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Ph relation between boiler and condensate
Monday, March 21, 2011 By: Arne Vestad [860]  Can anybody on this forum help me with an answer to this question when you have Condensate return at pH 8 to 8.5, is it possible to have lower pH in the boiler? We are here talking about a turbine plant with 900 psi in the boiler. The boiler water tested with pH 7, Conductivity 24uS/cm, Iron 0, Copper 0, Sulfate 0, Chloride 1.5 mg/l, Hardness 0 and O2 0.
It is very difficult to test for pH in very low conductivity water and in this particular boiler, the water is just clean and pure. Any help is greatly appreciated. Post a Reply... Viewed 5687 times
Monday, March 21, 2011 By: Ross [390]  The condensate return at pH 8 to 8.5 is good!
Boiler water at pH 7 is very bad! But I think you already know that... You need to get your alkalinity higher to prevent corrosion! Corrosion prevention is the primary reason for boiler water treatment regardless of the pressure rating or usage. My guess is the thinking at your plant is super clean water is the ultimate achievement, but it should not be. Post a Reply... Viewed 5673 times
Monday, March 21, 2011 By: Jim Watts [764] It is certainly possible for the PH to be lower in the Boiler than in return condensate.
This can occur when the substance dissolved in the condensate causing the high PH is volatile in the Boiler and the ammount that remains in equalibrium in the water results in a lower PH. This is the whole basis of treating condensate systems by dosing the boiler with amines. The results you are getting in the boiler indicate that there is something in the water not being analysed or the PH measurement is wrong. a conductivity of 24mS could indicate about 12 ppm of dissolved solids at PH 7 or about 2.5 ppm of TDS at higher or lower PH My inclination is that the boiler is normal but the PH is wrong, and it should be higher. Try adding a drop of Phenolphthalein to the water sample. If the water turns pink the PH is above PH 8.2 and everthing is ok except your measuring procedure. If the sample doesnt turn pink you have something in the water that probably shouldnt be there and I would be wondering if the chloride is right and not 15.0 instead of 1.5 Post a Reply... Viewed 5667 times
Sunday, April 3, 2011 By: Glencannon [28]  This is kinda why I wish we still titrated for pH. Most commercial pH probes only have a resolution of approx 0.2 pH. You can titrate with sulphhuric acid to a phonolpthalene end point more accurately, or you can use methyl orange, I think its methyl orange, and an optical spectometer for a slightly less accurate reading. Both would be better than a probe.
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