Evaluation of dry fly-ash particles causing difficult deposits for acoustic soot blowing of boilers

Abstract: This thesis compares ash collected from different boilers cleaned using infrasound cleaning. The samples were evaluated from their physical properties, in an attempt to find connections between the difficulty to remove ash and its physical appearance. To get a deeper understanding of the mechanisms behind adhesion and fouling, and possibly explain results from the study of the ash samples, a literature review was carried out. The ash was also evaluated to see if any connections could be drawn between the physical properties of the ash and its fouling capabilities. A strong connection was found between ash density and its fouling capabilities. It was found that no dry ash with a density higher than 0.4 g/ml were difficult to remove with infrasound cleaning, and no ash with lower density was easy to remove. The ash density was calculated from a measurement of the weight of a certain volume of ash on a scale. Optical microscopy was used to study the ash samples, and gave an estimation of particle size, shape, and porosity. However, no clear connection could be observed with this method between the different samples and which were difficult to remove. The particle size for a few of the samples were also measured by a wet laser sieving method, and while it does give a good picture of particle size, the size was not found to be a useful prediction of the ash fouling behaviour. The exact mechanism giving rise to the density dependence need to be further investigated.