Modeling and simulation of flue gas desulfurization over sorbent synthesized from CaO/CaSO4/coal fly ash in a fixed-bed reactor has been studied. A mathematical model was proposed based on the material balance for the gaseous and solid phase using partial differential equations to describe the adsorption of SO2 from a moving gas stream to the sorbent-bed of changing composition. The kinetic parameters of the mathematical model were obtained from a series of experimental desulfurization reactions carried out under isothermal conditions at various operating parameters; initial concentration of SO2 (500 ppm <= C-o <= 2000 ppm), reaction temperature (333 K <= T <= 373 K) and relative humidity (40% <= RH <= 70%). The partial differential equations were solved using a finite difference method. The model was found to give a very good description of the experimental data with an error less than 10%. The validated model was then used to predict the reactor performance under different modes of operation. It was found that higher relative humidity in the feed gas and higher reaction temperature increases the desulfurization activity of the sorbent. On the other hand, higher initial concentrations of SO2 reduce the desulfurization activity of the sorbent.