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Overview of Deaerators

Deaerators are devices that are used to remove dissolved gases, primarily oxygen but also carbon dioxide, from the feedwater of boilers through a process known as deaeration. Deaerators are necessary because dissolved oxygen can cause boiler feed water (BFW) corrosion, which can be incredibly detrimental to a boiler if left unchecked. This type of corrosion generally takes the form of pitting in the front end of the boiler, the treating system, feedwater lines and pumps, and the preheat coils.

Also, this process causes the boiler water to become more heated, which can reduce the risk of thermal shock in the boiler. The process of deaeration also increases the temperature of the water which helps to reduce the amount of fuel required to convert the feedwater into steam, thus improving the efficiency of the boiler.

Deaeration can be done in one of a few different ways. The primary methods of deaeration are tray type and spray type deaerators.

In both methods, the process begins as water is fed into a deaerator. In tray type deaerators, the water flows down into a chamber while steam simultaneously flows upwards out of the chamber through the water. This steam heats the water to its saturation temperature allowing it to strip the water of it’s dissolved oxygen before flowing out of the deaerator and into the atmosphere.

The spray type method is different because, while the water is still fed into a steam chamber, it is done so via being sprayed, rather than being allowed to flow. This, along with a preheater, causes the water to heat to its saturation temperature so that as steam is pumped into the chamber it is able to easily strip the water of it’s dissolved oxygen.

There are other methods as well, such as vacuum deaeration and deaerating condensers, but these are not as common.

 

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Articles about Deaerators
  • May/June 2005 Inspectioneering Journal
    By John Reynolds at Intertek

    Boiler feed water (BFW) corrosion is mostly the result of dissolved oxygen in the feedwater, but is also related to the quality of the BFW and the quality of the treatment system. If the treatment system is effective, then a layer of iron oxide (magnetite) will provide the protection needed to minimize boiler corrosion.

  • January/February 2005 Inspectioneering Journal
    By John Reynolds at Intertek

    Corrosion fatigue is closely related to mechanical and vibration fatigue cracking, except that it is initiated and accelerated by a corrosion mechanism, especially one that gives rise to pitting, from which cracks often initiate. But that corrosion mechanism need not be very severe in order to give rise to corrosion fatigue. Probably the best known case of corrosion fatigue, in a lightly corrosive environment, stems from deaerators in boiler systems.

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