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Solids Handling & Processing Supplement
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January - February 2015
PRUDENT PROCUREMENT By Gus Bishop – Solids Handling & Processing Association
In it together... We are all customers at times, whether as mere consumers or maybe as professional industrial buyers with challenging technical aspirations and even more challenging budgets. We all have increasingly ambitious expectations of the “shopping experience”. Gone are the days of the surly shopkeeper for whom the customer was an intrusive irritation. The sheer range of goods in all fields is so vast that we cannot be universal experts; we expect to be led honestly and economically as we narrow down both needs and available options. We expect patience, the opportunity to modify our desires (change our minds...) and the timescale and budget for intended purchases.
A STEP FURTHER
What more, therefore, should a professional industrial buyer demand when on business? For a start, all of the above. However, unlike the typical personal shopper, he or she will probably be using someone else’s money to procure goods and services that must satisfy the employer’s need – for a long time. The purchaser needs total confidence in the chosen vendor or supplier, who must commit to long term support. The procurement officer is a shopper with an agenda upon which his or her livelihood may well depend. So, suppliers shoulder a great burden of responsibility and must enter into a high quality reliable partnership with the buyer. But what about the process machinery supplied? In its own way it is both customer and supplier. To operate effectively it must receive properly prepared material in the correct quantity and condition. Whether the equipment in question is used to convey or grade or mix the material, its working parameters must be met. The equipment then supplies its finished material to the next stage. The receiving machinery will expect it delivered in the right quantity and condition – and so on to the very end, perhaps to bagging, palletising and outloading. Good suppliers will see their offer from the customer’s viewpoint. The purchaser really wants to feel that the best choice has been made; no nagging doubts, sleepless nights or awkward edgy meetings with the boss or indeed, colleagues. “Where on earth did you buy this ****?” is not a question the purchasing professional will want to be asked.
THE EASY WAY IS NEVER EASY
The economy is recovering, but the path is neither broad nor straight. This last year has seen many pitfalls, with stalling export markets, slackening pace of development in major prospective markets such as China, abrupt stock exchange fluctuations, political jitters on many fronts, all hitting confidence amongst investors: the list goes on. Recently there have been further rumblings within the Eurozone, with visions of deflation, stagnation and generally difficult trading conditions. The wildly fluctuating oil prices, down in January by more than 50% have been seen as both good and bad news depending upon the viewpoint. However, business continues, indeed impressively buoyantly in some sectors and purchasers continue to purchase, albeit with added WESTINGHOUSE vigilance and care.
the Association’s inception in 1981. The SHAPA mission statement includes such aims as reducing capital expenditure, cutting operating costs and increasing product reliability. Technical papers published and cogent seminars held as and when the need arises arm members with up to date, high quality tools to assist their customers to achieve these aims. Again, members benefit from assistance with export markets, with trade missions and oversees contacts. Because of the huge range of equipment and services that are required within our industries, many members find themselves suppliers to or customers of other members, sometimes both concurrently. Quarterly General Meetings have become an ideal forum for exchange of ideas and commercial networking as well as sources of good intelligence from the regular high profile invited speakers. For example, at the recent January meeting a number of members delivered presentations on various aspects of ATEX compliance.
VERY USEFUL INFORMATION
The seventh annual Digital Marketing Workshop is scheduled for 11th March. Originating as a “one-off” event, it has returned year after year by popular demand – its relevance and importance increasing steadily. Subjects professionally explored include what’s new in Google, selling on LinkedIn, a web clinic and an email masterclass, all to offer the best opportunities in digital marketing. Whilst this is a members only event, a browse through the recently updated website at www.shapa. co.uk will reveal a plethora of useful technical, commercial and legislative information, open to all. There are now twenty Technical Papers on subjects ranging from sources of useful information, ATEX legislation, powder characterisation, various processes and equipment to directives old and new. In addition there are now six Application Sheets also freely available, as well as technical advice at the click of a mouse upon request. For suppliers of solids handling machinery and services, the benefits of SHAPA membership are compelling at any price – our persistently low annual fee puts this beyond doubt! For project managers, process engineers and procurement professionals with quality processing projects to develop, install or simply to maintain, then the SHAPA website Equipment Finder at www.shapa.co.uk will offer a secure starting point, with all companies displayed there able to benefit from decades of SHAPA accumulated knowledge, experience and insight.
ENJOY THE FOLLOWING PAGES.
ss e c o r p r u o y d e e F
SHAPA COMMITMENT
Nobody takes the supply of engineering products more seriously than the 100+ strong member companies. For well over 30 years the Association has been developing a knowledge and skill base to assist the members – key manufacturers and suppliers of burden they have been eager to lighten on a continuous basis. As you scan the pages of this SHAPA supplement it will become clear that SHAPA member companies number amongst the most knowledgeable and technically capable in all aspects of solids material handling and processing. Furthermore, the membership also includes advisory and research bodies involved in continuously refining experimental data on material flow and characterisation. Many companies have been part of the SHAPA family for many years, with some founder member companies involved since
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COMPONENTS FOR BULK SOLIDS HANDLING
We expect the seller to “know their stuff” and have information and samples readily available. We expect all goods to be delivered on time, to actually work as promised and be accompanied by appropriate guarantees and service packages, all with clearly defined prices. If optional extras are offered, we assume that they will be appropriate to our needs and not mere costly embellishments. In short we as customers expect a lot – and we take it for granted that our wishes will be fulfilled to the letter.
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PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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SOLIDS HANDLING INDUSTRY AWARDS The Solids Handling & Processing Association (SHAPA) in association with Solids & Bulk Handling magazine are delighted to announce that these new awards to promote success and achievement across our collective industries, will be open to all companies registered in UK, whether or not SHAPA members, who are directly involved in the solids handling and processing industry. This exciting opportunity will comprise awards in three categories: the Export Award, the Innovation Award and the SHAPA Company of the Year Award.Full details about how to enter your company and applicable conditions are available on the Association website at www. shapa.co.uk, but please act quickly – the closing date for all entries is 28th February 2015 Briefly, the Export Award will go to the company who shows the best achievement relative to their size, with export sales either in one market or across several markets. Imaginitive and novel methods that have brought good results will be considered within the assessment of this award. The Innovation Award will be made to the company or collaborative organisations who have introduced significant new products or services, or valuable modifications that help drive the industry to further success. SHAPA will be looking for truly ingenious thinking, applied with flair. Finally, the SHAPA Company of the Year will be that organisation considered to have achieved the most in any category, relative to their size, by promoting best practice, setting All winners may use their award for their own marketing and publicity purposes as they see fit, provided that they quote the year of attainment. Awards will be announced and presented at the awards ceremony to be held on 14th April 2015. Please contact SHAPA now either via www. shapa.co.uk or by email to info@shapa.co.uk. Remember – closing date for all entries will be 28th February.
