Investigation of heat transfer characteristics of CaCO3 pellets during the thermochemical energy storage process in a packed-bed reactor: A dual-scale (2D + 1D) transient numerical study

Abstract

Compared with powdery CaCO₃ materials, milli-sized CaCO₃ pellets offer remarkable advantages in large-scale thermochemical energy storage (TCES) applications. However, there is a lack of a dual-scale packed-bed reactor model that couples the pellet scale and the reactor scale for CaCO₃ pellets TCES. Based on model validation by comparing it with existing experimental data, this study develops a dual-scale packed-bed reactor model for the CaCO₃ pellets TCES reaction. Firstly, the impact of pellet structural parameters and operating conditions on the heat transfer behavior of reaction pellets is evaluated. Then, a sensitivity multivariate analysis reveals the interplay between these key design parameters. The results show that the heating temperature is the most critical factor affecting the TCES performance of CaCO₃ pellets. When the heating temperature is raised from 1073 K to 1223 K, the overall conversion of pellets increases from 39.15% to 85.50% after 12 h. The size of the pellets significantly affects the heat transfer between the heating fluid and the pellets, as well as within the pellets. As the pellet radius increases from 0.25 mm to 5 mm, the maximum radial average temperature difference between the pellets and the heating fluid (HTF) increases from about 0.23 K to 19.03 K. Increasing the porosity of the pellets and accelerating the inlet velocity of the HTF both enhance the surface heat transfer between the HTF and the pellets. These results contribute to predicting the conversion behavior and the coupled multi-physics transport processes of CaCO₃ pellets in packed-bed reactors.