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Show • Plant operational data for stack opacity, and process pressures, temperatures, and flowrates Results are summarized below. Warmup. Following the retrofit, the boiler was warmed up from a cold start using the gas burners. This gave a much cleaner and convenient startup than the normal procedure of warming up with wood and coal lit with oily rags. Figure 6 shows opacity strip charts for conventional warmup and lightoff (6a) and gas warmup and lighter fluid lightoff (6b). Time averaged (6-minute) opacity traces are recorded from the center zero position. Clearly, with conventional warmup, the unit experienced periods of several hours with opacity of nearly 100 percent. With gas warmup, the opacity was below 20 percent for the entire startup campaign except for a few minutes during lightoff. During the first two startups following retrofit, it was not possible to lightoff completely on gas. As a cautionary measure to protect the bare grate prior to feeding coal, the gas burner management system required the undergrate air forced draft fan to be operational with 25 percent flow. This procedure gave excessive air flow through the grate during warmup which overly compensated for the heating by the gas burners. Experience during warmup with the undergrate air showed the grate rail temperature did not exceed 150°F. Coal fed during warmup was dry and hot and easily ignited with lighter fluid at the end of the warmup sequence, but did not ignite solely with gas. Gas lightoff with reduced undergrate air flow will be attempted at the conclusion of an outage scheduled for October 1995. Derate Recovery. The boiler derate at Dover Light & Power is strongly linked to the coal variability. The plant has a low-cost coal supply but in return experiences wide fluctuations in coal sizing and coal quality. Tables 1 and 2 list the ranges experienced during a 3-week test period in August 1995. These types of variations would normally have limited the boiler load to around 145,000 to 150,000 lbjhr except for rare cases where the coal sizing and quality was exemplary and could be tolerably fired. With approximately 12 percent cofire, the boiler was operated for 2 weeks of an August peak generation period 14 |
