Simulation For CO₂ Seperation Process In All Periods Of EOR Natural Gas

With the development of EOR technology, the EOR natural gas contains a large of CO₂ which lead to a lower value of the nature gas. If we discharge the gas directly, it not only wastes the energy, but also increases the greenhouse effect. At the historic moment, CO₂ seperation technology is invented. This technology can achieve the efficient use of EOR natural gas and be responsed to the requirements of environmental protection. This paper mainly researched the analysis of the EOR natural gas, design of the chemical process and membrane separation process, analysis the mixed amine absorption process with Aspen HYSYS, simulation the membrane separation process with MATLAB.Based on the siteinvestigation of the Shengli EOR natural gas, the study analyses the composition characteristics, especially the change law of CO₂ and heavy hydrocarbon component in the gas. Results showed that at the beginning of the CO₂ flooding injection, CO₂ content in the gas below 30%, but during the middle and later periods, the CO₂ levels rise sharply to 70%. There are C3+ and C5+ in the EOR natural gas, and C5+ is atable as well as lower levels. The heavy hydrocarbon of C3+ is higher but gradually reduce with the increase of injection.According to the characteristics of the EOR natural gas, this paper contrast the chemical absorption method, PSA, membrane separation method and low tempture fractionation method’s applicable scope and the treatment effect. Finally the mixed amine absorption method and membrane separation method were selected and designed. To prevent the heavy hydrocarbon in the natural gas pollution the membrane, the pretreatment of the membrane separation is required.The simulation of mixed amine absorption process is taken out with Aspen HYSYS. The influence of the lean solution flowrate, absorber plate number, lean solution temperature,absorbing pressure, CO₂ content in lean solution and desorption tower plate numberis analyzed to draw the conclusion: when the lean solution flowrate is 18t/h, absorbing pressure is 0.5MPa, lean solution temperature is 40℃, absorber plate number is over 20 and desorption pressure is 0.1MPa can achieve CO₂ treatment. In addition, the CO₂-CH4 system and the actual gas system were study respectively, and the results show that the actual gas system under the operating parameters of the CO₂-CH4 system can also meet the processing requirements. This study can offer guidance for experimental analysis and fieldoperation.For the the EOR natural gas which with 60% content of CO₂ is analyzed by MATLAB. Based on the study of the membrane area and the operating pressure, the membrane separation process has a large elasticity. The process can adapt to the CO₂ content is 50% to 80%, and only need to adjust the pressure of the membrane to meet the requirement of the high purity of CO₂, high recovery rate of CO₂ and low loss rate of CH4.