Reduction on the inefficiency of heat recovery storage in a compressed carbon dioxide energy storage system

A growing boom can be noticed at the area of energy storage in recent years as this technology can address the supply-demand problem of power generation. As one of the most cutting edge energy storage technologies, the compressed carbon dioxide energy storage captures an increasing number of eyes all over the world. However, large inefficiencies occur within heat exchangers in supercritical pressure with resulting in low system efficiency. Therefore, a new thermal energy storage configuration is designed by separating the supercritical heat exchangers into two parts in which different mass of thermal storage medium is provided to adapt to the specific heat of supercritical CO2, such as 0.45 kg/s for the high-temperature part and 0.76 kg/s for the low-temperature part. Detailed thermodynamic analysis is conducted to identify the superiority of the new configuration compared to the traditional one. The analysis results indicate that the heat transfer between supercritical CO2 and water enjoys much better temperature match in the improved system. The round trip efficiency of improved system can arrive at 57.85% with the optimized final cooler temperature at 32 °C, 5.26% higher than the baseline system with optimized final cooled temperature located at 48 °C. In the improved system, the optimized operation ranges of charge pressure and discharge pressure are at 15–17 MPa and 14–16 MPa, respectively. Equal split ratio should be suggested to the charge and discharge CO2 to properly utilize the self-cycling cold energy.