| OCR Text |
Show -9- The pre-retrofit test program was limited due to unit operating problems. Only mid- and low-load tests were performed during this time, since full load could not be achieved without co-firing oil. Intermediate load NOx emissions ranged from 0.55 to 0.35Ib/MMBtu over the same NSR range. The data showed that SNCR performance increased with decreasing load at a fixed NSR. This is most likely due to more favorable injection temperatures and increasing residence times. At intermediate load, NH3 slip varied from 20 ppm to 63 ppm over the range of NSRs tested. At minimum load, NH3 slip varied from 18 ppm to 94 ppm. Figures 11 and 12 show the effect of changing injection level on NOx emissions and NH3 Slip for tests performed at full load. Data are presented for tests performed using both 2/3 and 3/3 OFA. Five different injection level combinations were evaluated; Levels 3, 2U, and 2L individually, and combinations of Levels 3 and 2U and Levels 2U and 2L. Figure 12 shows NOx emissions plotted versus injection level for tests performed at an NSR of nominally 1.0. For both OFA operating conditions, the lowest NOx emissions were measured with two level injection. The combination of Levels 3 and 2U provided the lowest NOx emissions, although the difference was minimal relative to injection with Levels 2U and 2L. NOx emissions were lower when using 3/3 OFA, primarily because of the lower initial NOx levels. Figure 12 shows NH3 slip plotted versus injection level. These data show two trends. First, NHa slip decreased as the reagent was injected into hotter zones. Recall from Figure 1 that Level 2L is closest to the burners and is hence the hottest zone. In comparison, Level 3 is closest to the convective section, making it the coldest zone. Second, note that NH3 slip was significantly lower when using 213 OFA. This is due to the increased furnace exit temperatures at this operating condition, relative to 3/3 OFA. Based on the desire to balance minimum NOx reductions and NHa slip, the combination of Levels 2U and 2L was selected for further evaluation. Figures 13 and 14 show the effect of variations in solution flow on NOx emissions and NH3 slip, respectively. The data show that NOx emissions decreased with increasing |
