The flue gas damper gate is the bridge connecting the boiler to the FGD and wet ESP equipment, and it has a large influence both on boiler operation and on the service life of the FGD and wet ESP plant. The gates in the system include the FGD inlet gate and the wet ESP outlet gate.
In normal operation the flue gas leaves the tail of the boiler electrostatic precipitator, passes through the FGD inlet gate into the absorber for desulfurization, then enters the wet ESP for further dust removal, and finally leaves through the wet ESP outlet gate to the stack. Isolation and connection between the boiler flue gas and the desulfurization island and wet ESP plant is achieved by opening and closing the gates in the flue gas system. The gates therefore play an important role in guaranteeing normal, stable operation of the boiler, the desulfurization and the wet ESP system, and the safety of the system equipment.
Three positions, three specifications
Raw gas inlet. Highest temperature and highest dust load. Carbon steel with a suitable lining is normally adequate, provided the blade edges and the sealing strips are stainless.
Clean gas outlet. About 50 °C, saturated, and carrying chlorides and gypsum carry-over. This is the corrosion-critical position: 316L or duplex stainless for wetted parts, or carbon steel with a glass-flake lining, plus sealing air heated above the acid dew point.
Bypass. Normally closed, but must open within seconds. It needs the same corrosion protection as the outlet plus a drive that can act without external power.
Getting this selection wrong shows up as pitting on the blade edges within two or three years, and as a gate that no longer seals. It is cheaper to specify per position at the enquiry stage than to replace blades later.