Characterization of Gaseous- and Particle-Phase Emissions from the Combustion of Biomass-Residue-Derived Fuels in a Small Residential Boiler

Biomass is considered as one of the most promising fuels worldwide, mostly because of its renewability and almost-neutral carbon balance. At the same time, numerous studies have shown that the combustion of biomass fuels results in emissions of multiple gaseous and particle phase pollutants. The aim of this study was to fill the gap in the data of emissions from the combustion of agricultural biomass fuels. Five agricultural residue-derived fuels were tested: sunflower stalk pellets, straw pellets, buckwheat shells, corn stalk pellets, and wheat grain screenings. In addition, wood and sewage sludge pellets were investigated as reference fuels. Experiments were performed in a commercially available domestic 13 kW pellet burner during optimal and stable combustion conditions. The characterization of the emissions of gaseous basic pollutants (CO, CO2, SO2, NOx), as well as combustion specific pollutants (size-segregated particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), as well as BTEX (benzene, toluene, ethylbenzene, xylenes) was conducted. The emissions of PM were mostly represented by PM1 fraction (PM1/TSP > 0.8) in the case of all fuels. Total PM emissions ranged from 0.28 g/kg to 5.23 g/kg. Total emissions of PAHs ranged from 469.4 mu g/kg to 7212.2 mu g/kg. Size-segregated PAH analysis revealed that the most of PAHs were detected in fine aerosol fraction (0.056-0.18 mu m). Sewage sludge pellets were determined as the most polluting fuel, including PAH emissions. Several fuels, including sunflower stalk pellets, buckwheat shells, and sewage sludge pellets, were found to be the least favorable fuels for combustion in a small-scale pellet-type burner, because of increased emissions of CO and PAHs.