Experts in filtration and separation

We advance and disseminate knowledge in the design and use of filtration and separation techniques in industry, commerce and other walks of life.

2005

Published papers: Volume 5, Issue 4

Author(s) Title, page numbers and abstract
B.B. Gönül and Ö. Özcan THE EFFECT OF SURFACTANT ON the PRESSURE FILTRATION OF CLAY MINERALS IN THE PRESENCE OF FLOCCULANT (pages 250-252)

Abstract

In this study, the effect of nonionic surfactant in the presence of flocculant on the pressure filtration of tincal ore clay minerals was investigated. The filtration of the clays was not possible without flocculation. In the presence of flocculant, the surfactant addition caused a decrease of the filtration rate in pressure filtration, which is different from what is suggested in the literature. The surfactant addition caused dispersion of the formed flocs of the clay suspensions and decreased the floc strength. As a result, the residual moisture content of the clay mineral filter cakes increased. The change of the filtration rate of clay minerals with the surfactant addition in the presence of flocculant has been investigated.
J. Binnig, N. Mao, J. Meyer, M. Hata, G. Kasper and C. Kanaoka COMPARISON OF SURFACE FILTER TEST RIGS ACCORDING TO VDI 3926 AND JIS Z 8909-1 (pages 253-258)

Abstract

Two test rigs for pulse-jet cleanable filter media were compared with regard to cycle duration, residual pressure drop and particle emission level. The two rigs each reflect a standardized design for evaluating cleanable filter media, and differ mainly in the design of the respective regeneration systems. The standard test protocol included 5000 cycles of accelerated aging; media tested were singed and calendared polyethylene felts. Particulate emissions were recorded in real time by an optical particle counter.Test results during the first 30 cycles before aging agree well, both in absolute terms between the rigs, and for the media relative to each other on either of the rigs. After aging the two rigs differ by factors of about 1.9 and 0.75 respectively, for cycle duration and residual pressure drop for each of the two media tested. The largest differences arise from the particulate emission levels, both before and after aging. The gap between the rigs widens substantially with aging, for all performance parameters.
A. Walker APPLYING FILTER AIDS TO ROTARY DRUM VACUUM FILTER INSTALLATIONS (pages 258-263)

Abstract

Rotary drum vacuum filters, with their ease of operation and continuous discharge of solids and filtrate, are a natural choice for many applications. With the appropriate use of filter aids, the performance of a rotary drum vacuum filter (RDVF) can be enhanced. This paper provides three possible variations on a typical filtration application to demonstrate the operational benefits of using filter aids.
D. Dubbin Concentrating on quality – membrane filtration case studies (pages 264-269)

Abstract

Crossflow membrane filtration offers some unique benefits to producers. It provides an economic means of water removal which can easily be integrated into existing concentration and drying systems, but perhaps the most exciting feature of the technology is the ability to simultaneously concentrate and purify, thereby making possible enhanced product quality and new product development. In this paper two case studies are presented which seek to demonstrate how these properties have been exploited.
R.W. Chin and C. Metcalf INTRODUCTION OF AN AXIAL FLOW HYDROCYCLONE (pages 269-272)

Abstract

Hydrocyclones have been used in the petroleum industry for de-oiling produced water for some time now. The typical unit consists of tangential inlets followed by a tapered body. A new design based on axial flow past a stationary turbine instead of tangential inlets to induce spin will be presented. The axial flow reduces pressure losses as well as shearing of the oil droplets. Laboratory results of pressure losses, throughput, and performance will be presented.
G. Rideal, J. Storey and T. Morris APERTURE TESTING OF SAND SCREENS USING CALIBRATION MICROSPHERES (pages 273-276)

Abstract

This paper describes the development of a new method for the direct measurement of pore sizes in sand screens. Pivotal in the calibration process is a sonic sieving device that energises the microspheres to efficiently transport them through the filter mesh. From the percentage passing, a calibration graph supplied with the standard is used to determine the filter cut point. The analysis time is only 1 minute. Sampling variations both from a single roll and across several rolls were examined on 3 sand screen grades. The uncertainty of the method was less than 5%. This unique method provides a direct traceability to the International unit of length, both NIST and NPL.
I. Fantom and C. Cotttingham SHOULD I REPLACE MY ELECTROSTATIC PRECIPITATOR (ESP) WITH A FABRIC FILTER (FF)? (pages 277-284)

