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.

Corporate association

You can now join The Filtration Society or renew your Corporate Association online using the link below. Once you have completed the details on the corporate association page you will then be redirected to our secure payment system where you can pay for your membership online by credit or debit card securely.

Corporate Association of The Filtration Society is a way for industry, commercial and research organisations and universities to become involved with the many activities of the Society.

Since its inception in 1964 the Society has been advancing and disseminating knowledge in the design and use of filtration and separation techniques in industry and other walks of life. It has provided Individual Membership, where members gain ready access to a wide range of filtration and separation information and research through the organisation of conferences, regular publications and networking opportunities.

These and other benefits are now available to those industries and organisations who choose to become Corporate Associates.

View a list of current Corporate associates.

 

Benefits of association

Annual subscription £525 (non-VATable). A Corporate Associate of the Society receives:

  • Three copies of FILTRATION, the the international journal for filtration and separation. FILTRATION details Society news and events, industrial news and developments, technical papers and other articles of interest as well as new and original refereed research papers that cover the broad field of filtration, separation, clarification, dust control and related processes
  • All Corporate Associates receive a ¼ page advert in the Journal.
  • A 50% discount on the Elsevier magazine Filtration and Separation.
  • A 15% discount on Elsevier Advanced Technology publications within the filtration and separation cluster.
  • Reduced registration at Filtration Society organised and co-sponsored meetings for up to three company employees.
  • Inclusion of a Corporate profile on the Society web site with a hotlink to a designated company homepage.
  • Use of the ‘Corporate Associate of The Filtration Society’ logo on letterheads etc.

A Corporate Associate is entitled to the benefits listed above as well as the opportunity to network and develop business links with like-minded Members and Associates.

The Society is a registered charity; for this reason Corporate Associates cannot be voting members of the Society, although Associates are encouraged to communicate their views on all matters to the Society Council through the Honorary Secretary.

Apply for or renew your corporate association online now.

Apply for corporate association using the forms below:

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Filtration image

About the journal The official journal of The Filtration Society

FILTRATION is the official journal of The Filtration Society and many other filtration societies and groups around the world including the American Filtration and Separations Society and The Nordic Filtration Society.

FILTRATION is given quarterly to members as a benefit of Individual Membership and to Corporate Associates as a part of their association package. This internationally recognised journal is intended to be a primary means of communication between both members and associates concerning matters related to filtration and separation. All papers published in FILTRATION are abstracted and indexed by Chemical Abstracts, GEOBASE, MEI Online and Scopus.

There are two principal sections in FILTRATION. The first contains articles that keep members abreast of news and events. Contents include:

  • Society News – a summary of Society Council business and discussions, including news from filtration societies around the world
  • Reports on sponsored meetings
  • Industrial news and developments

The second section contains informative papers about technical developments and updates in filtration and separation. The main foci are industries that are reliant on filtration technologies and research and development in industrial and university laboratories. FILTRATION aims to publish original contributions in the broad field of filtration, separation, clarification, dust control and related processes. All papers are professionally reviewed and the journal is overseen by an international Editorial Board. Abstracts from these papers can be viewed using the dropdown menu under “Journal” at the top of this page.

To view examples of previously published papers  use the links below:

General guidance notes on the form of papers are available in the Notes for Authors, including submission instructions.

FILTRATION also accepts advertising, principally in the form of quarter,  half and full page adverts.

If you are interested in contributing an article or a paper, or you are interested in placing an advert, then please contact the Editor :

Dr Steve Tarleton
Tel: +44 (0)1509 222535
E-mail: e.s.tarleton@lboro.ac.uk

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2000-1

PUblished papers: Volume 1, Issue 4

Author(s) Title, page numbers and abstract
S. Weir and G.M. Moody TRENDS IN THE DEVELOPMENT OF FLOCCULANTS AS AIDS TO SOLID/LIQUID SEPARATION (pages 11-12)

bullet Abstract

bullet Trends in the development of commercially available flocculants and their utility have been identified. Increased molecular weight flocculants are finding use in the alumina industry and for sewage sludge pre-treatment. Highly crosslinked flocculants offer benefits in performance for sewage sludge dewatering, whilst the use of encapsulated flocculant technology is leading to enhanced performance for the dewatering of coal slurries. In biotechnology, fermentation cell broth separation is enhanced by low molecular weight flocculants.

R. Reed SOME APPLICATIONS OF MEMBRANE TECHNOLOGY TO BEER PRODUCTION: CROSSFLOW MICROFILTRATION FOR BEER CLARIFICATION AND HYDROPHOBIC MEMBRANES FOR THE TRANSFER OF GASES TO/FROM BEER (pages 13-17)

bullet Abstract

bullet This article summarises work carried out under the direction of the author whilst working for Brewing Research International on the application of crossflow microfiltration for beer clarification and hydrophobic membranes for the control of gas content in beer.

In the case of crossflow filtration of beer, technical issues surrounding the impact of fouling on the removal of critical components form the beer can largely be overcome by selection of appropriate membranes and backflushing. However, commercial considerations have prevented full-scale implementation. Hydrophobic membranes are in commercial use for the addition of nitrogen and the removal of oxygen and excess carbon dioxide from beer.

B.M. Verdegan, P. Herman et al. ENGINE OIL FILTRATION – TECHNICAL RESPONSES TO CHANGING CUSTOMER NEEDS (pages 17-19)

bullet Abstract

bullet Engine owners are increasingly aware that oil filters not only protect against wear, but also play a major role in improving engine reliability, improving fuel economy, controlling costs and protecting the environment. This has resulted in trends towards extended service intervals and the need for environmentally responsible filters.

This paper discusses these trends, focusing on four technologies developed to meet these needs: venturi combination filters, cone-stack centrifuges, incinerable filters and in-place cleanable oil filters.

K.C. Plumb and A. McLeish CLEAN IN PLACE DUST COLLECTS WITH SINTERED METAL ELEMENTS (pages 20-23)

bullet Abstract

bullet This article covers the use of sintered metal filter elements within dust collectors connected to pharmaceutical equipment. The dust collectors have a reverse air jet system and contain a number of filter elements. These are used to collect product powders that can then be transferred back into the process. Sintered metal elements have been used to allow the whole system to be cleaned in place using water or solvent and this in turn overcomes the need to break the primary containment of the equipment. The requirements of the reverse air jet system within the collector and in place cleaning techniques can be conflicting, however the resulting problems have been overcome. Those systems that are now operational have indicated that systems using sintered metal filter elements can be validated and meet with the requirements of the pharmaceutical industry.

A. Jena and K. Gupta A NOVEL TECHNIQUE FOR CHARACTERIZATION OF PORE STRUCTURE OF CERAMIC MEMBRANES (pages 23-26)

bullet Abstract

bullet Ceramic membranes find extensive applications because of their corrosion resistance and high temperature resistance. Pore characteristics of the modern ceramic membranes are controlled by the composite nature of their structure. A new technique has been developed that may be used to characterize such membranes. The membrane sample is soaked in a liquid that fills all the pores in the sample. Air pressure on one side of the sample is increased so as to remove the liquid from the pores. Because the pores in the coating are usually much smaller that those in the base material, the flow rate becomes a measure of the pore characteristics of the coating. A completely automated instrument is used to record gas pressure and flow rate. These data are analysed to find the largest pore size, mean pore size, pore size distribution, gas and liquid permeability, and surface area. Data obtained with a ceramic membrane are presented. Besides being appropriate, this technique has many operational advantages.

V. Kochergin and R.W. Howe MEMBRANE FILTRATION OF RAW BEET JUICE (pages 26-30)

bullet Abstract

bullet Over the past thirty years many sugar technologists have researched and evaluated the use of membrane technology within the sugar industry. The unit processes in which membranes may be applicable are clarification, purification, concentration and colour removal. Although there are opportunities for membrane technology in the sugar industry, the initiatives to date have generally proven to be uneconomical and unreliable to introduce on a larger scale. More recently, Amalgamated Research Inc. (ARi) sponsored by nine sugar companies worldwide have been researching a particular application of membrane technology which when coupled with chromatographic separation offers a potential re-configuration of the beet sugar process. Were the development of this technology to be successful then it could provide an alternative juice purification technique for consideration. Although at an early stage in its development the process offers improvements in efficiency, operating costs and environmental impact.

The purpose of this paper is to present the process and economic factors that need consideration for applications of membrane filtration in the sugar industry.

TRANSACTIONS PAPERS
E.S. Tarleton and S.A. Morgan AN EXPERIMENTAL STUDY OF ABRUPT CHANGES IN CAKE STRUCTURE DURING DEAD-END PRESSURE FILTRATION (pages 93-100)

bullet Abstract

bullet An automated apparatus has been used to obtain experimental data for the dead-end, constant pressure filtration of aqueous zinc sulphide suspensions. The apparatus and particulate/suspension properties are described and filtration data typical of that acquired during the investigation are presented. The conditions under which intuitively unexpected changes in cake structure occur are identified. It is shown how filtration parameters such as pressure, filter cell diameter and particulate dispersion all influence the onset of both irreversible and essentially reversible changes in cake structure and how these changes induce disturbances in the expected filtrate flow. Analyses of the experimental data and their relation to previous studies suggest that more localised changes in cake structure are responsible for the effects observed. The most probable mechanism is the migration of particle fines within a forming cake leading to the establishment of preferential flow channels; alternative mechanisms are also presented and discussed.

It is concluded that an abrupt change in cake form is more likely during the filtration of suspensions containing loosely networked particles and when filter cell dimensions are larger.

Keywords: Filtration; tomography; structured solids; networked particles; cake collapse; compressibility.

M. Mota, J.A. Teixeira, W.R. Bowen and A. Yelshin BINARY SPHERICAL PARTICLE MIXED BEDS: POROSITY AND PERMEABILITY RELATIONSHIP MEASUREMENT (pages 101-106)

bullet Abstract

bullet A continuous function relating the porosity of a mixture, ε, and the large particle volume fraction, xD, on binary mixtures of spherical particles has been established. The incorporation of the proposed porosity model into the conventional Kozeny-Carman equation gives a good agreement between the measured and the predicted permeability vs. xD. Based on this relationship and on the dependence of ε vs. xD a model predicting tortuosity and permeability was obtained, having demonstrated that the tortuosity may significantly alter the permeability of a mixed bed. The proposed model shows that the simulated permeability curve presents a minimum for xD values that are specified by the particle size ratios. The proposed model may be useful for the analysis of transport phenomena in granular beds as well as in engineering applications.

Keywords: Mixed beds; porosity; tortuosity; permeability; modelling; experiment.

W. Koch, W. Höflinger, E. Pongratz and D. Oechsle MULTIPLE- AND SINGLE-PASS OPERATION IN A CONTINUOUS PRESSURE FILTER WITH ROTATING DISCS AND CAKE THICKNESS LIMITATION BY SCRAPERS (pages 107-110)

bullet Abstract

bullet In this paper the differences between multiple- pass and single- pass operation were investigated for a continuous pressure filter with rotating discs and cake thickness limitation by a knife scraper. The filtration principle of the investigated pressure filter is similar to the thin-cake filter described in1-4. However, the filter investigated in this paper works with rotating filter discs and stationary scrapers. In many cases single-pass operation is designed on the basis of multiple-pass operation tests at laboratory scale. It is therefore interesting to clarify the differences in the cake build-up mechanism and the resulting cake resistances for these different modes of operation in order to estimate failures when single-pass operation is designed on the basis of multiple-pass tests. The results of the filtration experiments in multiple-pass and single-pass operation showed that the formation of the filter cake essentially depends on the rotation speed of the filter discs. At high rotation speeds the limitation of the filter cake thickness occurs due to turbulence effects and the effect of particle segregation dominates the filter cake formation. Hence, the constant amount of fine particles in the feed throughout filtration for single-pass operation (due to a larger total volume of suspension to be filtered compared with multiple-pass operation) leads to increased deposition of fine particles in the filter cake. At low rotation speeds the limitation of the cake thickness changes from turbulence effects to the cutting action at the scraper edge, hence the filter cake thickness becomes greater than at higher rotation speeds.

Furthermore, the effect of particle segregation influences the filter cake formation less than at higher rotation speeds because of the lack of vertical particle movement relative to the disc surface in laminar crossflow conditions between the filter discs. At low rotation speeds equal cake resistances occur, while at high rotation speeds the cake resistance is higher for single-pass operation compared with multiple-pass operation.

Keywords: Continuous cake building filtration; rotating discs; scrapers; cake thickness limitation.

D. Condie, C. Veal, R. Amal and I. Tsui Improving understanding of the effect of floc properties on the vacuum filtration of fine coal (pages 111-116)

bullet Abstract

bullet Despite the widespread use of polymer flocculants, their application to enhance the vacuum filtration of fine (-0.5+0 mm) coal is still poorly understood. In this paper small angle light scattering was used for determining the size and structure of conditioned coal flocs and the results correlated with cake moisture from bench-scale vacuum filtration tests. Floc size was characterised primarily as the proportion of the solids passing 25 m m, since these finest particles exert most influence on filter performance. Floc structure was characterised by a fractal scattering exponent (FSE), which was assumed to be a measure of floc compactness. The work has provided a new insight into the relationships between floc conditioning, floc properties, cake properties and filtration behaviour. Ultimately this might form the basis of an on-line technique for maximising filter performance.

Keywords: Vacuum filtration; coal; flocculation; light scattering.

R. de Lima Isaac and C.S.B. Fitzpatrick UPFLOW DIRECT FILTRATION: PERFORMANCE EFFECTS OF DIFFERENT BACKWASH STRATEGIES (pages 117-120)

bullet Abstract

bullet The influence of backwash method on upflow direct sand filtration, followed by downflow filtration, was investigated. The influent was a kaolin suspension coagulated with aluminium sulphate. Two different backwash methods were tested: water only, at 20% expansion and simultaneous air and water at collapse-pulsing conditions. Filtrate turbidity and particle counts were monitored for filtration rates of 5 and 10 m3 h-1. The influence of backwash conditions on filtrate quality was assessed. For an influent turbidity of 20 NTU (30 mg l-1 of suspended solids plus coagulant dosage of 5 mg l-1), the upflow filter produced a high quality filtrate. For an influent turbidity of 100 NTU (150 mg l-1 of suspended solids plus an alum dose of 10 mg l-1) subsequent downflow filtration was needed to obtain acceptable filtrate quality. Particle count data during the ripening period, including size ranges for Cryptosporidium and Giardia, show the ripening period to be independent of wash regime, but the peak is higher when a combined air and water wash is used.

Keywords: Upflow direct filtration; backwashing; ripening; particle counts.


PUblished papers: Volume 1, Issue 3

Author(s) Title, page numbers and abstract
A. Urkiaga, L. de las Fuentes et al. RED WINE CLARIFICATION BY MICROFILTRATION (pages 4-7)

bullet Abstract

bullet Wine making differs from other beverage production technologies in that the quality properties of the final product are not exactly predictable as many factors (e.g. weather, soil conditions) affect grape composition. It is also subject to numerous rules and restrictions dictated by local, national and international regulations and laws, and by culture and tradition. Although different technologies have been implemented in wine manufacturing, it is still a very traditional process. One of the most common operations includes a filtration stage to remove residual yeast, solids and colloids, normally achieved by conventional depth filtration with diatomaceous earth filters. However, the used diatomaceous earth from these filters will soon be considered a hazardous waste and its disposal will involve significant costs.

Alternatively, membrane filtration is emerging as a promising technology for this purpose. Its main advantage lies in its ability to perform wine clarification/filtration/pasteurisation in a single step in continuous operation with clean in place (CIP) strategies. Its use for white and red wine clarification has become common. However, for red quality wines the maintenance of organoleptic properties in the final product restricts its application. The viability of the technology has been proved by normalised sensorial evaluation of Rioja Alavesa microfiltered red wine compared with traditionally produced wine.

B. Jefferson, A. Laine, C. Bedel, P. LeClech and S. Judd SUBMERGED MEMBRANE BIOREACTORS AND THEIR ROLE IN WASTEWATER TREATMENT AND REUSE (pages 8-9)

bullet Abstract

bullet The potential of advanced biological unit operations for the recycling of grey and black waters has been evaluated. The membrane bioreactor (MBR) demonstrated the greatest efficacy towards water recycling in terms of all the usual quality determinants. The initial flux rate through the system was 28 l m-2 h-1, which then gradually decreased to a stable level of 8 l m-2 h-1, with no further decline and so no cleaning required. This demonstrated the process to be operating under sub critical flux conditions where no irreversible fouling occurs. Wastewater recycling is emerging as an integral part of water demand management throughout the world. The major benefit associated with it is the preservation of high quality supplies, alleviating current stresses on potable resources as well as offering environmental and economic advantages. Preference in the UK is for internal water recycling such as domestic grey and black water reuse, whereby water is reused from sources local to the demand. Domestic water recycling is an attractive option in the UK due to a relatively high domestic water consumption coupled with an intensive population. Domestic water use accounts for 40% of the total water usage in the UK. Given that over half the population lives in towns of 100,000 population or greater, water recycling in urban regions is an attractive option.

C.J. Sherwin, C.T. Ta, R. Scriven and D. Richardson SEDIMENTATION TANK PERFORMANCE STUDIES USING COMPUTATIONAL FLUID DYNAMICS (pages 10-12)

bullet Abstract

bullet The performance of sedimentation tanks is studied using computational fluid dynamics (CFD). The flow and solid particle concentration profile under steady state conditions are simulated using the two-phase (solid/water) Lagrangean coupled model. Flow velocity vectors are compared with Acoustic Doppler Velocimetry (ADV) measurements. The results show qualitative agreement. A tracer test is simulated using the flow profile to obtain the residence time distribution (RTD). Simulation is carried out for both a circular final settlement tank and a rectangular primary tank.

TRANSACTIONS PAPERS
W.W.-F Leung and A.H. Shapiro AN ACCELERATING VANE APPARATUS FOR IMPROVED CLARIFICATION AND CLASSIFICATION IN DECANTER CENTRIFUGES (pages 61-67)

bullet Abstract

bullet In an improved feed accelerator system for solid bowl and screen bowl decanters, a continuous feed stream is accelerated to full tangential speed as it is laid onto a separation pool in the centrifuge bowl. The full centrifugal force thus generated provides good performance in terms of the clarification or classification of fine slurries. Conventional accelerator designs, on the other hand, have poor acceleration efficiency, resulting in lower throughput and poor process performance. The improved accelerating apparatus is installed in each port of the feed compartment. An inwardly extending baffle at the trailing face of the port counteracts the Coriolis force generated by the discharge of feed slurry through the port. As the feed moves through the vane apparatus, it gains a high velocity (that is the feed is overspeeded), so that its tangential velocity is greater than its tangential velocity at the discharge radius. Then, as the feed passes to the larger radius at the pool surface, conservation of angular momentum causes a reduction in tangential velocity and an approximate match where the feed enters the pool. Turbulence, mixing, inefficiency and wear are thereby reduced. An additional feature – a “smoothener”, spreads the feed circumferentially, thus minimising concentrated jets that impinge upon and disturb the pool surface. The more quiescent pool facilitates settling.

The technology has been thoroughly tested and proven in the laboratory. Many field installations with the vane apparatus design have demonstrated process benefits in terms of either higher throughput or better process quality in both clarification and classification applications. In cases where polymer is used for the agglomeration of fines or low-density biosolids, polymer dosage can be reduced as the floc is gently accelerated, thus minimising floc breakage.

Keywords: Feed acceleration; decanter centrifuges; overspeeding vane; Coriolis; feed ports; efficiency.

S.K. Sharma, G.F. Ijpelaar and J.C. Schippers IRON OXIDE COATING DEVELOPMENT ON FILTER MEDIA (pages 68-72)

bullet Abstract

bullet The development of an iron oxide coating on filter media is a prerequisite for effective iron removal from groundwater. The rate of development of the coating and its characteristics may be influenced by raw water quality, process conditions and characteristics of the filter media. Laboratory scale short column experiments were conducted to study the effect of pH, influent iron concentration and type of filter media on the development of iron oxide coatings on the filter media. Increases in the surface extractable iron content (SEIC) and iron(II) adsorption capacity (AC) of filter media with the coating development were measured. Coating developed faster on filter sand at pH 7.0 than at a pH 6.0. Coated sand developed at pH 6.5 and 7.0 had a higher iron(II) AC compared to coated sand developed at pH 6.0.

Coating development was faster at the influent iron concentrations of 4.0 and 6.0 mg l-1 compared to 1.0 mg l-1 and the coated sand developed at an iron concentration of 6 mg l-1 had the highest iron(II) AC. The AC for iron(II) increased rapidly with increasing SEIC until the sand was fully covered with iron oxide. Thereafter, the iron(II) AC increased very slowly despite a steady increase in the SEIC.

Among the three media tested basalt had the highest iron(II) AC and coating development was fastest on basalt followed by olivine and then sand. Conditioning of new media at higher feed water pH and/or higher iron concentration could be a strategy to reduce ripening time and to develop media with high iron(II) adsorption capacity.

Keywords: Groundwater; iron removal; iron oxide coating; adsorption capacity.

