Impact of vapor recompression in batch distillation on energy consumption, cost and CO2 emission: Open-loop versus closed-loop operation

• We develop a vapor recompressed batch distillation.
• An open-loop control policy is devised for optimal use of internal heat source.
• We examine the impact on energy savings, cost and CO2 emissions.
• A variable gain control scheme is employed for constant composition control.

This paper aims at analyzing the thermal integration of direct vapor recompression system with a distillation column operated in batch mode. The unsteady state nature of the batch processing makes the use of vapor recompression a challenging task. For a meaningful comparison, it is attempted to run the vapor recompressed batch distillation (VRBD) column at same dynamics with its conventional counterpart. With this operating objective, the manipulation of a few process variables is proposed in open-loop fashion. Along with the energy savings and total annualized cost, the CO2 emission level is also used for quantitative performance evaluation of the proposed VRBD column. Aiming to produce a constant and high-purity distillate product, a gain-scheduled proportional integral (GSPI) controller that targets to keep the stability margin constant is devised for the VRBD process. Finally, this heat integration mechanism is illustrated by a binary batch distillation example in both open-loop and closed-loop modes. It is investigated that the VRBD shows a slightly higher energy savings (62%) compared to its closed-loop version (59.13%) but at the expense of distillate purity. The heat integration also achieves a significant savings in cost and CO2 emission.