 2.1 μm.

3.3 Flow simulation

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By means of flow simulation on the basis of the LatticeBoltzmann method, the pressure drop in the filter medium can be calculated among other things, and/or its permeability and/or flow

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Fig. 5: left: Flow profile through a pore; right: Particle deposition in the pore area

described results, it was assumed that a particle will adhere upon contact with a fibre. Also the sieve effect is considered for an interaction of a particle with several fibres. Deposited particles can be detected and considered in the next iteration step through a modified geometry. For the following results, precipitation efficiencies were calculated on unloaded filter media, so that this possibility was not considered.

Because this concerns uncharged filter media, electrostatic precipitation effects were neglected.

For the validation of the fabric model, the air permeability of the generated model was calculated with DNSlab and compared to the permeabilities of the actual fabric determined experimentally.

The experiments were carried out with the Pore Size Meter 165 from Topas GmbH. In the field of a viscous flow, there is a linear relationship between pressure loss and volume flow according to the Darcy equation. From the measured results, the permeability at a viscous flow can be calculated. The permeability of K1 = 3.66*10-13 1/m2 determined from the simu-

lation deviates by 5% from the permeability determined experimentally.

In conjunction with the calculation, the influence of the voxel size on the calculated permeability was also examined. In Fig. 4, values of the calculated permeability of different voxel sizes are plotted. In the examined case, it can be seen that the influence of the voxel size on the calculated permeability is minor below a length of 3 μm. Coarsening (grey area) can lead to deviations of up to 20%. The results also confirm the abovementioned rule for determining the voxel size.

On account of the high number of closely spaced individual filaments, it can be assumed that a negligibly small amount of air flows through the monofilament yarns. To detect this proportion of the flow, the multifilament yarn was replaced in the generated computational model by a monofilament thread of the same outer shape. By neglecting the multifilament structure, the pore structure was changed so much that there were clear deviations in the permeability. This simplification was therefore no longer applied.

3.4 Simulation of the particle precipitation 3.4.1 DNSlab program With the created fabric model, the particle precipitation was also simulated on the basis of the precipitation mechanisms implemented in the program. With precipitation mechanism “one”, particles which touch the surface are precipitated. In Fig. 5, it can be seen that the particles deposit in the area of the pores. Precipitation mechanism “two” considers the sieve effect, i.e. only particles that are bigger than the pore dimensions are precipitated. This precipitation mechanism is not suitable for the simulation of a bridge formation. Because no adhesive forces are taken into account yet in the precipitation models implemented in the program up to now, particles which are smaller than the pore dimensions and touch the surface either cannot be moved any further (precipitation mechanism “one”), or cannot be precipitated (precipitation mechanism “two”). Because of this, the process of bridge formation could not be simulated up to now.

Velocity / m/s

Fig. 6: left: Model for the flow simulation of the crossflow filtration; centred: Flow field; right: Pressure field

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Within the scope of an upgrade of the program, the flow boundary conditions can now be selected in DNSlab so that both a crossflow and also a throughflow of the fabric can be simulated. For the calculation of the flow, the pressure is specified as boundary conditions in the flow input, the flow output and in the downstream exit side (Fig. 6, left).

In Fig. 6, centre, the calculated flow field above and below the fabric can be seen, as well as in the biggest pores of the fabric. The maximum velocity occurs in the narrowest cross-section of the pore. On the right the pressure field is shown. It can be seen that the pressure drops sharply on account of the flow resistance within the pore.

In a subsequent step, particles of 15 μm size were given up during the simulation and were precipitated according to precipitation mechanism “one”. During the simulation, the particles are precipitated mainly in the mesopore range, like with static filtration carried out experimentally (Fig. 7). However, the process of bridge formation cannot be simulated yet with modelling, due to the unimplemented adhesive forces. But an appropriate further further development of the DNSlab program is planned.

3.4.2 Coupling of the Fluent and EDEM simulation programs The effect of bridge formation could be simulated simplistically for the first time with a coupling of the CFD simulation program Fluent and the DEM simulation program EDEM. Here, the flow field is calculated with the CFD program and the motion of the particles having a predetermined size or size distribution is calculated with the DEM program. Interactions of the particles with each other and with the fabric are also considered in the calculation.

In one simulation, a 20 μm large cylindri-

Fig. 7: Comparison of the simulation of the particle precipitation with experimental results

cal pore that was overflowing could be sealed by 5 μm large particles down to a minimum concentration of 0.1% by mass.

The process is substantially influenced by the specified interaction between the particles and the particles and the fabric. As is shown in Fig. 8 as an example, the bridge is formed after a certain time. Up to this time, particles can pass through the pore, something that corresponds in practice to so-called “turbidity shock” occurring.

Due to the additional flow resistance of the bridge, the filtrate stream decreases at the same time. The relationship of the influencing factors particle size / pore size, pressure difference, particle concentration and interaction parameters should now be examined in further simulations.

4. Summary and Outlook The results presented show that the calculation and forecast of the flow and particle precipitation in fabrics were clearly improved during the recent years. The coupling of the CFD simulation program Fluent with the DEM simulation program EDEM allows the simulation of the process of bridge formation, but the implementation of fabric structures and the calculation of the process in bigger fabric cut-outs are very costly. It is therefore the

objective to further develop the DNSlab simulation program so that interaction forces can be considered between the particles and between the particles and the fabric. Hence, it becomes possible to carry out the realistic generation of the fabric structure and also the calculation of the flow and particle precipitation with one program.

The effect of bridge formation could be simulated simplistically for the first time with a coupling of the CFD simulation program Fluent and the DEM simulation program EDEM. Expression of thanks: The presented works were carried out within the scope of the DFG project “Grundlagenuntersuchungen zur Partikeleinlagerung in Gewebeporen und der dadurch veränderten Veränderungen der Barriereeigenschaften” (Ri 776/28-1). The authors would like to thank DFG for its support.

Literature: /1/ Ch. Schnitzer: Filtrationsspezifische Charakterisierung von Multifilamentgeweben unter besonderer Berücksichtigung der Brückenbildung. Dissertation TU Kaiserslautern (2009) Vol. 1 of the progress reports of the Department of Mechanical Process Engineering ISBN 9783-941438-09-5 /2/ Ch. Schnitzer, S. Ripperger: Barrierewirkung von Geweben. Part 4: Modellierung der Durchströmung von Multifilamentgeweben. Filtrieren & Separieren 21 (2007), No. 4, pp. 226-231

Fig. 8: Simulation of the bridge formation; left: Time t = 0, pore not sealed; right: Time t = 0,03 seconds, pore sealed

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Flotation-filtration-process with ceramic membranes for water treatment J. Ludwig*, M. Beery*, L. León*, S. Ripperger** The process developed by akvola Technologies, Berlin, for water treatment that is offered under the name of “akvoFloat” includes a combination of a flotation where fine gas bubbles are generated by means of rotating porous ceramic disks and a microfiltration or ultrafiltration with submerged ceramic membranes. Both methods are arranged in one single open container. With the akvoFloat pilot plant, which was designed for a throughput of 12 to 20 m³/d, pilot testing was and is taking place. The results of an application for the treatment of surface water are presented in this paper. Other possible applications of the process combination are described.

1. Introduction The application of the two methods, flotation and membrane filtration, for the treatment of liquids with suspended or emulsified substances is not novel. What is new, however, is the skilful combination of the two methods in one container so that they complement each other perfectly (Fig.1 and 2). Conventional Dissolved Air Flotation (DAF) was replaced through an Induced Gas Flotation (IGF) with rotating ceramic disks generating microbubbles in the range of DAF. The energy requirements necessary for the flotation could thereby be clearly reduced (up to 90%).

The optimised arrangement of the ceramic disks used for the flotation and the ceramic membranes used for the vacuum filtration prevents that the substances discharged by flotation hinder the filtration.

The fouling of the ceramic membranes is thereby clearly reduced. The process can be implemented in technically interesting sizes in a container construction method.

The combination of both methods in one container goes hand in hand with simplified plant engineering and considerable space savings.

Through the flotation, fine particles, emulsified drops and colloid organic substances are continuously transported to the water surface of the tank together with the gas bubbles. The ceramic membranes are arranged in an area in which the content in colloid substances is clearly reduced on account of the flotation. The membrane stage can thereby be operated for a longer *Dipl.-Ing. Johanna Ludwig Dr.-Ing. Matan Beery Dipl.-Ing. Lucas León akvola Technologies Fasanenstr. 1 10623 Berlin Tel. +49 30 314 75656 Fax +49 30 314 26915 Mob. +49 163 3617076 ludwig@akvolution.de ** Prof. Dr.-Ing. Siegfried Ripperger Institut für Mechanische Verfahrenstechnik, TU Kaiserslautern

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time span with a low pressure difference without cleaning. Every now and then, an effective backwashing is possible.

The „akvoFloat“- technology was examined and tested for water treatment with a pilot plant under realistic conditions with the water from a ship channel in Berlin over several months. In the course of this, the effect described on top was demonstrated. Without switched on flotation, a clearly reinforced fouling of the ceramic membranes was observed. It can be expected that the data determined with this test series are also achieved with bigger plants concerning the precipitation and the specific throughput performance for the examined application.

2. Description of the pilot plant The pilot plant of akvola Technologies has a capacity of at least 12m3/d. Key element is a 300 l tank (B2), in which flocculation, flotation and filtration take place. Fig. 1 shows the plant flow scheme.

After passing through a 300 μm sieve for the removal of coarse sand and other big particles, the raw water arrives in the feed tank B1. Before tank B2, the flocculating agent FeCl3 (Iron(III)chloride) is added turbulently inline, in the subsequent flocculation track, the flocs grow further under addition of a flocculation aid (polyacrylamide) for stabilisation. The flocculation time amounts to less than 10 minutes.

The flocs and suspended matter come in

Flotation unit Filtration Membrane

Fig. 1: Plant flow diagram of the pilot plant

Fig. 2: Image of the pilot plant (viewed from the side)

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The temperature corrected specific filtrate stream (in l/m2h) is determined according to the above equation with the actually measured specific filtrate stream (l/m2h) and the water temperature (T in °C).

Temperature [°C]

Temperature

Acquired data averaged per month

Fig. 3: Values for temperature, pH and the content of „Total Organic Carbon (TOC)“, averaged over one month respectively

contact with the induced micro-bubbles in the flotation zone and rise together to the water surface, where a flotate layer forms. The bubbles are generated through ceramic diffusers with an admission pressure of the air of 2 bar and a flow rate of 50 Nl/m3 in the water.

The average bubble diameter results at approx. 50μm. The flotate layer is continuously hydraulically removed from the tank. Below this, there are submerged plate membranes from aluminium oxide with a pore size of 0,2μm. With a frequency-controlled gear pump (P2), the permeate is drawn off from the tank at constant permeate flow via the membrane surface and is collected in the permeate tank B3.

For the backwashing of the membrane the rotation direction of the pump P2 is reversed. The transmembrane pressure (TMP) will be continuously measured with a pressure transducer while the volume flows are measured with a rotameter and/or magnetically induced flow meter. Pump P3 is used for the draining of the tank and for the removal of the residues after a backwashing. The maximum filtration-TMP amounts to 0,5 bar, when exceeded, a backwashing is automatically initiated. The backwash effectiveness can be increased via an air scouring system. A backwash lasts 2 minutes as a rule, at a pressure of 2.1 bar and a volume flow of 1.2 m3/h.

The specific permeate stream is standardised with the following equation concerning the temperature, in order to guarantee comparability between the tests and with other applications /1/.

3. Tests with the pilot plant at the Landwehrkanal in Berlin In summer, 2013, tests were carried out with the pilot plant described above at the Berliner Landwehrkanal. Here, in particular the fouling behaviour and the cleanability of the membranes were examined. Fouling is caused through the forming filter cakes on the membrane plates of the filtration stage. Particles of a size smaller than the membrane pores, deposit on or in the pores at the beginning of the filtration. Bigger ones cannot penetrate into the pores and, rather, they deposit on the surface. With a nearly steady permeate stream, both lead to an increase of the trans-membrane pressure (TMP). The objective was to keep the TMP increase as low as possible. The test planning is based on a Directive of the American Membrane Technology Association (AMTA) /2/.

3.1 Water parameters of the raw water The water of the Landwehrkanal was characterized for the period of the long test duration by strong fluctuations in the total carbon (TOC, Total Organic Carbon) and in the turbidity. The low flow velocity in the duct (ca. 10cm/s) and the low duct depth of 2 m contribute to summery algae blooms. In addition, the duct is used with strong rain as a relief for the municipal sewage network.

Nearby the water extraction point, there was a well-used sluice, which significantly influenced the turbidity of the raw water.

During the test period, the turbidity value was > 10 NTU. Fig. 3 respectively shows the averaged over one month values of temperature, pH value and TOC. 3.2 Influence of flotation At the beginning of the test series, an operation without flotation and merely with the filtration was set, so as to demonstrate the positive effect of the combination of both process steps. The TMP- development without flotation at a flux of 112 l/m2h is shown in green in Fig. 4. The filtration started at a TMP of -0.15 bar (vacuum pressure because of the out-in operation of the membranes). Without flotation, the maximum TMP of -0.5 bar was already achieved after four hours. Within two hours a TMP of almost -0.3 bar was achieved that subsequently rapidly dropped.

Subsequent backwashings showed no effect and the TMP could not be improved any more. This so-called irreversible fouling could be removed through a chemical cleaning of the membrane.

With flotation

Transmembrane pressure [bar]

Without flotation

Filtration time [h:mm]

Fig.4: Time profile of the transmembrane pressure difference when the plant is operating without (green) and with activated (blue) flotation

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Avg. TMP decline

TOC removal

Total recovery

Fig.5: Process parameters and TOC removal during operation without (green) and with (blue) flotation

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Transmembrane pressure [bar]

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Filtration time [hh:mm]

Fig.6: Sludge layer in the tank during operation with flotation

Fig.7: Time profile of the transmembrane pressure difference during operation of the plant with flotation and chemical cleaning of the membrane

Under application of the flotation, the temporal TMP development was substantially improved. This fact in itself is known in the literature, e.g. /3/. Then, in the test series, in particular the backwash strategy was examined and a two hour-cycle turned out as the best. As can be seen in Fig. 4 in blue, the TMP after two hours, at the same initial value, amounted to only -0.24 bar and the maximum-TMP was not achieved during the test period of 9 hours. The introduction of a periodical backwashing and the flotation had a further positive effect. The plant could be operated with an approximately constant TMP of -0.28 bar and a steady filtrate stream. Periodical backwash in connection with the flotation prevent the formation of an irreversible blockage on and in the membrane and permit a quasi-continuous filtration operation.

The turbidity of the feed was always reduced by 95 %, something that led to filtrate-values of 0.3-3 NTU. Fig. 5 summarises the positive effects of the flotation on the total process. For, besides a more advantageous TMP development, the filtrate quality was also better, because small particles and organic matter were already removed before the filtration. That’s why the average TMP increase amounted to only 0,009 bar/h, in contrast to 0.022 bar/h.

The TOC removal (Total Organic Carbon) increased from 32% to 40%. The major part was removed through the flotate layer (see Fig. 6). In addition, the total water yield could be increased.

The air scouring of the membrane during a backwash was activated now and then in the form of an impulse to support the removal of the deposits on the membrane and to increase the backwash effectiveness.

different chemical cleanings were examined. After six hours of filtration (Label 1), a combined CEB/CIP was carried out. Citric acid (2100 ppm) was initially introduced with a CEB, afterwards, a CIP with the same concentration took place (exposure time 120 minutes). During the subsequent filtration, a strong TMP deterioration occurred, since the inorganic components were partially dissolved and therefore could penetrate into the membrane. Nevertheless, the previous starting-TMP could almost still be achieved in the subsequent backwashing. After another ten hours (Label 2), the following were carried out: a CEB with Sodium hypochlorite (1000

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3.3 Chemical cleaning After a certain filtration time, a chemical cleaning must be carried out since, in spite of regular backwashings, fouling appears during long operating times. The period of time until a chemical cleaning is necessary must be determined experimentally.

Nevertheless, it should normally not amount to less than to less than 24 hours. For the chemical cleaning, two execution manners were developed: a) Chemical Enhanced Backwash (CEB) and b) Chemical Cleaning in Place (CIP).

Often a combination of both methods is carried out /4/, /5/. As chemicals either acid, bases or oxidizing agents can be used. Here a base, e.g. sodium hydroxide, removes primarily organic fouling and an acid, e.g. citric acid, inorganic (for example, iron deposits as a result of the flocculant).

Fig. 7 shows the TMP course of 26 hours of filtration with a flux of 110-120 l/m2h. Within this period, the modes of action of

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ppm free Cl), 30 minutes of CIP with citric acid. The subsequent TMP was good, both with regard to the initial value as well as with regard to the development. Seven filtration hours later (Label 3) a 60-minute CIP took place with citric acid, which included an intensive intermixing of the solution with the air scouring equipment.

The effect was similarly good as with the second cleaning.

3.4 Summary of the test results The operation of the pilot plant has shown the high effectiveness of the flotation as a preliminary process of the filtration in the respect that less fouling and a better yield could be achieved on the basis of reduced irreversible fouling.

A periodical backwash (every 2 hours) and a flux of 110-120 l/m2h were optimum with the given conditions. In addition, a cleaning consisting of an alkaline CEB and an acid CIP has shown to be effective and has caused a complete cleaning of the membrane.

The test phase has shown that the akvoFloat- technology is suitable for the treatment of organically polluted surface water and that more than 60% of the organic matter is removed. The turbidity is removed almost completely.

4. Potential application areas of the “akvoFloat” technology The application areas of the “akvoFloat” technology are varied and not limited to the treatment of surface water.

Hereinafter, five potential application areas are described in more detail.

4.1 Pre-treatment of raw water for drinking water production by means of reverse osmosis Nowadays, reverse osmosis is the preferential method for drinking water production from brackish water and sea water. In many countries of the earth, such plants are being operated and their number will continue to rise. The “akvoFloat” technology was originally designed for pre-treatment of sea water desalination via reverse osmosis (RO). This pretreatment of the raw water is necessary to avoid deposits of finest particles, colloids and microorganisms on the RO membranes and to guarantee a service life of the membranes of several years. The suppliers of reverse osmosis membranes substantiate their requirements for water pretreatment on the basis of empirical values that are to be kept to for the operation of the membranes. Also, the warranty in connection with the RO membranes is subject to the fulfilment of the requirements.

Because the raw water quality can strongly differ in different locations and is also subject to strong temporal variations,

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treatment processes are in demand that do justice to the highly fluctuating inlet conditions. Hence, multistage processes are often implemented. The combination of the flotation and microfiltration within an akvoFloat plant is a multistage process in an especially compact construction method, suitable for application. The test results on the Landwehrkanal in Berlin show that the implemented treatment process with fluctuating inlet conditions and with a high organic pollution level, as may occur, e.g., climate-induced with an algal bloom in public waters, guarantees a treatment of the raw water that is sufficient for RO applications. Hence, it is suitable for the pretreatment of sea and brackish water for drinking water production by means of reverse osmosis.

4.2 Pre-treatment of raw water for pure and ultrapure water production by means of reverse osmosis The steadily rising demands on quality for products have the consequence that in the industry the demands on quality of process water often go beyond the requirements for drinking water. The supply of such pure and ultrapure waters is the main application area of reverse osmosis in the industrial countries that have sufficient drinking water resources.

Accordingly, reverse osmosis is increasingly used to meet the industrial demand for pure and/or ultrapure water. One generally calls processed water pure water.

The designation ultrapure water is used if, by means of treatment processes, foreign matters was extensively removed from the water. The foreign matter includes, among other things, minerals, dissolved organic matter, colloidal contaminants as well as micro-organisms and particles. Ultrapure water is required among other things in the pharmaceutical industry, the electronic industry and in power stations as boiler feed water. The softening of drinking water for households and municipalities is still more of a niche application. The application of reverse osmosis is necessary if the content in salts and further dissolved solids in the raw water exceeds the value allowed for drinking water or if pure and/ or ultrapure water with a low content in dissolved solids is required. For the preparation of ultrapure water, additional processes are usually still applied upstream of the reverse osmosis, such as for example ion exchangers for the separation of the remaining ions, an ultrafiltration for the further reduction of the colloidal substances content and a microfiltration on the “Point of use” for the guarantee of a very low particle quantity. In this process chain, application possibilities arise in the industrial sector for akvoFloat plants for

the pretreatment of raw water for the pure and ultrapure water preparation by means of reverse osmosis.

4.3 Treatment of process water and waste water for reuse The industry uses a large part of the available water resources among other things as cooling water as well as for solvents and as cleaning agent. In general the trend towards water recycling exists with the objective to reduce the environmental impacts and to increase the cost efficiency. Depending on local regulations, fresh water fees and waste water fees can be reduced. In the case of membrane processes, an increased water quality often also means improved product quality. The separated substances can also often be purposefully supplied again to a utilisation.

Hence, many industrial firms have drastically reduced their fresh water demand during the last years by a recycling of the process waters. These include, for example, the paper mills, the breweries and food processing operations. Also in metalworking and machining and in chemical operations, water is used more and more often in closed loop plants. Closed water loop plants reduce the water consumption, allow the recycling of valuable materials, minimise the waste water volume and also reduce the energy requirements in connection with the recirculation of hot waters. In numerous cases, the used water is treated with membrane processes.

For akvoFloat plants, there are good application possibilities in the field of process and wastewater treatment when favourable operating conditions arise for a flotation, i.e. if hydrophobic substances, such as for example oils and fats, soot, coal should be separated. Such application areas can be found in the food industry, chemistry, metal processing and environmental engineering. In connection with the addition of various substances e.g. of powdered activated carbon for the adsorption of organic compounds dissolved in trace amounts ozone for oxidation of compounds as well as coagulants and flocculants, the functionality of the plant can be enhanced without big expenditure.

Often, a sufficient water quality for a new reuse can be achieved with microfiltration or ultrafiltration, like is implemented with an akvoFloat plant. If a low content of dissolved substances is required, the effluent water quality mostly allows that a reverse osmosis can be added downstream without further treatment steps. A safe disinfection of the effluent water can be achieved through a downstream UV irradiation. This has an especially good effect after the membrane filtration, as, through the microfiltration, all components that cause turbidity were removed.

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4.4 Processing of oil-containing waters

4.5 Separation of biological matter from waters

In the oil and gas industry as well as in production engineering and environmental engineering, flotation is used for the treatment of oily waters. Here, oil or other water-immiscible hydrocarbons are emulsified in the water and form an oil-in-water emulsion (O/W-Emulsion). In connection with such waters, there are good chances for an application of akvoFloat plants.

Here, it must be distinguished between stabilised and not stabilised emulsions.

With a stabilised emulsion natural or artificially made and added interface-active compounds (surfactants) are adsorbed on the droplets, owing to which the deposition on phase interfaces (solid surfaces, further oil droplets and air bubbles) is hindered extensively. Accordingly, the phase separation through flotation is thereby also more complicated. Many additives which are added to water, for other purposes in practice, have in addition also an emulsifying effect. These include, e.g., cleaning agents, corrosion inhibitors, lustres and biocides.

Through the addition of a demulsifier (also called emulsion splitting agent or emulsion separating agent) adsorbed interface-active compounds can be displaced or influenced so that their stabilising effect on the emulsion is voided. The emulsion is thereby destabilised and a separation of the oily phase through flotation is possible.

In this manner e.g. the akvoFloat plants can be applied on oily washing waters of the food industry and production engineering.

Emulsions with the finest droplets may also be stabilized by electrical surface charges. In this case, a destabilization of the emulsion can also be achieved through a change of the pH value through addition of an acid or alkali.

Demulsifiers are often added in the influent stream in combination with flocculants so that macroflocs of fine oil droplets form, which are well floatable.

Here, it must also be considered that overdosing of demulsifiers can foster renewed emulsifying.

Oily waters occur among others as a so-called Produced Water in oil extraction and gas extraction, as washing waters in connection of processes of surface treatment (coating, spraying, galvanisation etc.), as cleaning solutions during parts and equipment cleaning and as flushing waters.

The tests for water treatment with an akvoFloat plant at a canal in Berlin have shown that flocculated organic matter with a high content in micro-organisms (e.g. algae, yeasts and bacteria) can be separated effectively through flotation and the downstream membrane filtration. H. Bennoit and C. Schuster /6/ describe the advantageous use of a degassing flotation for separation and concentration of excess sludge from an aerobic biological wastewater treatment plant in a paper with the title „Fortschritte des Flotationsverfahrens in der Abwassertechnik und Schlammbehandlung“. In connection with the flotation, cost savings are indicated that could be even more significant with the use of an akvoFloat plant.

Application possibilities arise in connection with the aerobic biological waste water treatment from this knowledge and the present experiences which are not yet being used nowadays. In the course of this, combinations with the membrane bioreactors that are increasingly being used in the waste water technology are also conceivable.

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5. Outlook The akvoFloat technology is currently being tested for the pretreatment of sea water for the reverse osmosis and for the oil -water separation with Produced Water. Results for this purpose will be published shortly.

Bibliography /1/ Allgeier S., Alspach B., Vickers J. (2005): Membrane Filtration Guidance Manual. US Environmental Protection Agency /2/ AMTA Guideline; American Membrane Technology Association (2011): Pilot Testing for Membrane Plants, November 2011, Florida USA. /3/ Dramas L., Croue J.-P. (2012): Algal Organic Matter (AOM) Fouling of Ceramic Membranes”, Expert Workshop Red Tides and HABs: Impact on Desalination Plants, MEDRC, Oman. /4/ Edzwald James K., American Water Works Association (2010), “Water Quality & Treatment: A Handbook on Drinking Water”, McGraw Hill, Chapter 11, p. 793-793. /5/ Raúl Pérez-Gálveza, Emilia M. Guadix, Jean-Pascal Bergé, Antonio Guadix: “Operation and cleaning of ceramic membranes for the filtration of fish press liquor”, Journal of Membrane Science, November 2011, Vol. 384 (1-2), pp 142-148. /6/ H. Bennoit und C. Schuster: Fortschritte des Flotationsverfahrens in der Abwassertechnik und Schlammbehandlung. Ripperger, Siegfried. „Der ProcessNet Technical Committee –„Mechanische Flüssigkeitsabtrennung (MFA)”„ Chemie Ingenieur Technik 79.11 (2007): 1748-1752.

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Separation processes on ships and offshore installations

S. Ripperger*

Introduction Separation processes for the wear protection of machines and the treatment of oils and fuels have been part of the equipment of ships with a motor drive for several decades. On account of increased internationally valid environmental standards for the protection of the seas, the application of other processes on ships became necessary in last decades. Also with the offshore-oil extraction, the application area of separation processes on the open sea was substantially extended.

Processes were added, hence, for the treatment of water, oils and gases on offshore drilling and extraction rigs.

The requirements for the plants are high. They must reliably fulfil the requirements concerning the separation, generally exhibit high throughput rates and be designed very compactly at the same time, since the space on ships and platforms is limited. Moreover, the plants must be robust and guarantee a high operational reliability. In this case, the definition of the separation limit often resembles a tightrope walk since, though the separation improves with its change to a lower concentration or smaller particle size, however, the effort and with it the overall size is substantially increased with respect to the throughput.

On account of the increasing use of the seas and the associated pollution, a further growing need of separation plants on the seas is to be expected.

International conventions for the protection of the seas The International Maritime Organization (IMO), a sub-organization of the UNO, decided in 1973 the worldwide applicable MARPOL agreement /1,2/ for the protection of the marine environment.

The agreement was supplemented by two protocols and six appendices. The appendices regulate the following kinds of contamination in connection with the ship operations.

Annex I: Prevention of pollution by oil (came into force in 1983), * Prof. Dr.-Ing. Siegfried Ripperger Lehrstuhl für Mechanische Verfahrenstechnik Technische Universität Kaiserslautern Gottlieb-Daimler-Str. 67663 Kaiserslautern Tel.: 0631-205-2121 www.uni-kl.de/MVT

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Annex II:

Prevention of pollution by noxious liquid substances (came into force in 1987), Annex III: Prevention of pollution by harmful substances carried at sea in packaged form (came into force in 1992), Annex IV: Prevention of pollution by sewage (came into force in 2003), Annex V: Prevention of pollution by garbage from ships (came into force in 1988), Annex VI: Regulations for the prevention of air pollution from ships (came into force in 2005).

In order to ensure established discharge requirements technical equipment aboard is specified in the annexes, among other things. Moreover, important operating procedures aboard are to be documented, such as for example the treatment and the whereabouts of separation residues such as oily bilge waters as well as waste.

According to Annex IV, the discharge of sewage from ships is generally prohibited. Exceptions apply when the ship has a plant for the treatment or processing of sewage or if the discharge is done from a waste water-collective tank at a distance of more than 12 nautical miles from the nearest shore.

The recently re-amplified awareness about marine pollution from plastics shows, that the present regulations are not sufficient. Other measures are necessary to protect effectively the seas against a contamination. Here, it must also be considered that the transhipment of goods at sea continues to rise. Thus, an increase by 1% was registered in 2012, compared with the previous year. This growth is far exceeded by the cruise industry in recent years. Compared with 2011, German citizens booked 11% more cruises in 2012. According to estimates of the UNEP (United Nations Environmental Program), approx. 120,000 tonnes of oil get in the Mediterranean Sea, for example, due to passing on the Mediterranean Sea by annually about 200,000 ships.

Greenpeace scientists assume an even a far greater amount.

Hereinafter, known application areas of separation processes on ships and technical installations on seas will be briefly described.

Application areas of separation processes on ships and technical installations on seas Fresh water supply While, on freighters, the drinking water supply of the crew can be ensured with seawater evaporators that are operated with the waste heat of the engines, this heat source does not suffice by far for the supply of the passengers and crew on cruise ships. On big cruise ships more than 1500 m3 drinking water are often required daily, which are gained from the sea by means of evaporation and/or reverse osmosis. On this occasion, one must consider that cruise ships with more than 1000 passengers today are no longer a rarity. The biggest cruise ships worldwide at the moment, the “Oasis of the Seas” and the “Allure of the Seas“ are able to accommodate 5400 passengers and approx. 2000 crew members. Both ships were built on the STX Europe shipyard Torku, Finland.

Waste water treatment on cruise ships For the disposal of the waste waters, modern cruise ships have a complete biological sewage treatment plant aboard.

They are mostly equipped with a membrane bioreactor (MBR), in which the contaminants are degraded and the activated sludge is separated from the water by means of membranes. The originating surplus sludge is further dewatered with filter presses or decanters and afterwards is burnt in the incinerators available on the ships.

Incinerator on cruise ships According to a provision for the prevention from 1988 of the contamination through ship waste, no waste may be dumped into the sea within special areas, including the North and Baltic Seas. To do justice to the requirements, big cruise ships have a waste incineration plant with boilers with a thermal output of approx. 2000 kW aboard, where combustible waste and dehydrated sewage sludge and organic waste is incinerated. The residual ash and other inorganic waste are delivered in the harbours and are disposed of there.

Exhaust gas purification of the ship engines The exhaust gases of the big ship engines are not being purified up to now.

Here, one must keep in mind that the engines are operated with heavy oil that results as a residual product during the

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with a residual oil content of maximal 15 ppm, in some special protective zones 5 ppm, can be discharged into the sea. It is already being discussed to define the lower limit value in general. The oil sludge is either incinerated in the main engine with the fuel (mostly heavy oil), or it is disposed of ashore. According to volume of the incurred bilge water and/or size of the ship, plants are offered with capacities between 0.1 and 10 m3/h. The limit value of 15 ppm can often be kept with centrifuges in the form of disk stack separators.

One system that also allows the observance of the limit value of 5 ppm residual oil content is illustrated in Fig.1. The GEA Westfalia Separator Bilge Master includes an adaptive adjustment of the throughput to the water temperature. For the observance of the limit value of 5 ppm, the system works with a diminished throughput. Should the throughput correspond to the nominal value of 15 ppm at 5 ppm, an adsorption filter is activated. Systems are being offered for throughputs of 500, 1200, 2500 and 5000 l/h.

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Bilge water treatment In the lowest space of a ship, the so-called bilge, an oil-water mixture accumulates that is still contaminated with fuel and cleaning materials as a rule. It is pumped out every now and then. In the inland waterway transport, there are boats in use which collect bilge waters, used oil and oil-contaminated waste from ships. The bilge water is mostly processed so that it can be discharged into the waters. A disposal is also offered ashore in- fixed installations or by special road vehicles.

