CaCO3 decomposition for calcium-looping applications: Kinetic modeling in a fixed-bed reactor

Abstract

Calcium looping can be used in various environmental applications such as post-combustion CO2 capture, sorption-enhanced reforming and thermochemical energy storage. The calcination reaction mechanism and the effect of CO2 partial pressure have not been fully clarified yet justifying further efforts; this work focuses on kinetic modeling of the reaction. Herein, calcination kinetics of limestone were studied experimentally in a fixed-bed reactor, and theoretically using different models previously reported in the literature. The Uniform Conversion Model (UCM) and the Changing Grain Model (CGM) described better the conversion-time data than the Random Pore Model (RPM). A Langmuir-Hinshelwood mechanistic model, which included the decomposition of CaCO3, the desorption of CO2 and the CaO* relaxation fitted well the reaction rate values leading to an activation energy of 210 kJ/mol and the pre-exponential factor equal to 18,860 kmol/(m2 s). The model was validated by predicting adequately the decomposition rates measured by other authors under different conditions.