D 11665 F
International Edition
2016
International Edition
MMTC 2000 EHF Test of Įlter media, beƩer than ISO 11057, heatable up to 250 °C, humidity control
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Highlights 2015
Dear Readers,
In Germany and the neighbouring countries, the magazine F&S has been quite an institution for the past 29 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 sixteenth 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 2015. 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 2015, 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 70).
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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MFP 2000 EHF – close to reality Įlter media tesƟng; temperature up to 250 °C, rel. humidity up to 80 % (90 °C) “Close to reality” is a very important aspect of Palas® Įlter test systems. This means the Įlter media must be tested under the same condiƟons as they are used in the applicaƟon. The MMTC 2000 EHF oīers for that purpose the following special advantages: - Test with diīerent powders from the process shows the inŇuence of the parƟcle material to the ĮltraƟon and cleaning characterisƟcs. - Adjustable temperature up to 250 °C to meet as well special condiƟons in high temperature applicaƟons. - Adjustable rel. humidity up to 80 % at up to 90 °C to test the inŇuence of rel. humidity on dust cake built up and cleaning requirements. - Special inlet for diīerent gas components to inŇuence the composiƟon of the carrier gas with regard to the process. - Special shapes of the supporƟng frame in the Įlter holder to simulate the so called “garland eīect” for Ňexible Įlter media. - Special inlet construcƟon for In-situ tesƟng by sucƟon of the dust from the real process.
W Highlights 2015
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Membrane technology – past, present and future within the water industry T. Peters
6
The chemistry makes the difference Membranes made from highly crosslinked polyamide for reverse osmosis J. Lipnizki
11
Use of membranes for process filtration and in industrial water management H. Lyko
14
The biggest drinking water production plant in the USA
19
Innovative feed spacer technology leads to enhanced reverse osmosis element performance J. Kidwell, St. Tielen, B. Paesen, J. Ogier, St. Lehmann, C. Schellenberg 20
In addiƟon, with the aid of the aerosol spectrometer Promo® the parƟcle concentraƟon and parƟcle size distribuƟon can be determined with the highest Ɵme resoluƟon and in temperatures up to 250 °C. The test specimens can therefore be accurately analysed during the cleaning pressure burst, and the cleaning parameters can be opƟmally Įne-tuned to the medium.
Zero liquid discharge – a futuristic model for water treatment processes? S. Ripperger
24
Improved treatment of landfill leachate by means of optimized flocculation technology Reducing leachate treatment costs, but how? Ch. Schröder
29
For an opƟmal process control, the measuring technology can be integrated into a data processing system.
Components and systems used in the processing industry for solid/liquid separation H. Lyko
36
Innovations and further developments in the food and beverage industries H. Lyko
40
New porous metallic-paper and its use as a filter medium L. Petersen, S. Ripperger, C. Kostmann, P. Quadbeck, G. Stephani, J. Strauß, S. Schramm
44
Performance of new filter media – expectations and experience in vacuum and pressure filtration D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer
48
Wire mesh used in sophisticated separating processes H. Schlebusch
53
The use of computational fluid dynamics for the development of filter fabrics S. Ripperger, K. Schmidt
55
The advantages of the MMTC system allow a clear, costeīecƟve, pracƟcal and useful comparison of cleanable Įlter media and exceed the requirements of the standards ISO 11057 and VDI 3926. The results can be evaluated automaƟcally and presented individually. The handling of Palas® Įlter test systems is simple and economical. With more than 130 built and delivered air Įlter test systems in more than 15 diīerent versions, Palas® is the leading manufacturer worldwide of Įlter test systems with integrated fracƟonal separaƟon eĸciency measurement. For more informaƟon, please contact us:
Palas GmbH Greschbachstrasse 3b 76229 Karlsruhe, Germany Phone: +49 721 96213-0 Fax: +49 721 96213-33 E-mail: mail@palas.de Internet: www.palas.de
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Contents
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No. 16/2016
Contents Highlights 2015
W Use of membranes for process filtration and in industrial water management Filtration in the future: Innovative filter media and their manufacture for air pollution control and fuel filtration H. Lyko
59
Improvements in aerosol technology facilitate aerosol research, filter development and filter testing H. Lyko
65
Testing of air filters in compliance with the new ISO 16890 H. Lyko, T. Stoffel
71 W Innovations and further developments in the food and beverage industries
Filtech 2015: Machines and processes used to manufacture filters H. Lyko
76
Imprint
70
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Highlights 2015
Membrane technology – past, present and future within the water industry T. Peters* The pressure driven membrane processes microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) have become definitively important instruments in water management and environmental engineering. Their performance has been comprehensibly verified from a technical and economical, as well as an ecological, point of view. These processes can be considered nowadays to be well-proven and very successful tools of chemical engineering, allowing for example to overcome water scarcity and to prevent water pollution, or to enable recovery and reprocessing of valuable substances. In combination with other processes the remaining water quantity can be significantly reduced by multiplied usage of the water, thus saving costs, but also facilitating the realization of environmental sustainable zero liquid discharge (ZLD) procedures. This development is partially based on results obtained during the operation of RO systems that were designed in the early days of the technology for the desalination of seawater (trendsetting patent 1964). Details addressing these membrane processes, example for their area of application in the past, present and expected developments, are considered for the discussion of decision supporting criteria for the selection of these technologies. 1. Introduction Membrane technology for the treatment of water and wastewater shows impressively how innovative, future-oriented and economically meaningful environmental protection technology can be. In the past 100 years of modern water and wastewater treatment for households and enterprises, no other new technology has been introduced that offers so many positive effects like membrane technology /1/. Numerous different problems in water treatment can be solved, simultaneously resulting in significant better cleaning of wastewater. Due to the wide range of available membranes and modules, including open channel systems for niche applications /2/, technically suitable systems for nearly every type of problem in water treatment can be found. Membrane technology also allows for internal recovery and reprocessing of solid and dissolved substances, thus creating added value. On one side the increasing world population, the rising living standard and the expanding industrialization are the main causes of the ever increasing demand for potable water and for water of high quality for industrial applications. The areas affected are not only arid regions of the world with their chronic water deficiency, but also at an increasing rate the urban agglomerations and industrial centres in which the capacity limits of natural supplies have almost been reached /3/. * Dr.-Ing. Thomas Peters Consulting for Membrane Technology and Environmental Engineering Broichstr. 91, 41462 Neuss, Germany, dr.peters.consulting@t-online.de
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On the other side, the phrase „WATER IS LIFE“ is generally used nowadays to very clearly express the problems of a lack of potable water. However, the statement should be rephrased to „NO LIFE WITHOUT CLEAN WATER IN SUFFICIENT AMOUNT“, as this helps to remind mankind that nearly every type of contamination can at least be a source for water pollution, and thus a danger for the basis of life. At the same time is clarified that water produced artificially has to meet well defined quality standards /4/, which is possible using membrane technology. 2. Advanced Water Management Strategies In many regions it is not possible anymore to satisfy the growing water demand by conventional methods of water procurement and processing. Therefore, an increased utilisation of advanced separation techniques like membrane technology is called for, based on three main strategies /5/: 2.1 PRODUCTION: production of potable water from saline and polluted waters in order to increase the amount of good quality water available in addition to the natural water resources. Example are: - Desalination of sea water or brackish water (RO) - Separation of sulphate from drinking water (NF) - Improved purification of river water (UF) - Disinfection of surface water (UF) 2.2 REUSE: improved purification of slightly polluted wastewater in order to increase the exploitation potential,
respectively to reduce the consumption of potable water by recycling or reuse of the purified water. Examples are purification of: - Pre-treated industrial wastewater for recycling in a semi-closed loop (low pressure RO) - Filter backwash water in swimming pools for use as bathing water (low pressure RO) - Filter backwash water in water works to increase the production of potable water (UF) - Effluent of sewage treatment plants and use for irrigation purposes (UF) - Gray water on ships and use as technical water (UF) - Gray water at hotels and use for toilet flushing and irrigation (UF) 2.3 PROTECTION: the prevention of further contamination of the water resources by improved purification of waste water and contaminated water. Example are purification of: - Landfill leachate (RO) - Effluent from sewage treatment plants to reduce contamination in the receiving river (UF) - Black water on ships or at hotels to protect the environment (membrane bioreactor (MBR) based on UF) The growing concern in recent years around the world regarding environmental pollution, more stringent legal requirements regarding the quality of drinking water or bathing water and the anticipation of tightened global waste discharge regulations have been further driving forces for the increasing acceptance and wider use of these technologies /6, 7/.
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M I C R O F I LT R AT I O N U LT R A F I LT R AT I O N
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Fig. 1: Flow diagram for a RO system, an example for the function of pressure driven membrane processes
Similar to the development of RO technology as a classical application for the desalination of seawater to produce potable water, the membrane processes MF, UF and NF become important instruments in water management and environmental engineering. The kind of process to be installed as a main step or in combination with other technologies for a specific application depends on the type of contaminants to be separated from the water to be treated and the quality requirements imposed for the produced water. 3. Membrane processes Even if membrane processes seem to be, or are, well known, and have been described in countless articles and descriptions, some technological details and nomenclature differ in publications. Therefore, some definitions and technical details that are usually used among experts are described here, together with some considerations resulting from long term experience in the field. The membrane processes considered are pressure driven separation processes, where the driving force is a pressure difference across the membrane. With the membrane the water to be treated is separated into a stream of filtrate (the usual denomination for the product water at MF and UF) or permeate (the usual denomination for the product at NF and RO), respectively, and a remaining quantity of retentate, also denominated as concentrate (Figure 1). In the retentate the contaminants or dissolved and undissolved components respectively contained in the feed water, which have been rejected by the membrane, are accumulated. Usually these processes are operated in the so-called crossflow mode that allows control of the formation of deposits or
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layers on the membrane surface, and a reduction in scaling, fouling and biofouling in a certain range. Thereby the negative effects of the inevitable biofouling in long term operation can be influenced positively using innovative cleaning procedures, e.g. air bubbles /8/. Such air bubble enhanced membrane cleaning has already been investigated ~30 year ago in context of an RO based technique for the reduction of nitrate in drinking water using a process that nowadays is addressed as ZLD /9/. For UF applications it was introduced years later as “Air-Pulsing”. In crossflow mode the liquid to be treated is pumped over the membrane(s) and split into the two streams mentioned above; the operating pressure provided by the pump and achieved by adapting the cross-section of the pressure control valve to the necessary level. For operation in deadend mode (possible only for MF and UF) this pressure valve is completely closed at well specified intervals. However, in all cases, flushing, rinsing, backwash, chemical enhanced backwash and/or cleaning activities need to be adequately selected and optimised during long term operation. Thereby it should be recalled, that the most important feature for the successful operation of membrane systems is the possibility to realise a highly efficient periodic cleaning of the membranes. The membranes used in these processes can be considered as well defined barriers. This allows for a continuous and reproducible control with robust measuring instruments. At the same time the barrier function of the membranes guarantees that a high quality of filtrate or permeate is always achieved, which is nearly independent from concentration changes of contaminants in the feed /5/.
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W W W. M I C R O D Y N - N A D I R . C O M
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Highlights 2015
possible to achieve a permeate recovery of up to 95 % from highly concentrated landfill leachate /10/. Transmembrane pressure is up to 5,000 kPa (50 bar), and usually in the range 1,500 to 2,000 kPa. 3.4 Reverse osmosis (RO): RO osmosis is operated with the tightest membrane types available. The organic and inorganic molecules are separated from the feed solution by a solution diffusion process with a rejection rate in the range of up to 99%. Typically, RO membranes are used to separate aqueous salts and ions with less than 200 D, where a Dalton (Da) is numerically equivalent to the molecular weight in g/mol. Applications range from ultrapure water for semiconductor and pharmaceutical use to desalination of seawater for drinking water production, and the purification of industrial waste water, like landfill leachate. Operating pressure for RO is usually up to 7,000 kPa (70 bar), for low pressure RO up to 1,500 kPa and for high pressure RO up to 15,000 kPa (150 bar). 4. Operational cluster of membrane plants
Fig. 2: Operating cluster of a membrane plant for process stream specification, /11/
Plants equipped with membranes show a high operating stability, as the process is switch operated. Also start-up and shutdown need no special attention and are realized in few minutes. The modular design of the systems is the basis for high flexibility against changes of the volume of water to be treated and for a small foot-print for the plant itself. These features result from the properties of the membranes and from their combination with an appropriate module configuration and plant design, that have to be strictly adapted to the needs of each specific application /5/. The basis for selection are the capabilities of the processes. 3.1 Microfiltration (MF): the membrane filtration process with the least restrictive membrane type. Its applications include bacteria and pigment removal and removal of other particulates with particle sizes in the submicron range. Porous membranes are used with pore sizes in the range of about 0.1 to 1.0 μm (1 mm = 1000 μm); the most common for commercial membranes is an average pore size of 0.2 μm. Transmembrane pressure are from 10 to 500 kPa (0.1 to 5 bar), usually around 100 kPa. In special applications like an MBR, a vacuum in the range of, for example, 0.1 bar is applied. 3.2 Ultrafiltration (UF): these membranes can remove bacteria and viruses and can separate macromolecules like proteins, as well as colloidal silica and pyrogens. The typical molecular weight cut-off ranges from 5,000 to 200,000 g/mol. Usual pore size is in the range of 0.05 to 0.02 μm. Transmembrane pressures are from 20 to 1,000 kPa (0.2 to 10 bar), and usually in the range 100 to 300 kPa. Again, in special applications like membrane an MBR, vacuum in the range of up to 0.2 bar is applied. 3.3 Nanofiltration (NF): the membranes used in NF operate on a solution diffusion principle, diffusing monovalent ions through the membrane, rather than blocking material from passing through the membrane due to pore size like MF or UF. NF is useful for colour removal, sugar and dye removal or for removing THM (trihalomethane) pre-cursers and hardness or sulphate from a water supply. Together with operation possibilities at low pH values it is also ideally applied to the purification of acid mine drainage (AMD). In combination with seeding technology and hydrocyclone classification it is
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While approved and well known technical solutions are usually available for the design and the manufacture of a membrane based unit, pre-treatment of the water to be processed, as well as the handling of the retentate and the different waste water streams produced during operation of a membrane plant, have to be adapted case-by-case to the specific conditions at the construction site of a plant. These can differ over a wide range, since apart from the influences determining the raw water quality, the details related to infrastructure as well as logistics, are usually very different, and consequently, have to be considered during the design, construction and operation of each membrane plant /4/. The above considerations include the systems for dosing and handling of agents for pre-treatment, agents needed during operation, agents for the cleaning of membranes, and, in addition, the treatment and discharge of the diverse waste water streams generated during these specific activities. A flow sheet has been developed for the specification and evaluation of the correlated interdependencies (Figure 2) which summarizes the main operational cluster of a membrane plant, here specified by way of example for a seawater desalination plant with RO. The term ICT refers to “Information and Communication Technology”, which is the basis for an efficient SCADA (Supervisory Control and Data Acquisition) system including remote control and data handling /11/. 5. Selected example for future applications A large number of scientific institutions, industrial enterprises, water suppliers and wastewater boards have participated in the development and application of membrane technology, partially supported by governmental R&D funds. This has been the case in the past, is valid for the current situation, and can be foreseen for the future development. In Germany, for example, membrane technology today represents a proven alternative to the classical processes of municipal and industrial waste water treatment. This pays off in terms of ecology and economy because the usage of membrane technology means fewer costs for water supply and wastewater disposal as well as industrial production, and also results in significantly less environmental stress /1, 12/. Beside the many conventional solutions in water management based on membrane processes that have been realized in the past and are actually implemented, more innovative solutions can be expected. Two solutions, that are considered to become increasingly important in related niche applications, are:
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a) NF for the decentralised production of safe drinking water from contaminated surface waters b) UF and RO in combination with other treatment steps to achieve a ZLD process for the treatment of brackish water in arid and semi-arid areas. 5.1 NanoďŹ ltration for decentralised production of safe drinking water The supply of clean potable water is, in the meantime, acknowledged as a basic human right. In semi-arid areas, and countries in tropical as well as sub-tropical climate zones, there is, in principle, enough water available from surface waters. However, often, and due to a high burden of polluting matter from extremely health damaging components, this water cannot, or shall not, be used as drinking water /13/. Thereby, the kind of contamination of surface waters can be very different. The spectrum ranges from microorganisms including algae, bacteria, parasites as well as viruses, and alarming harmful organic micro pollutants, over contamination with chemicals and diverse poison residua from industry and agriculture up to particles and suspended solids of organic or inorganic origin. Related water treatment plants or units have to be adapted to the requirements existing on site. In the case of a centralised drinking water supply usually large-scale plants are installed. For the production of drinking water from seawater by RO, plants typically have a production capacity in the range of 50,000 to 100,000 m3 per day, with single cases up to 500,000 m3/day. Adjusted to the conditions required of a decentralised potable water supply, smaller or small units with a production of potable water of a few m3 per day down to few hundred litres per day are available, especially for disaster and emergency situations /14/.
Fig. 3: Compact NF unit for decentralised potable water supply, /15/
In connection with the decentralised supply of (only) drinking water, a compact unit designed for robust operating conditions is considered to be a very promising solution (Figure 3); this is a membrane module equipped with a NF membrane /15/. The peculiarity is the membrane element itself which is designed according to the open channel construction that is used very successfully worldwide and has also proven to be suitable for other applications in water treatment /16/. Based on the usual conditions concerning temperature and contamination of the raw water to be treated, at about 5 bar operating pressure a permeate production of up to 1,500 litres per day can
be achieved. With a power demand of about 250 W at these conditions, for the supply of the electrical energy necessary for the operation of the unit even the use of, for example, photovoltaics is possible. Such an approach allows the unit to be particularly used for the production of drinking water in emergency or disaster situations where the whole infrastructure has been destroyed, for instance, after a tsunami. Alternatively, it can be used for initiatives which aim to “help people to help themselves� in remote areas with no clean water resources, or even addressing “microbusiness in selling drinking water� in (for example) 10 liter bottles.
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Highlights 2015
5.2 Multistep Zero Liquid Discharge (ZLD) process Adapted to the special demand in arid and semi-arid areas with very limited access to water of good quality, but availability of wells with brackish water, a combination of UF and RO for the purification of usually complex and difficult to treat water has been developed and operated successfully /17/. For this concept, different processes with diverse driving forces for the treatment of the retentate are integrated which allows for a high recovery rate for the different main water streams as basis for a ZLD approach /18, 19/. 6. Future Development of Membrane Technology At present, important developments are taking place in industrial membrane applications focused on the integration of different membrane processes in thermal separation technology and chemical or biological transformation. Bearing these in mind, better product quality, highly compact production plants and processes with improved efficiency, reduced energy consumption and sustainable environmentally friendly operation can be achieved /5 - 7/. The future development of membrane technology will be influenced by factors such as /5/: - A reduction in treatment costs because of increasing operational experience and longer membrane life time. - The production of membranes adapted to specific applications. - Increased efforts to reduce biofouling on the membrane surface. - Increased efforts to develop and optimize processes, e. g. forward osmosis and membrane based processes focussed on ZLD. - Reliable process monitoring. - Reliable discharge control. - Standard plant concepts with easy adaptation to each individual situation on site. - Realisation of “plug & play” concepts. - Broader use of Build-Own-Operate or Build-Operate-Transfer agreements. - Integration of membrane technology in a total water management based on “graduated quality requirements”.
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All in all, described here by way of example for seawater desalination with RO, improved membrane technology related aspects will contribute to lower the specific energy demand, and thus to reduce the carbon footprint. This includes, for example, RO membranes with higher specific permeate flux and/or higher salt rejection, as well as pumps and energy recovery devices or energy saving systems with higher efficiency. However, of the same importance are improved and environmentally sound systems for seawater intake and partial pre-treatment, that avoid the negative impact of the operation of seawater RO desalination plants on the environment and reduce overall operating costs. So, for eample, sub-seabed drains allow operation that is independent from the growing number of natural disaster scenarios such as algae bloom, that are causing increasingly problems in this area of water treatment /20/. Similar strategies will also improve the integration of MF, UF and NF. 7. Conclusions The need for clean and affordable water for an increasing population on the one hand, escalating energy costs and water scarcity, overstressing and/or contamination of the natural resources in many areas of this world, on the other, are the most important driving forces for the increasing demand for improved technology for water and wastewater treatment or purification. In this regard, membrane technology has been used, is used and will be used successfully, and increasingly, for different purposes and for a wide range of applications within the area of treatment and purification of water and wastewater. Such an evolution is based on features including compactness of the plants, short construction time, clean, easy, economical and long term reliable operation with high rejection rates of components/contaminants. The high operational performance is achieved mainly due to the barrier function of the membranes, but is also based on the experience gained in the last decades and the improvements in material selection for the manufacture of the membranes and the plants, as well as the increasing optimisation of operational
aspects including capacity building and preventive maintenance. Literature: /1/ Pinnekamp, J., Friedrich, H.: Membrane Technology for Waste Water Treatment. FiW Verlag, Aachen, 2006 /2/ Peters, Th.: High advanced open channel membrane desalination. Desalination 134 (2001) 213-219 /3/ Peters, Th.: Modern Water and Waste Water Purification. Structural Change in Europe, Hagbarth Publications, Bollschweil, June 2000 /4/ Peters, Th.: Desalination of sea water and brackish water with reverse osmosis and disc tube module DT. Proceedings WSTA Forth Gulf Water Conference, Bahrain, 13-18/02/1999 /5/ Peters, Th.: Membrane processes for the treatment of water and wastewater. Proceedings, International Conference for Filtration and Separation Technology FILTECH 2011, Wiesbaden, Germany, 22-24 March 2011 /6/ Peters, Th., Kraume, M.: Entwicklungen und Perspektiven druckgetriebener Membranverfahren [developments and perspectives for pressure driven membrane processes]. Chemie Ingenieur Technik, 2005, 77, No. 5 /7/ Macedonio, F., Drioli, E.: Membrane engineering progresses in desalination and water reuse. Membrane Water Treatment, 2010, 1 (1), 75 /8/ Chesters, S., Armstrong, M.: Bubble power – enhancing a weapon for RO membrane cleaning. WATER & WASTEWATER INTERNATIONAL, June-July 2014 /9/ Peters, Th.: Reduzierung des Nitratgehaltes im Trinkwasser mit Umkehrosmose [Reduction of the nitrate content in drinking water with reverse osmosis]. WASSERWIRTSCHAFT, 10/83 /10/ Peters, Th.: Purification of industrial waste water by separation of sulphate using nanofiltration and seeding technology. Proceedings, ACHEMA 2012, Frankfurt a. M., Germany /11/ Peters, Th., Pintó, D.: Seawater Intake and Pretreatment Using Neodren Technology Based on SubSeabed Drains. Proceedings, IDA World Congress on Desalination and Water Reuse. Maspalomas, Gran Canaria, Spain, October 2007 /12/ Peters, Th., Günther, R., Vossenkaul, K.: Membrane bioreactors in wastewater treatment. Filtration + Separation, January/February 2000 /13/ Peters, Th.: Safe Drinking Water Abstraction from Surface Waters. Arab Water World, 10/2013 /14/ Al Naqib, B., Bundesanstalt Technisches Hilfswerk [German Federal Agency for Technical Relief], personal communication, Bonn, April 2014 /15/ ROCHEM Technical Services, company brochure, Hamburg, 2013 /16/ Peters, Th.: Membrane Technology for Water Treatment. Chem. Eng. Technol. 8/2010, 33, No. 8 /17/ El Maraghy, N., personal communication, Cairo and Oman, October 2014 /18/ Peters, Th.: Visit and inspection of the AGRO-ZLD system from INTERNATIONAL DESALINATION & WATER TREATMENT GROUP. Internal report, Neuss, October 2014 /19/ Peters, Th.: Improving the Performance of Seawater Desalination Technology by Using an Optimized Intake System and Recovering Valuable Components from the Brine. Presentation at BIT’s 2nd Annual World Congress of Ocean – 2013, Hangzhou, China, 23-25 September 2013, /20/ Peters, Th.: Improving seawater desalination with reverse osmosis. FILTRATION, 8 (4), 2008
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The chemistry makes the difference Membranes made from highly crosslinked polyamide for reverse osmosis J. Lipnizki* Since 2012 reverse osmosis (RO) membranes “Made in Germany” are available. The main reason the German company LANXESS entered this market is both the rapid market growth and its existing access to the market through the company’s ion exchange resins. It added the RO manufacturing operation to the existing production of monodisperse ion exchange resins in Bitterfeld near Berlin. LANXESS used tried-and-tested polyamide-based composite membrane tech-
Highly crosslinked composite membranes
* Dr. Jens Lipnizki LANXESS Deutschland GmbH Liquid Purification Technologies business unit Head of Technical Marketing Membranes Phone: +49 (0)221 8885-2013 Email: jens.lipnizki@lanxess.com Website: www.lpt.lanxess.de
TMC in n-decane
nology for this new operation. From the outset, however, the goal was to achieve highly automated production and apply the company’s many years of experience in polymerization processes. This led to the concept of highly crosslinked polyamide membranes. With several tens of thousands of membrane elements installed in just under three years on the market, the product launch can be considered a success.
A composite membrane comprises three layers – the non-woven fabric (polyester), a polysulfone support structure and the selective polyamide layer. The latter is formed through surface polymerization
of trimethylene chloride (TMC) and meta phenyl diamine (m-PDA). Ideally, the network structure should develop fully, but the chlorine-carboxyl group also reacts quickly with water to form a carboxyl group that produces a surface with a negative charge, as shown in figure 1. This secondary reaction creates a less crosslinked polymer structure and a negatively charged surface. While the lower crosslinked structure reduces a membrane’s durability, the negative charged surface leads to interactions with ions that affect membrane rejection. This interaction is depending on the ionic composition of the feed and lead to changing rejection if the feed changes. The data sheet values for RO membranes are comparable under the specified
m-PDA in water
Fig. 1: Polymerization to form a polyamide layer
Fig. 2: pH dependency of Boric acid
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Highlights 2015
Tab. 1: Costing assumptions
Tab. 3: Calculation for comparable RO process
Tab. 4: Parameters for testing the rejection of organic substances
Tab. 2: Calculations for highly crosslinked RO, HF
test conditions, but the differences are apparent in process flows with different cations and anions. Rejection in the case of inorganic compounds, whose charge can be influenced by the pH, is a particularly good indicator of the electrostatic interactions and thus the membrane’s surface charge. The results set out below highlight these effects. Influence on rejection Flat membranes were investigated in test cells and their flux and rejection recorded. The data were normalized to the same flux value to compare the rejection for different fluxes. The best-known example of rejection changing along with the pH is boric acid. The World Health Organization (WHO) recommends a boron concentration of < 2.4 mg/l in drinking water. This value can be achieved in a single RO filtration process. In some countries that also use drinking water for agricultural applications, however, the concentration must be < 0.4 mg/l, because crops such as citrus fruits are very sensitive to boron. An RO process with permeate stages is used in this case, with the pH being increased to 10 after the first stage to achieve the required boron rejection. This process, which is demonstrated in figure 2, makes use of the fact that boric acid has a predominantly negative charge at a pH of 9.5 or higher.
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This negative charge and the electrostatic interactions with the negatively charged surface increase the rejection of the boron, which is present in the form of boric acid as given in figure 3. Since the salt concentration is low at the second permeate stage, low-energy (LE) RO methods are often used here. The measurements clearly demonstrate the influence of the surface. While the highly crosslinked LE membrane achieves a rejection of 80 percent at pH values of less than 8, the membrane with less crosslinking only does so at pH values higher than 9. The rejection of the competitor LE membrane depends on the boric acid’s charge to a far greater extent than with a highly crosslinked membrane. A further example that is primarily seen in the treatment of boiler feed water is silica rejection. Si(OH)4 + OH– =HSiO3– + 2H2O Silica is soluble in concentrations of less than 75 mg/l. As a weak acid, it is not dissociated in the neutral pH range. As soon as the pH rises, however, the acid dissociates and the rejection increases due to the negative charge. This is clearly noticeable at pH values of 9 or higher. For the results shown in figure 4, a standard bracksih water membrane was used. The influence of the temperature was also investigated, see figure 5, which revealed that the higher degree of crosslinking also has a positive impact on rejection at differ-
ent temperatures. To explain this phenomenon, it is important to bear in mind that several effects have an impact on the rejection as the temperature increases. Higher temperatures cause the membrane to swell and lead to higher water fluxes due to the increase in water permeability. This higher flux results in a higher surface concentration of salts, called concentration polarization, which may reduce the rejection. The greater the degree of crosslinking, the less pronounced the swelling as the temperature increases, which means the membrane’s rejection remains more constant. In the competitor membrane, the rejection decreases because this cannot be compensated by the increased permeate flux. Influence on the process Especially when treating boiler feed water, consistently high silica rejection is important, as this reduces the capacity of the mixed-bed ion exchange unit. The influence on the mixed bed was calculated using LewaPlus®, LANXESS’s design software for reverse osmosis and ion exchange resins, and compared with various silica rejections. Provided the silica rejection measurements are correct, the following assumptions can be made for the calculation: The calculations showed that higher silica rejection resulted in significant savings. While the regeneration costs for the mixed F & S International Edition
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Fig. 3: Boron rejection; Test conditions: boron concentration 200 ppm + 2000 ppm NaCl, pressure 10.3 bar
bed are less than €10,000, even at temperatures of 35 °C, they are significantly higher with a lower rejection. Rejection of organic substances The rejection of organic substances is much harder to predict, because both the molecule’s volume and its polarity affect the diffusion behavior and thus the substance’s rejection. Since surface effects are less significant in uncharged substances, however, the higher degree of crosslinking is particularly apparent in substances with a lower molecular volume. In this test, the rejections of standard brackish water membranes (Lewabrane® HF and competitor) and low-pressure elements (Lewabrane® LE and competitor LE) were investigated. The test parameters used are listed (see Fig. 6). The tendency with organic substances is the same as with inorganic substances. While there are no differences for substances with higher rejections such as isopropyl alcohol (IPA) and glucose, the differences are significant for substances with lower rejections such as dimethylformamide (DMF) and uric acid. The difference is particularly pronounced in the case of standard brackish water membranes (Lewabrane® HF and competitor). Impact on flux and fouling No long-term effects on the permeate flux have been identified to date due to the higher degree of crosslink-
ing and the resultant denser structure of the polyamide layer. Although fluxes were lower shortly after the startup of a plant fitted with a new membrane, they returned to normal after a brief period. Similarly, it is not yet clear whether the higher degree of crosslinking or the lower surface charge affects the membrane’s fouling behavior, because there are too many different parameters that cause fouling. For example, most organic substances in surface water have a negative charge and are therefore expected to be repelled by a negatively charged surface. In the presence of calcium, however, these substances form a complex with the negatively charged membrane, which increases the adsorption at the surface. The complex fouling behavior is also one reason why there is still no blanket solution for significantly reducing fouling by modifying surfaces in membrane chemistry. Future developments One possible way of improving fouling behavior is to optimize the flux in the spiral-wound membrane module. Feed spacer developments have already helped reduce low-flux areas. This inhibits biogrowth and the depositing of particles without increasing pressure losses and thus energy consumption. LANXESS will be unveiling an element with a spacer of this kind in the near future. At present, extrusion tech-
Fig. 5: Silica rejection; Test conditions: silica concentration 75 ppm + 2000 ppm NaCl, pressure 15.5 bar
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Fig. 4: Silica rejection; Test conditions: silica concentration 75 ppm + 2000 ppm NaCl, pressure 15.5 bar
nology only makes it possible to produce a structure with a variable length or width during feed spacer production. However, this would be useful for a spiral-wound membrane module, because the flux in the pressure pipe is not uniform and there is a far greater fouling tendency in the intake area than in the outlet area. In the future, feed spacers could bring about improvements that take into account the different flux conditions in the spiral-wound membrane module in terms of both length and diameter. 3D printing technology opens up new opportunities for adapting the spacer accordingly. Summary Anyone who has tried out various RO manufacturers knows that, although the membrane chemistry and the design of the elements are similar, there are differences when it comes to permeate performance and rejection. Membrane crosslinking influences rejection and stability, which means it plays a key role. In addition to being important for industrial applications such as the production of ultrapure water for power plants, high rejection is also becoming ever more significant in drinking water production. Stricter limits and better analysis methods are increasing the pressure to improve water quality, especially in terms of organic compounds. As the example showed, however, higher water quality does not necessarily mean higher operating pressures.
