- The Filtration Society - http://www.filtsoc.org -

2006

Published papers: Volume 6, Issue 4

Author(s) Title, page numbers and abstract
T. Jaroszczyk, S.L. Fallon, Z. Gerald Liu, S.W. Schwartz, C.E. Holm, K.M. Badeau and E. Janikowski DIRECT FLOW AIR FILTERS – A NEW APPROACH TO HIGH PERFORMANCE ENGINE FILTRATION (pages 280-286)

bullet Abstract

bullet Direct Flow axial filters utilize a unique patented alternating seal technology that enables tangential filtration and extreme flexibility of packaging options. The compact, high performance filters were developed for diverse environments including off-road high dust concentration applications. The most favourable design of this filter contains unlocked pleats at the upstream and downstream ends, allowing the air to flow relatively straight without changing its direction. Alternating sealing technology in the patented Direct Flow design enables the use of high-speed rotary pleaters. The incorporation of the angled sealing mechanism in this design leads to a space-saving advantage. The reduced-space feature is particularly important in air cleaner design where the filter is located in space-constrained areas behind the cabin or under the hood. Moreover, while other reduced-volume designs are susceptible to clogging due to the edge phenomenon, the Direct Flow design incorporates equalized contaminant passages in the form of spaces between individual pleated elements, which prevents such clogging.Due to new engine exhaust particulate and evaporative emission regulations, the importance of the engine air induction system has increased. Engine lifetime, fuel consumption and engine emissions depend greatly on the air induction system design and its performance. Providing optimized solutions for these requirements dictates filter development trends. This drives the need for media to become more efficient with higher permeability. The operation efficiency for fine particles can be drastically improved by applying a layer of fine meltblown fibres or nanofibres to a substrate. The substrate can be either a cellulose or synthetic medium.

V. Kalayci, M. Ouyang and K. Graham Polymeric Nanofibres in High Efficiency Filtration Applications (pages 286-293)

bullet Abstract

bullet Over the last three decades, nanofibre filter media have fueled new levels of performance in air filtration in commercial, industrial and defence applications where efficiency requirements have been low in comparison to HEPA (High Efficiency Particle Air) or ULPA (Ultra Low Penetration Air) levels. This paper discusses recent advancements in the nanofibre enhanced filtration field that extended the usability of nanofibres into applications with higher filtration efficiencies. In particular, these nanofibre matrices provide comparable performance to other commercially available HEPA media composed of sub-micron glass or expanded-PTFE membranes. Evidence of such performance along with benefits and shortcomings of the technology are presented. Furthermore, this paper covers another unique nanofibre filter media that will help fuel further growth in multiple diverse applications: an improved HEPA filtration media with outstanding cleanability. Nanofibre filter media is a viable solution in high efficiency applications with strict performance requirements.

D-J. Chang USE OF MICELLAR ENHANCED MEMBRANE FILTRATION SYSTEM FOR HUMIC ACID REMOVAL FROM WATER (pages 293-296)

bullet Abstract

bullet A micellar enhanced membrane filtration system was used for humic acid removal from water. Experiments were conducted using various pore size tubular ceramic membranes whose inner tube was packed with activated carbon or sands to enhance humic acid removal. It was found that the removal of humic acid was 45-75% when the inclusion of packed materials were absent, and the removal performance was decreased with an increase of membrane pore size. It was also found that the packed adsorptive materials can enhance humic acid removal, with removal values up to 98%. The removal performances were increased with an increase in specific surface area of adsorptive material. In addition, the permeate fluxes were increased with an increase of membrane pore sizes when the packed materials were absent.

C. Peuchot TESTING OF FILTER MEDIA FOR LIQUID FILTRATION – INTRODUCTION AND REVIEW (pages 297-300)

bullet Abstract

bullet Liquid filter media all have the same role of letting the liquid flow through whilst retaining a part if not all particles from the feed suspension. Clarification is the operation of reducing to a minimum the solid content of a liquid whilst concentration/dehydration is that of reducing to a minimum the liquid content of a solid phase. The variety of available techniques, processes and liquids to be filtered create a broad spectrum of technical requirements and properties. Tests are developed to evaluate these properties in conditions that are accelerated and cheaper compared to those at the full scale. An overview of the characteristics of filter media (from granular varieties to sterilizing membranes) classified in to four families (structural, hydraulic, mechanical and performance) is presented and the main test procedures (particularly standard ones) are summarised.

L. Hall, F. Heese and P. Robson QUANTITATION OF FILTRATION BY MAGNETIC RESONANCE IMAGING (MRI) (pages 301-303)

bullet Abstract

bullet This paper provides a brief overview of some of the methods whereby MRI can be used non-invasively to visualise the internal structures of a range of filters and to quantitate their function, including all the associated flow fields.

C. Ehrenberg and W. Höflinger DETERMINATION METHOD TO FIND AN OPTIMAL DEPTH FILTER LAYER COMBINATION FOR AEROSOL SEPARATION IN THE MINERAL WOOL INDUSTRY (pages 304-308)

bullet Abstract

bullet Mineral wool sheets are commonly used, e.g. for insulation purposes. The production of mineral wool generates large amounts of fine aerosols, which should be separated due to environmental reasons. The idea was to use mineral wool sheets as filter media for aerosol separation. The advantage is that the used filter sheets can be fed back into the production process and no deposit problems occur. The aim of this work was to investigate mineral wool sheets for their separation ability using a test rig and to find an optimal combination of several sheet qualities which can act as a good depth filter medium. For different sheet qualities, originally produced for use as insulation material, the fractional separation efficiency and the pressure drop were determined. By using the minimum value of the fractional separation efficiency, which is defined as the most penetrating particle size (MPPS), in connection with the corresponding pressure drop, a calculation method was worked out by which the optimal combination (number, thickness and different qualities) of a depth filter sheet can be found. As a basis of the calculation method the filter quality q is used. This is a useful criterion for the optimisation of filter media combinations consisting of different qualities such that q = |ln(P(x))|/Δp where the filter quality has the units Pa-1, P(x) is the penetration of the most penetrating particle size, and Δp is the pressure drop measured in Pa.

P.R. Johnston Pore-Size Distributions on the Surfaces of Filter Media Determined via Image AnalyseS (pages 309-311)

bullet Abstract

bullet A freely available software measures pore-diameter distributions in micro-photographs of the surfaces of filter media composed of random arrays of their constituent (building) materials. Pore diameter refers to the ratio of the cross-sectional area to the perimeter. Plots of the number of pores vs. diameter follow the gamma distribution with ratios of the standard deviations to means close to 0.707.

