This paper presents a case study of a heat recovery system in an incinerator of waste sludge from a pulp mill. The aim of this study is to find an optimized design of additional measures to be installed in the exhaust duct of the incinerator to help prevent fouling in a connected heat exchanger. A Computational Fluid Dynamics (CFD) approach is a natural choice for this application as no experimental evaluation of the proposed solutions can he performed. Input data are obtained from the process using simpler, balance-based approaches. CFD analysis is first used to determine what causes the finding and then optimize the duct design in order to eliminate the undesirable phenomena. Several solution alternatives are proposed consisting of sets of vanes with different geometries. The finite volume model employed in the computations is described, and the adopted approach, assumptions, and simplifications are discussed. The studied alternatives are evaluated and the best of them 's found using a flow uniformity index based on velocity distribution in a reference cross-section. It is concluded that the insight gained by CFD analysis is decisive for arriving at an improved design in this application.