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PARTICULATE FLOW RATES FROM VESSELS IN PROCESS PLANTS By Richard J Farnish, CEng MIMechE, Consultant Engineer, The Wolfson Centre for Bulk Solids Handling Technology
For many plants the consistency and repeatability of discharge or feed rates into a process are critical to the efficiency of the next process step. Inevitably this feeds into not only the quality of the final product but also the overall profitability of the exercise. A feeder exists to moderate the discharge rate achievable from a given bulk solids exiting a vessel into a process. However, where flow limitations occur or transfer rates are unreliable, many operators tend to resort to the time honoured approach of beating the offending vessel into submission. Typically, despite short term intimidation of the equipment to an operating condition, unacceptable behaviour is often lurking just around the corner and soon returns. The mistake made by operators and engineers tasked with ‘sorting out’ is that where irregular flow is occurring the true source of the problem is often not immediately obvious. The reality of the situation is typically that it is the interaction of the vessel or chute with the feeder/flow control device. A common cause of flow rate irregularity is the flow channel that is propagated through the vessel from the flow control device. However even in situations where a vessel discharges in gravity flow the presence of geometries that are inappropriate for the process requirement is also a common issue. If consistent and reliable flow is required (particularly where a high accuracy feed is sought) it is critical that during operation regions of non-flowing are minimised (or preferably eliminated) through careful equipment design with these objectives in mind. Examples of Fig.1: Preferential where non-flowing regions of material might develop draw down on to a include, above fixed capacity feeders (i.e. constant pitch screws, rotary valves), within vessels (i.e. core screw flow or poorly interfaced mass flow bins), through poor feeder interface design (i.e. direct onto vibratory trays, belts or drag link conveyors), or where gravity flow is throttled using slide gates, butterfly or iris valves. As you can see, there is plenty of scope for error. In one recent industrial project pack weights were found to be varying by +/-140g on a 25kg sack fill, resulting in substantial losses through ‘give-away’ on a plant operating 24/7 over a year. At an entirely different scale, a discharge accuracy of +/-2.5te on Fig. 2: Extended non flowing material a 30te fill was occurring at wagon in chute loading operation. In both cases the root cause was similar in that the flow channel that was established during discharge was encouraged to propagate through regions of non-moving material which were supported from the flow control device. Relatively simple modifications (which could have been readily implemented into the original construction) resulted in an improvement to +/45g in the first example and +/-500kg in the second example. The common mistake made when designing or modifying systems through which bulk materials will flow is to make the assumption that provided the granule (or powder) flows from the equipment, then all is well. The reality is that most process problems relating to bulk particulates originate from a failure to take time to understand their bulk characteristics. Most people that deal with bulk particulates will be Fig. 3: Flow against non of the opinion that cohesive (poorly flowing) materials are very difficult to work with – moving product
however, this is usually based on the usually frustrating experiences gained from the use of standard equipment types in conjunction with these types of powders. The reality is that, following characterisation for flow, such powders can be handled very successfully provided that the equipment with which they are used incorporates geometry, interfacing and feeder specifications that are appropriate. By contrast many believe that free flowing materials are much easier to work with – and to a certain extent they’d be correct. However, the presence of constrained flow channels can give rise to unacceptable flow variability even for ‘easy’ to handle bulk materials. The key to controllable and efficient discharge of free flow or cohesive powders lies in the incorporation of an understanding of the bulk characteristics at an early stage in projects to modify or purchase new equipment.
INDEPENDENT EXPERTISE: PROVIDING COST-EFFECTIVE SOLUTIONS TO INDUSTRIAL PROBLEMS
The Wolfson Centre for Bulk Solids Handling Technology is internationally recognised for its expertise in fields associated with bulk particulate handling and in the science and practical application of technologies to deliver improved process efficiencies. Our mission is to help industry to get powders and bulk materials to behave predictably through processes. Industry sectors benefiting from our services range widely and include power generation, chemicals, pharmaceuticals, foods, plastics, paper, minerals and cosmetics. Our clients are predominantly based in the UK, although many European and overseas companies take advantage of the independent and bespoke nature of our work. We have developed our portfolio of services over nearly four decades of interaction with industry, trade associations and professional bodies. We offer consultancy services to industry, conduct industrially focused research related to bulk solids handling issues and offer specialist short courses targeted at industry professionals. For information about these courses please use this link. http://www2.gre.ac.uk. If you have a problem with your plant or process, we have the knowledge and experience to provide cost effective answers that you can rely on. The centre is situated at the University of Greenwich’s Medway Campus, where we are part of the School of Engineering. Our location offers excellent transport links within the UK and EU enabling us to provide a prompt and flexible response to site visit requests and client meetings. Our experts have between them over one hundred man-years of experience of solving problems in the flow and processing of powders, granules and lump materials, in all industries from pharmaceuticals and food to mining and chemicals; from biomass waste and recycling to household goods and pet foods. They concentrate on the needs of the industry and share their knowledge through the provision of technical research papers, articles and editorials through the media and at conference and exhibitions where they often present papers or hold workshops. Our industrial-scale pilot plant is available to test a processing step, or mock up a whole handling process or logistics chain, at full scale or near full scale. This can be used to find and solve the problems off-line, then when you transfer the same process or material to your own or your customers’ plant, you can be confident it will work!
Contact us now on Tel: 020 8331 8648 or E-mail: wolfson-enquiries@gre.ac.uk to find out how we can help you.
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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ACCURATE FEEDING AND DISCHARGING The GYRO EX Bin Activating Feeder/Discharger is a bin discharger and an accurate feeder, with up to a 100 to 1 turn down ratio, all in one piece of equipment. It produces a controlled gyratory motion to positively withdraw granular materials from bins, storage silos and hoppers. The GYRO EX Bin Activating Feeder/Discharger uses a radial force to create a uniform circular motion on both the upper activation cone and the lower discharge cone. The stored material load is completely supported by the upper bin activation cone, which has a discharge angle less than the discharge cone. This means all material feeds faster from the lower discharge cone than from the upper bin activation cone, preventing the head load from compacting material in the lower cone as sometimes seen in traditional vibrating bin dischargers.
GET DOWN WITH HOSOKAWA MICRON LTD - LEADERS IN SIZE REDUCTION
For more information contact Dynamic Air Ltd, Milton Keynes, Buckinghamshire. Tel: +44 1908 622344 E-mail: sales@dynamicair.co.uk Web:www.dynamicair.com Need to micronise just 1g of material for NPD trials – no problem. Want high throughput milling of 10 tonnes per hour – no problem. Want advice on how to transfer small quantity milling operations to full production rates – no problem. With over 50 years of size reduction experience and an unparalleled range of equipment, Hosokawa Micron Ltd has the expertise and the right equipment to do the job. With a range of equipment from laboratory mills such as the Picojet, capable of processing very small batches down to below 1g to rugged Hosokawa Micron Prebreakers designed for heavy duty size reduction requirements Hosokawa Micron can deliver coarse crushing down to ultrafine milling of submicron particles across a range of wet or dry processing applications in the chemical, food, pharmaceutical, mineral and other industries. In supplying a range of milling technologies including ball mills, granulators and crushers, fine impact mills, jet mills and air classifier mills, with many units available in different sizes from lab to production scale, Hosokawa Micron customers can select the most appropriate milling technology to achieve their required result and benefit from easy production scale up as well as a range of non-standard options that deliver an individual engineering response to processing problems. Powder processors can select mills by particle size production capabilities at http://goo.gl/2WXiRh For further information/reader enquiries, please contact Hosokawa Micron Ltd, Runcorn, Cheshire, Tel: (01928) 755100 Fax: (01928) 714325 Email: info@hmluk.hosokawa.com Web www.hosokawa.co.uk
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PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
FLEXICON® WEIGH BATCHING AND BLENDING SYSTEMS
FLEXICON® Automated, Gain-In-Weight Batching And Blending Systems convey bulk ingredients from nearby or distant sources, weigh the ingredients in sequence, blend the batch and deliver it to downstream destinations. Typical material sources include FLEXICON Manual Dumping Stations (shown), TIPTITE® drum dumpers, BULK-OUT® Bulk Bag Dischargers (shown), screeners, rail cars and silos. Typical destinations include downstream process equipment, FLEXICON bulk bag fillers (TWIN-CENTREPOSTTM shown), storage vessels and packaging lines. Weigh batching controls receive weight gain or weight loss information from load cells to automatically actuate conveyors, valves, blenders and other system components. Material can be transferred by integral FLEXICON Flexible Screw Conveyors (shown), FLEXI-DISC® Tubular Cable Conveyors, PNEUMATI-CON® Pneumatic Conveying Systems, other conveying systems or by gravity. Complete engineered systems are available as well as stand-alone components, to food, dairy, pharmaceutical or industrial standards, with FLEXICON’s Lifetime Performance Guarantee. Lab testing on full-scale equipment using customersupplied material verifies system performance.
