How Deaerators Work (Engineering)

How Deaerators Work (Engineering)

Learn how deaerators work! This 3D animated video introduces the spray and tray type deaerators. You will learn all of a deaerator’s main components, its typical operating conditions, different designs and how it works.


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Deaerators are required to remove dissolved gasses from the boiler feedwater system. The two gasses removed are primarily oxygen and carbon dioxide. It is necessary to remove these gasses as a failure to do so may lead to corrosion of boiler components.

Deaerators are classified as un-fired pressure vessels, although they often operate at very low pressures e.g. 0.5 bar / 7.5 psi, 105 C / 130 F respectively.

Deaerators mechanically remove entrained non-condensable gases by raising the temperature of the water to its saturation point. The solubility of the gases reduces as the temperature increases, so the level of entrained gases reduces as the temperature increases. A deaerator is essentially a pressurised feed water tank, although non-pressurised (atmospheric) tanks can be used for smaller steam systems.

High levels of oxygen will lead to corrosion of boiler parts, which may lead to failure of the boiler. Typical problems associated with high dissolved oxygen levels include flaking of the water side boiler surfaces and oxygen pitting (deep holes in the metal surfaces).

High levels of dissolved carbon dioxide leads to a lower pH, which will make the boiler feedwater acidic. Low pH water causes corrosion of the carbon steel parts of the boiler and steam system components.

Two common deaerator designs are used in the engineering world, these are the spray type, and tray type. Both deaerator designs require a large contact surface area between the water and steam, in order to aid heat transfer. The steam heats the water to its boiling point, or very close to it.

Condensate from the steam system is returned to the deaerator and make-up water is fed into the deaerator. Chemical treatment also occurs in the deaerator; typically an oxygen scavenger is injected into the deaerator to remove the final traces of oxygen. Bicarbonate and amine-type chemicals are used to control the boiler water pH, they are usually injected with the make-up water or between the deaerator and boiler.

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