Bubbling Fluidized Bed Reactors for CaO-Based CO₂ Capture with Geldart Group B Particles: A Critical Review of the Coupling Between Bubble Hydrodynamics, High-Temperature Heat Transfer and Carbonation Performance

ABSTRACT: Bubbling fluidized beds are used in calcium looping for sorbent testing, thermochemical energy storage, and selected carbon-capture and sorption-enhanced processes. Their performance depends on gas distribution between bubbles and emulsion, the evolving properties of CaO/CaCO₃ particles, sorbent circulation, and heat removal. This critical narrative review examines these interactions for particles exhibiting Geldart Group B behaviour. Coupled fluidized-reactor modelling is established, including earlier bubbling-bed calcium-looping models; the contribution here is a synthesis of that literature with transparent screening calculations and an evidence-based validation agenda. A four-constraint representation organizes equilibrium; interphase transport; kinetics and sorbent supply; and thermal feasibility at a specified operating state. The constraints interact, and their minimum is not a substitute for a coupled reactor solution. Calculations account for gas-flow contraction, compare alternative bubble-growth correlations, and examine sensitivity to interchange coefficients, bubble-size distributions, and immersed internals. A reduced coupled example illustrates how finite kinetics and thermal feedback can lower capture below separate limiting estimates. Conversion-dependent particle properties are represented by a conditional constant-envelope calculation and contrasted with measurements of fluidization, bulk density, and fragmentation. Bubble growth can limit capture, but the binding constraint depends on operating conditions and available sorbent. Likewise, the relationship between bubbling and bed-to-surface heat transfer is regime dependent. Reproducible calculations and plotting data accompany the review, and a proposed validation programme identifies the simultaneous measurements needed to evaluate these screening concepts in hot reacting beds.