www.saVRee.com Deaerators Explained| pg. 4
Systems with low condensate returns must continually add large amounts of makeup
water. Continuously adding makeup water introduces more untreated water to the
system compared to when reusing condensate that has already been treated. For these
reasons, a deaerator is much more likely to be installed on a system with low condensate
returns than one with high condensate returns. It should be noted that systems with low
condensate returns will have larger operating costs due to higher water consumption,
higher heat/energy consumption (water has to be heated before entering the boiler) and
higher chemical treatment consumption.
The solubility of dissolved gases in water reduces as the temperature of the water
increases. In order to raise the boiler feedwater temperature, low pressure steam is
supplied. The steam transfers its heat to the feedwater until the feedwater approaches
its 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 ori�ce (hole) to control the
rate at which gas is vented. If the ori�ce is too large, steam will be vented, which reduces
the overall plant e�ciency (because of the reduction in steam cycle e�ciency) and drives
up costs. If the ori�ce is too small, some gases may return to the feedwater, which is also
undesirable.