RAPID RIBBON MIXING FOR TATE AND LYLE FROM JOHN R BOONE LTD John R Boone manufactured a 600 Litre Horizontal Helical Blade mixer for Tate and Lyle. This was constructed to meet the factory’s stringent hygiene and safety standards in stainless steel, with ‘u-trough’ adaptations for rapid discharge, larger batch sizes and fullwidth top doors for easy cleaning that include special safety interlocks. Tate & Lyle manufacture high-purity food additives and ingredients in hundreds of different types. Therefore when they were looking at replacing an old mixer their key objectives included improving the ease of cleaning and speed of changeover. The Horizontal Helical Blade Mixer is ideal for this application as it has four mixing elements forming an interrupted spiral and a short length compared to its width. This combination gives the mixer substantial advantages over conventional ribbon or spiral mixers. The slow-moving mixer arms gently lift and fold the blend end-to end, in an action that is so efficient that ‘trace’ components can be added directly to the mix with no need to pre-mix. This machine is fitted with two full-width doors to make it easy to clean so that cleaning only requires around ten minutes. The Horizontal Helical Blade Mixer is designed to discharge quickly with the two outer spirals sweeping the entire shell with every revolution, so there is only a very minimal amount of material remaining in the mixer after each batch.
For more information contact John R Boone Ltd, Congleton, Cheshire. Tel: +44 (0) 1260 272 894 Fax: +44 (0) 1260 281 128 E-mail:sales@jrboone.com Web:www.jrboone.com
For more information contact FLEXICON (EUROPE) LTD Tel:+44 (0)1227 374710 E-mail: sales@flexicon.co.uk Web: www.flexicon.co.uk
RMIG BRIDGE SLOT SCREENS CUT PROCESS DRYING TIMES An innovative range of drying screens has been launched in the UK by RMIG, one of Europe’s leading manufacturers of precision perforated products. Bridge Slot screens are specially designed for use in drying and storing all sorts of solid materials, such as grains, herbs, and more recently wood-chip, which is now primarily used to fuel biomass boilers. RMIG’s Bridge Slot screens are designed to enable a unique flow of air through the slots. This significantly improves air circulation, reducing drying times and increasing efficiency. With the right heating and storage conditions moisture content in wood-chip for example, can be reduced from an initial 50% to an ideal 18-20% in just 48 hours. The screens are manufactured in mild steel between 2mm and 5mm thick and this makes the screens ideal for use as “drive-on” flooring in large storage areas. With the right support system, the screens can take wide wheeled trucks for bulk loading and off-loading. Offering applicationspecific guidance, bespoke services and short delivery times makes RMIG the ideal partner for providing ventilation solutions for industry and agriculture.
For further information about RMIG’s Bridge Slot screens visit: www.rmig.co.uk.
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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CHOOSING THE RIGHT TECHNOLOGY FOR ACCURATE & RELIABLE SOLIDS LEVEL MEASUREMENT In this article Ingemar Serneby, Emerson Process Management, discusses the difficulties of measuring the level of solids in vessels and silos, and reviews some of the available technologies considering their suitability for different applications. INTRODUCTION
Selecting a suitable technology to measure the level of solid materials in vessels and silos can be a frustrating experience for many users. The material being measured often behaves in a manner that makes level measurement difficult and the results unreliable. Many applications need to convert level measurements into mass, and accurate results rely on a consistent density of the material being measured, and a complete understanding of the dimensions and characteristics of the storage vessel. The traditional approach to level measurement in the industry has been to use mechanical devices known as yo-yo’s. These are based on a weight attached to a wire being lowered onto the surface of the solids at scheduled times. The device calculates the level of the media based on the length of wire required before the weight makes contact with the surface. However, as the spool mechanism is in contact with the media, these systems require regular maintenance - exposing operators to the hazardous conditions on tall silos. Where continuous measurements are required, there are a number of options
that cover a wide range of applications in the process industries. These include Guided Wave Radar (GWR), non-contacting radar, ultrasonic, acoustic, laserbased technologies and load cells. In addition, for special applications where nothing else works, nuclear technologies can be
WHY ARE SOLIDS SO DIFFICULT TO MEASURE?
Surface inclination During the fill and emptying cycles, the surface of solid materials is rarely flat or horizontal, with a tendency to peak under the inlet and ‘rat hole’ above the outlet. The angle of repose, or surface inclination, will change as the vessel fills and empties, and this angle affects the recommended due to signal loss. Dust One of the most common problems for solids level measurement technologies is the effect of dust generated during the fill cycle. Many materials produce large amounts of dust in the silo and this can be problematic for ultrasonic and laser devices. The presence of dust affects the signal strength and subsequently the reliability of the measurement data. As a result, ultrasonic and laser devices are unsuitable for some of these applications. While radar signals are unaffected by dust, the antenna on non-contacting radar systems needs to be protected from dust build up, for example by using a PTFE bag which has non-stick properties, preventing dust from adhering to it. Air purges are also often used to clean dust off the sensor surfaces. Acoustic based systems use low frequency pulse signals that are unaffected by dust, filling noise, humidity, or temperature. In addition, they can be made selfcleaning by using the vibrating membranes to drive out any dust particles that coat the horns. Types of media There are many different types of media and their physical characteristics vary widely. For example, particles can vary in size from fine micron size to large particles, rocks, pebbles or granules. They can be smooth or have sharp edges. Parts that are in contact with abrasive media – such as GWR probes will require regular maintenance. Lightweight aerated materials have sound absorbing characteristics that affect the performance of ultrasonic and acoustic level devices. Some materials are hygroscopic - readily absorbing or trapping moisture and this can cause caking or clumps inside a vessel. In particular, coarser materials are more likely to clump, bridge, leave voids and pile up. Products like grain have variable characteristics dependent on the specific crop and moisture content. This makes it difficult to determine a consistent crop density that will provide accurate volume results. Dielectric Constant The dielectric value of many solids is fairly low. For radar technologies, the dielectric constant is a key indicator of the amount of signal that will be reflected back to the gauge. If the dielectric constant of the measured material is very low (<2), this may require the use of a GWR device that uses signal processing techniques to overcome the effects of poor signal strength. Bulk Density The weight of the material per volume is important when monitoring bulk solids inventories so it is important that the bulk density (usually in Kg/m3) is
Figure 1: Solids particles can vary in size from powders to pebbles and rocks
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representative of the material. Continuous level sensors will convert a distance measurement from the sensor to the material surface, to volume and weight/mass. Any errors in the bulk density will be translated into errors in volume and weight/mass.
Pull Forces
This is a particular problem for GWR where heavier materials can create a pull force that can break GWR cable probes or transfer loads to the silo roof, causing it Fig. 2: to collapse. While Guided this is more likely to be an issue in Wave Radar vessels taller than transmitter 50 ft. (15 m), care must be taken to guard against this possibility. A further consideration is that the weight of the material may push flexible GWR probes towards other structures in the tank, creating false targets.
