Particulate fouling of convective heat-transfer surfaces is usually assessed by empirical correlations. Nevertheless, constant progress in numerical calculation methods allows for prediction of deposition. This paper presents results of 2D modeling of powdery, medium-temperature deposit formation on superheater tubes. In contrast to other studies, presented approach results in shape prediction of deposits versus time of boiler operation. The mechanism includes the force of gravity, elastic rebound and adhesion forces acting at the moment of ash particle impaction. The forces determine if the particle bounces off the surface or stays onto it building up the deposit. Two practical cases are considered - an upward flue gas flow and a downward flow in the boiler. The results of simulations are compared with measurements in real boilers published earlier. The full-scale results are reproduced well. The simulations are carried out with use of Fluent code by means of User Defined Files. The described mechanism is implemented in Define_DPM_Erosion, and shape prediction is mirrored using Define_Grid_Motion functions of the Fluent code. (C) 2012 Elsevier Ltd. All rights reserved.