Experts in filtration and separation

We advance and disseminate knowledge in the design and use of filtration and separation techniques in industry, commerce and other walks of life.

Volume 8, Issue 3 Abstracts from the FILTRATION journal

GUARANTEE HIGH DUST COLLECTOR EFFICIENCY AND PRESERVE PROFITS
A. Dotti (pages 194-197)

Tyco Environmental Systems, through its Goyen and Mecair brands, provides a unique service to fabricators of dust collectors and those who use them. The GOCO software accurately models the cleaning of filters in on-line reverse pulse jet applications. This tool allows the full optimisation of the dust collector’s filter cleaning system taking into account the details of the particular application. More than ten years of operation and improvement to the software have shown GOCO to be a highly effective way to eliminate risk in the design and minimise operating costs associated with filter replacements and compressed air energy.

Now, the global experience and capability of Goyen Mecair is taking the GOCO configuration a step further by supplying the complete cleaning system ready to go to the fabricator. Such capability markedly reduces the fabricator’s risk of a failed filter cleaning system.

AHLSTROM DISRUPTOR™: NANOALUMINA FIBRE WATER FILTRATION MEDIA
R. Komlenic (pages 197-201)

Historically, there have been relatively few significant changes in filter media. With its natural electrokinetic potential and the ability to function through both electroadhesion and mechanical entrapment to effectively remove viruses, bacteria and particulates at high flow rates, nanoalumina fibre based Disruptor™ technology represents one such change. It is a multifunctional depth filter medium, effective for many water polishing applications. The nanoalumina media can also be used as a support scaffold for a wide range of very fine or nanopowders to impart compound specific adsorbance.

MICROFILTRATION WITH ROTATING MEMBRANES
Y. Taamneh and S. Ripperger (pages 202-207)

In many processes in the chemical industry and in environmental techniques it is necessary to separate finely dispersed solid/liquid systems in order to get either the regenerated solids or the solid-free liquid. Membrane filtration often relies on the presence of a shear stress at the membrane surface to reduce the accumulation of foulants. In classical crossflow filtration with membrane modules, the shear stress is brought about by tangential flow along the membrane surface which leads to pressure drops. For high concentration suspensions, the shear stress to reduce fouling may be so high that the required flow rate would induce an unacceptably high pressure drop. In cases of fractionation or classification a uniform trans-membrane pressure is needed for a high efficiency separation. For the rotating disc filter, the shear stress and flow are not alike since shear stress is only a function of the rotational speed. Therefore, these filters appear to be most applicable to the filtration of high concentration suspensions. Commercially, rotating disc filters have been implemented both as membrane discs rotating between stationary baffles and as fixed membrane discs next to rotating baffles.

In the following, filters with rotating membranes will be presented and their special advantages explained. The multi shaft disc (MSD) separator is designed in such a way that the membrane discs are mounted on two hollow shafts and form a shear gap. The opposite movement of the discs enhances the shear stress over the surface of the membranes. The solid/liquid separation process using such rotating membranes is often performed as a continuous operation to ensure an uninterrupted production process and a high efficiency (high filtrate flux at minimum energy input). Experimental results with an MSD separator and centrifugal disk (CD) filter are presented. The machines could be used as a new classification technique for the separation of a fraction of very fine particles, thereby avoiding cake formation.

A STUDY OF THE MECHANISM OF WET AND DRY FILTRATION USING NIST TRACEABLE GLASS MICROSPHERES
G. Rideal, E. Roberts, A. Stewart and J. Storey (pages 207-210)

This work investigates the performance differences in filter media depending on whether the challenge test is conducted in the dry state or using a liquid suspension of microspheres. Comparisons of filter cut points between a pulsed air flow and a single pass liquid suspension method were used to investigate the mechanisms of filtration. Depth filtration effects were examined by comparing 2-dimensional filters (precision electroformed filters) to moderate depth filters (pillow fabric and needlefelts) and a 3-dimensional depth filter (water cartridge filter). No differences were found for 2-dimensional filters but significant differences in performance were found between wet and dry analysis of 3-dimensional filters. There was little evidence of secondary filtration in the suspension method for concentrations from 0.2% down to 0.025%.

DEFOULING OF POLYMERIC MEMBRANES DURING MICROFILTRATION PROCESSING USING ULTRASOUND IN VARIOUS MEMBRANE MODULES
A. Maskooki, S. Ali.Mortazavi and A. Maskooki (pages 211-217)

The cleaning effects of ultrasound on the surfaces and pores of polymeric membranes have been proved for many years. In this paper, the defouling of three kinds of membrane at various ultrasound frequencies were investigated. The three membrane modules, hollow fibre, flat sheet and spiral wound were cleaned by irradiation at 28, 45 and 100 kHz and a constant intensity of 300 W during forward flushing with ultrapure distilled water for 30 mins. after fouling by 1% skimmed milk. The statistically analyzed results showed that the best cleaning effects are obtained for the hollow fibre membrane, using all tested frequencies during the first 5 mins. of ultrasound application; this is due to the lack of barriers such as a holder or membrane support in the module design. Although cleaning effects were observed for the flat sheet membrane module using ultrasound, especially at a frequency of 28 kHz, the cleaning efficiency at the same conditions was lower than for the hollow fibre system. The stainless steel and acrylic holders used in the module design prevented sonic power from reaching the surfaces and pores of the membrane which may be mostly due to turbulence of the feed and permeate solution by ultrasonic waves. The minimum ultrasonic cleaning effects were obtained with the spiral wound membrane module in which only the outside layers were affected. This is a consequence of the special module design and the barrier effects of the configuration and membrane holders.

