Electrostatic vs. Absorption

Roger,

Is this the first time that you have varnish problems in your turbines?
Did you already perform an oil analysis? what are the results?
From my previus experiences absorption medias can not deal with varnish, electrostatic filtration can.
However my recomendation is play a proactive rol. Prevention is 10 times cheaper than correction. Identify the causes for this abnormal varnish formation will drive you to really solve the problem. Filtering the fluid whith out found the real cause of the problem only guarantees you that you will be in the same situation shortly.
If you give me your email I can contact you directly.

Roger.

Some comments.

1.
Electrostatic filtration can only be used when water content is relatively low. (I think <2000ppm -not sure). By choosing absorbtion (ie. 1 micron depth type cellulose media) you will remove both moisture and varnish/particles.
(Electrostatic will not remove moisture)

2.
Electrostatic filtration tends to be messy when removing varnish from the unit. Vs. absorbtion elements only needs replacement.

3.
Cost of electrostatic filtration is allways higher priced than by-pass absorption equipment. But then again you will have a running cost for absorption elements.

I have to agree with Luis. Cellulose filters have limited capacity for removal of oxidized by products. If it is a serious problem then the ongoing cost of element replacement would be prohibitive. Electrostatic filtration is a very good method but it has a high capitol investment and it works very slowly. As Luis said, find the cause and save a lot more then you can see from the face of it.

Varnish formation is due to thermal and oxidative degradation of lubricant.Varnish
acts as insulator,increases thermal gradients,
If left unattended it can result in reliability and performance problems.The bottom line is increased maintenance costs.

High density sieve absorption filters along
with eltrostatic oil cleaners is the solution.
Electrostatic oil cleaners removes varnish
precursors and eliminates oxidation by-products
from internal surfaces.Main lube reservoir can
be cleaned by confined space tank cleaning.

RPVOT,FTIR analysis can be used to verify the
analytical results.

Bala.

Varnish problems in turbines are very common. Although root cause analysis will sometimes point to a specific cause, in most cases, it is an inherent problem in gas/steam turbine environments and cannot be fixed.

Both cellulose adsorption filters and electrostatic oil cleaners have been successful in these applications as permanent band-aids however. I have had more experience with electrostatic oil cleaners and have seen them solve varnish problems in steam turbine applications.

Regardless of the technology that you choose, I have two suggestions for you:

1. Determine a methodology to test the performance of the technologies. ISO Particle Count, AN, RPVOT, FTIR and other routine tests will not detect the removal of oxidation by-products which are almost always under 1-micron in size. The ultra-centrifuge test can sometimes be helpful, although I have not found it to be very sensitive and slight elevations in particle count can interfere with the results. I have some information on a test that you can use if you'd like to e-mail me.

2. Test and compare the technologies in your specific application prior to purchase. You should be able to use a small test-rig to compare the technologies.

As other posts have pointed out, these investments can be sizeable. But, the initial investment is much, much less than an unplanned outage - which varnish is capable of causing. If you already have varnish, you should not have a problem justifying the expense.

Best of luck!

Varnish is not a problem caused by oxidation products only.It will be produced if there is moisture too in the oil.So any filtration system which removes solid contaminants like oxidation products and wear particles and at the same time removes even dissolved moisture from the oil will be a Long term permanent solution for this problem. I know one Electric Refiner 'Klarol'which removes solid particles by absorption in cellulose filters upto 1 micron and eliminates moisture by Thin Film Evaporation Theory.If both the root causes of varnish-production are removed, the oil life may be extended tremendously.This cleaner can restore back even the emulsified oil without heating it beyond 60 degree centigrade.For more details I may be contacted by email myminimac@yahoo.com

Some comment on the root cause analysis of this case:
Generally, the initiation of a performance problem can occur long before analytical results from routine oil analysis indicate a problem. Therefore, supplemental tests are required to identify the presence of insoluble oxidation by-products, the root-cause of varnish.
The following series of tests, called the Varnish Marker Series can be of help:
· colorimetric analysis
· gravimetric patch test
· Fourier transform infrared (FTIR)

We have successfully enabled existing filters to remove submicron material and precursors of varnish by applying balanced charge agglomeration to the oil. Since water can be an issue in steam turbines, a system that does not use a grid to attract particles is more reliable than one that does. Bypass filters which use small pore-one micron pore size-may miss a significant amount of meterial since varnish precursors and soot particles are often 0.1 to 0.3 microns.In addition, in the fyrequel applications on some steam turbine EHC systems, the ability to maintain and enhance the resistivity of the fluid while removing the submicron material is a significant advantage.
Chuck Mitchell Isopur

Dear All

We here in México have been trying with the varnish problem since two years ago. First we tried with Electrostatic Filters but we did't reach good results.

