Boiler Water Chemistry

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Hi Muddasser,

The phosphate addition is done for a couple of reasons. But mostly they are to prevent problems associated with precipitation of dissolved minerals. As the water is boiled off, the dissolved minerals concentrate up, eventually they form scale inside the boiler.

Phosphates are added to react with the hardness in the water (Mg & Ca) to preferentially form Magnesium Phosphate & Calcium Phosphate as it is far easier to clean, than Calcium Sulfate / Magnesium Sulfate.

Phosphates also buffer the water to prevent pH changes.

Alternatives to using phosphates, are ...

1. Don't let the concentration of the water increase to the levels where minerals precipitate out. Requires far more frequent purging of high tds water from the boiler (increased energy & water costs).

2. Pre-treat the boiler feed water to remove the dissolved minerals. Usually done with reverse osmosis / EDI water treatment plant. Again adds cost.

Hope this helps.

Anthony