Why is an FGD booster fan different from a normal ID fan?
A dry ID fan sits in hot flue gas above the acid dew point, so its wetted surfaces stay dry and the failure modes are erosion and wear. An FGD booster sits after the absorber, where the gas has left the scrubber saturated and acidic and runs permanently below the water dew point. The casing and wheel never dry out, so the dominant failure mode is wet acid corrosion, backed by droplet carry-over and gypsum or lime fouling. That is why the design leads with metallurgy, lining and drainage rather than wear plates. We size the fan to your absorber outlet gas, not a generic ID rating.
What materials do you use on the wetted surfaces?
It depends on your condensate chemistry, which we take from the absorber outlet gas analysis. For mild acid we use 316L. For aggressive chloride-bearing gas we move to duplex or super-duplex stainless. Where the chloride level rules out austenitic stainless we use an FRP construction, or a rubber or ebonite lining on a carbon-steel shell. The corrosion allowance and lining specification are set against your gas analysis and dew-point margin, not a default, because the wrong metallurgy on a wet acidic gas thins through in months.
The gas is saturated and carries droplets. How do you handle the condensate?
We design the fan to stay self-draining. The scroll is sloped to a low-point drain so condensate cannot pool, the shaft seal is rated for the wet acidic gas, and on a downstream-of-absorber position the inlet arrangement sheds entrained droplets rather than pooling them. Standing liquid is what accelerates corrosion at the low point and unbalances the wheel as it swings with load, so continuous run-off is a design requirement, not an accessory. Tell us the droplet and mist-eliminator carry-over and we build the drainage to it.
Our scrubber carries gypsum and lime. Will the fan foul and go out of balance?
Wet-limestone and semi-dry scrubbers carry fine gypsum or lime solids that build up on the blades. The deposit is sticky and uneven, so the wheel drifts out of balance and vibration climbs before there is any structural wear. This is a fouling problem, not an erosion one, so we use a backward-curved or radial-tip wheel that sheds solids from the blade root rather than packing them, add a wash-water connection and access doors for in-place cleaning, and hold balance margin so a modest deposit does not push the fan past its vibration limit. Heavy hard-facing is the wrong answer here.
Should the booster sit upstream or downstream of the absorber?
Both positions are used and the answer changes the whole build. Upstream of the absorber the gas is hotter and drier but the fan still adds the train pressure drop; downstream the gas is saturated, acidic and droplet-laden, which is the harder, fully wet duty. A downstream fan gets the full wetted-metallurgy, drainage and seal package; an upstream or reheated position may allow a lighter build. Tell us where the fan sits and the reheat scheme, and we build to that position rather than assuming the worst or the best.
It is a retrofit into an existing flue-gas path. Can you size to the real system?
Yes, and a booster is usually a retrofit. We size to the measured system resistance across the added FGD train, not a nameplate figure, so the fan makes up the real pressure drop without robbing the upstream boiler or kiln of draught. We reverse-engineer to the existing duct orientation, bearing centres and foundation where you want a drop-in fit, and we account for the wet-gas density at saturation, which is lower than the dry gas the original path was sized for. Send the measured train resistance, the gas analysis and the existing GA and we match it.
Do you supply just the fan to a scrubber or FGD OEM as a sub-package?
Yes. We supply booster fans separately to wet-scrubber manufacturers and FGD builders. You specify the duty, the absorber outlet gas analysis and the integration interface — flange dimensions, wetted metallurgy or lining, drainage and seal scope, electrical interface and control protocol — and we document it up front and deliver the fan ready to mate. The engineering is identical to a direct-buyer fan; only the integration interface and who buys it differ. We have executed this duty on a handful of projects and build every one to its own gas analysis.
Do you build to API 673, CE and ATEX, and what do those claims actually mean?
We design and build to API 673 for oil and gas and refinery duty as project-specific scope (allow 7 to 10 working days for the offer). CE is self-declared per 2006/42/EC and 2014/35/EU, and ATEX Zone 2/22 is self-declared per 2014/34/EU (Category 3) where the area classification calls for it. To be precise, those are self-declarations of conformity, not third-party certifications. Performance is tested in-house to the AMCA 210 / ISO 5801 method on our 200 HP VFD test rig, not AMCA-certified, and we are not an AMCA member. Balance is to ISO 21940 G6.3 as standard, with G2.5 or G1.0 on application, and bearing life is a design target of L10h at or above 40,000 hours. Our only third-party certification is ISO 9001:2015.
