OCR Text |
Show amount of fuel exceeded the available oxygen limit and unburned fuel exited the reactor. Reduction of NO in diffusion flames, by passage through the flame zone, has also been found (reference 4). In these cases, NO was either injected into the fuel jet or into the combustion air. In passing through the flame zone, either from the rich or lean side, the NO was observed to decrease. The NO reduction from passage through the fuel-rich side, or fuel side, appeared to be higher than from the fuel-lean or air side. The same types of reductions can be seen in pulverized-coal-fired systems where heterogeneous as well as homogeneous processes are active. NO dopant has been injected into a variety of firebox locations in a pulverized coal, pilot-scale, tangentially fired system (reference 5). In this single-burner-level system, dopant was injected below, at, and above the fuel entry location for both air-staged and unstaged conditions. Up to 94 percent of the NO dopant was reduced. The reduction was most effective in intensively burning rich flame zones and rich postflame zones, and was much less effective in lean postflame zones (reference 5). Mitsubishi Heavy Industries (MHI), in a joint project with Tokyo Electric Power Company, performed sub- and pilot-scale fuel-staging tests (reference 6). This study was directed at gas-, oil-, and coal-fired utility boiler applications. In the subscale reactor tests, gas, oil, or coal was added to premixed and electrically heated mixtures of NO, O2 and N2 in a downstream section to reduce the NO concentrations. For these fuels, a maximum NO reduction of approximately 90 percent is achieved at stoichiometric ratios between 0.8 and roughly 0.4. For propane fuel, the reduction process appears to be roughly completed by 0.1 sec and is independent of inlet NO concentration from 40 to 1,000 ppm inlet NO. Also, for fuel-rich conditions, NO decomposition appears to increase 8-3 |