Abstract

Size separation, an important industrial unit operation, is a solid–solid separation process that produces minimally two streams from a feed stream of particles: one of coarser particles and one of finer particles. Devices that perform such separations fall into two general categories: those that separate by passing particles through apertures (screening) and those that separate using the forces of fluid dynamics (classification).

The performance of a separating device can be characterized by its size selectivity curve which, in turn, can be characterized by three parameters that describe completely the separation capability of a device. These parameters, which depend on the size of particles as well as on the design of the equipment, can also be used to predict the separation.

Size separation devices include inclined vibrating and stationary screens, probability screens, settling-pool classifiers, hydrocyclones, mechanical classifiers, free and forced vortex classifiers, and transverse flow classifiers. The separation achieved by a single unit can be improved by staging several units in prescribed configurations. Pneumatic classification systems should be designed to handle hazardous dust.