Performance of new filter media expectations and experience in vacuum and pressure filtration

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1 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 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 Fig. 1: Pore count development of different Double Layer Weave fabric generations Fig. 2: Number of pores vs. filtration time of DLW of the same pore size Fig. 3: Filter media resistance vs. filtration time 48 F & S International Edition No. 16/2016

2 Chemical Environmental Food Mineral Life Science 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. 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 F & S International Edition No. 16/2016 More than 50 years experience in process filtration Sefar AG Hinterbissaustrasse 12, CH-9410 Heiden Tel , Fax filtration@sefar.com,

3 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 F & S International Edition No. 16/2016

4 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 (m 3 /(m 2 *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 /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! STEINHAUS GmbH Platanenallee Mülheim an der Ruhr Germany Phone +49 (0)208 / Fax +49 (0)208 / filter@steinhaus-gmbh.de spaltsieb@steinhaus-gmbh.de website optima c F & S International Edition No. 16/

5 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). 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. Fig. 7: Square mesh fabric: Pressure increase to 0.6 bar- achieved within 30 min. Throughput rate avg. is at 103 m 3 Fig. 8: New double layer fabric: Pressure increase to 0.6 bar - achieved within 90 min. Throughput rate avg. is at 119 m 3 Fig. 9: Comparison of metal impurities at different pressure levels 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 m 3 /(m 2 *h) - Filtrate clarity - Cake dryness and quality 52 F & S International Edition No. 16/2016

6 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 cm 2 - 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. Summarized: 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 processes or when optimization of the current process is done. Through that, the overall cost of ownership can be reduced and competitiveness increased. Literature: /1/ VDI Guideline 2762: Mechanical solid-liquid separation by cake fi ltration, Determination of fi lter cake resistance. Part 1 and 2; Beuth Verlag GmbH, Berlin /2/ B.Sc Christoph Maurer: Publication, next generation of vacuum belt fi lter media. Achema 2012 /3/ H. Anlauf: Filtermedien zur Kuchenfi ltration - Schnittstelle zwischen Suspension und Apparat. CITplus 12/2003, GIT Verlag GmbH & Co. KG /4/ E. Ehrfeld: Infl uence of Filter cloth behavior on the layout of cake forming fi lters. Company BOKELA /5/ D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer: Eigenschaften von Filtermedien und ihr Einfl uss auf die Vakuum- und Druckfi ltration. Teil 1: Design von Filtermedien und Laboranalysen. Filtrieren und Separieren 29 (2015), Nr. 2, S /6/ D. Bartholdi, I. Erlenmaier, A. Seitz, Ch. Maurer: Eigenschaften von Filtermedien und ihr Einfl uss auf die Vakuum- und Druckfi ltration. Teil 2: Resultate aus Feldversuchen Filtrieren und Separieren 29 (2015), Nr. 3, S 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 Düren / Germany Phone: +49 (0) 2421/803-0 Fax: +49 (0) 2421/ 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 F & S International Edition No. 16/