Plants must be installed aboard sea ships which process the bilge water according to the legal requirements. The clear water

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crude oil processing in the refineries. Mostly, this oil contains a high sulphur-content. The environmental impact originating thereby during the combustion is being discussed controversially. In particular also because time spent in port, the energy requirements on the ships must be covered through running ship diesel engines, owing to which not unimportant volumes in sulphur dioxide, nitrogen oxides, soot and particulate matter are emitted in part into urban areas. Hence, it has been suggested during the last years to set up access to shore power for ships, by means of which their electric energy requirements can be covered at shut-down motors.

However, an electricity supply from the shore is possible up to now only in very few harbours. In Germany, the possibility exists in the seaport of Lübeck.

The IMO leaves the kind of the solutions for the reduction of sulphur emissions to the shipowners. It is vital that the mandatory standards according to MARPOL Annex VI are fulfilled. At European level, the pollution through sulphur dioxide was further reduced. The allowed sulphur content in the fuel for sea ships which moor in the EU was reduced at the beginning of 2010 to 0.1%, while on the open sea, in the North and Baltic seas, up to 1% are allowed (see also /3/). From 2015 onward, only ship fuels with a sulphur content of less than 0.1 percent may be used in the North Sea and the Baltic Sea as well as along the North American coast. In diesel fuel for passenger cars and trucks, only a sulphur content of 0.001% has been allowed in Europe since 2009. Also the nitrogen oxide emissions should be clearly reduced for ships produced after 2016.

Against the background of the increase of environmental requirements in the waterway transport, environmentally friendly fuels increasingly get to be part of the discussion. A possibility for the achievement of future environmental requirements in waterway transport is the use of natural gas. While a use of liquefied gases was not permitted up to now, a transition directive of the IMO came into force in June, 2010, which permitted the use with approval of the flag state. Since then, there is a steadily rising interest to be identified concerning the ship fuel of natural gas. A form of use is the conversion to LNG (Liquefied Natural Gas), which will be discussed in more detail in one of the following sections.

Ballast water treatment Ballast water is taken up for stabilisation by sea ships in ballast tanks or in hollow cavities between doubled side walls of the ship hull in order to guarantee the seaworthiness during empty runs.

It is taken up as a rule in coastal areas and is discharged again in the port of destination, possibly on the other side of the world.

Thereby, numerous organisms are deported into foreign ecosystems. This is partially connected with disastrous results /4/. To address the “environmental pollution” by ballast water, the IMO had adopted a Ballast Water Convention in February, 2004 /2/.

This calls by 2016 for that ballast water be treated aboard every ship through corresponding ballast water treatment systems prior to discharge into the marine environment, so as to satisfy the standard required.

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Fig.1: GEA Westfalia Separator BilgeMaster

G. BOPP + CO. AG CH-8046 Zurich Phone +41 44 377 66 66 info@bopp.ch

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Fig.2: The system BallastMaster ultraV of the GEA Westfalia Separator Group

During the last years, numerous systems were developed which ensure that the standard is fulfilled. This is also guaranteed through the approval procedures of the IMO and/or of the national permit authorities. The plants comprise two essential stages as a rule: 1. A mechanical separation stage for the separation of microorganisms and sediments with a separation limit in the range of 20-50 μm, and 2. a disinfection stage for the killing of microorganisms which are not separated in the first stage.

In the second stage, disinfectants are added e.g. (e.g. hydrogen peroxide, peracetic acid, chlorine compounds) or these are produced in situ (e.g. by means of electro-chemical ozone generation or chlorine electrolysis). A physical disinfection is present in this stage when a short-wave UV-irradiation is employed. Its disinfecting effect is where appropriate reinforced by a combination with ultrasound or a substance with biocidal action. Systems have been developed that can treat up to 3000 m3/h water.

Fig. 2 shows the system BallastMaster ultraV by GEA Westfalia Separator Group for a crane lifting vessel by Hochtief for the installation of offshore wind turbines.

The plant includes a filtration and a UV-C treatment of the water and can put through 500 m3/h. It has the BSH type-approval according to IMO MEPC. In a study by Frost & Sullivan /5/, the global market for treatment systems of ballast water is estimated at a turnover of 466.6 Million Euro in 2013. It is expected that the market will grow by 2023 at an average annual growth rate of 21 % to 3.14 billion US dollars. The retrofit market is expected to take a significant share of global sales and reach its highest demand in 2018. Bulk carriers, as well as oil and chemical tankers, are the most important end-users.

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Fig.3: Representation of the Floating Liquefied Natural Gas facility (Floating Liquefied Natural Gas – FLNG) Prelude of Shell

Oil treatment and fuel cleaning on ships Since the mid-twenties of the last century, centrifuges have established themselves in the form of plate separators for the cleaning and dewatering of oils and fuels in marine engineering. Nowadays, they are used for the treatment and supply of lubricating oils and insulating oils as well as for the treatment of heavy oil, which serves as a fuel. The large range of models enables it to cover throughputs during a continuous treatment over a range of up to 80 m3/h. Adapted temperature and dwell time within the centrifuge are decisive for the separation.

For the two biggest cruise ships mentioned above, the “Oasis of the Seas” and “Allure of the Seas”, the GEA Westfalia Group delivered in each case six separators for heavy oil treatment, in each case six separators for lubricating oil treatment of the three main drives and three auxiliary drives as well as a separator for cleaning of bilge water, hence a total of 13 separators per ship.

Treatment of water on offshoredrilling rigs Treatment plants for water for crude oil extraction are required worldwide to fulfil the quality standards for discharging the drilling and formation water resulting in oil extraction. The limit values of the International Maritime Organisation (IMO) and/or those of the national legislators are also valid for discharging these waters. The drilling water and formation water resulting on the offshore rigs is often also used as injection water to maintain the reservoir pressure for an optimum oil production. The drilling water contaminated with sand, oil and chemicals, which surrounds and cools down the drilling head and the drill rod assembly, is normally roughly purified and again pumped to the drilling bit. A portion enters the bilge of the platform during the cleaning of the system and through leakage or rising gas

bubbles via drains. A treatment for further usage or before recirculation into the sea is mandatory. For this purpose, disk stack separators are also used among other things, like on ships. For treatment of formation water mixed with oil, coalescence separators and flotation plants, often in combination with centrifuges and/or filters, are used. The application of ceramic membranes is being reported on in/6/.

Effects of „Liquefied Natural Gas (LNG)“ on waterway transport Among the fossil fuels, natural gas (NG - Natural Gas) has by far the highest growth rates. Big new natural gas fields in different parts of the world and the shale gas in the USA have led to that the gas market got moving and the gas prices uncoupled themselves from the oil prices.

This development led to that it paid off to liquefy natural gas more and more and to offer it as “Liquefied Natural Gas (LNG)“. Accordingly liquefaction plants were planned or were already established in many countries. In these, natural gas is liquefied through cooling with a high energy input to -162 °C. About 12% of the original energy content of the gas is used for this. Then the density is increased compared with the gas at normal temperature by approx. the factor of 600 and the volume decreased accordingly, so that the transport by ship pays off.

It is expected that a global LNG trade by ship will increasingly develop, which functions similarly to the trade with crude oil. Differently than with a supply via pipelines, competition can originate from this between the supplier countries, owing to which the prices for natural gas are also influenced. It is expected that LNG will become increasingly important for Europe’s energy supply.

During the liquefaction, sulphur and other impurities are also removed from the gas, among other things. The liquefied natural gas is transported among other things by ship to its destination where it

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can be transported further by truck, train or bunkering vessel. In the course of this development, the infrastructure for liquefaction and for transport of natural gas is being further developed in many countries. Thus, the first LNG tanker has unloaded LNG in 2011 in a previously established terminal in Rotterdam. At the moment, there are approx. 370 LNG tankers travelling on the seas and their numbers will continue to rise.

In the shipping industry, it is expected that the maritime diesel oil will increasingly be replaced through LNG. In many major ports, among others in Emden, Hamburg and Bremerhaven, there are terminals in planning with which ships can be supplied in future with LNG as a fuel. In order to promote the transition, the “LNG-Initiative Nordwest“ was founded /7/. Methane fortifies the greenhouse effect in the atmosphere approximately 25 times stronger than carbon dioxide (per kg).

One milestone in this development is the launch of the world’s biggest ship hull in December 2013 at the shipyard of Samsung Heavy Industries (SHI) in Geoje, South Korea. The 488-meterlong ship hull belongs to the floating LNG facility (Floating Liquefied Natural Gas – FLNG) Prelude of Shell. Upon completion, the Prelude FLNG will be the largest floating facility ever built and produce approx. 3.6 million tonnes in liquefied natural gas (LNG) per year about 200 km off the west coast of Australia (see Fig.3). It allows the extraction of natural gas on the seabed, to liquefy it on board and then to pump it directly into ships, which then transport the LNG to consumers or customers. This eliminates long pipelines to shore facilities, whereby gas resources can be developed whose development is not practical from the mainland.

In addition, the surrounding water is also employed for cooling.

The Prelude FLNG- facility should remain in operation off the west coast of Australia for about 25 years.

Information on the German shipbuilding and offshore suppliers Information on the situation of the German shipbuilding and offshore suppliers was recently published by the VDMA /8/. In this association, companies have joined up together more than 30 years ago in a working group Marine and Offshore supplier industry. Today, it has approximately 200 member companies.

They generated sales of 11.6 billion euros in 2012, with about 68,000 employees. The export rate increased to 74 percent. After a dramatic decline of the shipbuilding orders from October, 2008 onwards and the slump at the suppliers in 2009, the incoming orders have increased again. According to assessment of the VDMA, the industry has coped well with the profound turmoil in the global shipbuilding industry.

Beside the big three shipbuilding nations of China, Korea and Japan, developing shipbuilding countries are coming to the forefront. This includes, for example, Brazil, whose growth is based on the demand from the oil segment and gas segment. In 2012, 1.977 sea ships were ordered worldwide, of this 651 in China, 231 in South Korea, 361 in Japan, 66 in Brazil, 11 in Russia and 148 ships in the EU-27, 10 thereof in Germany.

The foreign business of German suppliers was distributed in 2012 at 39 % in Asia and 33% in other European countries. China, in spite of clear decline, is still the biggest foreign market with 17% of the exports, followed by Korea with 10 %. New markets in Asia achieved clear increases. In the background are the projects coming from the offshore boom in Singapore and India, however, also the projects of the young shipyards on the Philippines.

Furthermore, the industry is observing the efforts in Asia and South America to develop their own supplier industry. Therefore, the objective of German suppliers is to keep the existing edge in the technical and logistical field and to further expand it through

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innovations and service. The know-how protection is becoming increasingly important, also within cooperation with local partners.

The offshore segment is a future market for the shipbuilding industry and supplier industry. Thus, numerous supply vessels and installation vessels were built during the last years for the offshore-wind industry as well as platform providers and ships for the offshore oil and gas industry. The high growth potentials of the offshore sector result among other things also from the fact that big oil reservoirs and gas reservoirs are only still to be found on the sea, hence offshore. They are found and developed in ever deeper water or even ice-covered regions. Thus, the Brazilian enterprise of Petrobras wants to pierce through an up to 2,000-metre-thick salt layer during the development of new oil fields off the Brazilian coast. Partially the oil deposits are in 7000 metre of depth. In the deep water, above all the high pressures in the seabed as well as the long vertical extraction pipes in the water represent high technological challenges. It is predicted that complete extraction plants and production facilities will be placed directly on the seabed in future and thus are removed from surface influence.

Another area is the offshore-wind industry. Besides the political framework that is still unresolved in the long term, the offshore-wind industry distinguishes itself through pioneering works.

These include the challenges during installation and construction of offshore wind farms as well as their operation and maintenance.

In 2012, Siemens counted for the offshore wind power on an installed capacity of more than 80 GW in Europe by 2030. This corresponds to the output of a bit more than half of the power plant fleet currently installed in Germany. Only six percent of these 80 GW are currently developed, according to Siemens.

Delays with the connectivity of offshore wind farms to the electricity grid as well as disasters on drilling rigs show that the offshore sector not only entails big potentials but also many challenges and possible environmental hazards.

The commitment of German suppliers in the offshore oil and gas industry, which das been increasing for several years, will continue to grow. The demand for high-quality and reliable equipment is great. High availability, quick response times and high environmental standards and safety standards are competitive advantages of German enterprises in this area. Another focus of the German supplier industry is the power-saving and cost-saving and at the same time environmentally friendly operation of ships and offshore installations.

On the occasion of the trade fair of the maritime industry taking place from the 9th to the 12th of September, 2014 in Hamburg, it was also communicated by the trade fair company that an upturn in sentiment can be felt in the maritime industry /9/. One indicator of the sentiment is, among others, the positive shipbuilding activities.

Numerous shipping-lines use the currently low price level and are getting ready for the next ship orders. Nevertheless, the financing of the numerous projects is considered as problematic.

Literature: /1/ St. W. Douvier: MARPOL – Technische Möglichkeiten, rechtliche und politische Grenzen eines internationalen Übereinkommens. Dissertation, University of Bremen, Department 7, (2004) /2/ www.bsh.de: Homepage of the Bundesamtes für Seeschifffahrt und Hydrographie /3/ NABU Background Paper “cruise ships” (2011) at www.NABU.de/kreuzfahrtschiffe /4/ S. Ripperger: F&S Filtrieren und Separieren 23 (2009), No. 6, p. 314-314 /5/ Frost & Sullivan: Global Ballast Water Treatment Systems Market (Study M966, 2014) www.environmental.frost.com /6/ M. Ebrahimi, M. Aden, B. Schnabel, F. Liebermann, P. Czermak: F&S Filtrieren und Separieren 28 (2014), No. 1, p. 6-10 /7/ See: www.lng-nordwest.de /8/ VDMA: Deutsche Technologien für den Schiffbau und die Offshore-Industrie bewähren sich auf neuen Absatzmärkten, Press release of 25.06.2013 | id:1716745 /9/ See: www.smm-hamburg.com.

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Highlights 2014

Ceramic hollow fibre membrane technology for the treatment of oil-field produced water M. Ebrahimi, St. Kerker, S. Daume, F. Ehlen, I. Unger, St. Schütz, P. Czermak* Hereinafter, we report about the development and application of an innovative ceramic ultrafiltration hollow fibre membrane for oil/water separation during the treatment of “produced water” that results during oil production and gas extraction. Produced water is a complex mixture of dispersed and molecularly dissolved oil, suspended solid matter and other dissolved substances. It constitutes the biggest process water volume which occurs in the oil and gas industry and is difficult to treat on account of its composition. For its introduction into the environment, different purity requirements must be considered which mainly depend on whether the water is introduced onshore or offshore. Here, the residual oil concentration must be in the low ppm range. Hence, the development of efficient and effective cleaning processes and methods is a decisive prerequisite for the environmental compatibility of corresponding crude oil and natural gas production techniques and for their economic potential.

The ceramic hollow fibre membrane examined in this study (Mann+Hummel GmbH, Ludwigsburg, Germany) represents a new generation of an inorganic membrane which combines the advantages of a ceramic membrane material with the geometry of hollow fibre membranes.

1. Introduction “Produced Water” (PW) incurred during oil production and gas extraction consists of a complex mixture of dispersed and molecularly dissolved oil, other dissolved organic components, suspended solid matter, dissolved chemicals used and possibly heavy metals and naturally occurring radioactive substances. PW constitutes the biggest process water volume which occurs in the oil and gas industry and is difficult to treat on account of its composition. For its introduction into the environment, different purity requirements must be considered, which mainly depend on whether the water is introduced onshore or offshore. Due to the current environmental legislation, PW can only be initiated into the environment if the residual oil concentrations are in the low ppm range. Hence, the development of efficient and effective cleaning processes and methods is a decisive prerequisite for the environmental compatibility of corresponding crude oil and natural gas production techniques and for their economic potential. * Dipl.-Ing. Mehrdad Ebrahimi a, b Dipl.-Ing. Steffen Kerker a, b B. Sc. Sven Daume a, Dr.-Ing. Frank Ehlen c, M. Sc. Ina Unger c, Prof. Dr.-Ing. Steffen Schütz c, Prof. Dr.-Ing. Peter Czermak a, d * Reference author: mehrdad.ebrahimi@kmub.thm.de, info@ehc-memtec.de a Institute of Bioprocess Engineering and Pharmaceutical Technology – IBPT, University of Applied Sciences Mittelhessen, Gießen, Germany b ehc-memtec UG, Giessen, Germany c MANN+HUMMEL GMBH, Ludwigsburg, Germany d Dept. of Chemical Engineering, Kansas State University, Manhattan KS, USA

36

The cleaning of PW is usually carried out in multi-stage processes. In the first stage, a significant reduction of dispersed hydrocarbons and suspended solid matter is carried out, for example, through sedimentation processes in the earth gravity field or in the centrifugal field. In order to achieve the permissible limit values for the existing contamination in PW before introduction to the environment, downstream membrane processes, such as microfiltration (MF) and ultrafiltration (UF) processes, are necessary in further stages.

Here, the ceramic hollow fibre membrane (CHFM) examined in this study (Mann+Hummel) represents a new generation of an inorganic membrane, which combines the advantages of a ceramic membrane material with the geometry of hollow fibre membranes. In this study, the filtration performance of the CHFM is examined during the separation of oil/ water mixtures at a low trans-membrane pressure (TMP) of 0.5 bar. Here, the resulting permeate flow and the residual concentration of oil and organic components (TC, total carbon) are respectively measured. The fouling behaviour of the CHFM during the oil/water separation is recorded depending on the operating conditions and the composition of the feed stream to be cleaned, and the efficiency of physical and chemically supported backwash processes is described. In all investigations, a CHFM is used that has a pore size of d90 = 40 nm.

The oil/water mixture to be separated is produced on one hand as a defined model system (OMS, oily model system) with 30

ppm to 200 ppm initial oil concentration in the water and on the other hand is available as real PW from the dewatering of crude oil tanks (TDPW, tank dewatering produced water), with an oil concentration of between 1,000 ppm and more than 5,000 ppm. During the examinations, a separation efficiency was measured of > 99.5% with respect to the oil retention and of between 61% and 94% with respect to the total carbon concentration.

Through mechanical backwashing of the membrane, up to 80% of the initial permeate flow rate could be achieved during filtration operation. With chemically supported cleaning, the initial permeability of the new membrane was nearly achieved.

Overall, the investigated membrane system also demonstrated a stable operating performance in experimental periods of several days.

Hereinafter, the most important background on the creation, composition and purification of PW is initially summarised.

2. Challenges of PW 2.1 PW and its management PW is defined as wastewater that has reached the surface by washing out the deposits during crude oil production and natural gas extraction. In view of industrial applications, PW constitutes one of the biggest (waste) material flows that generally occur in processes of crude oil production and natural gas extraction. Here, the PW is often mixed with spring water that occurs naturally in rock strata [1]. At the moment, two measures are primarily used for the disposal of PW: reinjection

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into the raw material deposit itself and treatment for further use and/or introduction into the environment. Currently, more than 60% of the PW is introduced back into the deposits. The reinjection as well as the treatment of PW primarily require the separation of crude oil from other organic components and suspended solid matter [2].

The composition of PW and its physical properties vary significantly depending on the geographical location of its origin and depending on the extracted raw material [3]. Produced Water often contains different volumes of dispersed crude oil, additional undissolved and dissolved organic components, process chemicals, corrosion products, heavy metals, inorganic salts and naturally occurring radioactive components.

During crude oil production, three barrels of PW per barrel of crude oil occur on average [2, 4]. This ratio increases with increasing age of a deposit and, in older oil wells, reaches values of 7-10 barrels of PW per barrel of extracted crude oil [5]. Alzahrani et al. [6] estimate that, with worldwide crude oil extraction of 72,000,000 barrels/day, at least about 216,000,000 barrels/day of PW will result.

On account of this huge volume of PW, the manner of handling it is of great significance for the public and for legislation [7]. The potential for the introduction of PW into the environment or for its sensible recycling is being extensively discussed [8].

The statutory requirements for the purity of PW during introduction into the environment are very restrictive. Table 1 shows an overview of the permissible

residual crude oil concentrations during onshore and offshore introduction of PW in different world regions [9].

On account of these specifications, it is necessary to develop and/or improve innovative technologies for the purification of PW, not only in order to fulfil the increasing legal requirements with regard to environmental protection, but also in order to increase the economic efficiency of the purification processes and in order thereby to take advantage of a possible new source of water [10].

2.2 PW treatment The objective of the purification of PW is the removal of crude oil, other organic components and suspended solid matter and desalination. Usually multi-stage purification processes are used in order to achieve the required low crude oil concentration. Customary process technologies, which are used as the first and second stage during cleaning of PW are sand filtration, sedimentation, flotation, as well as apparatus hydrocyclones and separators, in order to significantly reduce the content of dispersed hydrocarbons and suspended solid matter [11, 12].

Membrane processes are usually used in the third treatment stage of PW, in order to achieve low residual crude oil concentration and to treat the PW for subsequent desalination through reverse osmosis.

Within the scope of these technologies, a great deal of research effort has been made for the treatment of PW by means of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), membrane distillation (MD) and/or corresponding combinations of these processes

[6, 13, 14]. Ahmadun et al. [15] give an overview of the different aspects of membrane technology in the treatment of PW. In a number of publications, the authors of this paper have previously described the possibilities offered by membrane technology in the treatment of PW [16-20].

During the treatment of PW the main technical challenges that are coupled with the application of membrane processes are the achievement of high flow rates, high purification efficiency and low fouling tendency of the membrane during operation, as well as chemical and thermal stability of the membranes used. In the treatment of PW, there are often conditions that preclude the use of conventional polymeric membrane materials, on account of the chemical composition or high temperature of the feed stream to be purified. In this context, using tubular or rotary ceramic membranes was suggested in order to treat PW. Ceramic hollow fibre membranes like they were used in this study are a new generation of inorganic membranes combining the advantages of an inorganic membrane material with hollow fibre geometry [21, 22]. In comparison with ceramic tubular membranes, they have a higher specific filter area with respect to the volume of a corresponding membrane module [23].

3. Overview on the experiments carried out In this study, tests were carried out for the efficient filtration of TDPW, and OMS by using an innovative ceramic ultrafiltration hollow fibre membrane

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Highlights 2014

Tab. 1: Allowed residual crude oil concentrations for onshore and offshore introduction of Produced Water into the environment.

(Mann+Hummel) with a pore size of d90 = 40 nm. Such a ceramic hollow fibre membrane is shown in Fig. 1.

Within the scope of the test series, the influence of the crossflow velocity (CFV) and the crude oil concentration in the feed stream on the membrane performance was examined. Other test series were used for the analysis of the cleanability of the membrane during filtration and the study of different physical and chemical cleaning procedures for the guarantee of a stable long term operation. In all examinations the TMP was 0.5 bar and the process temperature was 40 °C. The clean water permeability of the membrane used was determined with trans-membrane pressures of 0.25 bar to 1 bar.

4. Ceramic hollow fibre membranes (CHFM) The contents of this section are the description of CHFM, as well as their production and characterisation.

Fig. 1: Cross-section of a CHFM

spinning mass

central fluid (water)

annular cross-section Fig. 2: Mouth cross-section of a two-component spinneret having an annular cross-section (spinning mass) and a circular cross-section (central fluid)

Fig. 3: Scanning electron microscope image of the CHFM which was used in the experiments: ceramic microfiltration layer as a carrier structure and on it the functional ultrafiltration layer as an active layer.

38

4.1 Typical features of ceramic membranes The most important material and application characteristics of ceramic membranes are: - High chemical and thermal stability, which allows the filtration of acids, alkalis, solvents and hot fluids, as well as the cleaning of the membranes using chemical cleaning agents - High mechanical stability during filtration of abrasive fluid ingredients - Low fouling and adsorption tendency for organic molecules - Very high membrane purity after production through the required sinter process Ceramic hollow fibre membranes, in particular, have other advantages compared with ceramic membranes of other geometries (ceramic tubular and disk membranes): - High packing density (high ratio of the membrane surface to the filter volume) - Defined flow conditions, in particular with in-out cross-flow filtration - Low cost of materials in view of the filter area - Sintering process with low energy costs and short sintering time, on account of the low wall thickness of the hollow fibre membranes The CHFM that was used for the examinations described below was made by a fibre spinning process in which, simultaneously with the spinning process, a phase inversion is carried out from the liquid spinning mass to the solid structure of the hollow fibre membrane.

4.2 Fibre spinning and phase inversion The starting materials for the preparation of the ceramic hollow fibre membrane by means of a fibre spinning process are a ceramic powder, a polymer powder, a corresponding solvent system and a number of additives. These components are homogeneously mixed into a viscous spinning mass. The finished spinning mass is guided through a two-component spinning nozzle into an aqueous precipitation bath. Here, the solid structure of the hollow fibre membrane forms from the liquid spinning mass through phase inversion. Here, in detail, the solvent in the spinning mass is displaced through the water of the precipitation bath. Because the polymer component in the spinning mass is dissolvable only in the solvent, but not in water, a solid structure develops in the form of the hollow fibre membrane.

The form of the hollow fibre is generated through the cross-sectional area in the nozzle mouth of the two-component spinning nozzle shown in Fig. 2. The external annular cross-section is permeated by the spinning mass. In the internal annular cross-section, an aqueous central fluid flows, which has the same or similar composition as the precipitation bath. The central fluid comes into

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Tab. 2: Features of the CHFM and the filter modules examined.

Figure 3 shows the active ultrafiltration layer and the carrier structure in an image of a scanning electron microscope.

5. Filter modules, test set-up, test parameters and substance systems All filtration experiments were carried out with different lots of the same ceramic hollow fibre membrane from Mann+Hummel.

The data of the membrane used and the filter modules are summarised in Table 2. Figure 4 shows a membrane bundle as it is installed in a filter module.

Fig. 4. Image of a filter module with ceramic hollow fibre membranes, which was used in these examinations.

contact with the spinning mass only in the nozzle mouth, so that precipitation of the spinning mass within the nozzle is excluded.

During the spinning process, the nozzle mouth is guided either at a short distance above the precipitation bath (spinning with an air gap), or it is immersed directly in the precipitation bath.

The so-called green fibre originating during spinning shows features of a polymer hollow fibre membrane. The ceramic particles from the spinning solution are enclosed in the polymer phase. The green fibre is washed after the spinning in order to remove solvent residues and afterwards it is sintered at high temperatures. During the sintering process, the polymer is burned completely out of the fibre structure and the ceramic particles combine with each other via sintering necks. At the end of the sintering process, there is a pure ceramic hollow fibre membrane. The dimensions of this hollow fibre membrane are smaller than the dimensions of the green fibre due to thermal shrinkage during sintering.

5.1 Experiment set-up and test parameters The experiment set-up according to Fig. 5 comprises a centrifugal pump for fluid pumping, a filter module with CHFM, as well as the line routings for the feed, the permeate and the retentate stream.

The maximum operating pressure of the plant is 3 bar and the maximum operating temperature is 80 °C. The backwashing of the membrane can be carried out with a maximum pressure of 10 bar.

During the experiments, the CFV was varied between 1.5 m·s-1 and 2.5 m·s-1. The tests were carried out alternatively in the FedBatch mode or with full recycling of the permeate and retentate (Total Recycle Mode). The purely physical backwashing is done in different, but regular time intervals by the fact that permeate is pressed from the outside to the inside through the membrane against the filtration direction. The mean TMP was determined through measurement of the static pressure before and after the membrane module in defined time intervals. All filtration experiments were carried out with a fluid temperature of 40 °C and with a low TMP of 0.5 bar. The initial crude oil concentration in

4.3 Specific design of the ceramic hollow fibre membrane used The CHFM which was used during examinations consists of two layers. The first layer is a ceramic microfiltration carrier structure with open pores and with a low trans-membrane pressure during operation, which results from the above-described spinning process during phase inversion. This carrier structure gives the necessary mechanical stability to the membrane. After the sintering, this carrier structure is coated with a functional ceramic ultrafiltration layer as a separation-active layer on the feed side of the membrane. Because the membrane is permeated in all studies from the inside to the outside, the functional coating is also done on the internal luminal surface of the membrane. Both layers consist of Al2O3 aluminium oxide.

With this coating process, the membrane is flushed with a ceramic suspension that adheres in a thin layer on the inner surface of the carrier structure. After this coating step, the ceramic hollow fibre membrane is sintered a second time, in order to obtain a stable connection between the ceramic coating and the ceramic carrier structure.

With the examined hollow fibre membrane, the separation active layer has a thickness of only few micrometers. This membrane structure allows a low trans-membrane pressure during operation and a high permeate flow rate through the membrane from the inside to the outside, since the pressure drop in the open structure of the ceramic carrier layer compared to the pressure drop in the active ceramic ultrafiltration layer can be almost completely neglected.

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6. Results Hereinafter the test results are presented for the membrane flow rate, the separation performance and the backwashing ability of the investigated ceramic ultrafiltration hollow fibre membrane. Here, the CFV, the crude oil concentration in the feed stream, as well as the process parameters for the membrane cleaning during operation were varied.

During the examinations carried out, the cross-flow velocity was between 1.5 m·s-1 and 2.5 m·s-1, from which corresponding Reynolds numbers result for the flow in the hollow fibre lumen of between 2,900 and 4,800, which indicates a turbulent flow. The Reynolds number is defined as follows: Fig. 5. Systems flow chart of the membrane filter system used in the laboratory, Fed-Batch mode and also operating with full recycling of permeate and retentate are possible.

TDPW amounted to 1,000 to 5,200 ppm, with OMS at 35 ppm.

The permeate flow rate was determined with an electronic scale (DS 36K0.2, core) that was read with the data acquisition software LabVIEW (National Instruments, Munich, Germany). The membrane was chemically cleaned after each experiment with 1% P3 Ultrasil-14 cleaning solution (Henkel, Duesseldorf, Germany).

After the cleaning, the clean water flow rate of the membrane was measured.

An overview of the effect of different test parameters during separation of crude oil/water mixtures with ceramic membranes can be found in earlier works of the authors [16-20].

5.2 Analysis of the crude oil/water mixture The continuous on-line measurement of the crude oil concentration was made until the concentration range of one ppm with an on-line measurement system, which was developed for industrial applications (DECKMA HAMBURG GmbH, Hamburg, Germany). With a multi-range conductivity meter (HI 9033, Hanna Instruments, Kehl am Rhein, Germany), the electric conductivity of the feed and the permeate streams was determined. Samples from the feed stream, the permeate stream and the retentate stream were characterised with regard to their total carbon concentration (TC) with a TC measuring instrument (Shimadzu, Duisburg, Germany). The off-line measurement of the TC concentration and the dispersed crude oil is done with a fluorescence-based measurement system (TD500D, Nordantec, Bremerhaven, Germany).

with the density ρ of the liquid, the mean flow velocity v in the hollow fibre lumen, the inner diameter d of the CHFM and the dynamic viscosity μ of the liquid.

The membrane fouling that occurs with all tests is due to the formation of a top layer on the membrane surface, or blocking of the membrane pores by particle adsorption, or through sterically-induced particle retention, or usually due to the combination of the named effects. Because membrane fouling leads to a reduction of the filtration efficiency, a variation of the operating conditions during cross-flow filtration can be a purposeful approach, in order to analyse the mode of action of individual parameters of influence on the fouling behaviour of membranes and on the permeate flow rate [24, 25].

Tab. 3: Physical properties of the TDPW and OMS at 40 °C.

5.3 Characterisation of the crude oil/water mixtures Oily water samples from TDPW were made available by Deutsche BP AG, Ölraffinerie Emsland, Lingen. The OMS were prepared through pre-emulsification of water with crude oil (Oilfield Bramberg) with a rotor-stator- homogeniser and subsequently with a high pressure homogeniser (Emulsiflex C5, Avestin, Mannheim, Germany) with an operating pressure of 450 bar.

The final concentration of the dispersed crude oil in the OMS systems was set through dilution with demineralised water. A summary of the physical properties of TDPW and OMS is shown in Table 3.

Figure 6 shows the representative drop size distributions in the feed stream of OMS (red curve), as well as in the feed stream of TDPW (blue curve). The drop size distributions were determined with a laser diffraction spectroscope (Mastersizer S, Malvern Instruments Ltd., Herrenberg, Germany).

40

Fig. 6. Representative drop size distributions (relative volumetric frequency) of the crude oil drops in the feed stream of OMS (red curve) and TDPW (blue curve).

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Water Solutions D-67056 Ludwigshafen Phone +49 (0)621 60-0

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Ahlstrom Filtration – setting benchmarks in filtration media

Ahlstrom Filtration – setzt Maßstäbe für Filtrationsmedien

Clean Water for the world

Ahlstrom Filtration is a global technology leader in design, development and manufacture of innovative filter media.

Ahlstrom’s large technology portfolio is a proof of our commitment to ensure that your specific filter media performance requirements are met.

