Thermodynamic optimization on supercritical carbon dioxide Brayton cycles to achieve combined heat and power generation

The development of combined heat and power (CHP) systems based on the supercritical carbon dioxide (SCO2) Brayton cycle is important to enhance the energy utilization efficiency and satisfy different energy demands. Therefore, this study summarizes and compares the SCO2 CHP configurations in terms of back-pressure heating (system without pre-cooler (PC)) and extraction heating CHP types (system with PC). The configurations proposed in previous studies and new configurations proposed in this work are involved. Thermodynamic analysis models are developed, and the genetic algorithm is used to optimize the multi-parameters of SCO2 CHP configurations to reach the highest exergy efficiency. For the back-pressure CHP type, the configuration based on the SCO2 recompression-reheat cycle has the highest exergy efficiency of 44.1%, which can generate 219.5 MW of power under the selected heat load of 300 MW. For the extraction CHP type, the demands of 300 MW heat and 315 MW electricity are selected as the comparison condition. Under the comparison condition, the energy and exergy efficiencies of the configuration E-2 proposed in this study are respectively 73.9% and 40.8%. The configuration E-2 is integrated by the recompression-intercooling cycle, high-pressure extraction heating and reheat. Moreover, exergy losses and destruction within the SCO2 CHP system are analyzed to reveal its energy-saving mechanism in this study.