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About Dampers : APPLICATIONS
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Applications Where Dampers Are Used
Damper requirements and service conditions are obviously so varied that no one type can meet every application need. Before considering selection and specification, you should obtain a clear idea of how the different types operate, and just what the design details are for each type, and for specific models.
COAL FIRED POWER PLANTS
Locations for dampers in a coal fired unit range all the way from the induced draft fan and the primary air system to the flue gas scrubber outlets. Because several elements, such as fans and precipitators, are often paralleled, the number of dampers can be much higher than that shown in the figure.
In general, control dampers will be of the opposed louver type, and isolation dampers can be either parallel louver or guillotine. Double parallel louver dampers and double guillotine dampers also get consideration. If a damper must open or close quickly, the louver type is the only practical choice. A few butterfly dampers have gone into circular ducts adjacent to flue gas desulfurization systems, but this type of damper is not common in power plant applications.
At the inlet to centrifugal fans, either a parallel blade louver damper or a radial vane damper is sometimes the choice. These damper types impart whirl to inlet air when damper vanes are partly closed, reducing power need. Fully open, however, the damper causes a slight loss in the system.
Service conditions vary widely through the unit. Clean low temperature air at the forced draft fan inlet contrasts with ash laden, wet, corrosive gas before or after the scrubber. Temperature changes of nearly 300°F can occur suddenly when an air heater fails.
GAS TURBINE EXHAUST
In gas turbine combined cycle or heat recovery systems, a damper directs hot exhaust to the stack or to the recovery boiler. Although the gas is clean, it can be corrosive, and it's always hot, around 900°F or higher. Specialized damper types are required. Fast opening and tight closure are important.
For baghouses, both regular dampers and special poppet types are in service. The poppet varieties meet the need for a quick acting short stroke and tight sealing inside the baghouse itself.
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