Design and control of energy-saving double side-stream extractive distillation for the benzene/isopropanol/water separation

Abstract A new energy-saving double side-stream extractive distillation (SSED) is proposed for the benzene/isopropanol/water separation. The energy-saving alternative can further reduce 13% in TAC and 14.31% in CO2 emission in comparison to the conventional arrangement. Five control structures (CSs) are developed to control conventional (CS1 and CS2) and energy-saving (CS3-CS5) double SSED. The response of five CSs are studied by ±10% feed flowrate and ±20% composition disturbances, and the performances of five CSs are quantitatively assessed by two criteria, deviation from the production target (DPT) and integral absolute error in product purity (IAE). It is found that CS1 fails to handle effectively the feed flowrate disturbance, but CS2 has good dynamic behavior in the face of both feed flowrate and composition disturbances. The values of DPT and IAE for CS2 are obviously smaller than CS1. CS3, CS4 and CS5 all can resist feed flowrate and composition disturbances, but CS4 and CS5 receive more favorable control outputs than CS3. The values of DPT and IAE for CS4 and CS5 are very close, and both are smaller than those for CS3.