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

Volume 7, Issue 2

DEFINITE AND QUICK CHARACTERISATION OF FRACTIONAL SEPARATION EFFICIENCIES IN UNKNOWN AEROSOL CONCENTRATIONS
M. Schmidt (pages 106-108)

In many applications, besides the laboratory, there exists a need for the exact characterisation of filters and separators, e.g. in the fields of lubrication oil separation, blow-by oil separation, automotive and engine air filters and compressed air filters. As the aerosol concentration in the different processes may change rapidly, a quick particle characterisation upstream and downstream of the filter is required.

Other problems arising are the different measurement conditions of the application with regard to, for example, the temperature, type of aerosol and pressure conditions during the process. In the past, a user tried to cover at least the problem of varying aerosol concentrations by using two particle counters upstream and downstream of the filter to perform simultaneous measurements. The difficulty in doing so is the exact comparison (calibration) of the two counters with regard to their classification accuracy, resolution and counting efficiency.

Palas® has developed the new aerosol spectrometer welas® 3000 with two integrated sensors for upstream and downstream which allow quasi-simultaneous particle size and particle concentration measurements to be carried out. The sensors may be equipped with different sizes of measuring volume in order to obtain optimised results with regard to different concentrations in a short time. Since the electrical parts, such as the lamp source and optical receiving unit of the scattered light, are the same, the device parameters of the two sensors, such as classification accuracy, resolution and counting efficiency, are the same as well.

The sensors are connected to the control unit via optical fibres. Thus, it is possible to switch quickly between upstream and downstream without losses in the sample lines by simply using an optical switch of the light connection to the sensors. The welas® system may be equipped with internal heating up to 120°C and an aerosol cuvette that is pressure resistant to 10 bar. Hence, the system can be used for the previously mentioned applications. This paper will focus on measurement results, e.g. in the field of lubrication oil separation and on measurements at pressures up to 10 bar with varying upstream concentrations.

CFD ANALYSIS ON THE EFFECT OF CALENDERING OF FILTER CLOTH ON TRANSIENT CHARACTERISTICS OF CAKE FILTRATION
K-L Tung (pages 109-112)

The effects of a filter fabric calendering treatment and the permeability of filaments with regard to the particle deposition phenomena onto or into filter fabrics at the initial stage of filtration are conducted quantitatively using a microscopic forces analysis. The flow pattern and the resistance to fluid flow in the calendered interstices were obtained numerically using the fluid flow software FLUENT™. Based upon numerical data for the continuous phase, a program was devised to simulate the transient behaviours of pore clogging and cake formation by way of the Lagrangian approach. This estimates the change of filtrate clarity during the initial stage of filtration for various calendered fabric porosities and various filament permeabilities.

Results show that in the case of tightly woven filter cloths the flow is predominantly through the yarns of the cloth, while flow will generally be directed around the yarns of a loosely woven cloth, especially if the yarn is twisted tightly. Therefore, filtrations with tightly woven but loosely twisted yarn can increase the unfavourable, but inevitable, clogging problem. The simulated results further show that although the filtration resistance of woven filter fabric increases after calendering, the permeability is rectified and the clogging of the filter pores is also improved. After the calendering of the filter fabric has taken place, only the cake formation mode (in accordance with the law of blocking for all types of pore) is evident. The critical concentration proposed by previous investigators is not observed for calendered filter fabrics.

NEW ISO STANDARDS FOR COMPRESSED AIR ANALYSIS AND FILTER TESTING
S. Smith (pages 112-116)

A large number of the International Standards used within the compressed air industry are either in the process of regeneration or are due for review. In addition, the first complement of compressed air filter testing standards, ISO 12500 Parts 1 & 2, are nearing finalisation with Part 3, Particulates, in development. Further, there are proposals to develop three additional standards for inclusion in the ISO 12500 series. This paper provides an up to date review of the position regarding these standards and details the proposed methodology for ISO 12500-3 coarse particulates testing.

RECYCLING OF PROCESS WATER USING MICROFILTRATION AND NOVEL COMPOSITE FILTER MEDIA S.
Volooj, C. Carr and R. Lydon (pages 117-123)

In this study dyebath recycling and decolourisation using a dual-flocculant system combined with microfiltration has been examined, and typically above 90% of dye removal was achieved. The effects of fluorine treatment on the surface and filtration performance properties of the composite filter media have been investigated, and filtrates with less turbidity and cakes with lower moisture contents were observed. XPS and contact angle measurement techniques were used to characterise the nature of the modification imparted by the fluorine treatment.