D. Tao and B.K. Parekh CERAMIC CAPILLARY FILTRATION OF ULTRAFINE COAL SLURRY (pages 73-80)

bullet Abstract

bullet Ceramic capillary vacuum filtration of ultrafine coal slurry (<0.15 mm) was investigated under various experimental conditions using a ceramic filter plate supplied by the Outokumpu Mintec Oy. Parameters examined included cake formation time, cake drying time, type and dosage of flocculants, surfactants and metal ions. Results showed that cake drying time had significant effects on cake moisture but cake formation time affected both cake moisture and solids throughput. The anionic flocculant substantially reduced cake moisture, but only slightly reduced solids throughput. The cationic flocculant provided a three fold increase in solids throughput at a dosage of 20 g t-1, while cake moisture essentially remained unchanged. Of three different types of surfactants, the cationic surfactant was most effective in reducing cake moisture and increasing solids throughput. The addition of metal ions significantly increased solids throughput, but also increased cake moisture.

The lowest cake moisture of 14% was obtained using 10 g t-1 anionic flocculant, while the highest solids throughput of 390 kg m-2 hr-1 was found using 1.0 kg t-1 cationic surfactant. All cationic reagents (cationic flocculant, surfactant and metal ions) are highly effective in increasing solids throughput of the ceramic capillary filter.

Keywords: Coal dewatering; vacuum filtration; flocculation.

S.K. Teoh, R.B.H. Tan, D. He and C. Tien A MULTIFUNCTION TEST CELL FOR CAKE FILTRATION STUDIES (pages 81-90)

bullet Abstract

bullet A new test cell to determine filter cake properties has been developed. This multifunction test cell can serve as an accurate Compression-Permeability (C-P) cell, as well as a variable-volume filtration chamber, thereby enabling direct comparison and correlation between data. It is equipped with a computerised test system that can automatically control the operating parameters, such as the applied loading and the moving speed and vertical travel of the piston. It also provides a means for the determination of the transmitted pressure, the wall friction exerted by the filter cake, the cake displacement rate and the filtrate flow rate. The C-P test data generated from this new multifunction test cell is able to provide a reasonable prediction, within 2-15%, of the average specific resistance, obtained from the actual filtration process in the pressure range of 1 to 8 bar g.

Keywords: Cake filtration; compression-permeability cell; porosity; specific resistance; permeability.


Published papers: Volume 1, Issue 2

Author(s) Title, page numbers and abstract
N. Bugli, C. Bennett and B. Smith PERFORMANCE AND Service Life of Engine Air Cleaners (pages 7-11)

bullet Abstract

bullet Initial efficiency is one of the key performance measures of automotive engine air cleaners (EAC). Performances of EAC are generally measured and evaluated in the laboratory using standard test procedures and test dusts that may or may not represent real world conditions.

Typical laboratory performance levels of initial efficiency and dust capacity for three major air filtration technologies are presented. Service life of an EAC is related to its dust/contaminant holding capacity and its restriction rise over time. Evaluating performances of EAC in real world conditions provide meaningful data. Field evaluations are also presented for light and medium duty vehicles (passenger cars, light/medium trucks) to understand EAC performance and service life requirements.

P. Gullett and A. Hayns REMOVAL OF TOTAL HYDROCARBONS FROM WATER AND AIR (pages 12-13)

bullet Abstract

bullet In January 1996 details of laboratory filtration trials showing that Clerify TM consistently removed over 90% of total (dispersed and dissolved, in particular BTEX) hydrocarbons from water were announced to a produced water seminar in the USA. This paper is a sequel covering 36 months work and case histories since January 1996. During this time, in conjunction with major oil and gas industry operators, field trials have been completed and a wide range of filter systems have been designed, approved, fabricated and are being operated in the field.

Work has started to quantify the performance of Clerify TM as an air filter in field trials. Laboratory results show adequate air permeability and excellent adsorption and loading characteristics. Clerify TM is a filter material that chemically bonds specifically with hydrocarbons and also some other pollutants e.g. heavy metals and corrosion inhibitor. Initially, Clerify TM is processed into sheets that are converted into cartridges for use in standard oilfield filter vessels or specific units produced by AMETEK Filters.

The principal markets identified are: gas and oil facilities; leisure and commercial shipping bilge water; tanker ballast water; and industrial process water.

T.J. Ptak ADSORPTION PROCESS IN THIN ACTIVATED CARBON MEDIA (pages 14-16)

bullet Abstract

bullet Pleatable adsorption media are widely used in a variety of gaseous pollutants control applications including commercial and residential HVAC systems as well as automotive cabin air filtration. Granular activated carbon is particularly suited as an adsorbent for this application.

The objective of this paper is to evaluate the dynamics of adsorption in thin filter media made of granular activated carbon. Experimental breakthrough curves do not follow those observed in thick bed adsorption systems, suggesting that the conventional packed bed adsorption models are not applicable. Conventional theory, on the other hand, can be utilised to predict the initial performance of carbon media and to optimise filter structure.

T. Nordman, O. Ristinen, H. Kuopanportti and M. Tolonen A new air cleaning device for a sintering plant (pages 17-18)

bullet Abstract

bullet A new type of electrostatic precipitator, Ion Blast® air cleaning device, was experimentally used to de-dust a sintering plant flue gas. Instead of having a corona wire, the device is equipped with a high-voltage electrode consisting of a combination of a metal tube and several discharge rings. The rings have sharp needle electrodes and the corona discharge takes place at the tips of the needles. A high voltage of up to 150 kV is led to the discharge electrodes.

The charging in itself is similar to that taking place in traditional electrostatic precipitators, with the exception that so many ions are generated that they form an ion blast effect, which accelerates the migration velocity of dust particles towards the grounded walls of the cleaning chamber. A pilot plant device was tested in the de-dusting process of a sintering plant flue gas. The results showed that dust emissions below 10 mg/Nm3 can be achieved.

C. Peuchot
and T. Hunt
DEVELOPMENT OF ISO STANDARDS IN CONTAMINATION CONTROL AND FILTRATION OF FLUID POWER AND LUBRICATION SYSTEMS (pages 19-20)

bullet Abstract

bullet Many international standards concerning contamination control of hydraulic fluids and lubricants have been considerably revised and new ones adopted. The stimulus for these revisions is primarily the non-availability of the standard test dust ACFTD. As a new ‘dust’ was to be applied an opportunity arose for improving the quality of relevant standards by instituting more rigorous processes in size measurement and relevance to real industrial situations. An important feature has been the introduction of new secondary and on-line calibration.

Previously, with ACFTD, particles had been assessed from the longest dimension, but the new dust uses each particle’s projected area. That meant that the ‘size’ of test dust particles took on a new meaning and a new value. In order not to change the respected ISO 4406 method of coding cleanliness of systems, a novel coding definition had to be devised.

Dust changes in shape have also meant test procedures having to be reassessed. For instance, the ‘multi-pass’ test (ISO 4572) is replaced by the ISO 16889 which is more precise and requires the use of a test stand which is closely validated and controlled. Similarly, for lube oil filters, ISO 4548-12 is now used.

C. Peuchot
and T. Frost
NEW EUROPEAN DRAFT STANDARDS FOR CERTIFICATION OF THE PERFORMANCE OF CARTRIDGE FILTERS AND OTHER DRINKING WATER FILTRATION MATERIALS (pages 21-22)

bullet Abstract

bullet European regulations specify more and more stringent parametric values to define the quality of drinking water. Despite advancement in municipal treatment processes, water distributed inside buildings may suffer from poor quality (e.g. odours and turbidity) due either to the age and length of the network or to the absence of adequate treatment of the many small private supplies. This leads the consumer to look for point of use and point of entry treatment devices, e.g. cartridges or activated carbon filters, UF or RO membranes, to improve the aesthetic quality and protect them against potential disease.

To clarify product specification, create the conditions for fair competition and to protect the interests of end users (by definition a neophyte in domestic water treatment equipment) some European industrialists have agreed on defining standards for the evaluation of product performance. The products include granular filter media (from carbon to diatomaceous earth), cartridge filters and membrane devices. The authors summarise progress on drafting of standards and briefly describe test methods.

TRANSACTIONS PAPERS
O. Larue, T. Mouroko-Mitoulou and E. Vorobiev FILTRATION, CAKE WASHING AND PRESSURISED ELECTROOSMOTIC DEWATERING OF A HIGHLY CONDUCTIVE SILICA SUSPENSION (pages 31-37)

bullet Abstract

bullet A pressurised electroosmotic dewatering process was investigated within a filter cycle on a highly conductive silica suspension. A lab-scale filter-press was electrically and mechanically enhanced to perform the pressurised electroosmotic dewatering under a DC electric field, after the formation and consolidation of a silica filter cake.

The suspension conductivity was too high (22 mS cm-1) to allow efficient electroosmotic dewatering. Two processes were chosen to decrease the conductivity, namely, washing of the filter cake and dilution of the suspension. The filter cycle phases were filtration followed by cake washing or filtration of the diluted suspension, pre-compression of the cake and pressurised electroosmotic dewatering. An attempt was made to minimise the energy consumption and cake water content. The influence of the filter cycle phases, the current intensity and the electrode material were also examined.

The experiments showed that cake washing was more attractive than suspension dilution since it reduced the process time and consumed less water. It was also found that filter cycle phases could be optimised to improve water removal and energy consumption.

Keywords: Silica suspension; pressurised electroosmotic dewatering; filter-press, conductivity.

W.W.-F. Leung DEWATERING BIO-SOLIDS SLUDGE WITH THE VARIGATE TM DECANTER CENTRIFUGE (pages 38-44)

bullet Abstract

bullet High-solids decanter centrifuges have been commonly employed for dewatering environmental or bio-solids sludges throughout the past decade. This paper presents an advancement of this popular technology in which a cake-flow control baffle is installed in the centrifuge to select the driest cake and reject a wetter cake. The baffle also provides high compaction pressure and increases the retention time for cake consolidation and liquid expression. A differential hydraulic head sustained across the baffle in a centrifugal field further facilitates cake conveyance. The opening of the baffle is adjustable for optimal performance depending on the rheology of the cake and the resistance to cake flow at the baffle, which is related to the feed rate to the centrifuge.

Tests on the VariGate TM decanter which was equipped with an adjustable cake baffle at a municipal wastewater treatment plant demonstrated both higher solids throughput and drier cake compared with a conventional high-solids decanter tested side-by-side on the same feed slurry.

Keywords: Decanter centrifuge; high solids; baffle; cake; bio-solids.

G.-M. Klein, J. Meier and V. Kottke USING THE SELECTIVE PARTICLE DEPOSITION DURING CROSSFLOW FILTRATION AS A NEW METHOD OF CLASSIFICATION (pages 45-49)

bullet Abstract

bullet The particle layer build-up during crossflow microfiltration has been studied experimentally. Filtration experiments have been carried out at constant transmembrane pressure and at constant filtrate flux using a polydisperse quartz powder suspension. The constant filtrate flux experiments allow an understanding of the complex and interdependent mechanisms of particle deposition during a constant transmembrane pressure experiment.

The influence of the parameters of crossflow velocity, filtrate flux, and suspension concentration, on the specific particle layer resistance, deposit mass flow density and the particle size distribution of the particle layer was studied. The influence of the density difference between the particle and the fluid on the particle deposition process was examined using bakers yeast as a biological test medium. A specially designed flat duct module that provides defined flow conditions was used for the filtration experiments. The mean particle layer thickness, and surface structure was determined off-line by means of a high resolution laser-distance-sensor.

The effect of the selective deposition of finer particles during crossflow filtration has led to a new method of wet classification of fine particles, where the particle layer is recovered as a fine product. A new classification pilot plant which incorporates membranes was put into operation and demonstrated the feasibility of the basic process steps of this new method.

Keywords: Crossflow filtration; membrane; particle deposition; classification; polydispersity; fine particles.

C.S. Chou, H.C. Lai, J. Smid, J. T. Kuo and S.S. Hsiau NUMERICAL SIMULATION AND EXPERIMENTS IN A LOUVRED MOVING BED FILTER PANEL (pages 50-57)

bullet Abstract

bullet The history of quasi-stagnant filter granule zones near the louvres in three asymmetrical louvre configurations was studied numerically and experimentally. Results of flow patterns obtained by experiments were compared with those obtained by the Discrete Element Method (DEM). Four different flow regions were observed in the moving bed using computer simulations and experiments. The vertical shift of the louvre wall considerably affected the flow patterns in a moving granular bed. In addition, increasing the exit width of the moving granular bed improved the fluidity of the granular flow between the louvred walls.

Keywords: Louvred moving bed filter; DEM; quasi-stagnant zone.


Published papers: Volume 1, Issue 1

Author(s) Title, page numbers and abstract
D. Shaw and M. Price Process and mechanical developments of a modern day filter press and its ancillary equipment to suit the requirements of industry today (pages 8-9)

bullet Abstract

bullet The Filter Press and its well proven technology as a dewatering machine is used extensively in industries covering a wide spectrum. Its application is not restricted or limited to the dewatering of biosolids, it can operate effectively in many other areas particularly in the chemical and pharmaceutical fields where complex filtration, cake washing and air drying techniques are required. In such cases, the filtered product and/or the filtrate can be recovered efficiently and economically. In such applications the filter press has been used successfully for many years, where it has proved to be reliable and consistent in its operation.

Whilst the basic filter press and its process principles are generally well known throughout industry, the modern day developments and levels of automation now available are not so well known or recognised. This paper reviews the process and mechanical developments of a modern day Filter Press.

J. Andries, Ö. Ünal, W. de Jong and P.D.J. Hoppesteyn Hot gas clean up downstream of a coal/biomass fuelled pressurised fluidised bed gasifier using ceramic channel flow filter (pages 10-11)

bullet Abstract

bullet A research programme consisting of a number of interrelated projects in the area of energy production from solids is being carried out using a 1.5 MW process development unit. The installation is equipped with a pressurised, bubbling, fluidised bed gasifier, a high temperature ceramic channel-flow filter and a gas turbine combustor.

This paper describes the experiences with the ceramic filter system during combustion and gasification experiments using coal, miscanthus and straw. The particulate removal performance, the residual pressure drop build-up and the regenerability have been determined during combustion and gasification tests with coal and biomass-coal mixtures.

W. Reimann Purification of agricultural waste water by membranes (pages 12-13)

bullet Abstract

bullet The importance of membrane technologies for waste water treatment has increased in recent years. In order to find out the application limits for liquid agricultural residues, for example by ultrafiltration and reverse osmosis, experiments were carried out on a pilot-scale. The investigations have shown that the permeability and selectivity of membranes for ultrafiltration and reverse osmosis is influenced by the concentration of organic matter, expressed by chemical oxygen demand (COD). This is caused by concentration polarisation at the membrane as a boundary layer effect.

Membrane permeability decreases with increasing concentration of organic matter in waste water, independently of the kind of waste water. Using ultrafiltration for example, COD of waste water is retained up to 92% for milkhouse waste water (feed COD = 1.26 g/l) and up to 35% for a pig slurry (feed COD = 31.6 g/l). Therefore the filtrate of ultrafiltration from waste water with a low concentration of COD can be treated by reverse osmosis to such a degree that the minimum requirements for waste water ingredients are in accordance with the German regulations.

J. Pink Storm water screening to meet the urban waste water treatment directive (pages 14-16)

bullet Abstract

bullet The Urban Waste Water Treatment Directive (UWWTD) cites screening of storm overflows, to prevent aesthetic pollution of our watercourses, as an important issue. The water companies’ asset management plans (AMP3) will be significantly attributed to the topic over the next five years. In March 1998, Huber Technology commenced trials at North West Water’s Wigan WWTW to evaluate the ROTAMAT RoK1 Storm Screen. These were carried out partly in conjunction with a trial programme operated by UKWIR CSO Research Group, and partly under its own initiative.

The first tests were with 6 mm perforations on a side weir installation. Further tests were conducted during the year with the screen mounted in a stilling pond end weir configuration and finally with a 4 mm version on a side weir installation. This paper concentrates on the performance of the screen, in side weir configuration, operating with incoming flows set at 30, 45, 60 and 100 l/s, each with continuation/spill flow splits of 0.1, 0.2, 0.4 and 0.6. The conclusions identify how current environmental demands are best served by equipment currently available.

TRANSACTIONS PAPERS
S. Reymann The intermediate stage of the dead-end filtration process: New insights (pages 3-7)

bullet Abstract

bullet The analysis of volume-time curves in a dead-end filtration experiment can be used to gain understanding of the cake formation process. Two limiting cases are discussed: (1) high zeta-potential, where the particles have a strong double layer interaction and (2) zero zeta-potential where the particles behave collectively as a dense gas.

For (1) the forming cake can be assigned a continuum stiffness and the shape of the volume-time curve is obtained. A micromechanical model for the continuum stiffness of the cake has been developed, which enables accurate predictions of this property. For (2) the ‘granular temperature’ theory is appropriate and characteristic features of the volume time curve are highlighted. Again very few parameters are required. A range of experiments is described which support the theoretical findings.

Keywords: Dead-end filtration; cake formation; particle interactions; granular temperature.

R.J. Wakeman and R. Kotzian Cu2+ and Cd2+ removal from aqueous solutions using lecithin enhanced ultrafiltration (pages 8-13)

bullet Abstract

bullet Copper and cadmium ions are bound to lecithin aggregates which are removed from solution using crossflow ultrafiltration. Feed solution properties such as aggregate size, zeta potential and aggregate shape have been investigated at various surfactant to metal ion ratios. The results of these analytical methods have been used to explain permeate flux profiles and rejection levels obtained during filtration trials. Energy Dispersive X-ray Analysis and Scanning Electron Microscopy were used to investigate interactions on the membrane surface.

The surfactant to metal ion ratio has been shown to have a significant effect on the steady state flux and metal ion rejection. Metal ion rejection increases with increasing surfactant to metal ion ratio, however the maximum metal ion rejection levels decrease with increasing metal ion concentration. Lecithin rejection is not affected by these factors.

Keywords: Ultrafiltration; surfactant enhanced separations; metal ion removal.

M. Beiser, W. Stahl and M. Stiborsky A summary of academic research on decanting centrifuges (pages 14-16)

bullet Abstract

bullet Recent studies have provided improved insights into the procedures for deliquoring bulk materials in decanting centrifuges. These bulk materials can be deliquored, because centrifugal forces can overcome the capillary force at the beach of the decanter.

Experiments with a transparent flow channel have shown, that the resistance of the product as opposed to the flow resistance of the gap between the screw and the bowl determines the deliquoring kinetics. From observations of the liquid flow in the flow channel, a new model for predicting the deliquoring of bulk materials in decanting centrifuges has been developed.

The second part of this article addresses the separation behaviour of sludges in decanting centrifuges. The main conclusion of this work is that the usual assumption of a solid free bowl (i.e., the theory of the equivalent clarifying area) is no longer sustainable. When separating fine grained material, a large amount of solid matter accumulates inside the bowl. This affects the operation as well as the design of such machines.

Finally, the results of studies on the residence time of the liquid phase (centrate) are presented. These studies have shown that there are essential differences in the residence time behaviour for the flow through of the decanter centrifuge when operating with pure water as opposed to with suspension.

Keywords: Decanter centrifuge; dewatering; separation; residence time distribution; drag effects; compression.

H.M. Huotari and M. Nyström Electrofiltration in industrial wastewater applications (pages 17-22)

bullet Abstract

bullet The effect of a constant dc electric field in the crossflow membrane filtration of industrial wastewater was studied. The average electrophoretic mobility of the charged particles and colloids in the samples studied was usually slightly negative. The best flux improvement in electrofiltration was achieved when filtering a sample with very high electrophoretic mobility. In that case the limiting flux could be increased many-fold. The conductivity of the samples studied was over 500 µScm-1. At such conductivities, gas was produced on the electrodes.

The flux enhancement decreased significantly when the membrane worked as an electrode and the gas was produced on the membrane. The problem did not exist when a non-conductive ceramic membrane was used and an electric field was applied across the membrane. However, the high conductivity caused high energy consumption, which is a problem of electrofiltration in industrial wastewater applications.

Keywords: Electrofiltration; fouling; wastewater; conductivity; energy consumption.

R.W.K. Allen, H.G.D. Goyder, J. Macinnes and K. Morris Fluid dynamics of the cleaning pulse in fabric filters (pages 23-28)

bullet Abstract

bullet This paper revisits the concept of the pulse jet Venturi as a pump first proposed by Bakke in 1974. Flows from the reservoir to the pulse tube and then from the nozzle to the filter bag are analysed to allow prediction, from first principles, of the characteristic curve of the Venturi pump. The models developed are compared with experimental measurements of characteristic curves. Reasonable agreement is found for operating ranges typical of operating pulse jet filters.

Keywords : Fabric filters; cleaning; venturi; pumping; modelling.


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2001-2

Published papers: Volume 2, Issue 5

Author(s) Title, page numbers and abstract
E.S. Tarleton and R.J. Wakeman Solid/Liquid Separation Plant Design – Equipment Selection By Computer Software (pages 4-10)

bullet Abstract

bullet Within the broad area of solid/liquid separation and plant design, the purpose of this paper is to provide guidance on what form of small scale tests and results analysis are appropriate for the selection of equipment. Through a knowledge of elementary experimental data, selection charts and an expert system approach, it is shown how interactive software can be used to identify and rank potentially suitable separation equipment. Both basic and more sophisticated examples of equipment selection are presented and additional tables indicate how ranked equipment can be further shortlisted for further investigation.

