Calcium chloride dihydrate as a promising system for seasonal heat storage in a suspension reactor

Abstract

The shift to renewable energy sources increases the demand for energy storage to balance supply and demand. The call for heat storage solutions is particularly high with heat dominating residential energy needs. Simultaneously, significant industrial waste heat potential could be seasonally stored in reversible chemical reactions using thermochemical energy storage technologies. This study investigates the reversible dehydration of calcium chloride dihydrate which has been recognised as a suitable thermochemical material in prior studies. A new method is introduced by investigating the reaction in a lab-scale batch-type suspension reactor. In the reactor, a mechanical stirrer suspends the solid thermochemical material in an inert liquid, to prevent agglomeration of the particles. The investigation involves a parameter variation that includes different suspension media, different mass fractions of the solid reactant, as well as different system pressures during charging. The experimental investigation renders 40 wt% solid or lower as the most promising mass fraction to avoid agglomeration. Vegetable oils show promising results as suspension media. However, they lack thermal stability in the temperature range of up to 210 °C. Mineral oil can ensure thermal and cycle stability. Furthermore, a notable reduction in the dehydration reaction temperatures (176 to 109 °C) is observed when the system pressure is decreased down to 50 mbar. The study concludes that calcium chloride dihydrate has the potential to be used for 22 stable charging and discharging cycles in a mineral oil suspension and that lowering the system pressure can reduce the required charging temperature of the system. To further enhance the suspension method, it is essential to focus on mass transfer and foam mitigation during the dehydration reaction.