We have manufacturing plants in North and South America, Europe and Asia. With our numerous Research & Development centers and global Sales network we are able to support and work closely with our customers in order to find the best solutions for filtration applications.

We serve our customers in Transportation Filtration and Advanced Filtration segments. Applications in the Transportation market include filter media for: Air intake, Oil, Fuel and Cabin Air. Our long experience in chemistries and fibers has been setting benchmarks in the filter media market. We develop new and innovative solutions for this market closely following and anticipating changes to filter media requirements in the market.

Advanced Filtration offers a wide range of filter media technologies ranging from Ahlstrom Disruptor® and Ahlstrom Trinitex® to Microglass, Fine Fiber and Nanotechnology. This range of filter media technologies assures that you will find the right technology to suit your needs. Advanced filtration applications include Water, High Efficiency Air, Gas Turbine, Hydraulic, Life Science and Laboratory and others.

Ahlstrom Filtration ist weltweiter Technologieführer auf dem Gebiet der Konstruktion, Entwicklung und Herstellung innovativer Filtermedien. Unser umfassendes Technologie-Portfolio stellt sicher, dass Ihre speziellen Anforderungen an die Leistung unserer Filtermedien erfüllt werden.

Unsere Produktionsstätten befinden sich in Nord- und Südamerika, Europa und Asien. Aufgrund unserer zahlreichen Forschungs- & Entwicklungszentren und unseres weltweiten Vertriebsnetzes sind wir in der Lage, in enger Kooperation mit unseren Kunden deren Suche nach der besten Lösung für ihre Filtrationsanwendungen zu unterstützen. Unsere Kunden sind im Bereich der Filtrierung für das Transportwesen und Advanced Filtration tätig. Zu den Anwendungen im Transportwesen zählen Filtermedien für: Luftansaugfilter, Öl-, Kraftstoff- und Kabinenluftfilter. Aufgrund unserer langjährigen Erfahrung in den Bereichen Chemie und Fasern setzen wir Maßstäbe bei der Entwicklung neuer und innovativer Lösungen. Advanced Filtration bietet ein breites Spektrum an Filtermedien, von Ahlstrom Disruptor® über Ahlstrom Trinitex® bis hin zu Mikroglas, Feinfasern und Nanotechnologie. Dieses Spektrum unterschiedlichster Filtermedien gewährleistet, dass Sie die Technologie finden, die Ihre Anforderungen erfüllt. Wir bieten zukunftsweisende Filteranwendungen für die Bereiche: Wasser, Schwebstoffe, Gasturbinen, Hydraulik, Biowissenschaften, Labor und andere.

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Sauberes Wasser für die ganze Welt

60 years' experience in solid-liquid separation

60 Jahre Erfahrung in der Fest-Flüssig-Trennung

Swiss quality meshes for premium filters

Schweizer Qualitätsgewebe für Premium-Filter

Innovation and experience for excellent solutions

Mit Innovation und Erfahrung zu starken Lösungen

Die Produktpalette der BASF umfasst die Schlüsselprozesse der industriellen und kommunalen Wasseraufbereitung. Wir zählen zu den führenden Anbietern von Chemikalien zur Wasserklärung bei der Trinkwasserherstellung, zur Behandlung von Abwässern und industriellem Prozesswasser, zum Schutz von Entsalzungsanlagen, Kühltürmen und Boilern.

The company BHS-Sonthofen, with over 300 employees, is an owneroperated group of companies in the field of machine and plant engineering. The group has a number of subsidiaries around the world.

Das Unternehmen BHS-Sonthofen ist eine inhabergeführte Unternehmensgruppe des Maschinen- und Anlagenbaus mit über 300 Mitarbeitern. Zur Gruppe gehören mehrere Tochtergesellschaften weltweit.

BOPP entwickelt und produziert erstklassige Edelmetallgewebe vom stabilen Gitter bis zum hochpräzisen Feinstgewebe. Neben dem Einsatz im Siebdruck werden die Gewebe vor allem zu hochwertigen Filtersystemen für anspruchsvolle industrielle Anwendungen verarbeitet.

Mit der hohen Durchgängigkeit vom Drahtziehen bis zum fertigen Filter im eigenen Betrieb sichert das Unternehmen den hohen Qualitätsstand. Nach umfangreichen Investitionen in Forschung und Entwicklung, Maschinenanlagen, Gebäude und Infrastrukturen hat BOPP die Führungsposition weiter ausgebaut. Markant ausgebaut wurde unter anderem der Bereich der Sinterprodukte sowie die Konfektion, wo die Filterprodukte vom Prototyp bis zur Serienfertigung präzis, effizient und wirtschaftlich hergestellt werden.

Die Verbindung aus Kompetenz, Erfahrung und Innovationsgeist gewährleistet den bewährten, langfristigen Nutzen der Zentrifugen von Ferrum mit einem breiten Produktsortiment und weltweiter Tätigkeit.

Filtrationstechnik Als Spezialist für die Fest-Flüssig-Trennung hat BHS über 60 Jahre Erfahrung in der Chemie, Pharmazie, Nahrungsmittel-, Kunststoffindustrie und Umwelttechnik. Mehr als 1000 Referenzen belegen die breite Kompetenz. Das Herstellprogramm umfasst Druck- und Vakuumfilter, die auch als Komplettanlagen angeboten werden.

BOPP develops and manufactures high grade noble metal meshes ranging from robust support meshes through to high precision fine meshes. Alongside applications in screen printing, the meshes are used primarily for high value filtration systems in demanding industrial environments. Total control of the process from wire drawing through to completed filters in the company’s own factories ensures the highest levels of quality.

Extensive investment in research and development, machinery, premises and infrastructure has strengthened Bopp’s position as the industry leader. The company is particularly noted for its sintered products and fabrications, where filter products are produced accurately, efficiently and economically from prototype to mass production.

The combination of competence, experience and spirit of innovation, together with a wide product range and worldwide business guarantee the proven and long-term benefits of the Ferrum centrifuges.

Filtration technology As a specialist for solid-liquid separation, BHS has over 60 years of experience in the chemicals, pharmaceuticals, food processing, plastics and environmental industries.

More than 1,000 references testify to the company’s broad expertise. The range of products manufactured comprises pressure and vacuum filters which are also offered as complete systems.

In collaboration with our customers, we supply troublefree solid-liquid separation solutions with maximum performance, minimum energy consumption and consistent, reproducible product quality. Our pusher and scraper centrifuges comply with toughest requirements in the pharmaceutical, fine chemical, food and environmental industries. The efficient centrifuges from Ferrum stand for quality, flexibility, reliability and durability.

In Zusammenarbeit mit den Kunden realisieren wir maßgeschneiderte Lösungen für eine störungsfreie FestFlüssig-Trennung mit maximaler Arbeitsleistung, minimalem Energieverbrauch und gleichbleibender, reproduzierbarer Produktqualität. Unsere Schub- und Schälzentrifugen genügen höchsten Ansprüchen in der Pharma-, Feinchemie- und Lebensmittel-Industrie sowie in der Umwelttechnologie. Qualität, Flexibilität, Zuverlässigkeit und Langlebigkeit zeichnen die effizienten Zentrifugen von Ferrum aus.

®

BASF ist der weltweit führende Technologieanbieter für inge® Ultrafiltrationstechnologie, einem Membranverfahren zur Aufbereitung von Trink-, Prozess-, Ab- und Meerwasser. Die extrem kleinporigen und belastbaren Filter der Multibore® Membranen halten neben Partikeln selbst Mikroorganismen wie Bakterien und Viren zuverlässig zurück und sorgen so für sauberes Wasser.

Continuous or batch solid-liquid separation The solutions cover the field of cake filtration and range from rotary pressure, indexing belt, rubber belt, candle and pressure plate filters to complete filtration plants for solid-liquid separation in continuous or batch operation.

From consultation to laboratory and technical testing to process engineering design and finally to the delivery and support of complex plants, you will find a competent partner in BHS-Sonthofen.

Die leistungsfähigen Ultrafiltrationsmodule sind schnell und leicht einzubauen. Die Wasseraufbereitungsanlage kann durch platzsparende Rack-Konstruktionen einfach geplant, kostengünstig installiert und betrieben werden.

Das Unternehmen ist weltweit direkt oder über Partner aktiv und hat zahlreiche Referenzprojekte rund um den Globus mit seiner Technologie ausgerüstet.

inge® Multibore® Membranes

Rotary Pressure Filter RPF X20 Druckdrehfilter RPF X20

inge® T-Rack® 3.0

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www.bhs-sonthofen.com

Kontinuierliche oder diskontinuierliche Fest-Flüssig-Trennung Die Problemlösungen decken das Gebiet der kuchenbildenden Filtration ab, diese reichen von Druckdreh-, Taktband-, Traggurt-, Kerzen-, Tellerdruckfilter bis hin zu kompletten Filtrationsanlagen zur kontinuierlichen oder diskontinuierlichen Fest-Flüssig-Trennung. Vom Beratungsgespräch, über Labor- und technische Versuche bis hin zur verfahrenstechnischen Auslegung und schließlich zur Lieferung und Betreuung von komplexen Anlagen finden Sie in BHS-Sonthofen einen kompetenten Partner.

Indexing Belt Filter BF 100-050 Taktbandfilter BF 100-050

As a world leader in the manufacture of fine wire meshes Bopp supplies almost every industry, from plant construction through to accessories, across the globe.

With manufacturing facilities in Switzerland, Germany, England, Italy, USA, Sweden, China and Koreas as well as representation in all significant industrialised countries, Bopp guarantees a first class service.

Als einer der weltweit führenden Hersteller von Feindrahtgeweben beliefert BOPP Firmen aus fast allen Branchen vom Anlagebau bis zur Zubehörindustrie in aller Welt.

Mit eigenen Betrieben in der Schweiz, in Deutschland, England, Italien, USA, Schweden, China und Korea und zahlreichen Vertretungen in allen wichtigen Industrieländern wird ein erstklassiger Service sichergestellt.

Our customer-oriented Aftersales Service is available to provide our customers with uncomplicated and fast support thanks to worldwide service centres and the careful stock management for spare parts.

Reliable used centrifuges from the original supplier offer an interesting alternative to new machines. If required we will modify the machine using optional equipment to suit your requirements.

Unser kundennaher Aftersales Service bedient die Kunden dank weltweiten Service-Stellen und sorgfältiger Ersatzteil-Lagerbewirtschaftung unkompliziert und schnellstmöglich.

Zuverlässige Gebrauchtzentrifugen vom Originallieferanten bieten eine interessante Alternative zu Neumaschinen. Bei Bedarf passen wir die Maschinen durch diverse Nachrüstmöglichkeiten den Kundenwünschen an.

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Fax +760 901 2578 info@hydranautics.com www.membranes.com

Nitto Group Company

Hydranautics is a part of the Nitto group and one of the global leaders in the field of Integrated Membrane Solutions.

Hydranautics gehört zur Nitto Gruppe und zu den weltweiten Marktführern auf dem Gebiet integrierter Membranlösungen

Hydranautics offers complete membrane solutions like Reverse Osmosis, Nanofiltration, Ultrafiltration and Microfiltration for water, waste water and process treatment and applications.

Hydranautics’ membrane based solutions are currently in use on seven continents throughout the world for diverse applications such as

Hydranautics bietet komplette Membranlösungen wie Umkehrosmose, Nanofiltration, Ultrafiltration und Mikrofiltration für die Aufbereitung von Wasser, Abwasser und Prozesswasser sowie für Anwendungen.

Hydranautics’ Membranlösungen werden gegenwärtig auf allen sieben Kontinenten für unterschiedliche Anwendungen benutzt, wie z.B.:

• • • • •

Seawater Desalination Industrial High-Purity Water Surface Water Treatment Waste Water Treatment Specialty Process Applications

• • • • •

Meerwasserentsalzung Industrie-Reinstwasser Oberflächenwasseraufbereitung Abwasserbehandlung Anwendungen für Spezialprozesse

Our parent firm, Nitto Denko Corporation, is Japan’s leading diversified materials manufacturer. Nitto and Hydranautics have over 50 years of experience in membrane technology. We remain committed to bringing innovative membrane technologies which provide clean water to a thirsty world. Our global membrane division is headquartered in Oceanside, CA, USA and we have three state-of-the-art manufacturing sites located in Oceanside - USA, Shiga - Japan and Shanghai – China.

For further information kindly visit our Hydranautics website www.membranes.com.

Unsere Muttergesellschaft, die Nitto Denko Corporation, ist Japans führender Hersteller diversifizierter Materialien.

Nitto und Hydranautics haben seit über 50 Jahren Erfahrungen in der Membrantechnologie. Unser Engagement gilt innovativen Membrantechnologien, die einer durstigen Welt sauberes Wasser liefern. Unsere weltweite Membran-Abteilung hat ihren Hauptsitz in Oceanside, CA, USA; wir verfügen über drei hochmoderne Produktionsstätten in Oceanside - USA, Shiga - Japan und Schanghai – China. Für weitere Informationen besuchen Sie bitte unsere Hydranautics-Webseite www.membranes.com.

Core competencies

Kernkompetenzen

• Global Leader in Total Membrane Solutions • Product innovations through state of the art R&D • Customer Satisfaction through Global Technical Services • Global Presence • Customizable Membrane Solutions

• Weltweiter Marktführer für Membran-Komplettlösungen • Produktinnovationen durch Forschung auf dem Stand der Technik • Weltweiter technischer Kundendienst • Weltweit vertreten • Membranlösungen auf Kundenwunsch maßgefertigt

Candle Filter Plant CF 21-049 Kerzenfilteranlage CF 21-049

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Core competencies

Kernkompetenzen

• Premium fine wire meshes • Volume manufacture • Development/production • Consultancy/support • Bespoke products

• Premium-Feindrahtgewebe • Konfektion nach Maß • Entwicklung, Produktion • Beratung, Unterstützung • Spezialanfertigungen

www.bopp.ch

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Core competencies

Kernkompetenzen

• Pusher centrifuges • Scraper centrifuges • Mobile centrifuges • Used centrifuges • Automation

• Schubzentrifugen • Schälzentrifugen • Mobile Zentrifugen • Gebrauchtzentrifugen • Automation

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www.ferrum.net

www.membranes.com

Content of the company profiles: Q

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Company presentations

Hydranautics

Ferrum AG

G. BOPP + CO. AG Fine Wire Weavers / Feindrahtweberei

Aunankaari 4 33840 Tampere, Finland Phone +358 10 888 14

Complete company name (headquarter), contact person, street, post code, city, country, telephone and fax number, email and Internet address Colour print of the company logo Printing of up to three colour photos/images/graphics/tables

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Separation Industry 2016 – 2018 d Separation Industry with a clearly definde target group, t. Completely bilingual (English/German)

How to showcase your company:

The design: Robust thread-stitching for intensive and frequent use, reinforced cover, high-quality paper: cover 300 g/m2, interior 115 g/m2

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Book format: 24 cm height x 17 cm width

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Volume: Approx. 420 pages Publication date:

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Spring 2016 Q

Publication period: Every two years Utilization period: 2016 – 2018 (at least 2 years)

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The price/performance ratio for your portrait: Q

1/1 page, 4-colour: including all layout and translation services: Introduction price: EUR 1,950 (with self-provided translation EUR 1,850)

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2/1 page (double page) 4-colour: Introduction price: EUR 2,950 (with self-provided translation EUR 2,800)

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Company presentations

MICRODYN-NADIR GmbH

R + B Filter GmbH

Breslauer Straße 8 D-89250 Senden Phone +(49) 73 07 8 01 0

Kasteler Str. 45 D - 65203 Wiesbaden Phone +49 (0)611 962 6001

Bössingerstraße 34 D-74243 Langenbrettach Phone +49 (0)7946 9127 0

Fax +(49) 73 07 8 01 113 mailbox@lenser.de www.lenser.de

We will take care of everything else for you.

Prior to publication you will receive a proof.

Deadline for bookings: 29 January 2016 Deadline for printing material: 19 February 2016

Copyright: VDL-Verlag GmbH, Eckhard von der Lühe Heinrich-Heine-Straße 5, 63322 Rödermark / Germany Phone: +49 (0) 60 74 92 08 80 Fax: +49 (0) 60 74 9 33 34 Email: vdl-verlag@t-online.de or fs-journal@mgo-communications.de www.fs-journal.de R

Company presentations

Company presentations

LENSER Filtration GmbH

Send us your short company profile (up to 1,000 characters) together with the headline (up to 50 characters) Provide up to three colour photographs of your choice (poss. with a short caption, max. 35 characters per image) State your core competence with at most 5 keywords (170 characters) Send us your company logo together with the complete company name including email address and internet address (and contact person, if available).

On the enclosed search term register, list the search terms in which your company is to appear.

Company presentations

Company presentations

Company presentations

Sommer & Strassburger GmbH & Co. KG

Sandler AG

SIEBTECHNIK GMBH

Anlagen- und Apparatebau

Fax +49 (0)611 962 9237 info@microdyn-nadir.de www.microdyn-nadir.de

Lamitzmühle 1 D-95126 Schwarzenbach/Saale Phone +49 (0)9284 60 0

Fax +49 (0)7946 9127 39 info@rb-filter.de www.rb-filter.eu

Fax +49 (0)9284 60 269 filtration@sandler.de www.sandler.de

Gewerbestr. 32 D-75015 Bretten Phone +49 (0) 7252 9395-0

Contact person/Kontaktperson Peter Reich

Fax +49 (0) 7252 9395-50 info@sus-bretten.de www.sus-bretten.de

Platanenallee 46 D-45478 Mülheim an der Ruhr Phone +49 (0)208 5801 00

Leading Manufacturer of filter elements made of thermoplastic materials

Führender Hersteller von Filterelementen aus thermoplastischen Kunststoffen

Micro, ultra and nanofiltration membranes made in Germany

Mikro-, Ultra-, Nanofiltrationsmembranen „Made in Germany“

Filter elements for Air and Dust Filtration

Filterelemente für die Luftfiltration und Entstaubungstechnik

Innovative Producer of Filter Nonwovens

Innovativer Hersteller von Filtervliesstoffen

Your Stainless Steel Specialists for Filtration

Ihre Edelstahl-Spezialisten für die Filtration

LENSER Filtration has been founded in 1969 for the manufacture of made-to-measure plastic sheets and semi-finished products by pressing high-quality plastics in various sizes and strengths.

Approx 2 years later LENSER began to specialise in the manufacture of filter elements.

LENSER Filtration wurde 1969 zur Herstellung von maßgeschneiderten Kunststoffplatten bzw. Halbzeugen durch Verpressen von hochwertigen Kunststoffen in verschiedenen Formaten und Stärken gegründet.

Erst ca. 2 Jahre später begann LENSER damit, Filterelemente herzustellen.

MICRODYN-NADIR GmbH with locations in Europe, Asia and the USA is the leading independent manufacturer of micro, ultra and nanofiltration membranes and modules.

As this will remain our core competence in the future, we pursue very intensive research and development activities at our Wiesbaden location.

MICRODYN-NADIR GmbH ist mit Standorten in Europa, Asien und den USA der führende unabhängige Hersteller von Mikro-, Ultra-, und Nanofiltrationsmembranen und Modulen. Da dies auch in Zukunft unsere Kernkompetenz bleiben wird betreiben wir am Standort in Wiesbaden eine sehr intensive Forschung und Entwicklung.

R + B Filter GmbH produces pleated filter cartridges, filter panels and filter cassettes for air and dust filtration.

The filter elements are used to de-dust industrial working processes and to keep the air at work places clean.

Sandler AG ranks among the 15 largest nonwoven producers worldwide and continues to strengthen its international market position as a supplier of highquality filter media.

Die Sandler AG gehört zu den 15 größten Vliesstoffherstellern weltweit und baut ihre internationale Marktposition als Lieferant qualitativ hochwertiger Filtervliese weiter aus.

One filtration process is not like the other. For efficiency and the filtration results of a filter press the choice of the suitable filter elements is decisive. If necessary application engineers analyse suspension and filtration parameters in order to gain the required results with the right filter element.

On request application engineers analyse suspension and filtration parameters in order to achieve the desired filtration results with the right filter elements.

Since decades LENSER is the expert for high quality filter elements for liquid/solid separation in industrially used filter presses.

Filtrieren ist nicht gleich filtrieren. Für die Effizienz und die Filtrationsergebnisse ist die Auswahl der richtigen Filterelemente entscheidend. Anwendungsingenieure analysieren bei Bedarf Suspension und Filtrationsparameter, um dann mit dem richtigen Filterelement das gewünschte Ergebnis zu erzielen. LENSER ist seit Jahrzehnten der Experte für hochwertige Filterelemente für die Fest-/ Flüssigtrennung in industriell betriebenen Filterpressen.

For more than 45 years our products have been used in various industrial and municipal applications, among others in the field of water and wastewater treatment, but also in many process-integrated applications. Our products’ outstandingly sharp cut-offs and reproducibility allow for a high application variety among others in the chemical and pharmaceutical industry.

Seit über 45 Jahren werden unsere Produkte in den verschiedensten industriellen und kommunalen Anwendungen eingesetzt: u. a. im Bereich der Wasser- und Abwasseraufbereitung, aber auch in vielen prozessintegrierten Anwendungen. Die besonders scharfen Trenngrenzen unserer Produkte ermöglichen eine hohe Einsatzvielfalt u.a. in der chemischen und pharmazeutischen Industrie.

R + B Filter produziert plissierte Filterpatronen, Filterplatten und Filterkassetten für die Luftfiltration und Entstaubungstechnik. Die Filterelemente werden eingesetzt zur Entstaubung von industriellen Produktionsprozessen und zur Reinhaltung der Luft an Arbeitsplätzen. Unsere Staubfilterelemente sind weltweit im Einsatz.

Um eine optimale Funktion der Filterelemente zu gewährleisten, werden sie genau auf den Anwendungsfall abgestimmt.

Techniker und Ingenieure analysieren die Funktionsbedingungen am Einsatzort.

Ausgehend von den technischen Gegebenheiten entwickeln sie Lösungen in Zusammenarbeit mit unseren Kunden. Je nach Anforderung kommen angepasste Standard-Filterelemente oder individuell für den Kunden entwickelte Filterelemente zum Einsatz.

Kontinuierliche Veränderungen von industriellen Arbeitsprozessen und gesetzlichen Richtlinien erfordern Anpassungen der Staubfilterelemente. Deshalb arbeitet R + B Filter ständig an der Entwicklung von innovativen Produkten.

The product range comprises carded and meltblown nonwovens as well as multi-layer composites. Fibre based, needle-punched nonwovens cover the grades G2 to M5. Fine dust filter media for filter classes up to E11 are produced using submicron fibres.

Zum Produktionsprogramm zählen kardierte Vliese, Meltblown-Vliesstoffe und Mehrlagenverbunde. Faserbasierende, genadelte Vliese decken die Klassen G2 bis M5 ab. Feinfiltermedien für Filterklassen bis E11 werden auf Basis von Submicron-Fasern hergestellt.

Sandler develops and produces media for HVAC applications, the automotive industry, synthetic vacuum cleaner bags, customised special filters for liquid filtration as well as medical and hygiene applications.

Self-supporting filter media are suitable for all common pleating technologies. Synthetic pocket filter media feature a low pressure drop, are shedding-free and bacteriostatic.

Sandler entwickelt und produziert Medien für HVACAnwendungen, verschiedene KFZ-Filter, synthetische Staubsaugerbeutel, Spezialfilter für die Flüssigkeitsfiltration sowie den Klinik- und Hygienebereich.

Eigensteife Filtermedien eignen sich für alle gängigen Plissiertechnologien. Synthetische Taschenfiltermedien haben niedrige Druckverluste, sind shedding-frei und wirken bakteriostatisch.

Latest developments in the field of pleatable filter media combine excellent filtration performance, low pressure drop and long operating lives with high mechanical and pleat stability. Sandler offers solutions for automotive cabin air filters and HVAC applications.

Neuste Entwicklungen im Bereich plissierfähiger Filtermedien vereinen sehr gute Filterleistung, niedrige Druckdifferenz und lange Standzeiten mit mechanischer Stabilität und Formtreue der Falten. Sandler bietet Lösungen für Automobil-Innenraumfilter und HVACAnwendungen.

For more than 40 years Sommer & Strassburger has been a competent partner for stainless steel processing in the filter industry. Whether membrane filtration, cartridge filters or filter bags – we not only have the right housing for you, but the entire plant as well. We offer a wide range of stainless steels and special materials, with certification possible in accordance with PED 97/23/EC, up to IV / module G. In the pressure vessel area, Sommer & Strassburger is one of the best known manufacturers of stainless steel membrane housings. Our MembraLine® product line is available in sizes from 1.8" to 8.3", for pressures 6 to 300 bar.

For your cartridge filter requirements, we offer our standard FiltraLine® series to accommodate from 1 to 48 cartridges, with all commonly used cartridge filter adaptions. In addition, we offer special filter housings for up to 80 bar. Hygienic filter bags in sizes 1 and 2 round out our product range.

Sommer & Strassburger offers components and plant construction from a single source – from design to final installation on-site your reliable partner as order contractor.

Around 120 fully committed employees and modern machinery are ready to see to your needs.

Sommer & Strassburger ist seit über 40 Jahren kompetenter Partner für die Edelstahlverarbeitung in der Filtrationsbranche. Ob Membranfiltration, Kerzenfilter oder Beutelfilter – bei uns finden Sie nicht nur Ihr passendes Gehäuse, sondern auch den Anlagenbau dazu.

Wir bieten Ihnen eine breite Palette von Edelstählen und Sonderwerkstoffen, Abnahmen nach DGRL 97/23/EG sind bis Kategorie IV / Modul G möglich.

Im Druckrohrbereich ist Sommer & Strassburger einer der namhaftesten europäischen Hersteller von EdelstahlDruckrohren. Unsere Produktlinie MembraLine® ist in den Abmessungen von 1,8“ bis 8,3“ erhältlich, für Drücke von 6 bis 300 bar.

Für Ihren Bedarf an Kerzenfiltergehäusen bieten wir Ihnen unsere Standardbaureihe FiltraLine® von 1-fach bis 48fach für Drücke von 4 bar bis 10 bar mit allen gängigen Filterkerzenadaptionen; des Weiteren auch Sonderfiltergehäuse bis 80 bar. Ergänzt wird das Produktprogramm durch Beutelfiltergehäuse in hygienischer Ausführung in den Größen 1 und 2.

Sommer & Strassburger bietet Ihnen Komponenten und Anlagenbau aus einer Hand – von der Konstruktion bis zur Endmontage vor Ort sind wir als Auftragsfertiger Ihr zuverlässiger Partner.

Ca. 120 engagierte Mitarbeiter und ein moderner Maschinenpark stehen für Sie bereit.

Core competencies

Kernkompetenzen

Core competencies

Kernkompetenzen

• Coarse and fine dust filter media • Pleatable filter media • Liquid filtration • Synthetic vacuum cleaner bags

• Grob- & Feinstaubmedien • Plissierfähige Filtermedien • Flüssigkeitsfiltration • Synthetische Staubsaugerbeutel

• Agitating tanks • Heat exchanger • Membrane housings • Cartridge Filter Housings • Bag Filter Housings • Plant design and construction

• Anlagenbau • Behälterbau • Filtergehäuse • Wärmetauscher • Membrangehäuse • Beutelfiltergehäuse

At our headquarters in Senden LENSER approx. 150 employees are producing round the clock raw moulded plates, which are afterwords finished not only in Senden, but also in our production departments in Malaysia and Romania. All products are custom made according customer requirements.

A worldwide distribution network guarantees that we are mostly close to our customers. Approx. 250 LENSER employees and representatives in many countries are speaking most of our customers languages.

LENSER produziert am Stammsitz in Senden mit ca. 150 Produktionsmitarbeitern rund um die Uhr Plattenrohlinge, die dann nicht nur in Senden, sondern auch an unseren Produktionsstandorten in Malaysia und Rumänien weiter bearbeitet werden. Alle Produkte werden entsprechend den Kundenanforderungen auftragsbezogen gefertigt.

Ein weltweites Vertriebsnetz sorgt dafür, dass wir immer in der Nähe unserer Kunden sind. 250 eigene Mitarbeiter und Vertretungen in vielen Ländern sorgen dafür, dass wir fast immer die Sprache unserer Kunden sprechen.

One of our most innovative products is the immersed BIO-CEL® module for membrane bioreactors. This backwashable module shows the advantages of flat membranes as well as it is featured with the packing density of hollow-fibre modules, which allows for fantastic application possibilities in the field of municipal and industrial wastewater treatment.

BIO-CEL® submerged module

SPIRA-CEL® spiral wound modules

Kernkompetenzen

Core competencies

Kernkompetenzen

• Kammer-Filterelemente • Membran-Filterelemente • Wärmetauscher • Sonder-Filterelemente • Filterplatten-/rahmen

• NADIR® membranes and formats • SPIRA-CEL® spiral wound modules • BIO-CEL® submerged modules • SEPRODYN® ultrafine filtration modules • MICRODYN® tubular and capillary modules for microfiltration

• NADIR® Membranen und Formate • SPIRA-CEL® Wickelmodule • BIO-CEL® getauchte Module • SEPRODYN® Module für die Feinstfiltration • MICRODYN® Tubular- und Kapillarmodule für die Mikrofiltration

www.lenser.de

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www.microdyn-nadir.de

There are standard filter elements as well as customized filter elements in the R + B Filter range.

Examples of applications: Chemical and pharmaceutical industry, metal processing, surface technology, product conveying and storing, hot gas filtration, separation of oil mist and aerosols.

Anwendungsbeispiele: Chemische und Pharmazeutische Industrie, Metallbearbeitung, Oberflächentechnik, Produktförderung und –lagerung, Heißgas-Filtration.

Abscheidung von Ölnebeln und Aerosolen.

Das Unternehmen Eine in mehr als 90 Jahren Firmengeschichte (1922-2012) konsequent umgesetzte Unternehmenspolitik des kontrollierten, eigenfinanzierten Wachstums sichert uns heute nicht nur eine gesunde wirtschaftliche Basis, sondern auch eine beeindruckende weltweite Präsenz.

SIEBTECHNIK is part of a corporate group with clear orientation on the processing of mineral bulk materials as well as solids/liquids separation in the chemicals and food industries. With more than 40 companies and more than 2,700 employees world-wide we are placed extremely well strategically.

SIEBTECHNIK ist Teil einer Unternehmensgruppe mit einer klaren Ausrichtung auf die Aufbereitung mineralischer Schüttgüter sowie die Fest-Flüssig-Trennung in der Chemie- und Lebensmittelindustrie. Mit über 40 Unternehmen und mehr als 2.700 Mitarbeitern weltweit sind wir strategisch außergewöhnlich gut aufgestellt.

Our Centrifuges

Unsere Zentrifugen

In nearly all cases of mechanical liquid/solids separation, continuously operating centrifuges are the best technical and economical proposition. They can dewater large quantities of solids to low final moistures, whilst needing little space, energy and time. SIEBTECHNIK is specialised in the development and manufacture of continuously operating centrifuges. Our technical experts are at your disposal to advise you on the most suitable centrifuge.

Machines are available for tests either on your premises or in our test establishment.

Für die mechanische Flüssigkeitsabtrennung sind kontinuierlich arbeitende Zentrifugen in fast allen Fällen die technisch und wirtschaftlich beste Lösung. Sie entwässern auch große Feststoffmengen auf niedrige Endfeuchten bei kleinem Raum- und Energiebedarf und mit geringem Zeitaufwand. SIEBTECHNIK hat sich auf die Entwicklung und den Bau kontinuierlich arbeitender Zentrifugen spezialisiert. Zur technischen Beratung stehen Ihnen unsere erfahrenen Fachleute zur Verfügung, für Versuche in Ihrem Betrieb oder in unserer Versuchsanstalt mehrere Versuchsmaschinen.

Core competencies

Kernkompetenzen

• Screening Machines and Process Equipment • Sample Taking • Size Reduction • Laboratory Equipment • Centrifuges

• Sieb- und Aufbereitungsmaschinen • Probenahmeanlagen • Zerkleinerungsmaschinen • Laborgeräte • Zentrifugen

MICRODYN® tubular module

Core competencies

Global Guide 2014-2016

Together with their customers R + B Filter develops complete solutions with new products. Applications are carefully analysed by engineers in order to make suggestions that guarantee customers the optimum function of their dust collectors.

Eines unserer innovativsten Produkte ist das getauchte BIO-CEL® Modul für Membran-Bio-Reaktoren. Als rückspülbares Modul auf Basis von Flachmembranen, mit der Packungsdichte eines Hohlfasermoduls, ergeben sich fantastische Einsatzmöglichkeiten in den Bereichen der kommunalen und industriellen Abwasserreinigung.