Abstract

Lodge Sturtevant explore the pros and cons of moving from ESPs to Fabric Filters. The case to move to barrier filtration is not always as clear as it may seem. For many industries ESPs remain the Best Available Technology (BAT) when taken in context with IPPC and BPEO. Will the operating and maintenance costs increase? Our process conditions fluctuate. How will these affect emissions? Will the upgrade plant be “future-proof”? Can the plant meet even lower emissions in say 10 years time? These are frequently asked questions. We try to unravel the complex technical and economic issues to make your decision easier.
T. Frising, D. Thomas,
J.-C. Appert-Collin, S. Callé-Chazelet and P. Contal
INFLUENCE OF LIQUID AEROSOL STOP-AND-GO ON THE PERFORMANCE OF FIBROUS FILTERS (pages 286-294)

Abstract

Fibrous filters are the most common means used to separate liquid aerosol particles from an industrial gas stream. The pressure drop and penetration are the most important performance criteria of the filter. This study investigates the influence of an aerosol generation stop and go on the filter pressure drop and penetration. Experiments carried out using a HEPA glass fibre filter show that the pressure drop increases by up to 20% after an aerosol generation interruption. The pressure drop increase could be countered by performing a clean air permeation during the break period. If a permeation velocity higher than the filtration velocity is used, the pressure drop of the filter is noticeably reduced compared to what it would have been without an interruption. The same aerosol interruption did not have a clear influence on the filter penetration. The permeation technique could thus be considered to optimise liquid aerosol filter cleaning and/or regeneration. Keywords: Droplets; generation interruption; pressure drop; efficiency; clogging.
K. Järvinen, M. Oja and P. Rantala DEVELOPMENT OF HIGH PRESSURE FILTRATION CLOTHS (pages 295-304)

Abstract

In targeting economical solid-liquid separation, it can be optimal to aim for filter cakes with as low a moisture content as possible from the first stage of filtration. In some cases, if it is possible to filter the cake mechanically to a moisture content of less than 30 %, for example, the product can be further processed without a need for further dewatering cycles. One way to take the conventional filtration process further and to reach a considerably lower filter cake moisture content is to raise the filtration pressure gradually to an exceptionally high level, such as 140 bar. This paper focuses on the high pressure filtration of calcium carbonate, which is not easily filtered given its average particle size of 1.2 mm, and also on the impact of different cloths on filtration efficiency. Typical problems with high pressure dewatering techniques include the adherence of the cake to the filtration medium, mechanical breakdown or folding of the filtration medium in the filter and premature blinding of the filtration medium. If the performance of the filtration medium can be ensured in a high pressure filter in the same way that cloths function in conventional filters, high pressure filtration could provide major economic benefits in a number of conventional liquid-solid separation applications.

Keywords: Filter media; pressure filtration; coated fabrics.

Published papers: Volume 5, Issue 3

Author(s) Title, page numbers and abstract
P. Burroughs THE APPLICATION OF LASER PARTICLE SIZE ANALYSIS TO JUICE FILTRATION IN THE SUGAR INDUSTRY (pages 173-179)

Abstract

Juice filtration is an important feature of sugar processing. The purification of raw sugar juice from beet is a continuous process involving lime and carbon dioxide. The calcium carbonate precipitate produced in the purification stages is removed from the juice by a combination of settling and filtration. The filterability of the juice is significantly influenced by the particle size distribution of the precipitate. By using laser particle size analysis it has been possible to improve the understanding of those factors which can influence the particle size distribution of the precipitate.
S. Das A CASE STUDY ON TEXTILE EFFLUENT TREATMENT (pages 180-182)

Abstract

Our biosphere is under constant threat from continuing environmental pollution. Impact on its atmosphere, hydrosphere and lithosphere by anthropogenic activities on water, air and land have negative influence over biotic and abiotic components on different natural eco-systems. In recent years different approaches have been discussed to tackle man made environmental hazards. Clean technology, eco-mark and green chemistry are some of the most highlighted practices in preventing and or reducing the adverse effect on our surroundings.Among the many engineering disciplines, textile engineering has direct connection with the environmental aspects to be explicitly and abundantly considered. The main reason is that the textile industry plays an important role in a country like India as it accounts for around one third of total export. Out of the various activities in the textile industry, chemical processing contributes about 70% of the pollution. It is well known that cotton mills consume large volumes of water for various processes such as sizing, desizing, scouring, bleaching, mercerization, dyeing, printing, finishing, and washing. Subsequently, large volumes of wastewater containing numerous pollutants are discharged. This stream of water affects the aquatic eco-system in a number of ways such as depletion of the dissolved oxygen content or settlement of the suspended substances in anaerobic condition and special attention is demanded.

The study of the different measures that can be adopted to treat wastewater discharged from the textile chemical processing industries to protect our surroundings from possible pollution has been the focus of many recent investigations. This paper highlights one such preliminary study that was carried out at the Amaravathi Common Effluent Treatment Plant situated in Karur, a place near the north-central part of Tamil Nadu, India which has recently been known for producing considerable amounts of home textiles. A detailed investigation is under progress.