T. Sobisch, D. Lerche, T. Detloff, M. Beiser and A. Erk Tracing the centrifugal separation of fine-particle slurries by Analytical Centrifugation (pages 313-321)

bullet Abstract

bullet Unit processes using centrifugal fields are often applied for the separation, deliquoring and classification of fine grained materials. Modelling of these processes requires information about the separation behaviour of the suspensions to be processed. To this end, direct measurements in centrifuges are obligatory. Moreover, these measurements have to gather kinetic information as a function of the processing conditions, particle interaction and particle concentration. In this paper we introduce a multisample analytical centrifuge with position and time resolved photometric detection and its application to determine the sedimentation velocity distribution of particles inside the centrate as well as the in-situ compression behaviour of the cake. To obtain an insight into the sedimentation/consolidation mechanism and gain essential data for modelling separation in the centrifugal field measurements were carried out on systems that covered the range from stable suspensions to strongly flocculated dispersions. The investigations were complemented by centrifugation with manometric detection and with a disc centrifuge. Results obtained by multisample analytical centrifugation fitted well to the results for velocity distributions determined by manometric detection and packing density obtained by compression in the disc centrifuge.

Keywords: Centrifugation; solid/liquid separation; sedimentation; classification; physico-chemical aspects; flocculation; dewatering; consolidation; packing density.

X. Zhang, M. Romzek, M. Keck, D. Tsang and C. Morgan 3-D NUMERICAL STUDY ON FLUID FLOW AND PRESSURE LOSS OF MIXING CHANNEL AND WALL FLOW INSIDE A DIESEL PARTICULATE FILTER (pages 322-332)

bullet Abstract

bullet A better understanding of three dimensional fluid flow and pressure drop characteristics is essential for modelling the heat and mass transfer associated with surface chemical reactions, soot loading and passive regeneration inside a Diesel Particulate Filter (DPF) by a simplified one dimensional simulation. In the current paper detailed numerical studies of fluid flow and pressure loss inside a single channel were conducted. In addition to general information about mixing flow through channels and filter walls, the effects of filter wall permeability, channel length and width on velocity distributions and pressure losses were also addressed. Wall flow velocity magnitude is found to be higher at both ends of a channel. Results show that for a given DPF structure and wall thickness, higher pressure loss occurs for a shorter channel and pressure loss decreases as channel length increases, however, beyond a critical channel length pressure loss increases again. This critical channel length, associated with minimal pressure loss, is dependent upon the substrate cell structure; a correlation based on the current study as a function of channel cell size is given. Comparisons between 1-D calculations and 3-D CFD simulation results show an under prediction of pressure loss in the 1-D case for a shorter channel and an over prediction for a longer channel. Studies on the effect of wall permeability show a clear transition region from channel flow at higher permeability to Darcy flow at lower permeability. Pressure loss results also show good agreement between 1-D calculations and 3-D CFD simulations over the lower permeability region and an over prediction for the 1-D calculation at higher permeability. As expected, the 1-D calculation cannot reveal the flow transition region captured in the more detailed 3-D CFD simulations. The effect of mass flow rate on pressure loss was studied and a comparison between a 1-D calculation and a 3-D simulation shows some discrepancy at higher mass flow rates.

Keywords: 3-D numerical simulation; channel flow; wall flow; pressure loss.

B. Fuchs, M. Stolarski, W. Stahl and H. Nirschl MAGNETIC FIELD ENHANCED CAKE FILTRATION (pages 333-339)

bullet Abstract

bullet Cake filtration is a widely used solid/liquid separation process. The design ranges from lab-scale discontinuous Nutsche filters to large-scale continuous rotary drum filters. Another common separation device, especially in the mineral industry, is the magnetic separator which uses magnetic forces to separate magnetic from non-magnetic materials. The combination of the two mechanisms described in this paper is a totally new approach and results in positive synergetic effects and an extension of the field of application for the cake filtration process. The work describes the phenomenology of this new hybrid separation which combines pressure forces with magnetic fields or forces and defines potential areas of applications like pigment separation or bio-separation as well as separation of nanostructured magnetic materials in the electronic industry. The experimental results show that the cake filtration of magnetic particulate products can be improved significantly by superimposing a homogeneous, as well as an inhomogeneous, magnetic field. The reason can be seen in magnetophoretic effects as well as magnetic field enhanced structure changes of the particulate system. These result in less solids breakthrough, a faster cake formation, a higher permeation rate through an already built filter cake and therefore an integral improvement of the overall cake filtration process. However, the experimental results also define a critical magnetic field strength, above which there will no longer be a homogeneous cake formation. The critical field strength is a function of the applied gas pressure as well as a function of the (magnetic) product properties. In addition to the experimental results this work also introduces a theoretical approach to describe magnetic field enhanced cake filtration. An excellent agreement between experimental results and theoretical predictions is shown.

Keywords: Magnetic filtration; field enhanced filtration; cake filtration; magnetic structuring; magnetic separation.

M-C. Chang, R-Y. Horng, H. Shao and Y-J. Hu SEPARATION OF TITANIUM DIOXIDE FROM PHOTOCATALYTICALLY TREATED WATER BY NONWOVEN FABRIC MEMBRANE (pages 340-344)

bullet Abstract

bullet The feasibility of using an improved nonwoven fabric material as separation media in a photocatalytic membrane reactor (PMR) to treat low polluted water at lower trans-membrane pressure (TMP) was investigated. In this work, the titanium dioxide (TiO2) photocatalyst was Degussa P-25. Aqueous suspensions of TiO2 containing 1 mg/l of methylene blue were tested in the reactor using a light wavelength of 360 nm. After photocatalytic treatment, the separated photocatalyst was recycled to the reactor for reuse. Experimental results showed that a stabilized permeate flux of ~0.1-0.2 m3/m2 day could be obtained at a TMP of ~1–2 kPa. The permeate quality indicated a high particle collection efficiency for the nonwoven fabric membrane and the chosen experimental conditions. Keywords: Nonwovens; photocatalysis; photocatalytic membrane reactor.

Published papers: Volume 6, Issue 3

Author(s) Title, page numbers and abstract
E. Mayer

LABORATORY TESTING PROTOCOLS USED FOR BIOSOLIDS DEWATERING (pages 193-199)

bullet Abstract

bullet Biosolids dewatering is widely practised throughout both municipal and industrial wastewater treatment facilities. Biosolids are generally extremely difficult to dewater because of their gelatinous, compressible nature, and as a result pretreatment with polymer flocculants, coagulants, or filter aids is necessary. This paper discusses laboratory testing protocols used to determine optimum pretreatment, primarily for filter press dewatering and subsequent scale-up. Case histories will be highlighted where those testing protocols were successfully applied.

