Performance evaluation of ZTA ceramic encapsulated calcium hydroxide pellets for thermochemical heat storage

The development of Ca(OH)2/CaO reaction system is promising for thermochemical heat storage. However, the challenges such as the cohesiveness of powder materials and volume change during cycling hinder the practical application of this reaction system. To address these issues, this paper developed the zirconia toughened alumina (ZTA) ceramic encapsulated pellets. Although the presence of a ceramic shell decreases the heat storage density, it can limit the volume expansion of materials and stabilize particle size, resulting in the improvement of cycling stability. The test results indicate that the pellets exhibit stable hydration and dehydration capacities of 90 % during 20 cycles. The shell with a high and stable porosity of 78 % permits water vapor to transfer and provides a stable crushing strength of 10 N during cycling. Additionally, due to the compression of internal materials, the heat storage rate of encapsulated pellets is faster than pure Ca(OH)2. The porosity of encapsulated pellets increases at first and then remains stable during cycling, leading to the initial increase and subsequent decrease in heat storage rate. The maximum heat storage rate occurs in the fifth cycle, and the decomposition onset and end time can decrease by 2.91 % and 3.20 % compared to the first cycle, respectively.