Oxygen transport membrane unit applied to oxy-combustion coal power plants: A thermodynamic assessment

The oxy-combustion process is one of the alternatives which have been evaluated to counteract the increase in CO2 emissions over recent years. This technology consists of a combustion process with oxygen instead of air, which facilitates the capture of CO2 after the flue gas treatment process. Nowadays, oxy-combustion has not been implemented full-scale because of the high energy and economic requirements of the air separation unit to provide oxygen to the process. This paper proposes to ion transport membranes as a replacement for the air separation unit in order to minimize their high energy penalty of the overall system power. In particular, this work presents four processes based on the oxygen-fired plant with an oxygen transport membrane unit. As benchmark cases used to quantify the energy penalties for CO2 capture, the correspondent air combustion process without CO2 capture and a cryogenic oxygen-fired process (Case1) were considered. The thermodynamic comparison between the proposal alternatives has been conducted through simulation models based on Aspen Plus tools. The net electric power and the net efficiency of electricity production have been used as key parameters, which have allowed achieving an optimal system design that provides reduces the power consumption related to separate oxygen from the air. As the results show, the oxygen transport membranes concept exhibits better net electrical efficiency (35.7% vs. 30.6%), lower efficiency drop (2.5% vs. 7.6%) and lower specific captured CO2 (986 gCO(2)/hkW(net) vs. 1140 gCO(2)/hkW(net)) compared to the cryogenic oxygen-fired process.