If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. Magnesium phosphate has a surface charge that can cause it to adhere to tube surfaces and then collect other solids. For this reason, alkalinity is an important part of a phosphate precipitation program.
Phosphate concentration-pH of boiler water when using coordinated phosphate Na/PO 4 ratio equal 3.0. Conductivity and pH of boiler water when using tri-sodium phosphate.
When the concentration of phosphate in the boiler water is too high, phosphate will react with boiler scale forming iron and iron sodium phosphates or precipitate to form a solid phase on the hot boiler tube surfaces and elsewhere. This phenomenon is called phosphate hideout and it can result in changes of pH, as well as the concentrations of phosphate and other chemical species in the boiler water.
Dec 01, 1995 · Phosphate treatments have been used in boilers for more than 70 years. As operating pressures increased, the frequency of corrosion-related failures in phosphate-treated boilers also increased. Many failures were attributed to ``free`` caustic generated by the nonstoichiometric precipitation of various phosphate compounds on boiler surfaces.
Using of congruent phosphate as equilibrium phosphate boilers water
The low pH values of boiler water compared to phosphate residue concentration can be attributed to two factors, first, di-sodium phosphate formed has no effect on boilers pH, and it has no ability to buffer any pollutant may inter the boiler, second, the use of sodium sulphite as oxygen scavenger in this
cessful in increasing the phosphate reading, the actual phosphate inventory in the boiler has not decreased. It has combined with oxide deposits to form a slightly lower Na/PO 4 ratio solid (approxi-mately 2.1:1), causing an increase in alkalinity in the liquid phase (bulk water) — hence the boiler water pH increases. When the load