Experimental study of the influence of secondary air on the formation of pollutants and soot from wood pellets combustion
Session chaired by Pr. Epaminondas Mastorakos
Experimental measurements in a small-scale boiler have been performed to investigate the influence of secondary air supply on the formation of pollutants and soot during the combustion of wood pellets. The boiler used is a domestic automatic wood pellet boiler with a nominal power of 10 kW. It has coupled primary and secondary air injections in its factory configuration and the secondary air supply can be completely cut off by a plug. Gas analyzers are instrumented to measure the combustion gases which trapped separately from the chimney and the combustion chamber. A laser diagnostic bench is instrumented to acquire the signals from laser-induced incandescence (LII), including a YAG laser for soot excitation, a photomultiplier system for collecting the LII signals from the chimney, and an ICCD camera for collecting the LII images from the combustion chamber. The concentrations of CO2, CO and total hydrocarbons (THC) in the flame and in the chimney have been measured separately in the conditions with or without secondary air supply. With the presence of secondary air, the concentrations of THC, CO and CO2 in the flame increase strongly. In the chimney, a decrease of the concentration of CO2, a slight decrease of the concentration of CO and an increase in the concentration of THC are observed. The evolution of the average values of the LII peaks as a function of the primary airflow in the chimney has been investigated. There is a clear reduction of the LII peaks in the absence of secondary air and the temporal evolution of LII peaks without secondary air shows greater stability.
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