Measures for the improvement of process waste gas (PWG) distribution into U-tubes of a tube bank heat exchanger, which is a part of a liquid and gaseous wastes incineration unit, are discussed. Since PWG is being preheated by high-temperature flue gas, increasing the distribution uniformity is crucial. A computational fluid dynamics (CFD) software is used to analyse the existing PWG flow in the entire tube-side subsystem of the preheater and also to optimize the geometry by means of comparing results obtained for several different inlet region designs. Due to the size of the preheater, however, simplified 2D geometries are usually evaluated with detailed 3D evaluations being done only in case of a few key configurations. Such an approach greatly speeds up the optimization process. In addition to PWG distribution, vorticity is taken into account as well in order to reduce fouling.