Development of a mechanistic fouling model for predicting deposit formation in a woodchip-fired grate boiler

Currently fouling is still a major issue for the woodchip-fired boilers, which limits the utilization of the woody type fuel. In this work, a mechanistic fouling model considering both ash deposition and removal mechanisms was developed to model ash deposition. New criterions for the sliding and rolling particle detachment were proposed, and the effect of impacts among multiple particles, particle sizes of the deposited particles and surface roughness on ash deposition were considered. Combining with the Discrete Phase Model (DPM), heat transfer model, and dynamic mesh model, and this newly developed fouling model, the simulation tool was applied to predict the growth of ash deposit on a single tube. Good agreement was obtained between the simulation results and the results from a lab-scale experimental setup. By further investigation, it was found to be necessary to consider the removal process even when the flue gas velocity was as low as 1.93 m/s, and increasing the flue gas velocity significantly reduced ash deposition. The Young’s module of ash particles was also identified as an important parameter for ash deposition. The results indicate that the developed mechanistic model is a promising approach for predicting ash deposition behavior in the woodchip-fired grate boilers.