Gas side fouling of waste-heat recovery boilers is mainly caused by deposition of particulate matter. The influence of the critical sticking velocity on the growth rate of particulate fouling layers is described. The critical sticking velocity (CSV) of an incident particle hitting a powdery layer is defined as the minimum impact speed by which a particle can rebound from the surface. Since the CSV is a key parameter in the deposition mechanism, a well-defined experimental set-up has been built to assign it. Experimental results showed that the CSV increases with the porosity of the fouling layer. A correlation is made between the CSV and the fouling layer thickness. This correlation is based on the experimental results and the variation of porosity with the thickness for thin sintered powdery fouling layers as modelled by Todorov et al [1]. This new correlation shows that the sticking velocity decreases exponentially as the thickness increases. Therefore fewer particles are likely to stick as the fouling layer builds up and consequently the deposition rate decreases. The change in the critical sticking velocity as the fouling layer builds up contributes to the explanation of the asymptotic growth of particulate fouling layers on the tube bundle of waste incinerators.
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