Fig. 6: Rejection of organic substances; Test pressures: HF and competitor1 : 15.5 bar; LE and competitor 2 LE: 10.3 bar
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Highlights 2015
Use of membranes for process filtration and in industrial water management H. Lyko* Membrane technology is considered to be a growth market not only in the application sectors in which it has strong traditional representation such as water treatment or in dairy technology, but it is always finding new applications in the processing industry. Most recently at last year’s Achema the main focus of the declared topic issues were the recovery of basic chemicals and pharmaceuticals made from biogenic raw materials (bio-based world), which requires optimised, economically and ecologically justifiable separation processes. Membrane technology can make an important contribution here. Together with the growth in fermentation-based production processes there is also increased potential for membrane technology as part of the so-called downstream processing. Membranes can be used here for more precise separation and/or with less expenditure with regard to materials, operating resources and energy. Furthermore, the international congress always holds a forum for the presentation of innovations that stand on the threshold of commercialisation. Process developments using pilot plants The development of processes for concentrating, cleaning and desalination of products manufactured the aqueous phase is supported by the use of laboratory and pilot plants in which the membrane materials and various processes can be tested. Osmo Membrane Systems GmbH have produced different systems for developing new, integrated membrane-processes. Membrane materials can be screened during cross flow filtration in the flat channel test plant Memcell. Modularly designed pilot plants are used to evaluate the processes under virtual industrial conditions, in which the different membrane processes can be tested using process parameter variations and over a long period. The different pilot plants cover pressures ranging from 2 up to 120 bar. Two years ago, the portfolio of test equipment was extended by the pilot plant Klara in order to take into account the growing demands from customers: This pilot plant can work as batch plant or continuously operated plant. It is fully automated and uses integrated data storage and can also be monitored remotely. All current membrane products can be installed and tested at working pressures up to 60 bar. Ceramic membranes Ceramic membrane R&D is focused on making them more tight, i.e. to make them available for use with separation limits that are clearly below 1,000 Da. Applications using ceramic membranes previously existed in the nanofiltration sector and Inopor GmbH was the sole commercial provider. Other developments are geared to the production of *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
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membrane types in which higher packing densities can be realised, so that weight and installation space can be reduced for each installed membrane surface and this should overcome the classic disadvantage of ceramic membranes when compared to polymer membranes. As with polymer membranes, an increase in permeability without losing separation efficiency is always a development objective. Mann + Hummel have been involved for a long time in the production of ceramic hollow-fibre membranes, which combines the higher packing-density of a ceramic membrane with a higher flow rate and also produces sufficient stability. Dr Stefan Schütz reported about the production of hollow fibres using a phase-inversion process at the Achema congress. Their possible applications can be seen in the microfiltration and ultrafiltration of solutions with a high fouling potential (high concentrations of organic ingredients). The ceramic hollow-fibres are installed in different modules with overall filtering surfaces of approx. 0.05 m2, 0.3 m2, 2.4 m2 and 8 m2. The application results shown are from the oil / water separation sector for treating waste water from metal processing as well as the so-called produced water from producing crude oil and natural gas. A detailed description of the spinning processes and the results of the oil / water separation can be found in Ebrahimi et al. /1/. The effects of the infeed volume flow and the crossflow rate on the permeate flow and the cleaning efficiency are shown in this publication. The Achema presentation also showed that the permeate flow can be increased if silicon-carbide (SiC) is used as the active separation layer instead of aluminium oxide (Al2O3), as SiC is more hydrophilic and exhibits a lower fouling risk. Another application for the hollow-fibre module is the separation of blood in plasma and blood cells in
addition to oil / water separation. This type of separation is currently carried out using centrifuges. The use of membrane filters is very promising with regard to the possibility of recovering plasma at the same time and in close proximity to the taking of blood samples, i.e. for urgent analyses in medical emergencies. The requirements placed on the membrane module for this process are completely different to those for oil / water separation as one has to work with very small volumes here, which have a high content of cells that have to be separated (approx. 40 - 50 vol-%). These cells are treated as carefully as possible and filtered out under high hygienic requirements. The membrane filter element has been designed as a disposable filter. Another application with completely different hollow-fibre module dimensions is being tested in the current NAWADES (Nano-techno-logical Application in WAter DESalination) EU project. This involves the pre-treatment of sea water through ultrafiltration using an integrated photocatalytic anti-fouling function before entering a reverse osmosis unit. Atech innovations GmbH, of Gladbeck, is known for their ceramic tubular membranes and associated modules. At the congress, the CEO, Peter Bolduan, reported about a completely new type of flat ceramic membrane. The way of manufacturing the support structure, on which the separation-active membrane layer is coated afterwards, is similar to the paper production process. The fundamental principle for the production of a flat material that can be produced as rolls and can be processed into a thin ceramic layer after the sintering process was developed by the Paper Technology Foundation (PTS) in Munich and technically implemented by atech. During the manufacture of paper the suspension that is fed into the paper machine consists of cellulose and
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inorganic filler materials (CaCO3, etc., in order to lighten the product) and organic binders. The proportion of inorganic filling material, which is approx. 20% - 30% for writing paper, is increased to approx. 80% for the ceramic paper and a material (aluminium oxide) capable of being sintered is used instead of kaolin. This is how “pre-ceramic paper” is produced with a thickness of approx. 1 mm, a surface weight of more than 1,000 g/m2 that can be rolled or cut and laminated if a special ceramic adhesive is used. Flat elements with an internal drainage structure can be produced from several layers of ceramic paper placed on top of each other (see Fig. 1). The material shrinks by approx. 15% as a result of the sintering carried out at around 1,300° to 1,600°C and it is then porous and can be provided with an active outer separation layer for microfiltration or ultrafiltration in conventional coating and baking processes. This type of production of flat ceramic membranes with an outside to inside filtration direction opens up new options for the production of submerged modules. Compared to extrusion, which is used during the production of conventional ceramic membranes, this process allows greater freedom with regard to selecting the surface and the structuring of the drainage layer. The membrane elements shown in Fig. 1 were manufactured from ceramic paper in two different ways: one with a continuous outer layer and four internal rod-geometry structured layers and another with two outer and two inner layers (see Fig. 2). The pure water permeability, both with and without fitted active separation layers for microfiltration and ultrafiltration was measured for both elements and compared to the measured values for a multi-channel
IFAT MUNICH CH
Fig. 1: Different membrane elements made from ceramic paper (141: each with one outer layer, 4 inner layers; 222: each with 2 layers on each outer side and 2 internal layers, image: atech innovations GmbH)
222 141
Fig. 2: Production of new types of flat ceramic membranes from different layers of ceramic paper (image: atech innovations GmbH)
tubular membrane (19/3,3). Due to its larger pores (6 - 8 μm), the pure substructure of the tubular membrane exhibited a higher pure water permeability as compared to the elements made from ceramic paper with approx. 2 μm pore widths. But measurements with complete membranes, including the respective active separation
CUT Membrane M Technology
Hall A2 / Booth 519 CUT offers its customers: • know-how in different industries: ustries: e.g. chemical, food & beverage, environmental, process and d waste water treatment • high level of expertise in the he use and manufacture of membranes • support in process solutions ns • tailor-made membrane and d module solutions • worldwide availability Please get in touch with us! s! CUT Membrane Technology GmbH H Part of the Bürkert Group Feldheider Str. 42, D-40699 Erkrath h Phone: +49 2104 17632-0 0 E-Mail: filtration@burkert.com m
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layers for microfiltration and ultrafiltration, showed that the flat elements have a higher water flow. The structure 141 despite having the same overall thickness revealed higher flux rates than element 222. The better flow properties of the flat elements can be traced back to the transport paths, which are shorter overall.
The application specialists
Highlights 2015
Fig. 3: Cadence inline concentrator for single pass tangential flow filtration available from Pall in three sizes with membrane surfaces of 0.065, 0.13 and 0,7 m2 (Photo: Pall Corp.)
nanofiltration at pressures of up to 40 bar and a maximum temperature of 90°C. Gas filtration with pressures ranging from 4 bar up to 100 bar is possible with this module shape. The optimised configuration of the separate compartments (the number of membrane pockets per compartment wanes in the through-flow direction) will take into account the withdrawal of the permeate volume in the through-flows in the module and the feed flow to the individual membranes will be homogenised. Specific chemical reactions are only favoured in solvent-based chemical production processes if highly diluted reagents are present. The ring closing of peptides is a typical example of this. If the concentration of the initiators is increased then the likeliness of the polymerisation of the monomers will also increase and the output of the required cyclic molecules will drop. In turn the compulsion to use high dilution means that it is necessary to have larger reaction volumes and greater quantities of solvent. The Volume Intensified Dilution (VID) process was developed by the Flemish Research Institute VITO in order to be able to implement these processes in compact units and use less quantities of solvent. The integration of membrane filtration in this type of reaction process, which continually removes product molecules from the reaction volume and new reagents can be added under control afterwards, means that solvent savings of up to 85% and a corresponding proportion of the reactor volume can be made. Downstream processing in the bio pharmaceutical industry
Fig. 4: Function principle of the FiT (Filter in Tank) system from GEA for treating fermentation broths (image: GEA Group Aktiengesellschaft) Supply from the fermentation filtrate
Organophilic membrane filtration Organophilic membrane filtration is a relatively new sector in membrane technology, which is gaining importance in the processing industry. Borsig provides membrane technology for product recovery, gas cleaning and conditioning in the chemical and petro-chemical industries and their subsidiary GMT Membrantechnik is very active in the organophilic membrane filtration of liquids sector. Not so long ago, the recovery of rhodium catalysts from the production of polypropylene oxide was carried out in industrial plants using
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organophile nanofiltration. Spiral wound or pocket modules can be used for liquid filtration, depending on the solvent being used. In due course the company produced and sold pocket modules that were developed by GKSS (known today as the Helmholtz Centre in Geesthacht). As opposed to the spiral wound module, this has the advantage that the membrane pockets that were used were welded and not bonded. Therefore the module is also suitable for use with solvents, for which no resistant adhesive is available. The pocket module is provided for organophile
Many disposable components are used in the preparation of solutions during research, in clinical applications as well as the industrial production of bio pharmaceutical products such as medicines or vaccines, as they are in membrane filtration. Pall provides Cadence TFF (for Tangential Flow Filtration) and Cadence SPTFF (Single Pass Tangential Flow Filtration) series of ready-to-use, gamma irradiated, disposable module products, which can virtually halve the number of processing stages and the associated plant technology when compared to reusable modules, as the pre-treatment of the membranes before feeding the solution to be treated is considerably easier and post-treatment (cleaning and sterilisation) is no longer needed. The TFF module is available in five different membrane surface sizes ranging from 93 cm2 up to 2.5m2 and they are fitted with polyether sulphone membranes. They can be integrated in sys-
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High temperature oxygen separation High temperature processes such as those used in the glass, ceramics or steel industries can be operated on an energy-efficient basis if the combustion air is enriched with oxygen. Furthermore, combustion in an oxygen / exhaust gas mixture (oxy-fuel process) opens up an easy way for CO2 separation in fossil-fuel-fired power stations, as the exhaust gas that forms in addition to the CO2 mainly contains water vapour, which can be separated through condensation. A demonstrator for O2 separation using mixed conducting BSCF membranes (Ba0.5 Sr0.5Fe0.2O3-∂) (see Figs. 5 and 6) was built and tested at the Fraunhofer-Institute for Ceramic Technologies and Systems (IKTS) in Hermsdorf, so that the technical feasibility of high temperature air separation could be proven. The system generates approx. 5.4 L of pure oxygen at 850°C (>99.9% volume) per minute (this corresponds to 250 Nl/h). The energy consumption of this membrane process, in which the permeate is removed by a vacuum, can drop, depending on how the process is controlled, to 40% to 60% of the energy requirement for cryogenic air separation. The process can be used in particular in small portable plants, as it replaces the need for potentially dangerous pressurised oxygen tanks. A more detailed description of the functional principles of
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GEA Separation Solutions & Systems Our action is consistent with a simple model: The machine in harmony with man and nature. Maximum yields and minimum consumption of utilities ensure added value for the customer and sustainabilty for the environment. The know-how gained in the development of over 3000 process engineering applications makes GEA a renowned partner for small to large-scale centrifuge installations. We provide value-adding solutions for the dairy and food industry, chemistry, pharmaceuticals, biotechnology, power, shipping and environmental technology.
GEA-GE-01-002
tems that have been specifically designed as disposable systems. The SPTTF modules, which only permit a solution to pass though the module or a module cascade once, are hold-up elements fitted with a retentate flow limiter. They are used for inline concentration of product flows. Only one element is needed to provide the permeation driving force (pump or other pressure source) and this can be implemented using two possible membrane separation limits of 10 or 30 kDa and concentration factors of approx. 2 to 4. Dispensing with the recycling of the working volumes will reduce possible dead volumes as well as improve product recovery when compared to conventional tangential flow filtration. The product will also be better preserved as a result of spending less time in the filter (flow path design) and the risk of it being damaged by shearing force or agglomeration will be reduced. The membrane material that is used in single-pass modules is regenerated cellulose. Centrifuges are frequently used to separate the cells from fermentation broths and, depending on whether the end product lies inside or outside the cells, several different processing stages are needed for recovering and purifying the product. The Filter-inTank (FiT) system presented by Knud Schöneberg at the Achema congress can considerably simplify cell harvesting. In a process developed by GEA together with Novo Nordisk, a pharmaceutical company from Denmark, the filtration and diafiltration uses rotating disc membranes fitted inside the tanks, in which the broth can be collected after fermentation (see Fig. 4). The rotation of the membranes produces the shearing effect needed to prevent the formation of a covering layer on the membrane surface, whilst the driving force needed for the filtration is already provided by the hydrostatic pressure in the tank. A pump is not needed as the filtration pressure will be generated by the column of liquid or an impressed gas pressure. The membranes are monolithic, circular discs with an active separation layer made from aluminium oxide or zirconium oxide and a cut-off of 0.2 to 1.4 μm. In the described application tests that used a fermentation broth from insulin production and media from E.coli based processes taken from different preparation stages, stable membrane flows as well as product transmission rates at high cell concentrations and low trans-membrane pressure differences were measured. Overall, considerable savings were determined using the FiT system with regard to the number of processing stages, the water, energy and space requirements with a simultaneous increase in the output, product quality and hygiene.
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Fig. 5: Segment with mixed conductance BSCF membranes manufactured as capillaries (Photo: Fraunhofer IKTS)
these membranes and the determining of the system’s energy requirements can be found in /2/. Process and waste water treatment – ZLD The shutting down of water circuits in industry is one of the core application areas for membrane technology, as their still exist water consuming processes or industrial sectors, whose potential for saving considerable quantities of fresh water and drainage costs through shutting down the circuits has not been fully exhausted. New applications are often implemented, as preparation through strict initiation limits is suddenly necessary and/or made economical through more efficient processes. Alfa Laval have been producing a PVDF membrane with a polyethylene support coating for a long time, which is hydrophilated by a cellulose layer. This so-called ETNA membrane is somewhat thicker than other polymer membranes and has a slightly uneven surface, which looks like a volcanic rock when enlarged under a microscope. Ultrafiltration membranes are available with two separation limits of 1,000 and 10,000 Da and remain very robust during processing and with very
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frequent cleaning cycles. This type of membrane recently experienced a renaissance for oil / water separation, even with regard to the quantities of produced water from natural gas and crude oil supplies that have to be treated, which is globally estimated to be a quantity of around 8.4 billion m3/a. Dr Frank Lipnizki, from Alfa Laval, presented an example of an application for preparing oily waste water on ships and offshore platforms at the Achema congress. The permeate from this preparation (membrane MWCO: 10,000 Da) only contains 1 - 2 ppm oil. Another example of industrial water preparation for reuse as process water, this time through reverse osmosis, was the purification of decanter water after PVC production. With an annual production of approx. 35 million t and a consumption of 2 to 2.5 m3 of demineralised water per tonne of PVC, the normal process for treating process water up to now has been the biological treatment of approx. 75% to 80% of a the clear phase delivered by the decanter, which is used to dewater the solid product. The remaining 20% to 25% of the removed water can be reused as rinsing water without any biological treatment. If a RO 98pHt reverse osmosis module is used, the treated decanter water is not only freed from remaining PVC particles but it is also demineralised. The permeate can be used again as process water. This method enables approx. 60% of the fresh water requirement to be saved.
The term Zero Liquid Discharge (ZLD, i.e. complete waste water free production) played a very important role during the presentation of industrial water preparation systems and membrane technology was not always the most important or most innovative part of the technology that was used. Hager + Elsässer as well as Membranfiltrationstechnik, from Köln, both now united under the Aquarion Group roof, presented innovative reverse osmosis technology as the centrepiece of their ZLD technology. The concentration of the dissolved matter was based on a three-stage plant. After the first two membrane separation stages, in which pressures up to 80 bar are used, a concentrate of approx. 20% of the total amount of waste water still remains, which is fed into the third stage. An especially developed circular disc module that can realise a pressure up to 200-bar is used in this stage, which provides the driving force for further concentration. When compared to other plants the result of the high concentration through reverse osmosis is a reduced evaporation stage, whereby correspondingly less cooling energy is needed for the condensation process. Literature: /1/ Ebrahimi, M.; Kerker, S.; Daume, S.; Ehlen, F.; Unger, I.; Schütz, S.; Czermak, P.: Innovative keramische Hohlfasermembran zur Öl/Wasser-Trennung bei „Produced Water“ Anwendungen; F&S Filtrieren und Separieren Nr. 28 (2014) Nr. 4, S. 196 - 205 /2/ Kriegel, R.: Einsatz keramischer BSCF-Membranen in einem transportablen Sauerstoff-Erzeuger. In: Deutsche Keramische Gesellschaft, editor. Handbuch Technische Keramische Werkstoffe [Loseblattwerk]: HvB-Verlag Ellerau, Ellerau, Deutschland, 2010; Kapitel 8.10.1.1
Fig. 6: Transportable oxygen generator (Photo: Fraunhofer IKTS)
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The biggest drinking water production plant in the USA The south-west of the USA has now suffered from a major drought for several years. They have been looking for solutions to prevent a water emergency for many years. Cutbacks are one solution. On the 1st April of 2015 the Governor, Jerry Brown, ordered that the State’s cities and municipalities must reduce their water consumption by 25%. The cuts were so severe that agricultural areas had to be abandoned. Technical measures, such as the construction of desalination plants were also considered as a solution to providing the ever-increasing population with drinking water. The situation in San Diego, the southernmost city in California with nearly 1.4 million residents, is particularly dramatic. The city was nearly dry. The resident’s drinking water supply comes from the Colorado river and they are also dependent on supplies from northern California. Water is also in short supply there, so the decision was made to produce drinking water from the water in the Pacific ocean. One of the biggest reverse osmosis plants ever built is being constructed not far from the city in Carlsbad in San Diego County and it covers an area of four hectares, which is located alongside the existing Encina power station. It should produce about 200,000 m3 of drinking water per day and protect the water supply. This quantity is sufficient for supplying approx. 300,000 people.
The 922 million dollar project is the first major desalination plant on the west coast of the USA that has been financed privately and developed by the Poseidon Resources Corporation. The project includes a pump station, a product water reservoir and a ten-mile long pipeline in addition to the reverse osmosis plant. However, the construction of the plant has proved controversial. For example, environmental activists have criticised the high electricity consumption and the related carbon dioxide emissions. They also fear that the Pacific coastal areas will become “oversalted” as the salt extracted from the water will be returned to the sea as brine. They are also worried about fish stocks in the surrounding area where the brine will be returned to the ocean. 14 suits were filed against the plant, but none of them were successful. Project development started in 2006. All of the approvals for constructing the plant were issued by the responsible authorities in 2009 and the initial construction phase started in November 2009. It was expected to come into operation early in 2016. The Carlsbad desalination project will be developed as a public / private partnership between local utility companies and municipalities in San Diego County and Poseidon Resources. 30-year contracts together with extension options were concluded. They include fixed prices for the delivery of water and also control sup-
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plies from nine public water facilities in San Diego. The plant has been constructed as part of an IDE Technologies joint venture and the company will also operate it for a period of 30 years. The membranes and membrane modules are supplied by Dow Water & Process Solutions. Specifications A partial flow from the cooling water used in the Encina power station will be used as the untreated water supply for treatment. The power station uses approx. 380,000 m3 of sea water for cooling every day. The drinking water yield will amount to approx. 50%, so that a cubic metre of drinking water will result in approx. one
cubic metre of concentrate. The concentrate is twice as salty as sea water (67,000 ppm). It will be released into the power station’s cooling water discharge channel and mixed with the cooling water from the power station before it is released into the Pacific ocean. A granular media filter (fixed bed filter) and membranes are used for pre-treating the water. Chemically enhanced backwashing of the membranes will take place every day as part of the pre-treatment process. The diameter of the pipes used for the untreated water is 48 inches and 24 inch pipes are used for discharging the brine. Approx. 80% of the pipes used in the plant are made from high density polyethylene (HDPE) or from plastic reinforced with
glass fibre. The reverse osmosis plant will consist of twelve operative module blocks with another block held in reserve. Each of the module blocks is supplied by a high-pressure pump. The plant will be operated fully automatically. It has been designed as an energy recovery system based on pressure exchangers. The pump motors have frequency converters fitted to them. The reverse osmosis plant’s membranes are scheduled to be cleaned every six months. The water from the reverse osmosis plant will be conditioned and chemically disinfected and pumped into the long-distance pipeline system and distributed from there. See: www.carlsbaddesal.com as well
Innovative feed spacer technology leads to enhanced reverse osmosis element performance J. Kidwell*, St. Tielen*, B. Paesen*, J. Ogier**, St. Lehmann**, C. Schellenberg** The world is running out of water. By 2025 nearly 1 billion people will lack access to fresh, drinkable water. Reverse Osmosis (RO) water treatment will play a major role in alleviating water scarcity but with this technique, energy costs are involved as well. Any improvement of the membrane or element technology can increase the efficiency of the process. In a co-research project, Conwed Plastics and LANXESS’ Liquid Purification Technologies business unit have proven that innovations in feed spacer technology leads toward enhanced RO element performance. Reverse osmosis, the process Reverse osmosis is a water purification technology to remove mainly monovalent ions (e.g. NaCl) that utilizes a semipermeable membrane. An applied pressure is used to overcome natural osmotic pressure. Such RO membranes are being offered as spiral wound elements for a huge variety of desalination applications. Frequently
known as scrim, mesh, net, or netting, feed spacers act as one of the layers of spiral wound RO elements and provide vital separation between the membranes to achieve superior filter performance. A spiral wound element refers to a membrane configuration which is comprised of “flat sheet membrane - permeate channel spacer - flat sheet membrane - feed channel spacer” combinations rolled up
around a permeate collection tube. As shown on Figure 1, the membrane element structure contains the feed spacer that separates the surfaces of adjacent membrane envelopes. The feed spacer, configured as a net, keeps the feed channel open, allowing feed water to flow inside the feed channels, along the membrane element; Figure 2 shows an actual RO spiral wound element.
Contact *Conwed Plastics Marcel Habetslaan 20 3600 Genk, Belgium Phone +32 (0)89 84 83 10 sales@conwedplastics.com www.conwedplastics.com Contact person: Bert Paesen, Business Development Manager **LANXESS Deutschland GmbH BU Liquid Purification Technologies IAB Ionenaustauscher GmbH Bitterfeld Postfach 1152 06731 Bitterfeld-Wolfen, Germany Phone: +49 (0)3493 358500 carsten.schellenberg@lanxess.com www.lpt.lanxess.com Contact person: Dr Carsten Schellenberg R&D Membranes
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Fig. 1: Construction of a spiral wound RO module in detail.
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Fig. 2: Typical 8 inch RO modules as being used in many water treatment applications.
RO challenges Three primary challenges are identified in the RO water treatment process. They are studied, analyzed and acknowledged as a concern for membrane manufacturers, winders and plant operators: - Pressure drop - Membrane damage - Biofouling and scaling These challenges have driven combined technology efforts of Conwed Plastics and LANXESS to develop more efficient RO products. Effect of feed spacer on pressure drop The feed spacer is an essential component of spiral wound membrane elements. Feed spacers are manufactured from polymeric materials and optimized to maintain stable performance of membrane elements in a wide range of feed water composition and process parameters. The configurations of feed channel and feed spacer net are shown schematically on Figure 3. The feed channel, shown here in unwrapped configuration, forms a rectangular opening of typically 0.7 – 0.9 mm in height. Due to the presence of spacer or netting strands in the feed channel, the actual cross section area open to the feed flow is smaller than the geometric cross section.
Fig. 3: Schematic of a standard (equal strands) feed spacer / feed channel.
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equal strands
alternating strands design (ASD)
bottleneck strands
netting pressure drop (bar)
Fig. 4: Typical and new feed spacer geometries selected for CFD calculations and flow cell tests.
volume fraction (with v < 0.01 m/s) Fig. 5: Overview of main results collected from work package CFD calculations.
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The length of the feed channel is about 1 m. The feed spacer net, filling the feed channel, has filaments or strands positioned bi-planarly. The bi-planar characteristic causes the feed stream to change flow direction as it flows above and below the subsequent filaments. The objective of the feed spacer, in addition to keeping the feed channel open, is to promote turbulence of the feed stream. The need for turbulence in the feed stream is related to the nature of the RO desalination process. The feed water and dissolved salts flow parallel to the membrane surface, with a fraction of the feed water passing through the membrane as permeate, leaving the dissolved ions in the retained fraction of the feed water stream. This process generates excess concentration of dissolved ions at the membrane surface, a phenomena known as concentration polarization. The feed spacer induced turbulence reduces extend of concentrate polarization, thus improving performance of the RO membranes. However, the feed spacer induced turbulence increases friction in the feed channel, which is translated into pressure drop of the feed stream between element feed and exit points. The current configurations of feed spacers, used for construction of RO spiral wound elements, have been developed based on practical experimentation and fundamental studies. The objective was to create condition of “mixing flow” even at the low flow velocities existing in the feed channels of the spiral wound membrane elements. Subsequent R&D work demonstrated the importance of feed spacer filaments’ geometry, angular configuration as well as alignment of feed spacer with the direction of feed flow. Based on experimental results and hydraulic modelling, the configuration of feed spacer for RO applications evolved into a bi-planar net with square or rhomboid openings. Rhomboid net configurations are commonly known as diamond netting. The spacer is positioned in the feed channel with net filaments at an angle of about 45° to the direction of the feed flow (shown on Figure 3). This configuration results in acceptable trade-off of sufficient turbulence and mixing of the feed stream without excessive pressure drop. This orientation of the feed spacer net is applied in a vast majority of RO and NF (nanofiltration) membrane elements of spiral configuration. The above orientation of feed spacers, relative to direction of the feed stream, and the presence of high density membrane support nodes, result in significantly blockage of the flow path in the feed channel. Therefore, very clean feed water with low concentration of suspended matter is required for a stable operation of the membrane units. If the feed channel is in clean condition, without particles that could block feed water flow, the pressure drop across a single element is about 0.1 – 0.2 bar. In RO systems, membrane elements operate while enclosed in a pressure vessel. A single pressure vessel usually contains 6 – 8 membrane elements, operating in series. Therefore, the combined pressure drop along a pressure vessel is in the range of 0.6 – 1.5 bar. Seawater RO systems are configured as single stage units. RO systems for brackish applications are mainly configured as two or even three stage units. Consequently, the combined pressure drop in brackish RO systems will be higher, frequently in the range of 1.5 – 3 bar. The required increase of RO system feed pressure, due to feed-concentrate pressure drop, is approximately equal to half of the pressure drop value. Therefore, the configuration of the feed spacer has to provide sufficient turbulence and mixing in the area adjacent to the membrane surface without significant increase of pressure drop in the feed channel. Friction losses in the membrane element feed channels contribute to overall energy usage of the RO unit. Based on the common efficiencies of feed pumps and motors, each bar of pressure drop is equivalent to additional energy usage of about 0.025 kwh/m3 of product water produced. During system operation some feed born particles will deposit in the feed channels of the RO elements, contributing to increase of the pressure drop. The elements can be F & S International Edition
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pressure drop (bar)
Fig. 6: Overview of feed spacer samples used for test program using membrane fouling simulator (MFS); flow cell experiments.
feed spacer code Fig. 7: Basic results on pressure drop for the feed spacer samples evaluated.
damaged by operation at very high pressure drop. Still, some systems will operate for long periods of time (between membrane elements cleanings) with pressure drop 50% to 100% higher than the initial pressure drop on system start-up. The rate of pressure drop increase mainly depends on quality of the feed water. However, feed spacers of lower initial feed pressure show lower rate of pressure drop increase. This results in smaller power usage of the RO plant over the length of operation.