A. Jena and K. Gupta Characterisation of the pore structure of complete filter cartridges using high flow porometry (pages 183-187)

Abstract

Measurement of the pore structure characteristics of complete filter cartridges is a real challenge because of the high gas flow rates through large cartridges, the large size of the sample holder, and other related problems. A high flow porometer designed and built for testing high gas flow samples has been described. The equipment yields highly reproducible and accurate data. Sintered metal, woven metal and ceramic cartridges have been tested and their pore structures successfully measured. These data are presented and discussed.
K. Sutherland THE WORLD OF FILTER MEDIA: A Look at the Marketplace (pages 187-192)

Abstract

The paper introduces a symposium of filter media developments, setting the scene of the filter media marketplace in nature, size and content. It reviews recent developments, and draws attention to the ways in which further developments are occurring or are needed.
A. Macias-Machín, J. Santana-Rodríguez and J. Umbría GAS CLEANING USING AN ATOMISED ULTRA FREEZING SEPARATION UNIT: VOCs RECOVERY (pages 193-196)

Abstract

There is an emergent need to reduce the emissions of toxic volatile organic compounds (VOCs) going into the atmosphere. The most common VOC control technologies in use today are thermal incineration, catalytic oxidation, adsorption, volume concentrators, absorption, flames, biofiltration, membrane technologies and condensation. This paper describes the development of a new atomised ultra freezing separation unit (FUA) which allows the filtration of particulate solids from a gaseous flow and the simultaneous recovery of volatile organic compounds. Liquid nitrogen vapour recovery (helical-coil condenser) is used to reduce the amount of VOCs emitted into the atmosphere from point sources and provide for the recycling or re-use of the VOCs that are recovered. In all the cases studied (xylenes, methanol, toluene and acetone) the recovery efficiencies were higher than 94%.
J. Kostuch, T. Hoskin and A. Phillips SELECTING THE LOWEST COST DEWATERING PROCESS FOR FINE INDUSTRIAL MINERALS (pages 197-201)

Abstract

This paper considers and contrasts a range of dewatering technologies including centrifuges, filters and thermal systems for the dewatering of micron size industrial minerals. Capital, operating and lifetime total costs are reviewed, making reference to practical examples.
W. Reimann MEMBRANE SEPARATION TECHNOLOGY FOR THE PURIFICATION OF LACTIC ACID AFTER FERMENTATION (pages 201-203)

Abstract

The reaction mixture coming from a fermentation contains not only the target product, but also biomass, residual substances of the nutrients and salts employed, secondary products of microbial metabolism, and non-converted nutrients. All suspended constituents, including the biomass, are separated during recovery of the culture filtrate solution by ultrafiltration, which represents the state of the art. In contrast, the purification of the target product from dissolved ingredients can be very laborious and cost-intensive.Using the example of model solutions and lactic acid, obtained from rye flour by fermentation in the form of sodium lactate, it is shown how chloride can be separated from the culture filtrate solution by membranes. With diafiltration up to 79% of the chloride is washed out by using a volume of washing liquid equal to 50% of the volume of feed from sodium lactate. By electrodialysis with mono- and bi-polar membranes the sodium lactate is concentrated and transformed into free lactic acid and caustic soda. Through the test results it is demonstrated that not only uncharged components such as sugar and proteins, but also external ions such as chloride ions, can be removed from the target product by using membrane separation technology.
P. Johnston PORE-SIZE DISTRIBUTIONS IN FILTER MEDIA DEDUCED FROM THE EXTENDED BUBBLE-POINT TEST (pages 204-210)

Abstract

The pore size distribution in a filter medium, built from a random array of building materials, is addressed by considering the medium to be composed of a stack of theoretical thin layers — thin enough that pores pass straight through. All layers have the same gamma distribution of pore sizes, yet a certain-size pore in one layer does not necessarily lie on the same spot in adjacent layers. Thus the overall flow-pore-size distribution is narrower than that in a single layer. Moreover when the porosity (ratio of void volume to total volume) is less on one face, that face has smaller pores. The “largest” pore on a face is deduced from the bubble point, that gas pressure from underneath required to cause this first flow of gas from the top of a liquid-soaked medium. Yet no standard method has been developed for that measurement. Moreover investigators have not compared the bubble points on the separate faces.

Analyses of two separate results of extended bubble-point tests indicate that the test measures the effective pore size distributions in the top two or three theoretical layers.

