Kinetic Analysis of High Temperature Thermochemical Energy Storage Based on Calcination–Carbonation Chemical Looping Reactions

This work aims to improve the performance of carbonate storage systems, a form of thermochemical energy storage (TCES) for concentrated solar power (CSP) technologies. TCES has great potential due to its high energy storage densities and inexpensive materials, making it highly competitive with commercial molten salt storage systems. The storage system is based on metal oxide calcination–carbonation chemical looping, a cyclic process for which a broad range of metal oxide candidate materials are considered. Metal oxide produced in the solar-driven endothermic calcination reaction is cycled to the exothermic carbonation reaction, from which thermal energy is released to drive a power cycle.

This work details a comparative thermodynamic and kinetic study of calcination and carbonation reactions, using commercial samples and synthesized mixtures of carbonates such as CaCO₃ and SrCO₃. Experiments are carried out under a CO₂ atmosphere using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and the materials are selected to attain the desired storage temperature (typically above 565°C), energy density and charging and discharging rates. Chemical and structural cyclability of candidate materials are evaluated as a function of the calcination–carbonation cycle number using several characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption and X-ray diffraction crystallography. We show how different mixtures and synthesis precursors can improve the cyclability of metal oxide–carbonate systems.