N. Pearson Selection Of Centrifuges – Why Big Samples? (pages 10-17)

bullet Abstract

bullet Why does a centrifuge manufacturer require a large sample of the slurry to be separated, whenever a meaningful “Process Guarantee” is requested? This paper endeavours to explain the commercial modelling techniques used (with their limitations) to select the size and type of machine and the validity of the “Process Guarantee”.

A. Walker Solid-Liquid SEPARATION Plant Design – Vacuum Filtration (pages 18-22)

bullet Abstract

bullet The use of vacuum to provide additional driving force for the filtration of solids from a liquid suspension is common throughout the chemical and process industries. There are certain benefits and constraints associated with vacuum filtration, as there are with pressure filters, gravity filters and centrifuges, and these need to be considered in some detail before choosing any filtration equipment. In the following paper, the technique for the selection and sizing of a vacuum filter will be discussed, as well as ways of applying this information to the system under investigation.

V.A Goldade and A.G. Kravtsov Fibrous Materials For Ultra-Fine Air Purification (pages 22-26)

bullet Abstract

bullet Electret and filtration characteristics of charged polypropylene based fibrous polymer materials were studied. Forming processes and those of additional electrification of melt-blown fibers in a corona discharge were combined in one cycle. The charge state of the fibrous plastic was analyzed using a thermal depolarization method, which involved measurement of thermally stimulated currents (TSC). Surface charge density was measured by compensation method. Filtration parameters of materials were studied, including skipping factor of oil aerosol through the sample and aerodynamic resistance.It was established that polymer electrification at the melt stage allows attainment of the highest electret charge value, even under rather low electric field intensity. The secondary melt-blown fibrous materials showed higher electret characteristics. The mechanism of fibres charging is discussed. Electret charge on polymer fibres was shown to lead to a considerable improvement of filtration rates. Owing to Coulomb forces, not only are charged particles entrapped on electret fibers, but neutral contaminants are also able to acquire a dipolar moment in the electret field.

The skipping coefficient was investigated depending upon testing time, aerosol particle diameter and filtration velocity for different kinds of samples. The best results were obtained using two-layer samples with charged and non-charged layers. Linear growth of aerodynamic resistance of the filtering materials has been recorded with filtration velocity increase. The conclusion is that among fibrous filtering materials used in fine purification systems, including respirators, the most efficient are those which combine electret and non-electret filtering layers.

A. Macías-Machín, J. Umbría and A. Lecuona New Gas Filter Using Atomised Ultrafreezing (Fua) (pages 27-28)

bullet Abstract

bullet Air pollution has harmful effects on man, animal, vegetation, materials and the biosphere. For this reason, it is very important to remove the different polluting agents from the air. Those in the form of particles can be removed by means of different devices and equipment in order to clean gaseous currents, which may be emitted into the atmosphere without danger. The removal of particles from gases can be performed by means of solid-gas separation, where filtration is the most common. However, it is important to take into consideration those processes that are inherently less polluting. Regarding new filtration techniques, a series of devices using the simultaneous removal of particulate matter and gaseous pollutants in a single collection unit have been developed. These devices, which have attracted attention due to the originality of their designs, are called Multipurpose Filters.

D. Schlegel A Filtering Screw-Conveyor Press For Finely Dispersed Sludges (pages 29-32)

bullet Abstract

bullet A new filtering screw-conveyor press for finely dispersed sludges, specifically for mineral sludges with particles in the micron range, works continuously and fully automatically and almost without an operator. A small pilot version has been tested and more than a thousand hours of endurance tests have shown that abrasion and blockages can be controlled. In the largest axial section of the screw, beginning with the inlet of the sludge into the screw-channel, the multiphase system in the channel is still fluid. A thin layer of filter cake in the gap between the inner diameter of the porous barrel and the outer diameter of the screw represents only a relatively small resistance against filtrate flow. Therefore the filtrate mass flow per unit area of the filter medium is much higher in the filtering screw-conveyor press than in the usual chamber filter press. It is envisaged that the filtering screw-conveyor press will be able to compete well against the usual filtration techniques.

TRANSACTIONS PAPERS
C. Meisl, A. Fuchs and
G. Staudinger
Research Note: A Study Of The Separation Of Activated Sludge (pages 122-126)

bullet Abstract

bullet The treatment of organic pollution in waste water plants is carried out in two steps, namely, reaction and separation. In the aerobic basin the pollutants are converted into biomass by bacteria that use oxygen, that is pumped into the basin. This so-called activated sludge is separated from the treated water in the secondary clarifier. The separation efficiency of the secondary clarifier must be higher than 99.9%. The efficiency depends on the hydraulic flow within the secondary clarifier and on the separation properties of the sludge itself. The sludge can principally separate according to two different regimes. At a low concentration of suspended solids the single flocs settle according to the laws of sedimentation (including hindered settling). This regime is called disperse separation. The supernatant that represents the effluent is contaminated with the smaller flocs that do not settle quickly enough. If the amount of suspended solids in the water is above a critical level that is defined not only by the sludge type, but also by the operating parameters of the plant, the particles mostly, but not always, form a floc network. If this regime, which is called crosslinked separation, occurs the solids concentration in the supernatant is considerably lower.

Investigations on crosslinked separation have shown that the sludge flocs form a network that has a certain tensile strength and in which the small flocs are intercepted when the water percolates through it. As such the network works like a deep bed filter. The structure is able to impede the passage of even very small particles that would otherwise pass into the supernatant. As the density of the network increases with time, the filter performance also increases. In this way the water that passes into the supernatant is always cleaner than the supernatant itself. A thin layer of very clean water is formed directly above the sludge level.

Just above the sludge level, in the range of the thin layer, the particle concentration is lower than in the average supernatant. The transparency of the supernatant is used as a measure of the particle concentration. By using both, the transparency in the thin layer and the transparency in the supernatant, the transient transparency can be calculated and thus the level of contamination in the effluent can be predicted.

For the determination of the transparency values and the corresponding separation regime a photometric method has been developed. This paper provides measurements taken at commercial wastewater treatment plants.

Keywords: Activated sludge; deep bed filter; flocculation; photometry; sedimentation.

C.J. Richardson and V. Nassehi Finite Element Modelling Of Concentration Profiles In Flow Domains With Porous Walls (pages 127-134)

bullet Abstract

bullet Free flow regimes in domains with porous walls are a common feature in processes such as the filtration of suspensions and various hydro-environmental systems. Prediction of the fluid dynamical behaviour of these regimes is not straightforward because factors such as fluid viscosity, fluid density and wall permeability vary continuously during the flow. Notably, a portion of the carrying fluid will seep through the porous wall boundary thus depositing solid particles as it passes. In this paper an adaptive algorithm for the prediction of concentration profiles in regimes with porous walls is presented. This algorithm is based on the Galerkin finite element solution of a flow model incorporating the combined Navier-Stokes and Darcy equations and a transport model represented by the convective-diffusion equation. The stepwise development of the Galerkin finite element model is explained and the important features of the process from both the fluid dynamical and rheological points of view are discussed.

The effect of fluid seepage on the rheological behaviour of the fluid is epitomised by an equation relating fluid viscosity and volume fraction of solids carried by the flow. The numerical description of this model is completely general and can be easily extended to incorporate other factors.

Keywords: Porous wall; concentration boundary condition; finite element method; convective-diffusion equation; initial value problems.

H.-J. Schmid and H. Umhauer Electrostatic Precipitator Efficiency In The Fine Particle Regime (135-141)

bullet Abstract

bullet Earlier investigations on the grade efficiencies of electrostatic precipitators (ESPs) yielded significantly higher separation efficiencies for small particles (diameters less than 2 µm) than predicted by any model. Therefore, several experiments were conducted in a laboratory scale plate-type model precipitator with flat plates and smooth wires using monodisperse 1 µm particles to verify and understand this phenomenon: an optical in-situ measurement yielded local particle flux profiles. By integrating these profiles, balances for several small parts of the precipitator could be made providing deeper insight into the local particle precipitation. Furthermore, particle charge measurements were conducted on an aerosol sample taken directly from the precipitator channel. The flux profiles show the development of a characteristic profile along the duct that gets steeper towards the wall. These profiles are very similar for different operating parameters if the Deutsch-number is kept constant. On the other hand, the local balances always show a much higher separation efficiency than predicted by the Deutsch theory and even higher than that predicted by the laminar flow model. Measured particle charges are also significantly higher than predicted by common charge models.

Keywords: Air quality; CFD; electrostatic charging; electrostatic precipitation; grade efficiency; in-situ measurements; modelling; particle deposition; sub micron particles.

A.P. Koscheev, A.E. Serzhantov and A.D. Shepelev Surface Chemistry And Sorption Properties Of Chemically Modified Carbon Fibres From Polymer Blend Precursor (pages 142-146)

bullet Abstract

bullet An activated carbon fibre (ACF) material obtained by the pyrolysis of a polymer blend precursor was subjected to different chemical treatments, including electrochemical oxidation and thermal oxidation by air in order to modify its surface properties. The surface chemistry of different samples was studied by means of temperature programmed desorption. The influence of surface modification on the hydrophobic properties of ACFs, the adsorption of Cr and Pt ions from aqueous solutions and the removal of I2 from the gas phase were investigated. Electrochemically oxidised carbon fibres exhibited hydrophilic surfaces and strongly modified sorption efficiency. The adsorption capacities for Cr and Pt ions from aqueous solutions increased by two orders of magnitude after oxidation. In contrast, the amount of trapped I2 was reduced by a factor of 7. It was concluded that the adsorption of metal ions is enhanced and the interaction with I2 was suppressed by the action of carboxylic and lactone groups that are formed at the surface during treatment. The modifications of the surface chemistry of ACFs caused by interaction with oxygen and NO2 at room temperature were also studied. Keywords: Carbon fibre; functional groups; electrochemical treatment; heat treatment; adsorption.


Published papers: Volume 2, Issue 4

Author(s) Title, page numbers and abstract
A. Strehlow and M. Schmoch Comparison of techniques for electrode rapping in electrostatic precipitators (pages 5-8)

bullet Abstract

bullet Dust from industrial flue gases is often removed by electrostatic precipitators (ESP). The dust particles collected in these devices need to be cleaned off the electrodes at adequate intervals to maintain the function of an ESP. The use of hammers to rap the electrodes to clean them is common practice.In principle, there are many ways to rap the plates with a hammer as there is an almost infinite choice of locations and orientations to install the hammers and anvils. The hammers are typically tumbling hammers that are fixed to a rotating shaft or cylindrical hammers that are lifted by an electromagnetic force.

Another parameter is the suspension of the electrodes, which has to be adjusted to the chosen type of rapping system because of its influence on the oscillation intensity of the electrodes. The most suitable way to determine the efficiency of a given configuration is to measure the acceleration of the electrodes in those sections where the dust has to be removed.

Various types of rapping systems have been investigated to evaluate their efficiency. Acceleration measurements with a frequency analyser were performed on collecting electrodes as well as on different types of discharge electrodes. Since electrodes installed inside an ESP are hardly accessible most of the measurements took place on a test rig, which allowed measurements of full scale electrodes. Additional site measurements were carried out to validate the test-data.

K-J. Schröder, T. Boger, K. Drury, G. Lachut and P. Makris A New Generation of Ceramic Membranes with Excellent Space and Cost Efficiency (pages 9-11)

bullet Abstract

bullet Ceramic honeycomb monoliths have been used for more than 25 years as catalyst supports for automobile catalytic converters. Corning Incorporated, the world leader in the production of ceramic catalytic converter supports, is now utilizing this honeycomb technology to produce extruded mullite (3Al2O32SiO2) honeycombs to obtain highly compact and cost effective ultrafiltration (UF) and microfiltration (MF) ceramic membranes for liquid filtration applications. Conventional alumina ceramic membrane products are well known for their high strength, chemical durability and long operating lifetime but have always been significantly more expensive than polymeric membranes.

The use of a high packing density honeycomb support incorporated by Corning reduces the cost per unit membrane area as well as associated systems costs to levels that are competitive with tubular polymeric membranes. Like conventional alumina membranes, these honeycomb-based filters offer the ability to withstand extreme use conditions such as pH extremes, high temperatures and exposure to oxidants and solvents. In this paper the function and design of these new membranes are described. The economic and operational benefit of units incorporating these new membranes are discussed.

F. Pedersen, B. Norddahl and S. Eriksen PURIFICATION OF ORGANIC ACIDS ON COMBINED NANOFILTRATION AND BIPOLAR ELECTRODIALYSIS (pages 12-15)

bullet Abstract

bullet A combination of ultrafiltration, nanofiltration and bipolar electrodialysis for the recovery of lactic acid is presented. The method simplifies so far known methods involving membrane technology and increases the recovery of lactic acid. Optimal operating conditions for the nanofiltration were investigated. It was found that the chemical composition has a great influence on lactic acid transport in the membrane. Also, the performance of electrodialysis was evaluated. It was found to correspond closely to the theoretical expectations.

S. Weir, J. S. Robinson and G. M. Moody IMAGE ANALYSIS OF SEWAGE SLUDGE FLOCS : THE EFFECT OF FLOCCULANT MOLECULAR WEIGHT (pages 15-17)

bullet Abstract

bullet In recent years there has been a tendency toward the use of increased molecular weight flocculants for sewage sludge dewatering. Such ‘ultra high molecular weight’ flocculants engender dose efficient dewatering performance compared with lower molecular weight analogues. Image analysis of sewage sludge flocs confirms the theory that a larger mean floc size is formed by higher molecular weight entities at a given flocculant dose. The use of image analysis is a useful analytical tool for the study of sewage sludge flocculation by synthetic polyelectrolytes.

R.J. Wakeman PRETREATMENT METHODS FOR MEMBRANE FILTRATION (pages 17-22)

bullet Abstract

bullet Pretreatment refers to process steps that are required before the membrane separation in order to enhance or maintain the membrane performance over an acceptable duration of operation. The types of pretreatment required to reduce the potential for membrane fouling (when pretreatment is used as a technique for the management of fouling) depend upon both the process stream and the membrane type. Some chemical pretreatment operations themselves (e.g. chlorine addition) may lead to membrane damage, in which cases a further process is required to remove the offending chemical before it reaches the membrane modules. Pretreatment is designed to extend the lifetime of the membrane, prevent fouling of the membrane and maintain the performance (i.e. rejection and recovery) of the system.

M. Middlebrooks and M. Baumgartner Airborne Molecular Contamination (AMC) Control and the Effect of Filter Media Technical Parameters (pages 23-28)

bullet Abstract

bullet This paper reviews the different adsorption mechanisms for AMC control (gas phase filtration) and explains the influence of different filter media technical parameters (e.g. adsorbent grain size, impregnation, filter configuration depending on media selection) on performance characteristics such as efficiency, life time and pressure drop. Technical test results are mainly explained with examples of clean room applications according to the SEMI F21-95 standard.

TRANSACTIONS PAPERS
K. Weber and W. Stahl Influence of an electric field on filtration in a filter press (pages 88-93)

bullet Abstract

bullet The combination of mechanical and electrical filtration seems to be an effective method to enhance the filtration kinetics, because the electrokinetic effects are enhanced with increasing particle surface. The effect of electrophoresis decreases the migration velocity of the particles. The electroosmosis moves the diffusive layer of water around the particles. Thus, it promotes the filtration flow. In this way the electrokinetic effects of electroosmosis and electrophoresis improve filtration in one direction. By the addition of an electric field to a filtration in a two-sided filter-cell the electrokinetic effects enhance the filtration on the one side and impair the filtration on the other side. However, experiments have shown that even this inhomogeneous distribution of the filtrate leads to an acceleration of the filtration kinetics.

Experiments using a pilot scale filter press confirmed the results of the laboratory tests and also demonstrated faster kinetics. This kinetic acceleration could even be improved by a new electrode arrangement, where an additional electrode, operated as the anode, was inserted between the filter plates, while the electrodes behind the filter cloths were operated as the cathodes. In this way the kinetic of a pressure filtration experiment using a filter press and a kaolin suspension at a pressure of p = 10 bar and a voltage of U = 120 V was accelerated by 66 %.

Keywords: Electrofiltration; electrophoresis; electroosmosis; filter press; filtration kinetics.

J. Dueck, D. Purevjav and Th. Neesse Surface Force Effects on Filter Cake Characteristics (pages 94-98)

bullet Abstract

bullet In order to validate a filtration model that accounts for the particle interactions within filter cakes, filtration experiments with a quartz suspension were carried out. The bonding energy of the particles was varied using the electrolytes NaCl, MgCl2 and AlCl3 via the different valencies of the counter ion. The measured filter cake porosities and permeabilities show a remarkable correspondence to measured zeta-potentials and adhesive forces.

Despite some differences between the experimental results and the model equations, the principal validity of the theoretical expectations was confirmed. The model considerations can be helpful in providing a deeper understanding of the influence of electrolytes and how they act as coagulants in fine particle filtration. Keywords: Coagulation; filter cake; particle-particle-interaction; permeability; porosity; specific bonding energy.

A. Kavouras and G. Krammer Determination of solid hold up in jet filters from periodic continuous operational data (pages 99-105)

bullet Abstract

bullet The cleaning of gas dust filters is often incomplete. In this study experiments using a pilot plant scale fabric filter system were carried out where the filter cake was removed from the fabric by jet pulses. In general the jet pulses do not remove the entire filter cake from the exposed area and the entire filter area is not exposed to the jet pulses. The filter cake, which is not torn off the filter by the jet pulses, remains unchanged on the filter medium. As a result of the incomplete filter cleaning, the distribution of the gas flow across the filter area can be highly uneven. As a consequence, the rise in the pressure drop over time throughout a filtration cycle is not strictly linear. A pressure drop versus time curve that deviates from linearity can indicate an uneven distribution of solids across the filter area. Due to the mal-distribution of the solid load over the filter area, the jet pulsed filter cannot be described as a uniform, single filter area. A simple transient two-zone filtration model is employed to estimate the solid hold up of a jet pulsed filter from easily accessible data (solid mass stream to the filter, gas volume stream, pressure drop curve and pressure drop coefficient of the filter cake). The model considers the mal-distribution of the solid over the filter area through division of the entire filter area into two discrete segments. The model results are validated with experiments.

The hold up of the dust on the filter cake, as well as its distribution over the filter area are important pieces of information for the modelling of chemical reactions in the filter cake.

Keywords: Two-zone filtration model; fabric filtration; hold up; jet filters; filtration modelling.

A. Schiel, A.P. Weber, M. Katzer and G. Kasper Precipitation of submicron aerosol particles at high temperatures by electrostatic means (pages 106-108)

bullet Abstract

bullet The thermal charging of submicron particles for model aerosols of TiO2 and SiO2 as well as milled slag at 1600°C has been studied with the aim to achieve electrostatic gas cleaning at high temperatures. The charging state of the particles was determined by evaluation of the Deutsch model for precipitation in an electric field applied to a parallel plate capacitor. The size dependent particle separation efficiency for the precipitation was determined. A dependence of the charging state on the particulate material was found in relation to the work functions of TiO2 and SiO2. The milled slag was considerably less charged compared to the pure metal oxides and thus was less well precipitated. For all materials the precipitation was found to be rather independent of the particle size, which could be a favourable feature for industrial application.

Keywords: Air quality; coal combustion; electrostatic charging; electrostatic precipitation at high temperatures; submicron particles; fly ash; high temperature gas cleaning.

V.A. Kirsch INERTIAL DEPOSITION OF AEROSOL PARTICLES IN A MODEL FILTER WITH DUST LOADED FIBRES (pages 109-113)

bullet Abstract

bullet The deposition of monodisperse spherical aerosol particles in a dust loaded model filter due to inertial impaction and direct interception is considered. A regular lattice of parallel cylinders covered with coaxial porous permeable shells that simulate the layers of deposit on the fibres was used as a model filter. A method of calculation of the process of clogging of the fibrous air filter by monodisperse solid particles is described. The method accounts for the deposit permeability and for changes in the flowfield in the vicinity of fibres.

The fibre collection efficiency was determined by computing the limiting trajectory of a particle as a function of the porous shell radius and the porosity of the deposit. The results of the theoretical study on the kinetics of clogging in the depth of filters at low and intermediate Stokes numbers are presented. The results obtained are in agreement with available experimental data. Keywords: Aerosol filtration; dust loaded fibres; kinetics of clogging.

M. Rainer and W. Hoeflinger Experimental and CFD Analysis of Particle Retention on Different Filter Media in Solid-Liquid Filtration (pages 114-119)

bullet Abstract

bullet A number of filtration tasks require the deposition of a cake layer above the supporting filter media that itself acts as the actual filter medium. This study illustrates the cake layer formation on two different filter media (a dutch weave and a slotted metal sheet that have the same maximum pore size) and the resulting particle retention properties. In the first part of the paper the flow behaviour on the unloaded supporting filter media is calculated using the commercial computational fluid dynamic (CFD) software Fluent 5.4®. The differences in local fluid velocities and the particle tracks of single particles approaching the two different filter media are also calculated.

