Solid-liquid filtration

In the separation of solids from liquids, it is possible that the product of the operation may be (a) the liquid fraction, as in the beer industry, (b) the solids component as in pigment manufacture, or (c) both liquid and solids, as in metallurgical refining where the primary target is an electrolyte solution whilst the separated solids may contain a quantity of precious and/or semiprecious metals for separate recovery. There are still further cases where there is no product at all, the operation simply being used to clean up a liquid prior to it being used, re-used or discharged into a river or sea. 

Although textile filter media are used in numerous types of filter, the mechanisms by which the particles are captured are commonly referred to as surface straining (alternatively screening), depth straining, depth filtration and cake filtration. These mechanisms are shown in Figs 7.8a-78d. 

In surface straining/screening, the filter fabric retains particles of known size whilst smaller particles are permitted to pass through (see Fig. 78a). This mechanism, which frequently utilises monofilament fabrics with precise apertures or mesh sizes, often features in food processing such as flour or corn milling, the separation of minerals or as a precursor to more intensive filtration down line. To ensure that the apertures in the fabric do not become blocked, a vibration mechanism is frequently engaged to keep the particles moving. 

8 Filtration mechanisms (a) surface straining (screening), (b) depth straining, (c) depth filtration and (d) cake filtration. 

Although this technique is widely used to chara(4 erise pore size, other techniques are also used, not least amongst which are challenge tests (see Rideal, 2005) in which the filter medium is challenged by a quantity of calibrated micro-spheres, which are fluidised, typically by sonic means, to assist in their passage through the filter. Comparison is then made of the particle size distribution of the micro-spheres before and after filtration. 

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A.Rushton, A.S. Ward and R.G. Holdich, Solid-Liquid Filtration and Separation Technology, 1996, VCH, Weinheim, Germany... 

Ward, A. S., Rushton, A. and Holdrich, R. G. (2000) Solid-Liquid Filtration and Separation Technology, 2nd edn (Wiley-VCH). 

The preceding discussions have focused on an analysis of the most common operating modes for solid-liquid filtration. The analysis however is general, and does not allow practical calculations without further development of working expressions and more careful consideration of proper boundary conditions and assumptions. We now focus on a series of special formulas developed specifically for assessing optimum conditions of filtration. These offer simplified calculation methods that can be readily performed on a PC, and in some cases with a hand-held calculator. 

Rushton, A., A.S. Ward, and R.G. Holditch. 1996. Solid-liquid filtration and separation technology. New York VCH Publishers, 411. 

A. Rushton, A.S. Ward, and R.G. Holdich. Solid-Liquid Filtration and Separation Technology. Weinheim, Germany VCH, 1996. G.H. Hultsch and H. WiUcesmann. In D.B. Purchas, Ed., Solid-Liquid Separation Technology, London, U.K. Uplands Press, pp. 493-559,1981. 

This chapter will provide the reader with a general introduction to the more common types of solid-gas (dust collection) and solid-liquid filtration mechanisms. The raw materials, polymers, fibres, and different types of fabric construction employed in filter media manufacture and some typical fabric finishing processes are discussed in detail. A brief look at filter market developments will also be considered. 

Solid liquid filtration and separation technology / A. Rushton A. S. Ward R. G. Holdich. -Weinheim New York Basel Cambridge Tokyo VCH, 1996 ISBN 3-527-28613-6... 

Key words industrial filtration, dust collection, solid-liquid filtration, cake filtration, thermal and chemical conditions. 

Fabric constructions and yarn types for solid-liquid filtration... 

Rushton A., Ward A.S. and Holdich R.G., 1996. Solid-Liquid Filtration and Separation Technology, VCH Verlagsgesellschaft, Weinheim. 

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