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.

Volume 11, Issue 1 Abstracts from the FILTRATION journal

REMOVAL OF FINE PARTICULATE MATTER FROM EXHAUST GASES BY METALLIC MICROSIEVES
Esther Stahl, Josef Robert and Görge Deerberg (pages 36-40)

Metallic microsieves are promising filter media for removing fine particulate matter from gases. Therefore, a study has been carried out to show their filtration performance (pressure drop and filtration efficiency) with respect to different boundary conditions (volume flow, temperature). Experiments showed high particle retention rates after a short time, depending on the hole diameter. By applying microsieves with an average pore diameter of 8 µm, a retention rate of more than 99% could be obtained after 90-160 s. The practical application of microsieves as a filter in the exhaust gas of wood fired furnaces is shown to give good results.

DESIGN OF A NEW HIGH PERFORMANCE DRUM FILTER FOR THE CHEMICAL INDUSTRY
Thomas Langeloh and Reinhard Bott (pages 40-45)

Drum filters represent the most important and most applied rotary filter technology that is used in a wide range of industrial applications with very different products. For filtration tasks in the chemical industry BOKELA has developed a new drum filter generation which satisfies the needs and requirements of these applications, e.g. the filtration of crystal suspensions. These modern high performance drum filters are characterised by high specific solids throughput, intensive cake wash, sharp filtrate separation, low moisture contents, complete cake discharge, reliable operation and ease of maintenance. The fundamental aspect is a well calculated and well-designed hydraulic system.

DETERMINATION OF THE PRESSURE DEPENDENCE OF PERMEABILITY CHARACTERISTICS FROM A SINGLE CONSTANT PRESSURE FILTRATION TEST
Eiji Iritani and Nobuyuki Katagiri (pages 46-50)

A single constant pressure filtration test procedure has been developed for easily determining the pressure dependence of permeability (or average specific cake resistance). The method makes use of the variation of the effective pressure drop across the filter cake with time generated by using a filter medium with high resistance. The validity of the method was confirmed by constant pressure filtration of bentonite slurry using an ultrafiltration membrane with a nominal molecular weight cut-off of 1000 Da. It was also revealed that the threshold value of pressure below which the average specific cake resistance remains constant can be readily obtained from the method.

MITIGATING AND MODELLING MEMBRANE FOULING BY BIOACTIVE MIXTURES
Zaid S. Saleh, Judie M. Farr and Steffen A. Friedrich (pages 50-57)

In this study, the fouling that occurred during batch nanofiltration processing to separate phenolic phytochemical compounds from clear apple juice concentrate was characterized and modelled using various operating parameters. Polysulphone SelRO® spiral wound membranes with a molecular weight cut-off (MWCO) of 1 kDa and 0.25 kDa were used on a pilot laboratory scale rig. The retention of various compounds including total and individual phenolics, total soluble solids, proteins and certain types of sugars were determined analytically. The effects of temperature, pH, trans-membrane pressure and feed concentration on permeate flux, fouling and membrane performance were determined.

Different types of fouling mechanisms, including reversible and irreversible concentration polarization, cake formation, pore blocking or a combination of the aforementioned, were investigated. The trends in fouling rates were compared with predictions from available fouling models, and the fouling mechanism was considered. It was found that cake formation was the dominant reversible fouling mechanism in the 1 kDa membrane and that pore blocking was the dominant type of fouling occurring in the 0.25 kDa membrane. Reversible cake formation was greater at higher feed concentrations and temperatures and lower at low pH values and pressures. Furthermore, performing diafiltration increased the permeate flux remarkably by reducing the concentration polarization effect.

POLYMER EXTRUSION FILTER DESIGN WITH A HYBRID PSO-GA OPTIMIZATION APPROACH
Kathleen R. Fowler, Eleanor W. Jenkins and Brian M. McClune (pages 58-64)

We discuss an optimization study of two layer extrusion filter designs using a three-dimensional computational simulator and derivative free hybrid optimization methods. The simulator models flow of a non-Newtonian fluid through a multi-layered filter with debris deposition. Previous studies used a derivative free sampling algorithm to maximize different performance measures of one- and two- layer filters, relative to changes in porosity and pore diameter in each layer. A challenge in those studies, and the motivation for this work, is that the single search optimization algorithm used would converge to a sub-optimal filter design for certain starting points.

In this work, we apply a new hybrid optimization algorithm that combines two heuristic search methods: a genetic algorithm (GA) and a particle swarm optimization (PSO) algorithm. Both are known to exhaustively search the design space and are less likely to stagnate at a local minimum. They do, however, require a significant number of calls to the simulator. This is computationally expensive, as each call may require over an hour of computation time. The efficiency is improved by incorporating surrogate functions (i.e. a cheaper approximation to the real objective function) into the search phase. This paper presents numerical results for a two layer extrusion filter design and discusses extensions to more complicated filter designs.

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Volume 11, Issue 2

STUDY OF DEPOSITION AND SEPARATION OF SUBMICRON PARTICLES IN NANOFIBRE COMPOSITE FILTERS
Thomas Bahners and Eckhard Schollmeyer (pages 93-99)

A growing interest in the integration of nanofibres in media for surface as well as deep bed filtration can be observed. The present paper summarizes a study of the morphology of deposition and mechanisms of separation in multi-layer deep bed filters, predominantly with regard to submicron particles in liquid filtration. The considered composite filters were prepared as stacks of alternating layers of commercial nonwoven and electrospun nanofibre webs with variation in the thickness of the nanofibre layers. Analogous stacks made-up of only commercial nonwoven served for comparison. While the results indicate geometric separation purely due to pore size, as well as some contribution of impact driven separation, for micron sized particles, scanning electron microscopy (SEM) and combined X-ray spectroscopy (SEM/EDX) show deposition morphologies of submicron particles that are exclusively due to particle diffusion, i.e. statistical variation of the ideal trajectories. Particle separation/deposition mainly occurred in the nanofibre layers.

FILTER MEDIA PORE SIZE COMPARISON BETWEEN POROMETRY AND CHALLENGE TESTING USING SPHERICAL STANDARDS
Graham Rideal and Jamie Storey (pages 99-104)

The accuracy of pore size measurement by porometry has been found to be dependent on the instrument and operator. Similarly, challenge testing using ISO test dusts is dependent on both the precision of the particle analysis of the irregular shaped particles and the laboratory protocols. To overcome the ambiguity of shape, a much simpler challenge method has been developed using NIST certified, narrow particle size distribution glass beads. This new high-speed method determines the filter efficiency (cut-point) using a novel dry sonic device for pore sizes above 20 µm and a wet suspension method for pore sizes below 20 µm. This paper compares porometry values obtained for a number of porometers after cross validation with the new microsphere challenge test method. A new multimodal standard has also been developed to measure the pore size distributions in submicron filters.

PRODUCTION OF CONCENTRATED YOGURT USING SUPERABSORBENTS AND A PERMEABLE MEMBRANE
Abdolmajid Maskooki, Ali Ahmadpour and Masoud Rezaee (pages 105-114)

Superabsorbent polymers (SAP) are materials that absorb and retain water and aqueous solutions up to several hundred times their own weights within their structure, even under pressure. Reducing the time of dewatering by permeable membrane and superabsorbent polymers for the production of traditional concentrated yogurt was investigated. Yogurt samples were dewatered using vertical and wide bed permeable membranes with and without SAP. The effects of SAP and position of the bed on the amount of dry matter and soluble solid during reduction of moisture content were evaluated at different time intervals and continued for 180 mins.

The results showed that using polymeric superabsorbent combined with a wide bed reduced the dewatering time by one third with respect to conventional methods. At a specific time interval, using superabsorbent with a wide bed increased the dewatering efficiency by approximately 68% compared to the conventional method, while dewatering using a wide bed without SAP increased dewatering efficiency only by 10% compared to the usual vertical bed method. The dewatering process did not affect the soluble solid content of the tested yogurt. The results may be practically applicable to the industrial dewatering processes of many other foods.