P. Collins FILTRATION – AN INTEGRAL PART OF THE MODERN INDUSTRIAL PROCESS (pages 211-213)

Abstract

Filtration covers a diverse range of products, services, and industries and is typically understood as a means of cleaning a fluid by separation of usually dissimilar substances. To qualify as an integral part of the modern industrial process suggests that each part, including filtration systems, must contribute towards the functionality of the process, and increasingly also be capable of delivering a financial benefit.Dust control has evolved as an important part of filtration and is typically regarded as the heavy duty end due to its potential to handle huge gas volumes, with contamination concentrations ranging from 0.5 g/m3 to 250+ g/m3, and capable of delivering cleaned gas where the remaining contamination has a concentration level of < 1 mg/m3. Therefore with a cleaning ratio of up to 250,000:1 there is no doubting its functional contribution, and the visible impact that a correctly applied dust filter can have on its surrounding environment. However, it is possible for initial discussions with potential end users to reveal that it is a reluctant purchase and perceived as equipment with no positive financial benefit to the business. This paper demonstrates that this perception is often completely incorrect.

H. K. Shon, S. Vigneswaran, J.-H. Kim, H. H. Ngo and N.E. Park COMPARISON OF NANOFILTRATION WITH FLOCCULATION – MICROFILTRATION – PHOTOCATALYSIS HYBRID SYSTEM IN DISSOLVED ORGANIC MATTER REMOVAL (pages 215-221)

Abstract

In this research, a NTR 729HF nanofiltration (NF) membrane was employed to remove synthetic organic matter (SOM) from wastewater. NF alone led to a removal of 92.4% of dissolved organic carbon (DOC). The performance of NF was compared with that of a microfiltration (MF) hybrid system consisting of FeCl3 flocculation, MF and photocatalysis. Flocculation and microfiltration followed by photocatalysis led to more than 96% dissolved organic carbon (DOC) removal. A detailed molecular weight (MW) distribution study of organic matter indicated that the photocatalysis initially breaks the large MW organics and then the small MW organics were removed by a photoreactor process. Flocculation with an optimum dose of FeCl3 (68 mg/L as FeCl3) gave rise to the highest removal of organics including small MW organics. The small MW organics remaining after the treatment of flocculation could successfully be removed by photocatalysis.Keywords: Flocculation: PAC adsorption; photocatalysis; molecular weight distribution; nanofiltration; microfiltration.
Xu J., Ding S., Wang W. and Xu H. IMPROVING FLOC CHARACTERISTICS BY NON-SYMMETRICALLY ALTERNATIVE ROTATING FLOW (pages 222-228)

Abstract

The effects of non-symmetrically alternative rotating flow on the characteristics of flocs, including floc size and sedimentation, were investigated experimentally. It is shown that when the positive flow occupied about 25% of the total mixing time, with the rest comprising negative flow (in the opposing direction), the formed flocs had higher density and similar size to those obtained by a conventional stirring flow. The mechanisms by which the alternative flow restructures the aggregates are qualitatively analysed. It was supposed that the relaxing, throwing and twisting effects induced by the alternative flow are responsible for the improvements.Keywords: Floc size; floc density; shearing rate; non-symmetric; alternative rotating flow.

Published papers: Volume 5, Issue 2

Author(s) Title, page numbers and abstract
C.-C. Lin, C.-H. Yang and Y.-J. Chung EVALUATION OF USING HEATED SOLUTION TECHNIQUES FOR REMOVING MEMBRANE FOULING (pages 95-98)

Abstract

The aim of this research is to evaluate the effectiveness of temperature for easing the fouling problems of membranes to prolong their lifecycle. The results show that when water of 30°C was used as solution to remove the fouling, the increase in water mass transfer coefficient ratio (MTCw ratio) of the membrane was 6% (from 92% to 98%). When using water of 40°C as solution the increase in MTCw ratio was 2%. When NaOH was added to adjust the pH of the 30°C cleaning solution, the increase of the MTCw ratio of the membrane was 19%. On the other hand, the increase in MTCw ratio of 40°C cleaning solution with pH adjustment was 23%. Comparing the efficiency of fouling removal, the efficiency at 40°C was higher than the efficiency at 30°C. The results also revealed that the increment of the MTCw ratio can be improved by the addition of strong base. Moreover, the heated solution with added KH2PO4 has a higher removal efficiency of foulants compared with adding the basic chemical K2HPO4. In order to understand the influence of the cleaning process on the removal of target characteristics (i.e. hardness and TDS), the study compared the concentrations of target characteristics at temperatures of heated solution. The result showed that the reduction rates of the hardness and TDS in the permeate side of membrane were over 95%. These removal rates do not cause damage to the membrane structure. So the hardness and TDS removal rates are similar to the removal rates before the cleaning process.
WJ. Silva, S. Duke and P. McFadyen METHODS OF VALIDATING FILTRATION MATERIALS USING POLYMER MICROSPHERES (pages 99-100)

