NITROGEN RELEASE FROM A RANK SERIES OF COALS DURING TEMPERATURE-PROGRAMMED COMBUSTION

This investigation has involved the study of NO(x) release during the combustion of a wide range of coals of different rank and geographic o rigin. Temperature programmed combustion studies of coals using a ther mogravimetric analyser-mass spectrometer (TGA-m.s.) show that the oxid ative gasification profiles of the coals have two main regions, corres ponding mainly to the gasification of volatiles and of the chars forme d in situ during pyrolysis. Calculation of the fuel N conversion to va rious nitrogenous species, using the integrated area under each gas ev olution profile, combined with the analytical data shows that coal N c onversion to NO is rank dependent, with the fractional conversion of c oal N increasing with rank especially for the low to medium rank bitum inous coals where the increase is most noticeable. The NO-fuel N ratio for all the coals studied varies in the range of 11-42%. The conversi on of fuel N to N2 does not show definite trend with rank. Significant amounts of HCN (10-15%) were also detected during gasification for so me of the coals investigated. The studies show that coal-char N conver sion to NO during combustion is related to reactivity with the more re active coals having lower NO-N ratios.