Design and optimization of waste heat recovery system for supercritical carbon dioxide coal-fired power plant to enhance the dust collection efficiency

Abstract The supercritical carbon dioxide (SCO2) power cycle is a potential power cycle for coal-fired power plants. In the SCO2 power systems provided in previous studies, the boiler exhaust temperature is about 120 °C. To enhance the power plant efficiency and the dust collection efficiency of electrostatic precipitator, SCO2 power systems should be advanced to cool the boiler exhaust fluegas to nearly 95 °C. Therefore, systems of waste heat recovery from low-temperature fluegas are proposed and optimized in this study. Thermodynamic and optimization models are developed. The double reheat recompression SCO2 cycle is optimized as benchmark system. The benchmark system is improved to decrease the exergy loss and boiler exhaust, decrease the irreversibility of air preheater, and recover waste heat of the SCO2 cycle to preheat air to the air preheater. When the main compressor intercooling or bypass fluegas ahead the air preheater is adopted, the temperature of boiler exhaust fluegas can be decreased to around 95 °C which can ensure a high dust collection efficiency of electrostatic precipitator. The power plant efficiency is also increased as a result. However, if only low-temperature economizer is integrated, then the power plant efficiency is enhanced slightly by 0.09%-pts. If the low temperature economizer is integrated with other system improvements, the power plant efficiency can be enhanced by 0.89%-pts. Exergy analysis is also performed to reveal the mechanisms of efficiency enhancement.