Abstract

Filtration systems configured for specialized applications require new testing methods to validate their performance specifications. Polymer spheres can be formulated for challenging and testing specific kinds of filters with various particle detection methods. This paper discusses some novel methods of leak testing and efficiency testing for several filtration applications. Fluorescent and dyed microspheres for high visual contrast with filter media are discussed, along with non-dyed microspheres for detection by particle counting. Test setups for various applications are also discussed.
S. Weir PRESSURE FILTRATION OF AGGREGATED SEWAGE SLUDGE (pages 101-102)

Abstract

Different aggregation mechanisms are described and their merits discussed in terms of dewatering of sewage sludge by pressure filtration. The aggregation of sewage sludge particles is common practice prior to pressure filtration. The increased effective particle size leads to rapid initial release of water, minimal filter cloth blinding and a structured filter cake, which can continue to release water under pressure. This paper discusses several aggregation mechanisms induced by the use of synthetic polyelectrolytes and explains the dewatering properties in relation to polyelectrolyte properties.
J. George, R. Forna and T. Cravero AIR FILTRATION WITH FINE POLYMERIC FIBRES (pages 102-105)

Abstract

The need for higher filtration efficiencies without adversely affecting the filter lifetime is growing. Fibre diameter is one of the controlling factors in achieving high particulate efficiencies. The most common fibrous raw material which has commercially available fibres with sub-micron diameters is microglass fibre.In recent years, we have seen renewed interest in other manufacturing processes which are capable of manufacturing polymeric fibres with sub-micron diameters. As a result, more tools for the filtration expert to approach their specific problem are becoming available. This paper will take a pragmatic approach to the enhancement of filtration media performance by fine polymeric fibres. Results show a significant impact of these polymeric fine fibres on filtration performance.

M. Day FILTER TESTING – GETTING CLOSER TO FIELD PERFORMANCE (pages 106-110)

Abstract

The level of particulate contamination (“dirt”) in a hydraulic fluid is the single most important factor governing the reliability and life of fluid components. Improvements in system design, management and filter performance have resulted in contamination levels falling dramatically over the past 30 years. Users continue to demand better filtration performance, and this drives filter manufacturers to continuously make developments and improvements to their product. Concurrent with the improved cleanliness levels, the service life of filter elements has increased considerably as users also demand a reduction operating costs. However, a longer life means that the filter is subjected to unsteady conditions for a longer period and it is essential that its performance is not degraded and it maintains the required Cleanliness Level (CL).Filter tests are normally performed in the laboratory, as field-testing is often not practical because of time and cost, and a range of standard tests have been developed by ISO to satisfy this need. The most widely known and used is the ISO 16889 Multi-pass test, which determines the element’s particle removal capabilities and its filtration or Beta ratio. Unfortunately, the test is “steady state” and as it does not subject the filter to unsteady conditions and so the performance should be viewed as the ‘best possible”. Also the test may not show up deficiencies or weaknesses in the structures of the element, but may cause disastrous consequences in service.

This paper explains the drawbacks of the Multi-pass test in trying to predict field performance, and describes the requirements for a dynamic performance test. The paper then presents a newly developed test, which is designed to study the effect of cyclic flow on various aspects of element performance throughout its life. It also introduces a new method of rating filter performance that enables users to clearly distinguish between filters that can withstand the cyclic stress and those that cannot.

M. Socorro, A. Macías-Machín , J. Verona and M. Macías GAS FILTRATION USING NEW GRANULAR MATERIAL (pages 110-112)

Abstract

This paper describes some results for hot gas filtration using Lapilli, a new material for granular packed bed filters. A laboratory apparatus is described and some preliminary measurements of filtration efficiency and Differential Thermal Analysis are shown.
S. Smith A REVIEW OF EXISTING AND NEW ISO STANDARDS FOR APPLICATION IN THE CLASSIFICATION AND MEASUREMENT OF COMPRESSED AIR PURITY AND FILTER PERFORMANCE (pages 113-118)

Abstract

This paper gives an overview of the current series of ISO 8573 Compressed Air Quality Standards Parts 1 through 9 and proposed ISO 12500 Filter Test standards as applied to oil aerosol, hydrocarbon vapour and particulate removal cartridge filters for Compressed Air use. This work is covered by ISO TC118 SC4 WG1 & 2.
Y. Fang, C. Kuang, F. Wang and H. Gu DEVELOPMENT OF METALLIC MEMBRANE AND ITS APPLICATIONS (pages 118-122)

Abstract

There is a continued need for filtration media with high filtration rating and efficiency, good permeability, high temperature capability, high strength and corrosion resistance. Owing to their high strength, rigid structure and non-secondary pollution in addition to high filtration efficiency, metallic microporous materials are being used increasingly in high purity and high safety filtration systems. This paper describes the development of metallic membrane media made of nickel and stainless steel that are available from AT&M, and several cases of its applications in gas separation, radioactive aerosol filtration and fluid purification are introduced.Metallic membranes with mean pore sizes from 0.01 to 1.0 μm were developed. This new filter media exhibits good separation efficiency and very high filtration efficiency; its filtration efficiency for 0.1 μm particles is higher than 99.999999%. The filter media possess very high strength compared with ceramic membranes. The asymmetrically structured metal membrane shows very good regeneration ability. These peculiarities of the metal membrane plus a good thermal resistance permit use at high pressure, high temperature and other stringent application conditions and environment.