The second part of the paper describes an experimental study using a laboratory filter. The filtration of a diatomite suspension was observed under the microscope to show differences in the structure of the cake layer formed at different stages of the filtration process on a slotted metal sheet and on a twilled dutch weave. Higher particle retention of the cake layers built up on the metal sheet are caused by differences in the horizontal fluid velocities near the top surface of the supporting filter medium. Characteristic pressure drops over time during the formation of the first cake layer are discussed for the weave and the metal sheet in terms of the results from the CFD analysis.

Keywords: Solid liquid filtration; CFD analysis; filter media; cake layer; cake formation mechanism.


Published papers: Volume 2, Issue 3

Author(s) Title, page numbers and abstract
C. Grimwood SAFETY ASPECTS OF CENTRIFUGES (pages 6-9)

bullet Abstract

bullet Aspects of the safety of centrifuges used in the process industries are discussed taking the widely used batch centrifuge as an example. Three aspects of safety are reviewed, firstly the recent BS standard and CE certification, secondly control systems and finally basket design and inspection. The purpose of the review is to illustrate both good practice and some common pitfalls rather than give a definitive overview. Whilst the discussion refers to batch centrifuges many of the comments applies to other centrifuge types.

E. Maus APPLICATIONS OF PERVAPORATION AND VAPOUR PERMEATION (pages 9-11)

bullet Abstract

bullet The implementation of membranes in industrial processes offers access to a variety of applications. Their tailor-made process design with economic viability is decisive for the implementation of this technique. With the development of new membrane materials, both polymeric and ceramic, a wide range of industrial applications can be covered and some of these are illustrated with examples in this paper.

N. Day IS IT RIGHT TO BLAME THE CENTRIFUGE? (pages 12-17)

bullet Abstract

bullet It is almost universally accepted by those involved in the separation processing industry that the separation of liquid-solid suspensions is a highly complex subject. This, in part, is due to the almost infinite and diverse nature of materials available for processing, coupled with the vast array of separating equipment currently available on the market. Many knowledgeable and learned individuals have, over the years, gone to great lengths to examine and study the field of liquid-solid separation, producing detailed technical papers, formulae and theories. Whilst not attempting to undermine or vilify their valuable contributions in any way whatsoever there is also, just as importantly, a highly practical aspect to this field.

It is therefore the intention of this paper to cover the practical issues surrounding the vertical batch basket filtering type centrifuge, although most will apply to similar equipment, that must be addressed if a safe and efficient separation process is to be realised.

G. Rideal and J. Storey A NEW HIGH PRECISION METHOD OF CALIBRATING FILTERS (pages 18-20)

bullet Abstract

bullet Although bubble point testing has been used to calibrate fine filters and meshes, the technique begins to lose accuracy above pore sizes of about 30 microns. Test dust permeation has had some success in assessing the performance of filters with pore sizes above about 10 microns but the technique is more qualitative than quantitative because of the wide particle size distribution of the dusts. Furthermore, there is no traceability back to an International unit of length such as NIST (The National Institute of Science and Technology, USA). This paper describes the preparation, certification and use of a new range of 20 narrow size distribution glass microspheres for calibrating filters and meshes from 10 to 500 microns. Because the size distributions are so narrow the results are extremely accurate and reproducible.

The glass microspheres are certified using precision Electroformed sieves calibrated microscopically using a NIST Graticule and a calibration graph of percent passing against aperture size is constructed. The microspheres are then passed through the unknown filter or mesh and, from the percentage passing, the mean aperture size can be read off the calibration graph.

The use of sonic energy in the transportation of the beads through the filters means that the testing is very fast because it is performed dry. Sifting times of 1 minute are common for most of the range with accuracies and repeatabilities down to 1 micron. The absolute upper end of the pore size can be determined by analysing the particle size distribution of the microspheres passing the filter.

M. Riera MULTIPURPOSE SOLUTIONS INCORPORATED INTO GMP PEELER CENTRIFUGES (pages 21-23)

bullet Abstract

bullet The Chemicals and Pharmaceuticals Industry encouraged in the past the development of peeler centrifuges because of their configuration and mechanical arrangement. Fine chemicals and particularly pharmaceuticals needed a machine, the concept of which allowed separation of the processing area from the rest of the machine.

J. Hamatschek and P. Schöttler LATEST DEVELOPMENTS IN HIGH SPEED DISC STACK SEPARATORS (pages 23-25)

bullet Abstract

bullet Since 1893 Westfalia Separator has produced machines for mechanical separation; initially these were only separators and for the last 50 years also decanters. These two technologies are defined as sedimentation centrifuges from the process engineering viewpoint, which demarcates them from other centrifuges such as filtering, peeler and strainer centrifuges, etc. Prerequisites for mechanical separation with centrifuges are a difference in density as well as non-miscible substances. Thus, solid-liquid, liquid-liquid or liquid-liquid-solid separation is possible.

S. Cameron and C.J. Williams An Investigation Into The Fouling of Fine Bubble Aeration Diffusers in Activated Sludge (pages 26-30)

bullet Abstract

bullet It is estimated that 50-90% of the energy requirement of wastewater treatment is dedicated to the aeration of activated sludge. Accordingly, any factor that influences aeration efficiency will have a major effect on the overall operational costs of sewage treatment. One of the most efficient and therefore popular means of aerating activated sludge (AS) is the fine bubble diffuser. These come in a variety of designs but all rely on forcing air through a porous media located on the bottom of the AS tank. The bubbles produced at the diffuser/liquid interface disperse throughout the mixed liquor and oxygen diffuses from the bubbles into the activated sludge. This dissolved oxygen supplies the respiratory requirement of the aerobic micro-organisms that carry out biological treatment of the wastewater.

B. Madsen DECANTER PROCESS PERFORMANCE STUDIES: Flow Patterns, Sedimentation and Solids Handling (pages 30-32)

bullet Abstract

bullet In the design of a decanter centrifuge one can choose between a number of different principles for the flow path inside the machine. Over the years each manufacturer has developed strong arguments for their own favourite principle and for many years the most important choice was considered to be the choice between a co-current or a countercurrent design. As many thousands of each design type are operating successfully in the field one cannot truly claim that the one design is superior to the other.

TRANSACTIONS PAPERS
A. Ghirisan, K. Weber and W. Stahl THE INFLUENCE OF AN ELECTRICAL FIELD ON FILTRATION AND WASHING (pages 56-60)

bullet Abstract

bullet The influence of an electrical field on the kinetics of the accumulation and washing of a pressed filter cake was examined using laboratory filtration equipment (with a double-sided filtration cell) at the University of Karlsruhe in Germany. Under electrofiltration, the experiments conducted using quartz sand (average particle size d50% = 2 mm) suspended in Karlsruhe tap water (conductivity l @ 700 mS cm-1) showed that the electrokinetic effects (electrophoresis and electroosmosis) accelerate the kinetics of the pressure filtration.

Permeation experiments carried out using the untreated (non-polluted) filter cakes, pressed without an electrical field, were used as the control experiment to investigate the effect of washing. The kinetics of permeation was strongly influenced by the polarity of the electrical field. The permeation was accelerated when electroosmosis acted in the permeating direction (positive E-field) and decelerated, if electroosmosis acts against the permeating direction (negative E-field).

Examination of filter cake washing showed a kinetic effect that was only slightly accelerated by using the electric field. The conductivity due to the impurity of the cake was higher when the cake was washed in the presence of an electrical field than without it. As such cake washing without an electrical field for quartz sand SF800 seemed to be more effective. Therefore, an additional electrical field for the washing of quartz sand is not worthwhile.

Keywords: Electrofiltration; electrokinetic effects; electroosmosis; electrophoresis; permeate flux; pressure filtration.

M. Kuosa and J. Kallas HYDRODYNAMICS OF DYNAMIC MEMBRANE FILTERS (pages 61-66)

bullet Abstract

bullet This research focuses on a Computational Fluid Dynamics (CFD) based approach for the design of dynamic membrane filters. In the investigation both geometry and process parameters are studied in order to achieve the required turbulence on the membrane surface. The hydrodynamics of these membrane filters are expected to be affected by variations in operating conditions, such as, flow rate, suspension density and RPM and also by geometric parameters such as disc or turbine radius and the distances between the membrane and the turbine. In this study two basically different industrially used membrane separation devices are investigated using a commercial computational fluid dynamics package. The filter is equipped with either a rotating membrane disc or with a turbine. The fluid is assumed to be Newtonian, incompressible and isothermal. The k-ε model is used to describe turbulent flow.

Pumping the solution through the separation units is the main cause of the operating expenses in a membrane separation plant. In addition, too high a pressure drop may rupture the membrane or its support. In this research the effect of the location of feed and the exit regions is investigated. Comparison of the different fluid entrance and exit alternatives using the CFD simulation helps to determine the minimum or satisfactory pressure drop. In addition, the effect of the rotational velocity of a rotary element and the feed velocity are considered.

The research also shows that the flow dynamic conditions at the membrane walls in a filter with rotating disc, change considerably with a relatively small change in feed velocity.

Keywords: CFD; cross flow filtration; dynamic filtration; dynamic membrane filters; fouling.

S. Metsämuuronen and M. Nyström CHARACTERISATION OF MEMBRANE FOULING BY STREAMING POTENTIAL AND FLUX MEASUREMENTS (pages 67-72)

bullet Abstract

bullet Fouling and changes in the charge on the membrane during the filtration of protein solutions were characterised by simultaneous measurements of the flux and streaming potential through the pores of the membrane. Myoglobin was used as the model substance and both hydrophilic and hydrophobic ultrafiltration membranes and one microfiltration membrane were tested. The charge on the hydrophobic track-etched polycarbonate PC0.1 and the polysulfone GR51 membranes changed towards that of the protein during fouling. The charge on the GR51 membrane changed the most, while flux measurements indicated that the PC0.1 membrane fouled more than the GR51 membrane. The hydrophilic membranes that were made of regenerated cellulose did not become permanently fouled and their charge remained unchanged.

Although the flux increased when the flow velocity was increased in the laminar region the streaming potentials remained the same. A higher velocity prevented the formation of a concentration polarisation layer but not the permanent adsorptive fouling that occurred at the beginning of the experiment.

Keywords: Fouling; microfiltration; myoglobin; streaming potential; ultrafiltration.

M. El_zahar, M. Salih and K. Fujisaki BASIC STUDY OF BUBBLE FORMATION IN DISSOLVED CO2 GAS FLOTATION OF WASTE ACTIVATED SLUDGE (pages 73-79)

bullet Abstract

bullet This research deals with the performance of very fine micro bubbles required for dissolved CO2 gas flotation of waste activated sludge. CO2 gas micro-bubbles are produced by dissolving CO2 gas in waste activated sludge under pressure and then injecting or spouting the sludge through a small nozzle to atmospheric pressure – the method is known as “supersaturate and release”. Discussion of the hydrodynamic performance of the CO2 gas micro bubbles is presented. The behaviour of micro bubbles is one of the most important factors in the flotation process and several researchers have previously investigated the behaviour of micro air bubbles. However, for the case of CO2 gas flotation, little is known, because the method is very new. In addition, CO2 has about 30 times higher water-solubility than air. Since the size control of CO2 micro bubbles is very important in new CO2 flotation its impact on flotation has been studied.

The best conditions for CO2 gas flotation and the case of the usual “supersaturate and release” method were investigated. As an extension of this research, another method for flotation using CO2 gas was examined where a weak vacuum was used instead of a release to atmospheric pressure. A comparison between the results of the two methods is presented.

Experiments were carried out to obtain useful data for the relation between CO2 micro bubbles size and flotation controlling factors. The principal factors are sludge temperature, the initial height of sludge, the bubbling pressure, nozzle diameter and the spouting pressure. Furthermore, some experiments were executed to check the effect of not spouting on bubble formation and flotation. The results clarify the relationships between the characteristics of CO2 micro bubbles and the principal flotation factors.

Other subjects that might have an effect on dissolved CO2 gas flotation of waste activated sludge were investigated experimentally including bubble formation, bubble size and bubble-particle interactions.

Keywords: Flotation; carbon dioxide; micro bubbles; sludge; waste activated sludge.

S. Obermair, J. Woisetschläger and G. Staudinger The Flow Pattern in the Dust Outlet Geometry of a Gas Cyclone and its Effects on Separation Efficiency (pages 80-85)

bullet Abstract

bullet Since the end of the 19th century many researchers have attempted to clarify the influence of all the different operating and geometric parameters on the separation efficiency of gas cyclones. However, the dust outlet geometry was rarely investigated. Tests performed by the authors prove that by changing the dust outlet geometry, the resulting change in flow pattern can lead to a significant improvement in the separation efficiency. For a cyclone with a bin, Laser Doppler Anemometry (LDA) measurements show a vortex moving downwards along the wall. A second vortex transports the gas back from the bottom of the bin into the cyclone. The maximal axial upward velocity is of the same magnitude as the inlet velocity into the cyclone. By using a cone insert the tangential and axial velocities in the bin are reduced, but the two vortices are forced into the gap between the cone insert and the wall causing high turbulence.

The flow pattern of a cyclone with a downcomer tube is similar to that of a cyclone that incorporates a bin. However, as a consequence of the high tangential velocities and lower turbulence in the lower part of the downcomer tube and in the bin, there is an additional separation. Once the particles reach the downcomer tube, they will circulate in the bin and downcomer tube. As a consequence those particles are unlikely to be re-entrained back into the cyclone chamber.

The findings of this study show that cyclones that incorporate a cone insert or a bin should be replaced by cyclones with a downcomer tube. The downcomer tube works as a concentrator for the particles that are carried in the boundary layer at the lower end of the cyclone.

Keywords: Gas cyclone; dust outlet; LDA; particle separation; particle deposition.


Published papers: Volume 2, Issue 2

Author(s) Title, page numbers and abstract
A. Willis Air Filtration Using Glass Filter Media (pages 13-15)

bullet Abstract

bullet Hollingsworth & Vose (H&V) Company Ltd. manufacture wet-laid, bound glass microfibre media that end users convert into forms suitable for removing particles from air or liquid. In this paper, an explanation of the key properties that air filter manufacturers look for in our media are described, along with how H&V can help custom design media to meet exact final filter requirements.

A. Gibson Use of Tetratex ePTFE Membrane laminates in fine particle filtration (pages 15-17)

bullet Abstract

bullet Air pollution control has become a major concern worldwide. Emission control standards are becoming more and more stringent. Today, dust control is a necessary part of any process and is subject to strict emission regulations.

Under the current climate a filter has to operate as economically as possible and take into consideration process parameters such as gas stream chemistry and flow distribution, water and acid dew points and dust characteristics. The end result should allow the filter to operate with a good air flow distribution, low pressure differential and to meet the demands of both the end user and regulatory authorities.

J. Mills ELECTROSTATICALLY CHARGED AIR FILTER MEDIA (pages 18-21)

bullet Abstract

bullet This paper focuses upon the development of electrostatically charged filter media. The topics covered include an introduction to Hollingsworth & Vose, the history and development of Technostat media, its manufacture and applications, a review of composite media and finally the use of appropriate test equipment.

S. Smith Activated Carbon Media and its Application in Compressed Air (pages 22-26)

bullet Abstract

bullet When specifying filtration for a compressed air system, the presence and likely effects of an oil vapour are often overlooked. Activated carbon is a versatile medium, available in a wide variety of formats, with a large capacity for the removal of these vapours and is the primary selection for the filtration design engineer.

This paper describes the source of these vapours, gives a brief overview of the range of activated carbon filter materials that are generally available and describes a novel test method, to help determine operating life for a specific filter design under conditions that more closely simulate operation.

P. Hodgson Low Density Ceramic Filters for Hot Gas Filtration (pages 27-30)

bullet Abstract

bullet Low density ceramic filters were developed over 10 years ago. Based on ceramic fibre, mineral fibre or calcium silicate they are capable of handling gases at temperatures in excess of 1000°C. The ultimate temperature capability is dependent on the composition of the filter element and of course very much on the material of the element supports and filter structure. They have had a chequered history, with a mixture of some success and some outstanding failures. However, with greater understanding of optimum plant design and operating conditions for this type of filter the list of successful applications is growing rapidly.

G-M. Klein, M. Durst and H. Banzhaf FILTRATION REQUIREMENTS AND NEW FILTRATION CONCEPTS FOR MODERN DIESEL INJECTION SYSTEMS (pages 30-33)

bullet Abstract

bullet Modern time controlled high pressure diesel injection systems require extreme fine fuel filters and an efficient removal of emulsified water. The required border values of the filtration efficiency and water separation efficiency are described. Fuel filters with star-pleated elements and cellulose based filter media do not fulfill these new requirements. The necessity of a huge increase of filtration performance in terms of particle retention efficiency and particle holding capacity presupposes a new filtration concept.

The new multigrade media generation consists of two single filtration layers. The upstream layer is made of polymer meltblown fibres with very high particle holding capacity, the downstream layer combines the functions mechanical support and of the final filtration step with high particle retention efficiency. Compared to common filter elements either an increase of capacity by a factor of 3 or an increase of the initial particle retention efficiency by one order of magnitude is possible. Together with the excellent removal of emulsified water by coalescence, the multigrade media fulfill all new requirements of modern diesel injection systems. A further increase of depth filter media perfomance requires a CFD supported design of fibre composition and arrangement. The simulation of the flow field and particle trajectories is done with FLUENT. The geometrical model is a 2-dimensional array of circular cylinders. The calculated initial particle retention efficiency is shown to be strongly dependent on the arrangement of the fibres.

T. J. Ptak, A. Tondreau and M. Bryson FACTORS AFFECTING THE GENERATION OF ELECTROSTATIC CHARGE IN AUTOMOTIVE FUEL FILTERS (pages 34-36)

bullet Abstract

bullet Electrostatic discharge of accumulated charge generated in vehicle fuel systems can occur when system components are made of insulating materials. Since charge separation is a surface effect and fuel filters provide a large amount of surface area, the electrostatic charge and potential on filters can reach high levels, which are sufficient to cause electrical breakdown, resulting in pinholes in fuel filters.

This paper investigates the factors affecting charge generation during the filtration process in automotive fuel filters. The experimental investigation was concentrated primarily on a determination of electrical currents and potentials encountered in fuel filter elements made of different filter media and different resistivities of filter housings at specific flow rates.

T. Ciach BIODEGRADABLE FILTERS (pages 37-40)

bullet Abstract

bullet Disposable air and water filter cartridges, because of their high chemical resistance and popularity, have a significant environmental impact. Biodegradable polymers and melt blow technology are used in an attempt to reduce this problem. Biodegradable polymers available on the market were the raw material for melt blown fibrous filter production. The filters were tested in water and air environments. A biodegradable electret filter was also made.

C. Holden and G. Lomax THE CLEANING AND VALIDATION OF COMPONENTS FOR THE POLYMER INDUSTRY AND ASSOCIATED ENVIRONMENTAL RESPONSIBILITIES (pages 40-42)

bullet Abstract

bullet Over the last 25 years cleaning technologies have changed little apart from refining process technologies for improved performance and efficiency. However, the future could be different. Industry needs to standardise validation procedures whilst performing continuous monitoring to serve customer requirements. The biggest change the industry faces is one of environmental responsibility and performance criteria to meet international standards.

V. Hughes A NOVEL MECHANISTIC INSIGHT INTO THE EFFECT OF SURFACTANTS ON AVIATION FUEL WATER COALESCER PERFORMANCE (pages 43-44)

bullet Abstract

bullet Fibres have been taken from a commercially available aviation fuel filter-water-coalescer cartridge and their surface affinity for water examined in an Environmental Scanning Electron Microscope (ESEM). The fibres present a mixture of silica and epoxy resin surfaces. Water droplets were found to form only on the silica surfaces.

Fibres that had been soaked in jet fuel containing a naphthasulphonate (a model surfactant), equivalent to “disarming” the coalescer, had unusual wetting characteristics consistent with this additive lowering the interfacial tension of the fuel water interface. Water spontaneously spread across the entire fibrous matrix. Aqueous film structures have been observed within the fibrous matrix pointing to a novel mechanism to explain some specific field observations of coalescence failure.

TRANSACTIONS PAPERS
R.J. Wakeman INCREASING SOLIDS RESIDENCE TIMES IN TUMBLER CENTRIFUGES (pages 35-44)

bullet Abstract

bullet The effective wobble angle is a special parameter used in tumbler centrifuge design and operation; its relationship with the structural wobble angle can be calculated. A model to describe the motion of a tumbler centrifuge is summarised, enabling the importance of structural and operational parameters such as the effective wobble angle to be explained and related.

Additional vibratory forces which are generated in a tumbler centrifuge and which affect cake dewatering are identified and analysed, together with the motion of particles in the centrifuge drum. An alternative drum design, the step drum, is analysed and shown to increase the solids residence times. Keywords: Centrifuge; filter; modelling; design; residence time; solids discharge; vibration.

