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Show 150 1.50 InjectJon Angle : • • • • • r 1.25 0 00 99.4 0 300 100 99.S E ~ .s )( 1.00 .... EJ 1400 CD .!l E 0.75 ~ %Comb. Eff. = 99.2 0 z ~ 'j rn 50 0.50 0.25 0.00 Velocity Configuration Figure 4: 50,000 Btu/hr Selected Results of NOx ' The results also suggest that the parameters which are available to the burner designer have complex interactions and that careful consideration must be given to all of the operating parameters in order to reduce NOx emissions while maintaining high combustion efficiency. The next step is to evaluate these fmdings at a different scale, and in a burner geometry with distinct differences in design detail. 100,000 Btu/hr Burner Figure 5 shows the NOx emissions (corrected to 3% 02) at various excess air and swirl levels for the axial injection nozzle. While NOx emissions and combustion efficiencies are relatively insensitive to excess air for this nozzle, an increase in swirl strength notably decreases both NOx and combustion efficiency. The two-dimensional plot in the bottom of the figure more clearly shows the correspondence between swirl strength and the burner perfonnance. For the 900 cone annular injection nozzle, the effect of swirl strength is also to reduce NOx at the sacrifice of combustion efficiency. In this case, however, NOx levels are markedly lower, and an increase in excess air significantly reduces NOx to levels well below those measured with the axial injector. These results are shown in Figure 6. The results for the radial injector are presented in Figure 7. While the 0% excess low swirl case is more similar to the axial injector results, the radial injector reveals the highest sensitivity to swirl of the three nozzles and results in the lowest emission of NOx. Note that the low swirl perfonnance is very sensitive to excess air, while the high swirl conditions are relatively insensitive to excess air. 7 |
