Numerical prediction of characteristics of ash deposition in heavy fuel oil heat recovery steam generator

Resolving ash-related problems such as fouling and slagging is crucial to the operation of a heat recovery steam generator (HRSG) in a power plant using heavy fuel oil (HFO). This paper presents numerical predictions of ash particle deposition using a model implemented with CFD code. The deposition model considers the force of gravity, elastic rebound, and adhesion forces acting at the moment of ash particle impact, which determine if the particle bounces off or stays on the surface and accumulates into a deposit. The 2D simulation results showed that ash deposition depends significantly on the particle size and velocity. The normal gravity force is a significant parameter that determines the position of deposition. The simulation results for ash deposition in an HFO-HRSG showed that ash deposits are highest (~34%) in the first and second rows, where the particles hit first, after which deposition decreases. However, ash deposits in the internal array increase again in the rear rows because rebounding particles decelerate and are deposited because of gravity, as confirmed by observations of actual deposit formation.