T. Brattberg, T. Blomberg and R. Lundberg

NEW CELLULOSE FIBRES FOR FILTER MEDIA (pages 200-202)

bullet Abstract

bullet Filter media production for the automotive industry is based upon cellulose fibres. Today all cellulose fibres used are produced through chemical pulping processes. Rottneros is a leading supplier of kraft pulps for filters from its Vallvik Mill. Rottneros AB has through customer contacts learnt that there is a need for cost efficient cellulose fibres with very high porosity. A development process within Rottneros has resulted in a high porosity CTMP pulp (Chemi Thermo Mechanical Pulp) now being commercially produced in two of the companies CTMP production lines. The new pulp (CP 065) has considerably higher porosity than chemical pulps. Some filter producers use CP 065 instead of mercerized pulp in some applications. Therefore, the new pulp is compared in this study with mercerized pulp. CP 065 and mercerized pulp have the same initial pressure drop and removal efficiency while CP 065 has higher dirt holding capacity.

B. Longworth, J.P. Millington, J. Norris, P. Norris and C. Reid

FLASH DECOMPRESSION: THE KEY TO A NEW FILTER CLEANING PROCESS (pages 202-206)

bullet Abstract

bullet As the market for polymers has grown, particularly over the past three decades, the need for a technology to enable the cleaning of the complex and costly filters used by the industry has grown in parallel. Presently, cleaning processes use high boiling solvents, superheated steam and various high temperature pyrolysis techniques. These technologies are under continuous review and no more so than at present when companies of all sizes are facing increasing international legislative pressure to reduce harmful emissions and improve their impacts on the world environment. There is little doubt that legislative pressure to drive down emission levels will continue. An example relevant to our business is the landfill directive where the UK Government clearly intends to stop the use of landfill at some point in the future by gradually increasing the costs. A second example arises from the use by the industry of additives such as antimony oxides, resulting in an almost ‘Catch 22’ situation. If waste polymer is sent to landfill the likelihood of antimony being leached out into the ground water is tiny, however, if waste polymer is incinerated the removal of fine particles of antimony pentoxide from pyrolysis gases to the existing low consent levels is a difficult technical problem. A third and final example is the disposal of contaminated glycols. As solvents for high temperature cleaning, glycols have the advantage that a large proportion of them may be recovered for reuse by vacuum distillation. In even the best run operations a small amount of residual high boiling waste will be produced. Whilst previously this material could be sent to landfill, it is likely that in the future it will become a special waste and thus require specialist incineration.

In this commercial environment a successful ethical company will be one that continually reviews its technology in the light of current and future legislative changes. Cleaner and more environmentally friendly technologies may involve additional cost, but not in every case and it is worth remembering that in Europe, at least in theory, all similar processes must conform to the same emission consent levels. The development of new technologies may be costly but clever use of existing skills and resources and the expertise offered by universities allows research to be carried out at costs that are acceptable to a small company. It is equally true that new technology may be sold and the market developed by the technology driving the legislation.

Against such a background the Longworth Group of companies continually review their existing technology and fund the development of new techniques. This paper describes a development that led to an entirely novel, patented, solvent free low temperature process, known as DEECOM.

P. Lippens, A. Vanlandeghem, P. Martens and M. Pauwels LOW PRESSURE VACUUM PLASMA TREATMENT OF NONWOVENS AND NEEDLEFELT FOR FILTRATION APPLICATIONS (pages 207-210)

bullet Abstract

bullet Vacuum plasma treatment has found its way into industry since the 1980s. Initially it was used for cleaning printed circuit boards and later on as an activation for structural plastic parts prior to painting, flocking or gluing. Recently, however, the filtration industry has taken a sincere interest in the technology. Such interest has resulted in several plasma production systems having been installed in the industry. Plasma treatment is used either for activation of nonwovens or for coating of such products, for example needlefelts using plasma polymerization. In the case of activation, a process gas is used to graft functional groups on the surface of the fibres of the nonwoven. A typical example is the hydrophilization of nonwoven polypropylene (PP) for blood filters using carbonyl-groups. In the case of plasma polymerization, one or more precursor gases are (partially) decomposed in the plasma and react on the substrate surface to form a thin film. Such a process can be used for filtration media. Using precursors which contain fluorine, hydrophobic coatings can be deposited on the fibre surface. Such thin films substantially reduce the penetration of the filter medium, such as a nonwoven PP, with DOP aerosols (P and R type filters).

Plasma treatments on nonwovens and needlefelts are typically carried out on roll-to-roll equipment. Such equipment allows multiple passages through the plasma zone so that web speeds of several tens of metres per minute can be used. At such speeds, a plasma coating costs typically less than 0.05 Euro/m2, the cost of a plasma activation is even lower.

A. Startin and G. Elliott NEW AND IMPROVED HOT GAS FILTERS FOR DIFFICULT APPLICATIONS (pages 210-215)

bullet Abstract

bullet Filtration utilising low density ceramic filter elements is a well established technology for air pollution control and product recovery. Ceramic elements combine high filtration efficiency with the ability to operate at elevated temperatures. These benefits are particularly applicable to high temperature processes subject to stringent emissions legislation. Applications include waste incineration, metals smelting, glass melting and minerals processing. Madison Filter has developed two new Cerafil filter products designed to meet the needs of arduous filtration duties. Cerafil Green is manufactured from engineered biosoluble fibres and offers improved strength and toughness while not compromising filtration performance. Cerafil TopKat takes ceramic filter technology a stage further by incorporating an integral catalyst. The filter has the ability to control dioxin, NOx and VOC emissions down to low levels. The new products are described in detail and case studies presented.

M. Baumeister, K. Dickmann, M. Duka
and T. Hoult

MICROFILTRATION MEMBRANES WITH STRAIGHT PORE CHANNELS FORMED BY HIGH-SPEED FIBERLASER PERFORATION OF STAINLESS STEEL FOILS (pages 216-219)

bullet Abstract

bullet In the expanding field of microfiltration technology membranes are made mainly from polymeric and sintered materials. These have tortuous pore channels with a stochastically distributed arrangement. The filtration parameters are inferior to membranes with straight pore channels. Different approaches to develop sieves featuring this straight pore channel in stainless steel have been investigated (e.g. Aquamarijn B.V.). In general, these technologies are laborious and time consuming, making the technologies unavailable for competitive and widespread industrial applications. The Laser Centre of the University of Applied Sciences Münster (LFM) have developed in collaboration with SPI a novel method to produce stainless steel microfiltration membranes with regular pore distributions and straight pore channels.This paper reports this novel process technology for micro sieve production, which is capable of performing large pore matrices (up to 106 pores/dm2) in thin stainless steel foils (10 µm < dfoil < 300 µm), maintaining high processing rates and pore widths <5 µm. It is a two-step technique consisting of a fiberlaser micro-perforation with a subsequent cold roll forming. It perforates the stainless steel foils by deploying high speed “‘on-the-fly”‘ laser perforation (1000 pores/second) followed by a cold roll forming of the laser treated foil. The pore size after the micro-perforation is approximately 20 µm. To further reduce the width of the inserted pore the process is followed by the forming process. At present we are using a basic cold roll forming mill with two cylinders intended for manual operation, enabling the foil thickness can be decreased significantly. Perpendicular to the rolling direction the width of the pore is reduced (in one dimension). Parallel to the rolling direction the length of the pore increases. Through this process combination minimum pore sizes of 3.5 µm have been achieved. The elongated pore shape with a high ratio between length and width is visible.

