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Show aspirator were measured by a rotameter and an orifice meter, respectively. In some cases, a 70 inch-long, 60° wedge angle water-cooled injector sprayed the powder along the furnace centerl i ne. RESULTS Experiments were performed at fuel flow rates of 760-1100 lbs/ hr, equivalent to 14-20 MBTU/hr. Both, air and fuel flow rates were adjusted automatically to maintain a desirable stack oXYgen concentration at all cyanuric acid feed rates. Powder injectlon was done at 6, 10, 15.5, and 20 ft from the burner throat. Aspiration air for cyanuric acid injection was supplied at room temperature and its flow rate ranged from 34-70 lb/hr «0.5% of the total combustion air). Visual observations indicated rapid sUblimation of the powder in the furnace within 6-12 inches from the injection nozzle exit. Figure 5 shows photographs of the spray pattern. Typical flames were 8-10 ft long. Temperature and gas composition in the vicinit¥ of the injection points and other ' locations on the furnace mld-plane were mapped using the HVT probe. Three sampling ports on the furnace side wall were chosen. At each port, measurements were made at three points along the probe path. At 6 feet away from the burner, there appeared to be a central zone of high CO and 02 concentrations. with further mixing and chemical reactions occurrlng downstream of this point, all species concentrations leveled off quickly to their steady state values measured at the stack. Meanwhile, temperature continued to decline towards the exit of the furnace. It should be pointed out that the maximum flame temperatures have been measured at 2-4 ft away from the burner. Temperature. Cyanuric Acid Feed Rate. and 02 Concentration Effects Normalized NOx concentrations (relative to baseline stack measurements) are plotted in Figures 6-8 as a function of molar ratio of cyanuric acid to NOx . It is clearly evident that significant NOx reduction occurs even in the presence of high excess oxygen as long as sUblimation and decomposition of the acid are complete within the available residence time. This is in contrast with the reported findings of Wicke et ale [7] who concluded that excess oxygen becomes a limiting factor at low cyanuric acid feed rates, by oxidizing it to form NO. For a given temperature and oxygen concentration, NOx decreased with increasing cyanuric acid feed rate until a minimum point was reached. Beyond this value, NOx increased as the acid began to transform to NO. At lower temperatures, this behavior was followed by higher CO emissions formed most likely by HNCO dissociation (Figures 6-8), without any appreciable effect on the opacity levels. Low temperature NOx removal improved when the acid was injected along the burner centerline, where better mixing with the bulk combustion gas and longer residence times were expected. Maximum NOx reductions were 73, 70, and 80% at 2.2, 3.2, and 5.4% excess 02' respectively. In view of the fact that injection temperature variations were restricted by the number of available ports, the percent reductions may not represent the optimum values. -4- |