Batch pressure precoat filtration

In cake or surface filtration, there are two primary areas of consideration continuous filtration, in which the resistance of the filter cake (deposited process solids) is veiy large with respec t to that of the filter media and filtrate drainage, and batch pressure filtration, in which the resistance of the filter cake is not veiy Targe with respect to that of the filter media and filtrate drainage. Batch pressure filters are generally fitted with heavy, tight filter cloths plus a layer of precoat and these represent a significant resistance that must be taken into account. Continuous filters, except for precoats, use relatively open cloths that offer little resistance compared to that of the filter cake. 

The material to be filtered is fed into the vessel under pressure, and separation takes place with the solids being deposited on the leaf surface, and the liquid passing through the drainage system and out of the filter. Cycle times are determined by pressure, cake capacity or batch quantity. Where particularly fine solids must be removed, a layer of precoat material may be deposited on the leaves prior to filtration, using diatomaceous earth, Perlite, or other suitable precoat materials. 

Leaf and plate filters are mostly relatively simple pressure-driven filters made up of fiat filtration elements, although they can also be vacuum driven. The overall configuration of the filter may be horizontal or vertical, and the basic choice between them is often made according to the space available in the factory. They are mainly used for batch-operated solids recovery, although in combination with precoat they can also be employed for clarification and decontamination duties. 

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