Predicting ash deposition behaviour for co-combustion of palm kernel with coal based on CFD modelling of particle impaction and sticking

A CFD model that simulates particle impaction and sticking has been developed for predicting the ash deposition characteristics for the co-combustion of South African Coal (SAC) and palm kernel expeller (PKE) in an entrained flow reactor. The numerical related errors, caused by interception and the improper resolving of the flow-field within the boundary layer near the deposition surface, are investigated. In order to minimize the numerical related errors without excessive meshing, a new revised particle impaction model has been developed and accomplished using an impaction correction factor. The particle sticking is predicted based on the molten fraction results that have been obtained from the chemical equilibrium calculations using the chemical fractionation data in order to consider the short residence time of fly ash particles. The simulation results show that a reasonable coarse mesh, coupled with the revised particle impaction model, is suitable to accurately resolve the particle impaction without using a prohibitive meshing size. The ash deposition behaviour is determined by the particle impaction and sticking properties. Good agreements are obtained between the predicted results and the experimental data for the ash deposition behaviour.