Optimal startup procedures for batch distillation

Abstract

Operation of a conventional batch distillation column can be conveniently described in three parts: 1) startup period, 2) production period and 3) shutdown period. For standard separation processes, the production period is the most time consuming. However, for difficult separations, such as for high purity or azeotropic separations, the startup time may also be significant. In this paper, we present results for optimal operation of a number of different separations taking the startup time into consideration. It is generally found that the startup time is significant compared to the total operating time for difficult separations (high purities and recoveries) and when the combined column and condenser holdup is large. It is also found that the exact value of the startup time is of limited significance unless it is very different from the optimal value. Alternative ways of reducing the duration of the startup period are discussed.