Evaluation of NO Index for Predicting the Formation of NO in the Combustion of Coals Used in the Steel Works

Nitrogen oxide (NO) gas is one of the major environmental pollutants being generated from the steel industry. Since there are no techniques that can predict how much of NO will be formed from coal, it is extremely required to derive some indices based on the understanding of how coal properties are related with the formation of NO. The current research investigated how coal properties such as nitrogen content, fixed carbon (FC), volatile matter (VM) and functional forms of nitrogen could affect the conversion of nitrogen to NO (XNO) for anthracite, semi-anthracite and bituminous coals. It was expected that coals containing high nitrogen would provide the highest values of XNO. However, there was no correlation between nitrogen content and XNO. A variable that related coal properties and defined the quality of coal was proposed by Cr (FC/VM). For all grades of coals, XNO tended to decrease as Cr increased. The relationship between nitrogen functional forms and XNO was highly dependent on coal grade. XNO value increased when pyridinic-N increased and pyrrolic-N decreased in anthracite and bituminous coals before combustion, and pyrrolic-N increased and pyridinic-N decreased in semi-anthracite coals before combustion. This suggests that pyridinic-N might be considered to be the major functional form that affects the conversion of nitrogen to NO for all the coals measured. NO index for each coal grade was derived by using the previously-mentioned variables affecting XNO. The linear coefficients of the relations between NO index and XNO was found to be 0.98, 0.62 and 0.64 for anthracite, semi-anthracite and bituminous coals, respectively. More coals should be measured to validate the proposed NO indices with increased accuracy.