Fluidsolid Separations

The separation of suspended solids from a carrier fluid is a requirement in many engineering operations. The most appropriate method for achieving this depends upon the specific properties of the system, the most important being the size and density of the solid particles and the solids concentration (the ''solids loading'') of the feed stream. For example, for relatively dilute systems 10% or less) of relatively large particles 100 ^m or more) of fairly dense solids, a gravity settling tank may be appropriate, whereas for more dilute systems of smaller and/or lighter particles, a centrifuge may be more appropriate. For very fine particles, or where a very high separation efficiency is required, a ''barrier'' system such as a filter or membrane may be needed. For highly concentrated systems, a gravity thickener may be adequate or, for more stringent requirements, a filter may be needed.

In this chapter, we will consider separation processes for relatively dilute systems, in which the effects of particle-particle interaction are relatively unimportant (e.g., gravity and centrifugal separation). Situations in which particle-particle interactions are negligible are referred to as free settling, as opposed to hindered settling, in which such interactions are important. Figure 12-1 shows the approximate regions of solids concentration and density corresponding to free and

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