Influence of coal composition on the fate of volatile and char nitrogen during combustion

Fifty coals from North America, Europe, Asia, South Africa and Australia were burned in a 21 kW, refractory-lined tunnel furnace to determine the influence of coal properties on the fate of volatile and char nitrogen. Excess air fuel NO emissions (as determined by combustion in Ar/02/C02) ranged from 415 ppm to 1380 ppm with a premixed burner. These results correlated with total fuel nitrogen, inert pyrolysis HCN yield, and non-volatile nitrogen content, rather than with the geographic origin of the coal. Minimum staged NO emissions (at optimum first stage stoichiometry) ranged from 140 ppm to 380 ppm. Detailed in-flame measurements indicated that as first stage stoichiometry (air/fuel) was reduced, first stage NO formation decreased, but was ultimately offset by increases in oxidizable gaseous nitrogen species and solid phase nitrogen retention. TFN (NH3 + NO + HCN) generally increased with increasing fuel nitrogen and the species distribution was dependent upon coal rank. In general, HCN was greater than NH3 with bituminous coals, but less than NH3 with subbituminous and lignite coals. Second stage TFN conversion to exhaust NO decreased as the TFN distribution was shifted in favor of HCN and NH3. Char nitrogen conversion was generally low (less than 20 percent). Exhaust emissions were correlated in terms of the gas phase TFN and the char nitrogen entering the second stage.