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Show 8 Char samples were taken from all three flames at several axial stations. Since the flame gas velocity could not be determined for all positions, isokinetic sampling was not applied. However, taking the char samples at a higher velocity than that of the flue gas could result in relatively small error. The C content of char for the nonstaged flames are given in Figure 8. The results indicate that the carbon burnout was higher for the staged flame than that of the non-staged flame for axial distance less than XlD=IS. At the exit, however, the concentrations were found the same. The results for the H content are given in Figure 9. Smaller difference was obtained for the H content of char for axial distances larger than XlD=S., however, it was still high for smaller axial distance. The release ofH from coal particles may indicate the amount of volatile matter still present in the particles. It follows that the volatile evolution was delayed for the non-staged flame. The same conclusion can be drawn from the results for the N content of char. The data, shown in Figure 10, clearly indicate that the char particles from the non-staged flame contained higher amount of nitrogen than that of the staged flame. The very rapid decay of nitrogen in the solids for the staged flame is most interesting. This result implies that the fuel nitrogen can be removed from the solid in the fuel rich region before the carbon bmnout is complete. Funher, by comparison with the hydrogen data of Figure 9, the nitrogen can be removed from the char before the pyrolysis is complete. This is by no means an unbelievable finding but is in contrast to the usual belief that fuel nitrogen is always retained in the char leading to NOx production in the final burnout stage. This is a clear area for funher study. Conclusions Experimental work was carried out at the MIT Combustion Research Facility with the Radially Stratified Coal Burner with an illinois #6 coal. The highlights of the results are: • 217 NOx (@3% O2) concentration with unstaged stratified IVM flame at 1.08 stoichiometric ratio and 99.54% carbon conversion, • 107 NOx (@3% 02) concentration with staged PPM flame at 0.92 first stage stoichiometric ratio and 99.S2% carbon conversion, • 70 NOx (@3% 02) concentration with staged flame at 0.82 first stage stoichiometric ratio and 99.3% carbon conversion. The parametric study showed relative insensitivity of exit concentrations to thermal load (between 1 and 1.8 MW), air preheat (S10-56O F) and exit 02 concentrations (2.S-4.S%). The effect of transport air on exit NOx concentration depended on where the air compensation was applied at staged conditions. |
