4
Filtration in a Centrifuge The removal of a liquid from slurry by introducing the slurry into a rapidly rotating basket, where the solids are retained on a porous screen and the liquid is forced out of the cake by the centrifugal action is called Centrifugal fi ltration. Centrifugal Filt ration tends to be used when the solids content in the liquid-solid slurry is relatively low. The filtration medium may be of woven screens, fabric, non-woven fabric, paper, or a porous membrane. The configuration may locate the medium i n a plate-and-frame apparatus, on horizontal plates, as circular or flat cartridges, as a belt, as a rotary drum, or as the wall of a centrifuge. Granular beds are also somet imes used for fil tration. There are three basic types of filtration. 1. Cake filtration. The solids build up on the surface of the fil ter medium and form a cake of steadily i ncreasing thickness. This cake act ually becomes t he filter . A filter aid (e.g., diatomaceous earth) may be added to enhance the filtration. However it must be r emoved from time to time as the pressure drop becomes excessive (Hayes K, 2001). 2. Cross-flow membrane filtration. The feed is passed through a membrane or bed, where the solids being trapped in the filter and the filtrate being released at the other en d(Hayes K, 2001). When filtration is carried out in a centrifuge, it is necessary to u se perforated bowl to permit remove of the filtr ate. The driving force is the centrifugal pressure due to the liquid and suspended solids. The resulting force must overcome friction caused by the flow of liquid through the filter cake, the cloth and the supporting gauze and perforation. The resistance of the
