Exergy Analysis of a 600 MWe Oxy-combustion Pulverized-Coal-Fired Power Plant

In an oxy-combustion pulverized-coal-fired power plant (PC), a high CO2 content flue gas could be obtained, and this allows CO2 sequestration in an efficient and energy-saving way. To better understand the thermodynamic characteristics of the oxy-combustion process, a detailed exergy analysis of a 600 MWe oxy-combustion PC was carried out. The whole oxy-combustion PC system was divided into four models: boiler, turbines and feedwater heaters (FWHs), air separation unit (ASU), and flue gas treatment unit (FGU). The exergy (including physical exergy and chemical exergy) of each model was obtained, showing that the oxy-combustion boiler could reach higher exergy efficiency than the conventional combustion boiler. There is a significant difference between the exergy efficiencies of furnaces in the two boiler models, and the combustion exergy efficiency in the oxy-combustion furnace is about 4% higher. In each boiler model, the combustion process contributes nearly 60% exergy destruction. The exergy efficiency of the air heater in the oxy-combustion boiler is 10.3% higher than that in the conventional combustion boiler because of the flue gas recycle in the oxy-combustion boiler. The exergy destruction in the turbine and FWH model is just 9.01% of the total fuel exergy, and the turbines contribute about half. The exergy efficiencies of the ASU and FGU processes are 15.84 and 73.45%, respectively. The exergy efficiency of the oxy-combustion system is 37.13%, which is 4.08% lower than that of the conventional system.