Fluid–Solid Separations by Free Settling

This chapter deals with the fluid–solid separation techniques employed widely in chemical and allied processing applications. Due to significant difference in the density of fluids and solids, gravity is frequently used as the driving force for such a separation. At low concentration of solids in the mixture to be separated, settling can occur with little interparticle interactions and one can thus use the settling velocity of a single particle to size such as settling ponds or chambers. At high solid loading, interparticle interactions retard the separation. However, to speed up the rate of separation, it is common to employ centrifugal force which can create up to effectively thousands of g values. These devices are called hydrocyclones or aerocyclones, which are available for very high processing capacities and if designed properly, lead to good separation efficiency too. In this chapter, their working principles are described, which are combined with the heuristics to design or select the most suitable equipment for a given duty. However, their performance is strongly dependent on the detailed geometrical design.