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Show a 90· injector located at the centerl i ne of the furnace. Th is injector allowed the reburning fuel, diluted/transported with argon, to flow radially outward through four 0.5 cm holes and mix rapidly with the oncoming primary effluent. Burnout air was also injected radially. The 3.0 MW, down-fired tower furnace2 used in the pilot-scale investigations wa~ refractory-lined and water-jacketed with inside dimensions of 1.2 x 1.2 x 8.0 m. The four main diffusion burners each consisted of an inner pipe for axial primary fuel injection and an outer pipe, equipped with swirl vanes, for the main combustion air. This four burner array produced relatively uniform velocity and composition profiles at the primary zone ex it. The furnace conta i ned seven rows of ports for reburn i ng fuel and burnout air injection. The temperature profile was manipulated by insertion of cooling panels, positioned against the furnace walls. The reburning fuel and burnout air injectors were designed to maintain jet mixing similarity between the pilot-scale furnace and a full scale boiler based on empirical correlations for entrainment rate and jet penetration. Exhaust gas samples were withdrawn through a stainless steel, waterjacketed probe and analyzed for NOx (chemiluminescence), O2 (paramagnetic), CO/C02 (NDIR), and S02 (NDUV). A water-jacketed probe with 1n internal water quencn spray near the front end was used for extracting in-flame samples. Gas phase HCN and NH3 spec i es were co 11 ected ina gas wash i ng un it and subsequently analyzed for CN- and dissolved ammonia using specific ion electrodes. Gas temperatures were characterized with a suction pyrometer. RESULTS Original Concept: Staged Air Addition Figure 1 summarizes a series of experiments6 which were conducted in the tunnel furnace with an initial NO concentration of 240 ppm and a -N to NO ratio of 1.5. The solid symbols and dotted lines show results for cyanuric acid or ammonium sulfate injection under classical "De-NOx" conditions with 25 percent excess air and indicate an optimum reaction tJmperature of approximately 1000°C as has been reported previously. Somewhat surprisingly, however, Significantly larger reductions can be achieved over a broader temperature range if the selective reducing agent is added under slightly fuel rich conditions (in this case S~ = 0.99), and the final burnout air is added subsequently downstream. The open symbols and solid lines represent these data, and for these tests the peak temperature refers to the temperature at which the final burnout air was added. The selective reducing agent was added into the fuel rich zone at 900·C. Other compounds such as ammonium sulfate, which are Significantly less expensive and potentially less toxic, can produce even larger reductions than those measured with cyanuric acid. Kinetic modeling suggests that the rich zone acts primarily as a source of CO. At the rich-lean transition the CO is oxidized and excess OH is produced by the usual chain branching reactions: CO + OH ~ CO2 + H H + O2 ~ OH ~ 0 o + H20 ~ OH + OH For low initial CO concentration the excess radicals are consumed by: NH3 + OH ~ NH2 + H20 4 |