OCR Text |
Show The N20 data from Figure 5 have been replotted In Figure 6. In Figure 6, the N20 Is shown as a fraction of the NOx reduction (e.g. the fraction of the NOx reduced that is converted to N20). These results indicate that for NH3 injection, 2-5 percent of the NOx reduced appears as N20 in the products. For urea injection, 10-25 percent of the NOx reduced shows up as N20. Cyanuric acid exhibits the highest conversion to N20 with up to 40 percent of the reduced NOx appearing as N20 In the products. The calculated values shown in Figure 3b are In qualitative agreement with the pilot scale results. Experimentally, NH3 exhibits somewhat higher levels of N20 than the calculations. Likewise, the conversion of NO to N20 with urea is higher experimentally than calculated . Finally, the calculations indicate virtually no N20 at temperatures of 1027°C (13000 K) and above while experimentally the window for N20 emissions is broader. Pilot scale results at a lower initial NOx level of 300 ppm are shown In Figures 7 and 8. Figures 7a and 7b show NOx reduction and N20 emission, respectively, as a function of injection temperature. The NOx reduction data show that NH3 Injection provided peak removals of 88 percent at about 980°C. Similarly, urea injection resulted in a maximum NOx reduction of 57 percent at 930°C. As with the higher initial NOx level, cyanuric acid injection did not exhibit any peak NOx removal over the range of temperatures investigated. The maximum reduction of 52 percent was measured at 1 100°C. With the exception of NH3 Injection, maximum removals were lower for the tests performed with 300 ppm initial NO than those performed with 700 ppm Initial NO. N20 emissions (Figure 7b) show that at an initial NO level of 300 ppm, cyanuric acid injection yielded the highest N20 emissions; 69 ppm at about 980°C. N20 emissions resulting from urea injection also peaked at 980°C, at 43 ppm. When injecting the NH3 , peak N20 emissions of 21 ppm were measured at 880°C. Figure 8 shows the ratio of N20 emission to NOx reduction as a function of temperature for each of the three SNCR chemicals tested at this lower initial NO level. Test results showed maximum values at temperatures similar to those seen at higher Initial NO levels (see Figure 6). The ratio peaked at about 880°C for NH3 and 980°C for urea and cyanuric acid. Again, cyanuric acid was shown to provide the highest conversion of NOx to N20 . For NH3, the peak value was about 9 percent, while a peak value of 42 13 |