Characterization of fly ashes from the combustion of post-consumer waste wood

A considerable amount of post-consumer waste wood is generated in industrialized countries. Usually, this waste is combusted in biomass combustion plants. Because of the contamination of the waste wood with heavy metals, the fly ash produced in the combustion process also contains higher amounts of some heavy metals. In the fly ash samples investigated, the concentrations of Pb and Sb were significantly increased. The concentrations of As, Cd and Cu were elevated to a lesser extent, and the content of Ca and SO42- was also higher when compared to fly ash from the combustion of untreated wood. Several physical properties (particle size distribution, effective angle of internal friction, wall friction angle and flowability) were quite similar to those reported for second-stage fly ashes from combustion plants using untreated wood and forest residues as fuels. In contrast, the density of the waste wood combustion fly ashes was distinctly lower while the bulk density was higher. As a result, the porosity in the waste wood combustion fly ash was lower, while the values for the angle of repose were somewhat higher.