Dry scrubbing processes, especially dry sorbent injection technology, offer a more economical technology for retrofitting than wet or semi-wet scrubbing processes. A simple realistic model for the in-duct desulfurization process has been developed. The model has been conceived as an approach useful for both analyzing results and aiding in design of an in-duct desulfurization process. The model of the process involved, which is the basis for the discussion in this paper, has been evaluated by comparing the model results and the experimental data, obtained in a pilot plant study. The predicted values agree reasonably well with the available experimental data, and the relationships in the model presented have been verified. The sensitivity analysis of variables is relevant for the design and operation of the in-duct process, allowing a parametric study that reveals the effect of the different operation and design factors. Although this model is specific to our in-duct pilot plant, it may be used with confidence in commercial DSI (dry sorbent injection) units as it was designed and implemented according to widely accepted engineering rules in this field. The model has been built in an open structure to allow for rearrangements of and extensions to the process. (c) 2008 Elsevier B.V. All rights reserved.