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Equilibrium Phosphate Treatment

To address the "hide-out" problem, the Equilibrium Phosphate Treatment (EPT) was developed by Ontario Hydro. It specifies low phosphate additions with tri-sodium phosphate and the maintenance of small amount of hydroxide (OH) alkalinity. 

Note: The EPT program eliminates the use of di- and mono-sodium phosphates, which helps in the reduction of "hide-out" in high pressure boilers, known to be caused by reversible reactions between aqueous phosphate and magnetite that result in the formation of sodium iron phosphate compounds.

The equilibrium phosphate treatment (EPT) is utilized to maintain the boiler water pH within desired specifications of 9.0 to 9.7 pH. If ammonia is present in the condensate, its buffering effect caused by ammonia to the condensed boiler water sample will result in a false high pH reading. 

It is recommended that the low EPT pH limit be adjusted to compensate for the ammonia buffering. For the SDG&E units, which have ammonia in the 0.3 to 0.5 ppm range the low boiler pH limit is maintained above 9.2 pH.

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