Glycine tailored effective CaO-based heat carriers for thermochemical energy storage in concentrated solar power plants

Calcium looping process (CaLP) is one of the most perspective thermochemical energy storage (TCES) strategies to meet the demands of developing the 3rd generation concentrated solar power plants (CSP) in the CO2 Brayton cycle. However, the CaO-based heat carriers inevitably experienced severe sintering over the cycles, and their energy storage capacities deteriorated drastically. Research on the energy storage capacity of the CaO-based heat carriers in a closed-loop calcium looping process for thermochemical energy storage (CaLP-TCES; i.e., calcining the CaO-based materials under CO2-rich stream, which is much practical in the industry) is rare. Hence, this work employed a novel recipe to synthesize a variety of organic acid-modified CaO-based heat carriers to explore their thermochemical energy storage performance in a new closed-loop CaLP-TCES system. The energy storage capacity of the materials was evaluated by a simultaneous thermal analyzer (TGA/DSC), and the mechanism behind their promising energy storage performance was explored by X-ray diffraction, field emission scanning electron microscopy, N2 physisorption, reaction kinetics method and so on. Results showed that glycine modified eggshell ("Glycine eggshell") was an effective heat carrier for the CaLP-TCES system. After 60 repeated cycles at "650 degrees C - 900 degrees C," "Glycine eggshell" accumulated an energy storage capacity of 110.124 kJ/g, which was approximately six times higher than that of "Raw eggshell". Comprehensively considered the effect of carbonation temperature and calcination temperature on the energy storage/releasing performance of the "Glycine eggshell" materials, "750 degrees C - 900 degrees C" was the best option for the closed-loop CaLP-TCES system for the concentrated solar power plants. After glycine modification, the rich mesoporous and macroporous structure in the CaO-based material was generated, thereby improved cyclic thermochemical energy storage performance.