Regarding boiler water supply

Before putting a new boiler into use, it must be cleaned with sodium hydroxide and trisodium phosphate; after it is operational, sodium hydroxide is no longer added, only trisodium phosphate. The function of trisodium phosphate is that, under the temperature and pressure conditions in the steam drum, it can react with salts such as calcium and magnesium salts present in the boiler water to form loose slag, which can be easily removed through continuous blowdown. The phosphate content in the boiler water should be analyzed to control the dosage of chemicals added. Incidentally, it was once suggested to add trisodium phosphate to the deaerator, on the grounds that the pressure in the deaerator is low, making it easier to add it. But this is completely wrong, because under the temperature and pressure conditions in the deaerator, trisodium phosphate cannot react with salts to form sludge.

Sodium hydroxide is used to adjust pH, while trisodium phosphate is used for descaling

Trisodium phosphate also has the function of regulating pH! Sodium hydroxide is generally used for alkali cleaning equipment during startup operations; it is not added under normal circumstances!

Yes, trisodium phosphate does have the function of regulating pH, but its effect is limited. Some units also add sodium hydroxide to adjust the pH, but ammonia is generally used for this purpose.

The parameters of boiler water include pH, total alkalinity, conductivity, iron ions, phosphate, etc. These parameters are usually adjusted by adding trisodium phosphate. Adding sodium hydroxide to the furnace at the start of operation is intended to form a protective layer on the vessel walls.