A. Yelshin, J.A. Teixeira, W.R. Bowen, and M. Mota ROLE OF FRACTIONAL CAKE COMPOSITION IN CAKE RESISTANCE (pages 45-48)

bullet Abstract

bullet A model for binary mixtures was applied in order to provide an explanation of the discrepancy between the calculated and experimentally measured specific cake resistance in TiO2 cakes. The case under consideration shows clearly that, even where physicochemical factors influence the particle size distribution, for some bimodal dispersed systems where the ratio of larger diameter particles to those of smaller diameter is greater than 4, the specific cake resistance can be defined by using the particle mixture approach.

Consideration of tortuosity as a variable parameter dependent on porosity may improve the degree of fit between the cake resistance modelling and experimentally measured results. Keywords: Microfiltration; porosity; tortuosity; specific cake resistance.

M. Beiser, W. Stahl and A. Erk A FLOCCULANT TESTING METHOD FOR PRACTICAL APPLICATION IN A CENTRIFUGAL FIELD (pages 49-53)

bullet Abstract

bullet Flocculation is a common method to increase the efficiency of a solid/liquid separation process for fine grained material. Operators are faced with a wide range of possible solutions to their specific flocculation problem because of the wide range of flocculants on the market. It is not easy to identify the best flocculant and the ideal flocculation conditions (flocculant dosage and energy input during flocculation) without considerable effort. Laboratory methods to determine the best flocculant for a given application lag far behind the high level of development of different flocculants. This particularly applies to the sedimentation of flocculated particles in a centrifugal field. There is still no method to characterise the effect of flocculating agents on the three main parameters that play a role in a separation:

1) The sedimentation velocity of the flocs,

2) The compression kinetics and

3) The stability (transportability) of the sediment.

These properties can be determined, independently of each other, using a transparent disc centrifuge. In operation only the sedimentation and the compression kinetics can be detected. This paper presents the results of a preliminary study using a disc centrifuge.

Keywords: Centrifugation; compression; decanter centrifuge; flocculant testing; flocculation; sedimentation.


Published papers: Volume 2, Issue 1

Author(s) Title, page numbers and abstract
P. Miller THE NUTSCHE FILTER COMES OF AGE (pages 5-10)

bullet Abstract

bullet An emerging technology is outlined that appears destined to play a major role in how liquids in the future will be purified in the major liquid processing industries. Instead of piecemeal tinkering with “case history” methodology accompanied by the proliferation of purification stages and a worsening of the environmental pollution problem, the possibility of a generic solution is now in the offing. The goal is the realisation of a liquid purification ROBOT.The paper outlines how this goal is to be achieved with reference to the chemical, pharmaceutical, beverage, food and water industries, whereby all waste stream pollution is to be eliminated at source. The R&D program to realise this goal is outlined with references to web-site detailed information including patents.

E. Hardman FILTER MEDIA SELECTION, SCIENCE OR BLACK ART? (pages 11-14)

bullet Abstract

bullet This paper describes the principal factors that affect the selection of woven and needlefelt filter media. These factors are discussed in relation to the basic forms of filter media, the finishing treatments that can be applied and the methods of testing media.

G. Clark DESIGN CONSIDERATIONS OF NEEDLEFELTS USED FOR AIR FILTRATION APPLICATIONS (pages 15-21)

bullet Abstract

bullet This paper considers some of the important design and manufacturing issues involved in the selection of needlefelts for use in hot gas and dust collection filtration applications.

R. Allen and R. Lydon IMPROVED ABRASION RESISTANT COATINGS FOR INDUSTRIAL FILTRATION APPLICATIONS (pages 21-23)

bullet Abstract

bullet In many industrial filtration applications, the life of the filter media can be limited by abrasive damage. Such damage can be caused by impact of hard and sharp particulate matter in the slurry against the medium, as well as fretting damage between the filter medium itself and the filter press. Increases in filter media lifetime are desirable, and will result in improved process up time and hence greater process efficiency. This paper describes a range of new composite filter media that have been specifically developed to address abrasion issues in liquid filtration applications. The new range of media is called Tuf-tex™ and consists of a specially formulated abrasion resistant resin system, which can be applied to both woven and non-woven substrates. The resin is applied as a liquid system in such a way as to provide an abrasion resistant impregnation into the surface of the substrate.

The influence of the coating on the abrasion resistance, permeability, filtration efficiency and filtration throughput is described. Results from laboratory tests are employed to illustrate the process savings that can be expected from the use of these new media in industrial filtration processes.

R. White and C. Murton STAR FLOW PROFILE CERAMIC MEMBRANES (pages 23-26)

bullet Abstract

bullet This paper describes ceramic membranes that have a star profile cross-section. Their use in solid/liquid and liquid/liquid separations is described and for the latter it is shown how contaminate concentrations below statutory limits can be achieved.

TRANSACTIONS PAPERS
M.G. Frey, A. Jensen, K. Dam-Johansen and S. Rasmussen BAG HOUSE FILTER PERFORMANCE STUDIED BY NUMERICAL SIMULATIONS (pages 3-12)

bullet Abstract

bullet This paper addresses aerodynamic considerations and the effects of particle separation in industrial bag house filters. A commercial Computational Fluid Dynamics (CFD) tool was applied to analyse the airflow and particle transport in industrial bag filter vessels. The aim of the study was to obtain a better understanding of both processes and to optimise current filter design. The study has investigated the effect of two commonly applied filter inlet configurations, namely the tangential bottom and top inlet types, on the particle deposition pattern on the filter bags. A considerable proportion of the particles were found not to reach the filter bags. This is attributed to a pre-separation caused by inertia effects. The CFD calculations further indicated that fewer particles are captured on the filter bags in a bag house with a tangential top inlet compared with the same bag house using a bottom inlet. In addition, different particle deposition patterns were observed for the two configurations and are discussed.

Keywords: Bag filter design; computational fluid dynamics (CFD); gas-solids filtration; particle deposition.

R.J. Wakeman, P. Wu and M.A. Koenders SIMULATION OF THE MOTION OF PARTICLES SETTLING TOWARDS A VIBRATING FILTER MEDIUM (pages 13-19)

bullet Abstract

bullet Sedimentation of a particle towards a vibrating filter medium is modelled to calculate the motion of the particle relative to the oscillating medium. The effects of particle properties (particle size and density), vibration characteristics (frequency and acceleration) and filtrate flow rate on the particle behaviour close to the filter medium are investigated. The simulation shows that the vibration of the filter medium directly affects the motion of particles in suspension. For a particle with particular properties, critical vibration conditions exist when the particle makes infrequent contact with the medium, leaving a liquid layer above the medium and hence a higher liquid flow rate through it. This is an unstable situation; under most circumstances the particle periodically contacts the medium and rebounds into the liquid above it, whence the particle settles again. The filtrate flow rate has a considerable dampening effect on the vibration induced motion of the particle; a high flow drags the particle onto the medium and can nullify any potential advantage that may otherwise be offered by the vibrations.

Keywords: Settling, vibration filtration, modelling.

P. Mikulášek and P. Pospíšil FLUX ENHANCEMENT BY GAS-LIQUID TWO-PHASE FLOW FOR CROSSFLOW MICROFILTRATION IN A TUBULAR CERAMIC MEMBRANE (pages 20-26)

bullet Abstract

bullet The promotion of convection within an aluminium oxide tubular membrane using gas-liquid two-phase flow was studied for the microfiltration of aqueous titanium dioxide dispersions. The influence of gas flow velocity and periodical gas flow is also presented. The results of these experiments show that a constant gas-liquid two-phase flow has a positive impact on flux. It may be concluded that two-phase flow seems to expand the particle cake as it increases both cake porosity and thickness, thus allowing higher fluxes. In the case of periodical gas flow the improvement in permeate flux is less. However, this phenomenon depends on the mode of periodical gas flow and on the concentration of the dispersion used. The most important consideration is that for all the dispersion concentrations tested, the injection of air was always associated with an enhancement of the permeate flux. There is no concentration for which air injection had no effect on the permeate flux.

Keywords: Microfiltration; gas-liquid two-phase flow; dispersion; particle cake.

H. Yoshida, K. Tanaka and M. Komatsu INFLUENCE OF ON AND OFF TIMES OF POWER APPLICATION ON ELECTRO-OSMOTIC DEWATERING UNDER INTERMITTENT ELECTRIC FIELD (pages 27-32)

bullet Abstract

bullet Electro-osmotic dewatering is typically operated under continuous direct current (dc) conditions, however it has recently been shown that intermittent power application using half-wave rectified alternating current (ac) improves the dewatering process. The conditions of electro-osmotic dewatering under intermittent power application are further investigated in this study. The effects of intermittent power application are experimentally investigated for a range of low ac frequencies and under pulsed dc for a range of on/off time ratios. The intermittent electric field was found to improve the performance of electro-osmotic dewatering. An optimal frequency of rectified ac in terms of the total amount of water removed was identified. The efficiency of electric power consumption was determined and an optimal on/off time ratio for pulsed dc was identified.

Keywords: Solid-liquid separation; electro-osmotic dewatering; intermittent power application; on/off time ratio; electrical contact resistance.


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2003

Published papers: Volume 3, Issue 4

Author(s) Title, page numbers and abstract
M. Rowlands, I. Schnieders and B. Heinz

NANOWEB® – THE ROUTE TO HIGH PERFORMANCE FILTER MEDIA (pages 191-193)

bullet Abstract

bullet The ever increasing demand for higher performance filter media continues to challenge development engineers throughout the supply chain. Over the decades, there have been several step-changes in filtration technology including glass microfibre, spun-bonds, meltblowns, tribo-electric charged media and multi-layer structures. These major technology steps have been interspersed with a lot of small, incremental improvements.In recent years, the need for increasingly efficient media has driven a desire to develop sub-micron synthetic media – especially in applications where glass microfibre is undesirable. The use of Nanoweb® to achieve a further reduction in fibre diameter is potentially the next significant step-change in universally available filtration technology.

S. Volooj, C. Carr and R. Lydon

INVESTIGATIONS INTO THE RECYCLING OF PROCESS WATER USING PRESSURE FILTRATION AND NEW FILTER MEDIA (pages 194-197)

bullet Abstract

bullet In this study the potential recycling of textile dyehouse water using pressure filtration and composite filter media has been examined. The recycling of hydrogen peroxide bleach baths has been demonstrated, with the benefits of cashmere fibre strength retention and whiteness improvements observed. A preliminary evaluation of acid dyebath recycling for keratin fibres has demonstrated that residual colour can be removed.

I. Townsend

DESIGN CONSIDERATIONS FOR AUTOMATIC PRESSURE FILTRATION OF FLOTATION CONCENTRATES (pages 198-203)

bullet Abstract

bullet Most major concentrators built in recent years have incorporated pressure filtration for dewatering of flotation concentrates. Plant expansions and upgrades frequently replace old vacuum filters with pressure filters. Reasons for the selection of pressure filtration are described, including developments to meet the current and future needs of the mining industry. Next, factors contributing to a successful pressure filter installation are considered. These include filtration testing, effective integration of batch equipment into a continuous process, selection and dimensioning of ancillary equipment, and plant layout considerations.

T. Stott and I. Boxall ADVANCES IN HOT GAS FILTRATION (pages 204-211)

bullet Abstract

bullet The environment and pollution are high on the agenda today, and the required standards are continually increasing, which means that operators of industrial processes have to ensure that any gaseous or liquid by-product is free from harmful contaminants. Where the effluent is gaseous it is often also hot and this imposes particularly stringent demands on the Particulate Control Device (PCD) which is employed. The paper reviews some of the PCD’s that are available, and the requirements for them, and identifies a technology which has the potential to be a significant step forward in the field.

A. Walker

OPTIMISING PRECOAT USAGE ON A ROTARY DRUM VACUUM FILTER (pages 211-215)

bullet Abstract

bullet Unlike the more conventional scraper, belt or string discharge rotary drum vacuum filters (RDVF), the precoated RDVF has an additional overhead with the usage of precoat in both the frequency of re-coating (labour and time) and the cost of the precoat powder. Optimising the filter will yield a higher throughput per tonne of precoat, although determining the ideal operating parameters can sometimes be difficult with a full-scale unit. It is not always practical, nor wanted, to undertake optimising tests on a production filter as maintaining a steady filtration rate is often of prime importance.Extended laboratory-scale or pilot-scale trials can provide useful data for existing filtration systems, as well as in the validation and development of new processes. This paper explains the principle of optimising precoat usage for a steady-state system, and is particularly relevant to extended laboratory-scale test work.

N. Pearson OBTAINING DATA FOR SIZING CENTRIFUGES (pages 216-221)

bullet Abstract

bullet Previous papers have discussed the various methods used by a process laboratory to evaluate whether a material is suitable for separation by a centrifuge, either by outward filtration (basket machines) or by accelerated sedimentation. This paper looks in more detail how the Laboratory moves forward from simply deciding what centrifuge may (or may not) be applicable, to obtaining enough information to allow the full size machine to be designed and a process guarantee to be offered.The subject is vast and to avoid too many generalities this paper will concentrate on sedimenting type centrifuges and more specifically one of the most common types, the countercurrent, solid-bowl decanter centrifuge. Although the paper specifically refers to the decanter centrifuge, the same general approach is also used for other types of sedimenting and outward-filtration centrifuges.

H. Saveyn, K. Weber, P. Van der Meeren and W. Stahl TWO-SIDED ELECTROFILTRATION OF YEAST SUSPENSIONS: FILTRATION KINETICS AND PHYSIOLOGICAL IMPACT (pages 224-230)

bullet Abstract

bullet Yeast (Saccharomyces cerevisiae) suspensions were filtered on a laboratory scale two-sided filter press with central suspension inlet. Electrodes were provided on both sides in order to apply an electric field during the pressure filtration stage. Cathode and anode filtration kinetics were measured and modelled according to a new model based on classical batch filtration equations and electroosmotic and electrophoretic phenomena. Both the experiments and the model revealed an improvement of the filtration kinetics. The new model proved to fit very well to the experimental data, indicating a decreasing trend in the specific cake resistance upon application of the electric field. The values of the electrophoretic mobility determined by regression analysis were in line with the expected physical values, supporting this phenomenological model.Moreover, the viability of the yeast cells at different positions in the filter cake was tested, to determine the damaging effect of electrofiltration. Untreated yeast suspension as well as electrofiltered yeast cake parts were inoculated in batch reactors and followed in time. From these experiments it became obvious that the cell concentration and cell dry mass evolution, the glucose metabolism and the Crabtree ethanol producing effect were not altered by the electrofiltration stage, indicating no negative effect on the physiology of the micro-organisms.

Keywords: Biological effect; electrodewatering; electroosmosis; electrophoresis; model; Saccharomyces cerevisiae.

F. Heese and L.D. Hall MAGNETIC RESONANCE IMAGING (MRI) FOR NON-INVASIVE VISUALISATION AND QUANTITATION OF FILTRATION AND SEPARATION PROCESSES (pages 231-236)

bullet Abstract

bullet Work from recent projects highlighting the application of magnetic resonance imaging (MRI) to the filtration and separation field are described. These include MR imaging of the internal structure of filters, determining the particle deposition pattern in a cartridge filter and qualitatively and quantitatively measuring the fluid flow fields in a blood filter. It will be shown that MRI can successfully evaluate a variety of important parameters and thus offers huge potential as a unique measurement modality to assess non-invasively many of the critical parameters before, during and after filtration.Keywords: Filtration; separation; magnetic resonance imaging; MRI.

R.J. Wakeman and P. Wu NEURAL NETWORK MODELLING OF VIBRATION FILTRATION (pages 237-244)

bullet Abstract

bullet Vibration has been considered as a method to reduce filter medium clogging and disrupt the cake during filtration. However, there is difficulty in the widespread practical application of vibration to filtration because of the absence of sufficiently understood and well-defined theory of vibration filtration. A new identification method for the cake resistance is provided for vibration filtration. It estimates accurately the development of the cake resistance during vibration filtration and provides a tool to predict the process. In addition, the neural network modelling method is used in vibration filtration to establish the mathematical relationship amongst the combined cake resistance (the resistance to fluid flow due to the packing density of the particles in the cake during vibration filtration), vibration parameters, concentration of the feed suspension and the filtration time. It can provide guidance during practical applications about such parameters as the cake discharge time and optimal vibration conditions. Keywords: Cake filtration; vibration; filter media clogging.


Published papers: Volume 3, Issue 3

Author(s) Title, page numbers and abstract
A. Bologa, H.-R. Paur and W. Baumann

REMOVAL OF SUBMICRON FLY ASH FROM A BIOMASS COMBUSTION UNIT WITH A NOVEL “CAROLA” ELECTROSTATIC COLLECTOR (pages 133-135)

bullet Abstract

bullet EU directives for PM10 and PM2.5 particles may require the development of cost-effective gas cleaning technologies for fine particles. The results of design and experimental investigations with the novel electrostatic collector CAROLA for the collection of sub-micron particles are presented. The advantages of the new equipment are discussed.

A. Donn

EFFLUENT TREATMENT IN THE TEXTILE INDUSTRY (pages 136-138)

bullet Abstract

bullet In many of today’s process industries there are increasing pressures to reduce the impact and cost of wastewater discharge. At the same time process water costs are increasing due to increasing supply water charges and decreased water resources available to utilities. Effluent treatment and reuse can be a solution to both these problems and membrane technology is ideally suited to providing part of that solution.

K. Järvinen and J. Hämäläine

DIRT-REPELLENT FABRICS FOR DEINKED PULP DEWATERING PROCESSES (pages 139-142)

bullet Abstract

bullet A major problem in deinking mills is fouling of the filter medium caused by stickies, printing inks and other, predominantly anionic impurities. Existing disc filter bags are mainly made from polypropylene, polyester and polyvinylidene fluoride yarns, and the dirt-repellence of these traditional materials has turned out to be insufficient.This paper presents experimental results achieved by incorporating anti-pitch monofilament yarn technology and chemical fabric surface treatment technology into the conventional waste-paper based pulp dewatering fabric manufacturing. The filtration performance, dirt-repellence and hydrophilicity/hydrophobicity of the developed fabrics were analysed. Based on the results, it is possible to enhance filter media performance by altering the surface properties of the fabric. As a conclusion, it seems that dewatering media manufactured by utilising these new developments enable pulp mills to enhance the process performance and filter media lifetime due to the improved dirt-repellence.

A. Startin and G. Elliott INDUSTRIAL EXPERIENCES WITH LOW DENSITY CERAMIC FILTER ELEMENTS (pages 143-146)

bullet Abstract

bullet Environmental legislation and the demands of process filtration duties have necessitated the development of effective barrier filter media that can operate under arduous conditions. There have been many interesting developments in recent years including needlefelts based on advanced polymers, treated fabrics, metallic filters and rigid ceramic filters. Low density ceramic filter elements were launched in the mid 80’s and were initially applied to thermal soil cleaning duties. Since then the introduction and subsequent development of a range of monolithic elements has seen application to an increasing range of pollution abatement and product collection duties.Low density ceramic filter elements offer a number of significant benefits to the end user – temperature resistance (refractoriness), corrosion resistance, high efficiency, the ability to operate under variable conditions and operational reliability. They have generally been applied to processes where the gas stream is at an elevated temperature and where low emissions from the filter plant are required. They are also particularly applicable to processes which generate fine (sub-micron) particulates that can be difficult to control efficiently and economically using established techniques such as the cyclone or electrostatic precipitator. Applications to date include coal processing, waste incineration, non-ferrous metal processing, chemicals manufacture, fluidised beds and thermal soil cleaning.

Low density ceramic elements offer a viable particulate removal solution to a broad range of processes which can utilise the benefits of the technology. This paper highlights applications where the benefits of low density ceramic filter elements have been effectively employed. One such duty involves the collection of trace amounts of catalyst intermediate from a calcining furnace. Stable operation and low emissions are critical to the process and this level of performance has been demonstrated by the ceramic filter plant.

H. van Heeren, W. Nijdam et al.

MICROFILTERS MADE WITH SEMICONDUCTOR TECHNOLOGIES: A REVOLUTION IN PARTICLE-FLUID SEPARATION (pages 147-150)

bullet Abstract

bullet The ultimate goal in membrane filtration is to achieve a membrane with a low flow resistance, a high chemical resistivity and a well-controlled pore size distribution. There is no better way of achieving these goals than using semiconductor technologies for membrane production. This industry has a long experience in volume production of products with extremely small dimensions with ongoing research towards decreasing dimensions. A few years ago, an innovative small company, Aquamarijn, introduced this technology into the world of microfiltration. The result, microsieves made out of silicon, offered very good mechanical properties and a membrane made of silicon nitride, one of the most inert materials. Thanks to the lithographic technologies employed, the pore size distribution is much narrower than can be achieved with conventional membrane fabrication methods. The absolute pore size is also very well controlled, leading to very good separation characteristics. As it is a very thin membrane, it has very low resistance to the liquid flux, making low-pressure operation possible and featuring small footprints of installation.

The fluxes achievable with these sieves and the durability against chemical attack proved invaluable in several areas. However, due to their low flow resistance, process settings are much different from conventional membranes and work had to be done to optimise the product and the filtration process. At this moment feasibility in different areas like yeast cell filtration and sample analysis has been shown. Other applications are currently under investigation. This paper gives an overview of production technology, filtration process considerations and possible applications of this new type of sieve.

