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Show Other problems which are all related are: waterwall wastage due to reducing atmosphere in the furnace, high furnace exit gas temperature resulting in shortened life of pendant tube surface and liquid phase corrosion, high convection pass gas velocity causing accelerated erosion and excessive sootblowing required to prevent bridging of pendant surfaces which causes large build-up of ash on convection pass horizontal tube surfaces. These large ash build-ups result in channeling of the flue gas and extremely high localized velocities which greatly accelerate erosion rates. Many of these problems were further aggravated when the gas recirculation systems were abandoned on both units in 1981 and 1982. At this time, increased emphasis was placed on trying to improve combustion through burner improvements. Poor and unequal air and fuel distribution to the burners was frequently blamed for incomplete combustion causing excessive slag in the upper and lower furnace regions as well as waterwall wastage. In 1984 and 1985, Eastlake 5 experienced several large slag falls from clinkers which formed on the secondary superheater pendants. These slag formations bridged across the pendants, forming at a rate that quickly got beyond the operator's control and weighing several tons. When they fell, they created major damage to the bottom slope and resulted in long forced outages and large expense. The areas of chronic slagging and other problems are pointed out in Figure No.1. Another chronic problem was continued tube wastage of the lower furnace side walls. Various gimmicks such as cutting air slots in these panels were tried to solve this. More recent practice has been to make extensive use of aluminizing to protect this area. In the first 10 years of service, the majority of these tube panels had to be replaced. Windbox and Burner Improvements Efforts to improve combustion were hampered by the mechanical design of the original cell type "daisy chain" air register and the wrap-around windbox arrangement. It was impossible to keep the air register dampers properly positioned because of constant binding of the daisy chain drive linkage. The wrap-around (plenum) windbox required the air register dampers to control secondary air to the burner. As a final solution to prevent burners from being starved and to reduce furnace 02 imbalance, all registers were permanently fixed in the open position. Tne B&W cell type register is shown in Figure No.2. This approach still didn't solve the problem since most of the time less than the full compliment of six pulverizers and 48 burners are in service simultaneously. This meant that a large portion of secondary combustion air was dumped through idle burners instead of being delivered to active burners. In addition, it was suspected that there might be an inherent flow distribution problem with the windbox. This would explain the large fly ash accumulation frequently found in the rear windbox. The initial burner improvement program, therefore, was twofold: (a) replace the original daisy chain air registers with a reliable air register; and (b) investigate windbox flow for possible maldistribution and make corrections if needed. After testing three candidates for replacement air registers in identical 50 MW six-burner, front-fired, Sterling boilers at CEI's Ashtabula Station, the |