NO x release and reactivity of chars from a wide range of coals during combustion

Abstract

NO x release from a wide range of chars prepared in an entrained-flow reactor from coals and vitrinite concentrates of different rank and geographic origin was studied. Temperature-programmed combustion of the chars using thermogravimetric analysis and mass spectrometry showed that the fractional conversion of char-N to NO increased with increasing rank of the original coal at first and then reached a plateau above a vitrinite reflectance of ~1.5%. The fractional conversion of char-N to N 2 was roughly constant throughout the suite of chars. The HCN level was significantly lower for the chars than for the parent coals. The HCN is believed to be a devolatilization product in advance of oxidation to N 2, NO and N 2O. The conversion of char-N to NO was correlated with char reactivity. Normalization by surface area halved the range of reactivity values, but the relation between char-N conversion to NO and reactivity was still apparent. The results suggest that as well as the surface area, the intrinsic reactivity of the char is important in determining the reduction of NO on the carbon during combustion.