Conversion of fuel nitrogen in coal volatiles to NOx precursors under rapid heating conditions

The formation of NO_x precursors during the rapid pyrolysis of three Australian coals has been studied by the determination of HCN using long path length Fourier transform infrared spectrometry and of nitrogen-containing species in the tars using gas chromatography with a nitrogen-specific detector. Significant differences in the release rates of HCN were observed, and these can be reconciled with differences in the composition of the nitrogen fraction of the tars. The stability of the species containing nitrogen in five-membered (pyrrole type) rings is significantly lower than that of species with nitrogen in six-membered (pyridine type) rings. This results in the more rapid formation of HCN from those coals with a greater proportion of nitrogen in pyrrole type structures. At high pyrolysis temperatures (1000 °C), these results suggest that nitrogen released from the decomposition of nitrogen-containing aromatics can be reincorporated into high molecular weight products.