A Carnot battery system integrating ca(OH)2/CaO thermochemical energy storage and supercritical CO2 cycles for long-term energy storage and residential heat supply

The long-term energy storage and high-efficiency Carnot battery system are imperative to developing the future carbon-neutral energy system. This paper proposes a Carnot battery system integrating the CaO/Ca(OH)2 thermochemical energy storage, supercritical CO2 Brayton power and heat pump cycles, and some industrial waste heat. By effectively converting thermal, chemical, and electrical energy, the system not only harnesses excess electricity but also provides residential heating while enabling on-demand regeneration of electricity to the grid. According to the differential evolution algorithm and the HEATSEP framework, a multi-level optimization workflow is constructed to optimize heat transfer processes and operating conditions for deriving the most favorable system configuration in the energy aspect. The optimized system showcases impressive metrics, achieving an energy efficiency of 49.19 %, an exergy efficiency of 40.48 %, and a round-trip efficiency of 71.52 %. The key to further enhancing system efficiency lies in reducing heat loss from the regenerators and minimizing exergy destruction in the heat exchangers. Effects of the temperature of flue gas and the effective mass fraction of Ca(OH)2 in fluidized particles on the thermodynamic performance of the system are also investigated. It is recommended to leverage flue gas temperatures exceeding 250 °C for preferable energy cascade utilization. However, mechanically enhanced Ca(OH)2-rich fluidized particles with only 40 wt% of Ca(OH)2 show no significant impact on system efficiency. This research provides promising insights for advancing the efficiency and effectiveness of Carnot battery systems.