ABSTRACT
A theoretical study was performed to investigate the effect of ash chemistry and non-constant thermal properties on the calculated heat flux through a coal ash deposit. A mathematical model, previously developed to describe the build-up of furnace wall deposits, was used to predict the rate of deposit growth, thermal conductivity, and porosity of the deposit, as well as the heat transfer through the deposit. In this study, a method to predict deposit emittance and absorbance as a function of composition and particle size was added to the deposition model. Simulations showed that the ash chemistry had a significant effect on the thermal and physical properties of the deposit and, consequently, the heat flux through the deposit. Significant differences in the predicted heat flux through the deposit were observed when constant values (not varying with time and/or position) for the deposit emittance and thermal conductivity were assumed. The observed differences are largely due to the inability of the constant properties to adequately predict the resistance of the inner layer of the deposit which significantly affects the heat transfer through the deposit.
