Effect of Al2O3 Particle Addition on Fluidized Bed Thermochemical Heat Storage Performance of Limestone: From Instability Mitigation to Efficiency Enhancement

This study elucidates the mechanism of fluidization instability during limestone carbonation under a 100% CO2 atmosphere and determines the influence of Al2O3 fluidization aids (dosage and particle size) on exothermic performance. The experiments demonstrate that rapid CO2 absorption in the emulsion phase, coupled with insufficient gas replenishment from the bubble phase, disrupts the balance between drag force and buoyancy, leading to localized defluidization. This instability impedes gas exchange between the bubble and emulsion phases, resulting in bubble coalescence and channeling across the bed. The fluidization instability reduces the maximum exothermic temperature and causes significant temperature heterogeneity in the bed. With repeated thermal cycles (20 cycles), the CO2 absorption capacity of limestone diminishes (the effective conversion rate drops to 0.25), and the instability disappears. The addition of 5wt.% Al2O3 (particle size: 0.05–0.075 mm) stabilizes the fluidization state during carbonation, significantly homogenizing the bed temperature distribution, with maximum and average temperature differentials reduced by 63% and 89%, respectively, compared to pure limestone systems.