Filter area, plate selection

Wet cakes can be produced by sending concentrated slurries to filters operating under pressure or vacuum. Liquid passes through a porous barrier (filter media), which retains most of the solid particles to form a wet cake. Filters are designed to operate either continuously (e.g., the continuous rotary-drum vacuum filter or the rotary pan filter) or batchwise (e.g., the plate-and-frame filter or the pressure leaf filter). Table 16.32 contains f.o.b. purchase costs for most of the widely used filters. All costs are based on filtering area, which must be determined by laboratory experiments with a handheld vacuum or pressure leaf filter. For preliminary cost estimates, in the absence of such tests, select a continuous rotary-drum vacuum filter operat-... 

A first step in the selection of a suitable filter of tins type is to dedde on the area required fl>r filtration. Provision of this area will be dedded 1 the size of plate selected and the corre anding number the filter area provided in each chamber (approximate twice the area availableperplate)willvaiyfitnndes todeagna8 ownin Table 11.5. 

Table 11.6 Filter area and economic plate selection...

Restriction of the first fines by poor drainage will increase the probability of retention by the medium, with concomitant bfinding. On the other hand, the modem dinqiled filter plate used in conjunction wife properly selected filter media has reduced the fiequoicy in fire use of backing cloths. An exan le of fee latter is described below in fee section dealing wife industrial information. An altemative to backing cloth is the use of reinforced filter febric in fee flmrge and stay-boss areas of the filter. See Section 4.4.11 below. 

The leaf and plate filters are batch filters, and a critical element in their selection is the capacity of the filter for the amount of cake to be treated in a single batch. Flow through the filter will depend upon the nature of the suspended soUds and their concentration, the liquid viscosity, the pressure available, and a number of other variables. The acceptable value for the flow rate through the filter medium will normally be measured in a test rig. Then the filter can be sized from the calculation of required area ... 

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