A mechanistic approach has been used for assessing the ash deposition tendency and has been used for predicting the ash deposition behavior of Australian bituminous coals in a pilot-scale test furnace. The detailed analysis of mineral matter in coal determined by QemSCAN analytical technique was incorporated into an ash formation model to estimate the character of ash particles. The detailed chemical composition and particle size distribution data of ash particles from the ash formation model were incorporated into a computational fluid dynamics (CFD) code to get the arrival rate and retention ability of each ash particle onto the heat transfer surfaces. The CFD code along with the ash character from the ash formation model was able to simulate trends in ash deposition along the furnace length similar to those in the test furnace. The approach was also able to distinguish coals with high ash deposition potential from low ash deposition problems and the results agreed with those in test furnace.