(Cream separation, Centrifugation, Tubular bowl centrifuge, Disc bowl centrifuge, Domestic cream separator)
The cream separation is a very important unit operation in dairy industry. The cream or fat is taken out of milk for standardisation purpose. Besides, cream is also required to prepare some value added products as ghee, butter, etc. Cream is usually separated from milk by the centrifugation process.
Sometimes gravity separation may be too slow because of the closeness of densities of the particle and the fluid, or because of the association forces holding components together, as in emulsions like whole milk. In that case centrifugation helps in separation of the components on the basis of differences in their densities.
• The centrifuge increases the forces on particles many fold.
• Thus the particles that do not settle readily or at all in gravity settlers can often be separated from fluids by centrifugal force.
• The relative settling velocities of small particles are not changed, but the disturbing effects of Brownian motion and free convection currents are overcome.
The equipment using this principle of separation is known as a centrifuge. The
centrifuges are used for:
• separation of immiscible liquids,
• clarification of liquids by removal of small amounts of solids, and
• for removal of solids from liquids
Centrifuges are also used for centrifugal filtration, where the centrifugal force is used (not the pressure difference) to separate the solids through a filter medium. The major applications of the centrifuges are shown in Fig. 8.1.