Abstract:

High heat storage density and cross-seasonal heat storage are two advantages of thermochemical heat storage. In medium-and high-temperature heat storage, the heat storage material of the calcium oxide/calcium hydroxide heat-storage system is easy to accumulate but is challenging to fluidize. This study wrapped calcium hydroxide pellets in a sintered silicon carbide ceramic shell to create a heat storage pellet with a core-shell structure. Although the internal pores of the shell and core of this core-shell structure particles show different pore size distribution, the pore size of the shell is larger than the pore size of the internal calcium hydroxide core, so the wrapping of the shell has less impact on the internal calcium hydroxide storage and exothermic reaction process. Compared with pure calcium hydroxide, the core-shell structure particles' reaction rate and mechanical properties have also improved. The characterization results show that the shell of the pellets is chemically stable and does not react with calcium hydroxide to cause a decrease in the thermal storage density.In addition, the core-shell structure particles have good cycling stability, and the prepared particles were subjected to 25 exothermic and endothermic cycles under an air atmosphere. It was discovered that the particles' loss in heat storage density was 20% or less, and there was no cracking or fragmentation. However, the reaction of calcium hydroxide with carbon dioxide in the air decreased the heat storage density of the pellets. Still, after high-temperature calcination to make calcium carbonate decompose into calcium hydroxide again, the heat storage density of the pellets could be restored to 96.7% of the initial heat storage density. In summary, preparing heat storage particles in this study is significant for applying thermochemical heat storage technology.

Key words: thermochemical heat storage, calcium hydroxide, granulation