OCR Text |
Show with reaction temperature, achieving maximum decomposition at about 1150°C. Pilot-scale, corner-fired furnace experiments with gas, oil, and coal fuels were also run with both regular and low-NOx burners. Figure 1 shows how fuel staging was integrated into the pilot-scale furnace. The lower furnace burner arrangement is typical of conventional tangentially fired furnaces. Figure 2 shows the NO reductions observed using the fuel-staging approach compared to the conventional or low-NOx burner approach. These results show that the fuel-staging process reduces NO by 50 percent or more, roughly independent of the fuel type and initial burner NO production. Following the Japanese work, Energy and Environmental Research Corporation (EERC) performed some bench-scale experiments (reference 7) with pulverized coal to further investigate the parameters examined in the Japanese work. The inlet gases were generated by a doped propane/air flame. For inlet NO concentrations of 633 ppm or higher, Beulah lignite and Utah coal fuels showed maximum NO reductions from baseline of over 50 percent at stoichiometries of 0.9 and 0.8, respectively. For the case of 148 ppm Initial NO concentration, NO emissions actually increased rather than decreased as the amount of coal in the reduction zone increased. Apparently, coal combustion in the second stage generated significant NO or NO precursors, which offset any reduction of first-stage NO. This paper describes tests which characterized the fuel-staging process in a well-defined subscale, pulverized-coal-fired combustor. The important parameters of stoichiometry, residence time, and the fraction of fuel burned in the second stage were defined by these experiments. The experimental investigation is continuing along with a data analysis task which will help define the mechanisms and rates of the fuel-staging process. 8-4 |