Microstructural evolution of tailoring CaO/CaCO3 composites with alumina particle of varied sizes for thermochemical heat storage

Calcium-loop (CaL) heat storage technology is a potential backup energy option for concentrated solar power plants. During repeated cycles, calcium-based materials face sintering and agglomeration, leading to a rapid decline in heat storage capacity. The most widely studied closed CO 2 Brayton cycle requires calcium-based materials to undergo repeated cycles in a carbon-dioxide-rich atmosphere, but such work has been limited in the past. In this study, we synthesized various millimeter-sized calcium-based heat carrier pellets using a novel forming method and evaluated their heat storage performance. Using a simultaneous thermal analyzer (TGA/DSC), we evaluated the materials' heat storage performance and investigated the effects of different particle-size alumina on the pore structure of calcium-based pellets through X-ray diffraction, field-emission scanning electron microscopy, N 2 physical adsorption, and reaction kinetics. The study found that calcium-based pellets with large-particle-size alumina formed a web-like pore structure during cycling, exhibiting better structural stability. In contrast, those with small-particle-size better maintained their initial pore structure. Alumina-added calcium-based pellets had more abundant pores, with the large-particle-size alumina group having a specific surface area 3.5 times that of pure calcium oxide pellets. Additionally, the accumulative heat storage density of calcium-based pellets with small-particle-size alumina after 20 cycles was about 1.72 times that of pure calcium oxide pellets. It was worth noting that we found that shortening the carbonation time within the scope of this research could slow down the degradation of the exothermic performance of calcium based pellets.