Hydrodynamic and reaction kinetic responses of CaO/CaCO₃ carbonation in bubbling fluidized bed reactors for thermochemical energy storage: Influence of CO₂ mole fraction, grain size, and reactor dimensions

The CaO/CaCO₃ thermochemical energy storage system offers a promising method for the efficient utilization of solar energy. However, the reactor design remains underdeveloped. In this study, the Eulerian-Eulerian two-fluid model is employed to systematically investigate the effects of CO₂ mole fraction, particle size, and reactor dimensions on the carbonation process in a bubbling fluidized bed reactor. Increasing the CO₂ mole fraction from 50 % to 80 % reduces the duration of the chemical-reaction-kinetics controlled stage from 118.5 s to 65.3 s, and the transition stage from 64.6 s to 36.7 s, with minimal impact on the final conversion rate. High CO₂ concentrations cause insufficient bed fluidization and uneven local conversion rate distribution within the bed. As the grain size increases from 150 nm to 300 nm and 600 nm, the duration of the chemical-reaction-kinetics controlled stage decreases from 118.5 s to 104.0 s and 76.2 s, respectively. This causes the reaction to enter the transition phase earlier, ultimately leading to a reduction in the maximum conversion rate. Altering the height and width of the reactor does not significantly impact the conversion processes within the reactor. These findings provide valuable insights for the optimization and practical industrial application of efficient reactors.