Performance evaluation and optimization of a novel compressed CO2 energy storage system based on gas-liquid phase change and cold-electricity cogeneration

Compressed CO₂ energy storage (CCES) system has received widespread attention due to its superior performance. This paper proposes a novel CCES concept based on gas-liquid phase change and cold-electricity cogeneration. Thermodynamic and exergoeconomic analyses are performed under simulation conditions, followed by an investigation of the impacts of various decision parameters on the proposed system. Next, a multi-objective optimization is conducted with the total energy efficiency and total product unit cost as the objective functions. Finally, brief comparisons are made between the proposed system and existing systems. The results indicate that the total energy efficiency of the proposed system reaches 79.21% under the given simulation conditions, outperforming the electrical efficiency of 61.27%. Additionally, the total product unit cost of the system is 25.61 $/GJ. A key component, T1, plays an important role due to its large exergy destruction rate (1.0591 MW) and total investment cost rate (154.85 $/h). Despite this, the exergoeconomic factors of T1 is only 41.08%, indicating that investing in T1 to improve the efficiency is practicable. The analysis shows that a lower CO₂ condensation temperature benefits the proposed system performance. While improving the isentropic efficiencies of the compressors and turbines enhances total energy efficiency, excessive isentropic efficiencies can lead to a significant increase in total product unit cost. Through multi-objective optimization, an optimal favorable operating condition is identified, yielding a compromise result with a total energy efficiency of 111.91% and a total product unit cost of 28.35 $/GJ. The proposed CCES system efficiently delivers both power and cooling energy, demonstrating clear superiorities over previous systems.