Dynamics and control of thermal- versus electrical-driven pressure-swing distillation to separate a minimum-boiling azeotrope

Abstract

The implementations of heat integration (HI, thermal-driven), vapor recompression (VRC, electrical-driven), and self-heat recuperation (SHR, electrical-driven) in pressure-swing distillation (PSD) are available for providing energy saving and CO2 emission reduction over the conventional design (CONV, thermal-driven), exemplified by a minimum-boiling tetrahydrofuran/water. Approximately a 20 % decrease in total annual cost (TAC) and over 25 % CO2 emission reduction can be reached by using these measures. However, these steady-state advantages sometimes go along with decreases in controllability, so it is necessary to investigate the dynamics and control of these highly integrated and interacting processes. Robust temperature control structures based on decentralized proportional-integral (PI) feedback controllers are developed to tackle ± 20% disturbances in throughput and feed composition. For the thermal-driven processes, the PSD-CONV is easily controlled with the single-end control strategy. Based on that, the effective control of PSD-HI is achieved by either pressure compensation or bypass strategy. Regarding the complicated electrical-driven arrangements, the dynamic responses of PSD-VRC and PSD-SHR indicate their controllability is comparable to those of a regular sequence. These results demonstrate that there are no conflicts between the steady-state advantages and dynamic controllability for this specific separation. Meanwhile, these electrical-driven processes can be considered to extend to other minimum-boiling azeotropes owing to their economic and environmental advantages.