Emissions reduction from wood pellet stoves by uniform feeding

The instantaneous fuel-to-air ratio in pellet stoves may vary because of the feeding mechanism. The pellet feed flow rate variability of a standard screw feeder was quantitatively assessed with real-time measurements. Temporary excess or deficit of pellets commonly occur. The variability can be significantly reduced with a new feeder, by approx. 70%, both at nominal (full) and partial (half) load operation. The analysis of the instantaneous emissions reveals that the fuel feed instabilities cause temporary sub-optimal fuel-to-air ratio and, in turn, peaks of pollutants emissions. The impact on the emissions of a more regular pellet feeder is impressive. A reduction of CO emission by 46% and 37.5%, and of PM by 52% and 44% at nominal and partial load, respectively was measured. NOx emissions are less affected by a more uniform feed rate, being predominantly from fuel nitrogen.