OCR Text |
Show Table 1. Coal sizing o to 1/4 in 1/4 to 3/4 in 3/4 to 1-1/4 in > 1-1/4 in Specification <15 35 50 Average 15 41.4 32.1 11.4 Maximum 45.2 53.4 47.2 21.9 Minimum 4.3 26.9 13 0 Table 2. Coal analyses Ash HHV Moisture Specification 5 to 10 12,500 o to 8 Average 12.3 12,355 3.4 Maximum 16.7 12,800 4.3 Minimum 8.6 11,800 3.0 with daily loads in the 150,000 to 160,000 range with no significant increase in opacity relative to low load operation. This behavior was observed even for one period where coal fines were 45 percent, far in excess of the maximum fines specification of 15 percent. The effectiveness of cofiring in controlling opacity at high loads is attributable to dual effects of carbon burnout by the gas flames and displacing coal firing by the cofired amount. In addition, during the high load operation, the boiler had higher induced draft fan reserve than with coal firing, where fan limits would frequently limit load. This is because overall excess air is lower with gas firing due to the improved thermal distribution and enhanced mixing, reducing overall gas flow to the ID fan. Furnace Probing. Probing was done through opposed ports at the lower front of the superheater pendants, above the rear burner, and through four opposed ports 18 inches over the grate. A water cooled suction pyrometer was used for temperature probing, a water cooled pitot for velocity probing, and a specially designed aspirated probe for gaseous specIe?_ The results are shown in Figures 7 through 12. Results are shown for baseline 16 |