Reduction of NOx emissions in a swirled coal flame by particle injection into the internal recirculation zone

Abstract

An internally air staged burner was designed and used to measure the possible reduction of NOx in a swirling pulverized coal flame. Two flames, generated by varying the coal gun position, were studied using a 2.5 MW burner. The NOx emissions were reduced by inserting the coal gun into the burner quarl. This increased the fraction of coal particles injected into the oxygen lean, internal recirculation zone (IRZ) where the coal volatile nitrogen species were preferentially reduced to N2. Inflame nitrogen chemistry was observed by measuring the temperature and concentration of major gas species, NOx, HCN and NH3. As well, finite difference modelling of the two flames was used to predict the particle trajectories. By adjusting the fraction of coal injected into the IRZ, the NOx emission level could be reduced from 1300 ppm (little particle penetration into the IRZ) to 500 ppm (complete particle penetration). The burnout was unaffected by adjusting the coal gun position as the carbon content of the ash was less than 3% in both flames. Predicted particle trajectories were supported by particle paths deduced from the gas species measurements. Thus, a minimization of NOx emissions in an internally air staged burner may be accomplished by applying a detailed understanding of the particle trajectories.