What are the objectives of water treatment?

To prevent scale formation from low remaining levels of hardness which may have escaped treatment.

Sodium phosphate is normally used for this, and causes the hardness to precipitate to the bottom of the boiler where it can be blown down.

1) To deal with any other specific impurities present.

These will be specific substances for specific applications.

2) To maintain the correct chemical balance in the boiler water - to prevent corrosion it needs to be somewhat alkaline and not acidic.

Typically a 1% caustic solution will be used to achieve a target pH of between 9 and 11. British Standards BS 2486 recommends pH 10.5 - 12.0 for shell boilers @ 10 bar, pH 9 could be used in higher pressure boilers only.

3) To condition any suspended matter.

This will be a flocculant or coagulant, which will cause the suspended matter to agglomerate and sink to the bottom of the boiler from where it can be blown down.

4) To provide anti-foaming protection.

5) To remove traces of dissolved gases.

These are primarily oxygen and carbon dioxide and the presence of these dissolved gases in the boiler plant and system will cause corrosion. It is, therefore, necessary to remove and / or neutralize them if damage is to be prevented.