Thermodynamic optimization of coal-fired combined heat and power (CHP) systems integrated with steam ejectors to achieve heat–power decoupling

The operational flexibility of combined heat and power (CHP) units is highly required owing to the high penetration level of intermittent renewable power. Traditional CHP units should run in heat-controlled mode, which limits their operational flexibility. Therefore, the heat–power decoupling of CHP units is necessary. In this study, steam ejectors are used in designing low-cost and highly efficient heat–power decoupling systems with simple structures. Three new CHP systems integrated with ejectors are proposed, and multiple system parameters are optimized. The heat–power decoupling performances and energy consumption characteristics of the three reformed systems are also compared. Results show that all three reformed systems can achieve heat–power decoupling, and System II (coupled with two ejectors in series) has the largest peak-load regulating capacity (ΔP_e) of 94.8 MW. System III (coupled with two ejectors in parallel) shows the best energy and exergy efficiencies. Compared with the Basic System, System III can enhance energy efficiency by 13.47% and the exergy efficiency by 13.46% at ΔP_e of 40 MW. This study provides a promising approach for utilizing steam ejectors in enhancing flexibility for CHP plants.