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.

2014 programme The Filtration Society programme for 2014

FILTRATION SOCIETY 50TH ANNIVERSARY CONFERENCE

The Filtration Society invites you to a landmark conference at the Riverside Innovation Centre in the historic city of Chester on 13-14 November 2014.

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This 2 day conference will mark the 50th Anniversary of our foundation and our aim is not only to celebrate the last half century, with a look back on our history, but also to look at the future of our diverse and important field. A number of leading authorities from around the world are already committed to speak and more are currently being added.

Alongside the conference, there will be an exhibition, featuring the latest technologies in wet and dry filtration and there will be plenty of opportunities to catch-up with old acquaintances and meet new people who are driving progress in business, research and the application of filtration.

Chester is a beautifully preserved city with Roman and Medieval history on show. On the evening of 13 November we will be holding a dinner to celebrate our Society in a more relaxed atmosphere. The city offers plenty to see in quiet moments, or for those not participating directly in the conference.

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The conference flyer, including a draft technical programme and registration details, is available here.

If you need more information about attending the conference or exhibiting then please contact the Honorary Secretary, Dr Steve Tarleton at steve.tarleton@ntlworld.com.

Book and pay online now.

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Volume 14, Issue 2 Abstracts from the FILTRATION journal

FINE MICROPOROUS FILTER MEDIA FOR INDUSTRIAL PROCESS FILTRATION
Shireesh Pankaj, Dominic Baron, Trevor Sparks and Richard Lydon (pages 84-86)

AzurtexTM and PrimaporTM is a family of filter media products from Clear Edge filtration that incorporate a microporous coating onto, and into, the surface. Over the last number of years, Clear Edge has developed this product for a variety of fine and ultrafine filtration applications, including titanium dioxide, kaolin, gold tailings etc. Clear Edge has developed a body of knowledge in fine filtration applications and built-up a strong scientific understanding using its state-of-the-art laboratories to understand the chemistry and structural properties required for solid/liquid filtration.

It is shown that microporous coatings improve blinding resistance, enhance throughput and improve filtrate clarity; these properties are mainly attributed to the surface filtration effects. The gain in productivity is also reflected by increased retention efficiencies and abrasion resistance of the coated media. The findings from a number of case studies show that the most economically viable solution for fine industrial process filtration is microporous coated media.

REGENERATION OF A CERAMIC FILTER MEDIUM
Riina Salmimies (pages 86-91)

In this paper it is shown how the ceramic filter media used for the dewatering of iron ore, both hematite and magnetite concentrates, can be regenerated to full initial permeability using oxalic acid washing. However, regeneration of the filter medium might not always be consistent with particle dissolution as this process could have stopped but changes in performance of the filter medium can still be seen. Furthermore, the dissolution of particles could still be ongoing although most of the initial permeability was already restored. Results indicate that changes in pore size distribution explain the increase in permeability. As more pore volume is liberated, so permeability increases, although, such data cannot differentiate between complete and partial blocking of the medium pores.

MODELLING FILTER CAKE CAPILLARY PRESSURE CURVES USING A DISTRIBUTION FUNCTION: EFFECT OF PARTICLE SIZE DISTRIBUTION
Jose Angel Sorrentino (pages 92-100)

Capillary pressure curves have been determined for a long time in both filtration technology and oil reservoir evaluation with different aims, but with quite similar modelling tools. It has been always accepted that the existence of a capillary pressure curve is the result of the pore size distribution (PSD) prevailing in the porous medium, otherwise, all pores in the porous bulk (cake or reservoir) would drain or fill to the same pressure. However, modelling of the capillary pressure curve has been mainly done in accordance with the work of Corey and Brooks1. This approach is based on the demonstrated fact that a double logarithmic plot of capillary pressure vs. pore saturation leads to a straight line, except in the neighbourhood of saturation (S) equal to one, where a concavity is present. Although that form has not been detected due to insufficient resolution of the measurement, it has led to the use of a very simple model based on the power function which has been extensively used by oil-related researchers to calculate relative permeabilities.

This paper incorporates the quite simple concept that if the capillary pressure curve represents a PSD then a distribution function should be used to fit it. Therefore, different distribution functions were applied. Normal and log-normal functions fail to fit the well known, straight line behaviour of the double log plot. Power functions satisfy this criterion, but only the Rosin-Rammler-Sperling-Bennett (RRSB) function was able to produce linear behaviour as well as a concavity near S = 1. Although mathematical handling of the RRSB function is more difficult, presently available computer programs provide the required capability. This approach was used to fit capillary pressure data obtained from filter cakes constructed from custom mixtures of limestone particles that were prepared by varying geometrical standard deviations between 1 and 3 to ensure a broad data spectrum.

