ABSTRACT
The operations are divided into two broad categories: “cake” and “depth” filtration. From the viewpoint of a driving force, cake filtration is further divided into pressure, vacuum, gravity, and centrifugal operations. In cake filtration, particles in a slurry form a deposit as a filter cake on the surface of the supporting porous medium while the fluid passes through it. After an initial period of deposition, the filter cake itself starts to act as the filter medium while further particles are deposited. In depth filtration (sometimes called filter medium filtration or clarifying filtration), particles are captured within the complex pore structures of the filter medium, and the cake is not formed on the surface of the medium. In many processes, a stage of depth filtration precedes the formation of a cake. The first particles can enter the medium, and with very dilute slurries, there can be a time lag before a cake begins to form. Smaller particles enter the medium, whereas larger particles bridge the openings and start the buildup of a surface layer. Depth filtration is generally used to remove small quantities of contaminants. Cake filtration is primarily employed for more concentrated slurries. In practice, cake filtration is employed in industry more often than depth filtration. The following discussion will be concerned with cake filtration.
