INTERNAL TREATMENT BY BOILER COMPOUNDS-----WATER TECHNOLOGY---CY2111 183101 –ENGINEERING CHEMISTRY –I Lecture Notes

INTERNAL TREATMENT BY BOILER COMPOUNDS:

The residual salts that are not removed by external methods can be removed by adding some chemicals directly into the boiler water.  These chemicals are known as ‘Boiler compounds’.  This method is known as ‘Internal treatment’. 

E.g)  Carbonate conditioning, Phosphate conditioning and Calgon conditioning

a)  Carbonate conditioning:   Used for low pressure boilers.  Here the salts like CaSO₄   are converted to easlity removable CaCO₃.  But sometimes it produces NaOH, CO₂ and hence Carbonic acid.  So it is less preferred.

CaSO₄  +  Na₂CO₃  à  CaCO₃  +  Na₂SO₄

b)Phosphate conditioning:  Used for high pressure boiler.  No risk of CO₂  liberation.   

3CaSO₄  +  2 Na₃PO₄  à  Ca₃(PO₄)₂ +  3 Na₂SO₄

Three types of Phosphate salts are used:

Na₃PO₄   - Tri sodium Phosphate - Used for highly acidic water

Na₂HPO₄ – Disodium hydrogen Phosphate – Used for slightly acidic water

NaH₂PO₄ – Sodium di hydrogen phosphate – Used for alkaline water

c) Calgon conditioning:

Calgon is the trade name of sodium hexa meta phosphate- Na₂ [ Na₄ (PO₃)₆].

With calcium ions it forms a soluble complex and prevents scale and sludge formation.  It is used for high and low pressure boilers.

2CaSO₄ + Na₂[ Na₄ (PO₃)₆]  à  Na₂ [Ca₂(PO₃)₆]   +  2 Na₂SO₄