Fluid Mechanics for Chemical Engineering

Chapter 17

Centrifugal Separation

Centrifugal separation of solid particles in a fluid, but also of non-miscible droplets in another liquid or of gas bubbles in a liquid, is a frequently employed process. Its principle has already been described in the previous chapter on the basis of the BBOT equations.

This chapter deals with several important applications. It describes in sections 17.4–17.7 the principles of dimensioning apparatus such as centrifuge decanters, centrifugal separators, centrifugal filters, and hydrocyclones. It seeks to describe the dimensioning methodology by considering simple but illustrative configurations based on real-life cases. It is not a substitute for technical documentation regarding centrifugal apparatus, which can be found in various technical publications.¹ The flow models employed are rudimentary. The flows encountered in centrifugal apparatus are classified into two typical flows, solid-body rotation on the one hand and vortex flows on the other hand. These are described in section 17.2. In order to understand the reasons that cause either of those flows to be produced in the different apparatus for centrifugal separation, it is necessary to have some theoretical knowledge, such as the notions of circulation and velocity curl, as well as Kelvin’s theorem. These are introduced in section 17.1.

Separation criteria are fundamentally different depending on whether the fluid flow is of solid-body rotation type or vortex type. By way of example, the ...