| OCR Text |
Show Figure 3a compares NO control performance for injection of H20 2, CH30H, and their mixture. In these experiments the initial NO level was 430 ppm, and MR = 1.5. At optimum injection temperatures the chemicals provided 64, 76, and 76% NO removal, respectively. Comparing this data with Figure 2a, one can see that all additives are more efficient in natural gas combustion and the difference in performance is about 20-25%. The optimum injection temperatures are about the same for natural gas and coal firing. Two factors could be responsible for the difference in performance: the presence of about 3000 ppm S02 and heterogeneous processes on the surface of fly ash. In order to explain the difference in NO control performance between natural gas and coal, tests were conducted in which various amounts of S02 and coal ash were injected in flue gas formed by natural gas combustion. Methanol was injected at 894 K in flue gas containing 400 ppm NO. Sampling was performed at 783 and 616 K. As shown in Figure 3b, initial NO conversion decreased linearly with increasing S02. The difference in NO levels at the two sampling locations was the same at different S02 concentrations, suggesting that S02 impacts initial conversion but not reconversion. For these experiments, NO-to-N02 conversion without S02 doping was 96 and 91 % for sampling at 783 and 616 K, respectively. In the presence of 4000 ppm S02' NO-to-N02 conversion was 86 and 81 % at 783 and 616 K, respectively. Thus, the presence of S02 in flue gas is capable of decreasing NO-toN0 2 conversion by about 100/0. In another set of tests, both S02 and ash from the baghouse were injected during natural gas firing. Sulfur dioxide was doped to the fuel, and ash was injected at 1670 K. Both S02 and ash decreased initial NO conversion. Figure 3c compares NO concentration in coal firing and natural gas combustion with doping S02 and ash. Initial NO concentration was 400 ppm (bar F). Methanol was injected at 866 K, and as bar A shows, about 85% NO removal was achieved with natural gas 8 . |
