Numerical Investigation on Development of Initial Ash Deposition Layer for a High-Alkali Coal

Burning high-alkali content coals frequently causes severe fouling and slagging problems, which greatly threaten the efficiency and safety of boilers. In this paper, a set of numerical models have been integrated and validated to predict the development of initial deposition on the tube of a superheater for high-alkali yield fly ash particles. Besides the normally used ash particles transport models (inertial force, turbulent eddy effect, thermophoretic force) and adhesion model (alkali coating surface model), a deposit erosion model based on the energy dissipation at impaction has been introduced. The predicted characteristics, such as mass, morphology of deposit, and particle size distribution of deposited ashes, are compared with experimental observations in a 350 MWe boiler and a 10 kW laboratory furnace, respectively. The results show that, for a coal with high-alkali content, the proposed models can well predict the development of initial ash deposit layer, especially the phenomena of windward deposit erosion at high Reynolds number surrounding flow in real facility.