Effects of flue gas recirculation on energy, exergy, environment, and economics in oxy-coal circulating fluidized-bed power plants with CO₂ capture

CO₂ capture and storage(CCS) are required for coal-fired power plants, which are major sources of anthropogenic CO₂ emission. In this study, energy, exergy, environment, and economic (4E) analyses were performed for a 500-MW_e oxy-coal ultra-supercritical circulating fluidized-bed (CFB) power plant with CO₂ capture. The effect of the location of flue-gas recirculation (FGR) on the 4E values was investigated for wet FGR (wFGR) at 170°C, dry FGR (dFGR) at 68°C, and 80% wet and 20% dry FGR (wdFGR). The net electricity efficiencies of the wFGR and dFGR power plants were 37% and 36%, respectively. The exergy loss was the largest in the combustor and boiler area, where process improvement was possible. The levelized cost of electricity was approximately 60 $/MWh. The return on investment was 6.7% and 6.1%/y for the wFGR and dFGR plants, respectively. The CO₂ emission rate decreased by 90% (from 690 to 76 kg-CO₂/MWh) in the oxy-coal power plants with CO₂ capture. Relative to the wFGR, the dFGR was advantageous for preventing material corrosion because of the lower sulfur content in the FGR stream. For the wdFGR power plant, the process performance was intermediate, that is, between that of the wFGR plant and that of the dFGR plant. The study provided an effective tool for identifying the technological and economic effects of the FGR location for the oxy-coal power plant with CCS via 4E analyses.