FILTRATION OF NANOPARTICLES: PRESENTATION OF FANA TEST BENCH
N. Michielsen, T. Lelandais, C. Brochot and S. Bondiguel (pages 114-117)

A test bench for the analysis of air filter penetration has been developed at IRSN. The paper introduces this nano-aerosol filtration test bench (FANA) and the methodology used to measure filter penetration as accurately as possible for nanoparticles. Two configurations are compared by measuring the penetration through a metallic grid. The results obtained are identical. In addition, penetration results using two filtration velocities and a particle size range of 2.5 to 400 nm are presented for different types of filtration media (F6, F9, HEPA).

EXPERIMENTAL STUDY OF THE INFLUENCE OF PROCESS VARIABLES ON THE PERFORMANCE OF A HORIZONTAL BELT FILTER
Mikko Huhtanen, Antti Häkkinen, Bjarne Ekberg and Juha Kallas (pages 118-123)

This paper introduces an experimental study that was carried out to determine the influence of several different process variables on the performance of a horizontal vacuum belt filter. Laboratory scale tests were performed according to the multilevel full factorial design by using a conventional Buchner test unit. The investigated process variables were the volumetric feed rate of the slurry, dewatering time, amount of wash liquid used and solids concentration of the feed suspension. The parameters that were used for describing the performance of the process were the cake moisture content, production capacity of the filter and the purity of the washed filter cake. The results obtained from these tests were used to create different kinds of regression models for all of the studied responses.

Several different kinds of test designs were also extracted from the initial full factorial design for defining the minimum number of tests required to obtain satisfactory results for the investigated application. Comparison of different models showed that the amount of test work could be efficiently reduced by utilizing the statistical design of experiments and empirical modelling tools.

EVALUATION OF CONSOLIDATION-SEDIMENTATION PROPERTIES FOR THE BATCH GRAVITY SEDIMENTATION OF CONCENTRATED SUSPENSIONS
Nobuyuki Katagiri, Takeshi Hashimoto and Eiji Iritani (pages 123-128)

Consolidation-sedimentation behaviour of consolidated sediments under the action of gravity was investigated using highly concentrated suspensions of titanium dioxide particles under conditions of various pH, initial height and initial concentration. The average consolidation ratio of the consolidated sediment was analysed on the basis of the simplified analytical solution obtained using the modified Terzaghi model with the moving Lagrangian coordinate system. The modified average consolidation coefficient increased in almost direct proportion to the total volume of solids per unit cross-sectional area, which changes the driving force of consolidation-sedimentation due to the overlying weight of the solid particles. The variations with time of the height of the consolidated sediment were adequately modelled using the analytical solution describing the average consolidation ratio with the aid of the relation that the equilibrium height was represented by a power function of the total volume of solids for a specified pH.

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Volume 11, Issue 3 Abstracts from the FILTRATION journal

A REVIEW OF EQUIPMENT SELECTION AND PROCESS DESIGN IN SOLID/LIQUID SEPARATION
Steve Tarleton (pages 151-161)

This paper presents a survey of the methods of equipment selection and process design for solid/liquid separation. It is shown how a combination of automated analysis, laboratory scale test work and computer aided calculations provide the most reliable results. Current best practice is highlighted, both in terms of the computer software available (e.g. Filter Design Software) and the advantages offered by automated filter apparati for data generation. Worked examples and example data are presented to show the capability of the overall process.

CLOGGING OF INDUSTRIAL PLEATED HIGH EFFICIENCY PARTICULATE AIR (HEPA) FILTERS IN THE EVENT OF FIRE IN A CONFINED AND VENTILATED FACILITY
Victor Mocho and François-Xavier Ouf (pages 162-167)

The IRSN and AREVA NC are currently conducting a fire research programme to improve knowledge of the clogging of industrial pleated high efficiency particulate air (HEPA) filters in order to develop an empirical model for clogging of such filters by combustion aerosols. The model must insofar as possible be independent of the nature of the fuel. This paper discusses the influence of various ‘direct’ factors such as the filtration velocity, mass of deposited aerosols per filter area, diameter and morphology of the combustion particles, condensate content of the aerosols, and ‘indirect’ factors such as the air flow feeding the fire and its oxygen content, which influence evolution in the aeraulics of a clogged filter.

OUTGASSING CHARACTERISTICS OF HEATED PTFE MEMBRANE FILTERS WITH A THERMOPLASTIC SUPPORT
Jacob Swanson and David Pui (pages 168-172)

Airborne molecular and particle contamination in clean rooms reduces product quality and yield. In this study we investigated the outgassing characteristics of heated, expanded polytetrafluoroethylene (ePTFE) membrane filters that were supported by a thermoplastic layer because these filters represent a potential source of contamination. Two filter types were evaluated: ePTFE membrane filters supported by PTFE and ePTFE membrane filters supported by a polyester laminate. Filters were heated in a cyclic fashion by varying the temperature of the particle free nitrogen challenge gas. During heating, the concentration and size distributions of particles downstream of the filter were measured.

The results show that at a temperature of 200°C, high concentrations (>107 particles/cm3) of ~20 nm particles formed downstream of the polyester filter due to the nucleation of organic vapours that outgassed during heating. Additional experiments showed that after the outgassing ceased and the filter was cooled, subsequent heating would generate more particles. Filters with PTFE support that were cyclically heated in a similar fashion generated no particles at 200°C and very few particles at 260°C suggesting they are more suitable for use in a manufacturing clean room when elevated temperatures are present.

CHALLENGE TESTING FILTERS USING CERTIFIED MICROSPHERES
Graham Rideal and Jamie Storey (pages 172-177)

Challenge testing is a long established method of testing the performance of filters by measuring their ability to trap particles of known size. Traditionally, sands and test dusts have been used but more recently a range of narrow particle size distribution spherical particles have been developed, which can give higher precision and more repeatable results. The pore sizes that can be tested are only limited by the sizes of the challenge particles available so filters from millimetres down to nanometres can be measured. Being spherical, there is not an orientation element to the filtration as in the case of irregular dust particles but the biggest problem, particularly in the sub-micron range, is finding a sizing technique that gives sufficient resolution to detect small changes in size as a result of passing through the filter. Furthermore, spherical particles should give results independent of the method of analysis.

This brief illustrated review summarises the challenge test methods using the new Whitehouse Scientific spherical particles. In addition to the traditional single parameter result, the cut point of the filter, the latest evolution of the method is also shown to provide information on the pore size distribution in a filter.

TRANSITION BEHAVIOUR OF FILTER LOADING CHARACTERISTICS FOR SUPERMICROMETRE OIL-COATED ARTICLES
Ta-Chih Hsiao and Da-Ren Chen (pages 177-187)

Liquid-coated particles are often encountered in ambient and industrial working places. The loading behaviour (i.e. the characteristics of filter pressure drop vs. loaded particle mass per unit area) of filters for liquid-coated particles is expected to be different from those for the cases loading solid only or liquid only particles. In this study, a system capable of generating oil coated particles in stable concentrations was first developed for filter loading testing. A series of filter loading experiments were then performed to investigate the transitional behaviour of filter loading for oil-coated particles. It is observed that the general oil-coated particle loading behaviour of filters transits from that of solid only particles to that of oil only ones as the liquid volume percentage in test particles increases.

Our study shows the transitional loading behaviour highly depends on the overall particle size, and property of filter media and coating liquids. We concluded that the loading behaviour is dominated by the effect of liquid surface tension when the liquid volume percentage in coated particles is less than 50%. Under the above oil-coated particle conditions, the filter loading curves for particles with various liquid percentages can be merged into one via the solid core particle surface area. When the oil volume percentage in coated particles is more than 50%, the effect of liquid viscosity becomes dominant and the loading curves of various liquids follows the order of the oil viscosity.

