Centrifuge Replacement at Hydro Plant

Vacuum dehydration and air stripping are the only technologies that can effectively remove free, emulsified and dissolved water. I would suggest these technologies for your application.

If you regularly had large amounts of water contamination, I would suggest coalescing since it has the ability to remove very high levels of free water contamination, quickly and inexpensively. Coalescing only works on fluids with good demulsibility characteristics, which your turbine oil should have. Filters are the most inefficient and expensive options.

There are new studies indicating that even small amounts of dissolved water can impact bearing life. Whatever option you choose, the lower you can keep the water level the better.

Hydropower,

It look like you need not only a vacuum dehidrator. You also need a humidity sensor to prevent future accidents like the one you mention.
You need to work in both sides of the problem: prevention and correction. If one part is missing your program, sooner or later, will fail.
Feel free to contact me directly to my email lvelasco@vsconsultores.com.ve to talk more about your situation.

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Originally posted by hydropower:
I am trying the decide between vacuum dehydration and adsorbing or coalescing filter system to replace our old centrifuge system.

This will be used primarily to filter new oil and dirty oil for the governor oil system. Are requirement for dryness is less than 150 ppm.

We don't have a high water ingression rate, but about every 5 to 10 years we have a cooling failure that causes gallons of water to enter the oil system.

Any suggestions?

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Using a properly sized and dedicated off-line low-flow 3-micron cellulose fiber filters on your governor sumps will be sufficient to take good care of your governor oil. It will clean up your oil (and keep it clean), and it will keep your oil dry by removing any water that is there due to condensation. I assume that you may have cooling water leaks in guide and thrust bearings sumps (but not in governor sumps), and periodic run of bulk oil through purifier is a good practice to keep your oil dry. The most efficient method of removing water in hydropower equipment (with low water ingression rate as you mentioned) is vacuum dehydration (chemical separation). Coalescers (based on physical separation) can remove large quantities of free and emulsified water from oil in a shorter period of time than vacuum dehydrators, but are not effective in removing dissolved water.

I would like to learn something about centrifuges so I have 3 questions about all this.
Can a centrifuge remove from oil :-
1 free water
2 emulsified water
3 disolved water

I look forward to any answers.

Cheers

John

Centrifuges can easily and quickly remove free water. In most cases and under the right conditions they can also remove a good quantity of emulsified water. They are generally speaking, useless at removing disolved water. This really becomes a problem on oils that can have a saturation point of 0.1% or higher. In choosing a method of moisture removal it pays to do your research. Centrifuges, vacuum dehydrators, air strippers and cellulose filters can all be used effectively in moisture control if they are correctly used. A lot of people don't get the full benefits due to incorrect usage but under the right conditions they all have their place and can be extremely effective. Hydropower, have you done a failure analysis on your cooling system? If you are effectively controlling moisture levels than it may be difficult to predict a problem in the future until it is too late.

Dear John

As MC says, centrifuges are very good equipment for using when you have a lot of free water. However they don't remove water from the oil at 500 ppm (0.05%) or lower.

The most important point is your desired water level in your machine. For example, if you have Steam Turbines, according to ASTM D-4378-03, the highest water content you should find is 100 ppm (0.01%). In this case, centrifuges couldn't help you to have the oil free of water.

Most Turbine Oils have their saturation point at 50 ppm (70 C), and 250 ppm (160 F). Under Normal Operation conditions, dissolved water has no significant adverse effect on lubricant properties.

Regards

Dear John,

In our experience, we have found centrifuges to be the culprit of water being dissolved or emulsified into oil. If the off-take to the centrifuge is located near the bottom of the reservoir then it is possible that free water is drawn into the centrifuge with the oil and then emulsified during the aggressive centrifuging process.

Cetrifuges will be able to reduce the larger particulates but are not effective at taking out the fines.

Medium cellulose fiber filtration is only effective at eliminating very small quantities of water, free, dissolved or emulsified. The cellulose media is paper which absorbs the water and separates it from the oil. When this happens, the filter element weakens and breaks down. Oil will always take the path of least resistance during filtration, if there is a weak area, then the contamination will channel through the element and create a path of limited filtration capability. This method can be costly, time consuming and limited results can be expected.

To solve both contamination AND water in oil problems, we have employed a method whereby filtration is stepped down through a bypass system. The first stage is to run the oil through 0.2 micron synthetic filter elements, with the second and final stage using simple cotton wound elements to polish and absorb free, absorbed and emulsified water out of the oil. The bypass system filters at a rate of about 18 litres per minute continuously. The results on a 100cst calcium based hydraulic oil is 100% removal of water with a final ISO code reading of 11/9

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Originally posted by hydropower:
I am trying the decide between vacuum dehydration and adsorbing or coalescing filter system to replace our old centrifuge system.

Between the two technologies mentioned I wouldn't waste much time looking into coalescing the water out of your oil. Reason: the water contamination that you will likely be confronted with will be rich in organics which will allow bacteria to grow and will disarm anybody's coalescer. Vacuum Distillation has come a long ways in the past 10 years and you may find it more affordable than years past. There are also more companies getting into the market place which will help keep prices down.

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This will be used primarily to filter new oil and dirty oil for the governor oil system. Are requirement for dryness is less than 150 ppm.

I assume your governor oil is ISO 32 oil???? Depending on your location geographically 150ppm could be the oil's ambient water saturation point. Compounded with the fact that your plant location is a HYDRO-Electric the presence of moisture in the atmosphere is a sure thing. The use of a properly sized Vacuum Distillation system will dry the oil well below its saturation point but unless the system reservoir has its own dedicated dryer system (desiccant etc.) the oil will quickly soak-up moisture until it reaches its saturation point.

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We don't have a high water ingression rate, but about every 5 to 10 years we have a cooling failure that causes gallons of water to enter the oil system.

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Any suggestions?

Adopt a PM Schedule for your coolers. Improve the hygiene of the turbine oil reservoir with kidney-loop style filtration where water adsorption technologies can be applied, (read: low water ingression rate) and a dryer type tank breather for the reservoir. Locate a vendor who can rent you a Vacuum Distillation system for when you need it, (read: 5 to ten years).