APPLICABILITY OF FABRIC FILTERS IN AIR POLLUTION CONTROL (APC) FOR WASTE INCINERATION PLANTS – LONG-TERM EXPERIENCE…
G.G. Pranghofer (pages 124-126)

Continuous development and improvement of high durability laminates led to a large number of reference applications in Waste Incinerators, the long-term performance of PTFE membrane filters in various configurations and different stages of APC systems is detailed. Experience has been obtained over 20 years in all stages of flue gas cleaning, e.g. collectors downstream from the boiler, downstream spray dryers and in end-of-pipe filter systems, covering a temperature range in the collector of 100 – 250°C. The results of the performance in different incineration plants is provided in this paper, including retention rates of PM 2.5, dioxins, heavy metals and, in combination with absorbents, of acidic components (SO2, HCl, HF) in compliance with BAT and the European Regulation (Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on the incineration of waste).

COMPARISON OF DIFFERENT FILTER AID PERMEABILITY TEST METHODS
W. Li, C. Kiser, Q. Richard and E. Mayer (pages 127-132)

Permeability is an important specification for evaluation and selection of filter aid products. However, there has not been a standard filter aid permeability test method in the US. Permeability results published by different companies may not be comparable due to different apparatus, filter paper, cake formation, sample amount, sample preparation, and different driving force used. The objectives of the study in this paper were to (i) investigate factors affecting permeability results in different filter aid testing methods, and (ii) develop a method and procedure providing consistent testing results on different testing apparatus. Three permeability test methods, three grades of rice hull ash and two grades of diatomaceous filter aids were involved in the study. It was found that filter paper or clogging of filter paper, testing pressure, sample preparation are critical factors affecting permeability results. A tight, low resistant and not easy to clog filter paper should be chosen for a permeability test. The testing pressure should be chosen carefully considering the compactibility of samples to be tested. Recommendations on other testing conditions are also given in the paper.

PHYSICAL MEASUREMENT OF PORES BY GLASS BEAD CHALLENGE TESTING
G. Rideal (pages 132-137)

Pore size measurement by the indirect method of porometry can produce varying results, especially for larger pores in excess of about 100 μm. Consequently, ‘bubble point’ rated filters often fail to stop the expected particles in real situations. Historical labelling of filters, and even nominal ISO standard specifications can therefore be very misleading. In this work, narrow particle size distribution glass microspheres from a few microns to several hundred microns were used as challenge particles to assess a number of filter media. A new Sonic filter tester could perform the test in 1 minute in the dry state. The challenge test results were unaffected by the porosity of the samples, unlike the porometry results where large variations were seen. In other examples, a sintered polymer air filter rated at 5 μm had a filter cut point of 140 μm while a nonwoven sand screen used in petroleum extraction rated at 125 μm had a cut point of 395 μm. Recovering and analysing trapped microspheres within the pore structure can be used to measure pore size distribution and also reveal subtle internal details in woven filter media.

TESTING FILTER MEDIA FOR LIQUID FILTRATION
R.J. Wakeman (pages 138-147)

Filter media exist in many forms and with a wide range of properties that are relevant to the filtration process. Not all media have to meet the same requirements when in service and different industries place differing demands on the media. This leads to the need and development of standards that are industry specific in some cases, or media design specific in others. The range of media available is overviewed together with some of the test methods that relate to the ability of a medium to capture contaminants from a liquid stream (other methods that relate to, for example, mechanical properties of the medium are outside the scope of this paper). Integrated within the overview are the standards that have been written by associations with responsibility for representing best practice in particular industries or by national/international standards organisations. Some directions of current research that may underpin future standards are indicated.

