Investigating the influence of sweep gas on CO2/N2 membranes for post-combustion capture

CO2 partial pressure difference is the driving force for CO2-selective membranes and is emerging as the critical issue, when applying CO2-selective membranes for post-combustion capture. Using sweep gas can be an option to increase the driving force for CO2 permeation without changing the total pressure. Hence, in contrast to the application of compressors and vacuum pumps, the usage of sweep gas achieves separation without extra energy consumption. Nevertheless, it has the inherent feature of diluting the permeate. In this paper, two membrane concepts using air as sweep gas for post-combustion capture were investigated. The influence of the sweep gas on membrane area and the degree of CO2 separation was explored. An energetic and economic analysis was carried out comparing this concept with the cascade membrane concept without sweep gas. The technical route using sweep gas makes it possible to achieve an efficiency loss of 3.8%-points with a 70% degree of CO2 separation for a 600 MW reference power plant.

► Investigation of different membrane capture concepts for post-combustion w/ or w/o sweep gas.
► A potential sweep gas concept facilitates an efficiency loss of 3.8%-points. for a 600 MW power plant.
► The capture cost of using sweep gas is practically the same as that of without sweep gas.