This paper has been written to provide a realistic approach to modeling an in-duct desulfurization process and because of the disagreement between the results predicted by published kinetic models of the reaction between hydrated lime and SO2 at low temperature and the, experimental results obtained in pilot plants where this process takes place. Results were obtained from an experimental program carried out in a 3-MWe pilot plant. Additionally, five kinetic models, from the literature, of the reaction of sulfation of Ca(OH)(2) at low temperatures were assessed by simulation and indicate that the desulfurization efficiencies predicted by them are clearly lower than those experimentally obtained in our own pilot plant as well as others. Next, a general model was fitted by minimizing the difference between the calculated and the experimental results from the pilot plant, using Matlab (TM). The parameters were reduced as much as possible, to only two. Finally, after implementing this model in a simulation tool of the in-duct sorbent injection process, it was validated and it was shown to yield a realistic approach useful for both analyzing results and aiding in the design of an in-duct desulfurization process. (C) 2008 Elsevier B.V. All rights reserved.