Investigation on application temperature zone and exergy loss regulation based on MgCO3/MgO thermochemical heat storage and release process

Abstract

Thermochemical heat storage (TCS) is an efficient technology for energy utilization with high heat storage density and seasonal storage. Among TCS carriers, MgCO3/MgO has a broad prospect at moderate temperatures. However, its definite application temperature range is not clear, and the issue of degradation of energy quality remains to be addressed. This research presented an intergrated test scheme to determine reaction temperature zone and optimal temperature by making connection with thermokinetics. In order to further control exergy loss, pressure regulation strategy with exergy evaluation was carried out. Results indicate that upper limit on what exothermic reaction occurs and lower limit for the endothermic deviate from thermodynamic equilibrium within 12 °C at P(CO2) = 1 bar. Exothermic reaction is motivated under the promotion of melting process for dopants, and the highest endothermic temperature depends on degradation level of TCS products. In the above temperature range, optimal temperature affected by multiple subprocedures keeps the same variation rule as the lower limit temperature either before or after adjusting pressure. Furthermore, exergy loss can be reduced to 9.97 kJ/mol with exergy efficiency 91.0% via lowering pressure of CO2 in charging process. This research provides an effective pathway to select TCS carriers and regulate its energy quality for engineering applications.