Co-research project leads to optimized feed spacer geometry called alternating strand design (ASD) Based on the above knowledge, a co-research project was initiated to develop a novel feed spacer technology addressing the outlined challenges. In a first step, basic feed spacer geometries were evaluated, using 3D printed samples. Next, detailed CFD (computational fluid dynamics) calculations towards decreasing pressure drop and minimized low flow areas
were made. Low velocity areas, seen as the starting point for e.g. biofouling, were calculated, making use of feed spacers with equal strands, alternating strands and bottleneck type strands (Figure 4). The basic results of these calculations are summarized in Figure 5 showing the system alternating strand type feed spacer well balanced with regard to pressure drop while minimizing areas of low feed water velocity. To prove the performance of alternating strand design feed spacers, a number of different feed spacer types, now produced using large scale netting production technology, were tested in a flow cell measurement program. The pressure drop performance got evaluated. The feed spacer samples were installed in a special flow cell* and tested using different conditions for e.g. feed flow, time or fouling conditions. A selection of tested feed spacer materials is shown in Figure 6 along with corresponding pressure drop results in Figure 7 at a given flow rate of 20 l/h. Similar to indications received by CFD calculations this research confirm enhanced performance of feed spacer material based on new alternating strand design (ASD) technology. Presented results do indicate target objective of the ASD feed spacer can be achieved. RO elements constructed with such an innovative spacer geometry achieve a low pressure drop. This leads to savings in power consumption as a consequence. In addition, new ASD type spacer show a fine tuned flow pattern resulting in reduced biofouling tendency. This is seen as an improvement towards durability of such RO membrane elements. * (MFS membrane fouling simulator [The potential of standard and modified feed spacers for biofouling control, Araújo, P.; Kruithof, J.; Loosdrecht, M. V. & Vrouwenvelder, J Journal of Membrane Science , 2012, 403 - 404, 58 – 70])
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Zero liquid discharge – a futuristic model for water treatment processes? S. Ripperger* 1. Introduction The term “Zero Liquid Discharge (ZLD)” has cropped up more and more frequently in conjunction with water and waste water treatment processes over the last few years. This should be understood to mean processes without liquid waste or waste water. Initiatives and measures to bring this idea closer to fruition or to implementation have been ongoing in various industries for many years. Some ZLD plants are already in use. The motivation to develop and construct such plants is complex and not standardised. The following objectives can be realised by a ZLD plant: - cost savings resulting from the recycling of water and ingredients and energy, - cost savings from the disposal of the contamination loads removed from the waste water (e.g. reduction in the waste water charges), - load relief on existing waste water plants, - preservation of the water supply and/or the water quality, - realisation of environmental benefits. Measures for reducing the waste water flows have been introduced and implemented in many companies over the last thirty years or even longer. These developments were encouraged in Germany, especially through the Waste Water Charges Act introduced on the 13th September 1976. A waste water charge has been levied since 1981, which has been gradually increased over several years. This has clearly reduced the water consumption and the amount of waste water in many industries. In the majority of cases this was linked to cost savings in the form of reduced fresh water and waste water charges. It is also possible that this was linked to water treatment and the procurement of internal water circuits. The amount of waste water could then be clearly reduced, but the amount of contamination loads from the waste water that has to be disposed of clearly increased. The water recycling spectrum in many companies ranged from 80% to 90%. However, the complete elimination of waste water flows does not exist, except for a few exceptions. * Prof. Dr.-Ing. Siegfried Ripperger IES GmbH Luxstr. 1 67655 Kaiserslautern, Germany Email: er@ie-services.eu
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The reduced waste water flow is disposed of in centralised waste water treatment plants or it undergoes further treatment in separate plants, so that the contamination level is reduced even further. Not all of the water-borne impurities can be removed or eliminated, which means that they have to be drained with the reduced waste water flow. The remaining flow normally includes salts, non-vol-
atile compounds and colloidal substances, which are measured as “Total Dissolved Solids (TDS)”. A large proportion is made up of salts, which form as the result of the neutralisation of acids or basic waste water, etc.. pH value shifts can also be made during waste water treatment, so that impurities can be reduced and separated mechanically. For example, waste water containing compounds that include met-
Cleaned exhaust air Contaminated additive
Additives
Exhaust air Raw material Product Production process
Auxiliary and operating substance Air Water
Waste water A
Additives
Unused operating substance
B
Waste water treatment
Cleaned waste water
Waste
Fig. 1: Diagram of a production line with centralised waste water cleaning (additive process for environmental protection)
Exhaust air Raw material Product Auxiliary and operating substance Air Water
Production process
Waste water A
Unused operating substance
B
Water for further use
Resource Fig. 2: Environmental protection provided by a membrane process integrated into the process
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als that have been detached by the metal and surface technologies can be treated using a pH value shift. The metallic compounds become hydroxide, hydrated oxides or metal salts, which can be separated through sedimentation or filtration and disposed of as sludge. The residual aqueous liquid will be neutralised. They can either be removed or undergo further treatment, depending on the contaminants. Treatment of a waste water flow to produce a solid residue is problematic due to the contaminants, the large variety of ingredients and the necessary complete separation of the liquid. A project was implemented back in the 1990s in which a waste water flow was treated until no more waste water could be drained from it. The following bywords are used to describe the project: - waste water-free grinding, - waste water-free breweries, - waste water-free laundries, - waste water-free power stations - waste water-free landfill seepage water treatment. In order to realise these objectives, the last stage was normally linked to evaporation or dilution. The limited availability of water in many regions throughout the world has resulted
in the increasing requirement for ZLD plants to exist in conjunction with the realisation of new production plants. The tendency to lower the limit values for the removal of the salt loads also exists in many parts of the world. The reason for this latest known development is the increasing use of reverse osmosis for the recovery of drinking water. 40% to 50% of the supply fed into coastal plants is concentrated brine. The effect on the ecological system in coastal areas linked to recovery from this saline concentrate is still being discussed controversially. This brine extraction process is already linked to problems in regions with a high density of reverse osmosis plants. A negative effect from the technical plants on other seawater users in their vicinity can often be proven. Problems linked to the release of the concentrate from desalination plants situated further inland are many times greater. The concentrate is waste water, whose release is normally strongly controlled and is burdened by charges whenever necessary. Quite often subsequent biological waste water treatment plants and other public waters need to be relieved of these salt loads. The “Zero Liquid Discharge (ZLD)”concept has been developed in this conjunction for waste water-free water or
waste water treatment. In certain cases, the objective has also been to recover other ingredients (e.g. sodium chloride, sodium sulphate and phosphor) from the waste water. The concentration of seawater resulting from the drinking water production using reverse osmosis can also be the first step in recovering the inorganic materials that have been detached. To be able to realise this, the frequently available organic ingredients must be removed from the water and this also requires specific treatment stages. 2. Possible ZLD process concepts 2.1 Processing stage requirements An important prerequisite for economical water recycling is that different waste water flows that occur in a company are not mixed together if possible and are reprocessed in a centralised cleaning stage through the intake of other materials. Additives for the separation or extraction of contaminants are adsorption agents, bacteria cultures for biological cleansing, precipitants and flocculants or filtering aids for precoat filtration. The mixing of the additional material feeds, as shown in Fig. 1, is still common in conjunction with a centralised waste water treatment
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Highlights 2015
Distillate
Heat exchanger Not wetted microporous membrane
Solution “L”
Concentrate
Feed
Distillate “D” Heat exchanger
Membrane module
Heat exchanger
Fig. 3: TMD diagram with direct contact between the membrane and the solution and distillate
plants. However, this prevents economical preparation of the residue and its further use and therefore increases the amount of residue that has to be disposed of. It is more economical to treat small waste water flows that occur on site, i.e. before they are mixed with other material flows (Fig. 2). Quite often certain ingredients can be recycled for other uses. The following requirements apply to the treatment processes: - selective material separation without additives, - a physical separation principle that does not change the components that have to be separated, - a continuous and automatic operating mode, - economical operation even in small plants, - easy integration into the production process.
Fig. 4: Flow diagram of a TMD plant with heat recovery
2.2 Use of membrane processes A material separation process using membranes always fulfils the requirement profile listed above. They are frequently used for the process-integrated treatment of waste water flows. The membrane process is mainly used as a dynamic process with overflowed membranes due to the required continuous operating mode. A single or multi-stage process is needed, depending on the requirements, for preparing the recycled water. Microfiltration and ultrafiltration Particulate and macro-molecular materials are separated and concentrated using microfiltration and ultrafiltration. The resulting permeate is largely free of micro-organisms, so that it is ready to be reused in a process or for it can be fed out for further treatment for use in nanofiltration or reverse osmosis.
Fig. 5: Test results for a TMD with microporous polypropylene tubular membranes for concentrating a saline solution /3/
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Reverse osmosis Reverse osmosis is used to concentrate solved ingredients in an aqueous solution, e.g. salts. The osmotic pressure increases with the ingredient contents. As a rule, reverse osmosis can be used for the recovery of water from seawater up to a pressure of 80 bar, whereby a salt content of up to 80 g/L can be realised in the concentrate in relation to NaCl. Reverse osmosis plants with a possible operating pressure of 150 bar have been developed for landfill seepage water treatment. Pilot plants can also be operated at 200 bar. The concentrate being treated will clearly be reduced by the relevant high-pressure plants, which will also be linked to significantly reduced investment and operating costs with regard to further treatment. The separated materials contained in the so-called concentrate are predominantly in solved or colloidal form. With regard to the further treatment of the concentrate it is beneficial that the harmful ingredients in the waste water flow are highly concentrated or fed into the smallest possible volume flow. Trans-membrane distillation Trans-membrane distillation (TMD) allows the concentrate of a reverse osmosis plant to be further treated. It can also be used for desalination and cleaning water and aqueous solutions as well as for concentrating non-volatile water ingredients. This involves two aqueous phases (concentrate and distillate) that are separated from each other by a hydrophobic micro-porous membrane (Fig. 3). Due to the hydrophobic membrane properties in conjunction with the reduced pore size the aqueous phase can only seep into the pore system, if the capillary penetration or wetting pressure is exceeded. Many commercial hydrophobic micro-porous membranes have a water wetting pressure in the 2 to 4 bar range. This membrane property can also bring about safe separation of the concentrate and the distillate through the
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liquid making direct contact on both sides of the membrane. Both are separated from each other by the gas-filled pore system in the membrane. The driving force for the material transport through the membrane is the vapour pressure difference between the phase boundaries, which build up on the pore openings in the membrane. The vapour pressure difference can be adjusted by a temperature difference, etc. This causes the liquid on the hot side of the membrane to evaporate as the vapour permeates through the membrane and condenses on the cold side. Direct two-sided contact with the membrane can easily be put into effect using hydrophobic micro-porous capillary membranes. The economical reverse flow principle can also be used easily in this case. Trans-membrane distillation can also be carried out using flat membranes in the form of special spiral wound modules. A combination of a TMD module and a heat exchanger can also achieve the same effect as multi-stage evaporator with regard to heat utilisation. The associated plant flow diagram is shown in Fig. 4. The energy emerging from the distillate in the form of condensation heat will be
partially transferred to the solution in the heat exchanger. Determining of the operating ranges in a TMD plant including heat recovery will be carried out on the basis of the cost optimisation. The proper functioning of trans-membrane distillation has been proven by many researchers. The latest results are included in the dissertations from Nikolaus /1/ and Winter /2/. The industrial introduction of TMD for preparing drinking water from seawater foundered previously and this was mainly due to the higher operating and investment costs when compared to reverse osmosis. The operating costs particularly include the costs of providing the energy for evaporating the liquid. Test results have shown, that also with concentrating salt solutions a destillate with very low conductance can be produced (see Fig. 5). This value is very low when compared to normal evaporation plants, as a salt transfer through the membranes is prevented by the very small droplets carried with it. It should be noted that the conductance of the distillate can be affected by the passing CO2 or other volatile components. Therefore, it must be ensured that a vacuum degassing occurs before the TMD stage so that water with
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low conductivity can be produced. This is why hydrophobic membranes are already in use as standard items. Aqueous solutions containing salts and acids can be concentrated using TMD. Experiments have shown that aqueous solutions with low volatile organic components can be treated without membrane wetting. As water shortages and abundant sunlight often occur together in the same region, and a TMD plant can also operate effectively using water temperatures ranging from 50° to 98°C, they can also be operated in conjunction with a solar-thermal plant. In particular, a TMD plant enables treating the brine of a seawater reverse osmosis plant. As very little energy is needed for pumps when a TMD plant is operating, self-sufficient energy plants based on photovoltaics and solar collectors can also be constructed. The first promising trials that were undertaken showed that TMD could also be used for crystallisation evaporation. Evaporation (concentration) is often the process that competes with TMD. A precise cost comparison can only be made between the two processes using a specific project, as the costs are frequently affected by project-related ancillary conditions.
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This also applies to selecting the materials, etc. TMD plants are mainly made from plastics, which is advantageous in the case of corrosive solutions. In the case of small and medium-sized plants the investment costs for TMD plants are usually considerably lower than those of conventional evaporation plants with the same performance factors. 2.3 Treating the concentrates Further processing stages are necessary for treating the concentrates produced by the previously mentioned processes. Volatile substances can be removed through stripping and subsequent condensation. Oxidisable and biologically removable substances can be partially removed in a corresponding treatment stage. Waste water-free means that the part of the ingredients detached from waste water, which is mainly salts, accrues in solid form and re-useable “pure” water can be produced. As previously mentioned, these requirements can be fulfilled using evaporation or vaporisation of the remaining liquid. As before, ingredients in the concentrate can be separated into solids through precipitation or crystallisation and subsequent centrifugation or filtration. The sediment or the filter cake that forms can be dried, so that only a solid substance remains. For example, the solids can be separated from the small waste water flows using continuous or cyclically operated belt filters and the residue on the belt will be dried and transported away afterwards. Solar drying can be used with small quantities of waste. Huge quantities can be dried if energy is used in the plants. The energy needed for drying could easily become the largest share of the overall process. In large drying plants, such as those used in paper technology, they are paying increasing attention to energy recovery. It should also be taken into consideration that the major share of the energy used for drying is latent energy that is used with the vapour. It is necessary to condense part of the water vapour in order to realise the greatest possible recovery of heat. In order to recover heat at the highest possible and therefore worthwhile temperature level, condensation must also occur at the highest possible temperature level. A correspondingly high dew point can be
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realised if an air flow that is saturated with vapour is discharged from the dryer. A dry residue forms during the drying, which can contain salts and other non-volatile ingredients from the waste water. The concentration or water evaporation can also be carried out in regions with high sunshine and little rainfall by using ponds, which can be used accordingly for recovering sea salt. Corresponding plants for waste water concentration were previously unknown in Europe. It should also be taken into consideration that the environmental regulations will make their implementation difficult. The situation is different in Africa or America, where so-called “ponds” have also been created for waste water treatment. Different types of evaporators are available for treating the concentrates. As crystallisation evaporation is normally used, it is beneficial to separate and concentrate the crystals by using centrifugation or filtration simultaneously. Then the evaporation will occur with a relatively low concentration of solids. An alternative to the procedure where the formed crystals are discharged is the so-called thin-film evaporator with moving wipers. In this system the crystals that form on the heated evaporator wall are scraped off and removed. A powder-type solid can be recovered after brief final drying using this method. The evaporation plant is normally designed as a multi-stage plant in order to reduce the evaporation energy requirement, i.e. the exhaust vapour from the first stage is the superheated steam used for evaporation in the second stage. The energy requirement is reduced with each additional stage, but the investment costs increase, so that the optimum number of stages can be determined based on a feasibility calculation. The overall costs can be minimised by comparing the investment and energy costs. Three or four stage evaporation stages are often the optimum configuration for treating concentrates. An alternative to the evaporation of concentrated waste water flows is injection into a fluidized bed that works with preheated air. Granulation of the solids will also be realised in parallel to the drying. Waste incineration is also an option in the case of waste water flows with an additional high proportion of organic compos-
ites, i.e. it is injected into a burner. Waste water incineration is normally combined with existing incineration processes. Noncombustible ingredients can be removed and disposed of with the ash. A part will also be removed as dust and separated in the downstream surface filters. Even applications in which the concentrate is injected and dried in a hot exhaust gas flow from an incinerator plant are conceivable. The exhaust gas is cooled at the same time here and the solids are separated as dust by the exhaust gas filter. 3. Concluding remarks The conception and the material selection as well as the corrosive effects of the ingredients in the waste water and their tendency to form crusts must always be considered with regard to ZLD plants. The plants can be operated with clear signs of wear linked to the mechanical loads. These can often be minimised using high quality material combinations, but this depends on the operating conditions. The operating costs and, through the possible use of existing plastics, even the investment costs can be minimised by the use of waste heat at a relatively low temperature level. The large amount of waste water to be treated requires that the respective process can be optimised to meet specific requirements and local conditions. In general it can be ascertained that the ZLD process is based on known processes for water waste water treatment. The integration of water treatment in existing processes in conjunction with continuous heat utilisation makes economical solutions possible. However, the technology can only be used if its efficiency is clearly apparent when compared to alternative solutions, especially with regard to the disposal of the concentrate. Literature: /1/ K. Nikolaus: Trink- und Reinstwassergewinnung mittels Membrandestillation. Dissertation TU Kaiserslautern (2013), Fortschritt-Berichte des Lehrstuhls für Mechanische Verfahrenstechnik, Bd. 10, ISBN 978-3-943995-49-7 /2/ D. Winter: Membrane Distillation. Dissertation TU Kaiserslautern (2014), Schriftenreihe der Reiner LemoineStiftung, Shaker Verlag, ISBN 978-3-84403706-7 /3/ K. Schneider, W. Hölz, R. Wollbeck, S. Ripperger: Membranes and Moduls for Transmembrane Distillation. Journal of Membrane Science 39 (1988), S. 25 – 42
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Improved treatment of landfill leachate by means of optimized flocculation technology Reducing leachate treatment costs, but how? Ch. Schröder* Introduction Leachate processing at landfills places significant demands on process technology. Landfill leachate contains a cocktail of various pollutants. In addition to biodegradable nitrogen compounds, this also includes a large number of other organic and inorganic pollutant groups that are fully or partially non-biodegradable. These substances have to be removed from the landfill leachate through cost-intensive physicochemical treatment. The requirements placed on the treated leachate depend on the way it is discharged. Legal framework specifications define the limits for direct or indirect dischargers. After biological pretreatment, the landfill leachate still contains pollutants that were not biologically decomposed. The chemical oxygen demand (COD) serves as sum parameter for non-biodegraded contaminants downstream of the biological treatment. Due to the non-biodegradable contents of the landfill leachate, another treatment stage must be provided downstream of the biological treatment stage; this stage removes the contents from the wastewater stream physicochemically. In the simplest case, this involves treatment of the leachate with activated carbon. Physicochemical treatment must ensure, that limit values for discharging are complied with. Activated carbon adsorption removes COD and AOX loads from the wastewater. This is accomplished through a concentration- and time-dependent process of adsorption of these substances onto the activated carbon surface. When the adsorption capacity of the activated carbon is exhausted, or if the prescribed limits are * Dr. Christian Schröder aquen aqua-engineering GmbH Bauhofstr. 31 38678 Clausthal-Zellerfeld Tel. 05323-94898-0 www.aquen.de
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Tab. 1: Limits for indirect dischargers in Lower Saxony (Germany)
exceeded, the activated carbon must be replaced and regenerated. The pollutants are not actually eliminated in this process, they are just captured and stored locally when the activated carbon is replaced. The adsorption process occurs selectively, with nitrogen compounds not being adsorbed. Because the adsorption process is concentration-dependent, it is important from an economical point of view for the pollutant load be reduced as much as possible before entering the activated carbon adsorber. Of course, high pollutant loads can be captured by the activated carbon, but the active life of the adsorber is shorter due to the faster-moving adsorption gradient. In this case, the activated carbon cannot handle as much of a load since the discharge limits are reached very quickly. When the loads are lower, the adsorption gradient moves slower and the absolute load can be higher. The activated carbon is understood to be fully-loaded (exhausted) when the concentration of the adsorbable substances are as high on the discharge side of the activated carbon as they are in the feed. The disadvantage to activated carbon adsorption, in addition to the high specific treatment costs, is that filterable substances from the biological treatment stage mechanically block the adsorber. To avoid this, a filtration stage should be placed
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Fig. 1: Schematic of a simplified landfill leachate treatment system with biological treatment and activated carbon adsorption
Fig. 2: Schematic of a landfill leachate treatment system with a biological treatment stage, physicochemical treatment and activated carbon adsorption
Fraction portion [%]
Fig. 3: Floc Sensor FlocSens
Test time [min]
Fig. 4: Temporal plot of the floc size fractions (with FlocSens)
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upstream of the activated carbon stage. In general, this involves sand or cloth filters. To reduce the treatment costs physical (physicochemical) separation processes are used which remove the contents, primarily the COD, from the wastewater stream. The separated contents can be disposed of as sludge. The function of the activated carbon adsorption process can at best be reduced to a policing filter (or none). To separate specific wastewater contents, separation methods such as floatation or filtration are used, for example. In these methods, it is simple mechanical filtration by gravity, as compared to floatation, centrifugation or membrane filtration, which is economically preferred because of the low operating costs. However, the disadvantage is that the separation performance relative to the filtrate is often lacking. The efficiency of the separation process is very much affected by the quality of the conditioning. A prerequisite for good separation performance is for the contents to be separated to be concentrated and joined together as completely as possible into filterable floc structures, which are thereby mechanically separable. It is particularly important to incorporate the fines into the floc structure. The “DeSiFloc” concept for landfill leachate treatment includes a new, internationally patent-protected flocculation process which can separate the pollutants much more efficiently compared to conventional processes. The separation performance of mechanical filtration processes is influenced primarily by the floc structure achieved. The most important tool for conducting targeted flocculation tests is a newly developed flocculation sensor, the “FlocSens”. The FlocSens uses a photo-optical measurement process based on a CCD line scan camera. The sensor makes it possible to determine, online, specific flocculation characteristics such as sedimentation or filtration characteristics of the flocced wastewater. Settling tests were carried out to confirm the measurement results. A two-stage flocculation process is used consisting of coagulation (micro-floc formation) and flocculation (macro-floc formation). Iron-III chloride (FeCl3, 40 %) is used as a coagulant, and the solution of a cationic polymer is used as a flocculant. The addition of the coagulant causes structures to form in the suspension. The fraction of small structures decreases and the fraction of large structures increases. The residence time of coagulation is about 15 minutes. During this time, it is clear that the forces of attraction of the coagulant are not sufficient to render the suspension stable against shear. Over time,
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the structures formed erode and become smaller again. Then, the addition of the polymer causes a jump in large structures. No discernible destruction of flocs occurs during the test time of about 5 minutes after the polymer is added; thus, the flocs are sufficiently stable against shear for the separation process to take place. Fig. 4 shows the temporal plots of the floc fractions consisting of large flocs, medium sized flocs and small flocs for the laboratory tests listed. Considering the distribution of fractions and the shear stability of the flocs formed, the results are congruent with those of the COD fraction in the supernatant and with the visual appearance of the settling tests. The tests showed that the best separation results are achieved with temporally constant floc structures, which are consequently the most stables structures mechanically. The FlocFormer as a floccing reactor is the heart of the largescale system. By using the FlocFormer, the landfill leachate treatment process is more consistent in terms of processing and costs compared to conventional treatment. Throughout the entire system, the focus is on removing all pollutants -(apart from the nitrogen components, which must be further biologically decomposed-) efficiently from the waste water using the FlocFormer process. The FlocFormer flocculating system uses two devices; a turbo mixer for introducing the polymer homogeneously into the sludge or water in a short time, and a floc forming reactor that promotes a specific floc structure. The conditioning system has four degrees of freedom for optimizing the floc structure. These degrees of freedom are: - flocculant dosing, - turbo-mixer speed, - floc forming reactor rate, - floc forming reactor gap
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Fig. 5: The FlocFormer, a combination of Polymer and Cone Mixer
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Specific floc structure Step 2 – Floc forming
Step 1 – Polymer mixing
Slurry / Wastewater Polymer
Fig. 6: Schematic of FlocFormer design
The turbo-mixer unit is designed to mix a highly concentrated polymer solution with the wastewater. The polymer metering and mixing intensity of the turbo-mixer can be controlled online. The floc forming reactor is a modified conical agitator in which the specific floc structures are formed. An inner cone rotates concentrically inside an outer conical shell. A gap of constant width is built by the two conical elements. Because of the varying cone radii, the distribution of centrifugal forces is not constant along the axis of rotation. This means that different flow conditions can exist next to one another during flow within the gap. The sludge flows from the base of the cone through the gap between the concentric cone surfaces to the cone tip. The floc structure is initially destroyed by the high shear rates at the larger diameter. When the mixing intensity decreases corresponding to the axial position, the flow regime changes. The flocs can roll down along the cone walls and one another, and are compacted in this way. The gap can be changed during operation since the inner cone can be shifted in the axial direction. This degree of freedom allows the reactor to be able to treat a broad spectrum of different volumetric and mass flows.
Fig. 7: Comparison of conventional landfill leachate treatment and the DeSiFloc method
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Fig. 8: Schematic of the DeSiFloc treatment stages
DeSiFloc – Functional schematic and components The installed system agglomerates and flocculates the contents of the process water and then separates the filterable materials. Fig. 6 shows the schematic of the process. The function of the components used is explained below. Coagulation In this stage, the biologically pre-treated landfill leachate is electrically destabilized. Organic materials precipitate as a result of the destabilization, which results in a reduction of COD and AOX, and microflocs form. The iron chloride lowers the pH, which can be used as a control parameter. The target pH is relatively high for a coagulation process. The advantage of this is that the amount of coagulant used can be low. Flocculation By adding flocculant (synthetic polymers), the microflocs which have formed are converted to stable macroflocs in the FlocFormer. Two phases form; the floc structure which contains solids and pollutants, and the relatively clear residual liquid. By tailoring the floc structure, the downstream separation process can be significantly improved. Primary COD separation
to a pH of about 6.5 takes place using a base. This is done through the addition of sodium hydroxide (50% NaOH). Example of the Hattorf district waste landfill site – direct discharger Up until 2007, at the district waste landfill of the Osterrode am Harz (Hatttorf) district, the leachate was treated through a biological pre-treatment followed by physicochemical treatment (coagulation, separation, activated carbon adsorption). The pollutant with the highest concentration downstream in the feed to the physicochemical treatment stage is the non-biodegraded or non-biodegradable COD. This is between 30 % and 70 % of the original COD, depending on the leachate composition. The relatively high water load in Hattorf at the time often resulted in operational disruptions in the biological treatment stage and in the downstream filtration stages of the leachate treatment plant. This circumstance necessitated a significant reduction in the treatable flow volume. This led to an expensive disposal process of the leachate in Hattorf. Problem: The physicochemical treatment and downstream activated carbon system being designed must treat the landfill leachate economically enough to ensure that the direct discharger limits are not exceeded.
Solution with the DeSiFloc process: In 2007, the landfill leachate treatment plant in Hattorf was retrofitted from the ground up. In addition to bolstering the biological treatment stage, the DesiFloc process was used for the first time as a physicochemical treatment stage. The newly developed “FlocFormer” floccing system, in combination with a simple disk thickener as a separation stage to reduce the COD, proved that this combination is very economical to operate and is also a very safe process. The FlocFormer provides a tailored floc structure during the floccing process. This makes it possible to bind a large fraction of the pollutants into the flocs, thereby making mechanical separation of them possible. The use of the FlocFormer has two effects that result in a lowering of the operating costs: 1. The actual COD separation process can be done using a technically simple gravity filtration process. The COD elimination no longer needs to be done in the upstream biological treatment stage. 2. The COD separation performance can be significantly improved by using the FlocFormer. The burden on the downstream activated carbon stage was reduced by 90 %.
