Influence of near burner combustion modifications on NOx formation from an all-axial multifuel burner

Tests were conducted with a naturally staged, axial jet burner firing pulverized coal to evaluate near burner combustion modification alternatives for controlling NOx emissions to ultra low levels in a combustor operating with hot, running slag walls. The study focused on the use of small amounts of natural gas rather than swirl air to aid the stabilization of the axial pulverized coal flames. The relative importance of primary jet velocity and primary air stoichiometry were determined for these gas stabilized flames. Decreases in primary jet velocity had a dramatic effect on near burner NO production while primary air stoichiometry appeared to have a negligible effect. Another near burner modification, the use of a vitiated secondary air stream, did not significantly affect NO levels. Ultra low NO levels (below 90 ppmv) were achieved in this hot-walled combustor by optimizing the performance of the gas stabilized burner in conjunction with staged combustion and reburning.