The microstructure and pore structure evolution of CaO-based sorbents in three particle size ranges of 0.075−0.1, 0.15−0.18, and 3 mm were investigated using field emission scanning electron microscopy with energy dispersive spectroscopy and nitrogen adsorption−desorption techniques. A clear heterogeneous distribution of elemental carbon across the sorbent particles was found. A particle carbonation reaction model considering the structural evolution effects and the heterogeneously distributed reaction profile were established and verified. It was found that the pore structure of different particle size sorbents all exhibited a transition from the bimodal distribution to the unimodal distribution, which has a great influence on the dynamic reactive characteristics during carbonation. Within the defined particle size range, the carbonation reaction regimes all transform from interface reaction control into mass-transfer control, and the obtained critical product layer thickness that marks the transformation of control regime are 22, 46, and 74 nm, respectively, at 923 K. The maximum relative errors between experimental data and the simulation results calculated separately under interface reaction control (X < 50%) and mass-transfer control (X > 55%) with the effect of pore structure evolution are 12.7% and 12.1% over the defined particle size range.

The pore structure evolution and reaction characteristics of limestone with different particle sizes during thermal decomposition were investigated experimentally. A kinetic model considering the effect of pore structure evolution was developed to simulate the multiscale coupling of the mesoscale pore structure with the macroscopic transport and microscopic chemical reaction. Over a defined particle size range, the calculated results were in good agreement with the experimental data including the influence of gas diffusion throughout the whole decomposition course. A dimensionless Thiele modulus Th was constructed for assessing the critical point corresponding to the transformation of controlled mechanisms.

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The particle reaction model and dynamic reaction characteristics of limestone over a wide particle size range from 0.15 to 10 mm were studied by thermogravimetric analysis and nitrogen adsorption‐desorption techniques. A clear boundary between the sintered porous product layer and the undecomposed part was found by field emission scanning electron microscopy (FESEM) analysis. A dynamic coupling model considering the effects of varied pore structure and transport resistances was established based on the appropriate particle reaction model, which allowed us to predict the decomposition ratio and reaction regimes in a broad range of particle sizes. The dynamic characteristics of pore size distribution and reaction mechanisms were discussed. Over the defined particle size range and calcination temperature range, the diffusion of gaseous product through porous product layer will become the rate determining factor as the ratio of (r0‐rc)/r0 corresponding to 25 % Damköhler number above 0.35.

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