The stable floc structures are separated from the residual liquid using a mechanical separation in the form of a screen. Secondary COD separation Another, very fine downstream filtration further separates agglomerated solids from the clear phase. This filter is primarily a protection function for the next stage, which is activated carbon adsorption Neutralization After mechanical separation, neutralization of the treated mixture of landfill leachate and MBA process wastewater
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Fig. 9: Schematic of the DeSiFloc treatment stages
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1. Disk thickener
2. Belt filter
Fig. 10: Flocced landfill leachate in the process
After the disk thickener, a belt filter was provided that removes any possible remaining suspended material from the DSW using a very high-mesh filter medium. After the mechanical filtration of the leachate pollutants, there is an activated carbon adsorption stage. Full adaptation and efficiency of the flocculation-initiated separation process reduces the function of the activated carbon stage to a policing filter for the COD parameter. Compared to the former cost (with high carbon consumption): a cost reduction of approx.. 80%. Economical benefits: The ecological advantages of a safe separation are inestimable even considering increasing environmental restrictions. Example of the Deiderode district waste landfill site – indirect discharger The landfill leachate plant in Deiderode is part of the district waste landfill of the district of Göttingen and was originally built to treat incident leachate from
the landfill heap. The leachate treatment facility is an indirect discharger of the treated leachate. The mechanical-biological treatment plant (MBA) of the Abfallzweckverband Südniedersachsen (Southern Lower Saxony Waste Disposal Association) also sends water to the leachate treatment plant to lower the hydraulic load on its system. This relatively high water load causes operational disruptions in the downstream filtration stages of the treatment plant and results in high costs in the activated carbon area. The existing landfill leachate treatment plant at the Deiderode landfill of the district of Göttingen was expanded to include an additional separation stage in order to safely allow the MBA of the Abfallzweckverband to send wastewater to the leachate treatment plant. Initially, a maximum of 1.5 m3/h of MBA wastewater could be added to the treated amount in the leachate treatment plant, but it was desired to be able to send about 6 m3/h. To achieve this goal, the treatment plant was bolstered by an intermediate DeSiFloc processing stage. This additional treatment stage was situated downstream of the existing bio-
Fig. 11: Treatment and clarification stages for the landfill leachate in the DeSiFloc system
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logical treatment stage and upstream of the existing activated carbon treatment stage. The amount of water to be sent and the landfill leachate treatment plant concentrations to be adhered to remain the same. The treatment stage treats a maximum amount of biologically-pretreated leachate of 288 m3 per day. The maximum throughput per hour comes to 12 m3 and the maximum throughput per second is 3.33 litres. The DeSiFloc process is designed to be scalable. Each module has a base throughput for landfill leachate of 6 m3/h. Parallel operation of multiple modules can be done easily. To achieve the maximum output of 12 m3/h, the separation technique was installed in two parallel lines. The advantage to this is redundancy and a partial load system range, also making it easier to operate. Fig. 13 shows the schematic of the two lines. The filtered landfill leachate and the separated thick sludge are further treated centrally. To make sure that the flocs approach the screen as carefully as possible, the landfill leachate flows through the separation stages by the force of gravity following the FlocFormer, see Fig. 13. The plant is designed in such a way that the separating machines are installed on a platform and the corresponding vessels for the individual components are installed at ground level. This ensures good access for cleaning the system parts. Fig. 14 shows a partial view of the installed system. The landfill leachate treatment plant in Diederode is an indirect discharger. The water is sent to the district wastewater treatment plant in Göttingen. After startup of the DeSiFloc system, it was possible to take the existing activated carbon stage out of service. The profitability of the process is very positive.
Fig. 12: Partial view of the DeSiFloc system in Hattorf
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The original operation of the landfill leachate treatment plant at reduced volumetric flow resulted in a calculated cost for the activated carbon stage of about 5.30 €/m3. However, the actual number was probably higher since the capacity of the activated carbon could no longer be achieved due to blockage by solids. The expansion of the plant to include a newly tailored biological treatment stage and the physicochemical DeSiFloc stage made economical treatment of the entire amount fed to the landfill leachate treatment plant possible. The annual savings in comparison to pure activated carbon adsorption are considerable.
Tab. 2: Example of consumption cost calculation for chemicals and activated carbon for Hattorf – direct discharger Consumption of FeCl³ FeCl³ costs Consumption costs for FeCl³ Consumption costs for polymer Consumption costs for activated carbon Thus, the specific consumption costs in the physicochemical treatment stage is only
3.7 l/m³ 0.24 €/l (0.17 €/kg) 0.89 €/m³ 0.04 €/m³ 0.26 €/m³ 1.19 €/m³
Tab. 3: Example of consumption cost calculation for chemicals at Deiderode – indirect discharger
Economical benefits: The ecological advantages of a safe separation are inestimable even considering increasing environmental restrictions.
Consumption of FeCl³ FeCl³ costs Consumption costs for FeCl³ Consumption costs for polymer Consumption costs for activated carbon Thus, the specific consumption costs in the physicochemical treatment stage is only
3.0 l/m³ 0.24 €/l (0.17 €/kg) 0.72 €/m³ 0.10 €/m³ - €/m³ 0.82 €/m³
Fig. 13: Process schematic for the DeSiFloc plant in Deiderode
Fig. 14: One line of the DeSiFloc plant in Deiderode
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Fig. 15: Partial view of the DeSiFloc system
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Components and systems used in the processing industry for solid/liquid separation H. Lyko* Whether centrifugation or filtration, wire cloths, non-woven or depth filter sheets for separating nano to course particles and process filtration ranging from aqueous media up to chemicals that are especially aggressive, viscous or adhesive media: no parts of the solid / liquid separation spectrum that could be said to be relevant to the chemical or pharmaceutical industries as well as bio technology were omitted from last year’s Achema. Many innovations made to the specific components showed clear improvements with regard to process efficiency and performance whilst other exhibitors showed completely new processes, which were previously unknown in this form with regard to their respective applications. Some examples are shown in the following. Filter braids with threedimensional pore geometry Woven wire filters are proving to be ideal for precisely calculating pore sizes, thanks to their type of weave and the wire thicknesses used. Haver & Boecker use formulas for forecasting the pressure loss in the flow through the fabrics and the diameter of the smallest sphere that can only just be retained by a specific fabric. The calculation program was developed as part of a joint research project run by Stuttgart university. The calculated minimesh fabric properties can also be confirmed using glass-bead tests and air flow measurements. Up to now the efficiency of fabrics for especially fine degrees of separation has been limited, as the reduction in the size of the pores was interlinked with a reduction in the flow quantity and/or the stability of the fabric made from extremely thin wires. Not all of the metallic materials can be processed into very thin wires. These conventional filter braid limits have now been overcome by the new RPD HIFLO mini-mesh range of fabrics. These fabrics exhibit three-dimensional pore geometry, as their warp wires do not all lie parallel to each other in one level but are spatially staggered so that the weave wires meander around the warp wires (see Fig. 1). This results in smaller pore sizes with relatively high porosity. The structure exhibits an open surface that has been significantly increased over the same area, so that the flow rate is increased with the same degree of separation. The pore sizes can be calibrated as planned within 5 to 20 μm batches. A new loom was specifically constructed in the factory for the production of three-dimensional fabrics. As the material can also be made from relatively thick wires, special materials such as *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
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avesta, hastelloy, inconel or titanium can now be woven for the small pore spectrum under 30 μm. Filters and filter apparatus Filter bags are used as disposable components in a variety of applications, such as in water treatment, the filtration of chemicals, inks and paint, petro-chemicals or for the preparation of cleaning solutions. As they are not regenerated during the filtration, their dirt-retention capacity per installation space and the resulting service life are decisive with regard to their efficiency. Operating safety also increases, as filter changes do not occur so often. The advantage of the increased dirt-retention capacity is evident in the MAX-LOAD filter bags made by Eaton. The capacity increase is put into effect by this type of filter pleating being used in the filter bags, so that the filter area in the cylindrical assembly is approximately four times as high as that of a non-pleated filter bag with the same external dimensions. The pleated filter bag fits in all size 01 and 02 Eaton standard holder baskets. Other properties are the silicone-free material, the special surface treatment, the nearly complete prevention of fibre migration and the patented, pressure-activated sealing ring, which ensures bypass-free filtration. Eaton provide their well-known, closed BECO INTEGRA layer filtration system in a 1,000 mm size for the deep filtration of liquids, for which there are frames available in five size categories ranging from 200 up to 1,000 mm. Filter apparatus for particle separation from liquids are selected according to the particle concentration and particle size distribution and whether only the solids or only the clarified liquid should be considered as the valuable material to be recovered as product. Barry A. Perlmutter, president and CEO of the American sub-
sidiary of BHS Sonthofen, describes pressure filtration systems with the main focus on the separation of fine particles /1/. The complete recovery of all particles is increased with fine materials, even the finest can be recovered and in some cases in which the focus lies on the liquid that has to be recovered, the highest purity standards can also be better fulfilled. The author looked at cartridge filters and pressure plate filters as fine filtration alternatives. Which of the two systems should be used should be decided according to the properties of the filter cake that will be formed and the question of whether it still has to be washed in another process or not. Cartridge filters are more suitable when hard, possibly crystalline and irregularly shaped particles have to be handled, whereas soft, flaky particles are more suited to being separated on the horizontal surface of a pressure plate filter. The later, due to its horizontal filter area alignment, allows much thicker filter cakes (up to approx. 75 mm) to be processed. Filter cakes with thicknesses between 5 and 20 mm accumulate in cartridge filters. The fact that gravity does not contribute to cake detachment also confirms the suitability of pressure plate filters for processes involving cake washing. Cake removal strategies also differ. Cartridges have an internal throughflow of air/gas against the filtration direction, so that the flexible filter media are inflated and discard the cake. The solids are removed by the filter surface oscillations in pressure plate filters. Cake removal systems for use with drum filters Precoat filtration using rotating vacuum drum filters is another standard process used for both dewatering existing solid material in a suspension as well as in cases in which the filtrate is the product.
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Fig. 1: Drawing of three-dimensional weave structures in RPD HIFLO media (image: Haver & Boecker)
Different discharge systems such as knife, roller, belts or cords exist for removing the ďŹ lter cake from the surface of the drum. The quantity and the properties of the ďŹ lter cake decide which system should be used. A British company, Filtration Services Limited, specialise in the design, construction, maintenance and updating of vacuum drum ďŹ lters. The Automatic Knife Advance System (AKAS) is a special further development of the cake removal system, in which the knife can be moved in small units of 0.5 Îźm. Knife removal
Fig. 2: View of the RPD HIFLO wire cloth (image: Haver & Boecker)
systems are used when the solid product is supposed to be as clean as possible. Other applications involve the presence of solids, in very low concentration, which makes the building up of a ďŹ lter cake difďŹ cult, the presence of jelly-like particles that tend to clog the ďŹ lter medium, or of particle sizes below 5 Îźm, or of impervious or waste solids. In the case that very ďŹ nely granulated product has to be recovered with the highest possible purity, then the ďŹ ne increments of the knife positioning system have the beneďŹ t of completely removing
the product, whilst the main section of the washed ďŹ ltering aids remain on the drum on the surface of the ďŹ lter. Filtration of viscous media Diverse media, which are viscous and sometimes sticky, are processed in the food industry and have to be freed of particles carried with it as part of the manufacturing process. Typical examples of such media are honey, liquid chocolate or liquid caramel. Russell Finex, a Belgian company who celebrated their 80th anniversary
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Eco filter is a cylindrical filter, in which a rotating spiral-shaped scraper frees the stainless steel filter element of the solids that have become attached to it. High-speed tubular centrifuges
Fig. 3: Z11 high-speed tubular centrifuge with an 80,000*g spinning speed (image: Carl Padberg Zentrifugenbau GmbH)
Fig. 4: CARR U2k principle diagram, the first disposable centifruge for GMP processes in the world (image: Pneumatic Scale Angelus)
at Achema, reported about their recent successful application of their self-cleaning Eco filters for use in the filtration of liquid caramel and installed at Mondelez, who manufacture biscuits and cakes. The caramel accrues as the remaining mass during the production of chocolate bars and contains waffle crumbs. In filtration tests using the Eco filter, the mass
remained runny at 35°C and could be freed of the crumbs. The installation of the filter system was completed after it was ensured that the cleaned caramel could be returned to the chocolate bar production line without any effects on the quality of the finished product. The installation results in a 20% reduction in product losses and improves the waste treatment process. The
High-speed tubular centrifuges are used mainly for the continuous clarifying of liquids in the processing industry, e.g. for removing solids from fermentation broths. This type of centrifuge is also suitable for separating non-mixable liquids and removing solids at the same time. In the fast centrifuges made by Carl Padberg Zentrifugenbau GmbH (CEPA), the suspension is fed into the rotor in the running centrifuge from underneath, so that the ingredients are coated in accordance with their thicknesses. The liquid or the liquids are continually discharged through the drainage trays, whilst the solids remain in the rotor and are manually removed afterwards. 0.25 up to 10 L can be removed, whereas up to 3,000 L/h of suspension can be processed, depending on the type of solids. The special feature of the Z11 model (see Fig. 3), which has been designed for throughputs of up to 30 L/h, is the high spinning rate of up to 80,000 x g. This makes the centrifuge especially interesting if large quantities of very fine particles have to be efficiently recovered from diluted solutions. This also applies to the separation of nanoparticles from liquids in quantities that are well above laboratory scales. The later was implemented at the Fraunhofer Institute for Silicate Research (ISC) in Würzburg. Primary particles were produced using a wet chemical method as part of the research into functionalised nano and micro particles and they lie in relatively large dilutions. With high-speed tubular centrifuges these particles can be recovered in suitable quantities that meet the industrial standards. The simple functional principle of a tubular centrifuge also allows for easy phase separation modelling using predictable separation results. The centrifuges are available for various industrial applications with open casings, with closed casings (for Ex-versions, etc.) and with closed casings and all components made from stainless steel (for GMP requirements). Centrifuges used as disposable systems
Fig. 5: Structure for the acoustic separation of solids from liquids (image: Pall GmbH Life Science).
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If a return to disposable systems is made in the pharmaceutical industry and bio technology in order to save on investment, water and cleaning chemical costs for CIP systems, then at present there are only disposable filter systems with depth filters or membranes available for use for solids / liquid separation that meet the industrial standards. This should have
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changed, as Carr Centritech announced to launch the world’s first disposable centrifuge in the market, which has a capacity of up to 30 L/m and can prepare the fermentation broths from 2,000 L reactors and corresponds to the current standards in the bio / pharmaceutical industries. The U2k centrifuges are bigger versions of the centrifuge that was first exhibited at Achema 2012, which is suitable for laboratories and pilot plants, but only the prototypes were on show this year. They should enter the market in 2016. Developments with decanter centrifuges Decanters are well-established in a huge variety of applications in the chemical and pharmaceutical industries, the beverage and food industries as well as for sewage treatment. They have also been established for a long time in the newer processes used in biomass processing. In particular, they are also used in applications for processing biomasses, fermentation broths and various foods that involve suspended solids that are soft and fluid. Flottweg provide their “Sedicanter” for these types of suspensions, which are difficult to process using standard decanters. In this type of machine, the solids are separated over a long clearing stretch with a low-turbulence flow and, for a decanter, a very high maximum centrifuge acceleration of 10,000 x g. The Sedicanter lies inbetween a classic decanter and a separator with regard to the particle sizes that have to be separated as well as the clarity of the centrate. It separates particles that are clearly smaller than those that a decanter can separate, but it can also process solid concentrations that are just as high. The adjustable impeller fitted at the end of the clearing stretch enables it be reset to match the compression of the solids and its dry matter content and this resetting also enables it to match the fluctuating amount of infeed. Typical applications for this centrifuge, which is also available in hygienic or explosion-proof versions, are biomass separation from fermentation broths, algae recovery, the processing of soya milk, clarification during the production of sugar syrup or starch, treatment of alcohol mash and other methods for processing vegetable raw materials. Hiller provides centrate monitoring with their decanter for monitoring and ensuring the required solid separation quality during centrifugation. The system also uses an object sensor, which measures the discolouration of the centrate at the centrifuge’s outlet and passes the measurement signal on to the plant’s PLC via Profinet/ Ethernet. Depending on the discolouration, the difference speed, the polymer quantity (as the flocculant) or the infeed pump can be changed via an especially developed PLC module. A warning signal will be generated if the centrate is poor. The centrate monitoring system can also be used to optimise the polymer consumption used for sludge dewatering. Separation using acoustic waves With the award of the exclusive license for the Acoustic Wave Separation (AWS) process from its copyright owner, FloDesignSonics (FDS), Pall have expanded their portfolio with a filterless process for separating cells from fermentation broths that can be operated both continuously and discontinuously and can also be integrated in a downstream processing chain. The separating principle used here consists of standing three-dimensional acoustic waves generated inside a flow channel. When a cell suspension flows through this channel, the single particles collect at the wave nodes and accumulate into large units, until they become so heavy and become sediment. The process runs without any high mechanical stresses on the cells, without any temperature increases or any damage being caused to the fermentation products (protein).
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Literature: /1/ Perlmutter, B.A.: Choosing a Fine-Particle Filtration System; Chemical Engineering Progress (CEP), Vol 110 (2014) No. 12, S. 35 - 39
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Innovations and further developments in the food and beverage industries H. Lyko* Anuga FoodTec, the international supplier trade fair for the food and beverage industries continued to build on its past success by setting new exhibitor and visitor records. More than 45,000 specialists from the industry were informed about the products and services by a total of 1,501 exhibitors from 49 countries. The corresponds to a near 13.5% increase in the number of exhibitors as compared to 2012 and an approx. 6% increase in the number of visitors. The exhibition is arranged into food processing, food packaging, food safety, ingredients and services and solutions sections. Different types of separation technology and separation processes accompanied by the relevant measures for contaminant detection and quality monitoring are now included in the processing technology and for guaranteeing product qualities. During the production of food and beverages, exhaust air and/or waste water flows are also generated and these have to be treated. Exhibits and processes from these sectors are described in the following. At the exhibition the International FoodTec awards from the German Agricultural Society were awarded for the 9th time in cooperation with specialist and media partners. These awards included 9 gold and 9 silver medals, whereby one of each was awarded for technological innovations in the separation technology sector and a gold medal was also presented for an analysing process. Centrifuge technology The Z5E-4/01 decanter from Flottweg was hygienically designed for the safe processing of food (Fig. 1). All of the components that come into direct contact with the medium, are made from rust and acid resistant stainless steel and finished with a surface roughness Ra of 0.8 μm. This ensures good cleanability. Typical applications in the food processing sector are the separation of coagulated proteins, the production of soya drinks and starch as well as the clarification of fruit juices. A decanter fitted with an adjustable centripetal pump can be used to achieve optimum separation efficiency from variable infeeds. The centripetal pump controls the draining of the clarified liquid from a closed system under pressure and as a result of an adjustment, the diameter of the outflow can be varied and the separation efficiency can be optimised to match the infeed characteristics. Milk processing systems are gaining in relevance that enable the processing to be carried out at the lowest possible temperatures, which increases the sensory quality with a simultaneous reduction in energy consumption. Andritz Separation exhibited a cold milk separator, which is the first of its type without a gripper / peeling disc and is equipped with a special abstraction tube. The design of the CremaViva model range from Andritz Frautech (Fig. 2) controls the discharging of the skimmed milk and cream as a result of the hydrostatic pressure difference being used as the driving force. This type of discharge enables the separation to occur at very low tem*Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
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peratures of around 5°C with a maximum temperature increase of one degree. The discharged products, whose viscosities at these low temperatures are relatively high, are better preserved. The raw milk is fed in from above, which enables the drive system and the parts that come into contact with the product to be completely separated from one another. Membrane technology Membrane filtration is one of the established dairy technology processes for concentrating product flows containing proteins. Reverse osmosis is used here to concentrate the proteins from the whey and the ultrafiltration permeate from the skimmed milk and whey filtration. Previously, it was normal and sensible to concentrate the whey up to an 18 30% DM concentration. The three-stage ALPMA PRO High DM reverse osmosis plant now enables the whey to be concentrated in an approx. 6% DM to 28 - 30%
DM process. The first two stages of this plant attain a concentration of approx. 18% - 20%. This ensures that the osmotic pressure of the infeed into the third reverse osmosis stage is very high. Special membranes are installed in it. The permeate from this third stage has a very high CSB value, which is why it is fed back to the plant’s inlet together with the concentrate as a polisher. This prevents dry mass losses, which reduces the contaminated load in the waste water and saves energy as opposed to evaporating a concentrate with 18% - 20% DM. The reverse osmosis plant described here was awarded the silver International FoodTec award. The ultrafiltration, nanofiltration and reverse osmosis membrane processes enable all of the ingredients to be concentrated, which cannot pass through a specific membrane. Advanced processes are aimed at selectively accumulating very specific whey proteins in order to allow natural binders and emulsifiers or functional
Fig. 1: Z5E-4/01 Flottweg decanter with hygienic design for processing food and other hygienicsensitive applications
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nutritional supplements to be gathered and used, e.g. in baby food. The Fraunhofer Institute for Interfacial Engineering and Biotechnology has been working on the further development of the electro-membrane process that was previously developed at Hohenheim university, so that specific proteins can be selectively accumulated. The process is based on combining ultrafiltration with an electrical field. This ensures that proteins are not only separated according to their size but according to their charge as well. This increases the output and reduces the cleaning effort when compared to pure ultrafiltration. Preliminary trials at Hohenheim university have shown that peptide or protein fragments, such as casein macro-peptide, can be separated from the whey proteins α- and β-lactoglobulin using an electro-membrane process. The EU’s “Whey2Food” research project, which has been running since 2013, is optimising the processes for industrially-relevant quantities and in accordance with the stipulated hygiene and cleaning standards. The process has been tested under real conditions in automated pilot plants installed at partner dairies. Food analysis Virtually gapless quality controls are imperative along the processing chain for the preparation of raw and auxiliary materials up to the filling or packaging of finished products. The controls are implemented in accordance with the trend towards automation of production processes as automatically running inline analyses or at least as bypass analyses. Infrared spectroscopy is used to analyse the chemical composition of the process flows. The Austrian company, Insort GmbH, calls this process “Chemical Imaging Technology“ (CIT), as it is based on the chemical composition of the food colour image generated at high resolution and it is
Fig. 2: Functional diagram of a CremaViva cold milk separator (image: Andritz Separation)
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Highlights 2015
tank. The juice forms a very thin film as a result of the outflow rate and the adhesive force. Utilising the surface of the tank, including the lid, reduces the overall tank volume that is needed. In addition to saving space, this also results in a reduction in the energy consumption as a smaller vacuum pump can be chosen to extract the discharged gas . This method of easy and energy-efficient degassing won a gold International FoodTec award. Innovations for food pumps
Fig. 3: Operating sites of inline-refractometers in a pipeline (left) and a tank (right) (photos: K-Patents Oy)
Fig. 4: Novalobe rotary piston pump (image: Grundfos GmbH)
classified and sorted in industrially-suited real time. The technology is realised in the SHERLOCK food analyser process diagnostics system, which was awarded the gold International FoodTec award. The refractometry used for determining the relative density of a process liquid is a probate resource that is used in production and especially in processes that measure the concentration of the ingredients in liquids. It is used in the form of manual or laboratory devices for determining the sugar content in must, wine, fruit juices, honey, etc., as well as inline process checks. One of the ways to implement the latter is to use the inline PR-23 refractometer made by K-Patents, a Finnish company, which is approved for use in the food industry under the American 3-A Sanitary standard and the EHEDG guidelines. The different sensor versions enable installation in both pipelines with relatively small diameters as well as in tanks and larger pipelines (see Fig. 3). The feature of this measuring device is that all of the components needed for measuring, such as the light source, the temperature sensor, the prism on which the incident light is
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partially refracted and partially reflected, as well as the CCD camera, which records the resulting sample in high resolution, are all installed in an environmentally and mechanically isolated nucleus. The measuring system delivers the liquid concentration in brixs, regardless of the suspended particles, bubbles, fibres, possible temperature or colour changes. It does not need to be recalibrated after being installed. Degassing of fruit juices It is necessary to degas the fruit juices prior to filling in order to avoid filling problems and prevent the tendency to oxidisation, e.g. by minimising the atmospheric oxygen and preventing the solid fruit content from floating. The liquid is distributed over a large surface in as thin as possible yeasty layers for the degassing, in order to keep the gas molecule diffusion path as small as possible. Krones AG has developed a swirling inlet for this as this was previously realised using an annular gap, atomiser or tangential nozzles. This ensures that the liquid already inside the especially designed tank lid fitted on the degassing tank lies on the wall of the
The design of the pumps that supply the food or beverages also plays a role with regard to hygienic aspects and easy cleanability as it does with centrifuges and filters. Grundfos presented three new pump models that have been designed for different food applications. The Maxa 250-400 food pump is a single-stage, end-suction centrifugal pump made from rolled CrNiMo steel (AISI 300), which is used for high delivery volumes up to 1,400 m3/h and a maximum delivery height of 55 m. Typical applications are suppling beer or milk, hot or cold water, brine or the circulation of large quantities of CIP liquids. Pumps from the F&B Hygia range are controlled pumps used in wet areas, such as breweries (fermentation cellars, bottle washing systems or bottling). The frequency converter for controlling the motor is integrated in these pumps. This has the benefit that the cost-effective, convenient decentralised alignment can be optimised for the pump application as opposed to an external frequency converter fitted in a control cabinet. Special protection against moisture, such as being sprayed from the operating areas, is provided in the MGE permanent magnet motor by the integrated anti-condensation heater, which protects the motor and the frequency converter from being damaged by condensation as well as the maximum IP66 protection class version. The pumps from this range are single-stage, end-suction centrifugal pumps for delivery heights up to 73 m, delivery flows up to 110 m3/h and operating pressures up to 16-bar. They are available with various nominal width connections. The Novalobe rotary piston pump available in the new 60/2.1 design size (see Fig. 4) is a pump for delivering viscous food such as honey or sauces, whose delivery volume per rev is 2.1 litres. All of the parts that come into contact with the product are made from 1.4404 stainless steel (AISI 316L) with a roughness of Ra ≤ 0.8 μm. The cleaning is ensured by the design, which is certified by the European Hygienic Engineering & Design Group (EHEDG) and the aggregate can be sterilised at temperatures up to 150°C.
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Fig. 5: KMA Aairmaxx filter systems consist of an electro-filter (right), gas-scrubber (left) and a ventilator (centre): The separated tar is collected in the blue tar-collecting vessel.
Eccentric spiral pumps are preferred for delivering pasty, mushy or lumpy media. Application examples in the food sector for the eccentric spiral pumps made by Seepex are such materials as tomato paste, mashed potatoes, chicken legs, marzipan or even melons, all of which are media that cannot flow freely or only with restrictions. The company has revised their BCSO and BTCS (hopper pumps) ranges in order to satisfy the higher requirements regarding cleanability and durability. The pumps are designed in compliance with the 3-A Sanitary Standards and the EHEDG guidelines. Well-proven open pin joints are used in addition to the optimised pump casings as both together enable virtually residue-free cleaning to be carried out. The pump manufacturer Netsch provides eccentric spiral pumps that have been optimised for the media that has to be delivered, which in addition to hygiene, cleanability and suitability for handling food also fulfil the safe media handling conditions as well as energy and resource efficiencies. Honey counts as one of the food media that is especially difficult to handle, as it is extremely adhesive and can have a viscosity of up to 10.000 cP. These properties are particularly problematic with shaft seals. An eccentric screw pump has to be installed to supply the honey and the parts that come into contact with the product are made from stainless steel. White tallowed cotton is used as the sealing element in the food-compliant packed gland. The pump is also fitted with a dry running protection system that permanently monitors the stator temperature and switches the motor off before it starts to run hot as well as a contact manometer for preventing any damage caused by overpressure.
systems are of a modular construction and use different processes in succession. For example, Ultravent can consist of units such as an electro-filter for particle separation (designed as a plate electro-filter), UV lighting system and an activated carbon filter for fume removal. The system can also be equipped with a heat recovery system. The Aairmaxx (Fig. 5) includes tube electro-filter, ventilator and gas-scrubber components. Electro-filters have an advantage over filter media made from fabrics or nonwoven fabrics here as separated tars and oils cannot block the electro-filter as they do with the pores in a textile medium. Both versions of the electro-filters are cleaned automatically and periodically, in the Ultravent system by an integrated CIP plant and in Aairmaxx by an integrated heating register, which heats up the electro-filter once every week. References are available for both systems and the energy savings are around 80% or more when compared to afterburning. The Ultravent hybrid filter is used for handling exhaust air at 7,200 m3/h from newly installed deep-fryers for fish-fingers and other frozen fish products. The operating cost savings are given as 94% when compared to afterburning and the CO2 pollution can be reduced by 95%. Aairmaxx systems prove themselves in meat production for cleaning the exhaust air from hot smoking plants. Grandi Salumifici have installed a plant in Italy for treating an overall exhaust air quantity of up to 2,250 m3/h. The operating cost comparisons are for the treatment of 2,000 m3/h exhaust air from a smokehouse that ran for 16 hours a day and 6 days a week between the AAIRMAXX system and an afterburning plant with a heat recovery system showed cost savings of 85% from the tube electro-filter, ventilator and gas-scrubber combination and this includes the filter cleaning and the waste water from the gas-scrubber.