K. Bell WET ELECTROSTATIC PRECIPITATION – EXPERIENCE AND LEGISLATION (pages 150-153)

bullet Abstract

bullet Electrostatic precipitation has been a reliable technology since the early part of the twentieth century. Originally developed to abate serious smoke nuisances from smelters, in particular lead and zinc, they were a cost efficient way of recovering material that would otherwise be lost.

B. Hoffner, J. Heuser and W. Stahl THE EFFECT OF A RELATIVE PARTICLE MOTION DURING THE WASHING PROCESS OF GRANULAR MATERIALS (pages 156-161)

bullet Abstract

bullet The moving bed washing process in a Sedimentator combines advantageous characteristics of both cake (displacement) washing and dilution washing. It is based on a continuously flowing moving bed. Particles inside the bed move relative to each other and to adjacent walls during their vertical movement. The moving bed is penetrated in the wash chamber horizontally by a wash liquid.Washing curves are displayed for two fractions of coarse quartz sand at a constant solids flow rate in an improved apparatus. The washing process is strongly dominated by the displacement of the mother liquid leading to extremely low residual impurity contents compared to the results usually obtained in cake washing experiments.

The comparison to cake washing curves obtained at constant wash liquid flow rates and low Pe numbers reveals that the level of residual impurity is far below that obtained in cake washing results with Pe numbers of the same order of magnitude. Due to the relative particle motion in the moving bed stagnant regions within or at the adjacent walls are broken up locally and temporarily. Additionally, the negative effect of a local maldistribution of wash liquid and mother liquid flows near the boundaries is reduced.

A displacement ratio is suggested as a physically motivated efficiency measure to rate the washing results taking into account only partial ideal displacement, and partial ideal mixing. The application of reported correlations for the dispersion coefficient does not have a practical outlet at present. A qualitative comparison reveals both a significantly decreased dispersion affinity and a slightly higher sensitivity with respect to the flow conditions. A quantitative description using the dispersion model is subject to further research.

Keywords: Washing; moving bed; displacement; purification; Sedimentator.

A. Brou, L.H. Ding, and M.Y. Jaffrin Extraction and concentration of polysaccharides using a rotating disk filtration system (pages 162-168)

bullet Abstract

bullet The recovery of exopolysaccharides (EPS) produced by Sinorhizobium meliloti bacteria has been investigated using a rotating disk filtration system. The main feature of our system is the use of vanes on the disk which produces a very important increase in permeate flux and an EPS transmission rate close to 100%. During the recovery of EPS produced under standard fermentation conditions (70 h at 30°C) by microfiltration, the mass flux has been raised to 650 g h-1 m-2 using a disk equipped with 2 mm vanes rotating at 2000 rpm against 380 g h-1 m-2 with a smooth disk at the same speed. The permeate flux Jf for various disks can be correlated by the same function of the mean shear stress at the membrane (τwm0.72 at 30°C) showing that the effect of vanes is merely to increase the shear stress by raising the fluid core velocity between the membrane and the disk. With 6 mm vanes, the core fluid angular velocity was found to be 84% of disk velocity versus 45% for a smooth disk. The same device has been equipped with a PES 50 kDa membrane to concentrate EPS by ultrafiltration. Permeate fluxes were of the order of 160 L h-1 m-2 at 2000 rpm and 30°C with nearly complete EPS rejection.

Keywords: Dynamic filtration; microfiltration; ultrafiltration; exopolysaccharides; rotating disk.

E.D. Archer and R.W.K. Allen REVIEW PAPER: DRY SCRUBBING OF FLUE GASES (pages 169-180)

bullet Abstract

bullet Dry scrubbing owes its origins to intense industrial activity driven by the imperative to satisfy, at minimum cost, public opinion and its resultant increasingly stringent pollution control legislation. This review examines the development of dry scrubbing systems, their performance and the factors that limit their performance.Keywords: Gas filtration; flue gases; scrubbing.


Published papers: Volume 3, Issue 2

Author(s) Title, page numbers and abstract
T. Golesworthy

A Review of Industrial Flue Gas Cleaning (pages 71-79)

bullet Abstract

bullet Environmental awareness has grown significantly in the last 10 to 20 years. The general public and green Eco groups have swayed public opinion through the media such that the legislators have put increasingly stringent emission limits on many industrial processes and activities. The US Environmental Protection Agency has led the way with many countries following its lead. The Environmental Protection Act in the UK is an example of new legislation that seeks to protect our environment from all known industrial pollution hazards whilst acknowledging the need for industry to remain economically viable.A necessary part of industrial activity is managing its wastes using processes such as incineration. Emissions to air from incineration plant involve a wide range of materials that can include: particulate matter, oxides of nitrogen and sulphur, hydrogen chloride, volatile organic compounds, polychlorinated bi-phenyls, di-benzo furans (dioxins) and heavy metals.

A range of mature and emergent control technologies exist for the control of these pollutants including inertial separation, filtration, electrostatic separation, wet and dry scrubbing and catalysis/conversion processes. These techniques are reviewed historically as well as current state of the art composite gas cleaning plant for total solutions to the emission of currently prescribed pollutants.

J. Heikkinen, P. Pirkonen, J. Koskinen, R. Lahtinen and A. Mahiout

METHOD FOR REMOVING HEAVY METALS FROM METAL PLATING EFFLUENTS (pages 80-84)

bullet Abstract

bullet The objective of this work was to study the removal of dissolved metals from industrial effluents. The sorption of Cu, Zn, Cr, Pb, Ni and Cd from multicomponent mixtures was studied in a flow-through column packed with different sorbents. The materials studied were peat, two types of tree bark, rock wool and wood fibres made of reclaimed (recycled) paper. The metal-containing waste waters were collected from several industrial plants representing different industrial sectors in Finland.The efficiency of the metals removal from wastewaters studied at the laboratory scale depended largely on the wastewater and the material used as the sorbent. The results from the laboratory scale experiments suggest that the following factors should be taken into account: pH of the wastewater, number of different metal ions in the wastewater, concentration of the metal ions in the wastewater, and the solid matter content in the wastewater.

This research demonstrates that easily available materials can be used to remove dissolved heavy metals from industrial effluents. At very high metal ion concentrations the system seems to be inadequate, therefore the main purpose could be polishing of conventionally treated effluents.

K. Sutherland

PHYSICAL AND BIOLOGICAL TREATMENT PROCESSES (pages 85-88)

bullet Abstract

bullet A brief introduction is given to the main processes used in the treatment of municipal and industrial wastewaters, with emphasis on the use of filtration and related techniques. The key features of each stage in the process are described together with the main problems currently troubling the sector, especially those of increasing quantities, and greater severity in the restrictions on ultimate water discharge quality. Some of the modern developments leading to solutions to these problems are highlighted.

S. Massingham DEVELOPMENT OF A ZERO DISCHARGE PROCESS FOR MDF EFFLUENT TREATMENT (pages 89-90)

bullet Abstract

bullet Conventional processes for the treatment of effluent arising from the manufacture of MDF panels fail to comply with increasingly stringent environmental requirements. Recent advances in polymer chemistry combined with membrane technology have enabled both water recovery and, more recently, solubilised organic compound recovery. The result is that a ZERO DISCHARGE system is now a reality.This case study of the first commercialised system at an MDF mill outlines the shortfalls of conventional systems, and how the benefits of the membrane system have resulted in it being viewed not as an effluent treatment plant but as process technology incorporated into the refining process.

D. Condie, B. Johnston, S. Nicol and C. Veal

RESIDUAL MOISTURE REDUCTION IN COARSE COAL CENTRIFUGES USING AIR PURGING (pages 91-94)

bullet Abstract

bullet Air purging is a novel process for reducing the moisture content of coarse coal products from vibrating basket centrifuges. The technique involves injecting a turbulent stream of compressed air, via a manifold inserted into the centrifuge, through the bed of coal particles as it is traverses the centrifuge basket. The air blows water from the coal bed into the centrate stream. Over the last few years CSIRO and Novatech Consulting have been developing air purging, with the objective of reducing residual moisture by 1 wt% compared with conventional centrifuge operation. Such a moisture reduction would provide the Australian coal industry, which is the world’s largest exporter of coal, with substantial financial savings in downstream transport and handling costs.

This paper describes the results obtained when air purging was scaled up from pilot plant (2-4 tph) to commercial (up to 70 tph) scale operation. Reductions in residual moisture close to the 1 wt% target were achieved. The costs of installing and operating air purging are predicted to be much lower than the financial savings that would accrue from lower moisture products.

B.B. Gönül and Ö. Özcan THE USE OF SURFACTANTS IN PRESSURE FILTRATION OF VERY FINE DOLOMITE AND QUARTZ MINERALS (pages 94-97)

bullet Abstract

bullet The effect of surfactants on the pressure filtration of fine grained (x50 = 15 μ m) dolomite and quartz minerals was investigated in this study. The relationship between the surfactant type, concentration and surface tension of the slurry and the filtration rate and residual moisture content of dolomite and quartz minerals was analysed. The laboratory experiments showed that all types of surfactants increased the filtration rate of minerals and decreased the residual moisture content of the cakes. In the dolomite filtration a nonionic type was the most effective reagent, in the quartz filtration an anionic surfactant was the most effective type.

J. Umbría, A. Macias-Machín, A. Lecuona and A. Espino GAS CLEANING USING AN ATOMISED ULTRA FREEZING SEPARATION UNIT (pages 100-105)

bullet Abstract

bullet This paper describes the influence of operating variables such as gas velocity, liquid velocity, dust particle size and temperature of the atomised water used in the venturi scrubber of an Atomised Ultra Freezing Separation Unit (FUA). In this device there are two different units. In the first (termed filter) a venturi scrubber cleans the polluting dust laden gas and in the second a helicoidal heat exchanger (termed condenser) volatile organic compounds (VOCs) are recovered using liquid nitrogen as a refrigerant.Dust collection was more effective when the liquid to gas ratio increased and a low atomising water temperature improved the overall dust collection efficiency by more than 34 % when the temperature decreased from 25 to 0 ºC.

Keywords: Gas cleaning; venturi scrubber; water temperature.

O. Gundogdu, M.A. Koenders, R.J. Wakeman and P. Wu PERMEATION WITH VIBRATED MEDIA: EXPERIMENTS AND MODELLING (pages 106-113)

bullet Abstract

bullet Experiments and theoretical modelling are presented on cake permeation effects with a vibrated septum in a dead-end filter configuration. The key effect is that there is a critical vibration amplitude. Below this amplitude the cake remains intact and may even densify somewhat to display increased flow resistance. Above the critical amplitude the particle-fluid mixture may fluidise. In the latter case the vibration is strongly attenuated to such a degree that it is felt in a localised region near the septum only. Under these circumstances the septum is unclogged and the permeability of the system as a whole increases dramatically. Modelling the locally fluidised state is done by considering the motion of one particle that interacts both with the septum and the rest of the cake via a rough lubrication interaction. The results of the model show that substantial loss of contact interaction between septum and particle is possible. The parameter range in which this occurs is predicted by the model and is shown to be in the right order of magnitude when compared with the experiments. Furthermore, an analysis of the completely fluidised cake is given.

Keywords: Permeation; vibration filtration; modelling.

C. Johansson and H. Theliander MEASURING CONCENTRATION AND PRESSURE PROFILES IN DEADEND FILTRATION (pages 114-120)

bullet Abstract

bullet A laboratory filter press has been constructed with the capability of producing both liquid pressure profiles and concentration profiles with respect to the height of the filter cake and time during the course of a filtration experiment. The pressure is measured at 8 heights by means of capillary tubes placed inside the formation zone of the cake. The solid material concentration is obtained by attenuation measurements using a γ-radiating 241Am source and an NaI(Tl)-scintillation detector. It is also possible to perform cake washing experiments with the piston press. Experiments on a lignin sludge, a compressible material that is difficult to filter, have been conducted and show that both the pressure and concentration measuring systems function correctly. In this paper, solid compressive pressure profiles, solidosity profiles and filtration data are presented for lignin sludge.Keywords: Cake filtration; solidosity and pressure measurements; specific resistance.


Published papers: Volume 3, Issue 1

Author(s) Title, page numbers and abstract
D.A. Patterson DETERMINATION OF BEST AVAILABLE TECHNIQUES: METHODS AND CASE EXAMPLES (pages 12-17)

bullet Abstract

bullet Under the European Integrated Pollution Prevention and Control Directive (96/61/EC) there is a need to define the best available techniques (BATs) for pollution prevention and control for a number of industries.A number of methods have been developed in Europe for determining BAT, including life cycle analysis (LCA) and multi-criteria approaches. In the UK, a simpler method has been recommended by the Environment Agency, the Scottish Environment Protection Agency and the Northern Ireland Environmental Heritage Service. This method consists of two basic components: the assessment of environmental impacts using a series of simple calculations to determine parameters such as emissions to air, emissions to surface water, global warming potential and photochemical ozone creation potential and the balancing of environmental impacts against capital and operating costs. Despite its simplicity, this methodology is modular and flexible, allowing the possibility of more advanced techniques (such as LCA) to be used in the modules to address any deficiencies.

Despite this, the method may need to be amended in the future, since the European Integrated Pollution Prevention and Control Bureau is compiling a BAT Reference (BREF) type document on the economic and cross-media effects of BAT determination, due in May 2003.

A. Merry THE USE OF ULTRAFILTRATION FOR COD REDUCTION IN PULP MILL EFFLUENT – A CASE STUDY FROM SWEDEN (pages 18-20)

bullet Abstract

bullet The Enso Stora Fine Paper mill at Nymölla in Sweden is one of the world’s largest manufacturers of bleached magnefite pulp. Commercial pressures in the early 1990’s were pushing the mill to reduce emissions of COD. The solution was to install an ultrafiltration plant reduce COD from the oxygen stage of the bleach plant by 50%.This paper describes the 18 month process of developing and refining the UF process prior to design and start-up of the full scale plant. The experience of successfully operating the plant for seven years are also discussed, and other applications that have been looked at are commented upon.

B.D. Arnold and G. C. Deka AIR FILTRATION PERFORMANCE – SOME REAL WORLD RESULTS (pages 21-23)

bullet Abstract

bullet The establishment of air filter test methods that adequately reflect actual in-use filtration performance is of great significance to the air filtration industry. A key issue in this regard is understanding the elements that impact the performance of filters in the field and developing a test which adequately simulates these elements. One crucial element is the nature of the dust that is entrained in the air to be filtered and ultimately accumulated within the filter media. It is qualitatively understood that dust properties, such as particle size distribution, affect filtration performance over time. Quantitative studies, however, are limited. This paper describes the results of studies conducted to investigate the actual in-use performance of pleat filters. Results are compared with the filtration performance described by ASHRAE 52.2 characterisation.

D. S. Liley and M. Pearse PRACTICALITIES OF FLOCCULANT SELECTION (pages 24-27)

bullet Abstract

bullet The paper describes practical aspects of selecting flocculants for solid-liquid separation using clarification, thickening and pressure belt filtration as examples. Particular attention is given to analysing the initial process requirements and obtaining a representative test substrate. Practical procedures are given and laboratory-scale simulation equipment is described.

S. Cole, P Koklitis and M. Weaver Characterisation and Optimisation of a Filter Medium containing Immobilised Activated Carbon and its Application in Large Scale Purification Processes (pages 28-34)

bullet Abstract

bullet A modern approach to the use of activated carbon in decolourisation and purification of solids and liquids at industrial scale is described. Immobilised carbon in a form that is safe and convenient to handle simplifies the process operation, reduces process time, improves safety and cleanliness, and enhances process control and consistency. Increases in process yield are also achievable. This paper outlines the background to the use of activated carbon, describes the implementation of immobilised carbon, summarises methods of qualification and presents case studies to illustrate process benefits.

F. Tepper, L. Kaledin, G. Lukasic and S.l Farrah FILTERS BASED ON BIOACTIVE NANOFIBRES (pages 34-37)

bullet Abstract

bullet Argonide produces a form of nano alumina fibre that is bioactive in that it attracts and retains virus and other macromolecules by electrostatic forces. These fibres have been incorporated into fibrous (“depth”) filters and have been found to have ~log7-8 retention for viruses even at flow rates several orders of magnitude greater than could be obtained using microporous membranes.

E.S. Tarleton and R.C. Hadley THE APPLICATION OF MECHATRONIC PRINCIPLES IN PRESSURE FILTRATION AND ITS IMPACT ON FILTER SIMULATION (pages 40-47)

bullet Abstract

bullet This paper describes a mechatronic approach to cake filtration where automated constant, variable and stepped pressure filtrations are performed in a consistent manner without altering the inherent characteristics of a feed suspension. Experimental data for the three pressure/flow regimes are presented where cake formation is monitored by micro-pressure transducers capable of providing up to seven independent measures of liquid pressure within 3.3 mm of the filter medium surface.For constant pressure and moderately compressible talc cakes the liquid pressure increased with cake height in a non-linear manner and generally exhibited a concave profile. When a pressure step was applied following a period of constant pressure filtration, the cake structure typically required up to 30 s to reach a new pseudo-equilibrium state. During this time the reciprocal filtrate flow rate vs. filtrate volume plot was non-linear and the liquid pressures in the cake increased rapidly before remaining nearly constant. When the cake was thicker or the pressure step larger, the liquid pressure measured at 0.5 mm above the filter medium either remained constant following the increase in pressure or increased slowly over the 360 s duration of the pressure step.

The constant and step pressure data were analysed to obtain scale-up constants. These were used in process models to give good simulations of constant pressure filtrations but less accurate predictions of constant flow filtrations where pressures were under-predicted at short times and over-predicted at longer times. The latter was attributed to the time delay in cake restructuring following a pressure change.

Keywords: Cake filtration; tomography; micro-pressure transducers; scale-up; stepped pressure.

H. Niemi, J. Kallas and S. Palosaari THE OPTIMISATION OF MULTISTAGE RECYCLE ULTRAFILTRATION AND REVERSE OSMOSIS PROCESSES: AN APPLICATION FOR WASTE WATER TREATMENT (pages 48-54)

bullet Abstract

bullet The simulation and optimisation method for tubular module multistage recycle ultrafiltration and reverse osmosis processes, developed by the authors, was used to study the effect of variations in process and cost parameters on the total cost of effluent treatment. The effect of the number of recycle stages, volumetric concentration ratio (VCR), operating pressure, price of electricity, membrane cost and pay-back time of the investment on the treatment costs were studied. The processes that were investigated included the purification of oil-contaminated water using reverse osmosis and the ultrafiltration of a cutting oil emulsion. In this study the most economic processes were 2 or 3 stage processes for VCR 5 and a 6 stage process for VCR 10. No significant change in the cost was found by varying the operating pressure or the price of electricity or the cost of the membranes by approximately 20% of their initial value. Three different modes of operation, based on the distribution of the total VCR of the process between the recycle stages, were studied. The modes, in which the VCRs of the recycle stages are equal (ECR, equal concentration ratios), gave practically the same results in terms of the costs as they did for the optimisation mode (OPT). In the optimised operation, the concentration ratios of the stages were determined in order to give the minimum costs of the separation. Although both methods can be recommended, the ECR mode requires less than a second in computing time compared with optimisation that may take up to several minutes.

Keywords: Effluent treatment; oil/water separation; process design; reverse osmosis; simulation; ultrafiltration; wastewater treatment.

O. Larue and E. Vorobiev COMPARISON OF ELECTROCOAGULATION BY IRON ELECTRODES AND COAGULATION BY IRON SALTS DOSING ON LATEX SUSPENSIONS (pages 55-60)

bullet Abstract

bullet Compared to more conventional processes such as chemical dosing, electrocoagulation (EC) offers an alternative electrochemical treatment for removing colloids from wastewater. In this paper EC with iron electrodes and chemical dosing with ferrous sulphate or ferric chloride were investigated for two types of latex suspension. The results of both processes were compared through the efficiency of solid/liquid separations performed by sludge sedimentation and filtration. Preliminary testing identified the processes conditions (i.e. pH, coagulant concentration, conductivity and current density in EC) needed to provide optimum coagulation and avoid excessively high energy consumption in EC. Comparisons of the coagulation processes at their optimum conditions showed that EC generated flocs of greater size and/or density accelerated sedimentation and filtration.Keywords: Electrocoagulation; iron electrodes; chemical dosing; iron salts; latex suspensions.


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2004

Published papers: Volume 4, Issue 4

Author(s) Title, page numbers and abstract
M. Waldenmaier

CORRUGATED HIGH EFFICIENCY FILTER MEDIUM VILEDON FE 2507 SINE – RESULTS FROM LONG-TERM FIELD TESTS AND A COMPARISON WITH LABORATORY TESTS (pages 249-252)

bullet Abstract

bullet Filter cartridges equipped with modern synthetic filter media are increasingly used for the separation of airborne particles. The need to separate particles from a carrier gas occurs in dust removal applications as well as in the case of recovering special products, e.g. in pharmaceutical industry. Particularly for the filtration of very fine particles (less than 5 µm down to the submicron range) the requirements on the filter media are still growing with respect to the capability of separating these particles and to the cleanability when cleaned by pulse-jet.

