Performance assessment of a compressed CO₂ energy storage system with absorption refrigeration cycle

In order to fully utilize the heat generated in the compressed CO₂ energy storage (CCES) system and improve the round-trip efficiency (RTE), this paper proposes an improved system configuration integrated with an absorption refrigeration cycle. The tailored integration strategy lies in the unique CO₂ processing strategy: after primary compression and heat transfer to the absorption refrigeration cycle, the CO₂ stream is divided into two branches. One stream of carbon dioxide is further compressed in the secondary stage to reach the storage pressure and then condensed into a liquid state for storage. The other stream absorbs the cooling capacity from the refrigeration cycle, transforms into a liquid state, and is subsequently pressurized to the storage pressure. Since less work is consumed during the compression of the liquid, the RTE of the system can be improved. To fully evaluate the system's performance, analyses of both thermodynamics and economics were conducted. Furthermore, multi-objective optimization was used to optimize efficiency and minimize expenses. Simulation results demonstrated that the RTE reached 61.27% under design conditions, and the total cost per unit of energy output (c_ptot) is 4.31$/GJ, representing a significant improvement compared to the reference system. Exergy analysis reveals that the first-stage compressor, turbine, and post-stage heat exchanger exhibit relatively high exergy destruction and significantly impact the economic performance. Sensitivity analysis shows that increasing the condensation pressure and the adiabatic efficiency of the compressor and turbine improves the overall efficiency, whereas higher storage pressure and refrigeration cycle inlet temperature degrade it. The system underwent multi-objective optimization in the end. After optimization, the RTE of the system reached 64.34% and c_ptot reached 3.46$/GJ, respectively.