Evaluation and performances comparison of calcium, strontium and barium carbonates during calcination/carbonation reactions for solar thermochemical energy storage

摘要

The efficiency and economic competitiveness of thermal storage for concentrating solar power plant can be improved by increasing the operating temperature (above 600 °C). Thermochemical energy storage is an attractive way of efficiently storing high-temperature solar heat, in the form of chemical bonds as a stable and safe solid material, when compared with existing sensible and latent heat storage materials. Among the most interesting materials, BaCO_3, CaCO_3 and SrCO_3 show high storage temperatures (typically above 800 °C), energy storage densities, and charging and discharging rates. Heat charge corresponds to the calcination (decarbonation) reaction of the carbonates (endothermal step) and heat discharge corresponds to the reverse carbonation of the oxides (exothermal step). A comparative thermodynamic and kinetic study of calcination and carbonation reactions involving commercial and synthesized CaCO_3, SrCO_3 and BaCO_3 powders was performed for application in thermochemical energy storage. An experimental study based on thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) was conducted to study the decomposition and carbonation reactions and to determine the enthalpy of reaction for each metal carbonate. While complete calcination was achieved regardless of the metal carbonate involved, partial carbonation was observed with loss in CO_2 capture capacity during cycling. The effect of the addition of a promoting agent such as magnesium oxide on thermal stability for improving chemical and structural cyclability of these three candidate carbonates was also investigated. Beneficial effect of MgO addition was demonstrated and noticeable performance stability was obtained in the case of SrCO_3/SrO during successive energy storage cycles.