Filter presses 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. 

Membrane Filter Press. Membrane filter presses use impermeable, flexible membranes, or diaphragms to squeeze the cake for further cake deliquoring, as shown in Fig. 15. This type of filter provides less dead time in a filtration cycle, better washing, and drier cake compared to traditional plate-and-frame and recessed plate filter presses. A comparison of a recessed press operated at 100 psi and a membrane filter operated at 25psi for sludge dewatering is shown in Table 4. ... 

Group A Filter press containing plate and fimnes (flush plates) or recessed plates. 

Multi-element candle Multi-element leaf Plate frame press Precoat Nutsche and multielement leaf Precoat plate frame press Recessed plate filter press Sheet filter Single leaf Nutsche Bag Cartridge Dead-end membrane Fibre bed Low shear crossflow Sand bed Simplex strainer Belt press Duplex strainer High shear crossflow Rotary disc Rotary drum Sand bed Tower press Diaphragm filter press Expression (screw) press Horizontal element tube press Vertical diaphragm filter press Vertical element tube press... 

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. 

Both flush plates and recessed plates can be specified. Recessed plates obviate the need for the frames but are tougher on filter cloths due to the strain around the edges. These presses are more suitable for automation 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 32 mm to limit the strain on the cloth, whereas plate-and-frame presses allow this to be more than 40 mm if necessary. 

The vertical recessed plate automatic press is shown schematically in Figure 15. Unlike the conventional filter press with plates hanging down and linked in a horizontal direction, this filter press has the plates in a horizontal plane placed one upon another. This design offers semicontinuous operation, saving in floor space, and easy cleaning of the cloth, but it allows only the lower face of each chamber to be used for filtration. 

The vertical recessed plate automatic press, shown schematically in Figure 15 and described previously, is another example of a horizontal belt pressure filter. Cycle times ate short, typically between 10 and 30 minutes, and the operation is fully automated. The maximum cake thickness is about 35 mm washing and dewatering (by air displacement) of cakes is possible. Apphcations include treatment of mineral slurries, sugar, sewage sludge, and fillers like talc, clay, and whiting. 

Recessed-plate filter press. This press is similar to the plate-and-frame press in appearance but consists only of plates (Fig. 18-113). 

Both faces of each plate are hollowed to form a chamber for cake accumulation between adjacent plates. This design has the advantage of about half as many joints as a plate-and-frame press, making a tight closure more certain. Figure 18-114 shows some of the features of one type of recessed-plate filter which has a gasket to further minimize leaks. Air can be introduced behind the moth on both sides of each plate to assist cake removal. 

For many years the plate-and-frame systems have used flush plates with separate frames to contain the cake. These filter presses had many sealing surfaces which were the main cause for leakages. As a result recessed plates were introduced in order to cut the number of surfaces in half and reduced the problem of drippings. The development of recessed plates has gone hand in hand with advances in cloth technology which enabled three-dimensional stretching as opposed to simple plate-and-frame where the cloth remains in one plain. Present recess depths are 16, 20 and 25 mm so the corresponding cake thicknesses are 32, 40 and 50 mm at... 

The filter press is one of two main types, the plate and frame press and the recessed plate or chamber press. 

The filter presses play a significant role in the SLS industry, where it is unnecessary to operate in a closed atmosphere. The most typical filter presses is the plate-and-frame filter press. The recessed filter press and the membrane filter press are revised, based on the plate-and-frame filter press. 

Alliot, E.A. Recessed plates, plate and frame, filter press their construction and use. J. Soc. Chem. Ind. 1920, 39, 261-28 5T. 

FIG. 18-126 Automated recessed-plate filter press used in mineral applications. (Dorr-Oliver EIMCO.)... 

Filter presses play an important role in SLS since the nineteenth century. They are used when enclosed operation is not reqnired. An excellent treatment of practical problems enconntered with presses was provided by AUiot (1920). There are basically three types of filter presses plate and frame, recessed, and membrane (diaphragm). 

The principle of pressure filters differs from that of vacuum filters only in the fact that a positive rather than a negative pressure is used to force the filtrate through the filter membrane. On this account, pressures as high as feasible can be attained. Consequently, materials not filterable on vacuum filters may be handled by this means. Filter presses are of three general types those employing both plates and frames, those using recessed plates, and continuous rotary pressure filters. 

FIGURE 58.3 Recessed-plate filter press. (From Shirato, M. etal.. Filtration—Principles and Practice, eds. M. J. Matteson and C. Orr, Marcel Dekker, New York, pp. 299—423,1987. With permission.)... 

Classification of automatic filter presses now in practical use are as follows recessed-plate type and plate-and-frame type lateral type and vertical type fixed filter-cloth type and filter cloth-traveling type. 

Most automatic filter presses are of the recessed-plate type because of its simple structure and high pressure. With the lateral type, filter chambers are formed when perpendicular filter plates are placed together in a horizontal direction. The lateral, fixed-cloth filter press has a cloth hung in an inverted V shape between the plates so that the cloth becomes inclined when the filter plates are opened, prompting the ranoval of cake on it (Figure 58.10). The cloth-traveling type (Figure 58.11) moves an endless filter cloth between the plates to peel off the cakes. 

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