Process Simulation And Improvement Of Carbon Dioxide Recovery Systems For CO₂Enhanced Oil Recovery Associated Gas

In recent years, the excessive emission of CO2greenhouse gas has lead to globalwarming and natural disasters and attracted national attention that we have to solveimmediately. CO2used as flooding agent injected into oil reservoirs is a moreeconomical measure to control carbon dioxide emission, not only improving theamount of crude oil extracted from the mined oil fields in an Enhanced Oil Recovery(EOR) process, but also achieving the greenhouse gas CO2permanently sealedunderground. Recovery and utilization of high concentration CO2from theoil-associated gas can reduce the cost of CO2-EOR while avoiding air pollution.Therefore, CO2separation and purification technology for the CO2-EOR oil-associatedgas is significant for the mitigation of global warming and greenhouse effect.This paper contrasted and analyzed the advantages and disadvantages ofabsorption, adsorption, membrane separation and cryogenic distillation methods ofCO2recovery, and adopted conventional low-temperature distillation method torecovery CO2from oil-associated gas. The paper mainly focused on studyingsimulation researches of conventional three-tower process, conventional four-towerprocess and improved three-tower and four-tower process systems.Firstly, the paper simulated the conventional three-tower and four-tower processesbased on the conventional low-temperature distillation process for recovery CO2in theCO2-EOR oil-associated gas using chemical process simulation software ProMax3.2,and optimized the relevant operation parameters using sensitivity analysis method.Simulations were mainly conducted to investigate the effects of the operatingparameters (feed temperature, feed inlet stage, additive inlet stage, and additive ratio)on the on separation effect and energy consumption. The simulation results showedthat the minimum total equivalent work of the conventional three-tower and four-towerprocess systems is1.249GJ/t and1.289GJ/t, respectively, under the optimizedoperating parameters.Secondly, aiming at solving the problem of high energy consumption inconventional low-temperature distillation process system, improvement of thethree-tower and four-tower processes were proposed and simulated using ProMax3.2software. The improved processes added two intermediate reboilers in the CO2recovery column of the conventional three-tower process and CO2-C2separation column of the conventional four-tower process respectively and a pre-cooling heatexchanger, which made full use of the waste heat and cooling in the system. And, tomake sensitivity analyses and study the effect of intermediate reboiler position,intermediate reboiler withdrawn ratio and additive ratio on the reboiler duty and CO2mole fraction. Under the same CO2recovery amount and CO2recovery rate with theconventional process, the reboiler heat duty of the CO2recovery column and totalequivalent work of the improved three-tower process were0.348GJ/t and1.084GJ/t,respectively, reduced by67.5%and13.21%compared with that of the optimizedconventional three-tower process. The reboiler heat duty of the CO2-C2separationcolumn and total equivalent work of the improved four-tower process were reduced to0.186GJ/t and1.150GJ/t, respectively,73.28%and10.78%lower than that of theoptimized conventional four-tower process.