Heterogeneous noncatalytic reactions are numerous and of significant importance in industrial applications. The capture of carbon dioxide (CO2) using a calcium-based sorbent as a heterogeneous noncatalytic gas?solid reaction has been widely proposed for CO2 capture process. In current study, the behavior of the carbonation reaction of the calcined Cadomin limestone used for CO2 capture is explored using a novel modified changing grain size (CGS) model, which takes into accounts the grain size distribution and sintering of the sorbent simultaneously. In the proposed model, grains have different initial radius and the evolution over time of grain size distribution function is computed using modified population balance model by addition of two birth and dead terms presenting the rate of appearance and disappearance of the grains due to sintering phenomena, respectively. To validate the modeling results, the overall conversion of calcined limestone was compared with experimental data points obtained at 650? and atmospheric pressure for carbonation reaction.