‘BUBBLE BOBBLE’ IN THE LAUTER TUN – A NEW WAY FOR MASH SEPARATION IN THE BREWHOUSE
Johannes Tippmann, Hans Scheuren, Jens Voigt and Karl Sommer (pages 188-192)

Beer production starts in the brewhouse where milled malt is mixed with water. Relevant ingredients of the malt are converted and dissolved into the wort. The solids have to be separated from the remaining liquid which is a step done in the lauter tun and still a very time consuming process. The developed system is the result of two principles, evaporation of unwanted flavouring substances and the prevention of the blocking of the filter cake. The approach described in this paper was the integration of a bubble generator in the lauter tun which blows nitrogen bubbles (inert gas, not oxidising) through the mash and the filter cake.

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Volume 11, Issue 4 Abstracts from the FILTRATION journal

DIXON RINGS – A REVOLUTIONARY RANDOM COLUMN PACKING
Robert Alford, Mark Burns and Neil Burns (pages 218-223)

Dixon rings were developed in 1946 by Dr Olaf George Dixon while working for ICI and are currently used where high performance is essential. There are a number of published papers on the characterisation of Dixon rings as used in distillation applications; however, there is little published work on the countercurrent (scrubbing) performance of Dixon rings. Croft Engineering Services have developed a revolutionary manufacturing method for Dixon rings that can be used in both countercurrent absorption (scrubbing columns) including scrubbing of CO2 from air, as well as hard distillation separations such as tritium from water. This cylindrical mesh item of small size in comparison to the market leaders (Pall rings, Intalox saddles) offers superior performance in a range of applications. The current paper contains a detailed analysis of Dixon rings in a random column packing operating within countercurrent absorption applications.

WET PARTICLE CLASSIFICATION BELOW 1 µm – CHALLENGE FOR BASIC RESEARCH AND TECHNICAL DEVELOPMENT
Harald Anlauf (pages 223-229)

The conventional processes of wet and dry classification in the particle range of more than 1 µm are sieving and the different variants of stream classification. Approaching particle sizes of 1 µm and below the conventional methods reach their present physical and technical limits. The economic relevance of particle systems below 1 µm, and especially between 1 µm and 0.1 µm, is constantly growing and thus a high demand for improved and new classification processes exists. The grade efficiency, selectivity and cost effectiveness of the methods used for such applications are unsatisfactory or don’t exist. In this paper the physical background of classification processes and the problems of fine particle classification are described and discussed. The different physical principles and phenomena are analysed with regard to their potential for technical classification systems in the sub-micron range. Examples are given for promising techniques together with ideas for new approaches.

EFFECT OF ACOUSTIC WAVES ON THE PERFORMANCE OF A MULTI-CYCLONE – FILTER SYSTEM
Leonid Moldavsky, Chaim Gutfinger and Mati Fichman (pages 229-232)

Many air filtration systems include cyclones for pre-cleaning. The performance of the system changes with time because of filter clogging. The cyclones reduce the concentration of aerosol particles, but their sizes are reduced as well, which leads to deeper particle penetration into the filter. Acoustic waves enhance filtration efficiency and cause sedimentation of the very small particles on the filter surface. They also cause the filter layer to be more porous, which leads to a reduction in pressure drop across the filter. In the present study a cyclone-filter system, similar to that in heavy vehicles, was used to assess the effect of acoustic waves on the pressure drop across the filter. It was shown that a low frequency acoustic field reduces the pressure drop across the filter and increases the flow rate through the system, which leads to a reduction of the time between filter replacements or regeneration, ensuring improved performance.

A POROMETER ROUND ROBIN PROGRAM USING FILTER MEDIA OVER A RANGE OF PORE SIZES
Uwe Beuscher, Jeffrey Brake, Michael Doby and Ernest Mayer (pages 233-242)

A round robin program was undertaken to evaluate the techniques and methods used during the operation of various porometers. Two companies participated in the round robin testing of a total of ten Porous Materials, Inc. (PMI) porometers at various locations throughout the world. A variety of filtration media with a wide pore size range were run on the porometer units for comparison. As fragility of some conventional filter media continues to increase primarily due to decreasing fibre diameter and media thickness, porometer testing can sometimes be quite tedious for certain samples. At high compressive load during porometry, damage can occur to the samples producing misleading results. Measures to safely handle samples and operate porometers when working with fragile media were addressed.

The aforementioned samples were processed on each porometer using identical wetting liquid, support plates and parameter files throughout the program. The experimental data are discussed with possible explanations for the deviations presented. The results indicate that the industry should focus on standardising equipment design and developing a procedure for testing to ensure an accurate comparison among porometers.

EXPLORING THE INFLUENCE OF FEED MATERIAL PROPERTIES ON FULL CYCLE OPTIMISATION OF FILL, SQUEEZE AND BLOW PLATE AND FRAME PRESSURE FILTERS
Ross G. de Kretser and Peter J. Scales (pages 243-248)

Investigation of the response of plate and frame filter performance to changes in design and operating variables is complicated by the large matrix of potential variables and the inter-dependent kinetics of the fill, press and air blow stages. However, through some key simplifying constraints an integrated optimisation framework has been recently developed. Initial demonstration of the utility of the framework for minerals filtration was completed on an incompressible iron ore fines material which illustrated a strong dependency of the optimum filling duration on filter specifications such as the ratio of pressing to filling pressure and cavity thickness employed.

The current paper extends this work by exploring how these trends change with varying material properties, specifically treating the cases where the compressibility and permeability are varied. Comparison of optimisation examples for a lower permeability lead-zinc tailings material and the higher permeability iron ore fines revealed a common feature of an optimum fill duration, generally at early times, beyond which throughput deteriorated. A significant difference was observed in the optimum split of cycle stage durations due to the strong effect of desaturation kinetics on the finer tailings dewatering. However, a generic trend was implied whereby an optimum cavity thickness existed, but that this was for a cavity thickness whose optimum fill duration was zero, i.e. the press stage was initiated as soon as the filter cavities were filled.

THE EFFECT OF FACE VELOCITY, PLEAT DENSITY AND PLEAT ORIENTATION ON THE MOST PENETRATING PARTICLE SIZE, PRESSURE DROP AND FRACTIONAL EFFICIENCY OF HEPA FILTERS
Iyad Al-Attar, Richard Wakeman, Steve Tarleton and Adel Husain (pages 248-256)

The increasing need for clean air in critical industrial applications has highlighted the importance of the role of air filters in providing improved air quality. Actual performance of air filters installed in air handling units and in the intake of gas turbines tends to deviate from the performance predicted by laboratory results. Therefore, accurate filter performance prediction is important to estimate filter lifetime, and to reduce energy and maintenance operating costs. To ensure that the desired efficiency of a HEPA filter is attained, the effects of face velocity, pleat density and pleat orientation on the Most Penetrating Particle Size (MPPS) of pleated HEPA filters must be examined. This paper compares the effects of varying these parameters on the MPPS. The paper also presents the initial pressure drop response and fractional efficiency curves using DEHS testing according to DIN 1822 for vertical and horizontal pleat orientations. It analyses the underlying reasons causing surface area losses for different flow rates, pleat density and orientation as well as the effects on filter permeability. The tests conducted in this study used full scale HEPA pleated V-shaped filters from Heating Ventilation and Air Conditioning (HVAC) and gas turbine applications.

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Volume 12, Issue 1 Abstracts from the FILTRATION journal

PRESERVING OUR VITAL RESOURCE
Graham Rideal (pages 26-31)

Discussion of our dependence on clean water, some of the steps we need to take to ensure its availability and the impact of new filtration techniques.

