Energy and exergy analysis of oxy-fuel combustion based on circulating fluidized bed power plant firing coal, lignite and biomass

Oxy-fuel combustion with circulating fluidized bed (CFB) is a promising technology applied in carbon capture and sequestration. In this work, a supercritical oxy-fuel combustion system based on CFB boiler firing coal, lignite and sawdust is established to evaluate the system performance. Five primary units are arranged including an air separation unit, a CFB combustor considering the fuel combustion characteristics, a steam generation cycle, a simplified power island and a CO2 purification and compression unit. After the validation, the influence of fuel types, oxygen concentration, flue gas recirculation forms and exhaust flue gas temperature on the system performance including adiabatic flame temperature, flue gas loss, net efficiency and exergy efficiency are evaluated. The results showed that compared to lignite and sawdust combustion, oxy-fuel combustion with coal has the highest net efficiency and exergy efficiency which is mainly because of the lower moisture and ash. However, the drying process will not significantly increase the net efficiency of sawdust combustion according to the electricity consumption of biomass drying. Also, a dry cycle is preferable in high moisture fuels combustion due to the better burnout performance and less recirculation fan work. To increase the net efficiency, reducing the exhaust flue gas temperature and increasing the combustion pressure are both effective.