A detailed model for a wet flue gas desulphurisation (FGD) pilot plant, based on the packed tower concept, has been developed. All important rate determining steps, absorption of SO2, oxidation of HSO3-, dissolution of limestone, and crystallisation of gypsum were included. Population balance equations, governing the description of particle size distributions of limestone in the plant, were derived. Model predictions were compared to experimental data such as gas phase concentration profiles of SO2, slurry pH-profiles, solids content of the slurry, liquid phase concentrations, and residual limestone in the gypsum. Simulations were found to match experimental data for the two limestone types investigated. A parameter study of the model was conducted with the purpose of validating assumptions and extracting information on wet FGD systems. The modelling tools developed may be applicable to other wet FGD plants.