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Show Gas samples are taken at the exit of the combustor with a water-cooled probe and transported to a series of gas analyzers (NO/NOx' N20 , CO, CO2, and O2), The continuous measurement of N20 was mad0. using an NDIR based technique developed by Montgomery, et al (1989). The pilot-scale tests Investigated the effect of temperature, chemical Injection rate, and initial NOx concentration on the production of N20 for selective non-catalytic NOx reduction with the following chemicals: N H3 (gaseous) Urea (pulverized solid) Urea (aqueous solution) Cyanuric acid (pulverized solid) Figure 5 shows the NOx reduction and N20 emissions as a function of temperature for NH3 (gaseous), urea (solid), and cyanuric acid (solid) at an injection rate corresponding to an NINO molar ratio of 2.0. For the test results shown in Figure 5, the initial NO level was 700 ppm. At these conditions, NH3 exhibited the highest NOx reduction with a peak removal of 88 percent at a temperature of about 930°C. The peak NOx removal with urea was 82 percent at a temperature of 980°C. The calculations discussed previously yielded peak NO removals for NH3 and urea at nominally 927°e (12000K) and 1027°C (13000K) respectively. These differences are most likely due to 1) the finite mixing time in the combustor, 2) the non-isothermal nature of the combustor, and 3) the finite evaporation and decomposition time for the urea. Cyanuric acid did not exhibit a peak in removal over the range of temperatures studied; NOx removals increased as the temperature Increased (at 110aoe, the NOx removal was 73 percent). Again, this difference In high temperature behavior of the cyanuric acid relative to the calculations is due to the relatively slow decomposition rate of the cyanuric acid in the combustor. Figure 5b shows the corresponding N20 emission data as a function of temperature. The data show that ammonia injection resulted In the lowest N20 emissions, while urea injection provided the highest in terms of absolute concentration. With ammonia injection, N20 emissions peaked at 877°C, while injecting either urea or cyanuric acid resulted In peak emissions at 977°C. 11 |
