OCR Text |
Show side NO. levels agree with the baseline results, the 450 ppm at the center pon indicates that some of the reburning fuel is being recirculated below the reburning burners. During coal reburning (cyclone burner at 72% load and 2% O2; reburning burners at 28% load), NO" levels of 900, 860, and 830 were measured, and recirculation was not observed. Measuring the NO" levels directly above the reburning burners showed that the majority of NO" reduction had occurred. These results substantiate that good mixing between the reburning fuel and combustion gases does exist Pilot Furnace Temperature Prorde. SBS furnace temperatures were measured during both baseline and reburning phases to determine the technology's potential effect on temperature variations. Figure 8 illustrates the resulting furnace exit gas temperatures (FEGTs) under various operating conditions. The data indicate that while utilizing reburning, rear-wall OFA ports, a cyclone stoichiometry of l.t zero percent FGR, and maintaining a constant 6-million Btu/hr furnace heat input, approximately a 500F FEGT increase (from baseline) was observed. However, when 10% FGR was added to the reburning system, a temperauue quenching phenomena occurred and a 500F FEGT decrease (from baseline) resulted. A ±500F variation in FEGT is considered to have a minimal (if any) impact to boiler performance. 2400 I r 0 2300 § I -0 BASELINE o------o-~ -00-----0-------- £ ~ --------0_ 2200 r 0 :::N-;;--- r 2100 I CYCLONE AT 10% EXCESS AIR FULL-LOAD CONDITIONS u GAS REBURNING o OIL REBURNING o COAL REBURNING o 2000L-~~~~~-J-~1-~~-~~-~~1 -L--L-~~~-~~-~1~ o 2 4 6 8 10 12 14 16 18 20 FGR, PERCENT OF TOTAL FLUE GAS Figure 8. Operational Effects on Furnace Exit Gas Temperature (FEGT) The in-furnace probing showed no significant temperature variations between the baseline/reburning conditions, except that again a quenching effect occurred in the reburning zone when FGR was added. Combustible Loss. Unburned carbon and CO emissions were measured at both the stack and throughout the furnace during the baseline and reburning phases. An inherent cyclone characteristic is that the majority of the combustion occurs within the cyclone itself. Since the cyclone will continue to be operated in an excess air mode, this combustion characteristic will not be altered. However, the amount of unburned char that does not bum within the cyclone will now enter a reducing environment in the reburning zone, with the remaining combustion air not to be introduced until the OF A ports. When coal and fuel oil are used for reburning, additional unburned 13 |