The objective of this work is to investigate the behaviour of the two main mathematical models used for the estimation of SO2 reduction with the application of the dry additive method. The shrinking-core and pore-tree models for the conversion of the reactant CaO to CaSO4 are tested for various parameters such a SO2 concentration, temperature of the flue gas, porosity and diameter of the sorbent particles. Furthermore, a comparison between the accuracy of predictions of these two models, using experimental test cases, is presented.