Deaerator

J_10

How does a deaerator work?

Brad White_9

I assume you mean steam deaerator not an air separator?

A deaerator is a device used to pre-treat boiler feedwater prior to delivery to the boiler via a boiler feed pump/unit.

In general principle it is a tank which stores returning condensate and into which is injected any make-up water. Sometimes these handle just the raw make-up water but often they are mixed; single series flow rather than parallel paths. (It is good to remove free oxygen from all boiler feed water anyway.)

Into this tank is a submerged perforated tube (called a sparger tube) and sometimes an immersed heat exchanger.

Steam is injected into either of these devices (sparger tube or HEX) to pre-heat the water above the vapor point, whereby the water gives off non-condensibles (free air, CO2 usually). The non-condensibles are vented out either by a pressure relief vent or the tank is vented straigt to atmosphere.

In general terms this is based on temperature, usually 205 to 210 degrees F. This tends to drive off enough free oxygen, down to the single digits of what was in there to start with, making it suitable for injection into the boiler. Chemicals may also be injected into this vessel to scavenge oxygen.

In high pressure steam plants, the deaerator may take the water to boiling (at low pressure of course) because the higher temperatures of the incoming steam allow this. In this case the tank is held under pressure by a relief valve device.

I am sure others can add more detail, but that is a general overview I would give to co-workers in my office.

Best,

Brad