What are boiler oxygen scavengers and why are they important?
Dissolved oxygen in the feedwater circulates metal particles
into the boilers, typically copper and iron oxides. If left untreated, pitting
and aggressive localized corrosion will occur. The deposition of these metal
particles can lead to inefficiencies by creating an insulating layer on the
lining of boiling tubes. The insulating layer increases the temperature
necessary to allow for consistent and even heating. Even in low concentrations,
dissolved oxygen can have a profound effect on corrosion, especially when it
comes in contact with ammonia.
Removing oxygen from the feedwater and boiler system
prevents dissolved oxygen and oxidation of metal, which causes corrosion. There
are two ways to remove oxygen: mechanical and chemical. These two approaches
are typically used in tandem to ensure the lowest possible dissolved oxygen
levels. An exception to the rule is when low pressure boilers are used, in which
case high doses of chemical input alone should be sufficient at removing
Deaeration is the mechanical removal of dissolved oxygen. Dearators
work by heating the water and venting the gases. This operation reduces oxygen
in the makeup water by more than 99 percent, leaving behind oxygen
concentrations measured in the parts-per-billion range. At feedwater and boiler
water temperatures, even this level can create severe corrosion. Therefore, the
last traces of oxygen must be chemically scavenged from the feedwater.
Chemical scavengers come in two varieties: volatile and
- Volatile chemical scavengers typically consist
of hydrazine, hydroquinone, hydroxylamine and ketoxime.
- Non-volatile scavengers consist of sulfite and
The selection of the proper oxygen control program can be
made after an assessment of the specific boiler operating conditions.