Fine particle and gas emissions from the combustion of agricultural fuels fired in a 20 kW burner

Emissions from the combustion of agricultural biomasses have not been studied extensively. In this study, the effects of different biomasses and mixed fuels on fine particle (PM1) and gas emissions from a residential cereal burner were investigated. The cereal seeds of oat and rape, rape bark pellets, and wood pellets were the main fuels. In addition, oat was mixed with peat and kaolin and wood with kaolin. The gas emissions of NO, SO2, and HCl were clearly higher from cereal or mixed-cereal fuels than from pure wood fuel. The emissions of carbon monoxide (CO), organic gaseous carbon (OGC), PM, and the particle numbers from the cereal fuels did not differ significantly from the emissions of wood fuels, although the fuel ash contents were substantially higher. The release of alkali metals varied substantially between different fuels, probably due to large differences in ash chemical compositions. In contrast to wood fuels, phosphate contributed significantly to the formation of fine particles in the cereal fuels. In rape fuels, probably due to high S/Cl and S/K ratios, all of the fuel chlorine was released in the gas phase and was not enriched in the fine particles. At least partly due to this, the PM, and alkali metal emissions from the combustion of rape seeds were low, considering the high ash content (4.4%) and high alkali metal contents in the fuel. The addition of 5 wt % of kaolin to oat grains seemed to decrease the alkali metal emissions but slightly increased the emissions of incomplete combustion. It seems that the formation of chlorides (e.g., KCl) affects significantly the emission of fine ash particles. Moreover, sulfation of alkali metals seems to decrease the emission of fine alkali metal particles.