Nitrogen transformations during secondary coal pyrolysis

A CO/H-2/O-2/N-2 flame was operated under fuel-rich conditions in a flat fl ame reactor to provide a high-temperature oxygen-free environment to study secondary reactions of coal volatiles. The distributions of fuel nitrogen i n the devolatilization products of four coals, ranging from high volatile b ituminous to lignite, were obtained at gas temperatures ranging from 1159 t o 1858 K. It was found that the initial nitrogen released was contained alm ost exclusively in the tar for all coals. Release of nitrogen from the char as light gases started at a later stage than tar nitrogen release. During secondary reactions the nitrogen contents in the coal tars were higher than the nitrogen contents in the parent coals at temperatures below 1300 K. A rapid decay in the tar nitrogen content was observed between 1300 and 1600 K, followed by a much slower decrease in nitrogen content at temperatures a bove 1600 K. Nitrogen release from the coal tar can be described with first -order kinetics using the same rate constant for all the coals studied. Nit rogen release followed different routes in the tar and in the char, despite similar nitrogen functionalities in both products. Thermal decomposition o f char was found to be an important source for nitrogen release at high tem peratures. For low rank coals, NH3 was released earlier than HCN. For high rank coals, NH3 was released at the same time as HCN.