Electrostatic discharges and Electromagnetic Interference
Guided Wave Radar (GWR)
Guided Wave Radar (GWR) has many applications in the process and manufacturing industries providing an accurate and reliable measurement of level in tanks and vessels. GWR is a top down, direct measurement, as it measures distance to the surface. Since GWR is not dependent on reflecting off a flat surface, it works well with many powders and grains including plastics, fly-ash, cement, sand, sugar and cereals. Radar provides a fast response to changes in level, making it suitable for closed loop process control and safety applications. GWR is based on a low energy pulse of microwaves being sent down the probe, when the pulse reaches the media surface, a reflection is sent back to the transmitter. The transmitter measures the time taken for the pulse to reach the media surface and be reflected back. The on-board microprocessor accurately calculates the distance to the media surface using ‘time-of-flight’ principles. Because there are no moving parts, maintenance costs are reduced and the problems of false readings, which can result in potentially hazardous situations, are avoided. In order to improve the maximum measuring range in low dielectric materials, technologies are available that allow for measurements when the surface pulse is weak. For example, Emerson’s Direct Switch Technology provides an echo signal that is two to five times stronger than other GWR transmitters. The improved signal to noise ratio means enhanced ability to handle difficult measuring conditions like long measuring distances and lower dielectrics.
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Ultrasonics
While ultrasonic level devices can be used for the measurement of solids they do have a number of issues that can affect the way the sound wave reflects off the surface and/or the generation of “false” echoes that can make detecting the true level signal very difficult. These include their inability to make measurements in applications with dusty conditions, vapour space changes, changing angle of repose, large particle sizes, internal vessel obstructions, and coating or formation of clumps on the internal vessel surfaces.
Acoustic
OVERVIEW OF THE TECHNOLOGIES
Non-contacting radar
Non contacting radar needs a clear view of the surface and the best results are obtained with relatively flat, rather than slanted surfaces. However, the specific challenges of sloping surfaces, low dielectric properties and high filling rates can be overcome by the use of specially developed software and algorithms that can manage some of the unique characteristics of the return echoes.
While modern designs and technical innovations have improved the performance of ultrasonic level devices, in many applications, newer technologies such as radar and acoustic will generally provide better results across a wide range of applications.
In some applications, for example the level measurement of plastic pellets, electro-static charges can build up and eventually discharge. It is therefore important to provide a good earth ground to protect the sensitive electronics in measurement devices. In addition, the device must be designed to handle the electrostatic charge and divert the excess energy away from the electronics. This design can help with electromagnetic interference from nearby equipment, which can be a problem with non-metallic silos.
The company also developed Probe End Projection (PEP) which enables reliable measurements to be made with low dielectric materials when the surface pulse is too weak to be detected. This method is based on the fact that microwaves propagate slower through product than through air. By monitoring the position of the probe end echo, an algorithm can calculate the surface position in case of an unavailable surface echo. The PEP function will only be activated as a backup if the surface echo is too weak.
Non-contacting radar devices can be considered as an alternative to GWR for applications where no-contact with the media is required, for example where aggressive and abrasive media can cause damage or wear to the probe. Like GWR, non-contacting radar provides a top-down, direct measurement as it measures distance to the surface. Non-contacting radar sends a signal through the vapour space that bounces off the surface and returns to the gauge.
Acoustic based devices measure level by transmitting low frequency pulses that reflect off the surface of the contents of the silo, bin or container. Because of the nature of the acoustic signal, which transmits over a wide area, it can be challenging to obtain the correct echo from the surface. Acoustic systems such as the Rosemount 5708 3D Solids Scanners, use three horn antennas that detect not only the distance to the surface, but also the direction of the echo to the object reflecting the signal. A Digital Signal Processor then samples and analyses the received signals to provide very accurate measurements of the overall surface of the stored contents, and generates a 3D visualisation of actual allocation of product within the container for display on remote computer screens. Using the silo dimensions calculating the volume is therefore easy. 3D Solids Scanners provide continuous volume measurements that are based on the representation of the material’s surface. They are ideally suited to measuring solids in silos, large open bins, bulk solid storage rooms, stockpiles and warehouses. They can measure practically any kind of material including grain, lime, cement, plastic powders, difficult-tomeasure fly ash and materials with a low dielectric. Self-cleaning designs require minimal maintenance even when used in the dustiest environments.
Laser based technologies
Laser transmitters for level measurement employ the speed of light, using a very narrow beam focused on a small area. They are extremely accurate and can operate over large distances. This makes them particularly suitable for applications that require level information at a precise location, for example at the emptying point of a silo. This provides operators with information about the ability of a storage vessel to deliver material when demanded.
Laser based systems can be used in high pressure, high temperature applications using specialised sight windows that isolate the transmitter from the process. However, an accumulation of dirt, dust or other coating on the laser level transmitter seriously weakens the strength of the laser signal affecting their performance. Regular Fig. 3: Non contacting radar transmitter for aggressive maintenance is important to prevent accumulations and ensure the correct and abrasive media
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
functioning of laser level measurement devices.
Specialist systems
Nuclear systems work by directing a fan of radiation across the vessel. As the level rises and falls the amount of radiation received at the detector also rises and falls. Since the measurement system is not exposed to the material, nuclear systems are ideal for corrosive, abrasive, high temperature or high pressure process conditions. However, these devices require special licenses, training and tracking, which add to the operating costs. In addition, serious consideration must be given future disposal and the associated cost implications. Load cells and strain gauge weight systems are usually chosen for applications where certified mass measurements are required, for example in the food, pharmaceutical and aggregate industries. They are used to support accounting applications or where all other technologies have failed. Load cells tend to be built into a system when it is designed and installed, although they can be retrofitted. Systems need to be engineered to individual requirements and are often difficult to calibrate.
the media being measured is aggressive or abrasive. Care needs to be taken with low dielectric solids or where there is long distance to the surface, or where there is a source of electromagnetic interference. These applications require products with technologies such as Probe End Projection which is incorporated in the Rosemount 5300 GWR transmitter. Probe End Protection enables reliable measurements to be made under low signal conditions. For applications where aggressive or abrasive media can cause damage or wear to the GWR probe, non-contacting radar should be considered as an alternative. However, signal reflections are low in the measurement of solids which makes correct installation and the selection of antenna very important. The latest generation products such as the Rosemount 5402 non-contacting radar use advanced software and algorithms to overcome the specific challenges of solids measurement which include inclining or sloping surfaces, low dielectric properties and high filling rates.
For larger vessels and silos up to 70 metres in height, acoustic based systems provide highly accurate measurements of stored contents. They provide continuous volume measurements that are representative of the materialâ&#x20AC;&#x2122;s surface and can measure practically SUMMARY any kind of material including grains, mineral ores and cement With such a wide choice of technologies available, the characteristics materials with a very low dielectric. Devices like the 5708 Series 3D of each application need to be carefully considered to ensure an Scanners map the uneven surface typically found in solids applications accurate and cost effective solution to each solids level application. and can provide the minimum and maximum level, the total volume For example, what are the dimensions of the storage vessel? Will and a 3D visualisation of the surface. The self-cleaning design of such dust in the vessel be a problem? Does the media being measured products require low maintenance even when used in the dustiest have a low reflective characteristic? With the surface of solids environments. being typically uneven, will a single measurement point provide For applications in large areas such as warehouses, several acoustic accurate results? devices can be combined to provide an accurate and reliable As a general guide, for applications in smaller vessels, measurement system for inventory and production GWR radar devices provide an accurate and reliable Fig. 4: Emersonâ&#x20AC;&#x2122;s Rosemount 3D process control in many industrial applications. method of providing continuous level measurement of solids. With their small connection size, GWR systems are Solids Scanners provide level, easy to mount and can adapt to a wide range of vessel volume and mass measurement of Care in selecting the most appropriate technology will minimise maintenance requirements and provide the types and shapes. They have a fast response time for rapid bulk solids and powders longest operational life. Most suppliers offer a range filling applications and the measurements are independent of technologies and their technical and application of moisture, and material fluctuations such as density and temperature. However, the selection of the correct probe type is important and engineers have experience of popular applications and are able to guide users special consideration needs to be given to installations in tall vessels or where through the selection process.
