This paper discusses the development of specialized subroutines used in a Computational Fluid Dynamics code (FLUENT(TM)) to accurately predict temperature, velocity, and species profiles in a down-fired, pilot-scale, pulverized coal combustor and in the t-fired industrial boiler. A Lagrangian particle tracking algorithm, along with an advanced char burnout kinetic (CBK) model, was used to accurately predict the representative particle trajectories, as well as the loss of carbon from coal particles. The devolatilization and burnout parameters for the full-scale industrial combustion model were generated using the first principles and the combination of drop-tube/pilot-scale experiments. Additionally, the moisture that evolved from coal/biomass char heating is included via surface reactions, which accounts for char burnout due to steam and CO2 gasification. Carbon conversion that is caused by steam gasification may be significant when the amount of moisture is high in char. This endothermic reaction also may play a significant role in the stability/extinction of the flame or flame lift-off. The predictions of the code were compared to experimental measurements of gas temperature and 02 and CO in both of these combustors. Good agreement was found between the temperature and species predictions and the measured values.