Energy and exergy performance evaluation of a novel low-temperature physical energy storage system consisting of compressed CO2 energy storage and Kalina cycle

To improve the overall performance of the Compressed CO2 Energy Storage (CCES) system under low -temperature thermal energy storage conditions, this paper proposed a novel low-temperature physical energy storage system consisting of CCES and Kalina cycle. The thermal energy storage temperature was controlled below 200 degrees C, and the Kalina cycle was used to optimize the reuse of the stored thermal energy. A thermody-namic model of the integrated system was constructed, and the system performance was analyzed from the energy and exergy perspectives. Several evaluation indicators, such as system exergy efficiency (SEE), round trip efficiency (RTE), system energy density (SED), Kalina exergy efficiency (KEE), and Kalina energy efficiency (KEnE), were defined to evaluate system performance. In addition, the influences of several core parameters (e. g., split ratio (r), storage pressure (ps), turbine efficiency (te), pinch point temperature difference (pt) of heat exchangers, and ambient temperature (T0)) on the system performance were analyzed. The results of the base condition showed that SEE, RTE, SED, KEE, and KEnE were 58.17 %, 59.38 %, 6.32 kWh/m3, 38.62 %, and 8.64 %, respectively. The exergy destruction in heat exchanger 3 was the largest, accounting for 71.7 % of total exergy destruction. The sensitivity analysis results showed that increasing r could increase the SEE of the system, increasing ps could lead to a decrease in the RTE of the system, and increasing T0 could cause the RTE and SED to increase. The increase in te could improve all evaluation indices, while the increase in pt could reduce the system's overall performance. This study provides a new solution for the integrated application and optimal design of CCES systems under low-temperature thermal energy storage conditions.