Stressman76
Mechanical
Have any of you fellow engineers heard about or seen a push to no longer use a deaerator for feedwater? Have the dissolved gas standards changed where they are no longer necessary?
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Deaerator Usage In Power Plants
- Thread starter Stressman76
- Start date
Hi,
You should talk to people selling chemicals and following the boilers to get meaningful answer.
I don't think that it's reasonable.
Note:
The chemistry of water is very complicated, out of the scope of a mechanical engineer, based on my experience (Cooling water, Boilers).
www.watertechnologies.com
Pierre
You should talk to people selling chemicals and following the boilers to get meaningful answer.
I don't think that it's reasonable.
Note:
The chemistry of water is very complicated, out of the scope of a mechanical engineer, based on my experience (Cooling water, Boilers).
Handbook of Industrial Water Treatment | Veolia
Industrial Water treatment Handbook Context
Last edited:
EdStainless
Materials
But even with 100% condensate return it is likely that there are air leaks in the condenser and you still need to DA.
I have yet to see a condenser with prefect sealing and perfect non-condensable removal.
I have yet to see a condenser with prefect sealing and perfect non-condensable removal.
As a corrosion engineer, here are my points:
In HRSGs, three primary chemical treatments are used. Additionally, solid alkalizing agents like trisodium phosphate may be added to HRSG water to enhance impurity tolerance and mitigate corrosion risks:
AVT(R) (All-Volatile Treatment – Reducing):
Oxygen is minimized using reducing agents like hydrazine, creating a low-oxygen, reducing environment.
Note: This method is no longer recommended for all-ferrous systems due to Flow-Accelerated Corrosion (FAC) risks.
AVT(O) (All-Volatile Treatment – Oxidizing):
Oxygen is maintained within a controlled range (10–20 ppb) alongside a high-pH environment.
This is one of the most widely used chemical treatment methods.
OT (Oxygenated Treatment):
Oxygen is deliberately kept within a specific range (typically 30–50 ppb at the economizer inlet for drum units) to passivate steel surfaces. OT is often the most suitable treatment here. During normal OT operation, deaerator monitoring is unnecessary (vents remain closed), though deaeration may be required during startup to manage oxygen levels. Note that in Heller cooling systems, pH must be carefully controlled to avoid aluminum alloy corrosion (aluminum is susceptible to high-pH environments).
In HRSGs, three primary chemical treatments are used. Additionally, solid alkalizing agents like trisodium phosphate may be added to HRSG water to enhance impurity tolerance and mitigate corrosion risks:
AVT(R) (All-Volatile Treatment – Reducing):
Oxygen is minimized using reducing agents like hydrazine, creating a low-oxygen, reducing environment.
Note: This method is no longer recommended for all-ferrous systems due to Flow-Accelerated Corrosion (FAC) risks.
AVT(O) (All-Volatile Treatment – Oxidizing):
Oxygen is maintained within a controlled range (10–20 ppb) alongside a high-pH environment.
This is one of the most widely used chemical treatment methods.
OT (Oxygenated Treatment):
Oxygen is deliberately kept within a specific range (typically 30–50 ppb at the economizer inlet for drum units) to passivate steel surfaces. OT is often the most suitable treatment here. During normal OT operation, deaerator monitoring is unnecessary (vents remain closed), though deaeration may be required during startup to manage oxygen levels. Note that in Heller cooling systems, pH must be carefully controlled to avoid aluminum alloy corrosion (aluminum is susceptible to high-pH environments).
michaelmiles
Student
- Apr 25, 2025
- 6
True, in practice it's nearly impossible to recover 100% of the condensate due to system inefficiencies, leaks, and operational issues like start-ups or equipment failures. But even partial recovery can lead to significant savings in energy and water treatment costs, so it's still worth optimizing wherever feasible
EdStainless
Materials
While oxygen is the biggest concern for corrosion of boiler tubes there are also problems associated with CO2 (lower pH) and nitrogen in the system.
So even in plats running OT there still may be a need for some DA during certain phases of operation.
So even in plats running OT there still may be a need for some DA during certain phases of operation.
georgeverghese
Chemical
In steam heated heat exchangers where steam temp is lower than process fluid temp, there is a risk of migration of the higher pressure process fluid into steam due to corrosion / pinhole leaks on tubes and seepage through tube to tubesheet joints. De aeration / degassing helps to vent off these components also.
Agreed, chemical scavenging of dissolved O2 is much more effective than mechanical / thermally induced de aeration in actual operations, especially for higher steam pressure applications where lower limits of dissolved O2 apply, but this unit operation still does have some use.
Agreed, chemical scavenging of dissolved O2 is much more effective than mechanical / thermally induced de aeration in actual operations, especially for higher steam pressure applications where lower limits of dissolved O2 apply, but this unit operation still does have some use.
To my knowledge, using chemicals such as hydrazine and creating a reducing environment will worsen the issue of single-phase FAC in HRSGs.
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