EFFECTS OF POST-COATING BY GENERATING A THIN SECONDARY PARTICLE LAYER ON SURFACE FILTERS FOR DUST SEPARATION
Qian Zhang and Eberhard Schmidt (pages 31-37)

Periodic cleaning is necessary in surface filtration to limit the pressure drop, which increases as more dust is deposited. Higher cleaning efficiency can be achieved with lower adhesion of the dust cake on the substrate on the one hand and higher cohesion in the dust cake on the other. The operational behaviour of surface filters can be influenced positively by raw gas conditioning, e.g. by dosing of additives. This paper introduces experimental investigations into the effects of the so called post-coat filtration, which is a novel conditioning concept for surface filtration. An additional thin particle layer is generated by filtration of aerosols on the main dust cake before cake discharge is done. Experiments were performed with needlefelts as the test filters, limestone as the main dust and carnauba wax or sodium chloride as the post-coat particles on a surface filter test apparatus (manufactured according to VDI guideline 3926-1). The effects observed in single filtration cycles are presented and discussed.

SOFTWARE FOR STATISTICAL DESIGN OF EXPERIMENTS AND EMPIRICAL MODELLING OF CAKE FILTRATION
Mikko Huhtanen, Antti Häkkinen, Bjarne Ekberg and J. Kallas (pages 38-49)

This paper introduces software developed to improve the efficiency and quality of typical test filtration tasks and to simplify and rationalize the interpretation of test results. The software consists of two different modules.

The first module creates experimental designs according to initial information provided by the user. The test designs are created by applying the basic principles of factorial designs in such a way that the variations in the investigated ranges of the desired process variables are taken into account systematically. The utilization of different kinds of factorial designs also means that the amount of experiments needed to achieve the required accuracy can be minimized. The second module of the software analyses the experimental results by utilizing standard multivariate data analysis techniques. The meaningful information from a given table of experimental data is extracted and used to create regression models that quantify the relationships between the studied process variables. These models can be further applied to predict new values, for visualizing the relationships between the different variables, or for selecting the variable combinations in order to reach the predefined process objectives.

The current software is capable of creating experimental designs for five different kinds of filters, namely the automatic vertical pressure filter, double-sided automatic vertical pressure filter, horizontal membrane filter press, horizontal vacuum belt filter, and the ceramic capillary action vacuum disc filter. The suitability of the applied techniques for each filter type has also been verified by performing a large number of experiments. Some of the experimental results with the automatic vertical pressure filter are presented in this paper to illustrate the procedure developed and also to demonstrate the quality of the final results obtained by the applied methods.

ROTATIONAL PARTICLE SEPARATOR: AN EFFICIENT METHOD TO SEPARATE MICRON-SIZED DROPLETS AND PARTICLES FROM FLUIDS
J.J.H. Brouwers, H.P. van Kemenade and J.P. Kroes (pages 49-60)

The rotational particle separator (RPS) has a cyclone type housing within which a rotating cylinder is placed. The rotating cylinder is an assembly of a large number of axially oriented channels, e.g. small diameter pipes. Micron-sized particles entrained in the fluid flowing through the channels are centrifuged towards the walls of the channels. Here they form a layer or film of particles, material which is removed by applying pressure pulses or by flowing of the film itself. Compared to conventional cyclones the RPS is an order of magnitude smaller in size at equal separation performance, while at equal size it separates particles ten times smaller. Applications of the RPS considered are ash removal from hot flue gases in small scale combustion installations, product recovery in the stainless environment for pharmaceutical/food, oil water separation and demisting of gases. Elementary formulae for separation performance are presented and compared with measurements performed with various RPS designs.

DEVELOPMENT OF INNOVATIVE FIBRE MATERIALS FOR TECHNICAL APPLICATIONS – FINE POLYVINYLIDENE FLUORIDE FILAMENTS AND FABRICS
Stephan Walter, Wilhelm Steinmann, Gunnar Seide, Thomas Gries and Georg Roth (pages 60-64)

Development of new materials and processes for technical applications usually requires extensive interdisciplinary cooperation. It is seldom that innovative and sophisticated materials evolve solely from one technical or scientific discipline’s efforts. In this paper the development of fine melt spun polyvinylidene fluoride multifilament yarns, the processing, fabric production and property investigation are presented. It outlines what it takes to exceed the state-of-the-art for existing fibre materials and their applications. The steps of material selection, experimental evaluation of a process window for melt spinning PVDF, yarn processing and fabric formation are reported in detail. Furthermore, a model for the crystalline structure formation during melt spinning and drawing PVDF fibres is presented.

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Volume 12, Issue 2 Abstracts from the FILTRATION journal

CABIN AIR FILTER MEDIA WITH BICOMPONENT SPUNBOND SUPPORT LAYER
Annemarieke Maltha, Edgar Berkhout, Pieter Zuuring and Martin Koerntjes (pages 95-98)

This paper presents how a specially designed bicomponent spunbond nonwoven contributes to an improvement in filter design and filter medium efficiency. The spunbond nonwoven is used as a support layer or prefilter for filter media. Its unique properties result in filter media with low pressure drop, high mass evenness, and a high stiffness. Application of this spunbond as a support layer in pleated filter media for cabin air filters, leads to stiffer and sharper (smaller radius of curvature) pleats, without a degradation in overall mechanical properties, thus facilitating a more efficient filter design. Additionally, the bicomponent yarn architecture and nonwoven design allow for adding desired surface functionalities in the skin polymer, like easy lamination, tunable hydrophobicity and colour.

INNOVATIVE LOW PRESSURE PLASMA COATINGS FOR GAS AND LIQUID FILTER MEDIA
Filip Legein (pages 98-102)

Plasma is the fourth state of matter. By adding energy, matter can be transformed from solid to liquid, from liquid to gas and from gas to plasma. In plasma the molecules are decomposed into neutral and charged particles that will interact with the surface of the material. In low pressure plasma technology a stable and effective plasma is created by an electromagnetic discharge of a gas at low pressure and at low temperature. In recent years low pressure plasma technology has been improved to achieve polymerization of monomers on materials, depositing real nanocoatings on the surface, and adding new and permanent functionalities to the material. Innovative plasma processes allow the deposition of coatings with high levels of hydrophobicity and/or oleophobicity for use in gas filtration, or coatings with permanent hydrophilic effect for liquid filter media and battery separators.

The use of low pressure plasma for surface modification of filter media has become more widespread because it is a dry and clean technology. Filter media producers adopt plasma coating to improve the quality of their products. At the same time it helps these companies to save costs because of a lower consumption of energy and chemicals.

TREATMENT OF HIGHLY VISCOUS LUBRICANTS BY HIGH GRADIENT MAGNETIC SEPARATION
Katharina Menzel, Johannes Lindner and Hermann Nirschl (pages 103-108)

Abrasive particles in gear and hydraulic oils are responsible for increased wear in machine elements like bearings or the breakdown of entire machine systems, e.g. the gears in wind power plants. The monitoring of the lubricant condition as well as its continuous treatment is therefore essential to increase the lifetime of the equipment. The separation of micrometre particles ranging from 1 to 20 µm of a high viscosity lubricant is still challenging in state-of-the-art deep bed filtration because of high pressure drop and the unintentional separation of additives. Wear particles of different chemical composition are magnetisable and therefore magnetic separation is a promising approach to separate these particle clusters, while avoiding the separation of oil additives. The magnetic force is effective at great distance from the separating wire. The HGMS filter is therefore configured to be more porous than a conventional filter material. Hence, the pressure drop in High Gradient Magnetic Separation (HGMS) is negligible which is a great advantage and helps to decrease operating expenses.