POLYELECTROLYTE CONDITIONING EFFECT IN SLUDGE ELECTRODEWATERING
H. Saveyn, G. Pauwels, R. Timmerman and P. Van der Meeren (pages 218-224)

Activated sludge is known to poorly dewater due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering of sludge can enhance the dewaterability by the electroosmosis effect.

A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge compared to mere pressure dewatering. It was found that application of the electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered pressure dewatering, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.

CHARACTERIZATION OF SLUDGE FILTRATION
H. Yukseler, U. Yetis and I. Tosun (pages 224-229)

Buchner funnel filtration tests using an activated sludge obtained from a nearby wastewater treatment plant are analysed in the light of the multiphase filtration theory which states that the controlling factor in filtration is not the resistance of the cake but the resistance of the cake-septum interface. Experimental results indicated that the pore size of the filter medium strongly affects the filter performance. It is concluded that up-flow Buchner funnel experiments must be carried out using an industrial scale filter medium.

A NOVEL METHOD FOR IMPROVING LOW SEPARATION PERFORMANCE OF TOLUENE FROM N-HEPTANE VIA EMULSION LIQUID MEMBRANES CONTAINING SUBSTITUTED CYCLODEXTRINS AS CARRIERS
M. Chakraborty and H.-J. Bart(pages 229-237)

The selective separation of toluene from n-heptane is investigated using unsubstituted α-cyclodextrin (αCD), β-cyclodextrin (βCD) and also with two substituted CDs as a carrier in oil/water/oil-type emulsion liquid membranes. The separation factor for toluene to n-heptane is evaluated from the extraction of an equimolar mixture of toluene and n-heptane. βCD shows the highest selectivity followed by αCD, hydroxypropyl-αCD and hydroxypropyl-βCD. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: contact time, concentration of carriers, volume fraction of the membrane phase and the relative amount of solvent. The dispersed drop sizes as well as internal droplets sizes define the interfacial contact area and are important in determining efficiency of extraction and stability of the liquid membrane. The effects of carriers and interfacial tension on dispersed phase drop size, internal droplets size and size distribution are also systematically investigated.

NUMERICAL STUDY OF FLOW AND PRESSURE CHARACTERISTICS FOR DIESEL PARTICULATE FILTERS WITH SQUARE AND TRIANGLE CHANNELS
X. Zhang (pages 238-247)

In a previous paper the effects of filter wall permeability, channel length and width, as well as inlet mass flow rate on velocity distributions and pressure loss were investigated for diesel particulate filters (DPFs) with square channels. The current study is focussed on investigations of fluid flow and pressure drops inside a comparable DPF with triangle channels. Two DPFs with equilateral triangle channels are considered: one has the same channel width as the square channel DPF and the other has the same total open frontal area. A triangle structure with the same channel width has more individual channels and larger total filter wall surface area. The total filter wall surface area is the same when both structures have the same total open frontal area.

The effects of filter wall permeability, channel length and width, as well as inlet mass flow rate were studied by 3-D numerical simulations. The velocity profiles along the centrelines of channels, as well as inside the filter wall, are compared. For the same channel width and length, triangle channels result in much lower filter wall velocity and much higher velocity along the centrelines of inlet and outlet channels which leads to higher pressure loss. For the triangle channel geometry, flow transitions are observed as wall permeability increases or channel length increases and (compared with square channels) the transitions occur at much lower wall permeability and shorter channel lengths. Flow transition is delayed for an increase of channel width. The optimal channel length for triangle channels is dependent on channel width and a correlation is given. Results show that a much smaller optimal channel length is required compared to a square channel with the same channel width. The advantages and disadvantages of using triangle channels are discussed regarding pressure loss and soot loading capacity.

A NEW METHOD TO OBTAIN INFORMATION ABOUT THE PORE SIZE DISTRIBUTION IN MICROPOROUS POLYMERIC MEMBRANES
J. Llorens, P. Marco, J. Sabaté, M. Pujolà, I. Felip and E. Plumed (pages 248-251)

Transport measurements of selected fluids through porous membranes provide information on precise statistical moments of the membrane pore-size distribution (PSD). It is assumed that membrane porosity, εT, is distributed on different pores sizes which are statistically distributed. Mean pore sizes are determined on the basis of statistical moment analysis. This paper focuses in the special case of determining PSD in microfiltration (MF) membranes from a collection of experiments that include porosity and bubble point determinations and liquid and gas permeations.

INTERDEPENDENCE OF FINE PARTICLE FILTRATION PERFORMANCE AND DUST LOAD FOR ELECTROSTATIC MEDIA
J.A. Schütz (pages 252-258)

In this paper changes of penetration and pressure drop in electrostatic filter media that are caused by the capture of fine particles from a gas stream passing through the medium are approximated by a set of fit functions. These functions are shown to provide excellent representations of experimental data obtained from an electret split-fibre medium, a highly charged tribo-electric medium and an uncharged needlefelt. The media are benchmarked by relative comparisons of respective quality factor dependencies.

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