NON-WOVEN FABRICS AS SOLID/LIQUID SEPARATION MEDIA IN A MEMBRANE BIOREACTOR
W-K. Chang, S-H. Chuang, A.Y-J. Hu and M-C. Chang (pages 149-153)

The characteristics of non-woven fabrics as solid/liquid separation media in a MBR application have been studied in this paper. To understand the effect of particle properties on filtration performance, inorganic and microbial particle filtrations were studied simultaneously. The results showed that there was no significant decline of permeate flux during 120 h operation for inorganic particle filtration. Comparatively, non-woven fabrics were fouled rapidly for microbial particle filtration and significant decline in permeate flux was observed during experimental periods. However, low effluent suspended solids was achieved rapidly due to the denser cake layer on the fabric surface. This study has demonstrated that non-woven fabric materials could be used as solid/liquid separation media in membrane bioreactors for wastewater treatment. An appropriate operating strategy, like optimum operating flux and fouling control, is needed for long-term stable operation.

Keywords: Membrane bioreactor; filtration; fouling; non-wovens; solid/liquid separation; wastewater.

MEASURING PARTICLE DEPOSITION WITHIN FIBROUS FILTER MEDIA BY MAGNETIC RESONANCE IMAGING
J. Hoferer, E.H. Hardy, J. Meyer and G. Kasper (pages 154-158)

This paper describes the application of magnetic resonance imaging (MRI) to obtain information on local particle mass deposition within fibrous filter media. The experimental set-up used for on-line loading experiments is also detailed. The required procedure to initially gather information on filter structure without destroying it, which is required when the same filter medium is later loaded with particles, is briefly presented as is the particle size distribution of the particle material used to load the filter in comparison to a conventional test dust. Preliminary results are discussed for recording the loading process within a medium by visualizing the local deposited mass at various loading stages. By using this non-destructive measuring technique which first allows measurement of the internal fibre structure followed by loading of the medium, it will be possible to compare the data with results of simulations and thereby allow validation of kinetic filter models.

Keywords: Depth filtration; fibrous filter; gas filtration; MRI; particle deposition.

FILTERABILITY AND AGEING OF CRYSTALLINE POTASSIUM SULPHATE SALTED-OUT WITH ETHANOL AND ACETONE
M. Louhi-Kultanen, A. Llansana Arnalot, L. Nyström and J. Kallas (pages 159-167)

The desupersaturation and ageing of a solid/liquid suspension consisting of crystalline and dissolved potassium sulphate, co-solvent water and an anti-solvent, i.e. acetone or ethanol, were investigated based on image analysis, measurements of electronic conductivity and determination of certain filterability parameters. The crystals were produced by salting-out precipitation at 25°C. The samples were taken after addition of the anti-solvent in a semi-batch process by pumping the precipitant at constant flow rate or in a batch process by adding all the anti-solvent at the beginning of the precipitation process. The studied ageing time was 60 mins. Ostwald ripening theory was utilized to compare the ripening tendency in the studied solvent systems. The precipitation conditions were changed by altering the flow rate of the precipitant. The solution composition was changed by adding sulphuric acid to decrease the pH from a neutral solution pH equal to 6.2. Ageing for 60 mins. decreased the cake resistances of both studied precipitant systems whereas cake porosities varied only slightly between fresh and aged precipitate cakes.

Keywords: Filterability; ageing; stability; out-salting precipitation; potassium sulphate; desupersaturation.

TUBE SETTLERS FOR THE ENHANCEMENT OF SETTLING TANK CAPACITY
K. Fujisaki and M. Terashi (pages 168-172)

A new type settler has been developed and its usefulness was confirmed experimentally. The device arranges inclined parallel plates in the vertical direction, contrary to the usual horizontal arrangement. In this method, the separated clear water is removed directly by suction from the top end of the parallel plates. For the removal of clear water, the right and left edges of the plates are closed in order to make a tube with a rectangular cross section. These are the unique and original features of the equipment. The treatment capacity is proportional to the number of settling tubes set in the suspension, since each settling tube acts as a small settling tank. The new settling tube module was set in a final settling tank and over a wide range of sediment concentration the relationship between the suction velocity and suspended sediment concentration of effluent was investigated. Based on the results of these on-site experiments, it is demonstrated that the new tube settler system is very effective for the enhancement of settling tank capacity. A numerical estimation of the application of this system to a practical settling tank also confirms the effectiveness of the device.

Keywords: Lamella settler; settling tank; tube settler; sedimentation; thickening; clarification; sewage secondary effluent; activated sludge.