Step-by-step gas separation system and method for coupling membrane separation with liquid absorption

The invention relates to a step-by-step gas separation system and a step-by-step gas separation method for coupling membrane separation with liquid absorption. The pretreated flue gas is primarily purified through a secondary membrane separation link and then enters a liquid absorption link to be purified, CO2 product gas with the purity larger than 99% is obtained, and an exhaust membrane assembly and a product gas membrane assembly are adopted for separation and recovery of absorption liquid. According to the invention, a circulation process between membrane separation and a liquid absorption technology is reasonably constructed, and the CO2 product purity is effectively improved while the CO2 recovery rate is ensured. And the content of O2 and other impurity components in the permeated gas is reduced through the secondary membrane separation module, the degradation of the absorption liquid is reduced, and the loss of the absorption liquid is reduced. Meanwhile, through separation treatment of the exhaust m