A model approach is presented here to obtain sorption isotherms that are connected with a low cost breakthrough analysis for dry desulphurization of flue gas in a fluidized bed reactor. Experiments were conducted at different temperatures (600-900 degrees C) providing constant feedstock concentration (0.6% SO(2)). The fluidizing gas entered the bed through a distributor and fluidized the single charge of 15 g sorbent. The space velocity ranged from 3100 to 5700 h(-1). Each run was terminated when the steady state was reached. Sulfate layer thickness was calculated from conversion ratio and the structural parameter. Inserting this value and the particle size parameter into the mass transfer equation then extracted the process parameters. Equilibrium relationships involving these parameters were compared with different isotherms. The agreement between the experimental and predicted values of the sorption isotherms validated the model. The latter may be successfully used to design reactors for e.g., sulfating or desulphurization.