Prediction of local deposition rates for gas-side particulate fouling in refuse waste incinerators

Waste heat recovery boilers as applied in refuse waste incinerators are susceptible to fouling. On the tube bundles in the boiler deposits are observed ranging from thin and powdery to thick and sintered with large ridges at the upstream side of the tubes. Both types of layers result in a decrease of the overall heat transfer coefficient of about 27%. To optimize the geometry of the bundle such that the formation of layers is minimized a model is developed that, as a function of the geometry, predicts the local deposition rate of particles. The model incorporates both the transport and the sticking of these particles to the surface. The applied sticking model is based on the two-body approach. The validity of this approach is shown using well-defined experiments in which the rebound characteristics of particles impacting on a powdery deposit are measured. Using the results from the impact experiments the deposition rate is calculated for a tube bank geometry with a varying pitch. The calculated deposition rates, when using the sticking model, are in the same order as the deposition rates reported for the industrial case. From these first calculations, it also appears that the pitch has a strong influence on the formation of a deposit on the tubes.