Chemical and Non-Chemical Methods of Boiler Deaeration

Deaeration is one of the most important processes used to maintain the working condition of a boiler. Water fed into a boiler usually contains dissolved gases like carbon dioxide and oxygen which can corrode the materials that make up a boiler or steam plant over time. Oxygen can create oxides that rust a boiler and carbon dioxide can turn into corrosive carbonic acid. High temperatures which are a natural part of a boiler’s operation can also speed up corrosion. This can lead to costly replacements and lost production time. Deaeration is performed by either chemical or non-chemical processes, such as using deaerator pumps to remove potentially harmful gases.

Chemical Deaeration

The addition of certain chemicals to the boiler feed water transforms the unwanted dissolved gases into chemical formats that are harmless to the material of the boiler. These chemicals, which are sometimes called oxygen scavengers, are usually added after mechanical deaeration has been performed to fully neutralize the atoms. Some of the most preferred chemicals are sodium sulfite and hydrazine. It is important to know the volatility of the water treatment program used before choosing chemicals for deaeration. The pressure can have an impact on the chemicals used.

Non-Chemical Deaeration

Also called mechanical deaeration, this method takes out dissolved carbon dioxide and oxygen instead of altering the gases in the boiler feed water. The mechanical deaerator heats the feed water near to its boiling point, then sprays the hot water over several trays with perforations. Some types of mechanical deaerators are designed without trays but still function efficiently. As the steam moves in the deaerator from this action, the carbon dioxide and oxygen gases separate from the boiler feed water. They exit the deaerator by way of a vent at the top of the tank. The de-gassed water remains in the deaerator to be fed to the boiler, now free of corrosive gases.

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