• Recessed filter plates • Membrane filter plates • Heat exchanger plates • Custom made filter elements • Filterplates and frames

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Coming from pleated filter cartridges for air and dust filtration in the early 1990ies R + B Filter set a new standard on the market for air and dust filtration with the first pleated filter panel for dust collection. More innovations, partly patented products, followed.

Fax +49 (0)208 5801 300 info@siebtechnik.com www.siebtechnik.com

The company A corporate policy of controlled, self-financed growth realised consistently for more than 90 years of the company’s history (1922-2012) secures for us today not only a healthy economic base but also an impressive presence throughout the world.

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Core competencies

Kernkompetenzen

• Technical Support • Innovative • Most flexible Service • Customer engineered Solutions • Excellent Quality

• Technische Beratung • Innovativ • Kundenspezifische Lösungen • Flexibelster Service • Hervorragende Qualität

www.rb-filter.eu

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www.sandler.de

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www.sus-bretten.de

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Fig. 7: Normalised permeate flow rate depending on the test time during TDPW filtration (oil concentration 1,000 ppm) and OMS filtration (oil concentration 35 ppm), cross-flow velocity 2.5 m·s-1

Fig. 8: Normalised permeate flow rate depending on the test time during OMS filtration (oil concentration 35 ppm), cross-flow velocities 1.6 m·s-1 and 2.5 m·s-1.

In the following Figures, the temporal course of the normalised flux performance is shown for different operating conditions. The normalised flux performance is defined as the ratio of the permeate flow rate at time t relative to the permeate flow rate at the beginning of the respective test. For the time t = 0, the normalised permeate flow rate hence has the value 1. Here, the drop of the flow rate performance over time is a measure of the membrane fouling that occurs.

a cross-flow velocity of 2.5 m·s-1. After a filtration duration of 4.5 hours, within the ranges (I) and (II), a clear drop of the initial flow rate value by 76% can be detected. During the whole test duration of five hours, the mean permeate flow rate amounted to 97 l/(m2h).

6.1 Influence of different initial oil concentration Figure 7 shows the temporal course of the normalised permeate flow rate for the ceramic ultrafiltration hollow fibre membrane used during treatment of different oily waste waters (TDPW with 1,000 ppm crude oil concentration and OMS with 35 ppm crude oil concentration), at equal process parameters (CFV = 2.5 m·s-1), without backwashing in the ongoing filtration process.

The permeate flow rate in the first process period (I) has a clear drop over time. Here, the fouling potential depends on the features of the feed solution and the process parameters, as well as on the surface features of the CHFM used. In the second period (II), there follows a variable length period with a diminished flow rate drop.

In the third period (III), the permeate flows are almost stationary.

The results in Figure 7 also show that the normalised flow rate performance during OMS filtration drops over time more than during TDPW filtration, with a several times higher oil concentration in the feed stream. On account of the fouling that increasingly occurs during TDPW filtration, an approximately stationary state is reached after a shorter time than during OMS filtration.

The stronger drop occurring in this representation of the standardised flow performance during filtration of OMS with the low oil concentration of 35 ppm is due to the absolute value of the permeate flow rate at the beginning of OMS filtration being clearly higher than during TDPW filtration.

6.3 Influence of filtration time To record the behaviour of the ceramic hollow fibre membrane for a filtration period of several days, the long-term tests for TDPW filtration in total recycle mode, as well as in fed-batch Mode, were carried out with and without backwashing. The crossflow velocity in these tests was 2.0 m·s-1, and the trans-membrane pressure was 0.5 bar.

6.2 Influence of CFV variation In Fig. 8, the temporal course of the normalised permeate flow rate is shown during OMS filtration for two different crossflow velocities (1.6 m·s-1 and 2.5 m·s-1).

The ceramic hollow fibre membrane has a permeate flow rate at the beginning of OMS filtration of 190 l/(m2h) with a cross-flow velocity of 2.5 m·s-1 and achieves a stable operating mode with a flow rate of 100 l/(m2h) within 3.5 hours test duration. During this test, the permeate flow rate has a drop of 43% within the ranges (I) and (II) in comparison to the initial flow rate. In this case, a mean permeate flow rate of about 124 l/(m2h) was achieved after a test duration of five hours in total.

Figure 8 also clearly shows the influence of a reduced cross-flow velocity of 1.6 m·s-1 on the membrane performance. The operating ranges (II) and (III) are shifted compared with their position with F & S International Edition

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Tab. 4: Summary of the separation efficiencies with regard to oil and TC with six different experiments.

TRM: Total-Recycle Mode; FBM: Fed-batch Mode; LT: Long-term (nine days); MT: Mean-term (18 hours); TDPW: Tank dewatering produced water; OMS: Oily model system

The temporal profiles of the permeate flow rate for two different, very high oil concentrations in the TDPW (TDPW1 with 5,200 ppm and TDPW2 with 2,100 ppm) over two trial runs, each with 30 hours duration, are shown in Fig. 9.

The occurring permeate flow rates are clearly dependent here on the feed properties (composition and concentration of oil and organic components in the feed). The results show that the continuous increase of membrane fouling reduces the membrane permeability.

Fig. 9: Normalised permeate flow rate depending on the test time during TDPW filtration with different oil concentrations (TDPW1: 5,200 ppm, TDPW2: 2,100 ppm) for a test duration of 30 h, crossflow velocity 2.0 m/s; with backwashing (for TDPW1) and without backwashing (for TDPW2).

A comparison of the different membrane flow rates during TDPW1 and TDPW2 filtration, with the same operating parameters and with a test duration of about 17 hours (1020 min), showed that a higher average permeate flow rate with lower initial oil concentration occurs with TDPW2. During the TDPW2 filtration, with an initial oil concentration of 2,100 ppm, the flow rate dropped in the Fed-Batch Mode within two hours from the initial value of 140 l/(m2h) to 90 l/(m2h). After subsequent switching to Total Recycle Mode, a roughly stable state appeared with a still only slightly dropping membrane flow rate during the next 7 hours filtration time. After 17 hours filtration time, the flow rate reached a value of 80 l/(m2h) and remained approximately constant up to the end of the test. The flow rate performance was high enough for the whole test time so that no backwashing was necessary.

Fig. 9 also shows a representative example of the results that were achieved during the TDPW1 filtration, with an initial oil concentration of 5,200 ppm. With this test, the permeability of the membrane decreased continuously during the first four hours, from 143 /(m2h) to 85l/(m2h), because of membrane fouling and dropped during the next twelve hours to a value of about 45 l/(m2h). Hence, during the TDPW1 filtration, with an initial oil concentration of 5,200 ppm, a purely mechanical backwashing was carried out after about 17 hours, in order to increase the flow rate again. In the process, permeate was pressed from the outside of the membrane into the inside of the hollow fibre during a backwashing time of 10 s. In this case, the backwash pressure was 3.5 bar. From Fig. 9 it is

Fig. 10: Normalised permeate flow rate depending on the test time during TDPW filtration (oil concentration 5,200 ppm) for a test duration of nine days, cross-flow velocity 2.0 m·s-1.

Fig. 11: Pure water flow rates depending on the trans-membrane pressure for new and for chemically purified ceramic hollow fibre membranes after the filtration of oil/water mixtures for a filtration time of eight hours (on the left) and 70 hours (on the right).

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M I C R O F I LT R AT I O N

6.4 Oil and TC separation performance Besides the permeate flow rate, the retention property of the membrane compared with crude oil and organic components (TC) is another important parameter that characterises the membrane performance. The separation efficiency of the examined ceramic hollow fibre membrane during six different tests is summarised in Table 4. With every examination, a very high oil retention of more than 99.5% appeared, both with OMS and also with TDPW, regardless of the initial oil concentration in the feed stream. During OMS filtration, with an initial TC concentration between 50 and 100 ppm, a TC retention of 90-95% was achieved. The separation efficiencies for TC during TDPW filtration were between 61% and 94%.

6.5 Effectiveness of backwashing For the determination of the effectiveness of the backwashing, a long-term test for TDPW ultrafiltration was carried out with a CHFM with a high oil concentration in the feed of 5,200 ppm. The test duration was nine days with the inclusion of backwash cycles. The standardised permeate flow rate depending on the test time is shown in Fig. 10.

With this test, the permeate flow rate decreased from 149 l/(m2h) initially to 107 l/(m2h) after one hour of operating time. In another 15 hours, the permeate flow rate decreased to 46 l/(m2h). In order to limit the minimum permeate flow rate to not less than 30% of the initial flux, two different backwash strategies were applied with different backwash frequencies.

In the first backwash mode (I), backwashing with permeate is done every 18 hours for 10 s with a trans-membrane pressure of 3.5 bar, and every three hours

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in the second backwash mode (II) under the same conditions. Immediately after backwashing, the permeate flow rate in the first backwash mode increased to a value of 118 l/(m2h), which corresponds to an increase of the permeate flow rate to 80% of the initial value. In the second backwash mode, a stationary flow rate of about 40 l/(m2h) occurred by the end of the experiment. The results of these examinations show that quick backflushing may be temporarily effective in filtration of PW with high oil concentrations, but that this effectiveness decreases with an increase in operating time.

6.6 Membrane chemical cleaning The chemical cleaning of membranes is an integral process step in the operation of MF and UF systems in wastewater treatment and it has a significant influence on membrane performance. In this study, the effectiveness of the chemical cleaning steps carried out was examined in a series of filtration experiments. For this purpose, the pure water flow rate of the new membrane with distilled water was measured before each filtration test at room temperature and at different trans-membrane pressures. Accordingly, chemical cleaning of the membrane was carried out after each filtration of a crude oil/water mixture and afterwards the pure water flow rate was determined once more. During chemical cleaning, the membrane was rinsed with the alkaline surfactant solution described above.

In Fig. 11, representative results are shown for the cleaning effectiveness of the CHFM used. The respective pure water flow rate is applied depending on the trans-membrane pressure. The left diagram shows the pure water flow rates of a new membrane in comparison to a chemically purified membrane, which was used for eight hours for the filtration of oil/water mixtures. In the right diagram, the membrane was in operation for more than 70 hours under the same boundary conditions.

After the filtration test and the membrane cleaning, a pure water flow rate of 94% was achieved for the new membrane, which was in use for eight hours, with respect to the pure water flow rate of the new membrane (left diagram in Fig. 11).

With an operating time of 70 hours, the pure water flow rate of the membrane after chemical cleaning was 83% of the pure water flow rate of the new membrane (right diagram in Fig. 11). This shows that permanent fouling increases during longer operating times. Overall, the results of all the experiments show that the effectiveness of chemical cleaning for the exam-

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clear that through this simple mechanical backwashing, 75% of the original flow rate was achieved.

Backwashing can always be applied for the optimisation of the operating conditions for cross-flow filters, in order to control the membrane fouling and/or reduce it [26]. The effective monitoring of the membrane fouling with MF and with UF processes also depends on the kind and on the effectiveness of backwashing.

Different experiments have shown that an increase of the backwash frequency and the duration of the backwashing significantly reduces the membrane fouling [27].

Hence, the effectiveness of a quick backwashing for the increase of the membrane flow rate during cross-flow ultrafiltration of Produced Water was shown in this study.

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Highlights 2014

ined ceramic hollow fibre membranes was between 70% and 100%, depending on the operating conditions of the oil/water separation (test duration, CFV and oil concentration in the feed stream).

7. Conclusions Produced water (PW) as wastewater, which reaches the surface during crude oil extraction and natural gas extraction, constitutes the biggest wastewater volume that occurs in the crude oil and natural gas industries and is difficult to treat on account of contaminations contained in it and the often high oil concentration.

In this study, tests were presented for the efficient treatment of PW, on one hand with the use of oil/water mixtures from crude oil tank dewatering (TDPW) and on the other hand on the basis of oil/ water model systems (OMS). In this, a new innovative ultrafiltration membrane was used, consisting of a ceramic hollow fibre with a pore diameter of d90 = 40 nm.

During experiments, the influence of the cross-flow velocity and the oil concentration in the feed stream was examined with regard to the permeate flow rate and the purification performance with regard to oil and organic components (TC). The trans-membrane pressure for all filtration tests was 0.5 bar.

During treatment of TDPW and OMS, separation efficiencies were achieved with regard to the oil of more than 99.5% and with regard to organic matters of between 61% and 94%. Here, the cross-flow velocities were between 1.5 m·s-1 and 2.5 m·s-1.

The ceramic hollow fibre membrane used combines the advantages of an inorganic membrane material with the geometry of hollow fibre membranes and hence allows the application of a compact filter system. This allows a reduction of the space requirements and the weight of the required filter facilities with onshore and offshore plants under realistic industrial operating conditions. The presented membrane design also leads to a low trans-membrane pressure during operation and to high permeate flow rates because, with the presented double-layered membrane, the pressure drop across the openpore carrier structure can be neglected in comparison to the pressure drop across the active ultrafiltration separation layer.

The examinations have shown that the ceramic hollow fibre membrane used is also a robust solution for the treatment of wastewater that is heavily polluted with oil. Filtration with ceramic hollow fibre membranes can be used as an effective technology for the separation of oil

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and organic matters from produced water.

Because the examined ceramic hollow fibre membrane can be exposed to high crude oil concentrations in the feed stream of several thousand ppm, the potential is shown for combining several process stages in the present methods for the purification of Produced Water into one stage through the use of membrane filtration with ceramic hollow fibre membranes.

In this study, the effectiveness was shown of a purely mechanical and a chemically supported cleaning of the membrane by fast backwash cycles. The increase of membrane permeability after cleaning was determined in TDPW filtration processes with high oil concentrations. The results have shown that with chemical cleaning, pure water flow rates of 70% to 100% of a new membrane are achieved.

To optimise the filtration of produced water, other examinations are in preparation. Here, the objective is the development of the optimum combination of important process parameters.

Literature: [1] Folarin Y., Dongshan An, Sean Caffrey, Jung Soh, Christoph W. Sensen, Johanna Voordouw, Tom Jack, Gerrit Voordouw: Contribution of make-up water to the microbial community in an oil field from which oil is produced by produced water re-injection. International Biodeterioration & Biodegradation 81 (2013) 44-50.

[2] Kose B. et al.: Performance evaluation of a submerged membrane bioreactor for the treatment of brackish oil and natural gas field produced water, Desalination 285 (2012) 295–300.

[3] Bakke T., J. Klungsøyr, S. Sanni: Environmental impacts of produced water and drilling waste discharges from the Norwegian offshore petroleum industry. Marine Environmental Research 92 (2013) 154-169.

[4] Bailey B., M. Crabtree, J. Tyrie, J. Elphick, F. Kuchuk, C. Romano, L. Roodhart: Water control. Oilfield Review 12 (2000) 30–51.

[5] Veil J.A., M.G. Puder, D. Elcock, R.J. Redweik Jr.: A white paper describing produced water from production of crude oil, natural gas, and coal bed methane. Argonne National Laboratory, U.S., 2004.

[6] Alzahrani S., A.W. Mohammad, N. Hilal, P. Abdullah, O. Jaafar: Comparative study of NF and RO membranes in the treatment of produced water—Part I: Assessing water quality. Desalination 315 (2013) 18–26.

[7] Wandera D., S.R. Wickramasinghe, S.M. Husson: Modification and characterization of ultrafiltration membranes for treatment of produced water.

Journal of Membrane Science 373 (2011) 178–188.

[8] Horner J. E., J.W. Castle, J.H. Rodgers: A risk assessment approach to identifying constituents in oilfield produced water for treatment prior to beneficial use.

Ecotoxicology and Environmental Safety 74 (2011) 989-999.

[9] Lee K., J. Neff: Produced water - Environmental risks and advances in mitigation technologies, Springer (2011).

[10] Xu P., J.E. Drewes: Viability of nanofiltration and ultra-low pressure reverse osmosis membranes for multibeneficial use of methane produced water. Separation and Purification Technology 52 (1) (2006) 67.

[11] Fakhru’l-Razi A., A. Pendashteh, L.C. Abdullah, D.R.A. Biak, S.S. Madaeni, Z. Z. Abidin: Review of technologies for oil and gas produced water treatment.

Journal of Hazardous Materials 170 (2009) 530–551.

[12] Robinson D.: Oil and gas: Treatment of produced waters for injection and reinjection. Filtration + Separation 50 (4) (2013) 38-43.

[13] Alkhudhiri A., N. Darwish, N. Hilal: Produced water treatment: Application of air gap membrane distillation.

Desalination 309 (2013) 46–51.

[14] Yuliwati E., A.F. Ismail, T. Matsuura, M.A. Kassim, M.S. Abdullah: Effect of modified PVDF hollow fibre submerged ultrafiltration membrane for refinery wastewater treatment. Desalination 283 (2011) 214–220.

[15] Ahmadun F., A. Pendashteh, L.C. Abdullah, D.R. Awang Biak, S.S. Madaeni, Z.Z. Abidin: Review of technologies for oil and gas produced water treatment.

Journal of Hazardous Material 170 (2009) 530–551.

[16] Ebrahimi M., O. Schmitz, S. Kerker, F. Liebermann, P. Czermak: Dynamic cross-flow filtration of oilfield produced water by rotating ceramic filter discs. Desalination and Water Treatment, DOI:10.1080/19443994.2012. 694197.

[17] Ebrahimi M., Z. Kovacs, M. Schneider, P. Mund, P. Bolduan, P. Czermak: Multistage filtration process for efficient treatment of oil-field produced water using ceramic membranes. Desalination and Water Treatment 42 (2012) 17-23.

[18] Czermak P., M. Ebrahimi: Multiphase cross-flow filtration process for efficient treatment of oil-field produced water using ceramic membranes. Proceedings 7th Produced Water Workshop, paper 5, 29th – 30th April 2009, Aberdeen, UK. [19] Shams Ashaghi K., M. Ebrahimi, P. Czermak: Ceramic ultra- and nanofiltration membranes for oilfield produced water treatment - A mini review. The Open Environmental Journal 1 (2007) 1-8.

[20] Ebrahimi M., K. Shams Ashaghi, L. Engel, P. Mund, P. Bolduan, P. Czermak: Investigations on the use of different ceramic membranes for efficient oil-field produced water treatment. Desalination 250 (2010) 991-996.

[21] Lee M., Z. Wu, R. Wang, K. Li: Micro-structured alumina hollow fibre membranes - Potential applications in wastewater treatment. Journal of Membrane Science 461 (2014) 39–48.

[22] Tan X., K. Li: Inorganic hollow fibre membranes in catalytic processing. Current Opinion in Chemical Engineering 1 (2011) 69–76.

[23] Gaspar I., A. Koris, Z. Bertalan, G. Vatai: Comparison of ceramic capillary membrane and ceramic tubular membrane with inserted static mixer. Chemical Papers 65 (5) (2011) 596–602, DOI: 10.2478/s11696-011-0045-y.

[24] Chen H., A.S. Kim: Prediction of permeate flux decline in cross-flow membrane filtration of colloidal suspension: a radial basis function neural network approach. Desalination 192 (2006) 415–428.

[25] Reyhani A., F. Rekabdar, M. Hemmati, A. A. SafeKordi, M. Ahmadi: Optimization of conditions in ultrafiltration treatment of produced water by polymeric membrane using Taguchi approach.

Desalination and Water Treatment (2013) 1–10, DOI: 10.1080/19443994.2013.776505.

[26] Abdelrasoul A., H. Doan, A. Lohi: Mass Transfer Advances in sustainable energy and environment oriented numerical modeling, Chapter 8: Fouling in membrane filtration and remediation, methods. Book edited by Hironori Nakajima, ISBN 978-953-51-1170-2, Published: July 24, 2013.

[27] Hong S., P. Krishna, C. Hobbs, D. Kim, J. Cho: Variations in backwash efficiency during colloidal filtration of hollow-fibre microfiltration membrane. Desalination 17 (2005).

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Water management in the paper industry with and without membranes H. Lyko* The paper industry, as a large consumer of water for the production, has a great need for methods for the efďŹ cient use of wastewater streams. On the one hand, clean water should be recovered for reuse and therefore fresh water and wastewater costs should be reduced and on the other hand recyclables can be separated from wastewater streams and be supplied to further use. Moreover, through the removal of contaminants from process waters, the paper production can be designed more efďŹ ciently and the product quality can be improved. The membrane technology can make important contributions to all ďŹ elds. About 50 participants of the symposium â&#x20AC;&#x153;membrane technology in the paper industryâ&#x20AC;&#x153; could convince themselves of this. This symposium was organised by the Papiertechnische Stiftung in Munich together with the German Society of Membrane Technology (Deutsche Gesellschaft fĂźr Membrantechnik e.V. (DGMT), represented by board member Dr. Ines Bettermann). Directly afterwards, the seminar â&#x20AC;&#x153;water circuits in papermakingâ&#x20AC;&#x153; provided an overview about the embedding of different technologies for the optimisation of the water management of paper mills and the different measures for the containment of lime deposits, bioďŹ lms, slime deposits and odours.

Water circuits in the paper industry Although, on this occasion, this concerns lecture contents of the second event â&#x20AC;&#x153;Water circuits in the paper industryâ&#x20AC;&#x153;, here, they will be preceding the examples of the membrane technology because they illustrate the opportunities and limits of the circuit constriction and therefore also the challenges for membrane systems. Holger Jung, PTS, showed in his introduction about water circuits which water qualities are necessary at which places of the production, which processes enter contaminants into the water circuits and according to which criteria fresh water supply and circuit water treatment are optimised. If one follows the development of the fresh water consumption and the speciďŹ c wastewater volume from the paper and pulp industry throughout Europe (/1/, Fig. 1) and in Germany, the low seems to have been passed some years ago. As a reason for this, one can name the reconcentration of contaminants through lower fresh water supply, which adversely affect the products (scaling, bioďŹ lms), lead to deposits etc. on system components and cause intolerable staining with high-quality papers. Especially clean water is required, for example, directly on the paper machine for free spraying of the sieves and a shortfall of the volume or quality leads to losses in product quality. How far one has come up to now with advanced water management without membrane application which, among the rest, includes the sepaFig.1: Water proďŹ le of the European pulp and paper industry (source: /1/). According to this, 92% of the used water is being released back into the environment

*Dr.-Ing. Hildegard Lyko Dortmund, E-mail mylko@t-online.de

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ration of the water circuits between paper machine and substance treatment as well as the counterflow management of process water was shown by Heiner Meister and

Klaus Müller-Gommert of the paper mill UPM Augsburg. Here, a restriction of the circuits could be achieved for a fresh water need for the production of graphic papers

Fig.2: Water balance of a production facility for cardboard and packaging papers (free after the lecture of Lucas A. Menke, Meri Environmental Solutions GmbH)

Fig.3: Concept for the integrated process water treatment in a production facility for cardboard and packaging papers (free after the lecture of Luca A. Menke, Meri Environmental Solutions GmbH)

to under 6 l/kg, however, the increases of the CSB load and/or the contaminants load in the paper machine circuit also became clear. For the production of cardboard and packaging papers from waste paper, Lucas Menke of Meri Environmental Solutions GmbH showed how to proceed with the design and planning of water circuits. As an example of the interconnection of different wastewater treatment processes, a solution with integrated circuit water treatment was shown in which the wastewater from the stock preparation is subjected to an integrated preclarification through flotation before it runs through an anaerobic wastewater treatment and a lime trap.

The thus purified water is guided back into the process either directly via a sand filter or via the detour of an aerobic stage.

Wastewater that leaves the production facility to the outside is released from the aerobic stage with secondary clarification (see Fig. 2 and 3) Dr. Benjamin Simstich, PTS, also spoke about the circuit closure or restriction through integrated biological wastewater treatment. Its big potential is in that it relieves the water circuits of organic water constituents (COD) and therefore also prevents odour and slime problems.

On the other hand, it causes no retention of dissolved salts, moreover, the calcium carbonate concentration is also increased through the entry of atmospheric oxygen in an activated sludge process. However, Simstich pointed out that the calcium concentration can still reduce in the total circuit. In waste paper- processing ope-

Fig.4: Functional diagram of vapour permeation through a hollow fibre membrane and arrangement of the modules in the waste gas channel in the EU-Project CapWa (www.watercapture.eu)

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rations, less CaCO3 is extracted from the waste paper - due to the higher pH value of the effluent of the biological cleaning step - during the substance treatment.

Typical applications of membrane technologies in the paper industry The application of membranes is not new in general in the paper and pulp industry. The Scandinavian enterprise of Alfa-Laval can point to more than 50 references since the 1970-s concerning this. Dr. Frank Lipnizki explained the basic principles of the liquid filtration with membranes as well as different module construction types and illustrated the diversity of the application possibilities for paper wastewater with the help of different examples. In detail, the following were described: the filtration of the wastewater after the chemo-thermal decomposition of wood with subsequent shredding for the production of pulp (CTMP process), the filtration of bleachery effluent from the kraft process as well as the treatment of printing presses wastewater. With the CTMP wastewater, different ultrafiltration membranes (different membrane materials and separation limits) were tested. The retention of TOC and the achieved flow rates as a function of the concentration

were positive in the laboratory tests and pilot test, as the next step, a long-term test of several months should follow. The permeate can be used again, for example, for washing the wood chips. With the treatment of the bleachery effluent, it was a matter, primarily, of retaining and concentrating the colour particles since they hinder the biological wastewater treatment. This was implemented with a 25μmprefiltration for the reduction of the fibre proportion and a subsequent nano/ultrafiltration. The chemical oxygen demand was thereby reduced by 80%, at a permeate yield of 92%. Printing machine wastewater includes of course high concentrations of dyes. Here, the conventional treatment with a precipitation and subsequent separation of the dyes through a filter press was replaced through a 50 μm- prefiltration and an ultrafiltration. Therefore, a volume reduction by the factor 35 could be achieved, as well as a clear reduction of investment and operating costs compared with conventional treatment. Lipnizki saw the future of the paper industry in its expansion to biorefinery on pulp basis, in which all incurred residual materials are being recycled.

Kurt Schloffer, managing partner of Added Value GmbH with headquarters in Kuchl, Austria, reported about the

recovery of lignin from pulp bleachery wastewater with the help of a dynamic membrane filtration system. The method was already introduced at last year’s PTS environmental symposium and is described in /2/.

Membrane materials that, among the rest, are also well suited for the lignin separation, are being developed by the working group membrane technology at the Fraunhofer Institute for Applied Polymer Research in Potsdam. Detlev Fritsch, IAP, presented the filtration results that had been obtained with polyacrylonitrile membranes made at the IAP. The tests were carried out with model mixtures containing lignin precipitated from black liquor. The model solution was set to pH 9 with NaOH. The solutions were filtered with membranes with pore width between 21 and 25 nm at a filtration pressure of 10 bar, wherein membrane flow rates of 20 to 40 l/(m2/h) could be achieved. Due to the top layer formation on the membrane, appearing with increasing filtration time, the measurable separation limit decreased from at the beginning 450 Da to about 350 Da. Moreover, the average molecular weight of the retentate increased slightly compared with the average molecular weight in the source solution – an indication that low molecular mass dissolved

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substances and salts pass into the permeate and, therefore, the membrane is also suitable for purification of the lignin.

This event “membrane technology in the paper industry” was already the fifth of its kind (the fourth one took place in early summer, 2012,p. /3/), still, Dr. Benjamin Simstich, project manager with focus membrane technology at the PTS, called membranes “exotics” within the paper industry. They would be used up to now only in special cases with limited fresh water supply or if they will be necessary to comply with initiating limits. This is partly because membrane processes are often not economical if they “only” recover water and possibly fibres as the only recyclables. The focus of the work of the PTS in the area of membrane technology, on the other hand, was in the development of integrated membrane processes that, in case of consideration of the entire papermaking process, hold a technological and economical advantage for the user.

As examples of such processes, Simstich named the treatment of bonnet condensate by means of reverse osmosis, the thermophilic application of submerged MBR, the direct ultrafiltration of circuit water as well as anaerobic membrane bioreactors.

Bonnet condensate occurs when drying processes are operated with two-stage heat recovery. During papermaking, about 0,4 l/kg of condensate originate, which are, depending on the paper machine, 1 – 15 m3/h.

Because the condensate in itself already has a high quality, the processing into boiler feed water for vapour generation in-house offers itself as an option.

The purification of circuit water in paper mills with a thermophilic MBR offers two essential advantages: on the one hand, the MBR technology delivers a water quality that is suited for reuse, on the other hand, the waste water treatment with a temperature level of 40 – 60 °C without cooling means a clear savings in vapour.

The feasibility of the method has already been proven (s. a.a. /4/), further projects for the monitoring and control of lime precipitations as well as for the development of the first large-scale plant are either already running or are in preparation.

On direct use of submerged ultrafiltration modules in sieve water ducts, there was a ZIM project for the development of a prototype. The super clear filtrate obtained in this way should be reused in the hose nozzles on the paper machine sieve, whereby, on the one hand, fresh water (approx.

5%) is saved as well as, on the other hand, energy, because the temperature in the water circuit increases.

An anaerobic membrane bioreactor (ANMBR) offers wastewater treatment and generation of biogas in one unit. The

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membranes provide for water absolutely free of solid matter and one counts on a higher degradation rate of organic load and a more stable operation than with the anaerobic fermentation without membrane filtration. On the other hand, anaerobic microorganisms are a bit more sophisticated than aerobic ones, regarding the process conditions, and the anaerobic biomass also constitutes a challenge for filtration.

The PTS investigated ANMBR- technology as a cooperation partner of Bauer Resources GmbH (cf. also /2/), in order to make available an energy-self-sufficient method for the treatment of partial streams for the paper industry.

Dario Gallottini of Kubota Membrane Europe Ltd., London reported about the application of Kubota-flat membrane modules in ANMBR- plants. The focus of the Kubota-ANMBR-Technology is on the treatment of wastewater with more than 50.000 mg/l CSB, which is why the industrial scale references can also be found in the food and liquor production.

The advantage of the membrane filtration here, beside the reduction of fermentation tanks because of the higher rate of degradation, is in the removal of fermentation inhibitors like ammonia through the membrane.

Also in paper mills, sudden emergency situations or bottlenecks can make the application of a mobile membrane system for water treatment necessary, for example, in establishments where the raw water quality is subject to seasonal fluctuations so that an actually functioning conventional water treatment is not sufficient during certain periods. For this purpose, Pall offers its Aria™ Mobile-PAMC60System, ready for connection with pre-filtration, control unit and equipment for cleaning and backwashing in the container.

Walter Mach demonstrated the details and the performance capacity of the system, at the core of which are the so-called Mikroza®- hollow fibre modules.

Operating experience with MBR plants The cardboard factory Albert Köhler GmbH & Co. KG in Gengenbach has been operating a wastewater treatment plant with MBR and subsequent reverse osmosis since 2009. The ultrafiltrate of the MBR, like the permeate of the RO, are guided back into the production process and only the RO concentrate is discharged as effluent into the municipal sewer system. The plant is the result of a research and development project in cooperation with Siemens AG. Bernd Müller, Siemens AG, and the technical director of the cardboard factory, Thomas Dörfer, presented the plant structure, the problems

that have appeared in the meantime and the solutions found. Ca-scaling turned out to be an essential problem, partially due to the deterioration of the quality of the recycled paper used in the period between plant planning and today. Here, a water softening plant after the preclarification could remedy the situation. To reduce the salination of the ultrafiltrate, moreover, the activated sludge is de-ashed. As additional measures, the membrane cleaning and the conditioning of the wastewater were adjusted after the softening (the latter became necessary through the softening).

All in all, the effluent quality of wastewater has now become so good that one is negotiating about direct discharge for the remaining 71m3/d of residual wastewater instead of the original 948 m3/d.

Moreover, through the high proportion of the re-use of treated wastewater, the fresh water consumption was reduced by about 80 %, at a slight increase in production.

The special paper mill Louisenthal GmbH has four years of operational experience with the integrated wastewater treatment with recycling. As a raw material, only fresh fibres are used, in contrast to the cardboard production named above, no wastepaper. As Hubert Bauer as representative of the operator and Alfred Helble, CM Consult, explained, the raw material contains spinnable fibres so that one decided for the application of flat membrane modules because with hollow fibre modules, there would be a risk for braiding. The MBR plant purifies a partial stream of about 790 m3/d of the production wastewater, so that the municipal sewage treatment plant is relieved of about 40% of the initiated quantity and the organic load.

The filtrate free of solid matter is recycled, whereby 50% of the fresh water is saved.

In the separate filtration basin, there are 12 flat membrane modules with a total of 2.700 m2 of membrane area installed in two trains. Initial operational problems rather concerned the biology (sub-optimal oxygen control, foaming) than the membrane filtration. The investment costs in the amount of about 2Mio. € amortise after about three years.

