Membranes are among a suite of technologies being considered for post-combustion carbon capture. Recent studies have shown the importance of process design in optimizing membrane system performance and setting guidelines for membrane materials development. In this study, the simulated performance of membranes based on a rubbery poly(ethylene oxide) block copolymer, a polyvinylamine/polyvinyl alcohol blend that shows facilitated CO2 transport, and a glassy thermally-rearranged polybenzimidazole is compared for a single-stage membrane operation treating humidified flue gas. Parametric studies were conducted to investigate the impact of different operating modes and conditions. For all cases, high membrane CO2 permeance minimizes membrane area requirements, while high CO2/N-2 selectivity improves the CO2 purity and reduces the energy needed for CO2 purification. The benefits of higher selectivity are accentuated at higher feed-to-permeate pressure ratios, at the expense of increased energy cost. The advantages of higher permeance are most pronounced at a lower pressure ratio. The effects of water vapor in flue gas on CO2 capture with membranes can be complex depending on possible interactions of sorbed water with the membrane. From a process standpoint, a slight positive sweep effect is generated from the co-permeation of water vapor which increases the CO2 separation degree at a fixed membrane area.