OCR Text |
Show (SR1 _1 1*°)» t n e N 0 reduction potential of fuel staging is not sensitive to fuel fraction. DISCUSSION Testing in the idealized combustor has shown that fuel staging can significantly reduce NO emissions to levels lower than air staging for equivalent fuel-rich residence time and stoichiometry. This NO reduction can be achieved even when the first stage is fuel lean, as long as the second stage is fuel rich. The major parameter for fuel staging is the second-stage stoichiometry. Optimum NO reduction is achieved for second-stage stoichiometries of 0.6 to 0.8. Maximum NO reduction from baseline was found to be 72 percent. For lean first-stage conditions, the mean reduction from baseline was 66 percent. Table 2 presents results from this effort and the primary results from several fuel-staging studies (references 2, 3, 6, 7) which preceded and paralleled this effort. These results were briefly discussed in the introduction. The results of Wendt (reference 2) and Myerson (reference 3) are small-scale doped gas studies, where some of the reactor exit conditions were substoichiometric. These nonpractical, substoichiometric combustor exit conditions were not run in the present study. Some of the recent Mitsubishi Heavy Industries (MHI) (reference 6) and Energy and Environmental Research Corporation (EERC) (reference 7) results were obtained under more practical excess air exit conditions. As discussed in section 1, the MHI pilot-scale data (reference 6) was obtained in a 23-MW (80-million Btu/hr) tangential-coal-fired research furnace. Because of flow and mixing difference and also a fuel difference, a direct comparison between the MHI and present data cannot be made. However, presently the MHI data is the only constant-load coal flame processed by a coal flame data available to which the present subscale test results can be compared. 8-19 |