S. Tennison

NANO- AND MACRO- FILTRATION MEDIA BASED ON CARBON TECHNOLOGIES (pages 219-224)

bullet Abstract

bullet A novel binderless preparative route is described for the production of phenolic resin derived carbons for use as filters and membranes. The carbons, sold under the tradename NOVACARB™, can be produced in a wide variety of physical forms ranging from simple granules to large monolithic structures. The fully interconnected macropore structure of the carbons, which derives from the interconnected voids between the primary resin particles, can be precisely controlled to give a mean macropore size of between around 1 and 50 microns. This gives rise to very high permeabilities that can be orders of magnitude higher than conventional porous materials and provide the basis for some novel filtration media. In addition the production route allows the manufacture of asymmetric carbon membrane structures with a pore size in the separating layer of ~0.8 nm. These materials can function as gas separation systems with unique properties for low pressure and high temperature separations.

I. Townsend

PRACTICAL CONSIDERATIONS IN PRESSURE FILTER SELECTION (pages 225-230)

bullet Abstract

bullet Design considerations are discussed for filter presses, tower presses and tube presses, but not hyperbaric filters enclosed in a pressurised chamber. This paper on pressure filtration refers only to cake filtration, with or without in-filter cake washing, and excludes solution polishing and is based on a chapter for a book (I. Townsend, J. Palmer and T. Bongartz, Pressure Filters, in “Solid/Liquid Separation: Scale-Up of Industrial Equipment”, Eds. R.J. Wakeman and E.S. Tarleton, Elsevier, 2005 (ISBN 1-85617-420-4)).

D-J. Chang COLOUR REMOVAL BY MICELLAR-ENHANCED ULTRAFILTRATION (pages 231-233)

bullet Abstract

bullet Traditional ultrafiltration membrane technology for textile wastewater decolourisation enables efficient colour removal. Micellar enhanced ultrafiltration (MEUF) has been used to improve the decolourisation and reusability of textile wastewater. It was found that the optimum conditions provided by a micellar enhanced ultrafiltration membrane were suitable for the removal of colour from textile wastewater. Our results showed the rejection coefficient of dye to vary from 65% to over 95% according to the test conditions. The rejection coefficient of dye and the decolourisation of textile wastewater increased with increasing dye concentration in the feed solution, and were dependent on the dye/surfactant ratio. Decolourisation of the dye was greater than 95% at the optimum operating conditions. Furthermore, a good permeation flux was also observed.

B.L. Allen and D. Tao ASPHALT EMULSION ENHANCED FINE COAL DEWATERING (pages 235-241)

bullet Abstract

bullet With the introduction of advanced fine particle separations such as column flotation and enhanced gravity concentration, fine and ultrafine coal can be effectively recovered from washery waste. However, the difficulty in subsequent dewatering hinders the application of these new technologies in the coal industry. In the present study, agglomeration by asphalt emulsion was investigated for enhancing fine coal dewatering. The agglomeration selectivity and agglomerate size enlargement rate were investigated and agglomerate strength and settling behaviour were characterized. It was found that use of 0.5% asphalt emulsion reduced vacuum filter cake moisture from 35% to 26% with a fine coal slurry sample. Significant effects of asphalt induced agglomeration on vacuum filter cake structure and handleability were also observed. Keywords: Fine coal dewatering; asphalt emulsion; vacuum filtration.

K.C. Ting, R.J. Wakeman and V. Nassehi MODELLING FLOW IN MONOFILAMENT FILTER CLOTHS: 2. EFFECT OF WEAVE STRUCTURE AND NON-NEWTONIAN FLUID PROPERTIES ON PRESSURE LOSSES (pages 242-249)

bullet Abstract

bullet In Part 1, we presented a 3-D finite element mathematical model for predicting Newtonian and non-Newtonian fluid flows through monofilament filter cloths. The model was shown to give theoretically consistent predictions, verified with purpose-designed test cases and experimental results of previous researchers. In this paper, we examine the effect of weave structure on the flow pattern in the interstices of woven media together with the associated pressure losses. Fluid flow through four basic pore types was examined, using a range of aperture to fibre diameter ratios. The effect of non-Newtonian fluid properties on pressure losses across the woven media was also investigated. Our results showed that Pore Type 1 gives the lowest pressure drop across the wire mesh while Pore Type 4 gives the highest pressure drop, consistent with the experimental results reported by earlier researchers.Keywords: Woven media; wire cloths; wire mesh screens; three-dimensional; Newtonian fluids; non-Newtonian fluids; pressure loss.

M. Herold, M. Lehmann, H. Brunner and G.E.M. Tovar SMART MATERIAL COMPOSITE MEMBRANES BASED ON MOLECULARLY IMPRINTED NANOPARTICLES USED FOR SELECTIVE FILTRATION (pages 250-253)

bullet Abstract

bullet The new separation approach described is an efficient and easy alternative to the established methods for separation of small quantities of specific substances, like preparative HPLC or common SPE kits. The composite membrane used consists of a polymer membrane disc which acts as a support and a selective coating of deposited, molecularly imprinted, nanospheres. In the outer shell of these spherical nanoparticles molecular imprints are accessible which bind the target molecule from the mixture to be treated according to the principle of molecular recognition; the mixture runs through the composite membrane. In this paper we investigate the feasibility of the approach by kinetic experiments, calculating adsorption isotherms and by process modelling. The principal hydrodynamic properties of the composite membrane set-up are evaluated by modelling and flow experiments. Concerning thermodynamic and kinetic parameters, models for affinity characteristics are set up for the entire mass transfer through the composite membrane.Our nanoparticle approach already allows a very thin layer to realise separation performance and binding capacities in an interesting working regime. The technology of molecularly imprinted nanospheres offers the potential to cover a broader range of template molecules such that customised separation solutions can be envisaged.

