www.saVRee.com Deaerators Explained| pg. 8
as the water cascades down through each successive tray. The upper trays are referred
to as heating trays, or �rst stage trays. The lower trays are referred to as deaeration
trays, or second stage trays. The water then exits the tray area and is discharged to the
feedwater tank.
Dissolved gases and some steam are constantly discharged through the vent. A typical
deaerator will vent between 5% to 15% of the steam that passes through the deaerator.
As steam costs money to generate, it is bene�cial to vent as little steam as possible.
Approximately 90% to 95% of deaeration occurs within the spray area with much of the
remainder occurring in the tray area. Mechanically deaerated water is usually designed
to lower the oxygen content to 7 parts per billion (ppb). Any remaining oxygen in the
feedwater is stripped using oxygen scavenging chemicals (sodium sulphite, hydrazine
etc.).
How Spray Deaerators Work
Condensate and makeup water enter the water box directly above the spray nozzles; the
spray nozzles are spring loaded. Water pressure causes the nozzles to open and water is
sprayed into the deaerator. Spraying the water into the deaerator ensures a large contact
surface area between the water and steam, which ensures good heat transfer between
the two �uids (�uids are de�ned as either liquid or gas).