A fundamental approach to the prediction of coal ash deposit formation in combustion systems

Abstract

A fundamental study encompassing measurement and prediction of ash deposit initiation was conducted under conditions representative of coal-fired boilers. Laboratory experiments were performed with four bituminous coals to determine the ash collection and adhesion efficiencies due to inertial deposition. Measurements of the ash particle size distribution and composition as well as the deposit composition were made. An ash deposition model was developed based on a new viscosity model relevant to silicate glass with viscosities in the 105 to 107 Pa·s range in combination with crystallinity criterion for iron and calcium-rich particles. At long furnace residence times, the collection efficiency and deposit composition were predicted successfully for all four coals by using a critical viscosity of 105 Pa·s and assuming iron to be predominantly in the +3 oxidation state. At short residence times, the assumption of the +2 oxidation state for iron appears to be appropriate for these coals.