Effect of flue gas recirculation on efficiency of an indirect supercritical CO₂ oxy-fuel circulating fluidized bed power plant

This paper deals with and oxy-fuel circulating fluidized bed (Oxy-CFB) power plant with air separate unit (ASU), CO₂ compression and purification unit, and an indirect supercritical CO₂ cycle. This novel power plant was designed and modeled by using Aspen Plus at commercial scale to investigate the possibility and the effect of recirculated flue gas conditions. The indirect S–CO₂ oxy-CFB power plant had higher net efficiencies compared with oxy-CFB power plant with steam cycles because the phase of CO₂ does not change during the operation. Also, the effect of the amount of water retained in flue gas stream generated at the CFB boiler on the overall net efficiency was analyzed. By decreasing the temperature of recirculated flue gas from 90 °C to 40 °C, water retained in flue gas decreased, and input O₂ concentration in combustor increased from 34.7 to 38.5 vol%. When flue gas recirculation temperature was 40 °C, the boiler efficiency was 99.6%, and the overall net efficiency was 43.1%. Although approximately 20% of the total power is the power consumption of the ASU and CPU, high net efficiency was achieved in this novel power plant.