Eco-efficiency analysis and intensification of cryogenic extractive distillation process for separating CO2–C2H6 azeotrope through vapor recompression strategy

Abstract

The cryogenic extractive distillation process for CO2-ethane separation from natural gas involves four distillation columns in series and a rather high amount of energy from boiler and refrigeration compressors. This study proposes the intensification of a real plant located in China using a vapor recompression (VR) strategy to revamp it. The conventional process and the intensification configurations were designed by simulation in UniSim software. A utility plant with cooling water, steam generation, and propane refrigeration sections was also considered for realistic results regarding water consumption, CO2 emissions, and utility costs. Additionally, in order to establish an overall means for performance analysis, such indicators were grouped in a joint evaluation approach using the Comparative Eco-Efficiency Index. Results show that the VR1 scheme applied between the depropanizer condenser and the deethanizer reboiler provides savings of 24.2 % and 24.5 % in energy and water consumption, respectively; therefore, savings of 25.5 % and 21.4 % in CO2 emissions and utility costs were achieved, respectively, which increased the process's eco-efficiency by 41.9 %. As a point of interest, 33 months are necessary to recover the corresponding investment on the compressor and heat exchanger.