M. Scholten FACTIVATED CARBON – ITS USE IN FILTRATION PROCESSES AND RELATED DISPOSAL ISSUES (pages 122-124)

Abstract

Purification by activated carbon is a proven, modern, state of the art technology for a multitude of purification needs. Nevertheless, the principles were discovered long ago, and activated carbon has had a rich history ever since. The ancient Greeks had already described the use of charcoal to soften the effects of food poisoning. At the time of Columbus sailors used to blacken the insides of water barrels with fire; they learned that the water would stay fresh much longer by doing so.
K. Järvinen A NOVEL TECHNIQUE FOR ESTIMATING THE EFFECTIVE PORE SIZE AND OPEN AREA OF DENSELY WOVEN FILTER FABRICS (pages 126-133)

Abstract

Densely woven multifilament filter fabrics (cover factor greater than 1) have been the standard in solid/liquid separation for decades. The effective pore size of a filtration fabric is an aggregate measure of the pore size distribution which, together with the total open pore area, determines the fluid flow resistance of a fabric. It also gives an indication of the size of solid particles that can be retained on the fabric. For monofilament fabrics having a cover factor less than 1 the effective pore size and fabric porosity are routinely estimated from the construction parameters of weave and yarn. However, for multifilament fabrics with cover factor greater than 1 the fluid flow inside the fibre yarns becomes important because the pores in between the yarns are squeezed to the minimum. Even with the most modern porometers it can be difficult to measure the intra-yarn pore size and total pore size area accurately. Consequently, different permeability measurements, and not pore size measurements, have become the standard in evaluating their filtration performance and particle retention. Permeability, however, is a function of many variables and does not correlate directly with effective pore size.The purpose of this study is to present a new method for estimating the effective pore size and open pore area of a densely woven multifilament fabric. The method is based on a combined use of standard textile analytical methods and modelling of liquid flow through a fabric. Measured fluid permeability, fabric electrical resistance and fabric thickness were used in the developed model to calculate the effective pore size and the total open area. The results are validated by comparing them to the measured bubble point pore size (largest pore size) and average pore size of the fabric. The developed model shows good correlation with measured values.

Keywords: Multifilament fabrics; modelling; fabric open area; effective pore size; permeability; electrical resistance.

N. Salmela and M. Oja ANALYSIS AND MODELLING OF STARCH DEWATERING (pages 134-145)

Abstract

In industrial pressure filtration applications it is common to filter the suspension at constant pressure, and then to consolidate the formed filter cake at another, usually higher, constant pressure. The filtration phase can be described by the well-known classical filtration equation. The theories for expression have not been tested to the same degree and the determination of the point where the filtration stage ends and the dewatering stage begins is especially unclear. This paper shows four methods for the determination of this transition point. The methods are tested with filter cycle data from filtration tests with different starches. The theories of expression are also tested in order to find an easy and proper way to model the dewatering of starches in filter presses, and thus to reduce the experimental work required. The starch slurries were filtered in a piston press filter (78.5 cm2) and in a small-scale pressure filter (0.1 m2). The consolidation periods were modelled using Terzaghi’s consolidation model, a simplified version of Terzaghi-Voigt’s consolidation model with two parameters, the Terzaghi-Voigt consolidation model with three parameters and Shirato’s consolidation model. The results suggest that the Terzaghi model is adequate for the prediction of starch dewatering, and the Terzaghi-Voigt model with three parameters can be used for the prediction of longer starch dewatering periods. In addition, Shirato’s model can be used for the rapid prediction of starch filter cake consolidation.

Keywords: Filtration; dewatering; expression; consolidation; data analysis; starch.

W. Reimann TREATMENT OF AGRICULTURAL WASTEWATER USING ULTRAFILTRATION AND SUBSEQUENT REVERSE OSMOSIS (pages 146-151)

Abstract

The production and processing of agricultural produce generates wastewater that must be cleaned. The use of membranes represents an alternative to conventional cleaning methods. Applications of the membrane methods ultrafiltration (UF) and reverse osmosis (RO) were therefore examined for various agricultural wastewaters with consideration given to fouling. More recent studies examined the use of membrane methods for cleaning different wastewaters with different levels of organic contamination in a pilot plant in order to determine the capacity of the wastewater to meet mandatory treatment values and its suitability for reuse in the process.No major impairment of the permeability (permeate flux) and the selectivity (retention of the chemically oxidisable substances) of the membranes as a function of the level of organic contamination of the wastewater could be ascertained for UF. Increasing organic contamination of the wastewater acts particularly on reverse osmosis membranes in the form of fouling and leads to their permeability and selectivity being reduced more quickly.

