The Appearance of Nitric Oxide and Cyanide in One-Dimensional Coal Dust/Oxidizer Flames

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Abstract
Temperature and species concentration profiles are presented for rich coal dust/oxygen/diluent flames burnt on a flat flame burner. Either argon or nitrogen was used as the diluent to study the fate of fuel nitrogen. 30-40 percent of the fuel nitrogen appears as HCN and NO with the leaner flames favoring NO. Experimental reaction rate profiles, which are compared to a simple model, indicate fuel nitrogen evolution occurs in two consecutive steps. The model assumes (1) only volatiles combustion occurs, (2) nitrogen is released early in the flame with the tar, (3) tar pyrolysis gives rise to HCN, (4) HCN oxidation produces NO, and HCN reaction with NO leads to N2, and (5) nitrogen is released later in the flame directly from the char as HCN. Reasonable qualitative agreement between measured and predicted rates is obtained. Quantitative agreement is precluded by uncertainties about the gas and particle temperatures and the rate constants for tar and char nitrogen release.