Numerical simulation of coal-fly ash erosion in an induced draft fan

Induced draft fans extract coal-fired boiler exhaust gases in the form of a two-phase flow with a dispersed solid phase made of unburnt coal and fly ash; consequently fan blades are subject to erosion causing material wear at the leading edge, trailing edge, and blade surface. Erosion results in blade material loss, a reduction of blade chord, and effective camber that together degrade aerodynamic performance. This paper presents a numerical study of the erosive process in an induced draft fan carried out by simulating the particle laden flow using an original finite element Eulerian-Lagrangian solver. The particle trajectories are calculated using a particle cloud tracking technique that considers drifting near wall and an algebraic erosion model. The numerical study clarifies the influence of fan operation to the determination of the erosion regimes and patterns. In particular, the study investigates the role played by the size and mass distribution of the particles by considering a real composition of the flying ashes in the exhaust flow from a coal-fired boiler. The results illustrate the critical blade areas and erosion rates as given by the particle dynamics of different sizes. A specific analysis of the material wear at the blade leading edge is also given.