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Show -8- After making measurements of ~NO, ~N02 and NH3 slip, the nitrogen balance is forced to close by calculating "a". The result of this calculation for an NOINOx ratio of 0.5 is shown in Figure 6. The dashed horizontal line in Figure 6 is the stoichiometric ratio for Reaction 2 (1.33). Over the range of space velocities tested, the results show an increase in the N02 stoichiometric coefficient as the NH/NOx ratio changes. As the NH3/NOx ratio increases above 1.0, the stoichiometric coefficient "a" increases above 1.33. This suggests a shift between Reactions 2 and 3. At NH/NOx ratios below 1.0, the stoichiometric coefficient "a" decreases below 1.33. This might suggest that the N02 is reduced to NO prior to reaction on the catalyst. Similar results were seen at other NO/NOx ratios. The final issue to be addressed is whether the NO or N02 is preferentially removed when the flue gas contains a mixture of N02 and NO. While this may not affect overall performance, it may have an impact on the specification for a CEM or the SCR process control system. Figure 7 shows NOx, NO and N02 removals for NOINOx ratios of 0.38 and 0.63. For these tests, the space velocity was 24,000 hr-1 and the temperature 650°F. At the lower NO/NOx ratio of 0.38 (Figure 7a), it can be seen that the N02 removal is higher than the NO removal. The trend is just opposite for the higher NOINOx ratio of 0.63 (Figure 7b); in this case, the NO is preferentially removed. Thus, it appears that when the flue gas contains a mixture of N02 and NO, the minor component will be preferentially removed during the reactions on the catalyst. CONCLUSIONS The bench-scale study has shown that in situations where combustion modification for NOx control lead to higher NOINOx ratios, a downstream SCR can be impacted. In this situation, the impacts are not all detrimental. • • A mixture of NO!NOx will increase the activity of a commercial titanialvanadia SeR catalyst. This results in comparable or higher NOx removal with lower NH3 slip for a given amount of injected NH3. The maximum activity occurs at an equimolar mixture of NO and N02 • |