Keywords: Adsorptive materials; membrane processes; bioseparation; amino acid; nanoparticles; filtration; molecular imprinting.

Huang Bin, Yao Qiang, Xu Hai-wei, Long zheng-wei and Li Shui-qing PRESSURE DROP AND PENETRATION FOR PRE-CHARGED AND NEUTRAL PARTICLES ON FIBROUS AND MEMBRANE FILTERS (pages 254-258)

bullet Abstract

bullet The differences in pressure drop and penetration evolutions for pre-charged and neutralized particles with fibre and membrane filter media has been compared experimentally. A novel experimental setup was developed to perform in situ monitoring of pressure drop, aerosol concentration and diameter distribution. The test aerosol particle was a form of Si bead. The results show that the presence of electrostatics has a positive effect on the pressure drop and efficiency of a membrane filter but a negative action on a fibre filter. Keywords: Charging; fibrous filter; filter cake; pressure drop; cake structure.

Published papers: Volume 6, Issue 2

Author(s) Title, page numbers and abstract
E.S. Tarleton and R.J. Wakeman

FILTER DESIGN SOFTWARE (FDS) FOR FILTER PROCESS SIMULATION (pages 103-107)

bullet Abstract

bullet This paper details Filter Design Software® (FDS), new Windows® software for the selection and simulation of solid/liquid separation equipment as well as the analysis of test data. FDS has been developed in collaboration with multi-national companies spanning a wide range of industrial sectors to provide a comprehensive calculation, education and training tool that maintains a balance between ease of use, level of knowledge conveyed and comprehensibility.The selection module of the FDS compares up to 7 user-defined selection criteria with information contained in databases to produce a numerically ranked list of potentially suitable equipment. The FDS allows access to text and pictorial descriptions of more than 70 equipment types and hyperlinks provide more specific equipment manufacturer details via the internet.

The data analysis module facilitates interactive analysis of leaf filtration, jar sedimentation and piston press test data. Calculations are performed in a hierarchical manner using the available information, if some data are not measured then the FDS performs the best possible analysis using approximations. The results of an analysis can be used to refine (shorten) a list of selected equipment or provide scale-up information for equipment simulation.

The two equipment simulation modules provide calculation sequences for more than 20 types of vacuum and pressure filters, potentially involving combinations of cake formation, compression, gas deliquoring and washing. The user is able to input filter cycle data in their preferred units and guidance is given as to suitable numeric ranges for the type of filter being simulated. Results are presented on-screen in graphical and tabular forms and a mass balance is given for the solid, liquid and dissolved solute components present. The results are also made available in data sheet form which can subsequently be imported into a spreadsheet.

R.A. Suozzo and D.J. Davenport

PRODUCTION OF POTABLE WATER WITH UF MEMBRANES: A CASE STUDY FROM PILOTING TO PLANT EXPANSION, NEW BRAUNFELS, TEXAS (pages 108-112)

bullet Abstract

bullet The Lake Dunlap Water Treatment Plant is owned by the Canyon Regional Water Authority (CRWA) and is located in New Braunfels, Texas. In June 2002, the plant upgraded its existing water treatment plant with ultrafiltration (UF) membranes. The UF plant treats surface water after pretreatment with chlorine dioxide. Initial piloting led to the construction of the current four million gallons per day (MGD) ultrafiltration membrane plant. Data from the piloting process allowed for an easy transition to a full-scale plant. This paper will discuss the original pilot testing and how the data was used to design the current 4 MGD plant.

It will also discuss the operation of the 4 MGD plant, including how very high recoveries are achieved, running through a severe weather event, and how the experience from this event was used in design plans for expansion to 14.4 MGD. Even before the first expansion is completed, space for a second expansion project is already being allocated. We will look at the history that has persuaded this plant to upgrade from its original 2 MGD traditional sand filters to discussions of possibly more than 23.1 MGD in the near future.

C. Grimwood

SCALING-UP FILTERING CENTRIFUGES (pages 113-118)

bullet Abstract

bullet The scale-up of filtering centrifuges from laboratory or pilot scale tests to full plant scale is discussed. Several aspects of full scale centrifuges and small scale testing are considered including the test sample size, collection method and physical characteristics of the sample. The information provided is intended to assist the potential filtering centrifuge user and provide an understanding of the scale-up process, its limitations and interdependencies.

G. Moody and P. Norman OPTIMISING USAGE OF PRE-TREATMENT CHEMICALS (pages 119-127)

bullet Abstract

bullet A major consideration for any solid/liquid separation is the requirement for pre-treatment chemicals. The type of pre-treatment required depends on a large number of factors: the substrate to be treated, the solid/liquid separation techniques being used, any throughput constraints, and the desired outputs. The majority of the pre-treatment chemicals used increase the effective particle size of the solids to be separated, by various aggregation mechanisms. It is important to understand the basic theory of the behaviour of particles in suspension in order to identify the most appropriate chemicals to evaluate.

The main chemical groups used are discussed in some detail, and guidance is provided in terms of the product types to consider under different circumstances. The importance of mixing and application techniques is highlighted, as are some of the pitfalls to avoid, together with a number of laboratory protocols appropriate for use with specific solid/liquid separation equipment.

D. Horn, P. Basařová
and V. Machoň
BUBBLE SIZE, SHAPE AND RISE VELOCITY IN THE FLOTATION PROCESS (pages 128-131)

bullet Abstract

bullet The fundamental process in flotation is the formation of the bubble-particle aggregate, which is formed due to the interaction between a bubble and particle. Prior to the treatment of particle-bubble interaction, the dynamics of particles and bubbles in flotation is considered. Since the flotation process takes place in an aqueous medium, the interaction between bubbles and particles is strongly influenced by the hydrodynamic forces generated by the surrounding liquid and the relative motion between bubbles and particles.

To bring our understanding of the flotation process closer towards the needs of applications under more realistic conditions, the several assumptions have to be relaxed considerably. First, a bubble of the required qualities must be produced. The bubble should be allowed to move freely, i.e. to deform and undergo shape oscillations, which results in changes in the surrounding flow field. The bubble moves not in an unbounded medium of a stagnant liquid but in a swarm of neighbouring bubbles in a flotation column. The hydrodynamic bubble interactions affect the bubble motion substantially. The motion of a bubble swarm generates a complicated liquid flow field, which affects the bubble behaviour: the gas and liquid phases are two-way coupled. When solids are present in the bubbly mixture, the interaction pattern becomes even more complex and the original overall flow structure in the bubble column can be strongly altered.

