Influence of air staging strategies on flue gas sensible heat losses and gaseous emissions of a wood pellet boiler: An experimental study

An effective air staging strategy is of great importance for achieving low emissions and sensible heat losses through flue gas extraction. In cases where a commercially available system needs to be optimised, often the only viable measure is the modification of process parameters. In this work, the aim is to (1) Discover a combination of the most suitable process parameters based on a multi-criteria decision-making method and (2) To unveil relevant correlations between the two process parameters under study (PA/SA ratio and excess air), emissions and combustion temperatures. A modified commercial small-scale hot water wood pellet boiler was installed into a laboratory heating system. Nine different cases have been addressed within a parametric study, differing in the PA/SA ratio and overall excess air. Emissions, temperatures inside the combustion chamber and the flow rate of air entering the combustion chamber were measured. A low PA/SA ratio of 0.53 (54.7% reduction from factory settings), combined with a low O2 concentration in the flue gases of 5.26% (39.8% reduction from factory settings), and the elimination of infiltration air resulted in a simultaneous reduction of NOx and CO emissions by 14.4% and 93.9% respectively and a flue gas sensible heat loss reduction of 31.6%.