| OCR Text |
Show oxi~ized NO better than each component individually. The optimum temperature window for rrethanol was sorrewhat wider than that for the H20/CH30H mixture. Choice of an additive system for a specific boiler application would be made based on regions of temperature access in the boiler and allowable CO emissions. Figure 2b demonstrates the NO removal efficiency for the three additives injected at their optimum temperatures versus initial NO concentration. Removal of NO was higher for 70 ppm NO during injection of H20 2 and the mixture, but injection of methanol is more effective for higher initial NO levels. Experiments were then conducted in which MR was varied. Figw·e 2c shows that conversion increased with increasing MR for all three additives injected at optimum temperatures. Injection of H20 2 and the H20/CH30H mixture at MR=1.0 caused 70% and 90% NO removal, respectively. At MR=3.0 from 94 to over 98% NO removal was achieved for the three additives. Oxygen level in flue gas was varied from 0.5 to 8% by variation of the air/fuel ratio. Figure 2d demonstrates the effect of oxygen on NO removal. Tests were performed at optimum injection temperatures for each additive, at MR = 1.5, and at initial NO concentration 200 ppm. One can see that at low oxygen concentrations, NO removal was slightly decreased for H20 2 injection and significantly decreased for CH30H injection. At oxygen concentrations between 3 and 8 % there were no significant difference in NO removal. Several tests were also conducted to quantify reconversion of N02 to NO. During hydrogen peroxide and methanol injection at optimum temperatures, NO was simultaneously measured just downstream of the injector (750 K) and at the end of the convective pass (500 K). The sampling location at 750 K corresponded to residence times of 0.5 and 0.8 s, and the location at 500 K - to residence times of 1.9 and 2.2 s for injection of H20 2 and CH30H, respectively. Initial NO levels of 70, 200, and 500 ppm were tested. Only slight 2-5% reconversion was observed in each case. 6 - |
