A deaerator is a mechanical device that eliminates dissolved gases, such as carbon dioxide and oxygen, from feedwater before it gets to a boiler and its pipeline. Deaeration is done to prevent corrosion, helping to reduce plant maintenance and operating costs. This can also reduce plant downtime. Two basic types of deaerators are commonly used: the tray-type and the spray-type.

In a tray-type deaerator, feedwater enters at the top through a distribution pipe. The water cascades down through layers of perforated trays. At the bottom of the tray-type deaerator, low-pressure steam is produced, which moves up through the perforated trays. The steam comes into contact with the feedwater and heats it to its saturating temperature, which causes oxygen and other corrosive gases to separate out. The dissolved gases exit through a vent at the top of the deaerator, while the deaerated feedwater falls to the bottom and into a storage tank.

Rather than dripping the water through trays, the spray-type deaerator sprays the feedwater in a fine mist. In many cases, the spray is introduced first into a preheated section, which raises the temperature to help release oxygen and other gasses. Steam is produced at the bottom of the deaerator, and it rises to meet the heated feedwater and scrub the gasses from it. These gases are released through a vent at the top. A storage tank is positioned below the deaerator to receive the processed feedwater.

Oxygen and other corrosive gases may not be completely removed by deaeration in steam systems operated under high pressure. In such cases, it may be necessary to apply a chemical that is a scavenger of oxygen. Sodium sulfite is the most popular oxygen scavenger; however it can break down into acidic gases at high temperature that will increase corrosion and defeat the purpose of deaeration. Steam systems using high pressure should use organic oxygen scavengers instead.

A deaerator, just like other equipment in a plant, will experience wear and tear and should therefore be regularly checked and maintained. It is a good practice to conduct regular off-line check-ups of the deaerator to keep it in good running condition. A checklist will help in the performance of routine checks to avoid missing any steps in the maintenance procedure.