Particulate Emissions From The Combustion Of Biomass Pellets

The combustion of biomass pellets in small-scale appliances for domestic heating is a common source of particulate matter (PM) emissions, especially in Europe. The diversification of biomass raw material associated with the growing pellet market has the potential to increase PM emissions, particularly fine inorganic particles. Global concerns on public health and environmental impacts have imposed limitations to the emission of particles creating a need for a better understanding of the formation of particles to develop appropriate mitigation strategies. This review addresses the quantification, formation and mitigation of PM emissions. The measurements of PM emissions can be considerably affected by sampling and measurement methods or instruments used; thus, there is a need for uniform standards and protocols. PM emissions from small-scale pellet boilers have been related to both fuel quality and operating conditions. Biomass characteristics, specifically the ash content and the ash composition, have a significant impact on PM emissions as the ashes of the fuel contain the precursors for the formation of inorganic particulate matter. Operating conditions have also an important impact as soot and organic particles are formed in poorly oxygenated environments. Mass and number concentrations, mass and number size distributions, and chemical compositions of PM emissions are reported from the most relevant related studies. On-going research on mitigation strategies focuses on the inhibition of PM formation by combustion optimization and fuel pre-treatment; or on the separation of particles in the flue gas.