The use of the proposed model allows a general plot for reduced saturation that yields reasonably consistent capillary pressure curves for all the tested mixtures. The parameters of the RRSB distribution were correlated with PSD data: Sr and pk’ as a function of the Sauter mean diameter (xSV) and the PSD index, ξ, with the PSD geometrical standard deviation, σg,3.

MICROBIAL AEROSOL FILTRATION: INFLUENCE OF HUMIDITY ON HVAC
FILTER COLONISATION AND THE CONSEQUENCES ON FILTER RELEASE
Audrey Forthomme, Aurélie Joubert, Yves Andrès, Xavier Simon, Philippe Duquenne, Denis Bemer and Laurence Le Coq (pages 100-108)

Microbial aerosols are captured by HVAC filters and can colonise those filters in appropriate conditions. The aim of the study is firstly to examine the influence of humidity at fixed temperature on microbial growth for two HVAC filtering media (synthetic and glass fibre), and secondly to estimate the microbial release downstream of these filters after microbial growth. An experimental setup has been developed to homogeneously contaminate several filters simultaneously by nebulising a microbial consortium composed of bacteria cells and fungal spores.

After filter contamination, the growth of microorganisms onto the filters and measurements of microbial release from the filters were studied after latency in specific conditions of humidity and temperature during 48 h and 168 h (which simulate stops of HVAC systems during a weekend and a holiday week). Microbial growth onto the filters was evaluated after extraction by CFU counting. In order to study release the tested filters were placed in a column where airflow, representing a restart of the HVAC ventilation, was imposed. The microorganisms released downstream of the tested filters were recovered by a high efficiency collection filter and evaluated by CFU counting.

FILTERABILITY OF MINERAL SUSPENSIONS PREDICTED WITH THE ANALYTICAL PHOTOCENTRIFUGE: METHOD OF MULTISTAGE CENTRIFUGATION
Maksym Loginov, Nikolai Lebovka and Eugene Vorobiev (pages 109-120)

This article describes an experimental procedure and data analysis for characterising the filterability of mineral suspensions with the help of a new method of multistage centrifugation (MC). MC is based on the combination of two experiments: centrifugal sedimentation-consolidation in a centrifuge tube with an impermeable bottom, and centrifugal compression-permeability in a centrifuge tube with a permeable bottom (filtration cell). The experiments were performed at different centrifugal accelerations with the help of the analytical photocentrifuge. The application of MC requires a relatively small quantity of suspension (a few millilitres).

The analysis of experimental data yields the constitutive equations, namely the dependence of local permeability on particle volume fraction, and the pressure dependencies of local filter cake dryness and local specific cake resistance. MC was used for characterisation of the model suspension of calcium carbonate. Application of MC allowed the estimation of specific resistance in the pressure range 104 to 105 Pa. The values of specific cake resistance, obtained with the help of MC, were in good correspondence with those determined from conventional constant pressure filtration experiments. The pressure dependence of specific cake resistance obtained by MC was also comparable with that estimated for a lower pressure region (103 to 104 Pa) by the method of centrifugal consolidation as proposed by Loginov et al.1

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Volume 14, Issue 1 Abstracts from the FILTRATION journal

CLEANING HOLLOW FIBRE MEMBRANES DURING AND AFTER MICROFILTRATION USING ULTRASOUND
Abdolmajid Maskooki (pages 22-30)

Membrane technology is recognised as one of the most promising separation technologies of the past 30 years. The greatest disadvantage of the technology, particularly in microfiltration (MF) and ultrafiltration (UF) processing, is fouling. The fouling phenomenon occurs due to plugging of surfaces and pores of a membrane that is created by organic and inorganic particles and results in the gradual decrease of permeate flux. Therefore, the fouling process must be prevented during a filtration or be removed by cleaning techniques after the separation process has taken place.

In this study, various frequencies (28, 45 and 100 kHz) of power ultrasound were applied during and after crossflow microfiltration in order to evaluate the cleaning efficiency in hollow fibre membranes. Results showed that permeate flux rate for all treated membranes was increased significantly by decreasing the ultrasonic wave frequency. Maximum ultrasound effects were observed in the first five minutes of an MF process and after backwash flushing under the sonication. Maximum flux recovery was achieved when 28 kHz ultrasonic waves were applied.

