Steam boiler and its various types
Boiler feed water treatment
In this lesson we will discuss Deaerator. Deaerator is an important part of power plant system.
Deaerator is used to remove the oxygen of DM water.
Deaerator is a contact type open heater in which dissolve oxygen in the feed water is removed as much as possible by mechanical means. Gases move from higher partial pressure to lower partial pressure. Partial pressure of oxygen in air is high (as air contains almost 21% oxygen by volume) than the partial pressure of dissolved oxygen in feed water. Hence, by simple mechanical means it is not possible to eliminate the dissolved oxygen from water.Hence, in deaerator the feed water is heated by LP or VB steam (pressure: 2.5 – 3.5kg/cm2, temperature: 110 degree C). Due to heating the partial pressure of dissolved oxygen in feed water increases and solubility decreases to considerable amount. Then by mechanical means dissolved oxygen is released in air. Hence Deaerator is another very important part of boiler feed water treatment plant. The mechanical means is same as that of in degasser. But instead of air, LP steam is blown from bottom to top and feed water is poured from top to bottom.
Deaerator also serves as header, to provide a net positive suction head (NPSH) to the boiler feed pumps (BFP) and here by protects the BFPs from any damage due to vapor lock and cavitations.
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 feed waters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust). The corrosion may also damage the tubes of boiler.
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