Effect of functional form of nitrogen in coal on the formation of NO in its combustion

Abstract

Nitrogen oxide (NO) gas is one of the major environmental pollutants from the steel industry. At present, there is not a technique that can predict how much NO will be formed from coal. Therefore, understanding how different coal properties are related with the formation of NO is extremely required to derive an index. The current research investigated how coal properties, such as nitrogen content, fixed carbon (FC), volatile matter (VM) and functional forms of nitrogen, affect the conversion of nitrogen to NO (XNO) for anthracite, semi-anthracite and bituminous coals. It was expected that coals containing high nitrogen provide the highest XNO. However, from combustion test results, there was no correlation between nitrogen content and XNO. A variable that related coal properties and defined the quality of coal was proposed, called Cr (FC/VM). For all coal grades, XNO tended to decrease as Cr increased. The relation between nitrogen functional forms and XNO was highly dependent on coal grade. As XNO increased: pyridinic-N increased and pyrrolic-N decreased (anthracite and bituminous) and pyrrolic-N increased and pyridinic-N decreased (semi-anthracite). Pyridinic-N based coals showed higher XNO than pyrrolic-N based one. This suggested that pyridinic-N might be considered the major functional form that affects the conversion of nitrogen to NO. NO index for each coal grade was derived by using the previous mentioned variables relationship with XNO. The correlation index (R2) between the NO index and XNO was found to be 0.98, 0.62 and 0.64 for anthracite, semi-anthracite and bituminous, respectively. More coals would be necessary to validate and increase the accuracy of the proposed NO index.