UFC 3-240-13FN
25 May 2005
Figure 3-12. Mechanical Deaerator Schematic (Tray Type)
Vent
Water Inlet
Steam Inlet
Spray
Tray Section
Storage
To Boiler
Feed Pump
3-2.6.2
Chemical Removal of Free Oxygen. Oxygen scavengers are chemicals
that react with oxygen. Oxygen scavengers remove the oxygen from the boiler
feedwater so it will not cause pitting corrosion.
3-2.6.2.1
Oxygen Scavengers for Boilers up to 6205 Kilopascals. Oxygen
scavengers for boilers up to 6205 kilopascals (900 pounds per square inch gauge)
include catalyzed sodium sulfite and uncatalyzed sodium sulfite, both of which are
oxygen scavengers and sources of sulfite. When a deaerator is used, any uncatalyzed
oxygen scavenger will suffice and can be fed into the storage area of the deaerator. Use
catalyzed sodium sulfite in systems without a deaerator. A cobalt sulfate salt, which is
present in the catalyzed sodium sulfite material, is used as the catalyst. Catalyzed
sulfite reacts more quickly with oxygen than does uncatalyzed sulfite. Both the sodium
sulfite and the catalyst must be fed into the feedwater upstream from the boiler so
oxygen can be scavenged before the feedwater enters the boiler. This addition scheme
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