A STUDY TO EXCLUDE EARTHWORMS FROM HARVESTED AND STORED RAINWATER
K.T. Oladepo, J.O. Jeje, O.O. Fadipe and M.O. Ogedengbe (pages 108-113)

People in the study area believe that rainwater, harvested and stored, would, in due course, have earthworms in it. They consider earthworms in water meant for cooking, let alone drinking, objectionable. These are the known reasons why rainwater harvesting has failed to be accepted. This study was intended to encourage dwellers of rural and semi urban communities to embrace the harvesting and storing of rainwater for domestic use and reduce their use of water from sources which potentially transmit pathogens to users. Rainfall data were collected. Dual media filters were built of palm kernel shells (PKS) over silica sand. Rainwater was harvested and passed to storage, filtered and unfiltered. During 30 days of storage the rainwater was not found to contain earthworms, although it was widely believed that it would. Passing rainwater into storage through the dual media filters produced better quality water. Any approaching earthworm would surely be filtered out.

INFLUENCE OF MEMBRANE TYPE ON THE CROSSFLOW MICROFILTRATION OF BLUE DEXTRAN
Kuo-Jen Hwang and Syuan-Jyun Lin (pages 114-119)

The effects of membrane type and operating conditions on the crossflow microfiltration performance of blue dextran are studied experimentally. Three 0.1 µm flat sheet membranes made of polycarbonate (PC), polyvinylidene fluoride (PVDF) and mixed cellulose ester (MCE) were used in experiments as the filter media to separate blue dextran with a molecular weight of 2000 kDa. The filtration rate increased with increasing crossflow velocity and trans-membrane pressure. The filtration rate was highest while the dextran rejection was lowest when the PVDF membrane was used. The use of the PC membrane resulted in the lowest filtration rate but the highest dextran rejection. Therefore, the comparison of the mass flux collected into the filtrate follows the sequence PVDF > MCE > PC membrane. The results indicate that using a PC membrane and operating under high crossflow velocity are optimal for dextran concentration in the original suspension, while the use of PVDF membrane results in the highest filtration rate and collects most blue dextran in the filtrate.

METHOD OF TESTING METAL WORKING FLUID MIST SEPARATORS
Thomas Laminger, Marcus Stecher and Wilhelm Höflinger (pages 120-128)

This work deals with the development of a standardized filter test method for metal working fluid (MWF) mist separators. In order to compare the separation behaviour of different filter media, a filter medium must reach its stationary condition, which can take a long time. In the study an accelerated filter ageing procedure was developed and tested with six real filter elements of different structure using a laboratory scale filter test rig. A relatively high filter loading value generated by a nozzle spray was used to shorten the time needed to reach a steady state liquid equilibrium, and hence a steady state pressure drop. Thereafter the nozzle spray was shut off and an aerosol generator was used alone to produce a real working fluid mist aerosol. This aerosol facilitated determination of the steady state filter separation efficiency by measurements of the raw and clean gas aerosol concentrations, respectively.

Filter tests with 10 %vol MWF emulsions as the test substance showed that with the accelerated filter ageing procedure all tested filter elements reached the steady state within a period of two hours. Thereafter a steady state filter separation efficiency was determined. According to existing classification norms for dust filters, a classification system with a minimum requested separation efficiency in four particle size ranges for MWF mist separators is proposed. The tested filter elements were also classified using the proposed classification system. The filter class of the elements increases as the filter structure becomes finer. With the developed accelerated filter ageing procedure and the classification system it is now possible to evaluate and compare different mist separators in a short time.

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Volume 12, Issue 3 Abstracts from the FILTRATION journal

NEW LABORATORY DEVELOPMENTS FOR BELT THICKENER OPTIMIZATION
Pascal Ginisty and Christophe Peuchot (pages 154-158)

Gravity belt thickening is commonly used for sludge volume reduction. In many applications it is preceded by chemical conditioning to enhance water release and solids capture. Laboratory tests are usually performed to select the best polymer and optimal dosage for full scale application. Drainage kinetics are very sensitive to mixing conditions during flocculation. Thus, a specific device called the ‘boo-test’ was developed to control these parameters and guarantee the repeatability of conditioning, necessary for a reliable comparison of products. Torque rheometer and laser diffraction granulometer measurements give complementary data for describing the flocculation process.

SINGLE PARAMETER SIEVE CALIBRATION USING PRECISION GLASS MICROSPHERES
Graham Rideal and Jamie Storey (pages 159-162)

Sieving is the oldest method of particle size analysis but unfortunately its reputation has suffered from bad practice, by both the manufacturer and user. A combination of using poor quality mesh or even putting the wrong mesh in a frame, combined with casual analytical practices has reflected very badly on the method. International standards have endeavoured to specify acceptable tolerances using microscopy but the resulting 13 parameter definitions are difficult to replicate when trying to match sieves. Also, only wire spacings rather than actual apertures are measured. This study investigates the use of precision glass microspheres for the NIST traceable certification of sieves. A new image analysis software program was developed to analyse the internal parameters of each aperture. Excellent agreement was seen between the optical techniques and the glass microsphere calibration method when analysing a 63 micron sieve.

REDUCING OPERATING COSTS OF BAG FILTERS USING A FILTER EXPERT SYSTEM
Gunnar-Marcel Klein, Peng Bai, Tim Neuhaus and Theo Schrooten (pages 163-169)

This article addresses the optimization, including upgrades, of bag filters to reduce the life cycle cost (LCC) of an industrial bag filter installation. Energy consumption, mainly by fan motors and by the consumption of compressed air, is the biggest portion of the LCC of a bag filter. Today, improved jet-pulse cleaning systems enable the use of very long bags, leading to a reduction of both, investment and operating costs. A systematic analysis of the process parameter ‘air tank pressure’ was carried out for bag lengths up to 12 m. The results are summarized in a decision matrix, which allows the cement producer to decide the maximum possible bag length in filter upgrades, as well as for new installations. The test series are performed using special high speed pressure transducers to precisely determine the interior pressure in filter bags over their length and for different operation parameters.

The second part of the paper focuses on a newly developed tool to determine the optimum operational set points of jet-pulse bag filters. The filter expert system ProExpertise, by Intensiv-Filter, is able to calculate the differential pressure, the consumption of pressurized air and the energy demand for different operating parameters. The program presented is able to predict the optimum cycle time, at which the sum of the energy consumption for the fan and for the jet-pulse cleaning has a minimum value. The results are dependent on operation parameters such as volume flow, raw gas dust load, filter media type, bag length, among others, and provide even experienced filter experts with valuable information to reduce operating costs.

ProExpertise is based on the well-known filter equations for cake filtration and contains experimentally determined specific cake resistances and residual pressure loss values for Pural SB dust, limestone (taken after the raw meal mill in cement production) and ground cement. The expert system can be used to reduce the energy demands of existing and new filtering installations in various industrial applications.

OIL REPELLENT NANO-COATINGS FOR INCREASED FILTRATION PERFORMANCE
Stephen Coulson and D.R Evans (pages 170-171)

Consumer and industrial products are manufactured from a range of materials that are selected for specific bulk properties, cost and/or ‘look and feel’. However, many materials chosen in this way do not display the optimum surface properties. This presents an opportunity for surface modifications to apply desirable properties such as fire retardancy, anti-microbial, protein resistance and water/oil repellency. It is critical that these modifications do not alter the bulk properties of the product and retain desirable physical attributes. Additionally, they should be ultra-thin and well adhered. For commercial success, the desired effect needs to be a cost-effective and robust industrial process.

CROSSFLOW MICROFILTRATION OF OIL FROM SYNTHETIC EFFLUENT WATER
Yousef Alanezi and Richard J. Wakeman (pages 172-183)

Crossflow microfiltration of oil from water was studied experimentally under various operating conditions using a multi-channel ceramic membrane. Crossflow velocities, oil concentrations, and ionic strength effects on equilibrium permeate flux were investigated. An increase in crossflow velocity for oil emulsions from 1.14 to 2.28 m/s caused an increase in the equilibrium permeate flux. In contrast, as feed oil concentrations increased from 300 to 2400 ppm, equilibrium permeate fluxes were decreased. Likewise, when the ionic strength for the feed emulsions was increased, the permeate flux declined. These different observations are discussed in term of the hydrodynamics and particle interactions in relation to the filtration process.

