Control comparison of conventional and thermally coupled ternary extractive distillation processes with recycle splitting using a mixed entrainer as separating agent

Abstract

This paper explores the dynamic control of thermally coupled ternary extractive distillation process containing two extractive columns with recycle splitting of mixed separating agent by taking the separation of tetrahydrofuran/ethanol/water as a demonstrating example. A series of control structures are devised and assessed by the large (20%) perturbations of throughput and feed composition, and the robust regulatory control is achieved since the purities of all three products are closely going back to their initial steady-state design specifications when facing the large (20%) feed flowrate and composition disturbances. Besides, the dynamic response performance for control strategy with product ethanol purity controlled by manipulating the reflux ratio is superior to that with manipulating solvent flowrate in terms of peak dynamic transients, settling time and steady-state offsets when facing the large (20%) throughput and feed composition disturbances for extractive rectifier column C2. The direct dynamic response performance comparisons for conventional and thermally coupled processes with mixed entrainer are also investigated and showed that there is no conflict (tradeoff) between the steady-state economics and dynamic controllability for this system.