Image: Flue gas damper door (site archive)
A damper door consists of the frame, blades, sealing structure, main shaft bearings, crank-link mechanism and electric actuator. In flue gas desulfurisation (FGD) systems, flue gas dampers must achieve near-100% sealing under considerable pressure differential — something blade sealing alone cannot deliver. That is exactly why a sealing air system is necessary.
1. How the Sealing Air System Works
Where sealing demands are high, flue gas dampers adopt a double-louver structure: elastic seals are fitted between blades and frame on each layer, and sealing air (supplied by seal air fans) is continuously fed into the cavity between the two layers, keeping cavity pressure above the flue gas side. Even with minor blade-seal gaps, gas is held outside — achieving zero leakage. Seal air fans are typically installed one-duty-one-standby and interlocked with damper operation: fans stop when the door opens and start when it closes.
2. Three Types of Flue Gas Dampers
FGD dampers fall into three classes by position, with different requirements: the raw gas duct damper sits on the untreated gas side — high temperature, with emphasis on sealing and temperature resistance; the treated gas duct damper handles wet, highly corrosive gas after desulfurisation, placing the highest demands on corrosion-resistant materials; the bypass damper stays closed in normal operation and must open rapidly in emergencies or maintenance, requiring high sealing, high corrosion resistance, fast opening and high reliability simultaneously.
3. Sealing Maintenance Essentials
In routine maintenance: regularly inspect the wear and compression of the elastic seal strips on blade edges — they are corrosion-resistant, bolt-fixed and individually replaceable; adjust link rod lengths to correct blade closure and ensure synchronous tight closing; while the seal air fan runs, check seal air leakage from the cavity to judge sealing condition. Double-layer blades achieve over 99% sealing after closing, approaching zero leakage when combined with the sealing air system.
We manufacture flue gas damper doors with complete seal air fan systems, customizable for raw/treated/bypass positions — contact us for selection advice.
