Parametric study of CO2 capture and thermal energy storage in a CaO/CaCO3 bubbling fluidized bed with polydisperse particles

Abstract

The CaO/CaCO₃ cycle system holds broad application prospects in high-temperature processes such as thermal chemical energy storage for concentrated solar power generation and CO₂ capture and utilization. However, most numerical studies typically employ calcium-based particles of a single particle size, making it difficult to reflect the influence of particle size distribution on fluidization and reaction behaviour within actual systems. To elucidate the fluidization and reaction characteristics of CaO/CaCO₃ in bubbling fluidized beds, this study employs polydisperse calcium-based particles as the research subject. Numerical simulations incorporating chemical reactions are conducted to investigate particle fluidization behaviour under varying gas velocities, inlet CO₂ volume fractions, and dynamic operating conditions from a parameterisation perspective. By comparing different particle size combinations, characteristic parameters such as bed solid content distribution, time-averaged CO₂ concentration, time-averaged axial solid content, and time-averaged velocity were analysed. Results indicate that at constant gas velocity, the bed’s CO₂ adsorption efficiency gradually decreases as particle size increases from 75 μm to 136 μm. In the mixed-particle-size system, at the same gas velocity, the CaCO₃ solid content in the single-particle-size bed was slightly lower than that in the mixed-particle-size bed, while the CaO solid content was higher than that in the mixed-particle-size bed. Under different inlet CO₂ concentration conditions, higher CO₂ concentrations led to decreases in the bed's time-averaged velocity and time-averaged axial solid content. Considering particle temperature distribution, CO₂ adsorption efficiency, CaO conversion rate, and energy storage density comprehensively, the calcium-based particle system demonstrated superior overall performance when the inlet CO₂ volume fraction was 0.85.