CONVERSION OF FUEL-NITROGEN IN THE PRIMARY ZONES OF PULVERIZED COAL FLAMES

Complete distributions of all major products and nitrogen species are reported for the oxidative pyrolysis and combustion of premixed suspen sions of subbituminous, Pittsburgh No. 8 hvA bituminous, and a low-vol atile bituminous coal after 150 ms. As inlet O-2 levels were progressi vely increased from 0 to 15% in successive tests, the process chemistr y moved through oxidative volatiles pyrolysis, volatiles combustion, s oot combustion, and char oxidation. However, the different fuel compon ents were consumed sequentially only with the low-volatility coal. Cha r, soot, and noncondensible fuels burned simultaneously with the subbi tuminous coal and, to a lesser degree, with the Pittsburgh No. 8, Cons equently, hydrocarbon gases from these coals, particularly CH4 and C2H 2, were present while most of the char and its residual fuel-N was con verted into gases. With all coals, the persistence of gaseous hydrocar bons profoundly affects the conversion of all fuel-N species in the ga s phase, As long as detectable amounts of CH4 and C2H2 are present, NO is absent with all coal types and total fixed nitrogen (TFN = HCN + N H3 + NO) is composed of only HCN with both bituminous coals, plus appr eciable amounts of NH3 during intermediate stages with the low-rank co al. But after the hydrocarbons are consumed, HCN and NH3 vanish and mo st of the remaining char-N and soot-N are converted into NO, so TFN is composed of only NO. The extent of carbon conversion up to the NO inc eption point is the primary coal rank index for early NO production in coal flames, falling from 38% with the subbituminous to 12% with the low-volatility coal.