For the modelling of experimental results in this work, the applications of back transport models (such as torque balance, inertial lift and shear-induced models) in the area of liquid-liquid separations contribute new knowledge. For the experimental critical flux results the shear-induced diffusion model showed a better prediction in comparison with other back transport models when particle size was used as the fitting parameter. From the particle size distribution analysis, the number frequency of these fine droplets was less than 5% in the polydisperse emulsions. Hence, the smaller particles are causing fouling, which is in agreement with the findings of previous studies.

SIMULATION OF PRESSURE DROP AND CAPACITY FOR PLEATED AIR FILTERS LOADED WITH DUST
Philipp Hettkamp, Gerhard Kasper and Jörg Meyer (pages 183-192)

Air intake filters for combustion engines are commonly pleated and made of thin filter paper. At high dust concentrations these media function as surface filters. The properties of the dust cake and its distribution within the pleat then become crucial to pressure drop evolution and filter lifetime. The dust distribution in turn depends on the flow field in the pleat and particle properties. In this paper the Navier-Stokes equations are solved numerically for a domain representing one model pleat and then calculate particle trajectories and local growth rates of the dust cake. Continuous cake growth is approximated by assuming stationary flow during the deposition of an incremental amount of dust. Using such an approach the influence of pleat geometry, particle inertia and volume flow is investigated. Additionally, simple analytical models for the loading of idealized pleats are presented.

U- and V- shaped pleats exhibit distinctly different loading behaviour. The pressure drop slope of U-shaped pleats is initially linear. V-shaped pleats show a non-linear rise of the pressure drop. Therefore, rectangular pleats will generally yield higher dust capacities than tapered pleats. Particle inertia can have a pronounced effect on the loading curve of U-shaped pleats, while it is less important for V-shaped pleats. It is shown how dust capacity varies with pleat width. An optimum width exists because decreasing pleat width increases filtration surface while it diminishes the volume available for dust deposition. The results of numerical simulation and analytical model agree almost perfectly for the V-shaped pleat, and match qualitatively for the U-shaped pleat.

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Volume 12, Issue 4 Abstracts from the FILTRATION journal

A TOOL FOR DESIGNING SUPPLY AIR FILTER CLASS FOR HVAC
Thomas Carlsson and Magnus Johnsson (pages 214-219)

Fine filters (F5-F9) rated according to the standard EN779: 2002 are classified on average removal efficiency for a particle size of 0.4 µm during dust loading of ASHRAE test dust. It is not possible to use the measured efficiency from an EN779 report in order to predict the particle removal from outdoor air passing the filter due to the artificial dust. Particulate matter (PM) is measured locally all over the world, and it is possible to find data for more or less every city in the world. A test method to overcome the problem with dust loading and a calculation procedure has been developed. The procedure is based on data from local measurements of PM and particle removal from a filter. The method makes it possible to design the PM removal for PM1 , PM2,5 and PM10 for a specific filter and from the calculated values an indoor air quality (IAQ) can be predicted. The paper describes the newly developed test method for the filter and the calculation procedure. The paper also presents in-situ measurements showing the correlation between predicted PM values and the actual measured IAQ.

LONG TERM FOULING OF CERAMIC FILTER MEDIA IN THE DEWATERING OF HEMATITE CONCENTRATE
Riina Salmimies, Antti Häkkinen, Bjarne Ekberg, Juha Kallas and Jens-Petter Andreassen (pages 219-222)

The long-term blinding of a filter medium can affect the performance and lifetime of the medium, but can rarely be observed or quantified in the laboratory. Pilot scale experiments can offer additional information for the design of the washing of the filter medium, however they still don’t provide enough time in operation to evaluate the effects of hundreds of dewatering cycles. The long term fouling effects of a ceramic filter medium were investigated in this study by characterising samples taken from an industrial hematite dewatering process. Chemical characterisation was done using X-ray diffraction (XRD) after which scanning electron microscopy (SEM) was employed to identify the shape and size of the foulants on the surface of the filter medium.

The study showed that the ceramic filter medium used in the dewatering of hematite concentrate was primarily affected by slurry particle blockage, and to a lesser extent by precipitate formation, after operation at the plant scale. Whether the sample was taken from the centre or from the edges of the filter element did not to play a role in determining the nature or the extent of blinding.

LIMITING AND CRITICAL FLUXES VERSUS CLEANABILITY OF A POLYETHERSULPHONE MEMBRANE USED IN SKIM MILK ULTRAFILTRATION
Ndéye Wemsy Diagne and Murielle Rabiller-Baudry (pages 223-229)

The main bottleneck in the ultrafiltration of skim milk is the mastering of fouling and thus the subsequent cleaning in place operation. Industrial filtration practice often uses a polyethersulphone membrane of low cut-off to achieve the maximum flux (‘limiting flux’), but this favours severe fouling with a highly irreversible part due to proteins. On the other hand, above and below the critical or threshold flux two fouling behaviours exist. Below the threshold flux, fouling is low and corresponds to proteins adsorbed on the membrane without any applied pressure, whereas above this flux, the irreversible part strongly increases. The increase can be modulated by hydrodynamics. What about the cohesion of the fouling layer and its cleanability? This study shows that regardless of the intrinsic chemical efficiency of the cleaning solution the membrane cleanability is increased when the fouling is formed at threshold conditions instead of limiting ones.

INNOVATIVE COALESCENCE MEDIA (SFM) AND ITS WATER REMOVAL APPLICATIONS IN FUELS
Ruijun Chen, Jino Jose, Patricia Majestic, Tim Mills and Bill Martin (pages 229-236)

An innovative, US patent pending coalescence filtration medium, called SFM, has been developed to effectively and efficiently clean heavy water contaminations from fuels, including petrodiesel fuels and biodiesel blends. The paper focuses on studying four technical issues related to SFM and its water removal applications in fuels. The first proposes the concept of SFM, including filter medium structure and the coalescence filtration mechanism. The second addresses the conceptual designs of two coalescer elements, denoted as advanced and standard – these are made of the SFM coalescence medium and more traditional nonwoven filter media, respectively. The third briefly describes water droplet motion on the downstream surface of the advanced coalescer element. The fourth introduces experimental studies of water removal performance with the two coalescer elements for a No. 2 petrodiesel fuel and a B20 biodiesel blend.

The preliminary experimental results shown demonstrate unprecedented water removal capabilities for the advanced coalescer element. For example, total volumetric water content in 4.8 GPM petrodiesel-water blend flow can be reduced from 10% upstream of the element to 200 ppm or less downstream of the element within a single pass.

ANALYSIS OF DUST DEPOSITION ON AN INDUSTRIAL SURFACE FILTER AS A FUNCTION OF ITS PHYSICAL PROPERTIES
Arunangshu Mukhopadhyay and Awadhesh K. Choudhary (pages 237-246)

This investigation embodies the analysis of dust deposition on an industrial surface filter as a function of its physical properties. The study is augmented by examining the role of inlet dust concentration and pulse cleaning pressure on the performance of the pulse-jet filtration process. The changes in physical properties of the filter media are largely governed by dust deposition on the different segments of a filter bag. There is a consequent decrease in air permeability and compressibility of the filter media depending on the extent of dust deposition over different segments of the bag height. Progressive dust deposition also results in an increase in media stiffness.