The studies showed that by using the process combination UF and RO for wastewaters with a low level of organic contamination it is possible to obtain water with a quality that meets the German mandatory requirements for treated wastewater.

Keywords: Wastewater treatment, ultrafiltration, reverse osmosis, fouling, water recycling.

Published papers: Volume 5, Issue 1

Author(s) Title, page numbers and abstract
D. Gough DEVELOPMENTS IN GRAVITY SEDIMENTATION (pages 22-28)

Abstract

Gravity sedimentation has been employed for many years as a pre-treatment, ahead of filtration, to increase filtration rate, and reduce the size of filtration equipment. Over the last few years there has been a quiet revolution in thickening technology, assisted by improved flocculants and better understanding of the factors affecting sedimentation. This paper discusses the effect of feed dilution in thickening, the evolution of the ultra-compact clarifier thickener, and more recently the paste thickener.

W. Chen, F. Parma and W. Schabel TESTING METHODS FOR BELT FILTER PRESS BIOSLUDGE DEWATERING (pages 29-32)

Abstract

Belt filter presses (BFP) are commonly used for biosludge dewatering. Laboratory tests are usually performed to understand the dewatering characteristic of the sludge and to guide the optimisation of BFP operations. This work compares different laboratory testing methods and their effectiveness to simulate a plant BFP. Methods such as capillary suction times, specific cake resistances and apparatus such as the belt press simulator and the Crown Press were evaluated. It was found that the Crown Press is a good laboratory apparatus for simulating the performance of BFP.

P. Polasek and S. Mutl ACCELERATION OF GRAVITY SEPARATION PROCESSES (pages 33-39)

Abstract

The IHDS and POA processes applied both individually or in conjunction with one another represent an ideal tool for a very effective but inexpensive upgrading of water purification works. The High Rate (HR) Clarifier with a fully fluidised sludge blanket, incorporating both the IHDS and POA processes is capable of operating at an upflow velocity at the sludge blanket of between 10-25 m h-1 and more.The course of the clarification process in its individual partial phases and its entirety is influenced by many chemical and physical factors. The influence of the chemical factors manifests itself most profoundly during the process of destabilisation of the impurity particles and the influence of physical factors during the process of combining destabilised impurity particles into separable aggregates.

During practical plant operation the chemical factors affecting destabilisation of the impurity particles are optimised with respect to raw water quality. This includes determination of the most efficient destabilisation reagent and optimisation of its dosage and reaction conditions. The hydrodynamic conditions under which aggregation of the destabilised particles takes place, influenced by the intensity of agitation and characterised by the mean velocity gradient G and its duration T, are not optimised with respect to quality of raw water, destabilisation reagent used, type of method used for separation of formed suspension, etc.

J. Schienke DIATOMACEOUS EARTH – PRODUCTION METHODS AND THEIR IMPACT ON ITS USE IN PRECOAT FILTRATION PROCESSES (pages 39-42)

Abstract

DE is widely used in the food industry, it is necessary to minimise its chemical and biological impact on the filtered product in order to maintain a reliable product quality for the filtered liquid over the course of the filtration process. Each DE filter aid must be as homogeneous as possible to prevent variations in the filtration performance initiated by the filter aid. As the food industry is working mostly with natural products, there are natural variations in the crude food products caused by different harvest or weather conditions of the crude product. This has an impact on the filtration and gives variations to the filtration process itself. Additional variations added by an inhomogeneous DE would further complicate the filtration process, hindering the filtration managers ability to control and adjust the filtration performance.

T. Frising, D. Thomas, P. Contal, D. Bémer and
D. Leclerc
SPECTRAL DYNAMIC EFFICIENCY OF GLASS MICROFIBRE FILTERS IN LIQUID AEROSOL FILTRATION (pages 43-48)

Abstract

Air quality has become an important occupational health, environmental, political and scientific topic over the past few decades. Liquid aerosols can be an important part of air pollution. For example, mists of metalworking fluids used in the mechanical industries can constitute a real health hazard. Filtration is most often the method of choice to rid the atmosphere of these liquid aerosols. Classical filtration theories that calculate the efficiency and pressure drop of new filters are available in the literature [1, 2], but these theories can only be applied to new filters or during the very early stages of the filtration [3]. Even after a short period the amount of liquid accumulated on a fibrous filter, which is influenced by drainage, re-entrainment and evaporation, affects the efficiency. Therefore filter efficiency largely depends on filter characteristics (e.g. fibre material, fibre diameter, packing density, thickness), filtration duration and velocity, and particle size distribution. Several publications deal with filter efficiency variations with particle size distribution [4-9], filtration time [6, 9-11] and filtration velocity [7, 8, 11].

