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Why does boiler feed water need to be deoxidized?
Source: | Author:demihwater | Publish time: 2019-03-07 | 201 Views | Share:
Why does boiler feed water need to be deoxidized? What are the methods?
Why does boiler feed water need to be deoxidized? What are the methods?

Oxygen corrosion is the most common and serious corrosion in boiler system. Oxygen corrosion may occur
in pipes and equipments through which water is supplied, because water is generally in contact with the
atmosphere and dissolved oxygen in water is basically saturated.


Oxygen corrosion usually takes the form of ulcerative corrosion and small-hole local corrosion, so the damage
to the strength of metal components caused by this corrosion is very serious. From the analysis of the causes
of industrial boiler damage and scrap accidents throughout the country, it is found that due to poor deoxidization
of boiler feed water, corrosion and damage are caused, and scrap or tube burst is proposed, which accounts for
a considerable proportion. Therefore, in order to eliminate the corrosion and harm of dissolved oxygen to boiler
water vapor system, the national standard stipulates that for boilers whose evaporation is more than 2t/h, the
feed water should be deoxidized, and according to the different working pressure of boilers, the dissolved
oxygen in feed water should be controlled within the qualified range.


At present, there are two main deoxidization methods for boiler feed water: thermal deoxidization and chemical
deoxidization.


What are the characteristics of thermal deaeration?

Thermal deaeration has the following characteristics:

Thermal deaeration can not only remove oxygen, but also remove gases such as C02, NH3, H2S, which can
reduce the corrosion of these gases to boiler water vapor system.


(2) The effect of deoxidization is stable, which can reduce the oxygen content in feed water to below O.01mg/L
after deoxidization, promote the decomposition of bicarbonate in water and reduce the total amount of carbonate
compounds in water.


(3) No pollution of water quality.

4. Steam heating is needed, and more consumption is needed.

What is the working principle of thermal deaeration?

The atmosphere is mainly composed of nitrogen, oxygen, carbon dioxide, water vapor and a small amount of
other gases. The atmospheric pressure is the sum of the partial pressures of the gases that make up the
atmosphere.


According to the law of gas dissolution (Henry's law), the solubility of any gas in water is proportional to the
partial pressure of the gas at the gas-water interface, but independent of the atmospheric pressure. That is
to say, the dissolved oxygen content in water is only related to the partial pressure of oxygen in the atmosphere.
The smaller the partial pressure of oxygen is, the dissolved oxygen content in water tends to zero.



When water is heated to boiling in the atmosphere, the saturated vapor pressure of water equals the
atmospheric pressure at the air-water interface, and the partial pressure of oxygen equals zero. At this time,
the oxygen solubility in water drops sharply and comes out of the water, which is the principle of thermal
deaeration.

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