Integration of Oxygen-containing Exhaust Gas into the Air Separation Unit of an Oxyfuel Power Plant

Abstract

The Oxyfuel process is one possible solution to lower the high specific CO2 emissions of coal-fired power plants. The flue gas generated by this process has a high CO2 content, due to the missing nitrogen. However the dried flue gas still contains approximately 15 vol% (dry) impurities (NOx, SOx, O2, N2 and Ar). To further increase the CO2 purity the flue gas needs to be treated in a gas processing unit (GPU). Additional downstream gas treatment approaches such as Polymeric Membranes or Pressure Swing Adsorption to capture CO2 from the offgas of the GPU, can raise the capture rate from 90% to 99%. The remaining CO2 and most of the impurities contained in the offgas downstream of the GPU are discharged to the environment with the exhaust gas of the GPU. The O2 contained in the exhaust gas downstream of the GPU amounts to 4-5% of the oxygen supplied by the ASU. The energy demand of the ASU can be lowered if the O2 contained in this exhaust gas was captured and recycled back to the firing system. The energy saving potential of such a recycle would amount to 4-5% of the ASU energy demand, but only if all O2 is captured from the exhaust gas and no energy is needed for the capturing process. So the capturing process and its integration into the overall process has a substantial influence on the achievable energy saving. Target of this work is to integrate and model the capture and recycle of the oxygen from the exhaust gas back into the Oxyfuel power plant process.