Rate-Equation-Based Grain Model for the Carbonation of CaO with CO2

Abstract

A rate-equation-based grain model was developed to describe and predict the complex behaviors of the carbonation reaction of CaO with CO2 in calcium looping. In the model, the assumption of a uniform CaCO3 film at the grain scale was replaced with the product island morphology, and the rate equation theory was used to calculate the growth of product islands; this modified grain model was integrated into a particle scale model in which gas diffusion inside a CaO particle and the pore plugging effect were considered. The macroscopic kinetics of the carbonation reaction—including the initial fast stage and the later product layer diffusion stage—could be predicted successfully using the developed theory and was validated by comparison with experimental data. The effects of structural parameters on the carbonation kinetics were discussed. Furthermore, a nanometer-scale grain design criterion for CaO sorbent was proposed to optimize particle structure and achieve maximum CaO conversion in the initial fast stag...