Performance enhancement of pressure-swing distillation process by the combined use of vapor recompression and thermal integration

Abstract

The intensified pressure-swing distillation (PSD) process is explored by applying vapor recompression and thermal integration. The evaluation indicators of second-law efficiency and CO2 emissions are adopted to rank different pressure swing-top vapor recompressed (PSDVRC) configurations. Compared to the conventional PSD process, the economically optimum flowsheet is the thermal integrated PSDVRC process with overhead vapor splitting since it can reduce 67.05% in energy consumption, 72.66% in CO2 emissions and 34.14% in total annual cost (TAC) as well as enhance 159.06% in thermodynamic efficiency. Besides, PSDVRC processes with overhead vapor splitting (PSDVRC-VS) are also superior to other PSDVRC configurations where economic-efficient process is PSD process (PSDSVRC) with single vapor recompression. Dynamic controllability for the highly integrated and interacting economic-efficient process is also investigated. An effective control structure is developed that only handles small (5%) disturbances in throughput and feed composition. The modified process is further developed to achieve robust control performance in terms of peak dynamic transients, settling time, oscillation and steady-state offsets. Meanwhile, control performance comparisons for PSDVRC-VS and PSDSVRC processes are also studied and showed that there is conflict between the steady-state economics and dynamic controllability.