The coal-fired Oxyfuel-process with additional gas treatment of the ventgas for increased capture rates

© 2014 The Authors. Published by Elsevier Ltd. The Oxyfuel-process could be a solution to lower the high specific CO2 emissions of coal-fired power plants. The carbon capture rate (CCR) in current research is usually set to 90% due to the increasing specific energy demand of the capture process (GPU) and lower CO2 purity of the product stream at higher CCR. The remaining CO2 and most of the impurities escape to the environment with the ventgas downstream of the GPU. In current literature it is recommended to increase the CCR from 90% to higher values of up to 98-99%. This can be achieved by adding an additional gas treatment to capture the CO2 contained in the ventgas downstream of the GPU. At high CCR like 99% the necessary recycle of the captured CO2 into the basic GPU process leads to an increase of the specific energy demand of the GPU and an efficiency decrease of the overall process. It is possible to lower this efficiency penalty by recycling the remaining impurities downstream of the additional gas treatment to the ASU to regain the contained oxygen. The feasibility of the recycle strongly depends on the capture rate of the additional gas treatment, because it influences the CO2 concentration in the recycled exhaust gas. In this work an overall process of a coal-fired Oxyfuel power plant with cryogenic ASU and externally cooled GPU as a basic process is modelled. This process is adapted to higher CCR by adding an additional gas treatment by a polymeric membrane (PM) downstream of the GPU. The ASU is modelled as a triple column process. This process enables an exhaust gas recycle downstream of the PM. The GPU is a two stage partial condensation. Furthermore the influence of the additional gas treatment on the GPU process and the overall process for different CCR is examined and the resulting exhaust gas concentrations are calculated to evaluate the possibility for an exhaust gas recycle. This evaluation is necessary, because the remaining CO2 in the exhaust gas that is recycled to the ASU has to be removed upstream of the ASU. This leads to an additional energy demand to regenerate the molecular sieves upstream of the ASU