CO2 Capture from Natural Gas Fired Power Plants by Using Membrane Technology

Simulations of membrane separation were performed for two alternative processes for CO2 removal from an exhaust gas stream at a natural gas fired power plant. One process considered is an integrated membrane separation with pressurized gas (16.5 bar) rich in CO2 (10 vol %), while the other alternative solution is a process for CO2 capture from tail-end flue gas where the content of CO2 is low (4 vol %) and gas is released at 1 bar. A gas stream of 700 000 Nm^3/h is considered for both cases. Flux data obtained for a fixed-site-carrier poly(vinylamine) membrane developed within the research group at NTNU were used. This membrane has moderate CO2 flux but very high selectivity in favor of CO2. A favorable process design with a single-stage unit without the extra need for compression, and also use of a sweep gas to meet the process specifications, was recommended for the pressurized gas. For the flue gas lean in CO2, the driving forces are too low for separation unless both a compression of the feed gas (-4 bar) and a vacuum pump on the permeate side are used. Also, in this case a small fraction of the sweep gas on the permeate side is recommended.