Exhaust air cleaning in food processing The exhaust air from operations in which a huge quantity of fat (e.g. deep frying) is used to cure or prepare the food, produces exhaust air flows, which being fumes or fat-droplet aerosols have high organic loads that also include a high concentration of odorous compounds. Thermal afterburning is a process that is frequently used here that also exhibits a relatively high CO2 footprint due to the use of combustible materials or electrical energy. KMA Umwelttechnik GmbH provides and their Aairmaxx fume filter and Ultravent hybrid filters as alternatives to burning, whose efficiency and eco-efficiency are higher than that of burning. Both
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New porous metallic-paper and its use as a filter medium L. Petersen, S. Ripperger*, C. Kostmann, P. Quadbeck, G. Stephani**, J. Strauß, S. Schramm*** New types of porous, sheet-like materials that can be made from different metals are presented in the following contribution. Methods used during the manufacture of papermaking and sintering technologies are combined for the production. The suitability of these materials for use as filter material was tested using different samples. The results are presented here. 1. Introduction Porous paper and sintered materials have been used as filter materials for a long time. Their manufacture and their typical filter material properties are described in /1/ and /2/. New types of porous sheet-like materials that can be made from different metals have been developed as a result of the cooperation between the Fraunhofer Institute for Manufacturing Technology, the Applied Materials Research Centre in Dresden and the Paper Technology Foundation in Munich. Methods used during the manufacture of papermaking and sintering technologies are combined for the production. The porous materials * Dipl.-Wirtsch.- Ing. Lars Petersen, Prof. Dr.-Ing. Siegfried Ripperger Technische Universität Kaiserslautern Gottlieb-Daimler-Str. 67663 Kaiserslautern, Germany Tel: +49 (0) 631 -205 -2121 www.uni-kl.de/MVT ** Dipl.-Ing- Cris Kostmann, Dr.-Ing. P. Quadbeck, Dr.-Ing. G. Stephani Fraunhofer Institut für Fertigungstechnik und angewandte Materialforschung Winterbergstr. 28 01277 Dresden, Germany Tel: +49 (0) 351 -2537 -301 www.ifam-dd.fraunhofer.de ***Dipl.-Ing. J. Strauß, Dipl.-Ing. S. Schramm Papiertechnische Stiftung Hess-Strasse 134 80797 Munich, Germany Tel: + 49 (0) 89 -12146 36 www.cepa.de
can then be called porous metallic paper. The first trials involving different samples used as filter materials were carried out at the University of Kaiserslautern. The typical properties determined during the trials were then presented. Possible filter material application fields were also presented. The production of the materials is described in greater detail in the following. 2. Production of metallic filter papers A combination of paper and sintering technologies are used during the production of porous metallic paper. Metal powder or metal fibres as well as wood and cellulose, which are both used during the manufacturing of paper, are mixed together in a liquid as the starting materials. Afterwards they are processed with a so-called sheet former or by using a paper machine into a flat material. The material is formed on a sieve during the dewatering process which results in a compaction compaction. The defined final thickness of the paper packed with metal powder can be realised through a further calendering process. The suspension properties (mixing ratio, particle shape, particle size distribution, interparticle friction) are of huge importance as the compaction properties depend on them. The typical metal powder content lies between 75% and 85%. Metal powder and metal fibre mixtures can also
Fig. 1: Cross-section of sintered and porous metallic paper 44
be used. With these it is possible to adjust the overall porosity, the pore size distribution and the resulting surface weight within a wide range. It became necessary to develop a suitable retention/binding system for paper manufacturing due to the relatively high density differences between the cellulose and the metal powder or metal fibres. In principle, metal powder with particle sizes in the diameter range between approx. 2 and 50 μm can be processed into paper. It is also possible to create graduated structures, i.e. a structure with differently sized metal powder particles formed through additional coatings. This creates a packed paper, which exhibits a functional coating with defined properties. Porous metal papers with thicknesses ranging from 0.1 up to 1 mm were produced previously. After the packed paper sheet has been formed, a so-called cauterizing and sintering step will be run to produce the metallic structure. The cellulose and other organic ingredients will be removed in a thermal process during the cauterizing, which typically occurs between 200° and 650°C. During the sintering, which occurs between 1050°C and 1,300°C for stainless steel, the diffusion process causes material bonding between the powder particles or the metal fibres, which gives the porous structure high stability. The porosity and the pore size can be adjusted within a wide range via the parti-
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cle size of the metal powder being used, the type of cellulose (short / long fibres) and the retention/binder system. Previously, paper was manufactured with an average pore size in the 2 to 40 μm range and with a specific weight of between 450 g/m2 and 2,000 g/m2. An example of the cross-section of a sintered and highly-porous paper made from 1.4401 (316L) stainless steel with a thickness of 0.6 mm is shown in Fig. 1. This can be used to produce metallic filter materials for a wide range of applications. The flexible manufacturing processes allow the product to be optimised to meet the respective requirements. One advantage of the new technology is that it is easy to further process the paper before it is thermally treated using conventional paper technology. It can be rolled, coiled, pleated, creped or corrugated and these processes enable it to be optimised to meet different requirements. Some examples are shown in Fig. 2. In addition to this, the sintered structures can be bonded onto other metallic structures through welding or soldering, which is of great significance with regard to further processing into filter cartridges or filter discs. 3. Properties of the tested samples A total of six different samples were tested, which are referred to as A, B, C,
Tab. 1: Material properties of the tested samples
Sample
Specific mass
Sintering Thicktemperature ness
D, E and F in the following. Materials A - C differ due to the fact that different sintering temperatures were used during the production process. The surface mass varies with materials D - F. 3.1 Material properties The bubble point was determined using flow porometry in accordance with the ASTM F 316 method /3/. The bubble point gives the gas pressure at which the first bubbles in a completely wet sample can be seen to form. The pressure corresponds to the opening pressure of the largest pores in the sample. If the surface tension of the wetting liquid σ is known, it can be converted into the pressure difference Δp in an equivalent, maximum pore diameter d: (1) C is an empirical capillary constant here. According to ASTM F 316, a value
Bubble Point
Maximum pore diameter
Porosity
of 2.86 is the optimum for determining the maximum pore size of the majority of technical materials. It should be taken into consideration here that the pore cross-section deviates from the shape of a circle. A PSM 165 porometer made by Topas GmbH was used for the measuring. Topor was the liquid used in the tests. According to the manufacturer’s details, this is a perfluorinated compound with a surface tension of 0.0163 N/m, which completely wetted the usual filter materials. The maximum pore diameters in the samples being tested lie in the 8.8 μm up to 14.7 μm range. It was to be expected that particles that were bigger than the maximum pore diameter in the respective materials would be completely separated during filtration. The porosity was determined using a gas pycnometer. The material thicknesses were calculated from the specific masses and the porosities.
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Tab 2: Filtration rates of the materials used
Sample
Filtration rate at 0.5-bar in m/s
Degree of separation / %
Degree of separation / %
3.2 Filtration properties So that the filtration efficiency of the specific samples could be tested, the samples were first subjected to distilled water flowing over them in order to test if it was possible to release particles from the clean sintered metal paper. This did not occur at an significant level. Afterwards the samples were fed into a funnel filter made by BHS Sonthofen with a flow surface of 20 cm2 from an aqueous ISO medium test dust-suspension as per ISO 12103-1 /4/ with a mass concentration of 0.025g/L at 24° ± 2°C. The filtrated suspension volume amount was always 300 ml and the filtration pressure was a constant 0.5 bar. The filtrate mass was recorded by electronic scales and displayed by a computer connected up to it. The filtrate flow rate during the filtration time was virtually constant with all of the samples. The narrowing of the pores in the sintered metal paper by the separated particles was not so high during the tests so
that there was always an appreciable flow with regard to the sample’s permeability. The filtration rates realised at a pressure difference of 0.5 bar are listed in Table 2 for the sintered material samples that were tested. The values were basically determined from the specific mass, the porosity and the pore size. Samples A - C showed that an increase in the sintering temperature during production was accompanied by a reduction in the maximum pore diameter, a reduction in the porosity and a drop in the filtration rate. The results for samples D and E showed that with using the same sintering temperature an increase in specific mass or thickness causes a decreasing filtration rate. Both the suspension that was used as well as the filtrate was analyzed using the V4A Abacus mobile fluid single particle counter made by Klotz. This enables to determine the fitration efficiency of the samples. The filtration efficiency that were determined for material samples A - C as well as D - F are shown graphically in Fig. 3. It can be seen that the separation curves for all of the sintered metal papers have a similar shape. Virtually all of the particles from a particle size of approx. 8 μm were separated in all of the samples. The slight decrease in the separation curves for samples D - F for particles sizes of approx. 13 μm is explained by measurement fluctuations. With larger particle sizes the total
Particle size / μm
Particle size / μm
Fig. 3: Fractional degree of separation for samples A - C (left) and D - F (right)
Fig. 6: SEM images from sample E, 2,000 x
number of recorded particles is very low at intervals, so that any mild fluctuations here will have a huge effect on the result. It shows that a small maximum pore size is linked with improved separation of the fine proportion of the particle spectrum in samples A to C. An increase in the specific mass or thickness of the sintered metal paper will result in an increase in particle separation, which can be seen in the results from samples D - F. Several scanning electron microscope images were made from the samples in order to provide more detailed information about the types of separation. SEM images from samples A - C taken after filtration at an enlargement of 700 x are shown in Fig. 4. The sintered material is shown in white in the images. The separated particles can be seen in the darker colours. It can be seen that the structure of the sintered metal changes as the sintering temperature increases. At low temperatures the metal exists in the form of many bonded spheres, whilst the original structure increasingly fuses as the temperature increases. This shows that the finer, open-pored structure of sample A resulting from a low production temperature exhibits better filtration properties than samples produced at higher temperatures (samples B and C). The pore system is more branched in
Fig. 4: SEM images from A, B and C (from left to right), 700 x
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Fig. 5: SEM images from D, E and F (from left to right), 700 x
sample A and exhibits better particle separation and higher permeability. It can be seen that far more particles have already been separated on the surface of sintered material A as opposed to the other two materials. This applies especially to large particles from approx. 10 μm. As the particles of this size are virtually completely removed with sintered paper B and C, it can be assumed that separation partially occurs within the filter medium. SEM images from samples D - F are shown in Fig. 5. As expected, there are no structural differences in the filter media that can be seen in the images from samples D - F. An enlarged supplementary sample E structure is shown in Fig. 6. The deposited particles can also be clearly seen in the darker colours. Sample D deviates from samples E and F especially with regard to its thickness. A similar proportion of relatively large particles were separated on the surface of each. Overall, all of the sintered papers showed a good filtration efficiency. All of the particles from a particle size of approx. 8 μm were completely separated. Smaller particles were only partially separated. The sintered paper particles were separated on the surface as well as within the material. A low sintering temperature resulted in a structure with a fine, open pore system, hence a low flow resistance and improved separation were achieved. An increase in the sintering temperature causes increased fusing within this fine structure. The pore system shows less than with larger pores, hence a higher flow resistance and poorer separation. An increase in the specific mass or the material thickness results in improved separation and increased flow resistance.
The filter paper can also be used in combination with a stable and large-pored carrier material under extreme mechanical loads. Combinations with fabrics are also conceivable – they could be layered into mats, pressed and then bonded by sintering. This will form a solid bond that can accept high pressures and can be used for the filtration of highly viscous liquids. Literature: /1/ S. Ripperger: Poröse Sinterwerkstoffe und ihre Anwendung als Filtermittel. Filtrieren und Separieren 24 (2010), Nr. 3, S. 124-126 /2/ S. Ripperger: Eigenschaften und Anwendungen von Filterpapieren. Filtrieren und Separieren 24 (2010), Nr. 4, S. 178-180 /3/ ASTM (American Society for Testing and Materials) F 316 - 86 Standard Test Method for Pore Size Characteristics of Membrane Filters by Bubble Point and Mean Flow Pore Test (1986) /4/ ISO 12103-1: Road vehicles -Test dust for filter evaluation (1997)
4. Possible application areas The high porosity and the thin and stable structure of the sintered papers are the best conditions for use as filter media both with gas as well as liquids. In particular, utilisation can be introduced when the known polymer filter media can no longer be used. As the choice of filter media is clearly restricted from approx. 250°C, which means that the specific advantages of metallic filter papers come to the forefront in this temperature range. In principle, the sintered paper can be produced from different metals. Porous metallic paper can be made from chrome / nickel / steel, FeCrAl, nickel-based alloys as well as copper alloys. Stability, fracture toughness, wear and thermal shock resistance all play a role as well as porosity and pore size distribution regarding the applications. Previous results have shown that a good performance can be demonstrated both with abrupt pressure loads as well as thermal load changes. Soldering and welding are also possible. This is a huge advantage when compared to other high temperature filter media, such as porous ceramics. Metallic filters are normally easy to regenerate. The filter is burnt out in some applications, e.g. when used as a particle filter.
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Performance of new filter media – expectations and experience in vacuum and pressure filtration D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer* In process filtration, filter media are a crucial element for performance. Current demand and trends in various liquidsolid separation applications require that the filter media be adjusted to the specific product characteristics and process requirements of the user. In the past, the industry had the choice between two types of filter media: one with low resistance, providing a high level of permeability, but with lower mechanical strength; or one with higher resistance, resulting in a lower level of permeability, but mechanically strong and stable. Concessions had to be made, especially in vacuum or pressure filtration. The intention of this report is to show how a major filter media manufacturer has tackled these issues and what benefits these developments could offer the industry in the coming years. 1. Introduction 1.1 History and development of woven filter media Separation systems are used in many industries to remove undesired compounds, or to recover desired ones. These systems are utilized for many purposes including purification, concentration and clarification of suspensions, washing of processed products and management of wastes. As one method, cake filtration is particularly versatile in the wide range of options it offers for separating particles from suspensions. In combination with different treatment possibilities (i.e. concentration, agglomeration), a particle range of several millimeters, down to just a few microns is covered. The various equipment designs and operating principles of cake forming filter devices require customized and specially matched filter media to meet the process and mechanical requirements of the filter unit /2, 3/. New techniques have enabled Sefar to drastically increase the number of pores (Figure 1) and optimize the pore shape, which increases the throughput without compromising the particle retention and mechanical properties of the filter media /5, 6/.
the expectations. The big question for the development team has been to what extent these results can be transferred to the field. Figure 2 compares the number of pores with the filtration time of DLW filter media Gen 1 to Gen 3 with a 20 μm pore size: The higher the number of pores, the shorter the filtration time. This conclusion has a significant influence on filter media selection: Not only are pore shape, pore size and air permeability relevant, but the number of pores should also to be taken into account. When looking at the filter media resistance and resulting cake resistance, Figure 3 compares selected double layer weave (DLW) fabrics and shows clearly that the filtration time depends on the filter media resistance – the higher the resistance the slower the filtration time. Choosing a filter media with a low filter media resistance is essential for the shortest possible filtration time.
1.2 Laboratory results The new optimized fabrics have been thoroughly examined for pore sizes according ASTM F 316-03. In addition, a number of laboratory filter tests have been performed according to VDI-Rules 2762 /1/. The results have been very encouraging and in line with * Delia Bartholdi, Isabell Erlenmaier, Alexander Seitz, Christoph Maurer Sefar AG Hinterbissaustraße 12, 9410 Heiden, Switzerland www.sefar.com
Fig. 2: Number of pores vs. filtration time of DLW of the same pore size
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Fig. 1: Pore count development of different Double Layer Weave fabric generations
Fig. 3: Filter media resistance vs. filtration time
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Chemical
Environmental
Food
Mineral
Fig. 4: Results of fabric measurement, laboratory trials and production trials
In the above mentioned filtration tests no significant differences were found in cake height or cake dryness. Information from the field shows differences concerning this matter, which leads to the conclusion that the internal filtration test and the filtrate volume is too small of size to point out definitive results. Additionally it has to be taken into account, that the formed cake undergoes further processes, such as washing and drying, in which a different cake formation can also have influences on results. These parameters are highlighted in the following field test cases.
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2. Results from the field – case: 1 Ore beneficiation The following chapter describes the initial results achieved in the customer`s laboratory (vacuum nutsche testing) and followed by the production scale up on a vacuum belt filter. It makes use of filtration theory and the laboratory trials (Figure 4). Calcined
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Sefar AG Hinterbissaustrasse 12, CH-9410 Heiden Tel. +41 71 898 57 00, Fax +41 71 898 57 21 filtration@sefar.com, www.sefar.com
Highlights 2015
Fig. 5: Laboratory evaluation of alternative fabric – Part 1 (Physical fabric data, filtration test)
comparison of residual debris
Fig. 6: Laboratory evaluation of alternative fabric – Part 2 (Physical fabric data, filtration test) 50
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zinc ore is leached with sulfuric acid. The selection was limited to fabrics, which suit the thermal and mechanical requirements for vacuum belt filters, considering the customers’ demands: - Provide a more stable filter belt in terms of lifetime (4000 hrs +) and no elongation - Improve average filtration rate and throughput (m3/(m2*h)) to cope with increased production rate and slurry feed - Filtrate clarity shall be kept stable (≤ 1 g/l) - Moisture content target: less than 45% 2.1 Results of trials in laboratory and production scale up First, the currently used filter medium was analyzed. A double layer weave fabric was then selected in accordance with the laboratory experience, and to the measured pore size distribution of the already used single layer fabric. The replacement fabric was selected by considering the thermal (max. peak temp. 90°C or 194°F), chemical (pH ~2), and mechanical requirements (longer belt lifetime and lower elongation). Meaning the polymer and fabric finishing was selected in terms of stability against the temperature and pH value of the suspension, and the construction was chosen in order to deliver a prolonged belt lifetime. 2.2 Conclusion When compared to the currently used single layer fabric, the recommended double layer weave fabric achieved the following objectives in the field test: - 7% increase in the filtration rate - Reduced cake moisture (%) and solid content (g/l) in the filtrate - Confirmation of the lab data during 40 production days - Improved mechanical performance/lifetime due to the double layer weave construction
In comparison to conventional single layer filter media, belts made from optimized double layer weave fabric delivered improved filtration results by combining the functions of fine filtration (pore size, pore count) with enhanced belt durability. Laboratory tests and field tests confirmed that apart from pore size and permeability, other factors such as pore count and fabric design are important. 3. Results from the field – case 2: Coolant filtration Following significant changes in the production of crankshafts for the automotive industry, coolant filtration went out of control. Fines in the filtrate increased and coolant throughput decreased. Consequently, costs for the tools and the secondary safety filter grew to an unacceptable level. 3.1 Laboratory results of pre-evaluation First, the currently used filter medium and the amount of particles in the current coolant emulsion were analyzed. The fabric selection was based on the already utilized fabric by determination of the physical fabric data and the pore size distribution (based on ASTM F 316-03 /5/)). The customer demand, in respect to the desired reduction of fine particles in the filtrate entering the production cycle again, also had to be considered. The replacement fabric was selected in accordance with: - Pore size (equal or lower pore size) - Number of pores (higher number of pores) - Pore shape (rectangular instead of square shaped pores) - Mechanical and chemical aspects had to be considered as well, in order to achieve a reasonable lifetime All results are displayed in Figure 5 and 6. To achieve the particle retention target, it was recommended to change from the currently utilized single layer fabric to a double
Spaltsiebe & Präzisionsfilterrohre Slotted Screens & High Precision Filter Tubes
Sieben, Filtrieren und Entwässern in höchster Qualität! Screening, filtration and dewatering in highest quality!
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+49 (0)208 / 58 01 - 01 +49 (0)208 / 58 01 - 500 filter@steinhaus-gmbh.de spaltsieb@steinhaus-gmbh.de www.optima-spaltsieb.de
optima-16-12.1-4c
STEINHAUS GmbH Platanenallee 46 45478 Mülheim an der Ruhr Germany
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layer filter media with a matching pore size and similar permeability to achieve the desired production rate. 3.2 Production results during scale-up After the evaluation of different fabrics in the laboratory scale, the most promising option – Alternative 2 – was used for the
scale up trials in production on a pressure belt filter. The results from production at different pressure levels during the filtration cycle, regarding metal impurities in the coolant are shown below (Figure 7 and 8). The needed filtration time to achieve the limiting pressure level was increased from 30 min (Figure 7) to 90 min (Figure 8).
Fig. 7: Square mesh fabric: Pressure increase to 0.6 bar- achieved within 30 min. Throughput rate avg. is at 103 m3
Fig. 8: New double layer fabric: Pressure increase to 0.6 bar - achieved within 90 min. Throughput rate avg. is at 119 m3
Fig. 9: Comparison of metal impurities at different pressure levels
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Through this increase, triple the amount of coolant emulsion was processed. This lead to an increase in filtration capacity and a higher cake build up. In addition, the amount of fines in the filtrate was reduced to an acceptable level again (Figure 9). 3.4 Conclusion: production scale-up The field tests confirmed the theoretical thoughts and the laboratory tests as follows: - Fines in the filtrate have been reduced by 29% - Liquid throughput increased by up to 66% - Lifetime of the pressure belt doubled as a positive side effect Media resistance and resulting cake resistance, depending on fabric construction, pore size, pore shape, pore count and permeability are key elements for a successful filtration. 4. Overall summary and guidelines for filter media selection Laboratory results as well as highlighted field test cases showed the importance of the filter media selection on filtration results. Before starting to carry out laboratory or field trials, important suitability criteria concerning the filter device and application environment have to be considered: - Chemical requirements (selection of filter media polymer) - Characteristics of suspension (max. working temperature and pH) - Post cake treatment (compatibility with washing agents) - Temperature resistance (selection of filter media polymer and finishing) - Process temperature filtration (keep dimensional stability) - Post cake treatment (compatible with washing and drying process) - Mechanical requirements (selection of filter media polymer and construction) - Size of filter unit (light fabrics may not withstand) - Filter media treatment (intensive washing/cleaning processes) - Fabrication and conversion from roll good to filter media in accordance with equipment requirements and installation conditions This pre-selection reduces the possible filter media utilized within the specific application. The next topic to be clarified is the separation performance: - Required filtration capacity (selection of filter media resistance) - Characteristics of suspension - Particle size distribution - Throughput in m3/(m2*h) - Filtrate clarity - Cake dryness and quality F & S International Edition
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The first step is to analyze the current processed suspension. This gives the user a first indication of which pore sized filter media is needed. Since a large number of different weave styles are available, the following aspects also need to be considered: - Pore size - Filter media air permeability - Number of pores per cm2 - Weaving pattern Underlined by the laboratory results, the number of pores in the weaving pattern is even more important than the air permeability. This will have a significant influence on the resulting flow resistance and liquid/particle percolation. These differences influence the results in the given filter media resistance, which itself is a major factor for the filtration capacity. Next to the throughput, the filter test results help to judge the acceptable
particle retention behavior and residual cake moisture. Laboratory testing can help answer this question before scaling up production.
cesses or when optimization of the current process is done. Through that, the overall cost of ownership can be reduced and competitiveness increased.
Summarized:
Literature: /1/ VDI Guideline 2762: Mechanical solid-liquid separation by cake filtration, Determination of filter cake resistance. Part 1 and 2; Beuth Verlag GmbH, Berlin /2/ B.Sc Christoph Maurer: Publication, next generation of vacuum belt filter media. Achema 2012 /3/ H. Anlauf: Filtermedien zur Kuchenfiltration Schnittstelle zwischen Suspension und Apparat. CITplus 12/2003, GIT Verlag GmbH & Co. KG /4/ E. Ehrfeld: Influence of Filter cloth behavior on the layout of cake forming filters. Company BOKELA /5/ D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer: Eigenschaften von Filtermedien und ihr Einfluss auf die Vakuum- und Druckfiltration. Teil 1: Design von Filtermedien und Laboranalysen. Filtrieren und Separieren 29 (2015), Nr. 2, S. 98-103 /6/ D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer: Eigenschaften von Filtermedien und ihr Einfluss auf die Vakuum- und Druckfiltration. Teil 2: Resultate aus Feldversuchen Filtrieren und Separieren 29 (2015), Nr. 3, S. 177-181
Filter media resistance and resulting cake resistance depend on the fabric design, pore size, pore shape, pore count and permeability – which are key elements for successful filtration. Not only filter media manufacturers, but also Original Equipment Manufacturers point out that the choice of filter media is an important factor to be considered during filter process layout and definition /4/. Considering the filter media is an important part in the filtration process, the industry can use this provided knowledge to address challenges that may arise in coming years. Properly selected filter media can help when defining new pro-
Wire mesh used in sophisticated separating processes H. Schlebusch* The chemical, pharmaceutical, automotive, aerospace and offshore industries: efficient filtration technology is a vital part of complex production and processing in almost every sector. However not everyone is aware that the required efficiency and reliability in complex filtration processes are often only possible with wire mesh. Wire mesh is often associated solely with its best-known application - screening. GKD - Gebr. Kufferath AG – was one of the first to recognise the potential of woven media for critical tasks in process technology. As a result they specialised in the development of optimised process-specific woven media as high-tech structures. Process industries worldwide are increasingly utilising the significant advantages of made-to-measure filter media which are making processes a great deal simpler, more efficient and more reliable thanks to new material combinations and weaving technology. The received wisdom is that wire or sieving meshes are woven structures made * Hans Schlebusch GKD – Gebr. Kufferath AG Metallweberstrasse 46 52353 Düren / Germany Phone: +49 (0) 2421/803-0 Fax: +49 (0) 2421/803-227 www.solidweave.de
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of monofilament metal wires and used for screening processes. Textile meshes, it is thought, are made of synthetic or natural fibres. Metal generally has no place here. The traditional weaving machine technologies and fields of application are correspondingly diverse. Therefore the substitution of textile meshes by wire meshes or vice versa is often impossible. For a long time processing companies at the planning stage could only choose between these two starting materials and their specific advantages. In practice, however, the ideal was more often a combination of the properties of both materials and weaving technologies. An insight that quickly matured at GKD and was further developed into cutting-edge technological solutions based on wire mesh as a composite mesh. As early as the 1960s GKD got this concept up and running with a combination of monofilament wires and stainless steel cables. This resulted in the creation of flexible meshes that soon became indispensable as conveyor and process belts in numerous applications. The basis for this innovation were the decades of accumulated know-how as wire weavers that successfully met the challenge to weaving technology set by the extremely varied behaviours of wires and cables. The machine technology and above all the weft
insertion systems had to be adapted to the very divergent behaviours of the media with regard to the flexibility and stretch performance. Almost simultaneously GKD developed a weaving technique for synthetic monofilament wires made of polyester and polyamide and thereby also broke new ground for a metal weaver. For these meshes synthetic monofilaments were woven with the diameters common for stainless steel wires of between 0.2mm and 1mm. Here too the very different material behaviour with regard to stretching and stability – compared to metal wires of the same diameter – demanded the development of a suitably-adapted weaving technology. With the development at the start of the 1970s of Duofil-mesh made of monofilament wires and rods of stainless steel and polyester or polyamide, GKD achieved the next milestone in filtration and process technology. As endless filter belts for dewatering applications they were the first to combine the material advantages of synthetics such as flexibility and surface smoothness with the mechanical stability and transverse rigidity of stainless steel meshes. This combination leads to radically improved service lives despite the load on fast-running plants caused by constant flexural fatigue and narrow roll radii. The
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Fig. 1: Filter pack clad with YMAX.
Fig. 2: Wire mesh cable monofilament made of metal.
design of polyester wires in the warp direction and high-strength stainless steel wires in the weft direction ensures reliable flatness without creasing and allows very open structures with a high open screen surface. Compared to purely synthetic meshes of a similar size the substantially increased through-flow improves the belts’ efficiency in gravitational dewatering. The continual assessment of materials and their specific possibilities led GKD to develop its YMAX® filter media at the end of the 90s. Up until then mechanical robustness and excellent filtration rates were considered irreconcilable, as high retention rates require mesh geometries with very thin wires. As a result GKD developed a completely new kind of mesh structure made of mono- and multifilaments. Its multi-layered woven structure of stainless steel wires and metallic fibres made possible hitherto-unknown filter rates up to 3 μm in applications with high mechanical stress such as large-scale backflushing filters or centrifuges. Porosity up to 60 per cent, mechanical stability, flexibility, high throughput rates with minimal differential pressure and absolutely uniform pore distribution makes the new fibre-wire structure the universally-deployable filter medium for solid/liquid separation in the 20-30 μm range. Shorter filtration times and reduced use of filter aids are further advantages of YMAX® filter media. The success of these two- and three-ply structures made solely of metal materials was transferred to a growing range of utilised materials. A constant range of new high-performance textile fibres such as PTFE, glass, aramide, ceramic or basalt fibres has been combined by GKD with the stainless steel wire basic structure by means of correspondingly
adapted weaving technology. The technical weaving mill is now looking to incorporate all weavable materials into a composite mesh. As a result they are devising application-specific solutions that were considered impossible just a few years ago. For example GKD is developing cost-effective mesh designs using intelligent material combinations. Material combinations using PTFE are proving themselves in high-corrosion applications. Within the high temperature range designs featuring heat-resistant metal and ceramic materials are showing great potential. The combination of conductive stainless steel media and non-conductive polymer materials is yielding important results, the significance of which is often greatly underestimated: these material combinations open the way for filter media which are not electrostatically charged and can therefore be used to handle problematic filtrations such as solvents in particular. Furthermore these electrostatic properties improve the filtration and flow mechanisms in liquid and gas filtration. The consistent expansion of the material range, new structures and the constant adaptation of the weaving technology to the associated challenges are characteristic of the integrated solution expertise of GKD’s SOLIDWEAVE business unit. As a developer and manufacturer of high-precision meshes, optimised for the individual customer, the business unit is a world-leader in the most varied sectors and fields of application. Close cooperation with the customer and technical requirements result in tailor-made hightech woven solutions which are far removed from the classic sieve: technical mesh with intelligent added value through efficiency and progress in new directions.
Fig. 3: Duofilament as a mixture of steel and synthetic rods.
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Fig. 4: Flow simulation of the twilled dutch weave.
