Raw gas inlet gate
Hot, dusty and slightly negative. Why the inlet gate is a wear problem rather than a corrosion problem, and how the seat survives it.
The raw gas inlet is the dirtiest position in the whole flue path. Gas arrives from the precipitator or, on a partial-bypass arrangement, straight from the air preheater, carrying fly ash at 130 °C to 160 °C. The gate has to close against that dust and hold a seal that protects anyone working inside the absorber.
Why single louvre gates fail here
Ash settles on the seat every time the gate opens. A single louvre closes onto that ash and stops a few millimetres short. The leak is small but continuous, and it carries dust into the absorber, which is exactly what the maintenance isolation was meant to prevent. A double louvre with sealing air pushes the ash off the seat as it closes and then holds a positive pressure in the cavity, so any remaining gap leaks air into the duct rather than gas out of it.
Wear surfaces
Blade edges take the abrasion. We fit stainless edge strips on a replaceable carrier so the blade itself is not scrapped when the strip wears through. Guide rails are machined and, on the worst duties, fitted with a hardened insert. The frame is lined flush with the duct so there is no ledge for ash to build on.
Sealing air
Flow is usually set at 0.5 % to 1 % of the flue gas volume at that point, delivered at 1 kPa to 2 kPa above the duct pressure. The number that matters is not the fan capacity but the differential at the seal, which is why we ask for the absorber pressure profile and not a single figure. A differential transmitter across the cavity, wired to the DCS, lets the operator confirm the seal before signing a permit.
Operation
Close the gate with the sealing air already on. Opening should be done with the air still on until the blades are clear of the seat. Running the gate without sealing air is the fastest way to destroy a seat that would otherwise last a decade.
Talk to us about this duty
Send the duct section, design temperature, pressure difference and the duty point. We reply with the gate type, the material selection, the drive and a general arrangement drawing for approval.