OCR Text |
Show Consistent with MHI and other results presented in table 2, SR2 has been shown to be a dominant parameter with optimal NO reductions achieved for SR2 <^ 0.8. The maximum percent reduction achieved by the different investigators for coal, oil, and gas fuel under superstoichiometric exit conditions is also consistent with the results of this study. MHI showed that, after 0.2 sec, the fuel-staging NO level had reached the asymptotic low level (reference 6). The small slope of the fuel-staging NO results with residence time found in this study, shown in figure 7, support this result. As shown in table 2, MHI used an f of 2 in their coal tests, which is between the cases run in this study. In this study, the amount of fuel injected into the second stage was less influential on NO than second-stage stoichiometry. The correspondence of MHI and the present results over a range of f supports the limited importance of f to NO reduction. Consistent with EERC results (reference 7), in this study first-stage stoichiometry was found to be less influential on NO emissions than second-stage stoichiometry. Based on the results of this study and others, the fuel staging process has similarities to air staging. The trends of NO with second-stage stoichiometry are similar to trends of NO with first-stage stoichiometry for air staging. Based on prior air-staging results, it may be speculated that the NO reduction process could be a result of the following homogeneous and heterogeneous reduction paths: Homogeneous .<N0 Fuel N HCN, NHt ^ ^ ^ N 2 8-21 |