OCR Text |
Show tre~hanism The additional 20 reactions include SO/S03 interactions, fonnation of HN03 from N02, formation and reactions of CH30 2 and CH30 2H. These molecules are likely to be stable and their reactions may proceed at the relatively low temperatures of H20 2 injection. The 20 reactions with rate constants in the form ~ = A Tn exp(-E/RT) are presented in Table 1. The rate constants were selected from the NIST database (1994). The entire mechanism (49 species and 284 reactions) was used for modeling H20/CH30H interaction with NO, CO, S03 and CH4• The objective of the modeling work was to determine the most important elementary reactions responsible for NO removal and to provide insight into the controlling factors associated with the process. The modeling was performed without any vruiation of rate constants, and in general, this approach gave satisfactory, qualitative description of H20/CH30H reactions with NO. However, the use of the selected mechanism and the rate constants did cause some important quantitative differences when compared to experimental observations. For instance, preliminary validation of the model on the SNCR process (i e., comparisons with EER test data on NO reduction in the presence of ammonia) demonstrated slightly higher NO reduction with predicted the temperature window of NO removal shifted to higher temperatures by about 30-80 K This difference between experimental and modeling data was evident in all other modeling runs. A similar shift in the predicted temperature window with predicted higher NO removal was also found when the mechanism presented by Miller and Bowman (1989) was used. The experiments were conducted in the BSF with different cooling configurations in the convective pass leading to different temperature profiles in the regions where the reagents were injected. Since most of the tests were conducted with a quenching rate of about 188 K/s, this temperature gradient was used for all modeling. Results of the modeling under the same conditions as the experiIrental runs in Figure 2a, are presented in Figure 4a. As in the tests, all three additives 11 - |