Short-Cut Design Procedure for Batch Distillations

Abstract

This paper presents a short-cut procedure for the design of batch distillations which is equivalent to the Fenske−Underwood−Gilliland procedure for continuous distillations. Given a separation task, we propose computing the minimum number of stages and minimum reflux ratio required to perform it by batch distillation. These parameters are quite different from the continuous Nmin and Rmin parameters for the same separation task, because of the difference in the form of the material balances (steady state in continuous but integrated differential mass balances in the batch case). We propose that they should be computed as the number of stages and reflux ratio required by hypothetical batch distillation columns that operate at total reflux or have an infinite number of stages, respectively. Then, it is shown that the performance of batch distillations does correlate in Gilliland coordinates constructed with these batch Nmin and Rmin. This produces a quite simple, straightforward method to do preliminary design of batch distillations.