| OCR Text |
Show blending affects of the secondary air and the primary air spin relationship. The parallel flow arrangement produces a tight flame pattern which extends towards the rear of the furnace in the shape of an elongated ribbon of fire. This results in the combustion process of a burner taking place within the space confined to the path of secondary air coming from that burner. The flame is projected straight back from the burner throat opening, but turns upwards before it reaches the surface of the rear wall. This impeller configuration causes very little flame contact with the back wall. This impeller set-up produces flames that have good ignition, stay close to the tip of the burner nozzle and look excellent when viewed from the side of the boiler next to the burner throat opening. When viewed from this location, the surface of the flame pattern shows signs that the combustion products are twisting or turning in a rotational direction towards the side wall of the furnace. This action is the direct result of the flow from the impeller and the secondary air path being the same relationship. The complementary action results in a flame pattern that is rather compact at the point of origin and the departure angle does not cause the burner throat opening to be totally filled with fire. The photos shown in Figure No. 13 were taken from video tapes of these flames. Again, the 30° flat blade and 45° curved blade produced very similar results, with the curved blade receiving just a slightly higher rating in overall appearance. From these studies, it was concluded that the parallel orientation produced the best flame characteristics. The burners in Eastlake 5 were installed with parallel spin RSC 45° curved bladed impellers. Furnace Exit Gas Temperature (FEGT) These two supercritical B&W boilers were designed for an FEGT of 2,150°F maximum. During the problem period with the Avon 9 burners, conditions existed which promoted delayed combustion in the superheater region. Average CO levels were around 1,000 ppm and FEGT measurements averaged 2,370°F, with highs at the center of the superheater of 2,600°F. The.se measurements were made with the unit at 620 MW, considerably less than the full load 650 MW. Similar conditions were found to exist in the Eastlake 5 boiler when performing the baseline testing with the B&W cell burners. With the unit at 660 MW, CO levels averaged around 175 ppm and FEGT averaged at 2~410°F, with highs in the center of 2,550°F. FEGT profiles obtained on Eastlake 5 with cell burner fixed in the open position are shown in Figure No. 14. As previously mentioned, this boiler experienced severe superheater slagging problems. A main objective of the testing program was to improve upper furnace conditions and lower FEGT. In the beginning, FEGT measurements were obtained by water cooled high velocity thermocouple probes. However, at these high temperatures, this was very costly and time consuming. Fortunately, it was found that a hand-held infrared optical pyrometer gave reasonably good agreement (on a direct reading basis) with the average HVT values. Also, good agreement was obtained with B&W's boiler model calculated FEGT. The majority of the furnace gas temperatures reported were obtained by optical pyrometer method. Furnace observation ports used for determining FEGT as well as other readings are indicated on Figure No. 15. |
