we are operating 4 nos 500MW steam turbine in INDIA. Presently in our lubricating system moisture level is maintaining as high as 180-200ppm continuously. We are running the centrifuge(MAB205 ALFA LAVAL make)continuously. But could not be able to reduce the moisture level below 100ppm as recommended.
Please suggest what can be done.

D Mandal,
Your centrifuge does quite well as what is supposed to do – physically separate phases (water from oil). However, it addresses only free and emulsified water, but does nothing to dissolved water in oil. From the recommended concentration of water (100ppm), it seems that you are using ISO 46 (most likely) or maybe ISO 32 oil, as this range of dissolved water is commonly present in this oil. Keep in mind that this recommendation is based on the best case scenario when oil was new. However, if you added some different oil as a make up oil, or if this oil has been in service for a while, the water solubility characteristic (oil’s natural affinity for water) may change (usually goes up). To make the story short, if I was on your shoes, I wouldn’t worry about it too much, as this is the best any centrifuge can do. And the difference from the ideal (100ppm) to the level you achieved is consistently up to 100ppm, which is only one-hundred of one percent (not much at all), and such amount is not detrimental to your equipment. If you really want to lower dissolved water in your oil, then you should use equipment that separates water from oil on the chemical basis instead, such as vacuum dehydrator or air stripping dehydrator. Good luck to you.

D. Mandal

I agree with John. The normatives ASTM D-4378 and 6439-05 comment that the water values must be manteined lower than 100 ppm (only dissolved water; no free or emulsified water). The 6439-05, even, comment that, "dissolver water has, however, been reported to cause bearing damage". In the same point of the normative (X.1.1.2), you can find "oil may hold 50 ppm of water at 21 °C (70°F) and 250 ppm at 71 °C (160°F)".

If you have 180-200 ppm is not bad. Anyway, if you want to have lower than 100 ppm (you should it), you have to use vaccum dehydrator or air stripping dehydraton, as mentioned by John. Centrifuge is very good for removing quickly free water.

Try the Allen Filters, Inc. Hydroscav.
It removes 100% of free and emulsified water and dissolved water down to 50 ppm or less.
www.allenfiltersinc.com