Why de-aeration units are employed in boiler systems?

Minimize oxygen content to prevent formation of Iron Oxide

One of the major issues in Boiler System is Corrosion which is caused by Oxygen. As well, if Carbon dioxide is present in BFW it will be present in Steam and when steam condenses in condensate recovery it will result in formation of carbonic acid which again will cause corrosion. To prevent these problems Deaeration is employed. It strips dissovled gases and because we use LS steam it result in increasing of temperature of water. Solubility of gases decreases with increasing temp thereby disolved gases is removed from water.

But Note that mechanical deaeration has its limitations it can reduce Oxygen content to maximum7 ppb which is sufficient enough to result in process upsets. Thus we use oxygen scavengers to remove that least amount of oxygen.

NOTE: to prevent problems arising by presence of carbon dioxide, amines are used in BFW.

Thanks

To remove oxygen from the BFW, it has to undergo de-aeration. Sometimes, oxygen scavenger is also dosed to completely remove oxygen n BFW because presence of it causes pitting in boiler tubes.

In order to meet industry standards for oxygen content and the permissible level of metal oxide in the feed water, almost complete removal of oxygen is required. This can be accomplished only by effective mechanical deaeration supplemented by a properly controlled oxygen reducer. Deaeration is carried out by the following principles: the solubility of any gas in a liquid is directly proportional to the partial pressure of the gas at the surface of the liquid, decreases with the increase of the temperature of the liquid; the efficiency of the removal is improved when the gas and the liquid are strongly mixed. The deaeration can be accomplished using physical means such as thermal degassers or vacuum degassers or chemical means such as oxygen reducers (refining process) or catalytic resins. Membrane contractors are increasingly used. Carbon dioxide is often removed using physical means. The purpose of a degasser is to reduce dissolved gases, particularly oxygen, to a low level and to improve the thermal efficiency of the installation by increasing the water temperature. In addition, they allow the storage of water and provide adequate suction conditions of the feedwater pumps.

De-aerators are required to remove non-condensable gases like oxygen and carbon di oxide from boiler feed water

To eliminate rust in the system.

A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feedwater to steam-generating boilers. In particular, dissolved oxygen in boiler feedwater will cause serious corrosion damage in steam systems.

Boiler deaerators commonly are used to remove oxygen and other gases from the water that feeds into boilers that generate steam. Deaerators are useful because they remove the gases that attach to the metallic components of the steam system and cause corrosion by forming oxides, or rust.

The gases are also removed to increase the fluid heat transfer

De-aerators are used to strip out dissolved gases from boiler feed water. This is mechanical mode to remove dissolved gases in the water. The purpose is to avoid any gases in the BFW. These dissolved gases cause corrosion in boiler systems.

Corrosion prevention in Boiler system.

Deaerators are mostly used in Refineries, CPI or in Power Plants where boilers are used for steam production from Boiler feed water (BFW). Deaerator removes unwanted dissolved gases and dissolved oxygen from the BFW before entering into boilers. Presence of dissolved gases are the cause of corrosion in Boiler systems. Most of the deaerators are designed in such a way that the dissolved oxygen content in the outlet water is about 7 ppb by wt%.

To prevent Oxygen gas goes inside system and causes high rate corrosion by help of high temprature.