K. Turner

TOWARDS PROCESS INTENSIFICATION USING A MINI ROTARY VACUUM FILTER (RVF) (pages 132-136)

bullet Abstract

bullet The mini RVF operates on the same basic principle as all vacuum drum filters. The filter is made up of an inner rotating drum encased in an outer cylinder, of which the bottom half serves as a trough. The surface of the inner rotating drum is covered with a filter medium. Feed enters the base of the outer drum and the level is maintained by an overflow from which the excess returns to the feed vessel. This paper describes the principal features of the mini RVF and outlines some applications.

P. Rantala

EXPERIENCES IN HIGH-PRESSURE DEWATERING IN FINE PIGMENT SLURRIES (pages 136-139)

bullet Abstract

bullet Fine pigment slurry dewatering with a normal pressure filter is quite challenging. Filling and coating pigment slurries, which are mainly used in the paper industry, set a greater challenge for dewatering. In this paper the behaviour of fine pigment slurries in high pressure (>100 bar) dewatering both in a laboratory and pilot scale is examined. During the tests feed slurry varied and the first slurry was estimated to contain 76% calcium carbonate, 20% kaolin, 3% latex and 1% other binding and coating materials. The dry solids in the feed were 43%.

It has been proven that waste pigment slurries can be dewatered only by adding chalk when the over pressure was 100 bar. The amount of burnt, ground, fine chalk was 2-3% DS of the feed slurry solid content. Without adding chalk the filtration is not economical. It must be taken into account that the filter cloth resistance is only 5-10% of the total resistance which mostly comes from the cake. At the pilot scale, several slurries, mainly carbonate-based pigments, were tested for dewatering. The remarkable conclusion was that with the same slurry the simultaneous tests conducted with a laboratory piston press resulted in 20-25% higher capacity values than tests made by the pilot tube press. In general, with the pilot filter the filtrate flow was 0.3 m/h while with the laboratory filter it was 0.4-0.5 m/h. At the end of the tests the solids contents of the cakes was comparable. After pretreatment, >75% DS in the cake was achieved with both filters, whereas without pre-treatment the value was 63% DS.

B.M. Verdegan and R. Fletcher

REDUCING UNCERTAINTY IN PARTICLE SIZE MEASUREMENT FOR LIQUID FILTER TESTING (pages 140-145)

bullet Abstract

bullet Contamination control is essential for reliable, cost-effective operation of hydraulic and engine systems. Particle counting provides the common, underlying basis for comparing filter performance and monitoring of contamination levels in hydraulic oil, lube oil and fuels. Since 1999, ISO 11171 has been the standard particle counter calibration method for hydraulic and engine applications. ISO 11171 requires the use of NIST certified SRM 2806 for calibration. Recently, questions have arisen regarding interpretation of the SRM 2806 Certificate of Analysis (CoA), stability of the SRM, and what can be done to improve the quality of future releases of SRM 2806. These were triggered when it was found that one batch of the SRM, Batch 5, had deteriorated. The recall of this batch, closely followed by the release of a new batch as SRM 2806a, prompted questions regarding current and future supplies of the material. In this paper we report on the Batch 5 deterioration issues, comparison of SRM 2806a to the original SRM 2806, and progress of work to reduce the uncertainty of future batches of SRM 2806.

W-L. Lai, L-F. Chen, J-H. Lin and B-M. Yang EVALUATING THE OPERATIONAL STABILITY OF a BIOFILTER (pages 145-148)

bullet Abstract

bullet Two parameters, including total bacterial count (TBC) and dissolved organic carbon (DOC) from the effluent of the filter, were selected to evaluate its biostability at three values of O3/DOC and two hydraulic residual times (HRT). The biostable filter is called the BDOC filter bed. The BDOC filter was tested by two artificial water samples containing sodium acetate and sodium oxalate to confirm its operational reproducibility and to understand its ability to decompose different organic characteristics. Results indicated that both TBC and DOC of the effluent through the filter can provide information for ascertaining when the filter can reach its biostability. Also, the log(Nt /N0) (Nt and N0 represent concentrations at any time and at the initial time respectively) was affected by O3/DOC and HRT. At HRT = 176 minutes, log(Nt /N0) of the stationary phase for 1.7 O3/DOC was less than that for 1.1 O3/DOC. Also, it was found that even though the filter was incubated without adding ozone, prolonging the HRT of the filter to 729 mins. has a similar log(Nt /N0) in the stationary phase.

K.C. Ting, R.J. Wakeman and V. Nassehi Modelling Flow in Monofilament Filter Cloths: 1. Prediction of Pressure Losses (pages 150-158)

bullet Abstract

bullet Monofilament woven cloths or screens are used as the media in filters or to enhance the integrity of the filter medium in, for example, filter cartridges. In this paper we present research results aimed at simulating non-Newtonian fluid flow through a woven cloth. Due to the complex geometry of a woven cloth, 3-D modelling is necessary to correctly visualise the structure of the flow and hence to predict pressure losses. The modelling in a 3-D domain was handled using a finite element method which is known to cope effectively with flow domains in complex geometries. The simulation results were found to be in good agreement with experimental data, showing the developed model to be capable of generating accurate results for flow of both Newtonian and non-Newtonian fluids through filter media. Keywords: Woven media; wire cloths; wire mesh screens; finite element method; three-dimensional; Newtonian fluids; non-Newtonian fluids; pressure loss.

M.J. Lehmann Improved cfd modelling of particle-wall collision by including interception (pages 159-162)

bullet Abstract

bullet The focus of this paper is collision efficiency by interception. Following a literature survey, it will be briefly demonstrated that the collision efficiency by interception cannot be predicted with the standard FLUENT program but can be predicted with the new enhancements. Then the good prediction of the improved CFD modelling is shown by a comparison of simulated data for the inertia and interception regime with collision efficiencies from literature.Keywords: Collision efficiency; CFD simulation; interception; inertia.

M. Furuta, Y. Mukai and E. Iritani CONTROL of structure of thin filter cake formed by psl particles (pages 163-168)

bullet Abstract

bullet Microfiltration of dilute PSL suspension was performed under constant pressure and the properties of the thin filter cake were investigated. The specific filtration resistance was calculated based on cake filtration theory and the cake porosity was calculated from the specific filtration resistance by applying the Kozeny-Carman equation. The cake porosity at latex concentrations above 5.0×10-7 by weight was constant, while the cake porosity obtained for the filtration of very dilute suspensions (with concentration below 5.0×10-7 by weight) was observed to decrease with decreasing concentration.

