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saturation point (boiling point). As the water approaches its saturation point, the dissolved
oxygen level approaches zero. In power plant, the steam supplied is often waste steam
from the steam turbine(s).
Gas Solubility Reduces as Temperature Increases
Dissolved gases released by the deaeration process are vented to atmosphere along with
trace amounts of steam. A typical vent will use a plate with an orifice (hole) to control the
rate at which gas is vented. If the orifice is too large, steam will be vented, which reduces
the overall plant efficiency (because of the reduction in steam cycle efficiency) and drives
up costs. If the orifice is too small, some gases may return to the feedwater, which is also
undesirable.
Chemical dosing occurs on the makeup inlet line, within the deaerator, or between the
deaerator and boiler. The chemicals needed, their quantity, and where dosing should
occur, depend upon the system design. For example, makeup water supplied from a
reverse osmosis (RO) plant will have a low pH and should be treated before it enters the
deaerator.
Deaerator Components
A deaerator is an unfired pressure vessel. Deaerators are typically manufactured from
carbon steel, although some industries -such as the pharmaceutical industry- use stainless
steel. The pressure vessel is cylindrical in shape with as few welds and penetrations as
possible.