Fundamentals of Multistage Separation

The coexisting liquid and vapor streams associated with phase separation may be brought about by phase creation or by phase addition. Phase creation is accomplished by heat transfer to and from the column as in distillation, where heat is added in the reboiler to vaporize some of the liquid, and heat is removed in the condenser to condense some of the vapor. Phase addition is accomplished by sending an auxiliary stream to the column a liquid absorbent to an absorber or a stripping vapor stream to a stripper. 

In contrast to phase separation processes, separation of species forming a single phase may be accomplished by several flow mechanisms through membranes. Membrane separations are discussed in Chapter 18. 

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In Chapters 7 through 11, the performance of multistage separation processes was analyzed qualitatively on the basis of fundamental principles developed in Chapters 3 through 6. The objective was to gain an understanding of the different types of separation processes and columns and the factors that affect their performance. Chapters 5 and 6 employed graphical and semi-quantitative methods to represent a limited set of separation processes, namely binary distillation. Chapters 10 and 11 also used combinations of graphical and analytical methods applied to binary or ternary systems to represent speciflc classes of nonideal separations. 

Various configurations have been developed for muitistaging of fluidized beds using the pneumatically controlled downcomer, as shown in Fig. 38. Figure 38A shows the fundamental concept of multistaging of fluidized beds, with a downcomer between two adjacent beds, each downcomer being supplied with a separate stream of control gas. Consequently, there are as many control gas streams as there are stages. 

Earlier chapters use simplified and binary models to analyze in a very informative manner some fundamentals such as the effect of reflux ratio and feed tray location, and to delineate the differences between absorption/stripping and distillation. Following chapters concentrate on specific areas such as complex distillation, with detailed analyses of various features such as pumparounds and side-strippers, and when they should be used. Also discussed are azeotropic, extractive, and three-phase distillation operations, multi-component liquid-liquid and supercritical extraction, and reactive multistage separation. The applications are clearly explained with many practical examples. 

The book may be used for a methodical study of the subject or as a reference for solving day-to-day problems. It follows a logical flow of ideas within each chapter and from one chapter to the next yet each chapter is quite self-contained for quick reference. The discussion starts with fundamental principles, prediction of thermodynamic properties, the equilibrium stage, and moves on to the different types of multistage and complex multistage and multicolumn processes, batch distillation, and membrane separation operations. Although computer simulation is a central theme of this book, no previous experience in the use of simulation software is required. 

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