Liquid filter cloth applications

Membrane processes are used to filter liquids. Instead of conventional filter materials (e.g. filter cloth, filter candles,) microporous membranes are employed with molecular size pores. First the industry had to learn how to manufacture membranes with controlled pore sizes. To optimise the filtration capacities specific filter structures had to be designed in which the liquid followed well defined flow patterns on one side of the membrane. Many different systems were developed for the varied applications, all having their advantages and also disadvantages, i.e. plate modules, tubular modules, spiral wound membranes, etc. Research and development in this field is far from being exhausted. Today membrane systems are available which are sufficiently resistant to chemical, mechanical and thermal stress. They are produced from plastic... 

Table 2.12 classifies different types of cloths for liquid filtrations, and example applications are then given in Table 2.13. These tables collate some experiences of cloth applications into a preliminary selection guide for filter cloths, giving guidance as to what types of cloths have been found suitable...

General purpose compact forms of filters for gases and liquids, also limited application in filter presses for facing filter cloth. 

PPS fiber has excellent chemical resistance. Only strong oxidising agents cause degradation. As expected from inherent resia properties, PPS fiber is flame-resistant and has an autoignition temperature of 590°C as determined ia tests at the Textile Research Institute. PPS fiber is an excellent electrical iasulator it finds application ia hostile environments such as filter bags for filtration of flue gas from coal-fired furnaces, filter media for gas and liquid filtration, electrolysis membranes, protective clothing, and composites. 

By comparison, because it is not uncommon in liquid filtration applications for cloths to be removed from the filter and subjected to a laundering operation, a laboratory test programme has to be devised that will reproduce the mechanically induced... 

A wide variety of filter media are available to suit most applications. Selection of a medium must take into account many factors and requires testwork to be undertaken to evaluate the suitability of a medium for any application. Bearing in mind the critical role played by the medium in a filtration process insofar as an incorrect selection may prevent correct functioning of the filter or lead to high running costs, or it may cause too frequent downtimes, or lead to a liquid product of low quality or to overly wet cakes selection of an appropriate medium becomes self-evident. An investment in cloth selection can prevent avoidable costs after installation of the filtration system. 

Chemicaiiy-Resistant Fibers. Fibers with excellent chemical resistance to corrosive and/or chemical warfare agents or extreme pH conditions (eg, very acidic or very alkaline) were initially used for protective clothing. However, applications for filtration of gases and liquids in numerous industrial facilities are now more important. For example, PPS is suitable for use in filter fabrics for coal-fired boilers because of its outstanding chemical and heat resistance to acidic flue gases and its excellent durability imder these end use conditions. Many high tenacity fibers are also chemically inert or relatively unaffected under a variety of conditions. Aramids, gel spun polyethylene, polypropylene, fluorocarbon, and carbon fibers meet these criteria and have been used or are being considered for applications where chemical resistance is important. 

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