To separate the dissolved salt in raw water, the demineralization plant uses a chemical method in which demineralization plant's function is to remove dissolved salt using an ion exchange method, resulting in pure feed water for the boiler.

There are three types of resin used in the DM plant for the boiler feed water treatment process –

• Resin for cation exchange

• Resin for ion exchange

• Resin in a Mixed Bed

Resins are chemical substances (typically polymers with a high molecular weight) that react with salts and eliminate them chemically. The cation exchange resin, as the name implies, exchange the cation and anion exchange resin, which exchange anions with salts dissolved in hard water.

• Cation Exchange Resin:

Equation is: NaCl + RHSO₃ = RNa⁺SO₃+ HCl

In this reaction, NaCl is Sodium Chloride

• Anion Exchange Resin:

   Equation is: HCl + RHNO₄ = RNCl +H₂O

In this, HCl stands for Hydrochloric Acid and RHNO₄ is a weak base. As a result of the elimination of Cl–, water is naturally acidic.

• Mixed Bed Resin:

Mixed bed resins are used in boiler feed water treatment demineralization plants to remove ions (particularly Na+ and SO₃^2-) that may remain in the water after the preceding purification process.