April 15, 2006

Air heater leakage: Worse than you think

—By John Guffre, Paragon Air Heater Technologies

To sum up . . .

Due to thermal expansion and contraction, all rotary regenerative air heaters have dynamic leakage gaps that widen and narrow with load.

Air heater leakage has a huge effect on a power plant's heat rate, required fan capacity, coal drying and mill performance, precipitator/scrubber efficiency, and the like. Many plants lose the chance to sell hundreds of megawatt-hours each day due to excessive air heater leakage alone. During periods of peak demand, the lost daily revenue may amount to as much as $100,000.

Despite the severe, negative economic impact of air heater leakage, most plants continue to grossly underestimate their leakage because they don't know how to measure it accurately. Leakage measurements must be based a multipoint traverse of both sides of the air heater and include measurements of both O2 and flue-gas velocity levels. Finally, the test points must be located to cover high-leakage sectors (typically, those very close to duct walls).

Relying on existing continuous O2 monitors will necessarily produce the false conclusion that air heater performance is much better than it actually is. The continuous performance monitoring systems that most plants rely on today can do a great job of mathematically calculating leakage, but they cannot overcome the inaccuracy of data provided by continuous O2 monitors. In this case, the adage "garbage in, garbage out" certainly applies.

The cure for excessive air heater leakage is a straightforward, two-step process. First, be sure you're accurately measuring the actual amount of leakage present, and then tighten up your air heater sealing system by installing modern, high-performance seals.

—John Guffre is the chief research scientist of Paragon Airheater Technologies (Corona, Calif.) He can be reached at 888-488-3100 or jguffre@paragonairheater.com.