Fig. 5: Emersonâ&#x20AC;&#x2122;s acoustic scanners provide a 3D visualisation of the surface
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NEW BULK BAG EMPTYING CONVEYORS FROM SCHRAGE CONVEYING SYSTEMS Discharging bulk bags into a process typically involves elevating materials from ground level to process machinery feed points. Whilst the bags can be transported at ground level with fork lift trucks, elevating the material can be a challenge. In response to these challenges, a new range of tube chain conveyors has been launched by Schrage Conveying Systems. (Exclusively available in The UK from Renby Ltd). With a capability of lifting product from a few metres to as many as 35 metres, the new compact design fits within the legs of a big bag stand. This keeps the space requirement to a minimum. The tube chain conveyor can be operated at any angle from horizontal to vertical. This way, it does not impose any restrictions on the plant designer. Furthermore, with such large lengths possible on a single conveyor, just one tube chain conveyor is used where previously several conveyors would have been needed. All of the original benefits of the tube chain conveyor are retained, such as gentle handling, low energy consumption, dust tight conveying and low wear rates. Variations of the new design are available offering rapid filling / emptying of road or rail bulk tankers directly into your process or into intermediate containers.
Renby Limited, Tarvin, CHESTER CH3 8JF Tel: 01829 740913 Web: www.renby.co.uk Email: info@renby.co.uk
web: www.schrage.de email: info@schrage.de
THE BENEFITS OF EXPLOSION VENTS OVER EXPLOSION DOORS A global leader in providing innovative ATEX certified explosion protection technologies, warns process industries that explosion doors should be selected with caution – and must only be used for specific higher pressure applications. Fike UK, based in Kent, stresses explosion venting is the most common and effective form of explosion protection offering overpressure protection from potential industrial explosions. Keith Avila, General Manager at Fike UK said: “As a progressive company we are constantly developing the most effective and cost efficient explosion protection solutions. Over the years we have researched the attributes and qualities possessed by both explosion doors and vents and have found the benefits of vents significantly outweigh that of doors – and our customers are in agreement.” According to Fike, an explosion vent has proved to be the most effective method of passive explosion protection and can protect processes against the excessive pressures generated by an explosion. The explosion vent will provide an intended route for expanding gases to discharge and, as such, will prevent damage to industrial equipment. Standard explosion vents will open at a defined activation pressure and the vent area will remain open preventing build-up of vacuum pressure on cooling – as such guaranteeing not to fail. Explosion doors will also open at a defined activation point, but will generally reclose after the operation, with a device often being used to keep them closed, which is considered by many in the industry to not be as fail safe as the vent. More recently, however, some explosion vents now have the ability to reclose, but not 100% seal, thus cutting off the majority of the oxygen supply to assist in firefighting but do not allow a vacuum to form on eventual cooling. These types of vents effectively provide all of the advantages of light weight explosion venting, with the reclosing function of doors. Manufactured from thin stainless steel sheets of 1mm to 2mm, explosion vents are extremely lightweight allowing them to open fully almost instantaneously. Also, being classed as a more consumable part, explosion vents will be easier and less expensive to produce from materials compatible with the process. Conversely, doors are much heavier and, in certain instances, have very low efficiency, resulting in a larger venting area, a reduced explosion pressure or low burst pressure (Pstat). Fike’s specially designed explosion vents are passive explosion protection devices – with no moving parts to fail – and because of this they do not require any special maintenance. Easy to install, even in the most awkward and restricted locations, all vents come with optional weather protection covers to eliminate any potential damage from the elements and general debris. Keith added: “Explosion pressure relief is best achieved through the use of devices with no moving parts as they offer the highest venting efficiency and cannot be tampered with. Vents are well known to provide superior process compatibility. “With all of our explosion venting technology, we take into consideration design variables such as normal operating pressures, reduced explosion pressure and vent efficiency to name but a few. As with all Fikeproducts, we follow industry best practice and in many cases exceed industry standards. Fike is fully committed to providing the most cost effective and safest solutions possible.”
For more information contact Fike UK, Maidstone, Kent. Tel: +44 (0) 1622 677081 - E-mail: info@fike.co.uk - Web:www. Fike.co.uk
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LIFTVRAC - ON-SITE TRIALS FROM GENESIS Liftvrac, the inventors of the amazing conveying systems of the same name recently shown at PPMA, has appointed Genesis Process Solutions as their agents for the UK and Ireland. Phil Cameron is the Sales Director of Genesis Process Solutions: “We started to talk to Liftvrac some months before PPMA and convinced them that taking exhibition space was a good way of introducing the system to the UK markets. The level of good quality response was excellent with the number of companies requesting on-site trials well into double figures. We have now taken delivery of a Model S Liftvrac and already conducted onsite trials with some companies” To state that the Liftvrac conveying system is revolutionary is something of an understatement. It is more efficient, more economic and easier to clean than any other short-range mechanical or pneumatic system currently available for handling powdered, fluid, fragile or sticky products. The key component is a polyurethane belt which forms a tube around the product and carries it the entire length of the elevation. The flat belt is formed into a tube just after the product inlet and this tube then carries the material up to the top of the Liftvrac, where the belt opens flat again. The belt always wants to become flat naturally so doesn’t squeeze the product. Once the speed and belt load is set up the product holds itself in position so there is no stress on the product itself. A lip system effectively seals the tube and holds the product in place until it’s discharged at the end of the line. The seal is so effective that any powdered product, for example, can be conveyed without any risk of leakage into the surrounding environment. But it isn’t just powders that Liftvrac can handle. Fish, cheese, pasta, meat, plastics and a huge range of other products can be conveyed without any fear of blockages or clogging thanks to a scraper located at the discharge end of the belt. With a small motor, ranging from 0.5 – 1.5kW the Liftvrac system is extremely energy efficient and can handle product at rates up to18m3/h. The entire system can be dismantled, cleaned and reassembled in around twenty minutes – ideal if different products are going to be conveyed. Liftvrac is available in two models, C and S which refer to their shapes. C has been designed for tight enclosed spaces where the product needs to be conveyed to a mezzanine while the S model is better where there is more space and the product needs elevating to a mezzanine or overhead production line. Typical installations including the conveying of finished goods to a multi-head weigher, feeding raw ingredients to a mixer or even transferring from one area to another, the beauty of the Liftvrac is how versatile the unit is.
To discuss an on-site trial or a free site survey please contact Phil Cameron on 01270 766300.
