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Show ... ".i"- ' ,. ,~. Cyclone Burner Stoichiometry. The effects of varying the cyclone burner stoichiometry and percent reburning fuel were investigated; the results are plotted in Figure 7. Although B&W recommends that minimal cyclone operation changes be employed, various cyclone stoichiometries were tested during this project in order to complete the technology data base. Figure 7 is based upon maintaining a constant reburning zone stoichiometry of 0.9. As the cyclone stoichiometries were varied between 1.0 to 1.2, the percentage of rebuming fuel to the reburning burners (versus coal to the cyclone to keep a constant6-million Btu/hr load) was changed accordingly to achieve the reburning zone stoichiometry of 0.9. The natural gas input varied between 13 to 31 %. The figure shows that NOll levels decreased from 420 to 260 ppm as the cyclone stoichiometry was increased from 1.0 to 1.2, respectively. 500 o 0'-----0 0 400 ~o ; 0 .... 0~ I (") 0 300 ~ '--------- 0 .... c w I .... 0_ 0 0 UJ ex: ex: 20t 0 u E REBURNING ZONE QQ.. STOICHIOMETRY OF 0.9 ic 0 GAS REBURNING 0 z I 0 OIL REBURNING 100 I 0 COAL REBURNING OL-__ ~ ____ -L ____ ~ ____ ~ __ ~~ __ ~ ____ -L ____ ~ ____ L-__ ~ ____ ~ ____ ~ 0.98 1.02 1.06 1.10 1.14 1.18 1.22 CYCLONE STOICHIOMETRY Figure 7. Effect of Cyclone Stoichiometry and Percent Reburnlng Fuel on NOx Emission levels During coal rebuming tests as the cyclone stoichiometry increased from 1 to 1.2, 17 to 37% coal had to be introduced to achieve the reburning zone stoichiometry of 0.9. The NO levels were almost insensitive to the II cyclone stoichiometry. During pilot coal reburning tests, the same coal was utilized at the cyclone and reburning burners, but with different grind size. Since the total heat input was constant at 6-million Btu/hr, the total fuel nitrogen input to the furnace was not changed at different cyclone stoichiometries. These results indicate that the reburning zone stoichiometry is the controlling parameter in NOll reduction in the reburning zone. In-furnace NOll measurements were taken throughout the SBS (nine sampling ports located on the side furnace wall) during both the baseline and reburning phases. Baseline NOll levels were unifonn throughout the test facility, thus substantiating that all of the NOll generation occurs within and/or immediately upon exiting the cyclone. Operating in the natural gas reburning mode (cyclone burner at 77% of load and 2% excess 02; reburning burners input a123% of load), NOll levels at an elevation between the cyclone exit and the burners were 900, 743, and 450 ppm at the right side, left side, and center of the furnace, respectively. While the right-/left- 12 |