DETAILED SIMULATION OF EXHAUST FLOW AND DEPOSITION OF SOOT PARTICLES IN POROUS PARTICULATE FILTER WALLS
Andrew Schermerhorn, Konstantin Khodosevich, Ameya Joshi and Thorsten Boger (pages 246-256)

Particulate filters are a key after-treatment component employed in all modern diesel engines. Key performance criteria of particulate filters are pressure drop and filtration performance. Both are determined by geometric design parameters such as size, cell density and wall thickness, as well as intrinsic wall scale material properties. The latter are usually related to the properties of the pore space such as porosity, pore size and pore morphology.

In this paper tools to simulate the motion and deposition of discrete diesel soot particles through and on a finite section of a porous filter wall are discussed. The tools and models developed are solved for the complex flow through the pore space, either using the commercial software (FLUENT) or an internally developed Lattice-Boltzmann solver. The flow is combined with an internally developed discrete particle dynamics tracking routine to advance the particle motions in time. In the model the flow field is continually updated, taking account of the accumulation of soot. The simulated effect of mean pore size and porosity are discussed for examples of synthetic microstructures. A comparison with experimental data shows good agreement for clean permeability.

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Volume 13, Issue 1 Abstracts from the FILTRATION journal

BEHAVIOUR OF TWO FILTER MEDIA TO REMOVE ARSENIC FROM DRINKING WATER
Sofia Garrido, Martín Piña, Isaías López, Dagoberto De la O and Raymundo Rodríguez (pages 21-26)

In recent years greater importance has been attached to the arsenic (As) content in water for human consumption. The maximum permissible limits have decreased from 0.050 to 0.010 mg L-1, with protection of public health in mind. The aim of this study was to compare two filter media to remove arsenic from water of well N° 75 located in Torreon, Coahuila, with arsenic concentrations averaging from 0.070 to 0.085 mg L-1. Tests were conducted at laboratory and pilot plant scale with manganese Greensand and sand-anthracite media.

From the batch and column experiments, equilibrium conditions and adsorption constants for manganese Greensand were established. Pilot scale tests were conducted in the well at a flow rate of 0.55 L s-1 and velocities of 4, 7 and 10 m h-1 in order to evaluate the efficiency of arsenic removal. The isotherm model that gave the best fit to the experimental batch experiments results was the Langmuir isotherm, with a maximum adsorption capacity of 0.00656 mg As g-1. In the pilot scale experiments, the difference seen in performance between the manganese Greensand and sand-anthracite filters is due to the size of the grain media. It is concluded that the reduction of grain size favours the very important capacity retentive iron (Fe) hydroxides associated with As.

LONG TERM PERFORMANCE AND MONITORING OF A 10 m3 PILOT PLANT USING TEXTILE FILTER MODULES FOR DIRECT ACTIVATED SLUDGE SEPARATION
Bernhard Gahleitner, Christian Loderer, Harald Schuster and Werner Fuchs (pages 26-31)

The implementation of the Mesh system in a 10 m3 pilot plant at the local wastewater treatment plant in Tulln (Lower Austria), as an alternative process to conventional activated sludge systems (CAS) and membrane bioreactors (MBR), is presented in this study. Separation of sludge and water is performed by a self-forming dynamic membrane which is retained by a woven coarse pore textile filter. The system was operated at high fluxes of 70 L m-2 h-1 at the beginning of the test period and increased to 150 L m-2 h-1. A constantly low pressure loss between 5 and 50 mbar for all fluxes and continuous filtration periods of 3-6 weeks without chemical cleaning could be achieved. The effluent quality of the new system was monitored over a long term period (approx. 6 months) and found to be equal to the new local CAS.

A NEW EXPERIMENTAL SET-UP FOR HIGH THROUGHPUT SCREENING OF FLOCCULANTS
Arthur M.C. Janse, Pim van Hee, Johan A. Vente, Henk Robers, Ton Verkaik and Emile J.A.X. van de Sandt (pages 32-35)

In the fermentation industry frequent use is made of filtration as a unit operation to separate biomass from the continuous aqueous phase. However, filtration is hampered in many cases by the small size of the microbial cells, typically in the order of a few microns. To facilitate the filtration so called flocculation agents have been developed over the years in order to increase the average particle size. Despite their widespread use, selection of the best flocculant and accompanying flocculation recipe is still empirical, mostly based on trial and error, and therefore time consuming.

At the DSM Biotechnology Center equipment is being developed to speed up flocculant selection and the associated flocculation recipe development and optimization. The new set-up is able to test a large number of recipes (100) within a very limited timeframe (24 h) and in a highly automated manner. In this set-up, a flocculation recipe is prepared, consisting of the fermentation broth, flocculation agents like salts and organic polymers, acids or bases and/or dilution water. During additions and a flocculation period (in total 15 minutes) the particle size distribution is followed in time. After the measurement, the flocculation vessel is emptied and cleaned automatically after which the next measurement takes place.

This approach for flocculant selection is valid in the case of a strong relationship between particle size or particle size distribution and specific cake resistance. These relationships are known from other industries, but are very scarce for biotechnology processes. The paper describes the experimental set-up and its capabilities together with the first results relating the particle size (distribution) to the specific cake resistance.

PERFORMANCE AND POSSIBLE INDUSTRIAL APPLICATIONS OF A NOVEL PULSELESS FILTRATION SYSTEM
Sunil D. Sharma, Keith McLennan, Michael Dolan and Alex Ilyushechkin (pages 36-45)

Particulate separation from gas under ambient as well as hot conditions is one of the most important operations in various industries. Depending on the conditions of operation, a number of issues and challenges are associated with a conventional bag or candle filter systems which are actually semi-continuously operated with intermittent reverse cleaning of the filter element. The reverse cleaning is achieved with an additional mechanism and infrastructure on the top of the filter elements that allows pulses of the filtered gas or an inert gas at nearly twice the filtration pressure to pass through the selected filter elements. Obviously, filtration does not occur through the elements being pulse cleaned, but filtration does occur through the rest of the elements which are not pulsed. Therefore, the conventional filtration could be called a semi-continuous process which does not really have any adverse effect on the filtration process, but there are additional costs and several technical issues associated with the pulse cleaning mechanism and its adverse effect on the filter element.

Amongst the generic issues are: (a) tensile strain on the filter elements during reverse cleaning with very high pressure pulse, (b) loss of filtered gas or contamination of product gas with the inert gas used for pulse cleaning, (c) cost of the pulse cleaning system, and (d) particle breakthrough via the cleaned filter element surface. There are specific issues with the filtration processes associated with specific applications, for example, corrosion of the filter element, permanent deposition on the filter and bridging, large pressure variation during filtration of a gas with a heavy loading of particles etc. In order to address some of these issues a pulseless filtration system has been developed at CSIRO. This paper describes a novel concept of pulseless filtration and compares its performance with the conventional pulsed filtration system. The paper also highlights other possible applications of the pulseless filtration system, its benefits and limitations.

NEW OPTIONS TO BETTER EVALUATE EFFICIENCY AND CAPACITY OF COMBUSTION ENGINE FUEL FILTERS
Christophe Peuchot and Nicolas Petillon (pages 46-52)

The new high pressure direct injection systems for road and off-road vehicles combustion engines have tighter clearances which make them more sensitive to fuel particulate contamination. New requirements appear on fuel cleanliness and on all components making the fuel system. To ensure correct fuel cleanliness, engine manufacturers have to specify more efficient filters. The filtration efficiency of fuel filters is traditionally evaluated by standard methods such as ISO 19438. This method is used worldwide and requires the use of a mineral oil with a viscosity of 13 mm2/s at a test temperature of 40ºC. The contaminant specified is ISO MTD according to ISO 12103-1 A3.

The experience of many test laboratories, both internal and via international round robin exercises, has shown that standard test results do not simulate real filters in modern operational conditions precisely enough. Research has been launched to study the impact of various standard test parameters (fluid viscosity, surface tension/contact angle, contaminant size distribution and concentration…) on the measured filtration efficiency and retention capacity. Other parameters related to fluid flow conditions also explain differences between laboratory test results and behaviours in actual conditions.

