Geometric behavior and minimum flows for nonideal multicomponent distillation

Abstract

A simple algebraic method for calculating the minimum flows for nonideal multicomponent distillation columns has been developed. The method, which is based on an analysis of the geometry of the composition profiles in the state space, is quite general and applies to ideal, nonideal and azeotropic mixtures. Using the set of composition transforms developed by Barbosa and Doherty (1988, Chem. Engng Sci. 43, 1523–1537), the procedure can be extended to include multicomponent reactive distillation columns. For systems with constant relative volatilities, our method and Underwood's method are shown to be identical. The technique provides an accurate and efficient procedure for determining the minimum flows without the necessity of lengthy iterative schemes, as is the current practice. The method is demonstrated using several different multicomponent systems, including the mixture acetaldehyde—methanol—ethanol—water, which exhibits a pair of binary azeotropes, a ternary azeotrope, and a simple distillation boundary in the three-dimensional composition state space.