Water recovery from waste gas / waste vapour During the paper production, about 1.5 to 2 m3 per tonne of paper are lost as a vapour into the atmosphere, this is about 10-30% of the total water consumed. For comparison: in the cooling tower of a conventional coal-fired power plant, about 500% of the water consumed for vapour generation pass into the atmosphere, in a gas and vapour combined cycle power plant after all 100 %. These figures were presented by Dr. Ines Bettermann, Cut

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Membrane Technology GmbH, in her review of the European research project CapWa (Capture of evaporated water, Details s. www.watercapture.eu). Here, the recovery of water from waste gases / waste vapour was developed by means of water vapour permeation from the waste gas / vapour mixture from the outside into the interior of hollow fibre membranes (see Fig. 4). Among the rest, pilot tests were also carried out at the papermaker SAPPI in Nijmegen (NL) with the waste gases of the drying units. The task of CUT in this project was the development of a suitable membrane module from hollow fibers that had been obtained through coating of PES for UF with sulphonated polyetheretherketone (SPEEK). Up to the completion of the project in autumn, 2013, the manufacturing process for the module was automated so that a total of 46 modules, each with 1 m2 of membrane area could be produced. The hollow fibers arranged in rectangular frames are subjected to vertical incident flow. With the pilot tests in the paper mill, up to 1.8 l(m2 h) of water could be recovered at 2-month continuous operation of the module. The conductivity, at 8.2 μS/cm, clearly fell short of the required limit value of 20 μS/

cm. Beside the recovery of pure water, the integration of this method into the paper drying process offers the advantage of more efficient heat recovery and therefore of a reduction of the energy consumption.

Optimisation of the effluent treatment in paper mills The performance efficiency and operational stability of membrane bioreactors for wastewater treatment is determined by a huge number of influencing factors.

Thomas Wozniak, Nalco Deutschland GmbH, reported about cases where existing plants have been optimised through various measures in such a manner that performance efficiency and operational stability could be increased. Thus, in a 10 year-old MBR plant in a French paper mill, the ventilation was automated and an oxygen monitoring introduced, moreover, the pH value was reduced permanently to a value below 8, in order to prevent calcium scaling, a polymer was metered in that improves the sludge structure, and the sludge re-circulation was provided with even greater flexibility through frequency control of the pumps and the interposition of a buffer tank. With these measures, the

permeability of the membranes and the solid matter concentrations in the bioreactor could be increased. Therefore, no more unfiltered wastewater had to be conducted in the bypass, the capacity of the plant was increased at concurrent reduction of the energy consumption and the surplus sludge accumulation. Additional practical examples related to the pretreatment of paper effluent prior to biological wastewater treatment by means of flotation. Here, the automatic control unit 3D Trasar™ was used, with which input and effluent quality of the flotation are determined continuously via a turbidity measurement and the additional chemicals are dosed automatically adjusted. In three applications of the paper and pulp industry, it could be shown that, with this system, the outlet turbidity can be decreased and can be made more uniform.

Treatment of printing effluent With offset printing, the printing plate is wetted with a thin dampening water film before the printing sites are dyed with printing ink by the inking rollers. Dampening water is spiked with a huge number of additives (e.g. tensides) for the optimisati-

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on of the chemical and physical interaction between printing ink, dampening water and printing plate, moreover running off dampening water is contaminated with flushed out printing ink and paper fibers.

The conventional methods of dampening water treatment consist of filtration with filter mats, bags or cartridges and/or sand filters that either have a low service life or are difficult to regenerate. As an alternative, Baldwin Technology GmbH, under the name Pure Filtration, offers crossflow-microfiltration with ceramic membranes. Ernst Engelhardt described the details of the entire dampening water treatment plant in which a sedimentation tank is added upstream of the membrane system, in which also a greater proportion of the dye floats up. The dampening water filtration is done in the bypass, the filtration plant is designed in stainless steel. For the prevention / elimination of membrane blockages through dyes, an automatic thermal-chemical purification takes place, approximately every 7 days.

Paper effluent as a raw material source In the Dutch Kenniscentrum Papier en Karton (KCPK), one is dedicated to the development of the waste-free paper mill, in which all components that arise within the industrial facility except for the product (paper or cardboard) are recovered as recyclables or can be processed in further steps into valuable chemical feedstocks. Michiel Adriaanse looked at the effluents of paper mills and cartonboard mills as a gold mine and reported about different already ongoing projects and visions for the future paper production in a so-called MIMO-(multiple input, multiple output)- factory, in which paper is only one of many products. Multiple Input in this context means that one also uses other (plant-based) raw materials for fibre recovery. These are also reflected in the CSB content of the effluent and in the concentrations and in the variety of utilizable wastewater constituents. As practical examples, already tested on a pilot scale, the production of greengas (biogas with 90% of methane content) through high- pressure fermentation with special bacteria and the recovery of fatty acids contained in the wastewater, were named.

The latter can serve later for the production of polyhydroxyalkanoates (biopolymers (PHA)). A further possibility of resource recovery from waste water is the biological wastewater treatment with the Nereda®- method (s. /5/), in which, inter alia, an alginate arises that can be used for the production of alternative adhesives.

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Effect and continuance of chemical additives In the paper industry, according to raw material state and product requirements, a huge number of process chemicals and functional chemicals are used that one can find again in products and solid residual materials, however, also in the waste air and in water circuits. Jürgen Belle of University of Applied Sciences Munich, described the systematics according to which the chemical additives are accounted for in ecologically relevant process sections and illustrated for the retention means of polyacrylamide that the calculated concentration of this agent in the water circuit amounts to maximum 10 ppb. This value is smaller by two orders of magnitude than values that have been found before in food. The possibilities for the disinfection of the fresh water were the subject of the talk of Elke Tiedtke, Kolb Deutschland GmbH. Particularly when using surface water, microorganisms can be expected. Moreover, the water quality fluctuates depending on the temperature, the amount of precipitation and the season. For disinfection, UV radiation and the use of biocides are on offer, wherein a combination of both methods with an online control of the biocide compensates the respective disadvantages of both methods. This consists essentially in that the UV disinfection has less of an effect in turbid waters and, moreover, has no controlled sustained release effect and that biocides also represent wastewater pollution and possibly affect the biological wastewater treatment. The Swiss enterprise Servophil AG also supplies biocides for the treatment of circulating waters.

Dr. Frank Dürkes introduced the different substance groups and illustrated which effects an adapted dosing technology can have on the effectiveness of biocides for preventing slime formation and how one can detect the distribution of agents in the water circuit. Because the actual biocide is absorbed too quickly by biofilms, it is difficult to detect.

Therefore measurements were carried out at a production site with lithium salt as a tracer. In this manner, the dosing technology was optimised. The mode of action of the combination of microbiological deposit monitoring and antiscaling dosage in paper machine cycle with circuit water treatment through sedimentation, anaerobic and aerobic biological stages of treatment, was demonstrated by Peter Dittmann of ICL Performance Products. Here, it was in the essentials about the prevention of lime precipitations in the anaerobic stage.

Chemical additives that are dosed either for the attainment of a certain paper quality or for the prevention of biofilms or lime deposits have been partially found again in circulating water and can affect the

biological wastewater treatment. Gabriele Weinberger, PTS, distinguished between the possible effects of different additives that either directly biostatically inhibit the biological degradation of water constituents or indirectly end up as an additional load in the sewage treatment plant. Thus, investigations on degradability were carried out for different chemicals. During anaerobic wastewater treatment, additives, through various forms of sludge degeneration, can impede the mass transfer and therefore the substrate degradation and reduce the biogas yield. Among the rest, as a consequence of problems that have appeared up to now, there is a requirement for coordinating the kind and dosage of additives with the persons responsible for the wastewater treatment.

Problems in the water circuit Raw materials, process waters and products from paper mills emit different odour substances that can become disagreeable, particularly with biological degradation processes and other transformation processes, for example, if not stored correctly.

Dr. Kerstin Keppler of Wöllner GmbH & Co. KG differentiated between the different odours that can appear in a paper mill and explained how one detects such smells with “electronic noses“, special gas sensor systems. Nevertheless, their evaluation is very time consuming and is done via statistical algorithms. To narrow down odour causes, it helps to create an odour database.

Holger Jung, PTS, in the last lecture of the event, laid the focus on calcium deposits and odour problems. Calcium carbonate is used as ingredient of coating paint and as a filler and accordingly dissolved increasingly when using waste paper as raw material and entered into the process water. Odour problems appear, for example, with anaerobic microbial processes. With the latter, organic acids originate that lower the pH-value and increase the solubility for CaCO3 and therefore the water hardness. Because of the complexity of these relationships, a huge number of methods was discussed for the reduction of calcium problems and odour problems in water circuits.

Literature: /1/ CEPI Sustainability Report 2013; s. www.cepi.org /2/ Lyko, H.: Papier- und Zellstoffindustrie auf ihrem Weg zur nachhaltigen Produktion – report of PTS Umwelt Symposium 2013; F&S Filtrieren und Separieren 27 (2013) No. 6, p. 389 – 394 /3/ Simstich, B.; Jung, H.: Water management in the paper industry: Solving scaling problems and recovering recyclable materials by means of membrane processes; F&S International Edition No. 13 (2013) p. 26 – 28 /4/ Simstich, B., Beimfohr, C.; Lyko, M.; Horn, H.: Thermophiler Betrieb eines getauchten MBR bei 50°C zur Prozesswasserreinigung in der Papierindustrie, KA Korrespondenz Abwasser, Abfall 2012 (59) No. 5, S. 465-472 /5/ de Kreuk, M.K., Pronk, M.; van Loosdrecht, M.C.M.: Formation of aerobic granules and conversion processes in an aerobic granular sludge reactor at moderate and low temperatures; Water Research Vol 39 (2005) No. 18, p.

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Technical solutions and innovations for wastewater treatment and sewage sludge treatment A report on the IFAT 2014 H. Lyko* With more than 135,000 visitors from all over the world and 3081 exhibitors from 59 nations, last year’s IFAT could achieve an impressive record. Under the keywords water and wastewater treatment alone, which also included the sewage sludge treatment, 846 exhibitors were registered with just about 300 different products. These figures underline the diversity of the offer of technologies, which in turn are an indication of the just as varied requirements through different users worldwide, given through local circumstances and legal boundary conditions. The possibilities to collect wastewater in a decentralised manner as well as centrally and to purify it, moreover, have led to a huge variation range in components and/or system sizes and the selection of a certain technology is often directed also on the wastewater volume to be treated. It is impossible to appreciate all relevant products and services. Hereinafter, current topics and some innovative products shall be looked at as examples.

Discussion topics related to water and wastewater The IFAT is not only a marketplace for products but its size and internationality also offered space for enterprise associations and national as well as international organisations to maintain and to develop their networks as well as to demonstrate also the topics which they consider to be most important to a wide audience.

Here, at national level, the new establishment of the „Initiative Verantwortung Wasser und Umwelt“ (initiative responsibility for water and environment) should be pointed out, which has originated from the working committee Civil Engineering in the discussion group Building Materials Industry in the Federation of the German Trade with Building Materials (Bundesverband Deutscher Baustoff-Fachhandel, BDB e.V). This initiative is committed to the rehabilitation of the sewer system in Germany. In the press conference in Munich, the spokesperson for the initiative, Rainer Mohr, managing director of Aco Tiefbau Vertrieb GmbH, and the chief executive of the BDB, Michael Hölker, pointed out a renovation need of the 540,000-kilometre-long sewer system in Germany at about 6.9 billion euros per year. This need, which was determined from the inspection of meanwhile 80% of the system and a presumed service life of 100 years, is contrary to the actually paid public sector investment of about 4 billion euros. The disproportion between required and effected investments was also named in the 2014 politics memorandum of the German Association for Water, Wastewater and Waste (Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V. DWA) /1/. Damaged ducts pose the dangers of infiltration of additional water and the exfiltration of untreated effluent into the soil and into groundwaterbearing strata. On inquiry, Rainer Mohr informed that one currently reckoned with an exfiltration rate of 10 – 30 % (depending on the condition of the sewer system of a city / municipality). Which hazard potential emanates from leaky sewers can be read up upon, among other things, in Jianmin Hua /2/. Wastewater ingredients which are not biodegraded in the soil on their seepage route can be found in the ground water later on and possibly also in the inflow of potable water treatment plants.

This applies with certainty also for the huge number of anthropogenic trace substances such as pharmaceutical residues or their by-products, which are discharged with municipal waste-

water. The recording and elimination of these substances was considered with many exhibitors in product development and process developments. Some examples were also to be seen at the booth of the German Federal Environment Foundation (Deutsche Bundesstiftung Umwelt DBU), which supports several research projects on the development of elimination procedures and has

*Dr.-Ing. Hildegard Lyko Dortmund, E-mail mylko@t-online.de

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been dealing for 15 years already with the subject of vegetated soil filters as a close to nature additional purification process.

In a panel discussion, Prof. Wolfgang Günthert, vice president of the DWA and Dr. Heinrich Bottermann, Secretary General of the DBU, faced the questions of the presenter and the audience on the handling of anthropogenic trace substances. The position of the DWA is published in a separate position paper /3/ and was set forth by Prof. Günthert. After better and better analytics have led to the detection of several hundred different substances in waters, a scientific evaluation of the resulting risks is necessary. With the environmental quality standards coming from the EU water protection law, one calls for a harmonisation with the substance investigation and substance-evaluation-program according to the REACH Ordinance.

An exhaustive introduction of the fourth cleansing stage independent of the initiating waters concerned is believed not to be appropriate. At the panel discussion, rather, strategies were also discussed with which entries of trace substances such as pharmaceuticals into the wastewater can be avoided. Among the rest, this includes the decentralised detection and treatment of particularly contaminated wastewater, for example, from hospitals and nursing homes, however, also the question as to whether the ecotoxicological effect of a drug should be relevant for approval, something that is not yet the case up to now.

Water and wastewater filtration There were various different filter construction types on display that can perform the particle retention from water or wastewater streams at various points of a municipal or industrial treatment plant.

For the protection of membrane elements in the potable water treatment and wastewater treatment, however, also for the filtration of sewage treatment plant effluents, Boll & Kirch Filterbau GmbH offers automatically operated edge filter candles with filter ratings of up to 50 μm.

For especially difficult filtration conditions, such as for example for non-pretreated river water or very fibre-contaminated process water from the paper production, the so-called bipolar filtration is implemented in the filter model 6.18.2 (Heavy Duty). In this case, the raw water flows into the filter candle from both sides.

During the backwash phase, a hydrodynamic element arranged in the middle of the candle increases the flow speed and thus the cleaning effect.

Alfa-Laval presented a new robust flat filter element (IsoDisc) that can be used for

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Fig. 1: RoDisc®- Disc filter - Pilot plant with upstream flocculation reactor on the sewage treatment plant Mannheim (Photo: Huber SE)

tertiary filtration, process filtration or the filtration of surface water. As a filter medium in the IsoDisc system that is based on technologies of the enterprise of Ashbrook Simon-Hartley acquired in 2012, a kind of pile material medium is used, and the driving force for the filtration is the gravity.

The filter element is completely immersed during the filtration. Particles of ≥ 10 μm can be separated and the filtrate fulfils the criteria for a reusability of the water, such as for example the Californian standard 22, which dictates an average turbidity of ≤ 2 NTU (24 h- Mean). The double-layer fabric plates are backwashed for cleaning with filtrate. When required, every individual filter plate can be taken out and be exchanged during the running filtration operation. The system can be installed in concrete basins as well as in steel tanks and is also suited for the retrofitting of existing wastewater treatment plants.

The filtration of the effluent of a biological wastewater treatment is also one of the application fields of the RoDiscdisc filter by Huber. This is recently also being used together with a cleaning stage for the adsorption of non-biodegradable trace substances in powdered activated carbon. The adsorption takes place in a contact reactor downstream to the secondary clarifier to which a sedimentation basin is connected. In this the biggest part of the carbon is separated under addition of precipitation and flocculation agents and is transported back into the contact reactor. The non-sedimented fine fraction is separated with the disc filter. With investigations of the effectiveness of the procedure on the sewage treatment plant in Mannheim (see. Fig. 1) values of the

filtrate turbidity were measured of less than 1 FNU. The ultrafiltration of wastewater with a solid matter content that is well below that which prevails for example in an activation tank, however, far above typical potable water applications can also be performed with from the outside inwards permeated hollow fibre membranes in a pressure-driven process. For this purpose, the hollow fibres are mechanically stabilised, in order to withstand the higher filtration pressures. Corresponding filtration systems are ZeeWeed 1500 by GE Water & Process Technologies or the system MegaPure™ by Koch. The cleaning of any top layers on the membranes is caused through blowing in of air. At MegaPure™, the module design of the submerged Puron-hollow fibre modules was taken over, in which the hollow fibres are only potted at the bottom of the module and at the upper end are freely movable so that the cleaning of the membrane surfaces through the air bubbles is facilitated. The stated solid tolerance in the raw water amounts to maximum 250 mgl/l. Among the rest, the following are indicated as possible applications for this ultrafiltration: the pretreatment for seawater desalination before a reverse osmosis and the tertiary cleaning of sewage treatment plant effluents.

MBR- technology MBR technology is experiencing international growth rates and this not only in view of the number of the installed plants but also increasingly bigger MBR plants are being built. Recent market forecasts are provided by the study by Transparency

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Market Research (www.transparencymarketresearch.com), in which one assumes an increase of the global market volume from 963.8 million US$ in 2012 to about 2.5 billion US$ by 2019, namely both for submerged as well as external membrane systems. One example of the increasing establishment of big plants is the successful installation of the submerged VRM system in the biggest municipal sewage treatment plant of Russia, about which Huber SE reported. In the plant, which was put into operation in autumn, 2013, a total of 92.160 m2 membrane area is installed in six ďŹ ltration streets with four VRM 30/640 each.

To further reduce with a big module for big sewage treatment plants above all investment costs and operating costs per square metre of installed membrane area was the motivation for Microdyn-Nadir for the development of the BioCel XL with 1.900 m2 of membrane area that was to be seen for the ďŹ rst time at the IFAT (see separate article within this issue). The ďŹ rst modules were already sold at the trade fair.

Also with the MBR technology, activities prevail to sensibly integrate an adsorption of not biologically degradable or poorly degradable substances into an overall plant. GE water & process does this with the MACarrier-MBR- process, wherein MACarrier is a carbon-based product developed in the Chinese technology centre by GE, which is particularly adapted to the ZeeWeed 500Dhollow ďŹ bre modules. The process should especially also provide for a further CSB reduction in industrial efďŹ&#x201A;uent treatment plants.

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Dewatering and thickening of (sewage) sludge The topic of sewage sludge thickening and - dewatering is still characterized by the pressure on sewage plant operators to minimise the costs for the sludge treatment and/or disposal. In the process of this, the optimum technical solutions vary according to the incurred sludge volumes and the local circumstances (incineration present on site, length of possible routes of transport).

Codecisive for the dewatering result (dry substance content of the dewatered sludge as well as clarity of the centrate / ďŹ ltrate) is, in addition to the machine parameters, the dosage of ďŹ&#x201A;occulation agents with which large, settleable ďŹ&#x201A;akes result from the originally small and difďŹ cult to separate sludge ďŹ&#x201A;akes and which, through the formation of ďŹ brous scaffolds, increase the water release capacity for sludges/3/. The optimisation of the operating costs of a sludge dewatering will always happen taking into account the costs for energy, ďŹ&#x201A;occulants and if applicable disposal costs of the dewatered sludge.

Drivers of the sludge dewatering are decanters and belt presses, moreover ďŹ lter presses and screw presses are also used. Decanters and belt presses are considered as the machine models that can process big sludge volumes and with which relatively high degrees of dewatering in the order of magnitude of about 25 % DS can be achieved. There, the achievable drying degree depends on the kind of the sludge and the volume of added ďŹ&#x201A;occulation agents. With newer generation decanters, one succeeds meanwhile to push the average energy requirements for the dewatering of thin sludge to a value of about 0,5kWh per m3. The manufacturers GEA Westfalia Separator report this independently of each other for their machine series waterMaster and Alfa-Laval for the decanter ALDEC G3.

Hiller GmbH showed at the IFAT with the help of its â&#x20AC;&#x153;ECO cockpitâ&#x20AC;?, with which simple economic efďŹ ciency calculations could be carried out, which saving potentials result through the optimised use of their decanter DekaPress for sewage treatment plants, particularly in view of disposal costs and polymer consumption. As a recent reference, one should point out the new installation of a decanter in the 10.000 PE- sewage treatment plant Augustdorf in the vicinity of the Teutoburg Forest in Germany, where a 27 year-old dewatering unit was replaced. Thereby, on

F & S International Edition

No. 15/2015

With 45 years' experience and more than 5500 decanters manufactured, HILLER is a world-leading manufacturer of decanter centrifuges and a specialist in the construction of entire plants for solid/liquid separation.

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Highlights 2014

account of the newly achieved dewatering result of 21-22% DS savings arose of annually about 45,000 disposal costs.

Up to 40% less energy consumption than with predecessor machines is also promised by Andritz Separation for the new series of decanter centrifuges (see Fig. 2), which are equipped with a direct gear unit for the screw drive, turbojet weir plates and the feature HPP (High Hydraulic Pressure, means a reduced diameter outlet, through which the loss of acceleration energy for liquid and solid matter is reduced).

Gebr. Bellmer GmbH is primarily represented in the area of sewage sludge treatment with the sieve belt press WinkelPresse as well as with the belt thickener TurboDrain. The product ranges Green Line™ of these two machine models are equipped with so-called Nanotechsieves. These, on account of their special surface properties, provide for it that the water can run off particularly well and sludge particles do not get stuck. This facilitates the filtration as well as the sieve cleaning and reduces the polymer consumption. The high quality of the filtrate of the TurboDrain belt thickener shows at the sewage treatment plant Benningsen of the city of Springe. There, this machine fulfils not only the task of the thickening of the surplus sludge but also functions as a secondary clarifier unit in case of overload of the secondary clarifier tank in case of strong rain events by filtering a partial stream of biologically treated wastewater.

The filtrate can be introduced directly into the receiving water body under observance of the Water Act requirements.

Screw presses are often offered as machines for the dewatering of structured sludges. In such implementations, they

cannot achieve the solid matter contents that are attainable with decanters and belt presses for sewage sludge. However, in view of investment and energy costs, they are attractive especially for smaller sewage treatment plants. Alfa Laval presented a screw press at the IFAT that was developed especially also for the requirements through sewage sludge and has been on the market since about two years. It should provide an alternative for mobile sludge treatment, particularly for smaller sewage treatment plants of about 5.000 to 10.000 PE. Since, with the wage dewatering, no expensive machines must be provided on site, however, odour-tight containers for temporary storage have to be present. In the screw press, the separation is done in an inclined drum, in which the sludge is pressed through a conveyor screw against a cylinder envelope designed as a wedge wire screen and is thus dewatered. The driving mechanism of the auger is a small electric motor with parallel shaft helical gear. In contrast to a decanter, a screw press runs very slowly and quietly. The energy requirements were stated as about 1.5 kWh for the dewatering of 8-10m3 of sludge.

The Bauer Group, with head office in Voitsberg, Austria, has its main business area in agriculture and also has been building for a long time screw presses for the solid-liquid separation of slurry and digestate. They used the IFAT for the presentation of the new sludge press separator with which they want to enter the market of the sewage sludge treatment. In a twoyear development phase, a machine was developed on the basis of an existing press screw separator that should dewater the sludges from sewage treatment plants in the order of magnitude of 20,000 to 50,000

PE, from the wastewater treatment from slaughterhouses or industrial sludges. Also here, the challenge lay in achieving a satisfactory dewatering performance for originally little structured sewage sludge.

Moreover, the equipment unit should be compact at high capacity, offer a high operational reliability and be reasonably priced. The prototype of the SPS 1200 (see Fig. 3) was completed at the end of 2012 and the first series could be released in September, 2013. One special feature is the auger, newly designed for sewage sludge dewatering, which is made from a kind of plastic which also withstands aggressive industrial sludges. The dewatering degrees achieved in the test were up to 30 % DS for digested sludge. The flocculant consumption necessary for the dewatering was stated with 9 – 15 kg WS/t of solid matter. The connected load of the machine, which processes 2m3/h of sludge with 2 – 9 % DS, amounts to 0,55 kW. In view of the newly presented screw presses especially for sewage sludge, it should be noted for the sake of completeness that Huber SE has for some time been offering screw presses for sludge dewatering. The large RoS 3Q 280 achieves, according to experience reports from an American sewage treatment plant, throughput rates from more than 25 m3/h and dewatering degrees of more than 30% and is also being used in large sewage treatment plants, e.g. in the 140.000 EWplant at the Georgian Black Sea Coast.

With their hydraulic presses that, in contrast to decanters and also the named above screw presses, can achieve very high dewatering degrees of up to 50 % DS in the filter cake, the Swiss enterprise of Bucher Unipektin AG offers an alternative dewatering technology. With the patented method, sewage sludge is filled into a chamber where there are drainage hoses via which the squeezed-out water is discharged while a hydraulically operated pressing piston restricts the sludge space.

This technology is not new but already executed in more than 2000 plants worldwide. One achieves the highest dewatering degrees above 35 % DS, by conditioning the thin sludge, beside a polymer addition, still through addition of 95% sulphuric acid and 50 % hydrogen peroxide solution (Kemicond method). The amount of polymer used thereafter is then relatively low, with 4 – 7kg/ t DS. At the IFAT, the enterprise for the first time presented its new mobile dewatering plant with complete equipment and a Bucher HPS 3700 press, which, as smallest of this machine series, can process 130 -200 kg of solid matter per hour.

Fig. 2: New Andritz-decanter with up to 40 % less energy consumption

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F & S International Edition

No. 15/2015

Highlights 2014

efďŹ ciency and strength, however, tend to have lower permeability and are more difďŹ cult to clean off, while monoďŹ lament fabrics rather have a high permeability, lower tendency to clog and good release behaviour, however, not as a high separation efďŹ ciency degrees and strengths. For application in ďŹ lter presses, media with air permeabilities from 2 l/(dm3 min) upward (measured at 200 Pa) are being offered.

In the course of this, rather ďŹ ner fabrics are used for industrial wastewater (about 5 â&#x20AC;&#x201C; 30 l/(dm3 min), while the sewage sludge dewatering in municipal plants takes place, depending on the ďŹ&#x201A;occulation agents used, with ďŹ lter media whose air permeability is in the order of magnitude of 500 to 1000 l/(dm3 min).

Fig. 3: New FAN-Sludge press separator from Bauer Group

Filter media for dewatering

process ďŹ ltration in Germany on a total of 32 of 49 looms. Mono- and multiďŹ lament yarns of different polymers such as polypropylene, polyamide and polyester are processed into single and multi-layered fabrics. The ďŹ lter fabric that is ideal for solid-liquid separation through cake-forming ďŹ ltration allows a high liquid throughput with very slow pressure increase. In the course of this, multiďŹ lament fabrics have the advantage of a high separation

An essential part with the dewatering of sludges from the municipal or industrial wastewater treatment with belt ďŹ lters and ďŹ lter presses, besides the conditioning of the sludge, is played by the structure, the pore width and/or permeability and the material of the ďŹ lter fabric used. The ďŹ lter medium manufacturer Saati (formerly FugaďŹ l Saran) produces fabric for the

Bibliography /1/ DWA-Politikmemorandum â&#x20AC;&#x201C; Positionen zur Umweltpolitik, Deutsche Vereinigung fĂźr Wasserwirtschaft, Abwasser und Abfall e.V., 2014 /2/ Jianmin Hua: Transport- und Umsatzprozesse bei der Abwasserversickerung aus undichten Kanälen; Dissertation TH Karlsruhe (2007) http://dx.doi.org/10.5445/ KSP/1000006122 /3/ Bayerisches Landesamt fĂźr Wasserwirtschaft: fact sheet No. 4.5/14: Wassergefährdende Stoffe in Hilfsmitteln zur Abwasser- und Schlammbehandlung; Ad of: 25.07.2005

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F & S International Edition

No. 15/2015

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Highlights 2014

IMPRINT Publishing house: VDL-Verlag GmbH Verlag & DienstLeistungen Address: F&S - Filtrieren und Separieren VDL-Verlag GmbH Verlag & DienstLeistungen Heinrich-Heine-Straße 5 63322 Rödermark/Germany Phone: +49 (0) 6074 92 08 80 Fax: + 49 (0) 6074 9 33 34 e-mail: vdl-verlag@t-online.de www.fs-journal.de Editor: Prof. Dr.-Ing. Siegfried Ripperger Birkenstraße 1a 67724 Gonbach/Germany Phone: +49 (0) 6302 57 07 Fax: +49 (0) 6302 57 08 e-mail: SRipperger@t-online.de Dr.-Ing. Hildegard Lyko Dortmund/Germany Publisher: Eckhard von der Lühe Advertising department: Eckhard von der Lühe Phone: +49 (0) 6074 92 08 80 Fax: + 49 (0) 6074 9 33 34 e-mail: vdl-verlag@t-online.de International Sales Manager: Margot Görzel Phone: +49 (0) 6196 65 32 11 e-mail: fs-journal@mgo-communications.de Printing Office: Strube OHG 34587 Felsberg/Germany Layout: Ralf Stutz, Gestaltung Hainer Hof 1 60311 Frankfurt am Main/Germany Nicola Holtkamp

F & S - International Edition is a special edition of the trade magazine F & S - Filtrieren und Separieren published in Germany.

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100 years of activated sludge processes

H. Lyko*

Aerobic biological sewage treatment, also called activated sludge process, has become an integral part of contemporary sewage treatment technology. The effectiveness of biological degradation is also an indispensable requirement for every contemporary membrane sewage treatment plant, because in this case the most important function of the membrane is the retention of the biomass and in this, the separation of extremely small particulate contaminants such as bacteria or viruses represents an important additional effect.

The removal of all degradable organic ingredients continues to be the responsibility of the biology.

Biological sewage treatment had its beginning as a technology with the lecture “Experiments on the oxidation of sewage without the aid of filters“ by Messrs. Edward Ardern and William Lockett that they presented on 3rd April, 1914 at the Grand Hotel in Manchester before the Society of Chemical Industry.

The two chemists were employed at the Manchester River’s Department, for which they conducted research at the Davyhulme Laboratories. The basic idea, to use naturally occurring microorganisms for the degradation of sewage contamination, can be attributed to the chemist Gilbert John Fowler, who headed the research operation at Davyhulme since 1904 and, moreover, taught at the University of Manchester.

Fowler, in turn, got his inspiration during a visit to the USA in November, 1912, when he was able to get an idea of the pollution of New York harbour and visit the experimental station in Massachusetts, in which they carried out experiments with ventilated algae and other organisms, which grew as biofilms on slate slabs.

After his return to England, his employees, Ardern and Lockett, began their own experiments, followed by further research

by Lockett on a larger scale. Thus, the large-scale technical and economic feasibility of the process could be verified.

Then, in spite of the outbreak of World War I in the summer of 1914, commercialisation took its course with patenting

by Messrs. Jones and Attwood, who, as producers of greenhouse equipment, also had the knowledge of how to implement the large-scale technical ventilation. In 1915, 15 English towns already had experimental facilities. *Dr.-Ing. Hildegard Lyko Dortmund, E-mail mylko@t-online.de

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The centenary of this groundbreaking technology was celebrated in the form of a conference on 2nd and 3rd April, 2014 at a historical site, the Lancashire Country Cricket Club in Manchester, organised by the CIWEM wastewater management panel in cooperation with aqua enviro technology transfer. Invited speakers gave lectures about the past, present and future of the activated sludge process. In addition, an industrial exhibition and an exhibition on the history of the process took place, and also an inspection of the sewage treatment plant in Davyhulme was offered.

Since the first days of the application of the activated sludge process, a solution has been found for a large number of the initially occurring operating problems.

The ingredients that impede the biological degradation are known, the processes of nitrification and denitrification have been mastered across a wide temperature range, and there are methods available by which the occurrence of floating sludge and bulking sludge can be minimised. However, the activated sludge process, as carried out today, is extensively a linear process in which all water constituents are more or less treated as waste and no recovery of recyclable materials and energy takes place. The biological sewage treatment of the 21st century should be a circular process with the possibility to recover resources in every step of the process. To make this approach more cost-effective, it is useful to minimise the dilution of the wastewater constituents and their heat content. This is achieved by separate wastewater and rainwater collection. The solid matter retained with rakes and/or sieves can be used for energy through fermentation or combustion. Turbines can be used in mountainous areas for generating energy from partial streams. Nowadays, the recovery of methane from the anaerobic digestion of sewage sludge is already being carried out in many sewage treatment plants. In this way, the phosphorus that was removed from the water during the activation and was bonded to the sewage sludge can be recovered. All in all, one sees the sewage treatment plant of the future less as a pure plant for the removal of undesirable substances, but rather as a nutrient or energy factory in which the activated sludge process is the essential process to ensure the quality of the effluent, whose energy requirements are largely covered through the energy inherent in the incurred sludge.

