The respective meanings of changing boiler water quality
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The quality of steam generated by the waste boiler in the conversion system is subject to certain requirements, but it is difficult to analyze the quality of this steam; generally, the boiler water in the waste boiler is analyzed instead. What should be included in a comprehensive analysis of boiler water, what do these elements mean, what are the typical values for each parameter, and are there any national standards such as GB?
General analysis of boiler feed water: 1 Dissolved oxygen ≤7 μg/L 2 P3O4 15～20 mg/L 3 pH 9.0～10.0 4 SiO2≤ 0.5 5 Conductivity 10～100, etc
Boiler feedwater alkalinity Boiler feedwater hardness Boiler feedwater Cl- Boiler feedwater oxygen content Water pH Boiler water Cl- Boiler water PO43- Boiler feedwater pH
The phosphate level and conductivity are too high.
The pH of low-pressure waste boiler water is 9–12, with a Cl concentration of less than 500; the pH of medium-pressure waste boiler water is 9–11, with a sulfate concentration of 5–15
9.8.1.1 Requirements for boiler water quality: A. Phosphates: A certain level of phosphates should be maintained in boiler water, primarily to prevent scaling; the amount of phosphates in the boiler water should not be too low nor too high. B. pH value: It must not be lower than 9; if the pH value is too low, corrosion of the boiler by water increases. Phosphate and Ca2+ can produce water slag that is easy to discharge only under high pH conditions. However, the pH cannot be too high, otherwise it will cause alkaline corrosion. The pH value is generally between 9 and 11. 9.8.1.2 Na3PO4 is added to the boiler water, causing PO43- to react with Ca2+ in the highly alkaline boiling boiler water to form basic phosphate sludge that can be easily removed. The reaction is as follows: 10 Ca2++6 PO43+2OH- == Ca10(OH)2(PO4)6 ↓ A small amount of Mg2+ that enters the boiler along with the feedwater reacts with SiO32- in the high-temperature alkaline boiler water to form serpentine sludge; the reaction is as follows: 3 Mg2++2 SiO32-+2 OH-+H2O == 3Mg2•SiO2•2H2O. This type of sludge can be easily removed through the boiler’s waste water discharge. 9.8.1.3 Hazards of excessive addition of Na3PO4: A. It increases the salt content and alkalinity in boiler water. B. The formation of adherent sludge Mg3(PO4)2 may lead to the formation of soft scale with very poor thermal conductivity. C. Excessive iron content may lead to the formation of iron phosphate scale. 9.8.1.4 Hazards of insufficient addition of Na3PO4: A. It cannot prevent the formation of calcium and magnesium scale. B. A low pH value of water can easily increase the silicon content in steam. 9.8.1.5 Control parameters for BW during Na3PO4 dosing. Phosphate: 5–15 mg/L; Silica: ≤200 mg/L; Salt content: ≤100 mg/L. 9.8.2 Importance of regular drainage from the boiler: As the water in the boiler evaporates, various ions such as Cl-, Mg2+, and Ca2+ remain in the liquid phase of the boiler. If no drainage occurs, their concentrations will continue to increase, and such elevated ion concentrations can cause varying degrees of damage to the boiler. A high Cl– content can cause intergranular corrosion in stainless steel tubes, and its presence in steam also affects the quality of the steam. High levels of Mg2+, Ca2+, etc. can cause scaling in the tubes of waste heat exchangers, affecting heat transfer. If the waste boiler water is acidic, it will also cause equipment corrosion. Water quality analysis parameters: Cl - ≤300 mg/L, Alkalinity 3~10 mg/L, pH 10~12
Adjust the water quality of the waste heat boiler: Clˉ ≤ 300 mg/l, hardness: 2–10 mg equivalents, pH: 10–12