Generation and elimination of defluidization caused by rapid CO2 absorption during CaO/CaCO3 energy storage process

CaO/CaCO 3 energy storage is a promising technology to solve the intermittency of solar energy. Fluidized-bed reactors serve as crucial devices for calcination and carbonation in CaO/CaCO 3 energy storage system . This work presents the first observation of defluidization occurring in CaO/CaCO 3 energy storage process. The mechanism of defluidization was investigated through the exothermic experiment and computational fluid dynamics-discrete element method. Furthermore, the defluidization in the exothermic stage was mitigated by simultaneous nano-silica coating and SiO 2 fines addition. The result indicates that high CO 2 concentration (>80 %), small particle size (0.075–0.18 mm) and low initial bed temperature (700–800 °C) result in the defluidization. The defluidization leads to low exothermic performance of CaO particles and serious uneven temperature distribution in the exothermic stage during CaO/CaCO 3 energy storage process. The simulation result indicates that carbonation proceeding at zero-order kinetics leads to rapid CO 2 absorption in the emulsion phase . The absorption of CO 2 in the emulsion phase surpasses the replenishment of CO 2 from the bubbles, resulting in the contraction of the emulsion phase, which is the cause of defluidization in the exothermic stage. The combination of nano-silica coating for CaO and SiO 2 fines addition enhances the porosity in the emulsion phase, thereby facilitating the diffusion of CO 2 from the bubbles into the emulsion phase. Thus, the defluidization of CaO particles is eliminated by simultaneously coating with 5 wt% nano-silica and adding 3 wt% SiO 2 fines (50–75 μm). After this improvement in fluidization , the bed temperature difference is only 12 % of that in defluidization. Furthermore, the effective conversion of CaO particles increases by 10 % compared with that in defluidization. These findings are helpful for solving the defluidization of CaO particles in CaO/CaCO 3 energy process.