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istaltic pumps and metered with rotameters. In order to maintain a constant thermal environment in the test section, the total amount of liquid injection was held constant at nominally 1 liter/hr. By diluting a concentrated reagent solution with distilled water, the amount of chemical reagent was varied while the total liquid flow rate was maintained. At a N/NO ratio of 2.0 the solution concentrations were 1.46 mole \ nitrogen (i.e., 2.4 wt\ for urea and 1.4 wt\ for ammonium hydroxide). For the cases where 00 was added to the process, this was done by injecting the CO along with the atomizing air. Gas samples were taken at the exit of the combustor with a water-cooled probe and transported to a series of gas analyzers (NO/NOx ' NH3' N20, CO, C02' and 02). The continuous measurement of N20 was made using an NDIR based technique( 5). NH3 was measured using a Perkin-Elmer Mekos 100 continuous analyzer. The Mekos 100 is an infrared analyzer; the entire sampling system including the sample cell of the analyzer is heat traced to 250oC. In the results which follow, removal of NO is presented rather than NOx (NO + N02). This was necessitated by the sampling train configuration utilized during the test series; however, previous tests have showed that for the range of parameters investigated, no N02 was produced (4). RESULTS Urea with Carbon Monoxide Previously, it has been observed that CO present in relatively small quantities during the urea SNCR process results in the following behavior (4): o Widens the effective temperature "window". o Shifts the temperature "window" to a lower regime. o Lowers the peak removal efficiency. o Reduces unreacted ammonia byproducts. o Increases N20 emissions. This behavior can be readily seen in Figures 2 through 5 for the case of initial NOx of 125 ppm, N/NO of 2, and CO levels ranging from 0 to 2000 ppm. As can be seen, N20 levels increase significantly as CO levels increase over the temperature range investigated. Peak N20 levels for the test conditions were about 25-30 ppm. The present data compare favorably with earlier data (4) collected on a different apparatus. In the earlier system, peak N20 levels of about 30-35 ppm were noted under similar conditions. Ammonia with Carbon Monoxide More recently, tests similar to those discussed above for urea have been conducted using aqueous ammonia a8 the selective reducing reagent. Results of these tests are shown in Figure 6 through 9. These figures present NO removal efficiency, CO characteristics, unreacted ammonia, and N20, respectively. Each of these results are discussed below. As in the case with 5 |
