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Causes of Low pH Corrosion
Acid leak from demin water plant
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Acid contamination in boiler make-up water or condensate return
BFW and condensate pH = 9.2 – 9.6 for all ferrous metallurgy and for Ferrous/Cu mixed metallurgy system pH = 8.8 – 9.2 Boiler water pH typically 9.3 – 10.3 at 5 15 ppm PO4
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贵厂锅炉现状
5、锅炉凝结水Fe含量0.69ppm，严重超 标（国标≤0.1ppm）； 危害：蒸汽未处理，造成凝结水PH偏低， 腐蚀设备管道，而且过高的凝结水Fe含量 会带入锅炉，会进一步对锅炉产生腐蚀， 影响锅炉的稳定运行。 解决方案：1、投加中和胺，调整蒸汽PH； 2、如果条件允许，增加凝 结水 精处理装置；
贵厂锅炉现状
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3、过热蒸汽SiO2含量高达296ppb，饱和 蒸汽SiO2含量高达140ppb，国标控制要 求为20ppb，严重超标 ； 危害：蒸汽中SiO2含量超标，会在汽轮机 等表面形成硅酸盐垢，难以清洗，会严重 影响设备的稳定运行，增加运行能耗 解决方案：1、加大排污； 2、检查混床；
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Boiler Water Treatment
Objectives
Prevent Corrosion cause by
Acidic pH (< 7.0) Too high pH (>12.5) Dissolved Oxygen in BFW
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Corrosive
Corrosive
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HIGH OR LOW BOILER WATER pH CORRODES BOILER STEEL
Boiler Corrosion
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Low pH Corrosion
Boiler metallurgy typically is made of carbon steel At water pH < 7.0 (acidic), it is corrosive to carbon steel Optimum pH control range
O2 Scavenger
Residual dissolved O2 to be removed by organic O2 scavenger, CorTrol OS7785 CorTrol OS7785 is hydroquinone
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Deaerator – Spray & Tray
At temp > 100 C, dissolved O2 in water can cause O2 pitting corrosion O2 pitting corrosion is very rapid and as such, it can cause tube leak in relatively short time To eliminate dissolved O2 corrosion in a boiler system (feed water/boiler water/condensate) dissolved O2 must be removed and maintained at less than 10 ppb
Relative Corrosive Attack
8.5 pH
12.7 pH
Safe Range
1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH
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Dissolved O2 Corrosion
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High pH Corrosion
In boiler operating temperature, pH > 12.5 is corrosive to carbon steel
NaOH leak from demin water plant NaOH or KOH contamination in condensate from process leak
Localized concentration of free NaOH due to high heat flux or steam blanketing
Process 8.6 MT/Hr
Demin H2O pH/Cond/SiO2
E-8129
2.4 MT/Hr
Steam Drum C-6130
LP Steam Condensate pH/Cond/F e Deaerator C-8108 EO Reactor E-6101
Blowdown
OS7785 O2 Scav
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EO Waste Heat Boiler Schematic
75.4 MT/Hr
MP Steam 16 MPa
pH/Cond/SiO2
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贵厂锅炉现状
今天现场分析，发现如下问题： 1、炉水PH 8.98，偏低，国标为9.0~11.0， 正常控制一般在9.5~10.5； 2、炉水Fe含量超标（0.69ppm）； 危害：过低的PH会造成锅炉腐蚀，产生爆 管现象； 解决方案：采用协调磷酸盐控制炉水PH， 防止腐蚀
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Dissolved O2 Removal
Mechanical deaeration in deaerator
Raise boiler feed water temp to 1-2 C of saturation temperature by steam stripping Remove dissolved O2 to < 10 ppb
Boiler Water
Alkaline PO4, OptiSperse HP2650
Stainless steel metallurgy is resistance low/high pH and dissolved O2 corrosion
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Causes of High pH
NaOH contamination in boiler make up water or condensate return
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pH Control to Minimize Corrosion
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Boiler feed waLeabharlann er and condensate
Use of volatile neutralizing amines, Steamate NA0880
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Boiler Water Treatment
Technical Training
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STEAM EQUALIZERS
DOWNCOMER
STORAGE TANK
TO FEEDWATER PUMP
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