Multicomponent Distillation Mass Transfer Models

Distillation trays are so simple... Sieve tray decks are, after all, hardly more than sheets of metal with a few holes punched in them. This of course is part of the fascination—that the behavior of something so simple can be so difficult to predict with regard to its hydrodynamic and mass transfer performance. 

Distillation retains its position of supremacy among chemical engineering unit operations despite the emergence in recent years of many new separation techniques (e.g., membranes). In fact, when choosing a separation scheme the first question that is usually asked is Why not distillation (King, 1980). 

It is beyond the scope of this book to describe distillation equipment at any length in depth treatments are available in, for example. Smith (1964), Billet (1979), King (1980), Fair (1984) Lockett (1986) and Kister (1992). However, some comments are needed to place the material in Chapters 13 and 14 in their proper context. 

Distillation is most frequently carried out in multitray columns, although packed columns have long been the preferred alternative when pressure drop is an important consideration. In recent years, the development of highly efficient structured packings has led to increased use of packed columns in distillation. 

The design of both types of distillation columns is a fascinating subject to which a great many books and papers have been devoted (some were cited above). The modeling of mass transfer on distillation trays and the use of these mass transfer models in the simulation of multicomponent distillation and absorption columns are the aspects of the process design function that we shall consider in this book. 

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