Abstract: A method and apparatus for controlling the density of the solids separated from a feed slurry by selectively recirculating the separated liquid component of the feed slurry to change the feed slurry's density when an unwanted density of the separated solids is detected. Further, the efficiency of the separation is increased by recirculating and recharging unused catalyst into the feed slurry where it is used to assist in the separation of the solids.

Abstract: A decanter centrifuge typically includes a bowl which is rotatable about its longitudinal axis and an independently rotatable screw conveyor mounted coaxially therein. A drive motor is provided to rotate the conveyor at a differential speed from that of the bowl, which has a separate drive motor. An engagement element, in the form of an indexing clutch, an over-running clutch or a selectively controllable clutching element, is provided between the conveyor drive motor and the bowl to simultaneously rotate the bowl and the conveyor during a cleaning in place operation of the centrifuge.