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Show Figure 3 replots the results In Figure 2a ,b showing the calculated N20 levels as a fraction of the NOx reduced. For ammonia InJection, the calculations Indicate less than 1 % of the NOx is converted to N20 . For urea Injection, the calculations Indicate a peak NOx to N20 conversion of 12% at 1200oK. For HNCO, the calculations indicate that over 50% of the NOx is converted to N20 at 1200oK. Additional calculations have been performed investigating the effect of 1) the presence of S02' 2) combustion product stoichiometry, 3) initial NOx level, and 4) amount of SNCR chemical added. These results show similar trends and have not been included In this paper. PILOT-SCALE TEST RESULTS A series of tests were also conducted in a small pilot-scale combustor. A schematic of the combustor used for these tests is shown in Figure 4. The pilot scale cC?mbustor fires natural gas, doped with NH3 to control the Initial NOx level. The combustor and test section are refractory lined with the test section being 15 cm in diameter and 240 cm long. At the firing rates used for these tests, the residence time in the test section is nominally 0.5 seconds, while the temperature drop along the test section is nominally 250°C/sec. The SNCR chemicals are injected into the combustion products in a venturi section above the test section. Gaseous and pulverized solid chemicals were injected pneumatically at the throat of the venturi using the two diametrically opposed injectors. The gaseous chemicals were metered with rotameters, and the pulverized solids metered with a loss in weight gravimetric screw feeder. Liquid solutions were injected at the throat through a small air assist atomizer. The atomizer was fabricated into a water cooled holder. The single atomizer was located at the center of the throat with the spray directed downward (i.e., co-flowing with the combustion products). The liquid solutions were pumped with variable speed peristaltic pumps and metered with rotameters. To vary the amount of liquid SNCR chemical being injected, the total liquid flow rate was held constant, at nominally 1 L/hr, and the concentration of the solution changed. 1 his was done to maintain constant thermal conditions in the test section. 8 |
