Pressure Leaf and Candle Filters

These units are sometimes described as pressure vessel filters the vessels used to contain the filter dements are cylindrical designs, positioned vertically or horizontally. These vessels operate in batch mode, with filter cycles similar to plate and fimne filters. The variations available in the type of elements (leaf or candle) and its position in the pressure vessel, lead to a large number of available designs [Purchas, 1981], General operating features of pressure vessel filters have been described [Bosley, 1986] these units are considered to be cleaner and more reliable than other pressure filters, provided adequate attention is given to filter cake properties. 

In this respect, a piinc al effect is the stability of the cake on the filter element. If the latter is in the vertical position, loss of pressure during the filter cycle can result in portions, or all, of the filter cake falling away from the element. On the other hand, sticking of cakes on filter media can produce difihculties in cake discharge. 

Such effects are often more inqjortant in dewatering filter cycle time than cake formation and washing practical information on the cake discharge problem [Carleton Heywood, 1983] is discussed in Qiapter 4. 

Kgure 11.48 Vertical leaf filters back-flushing and sluicing discharge (Courtesy of U.S. Filter Co., Vanpipe Co. Ltd, Burslem, Stoke, U.K.) 

filtration proceeds only on the iqiper sut ce of the leaf The latter may be provided in the form of a tray, to ensure throng washing of the cake. A typical airang noit here would be the provision of a stack of leaves or trays (iq to 25 fihei area). A fihratitni, the pressure vessel has to he opened for removal of the fiUed stadr. Nonna%, the latter would be r laced immediately with a dean stack. Horizontal leaves are also usefid in the processing of st sedimenting solids. 

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