Pyrolysis of superfine pulverized coal. Part 3. Mechanisms of nitrogen-containing species formation

With more stringent regulations being implemented, elucidating the formation mechanisms of nitrogen-containing species during the initial pyrolysis step becomes important for developing new NOx control strategies. However, there is a lack of agreement on the origins of NOx precursors during coal pyrolysis, in spite of extensive investigations. Hence, it is important to achieve a more precise knowledge of the formation mechanisms of nitrogen-contain species during coal pyrolysis. In this paper, pyrolysis experiments of superfine pulverized coal were performed in a fixed bed at low heating rates. The influences of temperature, coal type, particle size and atmosphere on the NH3 and NO evolution were discussed. There is a central theme to develop knowledge of the relationship between particle sizes and evolving behaviors of nitrogen-containing species. Furthermore, the catalytic role of inherent minerals in coal was proved to be effective on the partitioning of nitrogen during coal pyrolysis. In addition, the conversion pathways of heteroaromatic nitrogen structures in coal/char during pyrolysis were recognized through the X-ray photoelectron spectroscopy (XPS) analysis. Large quantities of pyridinic and quanternary nitrogen functionalities were formed during the thermal degradation. Finally, the relationships among the nitrogen-containing gaseous species during coal pyrolysis were discussed. In brief, a comprehensive picture of the volatile-nitrogen partitioning during coal pyrolysis is obtained in this work, involving the formation mechanisms of the main nitrogen-containing gaseous products such as NH3, HCN, NO, NO2 and N2O.