Parameter analysis of discharging process for CaCO₃/CaO thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) system is one of the promising technologies to overcome mismatch between solar energy supplies and variable electricity demands mainly benefiting from its high energy density, superior reversibility and low cost. This TCES system is divided into three processes, energy charging, energy storage, and energy discharging. The discharging process is the most important due to the involvement of CO2 in the conversion from CaO to CaCO3 for power generation. In this paper, a simplified discharging process is proposed and the mathematic models are developed based on mass and energy balances. Theoretical investigation is carried out to explore the effect of different parameters (gas solid ratio, solid inventory in the carbonator, and carbonator pressure) on discharging performance, which is determined by expansion work of turbine and CaO conversion. The results indicate that the gas solid ratio is the most critical parameter in regard to expansion work of turbine, followed by carbonator pressure, while the effect of solid inventory in the carbonator is little. On the other hand, solid inventory is the most significant among three parameters for CaO conversion, and the effect of carbonator pressure can be ignored.