For more information, see www.activatedsludgeconference.com

F & S International Edition

No. 15/2015

Highlights 2014

Extra-large modules for membrane reactors

M. Lyko*

MICRODYN-NADIR introduced their new BIO-CEL® XL module for large-scale applications at the IFAT fair in Munich.

The size of the world remains the same – just the population steadily grows.

Nowadays, water is one of the most important and scarce resources on earth.

In order to also have access to high quality drinking water in the future there is a need to treat the wastewater efficiently.

Today a large variety of treatment processes adapted to different municipal or industrial needs are in use. Nowadays, the activated sludge process is the most common treatment process and has been in use for more than a 100 years.

Membrane bioreactors incrementally get into the focus and are already an indispensable process technology when talking about wastewater treatment.

Compared to conventional activated sludge processes they provide better effluent qualities. Moreover, they offer larger treatment capacities using the same amount of membrane area. Beyond that, with MBRs wastewater recycling for reuse becomes possible.

In a MBR process the cleaning of the wastewater takes place in the biological treatment (mainly the activated sludge process). The separation of clean water and biomass is not done by sedimentation anymore, but with the help of the membranes by micro- or ultrafiltration.

Compared to other biological and physical-chemical processes for wastewater treatment and other pressure driven memMichael Lyko Manager International Sales MICRODYN-NADIR GmbH

brane methods the MBR technology is quite “young”. First, MBR plants were realized for smaller industrial applications.

In Germany a lot of plants with external tubular membranes for leachate treatment on landfills were put into operation in the beginning of the 1990s.

At the turn of the millennium new submerged membrane modules were developed and helped to reduce the cost of the technology. Ever since, it was also possible to build larger plants. At this time mainly two different concepts of submerged membrane modules were commercially available, that is to say

modules with vertical hollow fibers and those with flat sheet membranes glued or welded onto rigid plates. Both types have advantages and disadvantages. Hollow fiber modules are backwashable and have a considerably higher packing density than the plate modules. However, with hollow fibers serious problems, such as “braiding” occur. Braiding is caused by hairs and fibers, which cannot be completely separated from the wastewater.

They become entangled by the membrane fibers. An automatic cleaning is nearly impossible. On the other hand, when using plate modules an effective backwash is

Fig.1 MICRODYN-NADIR´s new BIO-CEL®XL module in a municipal plant

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Fig. 2: Structure of the BIO-CEL® laminate

Fig. 3 The new BIO-CEL®XL module

impossible, the package density is low, but braiding cannot occur due to the hydraulic design.

MICRODYN-NADIR which emerged from the membrane activities of Akzo-Nobel Group and the Hoechst AG has been driven by this development from the beginning. First they delivered tubular modules for MBRs with external pressure-driven membrane filtration. Later additionally flat sheet membranes were supplied to different producers of submerged modules.

In 2005, the company introduced the first BIO-CEL® module commercially available. The BIO-CEL® is based on a hollow structure made of two membranes and a spacer in between. Both of the membranes are laminated onto a spacer – a MICRODYNNADIR patented process for liquid filtration (Fig. 2).

The BIO-CEL® concept includes all advantages of both hollow fiber and plate module types without displaying their inherent disadvantages: - Backwashability - High packing density - No Braiding - Perfect inside and outside hydrodynamics 62

In 2008, the company introduced the up to this point largest BIO-CEL® module at the IFAT trade fair - the BIO-CEL® BC400 with 400 m2 membrane area. In the following years a lot of municipal and industrial references have been realized with this module.

Today there are more then 100 references all over the world. Since December 2014 the BIO-CEL® BC 400 is equipped with 4% more membrane area while offering the same outside dimensions as before, and is now called the “BIO-CEL®BC416 with 416 m2 membrane area. Not only does it offer an increase in packing density but also a decrease in energy consumption.

In 2009, MICRODYN-NADIR (Stefan Krause), the Technical University of Darmstadt (Peter Cornel) and the University of Osnabrueck (Frank P. Helmus and Sandra Rosenberger) jointly developed the Mechanical Cleaning Process (MCP) for BIO-CEL® modules.

In this patented process plastic granules are added to the biomass, which are forced to circulate along the membrane surface by the crossflow, which is induced by the aeration. The plastic granules perform a continuous mechanical cleaning of the membrane surface and prevent the build-up of permanent fouling layers. As the membrane remains cleaner throughout the entire filtration process, higher flux rates can be realized. Higher fluxes mean higher plant capacities using the same membrane area. Additionally, with the MCP costly and labour-intensive cleaning procedures with accompanying breakdown times turn out to be dispensable.

Progressively, a need for MBR solutions for larger wastewater treatment plants emerged. For an easy handling these “XL WWTP’s” also need bigger modules. With the BIO-CEL®XLmodule (Fig. 3) this need can totally be addressed. The XL module was initially introduced at the IFAT 2014 fair in Munich, Germany.

1920 m2 of membrane area are subdivided into four integrated membrane units. The already extremely high packing density of the previous module types is now increased by another 10 to 15 % due to the larger membrane units. A decrease of the energy consumption of the same amount is expected.

The module itself is divided into two parts. The membrane unit is now optimized not only for the use in the treatment plant but also for the standard transportation procedures. The aeration part is installed below the membrane unit and is easily exchangeable.

Both units have a frame made of stainless steel. Extra feet are available for a standing installation of the module in the basin but they can also be installed hanging in the water. One target in the design process was to again improve the easy onsite handling of the BC400.

The XL module will be delivered fully mounted – only membrane and aeration unit are separated.

The possibility to change membrane units is consciously abandoned. MICRODYN-NADIR has shown in several tests that damages of the membrane have no influence on the excellent filtrate quality. Due to the self-healing effect of the laminated membrane sheets, damages “heal” in less than two minutes by the help of the biomass in the system, may it be scratches in the membrane, cut edges or even holes.

Additionally, all other advantages of the previous types of the BIO-CEL® modules remain with the new BIO-CEL®XL module.

- The module is backflushable – not only during the periodic backwash, but also during the regular maintenance cleaning and the rarely needed intensive cleaning.

- The small distance between membrane and frame prevents edge clogging.

- The membrane pockets are flexibly mounted within the module and can move during filtration. This avoids gap clogging.

F & S International Edition

No. 15/2015

Highlights 2014

- The module is based on flat sheet membranes. Therefore, difficulties, such as braiding cannot occur.

- The module has bottom open channels. So it is unsusceptible to silt-up.

- The membrane is designed for low fouling and scaling - The design of the module allows for easy cleaning. Additionally, easy pre-treatment is another benefit – pre-filtration with 2 mm punched holes is sufficient.

The reliable performance of the XL module and its advantages have been proven during a test in an existing wastewater treatment plant. The test was performed by directly comparing the XL module to the previously installed BIO-CEL® BC400 modules.

In this existing wastewater treatment plant with four identical lines the BC 400 modules of one line had been replaced by two of the new BIO-CEL®XL modules. The new modules were operated under the old adjustment of the control unit. An optimization of parameters had been delayed to the time after the initial test. Tests showed that especially the permeability – the flux in relation to the trans-membrane pressure – had been constant and identical to the long-term values of the installed BC 400 modules. The values are independent of the feed flow of the system. The values of the first six-month of the test are shown in Fig.4 Summing up, it could be proven that with BIO-CEL®XL we can now offer a module that addresses the plant manufacturers´ need to build large wastewater treatment plants world wide in an economically and technically efficient way. Easier handling, less piping and optimized transportation significantly helps to save money.

The success could be proven for almost 2 years.

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Fig.4: Permeability and Feed flow – averaged monthly values

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No. 15/2015

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H AV E R & B O E C K E R

Highlights 2014

Washing of suspensions by means of dynamic disk filters D. Goldnik, S. Ripperger* While washing particle systems the dissolved substances in the liquid of a suspension are displaced and flushed out by a washing fluid. During cake filtration, the washing takes place after the cake formation or the subsequent mechanical dewatering. The washing of filter cake with the finest particles is problematic on account of high flow resistance and/ or cracking of filter cakes during the mechanical dewatering. Dilution washing or diafiltration is therefore often carried out with such material systems, i.e. washing of the particles in as highly concentrated suspension as possible. For diafiltration, dynamic filtration processes are used mostly in the form of cross-flow filtration. Highly concentrated suspensions can be advantageously filtered and/or washed with dynamic shear gap filters. In the following, a report about the washing of concentrated suspensions with a filter with rotating disks that are arranged on one or more hollow shafts is presented. The rotation of the disks and the constant movement of the suspension prevent the formation of a filter cake and thus facilitate the handling of suspensions with high concentrations of solid matter.

1. Introduction The washing of particle systems includes the displacement and/or flushing of dissolved substances from the liquid of a suspension and/or a filter cake by means of another liquid, the so-called washing fluid. The original liquid is colloquially often also called “mother liquor”.

While washing, substances will also be discharged which adhere to the particles or are included within them if these are dissolved in the washing liquid.

During cake filtration, the washing takes place after the cake formation or the subsequent mechanical dewatering. Here, displacement washing is sought, i.e. the washing liquid should displace the mother liquor from the pore system. Because the cake is permeated in the process, one also speaks of washing by permeation. As a key figure, the washing ratio W* was introduced, which is defined as follows: (1) Vw,ges represents the total supplied washing fluid volume. Vf,0 is the liquid volume in the filter cake and/or the suspension.

With an ideal displacement washing of a filter cake saturated with liquid, at a washing ratio of W* = 1, the starting liquid is just displaced and/or replaced through the washing fluid. Since diffusion effects and other mixture effects appear at the penetration front of the washing liquid, washing ratios greater than 1, i.e. W* > 1, are necessary for leaching of a substance. Hence, an ideal displacement washing is not feasible in practice. Big deviations from the displacement washing occur when a filter * Dipl.-Ing. (FH) Denis Goldnik, Prof. Dr.-Ing. Siegfried Ripperger Lehrstuhl für Mechanische Verfahrenstechnik Technische Universität Kaiserslautern Gottlieb-Daimler-Str., 67663 Kaiserslautern Tel.: 0631-205-2121, www.uni-kl.de/MVT

64

cake is being permeated unevenly. In particular, while washing the filter cake with fine particles, big problems can occur as a result of the cracking of compressible filter cakes during the mechanical dewatering.

Washing the filter cake with particles in the size range of dP < 10 μm is also problematic on account of the high cake resistance, since this entails long washing times.

The cake resistance can be reduced in this particle size range through flocculation, but the internal structure thereby becomes uneven, so that uniform permeation is not achieved. However, this is aimed at with washing by permeation. Often, it will become necessary to redisperse the previously largely mechanically dewatered filter cake in the washing liquid again and to filter it. In this case, one also speaks of a dilution or redispersion wash. In the process, the pore liquid and the washing fluid are mixed with each other. If both liquids are soluble in each other, substances dissolved in the pore liquid are diluted. This process can be repeated often, until the filter cake has the desired purity.

As an alternative to this, Heuser /1/ examined jet washing of filter cake with low thickness. In the process, the supply of the washing liquid was done as a jet with local resuspension of a part of the filter cake. Hoffner /2/ developed an apparatus in which fluid-saturated agglomerates move bulk-like through one or several serially aligned washing chambers.

An alternative to washing with cake formation is so-called diafiltration. It is applied in particular in the presence of fine particles in suspensions that are difficult to filter, which include e.g. biosuspensions. With diafiltration, washing is carried out in conjunction with dynamic filtration. Thereby the original suspension is concentrated up to a certain degree; afterwards the washing fluid is metered in continuously or discontinuously. Dynamic

filtration is mostly carried out in the form of cross-flow filtration. It is advantageous if no deposit layer forms in the process from deposited particles of the suspension. This can be best achieved if the cross-flow filtration is operated with a high wall shear stress and simultaneously with a small pressure difference. Filters with rotary disks that are arranged on one or more hollow shafts comply with these requirements. The rotation of the disks and the constant movement of the suspension prevent the formation of a high deposit layer and thus facilitate the handling of suspensions with high concentrations of solid matter. In the course of this, the hydrodynamics play an important role in conjunction with the rheological properties of the suspension. These are influenced by the kind of particle system, the solid matter concentration, the physical-chemical properties and the process parameters. All these influences affect the washing result, the necessary washing fluid volume and the washing time.

As a target variable of a washing a residual concentration of a particular substance is often determined, which should be exceeded after washing in the washing solution or in the rest of the suspension.

The degree of leaching is detected with a concentration ratio of this substance: (2) In some cases, the concentration of this substance can rise again in the washing liquid of the suspension after the washing. In such a case, the particles on these substances pass from their interior out to the washing liquid, as in an extraction of solid matter. In this case there is a disequilibrium, i.e. a dissolution capacity and a concentration difference, which equalises on the basis of the diffusion processes. As a result of that, the concentration in the washing liquid can increase again.

F & S International Edition

No. 15/2015

Highlights 2014

Lift

Drag Diffusion Centrifugal force

Radius r /mm

Filterfläche

Hollow shaft Reynold’s number

Filtrate

Disc rotational speed n / min-¹

Fig. 1: Transition radii as a function of the disk rpm and water (ϑ = 20°C) as a fluid

2. Filters with rotary disks In filters with porous rotary disks, the disks within a pressure vessel are exposed to the suspension from the outside. In the process, the filtrate flows into the inside of the disks, on account of the pressure difference, and from there through radially extending filtrate ducts to the hollow shaft. The porous membrane filter disks are mostly made out of ceramics. There are also disks where metal mesh or polymeric flat membranes are fastened on a porous carrier.

The pore size of the membrane is chosen so that the particles of the suspension are separated reliably.

In practice, two different models of filters with rotary disks have established themselves. In a filter with one hollow shaft, several filter disks are arranged at a specific distance. In other filters with two or more shafts, the disks are arranged in those at a specific distance on the shafts so that the individual disks overlap and form shear gaps.

On account of the rotation of the disks and the constant movement of the suspension, there is dynamic filtration. In this case, hydrodynamic effects particularly hinder the formation of a filter cake and cause a higher filtrate flow than with cake-forming filtration. Furthermore, nearly ideal mixing can be guaranteed on account of the constant movement of the suspension in conjunction with the disk rotation in a filter with few disks.

During the rotation, different forces act on the particles in the suspension at the surface of the filter disks. The drag force (resistance force) as a result of the filtrate flow causes a force effect, which promotes an accumulation of the particles on the disk surface. This movement onto the filter disk surface and the deposit there of the particles counteract the lift force (dynamic lift), the resistance force of the cross-flow and the centrifugal force. In the steady operating state, a dynamic balance is established on the surface between particle supply and particle removal. This steady operating state of dynamic filtration is essentially determined by the wall shear stress on the disk surface and by the trans-membrane pressure difference /3/.

In contrast to classic cross-flow filtration with membrane modules, the wall shear stress of a disk filter is primarily influenced by the rotation speed of the disks and the geometric conditions in the suspension space. Thereby it is possible to realise relatively high wall shear stresses with a low filtration pressure difference.

With respect to an operation without deposit layer formation and with very high solid matter concentration, it is desirable for high wall shear stresses to be achieved with non-shear-prone suspension. This is particularly achieved through very high relative speeds between two filter disks with a shear gap. In disk filters with only one shaft, stators and/or baffles are installed for this purpose in the pressure vessel, in order to interfere with rotary flow of the suspension with the disks.

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Filtrate

Fig. 2: Schematic diagram of the flow ratios of two overlapping disks.

The pressure and flow conditions are not steady with an implementation of a shaft over the radius of the disks. The flow on a disk in a container was described in more detail by Tonhäuser et al. /4/. Under certain conditions, the flow can be divided near the disk surface into three ring-shaped regions. There is laminar flow on the inner radius of the disk. From a certain radius, this flow becomes unstable and forms Taylor-Görtler vortices in the form of logarithmic spirals. On the outer region of the disks, a highly turbulent flow can form. The regions are defined by the radius rinst < r < rtrans. In the process, the inner radius rinst marks the beginning of the region where the vortices are formed (primary instability). The radius rtrans marks the beginning of the transition to turbulent flow (secondary instabilities). In both regions, there is

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Highlights 2014

Degree of leaching c* / -

Continuous washing W* = 4 Discontinuous washing W* = 4

Number of dilution steps m / -

Fig. 3: Degree of leaching depending on the dilution stage number for a washing ratio of W* = 4

a complex three-dimensional flow, which further increases the cross-flow on the disk surfaces.

The transitions are described in the literature by a Reynolds number, which is defined as follows: (3) Gregory et al. /5/ show the following values: Reinst = 1.9·105 and Returb = 2.84 ·105. In Fig. 1, the transition radii thus calculated are plotted for water (ϑ = 20°C) as a fluid in relation to the disk rotation speed. Slightly different values are specified for the Reynolds numbers by Kobyashi et al. /6/ and Chin et al. /7/. The values apply to a disk in a large container in which the flow is not affected by walls, baffles or similar.

With the formation of a vortex flow, the wall shear stress also rises. Therefore, such an operating mode is worthwhile in order to avoid a growing deposit layer.

Taamneh et al. /8/ investigated the use of multi-shaft filters with overlapping disks. In the process, it could be observed that with a twin-shaft shear gap filter, the growing of a deposit layer can be efficiently prevented. In Fig. 2, two overlapping disks are shown schematically.

Because of the overlap, it is possible to ensure nearly identical flow conditions over the entire disk radius. With the same direction of rotation of the disks, there is a counter-rotating movement at a constant relative speed in the shear gap between the two disks. This effect increases the wall shear stress.

3. Operating modes of diafiltration and their theoretical treatment In the following, for the treatment of the washing of a suspension with filters and membrane systems, it is assumed that: - the suspension is mixed ideally, - the solid matter is separated completely

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Fig. 4: Arrangement of the disks in the Multi-Shaft-Disc-Separator

from the filter medium, and/or the membrane, - the dissolved material to be washed out can pass freely through the filter medium and/or the membrane and - the supplied washing liquid does not contain the material to be washed out.

The dissolved components in the suspension liquid can be washed out discontinuously or continuously. The solid matter of the suspension is often concentrated initially at the concentration cs,0. Thereby, the source volume V0 of the suspension is adjusted for the washing. If it is assumed that the component to be washed out is dissolved only in the liquid, then one obtains Vf,0 for the initial volume of the liquid of the suspension and the concentration c0 for the dissolved substance volume: (4) For the change over time of this volume, one can write: (5) 3.1 Discontinuous washing in relation of the suspension volume For discontinuous washing of an initial volume V0, a certain volume of the washing liquid VW is supplied, so that the solid matter and also the dissolved component in the suspension are diluted. Then the solid matter is concentrated by the filtration again to its initial volume V0. According to the above assumptions, which can be met through a suitable choice of the filter medium, only the liquid volume is thereby changed and the concentration of the substance to be washed out, that is diluted in the first step, is the same in the suspension and in the filtrate. Hence, the second term in equation 5 is equal to zero. The volume of the suspension changes, because the supplied washing fluid volume is drawn off again as filtrate due to the filtration.

Accordingly, the solid matter concentra-

tion of the suspension cs increases. With the defined solid matter concentration, the initial volume Vf,0 and/or V0 is reached again. Then the filtration is interrupted and in another step, the same volume of washing liquid is supplied again. Afterwards the suspension is usually concentrated again to its initial volume Vf,0. The process of dilution and concentration can be repeated several times. With step m, the concentration cm is adjusted after the dilution and concentration. The following applies:

(6) In this, VW is the added washing fluid agent that corresponds to the filtrate volume VF discharged afterwards. The cycle number m necessary to achieve a certain final concentration is dependent on the respective dilution of the source concentration and hence on the selected supplied washing fluid volume. For the washing ratio after the m step defined in equation 1, one gets: (7) Hence, equation 6 can be written as follows:

(8) The specific filtrate flow is usually reduced with rising solid matter concentrations. If one assumes that the filtrate incurred in the concentration process is detected in a cycle with the average filtrate volume flow and that this is adjusted again after every dilution, one can write the total required filtration time tF,ges: (9)

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3.2 With reference to the suspension volume continuous washing In so-called continuous washing, the suspension is concentrated on the specific solid matter concentration cs,0 and then the washing liquid is continuously added at a constant suspension volume V0.

For this, the added washing fluid flow must correspond with the filtrate flow. The concentration of the substance to be washed out within the suspension thereby changes with the time t, i.e. the first term in equation 5 is zero. If the desired final concentration of the substance to be washed out is achieved, the washing is terminated.

For the change of concentration, one obtains: (10) Integration with the corresponding boundary conditions provides: (11) It can be shown that the leaching degree of continuous washing achieved with a specific washing ratio can be approximated with intermittent washing through a lot of dilution stages. It theoretically corresponds to intermittent washing with infinitely many stages.

In Fig. 3, the degree of leaching is applied for a washing ratio of W* = 4 according to the context of equation 8. The dashed line is the value for continuous washing (equation 11), which is theoretically achieved with intermittent washing with infinitely many stages. Other values for other dilution stages are entered in Table 1.

Because, in the case of continuous washing, one washes with steady solid matter concentrations and steady operating conditions, one can assume that a steady filtrate flow will result. Accordingly, the following applies: (12) 4. Tests for dynamic washing of suspensions 4. 1 Experimental facility The experiments described hereafter were performed with a Mulit-Shaft-Disc-Separator (MSDS) manufactured by Membraflow GmbH. The filter consists of two horizontal hollow shafts, on which a maximum of 11 filter disks can be aligned offset to each other. Thereby, they form a shear gap of 4 mm. The outer diameter of the disks is 90 mm. This leads to a maximum filter area of 0.11 m2. Disks can be produced with different filter media.

With the performed tests, disks were used in the form of ceramic membranes with a mean pore size of 0.2 μm. Fig. 4 shows the arrangement of the disks in the Multi-Shaft-Disc-Separator.

The suspension is conveyed via a pump from an agitated, 12 litre capacity, tempered feed vessel into the filter chamber. In the filter, part of the liquid is separated from the suspension as a filtrate. On the concentrate and filtrate side, the current volume flows can be read out at any time of the experiment. To be able to detect the washing success, the suspensions are marked with a 0.1 molar saline solution. Consequently, the salt is the substance to be washed out. By means of a conductivity measuring cell, the salt concentration in the filtrate can be recorded and displayed. The degree of leaching is detected according to equation 2.

The pressure drop of the filtration, which was always kept at Δp = 1 bar in the presented results, is determined by means of pressure sensors in the filter chamber and filtrate pipe. Discontinous and continuous washings were realised in this filter.

4.2 Properties of the suspension Because the hydrodynamics have a decisive influence the efficiency of the dynamic filtration, the flow behaviour of the suspension is of great significance. With high solid matter con-

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Tab. 1: Degree of leaching for different dilution stage numbers and different washing ratios

centrations, the flow behaviour of suspensions often deviates from that of Newtonian fluids. Hence, the flow behaviour of the suspension was determined with a rotation viscometer (model: HAAKE RheoStress 6000) at different solid matter concentrations.

Highly concentrated and highly viscous suspensions were measured using a parallel plate shearing geometry. With low viscosity suspensions, a cylinder beaker arrangement was selected. With the latter arrangement, the rotary cylinder has a helical spiral groove.

This prevents the sedimentation of the particles in the double crack and provides a steady distribution of all particle sizes in the measured volume.

Watery suspensions were made with aluminium oxide (manufacturer: Almatis GmbH, type: CT 3000) and titanium dioxide (manufacturer: Sachtleben, type: R 611) and examined. The suspensions were prepared in 0.1 molar saline solution. In this case, with the suspensions that have the isoelectric point set at pH = 8, there occurred a mono-modal particle size distribution. With Al2O3, this ranges from 0.1 μm to 9 μm, wherein the modal value is

w w w . w e i s s e . d e

Hence, a connection is produced with the required filtration time tF and the filter area AF.

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Residual content c* / -

Dynamic viscosity η / mPas

Highlights 2014

Duration of washing tw / s

Shear rate γ / s-¹

Fig. 6: Influence of the disk rpm on the washing time of an aluminium oxide suspension with initial solid matter concentration ccs,0 = 0.1 and final concentration cs = 0.2 and ϑ = 20°C

Residual content c* / -

Residual content c* / -

Fig. 5: Viscosity of Al2O3 and TiO2 suspensions at ϑ = 20°C as a function of the shear rate γ

Water Water Water

Duration of washing tw / s

Duration of washing tw / s

Fig. 7: Influence of the solid matter concentration and disk rpm for the washing duration of an aluminium oxide suspension with ϑ = 20°C

approx. 3.5 μm. TiO2 is substantially finer and has a modal value of 0.45 μm. With TiO2, the size distribution ranges from 0.1 μm and 2.0 μm.

For the viscosity measurement of suspensions with different solid matter volume concentrations cs, the shear rate was initially gradually increased and was afterwards reduced again in steps upon reaching a defined maximum value.

Fig. 5 shows the course of the suspension viscosity of TiO2 and Al2O3 as functions of the shear rate γ. In the figure, it can be seen that suspensions with a low volume concentration of cs = 0.01, suspensions of both systems have a Newtonian flow behaviour. With increasing concentration, the Newtonian flow behaviour turns into a pseudoplastic behaviour.

Accordingly, with increasing shear rate, a drop in viscosity is observed. The causes for this are a change of the internal structure and the particle-particle interaction.

Because the particles deviate from the spherical shape, shearing can also cause alignment of the particles. With very small particles, the Brownian motion counteracts this alignment.

Suspensions of the same solid matter concentrations of aluminium oxide have

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Fig. 8: Influence of the suspension temperature on the washing time for an aluminium oxide suspension with cs,0 = 0.01 with rpm of n = 1000 min-1

a higher viscosity in comparison to those of titanium dioxide. This can be due to the lamellar structure of the Al2O3 particles.

Titanium dioxide particles have a rounder form.

For the washing of suspensions, low viscosities, with high solid matter concentration, are desirable in the disk filter.

This allows the washing to be carried out with high solid matter concentrations, i.e. with a small source volume of V0. In this manner, the washing fluid volume can be minimised. Furthermore, under the aspect of good mixing in a turbulent flow, a low viscosity is of advantage.

4.3 Influence of experimental parameters on the washing duration Tests were carried out for washing of aluminium oxide suspensions with different disk rotation speeds, solid matter concentrations and temperatures.

Firstly, the influence of the disk rotation speed on the temporal course of the leaching was examined. Here, aluminium suspensions have been washed cyclically at cs = 0.01 and ϑ = 20°C. In this case, 2 litres of filtrate were first withdrawn from the suspension and were afterwards replaced by washing fluid (water). During

the cycles, the suspension concentration was increased to cs = 0.02. Fig. 6 shows experimentally determined values at disk rotation speeds of n = 250 min-1, n = 500 min-1 and n = 1000 min-1. In the Figure, the salinity residual content is plotted against the washing time. It can be seen that, with rising rpm, the washing time decreases in order to reach a certain salinity residual concentration. With higher rpm, the wall shear rate increases and the viscosity decreases on account of the shear stress. A turbulent vortex flow over the membranes results. This reduces the formation of a thick deposit layer.

Thereby, the filtrate volume flow rises and cyclic addition of the washing fluid can be done faster.

For investigation of the influence of the solid matter concentrations, intermittent washing experiments with aluminium oxide were carried out. The results are shown in Fig. 7. The diafiltration was done under the same conditions that were applied in the investigation of the rotational speed influence. The solid matter concentrations and disk rotation speed have an essential influence on the filtrate flow and the washing time thus resulting. In the figure, the salinity residual content for the washing time is applied for aluminium

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suspensions with the source concentrations of cs,0 = 0,01, cs,0 = 0.03 and cs,0 = 0.05 at disk rotations of n = 250 min-1 and n = 1000 min-1. Here, the concentration of the suspensions was increased to cs = 0.02, cs = 0.04 and cs = 0.06 during the cycles.

With increasing solid matter concentrations and suspension viscosity, the washing time increases. In the process, it could be observed that the filtrate flow decreases relatively strongly, especially with the low rpm in the first third of the experiment, and then remains steady afterwards across the remaining experiment. Therefore, one can conclude a deposit layer formation.

If the steady viscosity that occurs with high shear rates is assigned to mean examined solid matter concentrations, the viscosity ηSus increases from 1.1 mPas to 1.6 mPas and finally to 2.1 mPas. In the process, this corresponds to a ratio of 1:1.4:1.3. With the rpm of n = 250 min-1, the washing duration increases for the achievement of c* = 0.1 at the different concentrations from approx. t = 2500 s to approx. t = 3500 s and, finally, to t = 4700 s. This, too, corresponds to a ratio of 1:1.4:1.3. Therefore, a similar relationship exists between suspension viscosity and washing time.

With increased disk rpm, this relationship between the viscosity change and the washing time is not detected anymore.

In this case, it is to be assumed that the deposit layer thickness is marginal. The influence of the solid matter concentrations is thereby considerably reduced at a higher rpm.

On account of the fact that the temperature plays an important part with the flow properties, the influence of the suspension temperature on the washing was examined. The experiment procedure also complies with the one that was also used during the investigation of the variable speed. In Fig. 8, the results are illustrated for washes of aluminium oxide suspensions with cs,0 = 0.01 and n = 1000 min-1 at ϑ = 10°C, ϑ = 20°C and ϑ = 38°C. With rising temperature and decreasing viscosity, the required washing duration decreases in order to reach a certain salinity residual content. Therefore, other than the concentration change, the temperature change plays a role at high rpm like, e.g., at n = 1000 min-1. Here, however, the suspension viscosity does not have the decisive influence but the viscosity of the permeating fluid does. Water has a viscosity of η = 1.3 mPas at η = 10°C, η = 1 mPas at ϑ = 20°C and η = 0.65 mPas at ϑ = 38°C. The ratio of the viscosity thus corresponds to 1:0.75:0.65. In the experiments, the required washing time decreases in order to reach c* = 0.1 at the respective temperatures, from t = 2700 s to t = 1750 s and, finally, to t = 1300 s. In

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considering the washing time relationship. the ratio of approx.. 1:0.75:0.65 can also be determined here.

With the withdrawal of large amounts of filtrate, the solid matter concentration in the suspension increases. Consequently, the viscosity also gets bigger. Therefore, it is of significance to examine the influence of the reconcentration of the suspension during diafiltration.

As already shown in Fig. 7, the concentration change affects the washing time only slightly at a high rpm. That is why experiments with aluminium oxide were carried out with an initial concentration of cs,0 = 0.01, ϑ = 20° and n = 1000 min-1.

In the process, a filtrate volume of 2 L, 4 L and 6 L was extracted before the cyclic addition of the washing fluid of the suspension with an initial volume of VSus = 10.5 L. As a result, there was a concentrated volume of V0 = 8.5, V0 = 6.5 and V0 = 4.5 L. The results are shown in Fig. 9.

It can be observed that the washing duration in order to reach a certain salinity residual content increases only slightly.

5. Prediction of the washing result In Fig. 10 it is shown that the relationship between the residual content c* and the washing ratio W* described in equation 11 applies for a wide range of different solid matter concentrations cs, disk rotation speeds n, temperatures ϑ and different solids and kinds of washing, discontinuously (DK) and continuously in the direct current (GS) or countercurrent (GG).

If equation 11 is converted according to the required washing volume, one gets: (13) The required washing fluid volume is therefore inversely proportional to the residual volume of the suspension before the addition of the washing fluid. In Fig. 11, the connection of equation 13 is compared to experimental results. Suspension of an initial volume of Vf,0 = 10.4 L was washed continuously in direct (GS) and countercurrent (GG). On the other hand, the original suspension volume of 10.4 L was first concentrated to Vf,0 = 8.4 L, Vf,0 = 6.4 L and Vf,0 = 4.4 L and was afterwards washed intermittently in m steps.

It can be seen that a stronger concentration of the solid matter in the suspension before the addition of the washing fluid has reduced the necessary washing fluid volume in order to reach a specific salinity residual concentration. However, the required washing time increases according to Fig. 9.

