Particulate matter emission characteristics of spruce, sunflower and maize: A comparison between nominal and reduced output in a small-scale boiler

Abstract

The applicability of spruce, sunflower and maize for residential heating was investigated. Emission factors of gaseous and PM pollutants were established at both nominal and reduced output. Since automatic pellet boilers often operate at reduced output, understanding the differences in PM release and behavior is crucial. The emission factors for sunflower reached the highest values at 111.6 mg MJ−1 and 139.2 mg MJ−1 for nominal and reduced output, respectively. PM emission factors reached 49.5/39.5 mg MJ−1 for maize and 8.6/21.4 mg MJ−1 for spruce. It was shown that PM size distribution does not vary significantly between nominal and reduced output and is highly dependent on the fuel composition. The PM size peak was in the range of 0.377–0.596 μm for sunflower, 0.252–0.377 μm for maize, 0.152–0.252 μm for spruce at nominal output and 0.0941–0.152 μm for spruce at reduced output. The entrainment of coarse ash particles was found to be negligible. Cd, Pb, Tl and Sb were found almost exclusively on emitted particles, due to their high volatility and modes of occurrence. The release of inorganic matter into the flue gas was severely inhibited in maize due to the formation of refractory phases.