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Oil Filtration
Oil Filtration
The vacuum dehydration process lowers the partial pressure, which assists in removing the water from the oil. Just like boiling water on top of Mount Everest, lowering the pressure allows water (and other volatile materials) to boil at a much lower pressure.
At the typical pressures used by most vacuum dehydrators (25" to 28" of mercury), water boils at 49°C to 55°C. By heating the oil, typically to 66°C to 71°C, water is vaporized inside the dehydrator, without causing excessive oil degradation due to thermal and oxidative stress.
In most dehydrators, the air is warmed and dried prior to being passed over the oil, encouraging the water to transfer from the oil into the air.
To maximize the process, the oil is thinned to obtain the greatest amount of surface area exposure possible. This is achieved by allowing the oil to pass over a number of surfaces internally in the vacuum chamber, or by creating an umbrella spray within the chamber through which the dry air passes.
The real benefit of this process is its ability to remove dissolved water and other low-boiling liquid impurities such as fuels and solvents. The removal of dissolved water makes it ideal for systems requiring low target levels of moisture.
It is particularly useful in environments where large volumes of oil are at risk from the process or system, such as in steam turbines or paper mills.
In fact, for lightly additized oils such as turbine oils and transformer oils, a vacuum dehydrator can remove as much as 80 percent to 90 percent of dissolved water, achieving water levels as low as a few ppm.
The main disadvantage of vacuum dehydrators is their cost and comparatively low flow rate. Because of the cost, many companies chose to rent dehydrators on an “as-needed” basis rather than purchase them.
The main advantage of vacuum dehydrators is that they offer the ability to remove moisture to very low levels. The greater the volume of oil and water, and the lower the target moisture level, the more cost-effective vacuum separation becomes.