On the basis of Fig. 12, it can be shown that this standard description is not always

Residual content c* / -

Residual content c* / -

Highlights 2014

Washing ratio W* / -

Duration of washing tw / s

Theoretical continuous Vf,0 = 10,4L Theoretical continuous Vf,0 = 8,4L Theoretical continuous Vf,0 = 6,4L Theoretical continuous Vf,0 = 4,4L Washing continuous GG Vf,0 = 10,4L Washing continuous GS Vf,0 = 10,4L Washing discontinuous Vf,0 = 8,4L Washing discontinuous Vf,0 = 6,4L Washing discontinuous Vf,0 = 4,4L

Fig. 10: Salinity residual content as a function of the washing ratio with variable process parameters

Experiment discontinuous Vf,0 = 4,4L Experiment discontinuous Vf,0 = 8,4L

Residual content c* / -

6. Summary For the case of suspension washing with a dynamic disk filter, the effects on the washing result, the washing fluid volume and the washing time were indicated for the kind of particle system, the solid matter concentration, the rpm, the temperature and the kind of washing operation. It was shown that the flow behaviour of the suspension in combination with the hydrodynamics has a decisive influence on the washing process.

On account of the non-Newtonian flow behaviour, the viscosity of the suspension is influenced through the process parameters. The fluid mechanics in conjunction with the viscosity also influence the possible formation of a deposit layer on the filter disks, which may reduce the filtrate flow and increase the washing time.

It could be shown that the washing in the disk filter can be predicted over a wide range.

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Theoretical discontinuous diafil. Vf,0 = 8,4L Theoretical continuous diafil. Vf,0 = 4,4L Theoretical continuous diafil. Vf,0 = 8,4L

Residual content c* / -

Fig. 11: Required washing fluid volume depending on the washing kind

valid for the examined disk filter. In the experiments, the washing fluid volume VW was carried out across the residual content c* for a diafiltration with an initial suspension volume of VSus = 10.4 L and starting concentrate volume of Vf,0 = 8,4 L, 6,4 L and 4,4 L.

Theoretical discontinuous diafil. Vf,0 = 4,4L

Washing fluid volume Vw / L

Washing fluid volume Vw / L

Fig. 9: Influence of the diafiltration kind on the washing duration of an aluminium oxide suspension with cs,0 = 0.01, ϑ = 20°C and n = 1000 min-1

Fig. 12: Comparison of the calculation for the required washing fluid volume

List of Symbols AF c* c

[-] [-] [mol/L]

c0

[mol/L]

cm

[mol/L]

cs,0

[-]

cs

[-]

n m m0

[1/min] [-] [kg]

r rinst

[mm] [mm]

rtrans

[mm]

Re Reinst

[-] [-]

Retrans [-]

t tF

[s] [s]

Filter area Residual salinity Concentration of the substance washed out in the suspensionn Initial concentration of the substance washed out in the suspension Concentration of the substance washed out in the suspenion in the mth stage Initial solid matter volume concentration in the suspension Solid matter volume concentration in the suspension Disk rotation speed number of washing steps Mass of the dissolved component Disk radius Radius at the beginning of the instabilities Radius at which the transition to turbulent flow occurs Reynolds number Reynolds number at the beginning of the instabilities Reynolds number at which the transition to turbulent flow occurs Washing time Filtration time

Vf,0

[L]

V0

[L]

VF VW VW,ges

[L] [L] [L]

W* γ Δp

[-] [1/s] [bar]

η ϑ

[mPas] [°C]

_ vF pSus ω

[L/h] [kg/m3] [1/s]

Initial Liquid volume of the suspension Initial Volume of the suspension Filtrate volume Volume of the washing fluid Total volume of the washing fluid Washing ratio Shear rate Trans-membrane pressure difference Dynamic viscosity Temperature of the suspension Middle filtrate volume flow Density of the suspension Angular velocity

Literature: /1/ J. Heuser, Dissertation, Universität Karlsruhe (TH) 2003. /2/ B. Hoffner et al., Chem. Eng.-Technol. 2004, 27 (10), pp. 1065-1071. /3/ J. Altmann, S. Ripperger, .Chem.-Ing.-Tech. 1996, 68 (10), pp. 1303-1306. /4/ M. Tonhäuser et al., Chem.-Ing.-Tech. 2004, 76 (1-2), pp. 114-118.

DOI: 10.1002/cite.200403314 /5/ N. Gregory et al., Phil. Trans. 1955, 248, pp. 155-199. /6/ R. Kobayashi et al., Acta Mech. 1980, 35, pp. 71-82. /7/ Y.-M. Chen et al., Heat an Mass Tranfer 1998, 34, pp.

195-201. /8/ Y. Taamneh, S. Ripperger, Physical Separation in Science and Engineering, 2008, DOI: 10.1155/2008/508617

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Highlights 2014

Viscose speciality fibres for filtration applications Ph. Wimmer* Viscose speciality fibres are cellulose fibres that are produced from natural cellulose in a chemical process. In the process, the fibre characteristics cannot only be adjusted specifically to match the processes for the production of filter media, but cellulosic raw materials of different origin can also be used used for viscose fibre manufacture without altering the properties of the final viscose fibres. Fibres with functional additives influence the result of the filtration not only with their physical properties, but also with the chemical properties of the incorporated additives.

Through the openness of the fibres to diffusion in aqueous systems and gases, the full effectiveness of the additives homogeneously distributed inside the fibres is preserved. The incorporation of the finest particles into the fibre matrix allows their inclusion into filtration products without the hazards and problems usually associated with dust. Viscose Speciality Fibres in many different lengths are used as raw material for filter paper production in order to regulate porosity as well as for the production of nonwoven materials and textiles for filters. Filter media for food filtration, for example, are an important field of application for viscose speciality fibres, since the fibres are taste neutral and physiologically as well as hygienically absolutely safe.

1. Introduction Cellulose is the polymer of beta glucose and thus belongs to the polysaccharides, just like starch. As a component of the cell walls of plants, it is the most widespread (bio-) polymer. Natural cellulose fibres occur in pure form in cotton, for example, but often also as the fibre component of natural composite materials like wood.

Due to their different geometrical shapes, these fibres can be processed into a huge number of extremely different products, for example textiles and paper. /1/ * Dr. Philipp Wimmer R&D Viscose, Technical Manager New Business Kelheim Fibres GmbH Regensburger Str. 109, 93309 Kelheim Tel.: +49 (0)9441 99-219, Fax: +49 (0)9441 99-1219 E-mail: philipp.wimmer@kelheim-fibres.com

Cellulose is biocompatible, physiologically neutral, completely biodegradable and non-allergenic. Therefore it is also suitable for food, medical and hygiene applications. Cellulose can store large amounts of water inside the fibre matrix, since it is extremely hydrophilic and has a high absorbency, but it does not dissolve in water.

Viscose speciality fibres are regenerated cellulose fibres and can be produced from nearly every cellulose-based raw material. They are usually produced from wood in a multistage chemical process, of which the first step is the pulping process known from paper production. In this step the cellulose is separated from other components of the wood, mainly lignin and hemicelluloses.

To be able to spin the cellulose into viscose speciality fibres, an alkali treatment with sodium hydroxide solution is first carried out in the viscose process. In the formed alkali cellulose, a white fibrous powder, the length of the polymer chains is adjusted and afterwards the reactive alkali cellulose is converted with carbon disulphide into cellulose xanthate, a yellowish substance. Through dissolving the freshly formed xanthate in sodium hydroxide solution, a highly viscous liquid with honey-like appearance is obtained, the so-called spinning dope.

While extruding the spinning dope through a spinneret into a sulphuric acid bath, the cellulose xanthate precipitates and coagulates to form viscose fibre filaments (cellulose), while the carbon disul-

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Unlike thermoplastic fibres like polyesters or polypropylene, viscose speciality fibres allow a quick diffusion of aqueous liquids and gases inside the fibres. Therefore, chemically effective additives that require a direct contact with reaction partners can also be incorporated.

Viscose speciality fibres have a high temperature stability and do not soften or melt. The decomposition point of the cellulose, which often constitutes the upper temperature limit of application, is clearly above the softening point of most thermoplastic fibres.

Fig. 1: Dependence of the fibre surface on the fibre count

phide which is formed in the reaction is re-used in the process.

In the following process steps the viscose fibre filaments are stretched, cut into fibres, washed, and dried. /2/ A further product of the process is sodium sulphate, an important raw material for the glass and laundry detergent industries.

Even though in the viscose fibre manufacturing process cellulose (pulp) is converted into cellulose (viscose fibres), the characteristics of the viscose speciality fibres differ substantially from those of the raw materials used, since the fibre diameters and fibre lengths are adjusted in the viscose fibre process. In addition, the process also allows the controlled chemical modification of the fibres.

2. Fibre modification for the production of filter media In nature, cellulose fibres occur only in a limited amount of fibre geometries. Differences exist between celluloses from different fibrous plants, for example cotton, bamboo or wood, but also between celluloses from the same plant species, but from other geographical growth regions. Seasonal and weather influences also have an influence on the fibre characteristics and unless the viscose fibre manufacturing process many processes to transform fibres into products are unsuitable to completely turn off natural variations.

For the production of textiles and nonwoven materials, for example, much longer fibres are required than for the production of papers. Among the textile and nonwovens fibres longer fibres are better suited for the production of needle felts, whereas shorter fibres are perfectly suitable for the production of hydroentangled nonwovens.

In the viscose process, the fluctuations of the raw material characteristics still present after the pulping process are compensated by adaptation of the process parameters, so that there are always the same product characteristics at the spinning jets. The spinning dope with consistent properties now allows a specific adjustment of the fibre characteristics.

The influence of the following fibre modifications on the characteristics of filter media will be explained more detailed below: - Changes of the fibre geometry (cross-section, length, thickness) - Chemical fibre changes - Embedding of functional additives into a viscose fibre matrix

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3. Influence of the fibre geometry on the filter and filtration characteristic The fibre length primarily has influence on the ability of the fibres to be processed into filters. The influence on the filter characteristics is usually indirect and arises from the fundamental differences between the processing technologies and the products resulting from these. Especially in combination with natural fibres, the adjustability of the fibre length is a big advantage as natural fibres can indeed be shortened with a loss of quality, but in no way can be lengthened. Filter papers are an important market for viscose speciality fibres. Such filter papers are usually made from pulps with fibre lengths of approximately 1 to 10 mm. Viscose speciality fibres are offered as short cut with precise, reproducible cut length in the range of 3 to 12 mm. These short cut fibres are fully compatible with wood pulp and can be dispersed well in the pulper and are hence ready for use for the paper process. In the filter paper itself, the fibre length has only a little influence on the filtration characteristics, but mainly influences the strength of the paper. In particular, the tear strength of the papers increases significantly with increasing fibre length.

Filter papers are not only used in industrial and vehicle filters.

In particular, they are used for food and beverage filtration. Due to the positive physiological characteristics of the viscose speciality fibres, even at high temperatures, filter papers suitable for food and beverage applications are an important market for viscose short cut fibres. Common filter papers containing viscose fibres are tea bag and coffee pad papers for liquid filtration and plugwrap papers of cigarettes for gas filtration. During cigarette smoking, these porous papers wrapped around the filter provide lighter smoke by regulating the air flow through the filter side into the smoke stream.

Viscose speciality fibres are added to these papers mainly to increase and control the porosity. The porosity of the filter papers can be influenced by the amount of Viscose speciality fibres used, as well as by their fibre count.

The fibre count is a measure of the diameter of the fibres (considered to be round) and is usually given in the unit dtex (1 dtex = 1 g / 10,000 m of fibre). Viscose speciality fibres are produced in the count range of approx. 0.5 dtex up to well above 10 dtex.

This corresponds to fibre diameters of approx. 6 μm to well more than 30 μm.

Fibres with high count lower the paper density and increase the porosity much more significantly than fibres with low count, which, on the other hand, increase the strength of the paper to a certain extent. /3/ The fibre count/fibre diameter influences the filter characteristics not only in paper filters. The fibre surface in filters, which is available to particles for attachment, or in chemically functionalised fibres is available as “membrane surface” for diffusion into the fibre itself, is directly linked with the fibre count.

For microfibres with < 1 dtex, a particularly large increase of the fibre surface with decreasing fibre count is observed (Fig. 1).

The fibre cross section, which can be regulated in the manufacturing process of the viscose speciality fibres, has a much stronger influence than the fibre count on the fibre surface in the filter. In comparison to the cloud shape of the “round” standard viscose

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fibres, the surface can be more than tripled at the same filter weight (Fig. 2).

Other filter properties, for example air resistance, can also be modified by the fibre cross-section. Filters from trilobal fibres have a low air resistance in combination with a high fibre surface area, which is the reason why cigarette filters are usually produced from trilobal cellulose acetate fibres.

Other cross-sectional shapes also significantly influence the filter characteristics.

The very deeply fissured, letter-shaped Umberto fibres have numerous hollow cavities well protected from the flow, in which trapped particles are firmly bound.

Segmented hollow Bramante fibres are collapsed in the dry state. In contact with water, they swell and store the water in their hollow cavities. The free filter cross-section is significantly reduced by the swelling and thereby the filter resistance is increased. The swelling is reversible and stored liquid water is discharged as humidity. Because the moisture is bound in a hollow cavity inside the fibres, trapped moisture cannot be discharged, even by high flow rates.

The fibre cross-sections also have a big influence on the characteristics of filter papers. As already explained before, round fibres increase their porosity by reducing the paper density, which leads to a lower filter resistance. Trilobal fibres act similarly.

In contrast to round and trilobal fibres, flat fibres increase the filter resistance and the density of the filter papers. The increase of the density is usually linked to a clear increase of the tensile strength of the papers.

4. Chemically modified viscose speciality fibres as an active filter medium In the preceding section, the influence of modifications of the fibre geometry of viscose speciality fibres on the filter characteristics was introduced, in particular on porosity, filter resistance and surface.

Round (normal viscous) surface 100%

Flat (thickness/width 1:5) approx. 150%

Ultra-flat, smooth surface (thickness/width 1:20) approx. 360%

Trilobal (thickness/width 1:5) approx. 240%

Hollow fibres

Ultra-flat (thickness/width 1:20) approx. 260%

Letter-form

Fig. 2: Fibre cross-sections of viscose speciality fibres, surface area of selected cross-sections compared to standard viscose

Furthermore, it was shown that viscose speciality fibres can be produced specifically for the requirements of the different filter manufacturing technologies.

In this section, the chemical modification of viscose speciality fibres, as well as application examples for these fibres in filtration, will be discussed. The fibre shape and the type of filter medium can promote the efficiency of the modification, but both are of secondary importance in this context.

The cellulose molecule offers various possibilities for chemical modifications (Fig. 3). If reactions are carried out on the hydroxyl groups of the monomer units, molecules can covalently bind to the polymer chain via electron pair bonds. Such chemical modifications are permanent.

The cellulose molecules of the viscose speciality fibres are bonded to each other through hydrogen bonds. Hydrogen bonds are strong interactions between protons and non-bonding ion pairs of some heteroatoms. If an ideally polymeric sub-

stance, which is also capable of forming a large number of hydrogen bonds is incorporated into the viscose fibres, even water-soluble substances can be immobilised in the polymer matrix of the viscose fibres. Due to the high number of hydrogen bonds as well as the steric hindrance of the macromolecules the bonding forces between incorporated molecules and the cellulose chains are stronger than the diffusion forces of the water. This means that even water soluble incorporated macromolecules cannot be extracted from the viscose fibres.

The cellulose backbone can also be modified, for example by oxidation. /4/ These reactions, however, will not be discussed here. In the manufacturing process, the chemical fibre modification is possible both, via the spinning mass before filament formation and after the filament/fibre formation during fibre washing, where the never-dried fibres are much more accessible to reactions than fibres having already been dried.

Covalent bond

Hydrogen bond Fig. 3: Examples of binding possibilities in the cellulose molecule

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Fig. 4: Dye absorption of cationic Danufil® Deep Dye Viscose Speciality Fibres (blue surfaces) in comparison to normal viscose (white surfaces)

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Relative water retention capacity [%]

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Normal viscous

Modified fibre Verdi

Hollow fibre Bramante

Modified hollow fibre Dante

Fig. 5: Water imbibition of modified viscose speciality fibres in comparison to standard viscose (measurement according to DIN 53814)

For use as a reactive filter medium, it is necessary to distinguish between reversible reactions where the filter medium can be regenerated, and irreversible reactions where the filter medium can only be used once, for example as a police filter.

Regardless of the reversibility, the viscose fibre can take part as a reactant in the filtration, or it can simply be a carrier for reactive substances.

Viscose speciality fibres that are chemically modified through active ingredients are always highly advantageous when the active ingredients required for filtration cannot be processed into filter media, either because they are water soluble

or because the produced filter media have considerable deficits in their physical properties, for example, differential pressure or available filter area. When the active ingredients are part of the carrier material viscose speciality fibres solely the processing and the technical/mechanical properties of the viscose fibres are relevant for filter manufacture but no longer the characteristics of the active ingredients anymore.

The technologies for the distribution of active substances in viscose speciality fibres, as well as for the fibre distribution in filter media, are fully developed and therefore a homogeneous active ingredient distribution is always guaranteed.

Fig. 7: Titanium dioxide particles incorporated inside viscose speciality fibres

Fig. 8: Tea prepared with hard water (left) and with soft water (right)

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Fig. 6: Hydrophobic Olea viscose fibre in water (left) in compared to standard viscose (right, fibres sunk in water)

Through incorporation of a cationic polyelectrolyte, the rather anionic viscose speciality fibres become cationic. This is associated with an increased affinity both for anions and also Lewis bases. An example of a cationic viscose fibre is Danufil® Deep Dye with quaternary nitrogen as cation. The application of these fibres as an anion exchanger is obvious. The ion exchange is reversible and the fibre can be loaded at any time with different counter-ions depending on the application.

The fibres have a high affinity to PEG (polyethylene glycol), a common active ingredient carrier for pharmaceuticals and cosmetics. PEG can simultaneously bind to several molecules, so that not only anionic pharmaceuticals, but also pharmaceuticals bound to PEG, can be filtered off from water through cationic fibres. An interesting aspect, not only concerning the dyeing of textiles, is the high affinity of the cationic fibres to dyestuffs, which increases with the number of cationic groups (Fig. 4). /5/ The phenomenon of dye transfer in laundry is not only a problem in household laundry, but also in industrial laundry. Cationic viscose speciality fibres can be processed into cloths for household laundry, which catch bleeding dyestuffs from the washing liquor, but they can also be processed into filters for chemical cleaning. The service life of the solvent, used for a longer time in a closed system with solvent filtration, is thereby extended.

As they are made from renewable raw materials, used filters from viscose speciality fibres can be incinerated CO2 neutrally, or can even be composted if the impurities in the filter allow this.

Anionic viscose speciality fibres, which are produced in analogy to the cationic fibres by incorporation of anionic polyelectrolytes (carboxylic groups), can also be processed into filter media.

Polycarboxylates are also used in medicine and and hygiene products. These are able to buffer the pH value in the skin-neu-

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tral range around approx. pH 5. The buffer effect for the pH is also of interest in the filtration of aquarium water, in particular if fish are kept from tropical waters that are often softened by humic substances in the soil and therefore are slightly acidic. Protons from the anionic viscose speciality fibres replace hardness- forming calcium and magnesium ions from tap water. At the same time, particles and excrements in the water are filtered off.

Like most ion exchangers, the anionic viscose speciality fibres can be loaded with different cations. Especially for pH regulation, different functions can be implemented, from alkaline ion exchangers with alkali metal loading to catch acids, to acidic proton-loaded ion exchangers to catch metal ions. Even ion exchangers with partial proton and metal loading are possible, which then buffer the pH over a wide range.

Cellulosic materials are also used for applications where flame-retardant materials are required for safety reasons, for example air filters for motor vehicles. The use of cellulosic fibres is only possible if they are treated with flame retardant chemicals.

These often release toxic gases in case of fire. Existing cellulosic solutions often reduce or eliminate the flammability risk but at the same time the risk of intoxication increases as toxic gases are released from the FR chemicals in case of heat and fire exposure.

Through chemical functionalisation of viscose speciality fibres, it is possible to incorporate silicate in the viscose speciality fibres.

The Danufil® BF fibre is an alloy of cellulose and silicate which combines the advantageous properties of both materials. The silicate component in the fibre provides heat and flame protection.

The LOI of the fibre is above 27. The cellulose component gives the fibre strength and flexibility. Only in direct exposure to flames, the cellulose part will slowly burn away. The silicate framework, however, remains stable and protects the underlying materials from damage by heat and flames.

As only “sand” is used for flame protection no toxic sulphur-containing or phosphorous gases can be released from the fibres.

Water, in particular liquid water, promotes corrosion and is therefore a big problem in many application areas, because the service intervals and the availability of machines are reduced.

The ability to absorb and store large amounts of water is a fundamental characteristic of cellulose. The water absorption of viscose speciality fibres, which is especially high in comparison to other cellulose fibres, can be multiplied through chemical modification, which itself can even be combined with a modification of the cross-section (Fig. 5). Viscose speciality fibres in filters reduce the risk of corrosion, because they bind water before it can cause corrosion. The water absorption is fully reversible and there is no risk of bleeding particles during swelling like it is the case for super absorbent particles. At elevated temperature, for example the operating temperature of machines, as well as at low air humidity, viscose speciality fibres release absorbed water in gaseous from so that the original absorption capacity of the filter is restored.

In addition to water absorption, viscose speciality fibres can also prevent corrosion by incorporated corrosion inhibitors, since these remove other corrosive substances from operating media.

The chemical modification of the fibres allows the integration of various further functionalities. A new development is a fluorine- and silicone-free, biodegradable hydrophobic viscose fibre, which, for example, can be used for protection against moisture (Fig. 6). /6/ This fibre is expected to have a higher affinity to oils and fats and therefore it should be suitable for the absorption of these media.

Cellophane films or Sausage casings are well-known examples.

They allow the drying of the sausages, e.g. Salami, by diffusion of water.

There is no interest of using viscose speciality fibres as membranes because the diffusion through the space between the fibres is always quicker than diffusion through the fibres themselves as it has nearly no diffusion resistance.

The possibility of diffusion inside the fibres is of much greater interest. The fibre diameter of only a few μm allows a very quick diffusion into the fibres. Many different materials, for example resins, activated charcoal, colour pigments and inorganic salts, are resistant to the conditions of the viscose fibre manufacturing process at least for the time required for fibre manufacture and can therefore be incorporated into the fibres. The incorporated particles are distributed homogeneously across the entire fibre cross-section and fibre length (Fig. 7).

In order to be able to be incorporated, the particles must be significantly smaller than the fibre diameter. Finely ground particles have a many times larger surface and therefore usually also a far higher activity than coarse particles. The disadvantage of such fine particles is their tendency to develop fine dust, which increases the health and fire risk. Their incorporation solves the dust problem, since the particles are permanently embedded inside the fibre matrix. The high diffusion rates through the viscose fibres still allow a high activity of the particles, especially as these are separated from each other and thus are easily accessible from every side.

A very clear example is water softening for coffee and tea preparation using serving machines, where a softening pad is used in addition to the coffee pad for water softening (Fig. 8).

5. Use of viscose speciality fibres as a matrix for active particles Cellulose is known for its openness for diffusion of gases and aqueous liquids. This is also used in filtration, for example for dialysis or ultrafiltration, but also in the food and packaging sector.

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Water hardness (Ca/Mg) [mmol/l]

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Poseidon fibre (with ion exchanger) Verdi fibre (anionic)

Ion exchanger (resin bead)

Mass of the exchanger medium (fibre/resin) [g]

Fig. 9: Softening of 150 ml water (cup serving) in 30 secs with different ion exchangers

A standard Senseo® coffeemaker prepares a cup of coffee of 150 ml volume in approx. 30 seconds. Hence, during this time the water hardness needs to be reduced to the optimum level. Fibrebased filter pads made from the anionic viscose fibre Verdi and from the viscose fibre Poseidon with incorporated ion exchange resin were compared to a filter pad filled with pure commercially available ion exchange resin. While 2 grams of fibres were already sufficient for adequate water softening, at least 10 grams of ion exchange resin were required for a comparable result (Fig. 9). The Poseidon fibre contains 35% of ion exchange resin. This illustrates that, in spite of a far lower content of active material, an equivalent result is achieved, since the available ion exchange capacity of the incorporated resin is used highly efficiently.

The reason for the advantage of the fibre-based solution is the quick diffusion through short paths combined with a high active surface area. The incorporated ion exchange resin is fully functional also within the fibres.

This example shows that viscose speciality fibres with incorporated active ingredient particles are particularly suitable for time-critical filter tasks, since the diffusion pathways in the fibre are short and the active ingredient particles in the fibre interior are isolated from each other and therefore easily accessible.

Just as it is possible to incorporate ion exchange resins into viscose speciality fibres, also other active ingredients can also be incorporated into the fibres without loss of activity. Certain titanium dioxide particles are suitable for photocatalytic air purification and some metals have an antibacterial effect. Also particles for filter identification, such as luminescent pigments, can be incorporated into filters via viscose speciality fibres.

Through the incorporation of doped, activated charcoal into a fibre matrix, the filter medium can even be utilised as a catalyst for chemical reactions. In the filtration process, there is no risk from charcoal dust.

Through the incorporation of phase change materials (PCM), heat can be exchanged during filtration. The technology of PCM microcapsules is known under the name Outlast®.

HME (heat and moisture exchange) filters for ostomy patients are usually made of creped paper and must take over the pre-heating and pre-moistening of the breathed air as a larynx substitute.

If nonwoven materials from Outlast® viscose speciality fibres are used, these allow better dust filtration, since, in contrast to creped paper, no flow channels exist. Moreover, the viscose fibres allow an extremely quick and effective moisture management. The PCM microcapsules in the fibres, as a latent heat accumulator, absorb and discharge much more heat than paper alone can do only by temperature change (Fig. 10). The crucial criterion for these filters, the low air resistance for breathing, can be maintained at the level of creped paper by a suitable design of the nonwoven fabric.

Just like the chemical modification of viscose speciality fibres or the adaptation of the fibre geometry, the incorporation of active

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Fig. 10: Outlast® viscose fibre with incorporated phase change materials (micro-encapsulated wax)

ingredients in the fibre matrix is also a possibility for the adaptation of viscose dpeciality fibres to the specific requirements of the most different applications in filtration. It could be demonstrated that viscose speciality fibres are highly suitable as a carrier matrix for particles, in particular for time-critical filter tasks.

6. Summary and Outlook Viscose speciality fibres are comparable to natural cellulose fibres in their environmental characteristics and their physiological properties, such as the non-allergenic effect, and, just like these, they are also suitable for food and medical applications.

At the same time, in contrast to natural fibres, viscose speciality fibres offer the possibility for the adjustment of the fibre geometry to the specific requirements of filter manufacturers.

Through chemical functionalisation or through incorporation of active ingredient particles, functions that are needed for specific filtration tasks can be selectively incorporated into the fibres. In this context, it could also be shown that Viscose Speciality Fibres allow a quick diffusion of liquids and gases into the fibres, so that molecules and particles incorporated inside the fibres retain their full activity.

The different possibilities for fibre functionalization can also be combined in order to achieve synergetic effects that result from the different functionalities and geometries.

The numerous examples show that viscose specialty fibres are an extremely versatile raw material, suitable for the production of filter media, and suggest that the application possibilities for viscose speciality fibres in the area of filtration have by far not all been exploited yet, just as on the fibre side, not all possibilities for functionalisation have been exhausted yet.

For the development of the filter media of the future, the cooperation between filter manufacturers, to whom the specific requirements of filters are known, and fibre manufacturers, who have the specific knowledge and skills about the functioning of fibres, seem to be the best pathway.

Literature: /1/ D. Klemm, B. Philipp, T. Heinze, U. Heinze, W. Wagenknecht: Comprehensive Cellulose Chemistry, Volume 1, Wiley – VCH Verlag (1998) /2/ K. Götze: Chemiefasern nach dem Viskoseverfahren, First volume, 3rd edition, Springer - Verlag (1967) /3/ I. Bernt, Fine-Tuning of Paper Characteristics by Incorporation of Viscose Fibres, Lenzinger Berichte 89 (2011), 78 – 85 /4/ M. Siller, W. Roggenstein, T. Rosenau, A. Potthast: Functionalisation of Viscose Fibres, Lenzinger Berichte 91 (2013), 81 - 44 /5/ R. Scholz, D. Dedinski: Cationic Activated Viscose Fibres – Dyeing of Fibres and Decolouring of Aqueous Solutions, Lenzinger Berichte 89 (2011), 86 – 90 /6/ P. Wimmer: Viscose Fibres for enhanced Fluid Management, Lenzinger Berichte 91 (2013), 61 – 66

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Recovery of beer from surplus yeast - System comparison of the separation technology used W.-D. Herberg* In beer production, yeast occurs as a by-product, which contains a lot of valuable beer that, however, cannot be reused in the process. Different separation technologies are used for the recovery of this beer, which are set out below.

Process overview Beer production can be divided into three main process steps: 1. For the production of the beer wort, the starch of the malt or other starch sources must be converted into soluble sugar. In the area of the purity law, this takes place by the malt-inherent enzymes, and outside this, synthetic enzymes are also used.

After separating the husks of the starch sources (e.g. malt) and boiling with hops, one obtains the wort that essentially consists of water, sugar, some proteins and minerals, as well as flavourings, colours and aromatic substances.

2. The wort is fermented into beer with the addition of yeast. This produces alcohol and CO2 from the sugars. Beside these main products, the yeast also forms aromatic substances, like for example higher alcohols, esters, organic acids etc., that influence the beer quality as well as the digestibility. The brewer has a big influence on this spectrum through the choice of the fermenting parameters (temperature, oxygen content, yeast concentration, pressure, wort composition, yeast strain). About one third of the extract of the beer wort remains unfermented; this so-called residual extract consists of polysaccharides, like for example glucans, proteins and minerals. The (bottom fermented) yeast settles at the end of the fermentation and is partially recycled. This fresh yeast from the fermentation is known as fresh yeast in the specialist language.

3. The beer is stored cold, filtered and is then bottled. Through the cold storage and the pH drop during fermentation, trub occurs that settles with the yeast and forms the so-called tank bottoms.

Filtration as a final process step before bottling removes all yeast cells, trub particles and also colloid ingredients.

material remains behind after drying at e.g. 105 °C. At this temperature, only water and alcohol are evaporated and the residues of the organic and inorganic substances remain behind.

A differentiation between dissolved and undissolved substances is not possible. The result is indicated as % DS. The main possibility of error here is the dissolved extract of a liquid, and so, for example, a clear lemonade with 11 % sugar content by weight has a DS of 11%, without including any solid matter.

2. The centrifugal sample in a laboratory centrifuge divides the sample into insoluble solid matter and liquid phase, thus simulating the actual process conditions. The result is shown as % by vol.

3. The yeast cell count is determined in million cells/ml suspension by means of a Coulter Counter or via the conductivity. The analysis is inaccurate in the range of concentrations of yeast and tank bottoms.

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Yeast mass balance in the fermentation of the beer To keep the yeast population young and thus vital for fermentation, a certain increase of the yeast is desirable. The yeast can work aerobically (respiration) and also anaerobically (fermentation).

During respiration, the energy gain is clearly higher and with it also the growth rate. This growth rate can be controlled through specific ventilation of the yeast or the wort at the beginning of the fermentation. Typically, approx. 20 million cells/ml are metered into the beer and a three-fold growth rate is aimed at. Thus at the end of fermentation, there results a maximum yeast cell count of approx. 80 million/ml, of which 20 millon/ml are then usually reused.

The solid matter content of yeast and/or the beer content of a yeast suspension can be determined in several ways: 1. The dry substance (DS) indicates what amount of residual *Wolf-Dietrich Herberg Director Beverage Department Membraflow / Head of Filtration GEA Westfalia Separator Group GmbH wolf.herberg@gea.com

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Fig. 1: Seen from the left: Beer from a centrifuge with tank bottoms operation, tank bottoms sample, beer with yeast operation and yeast samples with typical massive CO2 release.

Fig. 2: Flow behaviour of concentrated yeast

Typically, the following applies: 40 million cells/ml = 1 % by vol.= 0.25 % DS. The quickest, easiest and closest procedure to the actual process method is the centrifugal sample, which also allows the easiest yield calculation.

The above-mentioned figures mean that 60 million cells/ml correspond to a yeast concentration of 1.5 % by vol. If the tank bottoms occur as a suspension with a yeast concentration of 50 % by vol., this suspension corresponds to approx. 3% of the produced beer (output) of a brewery.

its dark colour, tank bottoms are rarely used in the food processing industry, but they are in demand as high quality feedstuff.

The quantity ratio of white yeast to tank bottoms is about 2/3 to 1/3, but the bigger volume of beer is contained in the tank bottoms.

The figures shown vary significantly from company to company and are accounted for only with great effort. Often green beer is centrifuged immediately after the primary fermentation and then, with appropriate raw materials and process selection, no tank bottoms result. However, beers that are produced according to the purity law requirements, have such a high protein load that tank bottoms always results.

White yeast often needs dilution with de-aerated water before being fed into a beer recovery system: 1. Concentrated yeast with more than 40 % by vol. makes high demands on the processing. These are reduced through the improvement of the flow properties.