U. Kohaupt FILTRATION OF FINE PARTICLES BY HIGH GRADIENT MAGNETIC FILTRATION (pages 48-50)

Abstract

High gradient magnetic filtration, as realised in the HGF described in this paper, has been developed in a cooperation between a research institute and a medium sized enterprise manufacturing magnetic separators. This development, resulting in a new product, is the state of the art in the magnetic treatment of process liquids. It works with permanent magnets and realises an efficiency of more than 90% for particles of 1 µm diameter. The advantages are high efficiency, less re-contamination of the process, no wear, nearly no power consumption and high reliability. The switchable magnet is realised in an industrial process for the first time and demonstrates the future prospects in magnet applications.Industrial degreasing and ultrafiltration processes are significantly more economical nowadays. Responding directly to more demanding requirements in the industry, high gradient magnetic filtration is an additional step towards more productivity.

X. Simon, D. Bemer, S. Calle, D. Thomas and R. Regnier DESCRIPTION OF THE PARTICLE PUFF EMITTED DOWNSTREAM OF DIFFERENT DUST SEPARATORS CONSECUTIVE TO PULSE-JET CLEANING (pages 52-61)

Abstract

The phenomenon of particle puffing downstream of pulse-jet filters during cleaning is mainly responsible for the increase in downstream concentration, combined with the decrease in filtration efficiency. Clogging and cleaning cycles were performed on three test rigs: a flat media device, an industrial dust separator and a pilot dust separator. The outlet particle concentration was continuously recorded during the filtration cycles and the mass emission after each cleaning was investigated. Cleanings were carried out with different operating conditions in order to differentiate the several mechanisms which participate in the global particle puff. The objectives were to determine the contribution of each one of these different particle removal mechanisms and to investigate the characteristics of the particle puffs during pulse-jet cleaning.The principal mechanisms are classified into two groups; (i) the seepage of particles or particle agglomerates, the resuspension of cake particles during their removal upstream of the filter surface, and the resuspension of particles having settled on the walls of the installation; (ii) the decrease in filtration efficiency following the removal of the cake.

The respective share of these groups of mechanisms seems highly dependent on the “filter media / filtered dust” combination under consideration.

Keywords: Aerosol; fabric filter; pulse-jet cleaning; dust emission; pressure drop; efficiency.

M.J. Lehmann, E.H. Hardy, J. Meyer and G. Kasper FIBROUS FILTERS: NON-INVASIVE DETERMINATION OF LOCAL 3D FIBRE STRUCTURE BY MRI (pages 62-67)

Abstract

The “inner structure” of a low density fibrous filter medium determines its pressure drop, fractional efficiency and dust load capacity. Suitable parameters describing this “inner structure” are key inputs for modelling filter performance accurately. We have reported in the past on ways to apply non-invasive magnetic resonance imaging (MRI) to obtain quantitative data on internal fibre packing density distributions1,2. Key aspects of the technique will be reviewed here, briefly.A difficulty specific to the MRI technique is to validate its results. Alternative methods for obtaining quantitative, highly resolved data are hard to come by. However, previous “intrinsic” tests have shown that reliable information about the packing density distribution can be obtained if the MRI resolution (voxel size) is of the order of the fibre diameter.

For further validation, we now compare the total pressure drop, as measured on real media, with that simulated on the basis of actual 3D packing density data by MRI. The simulation is based on our cellular model, which was implemented in FLUENT, in combination with the classical single fibre theory. Due to an enlarged field of view, for the first time we were able to record the structure of the filter sample over its full thickness. Good agreement of simulated pressure drop on the basis of MRI data indicates that MRI is a very useful tool for obtaining the necessary structural information for filtration modelling.

Keywords: Fibrous filters; packing density; magnetic resonance imaging; CFD.

R. Dias, M. Mota, J.A. Teixeira and A. Yelshin STUDY OF TERNARY GLASS SPHERICAL PARTICLE BEDS: POROSITY, TORTUOSITY AND PERMEABILITY (pages 68-75)

Abstract

Ternary mixtures of glass beads were constructed as a model of granular packing. Porosity and permeability were experimentally determined in a wide range of mixture composition. Based on experimental data, tortuosity was calculated using the Kozeny-Carman equation. Applying the conventional relation that expresses tortuosity as the inverse of the power order of porosity, it was found that the parameter n varies with the fraction content. The observed phenomenon was explained by wall effects between particles of different sizes.Keywords: Ternary mixed bed; porosity; tortuosity; permeability.
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