The paper presents results obtained at various conditions for actual diesel and petrol fuel filters and quantifies their impact on apparent behaviour. Tests performed using the low viscosity fluid ISO 4113 and ISO FTD in steady flow conditions with steady and variable contaminant concentrations are reported. A new approach, based on the principles of the European standard method EN 13443, is presented. It consists of using alternate contaminant concentrations: low ones close to that measured on industrial fuels to give efficiency results close to reality and high ones to accelerate the clogging whilst checking the downstream fuel quality is constant whatever the contamination level of the fuel to filter.

EXPERIMENTAL STUDY OF FILTER CLOGGING WITH POLYDISPERSE PARTICLES
Ryan Sothen, Yanli Chen, Pengfei Zhao and Bruce J. Tatarchuk (pages 53-57)

The influence of dust loading on pressure drop was examined for two filtration media loaded with polydisperse particles under various face velocities. Each media displayed the traditional depth and surface loading pressure drop growth found in previous research. However, this research observed a fundamental correlation between the loading coefficient and the face velocity at which the media was aged. Media loaded at lower face velocities were found to transition from the initial depth loading stage to surface loading at lower mass captured per available filtration area and possessed higher loading coefficients. These effects were the result of dendrite shaped structures being preferentially formed at lower velocities due to a shift in deposition mechanisms from impaction to interception. The dendrite shaped structures eventually caked the upper layers of the filter and prevented subsequent particles from loading into the depths of the fibrous media. Scanning electron micrographs were used to verify the cake formation.

DETERMINATION OF FILTRATION PROPERTIES OF MINERAL SUSPENSIONS FROM ANALYTICAL CENTRIFUGATION DATA
Maksym Loginov, Nikolai Lebovka and Eugene Vorobiev (pages 58-64)

This work is focused on the use of data obtained by centrifugal consolidation of mineral suspensions for the prediction of deadend filtration. The new method for analysis of centrifugal consolidation data and the evaluation of pressure dependencies of particle volume fraction, specific filtration resistance and consolidation coefficient of mineral sediments in the low and moderate pressure region (<100 kPa), is proposed.  The applicability of the method for analysis of centrifugal consolidation of different mineral suspensions (calcium carbonate, bentonite, laponite) is discussed.

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Volume 13, Issue 2 Abstracts from the FILTRATION journal

SEPARATION CHALLENGES FOR BIOTECHNOLOGY – SMART IS ONE ANSWER
Karsten Keller (pages 92-98)

Downstream process costs in biotechnology are responsible for up to 80% of the total process costs due to the challenging separation tasks. The valuable products are embedded in a complex mixture and the product concentration is very low. Traditional chemical engineering approaches are lacking economical solutions. New processes need to be discovered to overcome these separation challenges. SMART is a systematic approach to find better separation solutions for the industry.

Selective separation technology
Manage the product properties
Advanced mechanical separation technology
Reorganize the separation forces
Treatment with enzymes

This paper provides examples of how SMART is changing the way of separation in biotechnology. SMART examples include membrane technology, magnetic separation, enzyme treatment and additional approaches. Some SMART examples are in the early research stage, while others are close to implementation.

DETERMINATION OF THE MODIFIED FOULING INDEX (MFI) AND COMPRESSIBILITY OF THE CAKE-LAYER ON A MEMBRANE DURING ULTRAFILTRATION FOR OILY WASTEWATER TREATMENT
Irena Petrinić, Arnela Murić and Morten Lykkegaard Christensen (pages 99-102)

Oily wastewater is one of the major pollutants that occur in many industrial fields and it is very harmful to the environment, especially aquatic life. All conventional methods for the treatment of oily wastewater, such as dissolved air flotation (DAF), coalescence and adsorption have their advantages, but none is effective enough. Therefore, membrane technology appears to be a promising method which offers many possibilities regarding membrane materials, process configuration and operational parameters (high pressures, temperature, crossflow etc.). However, the main problem in membrane filtration is fouling. In this study the Membrane Filtration Index (MFI) was extended to improve the precision of MFI for oily wastewater. A tubular module with a PES membrane was used in a crossflow ultrafiltration mode. In order to examine the correlation between the measured cake resistance and rejection of different feed components (COD, TSS, Fe, etc.), laboratory analyses were performed. It was found that formed cakes were compressible and the values of cake resistances were almost the same for different parameters even if rejection values increased.

UNDERSTANDING THE ROLE OF THE TWO CALCIUM POOLS ON CENTRIFUGAL DEWATERABILITY OF SLUDGE TO AVOID STICKINESS PROBLEMS IN CENTRIFUGE-DRYERS
Bart Peeters, Raf Dewil, Luc Vernimmen and Ilse Y. Smets (pages 103-112)

The purification of wastewater with activated sludge generates huge amounts of excess sludge, which is most often incinerated after mechanical dewatering and drying. During the dewatering-drying process, i.e. to within a certain range of dry solids content, the sludge passes through a sticky phase. Its sticky consistency causes the sludge to cling to the dryer walls, causing operational downtime. Hence, it is of utmost importance to control the dry solids content of the sludge at the end of the mechanical dewatering step (i.e. before it enters the drying step) to avoid the sticky issues.

Ca2+ ions play a crucial role in the bioflocculation process and, hence, in sludge dewatering, by means of (i) the exchangeable Ca2+ and (ii) the enmeshed CaCO3 solids in the flocs. It is demonstrated that both Ca2+ pools improve the cake dryness obtained after centrifugal compaction. More specifically, in the case when exchangeable Ca2+ is present in the sludge, in this way stabilizing the floc structure, the cake dryness increases by about 2% DS. An increase of the sludge CaCO3 fraction from 30% to 70% raises the cake dryness by 10% DS.

At the Monsanto Antwerp WWTP, Belgium, for sludge characterized by too good a natural dewatering capacity due to the presence of both Ca2+ pools (and, in particular, due to the incorporation of the CaCO3 solids in the sludge), the traditional addition of clay mineral as a skeleton builder is reduced in the sludge feed to the centrifuge-dryer apparatus. In this way the cake dryness after the centrifuge is controlled which avoids the stickiness phenomena in the dryer operation.

INVESTIGATING SKIN FORMATION DURING THE FILTRATION OF MICRO-CRYSTALLINE CELLULOSE
Tuve Mattsson, Maria Sedin and Hans Theliander (pages 112-119)

Separating solids from liquids through filtration is an important unit operation employed in a wide range of industrial sectors. It is vital that accurate and applicable models are employed when designing industrial sized filters. Comprehensive models are readily available for materials that form incompressible cakes, whereas those for compressible cakes are lacking. Materials that form compressible filter cakes may also form a dense initial cake close to the filter medium, i.e. a ‘skin’. In this study the local filtration properties of a model material, TiO2, and micro-crystalline cellulose (MCC), are measured to investigate skin formation in a compressible filter cake. Indications of the formation of a skin in the filtration experiments using MCC could be observed; local pressure measurements were found to be useful in the investigation of its formation. Both the choice of the filter medium and the electrostatic interactions affected the skin formation. The tendency for skin to form was reduced at a lower pH, this lower pH corresponding to less charged particles and filter media.

FILTRATION OF FIBRE/PARTICLE MIXTURES
Steve Tarleton, Kuhan Chellappah and Richard Wakeman (pages 120-126)

New data are reported for the filtration of binary fibre/titania (rutile) mixtures. The combined use of the Kozeny-Carman equation and Darcy’s law is discussed in relation to the filtration of these mixtures. Upon study this approach is shown to have its limitations, particularly when significant aggregation takes place between the two solids species. The difficulties in overcoming these limitations from a fundamental basis are highlighted and a semi-empirical model is presented and discussed. This model is shown to better represent the specific resistance trend with solids composition for a range of binary mixture filtration data.

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