Energy saving in batch distillation for separation of ternary zeotropic mixture integrated with vapor recompression scheme: dynamics and control

Abstract

Abstract In this work, tight composition control and in parallel the operation is integrated with vapor recompression scheme (VRC) is proposed to achieve energy savings and maximum product at a specified high purity for the separation of ternary zeotropic mixture in batch distillation. Firstly, the model representing a ternary system of hexanol/octanol/decanol has been simulated to analyze the open-loop and close-loop dynamics of the process. Secondly, the open-loop and closed-loop operations are integrated with single stage VRC scheme to achieve energy savings. Single stage VRC is operated at very high compression ratio (CR) due to the large temperature difference of the top and bottom streams in batch distillation column. To further improve the thermodynamic efficiency of single stage VRC, double stage compression without intercoolers between the stages of VRC is proposed. Two control schemes have been implemented for constant composition, namely proportional integral (PI) controller and nonlinear gain scheduling proportional integral (GSPI) with and without VRC in closed-loop. The results shows that double stage VRC with GSPI algorithm provides better performance than conventional in terms of energy, product amount and Integral Square Error (ISE).