Importance of solid fuel properties to nitrogen oxide formation through HCN and NH3 in small particle combustion
✍ Scribed by Martti J. Aho; Jouni P. Hämäläinen; Jouni L. Tummavuori
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 659 KB
- Volume
- 95
- Category
- Article
- ISSN
- 0010-2180
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✦ Synopsis
The formation of nitrogen oxides from fuel-nitrogen through intermediates was studied by measuring first fuel-O/fuel-N ratios and nitrogen functionality in selected solid fuels. Then the ratios of the yields (fuel-N ---} HCN)/(fueI-N --* NH 3) in a nearly inert atmosphere at 800°C in an entrained flow reactor was measured and finally the ratio (fuel-N ---} N20)/(fuel-N ---} NO) in an oxidizing atmosphere at 800°C. The fuels studied were coal, brown coal, S-and C-type peat, fir bark, birch bark and pine bark, all milled to a particle size < 63/xm. The ratios of O/N in the fuel, measured by elemental analysis, ranged from 7 to 150. Nitrogen functionality (mass percent of the total nitrogen content) was determined by XPS. The (fuel-N HCN)/(fueI-N -~ NH 3) conversion ratio in the absence of 02, and also the (fuel-N ~ N20)/(fuel-N ~ NO) conversion ratio with O 2 present, decreased with increasing ratio of fuel-O/fuel-N, but neither ratio decreased regularly with the increasing ratio of pyrrolic to pyridinic nitrogen in the fuel. Thus, fuel-oxygen plays a more important role than nitrogen functionality in the chemistry of nitrogen oxide formation. The strong effect of (fuel-O/fuel-N) ratio on the (fuel-N ~ HCN)/(fuel-N -~ NH 3) ratio may be due to the reaction between OH radicals and HCN to form NH 3 near the fuel particle. The importance of this reaction is considered. Charring the fuel sample before combustion led to a sharp drop in the conversion of fuel-N to N20 compared with the virgin fuels. Thus, heterogeneous combustion reactions produced much less N20 than homogeneous combustion reactions.