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. As a consequence of the particles that comprise the fly-ash, the axial fan blades are subject to erosion resulting in material wear at the leading edge, trailing edge and blade surface. Erosion results in a loss of the blade aerodynamic profile, a reduction of blade chord and effective camber that together degrade aerodynamic performance. In this paper, the authors use a numerical study to predict the aerodynamic performance of the as-new blade and the same blade as-eroded after 9,000 hours in-service. The authors predicted fan performance and stall margin for both the as-new and as-eroded blade, and evaluated the impact for fan operation at a constant duty point. The authors calculated particle trajectories using an in-house Computational Fluid Dynamic (CFD) solver coupled with a particle cloud tracking model predicting solver based on an original finite element interpolation scheme. The numerical study clarifies the influence of fan aerodynamic operation to the determination of the erosion regimes and patterns. The authors also investigate the coupling between the three-dimensional flow structure at high- and low-volume flow rate and the particle motion to provide insight into the performance degradation process, and the risk that continued operation poses to the fan's mechanical integrity.