Multi-physics modeling of Ca-based energy carrier for thermochemical energy storage: Revealing the energy release behavior coupled with pore evolution

Calcium looping (CaL) for thermochemical energy storage exhibits high energy density and stable reaction characteristics, indicating significant potential for large-scale application. The calcium-based particle, as the energy carrier, however, occurs to be blocked easily during the carbonation process, which causes the abrupt discontinuation of reaction and then affects the exothermic performance seriously. Investigating the pore evolution and exothermic behavior within energy carrier is thus crucial to improve the reaction performance. In this work, a multi-physics random pore model focusing on pore evolution is developed, which simultaneously reflects both the reaction processes and heat-mass transfer processes within particles. The results show that a faster reaction rate in outer layer leads to the obviously uneven distribution of conversion within the particle. This uneven distribution causes pore blockage to tend to occur on the outermost layer. In order to inhibit the pore blockage, and balance the reaction rate and conversion, the optimal carbonation conditions, with a gas flow temperature of 923 K, a low CO₂ partial pressure, a particle radius of 300–500 μm, and an initial porosity greater than 0.47, is achieved. Furthermore, based on understanding the pore evolution and reaction behavior of energy carrier, a pore structure with a gradient design is proposed for CaL, confirming their superior ability for inhibiting pore blockage and homogenizing reaction. This study presents an effective method for inhibiting pore blockage during carbonation reaction and provides practical guidelines for the manufacture of calcium-based energy carrier.