EFFECTS OF POST-COATING BY GENERATING A THIN SECONDARY
PARTICLE LAYER ON SURFACE FILTRATION
Qian Zhangang and Eberhard Schmidt (pages 30-37)

Periodic cleaning is necessary in surface filtration for dust separation to limit the pressure drop, which increases as more dust is deposited. Higher cleaning efficiency can be achieved with lower adhesion of the dust cake on the substrate on the one hand and higher cohesion in the dust cake on the other. The idea of an innovative conditioning concept for surface filtration, the post-coat filtration (also called post-coating), is introduced and realised on a laboratory scale.

An additional thin particle layer is generated by the filtration of aerosols on the main dust cake before cake discharge is performed. Experiments were done on a surface filter test rig according to VDI guideline 3926-1, Application 1. Results with needlefelts as test filters, limestone as the main dust and several post-coat particles are presented and discussed. The effects of increased formation of larger cake fragments during particle layer detachment, compared to the corresponding results in cases of conventional filtration without post-coating, were observed for selected material combinations and operating conditions. Comparatively positive effects of a selected post-coat on the operating behaviour of the test filters were observed during filtrations over several filtration cycles.

USING MICROWAVES TO ACCELERATE AGEING OF AN ULTRAFILTRATION PES MEMBRANE BY NaOCl TO OBTAIN A SIMILAR AGEING STATE TO THAT FOR MEMBRANES WORKING AT THE INDUSTRIAL SCALE
Murielle Rabiller-Baudry, Cindy Lepéroux, David Delaunay, Houda Diallo and Ludovic Paquin (pages 38-48)

Looking for a laboratory scale protocol that leads to aged membranes that could be representative of the aged state obtained at the industrial scale, this paper proposes a systematic study of the degradation of a polyethersulphone (PES)/ polyvinylpyrolidone (PVP) flat membrane by sodium hypochlorite. Different protocols are compared: ageing by immersion in static conditions with or without the coupling of applied microwaves as well as in dynamic conditions, namely directly on an ultrafiltration (UF) pilot. Regardless of the protocol, the physico-chemical evolution of the pristine membrane always highlights the progressive removal of PVP and slow degradation of the PES matrix itself. The use of microwaves appears a very interesting way to significantly decrease the duration of the treatment required to damage a membrane close to the aged state at the industrial scale. Nevertheless, some limitations are also evident thanks to UF behaviour in terms of both water flux and protein filtration.

ANALYTICAL CENTRIFUGATION: IN-SITU VISUALISATION AND CHARACTERISATION OF SEPARATION BEHAVIOUR FOR FILTER FEED DISPERSIONS
Dietmar Lerche (pages 49-60)

Dispersion behaviour is important in many technical applications and especially in solid/liquid separation. While for some applications sedimentation and sediment formation have to be avoided or minimised (e.g. food products), for solid/liquid separation processing or waste recycling these are essential. Besides volume concentration and rheology of the continuous phases, agglomeration, agglutination or flocculation are crucial in this respect. It is quite common to use zeta-potential to differentiate between flocculated and non-flocculated dispersions. However, this approach is not always applicable, especially in cases of sterically or rheologically stabilised dispersions and products made from soft particles.

Analytical centrifugation based on space and time resolved detection of extinction profiles over the entire sample height was used to characterise the sedimentation and consolidation behaviour as well as particle interaction (degree of flocculation) in dispersions at their original concentration. Depending on initial turbidity of the suspension, NIR- and visible light or mono-energetic X-ray radiation was employed.
Sedimentation and consolidation behaviour of stable or flocculated polydisperse suspensions made from quartz, limestone, mixtures of metallic oxides or magnetic therapeutic carrier and enzyme coated nanoparticles were investigated by in-situ visualisation of the separation process during centrifugation. The state of a dispersion can be easily recognised by the typical fingerprint pattern of the evolution of transmission/intensity profiles. Colloidal stable dispersions (stable against flocculation, agglomeration) show typical polydisperse sedimentation behaviour, whereas flocculated dispersions exhibit zone sedimentation and gradual consolidation. Zeta potential did not always predict the state of dispersion regarding flocculation.

While the packing density for colloidal stable dispersions only slightly depends on the excess pressure acting on the sediment it strongly depends on pressure for flocculated dispersions, and it takes much longer to reach the corresponding equilibrium packing density. Instead of carrying out measurements at different accelerations it is also possible to evaluate the compressibility of sediments (or cream layers) by increasing the acceleration step-wise and recording the kinetics of the sediment (cream layer) height or sediment packing concentration. It was shown in the literature that based on these data filterability and compressive yield stress can be predicted.

