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What are Deaerators?

12/9/2013 2:54:10 PM | by Anonymous

Deaerators

Deaerators are devices that are widely used for removing of oxygen and some other dissolved gas from the feed water to steam the generating boilers. The dissolved oxygen in the boiler feed waters can cause a serious corrosion damage in the steam systems by attaching it to the walls of the metal piping and some other metallic equipment as well as forming oxides. Furthermore, the dissolved carbon dioxide combines with water form carbonic acid that may cause further corrosion.

 

The deaerator is a mechanical device that can eliminates dissolved gas such as carbon dioxide and oxygen from feed water before it gets to the boiler and pipeline. Deaeration is done to prevent corrosion by helping to reduce plant maintenance and operating costs as well as they can reduce the plant downtime.

 

Most of the deaerators are designed to remove the oxygen down to level of 7ppb by the weight (0.005cm³/L) or less and it can eliminate carbon dioxide. The two basic types of deaerators are the spray and tray types.

 

The spray type consists of horizontal and vertical cylindrical vessels which can serves as both the deaeration section and the boiler can feed the water storage tank. Deaerator can spray the feed water in a fine mist and it is introduced first into a preheated section which will raise the temperature to help release oxygen and some other gas.

 

The steam is produced at the bottom of the deaerator and it will rise to meet the heated feed water to scrub the gas. The gas is then released through at a vent on top of the storage tank and it is positioned below the deaerator to receive the processed feed water.

 

The oxygen and some other corrosive gas may not be completely removed by the deaeration in steam systems which are operated under the high pressure therefore it may be necessary to apply a chemical that is scavenger of oxygen. The most popular oxygen scavenger is the sodium sulfite however it can also break down into acidic gas at the high temperature which can increase corrosion as well as defeat the purpose of deaeration. The steam systems use high pressure should also use organic oxygen scavengers.

 

In the tray type of deaerator, the feed water can enter at the top through a distribution pipe. The tray type is also known as cascade type which also include a vertical domed deaeration section that has a mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feed water storage tank. At the bottom of the tray type deaerator, the low pressure steam will produced and moves up to the perforated trays.

 

The steam will come into contact with the feed water and heats it to its saturating temperature which will cause the oxygen and other corrosive gas to separate out. The dissolved gas will only exit through a vent at the deaerator while the deaerated feed water falls to the bottom and into the storage tank rather than dripping the water into the trays.

 

These deaerators are just like other equipment in a plant that will experience wear and tear therefore it should be regularly maintained and checked. It is also a good practice to conduct regular checkups of the deaerator to keep it a good running condition. A check list will also help in the performance of the routine checks to avoid any missing steps in the maintenance procedure.

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