Why is chemical dosing performed in the steam drum?

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Although boiler feed water is treated rigorously, it is impossible to completely remove all impurities, and some impurities still make their way into the boiler. As the water in the boiler continues to evaporate and concentrate, its salt content gradually increases, which may lead to internal scaling. To prevent scaling, chemicals must be continuously added to the boiler water during operation. These chemicals undergo chemical and physical reactions with the calcium and magnesium salts present in the water, resulting in non-adhesive, loose sludge that settles at the bottom and is removed from the boiler through regular slag discharge. The chemical added to the boiler water is usually Na3PO4 (sodium triphosphate), which, after being diluted, is pumped into the boiler water in the boiler drum by a dosing pump. Adding trisodium phosphate to the boiler water not only causes the calcium and magnesium salts in it to form non-adherent, loose sludge, but it also helps to adjust the alkalinity of the boiler water, keeping its pH value within the range specified by the regulations.