Thus, the filter cake had a dense structure when the suspension was too dilute. The variation of the cake structure was also confirmed by SEM. Furthermore, microfiltration of saline PSL suspension was performed for various sodium chloride concentrations. As a result, it was shown that the addition of sodium chloride brought about an increase of cake porosity because the flocculation of particles was caused by the reduction of electric double-layer thickness. In addition, the average pore size of thin filter cake estimated from the porosity was in the range of 20-70 nm. Hence, the structure of the filter cake in microfiltration of a dilute particulate suspension can be controlled by the suspension and electrolyte concentrations.Keywords: Microfiltration; filter cake; porosity; filtration rate; polystyrene latex.

S. Rief, A. Latz and A. Wiegmann COMPUTER SIMULATION OF AIR FILTRATION INCLUDING ELECTRIC SURFACE CHARGES IN 3-DIMENSIONAL FIBROUS MICROSTRUCTURES (pages 169-172)

bullet Abstract

bullet The dependence of filter properties such as pressure drop, filter efficiency, and filter lifetime on the geometric structure of fibrous filter media is of great practical importance. In particular electrostatic forces are highly dependent on this structure. Many textiles have an irregular structure, which cannot be represented by functions of, say, porosity. Thus, it is necessary to model the three-dimensional structure of the textiles and electrostatic charges on their surfaces. To study the filtration properties, we use a Lagrangian formulation of particle transport in the calculated complex flow field and solve a Poisson equation with jumps in the electric conductivity and singular source terms on the fibre surfaces.

The dependence of filter properties such as pressure drop, filter efficiency, and filter lifetime on the geometric structure of fibrous filter media is of great practical importance. In particular electrostatic forces are highly dependent on this structure. Many textiles have an irregular structure, which cannot be represented by functions of, say, porosity. Thus, it is necessary to model the three-dimensional structure of the textiles and electrostatic charges on their surfaces. To study the filtration properties, we use a Lagrangian formulation of particle transport in the calculated complex flow field and solve a Poisson equation with jumps in the electric conductivity and singular source terms on the fibre surfaces.

The electric field is obtained as the negative gradient of the potential. Depending on the size of the particles, the microstructure of the filter, the electric field and the shape of the fibres, we simulate pressure drops, filter efficiencies and filter lifetimes. Since controlled variations of structural parameters like fibre orientation, fibre shape, spatially varying pore size distribution or gradients in the fibre density and the distribution of electrostatic charges on the fibre surfaces are easily achieved within the simulation, our results constitute a systematic and quantitative approach for the simulation of air filtration in fibrous filter media.Keywords: Simulation; nonwoven; particle separation; electrofiltration; clogging.

Published papers: Volume 6, Issue 1

Author(s) Title, page numbers and abstract
R. Wengeler, H. Nirschl, F. Herbstritt and W. Ehrfeld

STUDIES ON A MICRO HYDROCYCLONE FOR LIQUID-LIQUID SEPARATION (pages 21-26)

bullet Abstract

bullet Micro process technology focuses on process enhancement by rapid mixing and exact temperature control for chemical reactions or upstream processing. Yet only a few examples show the capabilities of microtechnology in downstream processing. One of the most important unit operations in this area is the separation of phases. Separation devices on the micro scale are so far not commercially available, which makes it difficult or even impossible to realize complex processes entirely within a micro reaction plant. Within this paper a micro hydrocyclone will be presented as being the first separation device on the micro scale. It has been investigated experimentally with respect to its separation capabilities for separating liquid-liquid dispersions with different densities of the phases. The investigations show the capability of micro hydrocyclones for mechanical separation of liquid-liquid dispersions. Further potential has been proven by classification and size reduction of droplets as well as the classification of solid particles.

The study shows new possibilities in processing multiphase flows in micro components. The capability of using micro process devices in downstream processing has especially proven the future potential of this technology. In the near future devices like the micro cyclone from Ehrfeld Mikrotechnik BTS may enable the realization of complex chemical engineering processes with separation steps on the micro scale.

D.G. Stevenson

SAND FILTER DESIGN AND WATER WASTAGE (pages 26-30)

bullet Abstract

bullet There are striking differences to be found in traditional filter designs especially between Europe and the U.S. These can affect the quantity of water wasted or to be recycled in washing and subsequent maturation. Ultimately this will affect the solids load that can be handled. To quantify such factors the displacement of solids from the pores in the beds of granular media filters during washing, into the supernatant water and then towards the weir or launder, has been simulated using a mathematical model.

The results confirm that the wash volume is a function of the height of weir or launder above the bed and hence the depth of supernatant water during washing. The figures are in line with experience and reported data. A similar model has been used to simulate the passage of transient turbidity events through the bed and the underdrain system during maturation and filtration. Again, an increased depth (under drain volume) leads to further delay and wastage, especially where the first filtrate is run to waste. Deep underdrains smooth out turbidity spikes, leading to a false sense of security but have no beneficial effect on the total solids going into the supply.

M.V. Melo, O. de A. Pereira, R.F. de Jesus and L.A. Duarte dos Santos

ADVANCES IN NON-CONVENTIONAL FLOTATION FOR OILY WATER TREATMENT (pages 31-34)

bullet Abstract

bullet The aim of this work is to present an alternative technique for the treatment of waters contaminated by dispersed oil. The treatment system should achieve high removal efficiencies even under unfavourable conditions, when oil is finely dispersed in the water phase, oil droplet sizes range from 10–30 μm and concentrations range between 100 and 200 mg L-1. The system presented in this work focuses the association of centrifugal separation in a hydrocyclone and the flotation operation. The system is characterized by the association of these two processes, resulting in a compact unit (centrifugal flotation system). The bubble generation, flocculation and the droplet-bubble contact were performed through a static mixer (in-line flocculator), while the separation of the phase rich in oil (froth phase) was promoted by a hydrocyclone. The oil-in-water emulsions were prepared using crude oil from the P-31 platform (PETROBRAS), with 29 ºAPI. The emulsions used were very stable with oil droplet sizes between 10 and 20 μm and concentrations between 90 and 125 mg L-1. Under the experimental conditions investigated and using a liquid feed flow rate of 2.0 m3 h-1 (ac = 200g), it was possible to remove up to 90% of the oil content in the feed. It was also verified that the split (QO/QU) has a small influence on the separation efficiency of the system. It was possible to achieve a water recovery above 95% with a treated water having an oil concentration below 20 mg L-1; the split was 5%.

T. Sparks CAN THE SUCCESS OF A PROCESS DEPEND ON SOLIDS WASHING? (pages 35-39)

bullet Abstract

bullet Washing soluble contaminants (or valuable products) away from solids can be of critical importance to the success of a process. Can the required washing level be reached? If so, then at what cost? This paper describes aspects of washing, their impact on overall performance and methods by which washing can be improved in practical applications. The opinions expressed in this paper may not necessarily be those of Larox Corporation.