X. Simon, D. Thomas, D. Bémer, S. Callé, R. Régnier and P. Contal

INFLUENCE OF CLEANING PARAMETERS ON PULSE – JET FILTER BAG PERFORMANCE (pages 253-260)

bullet Abstract

bullet The aim of this study is to characterise pressure drop and acceleration profiles along a filter bag subjected to different conditions of pulse-jet cleaning. A flow of clean air is imposed on the 24 bags of a pilot-scale dust collector. Pulse-jet cleaning can be achieved either on the single instrumented filter bag, or on the 24 bags simultaneously. Various parameters (initial bag tension, filtration velocity, compressed air tank pressure, impulsive flow duration and geometry of the nozzle or tube injector) were investigated and their influences on the cleaning performances of a filter bag are discussed and compared. Results permit better understanding of the effects of pulse-jet cleaning and identification of the areas where cleaning seems to be most effective. Choice and combination of those parameters (compressed air pressure, geometry of injector nozzle and number of bags cleaned simultaneously) seem to be crucial stages for the optimisation of bag cleaning in pulse-jet filters.

A. Karabach and I. Dun

THE TURBO MAGNETIC OIL FILTER “URAGAN-M” (pages 260-261)

bullet Abstract

bullet No abstract available.

R.A. Smith EXTENDED AREA FILTRATION IN NONWOVENS POLYMER PROCESSING (pages 262-266)

bullet Abstract

bullet As the application of nonwoven materials into more critical end uses such as filter media has evolved along with a highly price competitive market, manufacturers have been increasingly interested in ways to distinguish their product in the market or improve their economic position. Many of these manufacturers have development efforts aimed at reducing fibre diameters, improving fibre/web physical properties and consistency while maximizing process efficiencies.Given the capital and operating cost impact of filtration requirements on a process, not to mention potential product quality or market position issues, it is extremely important that the right decisions are made relative to filter medium, size, and design. Without a fundamental understanding of filtration concepts and technologies, including an understanding of the end users own basic filtration needs, knowing the strategic questions to ask of a supplier or how to interpret their answers is difficult. In the absence of this knowledge, they must find an unbiased company or consultant that can provide them with the necessary guidance and direction.

D. Kunz, E. Schmidt and T.A. Peters OPTIMISATION OF SLUDGE MANAGEMENT IN LEISURE PARKS BY LOW-PRESSURE REVERSE OSMOSIS (pages 267-270)

bullet Abstract

bullet Water treatment has become more and more important due to increased costs for municipal water and wastewater during the past few years. The membrane processes have been developed continuously during recent years. Increasingly they have replaced approved processes like adsorption and reverse osmosis is already established for sea water desalination and other applications. In the “Bergische Sonne” leisure park in Wuppertal, the so-called project “SAMRO” has been developed.In this project, a specific vibration screen is used to separate the solids material in addition to a low-pressure reverse osmosis membrane process. By using this combination, the filter backwash water, which is accumulated during the backwashing of the filters, is purified by a low pressure reverse osmosis so that it can be used as filling water for the basins again. The filter backwash water is pre-cleaned over a Sweco vibration separator to separate particles which are bigger than 60 µm. The filtrate flows over a police filter (a bag filter) afterwards and then over the flat membrane modules of the low pressure reverse osmosis system. The results show that the drinking water and sewage quantity has been reduced by 80 %.

The savings made are also based on the lower energy demand required to heat the potable water. It contains a credit of 0.40 €/m3. The hygienic conditions are improved since sludge storage is avoided.

T. Sobisch and D. Lerche

USE OF ANALYTICAL CENTRIFUGATION FOR EVALUATION OF SOLID-LIQUID SEPARATION IN DECANTER CENTRIFUGES: APPLICATION TO SELECTION OF FLOCCULANTS FOR SLUDGE DEWATERING (pages 270-274)

bullet Abstract

bullet The paper reports on a new laboratory method for the evaluation of solid-liquid separation in decanter centrifuges based on analytical centrifugation. The method allows determination of the two critical parameters for sludge dewatering – separation rate of sludge flocs and the compressibility (dewaterability) of the sludge cake. The initial separation rate gives information on whether or not the sludge flocs are separated fast enough from the bulk liquid. This relates to the maximum throughput performance at which the decanter can operate. The content of total solids after centrifugation measures the extent that the separated sludge cake can be compressed further. This is proportional to the total solids, which can be obtained if the throughput rate is not critical. The action of high shear stresses during mechanical processing was modelled by adapting the sample pre-treatment, so that similar changes take place in the sludge samples as in practice. The performance of the newly developed method was demonstrated by investigations of the effect of the initial total solids of a sludge, of mechanical stresses on sludges before flocculant addition, by an example of flocculant selection and by comparison with results obtained under field conditions.

K. Velten, M. Günther, B. Lindemann and W. Loser OPTIMISATION OF CANDLE FILTERS USING THREE-DIMENSIONAL FLOW SIMULATIONS (pages 276-280)

bullet Abstract

bullet A model has been developed to compute 3D quasi-stationary flow patterns in candle filter systems. It is based on the Navier-Stokes and Brinkman flow equations and a shape optimisation procedure to estimate the filter cake shape in 3D. Finite elements and an iterated grid search algorithm are used to solve the mathematical problems. Since an unnecessary detailed modelling of the process is avoided, the approach is particularly efficient in terms of computation time and memory requirements. It allows for a scenario-based optimisation of the filtration process. Among the results, the 3D flow pattern in a particular candle filter system (FILTROjet 2300®) has been obtained. Also, the dependence of the filter cake’s shape on its thickness has been derived, which will be used for experimental validation.

Keywords: Cake filtration; candle filters; CFD; Darcy equation; finite element method; liquid filtration; modelling; Navier-Stokes equations.

A. Marquard, J. Meyer and G. Kasper EFFECT OF AEROSOL CONCENTRATION ON THE ELECTROSTATIC PRECIPITATION OF NANOPARTICLES (pages 281-286)

bullet Abstract

bullet This paper presents experimental data on the relevance of particle space charge effects during electrostatic precipitation of SiO2 nanoaerosols in a cylindrical ESP. The influence of particle concentration on the ESP-operation is characterised by measurements of voltage (U) – current (I) characteristics, particle collection efficiencies and mean particle charges at the ESP exit. Variation of particle concentration between 5×106 and 1.8×108 #/cm3 was achieved by diluting the aerosol without changing the particle characteristics (size and morphology) and gas conditions (temperature and humidity). With increasing concentration a decrease of the voltage-current curve was observed, but for the highest voltage applied, precipitation still remained high (total number collection efficiency 98 % for 45 nm aerosol and 96 % for 75 nm aerosol).The transition from low to the high particle concentration regime where particle space charge effects start influencing the ESP-operation was determined. Derived from the U-I curves, the threshold concentration lies between 5×106 #/cm3 and 9×106 #/cm3 and derived from the measured collection efficiencies, it is located around 1.5×107 #/cm3.

For the low concentration regime a theoretical analysis of the charge and grade efficiency measurements based on two migration models (Deutsch1; Leonard et al.2) and a charging model (Fuchs3; Adachi et al.4) was performed. Whereas the charge calculations based on measured grade efficiencies and the Deutsch model showed good agreement with the direct charge measurements, the charge calculations based on the established Fuchs model at the measured electrical conditions resulted in a significant underestimation of the particle charge.

Keywords: Corona-quenching; Deutsch equation; electrostatic precipitation; Fuchs charging model; nanoparticle charging.

S. Tanaka and C. Kanaoka DURABILITY VALIDATION OF SYNTHETIC FILTER BAGS (pages 287-294)

bullet Abstract

bullet The use of filter bags as high temperature air-cleaning media is one of the most promising methods for preventing the release of hazardous emissions such as dioxins from incineration exhausts. High-temperature and chemical resistant fibre felts are preferable for filter media to establish high collection efficiency and strong durability. The felt shape materials must have quite different durability compared with bulk polymer material because there are so many factors related to polymer morphology and felt structure. However, no systematic method to evaluate the durability of filter materials has been established. The dominant degradation mechanisms of filter bags (FBs) is also unclear.In this study, a systematic evaluation method for high temperature application is proposed and validated on an experimental basis. Commercially available synthetic FBs for high temperature operation made of poly-fluoroethylene, poly-phenylene sulphide, poly-imide, and poly-metha-phenylen isophtalic amid showed excellent durability and high application potential in municipal incinerators at temperatures of less than 210ºC. Not only temperature, but also oxygen and water content, significantly affect the durability of FBs by a mechanism of oxidization or hydrolysis. PTFE showed strong durability against all acid gases tested but its tensile characteristics are significantly affected by temperature change. The degradation mechanism was investigated by a comprehensive chemical analysis.

Keywords: Bag filter; durability; acid gas; hot gas cleaning; synthetic bag filter.

J.-L. Lanoisellé, G. Piar and E. Vorobiev High-pressure expression of cocoa suspensions: an overview of the butter extraction mechanism (pages 295-303)

bullet Abstract

bullet Expression is a unit operation that is very widespread in food industries, and is used in particular to extract oil from a plant. This process is important for the first transformation of cocoa (54% fat) as a prelude to the manufacture of chocolate. The objective is to obtain cocoa butter (fat), which will be added to the cocoa mass (liquor) and sugar to form chocolate. Classically, expression is performed at 100°C in high-performance hydraulic presses that work with pressures of 80 MPa. The cocoa expression operation is considered complete when the cake butter residual content is 10%. The operation takes place within 20 minutes to produce a cake butter residual content of 10%, and may be divided into five phases with regard to recordings of pressures, variation of thickness of the pot and extracted mass of butter: i) a feeding phase, including an over-filling stage, which corresponds to a filtration with constant pressure; ii) a filtration phase characterised by a constant butter outflow and a linear increase of pressure with time; iii) a constant rate compression phase with a rapid increase of pressure; iv) a compression phase with a decreasing rate of deformation of the pot limited by the forward movement of the piston resulting from the performance of the hydraulic pumping unit; and v) a constant pressure compression phase due to the pressure regulation of the hydraulic pump unit.

For each of these phases, an empirical model is proposed, which allows the calculation of the volume of butter extracted according to time.

Keywords: Compressible porous media; consolidation; constant pressure; solid-liquid expression; filtration; fine particle.


Published papers: Volume 4, Issue 3

Author(s) Title, page numbers and abstract
A. Jena and K. Gupta

Characterisation of nanofibRE filtration media by Capillary flow Porometry (pages 176-180)

bullet Abstract

bullet Comparison of the capabilities of pore characterisation techniques suggests that liquid extrusion techniques are most appropriate for the characterisation of nanofibre filtration media. The extrusion techniques, Capillary Flow Porometry and Liquid Extrusion Porosimetry, were used to successfully measure all the pore structure characteristics of through pores. Pore throat diameter, bubble point pore diameter, mean flow pore diameter, flow distribution and gas permeability were measured by capillary flow porometry. Through pore volume and volume distributions were measured by extrusion porosimetry. It is shown that through pore surface area and liquid permeability are measurable by both techniques. It is concluded that techniques based on liquid extrusion are suitable for characterisation of nanofibre filtration media.

W. Polonio

PERFORMANCE OF DIFFERENT PRIMARY FILTERING MEDIA IN ROTARY VACUUM DRUM FILTERS FOR SUGAR-CANE MUD (pages 181-185)

bullet Abstract

bullet This study aims to evaluate the development of 13 different types of primary filter media. These were developed for use in the vacuum filtration of sugar-cane mud to simulate the cake formation and dewatering operations in the Rotary Vacuum Drum Filters employed in sugar and alcohol mills in Brazil. The primary filtering media tested were divided in perforated boards by mechanical process and chemical photo corrosion, with round bores, different procedures, open areas, superficial types of finish, thickness and chemical corrosion attack of the boards. Other types were also built with trapezoidal bars to form a metal grid having rectangular openings of different open area. All the experiments were made in a pilot plant attached to the real filter that aimed to reflect the truthfulness of the operational variables of the sugar-cane mud in a Rotary Vacuum Drum Filter. For each experiment, the analyses of the mud, cake and filtered juice were made at the mill’s own laboratory, raising quantitative and qualitative data that was contrasted with the standard filtering element commonly used. The results are presented graphically, comparing the filtering indices obtained in the formation and cake dewatering steps, for variations in vacuum, temperature and concentration of the filtering auxiliary.

As a conclusion, the user is shown a new way to significantly improve the performance of vacuum filtration through low investment, without the need to increase the area of the filtering unit.

H. Nirschl and V. Denk

THE WHIRLPOOL SEPARATION SYSTEM AND ITS INDUSTRIAL APPLICATION (pages 186-189)

bullet Abstract

bullet The whirlpool is in general a device for solid-liquid separation. The physical phenomenon is also known as the so-called teacup effect: tea leaves in a tea cup which has been stirred do not move to the outside, in accordance with centrifugal force, but contrary to the direction expected they move towards the centre of the bottom of the cup where they settle. The separation of the particles takes place in the bottom boundary layer of the vessel. The equilibrium forces arising from fluid rotation are disturbed there so that resulting eddies force the particles to move to the centre of the vessel.Various undesirable secondary flows arise in the system. A so-called torus eddy with a shape of a car tyre tries to whirl up the settling trub in an undesirable manner. As a result the entrance velocity may be limited to a special inlet velocity which makes sure that the shear stresses on the trub particles are not too high and no destruction can occur. The limitation of shear stresses is of high importance because not just in the whirlpool but also in the surrounding parts, for example in pumps and pipes, a degradation of the particles is possible. Besides, there are constructive ways to get rid of undesirable secondary flows.

The torus eddy can be ‘sliced’ be means of suitable inserts. The inserts can consist of concentric rings installed near the bottom. A work programme has been developed to ensure the separation system for use in the brewing industry. The system has now been installed and approved in several breweries.

M. Schmidt and L. Mölter NEW TEST SYSTEM FOR PRACTICAL FILTER TEST OF CLEANABLE SURFACE FILTER MEDIA AT TEMPERATURES UP TO 250°C AND IN RELATIVE HUMIDITY UP TO 80% (pages 189-193)

bullet Abstract

bullet No abstract available.

N. Salmela and M. Oja FILTER MEDIA TESTING FOR STARCH FILTRATION SYSTEMS (pages 194-198)

bullet Abstract

bullet Pressure filtration of starch slurries in starch production is increasing. Because the filter medium is a keystone of any filtration system, it is important to find the best possible medium for a certain process. The change of the medium can significantly alter the economics of the starch filtration process. Every starch type has its own special mean particle size and particle size distribution. The differences between sizes of different starches are quite large: from a couple of micrometers to one hundred micrometers. However, different starch types are filtered in the same filter press. The filter media used has to be as suitable as possible for all starch types.In this work, different types of filter media used in commercial starch production processes were tested. The aim was to find the most suitable medium for wheat starch filtration. The resistance of the clean and used medium was measured before filtration and between the filtration runs by flowing water through the medium. The medium resistance was measured with the same test filter as the actual filtration tests, but using special water piping. Clean and used media were also compared microscopically.

Because every starch type has its own special properties, it is important to find the media most suited to each application. North European starch production consists mainly of wheat and potato starch production, whereas American and Southern European starch production consists mainly of maize starch production. This sets different demands for the filter media.

R.A. Smith

METALLIC FILTER ELEMENTS: DETERMINING AN ELEMENT’S SUITABILITY FOR REUSE AFTER CLEANING (pages 198-202)

bullet Abstract

bullet There are a number of metallic filter element configurations and media used in liquid/solid as well as gas/particle separation. Their high cost requires that they remain on stream for a long time or are cleaned on/off-line and subsequently returned to service. At some point, some sort of cost effective non-destructive test must be applied to assess suitability for continued service.There are a number of tests used to define the largest pore in an element, mean pore size, permeability, tortuosity, etc. when new. The picture becomes cloudy once an element has been used. This is due to subtle changes in the media as a result of a multitude of possible causes. Changes could be minor with no measurable or minor increase in largest or mean pore size to significant changes that compromise an element’s integrity from a performance or product quality perspective. It may also be necessary to determine the effectiveness of cleaning. It is important that the end user be able to determine if an element is suitable for reuse or must be replaced. What tests, criteria and limits does he /she use to make this determination?

It basically becomes a risk assessment for the end user. Standards or limits set too high will result in higher operating costs due to element replacement. Limits set too low may result in process upsets, productivity or product quality issues. This paper addresses the test methods and criteria commonly used today and provide some insight into the significance of test results relative to minimising the risks associated with setting these limits.

D. Šmidová, P. Mikulášek et al. CHARGE EFFECTS OF DISPERSED SYSTEMS AND MEMBRANE SURFACE ON CROSSFLOW MICROFILTRATION (pages 204-209)

bullet Abstract

bullet The influence of particle size and ζ-potential of the feed particles (TiO2) and a membrane surface (α-Al2O3) with changes of pH on permeate flux during microfiltration using a tubular ceramic membrane have been studied. The properties of alumina tubular membranes and the aqueous titania dispersions were measured and related to the filtration characteristics. The experimental system is also described. It was found that permeate flux was dependent on the surface charge of the suspended particles and to some extent dependent on the surface charge of the membrane. This phenomenon was especially pronounced during microfiltration of a dispersion around its isoelectric point, when permeate flux increased significantly.

Keywords: Microfiltration; zeta potential; particle size; pH.

M. Beiser and W. Stahl INFLUENCE OF ADDITIVES ON THE SEDIMENTATION BEHAVIOUR OF FINE GRAINED SOLIDS IN THE CENTRIFUGAL FIELD (pages 210-215)

bullet Abstract

bullet The influences of solids concentration and additives on the sedimentation behaviour of quartz and limestone suspensions in centrifugal fields are described. These solid/liquid systems showed similar physical properties (e.g. particle size distribution, particle shape, density) but different physicochemical properties. Quartz/de-ionised water-suspensions were inherently stable, that is the quartz particles did not tend to coagulate, whereas limestone suspensions were destabilised in their natural state. Within this paper, the influence of electrolyte concentration (AlCl3) and pH-value (HCl) on the sedimentation behaviour of quartz particles is discussed. Both additives induced coagulation of the quartz. Additionally, the influence of dispersing agents on the sedimentation of limestone particles is presented. The comparison of the settling behaviour of these two products revealed both similarities and differences.

The experimental results show how the sedimentation behaviour of fine grained solids can be readily influenced by additives. The well directed control of physicochemical parameters implies the possibility of adapting the sedimentation behaviour of particles to a particular process in an optimal way.

Keywords: Sedimentation; centrifugal field; physicochemical properties; coagulation; additives.

H. Saveyn and P. van der Meeren FILTRATION AND WASHING CHARACTERISTICS OF CONCENTRATED COBALT HYDROXIDE SUSPENSIONS (pages 216-219)

bullet Abstract

bullet Cobalt hydroxide Co(OH)2 suspensions were made by a precipitation reaction and the suspensions were consequently adjusted to different pH values, ranging from about pH 6 to 10. It appeared that the suspension viscosities showed a maximum at pH 8.8 because of strong interparticle attractive forces, leading to bridging as was confirmed by the high sediment volume upon prolonged sedimentation.The rheological behaviour of the suspensions was reflected in their filtration behaviour, indicated by the fact that suspensions with the highest apparent viscosity were the easiest to filter, with the lowest filter constants and shortest filtration duration times. The porosity of the cake structure was demonstrated through the filter cake thickness and the water content, which showed maximum values around pH 8.8. It appeared, however, that the good filterability at pH 8.8 was compensated by an increased retention of sodium in the filter cake, because of the large pore liquid volume.

Upon washing, it appeared that the filter cakes formed from suspensions at pH 8.8, were washed out most quickly. The mixing of pore liquid with wash liquid was more pronounced in these cakes, due to high wash liquor velocities in the larger pores. It is discussed how this optimum pH is related to the point of zero charge of two cobalt (hydr)oxide compounds.

Keywords: Cake filtration; cake resistance; filter cake structure; metal hydroxide suspension; porosity; particle bridging; porosity; viscosity; washing.

R.L.R. Salcedo, V.G. Chibante and I. Sôro LABORATORY, PILOT AND INDUSTRIAL-SCALE VALIDATION OF NUMERICALLY OPTIMISED REVERSE-FLOW GAS CYCLONES (pages 220-225)

bullet Abstract

bullet This paper addresses the experimental validation of the optimum design of reverse-flow gas-cyclones, obtained through the solution of a numerical non-linear optimisation problem, viz. maximizing cyclone collection. The simulation model is based on the predictive properties of a finite diffusivity model, where the particles’ turbulent dispersion coefficient is estimated through an empirical correlation between the radial Peclet and Reynolds numbers. The optimisations were formulated with constraints on pressure drop, saltation velocity and geometrical considerations, such that feasible cyclones could always be obtained.The optimum geometry, named RS_VHE, is different from the available high-efficiency designs, and represents reverse-flow cyclones with a significantly improved predicted performance. An innovative partial recirculation system within a collector-first arrangement further reduces emissions with only a moderate increase in pressure drop. The generally observed, but unexpected, high collection of sub-micron particles is attributed to capture by larger particles in the turbulent flow field due to turbulent dispersion, much like what occurs in re-circulating fluidised beds.

