Investigation on energy grade improvement and regulatory mechanism enabled by MgCO3/MgO thermochemical energy storage

Thermochemical energy storage (TCES), by virtue of high energy density and cross-seasonal storage capability, makes a difference in the time–space mismatch between energy supply and demand. However, traditional TCES leads to exergy loss due to thermal hysteresis effect, and its ungovernable exothermic temperature limits industrial application. In this study, a novel high pressure TCES scheme was developed based on modified ▪ for improving thermal energy grade with flexible exothermic temperature. Van’t Hoff thermodynamic equilibrium and chemical reaction kinetics equations were predicted by thermogravimetric analysis for MgCO3 decarbonation and MgO carbonation. The regulatory mechanism combined with the thermodynamics was further explored. Results show that energy grade improvement rate increase with the increase of the pressure of CO2. It can reach 5% at 2 MPa, and then increase to 10∼15% at 10 MPa close, gradually approaching to the limit after 20 MPa. TCES high-pressure platform proposed in this study could store heat in the range of 320∼380 °C at pressure of 0.1 MPa N2 with a satisfactory thermal storage power, finally thermal energy could be flexibly raised to 430∼500 °C at 2∼2.5 MPa CO2 with a fast reaction rate for energy user side. The actual energy grade improvement rate of the system can reach 4.24∼16.45%. The theoretical model guides practical TCES application for improve energy grade.