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The use of computational fluid dynamics for the development of filter fabrics S. Ripperger, K. Schmidt* Programs for numerical flow simulations resp. for Computational Fluid Dynamics (CFD) enable flow fields and their interlinked processes to be simulated and visualised inside apparatus and machines. This tool can also be used to intensify the development of filter media. The significant filter media features that have to be taken into consideration are covered in the following. 1. Introduction Numerical flow simulations resp. Computational Fluid Dynamics (CFD) is increasingly being used for analysing and developing technical systems. Flow fields and their interlinked processes can then be simulated and visualised inside instruments and machines. CFD provides numerical conservation equation solutions for momentum, masses and energy, at which the fluid phase properties have been taken into consideration. The most common form is a Newtonian fluid in the form of a laminar or turbulent flow that flows through the flow channel or the pore system. The equation solutions for the many very small computed cells, which fill out the geometry of the flow channel, enable the flow and the associated mass and heat transfer processes to be simulated. The benefit of this is that the corresponding flow profile is viewable before the apparatus or component is realised and the pressure loss can be determined. The flow can also be shown spatially. This in-depth knowledge enables filter media and filter units to be better optimised and updated to meet the practical conditions. The geometrical shape of the flow channels must be defined before the flow simulation can be conducted. A textile filter medium will be affected by the pore morphology, which determines the important functional properties of a filter medium. In particular, this includes the separation effect on the particles and the flow resistance from the fluids, which flow through the filter medium when pressure is applied. The complex relationship between the 3D pore structure in the fabric and its permeability and retention properties are usually determined experimentally. In this way the effect of the micropores (pores in the yarn) and the mesopores (pores inbetween the yarns) that occur in fabrics with multifilament yarns can be recorded and the thread deformations that occur during manufacture and further processing can also be taken into consideration. A lot of experimental work is needed in order to develop filter media that meet the requirements, as optimum retention and permeability properties have to be created using the trial-and-error method. Structure generators, which enable the geometry and pore morphology of fabrics based on fabric parameters (e.g. type of weave, diameters and number of filaments, mesh widths) to be generated virtually, can, by using aligned filter media in conjunction with the flow simulation, make the development of a specific application considerably easier. However, what is important here is that the respective 3D pore morphology is generated to be as realistic as possible. The stochastic geometry generation methods and the associated parameters must be taken into consideration here in * Prof. Dr.-Ing. Siegfried Ripperger, Dr.-Ing. Kilian Schmidt IT for Engineering (it4e) GmbH Luxstr. 1, 67655 Kaiserslautern Tel.: 0631-53444433 E-Mail: www.it4e-gmbh.de
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Fig. 1: Top view of a real (left) and generated (right) multifilament fabric
the case of fabrics, e,g, the deviations from the ideal structure that occur during production and further processing. The structure generation is interesting, especially with regard to the development of optimised, multilayer fabric composites or composites made from fabrics and other filter media, such as non-woven materials or perforated sheets /1, 2/.
WOVEN STRUCTURES FOR INDUSTRIAL APPLICATIONS
FILTRATION SOLUTIONS MADE OF TECHNICAL METAL WEAVES – Reliable and precise – Optimized flow properties based on simulation – Easy to maintain
GKD – GEBR. KUFFERATH AG | BUSINESS UNIT SOLIDWEAVE Metallweberstraße 46 | D – 52353 Düren | www.gkd.de
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Fig. 2: Monofilament plain weave fabric (square mesh), mesh size 50 μm, wire thickness 30 μm
2. Fabrics Fabrics rank amongst the oldest woven textiles and have been used as filter materials since very early on. The barrier effect of the filter fabric that occurs during the start phase of the filtration up to the creation of the filter cake is of decisive importance in cake filtration. The filter cake takes the separating function and the filter medium takes the support function for the cake being formed in other filtration processes. Cake formation is initiated by bridges of separated particles building up on the pores in the fabric. The result of the formation of a cake is that the separation limit will be shifted to smaller particles. Fabrics are not depth filter media. Nevertheless, this must be expected in multilayer fabrics and fabrics made from multifilament yarns, even with particle separation in the inner structure. The filtration characteristics in a cyclic operating mode that uses periodic filter media cleaning can be altered by changing the number of filter cycles used. Technical textile characterisation of fabrics The texture of a fabric results from this type of interweaving of the warp and weft threads, i.e. the weave pattern. The smallest unit is the rapport. Different types of fabrics can be produced through allocating different warp and weft thread crossover points. The simplest is the plain-weave, in which a weft is feed over and under the warps in turn. Monofilament and multifilament threads can be used as the threads. A multifilament yarn consists of a great number of fibres (filaments), which can be warped, swirled around or crimped with each other. The cross-section of the fibre can be round or any other cross-section shape. A monofilament is a thread that consists of a single filament. A wide range of fabrics can be produced based on the different types of
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Fig. 3: Pressure drop depending on the filtration velocity of water for plain weave fabric with a wire thickness of 20 μm; Solid line: simulated results for a mesh size of 20 μm (blue), 22 μm (green) and 25 μm (orange); Points: calculation according to Eq. 1 for a mesh size of 20 μm with constants from /6/
thread and the different types of warp and weft thread combinations. The pore areas in the threads between the individual fibres must also be considered with regard to a simulation in the case of fabrics with multifilament threads. In this case the 3D pore structure in the raw fabric is determined by the type of warp and weft threads (monofilament, multifilament) used, the associated fibre fineness, the warp and weft thread thicknesses and the type of mesh. A regular mesh is needed to produce an ideal fabric structure. A maximum particle diameter for a particle that passes straight through the fabric can be determined for such an “ideal” structure. However, a divergence from the ideal structure cannot be avoided in practice. Materials Fabrics are made from different materials. Filter fabrics are mainly made from synthetic or metal fibres. Natural fibres are seldom encountered. Even fabrics in which the warps and wefts are made from different materials are used. After-treatment procedure The fabric properties will be subsequently affected by the so-called after-treatment in the case of filter fabrics. Shrinking and fixing the fabric structure in place can be realised through thermal treatment. The fabric is fed through heated rollers of a calender. The high temperatures and/or the increased pressure cause the pores in the fabric to constrict as well as smoothing the surface. The calender also causes the fibres and threads near the surface to be flattened. Fabric properties Air and water permeability of fabrics are determined experimentally in addition to the technical textile parameters. The surface properties are determined in conjunction with the wetting of the pore
structure when a liquid is applied. If the surface tension of a test liquid and its contact angle in relation to the material are known, then a pore diameter distribution can be determined using the flow-pore porometry /3, 4/. Particle retention can be due to a spatial separation effect (sieve effect), formation of bridges or clusters as well as adhesion. The development or selection of a fabric for use as a filter material is treated as an optimisation process, in which these mutual dependencies have to be taken into consideration. The dependency of the pressure drop – (flow rate, on the specific filtrate flow w filtration rate), the fluid properties (density ρ, dynamic viscosity η) and the fabric structure can all be ascertained using the following equation: (1) The constants Kl and Kt are dependent on the fabric structure. The first term takes into consideration the viscous (laminar) flow and the second term is only significant if turbulence occurs. The second term can be ignored in the case of a viscous flow, so that a relationship in accordance with the Darcy equation occurs. If turbulence occurs, Philipp Forchheimer /5/ has proposed the extra term, whereby the parameter Kt will also be significantly affected by the pore structure. The pressure drop and the particle retention are normally determined experimentally in traditional filter media development or selection. The complex structure and the small structure dimensions cause minor structural changes that have a huge effect on the flow and the barrier-effect on the particles. It also presents a great challenge today with regard to theoretically generating real porous structures in filter media that deviate from the ideal structures. Up to today, the experimental results have proved to
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Fig. 4: Dutch weave (plain), cut point 20 μm, wire thickness: 50 μm warp and 36 μm weft
be a safe basis for ascertaining the actual properties of structures. However, theoretical trials based on a virtual fabric model can contribute to a significant reduction in experimental trials. Composite fabrics that are made from several different metal-wire cloths and are firmly bonded together are being increasingly used for filtration. This results in robust composite fabrics that, depending on the choice of the ply, can be optimised to meet the filtration requirements. However, it should also be taken into consideration that “additional” transfer resistance exists in the transfer area between the fabrics, so that the overall resistance can be greater than the sum of the individual resistances.
The Digital Material Laboratory for Digital Gas and Liquid Filtration
Fig. 5: Pressure drop depending on the filtration velocity of water for the Dutch weave of Fig. 4; points: simulation; dashed curve (blue): calculated according to Eq. 1 for a cut point 20 μm with constants from /6/; dashed curve (red): calculated according to constants from documents of Haver & Boecker
3. Description of the flow through a fabric using CFD The geometrical structure of the flow area must be rendered or read in and a lattice must also be created using many cells (computational grid) before running a CFD simulation. The relevant conservation equations for each separate cell will be solved afterwards. Applying the method to very fine structures presents a challenge with regard to how they exist within filter media. The fabric structure or a fabric composite can either be generated mathematically or ascertained using three-dimensional, high-resolution computer tomography and then transferred to the computer program. The three-dimensional, geometric structure of the filter
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Fig. 6: Double-layered fabric consisting of the monofilament plain weave fabric (square mesh) and a Dutch weave fabric, each with a cut point of 20 μm
medium is the start point for the numerical simulation. The results generated using the DNSlab-software are shown in the following. The program, which is continuously being expanded, also includes a structure generator for monofilament and multifilament fabrics. The virtual model that was generated was based on the default fabric parameter values. Fig. 1 shows an actual multifilament fabric and the associated 3D model generated by DNSlab. Structures based on 3D image data, as produced by micro-computer tomography (μ-CT), can also be read in and taken into consideration. Multi-ply asymmetrically structured filter media and severely deformed calendered fabrics can also be included. The discretisation for numerical calculations is based on a voxel structure in the DNSlab-software, i.e. the flow area within the filter material will be structured as a uniformly computed lattice from cubic cells (voxels). This will fill the flow channel in the filter material. The voxel size will be oriented towards the dimensions of the pores at the crossover points and the diameters of the warp and weft threads. The flow simulation can be used to calculate the pressure drop in the filter material or its permeability or flow resistance, etc. The Lattice-Boltzmann method was used for calculating the flow in the example shown here /7/. The method can be used efficiently with a voxel lattice and the transition regime from laminar to turbulent flow. Geometrically recording the pore structure and digitising it is not a problem if the DNSlab-software is used in conjunction with this method. A plain-weave monofilament fabric is shown in Fig. 2. Fig. 3 shows the pressure drop dependency on the flow rate during a
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Fig. 7: Simulated pressure drop depending on the filtration velocity of water for the double-layered fabric as shown in Fig 6 (blue curve); dashed curves: pressure drop of the single fabric layers
water flow on a fabric with a 20 μm wire diameter and mesh widths of 20 μm, 22 μm and 25 μm. The dotted curve shows the dependency on equation 1 for a fabric with a mesh aperture of 20 μm, whereby the constants Kl and Kt were taken from the book by Bruncher /6/. Appropriate calculations can also be made for a plaited fabric (Figs. 4 and 5). The simulated values are shown as red dots in Fig. 5. Constants Kl and Kt taken from the book by Bruncher /6/ (blue curve) and documents from Haver & Boecker (red curve) were used for this fabric. The results show that in the calculated cases even the smallest geometrical changes affect the pressure drop. Fig. 6 shows a composite fabric (double-layered fabric), which was generated from a monofilament plain weave fabric (square mesh) and a Dutch weave fabric, each with a cut point of 20 μm. The associated simulated values for the pressure drop for a water flow are shown in Fig. 7. The solid curve for the separate fabrics can also be determined from the addition of the pressure drops. This also corresponds to the values simulated for the composite fabric in the case under consideration, so the transfer resistance can be ignored in this case. The generated geometrical structure enables the largest diameter of a sphere to be determined using the software, which can barely be optimised for the pore system. The particle size in the two virtually generated fabrics is 20 μm. This particle size was also determined experimentally during the fabric development using complex test filtrations and spherical-shaped particles.
4. Outlook It has been shown that a numerical flow simulation can also provide good service in addition to the empirically determined methods for calculating the flows through filter media. A reduction in the development time and a lower development costs can be realised by using the simulation method. This is especially the case when the complex production of samples and their experimental trials are restricted to a minimum by a simulation. However, it must be mentioned that a complete abandonment of experimental trials cannot be recommended. Calculating multi-phase flow fields including particle/ particle, particle/wall and particle/fluid interactions during the simulation still presents a challenge. Literature: /1/ A. Wiegmann, O. Iliev, A. Schindelin: Computergestützte Entwicklung von Filtermaterialien und gefalteten Filtern. F&S Global Guide oft the Filtration and Separation Industry (2010), S. 265-272, ISBN 978-3-00-029751-9 /2/ D. Hund, K. Schmidt, S. Ripperger: Numerische Berechnung der Strömung und Partikelabscheidung in Filtrationsgeweben. F&S Filtrieren und Separieren 28 (2014), Nr. 4, S. 221-225 /3/ S. Ripperger, Ch. Schnitzer: Die Barrierewirkung von Geweben. Teil 1: Textiltechnische Charakterisierung und Barrieremechanismen. F&S Filtrieren und Separieren 28 (2014), Nr. 3, S. 110-117 /4/ Ch. Schnitzer, S. Ripperger: Die Barrierewirkung von Geweben. Teil 2: Experimentelle Methoden zur Bestimmung von Gewebeeigenschaften. F&S Filtrieren und Separieren 19 (2005) Nr. 4, S. 166-173 /5/ Ph. Forchheimer: Wasserbewegung durch Boden. Zeitschrift des Vereines Deutscher Ingenieure (VDI-Z), Vol. 45 (1901). /6/ B. Bruncher: Filtration and Wire Cloth. Wire Cloth Division Gantois Co. (1984) /7/ A. A. Mohamad: Lattice Boltzmann Method, Springer Verlag (2011)
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Filtration in the future: Innovative filter media and their manufacture for air pollution control and fuel filtration H. Lyko* Edana, the international Association of Nonwovens Industries, have been hosting the FILTREX conference together with the accompanying industrial exhibition for the last 12 years. In autumn 2014, the general manager of Edana, Pierre Wiertz, welcomed more than 150 participants to Berlin. Admittedly, filter media only have a share of around 8% of total nonwoven industry sales, but have a growth rate of around 9% per year in Europe for all types of filter media, which is an outstanding share of the nonwovens. Two trends that have a significant influence on the global market for filter media were the main focus of the event. The first is the call for new requirements regarding fuel qualities and the new conditions stipulated in the environmental legislation, which require continuous further developments in the fuel filtration sector. The other covers the challenges presented by increasing urbanisation in many countries with regard to air pollution control and in fact, both apply to protection from emissions as well as for improving the air quality in indoor areas. The answers to these challenges are new filter media developments and production processes for air and liquid filtration. Passenger transport changes Developments in the car sales markets are decisive success factors for the automobile industry as well as the manufacturers of car filters. Philip G. Gott, senior director for long-term planning in the automotive sector at IHS, a market research company, reported on the effect of urban mobility on the automobile industry and the decline of motorisation by the population in many urban centres as part of his keynote address. In his opinion, this not only depended on the economic recession but also on the fact that motorisation *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
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in large towns has reached its limit due to increasing traffic jams. New transport scenarios focus on expanding public transport services. This trend manifests itself in reduced growth chances for automobile filters. The number of new car registrations between 2020 and 2035 should reach an upper limit of around 100 million vehicles, which is approximately 30 million less than originally expected. This loss of market prospects for automobile filtration can be countered by the filter industry if they orient their activities towards future means of transport. Calls are being made for more public announcements about implementing even greater measures for improving innercity air quality, especially in buses and bus stations.
Fuel filtration trends Modern diesel engines have high requirements regarding the fuel quality directly before the injection nozzle, namely with regard to the limits for concentrations of particles of different size fractions as well as the proportion of water. During a podium discussion that was chaired by Philippe Wijns, of Hollingsworth & Vose (D), Harald Banzhaf, of Mann und Hummel, as well as Andrew Shepard, also of Hollingsworth & Vose, as representatives from filter and filter media manufacturers, Mark Wolfinger of the Lubrizol Corporation, which also produces fuel additives as well as other items, and Tobias Asam from SGS (D), a testing
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Tab. 1: Permitted number concentrations of particles in diesel fuel as per WWFC requirements and as per an injection pump manufacturer’s technical specifications
Tab. 2: Effect of the fuel parameters on the exhaust composition
and certification service provider, they discussed fuel filter requirements with regard to maintaining emission limits, the smooth running of engines and the necessary maintenance intervals. As the numerous analyses made by SGS have discovered, the qualitative differences between the fuel samples collected throughout the world are enormous and a considerable number exceed the limits set by the WWFC (World-Wide Fuel Charter, 2013 issue) for particle content. Diesel fuel should correspond to an 18/16/13 quality class before the filter. A commercial injection pump has to have an 11/8/7 quality class. The quality classes denote the number of particle concentrations that are bigger than 4 μm / 6 μm / 14 μm. The concentration ranges in accordance with ISO 4006 for the mentioned examples are itemised in Table 1. Typical particles are metallic (iron, steel), mineral (aluminium, silicate) particles as well as corrosive salts, which get into the fuel during manufacture, transportation and storage. A diesel filter must not only retain particles, but also water, which is why they are made with at least three layers, one as a particle filter medium, one as a coalescence separator and one as a drainage medium. Modern diesel filter media must have a particle retention factor greater than 99.9% and a water retention factor that is also greater than 99% and the service intervals must be between 60,000 and 180,000 km. In the future there will be an increase in the use of highly efficient filters with multi-layer / more efficient filter media, whose β value (relationship of the number of particles (4 μm) in raw fuel to the number of particles in filtered fuel) will lie at 2,000 or higher. The filter size has decreased, despite increased efficiency, as a result of the decrease in available installation space. 60
The transport sector is responsible for approx. 23% share of global CO2 emissions. In particular, the emissions from heavy lorries, construction and agricultural machines are the cause of tremendous discrepancies between the USA and the EU on one side and the rest of the world on the other side with regard to the applicable emission regulations. Even the regulations covering the fuel qualities cause huge differences. The effects of the fuel quality on vehicle emissions were discussed in detail. An overview of the important fuel parameters and their effects on the exhaust gas properties are shown in Table 2. Air filter media innovations Representatives from three manufacturers as well as two nonwoven machine suppliers presented their innovations in a discussion chaired by Monica Capello, of Ahlstrom Italy. Christian Desquilles from the filter media manufacturer, Lydall, reported on the new developments for glass-fibre filter media used in Classes F7 to E12. He showed filter test results obtained with a class new F9 V-shaped filter, the design of which was not described in detail, compared with an old glass-fibre medium, both were tested in accordance with EN779. The initial pressure loss as well as the filter’s average pressure loss of the new V-filter could be reduced by approx. 25 Pa, which resulted in a reduction in the energy consumption from 1,721 to 1,423 kWh. The low energy consumption only slightly affected the separation efficiency, but the Class F9 filter remained intact. The dust absorption capacity was somewhat higher than that of a comparable medium. Dr Jörg Meier from Johns Manville showed a hybrid filter medium made from
a glass-fibre layer, which can be embedded inbetween two layers of synthetic fibres. In this medium, which has been designed for pleated assemblies, the glass-fibres ensure filtration efficiency, whilst the synthetic coatings provide the stability. The glass-fibre medium was produced in a dry way in the cases described here. The synthetic media are dealt with as spunbond media. A particular benefit here is ability to use bi-component fibres. The three layers are bonded by calendering. When a new, three-layer medium for a Class F7 filter is compared against a conventional F7 medium made from wet-formed glass-fibres, the hybrid medium appears heavier with a surface weight of 104 g/m2 as opposed to 67 g/m2 and thicker (0.8 mm instead of 0.54 mm), but it also exhibits air permeability that is a good 10% higher. The separation efficiency in the critical particle range of around 0.3 μm increased slightly when compared to a pure glass-fibre medium. Particularly impressive for the listeners was the presentation of the screwdriver tests, in which a screwdriver is dropped vertically onto a stretched filter sample and it does not penetrate the medium. The glass-fibre medium did not pass this test. Dr Ina Parker from Ahlstrom presented the benefits of the new Flow2Save™ and Pleat2Save™ media. The Flow2-Save™ medium is available in efficiency classes F7 to H13 and it is based on a gradient structure made from synthetic fibres. It is thicker and has a higher surface weight than comparable glass-fibre media and it also has higher mechanical stability than a standard micro-glass medium. Tensile strength measurements showed that the value was 2.5 times as high as that of a micro-glass medium for the flat material test and the difference for the pleated media was even higher. Long-term comparisons of V-shaped elements against Filter Class F9 pleated media show that Flow2Save™ is clearly more efficient with regard to energy consumption (1,300 kWh) than a two-layer glass-fibre medium (1,900 kWh). The Pleat2Save™ medium mainly consists of synthetic fibres, but it also has a small glass-fibre content. It is available in M5 to F9 efficiency classes. The pressure loss difference against the glass-fibre media is not so grave, but it does affect the mechanical stability. This has resulted in the distance between the adhesive applicators for stabilising pleated packages being increased, which can save adhesive. The production of new synthetic filter media has been made possible by the development of powerful fibre spinning plants. The American BIAX Corporation, which was founded by Dr Eckhard Schwarz from Germany in 1947, was one of the pioneers of the meltblown and spunbond technologies. Prof. Behnam F & S International Edition
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Fig. 2: Simplified process diagram of a meltblown process Fig. 1: New generation diesel filters Individual component names: 1 – Particle separator 2 – Coalescence separator Type 1, 3 – Coalescence separator Type 2,4 – Sedimentation chamber 5 – Hydrophobic water barrier (image: Mann + Hummel)
Pourdehimi from the Nonwovens Institute in Raleigh, North Carolina, presented the address by Douglas Brown, BIAX. He demonstrated the basics of meltblown technology, in which the polymer with the low viscosity melts is pressed through a fine nozzle into a hot air flow (see Fig. 2). The spunbond process runs similarly in principle, whereby high viscosity melts can be used and after spinning the fibres can be positioned on the underlay and are bonded together in an additional processing stage. The significant differences between the two processes, according to Blatt und Hietel /1/, is that with the meltblown process the polymer melt threads come out of the nozzle as stretched free jets in hot air and are then laid on or rolled onto the drum, whereas in the spunbond process the already stretched and cooled fibres are swirled around and then laid down. BIAX has developed the so-called “spunblown” process, which can process both low as well as high viscosity polymer melts, whereby the additional bonding process stage becomes optional. This industrial spinning process uses multi-nozzle systems, in which there are up to 20 rows of nozzles with up to 120 outlets per cm. The process is very flexible with
regard to the polymer that has to be processed, the molten volume flow and other operating parameters. Fibre diameters between 0.2 and 10 μm are now possible. The fibre diameter of fibres from a spunblown process has a broader distribution than fibres from a meltblown process, but these fibres have a higher tensile strength. The German company, Reifenhäuser Reicofil, a member of the Reifenhäuser Group, specialises in spunbond fabric, meltblown and composite plants for the production of nonwovens. Markus Wüscht gave an insight into the relationship between the different nozzle heads and the production quantities, between nozzle diameters and fibre diameter distribution and the final effect that they have on particle retention. The use of multi-row nozzle systems includes cooperation with BIAX in this respect. All of the plant components that have to be changed or cleaned from time to time when switching production, must be designed in cartridge form. The fibre placement geometry also plays an important role with regard to the structure of the final medium in addition to the polymer that is used, the melt volume flow and the nozzle diameter. If the fibres are positioned horizontally then a relatively thin medium with small pore sizes, low permeability but with a high retention capability will be created. If positioned on a rounded and sloping downward surface the pore widths and permeability will increase but at the retention capacity’s cost. A new development, the
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so-called “high-loft meltblowns”, has been created using a special positioning design in combination with a two-drum system. They should be especially used as pre-filters with a high dust retention capability. It should also be pointed out that the fibre production and positioning also affects the filtration support during the charging of the fibres, but unfortunately, the charging principle that was used was not explained. Flame-retardant filter media A fibre composite made from cellulose or a combustible plastic will have to be made flame-retardant using an appropriate binder. Mark Wolfinger, from Lubrizol, reported about the development of such bonding agents. The development objective was formulated as being the freedom from halogens. Six different binding systems were used with one cellulose medium not only to check the flame-retardant effect, but rather more with regard to examining the resulting filtration properties. Flame-retardant chemicals should never be washed out. The cellulose medium was impregnated with 30% of the binder being tested and always dried using the same procedure. The bursting pressure, tensile strength and flexural rigidity were all determined in addition to the flame resistance, the air flow pressure loss was measured as well as the running of a complete filter test for determining the fraction separation efficiencies and dust retention capabilities. The chemical composition of the binder system that was evaluated as being the best was not divulged. Optimisation of media for liquid filtration The surface properties of filter media have an enduring effect on the filtration efficiency of liquid filters. One option that can be used for media surface treatment is low-pressure plasma coating. Eva Rogge from the Belgian company Europlasma, explained the advantages of the Nanofics® process, whereby 50 - 250 nm thick coatings are applied to filter media. The reduced chemicals consumption of under 1 g/m2, which in turn reduces the energy expenditure by a factor of 2.5 and the discontinuation of waste water or waste makes the plasma coating considerably more environmentally friendly than conventional dip-coating processes. In the meantime the process has also become feasible as a roll-to-roll system (see Fig. 3). Hydrophilated battery separator membranes, hydrophilated PTFE and especially hydrophobic diesel filter media were some of the application examples that were mentioned. At the University of Leeds, in the UK, Hamidreza Arouni has been working on the development of new media for the coalescence separation of water from diesel. This involved the basics of coales62
Fig. 3: Low pressure plasma coating plant for the nano-coating of material webs (image Europlasma NV)
Fig. 4: Global distribution of PM 2.5 concentrations, determined by van Donkelaar et al, /2/ through evaluating the spectro-radiometric data from two NASA satellites.
cence and the separation of water-droplets from the fibre structures and how the separation and the pressure loss change with the media’s structure parameters. In this conjunction the presence of tensides should also be noted, as they stabilise the water-droplets in diesel oil and can make coalescence more difficult. Fibre structures are a great help here as they stop the droplets from moving and their surface properties also help by attracting the ambient tenside molecules in the water-droplets. The effects on health from air pollution and climate change In a keynote lecture at the start of the second day of the conference, Prof. Dr Christian Witt from Berlin University’s Charité clinic, presented an extensive overview about the relationship between air pollution, heat events and medical emergencies. Accordingly, there is a correlation between the number of patients with chronic respiratory, lung or cardiovascular system illnesses and the population density. Heavily populated areas are always areas with increased temperatures, which was duly demonstrated by the temperature distribution at the Berlin conference venue and the surrounding areas. Heavily populated areas are also often linked to increased air pollution, which is clearly evident in the parts of China shown in the map in Fig. 4. An increase in medical emergencies (respiratory illness-
es) is always seen just a few days after a heat event. Around 22,000 to 45,000 deaths were traced back to heatwaves that occurred during 2003. Many people in countries with high air pollution consider the poor air quality, especially indoors, to be a catastrophe. Dust particles get into the air as a result of gaseous impurities from exhaust gases, fittings and construction materials as well as people, pets, home textiles and especially open-hearth fires. If letting air from outside in cannot contribute to an improvement due to the general air pollution, then the pollution of the interior air will be higher than that of the atmospheric air. According to details released by the WHO (2012) around 3.3 million deaths throughout the world can be directly linked to indoor air pollution. Effects on indoor air quality Dr Jörg Sievert, who represented the filter media manufacturer Freudenberg, chaired the session of lectures, in which the relationship between air filtration in ventilation systems, the polluting of atmospheric air as well as the achievable internal air quality were all discussed. Dr Claus Händel from the European Ventilation Industry Association (EVIA) reported on the current status of the revision of EN 13779 /3/ for ventilating non-residential buildings and the limitations in EN 15251 /4/, which focus on the energy efficiency of buildings and the indoor climate. Filtration is just one F & S International Edition
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function used in different types of air conditioning systems. The choice will be influenced by the quality of the atmospheric air and the supply air quality required by the constructors. The supply air cannot be equated with the interior air quality. Three quality classes exist for atmospheric air and these are considered separately for particles and gases as they differ in impurity types and concentrations, whereby only the first class lies within the WHO guidelines with regard to fulfilling the national standards. The gaseous impurities have their own EU or WHO ratings according to the specific substances used and the measuring times also differ (see TR 13779). The quality of the air fed into the buildings is sub-divided into a total of 4 different classes, of which the poorest lies at the WHO level. If the quality of the atmospheric air is poor, then the filter system should consist of a suction filter and a filter with a higher efficiency class in the outlet section going into the interior and one filter is sufficient if the atmospheric air pollution is low and a higher class filter is not needed at the outlet into the building. Filters should also be chosen according to their life-cycle costs as well as the filter class and the overall separation efficiency. Indoor air scrubbers can be used if the interior pollution is very high. The need
Fig. 5: Principle diagram for determining the local fractional separation efficiency for particulate matter filtration.
for indoor air scrubbers is especially high in China, which is why these units are widely used there. The efficiency of such units has been tested at the Institute of Energy and Environmental Technology (IUTA) in Duisburg. Dr Christoph Asbach showed the design of such indoor air scrubbers and how their efficiency is measured in the form of the Clean Air Delivery Rate (CADR) using cigarette smoke as the test aerosol. The room air that is sucked in passes through a pre-filter inside the unit being examined as well as a HEPA filter and an activated carbon filter. An UV source with a photocatalytic filter and an ioniser is connected up for this.
