Design, operation, and case analyses of a novel thermodynamic system combining coal-fired cogeneration and decoupled Carnot battery using CO₂ as working fluid

In the context of energy transition, coal-fired power generation systems must be more efficient and flexible. This study proposed a novel thermodynamic system that combines the coal-fired cogeneration (CG) and decoupled Carnot battery (CB) using CO₂ as the working fluid. The ''design-operation-case'' model and analysis framework were constructed for this novel system. In the design stage, the optimal layout and design parameters for each subsystem were determined. In the operation stage, the operating domain of the novel system was explored. Finally, the feasibility of the novel system was evaluated through a case analysis. The findings include that the optimal arrangements with the highest exergy efficiencies for the CG, heat pump, and heat engine subsystems are the recompression, recuperative, and non-recuperative layouts, respectively. After parameter optimization, the exergy efficiencies of the three subsystems reach 46.24%, 69.23%, and 54.04%, respectively. The round-trip exergy efficiency of the CB is improved by 1.41%pt after decoupling. Moreover, the operating domain factor of the CG subsystem is 0.941, which is 43.87% higher than that of the traditional steam CG system. By incorporating the general CB into the CG subsystem, the operating domain area increases by 0.379 m², which further increases by 1.467 m² after decoupling the CB. The novel system is ultimately proven feasible.