Oxygen Transport Membranes for Ultra-Supercritical (USC) Power Plants With Very Low CO2 Emissions

Abstract

Coal combustion for electric power generation is one of the major contributors to anthropogenic CO2 emissions to the atmosphere. Carbon capture and storage (CCS) technologies are currently intensively investigated in order to mitigate CO2 emissions. The technique which is currently the most pursued is post combustion scrubbing of the flue gas, due to the potential to retrofit post combustion capture to existing power plants. However, it also comes with a substantial energy penalty. To reduce the energy demand of CO2 processing, the so-called oxyfuel technology presents an option to increase the concentration of CO2 in the flue gas. Here, the coal is burned in a mixture of oxygen and recycled flue gas. Hence, the flue gas primarily consists of CO2 and water vapor, which can be easily condensed. In general, there are two different techniques for oxygen production in oxyfuel power plants: cryogenic air separation (it is a method which can be easily implemented since it is already well established in industry) and a mixed metal oxide ceramic membrane (ITM or OTM) operating at high temperatures (it is a new process for O2 production, which is under development). In the last ten years, efforts in the efficient utilization of energy and reduction of emissions have indirectly stimulated research in mixed conducting membranes. In fact, the presently available cryogenic air separation process consumes a significant fraction of the generating plant’s output and reduces its efficiency. Oxygen transport membrane (OTM) integration with an ultra-supercritical (USC) power plant is, indeed, considered a promising technology that will lead to economic and energy savings compared to the previous solution. In this paper, we discuss the actual potentialities and limits of OTM and their integration in USC power plants.