www.saVRee.com Deaerators Explained pg.
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Spray Tray Deaerator
Once the water has passed through the spray nozzles, it comes into direct contact with the
steam. The steam flows in a counter direction to the water. As the steam heats the water,
the dissolved gases are liberated. The quantity of dissolved gases present reduces as the
water cascades down through each successive tray. The upper trays are referred to as
heating trays, or first 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 beneficial 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.).