Synergistic Energy Transfer Regimes of Carbonation Processes in Solar-Driven Calcium Looping: Tracking from Energy Carrier

Calcium-looping (CaL) energy storage technology presents a promising solution to the instability challenges associated with solar energy utilization. Carbonation serves as the crucial step for energy release within the CaL process. Both the heat transport network and underlying mechanisms exert a pivotal influence on the energy conversion performance of the integrated system. In this work, taking the carbonation reaction at the grain scale into account, a cross-dimensional multiphysics model based on the computational fluid dynamics–discrete element method (CFD-DEM) is proposed and developed to quantitatively characterize the spatial–temporal correlation between the non-uniform flow structure and the heat flux distribution in a fluidized bed by employing particle tracking techniques. The energy transfer regime, highlighting the synergistic effect between macroscopic gas–solid hydrodynamics and microscopic carbonation kinetics, is elucidated. It is revealed that a typical core-annulus flow structure is observed during the carbonation process in the fluidized bed, wherein particles manifest complete mixing characteristics. Under the influence of this flow structure, a quasi-periodic oscillatory heat transfer network is established within the initial 12 s of the reaction. The reaction heat and convective heat transfer contribute more than 70% of the total energy transfer, with reaction heat being the most significant. The conduction and radiation heat transfer exhibit comparable magnitudes, but the contribution of radiation heat will further increase associated with the temperature of the energy carrier exceeding 1025 K. Particle tracking indicates that the height of the energy carrier directly affects the carbonation reaction rate, leading to fluctuations in the heat transfer network. Furthermore, the influence of inlet temperature demonstrates that elevated inlet gas temperatures accelerate attainment of carbonation equilibrium and raise the equilibrium temperature, albeit at the expense of diminished reaction driving force. This work will make contribution toward gaining profound insights into the intricate mechanisms underlying mass and heat transfer and offering invaluable guidance for the industrial design of CaL systems for thermal energy storage.