Optimising deaerator venting
Deaerator venting optimisation is the tuning of the vent that releases non-condensable gases from a deaerator so it removes dissolved oxygen and carbon dioxide effectively while losing the minimum steam. Too little venting leaves corrosive oxygen in the feedwater; too much throws away steam through the vent plume.
What it is
A deaerator strips dissolved oxygen and carbon dioxide from boiler feedwater by heating it to near saturation and venting the liberated gases. The vent must carry those non-condensables out, but it inevitably carries some steam with them. Optimisation finds the vent setting that achieves the required low dissolved-oxygen level without venting more steam than necessary — a balance read from the small, steady vent plume and the feedwater oxygen result.
Why it is done
Dissolved oxygen is a primary driver of boiler and feed-system corrosion, so under-venting risks pitting of pressure parts and pipework and increases oxygen-scavenger chemical demand. Over-venting, on the other hand, sends a large steam plume to atmosphere continuously — wasted energy and treated water. Because the correct vent is a thin, steady wisp rather than a roaring plume, an untuned vent usually errs toward waste. Setting it properly protects the boiler and stops a continuous, visible steam loss.
How it is done
Deaerator operating pressure and temperature are confirmed at saturation, since deaeration only works when the water is heated close to the boiling point at that pressure. The vent orifice or valve is adjusted to give a small, continuous plume that clears the non-condensables, and feedwater dissolved oxygen is measured to confirm it meets the target. Oxygen-scavenger dosing is reviewed against the achieved level so chemical is not masking poor venting. The setting is checked across load, and the vent path is verified clear of restriction or condensation.
- Confirm saturation conditions
- Set steady vent plume
- Measure dissolved oxygen
- Review scavenger dosing
- Check across load
- Verify vent path clear
What to watch for
Closing the vent down to save steam without measuring dissolved oxygen invites corrosion that only shows up years later as pitting. A large roaring plume wastes steam continuously and is often mistaken for good deaeration. Running the deaerator below saturation — too cool for its pressure — means no amount of venting removes the oxygen, and masking the shortfall with extra scavenger hides the real fault.
Related practices
Changing over a boiler feedwater treatment programme
Adopting condensate recovery
Establishing a steam-trap survey programme
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