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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THE SIX GUIDELINES YOU NEED T Exponential growth in the use of bulk bags has spawned an entire manufacturing segment dedicated to producing specialised equipment that not only fills and discharges bulk bags, but offers various degrees of automation and integrates filling and unloading operations with upstream and downstream equipment. As the number of equipment options increases, so should the ability of the specifier to evaluate stand-alone equipment and integrated systems against current and anticipated needs. The author addresses the “filler” half of the bulk bag handling equation, offering the six most important parameters to consider when satisfying any individual bulk bag filling requirement with top efficiency and cost effectiveness. 1. ANTICIPATE MAXIMUM CAPACITY
such,
The difficult but critical question: How many bulk bags will you need to fill per week during the useful life of your next bulk bag filler? With few exceptions, buying a more costly filler with higher capacity than you now need will be less costly than replacing a filler you outgrow, unless that filler can be retrofitted with performance enhancements at a later date. Capacity requirements run the gamut, from one bag per week to 20 bags per hour. Where your volume falls should, in part, influence your decision to specify a manual, semi-automated or fully automated machine. Generally speaking, the more manual the filling operation, the more output is subject to variation. When gauging the capacity and payback of manual equipment against automated equipment, you need to determine the average pace at which operators can attach, detach and cinch bag spouts, remove filled bags, load pallets and conduct all other filler-related operations. When estimating the time allocated to these manual functions, it is advisable to anticipate a pace that an operator can realistically Fig. 1 maintain throughout an entire shift while avoiding fatigue or injury. For the lowest volume applications, a basic filler operated manually will maximise your return on investment. One example is a medium-gauge Twin-CentrepostTM filler (FIG. 1) which offers the structural integrity of four-post fillers but at significantly lower material and fabrication costs and with less weight. This two-post design also affords unobstructed access to the bag spout and loops, facilitating rapid manual insertion and removal of bags. This class of filler is typically equipped as standard with fill head height adjustment via fork truck to accommodate all popular bag sizes, a feed chute vent port for dust-free air displacement during filling, and an inflatable cuff to seal against the bag inlet spout and ensure it does not collapse on itself during filling. Limited performance options, which can be added initially or retrofitted, include an inflator to expand the bag prior to filling, and a programmable scale system with flow Fig. 2 control valve for filling by weight. The cost of a scale system can be avoided by placing the entire filler onto an all-purpose plant scale, providing the filler is properly equipped for in-plant mobility (FIG. 2). If a forklift is unavailable to remove filled bags, as is required by the above-mentioned fillers, configurations are available with a three-sided base that provides access from the open side using a pallet jack (FIG 3).This lowprofile configuration can also be utilised to conserve height in low headroom applications. The time required to prepare empty bags for filling, and to remove filled bags from beneath the filler, can have as much or greater influence on maximum filling capacity than the rate at which material enters the bag. As Fig. 3
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adding a roller conveyor allows filled bags to be rolled out of the filling area for spout cinching and pallet/bag removal while another bag is being filled. Adding such a conveyor system, however, generally requires a filler with rear posts (FIG. 4) and a cantilevered fill head equipped with hooks that release bag loops automatically, so if higher capacity is in your future, a rear post configuration may be your best choice today. Increasing the capacity of systems equipped with roller conveyors to the next level generally entails adding an automated pallet dispenser (FIG. 5) which places pallets and slip sheets onto the roller conveyor upstream of the filling operation, further Fig. 4 reducing the time required for each filling cycle by limiting manual operations within the filling station exclusively to loading an empty bag. To further reduce the time needed to attach the spout of an empty bag to the filler, this Swing-Down® filler (FIG. 6) lowers the entire fill head to within an arm’s length of an operator standing on the plant floor. Further, it pivots the bag spout into a vertical position, enabling the operator to connect the spout of an empty bag to the inflatable bag spout collar in several seconds, after which the spout pivots back to horizontal, the entire fill head returns to fill height, the bag is inflated, and filling commences. Additionally, when the bag reaches its target weight, the bulk material delivery system deactivates automatically, the spout collar deflates, the fill head raises to decouple from the spout, and the powered roller conveyor sends the bag downstream of the filling area--automatically, Fig. 5 rapidly and safely.
2. EVALUATE SAFETY AGAINST MANUAL OPERATIONS REQUIRED AT ANY GIVEN LEVEL OF CAPACITY
With manual and semi-automated filling operations, the potential for worker fatigue and injury can increase according to required output per shift, relative to the type of bulk bag equipment specified. Consider that the connection points of a conventional filler are often beyond the reach of most operators, even when short bags are being filled. But adding the height of a roller conveyor to the height of a bulk bag to the length of its bag loops puts the connection points for bulk bags of only 122 cm in height at approximately 213 cm above the floor! This requires an operator to stand on a platform, a ladder or on the roller conveyor while straining to reach overhead spout connection points and inserting hands between temporarily disabled moving parts. Difficult-to-reach spout connection points can therefore compromise safety as well as capacity—two problems that can be solved with the addition of a fill head that lowers and pivots to the operator at floor level. Repetitive manual tasks such as releasing bag hooks, placing pallets on a roller conveyor or actuating bulk Fig. 6 material delivery, also increase the potential for error
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
TO SPECIFY A BULK BAG FILLER By David Boger, Vice President Sales and Marketing, Flexicon Corporation and injury, justifying semi or fully automated equipment for all but the lowest volume applications.
3. ENSURE CONTAINED
DUST
IS
Even the most rudimentary filler is likely to be equipped with an inflatable spout seal (FIG. 7) to hold the bag spout firmly in place during filling. However, not every fill head is vented to a dust collector to filter displaced air and Fig. 7 dust, and to vacuum ambient dust in the operatorâ&#x20AC;&#x2122;s vicinity during disconnection and cinching. It is therefore important to confirm that the filler you are considering is so equipped, particularly when contamination of the product or plant environment cannot be tolerated.
4. DETERMINE YOUR NEED FOR MULTI-FUNCTION FILLING If your plant fills drums, boxes or other containers as well as bulk bags, multi-function fillers (FIG. 8) can boost production, undercut the cost of separate equipment and reduce the amount of floor space required. Multi-function fillers can be switched from bulk-bag to drum-filling mode in seconds by positioning the swingarm-mounted drum-filling chute under the fill head discharge port. The chute automatically rotates to deliver material to all four drums on a pallet. Similar adapters for boxes, totes or other containers are also available with varying levels of automation.
5. MATCH THE FEED SOURCE TO YOUR MATERIAL AND YOUR FILLER
Filling capacity, accuracy and efficiency are often limited by the ability of upstream equipment to feed Fig. 8 material consistently and in sufficient volumes. High capacity, semi- or fully-automated fillers therefore require highcapacity feeding systems that are typically automated and feed material into the filler by gravity or by a metering device. The ability to gravity-feed material depends on whether a material storage vessel can be located above the filler, and on the materialâ&#x20AC;&#x2122;s flow characteristics. The more free-flowing it is, the more accurately its flow can be varied (down to dribble-feed rate) by a slide gate or other valve that must close the instant a precise target weight has entered the bag. Non-freeflowing titanium dioxide (TiO2) for example, may flow in a trickle and then in clumps, and it may bridge above the flow control valve, making it a poor candidate for gravity feeding. For non-free-flowing materials, a metered feeding system is required to feed the filler accurately and consistently. Metering systems can include a flexible screw conveyor (FIG. 9), screw feeder, rigid auger, drag disk, bucket elevator,
rotary airlock valve, or other device that does not rely on gravity alone to deliver material to the filler. The selection of a metering system can hinge on the available space above the filler, since surge hoppers and filter receivers with rotary airlock valves may require more headroom than is available. In these cases the discharge housing of a flexible screw conveyor can often fit between the filler inlet and the ceiling joists, while eliminating the need for a flow-control valve. For products that are easily aerated, pneumatic conveying systems should be avoided, since the conveying process can cause the material to Fig. 10 require a much lengthier densification/deaeration cycle to achieve the desired fill weight and package stability. If sufficient headroom exists above the filler, a surge capacity equivalent to the weight of a filled bag can be employed to reduce cycle times while maintaining accurate fill weights. This configuration allows bag change-over to occur while the subsequent batch is in the process of being weighed. When a pneumatic conveyor is used as the material delivery system, the filter-receiver can be sized to hold the weight of an entire bulk bag (FIG. 10) to apply this method. For the same reason, a surge hopper above the filler can be considered when utilising mechanical metering devices moving material to the filler from both storage vessels and plant processes.
6. COMPLY WITH SANITARY REQUIREMENTS
While all fillers can be constructed of stainless steel with ground and polished welds, their designs can preclude sanitising according to government standards. If your application must meet sanitary requirements, your choices should be limited to designs that are accepted by the USDA Dairy Grading Branch (FIG. 11) or other agencies to which you must comply, or to which you elect to comply for assurance that sanitary conditions can be maintained.
