BATCH DISTILLATION OF MULTICOMPONENT SYSTEMS WITH CONSTANT RELATIVE VOLATILITIES

A method is proposed for the shortcut simulation of multicomponent bat ch distillation operations. The method relies on the assumption that a given batch column can be approximated with one having an infinite nu mber of stages, so that the Underwood equations developed for the desi gn of continuous columns can be applied to evaluate the evolution of p roduct compositions during the batch. The results obtained represent t he limiting fractionation that can be obtained when the number of stag es becomes large. A rigorous, computationally efficient model is also developed within the assumptions of constant relative volatilities, co nstant molal overflows, and negligible stage holdup. Three operating m odes are considered: constant reflux ratio, constant composition of on e component in the overhead product, and total reflux. Examples are pr esented showing that the shortcut model allows close approximation to the results given by the rigorous model. The computational demand of t he shortcut model is very low, so that it can be profitably used as a tool for preliminary batch distillation process design, simulation, an d optimization.