Since one year ago we are using the Balance Carge Aglomeration Equipments, and we are having more good results, even in improvind ISO Code (until ISO 14/12/9).

Regards.

Hydropower facility in US has seen benefits in controlling varnish particles in lube oil with a dedicated off-line 3-micron absolute cellulose fiber filters. The removal was effective at low-flow operation (6-10 gpm). Low flow seems to be the key, as electrostatic filters could rarely be found with flows above 1 gpm (which I read as being ineffective at higher flows). It make sense that with low flows even particles <3 microns can be captured at 3-micron filter. Also, the efficiency seems to be greater if filter surface area is bigger (at given low flow). One cannot prevent varnish from forming (inherent to the operation process as Greg said before), but one can control it at levels, which do not cause significant problems. Absorbent cellulose fiber filters also continually take out any moisture out from lube oil (present there as the result of condensation). Any amount of moisture/water in oil decreases efficiency of electrostatic filters. For this reason, some manufacturers of electrostatic filters incorporated a separate absorbent filter (cellulose fiber) to take care of possible moisture present in oil.

Electrostatic oil cleaners are slow, cannot remove moisture, in fact they trip if the moisture content in the oil is more than 0.5%, malfunction if the metal content of the oil is on the higher side, have filters which are expensive and remove very little contamination. When we talk about Turbine oils, we are talking about large quantities of oil. There is no way an electrostatic system can clean large quantities of oil unless you are planning to instal 5 such machines. There are two possibilities here. One, take out the oil, re-refine it and put it back in the system. Second, go in for the Klarol oil cleaning system. This system will remove solid contamination down to 0.25 microns, moisture, dissolved gases and air. Also,Klarol replaceable filters have a very high contamination removing capacity, thereby making it very economical to operate. In certain cases, where the molecular bonding in the oil is weak, the Klarol system can also help to reduce the total acid number of the oil.

I believe that you are referring to the difference between electrostatic and AD-sorption. There is a difference between ab-sorption and ad-sorption, and it can mean a lot.

I sell an industrial hydraulic and lubrication oil filtration device that filters down to 0.1 micron, minimizes moisture to the PPM level, removes oxides, and acids, and prevents the formation of varnish. This is what we call Deep Ad-sorption technology.

It can prevent the varnish from forming by preventing the components that cause varnish to affect the oil.

For more information, please email me @ jprzybylski@meijicorp.com

The adsorption process using cellulose to remove varnish is very effective but depends a lot on the amount of cellulose and composition of the element. CC Jensen filter 3 micron elements contain approximately 8 pounds of cellulose. Using extraction methods devised by Noria (Jim Fitch)and conducted by South West Research it was determined that each CJC "B" element held in excess of 12 pounds of varnish and the "BLA" was over 15 pounds. Even with this amount of varnish in the element the differential pressure did not increase significantly so we recommend that the elements be changed initially at 4 to 6 months and then yearly after that. CC Jensen filter systems are used extensively for Turbine applications for fine particulate removal, varnish removal, and water removal. Our website contains many additional applications.

I have not seen testing on any electrostatic methods that show any actual amounts of varnish removed. Does such data exist? To see the data on the CC Jensen elements please visit our website [URL=klassenhydraulics.com ]klassenhydraulics.com[/URL]or email me at
cjccanada@telus.net

Thanks, Harv

working in a refining industry, i have concerns about the electrostatic technique as they work on high voltages.since i am reviewing this method for use, are they available with 'intrinsically safe -Ex' tag? do they comply to strict safety norms in flammable gas environments, in other words?

The Isopur Balanced Charge Agglomeration system, BCA, has been tested for compliance with Explosion proof NFPS Class 1 Div 2 Group C and D in both Purge and NEMA 7 versions. It also has been tested for the European ATEX equivalent.

As far as how much varnish our system can hold, It is limited by the filters. BCA causes particles to stick together to form larger particles. These particles are removed in the filter system that is part of the unit. The filters used are high efficiency filters that are similar to those available from many manufacturers. The amount of material they hold is the same as most filters. They would hold about the same amount of material with or without BCA. The technology makes the filters more efficient, in that they remove smaller size particles without resorting to small pore size filters. Many companies are finding that very small filter pore size contributes to static discharge and oil degradation.