Why must the pH value of boiler water be kept at 9

Reason for controlling the pH of boiler water at 9-12: 1. To keep the boiler water slightly alkaline; if it becomes acidic, it can corrode equipment under high-temperature steam conditions. Corrosion in high-pressure equipment is particularly dangerous and can lead to explosion accidents. Therefore, we maintain the pH at 10-12. 2. Generally, treatment is carried out by adding a chemical, sodium hydrogen phosphate, which creates an alkaline environment. 3. For the control of the boiler water pH value, it is also possible to regulate it through regular blowdown and continuous blowdown. 4. Boiler water is generally hot water at around 100 degrees Celsius after deoxygenation, and the deoxygenation method is usually thermodynamic deoxygenation, that is, the steam-driven oxygen removal method. 5. The boiler control should be stable; large fluctuations should be avoided to prevent damage to pressure equipment and resulting accidents. 6. A regular inspection system must be implemented, with inspections generally carried out every 1–2 hours, to check the safety accessories and prevent accidents. 7. Regularly check the analysis results of the boiler system; once any fluctuations are detected, immediately identify the cause to prevent accidents

Sometimes it is also controlled at 6.5 to prevent catalyst charring, but for a short period of time. This post was last edited by WSL01218 on 2008-7-7 09:55.]

It is mainly to prevent equipment corrosion, with the value generally kept between 9 and 11; values that are too low or too high are not favorable. This is achieved primarily by adding sodium phosphate and liquid ammonia

In alkaline water, Na3PO4 reacts with the Ca2+ ions and PO43- ions present in non-carbonate hardness as follows: 10Ca2++6PO43-+2OH-——Ca10(OH)2(PO4)6. The resulting basic phosphatite is a soft sludge. It can be removed during wastewater discharge. When the pH level is low, Mg2+ present in compounds other than carbonates easily combines with PO43- to form magnesium phosphate. This magnesium phosphate tends to cause scaling on the heating surfaces; therefore, it is necessary to control the pH level of the water. Otherwise, phosphate deposits will form and adhere to the heating surfaces, resulting in scale formation.

The pH level in the boiler water should be maintained at least at 9, and this is because: 1. When the pH level is low, the corrosive effect of water on the boiler’s steel components increases； 2. The reaction between phosphates and calcium ions in the boiler water can produce slag that is easy to remove only when the pH level is high enough ； 3. To suppress the hydrolysis of silicates in the furnace water and reduce the amount of silicic acid carried away in the steam, the pH value should be kept at a higher level. However, the pH value of the boiler water should not be too high either; otherwise, there will be an excess of free NaOH, which can easily lead to alkaline embrittlement.

Adjusting the pH value with ammonia can effectively remove CO2 and reduce its corrosion on pipelines. Keep the PH range at 8. 5–9. 2 An excessively high pH can cause ammonia to corrode the pipes itself. By keeping the pH of the boiler water at or above 9, the boiler steel remains in a passivated state, which prevents corrosion. 1) At low pH levels, the corrosivity of the boiler water on the boiler steel increases. 2) The reaction between phosphate ions and calcium ions in the furnace water allows for the formation of slag that can be easily removed, only when the pH value reaches a certain level. 3) To suppress the hydrolysis of silicate in the boiler water and reduce the amount of silica carried in the steam. However, the pH value of the boiler water should not be too high either. If the pH value of the boiler water is very high, it can easily lead to alkaline corrosion. This post was last edited by dea586 on 2008-7-6 11:24]

I would like to ask what purpose the adjusting blowdown angle valve on the boiler blowdown pipeline serves? Why add a corner valve? Thank you!

Ugh, I kept looking everywhere for reasons why PH needs to be kept at an alkaline level; turns out there’s an explanation right here. :Victory: But there’s still one thing I don’t understand: 1, why at the pH value

It seems you need to learn some skills related to boiler water treatment. The control of the pH level of boiler water is related to the pressure rating of the boiler: 1. For low-pressure boilers, the feed water is usually softened water, with a hardness level kept below 0.03. Phosphate-based chemicals are used for treatment inside the boiler, and the pH of the boiler water is maintained between 10 and 12. This helps to remove hardness by forming sludge that can be disposed of, while also neutralizing acidic substances and preventing corrosion of the boiler. 2. Medium-pressure boilers generally use deionized water, with a hardness level kept below 0.003. Treatment is carried out using phosphates and sodium hydroxide inside the boiler; the oxygen content in the feedwater is kept below 15 ug/l, while the pH of the boiler water is maintained between 9 and 11. 3. High-pressure boilers typically use two-stage deionized water, with a conductivity level below 0.2, silicon content below 20 ug/l, and a pH between 8.5 and 9.3. There are various methods for chemical treatment in such boilers, with phosphates and sodium hydroxide being the most common ones. The oxygen content in the feedwater is kept below 7 ug/l, and the pH of the boiler water is maintained between 9 and 10.5. 4. In subcritical and supercritical boilers, the feedwater is basically pure water, as higher pressures result in greater solubility of salts in the steam, leading to an increase in the amount of salts carried by the steam. This has a significant impact on the superheaters and turbines

Thank you. However, for boilers of the same pressure rating but in different installations, the operating methods vary. One is 3.2 MPa and the other is 3.8 MPa; they should be of the same pressure grade. One uses only trisodium phosphate, while the other does not use trisodium phosphate but instead uses hydrazine and ammonia water. The other boiler at 1.6 MPa does not have anything added. At the same time, the latter two boilers basically do not discharge waste water, and their test results are all within acceptable limits?