(401ad) Polymeric Membrane Systems for CO2 Capture from Flue Gas: A Techno-Economic Analysis
The increasing consumption of fossil fuels has resulted in immense CO2 emissions after the Industrial Revolution. Membrane processes have been suggested as an alternative to amine absorption for post-combustion carbon capture. Despite of the tremendous research efforts, CO2-selective polymeric membranes typically exhibit a trade-off between CO2 permeance and CO2/N2 selectivity. This presentation will show how to overcome the limitations as a result of this trade-off by noval membrane process designs. In the first membrane process, called the hybrid air sweep process, the flue gas flows to a vacuum membrane stage using a membrane with high CO2/N2 selectivity and moderate CO2 permeance. The retentate gas then flows to an air-sweep membrane stage employing another membrane with high CO2 permeance but low CO2/N2 selectivity. The CO2-laden sweep air is fed to a power plant boiler as combustion air. A highly selective amine-containing membrane with a CO2 permeance of 1100 GPU (1 GPU = 10-6 cm3 (STP)·cm-2·s-1·cmHg-1) and a CO2/N2 selectivity >140 is used for the vacuum stage to enrich the CO2 to >95% purity whereas a highly permeable poly(ethylene oxide)-based membrane with a CO2 permeance of 2000 GPU and a CO2/N2 selectivity of 20 is employed for the air sweep stage. This hybrid membrane configuration yields a capture cost of $40.2/tonne CO2 in the 2007 dollar basis for 90% CO2 recovery, which nearly meets the target of the Department of Energy (DOE) set for 2025. In the second membrane process, i.e., retentate recycle process, the flue gas is passed to two stages employing the membrane with high CO2/N2 selectivity; these two stages are placed in an enriching cascade. A portion of the CO2-depleted retentate of the first membrane stage is recycled as its own sweep gas. It is identified that the highly selective amine-containing membrane is needed for both stages and a 20% retentate recycle renders a capture cost of $43.1/tonne CO2. These cost calculations in the 2007 dollar basis have included both membrane module installation cost and 20% process contingency.