Thermodynamic Model Optimization And Process Calculation For Low Temperature Methanol Washing

The low temperature methanol washing process was widely used in the large-scale ammonia synthesis and coal gas plants,due to the acid gas such as:CO2,H2S,COS could be selectively dissolved in methanol under low temperature and high pressure.In the process of indirect coal liquefaction,the products such as gaseous hydrocarbon,liquid hydrocarbon and synthetic wax can be obtained by gasification,purification and Fischer-Tropsch(F-T)synthesis processes.However,the tail gas of F-T synthesis process contains a lot of lower hydrocarbons.Therefore,the lower hydrocarbons effective separation and syngas(CO and H2)reutilization can greatly improve the energy utilization efficiency and economic benefit of the synthetic oil plant.In aim of this paper was to optimize the tail gas treatment process of F-T synthesis.Aspen Plus was used to simulate the absorption process for the F-T synthesis tail gas by low temperature methanol washing process,and the optimum process of low temperature methanol washing was put forward.The results of the work are detailed as follows:1.Investigating the research progress of low-temperature methanol washing process,including the process improvement,related gas solubility data measurement method and thermodynamic model improvement;2.An apparatus for measuring the solubility of gas is established with the Setaram BT2.15 temperature control system.The reliability of the determined device was verified by measuring the solubility of CO2 in methanol at 50 ℃,-15℃ and-30℃;3.The solubility of CH4,C2H6 and C2H4 at-30～-20℃ was measured by constant volume method,and the accuracy of Henry’s coefficient and PC-SAFT model was compared.The results show that the PC-SAFT equation can well correlate the solubility of gas in methanol,and can accurately describe the variation trend of gas solubility with temperature and pressure.Thus,the PC-SAFT equation can be used to calculate the process of carbon gas absorption;4.Based on the above results,the PC-SAFT thermodynamic model was regressed,and the process simulation of F-T tail gas absorption was carried out on the Aspen Plus.The naphtha pre-washing and methanol pre-washing schemes were put forward,and the best scheme of low temperature methanol pre-washing was determined by comparing the process steps,energy consumption,recovery rate and other indexes.