Demin Water ( Demineralisation Boiler Water)

Demineralization Plant

The function of demineralization plant is to remove dissolved salt by ion exchange method (chemical method) and there by producing pure feed water for boiler.

DEMINERALIZATION PLANT
The salts which make the water hard are generally-chloride,
carbonates,
bi-carbonates,
silicates and phosphates of sodium,
potassium,
iron,
calcium and
magnesium.

In D M plant there are three types of resin used for boiler feed water treatment process -

1. Cation exchange resin
2. Anion exchange resin
3. Mixed Bed resin

Resins are chemical substances (usually polymers of high molecular weight) used to react with salts and eliminates them by chemical process.
As the name suggests, the cation exchange resin, exchanges the cation and anion exchange resin, exchanges anions with the salts dissolved in hard-water.

Cation Exchange Resin
Thus H2SO4, H2CO3 are also produced.
We have removed Na+ but the water has become acidic.

Anion Exchange Resin
This way we have eliminated Cl- and thus acidity of the water.
Similar reaction for H2SO4 also. dm plant

Mixed Bed Resins
These mixed bed resins are used in Demineralization plant of boiler feed water treatment, to remove the ions (especially Na+ and SO32-) which may further present in the water after foregoing process of purification.

Degasser
The function of degasser tower is to remove carbonate ions by forming carbon-di-oxide. In degasser tower stream of water is poured from top and air is blown from bottom to top. In the pressure of air the carbonic acid (H2CO3) present in the water dissociates into H2O and CO2.

This CO2 is free to mix with air.

Benefits of using degasser are:
It removes the carbonic acid and other gases mixed with water by simple physical method and thereby reduce the chances of corrosion.
It saves the resins which are very costly chemicals and thereby improves the economy of boiler feed water treatment process.
The H2CO3 free water is now collected in degasser sump and then pumped to anion exchange resin inlet.