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Volume 13, Issue 4 Abstracts from the FILTRATION journal

PURIFICATION OF CRUDE BIODIESEL USING POLYMERIC COMMERCIAL MEMBRANES
Magno José Alves, Suellen Mendonça Nascimento, Iara Gomes Pereira, Vicelma Luiz Cardoso and Miria Hespanhol Miranda Rei (pages 216-221)

The water washing step is a concern in biodiesel production, since it uses large quantities of clean water and generates wastewater to be treated. This paper proposes the application of a microfiltration process to purify crude biodiesel. The crude biodiesel was microfiltered in a deadend process at 1 and 2 bar trans-membrane pressure and with a membrane of 0.22 μm pore size. Observed permeate fluxes showed that there was a pronounced flux decline during the first 2 mins. of filtration. The stabilised flux was greater at 2 bar than at 1 bar, showing that a greater trans-membrane pressure enables greater fluxes. Density, viscosity and the acid value of water washed and permeate biodiesel samples were in accordance with international legislation.

Both water washing and membrane separation processes were able to reduce the amount of soap detected in the crude biodiesel. However, the proposed membrane process was not as efficient as the water washing method in reducing free glycerol content in the crude biodiesel. Especially at the highest applied pressure (2 bar), the permeate obtained was not in accordance with the legislation for free glycerol content (<0.02 wt%). The obtained results showed that the membrane process can be a suitable process for biodiesel purification. However, more specific pore size and material must be analysed in order to achieve the desired level for free glycerol content.

INFLUENCE OF WINDING PARAMETERS ON THE PERFORMANCE OF STRING WOUND FILTER CARTRIDGES – PART I
Pragnya S. Kanade and Someshwar S. Bhattacharya (pages 222-231)

Out of the many disposable filters options available, string wound cartridges/candle filters account for a significant proportion in terms of their application. Wound cartridges are produced by laying a yarn spirally around a perforated core, however, relatively little has been reported on the effect of winding parameters (such as wind ratio, yarn tension, gain etc.) on their performance. Apart from winding variables, the yarn properties, fibre fineness and testing parameters like flow rate and slurry concentration, play a deciding role in filtration behaviour.

This paper reports how wound cartridges have been produced on a newly developed filter winder with electronic controls and their performance assessed on a prototype single pass test rig. Both of these have been developed by the authors. Water or aqueous suspensions of standard test dusts were used as challenge media and comparisons between the cartridges produced on the newly developed winder and a commercial filter winder are reported. Validation tests were performed under the same test conditions. The analysis of filtrate samples was carried out to evaluate the performance of cartridges that had been formed using different winding variables.

PVSC SEWERAGE SLUDGE FILTER PRESS REHABILITATION PROJECT
Ernest Mayer, Sheldon S. Lipke, Marques D. Eley and P. Scholtyssek (pages 237-247)

Passaic Valley Sewerage Commissioners (PVSC) have experienced some sludge dewatering problems with their five ductile iron (DI) plate standard recess presses over the past 10 years. These problems are mainly associated with long dewatering cycles, filter plate scaling, press cloth blinding, and the lack of suitable lab tests for predicting performance. This paper will address these issues, provide some suitable lab test procedures, and suggest future press modifications for improved performance.

NEW CROSSFLOW FILTER MODULE DESIGN PARAMETERS: A THEORETICAL ANALYSIS OF CROSSFLOW FILTER PERFORMANCE LIMITS
Nicos H. Andreas and Christopher L. Cox (pages 247-256)

Exact analytical solutions for the pressure and flow distributions for a cylindrical crossflow filter operating at steady state laminar flow conditions are presented. New characteristic parameters and dimensionless groups that emerge from analysis of the solutions are identified and their significance demonstrated. The solutions obtained are valid only for zero fouling and quantify a performance envelope that can never be exceeded by any real crossflow filter. Two new dimensionless numbers that determine solution trends and are useful in scale up and generalization of empirical data are also identified.

Analysis is used to quantify the interdependence between the model parameters and to determine limiting values, such as a maximum crossflow filter tube length that may not be exceeded in order for solutions to be physically meaningful. The model also provides a theoretical prediction of the minimum surface area required to achieve a design average permeate flux, and can be used to design meaningful experiments and to extract model parameters from empirical measurements. The mathematical model developed and the solutions obtained can serve as a sure foundation for the rational and systematic addition of incremental complexities, e.g. variable viscosity, media fouling and cake build-up inside the tubes. Despite the simplicity of the model used it is shown that the solutions obtained provide useful tools for designers and operators of crossflow filters.

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