The fate of nitrogen during pyrolysis of German low rank coals - a parameter study

Proceeding from the knowledge of the functional forms of nitrogen in coals it should be possible to draw conclusions on the mechanisms of its release during devolatilization. Pyrolysis experiments were carried out with a seri es of lignite from the main German mining districts in a temperature range from 673 to 1173 K. Nitrogen functionalities of the coals and the obtained chars were determined by XPS. The nitrogen content of the residual pyrolysi s chars was found to be dependent on a wide variety of parameters: coal typ e, temperature, residence time, mineral matter. An increasing N/C ratio was detected for chars obtained under conditions of oxopyrolysis. The conversi on of fuel-bound nitrogen to NOx-precursors (HCN, NH3) is also strongly dep endent on coal type The mineral matter of the parent coals was found to aff ect both the primary devolatilization process and the reaction paths to for m ammonia. The balance of the nitrogen distribution during pyrolysis shows a large amount of N-2 to which the coal-N is converted. (C) 1999 Elsevier S cience Ltd. All rights reserved.