Optimal operation policy for total reflux and multi-effect batch distillation systems

The optimal operation policy which minimizes energy consumption is derived for a total-reflux-type batch distillation system and for a new type of separation system called 'multi-effect batch distillation system (MEBAD)'. The results of optimizations for the binary system show that the separation performance of the total reflux column is increased remarkably by optimizing the reboiler hold-up as a function of time, and that the performance is the same or even better than that of the rectifying column if the hold-up is optimized. The MEBAD can be regarded as a heat-integrated batch distillation system. Thus, for ternary systems the separation performance of the MEBAD is better than the conventional batch distillation column even if the hold-up of each vessel is kept constant during the entire operation period. Furthermore, the simulation results indicate that by optimizing the hold-up of each vessel as a function of time the separation performance of the MEBAD can be improved to the level of a continuous distillation system. (C) 1999 Elsevier Science Ltd. All rights reserved.