Apart from using the existing test standards, the units were also tested using old filters, whereby the CADR ratings clearly dropped. Dr. Thomas Klamp, of Trox GmbH, talked about the current and future state of standardisation of the testing and classification of air filters. Currently, Class G - F dust filters are considered under EN 779:2012 /5/ and HEPA and ULPA filters under EN 1822 /6/. Under EN 779 the lowest separation efficiency for a filter unloaded using isopropanol is considered to be that for 0.4 μm particles. The speaker’s criticism was that the ASHRAE test dust that was applied bore little rela-
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tion to typical atmospheric pollution. At the time the conference took place, relevant bodies were proposing a draft for a new standard (ISO 16890) in which the measuring of the separation efficiencies of the different dust fractions PM10, PM2.5 and PM0.1 are described separately. Dr. Thomas Caesar, from Freudenberg, presented a correlation between the construction of energy-efficient houses that meet the latest standards and the necessity of air filtering in order to guarantee adequate internal air filtering. Like Prof. Witt before him, he suggested that the quality of the internal air is normally poorer than that of the atmospheric air. This downgrade will be much more severe if the exchange with the atmospheric air is limited, as is the case in energy-saving houses. When planning filter plants as part of the ventilation system a balance must be made between gaining energy through the saving of heating energy and the energy that will be expended by a reasonable filter plant. Energy efficient filters were mentioned as the solution to this. If the exchange of air is limited due to the construction, i.e. if only little filtered air is fed in from the outside as supply air and fed out as interior air, then, in the author’s opinion, the effect of the filtration on the interior air quality will certainly be limited. In this session of lectures, the podium discussion was once again followed by a challenge to the design of ventilation filters. Accordingly, HEPA filters are not used in the majority of cases for energy reasons. It must also be pointed out that the volume flows for filter testing used in compliance with EN 779 clearly exceeded the real air quantities in ventilation plants used in small buildings. Filter testing, modelling and optimisation aspects Prof. Jing Wang from ETH Zurich chaired the last session of lectures, in which Sven Schütz, of Palas GmbH, reported on the importance of generating aerosols for filter testing. In the example, a Laskin aerosol generator was used as the droplet aerosol and a brush-generator for the dispersal of the test dust, the measures for checking the constant dosing showed up in the form of deviations from the average value as well as in the form of a drift away from the starting value with increased measuring times. Another property that must be considered in accordance with VDI Directive 3491 /7/ is the reproduction capability of an adjusted number of concentrations with more switching operations made by the operator. A brush-generator is driven by dry, cold air. Before it is applied to the filter that is about to be tested, the aerosol is diluted using an extra air flow, which has a specific, relative humidity. As the dust capacity of a test piece changes with the relative 64
humidity, an intermediate switching of the humidifier is recommended so that the effects of the mixture ratio between the dust generator and the dilution air on the test result can be avoided and the air humidity needed for the test piece can be set so that it remains constant. The production and testing of clean room filters showed that, in so far as it is exigent, a particle retention of 99.999% or higher in the MPPS sector must also be realised using lower raw gas concentrations. Mikael Eriksson, of Camfill, mentioned these requirements based on the practical use of the equipment in so-called biosafety laboratories and the requirements of the electronics industry. Class 15 - 17 ULPA filters could be used in the latter case as the low particle diameter that amounts to approx. 15 nm has to be taken into consideration and 99.999998% retention must be maintained. Filter testing of HEPA and ULPA filters not only includes the recording of integral values, but the local minimum separation efficiencies listed in EN 1822 are included as well. The filter testing was carried out using a spray probe that could be moved along the entire surface of the filter (see Fig. 5). The typical minimum separation efficiency of HEPA and ULPA filters lies at particle diameters of around 150 nm. The physical mechanisms for loading a filter and the development of the pressure loss with increased loading and the separation efficiency for deep bed filters is known for particles around 300 nm. Different trials carried out in the 2,500 m2 Camfil R&D Centre in Trosa, Sweden over the past few years have contributed to an understanding of the mechanism for the filtration of nanoparticles. For example, in a trial project using silver nanoparticles on filter media of different thicknesses, it was determined that the particle retention could be traced back to the effect of the media rather than the surface filter and afterwards the thickness of the filter media was increased due to the low deep bed filter effect and this did not have an improved effect. In the meantime, filter efficiency has succeeded and has been proven with particles sizes of up to approx. 1 to 2 nm. Prof. Behnam Pourdehimi from the Nonwovens Institute in Raleigh, NC (USA), reported on particle separation simulation on filter media and the development of new structures. The modelling of fibre structures has continued as part of the research work at the institute and this has ranged from single fibres to a microscale fibre entanglement and a finished nonweave up to a whole filter element. In particular, the effects of fibre orientation on the properties of the filter media being generated were recorded here and in fact they were within a specific plane as well as being perpendicular. The separation of the particles, which were clearly smaller
than the diameter of the fibre, played a minor role with regard to whether the fibres should lie parallel or not in the plane. The effect of the orientation will increase the more the fibres are orientated vertically to the surface of the filter under consideration, i.e. the fibre structure will become more three-dimensional. In addition to this the pressure loss is not appreciable when the fibres within do not lie in parallel within their plane, providing that the SVF (Solid Volume Fraction) value is preserved. The SVF value also changes when a fibre structure is calendered and flat-lying fibres start to buckle as a result of the pressure and the medium then becomes tighter to a known three-dimensional extent. The last address of the event was once again devoted to the production of nanofibres. Fred Lybrand , from Elmarco USA, presented the latest developments in NanoSpider™ technology, which is a spinning technology that does not use nozzles, but is orientated to the industrial coating of filter media. The use of the technology on an industrial scale here is clearly influenced by market requirements and prospects and some “exotic” processes such as the production of inorganic nanofibres, which has already been proven as being possible, are not taken into consideration. The intended front-line use of the technology is aimed at ventilation filters. The main focus of a quality analysis of nanofibre-coated media is on the uniformity of the medium properties in the surface. This was certified by measuring the air resistance at the measuring points distributed over the cross-section of the material web in relation to the movement feed direction. The measured variations in the transverse and longitudinal directions were less than those for micro-porous membranes. The stability of the production processes over a long period of time and with up to nearly 18,000m2 of filter medium can be confirmed. Literature: /1/ Blatt, T., Hietel, D.: “Nano”- Meltblown-Fasern: Technologieentwicklung durch Verknüpfung von Simulation und Experiment, Vortrag, 27. Hofer Vliesstofftage 2012 /2/ van Donkelaar, A.; Martin, R.V. et al.: Global Estimates of Ambient fine Particulate matter Concentrations from Satellite-Based Aerosol Optical Depth: Development and Application; Environmental Health Perspectives June 2010, 118(6), S. 847 – 855 /3/ DIN EN 13779: 2009 Lüftung von Nichtwohngebäuden – Allgemeine Grundlagen und Anforderungen an Lüftungsund Klimaanlagen /4/ DIN EN 15251: 2007 Eingangsparameter für das Raumklima zur Auslegung und Bewertung der Energieeffizienz von Gebäuden – Raumluftqualität, Temperatur, Licht und Akustik /5/ DIN EN 779: 2012 Partikel-Luftfilter für die allgemeine Raumlufttechnik /6/ DIN EN 1822: 2011 Schwebstofffilter (EPA, HEPA und ULPA) /7/ VDI 3491:2012 Messen von Partikeln – Herstellungsverfahren für Prüfaerosole F & S International Edition
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Improvements in aerosol technology facilitate aerosol research, filter development and filter testing H. Lyko* Manufacturers and users of filters and separators now and then ask the question as to whether the efficiency parameters determined in a laboratory really do equate to those of working plants and this is not only since the VW exhaust gas scandal became known. The reason for any discrepancies is not normally the conscious need to secure an economical advantage, but is mainly to do with the difficulties of creating a real operating situation, especially with regard to long running times under changing conditions that are sufficiently representative in a test scenario restricted by time and space. The test piece efficiency requirements (emission limits or MAC values) also change with growing recognition and increased understanding of the effects of airborne pollutants as well as the efficiency of the measuring technology used for testing filters. Last year’s 29th Palas aerosol technology seminar yet again provided numerous opportunities to discuss the status of test equipment, test procedures and the status of national and international standards covering the generation, measuring and separation of particles as well as those for diverse application sectors. This ranged from aerosol and particle production to medical issues, exhaust gas testing of automobiles, air measuring processes and classic filter testing up to the ongoing filtration technology research work. Developments at Palas The event started off with the CEO of Palas, Leander Mölter, presenting an overview of the latest developments in the company’s structural organisation and the products. The company, which has now existed for 32 years, can refer back to 4,450 units being sold (up to the point in time of the seminar) and this figure includes nearly 2,000 aerosol generators. The generation change at the top was initiated by the involvement of Dr-Ing Maximilian Weiß as a partner and his *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
further appointment as the director of development and production. By their own account, Palas is market leader for product groups such as filter test systems, aerosol spectrometer systems, particle generator systems, diluting and calibration systems. The company’s know-how is protected by more than 60 patents and 100% in-house production. Every year the portfolio is extended by several new products or model versions every. A new measuring system, which was not described in detail as part of the presentation, is a condensation nuclei counter, which has been designed for measuring atmospheric air over long periods without any dilution. The ENVI CPC (Fig. 1) has a cut-off of
7 nm and it can count particles up to a concentration of 2 million/m3. Current status of exhaust gas technology used in diesel vehicles The evaluation of the quality of the exhaust gas emitted by diesel vehicles not only includes the noxious gas concentration and the emitted particle mass but also the particle count emitted per kilometre, which has been stipulated since the introduction of the Euro 5b Emission Standard (see Table 1). A condensation nuclei counter is used in a defined test set-up (i.e. a PMP measuring section) for measuring this particle count. The exhaust
PM1, PM2.5, PM4 & PM10 ͕ ƉĂƌƟĐůĞ ƐŝnjĞ ĚŝƐƚƌŝďƵƟŽŶ EĞƚǁŽƌŬͲĐŽŵƉĂƟďůĞ͕ ƌĞŵŽƚĞ ĐŽŶƚƌŽů ďLJ ƚĂďůĞƚ /ŶƚĞŐƌĂƚĞĚ ĐĂŵĞƌĂ ĨŽƌ ĚŽĐƵŵĞŶƚĂƟŽŶ ^ĞŶƐŽƌ Θ ĂůŐŽƌŝƚŚŵ ŝŶ ĂĐĐŽƌĚĂŶĐĞ ǁŝƚŚ ĐĞƌƟĮĞĚ &ŝĚĂƐΠ ϮϬϬ ^ ϬϬ ^ &ŝĚĂƐΠ &ƌŽŐ DŽďŝůĞ ĮŶĞ ĚƵƐƚ ŵŽŶŝƚŽƌŝŶŐ ƐLJƐƚĞŵ
less is not enough
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Fig. 1: ENVI-CPC 200 condensation nuclei counter for monitoring atmospheric air without using a dilution system (the system includes a butanol tank, image: Palas GmbH)
gas is diluted with air before it can reach the particle counter and larger particles (> 2.5 μm) are separated in a cyclone afterwards and the volatile particles are removed in an evaporation zone or a catalytic stripper. As Prof. Reinhard Niessner from the Institute for Hydrochemistry at the TU Munich explained, deviations of up to 25% of the measured particle counts can occur when different test stands are used. These differences can be traced back to the performance characteristic variations of the counters made by different manufacturers, which show deviations of around 18%. This could be confirmed by measuring the counting rates of different condensation nuclei counter (CPC) by using model aerosols. The same aerosols were classified with a diffusion battery and subsequently measured by using a reference CPC as well as a SMPS system for comparison purposes. In addition to the deviations in the counting efficiency of CPCs made by different manufacturers, the measured particle count and the particle size distribution were also affected by the surface modification of the exhaust particles (soot particles). Such surface modifications occur in real exhaust gas measuring, when volatile hydrocarbons accumulate on the soot particles. This relationship was made visible in the test set-up by coating with n-hexadecane. The particle number measured in the PMP section was also considerably affected by the proportion of volatile particles that had not been eliminated previously. It was shown that the count difference of H2SO4 nanoparticles and oxidised tetracontane particles was a lot higher than that of pure soot particles due to their better wettability, so that overall, there was a higher particle concentration in the exhaust gas.
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Fig. 2: Design of the AIDA cloud simulation chamber and measurement curves for a typical cloud experiment using desert dust (imag: Institute for Meteorology and Climate Research Atmospheric aerosol research at KIT.
The effect of the CPC count efficiency on the measurement result from the PMP section was also very explicit in the presentation given by Dr Maximilian Weiß, of Palas. According to the PMP measuring section requirements, the counting efficiency of a CPC for particles sizes of 23 ±1 nm must be 50% and 90% for 41 ±1 nm. These requirements correspond to the existing definitions of the options for a commercial condensation nuclei counter. The CPCs made by other manufacturers exhibit other counting efficiencies that depend on the particle size and this proof was based on the measurements carried out in the calibration laboratory at the Leibniz Institute for Tropospheric Research in Leipzig using a CPC from Palas. The cut curve in the Palas unit runs in a very steep range between 23 and 41 nm and the counting efficiency of 41 nm clearly lies above 90%, so that overall, more particles can be recorded in this size range. Palas also provide a thermal dilution system for removing the volatile particles in addition to the measuring set-up for particle counting. The PMPD 100 “thermal diluter” consists of a 1 m long, flexible and heated tube in which the exhaust gas is heated up to 200°C and two dilution stages, in which an overall dilution ratio of 1:100 can be realised. According to the instructions for the PMP measuring section, the volatile tetracontane (C40H82) particles with a mobility diameter that reaches 30 nm must be completely removed (evaporation). The thermal diluter was used at the Swiss Federal Institute for Metrology (METAS) for measuring together with a 30 nm tetracontane aerosol and with a VPRE (Volatile Particle Removal Efficiency) of 99.967% and a measuring inaccuracy of 0.024%.
Aerosol measuring in special application cases Basic particle measuring units have been designed for use with applications under normal pressure and temperatures. The unit’s performance characteristics must be known for conducting tests under clearly different conditions. A typical application area for a particle counter working under reduced intake pressure and very low temperatures is cloud research and this is implemented in real time using aircraft measurements from the upper troposphere as well as in a simulation reactor, in which the pressures and temperatures can be simulated within the different air layers in the Earth’s atmosphere. Dr Ottmar Möhler from the Institute for Meteorology and Climate Research at the Karlsruhe Institute for Technology (KIT) reported on comparative measurements made using TSI CPC 3025 and 3772 condensation nuclei counters as well as the Palas UF-CPC 200 in the aerosol chamber at the AIDA reactor in Karlsruhe (see Fig. 2). Starting from a pressure of 1,000 hPa the pressure is reduced in decrements of 200 hPa during a series of measurements until it has dropped to 200 hPa and it is then increased in two 400 hPa increments back to 1,000 hPa. These pressure variations were carried out using aluminium sulphate test aerosols (in two concentrations), Arizona test dust and soot (produced by spark discharching from a graphite electrode). The two TSI 3772 and UF-CPC 200 counters provided particle measurement values at all pressure levels and the same particle concentrations in the ranges between 1,000 and 500 hPa. The counting efficiency of the TSI unit dropped with the further drop in pressure, whilst that of the Palas unit increased. The latter reacted to pressure changes and pressures under
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Tab. 1: Development of emission limits for cars with diesel engines in Europe
500 hPa with severe fluctuations in the particle concentrations that were displayed. These were traced back to fluctuations in the sample flow rates, so that the measurements had to be repeated using a stabilised sample flow rate. Another special aerosol technology application was presented by Dr Otmar Schmid from the Helmholtz Centre in Munich, where practical studies into administering medication from an aerosol are taking place as part of the development of medication against lung diseases. During the pre-clinical phase a newly developed active agent was previously pipetted directly onto the cells, which formed an air / liquid boundary layer. Aerosols were hardly ever used for this beforehand. Schmid presented a new type of system, in which a test aerosol purposely makes contact with a cell culture, in a method that is similar to inhaling medication into a lung. In this system, which is called ALICE-CLOUD (Air / Liquid Interface Cell Exposure Cloud, see /1/) the cells are found with the liquid in a microtitre plate on the floor of a cubic chamber and an aerosol cloud is sprayed over its surface. The air resistance slows this cloud as it drops down and flow turbulence occurs at the same time, which ensures even horizontal distribution of the particles or droplets. This creates an even mist from the cloud, which slowly falls down onto the cells. The process runs at a small scale, as new active agents are only available in very small quantities for pre-clinical studies. A quartz-crystal micro scales is used with the dosing and the atomiser is a commercially available aerosol generator, which is also used to administer medicaments during artificial breathing. Biomass combustion is another application field for aerosol measuring technology and it has high relevance with regard to the formation of fine dust. The need for low emission plants exists for households, whereby an increase in emissions through user errors should be excluded as far as possible. A ventilation-controlled small furnace with a fully automated feeding system has been developed at the German Biomass Research centre in Leipzig.
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Dr. Ingo Hartmann reported on the simultaneous use of SMPS measuring units, Optical Particle Counter (OPC) and a Photoelectric Aerosol Sensor (PAS) for detecting PAC accumulated on the particles as well as a gravimetric dust measuring device and a measuring system for gaseous exhaust gas ingredients in this small furnace plant. An application for a patent covering the design of this plant had been made. The goal was to evaluate the effect of the combustion conditions and the adjustable parameters such as air and the supply of fuel as well as the effects of the starting-up and shutting-down processes on the emissions. Catalysts were also tested on ceramic sponge carriers. The results of the exhaust gas tests have shown that with this furnace it is possible to obtain dust values with a factor of 100 lower than the presently installed domestic heating systems. The dust concentrations amount to less than 5 mg/ m3 as is the CO content of the exhaust gas when the furnace is run with a Lambda value for the excessive air is 1.2 to 1.8. In general, reproducible test conditions can also be accieved. The plant is used for studying catalysts and work on the transferring of plants that are close to market is also planned. Industrial production of nanoparticles In 2013 Prof. Andreas Schmitt-Ott, from the TU in Delft, presented and showed options for producing metallic nanoparticles through spark discharges that are part of the BUONAPART-E (Better Upscaling and Optimisation of Nanoparticle and Nanostructure Production by Electrical Discharges) EU project, which started in 2012 /2/. An alternative production method was developed as part of this EU project at the Institute for Nanostructure Technology at Duisburg University in Essen, in which the principle of discharging a flashing arc was optimised and optimised production units were upscaled through parallel switching. Dr Matthias Stein explained this process (see /3/), in which thermal plasma is formed by igniting an arc between two electrodes. This process vaporised the anode material
and the corresponding nanoparticles were created from the vapour whilst it cooled down. In essence, the factors that affect the production rate, which were also tested during the development of this system, are the choice of the anode material and the applied current, the shape of the crucible (which also includes the gap between the electrodes) and the composition of the carrier gases. Fig. 3 shows the optimised crucible. The amount of current applied can only increase the production rate in a limited manner as the particles become too big, if a material-dependent limit is reached. This arcing process produced even bigger quantities of particles than they can be supplied by the spark discharge process that was described in 2013 as the primary particles were somewhat bigger. For example, the silver particles created here were between 10 and 120 nm, whereas it is also possible to create primary particles under 10 nm using spark discharging. If a carrier gas component that reacts with the anode material is chosen for the arcing process, then reactive nanoparticle synthesis (e.g. the production of nitrides) is also possible. In the meantime there now exists a plant with 8 parallel electrode chambers (see Fig. 4). Assessing health risks from nanoparticles Nanoparticles, which cannot be solved in human bodies and do not have to be classified as toxic due to their chemical composition, are also ascribed a harmful health effect, as they exert so-called inflammatory stress, in which intruding foreign bodies overstress the necessary macrophage by depleting it /4/. Dr Otmar Schmid, from the Helmholtz Centre in Munich, answered the question about which dosing parameter is the most suitable to use for risk assessments. Ten different published studies involving laboratory animals were evaluated in the literature for clarification and the doses for an inflammatory reaction from the pulmonary tissue were compared in relation to the surface of the lungs. When compared to the particle mass, particle volume, characteristic length and BET surface parameters with regard to their correlation for a cell tissue reaction, the BET value exhibited the best correlative value for low soluble and low toxic particles. In addition, the inflammatory effects were increased by metallic particles and sharp-edged quartz particles. The particle count is relatively unreliable as a parameter, as the flammable dose clearly depends on the particle size. Special status is given here to fibres with lengths from approx. 5 μm as particles with expansions above this length can no longer be processed by the macrophage, so the number of fibres is once again relevant.
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Fig. 3: Optimised crucible for producing metallic nanoparticles by discharging a flashing arc (image: Nanostructure Technology Department at Duisburg-Essen University)
Status of standards and guidelines for different aspects The preparation of test aerosols plays a decisive role during the quality testing and calibration of particle test equipment as well as during filter testing. Dr Nobert Höfert from the VDI’s Commission on Air Pollution reported on the status of the revision of VDI Directive 3491, which was published during the 1980 to 1996 period and contained a total of 16 sheets. 6 sheets have now been withdrawn during the revision, as single types of aerosol generators are no longer described and the classifications are now based on the unit’s active principle. In addition to Sheet 1 (“Basic principles and overview”) and Sheet 6 (“Transport and conditioning”) the other remaining sheets are Sheets 2 to 5 for the “Dispersion of liquids”, “Dispersion of bulk materials”, “Condensation processes” and “Chemical reaction” active principles. The possible particle materials, the active principles and the currently available technical realisations are described in these sheets. Anyone who wants to produce an aerosol in accordance with this directive, is not obliged to buy a commercial unit. In the meantime, the well-known, non-commercial particle generator developed by Scheibel and Porstendörfer, in which the particles are created through condensation /5/, has frequently been copied. Increasing quality improvements to filter media and the updating of filter testing standards have resulted in the necessity to adequately define the test dust that is used for the testing in detail and to control the test dust quality during production. The DMT Group is involved in both testing products with regard to air quality by using test dusts as well as producing test dusts. Dr Dirk Renschen showed which
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Fig. 4: Plant with 8 pairs of electrodes for producing metallic nanoparticles by discharging flashing arcs (image: Nanostructure Technology Department at Duisburg-Essen University)
test dust listed in the various test standards can be used and where possible ambiguities and measuring inaccuracies caused by poorly defined test dust can be expected. This applies, for example, to the Pural NF test dust when testing regenerable filter media. As the manufacturer cannot give a guarantee with regard to the particle size distribution, this dust, an aluminium hydroxide derivative, is only suitable for comparative measurements. In the testing carried out in compliance with EN 779, ASHRAE test dust is allowed to be dusted on in undefined concentrations and it was feared that an inaccuracy was caused with regard to the state of the charge by the effect of the dust concentration on the media. The ASHRAE dust, a mixture whereby 72% of the weight is A2 Fine Test Dust (as per ISO 12103-1), 23% of the weight is carbon powder and 5% of the weight is ground cotton linters, is specified in great detail, but despite this it is impossible for different providers to produce the same test dust, so that comparable measurements should only be made using test dust from the same provider. The testing of air filters for household applications was carried out using a synthetic dust, which is similar to ASHRAE dust. Renschen described the quality control measures carried out with DMT’s Type 8 synthetic house dust, which consists of 70% mineral dust, 20% short-fibre cellulose and 10% chopped cotton fibres. The quality control starts with the incoming goods checks for the raw materials being used. The particle size distributions of mineral raw materials and products are determined using laser diffraction and sieve analyses. Lengths of up to 4 mm for the relative fibre quantities and permitted deviations have been defined for a total of
6 length classes of the cotton fibres. A test cutting is carried out from a fraction of each new incoming batch of cotton and the cutted material is measured in an external test laboratory. The bulk density and the fibre moisture are determined during internal quality checks and the introduction of a fibre length determining process using digital image processing is also planned. The new ISO 16890 test standard has already been announced for the Palas ATS 2014. Thorsten Stoffel from DencoHappel (previously known as GEA Air Treatment), who is a member of the standardisation committee, reported on the expected changes. They are described in detail in the following article. Fidas certification news The official announcement of the suitability of the Fidas fine dust measuring unit for “the continuous parallel immission measuring of the PM 10 and PM 2.5 fractions in airborne particulate matter in stationary use” was made in April 2014 in the German Federal Gazette (see: www.qal1. de). Karsten Pletscher, of Palas, reported on the progress of the certification during previous years /6/. This time he referred to the specific and controlled further development of the measuring device, which will have to be optimised in compliance with the amendments to the EN 15267-2 standard that is expected to be announced in 2016. Previouly it was only permitted to make changes to an initially certified unit without it having to lose its certification during a period of 5 years after the first certification. In accordance with the new standard the option exists to further optimise a measuring device over its entire service life. Depending on the magnitude of the changes, which relate to the unit’s
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hardware as well as its software, it must be certified either internally (by the manufacturer) or through external testing that the changes do not degrade the unit’s performance. Relevant changes require a notification or a supplementary test report to be sent to the certification office, so that the revised certificate can be published in the German Federal Gazette. Since the initial certification was issued, the indoor version, Fidas 200 has already been approved as well as the detailed changes such as a new LED, another digital output jack socket, the current unit firmware and a new display structure for the unit’s software. Filter testing for different application cases Industrial dedusting using regenerable filter media often has to take place at high temperatures, i.e. at cement producers or waste incineration. High air humidity can also occur. Such extreme conditions are not foreseen in VDI 3926 for testing regenerable filter media. A suitable test stand for this that can also be operated using different, industry-oriented dusts, is often required by filter manufacturers. Palas have now satisfied this requirement with their new MMTC 2000 EHF (Fig. 5) test stand and Martin Schmidt described the design of this test stand, which can realise test temperatures of up to 250°C as well as relative humidity of 80% (at a test temperature of 90°C). Directly generated water vapour is diluted with air in the mixing chamber for creating the relative humidity. The test dust is dispersed by the RBG 2000 brush generator and is fed into the system with the help of the dispersing air, than it is heated together with the humidified air. Measurement curves were shown during the presentation, in which the precise settings for a constant temperature and humidity were confirmed. The volume flow measuring takes place behind the gravimetric final filter and therefore within the heated zone. Test operations in which Pural NF test dust was used for the dusting were checked to see how good and how quickly the different relative humidities could be set up inbetween the different test sequences. They showed that cycle times with the temperature increased to 250°C were shorter and that the dust emissions increased simultaneously. The air was also very dry at this temperature (relative humidity <10%). A lower temperature of 90°C and a higher humidity of 80% will result in longer cycle times and less residual pressure losses. The new DIN EN ISO 10121-1:2015-10 standard for testing adsorptive filter media was published in October last year /7/. The Institute for Energy and Environmental Technology (IUTA) in Duisburg and
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Fig. 5: MMTC 2000 EHF test stand for regenerable filter media, increased temperatures and air humidity (Photo: Palas GmbH)
Fig. 6: Typical pressure drop gradient for regenerative surface filters (wird noch mit englischer Beschriftung versehen)
the Institute for Nanoparticle Process Technology at the Duisburg University in Essen have been running a joint research project for evaluating and optimising test procedures for adsorptive filters for updating this standard. Dr Uta Sager described the different test stands used at IUTA, which, partially through modification, are suitable for the testing of adsorptive filter media as well as the series of measurements that were previously carried out. The test stand at IUTA that has been modified for toxic substances as well as the test stand for cabin air filters at Duisburg University, which is equipped with a bypass adsorber for media samples up to 113 mm in diameter, can be called upon for the testing of adsorptive filter media. A ventilation filter test stand that complies with EN 779 was used at IUTA for
testing entire filter elements. The cleaning capability of a filter medium corresponds to the quantity of hazardous gas that is adsorbed until penetration of this gas component to the clean gas side of the filter is detected. The test gas concentration can be increased in order to accelerate the measuring up to penetration comparative to real operating times. In the first measurements that used toluol and butane as the front line test gases, run on different test stands under the same test conditions (temperature, relative humidity, flow rate) produced results that could be compared against one another. Comparable results were obtained both from the testing of the same media on different test stands as well as through comparisons between the medium and the resulting finished filter element.
