A comprehensive kinetic mechanism is proposed for the release of char-bound nitrogen in coal (char-N) into the gas phase during the combustion of coal char particles. The salient feature of the proposed mechanism is that char-N is converted competitively to NHias well as to NO at the surface of the particles. Based on the proposed kinetic mechanism, a mathematical model is developed for the transient formation of char-NO originated from char-N during the combustion of a single particle of coal char in an O2/Ar stream. The theoretical predictions of the model are compared with the experimental data for three kinds of chars, of which the parent coals are Taisei (anthracite, China), Taiheiyo (non-caking bituminous, Japan) and an activated sludge (a pseudo low-rank coal from waste-water treatment): their fuel ratios range from 0.12 to 4.16. Quantitative agreement is found between the predictions of the model and the measured values for the transient formation of char-NO and for the overall fractional conversion of char-N into char-NO. This proposed mathematical model, based on a comprehensive kinetic mechanism, is recommended for modeling the char-NO formation step in practical coal combustors. © 1988 Combustion Institute.
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