Effect of chemical additives on hard deposit formation and ash composition in a commercial circulating fluidized bed boiler firing Korean solid recycled fuel

Abstract

Combustion of SRF (solid recycled fuel) and biomass with potassium (K), sodium (Na), and chlorine (Cl) contents can result in operational problems such as hard deposit formation and convection pass tube corrosion. Two types of commercially available chemical additives, ammonium sulfate [(NH4)2SO4] and borax solution, were examined to elucidate their effect on hard deposit formation and the particle composition of fly ash on the convection pass of a commercial CFBC (circulating fluidized bed combustion) boiler. The addition of ammonium sulfate/borax solution hindered metal chloride formation and reduced the amount of hard deposit formation on the convection pass tubes. Both the alkali and potassium chloride content and the point load hardness of the hard deposit were reduced, while the melting temperature increased according to the borax solution use. When chemical additives were employed, the particle size distribution of the fly ash shifted to coarse particles. In particular, SEM (scanning electron microscopy) images of the fly ash particles revealed the attachments of fine particles to the ash particles. These were assumed to be mineral salts attached to the coarse particles, which increased the overall particle size distribution.