A. Startin HOT GAS FILTRATION CASE STUDY – TESTING AND MONITORING (pages 40-44)

bullet Abstract

bullet Filtration using ceramic elements is now an established technique for hot gas clean up. Advancements in the design and composition of ceramic filters have been accompanied by the development of monitoring and testing techniques. Plant monitoring is employed to assess the performance of filter elements in service while a range of destructive and non-destructive tests are used for element characterisation.

E. Hardman

FILTER MEDIA SELECTION – AN OVERVIEW & MANUFACTURER’S PERSPECTIVE (pages 45-53)

bullet Abstract

bullet The separation of solids from liquids, which is an intrinsic feature of countless industrial processes, can be achieved in a number of ways. In the present paper the focus will be principally on systems involving pressure, vacuum, centrifuge and gravity, with a particular emphasis on pressure and vacuum. In addition, whilst there is a plethora of filter media types the paper will concentrate mainly on those of textile origin. With the above in mind, the purpose of the paper is to provide the reader with a basic overview of filter media selection criteria as seen through the eyes of the media manufacturer, reviewing what is currently available and taking a brief look at some advanced treatments and where it is believed development activity should be directed in the future.

P. Trautmann, M. Durst, A. Pelz and N. Moser

HIGH PERFORMANCE NANOFIBRE COATED FILTER MEDIA FOR ENGINE INTAKE AIR FILTRATION (pages 53-56)

bullet Abstract

bullet Filtration functions in motor vehicles have become extremely diverse and complex as a result of the precise requirements of modern engines, increasing stringent environmental legislation and, last but not least, rising demands for greater comfort and convenience from customers. Modern air filter media are expected to comply with the filtration values stated in the relevant specifications, for example, dust holding capacity and the full life filtration efficiency under all operating conditions. The filter media exhibit high stability under pulsating forces and do not allow any dust to permeate even under dynamic conditions, such as engine pulsation. Furthermore, a good quality air filter medium must be resistant to water, engine oils, fuel vapours and crankcase gases which reach the medium from the intake air or as a result of diffusion e.g. when the engine is stopped. Finally, materials must exhibit high thermal stability, since the temperatures at the filter element can rise to 90°C when the vehicle is driven. Today, cellulose based filter media are standard in most air intake systems.

A lot of effort has been expended in the past to optimise these media regarding efficiency, dust capacity, and pressure loss. To cope with increased requirements, the use of nanofibre coated filter media is an effective solution. Nanofibre coated filter media enable the selective optimisation of the filtration performance of air filter media for engine air filtration. Efficiencies in particular can be increased remarkably by adding a nanofibre layer on a carrier paper.

W. Li, C. Kiser and Q. Richard

DEVELOPMENT OF A FILTER CAKE PERMEABILITY TEST METHODOLOGY (pages 57-60)

bullet Abstract

bullet Permeability is an important characteristic of filter aid products. It can be tested by liquid flowing through an already formed cake approach (Method I) or by the cake filtration approach (Method II). Although in Method I permeability is easily calculated, two test runs are required. The method also requires a longer time compared to Method II. Method II requires the effective suspending of unfiltered feed to prevent sedimentation during filtration, and calculations are also more complicated than Method I. To simplify test and calculation procedures, a new filter cake permeability test method has been developed where filter medium resistance is also included. Test results on Rice Hull Ash (RHA) filter aids using the new method could be repeated consistently and correlated very well with results from tests based on the other two methods.

J. Dueck, D. Purevjav and Th. Neesse POROSITY MODEL FOR CAKE FILTRATION OF FLOCCULATED SUSPENSIONS (pages 62-70)

bullet Abstract

bullet A porosity model for the filter cake is presented that considers the adhesive forces caused by polymeric flocculants. Based on this model, cake permeability can be determined using a modified Kozeny-Carman equation. The theoretical considerations were validated by filtration experiments, using quartz suspensions and cationic polyacrylamide as flocculant. The filtration behaviour of flocculated quartz suspensions can be sufficiently explained with this model. Keywords: Cake filtration; modelling; cake porosity; permeability; adhesive forces.

M.L. Christensen, N.P.R. Andersen, M. Hinge and K. Keiding CHARACTERISATION OF THE TRANSITION BETWEEN THE FILTRATION AND CONSOLIDATION STAGE FROM LIQUID PRESSURE MEASUREMENTS (pages 71-78)

bullet Abstract

bullet Constant pressure, deadend filtration is a widely used method for estimating filter cake resistance and compressibility. An accurate estimation of these parameters involves identifying the transition between the filtration and consolidation stage, i.e. the point in time when the piston touches the filter cake. This paper presents a method for determination of the transition point by measuring the liquid pressure at the sample-piston interface. The method is compared with the conventional method based on measuring filtrate volume, and it is found that the transition point occurs earlier when using liquid pressure measurements. This is consistent with calculations, which show that the filter cake compressibility is high in the initial part of the consolidation stage while the hydraulic resistance is low. Hence, the filtrate flux in the initial part of the consolidation stage is of the same order of magnitude as the filtrate flux obtained during filtration, which explains why the estimated transition time is delayed using the conventional method. While this finding does not affect the determination of the filtration characteristics, it is important for determining the proper consolidation characteristics.

Keywords: Cake filtration; consolidation; liquid pressure.

J.A. Gantt, E.P. Gatzke, V. Van Brunt, T.J. Deal, R.B. Haggard, M. Poirier, S. Fink and C. Nash DYNAMIC MODELLING OF A PILOT-SCALE CROSSFLOW FILTRATION PROCESS (pages 79-86)

bullet Abstract

bullet The Filtration Research Engineering Demonstration (FRED) facility at the University of South Carolina is a pilot plant designed with the Savannah River Site (SRS) to test operational aspects of separation of high level from low level radioactive waste currently being performed at the SRS. This paper presents a dynamic crossflow filtration model for the FRED facility based on experimental data. The resulting model includes the effects of trans-membrane pressure, slurry concentration, and the role of backpulsing. The model was created using a statistical modelling program, JMP (SAS Institute), and the model was based on Darcy’s Law.

The model successfully fits the given data from a non-radioactive sludge test performed at FRED to an accuracy of 90%. This dynamic model can be used to predict how the filtration process may respond to variations in parameters, such as trans-membrane pressure, backpulse interval or axial velocity to improve cycle times at the Savannah River Site.Keywords: Membrane; radioactive; dynamic modelling; resistance; backpulsing.