Thermodynamic analysis of compressed and liquid carbon dioxide energy storage system integrated with steam cycle for flexible operation of thermal power plant

In order to achieve global carbon neutrality, it is expected that the proportion of renewable energy will increase. As the share of renewable energy increases, the problem of renewable energy intermittency will become more pronounced and has to be resolved for the sake of grid stability. To address this issue, an enhanced thermal power plant's load-following capability will be demanded. To effectively operate thermal power plant more flexibly, an integration concept of the energy storage system with the steam cycle of the thermal power plant is suggested in this work. Moreover, a compressed carbon dioxide energy storage system is specifically recommended as a promising Energy storage system technology for this purpose due to its advantages of having competitive round-trip efficiency, good possibility of realizing large capacity, and delivering adequate power. In this paper, four process layouts using carbon dioxide for energy storage system are suggested and evaluated thermodynamically. From the analysis, it is first shown that this system can achieve round-trip efficiency of 64% and energy density of 3.8 kWh//m3. In order to further improve the energy density, three layouts of liquefied carbon dioxide energy storage systems are suggested by adopting idea from a liquefied air energy storage system. These proposed system processes were designed and evaluated to achieve maximum round-trip efficiency of 46% and energy density of 36 kWh/m3, increasing by nine times than the previously reported value for compressed carbon dioxide energy storage system, which shows that there is a trade-off between round-trip efficiency and energy density in compressed carbon dioxide energy storage system.