Recessed plate press

Filter Press The filter press, one of the most frequently used filters in the early years or the chemical industry, is still widely employed. Often referred to genetically (in error) as the plate-and-frame filter, it has probably over 100 design variations. Two basic popular designs are the flush-plate, or plate-and-frame, design and the recessed-plate press. Both are available in a wide range of materials metals, coated metals, plastics, or wood. 

Recessed Plate Recessed plate press shown... 

The recessed plate press as shown in Figure 22.40 does not require a frame. The edges of the plate are extended outward, leaving a space for a cake. Recessed plate presses are somewhat simpler than plate and frame presses. A center feed as shown in Figure 22.40 is common with recessed plates. 

Recessed plate press Here, the functions of the plate and frame are combined such that cake is formed within a recess on each plate. Unlike the plate and frame press, cake thickness is restricted to 32 mm unless additional... 

Horizontal diaphragm, plate and frame, and recessed plate presses... 

Figure 6.3 Schematic diagram of the horizontal diaphragm press cycle (side view of one chamber shown and cake discharge omitted), (a) Filtration via pump (b) filtration via diaphragm (c) compression deliquoring (d) displacement washing (e) gas deliquoring. Plate and frame and recessed plate press cycles are similar but the filtration phase using the diaphragm (b) and the compression deliquoring phase (c) are omitted.

Both flush plates and recessed plates can be specified, the latter obviating the need for frames but being a little tougher on filter cloths due to the strain around the edges. Recessed plate presses are more suitable for automation, however, because of the difficulty of the automatic removal of residual cake from the frames in a plate-and-frame press. Recessed plates with no frames limit the chamber width to less than about 32 mm (to limit the strain on the cloth), whilst plate-and-frame presses allow this width to be more than 40 mm if necessary. Plate sizes range from 150 mm to 2 m, giving filtration areas up to 200 m. The number of chambers varies up to 100, and exceptionally up to 200. 

It is possible that the filtration cycle should be stopped short of maximum cake thickness, since the pressure starts to iuCTease well before that point, and filtrate rate may fall to an unacceptable level. The question of optimum cake thickness is an important parameter in filter press design. The plate and frame and recessed plate presses do not allow much freedom to vary cake thickness, very much decided by the width of the recess, should a very dry cake be required. 

The filter cake is formed at pressures up to around 8 bar, but then the diaphragm exerts a pressure of up to 15 bar or more to dewater the cake, enabling capacity increases of 50% on a corresponding recessed plate press. 

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