(70a) Technical and Economic Assessment of Membrane-Based Systems for Capturing CO2 From Coal-Fired Power Plants

Coal-fired power plants contribute nearly 50% of U.S. electricity supply and account for about a third of national emissions of carbon dioxide (CO2), the major greenhouse gas associated with global climate change. Post-combustion carbon capture and storage (CCS) has been considered a key technology for deeply reducing CO2 emissions from existing and new coal-fired power plants. Membrane systems are among the advanced technologies being developed for more cost-effective capture. Membranes have been used commercially to separate CO2 from natural gas and other industrial gas streams, and have the potential for application to power plant flue gases. The objective of this study is to evaluate the technical feasibility and cost of membrane systems for CO2 capture at coal-fired power plants using newly developed cost and performance models.

Performance and cost models of polymeric membrane capture systems have been developed for use in this evaluation. We investigate the performance and cost of different capture system configurations including single- and multiple-stage modules to identify feasible membrane systems that are able to simultaneously achieve 90% CO2 capture and above 95% purity of CO2 product. We also examine a range of key factors affecting the capture system performance and cost. These factors considered include the inlet CO2 concentration, gas flow patterns, feed-side versus permeate-side pressure ratio, membrane properties, and other parameters. In particular, this study systematically evaluates the effects of membrane driving force designs for CO2/N2 separation. This is important since power plants flue gases are at atmospheric pressure, and typically have 10% to 15% CO2 by volume, which results in a low CO2 partial pressure. Furthermore, to increase the inlet CO2 partial pressure and decrease the energy required to generate a pressure difference across the membrane, boiler combustion air is used as a sweep gas for a two-stage, two-step membrane capture system.

The preliminary results show that multiple-stage membrane systems are capable of meeting the CO2 capture performance targets (90% capture and above 95% product purity) for given membranes. A hybrid design using both compressors and vacuum pumps for producing the separation driving force between feed and permeate sides is effective in reducing the energy requirements and cost of CO2 capture. A combination of combustion air sweep with the two-stage, two-step membrane capture system would further reduce the energy use and cost of CO2 capture. Plans for further model development also are discussed.

This work is supported under a contract from the U.S. Department of Energy's National Energy Technology Laboratory (DOE/NETL).