Filter Solutions for Turbomachinery Operators in Power Plants

Submitted by Cory Calderon
The importance of maintaining a low TAN number

For natural gas, coal and steam-powered turbomachinery operators, reducing the amount of acid in lube oil and hydraulic systems is an ongoing challenge. The systems that lubricate all of the mechanical equipment will develop acid that, if untreated, will cause a variety of problems that can ultimately lead to a complete shutdown of the system. Consequently, it is always a goal for turbomachinery operators to eliminate or neutralize as much of the acid as they possibly can in order for the system to run uninterrupted. The total acid number (TAN) is an industry standard that measures the acidity of the system and is determined by the amount of potassium hydroxide that is needed to neutralize the acids in one gram of oil. The goal is to reduce this TAN number and bring it down as close to zero as possible.  The higher a system’s TAN number, the worse the problem is.

Filter Solutions

So what solutions currently exist for turbomachinery operators to reduce their TAN number and prevent the accumulation of acid?

Standard industry practice is to use some kind of element to address this issue. Two of the more popular types of filters in the industry are based in clay and wet resin. Both of these filters are designed to reduce the amount of acid that forms in the system and both do an adequate job. The clay filters have been around for more than 30 years. It is fairly inexpensive and works very well with new electrohydraulic fluid, which has led to its popularity. Operators, however, were still looking for better ways to control their TAN numbers in their system. The clay filters did not control the acid as well as many would have liked, and although it was effective with new electrohydraulic fluid, after a few years, its effectiveness would begin to wear off.  This led operators to search for new, more effective ways to control TAN numbers in their systems.

Wet resin filters were introduced to more effectively reduce the amount of acid and maintain a very low TAN number in hydraulic and lube oil systems. When introduced, the filters boasted longer fluid life, increased equipment life and superior efficiency. Wet resin elements were a bit more expensive than the clay variety but they would need to be replaced less often and were able to drop TAN numbers down even further. One of the main drawbacks for operators, however, is that in order to replace the clay filters with wet resin elements, the system would need to be flushed. This process can cost between $15,000 and $20,000 and can additionally take a few days to complete. Regardless of this upfront expense, many operators chose to make this switch due to its long-term benefits. There are still several power plants today, however, that use clay filters in their system.

The biggest drawback with both of these industry standard cartridges is that the way they are designed to reduce acid varnishing is by producing a powder that reacts with the acid.  During this process, the acid is neutralized and thus the TAN number is reduced. However, because these filters use a chemistry to neutralize the acid, particulate is left behind as a result. Unfortunately for operators, this means that one problematic substance is being substituted with another. In order to avoid this particulate that is left behind, a new kind of cartridge was introduced, the dry ion exchange cartridge. 

Dry ion exchange cartridges

Dry Resin Ion-Exchange Cartridges
Dry ion exchange cartridges are an absorption filter medium that do not use a chemical reaction to neutralize acid. This approach allows for no problem-causing particulate to be left behind in the process. Additionally, the dry resin cartridges can handle four times more flow than the alternative options.

By using dry resin beads as opposed to wet resin beads, moisture can be more effectively captured by these cartridges. Capturing moisture is a critical part of the equation for two key reasons. First, moisture that is left uncaptured can cause varnishing issues. Secondly, and just as important if not more, moisture will contaminate the oil and as a result, the conductivity of the oil will go down. When this process occurs there will be a static discharge that can be so strong that it can actually damage mechanical parts, the filter media itself and the inner core of the system. When static discharge occurs due to low fluid conductivity of the lubricant, there are anti-static filter elements available that can improve and maintain the lubricating oil’s conductivity for extended periods of time, eliminating the static discharge problem. This means if an operator is using a wet resin filter, it is likely they will also need some kind of anti-static filter element in order to avoid unnecessary shutdowns.

As electrohydraulic fluid is fire retardant, operators are well aware that it is a fairly expensive liquid.  As stated previously, there was always a hesitancy to switch filter types because of the need to flush the system and replace the very costly fluid. However, what many operators do not know is that when switching to a dry resin ion exchange filter, the system does not need to be flushed. This is due to the fact that a dry resin ion exchange filter is an absorption filter medium as opposed to a chemical reaction filter medium like one would find in the wet resin varieties.

While wet resin filter mediums are effective, a dry resin cartridge can significantly reduce the TAN numbers as opposed to other technologies. Wet resin filter mediums need to be changed on a regular basis and eventually, they simply will no longer be effective.  Dry resin cartridges do need to be changed but not nearly as frequently as their wet resin counterparts, lessening the burden on operators.

For more information, please contact Patrick Hyland at (844) 705-0495, or email Patrick at

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