2. The water dilutes the liquid surrounding the yeast cells, whereby alcohol and residual extract diffuse from the cell because of the concentration gradient. Thus the yield of the process increases.

The performance information in the following process comparison refers to a concentration of 50 % by vol. of releasable materials in the incoming yeast suspension.

Characteristics of white yeast The solid matter concentrations of white yeast lie in the range of 40-70 % by vol., corresponding to about 10 – 17 % dry matter.

It has a pleasant fresh smell, contains a lot of CO2, is very sticky and has a complex flow behaviour. In the laboratory centrifuge, it is deposited clearly, but is compacted during prolonged centrifugation so that identical centrifuging times must be kept for the comparison of different samples. Through its white colour and high vitality, it is a valuable resource as a base material in the food industry.

Characteristics of tank bottoms In contrast to the rather homogeneous white yeast, a 3-fold layering of the sediment under a turbid supernatant often appears during centrifugation of the tank bottoms: 1. A lower dark layer of hop resins and dead yeast cells 2. A brighter middle layer that is similar to the white yeast 3. A dark layer over this that consists of fine trub particles.

With the tank bottoms, the concentration varies in the range of 5-60 % by vol. which is a challenge for the separation technology used in conjunction with the bad clarification capacity and the inhomogeneity. On average, one can assume solid matter concentrations of 25%. Because of Fig. 3: Centrifuge sample of white yeast

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Yield calculation The yield of the processes can be determined in different ways.

The simplest and thus the most accurate is the analysis based on the centrifugal samples with the laboratory centrifuge. If one looks at the yield of a system, in principle the following applies: The yield of a system is always the mass of the valuable substance obtained with respect to the incoming mass.

In this case this means: Mass of the outbound extract Yield % = x 100 Mass of the inbound extract Or Volume out x extract concentration out Yield % = x 100 Volume in x extract concentration in Hence, one determines the volumes and the extract concentrations of the two streams: Feed: Volumes x Proportion of liquid phase x Concentration, in the Fig. 3 example with a volume flow of 10 hl/h: 10 hl/h Yeast x 50% Liquid proportion x 12 kg/hl Extract = 60 kg/h Extract flow rate Outlet: 4.75 hl/h Beer x 12 kg/hl Extract = 57 kg/h This results in a yield of 95%. This would be a typical yield of a centrifuge operation without diluting the yeast in the inflow.

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Fig. 4: Diagram of a cross-flow system for beer recovery

If the yeast is diluted 2:1 with water before the centrifuge, the feed conditions remain unchanged. However, the outlet side changes drastically through leaching of the extract from the yeast cells: 9.75 hl/h Beer-Water mixture x 7.4 kg Extract/hl = 72.15 kg/h Extract.

This corresponds to a yield of 120%.

This is also a typical value for the practical use of a self-cleaning separator and yeast dilution in the inflow.

Economic efficiency of a beer recovery system: The installations amortise very quickly.

An example is a brewery with 2 million hl/a annual output, wherein a system should perform about 20 hl/h for the coverage of the seasonal peaks: A 3% yeast proportion of the annual output results in an annual consumption of approx. 60,000 hl of yeast. Typically, about 25,000 hl/a of beer are recovered from the yeast.

With a beer value of 15E/hl, 375,000 €/a can thus be generated. Depending on the scope of the integration effort and, depending on the selected system, the investment lies in the range of 400,000 – 800,000 €.

This means that the ROI can amount to one year in the best case. So beer recovery systems are very economical.

Minor transport costs must be added for the concentrated surplus yeast, which is used in food processing industries or agriculture.

System for beer recovery Besides belt and chamber filter presses that are no longer commonly used, the usual methods are centrifugation or filtration.

Self-cleaning separators

Fig. 5: HFE 45 nozzle separator installed in a brewery

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Self-cleaning separators combine simple process management with a good yield. The yeast is fed to the separator from a buffer tank. Because of the high solid matter proportion of the yeast

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Fig. 6: Ceramic membrane

suspension, the partial ejection of the separator bowl is done in short intervals of 90 - 150 s, in order to achieve the necessary performance. When processing white yeast, low turbidity is achieved in the clear phase, and in the pure processing of tank bottoms, the turbidity is clearly higher, at about the same level as German wheat beer. The range of performance per machine lies between 3 hl/h - 25 hl/h feed volume. Performance control is done using the ejection frequency, since this correlates directly with the introduced solid matter volume. When using GEA Westfalia Separator Hydrostop separators with a very effective ejection system, a solid matter concentration of 95 % by vol. is achieved. With an inflow performance of 25 hl/h, the power consumption is approx. 40 kW. Nozzle separators The integration is similar to self-cleaning separators, but as nozzle separators react sensitively to concentration fluctuations, circulation is advised and dilution to approx. 30 % by vol. in the feed is absolutely necessary. Because the solid matter is ejected continuously via nozzles, the performance per unit is high, even when using relatively small machines.

The machine illustrated in Fig. 5 performs up to 50 hl/h with a bowl diameter of only 540 mm and with this has a power consumption of approx. 40 kW. The clarifying efficiency is on a par with that of the self-cleaning separators, but the achieved solid matter concentration of the separated yeast is clearly lower at approx. 80 % by vol.

Decanters Decisive progress in decanter construction with respect to oxygen pick up and hygienic design allows the application of decanters for beer recovery. Decanters that have a much smaller clarifying area 80

than disk-type separators are ideal for the processing of high solid matter volumes.

With white yeast, the performance is high and the clarification good, because the yeast cells sediment well. However, with tank bottoms almost no protein is separated which results in very turbid and indeed yeast-free clear phases, but still with solid content. Post-clarification is recommended by means of a separator. The concentration of the separated yeast lies at about 95 % by vol. Decanters are the only system with which the yeast in the feed does not have to be diluted.

With all centrifugal processes, the beer has a residual turbidity and contains small amounts of yeast. However, depending on the point of return into the system, this is insignificant since the beer is usually blended back before fermentation or during the transfer from fermentation to storage.

Cross-flow Filtration For beer recovery, systems with ceramic elements have prevailed, not least because of their superior durability and easy cleaning. There are only a few systems with polymer flat membranes.

The systems are equipped with multi-channel elements, and 6 mm or better 8 mm channels, are used because of the high viscosity of the yeast. The pore width used is 0.2 - 0.8 μm, but the influence of the pore width on the clarity of the product is low. The filtrates are free of yeast and largely sterile. Because fine turbidity is also retained, the blending into the beer can take place during the filtration. Through this, the imputed value of the recovered beer increases somewhat.

The electric power input for a system of approx. 25 hl/h inflow performance is about 60 kW. The membrane systems are operated in three variants: 1. Continuous operation: The suspension is supplied and concentrated in the filtration loop, and the concentrate is continuously discharged. This leads to short dwell times of the yeast in the system, but it is always filtered with maximum concentration so that the flux is low and the power input is high. Because the concentrate still contains undiluted extract, the yield is low.

2. Continuous operation with dilution of the yeast in the inflow: like 1, but through the water addition in the inflow, the losses decrease because the extract was diluted in the concentrate.

3. Batch process with diafiltration: a batch tank is concentrated via the filtration loop. If the final concentration is reached, the mixture is diluted with water. This variation achieves the best yields, but the process duration is approx. 20 h.

In the processing of pure tank bottoms, there can be shorter operation times of the membranes between the cleanings, because the pores of the membranes become blocked through the fine trub.

However, the general service life of ceramic membranes is virtually unlimited.

Comparison of the systems For the system comparison, there are four aspects in the foreground: 1. Product quality: a. In taste, the systems are comparable in the blends (max. 3% dosage of recovered beer) b. Turbidity: the dosage of yeast beer from the centrifuge processes directly before the beer filtration can influence the turbidity of the filtrates, and so the blending should be done earlier. This effect does not appear with yeast beer from membrane systems.

2. Integration expenditure: a. Membrane systems need their own CIP (purification plant) and centrifuges are cleaned together with the conduit. b. Separators need little space c. For the integration of decanters, post-clarification through separators is recommended 3. Operating mode: In the processing of mixtures of yeast and tank bottoms, membrane systems work better than for tank bottoms processing alone. The sales yeast thus obtained can be difficult to use as a food base material. This also applies to a lower extent for nozzle separators.

4. Operating costs: The use of nozzle separators is the best solution. The running costs (electricity, cleaning) of membrane systems are above those of centrifuges, but the latter have higher maintenance costs. Because centrifuges are produced only in graduated sizes, the investment costs of certain system sizes can speak respectively for one or other system.

Summary: With beer recovery systems, approx.

1-2% of the annual output of a brewery can be economically recovered from the yeast. The established systems are centrifuges and ceramic cross-flow filtration.

If clear filtrates are required, cross-flow filtration is used, which requires separate CIP in addition. Nozzle separators offer high performance with low investment.

Simple installation, maximum yield and great flexibility can be combined with the installation of self-cleaning separators.

A detailed analysis of local conditions is required in each case.

F & S International Edition

No. 15/2015

Highlights 2014

Adhesives for the manufacture of ďŹ lter media for vehicle component assembly M. Dressler * In the manufacture of air ďŹ lters, user-friendly, intelligent adhesives are a crucial factor for process efďŹ ciency and make air ďŹ lter systems resistant and reliable.

The product range for air ďŹ lters is not only huge but also covers all kinds of special variations. Even when considering only the limited spectrum of air ďŹ lters for vehicles, this still refers to a product range where structural forms, sizes and material choices are almost unlimited. Air ďŹ lters are manufactured in fast production processes with speciďŹ cally tailored adhesives which have to fulďŹ l all the challenges during production as well as in the utilisation of these high-tech ďŹ lter systems later on.

Adhesives are responsible for the optimum connection of the most diverse structural components and material combinations â&#x20AC;&#x201C; for ďŹ&#x201A;at surface bonds of the ďŹ lter medium, for the strength of small surfaces in pleating, and for the ďŹ&#x201A;exibility of the frame assembly. Specially formulated adhesives facilitate high-speed manufacturing cycles, a problem-free engineering and application technology, and an accurate production with the highest quality for each intermediate product that undergoes further processing, up to the ďŹ nal step.

1. Flat surface compound of ďŹ lter media with activated charcoal During the laminating process and for the end product of activated charcoal ďŹ lter media, modern adhesives like the thermoplastic Jowat-Toptherm and the reactive PUR adhesive system Jowatherm-Reaktant ensure quality and efďŹ ciency.

Quality, because the performance of the activated charcoal ďŹ lter is substantially determined by the adsorption capacity of its ďŹ lter medium. The new Jowat laminating adhesives reach good strength levels of the activated charcoal medium in the laminating process, even when the adhesive grammages are low. This ensures that the open surface of the activated charcoal remains as large as possible with only minimal reduction of adsorption and air permeability â&#x20AC;&#x201C; even when the ďŹ lter media consist of several layers. When bonding the activated charcoal onto the carrier material a low adhesive grammage is crucial for maintaining the actual function of a ďŹ lter the ďŹ ltration and constant supply of clean air â&#x20AC;&#x201C; to a superior extent.

EfďŹ ciency, because the new adhesives based on polyurethane or polyoleďŹ n have good spraying properties, and the high green strength allows fast downline steps, thereby supporting the manufacturing processes. The open time of the adhesives (see table 1) is adapted to the individual manufacturing methods when the ďŹ lter ďŹ&#x201A;eece materials are coated with activated charcoal. Even when the adhesive bond is subject to downline stress resulting from operations like reeling and unreeling, cutting and pleating of the coated ďŹ&#x201A;eeces, the excellent ďŹ&#x201A;exibility of the Jowat adhesives will also withstand these mechanical stress factors.

The selection of the approriate adhesive system must be made under consideration of the manufacturing process and the characteristics required from the end product when in actual use. The table below shows a comparison of the relevant process parameters of both adhesive systems. * Michael Dressler Produktmanager Jowat AG Ernst-Hilker-StraĂ&#x;e 10 - 14 32758 Detmold Phone: +49 (0)5231 749-300 E-mail: michael.dressler@jowat.de Internet: www.jowat.de

F & S International Edition

Following the basic choice of either thermoplastic or reactive system, the speciďŹ c adhesive is selected according to the requirements of the manufacturing processes and the performance criteria of the ďŹ lter media which have to be met.

When comparing a purely thermoplastic to a reactive adhesive, the reactive system is exhibiting a much better performance, with an outstanding ďŹ&#x201A;exibility, very long open time and high heat resistance. All of these are properties which the reactive adhesive achieves due to the chemical crosslinking reaction that takes place after application.

Bonds with either Jowat-Toptherm or Jowatherm-Reaktant permit a high functionality of the ďŹ lter medium due to the formulation ingredients which are low in VOCs; both adhesives also have no recognizable odour in the ďŹ nished product. Characteristics which are expected especially when they are used for the manufacture

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Highlights 2014

Table 1: Relevant process parameters and characteristics by comparison (source: Jowat)

Table 2: Processing parameters of selective Jowat adhesives for the lamination of activated charcoal filter media (source: Jowat)

Table 3: Examples for formulations with different viscosities, open times and processing temperatures (source: Jowat)

of passenger compartment filters. Beyond this, the low adhesive consumption also results in lower energy requirements, and in consequence reduced manufacturing costs.

2. Pleating and filter frame assembly The thermoplastic Jowat filter adhesives for pleating and frame assembly have been developed for sealing and forming properties which also promote the largest possible process safety. Apart from the good adhesion to the papers and fleece materials, structural properties are also required. This means the the shape of the filters must remain unchanged over their entire life, even when the material compound is exposed to mechanical forces or high temperatures. The special adhesives for pleating and frame assembly ensure that the filter elements have a lasting product life and a high quality.

Pleating: The diverse filter materials and manufacturing methods require adhesives for the pleating step with special processing characteristics: Jowat adhesives support fast manufacturing by an open time adapted to this necessity, while the high

Fig. 1: Activated charcoal filter media pleated (source: Jowat)

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The processing characteristics and their impact on the process times can be tailored to the requirements of the manufacturing process (see table 3).

In order to provide adequate stability to the filter media after pleating, the adhesive is applied in bead form for the lateral bonding of the filter pockets, and to hold the folds in place. When assembled into the frame, the adhesive can also be applied with a flat slot nozzle. The necessary strength, flexibility and tightness on the frame is given by the embedding of the ends of the pleats in the adhesive layer (see photo 3). The products listed in table 3 have proven to be successful for pleating as well as for assembly into the frame.

Filter frame assembly: The engine compartments of cars are becoming increasingly more compact, in consequence the air filter placement often permits only a filter exchange under heavy deformation (see photo 2 ) This in turn demands for frame bonds with high levels of strength and excellent flexibility. The adhesive, or better the bondline, may not fail and the filter pockets may not develop leaks, respectively the performance of the filter element may not be impaired. Apart from this, the assembly inside the engine compartment also necessitates superior levels of temperature resistance - depending on the placement of the filter, the filter bond may be exposed to temperatures from 80 to 130 °C.

Conclusion: The filters used in an automobile play a non-negligible role when considering its ecological footprint. All air filters have a series of properties in common: The optimum air filter is tailored to the surrounding component architecture, it is tightly sealed and creates minimal differential pressure in spite of its superior capacities of particle removal and absorption. The filter should maintain constantly the full and highest possible performance up to the time of exchange. When the adhesive is perfectly matched to the substrates used and their surface properties, to the production processes and the future wear in actual operation of the filters, major savings in processing costs are possible without loss of quality of the end product. Jowat filter adhesives meet the stringent heat resistance demands by the car manufacturers, and allow the manufacture of vehicle compartment cell filters and engine intake air filters in OEM quality. Using modern adhesives with special formulations which have no detrimental impact on the performance of the filter is therefore an absolute must, from the ecological as well as from the economical perspective.

To take full advantage of all positive characteristics of a modern adhesive, Jowat provides competent technical consultation to all customers in all phases of use of the products. From the provision of samples over the test phase to taking-into-operation of the machines, Jowat engineers are ready to supply help and advice.

Fig. 2: Adhesives for pleating and frame assembly, major quality factors for the filter performance. (source: Jowat)

Fig. 3: Examples for embedding of the filter pleats into the layer of adhesive on the frame (source: Jowat)

green strength data are maintained, which ensures fast downline production cycles of the pleated filter media. The adhesives additionally have a wide spectrum of adhesion for safe bonding of substrates made of paper, fleece and other materials like nano-fibres. When papers impregnated with phenolic resins are used a high temperature resistance is required since curing takes place after pleating, and usually at temperatures distinctly above 150 °C.

F & S International Edition

No. 15/2015

Highlights 2014

New standards for surface purity, energy efficiency and nanoparticles under discussion A Report on Cleanzone 2014 The concept of “pure” is usually associated with the notion of an ideal.

Nevertheless, in terms of clean rooms, there are different philosophies in different regions. According to a report on the Cleanzone 2014, the USA is considered here as fond of regulations , Japan as driven by technology and Europe as a leader in application-oriented engineering skills. This results in a variety of pulses, which currently lead to further developments of the recognized standards.

Koos Agricola, Secretary General of the ICCCS (International Confederation of Contamination Control Societies) and the ICEB (International Cleanroom Education Board), puts it in a nutshell: “In the USA, on the one hand, one holds on to familiar processes for a very long time while the US researchers, on the other hand, produce a variety of new technical cleanroom solutions.

Differently than in the past, less prominent innovations come from Japan at the moment, on the other hand, one has perfected an extremely conscientious quality control there.”

The ideas for the optimisation of existing standards and directives mostly come from Europe. Emerging countries in Asia and South America, where new cleanrooms now originate increasingly, like resorting to this groundwork. “Often, they are using European products, however, more and more, there are also alternatives available from China”, Koos Agricola observes: “Here, the training of the staff plays an essential part. Here, Europe could play a much bigger role than is currently the case.”

In spite of different national regulations, VDI Directive 2083 (Association of German Engineers) and ISO EN DIN 14644 have been developed as the basis for the operation of cleanrooms and these have also largely prevailed internationally. “The confusion that was still there 50 years ago with numerous national cleanroom standards, has been overcome with ISO 14644” Thomas Wollstein explains, who is the responsible person in charge at VDI for the field of cleanrooms. “According to this example, numerous useful standards have been set. Currently, there are new burning questions on the agenda.” The answers serve to change the operation of cleanrooms in important details.

Detection of smaller particles and viable organisms For the definition of air purity classes, particle size distributions up to the micron and submicron range were used as a basis, which are orientated on the distribution of the “natural aerosol” in ambient air. After expansion of the purity classes to nanoparticles, which have their own agglomeration behaviour, these must now be considered in new particle size distributions and new measuring methods. The development of suitable standards is still at an early stage.

Besides nanoparticles, reproductive bacteria are also a problem.

Their viability cannot be detected immediately, but they have yet to multiply for several days in culture in order to detect them, or evidence has to be provided for the freedom from viable bacteria.

Concerning cleanrooms, for this purpose there is VDI Directive 2083, Sheet 18 Cleanroom technology - biocontamination control, which takes into account the need for rulemaking for the hygienic design of cleanrooms. Like the other directives of this series, it was compiled by the VDI Technical Committee Cleanroom F & S International Edition

No. 15/2015

Fig.: Cleanrooms are part of the standard equipment of a production operation in many fields, e.g. as illustrated in food processing

Technology (FA RRT) founded in 1972. This directive finishes with a short introduction to the GMP clean room classes, their application areas and the underlying limit values. This raises the question: How important is cleanroom classification according to GMP in comparison to ISO? In the application, the following shall apply: Those who manufacture medicines must work according to GMP, as otherwise they will not pass an audit by the responsible authorities. The certification according to ISO standards may also bring additional benefits beyond that, for example in the optimisation of workflows, the exploitation of cost reduction potentials or with special customer requirements. With GMP compliance, an enterprise has fulfilled roughly 70 to 80 percent of ISO requirements. Both classification systems assume air purity. Maximum limits of the number of particles of a certain size per cubic metre are always specified.

Cleanable, cleanroom compatible: Surfaces and materials “In addition, more and more parties involved find that clean air is by no means the be all and end all by itself in the cleanroom” noted Koos Agricola. “All surfaces should also be cleaned accord83

Highlights 2014

ing to the specification of ISO 14644-9. Among other things, what is lacking here is a standard for the depositing of particles on furnishings and walls.” Important points in this context are materials and material combinations. Because sometimes material mating can be observed, like for example a roller that rubs over a surface.

“So we have recently described a method in Sheet 17 which imitates the actual conditions of use” reports Thomas Wollstein. “In this, one lets a ball run on a plate, so as to define a standard contact load. The model is based on relevant research at Fraunhofer Gesellschaft.”

Potentially much more energy efficient Headway has been made in the German language area with regards to energy efficiency in the cleanroom. Michael Kuhn, Steinbeis-Transfer-Zentrum (STZ) für Energie-, Umwelt- und Reinraumtechnik, Offenburg (“EURO”), has demonstrated how high the saving potential is in several case studies. This is almost always from ten to twenty percent and it can even be 50 percent if one exhausts all leeway. At the moment, standardisation in the

form of standards is underway at VDI. The British Standards Institution, the counterpart to the German DIN, is already proposing to discuss this issue in an international context.

Pole position for Europe - update for everybody on the clean zone In summary, it can be stated that many things are in motion with the standards for cleanrooms. A whole series of questions relating to standardisation problems will first be taken up in the region of Germany, Austria, Switzerland and The Netherlands. Currently, these include surface cleanliness, biocontamination with viable organisms and also the expansion of particle detection down to nanoparticles.

Visitors can find information, ideas and tips for implementation and innovative technical solutions at the next CleanZone, International Trade Fair and Congress for Cleanroom Technology, from 27th to 28th October, 2015, in Frankfurt am Main. It represents an opportunity to get comprehensive information and to make important personal contacts.

Future importance of natural product-process technology for chemical production

S. Ripperger*

1. Natural product-process technology and its development As long as man has existed, he has resorted to the resources of nature. He uses plants and animals for food, as well as natural products for building houses and as an energy source in the form of fuels. For centuries, materials have been obtained that are synthesised by plants and are often today called natural products in the narrow sense. This concerns a large product range, extending from intermediate products and end products up to medicinal products, cosmetics and dyestuffs.

Today in the broader sense, natural products are used for food production and as renewable resources. According to a definition of the Agency for Renewable Resources (FNR) /1/, renewable resources are “regional and forest generated products that are not used as food or feed, but are used materially or to generate heat, electricity or fuels.” This concerns products that are grown in agrarian areas or wood. * Prof. Dr.-Ing. Siegfried Ripperger Lehrstuhl für Mechanische Verfahrenstechnik Technische Universität Kaiserslautern PO Box 3049 67653 Kaiserslautern Tel./Fax: 0631-205-2121/3055 E-mail: ripperger@mv.uni-kl.de

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Large amounts of wood were used until the 18th century in the production of iron and for heating. Large amounts were required e.g. for the production of charcoal for making steel and for salt extraction by boiling brine that was carried out on brine sources. At the end of the 18th century, wood was replaced more and more with coal. This was also used for steam generation for driving the emerging steam machines and afterwards was also increasingly used in the form of coke for steel making. With the industrial revolution in the 18th and 19th centuries, bituminous coal tar resulted as a by-product from the generation of metallurgical coke and illuminating gas in increasing volumes.

In the middle of the 19th century, this “waste” was increasingly processed in bituminous coal tar refineries into impregnating oils and then further into aromatic tar compounds. The aniline dye industry originated from this. Many of the chemical companies known even today were founded at this time. They were based primarily on the developing coal chemistry, which resulted from wood consumption and, accordingly, deforestation being reduced in Europe.

With the development of oilfields and natural gas fields in conjunction with the increasing motorisation in the 20th century, industrial chemistry changed over to the raw materials crude oil and natural

gas. Both products were cheap, easy to transport in pipelines and easier to process. With this change in raw materials, the petrochemical industry developed, that constitutes today the chemical industry for the most part. According to a communication of the Chemical Industry Association from 2012/1/, derivatives of crude oil, above all naphtha, today form by far the largest part of the raw material basis for organic-chemical synthesis in chemistry (see Fig. 1).

Since the middle of the seventies in the last century, a chemistry of renewable resources has increasingly developed (again). The cause for this development within the chemical industry is the expectation that, on account of the worldwide high demand for crude oil, a shortage and the increase of crude oil prices, the significance of petrochemistry will decrease. The compound systems in today’s chemical sites in the so-called chemical industry parks guarantee that the processes are operated with high resource efficiency, so that in future, clear efficiency increases are not to be expected. Hence, for several years, research projects and development works for the improvement of biotechnological processes have been partially funded with considerable public funds.

Besides “green biotechnology” (agricultural application) and “red biotechnology” (medical-pharmaceutical application), F & S International Edition

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Highlights 2014

Renewable primary products 13% Coal 1%

Natural gas 14% Naphtha, natural oil derivatives 72%

As of 2008, since no newer data are available for renewable primary products Source: VCI, FNR; Basis: Tonnes of raw material

Fig. 1: Raw material basis of the German chemistry industry; proportion of raw material sources on the basis of the tons of raw materials used; source: VCI, Agency for Renewable Resources

“white biotechnology” has been established for biotechnologically-based production on an industrial scale. Many see in it the potential for sustainable development within chemistry, since they could one day develop into an essential carrier of organic chemistry. Industrial (“white”) biotechnology includes biotechnological production processes for the industrial processing of natural products with the objective to replace fossil raw materials. According to Fig. 1, in today’s chemistry processes, renewable resources are already used for about 13 percent. Thus renewable resources are now already an important basis for some products of the chemical industry.

Source products for chemistry are among other things oils, starch, sugar and cellulose. Sugar is gained e.g. in the respective cultivation regions from sugar beet or sugar cane. The production of glucose through hydrolysis of starch is also gaining momentum.

In the processing of the raw materials, the question must also be asked about the utilisation of the by-products. Large amounts of biomass originate in the processing of the source materials, which up to now can be used only in a limited manner as animal feed.

In the long term, a more efficient use of the co-products is necessary. A starting point is the so-called “biorefinery”, which has the complete material and energy use of renewable resources as the objective. In this, biogas generation, which is part of the state of the art, can also be used. The objective, with the help of “white biotechnology”, is to further process renewable resources and possibly also waste materials from food production in so-called biorefineries into the desired products of the pharmaceutical industry and chemical industry. White biotechnology would thus also be associated with integrated environmental protection that largely avoids toxic waste and waste problems.

The use of biotechnology in chemistry is not new, but was limited some years ago mainly to the production of enzymes, some food additives and active pharmaceutical ingredients. It was found that in some cases biotechnological processes may have more positive business results than purely chemical processes. This concerns in particular the synthesis of complex organic compounds.

Bulk and fine chemicals, food products and food additives, feed additives, agricultural and pharmaceutical intermediates, enzymes and biofuels and bioplastics belong to the products of white biotechnology. In isolated cases, process costs could be reduced through the use of white biotechnology. Thus, a change from a chemical to a biotechnological process took place e.g. with the production of some vitamins and amino acids. It is expected that white biotechnology has considerable influence also on the production of bulk products and polymers. One speaks of bulk products if more than 10000 tons of it are produced annually. Even now, bioreactors with 500 m3 size (and more) are used for the production of bulk products such as L-glutamate flavour enhancer, F & S International Edition

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L-lysine feed additive, antibiotics, vitamins or for the generation of succinic, citric and lactic acid.

Ethanol, acetone and butanol are examples of products that are supplied mainly from the petrochemical industry even today, but that in future could also be produced biotechnologically in large quantities. Regardless of the assessment of how urgent the need currently is for the substitution of crude oil, there is the growing recognition that renewable resources are the only self-renewing source of organic carbon compounds and constitute an alternative resource for the future. With the increased use of renewable resources, a structural change within the petrochemical industry is unavoidable, like with the transition from coal chemistry to the petrochemical industry.

As with the so-called energy revolution, the results that are connected with an increased application of white biotechnology are not yet clearly recognisable. Much like it was hard to imagine that in the energy sector nuclear power plants can be partially replaced by many thousands of wind turbines, today it cannot be estimated yet how the raw material volumes converted in today’s steamcrackers can be replaced through processing renewable resources.

In today’s big steamcrackers, more than a million tons of longchain hydrocarbons (e.g. naphtha) are partially converted annually, by thermal cracking in the presence of water vapour, into shortchain hydrocarbons as source materials for the further syntheses.

It can be expected that with the development of white biotechnology, varied applications result for separation techniques. To illustrate this, a process diagram for the production of potato starch is shown in Fig. 2. The objective is that the material transformations are carried out so that the source materials are converted into the state of the ideal product with as few intermediate steps as possible. Nevertheless, it is clear that a number of process

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seasonal occurrence of the raw materials.

Smaller process technology plants are planned and are increasingly established on the basis of standardised modules, partly in container size. Partially decentralised processing of products under optimised conditions therefore appears possible.

3. Raw material situation in Germany

Fig. 2: Process diagram for the production of potato starch

steps are required in order to obtain the starch. In the colour-coded stages of the process, mechanical separation processes are applied.

2. Process technology procedures for the processing of renewable resources Process technology procedures for the processing of natural materials are already used on a large scale in the cellulose and food industries. In this, one is anxious to design the material change as effectively as possible and to minimise the investment costs and operating costs. The cost structure arising here is also a basis for a rough cost estimate for applications in the chemistry field.

Separation techniques like centrifugation, filtration, separation of materials with membranes and extraction are only some of the traditional procedures that are applied at many places within the processes. Products with a high natural water content are usually processed and converted in the form of more complex, partially colloidal dispersed suspensions. Such suspensions are to be found in the production of starch, sugar, juices, alcoholic beverages and milk products. The density difference between solid and liquid is mostly very low. These features complicate the separation of materials. Small particles and a low density difference result in very low settling velocities of the dispersed phase.

The economical use of sedimentation is achieved with this combination only with high speed disk separators. Gravitational sedimentation is only of importance in connection with the long-term storage of products in containers.

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The large specific surfaces of the material systems, in combination with an identical surface charge and the repelling surface forces resulting from it, hinder sedimentation and the dewatering of the sediments and sludges. When using cake filtration, very compact and compressible filter cakes thereby arise, which accordingly result in low specific filtrate flow rates.

Filtration can often be carried out with an adequate result only through the use of filtration aids or dynamic filtration processes with a high specific energy input.

The solid matter is often dried for further use. For reasons of energy conservation, a very high solid mass content is aimed for after the mechanical separation.

Because of the heat sensitivity of many products, separation processes that require high temperatures are only applied to a limited extent. In relation to fermentation, batch operation is usually still predominant. As in other industries too, there is still a trend towards automated operation.

In the production of source materials for chemical production, the “Economy of Scale” is exploited in the chemical industry, which means that production costs are reduced with increasing production volumes and corresponding plant size. The optimum plant size and plant configuration is developed on the basis of the product requirements of the market, the available raw materials and the environment in which production takes place.

In the case of natural raw materials, the distances must be considered between the cultivation of the materials, the transport possibilities and the possible spoilage of the raw materials. Temporary storage facilities are necessary for the continuous operation of the plants on account of the

According to FNR/2/, in 2013 renewable resources were grown in Germany on one fifth of the arable field surface. In addition, wood grows on approx. one third of the German Federal total area that can be used industrially and for the power supply. The average annual wood production of the last ten years was 56.8 million m2, of which nearly half was used for material and the rest for energy. One can assume that wood production cannot be significantly increased anymore in Germany.

According to the Bundesvereinigung der Deutschen Ernährungsindustrie e.V. /3/, about three quarters of raw materials processed into food in Germany are also grown here. Four fifths of the arable land is used for this. A quarter of the raw materials necessary for food production are bought in European and non-European foreign countries. This also includes products that cannot be grown in Germany, like for example coffee and cocoa.

A growing world population and a higher buying power in many countries led during recent years to an increasing demand for agricultural products and to an upward trend in prices. Moreover, harvest variations influence the supply at short notice. In addition, due to the depicted development, there is increasing competition for the use of agricultural land in the choice between food and renewable resources.

Many agricultural raw materials have been internationally traded for a long time on stock exchanges. During recent years, agricultural raw materials have developed into short-term financial investment products, so that the respective market situation is also increasingly influenced by financial investors. Hence, many worry about the raw material supply for food production and about the price of food. Also against this background, a significant raw material change in the chemical industry has been difficult to imagine up to now. Even if it slowly takes place, it is a big technological challenge. The economic risks are manageable only for individual products or a product group. However, the depicted raw material change offers an opportunity for sustainable development, with the use of partly known technologies.

Sources: /1/ www.vci.de /2/ www.fnr.de /3/ www.bve-online.de F & S International Edition

No. 15/2015

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