Comparison and sensitivity analysis of the efficiency enhancements of coal-fired power plants integrated with supercritical CO2 Brayton cycle and steam Rankine cycle

Abstract

The supercritical CO2 (SCO2) power cycle, which is highly efficient and cost effective and features a compact structure, is expected to replace steam Rankine cycle and bring technological revolution to coal-fired power plants. To obtain the quantitative energy saving potentials of the SCO2 power cycle, this study compared the thermodynamic performances of coal-fired power plants with SCO2 cycle and 10 in-service coal-fired power plants with steam as the working fluid. The efficiencies of 538 °C, 566 °C, and 600 °C typical power plants were increased by the SCO2 cycle by 2.52%, 2.39%, and 2.84%, respectively. Exergetic analysis revealed that the decrease in heat transfer irreversibility in the boilers mainly caused the efficiency enhancement. Then, the main devices’ performance parameters, including the isentropic efficiency of the compressor, isentropic efficiency of the turbine, pressure drops of the heat exchangers, regenerator terminal temperature difference, and leakage ratio, were analyzed in terms of their sensitivity to the efficiency enhancement of coal-fired power plants integrated with the SCO2 cycle. The influence of these parameters on the internal irreversibility of coal-fired power plants was also studied. With a 600 °C power plant as an example, the energy saving limits of the main devices’ parameters of SCO2 cycle in comparison with the steam Rankine cycle are as follows: the compressor isentropic efficiency exceeded 75%, the turbine isentropic efficiency exceeded 86%, the pressure drop of the heat exchanger was less than 0.35 MPa, the temperature difference of the regenerator terminal was less than 21 °C, the leakage ratio was less than 2.5% when the leakage was not recovered, and the leakage ratio was less than 16% when the leakage was recovered.