Release and transformation mechanisms of trace elements during biomass combustion

Abstract

The release and transformation mechanisms of trace elements (TEs) during biomass combustion and the environmental impact of TEs in biomass ash were evaluated in this study. Three types of biomass were selected as fuels, with a type of bituminous coal used as a comparison. The quantitative contents and chemical fractions of the TEs in the fuels, ash and char obtained after combustion and pyrolysis were analyzed. The results indicated that during the biomass combustion, the amounts of TEs released were ordered as follows: As > Cd, Pb, Zn > Cu. The TEs in the different chemical fractions both in the fuels and the solid products were shown to be in the forms of different specific compounds, and the transformation of each TE was discussed in depth. Cd, Cu and Zn were found to be released in higher quantities during pyrolysis than combustion and the reason may be that more nonvolatile TE oxides but less volatile TEs chlorides were formed during combustion. The assessment of the environmental impact of the TEs in biomass ash indicated that the environmental risks of Zn and Cu in biomass ash are higher than those in coal ash.

Keywords: Biomass; Combustion; Release; Trace elements; Transformation.