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Ralf Heidenreich from the Dresden Institute for Air Handling and Refrigeration described a plant for testing the efficiency of filtering separators in 2014 /6/. This type of efficiency test is similar to the filter classification used for ventilation filters. The testing of filter plants that are installed in dusty workplaces and that return the cleaned air to the room were relatively difficult, as the low clean gas concentration required by the corresponding standards was often at or below the detection levels of the test instruments that were being used, especially when it was a gravimetric measurement that had to be made. The gravimetric determination of the clean gas concentration was supplemented here using counting measuring processes (CPC) or optical processes (photometer). The filter surface stress stipulated by the test standard was difficult to produce on the raw gas side in many cases, as the existing ventilators could not provide the required quantity of air. The resistance characteristics of the filter elements must be taken into consideration during possible classifications. The pressure drop coefficient of a typical low pressure filter element (filter pocket) can, using the same Reynolds number, be lower than a high pressure filter element (filter plate) by up to two orders of magnitude. In future application cases, the tests should also be run using nanoscale particles and the filter cake properties should also be taken into consideration. Measuring the fractional separation efficiency, i.e. the retention by a filter medium of each specific size class, is an important component of filter testing, and optical particle counters are used here as standard test equipment. Sven Schütze, from Palas, showed that concentration measurement variations for raw and clean gas could be realised in different test stands. If the raw gas concentration can be stabilised, then this can be measured in the clean gas channel before installing the test filter. Then the test filter is installed and the clean gas concentration is measured behind the filter. The separation efficiency is calculated from concentrations and particle size distributions in raw and 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
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clean gas. Another option when using a single aerosol spectrometer is to switch between the sample probes in the raw and clean gas channels. With the installation of optical fibre cables, which transfer the signals from each of the aerosol sensors in the raw and clean gas channels to a joint control unit, then errors in the next stage caused by the build-up of particle deposits in the air lines or at the switchover valve, which is always possible in the version with two sample probes, will be prevented. In order to ensure that the optical switching between the raw and the clean gas sides fitted on the filter test stand can produce reproducible measurement values, a “round-robin” test was run using units of three different ages (3 and 8 years and a new unit) to prove this. The latest development for determining the filtration efficiency factor is simultaneous measuring using two Promo measuring systems at two measuring points in front of and after the filter, in which both evaluation units are connected to the evaluation computer via Ethernet. Simultaneous measuring is enabled by the new MPSlave software that controls both measuring systems. Current filtration research work Dr. Kilian Schmidt from the Institute of Mechanical Process Engineering at TU Kaiserslautern reported on the comparisons between the measurements and the calculations of the efficiency of wire meshes used for droplet separation. The measuring technology is described in greater detail in /6/. The simulation procedure used the DNSlab program is clarified in this magazine using a wire mesh example (see Page 55). Dr. Qian Zhang from the Institute for Particle Technology at Wuppertal University presented a research concept for quantitatively forecasting the longterm operating characteristics of cyclically regenerated surface filters. It is generally known that the residual pressure drop continually increases in surface filters as the number of loading cycles increases (see Fig. 6) and the filter irreversibly ages. The filtration cycles between two cleaning
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
phases can be extended through the use of specific filter structures / surface fittings and the increase in the residual pressure drop gradient also depends on the filter medium, but the relationship between the filter structure and changes to the operating characteristics has still not been quantified. This should now be investigated by combining the measurement of the pressure / time curves during the dusting and the determination of the time-dependant residual pressure drop with the analysis of the dust deposits and the medium’s structural changes by using imaging techniques at different points in time whilst the filter ages. These extensive tests should be carried out for differently structured filter media, so that it would be possible to describe the surface properties of the filter media using quantitative parameters. The changes to a filter medium’s operating characteristics over time can be predicted if they are based on these parameters. Literature: /1/ Lenz, A-G.; Stoeger, T.; Cei, D.; Schmidmeir, M.; Semren, N.; Burgstaller, G.; Lentner, B.; Eickelberg, O.; Meiners, S.; Schmid, O.: Efficient Bioactive Delivery of Aerosolized Drugs to Human Pulmonary Epithelial Cells Cultured in Air-Liquid Interface Conditions; American Journal of Respiratory Cell and Molecular Biology Vol. 51 (2014) No. 4, S. 526 - 535 /2/ Lyko, H.: Höhenflug der Aerosoltechnologie – Bericht vom 27. Palas Aerosoltechnologieseminar, F&S Filtrieren und Separieren 27(2013) Nr. 6, S. 379 - 385 /3/ Stein, M.; Kiesler, D.; Kruis, F.E.: Adjustment and Online Determination of Primary Particle Size in Transferred Arc Synthesis of Copper Nanoparticles; Aerosol Science and Technology 47 (2013), S. 1276 – 1284 /4/ Lyko, H.: Nanomaterialien am Arbeitsplatz: Herausforderung für den Arbeitsschutz?, F&S Filtrieren und Separieren 25 (2011) Nr. 4, S. 230 – 232 /5/ Scheibel, H.G.; Porstendörfer, J.: Experimental results on saturation ratios and detection limits of an absolute condensation nuclei counter; Journal of Aerosol Science Vol 14 (1983), Issue 3, S. 383 – 387 /6/ Lyko, H.: Partikelmesstechnik und Filterprüfung nach neuestem Stand; F&S Filtrieren und Separieren 28(2014) Nr. 6, S. 337 – 343 /7/ DIN EN ISO 10121-1:2015-10 Methode zur Leistungsermittlung von Medien und Vorrichtungen zur Reinigung der Gasphase für die allgemeine Lüftung – Teil 1: Medien zur Reinigung der Gasphase (ISO 101211:2014, deutsche Fassung)
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Testing of air filters in compliance with the new ISO 16890 H. Lyko*, T. Stoffel** The new ISO 16890 test standard has been available in draft form since 2015 /1/. It is to be expected that it will be harmonised in various countries during 2016 and that it should come into force in 2017. ISO 16890 will supersede the currently used EN 779 /2/ standard at European level for Class G1 to F9 air filters. This will also affect the areas of application of the ANSI / ASHRAE standards 52.2-2012 /3/. For the first time ISO 16890 will determine an air filter‘s efficiency class by using its efficiency factor for the environmental measuring of the relevant PM10, PM2.5 and PM1 particulate matter classes. Certain test procedure details will also be changed when compared to the existing standards in addition to the classification of the filters into efficiency classes. The previous filter classes according to EN 779 and the ANSI / ASRAE standards still remain important criteria for selecting filters and filter combinations for ventilation systems. The European EUROVENT manufacturers association has accepted the classification of filters into energy efficient classes in accordance with the efficiency classes listed in EN 779. All of these measures must be revised and optimised by the time that the new ISO 16890 comes into force. 1. Introduction For many years now, particulate matter pollution in the atmospheric air has been measured by measuring stations in the German Federal States and by the Federal Environmental Agency as well as by public measuring stations in other EU countries. Up-to-date values for the PM10 and PM2.5 particle fractions are published on the appropriate internet sites belonging to the Federal States‘ environmental agencies and the Federal Environmental Agency (FEA) and annual particle fraction evaluations are also issued by the FEA. The PM1 fraction, which is also examined for respirable particulate matter, cannot be explicitly measured overall. If the evaluation of air quality is based on the concentrations of the particle fractions mentioned above, it seems only logical to evaluate air filters using the same criteria. However, this is not the case with the current valid EN 779:2012 test standard, as the overall filtration efficiency of a particle collective (for coarse dust filters) or the efficiency factor for size 0.4 μm particles (for M and F classes) are used as the criteria for the classification of filter classes. The American standard already defines the minimum efficiency factor for various particle size classes /4/. The fact that a filter test according to EN 779 does not directly provide information about the air quality to be achieved by the respective filter with regard to the relevant particle size classes was certainly an important motivation for preparing the new ISO 16890. This draft will be harmonised in various countries this year, so that it can come into force in 2017. The most important and up-to-date parts of the new standard are described in the following as well as the resulting changes applicable to the manufacturers, testing institutes and equipment manufacturers.
Fig. 1: Example of air filters installed in a HVAC plant (photo: DencoHappel GmbH)
average efficiency factor for 0.4 μm particles with Class M and F filters. The filter‘s dust collecting capacity is determined by loading it with synthetic test dust until the final pressure difference listed in the Table 1 can be determined. Dust that complies with ASHRAE is used as the test dust, which consists of 72% mineral dust (A2 fine test dust as per ISO 12103-1), 23% carbon powder and 5% chopped cotton fibres. Class F particulate matter filters First filter test system according ISO 16890
2. State-of-the-art filter testing according to EN 779 and ASHRAE 52.2 Under the European EN 779:2012 standard, air filters are classified according to the average filtration efficiency using synthetic test dust (Class G coarse substance filter) or according to the *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696 ** Thorsten Stoffel M.A. Filter division product manager, DencoHappel GmbH Südstraße 48, 44625 Herne, Germany Tel:+49 (0) 2325 46843 Email: thorsten.stoffel@dencohappel.com www.dencohappel.de
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ALF 114 General Air Filter Test System
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Tab. 1: Classification of air filters into filter classes in accordance with EN 779:2012
Tab. 3: MERV (Minimum Efficiency Reporting Value) criteria in accordance with ASHRAE 52.2:2012, 2015 supplement /4/
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determined from the six test cycles that are run consecutively. A new filter medium is used in the first of the six test cycles. The test piece is loaded with synthetic ASHRAE test dust during the following test cycles /5/. The E1, E2 and E3 range efficiency factors are the result of the classification in accordance with MERV (Minimum Efficiency Reporting Value), which can be found in Table 3. It is not just the MERV value that is needed to determine this value as the filter flow rate is also required for the final classification of a filter in compliance with ASHRAE 52.2. The standard specifies a total of seven different possible velocities for testing the filters and these range from 0.6 up to 3.8 m/s [118 up to 748 FPM (feet per minute)]. For example, a precise filter designation would be MERV 8 @ 492 FPM. 3. Terminology, classification and testing instructions in accordance with ISO 16890
Tab. 4: ISO 16890 terminology
will also be examined with regard to the filter medium‘s minimum efficiency factor for the 0.4 μm particle size. The minimum efficiency factor listed here is the lowest of the values measured for the initial efficiency factor, the unloaded filter‘s efficiency factor and the efficiency factor measured for this particle size during the loading process. Table 1 shows the criteria used for filter class classification in accordance with EN 779.
Tab. 2: Classifying the particle size classes in accordance with ASHRAE 52.2
According to the US ASHRAE 52.2 standard (/3/, /4/), the 12 particle size classes, in which particles are counted before and after the test filter (see Table 2), are sub-divided into three ranges. The average minimum efficiency factor value for the size classes concerned is given for these three ranges (PSE = average Particle Size Efficiency). Therefore the minimum efficiency factor for a size class is the minimum filtration efficiency value
The new ISO 16890 Air filters for general ventilation standard covers four parts, which are shown in the following: - Part 1: Technical specifications, requirements and efficiency classification system based upon Particulate Matter (PM) - Part 2: Measurement of fractional efficiency and air flow resistance - Part 3: Determination of the arrestance and the air flow resistance versus the mass of test dust captured - Part 4: Conditioning method to determine the minimum fractional efficiency. 3.1 Terminology and classification into efficiency classes The terminology listed in Table 4 should be used in compliance with the new ISO 16890 for evaluating the particle size distribution in crude and clean gasses and determining the filtration efficiency factor (efficiency value E). F & S International Edition
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Filters will be classified in accordance with their efficiencies with respect to the PM10, PM2.5 and PM1 particle fractions under the new standard (see Table 3). These particle fractions comprise all measured particles with aerodynamic diameters equal to or less than 10, 2.5, or 1 μm respectively. E (ePMx) shown in Table 5 represent the efficiencies that are averaged over all measured particle size classes belonging to the respective size range PMx (calculated using the specific EA,i value), and Emin(ePMx) mean the minimum efficiencies for the IPA conditioned filters and are calculated in the same way from the specific ED,i values. All of the size classes, of which the upper margins do not exceed the value of 1μm, are used for determining Emin(ePM1) and E(ePM1) and the evaluations for PM2.5 and PM10 are made analogous to the 2.5 and 10 μm upper margins. For this the geometrical average value of every particle size range is taken into account. All of the E(ePMx) and Emin(ePMx) are the initial efficiencies for a new filter medium that has not been loaded by dust beforehand. The determination of the filtration efficiencies for a filter that was aged by being loaded with test dust is not included in this standard.
Tab. 5: Filter classifications in accordance with ISO 16890
A filter test report includes all of the details from the efficiencies listed in Table 5 together with the E(ePMx) measured values rounded down to the next 5% step. Table 6 exemplarily shows the measured efficiencies of filters that have been classified in accordance with EN 779 as Class F7 or F9, the efficiency values rounded to the next 5 % step as to be listed in the test reading and the resulting classification in the relevant filter class according to ISO 16890. Due to its minimum Emin (ePM1) efficiency, the F7 filter does not meet the ISO ePM1 class filter requirements (see Table 5) and is therefore classified as an ISO PM2.5 filter. The F9 filter is an ISO ePM1 class filter. Every filter can be clearly specified using the numerical value details from the test report, which form the average efficiency factors for the loaded and unloaded test pieces and are rounded down to the next 5% step.
The authors do not have an example that uses the measured values for a filter tested in accordance with ASHRAE that could be evaluated using the ISO 16890 criteria. If you compare the MERV criteria given in Table 3 against the values given in Table 5 for the specific classes in accordance with ISO 16890, you will come to the conclusion that an ISO ePM1 category filter at least corresponds to a MERV13 filter. If a geometric diameter of 2.57 μm is used for the upper size classes in Range 2, i.e. 2.2 up to 3 μm (Table 2) and this fraction is then used to calculate the PM2.5 fraction, then an ISO (ePM2.5) class filter will be an approximate match to MERV 11. However, the US standard does not state a filter discharge procedure as mandatory. There is the possibility of conditioning the filter by using KCl to simulate efficiency losses like they may occur in field applications /4/. The fil-
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Tab. 6: Example of the measurement results obtained during the testing of two air filters and their classifications according to ISO 16890
tration efficiencies determined with KCl conditioned filters are named Ei,A with corresponding efficiency classes MERV A. Filter rating is done by using the same efficiency values listed in table 3 as for the unconditioned filters. 3.2 Filter testing process details In addition to the previously shown differentiated evaluations of the fractional filtration efficiencies, other changes have also been made to the filter testing process as opposed to testing in accordance with EN 779. An important change here concerns the defining of test aerosols. Under ISO 16890 the filtration efficiencies of the different sizes ranges are measured using a DEHS aerosol together with an A2 fine (as per ISO 12103) for the particle size range up to 1 μm (PM1) and an aerosol with a 20% KCl solution is used together with the A2 fine for the particle size range above 1 μm. The DEHS is used over the entire size range for determining the filtration efficiency factor fraction under EN 779. Fig. 2 gives an example of an aerosol generator for KCl that supplies particle concen-
Fig. 2: Aerosol generator for producing highly concentrated KCl particles from 0.1 to 10 μm (photo: TSI GmbH)
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trations and size distribution as required for testing according to ISO 16890. The distributions from the DEHS and KCl aerosols over the two size ranges ensure that there are an adequate number of particles of all relevant size classes on the filter. Measuring over two cycles is recommended for the practical filter testing, whereby one cycle uses DEHS and the other KCl, each together with the test dust being added at the same time. The ASHRAE test dust that was heavily criticised is no longer used. Another difference to testing under EN 779 is that determining the dust collecting capacity through loading with test dust up to a pressure loss of 450 Pa is no longer mandatory. The standards commission gave a lot of thought with regard to how to apply isopropanol to discharge the test filter. EN 779 also requires the filter medium to be discharged for determining the minimum efficiency, but it does not include any specific details with regard to the conditioning procedure. The new standard defines the discharging procedure more precisely. It calls for discharging not only filter samples but entire filter elements before the testing procedure. In order to enable complete filter units to be discharged, the test specimen must be stored in a chamber for a predefined period of four hours, alongside slide-in racks that are filled with isopropanol up to different levels instead of submerging it in liquid IPA. This requirement should ensure that the chamber‘s gas-filled compartment is saturated with isopropanol vapour, so that the sample filter is completely and evenly loaded with IPA after the predefined storage period has expired. This type of test filter conditioning is somewhat controversial, as a high concentration of isopropanol vapour is released into the environment when the chamber is opened to remove the conditioned test specimen. This requires higher expenditure to maintain work safety and explosion prevention in the affected laboratory.
3.3 What has changed with regard to the test rig setup? Whereas only the overall filtration efficiency and the filtration efficiency of a specific size fraction (0.4 μm) were used for filter classification under EN 779, determination of the size-dependent filtration efficiencies is also implemented by the relevant test equipment. It can be initially assumed that the procedure for collecting data during filter testing with regard to the measured particle size classes remains the same with respect to the number of particles being used and the concentration measuring process. Filter testing in compliance with ASHRAE 52.2 is fulfilled with classification into twelve particle size classes and this is also the most important prerequisite for evaluating the measured filtration efficiency factor under the new standard. In all cases the test rig setup that complies with the standards (ISO 16890, EN 779 and ASHRAE 52.2) always uses a 610 mm x 610 mm (24 x 24 inch) filter element as the test piece. The range of the permitted air volume flow rate of 0.25 up to 1.5 m3/s stipulated in the draft of the new standard gives a filter flow rate of between 0.67 and 4 m/s and this virtually corresponds to the value range for the permitted filter flow rate listed in ASHRAE 52.2. All-in-all it can be seen that the filter testing in compliance with ISO 16890 can be undertaken using an existing EN 779 or ASHRAE 52.2 test rig after choosing the relevant aerosols and test dust and modifying the evaluation routine. 4. What will happen to the energy classes? At present, the G1 - F9 filter classification under EN 779 forms the basis for classifying the filters into the energy classes defined by the European Eurovent manufacturers association (see /7/). The energy classifications were revised during the 2014 and the present version has been inforced since the start of 2015. The value range that has to be maintained for a specific energy class has to be separately defined with regard to the annual energy consumption for each filter class. In doing so, the physical relationship is taken into consideration, that a filter‘s pressure loss and the resulting energy consumption will increase with increasing filter efficiency. Due to these dependencies we can conclusively calculate the energy efficiency indicator in relation to the average filtration efficiency and the average pressure loss, albeit an energy-evaluation of this type could not be used directly beforehand. Classification into filter classes in compliance with EN 779 means that the filter covers a class with a larger range of energy values and a classification into
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discrete value ranges must also be made here, as naturally, it cannot be transferred directly to the filters evaluated under the new standard. The energy evaluation of an ISO 16890 classified filter made under today‘s standards will take you back to the direct calculation of an energy efficiency indicator. However, dust loading is needed for determining the significant pressure losses. This should be orientated to the average dust quantity that an ISO (ePM10), an ISO (ePM2.5) or an ISO (ePM1) filter handles during an operating year. Furthermore, the influence of the filter geometry on the pressure loss must be taken into account by an extra factor. In order to determine this and also to check the suitability of the previously proposed dust quantities that are being discontinued, a variety of experiments must be run using commercial filters with different efficiency classes. This study was still not concluded at the time of editorial deadline.
tion recommendation for air filters issued by the National Air Filtration Association (USA) /9/ is orientated towards the particle size, which must be maintained without fail in the filter for specific uses. For example, a MERV 15 class filter is needed to stop any bacteria from getting into a hospital‘s internal ventilation system. 6. Summary
5. Filter choice consequences to be considered when planning ventilation systems
Important changes to the testing of filters are described here and they will come into force with the introduction of the new ISO16890 standard. The definition of filter efficiency classes, which is orientated to the filtration efficiency of the PM1, PM2.5 and PM10 particulate matter fractions, corresponds to the standards used in environmental monitoring stations for evaluating the atmospheric air. The new method of evaluating filter efficiency makes a direct transfer of the previously applicable energy efficiency classes impossible, as filter selection recommendations for the design of air conditioning systems also have to be reviewed.
When designing ventilation systems for non-residential buildings, filters with specific efficiency classes should be chosen in compliance with the details given in EN 13779 /8/. The outdoor air quality classes (ODA 1 to ODA 3) for the air to be filtered and the required indoor air quality, which is sub-divided into a total of 4 categories (IDA 1 to IDA 4) should be used as the basis for selecting the filter or filter combination.The outdoor air categories are classified according to CO2, NO2, SO2 and PM10 concentrations, whereas the indoor air categories are classified according to the proportion of incoming outdoor air and the proportion of CO2 content that exceeds the outdoor air concentration. There is a recommended filter class or a combination of filters from different efficiency classes for each ODAx / IDAx combination. These recommendations also need reviewing, as a more precise specification for the atmospheric air quality with regard to PM2.5 and PM1 concentrations would be much more helpful. The selec-
Literature: /1/ Draft International Standard ISO/DIS 16890-1: Air filters for general ventilation – part 1: Technical sepcifications, requirements and efficiency classification system based upon Particulate Matter (PM) /2/ DIN EN 779:2012-10: Particulate air filters for general ventilation – Determination of the filtration performance /3/ ANSI/ASHRAE Standard 52.2-2012 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size /4/ ANSI/ASHRAE Addenda a,b, and d to: ANSI/ASHRAE Standard 52.2-2012 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, 2015 /5/ National Air Filtration Association (NAFA): Understanding MERV /6/ Stoffel, T.: Filter Classes acc. to ISO 16890 expected to become effective as of 2016, Vortrag, 29 Palas Aerosol Technologie Seminar, 27,/28. September 2015 /7/ Lyko, H.: Particle measuring technology and filter testing according to the latest state of the art, F&S International Edition No. 15/2015, pp 14 – 20 /8/ DIN EN 13779:2007: Ventilation for non-residential buildings - Performance requirements for ventilation and room-conditioning systems /9/ NAFA User’s Guide for ANSI/ASHRAE Standard 52.2-2007, rev. Nov. 2009
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Filtech 2015: Machines and processes used to manufacture filters H. Lyko* Filtech is not only the most important traditional industry meeting point for the filter industry, where the newest developments in the filter media and separation process sectors can be discussed on the exhibition stands and during the conference presentations. The exhibition has also become an important market for machines and fittings used in the production of filters as well. The new types of filter media and filter elements need new and optimised production processes to be able to introduce them in the market in industry-relevant quantities. Conventional production machines can be optimised with regard to time, material and energy and this will save filter production costs. For example, fully automated, highly specialised machines are needed for large-quantity production of air and fuel filters for the automobile industry or for ventilation systems. Examples are shown in the following. Pleating machines Pleating machines are designed as either knife or roller pleating machines, whereby roller pleaters tend to run at higher pleating speeds, whilst knife pleaters are more precise, have variable pleating heights and can process multi-layer filter media. A knife-pleater model with a very high processing speed of 600 pleats per minute for this type of machine that, depending on the material, can run even faster, is produced by SP-Sondermaschinen GmbH. This pleating machine processes activated carbon filter fleeces, polyester meltblowns, HEPA and ULPA materials with a pleat height of 20 – 40 mm with a maximum width of 650 mm. It can be integrated into a production plant producing interior air filters with integrated two and four side adhesion and a slitter (see Fig. 1). The digital CNC controlled knife-pleater made by the Swiss manufacturer, JCEM, can also score here, even though it does not have such a high pleating speed, but has larger and variable dimensions for the web widths and pleat heights that have to be processed. Pleat heights of 4 to 150 mm and more as well as working widths of 500 to 2,400 mm can be achieved at a production speed of 300 pleats/min. The newest development, the “Power Pleater P6”, processes multi-layer filter media that also include stainless steel weaves with very high compression. Sewing and welding plants
of welding (the process variants are shown in Fig. 2), lies in the fact that the surface of the medium is not or is only slightly affected. Several product innovations by Pfaff for welding processes have received industry awards over the last few years. As a result of discussions held with customers, new and reliable special processing and streamlined machines have been developed for the production of star filters, hot-air production lines for filter bags or automatic ultrasonic welding systems with up to five welding heads for the production of filter plates or bags. Four different systems were presented at the exhibition. These include a programmable duplex wheel ultrasonic welding machine solu-
tion, which cuts and seals edges during a process and has a second reinforcing welding seam; a programmable hot-air welding machine with adjustable hose infeed for producing filter bags; a single-head ultrasonic system for cutting and sealing edges / welding membrane filters and textiles in the form of plates and panels as well as a programmable free-arm hot-air welding machine for sealing seams with tape. Manual, semi-automatic and fully automatic machines for bonding pleated filter media using different processes are the speciality of Massman, an American manufacturer. The basic variants for longitudinal sealing of the filter media during the production of filter cartridges are shown in
Fig. 1: Interior air filter production plant from SP Sondermaschinen GmbH with an extremely fast knife-pleater (image: SP Maschinenbau GmbH)
The technology of assembling filters by sewing and welding has been further developed together with the advances in materials and the material combinations from which the filter-media are produced. According to reports, Pfaff, a machine manufacturer from Kaiserslautern, is the only manufacturer who provides both sewing and welding bonding technology solutions for filter media. The advantage *Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696
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Fig. 2: Various filter media welding processes (image: PFAFF Industrial)
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Fig. 3. The market presence shows a clear trend with regard to the support of ultrasonic welding /1/. Admittedly, the overlapping bonding is environmentally friendly, but the danger of unwanted bypasses exists. The metal clip holds the medium together, even under high pressure loads, but remains after the complete incineration of a plastic filter at the end of its service life. The hot-adhesive bond can also be incinerated, but polyamide-based high-performance adhesive, which is suitable for use with oil, diesel and alcohol, is difficult to apply and distribute according to George /1/. All of these obstacles do not occur with ultrasonic welding and it is also more cost-effective than adhesion or using a metal clip for the bonding. Ultrasonic welding, which does not use any other resources, can also be used on compound media, provided that Fig. 3: Different options for bonding pleated filter media (free as per /1/) the plastic content of the medium is at Bonding of filter media with end caps or frames least 65%. Jentschmann, a Swiss machine manufacturer, exhibited their Different components are nearly always bonded to one another Weldsonic filter system, which is an ultrasonic welding machine when filter elements are assembled or else liquid plastics are cast for sealing modular pleated filter packages and is able to fulfil with each other. In addition to the adhesive properties, the media all of the various customer requirements. The single modules are and temperature consistency and the mechanical stability of the available in different versions as a guiding device, an automatic adhesive bonding also play a role when choosing the dosing and adhesive tape cutter, the ultrasonic welding head, an edge cutter, mixing technology with regard to the efficiency and performance another ultrasonic welding head for increasing the production of the production processes. This is acknowledged by Reinhardtspeed and a seam press. More specifically, the welding seam Technik GmbH, who provide dosing and mixing systems for the can either be positioned directly on the root of the pleat or freely selectable between the root of the pleat and the top of the pleat and the design of the welding seam can also be optimised to meet the customer’s requirements. An electrically adjustable table is set to the pleat height of the filter package in order to ensure optimum pleat guidance without any crushing or stretching and in the case of non-weldable filter media, a hotmelt adhesive tape can be inserted in the welding seam and cut off automatically at the end of the pleat package. Modern ultrasonic welding machines that undertake the previously mentioned work using roller seam processes, in which the material to be welded is continually welded inbetween two discs rolling on one another. Continuous seams are produced by this process and even curved seam contours are possible at welding speeds up to 20 m/min. Nucleus GmbH provide this option with their computer-controlled Rotosonic V4E series o f machines that are equipped with a new sonotrode generation and a variety of new functions. The system, which can be equipped with different flatbed and free-arm models and accessory packages, is operated from an 8.4“ touch-screen. It has Ethernet support, so that the settings and welding parameters can be loaded by accessing an external network drive or storage media or passed on to other machines. The relevant parameters are displayed and saved in an external database during the welding process. Filter bags for air and liquid filtration can be efficiently produced in large quantities in automatic production plants, such as those provided by Keilmann Sondermaschinenbau GmbH. The FPS 300 system produces up to 36 separate filter bags per minute from roll material at a maximum speed of 20 m/min. Such filter bags are fitted in filter bag frames for air filtration. The machine used a myriad of technical details that enable glass-fibres and synthetic media with different material thicknesses to be processed into bags with conical or constant stich loosening, straight or tapered external shapes and special shapes in the outer seam areas. Other technical features include a swivelling side seam sewing machine with stich loosening up to 60 mm, a multi-needle sewing station, a hot-pasting system and a high-speed cutting system, etc.. F & S International Edition
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the capacity in m/a. The stipulated capacities are considered for fibre diameters of 400 ± 50 nm. Refer to the article by Luo et al. /3/ for a comparison of commercial electro-spinning processes as well as other fibre production processes.
Fig. 4: A look at an Ecofilter production plant for manufacturing cylindrical filter elements (image: GUSBI)
production of cylindrical filter elements such as cartridge and bag filters. The dosing system consists of gear wheels and eccentric spiral or piston pumps. They are integrated in an automatic production plant of that they developed themselves, in which the processes, ranging from pre-treatment, preparation and the application of adhesive or sealant to one, two or more components up to the automatic hardening process are carried out. Various robotic and handling systems are used for this. Gusbi, an Italian provider of filter production machines, does not use adhesive in their Eco-Filter range of machines. In fully automatic plants in which automobile filters are assembled, end cap elements made from a thermo-plastic material (polyurethane) are used, which is heated and then bonded to the filter media. Fig. 4 shows a section of the production plant. Production of nano-fibre media Nanofibre media are gaining in significance with regard to filtration as the filtration efficiency in the MPPS (Most Penetrating Particle Size) area increases due to the reduction in the diameter of the fibres (see /2/) and this enables the overall filtration efficiency to be increased without the surface weight of the filter medium and the nominal value of the induced pressure loss through the medium being increased. FIBRANE, a Korean company, has developed and patented the so-called Aerodynamic Electro Spinning (AES) process, which is termed the first nano-fibre mass production process in the world. Whether it really is the first mass production process is difficult to prove, as there are other nano-fibre media manufacturers in the market. Whether this is a mass production process or not, has to be evaluated by comparing the stated capacities against other processes. A nylon spinner unit spinning at approx.6 million m/a with a surface weight of 5 g/m and another made from PVDF approx. 0.9 million m/a with the same surface weight and made from PVDF can be produced. The use of two or four spinning units increases the production quantity, but the production of nano-fibre media with higher surface weights reduces
Fig. 5: Additive production processes have opened up new options for manufacturing machine components and filter elements (image: ExOne GmbH) 78
Additive production of filter components The option of transferring the data for a CAD generated object straight to a production machine opens up new possibilities for the manufacturers. The so-called 3D printing of complicated, detailed and fragmented objects appears particularly attractive and these can be bonded together in multi-stage production processes through adhesion or welding or it could even be used for complex casting moulds (if this can be realised). This also applies to filter components, especially if they are treated as multi-layered, rigid elements (see Figs. 5 and 6). Two exhibitors showed processes for the additive production of metal filter media. The machines from ExOne and Croft Additive Manufacturing use powder as the raw material, but different bonding processes are used. ExOne uses a so-called “binder-jetting” process that was developed by MIT (Massachusetts Institute of Technology) and this ensures that the metal powder is distributed thinly over the surface. A print head then sprays a predetermined pattern on the powder coating, which is similar process to ink-jet printing on paper. This process is repeated layer-by-layer, so that very large objects can also be produced in this way. The process is suitable for sand, ceramics and metal-powder. The finished “printed” objects must be sintered afterwards so that components made from ceramics and metal can be finalised. An example of a component already in use in separation technology is ExOne’s production of strike-through plates for decanter centrifuges, which are used in the mining industry (see Fig. 6). These components are extremely stressed as a result of the abrasive media and they can also be produced using complex welding processes. Croft Additive Manufacturing, a British company, uses a laser to bond the metal-powder particles. The powder is also distributed in a thin layer over one level and then it is irradiated by a laser following a pre-determined pattern, so that localised fusion of the metal powder occurs and the small parts are then bonded to one another. This process is also repeated layer-by-layer. Posttreatment through sintering is no longer needed as the powder on each layer is immediately bonded by the laser. The laser printing processes are more time-intensive than the “binder-jetting” process. With the latter, the pieces also have to undergo final sintering afterwards, but hermal post-treatment can also be applied simultaneously to several workpieces. Literature: /1/ George, L.: Premium Pleated Filter Seaming Technology; Int. Filtration News Vol. 31 (2012) No. 5, www.filtnews.com /2/ Lyko, H.: Filtrationsforschung für leistungsfähige und energieeffiziente Filtermedien – Bericht vom 6. IUTA-Filtrationstag; F&S Filtrieren und Separieren 29 (2015) Nr.1, S. 52- 56 /3/ Luo, C.H.; Stoyanov, S.D.; Stride, E.; Pelan, E.; Edirisinghe: Electrospinning versus fibre production methods: from specifics to technological convergence; Chem. Soc. Rev. 2012, 41, 4708 -4735
Fig. 6: Abrasion-proof strike-through plates for decanter centrifuges, produced using the “binder-jetting” of metal powder and final sintering (image: ExOne GmbH) F & S International Edition
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