This work presents a model of ash deposition growth in the ash hopper of utility boilers when the nozzles are tilted downwards. The model consists a comprehensive combustion code to predict the flow field, temperature field, the gas and solid combustion and the deposition growth behavior. The results show that burner tilting has a significant effect on the deposition in the ash hopper. The work indicates that the numerical model can be used to optimize the design and operation of pulverized coal-burning boiler equipped with tilting burner systems. (C) 2002 Elsevier Science B.V. All rights reserved.