Process Optimization of Heat-Integrated Extractive Dividing-Wall Columns for Energy-Saving Separation of CO2 and Hydrocarbons

Large amounts of gas mixtures of CO2 and hydrocarbons are generated in the CO2-enhanced oil recovery (CO2-EOR) process, and their separation is very challenging due to the formation of a minimum-boiling azeotrope of CO2 and ethane. Hence, in this work, an intensified triple-column extractive distillation (ITCED) process, based on the triple-column extractive distillation process proposed by Ebrahimzadeh et al. [Appl. Therm. Eng. 2016, 96, 39-47], is developed and optimized using a mixed-integer nonlinear programming (MINLP) method in terms of the minimal total annual cost (TAC) to separate the CO2-hydrocarbons mixture effectively. Furthermore, based on ITCED, two types of extractive dividing-wall column (EDWC) processes, i.e., vapor split EDWC (VSEDWC) and liquid split EDWC (LSEDWC), are developed and optimized. Then, the thermodynamic efficiency and CO2 emissions of these processes are calculated to evaluate their energy efficiency and environmental impact, showing the advantage of LSEDWC over the other processes. Finally, a heat-integrated LSEDWC (HI-LSEDWC) process is proposed and demonstrated to be able to substantially improve the original tripe-column extractive distillation process with a 33.04% decrease in TAC from $118.93 x 10(6) to $79.63 x 10(6), a 78.07% increase in thermodynamic efficiency from 12.28 to 21.87%, and a 37.22% reduction of CO2 emissions from 82.56 x 10(3) to 51.84 x 10(3) kg/h.