Deaerators

Corrosion of iron or steel in boilers or boiler feed water piping is caused by three fundamental factors:

• Feedwater Temperature
• Feedwater pH Value
• Feedwater Oxygen Content

Temperature and ph value influence the aggressiveness of corrosion.  The higher the temperature, and the lower the pH value the increased aggressiveness of the feedwater.  The dissolved oxygen content of the feedwater is a large factor in determining the amount of corrosion that will take place.  The presence of oxygen, and other non-condensable gases, in the feedwater  is  a major cause of corrosion in the feedwater piping, boiler, and condensate handling equipment.

Deaeration is the mechanical removal of dissolved gases from the boiler feedwater.  There are three principles that must be met in the design of any deaerator. 

• The incoming feedwater must be heated to the full saturation temperature, corresponding to the steam pressure maintained inside the deaerator. This will lower the solubility of the dissolved gases to zero.
• The heated feedwater must be mechanically agitated. This is accomplished in a tray deaerator by first spraying the water in a thin film into a steam atmosphere. Creating a thin film reduces the distance the gas bubble has to travel to be released from the water. Next, the water is cascaded over a bank of slotted trays, further reducing the surface tension of the water. This allows the for the removal of any gases not liberated by the initial spraying.
• Adequate steam supply must be passed through the water, in both the spray section and the tray section to sweep out the gases from he water