Novel integrated system for cryogenic CO2 capture and liquefaction of natural gas using natural refrigerants

The high triple point temperature of CO2 makes it difficult to remove CO2 from conventional natural gas by cryogenic distillation. However, for natural gas rich in ethane, CO2 can be separated from natural gas in a liquid state along with ethane during the cryogenic distillation process without freeze-out problems due to the azeotropic characteristics of CO2-C2H6 mixtures. In this study, the freeze-out temperature of CO2 under certain distillation conditions is obtained from HYSYS and verified by a phase equilibrium analysis to obtain the maximum allowable CO2 content for typical feed gas compositions. On this basis, an integrated system for cryogenic carbon capture and liquefaction of natural gas rich in ethane is proposed, which adopts dual mixed natural refrigerants to provide the required cooling capacity. Through process optimization, the system achieves an exergy efficiency of 57% with a specific power consumption of about 0.4 kWhxNm(-3)(NG).