Continuous filtering centrifuges
A continuous centrifugal separator for coarse crystals is the reciprocating conveyor centrifuge shown in Fig.29.11. A rotating basket with a slotted wall is fed through a revolving feed funnel. The purpose of the funnel is to accelerate the feed slurry gently and smoothly. Feed enters the small end of the funnel from a stationary pipe at the axis of rotation of the basket. It travels toward the large end of the funnel, gaining speed as it goes, and when it spills off the funnel onto the wall of the basket, it is moving in the same direction as the wall and at very nearly the same speed. Liquor flows through the basket wall, which may be covered with a woven metal cloth. A layer of crystals 25 to 75 mm (1 to 3 in.) thick is formed. This layer is moved over the filtering surface by a reciprocating pusher. Each stroke of the pusher moves the crystals a few inches toward the lip of the basket; on the return stroke a space is opened on the filtering surface in which more cake can be deposited. When the crystals reach the lip of the basket, they fly outward into a large casing and drop into a collector chute. Filtrate and any wash liquid that is sprayed on the crystals airing their travel leave the casing through separate outlets. The gentle acceleration of the feed slurry and deceleration of the discharged solids minimize breakage of the crystals. Multistage units that minimize the distance of travel of the crystals in each stage are used with solid cakes that do not “convey” properly in a single-stage machine. 1,200 mm. (12 to 48 in.). They dewater and wash 0.3 to 25 tons/h of solids containing no more than about 10 percent by weight of material finer than 100-mesh.