Fig. 9
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
CONCLUSION
Fig. 11
With an almost unlimited combination of filler designs, features and upstream equipment from which to choose, specifiers have the ability to tailor bulk bag filling systems according to capacity requirements, expandability, safety concerns, plant hygiene considerations, ancillary filling needs, upstream equipment and sanitary standards. While numerous available options can complicate the selection process, they can also yield a highly efficient and cost effective solution to any given filling problem, providing that fundamental steps are taken to evaluate equipment against precise requirements.
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CONTINUOUS WET AGGLOMERATION BY INSTANT MIXING TECHNOLOGY By Stewart Bryan, Commercial Manager, Hosokawa Micron Limited, Runcorn, Cheshire
Agglomeration can be defined as a process of particle size enlargement where fine powder particles are bonded to form large, relatively permanent masses in which the original particles are still identifiable. These agglomerates have a coarse, open structure and a mean particle size ranging from 0.1 to a few millimetres. The process uses agitation in the presence of the required proportion of a liquid phase or other binding agents and is normally followed by evaporative drying. Applications for instant mixing are, for example, found where rapid dissolution, dispersion and wetting are important in the product end use. Powders suitable for processing with this process include most water soluble powders, including sugars, milk powder blends and water soluble chemicals.
APPLICATION: CHOCOLATE DRINKS
BENEFITS
The goal of any particle size enlargement process is to reliably produce particles exhibiting required end use properties - simple de-dusting, to engineered particle of specific size, shape, density and dissolving rate or compressability.
INSTANT MIXING AGGLOMERATION
Instant mixing agglomeration is a wet agglomeration method. This means powders and a liquid are required by the process which typically includes mixing, drying, conditioning, size reduction, size classification and material transport.
MIXING
Instant mixing agglomeration maximises control of mixing conditions which give rise to yielding ‘perfectly’ formed uniform granules. With high level mixing intensity, instant mixing agglomeration delivers uniform wetting of particles and uniform particle growth. Because newly formed wet agglomerate is malleable, particles are easily deformed. It is important therefore that residence in the mixer is limited; 0.2 seconds to a maximum of a few seconds. Saturated powders exhibit extremely poor flow characteristics which can cause mixer blockage. A self cleaning mixer offers the answer. However insufficient cleaning of material from the wall can give rise to non-uniform, non-homogenous product characteristics which in application show up as ‘sinkers’ or undissolved, undispersed product. Liquids are introduced typically near the feed end of the agglomerator. The liquid feed stream can be atomised using air; also steam can be injected. The mixer itself can provide the remaining mechanical atomisation to disperse the fluid.
CONDITIONING
clusters of smaller particles. Because of the irregular surface, the instant agglomerate will have more surface area than a solid ‘regular’ granule – properties which aid dispersibility, fast dissolving and compressibility of the agglomerate. If, however, a more defined shape is required, a secondary forming process prior to conditioning can be done.
The consumption of cocoa in chocolate drinks has increased considerably over the past decades. This is mainly because products have been developed that make it easier to transform cocoa powder into hot and cold drinks. These products must have instant properties. The final product is judged by the following criteria: * bulk density * colour * flowability * wettability * sinkability * dispersibility * homogeneity of product, no segregation * dissolving time in hot or cold liquids * appearance
AGGLOMERATION PROCESS
Before the actual agglomeration takes place, all powdery components will have to be blended. This can be done in different ways, the choice of which depends on the production capacity. For a production capacity between 500 and 1000 kg/h the most practical way is to pre-blend all powdery components in a Vrieco Nauta Conical Mixer After preblending, the mixture is fed to a buffer hopper. From this hopper, the blend is fed to the Flexomix agglomerator, in the correct proportion by a constant weight feeder. For agglomeration with water, 2 - 8% water is generally needed. This is an important parameter to influence the grain size of the product. The grain size of instant cocoa is generally between 300 and 600 μm. The use of water in combination with steam gives special quality characteristics on the end product. Emulsifiers and flavours could be dissolved in water using a liquid premix tank. Part of the sugar can also be dissolved in the water, which influences the instant effect. The wet granules fall directly from the Flexomix into the Fluidbed Dryer. Warm drying air is blown through the perforated base plates. The temperature of the drying air and the maximum temperature of the product during drying are very important factors for the quality and the taste of the end product. After passing the drying section of the fluidbed, the product transfers to the cooling section in the same bed. Dependent on the behaviour of the end product, cooling is done by ambient air or conditioned air. The blow-over air is cleaned by a (cyclone and a) filter and exhausted. The separated dust is either collected in a small hopper or transported directly to the packing line, together with the on-size product. After cooling the product is discharged from the Fluidbed Dryer and passes a sieve to eliminate any oversize particles which may be present. The oversize is continuously crushed and added to the end product stream. The total stream of end product is fed to a storage hopper from where it is transported to the packing lines. The total
Mixed, agglomerated product is discharged directly to a conditioner, typically a dryer, to stabilise the agglomerate. Because of the malleable nature of the wet granule, physical handling will affect ultimate product quality, size, shape, density, etc. Further mechanical handling methods need to be carefully considered in light of desired end product qualities. Options for further processing after the wet agglomeration step include: Drying When no further sizing is required and a dispersible granule with maximum surface area is required for products including chemicals or instant beverages fluidbed drying is preferred, providing minimal mechanical force and maximum drying rate. Wet granules are suspended in and surrounded by drying air. The fluidbed dryer effectively classifies the particle returning fines to the agglomerator for rewetting resulting in a dust free product. Cooling Cooling stabilises the malleable granules. Forming The instant mixing process is most efficient in producing a fine agglomerate in the range of 100 μm to 1000 μm. Due to the instant forming process, the agglomerates are Figure 3: Flexomix Mixing System
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Agglomeration Plant is controlled by a SCADA system as Operator interface.
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
SPIROFLOW’S BULK BAG FILLING SOLUTION BOOSTS BABY FOOD PRODUCTION Spiroflow Ltd, world-leading manufacturer of conveying and weighing systems, has boosted productivity at a household name baby food manufacturer by installing a bulk bag (FIBC) filler and vacuum conveyor system to significantly reduce the need for manual handling. Shifting millions of tonnes of very fine ingredients is part and parcel of the production process for food companies, which must have systems and equipment in place that adhere to regulatory requirements. The company specified a bulk bag (FIBC) filler for various infant formulas and powders. The equipment is manufactured entirely of stainless steel with automatic height adjustment for different-sized bags, and offers bag inflation and a vibration facility for an even, accurate fill and effective compaction – resulting in a stable load for both storage and transportation. Completing the ATEX approved conveying and bulk handling solution is a gas flushing connection and vacuum conveyor system for the safe, accurate and dust-free filling and transportation of powdered milk. Deploying a filling machine for bulk bags and vacuum conveyor system for transporting the product is saving the company the equivalent of 40 25kg sacks per filling and reducing handling downstream, as the product is emptied automatically rather than manually. The firm’s site engineer chose Spiroflow as he had positive previous experience of its conveying equipment, having previously purchased flexible screw conveyors from Spiroflow several years ago - which are still operating satisfactorily to this day. The customer used bulk bags to reduce manual handling and increase hygiene levels: bulk bags are one of the most convenient, cost-effective methods of packaging, storage and transport. Market-leading customers in industries ranging from food and pharmaceuticals to plastics and building products, use Spiroflow’s handling systems for bulk bags, usually for filling or discharging fragile or fine-particle products quickly and with the minimum of fuss. In addition to bulk bag fillers and vacuum conveyors, Spiroflow also manufactures flexible screw conveyors, aero mechanical conveyors, tubular cable and chain drag conveyors, bulk bag dischargers, ingredients handling and weighing systems. The company’s technical and engineering expertise has led to it developing an international reputation for an unrivalled range of products with state-of-the-art control systems.
PS: Spiroflow recently open their new Technical Centre and you can learn about it by turning to page 5 of the magazine. For more information on Spiroflow’s products and services visit www. spiroflow.com or call +44 (0)1200 422525.
