Formation of NOx precursors during the pyrolysis of coals in a fluidized-bed reactor
- CSIRO, North Ryde, New South Wales (Australia). Div. of Coal and Energy Technology
Conversion of coal nitrogen to NOx and N{sub 2}O is the most important source of NOx and N{sub 2}O produced in modern coal combustion processes. A suite of rank-ordered coals from Australia, Germany and the USA were pyrolyzed at high heating rate in a fluidized-bed reactor. Nitrogen functionalities of the coal samples were determined by X-ray photoelectron spectroscopy (XPS). The yields of gas-phase nitrogen-containing species (mainly HCN and NH{sub 3}) and the functionality of the nitrogen in the coals were all found to change with rank. However, coal nitrogen functionality alone was found to be insufficient to predict the nitrogen distribution during pyrolysis. Further experimental evidence supporting this conclusion has been obtained in the ongoing efforts to trace the changes in tar nitrogen functionality during thermal cracking with a combination of preparative size exclusion chromatography (SEC) and XPS. Nitrogen functionalities were determined by XPS for tar samples from the pyrolysis of a German bituminous coal at temperatures in the range 600--900 C. These measurements showed that tar nitrogen functionalities changed with both temperature and molecular mass. In the case of this coal, no quaternary nitrogen was found in any of the tar samples. Furthermore, the XPS data for the tars appeared to indicate that pyrrole nitrogen structures were more stable than the corresponding pyridine nitrogen structures. It is clearly necessary to extend the current study to other coals and other methods of tar sample preparation. There was a large decrease in pyridinic nitrogen and an increase in nitrile nitrogen at temperatures between 600 C and 800 C. This change in nitrogen functionality was observed to coincide with the onset of significant thermal cracking of the tars, as observed using analytical SEC of the same tar samples. On the whole, the thermal stability of tar nitrogen during thermal cracking in the freeboard of the fluidized bed reactor is consistent with that of nitrogen-containing model compounds reported in the literature.
- OSTI ID:
- 324756
- Report Number(s):
- CONF-970931-; TRN: IM9911%%453
- Resource Relation:
- Conference: 14. annual international Pittsburgh coal conference and workshop: clean coal technology and coal utilization, Taiyuan (China), 23-27 Sep 1997; Other Information: PBD: 1997; Related Information: Is Part Of Fourteenth annual international Pittsburgh coal conference and workshop: Proceedings; PB: [1500] p.
- Country of Publication:
- United States
- Language:
- English
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