Chapter 7: Membrane Gas Separation Processes for Post-combustion CO₂ Capture

This chapter provides an integral view on membrane-based CO₂ capture from coal-fired power plants. Since gas separation membranes do not feature the same selectivity towards CO₂ as chemical absorption processes, a specification of the process boundary conditions up- and downstream of the membrane unit was performed first. The ongoing uncertainty regarding CO₂ purity requirements resulted in the derivation of different purity scenarios. Subsequent to the selection of an appropriate membrane material, the generation of the driving force for CO₂ permeation across the membrane was studied. Different options such as feed compression, suction at the permeate side or sweeping were reviewed with focus on large scale implementation in power plants. Since single-stage membrane processes are not able to achieve the required CO₂ purity in conjunction with high CO₂ recoveries, only two-stage membrane processes were examined in this work. A techno-economic analysis of two-stage membrane processes with and without recycling streams provided insight into economics and related energy consumption, CO₂ recovery and CO₂ avoidance costs. The techno-economic analysis revealed that post combustion CO₂ capture by membranes appears feasible. Nevertheless, the CO₂ product stream contains at least 1 vol.% of O₂, thus violating strict purity requirements as for enhanced oil recovery.