OCR Text |
Show 8 stability limits. The identification of these regions, however, required the complete emissions mapping over the stability limits for each nozzle. The results also show that the regions of high performance tend to be near the stability limits. These two issues, i.e., the need for a complete emissions map prior to identification of high performance regions and the need to operate near the stability limits, may be addressed through the use of active control. With an active control scheme, the burner's performance "space" could be searched and evaluated in real time such that a priori knowledge is not required. The burner performance would also be continually monitored such that if a drop in performance occurred due to a change in load or system degradation, the active control algorithm would seek out the new region of optimum performance. This type of active control experiment has been conducted on this burner using the co-swirl nozzle [10]. If a fast stability sensor is also incorporated, the active control scheme could then operate the burner in narrow regions very close to the stability limit Another advantage of the performance function approach is that the function itself can be tailored to address particular regulatory or financial requirements. For example, the functions f and g can be changed to reflect higher or lower rewards, by changing the slopes of the curves, in accordance with local regulatory requirements. Alternatively, the weighting factors can be changed to favor either higher efficiency or lower NOx. Figure 7 shows the effect of changing w1J to 0.75 and WNOx to 0.25; the areas of acceptable performance are seen to broaden since the NOx emissions are less weighted. 35 30 25 '#. ....- 20 ~ UJ UJ CD u 15 x W 10 5 - - ...... 0 0.3 0.4 , , ------------------ I I I 0.5 0.6 0.7 Swirl,S' 0.8 0.80+ 0.69 to 0.80 0.57 to 0.69 0.46 to 0.57 0.34 to 0.46 0.23 to 0.34 0.11 to 0.23 0.00 to 0.11 ............ 1- ............... Counter-Swlrl 0.9 Figure 7: Performance Index (1) Maps for Co-swirl, Radial, and Counter-swirl Nozzles NOx weighted at 0.25 and Efficiency weighted at 0.75 |