Microwave-assisted dehydration of calcium hydroxide for thermochemical energy storage

This study demonstrates the successful dehydration of calcium hydroxide (Ca(OH)₂) under microwave heating, employing silicon carbide (SiC) as a passive heat-sorbent and heat-transfer enhancer. The experimental setup involved compacted powder samples in pellet form composed of Ca(OH)₂ and SiC (β form). These pellets were loaded onto a quartz-glass tube and positioned within a cylindrical microwave cavity operating in the single TM₀₁₀ mode, which concentrates the microwave's electromagnetic field along its axis. Under identical 30 W power input, the Ca(OH)₂-SiC blend achieved a temperature of 418 °C, while the precursor Ca(OH)₂ pellet only reached 85 °C. Notably, an analysis of the microwave cavity's resonance frequency revealed fluctuations in the spectrum during the experiments, indicating the ongoing dehydration reaction. This observation was corroborated by a multiphysics model that accurately predicted the system's temperature evolution and provided insights into the temperature distribution within the sample and the progression of the reaction. Microwave heating at 30 W is expected to raise the pellet's temperature to over 600 °C, ensuring a uniform and elevated temperature distribution. This, in turn, facilitates rapid reaction rates, ultimately leading to a potentially high power density of 1.21 MW m⁻³. In conclusion, the incorporation of SiC powder proves to be a promising strategy for efficiently heating packed bed reactors in thermochemical energy storage, offering a viable alternative to traditional methods such as Joule heating or heat exchange with heat transfer fluids. Furthermore, the ability to monitor chemical reaction progress via resonance frequency analysis and change of dielectric properties opens avenues for exploring chemical reactions kinetics as an alternative to thermogravimetric measurements.