From Chemical Process Equipment: Selection and Design, Second Edition
13.4. BINARY DISTILLATION
Key concepts of the calculation of distillation are well illustrated by analysis of the distillation of binary mixtures. Moreover, many real systems are essentially binary or can be treated as binaries made up of two pseudo components, for which it is possible to calculate upper and lower limits to the equipment size for a desired separation.
The calculational base consists of equilibrium relations and material and energy balances. Equilibrium data for many binary systems are available as tabulations of x vs. y at constant temperature or pressure or in graphical form as on Figure 13.3. Often they can be extended to other pressures or temperatures or expressed in mathematical form as explained in Section 13.1. Sources of equilibrium data are listed in the references. Graphical calculation of distillation problems often is the most convenient method, but numerical procedures may be needed for highest accuracy.
MATERIAL AND ENERGY BALANCES
In terms of the nomenclature of Figure 13.5, the balances between stage n and the top of the column are
Figure 13.5: Model of a fractionating tower.
is the enthalpy removed at the top of the column per unit of overhead product. These balances may be solved for the liquid/ vapor ratio as
and rearranged as a combined material and energy balance as
Similarly the balance between plate m below the feed and the bottom of the column can be put in the form
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Topics of Interest
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Overview M. F. Doherty, Ph.D. Professor of Chemical Engineering, University of California Santa Barbara (Section Editor) Z. T. Fidkowski, Ph.D. Process Engineer, Air Products and Chemicals...