Characterisation of wood combustion particles using electron probe microanalysis

Abstract

Biomass combustion for energy production has increased in recent years, mostly in domestic households and for the space heating of some public and agricultural buildings. Small wood combustion boilers are not equipped with any flue gas filtering system, and they release most of the small particles generated on combustion to the air. Particulate emissions from a 400 kW wood-fired heating plant were measured during standard winter operation. Cyclone fly ash and bottom ash, as well as ambient aerosol samples, were collected on site. The samples were analysed using conventional single-particle electron probe microanalysis (EPMA) including use of a thin-window detector allowing the determination of low- Z major elements such as C and O. The particles were classified based on the analyses obtained and using hierarchical cluster analysis. The majority of stack-gas particles were found to be in the respirable size range. Using EPMA, the wood combustion particles could be traced in the neighbouring air because of their characteristic potassium content. The cyclone- and bottom-ash particles have lower potassium contents due to alkali release during the combustion process.