Smoke damper doors usually require 100% sealing performance under large differential pressures. They are typically designed with double louvre-style doors. In addition to the sealing elements on each air door, the sealing gas often further modifies the sealing performance of the air door by passing through two air door chambers.
When the entrance and exit damper doors are not equipped with a sealed air system, and the FGD stops operating, gaps in the damper blades allow hot smoke to leak into the FGD, causing system corrosion.
Sealing Principle
Double-slat louvers are commonly used for desulfurization damper doors. Each louvre is composed of multiple slats, each equipped with a sealing element. When the damper door is closed, an elastic contact seal is achieved between the slats through the sealing elements. Additionally, to enhance the sealing effect of the damper door, sealed air is blown into the cavity between the two slat louvers, with the pressure being greater than 500Pa of the flue. This high-pressure air prevents desulfurization backflow, thereby achieving the sealing objective.
The primary reasons for inadequate sealing are as follows:
Leaf (Sealing Element) Clearance Too Large
Due to technical and cost considerations, the sealing gaskets used in the engineering baffle doors are predominantly made of metal elastic strips. These strips are constructed from materials such as stainless steel and special nickel-based alloys, which are then treated with thin plates. The elastic linear contact sealing metal strips are in contact with the baffles.
During the manufacturing and inspection of the shutter doors, blade gaps are typically not an issue and ensure proper sealing performance. However, the shutter door frames are prone to deformation during transportation and installation. Especially, some manufacturers cut corners on the shutter door frame to save costs, resulting in insufficient strength and rigidity. Additionally, at higher desulfurization temperatures, the metal strips are prone to deformation, and the double shutter structure accumulates a large amount of dust. This increased dust accumulation also leads to incomplete contact between the elastic seals and adjacent shutters.
During the installation of the damper door actuator on-site, attention should be paid to ensure the stroke of the actuator matches the damper door's stroke perfectly. The stroke is in place, but the damper door is not fully closed—this should not occur. Such a situation would cause the sealing elements to come into close contact, increasing the gap, and significantly reducing the sealing effect.
2. The air volume of the sealed air is small.
Through special formula calculations, the sealed air volume is related to parameters such as the size of the baffle door, blade gap, blade upwind and downwind pressure, and sealing air pressure. If the air volume of the sealed air is very small, even if the air pressure of the sealed air is very low, it is impossible to form sufficient sealed air positive pressure in the cavity between the double louvers. Above the desulfurization pressure, positive pressure desulfurization will backflow.
Strategies and Measures:
If traditional metal elastic seals are used, strict monitoring of the manufacturing quality of the shutter door is required to ensure the rigidity and strength of the shutter door frame. Additionally, the blade seals should be installed flatly without arc deformation. When the shutter door is closed, the blade seals should be in close contact with the other blade, with the gap within the guaranteed range.
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