RINGING IN THE CHANGES FOR 2015? Does 2015 represent an opportunity to get more performance from your process equipment or simply another year of coaxing the plant along from one problem to the next? Unfortunately, for too many companies, manufacturing rates or product quality are often let down by powder handling equipment that either flows material erratically or not at all. The causes of many of these types of problems have been recognised for many decades, but the knowledge to provide an initial diagnosis is often not available to those tasked with keeping production running. The Wolfson Centre for Bulk Solids Handling Technology has developed just the range of short courses that industrial end users and designers need to keep themselves up-to-date with the latest technologies and established test methods that can be applied to solve many types of flow problems. Pick up the phone, not the hammer
For more information visit: www.bulksolids.com wolfson-enquiries@gre.ac.uk 020 8331 8646
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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POWDER STORAGE SILOS – DISASTERS WAITING TO HAPPEN?
The latest silo protection technology provides much more than a safety system to prevent over-filling and over-pressurisation. INTRODUCTION
According to Hycontrol’s MD Nigel Allen, many powder storage silos are disasters waiting to happen, putting lives at risk and posing serious threats to the environment. Level measurement specialists Hycontrol have been designing specialist silo protection systems for over 20 years and have extensive experience of the potential problems that exist on sites, especially in the quarrying, cement, bitumen, food, plastics and waste water industry sectors. “Our findings are worrying to say the least and the photos taken by our installation engineers speak for themselves”, says NigelAllen. “Companies just don’t seem to understand the consequences of poorly maintained protection systems. It’s quite frightening that operators accept pressure blow outs via the pressure relief valve (PRV), erroneously citing that ‘It’s OK - the PRV is doing its job’. This couldn’t be further from the truth PRVs are there as a last resort. If the silo protection system is working correctly and is fitted with an automatic shut-off feature to prevent over-filling, the PRV should never be used. If a PRV blows then there’s an inherent problem with the system or the filling protocol and corrective action must be taken.” “Material in and around a PRV is a tell-tale sign that there’s something wrong and a catastrophic blow-out is waiting to happen” continues Allen. “The material blown out from the silos will almost certainly solidify over time and this will, at best, prevent the PRV from working correctly and, at worst, completely clog it up. Unfortunately many Fig.1: A PRV that’s completely maintenance engineers just don’t realise solid! the potential dangers that lurk beneath. They often think that simply cleaning off the material on and around the PRV is good enough. They don’t realise that if the PRV doesn’t lift next time an ‘event’ occurs, the over-pressure could easily rupture the silo or eject the filter housing from the top. On an ATEX rated silo the over-pressure could be sufficient to simulate an explosion and open the protective blast panels, resulting in costly loss of product and silo contents being left open to the elements”. With regard to filter housings, Hycontrol engineers have witnessed another worrying practice at a number of sites where companies fit chains to prevent the housing being blown off the top of the silo, almost accepting the inevitable is going to happen.
WHAT CAUSES PROBLEMS?
OVER-PRESSURISATION
Silo protection systems are designed to prevent the damaging and potentially dangerous Fig.2: Believe it or not there consequences of silo over-filling or overis a silo protection system pressurisation when powdered material is being transferred pneumatically from road tankers to underneath silos. Unfortunately, perched out on the top of silos, such protection systems are all too often ‘out of sight - out of mind’ - that is until a major problem occurs! Problems during the filling process usually arise through an inherent problem with the silo protection system or with the air filtration system on top of the silo. Problems can also occur through tanker driver/operator error. Delivery tankers are pressure-tested vessels typically capable of withstanding up to 2 bar (29 psi) pressure. Storage silos are designed to withstand the weight of material stored in them and can rupture at pressures as low as 1-2 psi above atmospheric pressure. The consequences of over-filling or over-pressurisation include: · serious or fatal injury to workers and the public. · catastrophic silo damage · loss of material and production plus · harmful environmental pollution · damage to company reputation A key issue with many silo protection systems is that without adequate ground level testing capabilities, operators don’t know if they will work when needed. Working at height restrictions limit silo top inspections and maintenance, especially in adverse weather conditions. However, the main problem is what can engineers actually do when they are at the top of the silo? How do you physically test a relief valve or pressure transmitter unless you remove them? Even if the protection system does do its intended job and prevents a major incident, companies rarely investigate the root cause of the problem so that remedial work can be carried out to prevent the situation re-occurring. Important ‘near miss’ events
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such as PRV (Pressure Relief Valve) lifts, high level events and high pressure events are routinely not recorded and often conveniently dismissed. Hycontrol have clear evidence that in practice there are more ‘near misses’ than realised and that the situation is a ticking time bomb. Filter housings at the top of the silos are designed to Fig.3: Now you don’t see it! vent the silo during filling, whilst preventing dust escaping into the atmosphere. Normally these are fitted with some form of self-cleaning system to keep filters clear. These are typically mechanical shakers or reverse jet systems. Although filter manufacturers give recommended check routines and filter replacement schedules, in practice it would appear these guidelines are regularly ignored. Faulty operation can be caused by a range of issues, including blockages and the Fig.4: Now you do! fitting of unsuitable or wrongly-sized filters. Most powders form hard compounds when mixed with water from the atmosphere, further exacerbating the problems at the top of the silo.
EFFECTIVE SILO PROTECTION
The MPA (Mineral Products Association) publishes comprehensive guidelines for silo protection systems in quarries and cement works, but there are little or no such recommendations for powder silos used in a broader range of industries including food and beverage, chemical, water treatment and plastics. However the primary principles are the same for protecting any pneumatically filled silos. Even with guidelines in place, the bench mark for the effectiveness of any silo safety protection system can only relate to the last time all the components were fully tested.
OPTIMUM SOLUTION
The only effective solution is to take an integrated approach to silo protection design whereby the PRV, pressure sensor and high level alarm can be tested at ground level, prior to each fill. Only when all these safety devices have passed the checks should the safety interlock allow the silo inlet valve to open and the delivery to commence. As an added benefit, an effective protection system can serve as a powerful predictive maintenance diagnostic tool by recording critical near-miss events that occur during the filling process. This information allows managers to carry out effective predictive maintenance by means of a logical step-by-step root cause analysis (RCA) process to understand why the problems are arising. For example, high pressure and PRV lift events may be due to filter problems, prompting questions such as: · Are the filters the correct size? · Is the filter cleaning regime fully operational? · Have the filter bags/cartridges been changed as per manufacturers’ recommendations? In parallel the logs will also indicate if the tanker drivers are routinely over pressurising during the fill process. In summary, the optimised silo protection system should incorporate: · Pressure sensor, hi-alarm level sensor and PRV testing (essential) · Simple ‘1’ button press to test all components · Silo filling auto shut-off control · Pneumatic cleaning of pressure sensor · Recording of the number of events on incidents of over-pressure (time /date stamp) · Recording of the number of events of PRV lift and opening (time /date stamp) · Recording of the number of events of high level probe activation (time /date stamp) · Filter ON / OFF output option to check filter status · Filter air supply monitoring alarm option
CONCLUSION
There is strong empirical evidence that many silos are ‘disasters waiting to happen’. The practical reality is that powder storage silos can split or rupture at pressures as low as 1 or 2 psi above atmospheric pressure. Malfunctioning filter housings can be ejected at similar pressures. Cursory visual inspections of silo protection equipment is woefully inadequate. Therefore it is imperative that any installed safety system must be capable of providing reliable protection that can be easily verified by testing critical components before each and every delivery – without having to climb to the top of the silo. This approach will provide total silo safety; protecting assets, the environment and most importantly site personnel and the public.
PROCESS INDUSTRY INFORMER January - February 2015 - SHAPA Supplement
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