8 - Incorporation of Cake Filtration Principles to the Analysis of Solid/Fluid Suparation Processes

Abstract

Besides cake filtration and expression, cake formation, growth, and/or consolidation are also present in several other solid/fluid separation operations. The present chapter is devoted to the analyses and discussions of such problems. As an example, for gas emission control, fabric filtration is often applied. In fabric filtration, particle-laden gas is passed through filter bags such that filter cakes are formed outside bag surfaces. Because of the large quantities of gases to be treated and to insure bags' repetitive use, filter bags require periodic cleaning. A study of fabric filtration therefore must be based on the principles of cake filtration and that of filter cleaning. Another example would be cross-flow membrane filtration that is an application of the so-called membrane technology, which has become popular and important in recent years. Cross-flow filtration is commonly divided into two categories: (1) microfiltration for removing particles of size ranging from 10-1 to 102 μm and (2) ultrafiltration for particles (or macromoleculars) with size up to 100 nm. Separation is achieved by the sieving effect and the membrane used functions as a sieve. The rejected (or removed) particles form cakes on the upstream side of the membrane. Unlike regular cake filtration discussed before in cross-flow filtration, the feed flow and the filtrate flow are not in the same direction. While the consequence of the cake formation is the same as that of regular cake filtration, namely, an increase of the total resistance to filtrate flow, the manner and the extent of cake formation in cross-flow filtration is quite different from the discussions given previously. This difference represents the main issues to be discussed in this chapter.