Influence of ash species on particle size dependence of water- and citric-acid-soluble potassium concentrations of woody biomass combustion ashes with low potassium content

Abstract

The dependence of the concentrations of water- and citric-acid-soluble potassium on particle size was investigated for two types of low-potassium-content woody biomass combustion ash discharged from different biomass power plants. For both types of ash, the potassium concentration increased as the median diameter decreased; crystalline potassium, such as KCl and K2SO4, was identified more in fine combustion ash, whereas crystalline SiO2 and CaCO3 were abundant in coarse ash. The potassium components could be present as finer ash particles or as cover over coarser ash particles composed of crystalline SiO2 surfaces. Differences in the existence forms of the potassium components caused differences in the dependence of potassium concentration on the median diameter of the ash. Moreover, the methods used to calculate the particle size distributions of three ash particle components (water-soluble, citric-acid-soluble, and insoluble) in the ash residues can be used to evaluate the particle size dependence of both potassium concentrations to some extent. The potassium enrichment process demonstrated in this study could be successfully performed on a factory scale via the surface grinding of bottom ash. The collected fine grinding debris containing rich potassium, separated from the surface of the silica, was found to be possibly reusable as fertilizer.