Flue Gas Recirculation during Biomass Combustion: Implications on PM Release

Abstract

The need for low-emission technologies in biomass domestic heating systems has encouraged the development of primary methods to improve the combustion process. Air-injection strategies are known to yield successful results regarding gaseous emissions; however, their implication on PM release still has some unknowns. This research analyzes how the concentration, types, and morphology of released particles can be affected by the air staging distribution and flue gas recirculation. This study was carried out in a lab-scale combustion unit to determine the main factors that affect temperatures and emissions. The results revealed significant CO and PM reductions associated with both flue gas recirculation and low primary airflows. In addition to the presence of small carbonaceous agglomerates, particularly for cases with a high primary supply, approximately 70% to 80% of the emitted particles were residues from incomplete biomass degradation, with sizes predominantly below 0.1 μm. The influence of the air-injection strategies on NO release was barely noticeable since the thermal NO formation mechanism did not play a major role in low chamber temperatures.