OCR Text |
Show analyzers were then calibrated with a certified gas mixture (211 ppm NOz in N2). Conversion of NH3 to NOz was measured using a certified gas mixture (80.7 ppm NH3 in N2) mixed with zero air in a 9:1 ratio. The gas mixture (NH3/air) was introduced to the system at the probe to simulate actual sampling conditions. Flow rates of the sample gas through the probe and through the analyzer were also established before each run. Data were recorded on strip charts continuously during each run. At the conclusion of each run, baseline for each instrument was re-established and the instruments were calibrated using the certified gas mixture . The final conversion of NH3 to NOz was also measured in the same manner as before the run . To calculate NH3 concentrations in the sample gas, the difference between the NOz readings from the two monitors was calculated. This difference was corrected for the conversion efficiency of the oxidation reactor to estimate total NH3 concentrations. The average of the two conversion levels (before and after each run) was used in the calculations for NH3 concentrations . RESULTS Laboratory Study To evaluate the oxidation of NH3 in the stainless steel reactor designed in this program, and subsequently determine the optimal operating conditions for the initial prototype NH3 monitoring probe system, a series of kinetic measurements were planned. Due to schedule/equipment constraints , only a portion of the measurements was completed. Table 1 summarizes the experimental conditions at which these tests were performed, and reports the conversion efficiencies measured. All runs were conducted using dry gas mixtures. Except in Run 14, the initial gas mixtures contained no NO. Several of the runs were repeated to ensure reproducibility. The deviations of all but one of the replicate tests from the mean was less than 15 percent of the mean value . To ensure that there was no reaction between N2 and 02 at the elevated temperatures employed in this study, zero air was passed through the reactor system . No NO formation that could potentially interfere with the NH3 measurements was observed. In these tests, it was not possible to directly investigate if decomposition of NH3 to N2 and H2 occurred. However, under the conditions of the experiments in this study (i.e, low NH3 concentrations in excess 02), decomposition of NH3 to N2 is considered to be insignificant . Although less than 15 percent decomposition of NH3 to N2 in He has been observed on a 430 stainless steel catalyst at 1,090 K, it is expected to be much less than this level in the presence of 02 ' 13-1S Reactions 3 and 4, conversion of NH3 to N2 and N20, respectively, are not expected to be significant at temperature levels greater than 700 to 800 K in the reactor. Although temperatures fall in the transfer line from the reactor to the analyzer, the absence of a catalytic surface minimizes the contribution from these reactions to the conversion of NH3 to undesired products. Other reactions that may occur in the laboratory system under study are: lmo/148 6 |