How To Know When To Change The BCA Collection Filter?
How Do I Monitor the Effectiveness of the BCA technology?
How Does Varnish Testing Correlate with Air Release Testing?
Varnish is a sub-micron polar gel, that is high in molecular weight. These gels differ from lubricating oil molecules, which are low in molecular weight, and are non-polar compounds.
We use polar attractive forces to join together, or agglomerate, the sub-micron gels into a larger gel that is sufficiently big enough to be captured by conventional filtration methods. We generally use Beta 200 3-micron filters for collection of the agglomerated gels. However, in the cases of trying to clean-up a heavily contaminated oil, we may recommend the use of a higher effeciency filter, like a Beta 200 1-micron filter for collection.
By using conventional filtration to remove the agglomeration, the operating costs of the BCA system are low, since the filters themselves are not electrical devices, like other Electrostatic Filtration systems (Electrostatic Precipitation devices, etc.)
To illustrate what the gels actually look like, both Before and After the BCA process, please see the below photos of Membrane Patch Colorimetry (MPC) patches, from a GE Frame 6 Gas Turbine, using a Group III basestock oil:
MPC Full View 100X magnification 400X magnification
MPC Full View 100X magnification 400X magnification
The photos in the After MPC patch clearly show how the BCA has attracted the many smaller gels into a much larger gel that is easy to remove by conventional filtration.
This is perhaps one of the most common questions about BCA Technology and the answer is also one of the most misunderstood concepts of BCA operation. The Best Practices for determining the proper time to change the BCA filter are, in order of the most preferred given first:
Most Industrial Engineers will try and quantify the proper BCA Collection filter life and performance by the Delta P across the filter. The problem with this approach is that the main physical property of the Varnish contaminant; the fact that it is a soft gel, makes Varnish a tricky substance to catch with pore-type filtration. The Varnish will block a pore space and remain there under a given micro-pressure, but as this pressure is increased, the Varnish gel shape will distort and push through the filter pore. The sensitivity of the Delta P measuring system required for this type of measurement is not suitable nor economically practical for heavy industrial use.
Using Oil Analysis Samples, if your MPC Patch examination shows large agglomerations coming into the BCA Charging and Mixing Unit, or if your MPC values into the CMU are roughly the same or greater than the MPC values coming out of the CMU, you are not changing the Collection filter frequently enough.
A General Guideline for Collection Filter changes, if you are not near a laboratory that can provide you with MPC testing, is 3,400 hours per filter change. The ISOPur purification units that are PLC equipped, come with a NAG-screen to remind you of this general interval.
There are occasions when extreme Varnish contamination will cause the ISOPur built-in Delta P sensing devices to shut the filter down. This is usually found in the first few hours of clean-up a highly contaminated oil reservoir. Another case would be high water contamination and the use of pleated paper finlters instead of the recommended glass fiber type.
The driving force behind using an electrostatic filter system is to reduce varnish related turbine-trips, to stop filter plugging and to increase the effectiveness of heat exchangers. These events should be recorded and monitored for the frequency of occurance to see how well your purification system is working.
As a secondary measure, you should make physical inspections of the primary hiding places of varnish, whenever a scheduled outage is available.
But lastly, most people aren't patient enough to wait to see these results, and they want to see some real proof of performance quickly. The way they usually try to accomplish this "quick-check" is through oil analysis. In recent years, ASTM has come up with a Varnish Potential test that is called MPC, in its' current draft form, which stands for Membrane Patch Colorimetry. Several labs around the world offer this test under their own trademarked names, like VsPI and QSA, to name a few of the leaders in the field. However, in addition to being able to monitor the Varnish Potential of the oil, it is also recommended to test for some of the more popular lubricant performance tests, to see how the varnish purification is affecting the lubricant performance. Some of these performance tests include ASTM D 3427 for Air Release Properties, ASTM D 1401 for Water Separation Characteristics and ASTM D 892 for Foaming Stability, to name a few of them.
The below graph shows typical results of what will happen to an R&O type oil as the Varnish is Agglomerated, and then removed. You can see the initial increase in the Air Release Time, and the subsequent decrease in Air Release Time, as a result of the oil being purified.
