Carbon dioxide capture,utilization and storage (CCUS) is a necessary means to achieve the goals of “carbon dioxide emission peaking” and “carbon neutrality”.In the whole CCUS process,the cost of carbon dioxide capture accounts for as much as 70% of the total cost.Therefore,reducing the cost of carbon dioxide capture is crucial for the large scale application of CCUS.Low pressure flash system in a Rectisol unit is one of the main sources of carbon dioxide emission in modern coal chemical projects.Based on Aspen Plus process simulation software,two kinds of low pressure flash process in a Rectisol unit of a 750 000 tons/year coal to ammonia plant are simulated and analyzed.The influences of main operating parameters on the content of CO₂ in the tail gas,the temperature of rich methanol,the content of CO₂ in rich methanol,CO₂ recovery rate,and the operation cost are explored,and the CO₂ recovery cost by these two processes are compared.Results show that the operating pressure for H₂S enrichment column should be 0.07-0.08 MPa,the nitrogen flow rate of nitrogen stripping process should be 900 kmol·h^-1,and the operating pressure of vacuum desorption should be -0.086 MPa.In order to improve the CO₂ recovery rate of Rectisol unit as much as possible,the conventional nitrogen stripping process can be revamped into vacuum desorption process to make CO₂ recovery rate exceed 97%,and can significantly reduce the operation cost of CO₂ recovery.