Current investigation status of oxy-fuel circulating fluidized bed combustion

Oxy-fuel circulating fluidized bed combustion (Oxy-CFBC) is regarded as one of the most promising and sustainable technologies for carbon capture, utilization and sequestration (CCUS) in coal-fired power plants. The investigation of Oxy-CFBC technology has been rapidly developed in the past 15 years. The Oxy-CFBC facilities are from lab-scale to industrial-scale. The inlet oxygen concentration increased from 21 to 30 % in first generation of Oxy-CFBC to higher inlet oxygen concentration up to 50 % in second generation of Oxy-CFBC. This paper reviews the published materials on the aspects of research status including existing models, heat transfer, combustion characteristics, pollutant formation and emission, and Oxy-CFB power plant system optimization. In particular, research fuels included coal, biomass, sewage sludge and oil shale, and the differences of NOx emission and desulfurization mechanism between air combustion mode and oxy-combustion mode are considered in the review. The NO emissions (in mg/MJ) are lower and the direct desulfurization will occur under Oxy-CFBC conditions as compared to that in air-fired conditions. In Oxy-CFBC, the increase in inlet oxygen concentration and temperature will improve the combustion efficiency and desulfurization efficiency, but increase NO emissions as well. Gas staging and oxygen staging are effective ways to reduce NO emissions. Moreover, the new generation of Oxy-CFBC technologies such as pressurized Oxy-CFBC and oxygen-steam combustion, the published patent status about Oxy-CFBC and the challenges of Oxy-CFBC technology in China are also analyzed for future research and technology industrial application.