Suppressed Nitrogen Evolution from Coal-derived Soot and Low-volatility Coal Ci-iars

This laboratory study uses a novel furnace to resolve nitrogen evolution during the three stages of pulverized coal combustion. primary devolatilization, secondary pyrolysis, and com­ bustion The behavior of six coals depicts continuous rank variations, as well as suppressed nitrogen evolution {i'om low volatility coals. During primary de volatilization of any coal, ar­ omatic compounds in tar and oils are virtually the only shuttles for nitrogen out of the coal matrix. The small amounts of HCN observed while primary devolatilization winds down prob­ ably come from the char, because char particles are significantly hotter than tar in these experiments. Secondary pyrolysis promotes additional HCN evolution Crom both char and tar Moreover, substantial {i-actions of the volatile-nitrogen from primary devobtilization is reincorporated into a carbonaceous soot matrix It)r all coal types The fraction of coal nitrogen incorporated into soot remains constant, even while soot· yields dramatically increase. Incorporation of nitrogen into soot has the potential to substantially reduce the amount of coal nitrogen amenable to aerodynamic NO, abatement strategies It)r coals with large tar yields_ This potential limitation is compounded by another limitation It)r low volatility coals. \Vhere~ls one-half to two-thirds of the coal-nitrogen is expelled by thermal decomposition /i-om other coal types, only .30 to 40% is expelled from low volatility samples This tendenc)! suggests that nitrogen functionalities become much more refractory as their surrounding ar­ omatic domains become more extensive, either in high rank coals or soot. For such systems, our measurements indicate that the only way to expel the nitrogen is to burn it away