Results obtained for the RS_VHE cyclones with partial recirculation at laboratory, pilot and industrial scales, for temperatures ranging from 300 to 600 K, gas flow rates from 1 to 104 m3/h and inlet loads from 15 to 104 mg/m3, show them to perform significantly better than equivalent diameter HE cyclones, or smaller diameter multi-cyclones. Under certain circumstances, with recirculation the proposed system shows better performance than on-line pulse-jet bag-filters.

Overall, the results show that the numerically optimised RS_VHE cyclones, when coupled with a partial recirculation system, open the applicability of these simple devices for fine particle collection which is typical of more expensive devices, such as venturis and on-line pulse-jet bag-filters.

Keywords: Optimised gas cyclones; recirculation; turbulent dispersion; fine particle; pilot plant; industrial practice.


Published papers: Volume 4, Issue 2

Author(s) Title, page numbers and abstract
C. Peuchot

EVOLUTION OF FILTER TEST STANDARDS (pages 99-103)

bullet Abstract

bullet Liquid cartridge filters are used in many processes and on many machines working on, or using fluids, where particles in suspension may reduce the performance. This creates a huge market in which a lot of suppliers operate with a broad variety of products, the quality of which can fully, or on the contrary not at all, comply with the user specifications or requirements.Standard test methods are necessary to evaluate the behaviour and performance of the filter in conditions that represent as closely as possible the actual working conditions. This is expected to make the preliminary choice of filter, before a validation on the real process, the right one.

The performance and ability for use of filtering cartridges can be divided into three classes: Hydraulic, Compatibilities and Performance.

The standard methods on which all industrial relationships should be based are drafted by experts from the three “partners” involved: the manufacturers, their client end users and testing laboratories, each one bringing to the discussion their own requirements and know-how to reach the best compromise possible.

Because of the constant evolution in market needs, the products offered and testing know-how and equipment, standards must be regularly updated and new ones drafted.

G. Glasgow and B.J. Morrow

TREATING COMBINED SEWER OVERFLOWS: PERFORMANCE OF HIGH RATE CLARIFIERS AND CONTINUOUS SAND FILTERS (pages 103-108)

bullet Abstract

bullet During wet weather conditions, wastewater flows in combined sewers systems can be enormous, resulting in untreated spills from combined sewer overflow structures to the receiving water. Where such intermittent discharges are judged to be unsatisfactory, the conventional solution has been to either increase the pass forward flow or store the wet weather overflow in large tanks for later treatment. An alternative to this storage solution, known as Equivalent Treatment, is to treat the overflow to a desired standard and discharge it as and when necessary directly to the receiving water. Process technology including clarifiers, filters and ultra violet disinfection is being trialed by United Utilities to assess this approach to solving unacceptable intermittent discharges. Results have shown that suspended solids concentrations, ultraviolet transmission levels and faecal coliform concentrations can be improved to a level where ultraviolet disinfection becomes viable for the destruction of microorganisms. United Utilities are actively pursuing this approach to storm water management for a number of intermittent discharges across the North West of England.

T. Yamamoto, C-L.
Yang et al.

ELECTROCHEMICAL METHODS FOR COOLANT OIL REGENERATION (pages 109-113)

bullet Abstract

bullet Coolant oil (an oil-in-water emulsion), widely used for machining metal pieces from various industries, needs to be clean before being disposed of or reused. The used coolant oil contains not only fine metals but also sludge, grease and other compounds which are the source of odours as time elapses. The conventional methods are to use the filters, and gravitational and centrifugal separation methods to remove those compounds but these have practical limitations in terms of maintenance, removal efficiency, and coolant oil quality for regeneration. In the present study, electrochemical methods were investigated to remove these compounds and to regenerate the coolant oil – this led to development of a maintenance-free and innovative coolant oil treatment process. The other advantage was to suppress bacteria generation by controlling pH in the coolant oil, being considered the main cause of the odour problem. More than 90% by weight of fine aluminium particles, grease and oil were removed by the filter. The coolant oil can be used for regeneration and its characteristics did not deteriorate when the treatment time was less than 20 s at 20 V.

T. Wharton APPLICATION OF THE OPTICAL SENSING ZONE METHOD TO FILTER MONITORING (pages 113-116)

bullet Abstract

bullet This paper presents some recent developments in optical sensing and its use in filter monitoring. The operating principle of the Accusizer is described and methods for incorporation within filter test environments is shown.

R. Buxton Use of Standard Test Dusts in Filter Challenge Testing (pages 116-118)

bullet Abstract

bullet Standard test dusts have a wide variety of uses in a range of industries. They are used as secondary calibration materials for measuring instruments, testing the integrity of enclosures and packaging, the reliability of components and equipment in dirty atmospheres and in the testing of filters and filtration systems. There are many test dusts – Particle Technology Ltd manufacture dusts to over 70 different specifications. This paper concentrates on the filtration uses of standard test dusts.

P. Pinacci, M. Radaelli, A. Bottino and G. Capannelli

MOLASSES PURIFICATION BY INTEGRATED MEMBRANE PROCESSES (pages 119-122)

bullet Abstract

bullet Molasses represent an important waste stream in the sugar manufacturing process but their value is very low because of the presence of impurities ranging from suspended materials to inorganic salt and colour substances. This paper deals with the possibility of purifying molasses by two consecutive membrane processes, i.e. microfiltration and electrodialysis, and to recycle them back to the sugar manufacturing process.

The results of laboratory feasibility tests indicate that, by feeding the electrodialysis with microfiltered molasses at a concentration of 30 Brix, it is possible to remove up to 80% of salts, thus obtaining a stream suitable for sugar crystallization. Fouling phenomena are negligible due both to the beneficial effect of the microfiltration pre-treatment and to the intrinsic characteristics of the ion exchange membranes. Preliminary economic figures indicate potential benefit due to the use of integrated membrane processes but crystallization tests of purified molasses are necessary in order to evaluate the actual yield of the crystallization process and determine the quantity and quality of recovered sugar.

E. Iritani, Y. Mukai, N. Katagiri and I. Yoshii CONSOLIDATION BEHAVIOUR OF GEL EMULSION CAKE IN THE FILTRATION OF O/W EMULSIONS WITH AND WITHOUT SOLID PARTICLES (pages 124-129)

bullet Abstract

bullet A method has been developed for preparing highly concentrated gel emulsions by the filtration-consolidation of O/W emulsions using an unstirred batch filtration cell. The cake was highly consolidated without cake cracking or the coalescence of oil droplets by applying the pressure longer after completion of filtration for the whole emulsion. A compressed cake formed by this method has a porosity much smaller than the value of 0.2595, which corresponds to the hexagonal close packing of undistorted spheres. During consolidation, the oil droplets separated by thin stable films of continuous water in the compressed cake lose their sphericity and increasingly deform.By considering cake compressibility, the properties for the filtration period were evaluated on the basis of the cake filtration equation. This revealed that the highly compressible filter cake formed on the membrane surface during filtration. Moreover, the properties of the consolidation period were analysed using the modified Terzaghi model. The variations over time of the average consolidation ratio and the average porosity in the compressed cake during the consolidation process were well described by the model.

Filtration-consolidation of O/W emulsions containing fine solid particles is also important from the practical viewpoint. It was found that a cake with two distinct layers, comprising gel emulsion and fine solid particles respectively, was formed, and that the properties of the cake in both the filtration and consolidation periods can be well described by the model proposed.

Keywords: Gel emulsion; O/W emulsion; filtration; consolidation; cake.

A. Bottino, G. Capannelli, A. Comite and M. Oliveri DEVELOPMENT OF NOVEL MEMBRANES WITH CONTROLLED POROSITY FROM FLUORINATED POLYMER (pages 130-135)

bullet Abstract

bullet This paper deals with the preparation and characterisation of a new class of porous membrane made from a fluorinated polymer (polyvinylidene fluoride) supported on various types of porous non-wovens. Flat sheet membranes were prepared from polymer solutions, initially cast at room temperature on the non-woven, and then exposed for a given period in air before being immersed in water. The effects of some of the preparative parameters (i.e. polymer concentration, type of non-woven, exposure period of the cast solution) on the membrane properties (air permeability, ultrafiltration performance, structure and morphology) were investigated.The stretching action of the non-woven on the nascent membrane during immersion in the water bath was found to play an important role in the formation of membrane pores. The action was strictly connected to the penetration depth of the polymer solution into the non-woven matrix that in turn was controlled by wetting the non-woven, or by varying the polymer concentration (i.e. the solution viscosity), as well as the exposure time of the solution before being immersed in water. Proper operating parameters were then defined in order to prepare membranes with controlled pore size and distribution in the range of tenths of micrometers.

Keywords: Porous membrane; membrane processes, micro- and ultra- filtration; liquid and gas filtration.

W.R. Ruziwa, N.S. Hanspal et al. COMPUTER MODELLING OF PLEATED CARTRIDGE FILTERS FOR VISCOUS FLUIDS (pages 136-144)

bullet Abstract

bullet The primary aim of this study is to develop and validate a software package for the design of pleated cartridge filters for aeronautical applications. This package is intended to develop into a cost effective, robust and reliable design tool to enable engineers to appraise the operation of a filter. A 2-D computer code has been developed to simulate both Newtonian and non-Newtonian flows in the filter. The model is based on the flow and mass transport models described by the Continuity and Darcy equations and the Convective-Dispersion equation for the porous flow region. These equations are solved by the weighted residuals finite element method. First order Taylor-Galerkin and implicit time-stepping schemes were applied for temporal discretization of the Darcy and the Convective-Dispersion equations, respectively.The streamline upwinding Petrov-Galerkin technique was chosen for the solution of the Convective-Dispersion equation to overcome the numerical problems caused by high Peclet (convection dominated) transport. Preliminary numerical experiments were based on simple geometries and the domain complexity was increased in steps to examine the model flexibility in dealing with various situations. The overall model was validated against experimental data. Domain variables of interest are velocity, pressure and concentration profiles, which are obtained through the solution of the governing equations taking into consideration the changes in the rheological properties of fluids being filtered.

Keywords: Modelling; porous flow; deadend filtration; pleated cartridge.

G.M. Queiroz, M.S. Oliveira et al. A STUDY OF THE INFLUENCE OF THE COLLECTOR ON PHOSPHATE FLOTATION IN A COLUMN (pages 145-149)

bullet Abstract

bullet The purpose of this work is to analyse the influence of some important operational variables of the flotation column. An apatite ore sample taken from the flotation circuit of the company Bunge, Araxá, Brazil, was used as test material. A laboratory flotation column was operated in discontinuous mode in order to examine two different types of fatty acid collectors, and the effects of their dilution, conditioning time and dosage. The effects of these variables on the content and recovery of P2O5 was evaluated through a factorial design.Recoveries between 32 and 55% were obtained in flotation with rice oil soap collector. This range was greater than the one observed in flotation with the soy-grape oil collector (38 to 50%). The dosage of the collector was the variable that exerted the greatest influence on the recovery.

Keywords: Flotation column; batch operation; apatite; fatty acid collectors.


Published papers: Volume 4, Issue 1

Author(s) Title, page numbers and abstract
G. Lindenthal and L. Mölter

QUICK AND RELIABLE FILTER TEST ACCORDING TO PREN-779 OR ASHRAE 52.2 WITH A NEW WHITE LIGHT SCATTERING SENSOR SYSTEM (pages 19-21)

bullet Abstract

bullet In order to characterise filters according to EN 779 or ASHRAE 52.2, the grade efficiency curve has to be determined. Therefore the particle size distribution by number of the test particles (e.g. DEHS or KCl) in the upstream and downstream positions must be measured exactly. To realise this task two experimental set-ups are generally possible, using one or two measuring devices.In this paper we first point out the basic principles for quick and reliable filter tests to the above standards. So a constant and reproducible aerosol generation, isokinetic sampling without losses of particles in the transportation tubes from the sampling point to the measuring volume and an unambiguous particle sizing and counting system are needed.

M. Oja, T. Knuutinen, P. Mörsky and H. Lehto

EVALUATION OF THE SCREEN PERFORMANCE IN A WET GRINDING CIRCUIT (pages 22-24)

bullet Abstract

bullet The purpose of this study was to find out the way to minimise the amount of fine material in a screen overflow. The experiments were carried out in the wet milling circuit that had a Derrick single-deck screen after a rod mill. The tests showed that increasing load on the screen increased the recycle load so much that the feed size distribution changed considerably. The current results suggest that the grade efficiency curve of the test screen depends on the feed size distribution.

K. Morris

CYCLONE DESIGN – AN INTEGRATED APPROACH (pages 25-28)

bullet Abstract

bullet Cyclones are widely used in industry as a cost effective means to remove relatively coarse particulate material (>25 μm) from gas flows. They are capable of much more sophisticated and fine grade separation and classification, but suffer from a lack of simple and convenient design procedures. This problem comes about, in part, from a lack of information about the problem species, but more fundamentally, from the interaction and interdependence of the physical and operational parameters, which describe the geometry and operations conditions in a cyclone.

G. Rideal, E. Mayer and R. Lydon COMPARATIVE METHODS FOR THE PORE SIZE CALIBRATION OF FILTER MEDIA (pages 29-33)

bullet Abstract

bullet For many years the main method of calibrating filter media has been via the ‘Frazer’ air permeability measurement. In more recent years the use of pore size has become more acceptable as a backup method of further calibration.Pore size measurement has been traditionally performed by the Bubble Point measurement whereby the maximum aperture size present can be related to the pressure at which a bubble appears on the top side of a wetted filter medium pressurised from below. Changes in flow rates are used to estimate the pore size distribution, while the efficiency in an actual filtration process is calculated by using a ‘tortuosity factor’ to estimate the retention properties of the filter medium. The limitation of this technique is that it is a second order method and only gives ‘equivalent’ or theoretical pore sizes often dependent on the pore structure within the filter medium.

An alternative method is the so-called ‘Challenge test’. In this method standard test dusts or glass beads are presented to a filter medium and the size distribution in the downstream flow analysed. The method gives a more absolute measurement of pore size because it measures real particles but, because the size distributions involved are often broad, there is a significant uncertainty in the measurement of the largest particles passing the filter medium.

A new set of narrow size distribution glass microsphere standards recently introduced has been used to accurately determine the filter efficiencies of double-layered woven filter media of nominal pore sizes from 20 to 200 μm. The results are compared to the more traditional method of bubble point testing and air or water permeability measurements.

R.G. Holdich, I.W. Cumming and S. Kosvintsev PRODUCTION AND USES OF METALLIC SURFACE MICROFILTERS WITH SLOTTED AND CIRCULAR PORES (pages 34-38)

bullet Abstract

bullet The filtration mechanism of a surface microfilter is simple rejection of suspended particles at the surface of the filter, in a similar way to sieving. Hence, the surface pore size of the microfilter, as viewed under a microscope, is the pore size rating of the filter. Conventional microfilters have pore sizes considerably in excess of the pore size rating of the filter; they rely on depth filtration mechanisms to retain the suspended solids – leading to internal membrane fouling and poor long-term flux performance. A method of production of surface microfilters is described in which the pore size of an existing filter is reduced by selective deposition. Methods of characterising the pore sizes of these filters include: image analysis, the bubble point test and experiments where the filters are challenged with a very low concentration of solids in suspension and analysis of the feed and permeate, to provide the rejection efficiency for each particle size, or grade.The method of production is applicable to commercial membranes for process-scale use, as well as laboratory applications. The filters are reusable, in most applications, and their use is likely to become widespread in separations involving particles within the microfiltration range. Backflushing is usually effective in keeping deposited material off the surface of the filter and fluxes in the 1000’s l m-2 h-1 result.

F. Deshun and R.J. Wakeman

INVERTING FILTER CENTRIFUGES – ADDING A SIPHON EFFECT AND AN IMPROVED CLOTH INVERSION MECHANISM (pages 39-43)

bullet Abstract

bullet The inverting filter centrifuge has a special solid transport structure. In order to improve this kind of centrifuge, two designs are put forward and discussed here. One design concerns the basket of an inverting filter centrifuge that leads to the siphon inverting filter centrifuge. The other is concerned with the solid transport mechanism of an inverting filter centrifuge. A more dependable and lower cost solid transport structure is described.

S. Judd and B. Jefferson WASTEWATER RECYCLING STUDIES (pages 43-48)

bullet Abstract

bullet This paper describes trends in wastewater recycling and highlights the potential benefits of membranes. Three case studies are used to illustrate what can be achieved with current technology.

J.P. Robinson, E.S. Tarleton, C.R. Millington and A. Nijmeijer Evidence fOR swelling-induced porE structure in dense PDMS NANOFILTRATION membranes (pages 50-56)

bullet Abstract

bullet A dense polydimethylsiloxane (PDMS) membrane was used to assess the flux and separation performance of a range of solutes (e.g. poly-nuclear aromatics and organometallics) and organic solvents (e.g. heptane and xylene). Solvent flux was modelled with the Hagen-Poiseuille equation and found to fit well with the degree of swelling influencing the effective pore size and porosity of the membrane.The rejection mechanism for low-polarity solutes was found to be predominantly size exclusion. The rejection varied with solvent type and rejections were higher in poorer-swelling solvents. For instance, the rejection of 9,10 Diphenylanthracene was 2% in a pure heptane solvent compared with 15% in xylene. It is postulated that dense PDMS membranes exhibit the characteristics of a porous structure when swollen with solvent, and that the degree of swelling impacts on the separation performance of the membrane. A comparison between the Hildebrand solubility parameters for the PDMS membrane and the challenge solvent was found to be a good indicator of flux/rejection behaviour.

Keywords: Nanofiltration, membrane, PDMS, non-aqueous, solute rejection, polymer swelling.

H. Hess and W. Höflinger Characterisation of the Resistance Behaviour and Separation Efficiency of Precoat-Layers built up during Crossflow Filtration (pages 57-64)

bullet Abstract

bullet In precoat filtration the filter aid layer can be built up by a crossflow technique. Due to selective particle deposition the structure and characteristics of the precoat-layer built up by the crossflow essentially differ from a precoat-layer obtained by deadend filtration. Thus the filtration resistance, the area mass and the separation efficiency of crossflow precoat-layers are greatly determined by the operating conditions (filtration pressure, crossflow velocity) during the cake build-up.In the first part of the paper a model for the characterisation of the resistance behaviour of crossflow precoat-layers is presented. Using this model the resistance behaviour can be described by two process specific parameters, the filter medium resistance β and a dimensionless resistance coefficient K. Both parameters can be determined from experiments at different operating conditions and their dependency on the filtration velocity determines the resistance behaviour.

The second part of the paper describes a model proposal for the estimation of the separation efficiency of crossflow precoat-layers. Based on the process specific parameters β and K a critical “cut-off” diameter can be calculated for precoat-layers built up at various operating conditions. Combining both models a new method was developed to determine the optimal crossflow velocity for the build-up of a precoat-layer with given separation efficiency and area mass with a filter aid with given particle size distribution.

Keywords: Crossflow filtration; precoat filtration; filter aid; classifying effect; selective particle deposition; separation efficiency.

P. Sedin and H. Theliander LOCAL FILTRATION PROPERTIES OF KAOLIN FILTER CAKES (pages 65-73)

bullet Abstract

bullet Simultaneous measurements of the local solid compressive pressure and local solidosity using γ-ray attenuation have been performed on kaolin during filtration. Based on these measurements, constitutive relationships for solidosity, specific filtration resistance and permeability were determined. Four different methods were used in the estimation of the parameters in the constitutive relationships. The empirical relationships fitted the data well, within the experimental error, and it was found that the estimates differed. The exponents in the relationships, on the other hand, were estimated to be almost identical and independent of the method used. The transition time between the cake build-up and expression phases was determined using three different methods, the agreement between the three methods was good. The pressure profiles at the transition were found to deviate from the assumed pressure profile used as initial condition in the commonly-used expression models, e.g. Terzaghi and Terzaghi-Voigt models.Keywords: Filtration; kaolin; local filtration properties; permeability; pressure and solidosity profiles.

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2005

Published papers: Volume 5, Issue 4

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Keywords: Filter media; pressure filtration; coated fabrics.

Published papers: Volume 5, Issue 3

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

Abstract

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

Abstract

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

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

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

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

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

Abstract

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

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

Abstract

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

Abstract

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

Published papers: Volume 5, Issue 2

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

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

Abstract

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

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

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

Abstract

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

Abstract

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

Abstract

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

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

Abstract

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

Abstract

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

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

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

Abstract

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

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

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

Abstract

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

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

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

Published papers: Volume 5, Issue 1

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

Abstract

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

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

Abstract

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

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

Abstract

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

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

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

Abstract

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

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

Abstract

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

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

Abstract

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

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

Abstract

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

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

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

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

Abstract

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

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

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

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

Abstract

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

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2007 Abstracts from the FILTRATION journal

Use the links below to view abstracts from FILTRATION volume 7:

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2008 Abstracts from the FILTRATION journal

Use the links below to view abstracts from FILTRATION volume 8:

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