Oil Dehydrator

Over time oils in lubrication systems can become contaminated with water. Most lubrication systems are vented to the atmosphere and readily allow the exchange of ambient air into and out of the oil reservoir. Ambient air contains varying amounts of water vapor. Once inside the reservoir, the water vapor dissolves into the oil. Water vapor or even liquid water may also enter lubrication systems through leakage at seals. Depending on the operating conditions, water in lubricating oil may be present as dissolved, emulsified or free water. The presence of dissolved water significantly modifies the lubricity, film thickness, load carrying ability and viscosity of the oil. In addition, water can react with oil additives and oxidize or hydrolyze the lubricating oil itself, generating sludge or acids. The contamination level of lubrication oil affects the service life of the associated components.

Surface corrosion is directly linked to the presence of water. Accelerated metal surface fatigue in bearings can be promoted even if only dissolved water is present. The effect of dissolved water in lubricating oil on the fatigue life of roller bearings has been investigated. The results of bearing life tests from one study are plotted in Figure 1. It may be observed from the data that reducing the lubricant water content to 25 ppm from 400 ppm, close to the saturation level at the test temperature of 150° F, improves bearing life by 500%. It may also be observed that most of the improvement is obtained by reducing the water content from 100 ppm to 25 ppm. This illustrates that even small amounts of water can significantly reduce bearing life.

Figure 1. Roller Bearing Life vs. Dissolved Water

(Source: R.E. Cantley. "The Effect of Water in Lubricating Oil on Bearing Fatigue Life." ASLE Transactions, American Society of Lubrication Engineers, Volume 20, No. 3, p. 244-248, 1977; from a presentation at the 31st Annual ASLE Meeting, Philadelphia, Penn.)

The Oil Dehydrator is a simple and effective means of reducing and controlling water in lubricating oils. Photographs of the protoype are shown in Figure 2. The system is designed for easy installation into an existing lubrication circuit using a kidney loop configuration. It has been tested in controlled laboratory as well as in industrial environments and has been shown to remove 100% of free and emulsified water, and reduce dissolved water to below 100 ppm and eliminate up to 70% of dissolved air. The test results presented in Figure 3 demonstrate that the water concentration can be reduced to below 100 ppm with less than 7 turnovers of the total oil reservoir volume even for very high initial water loadings. At the typical operating fluid flow rate of the system, water concentrations can be reduced to less than 100 ppm in a 50 gallon lubrication system in about 24 hours.

Figure 2. Oil Dehydrator Prototype

Figure 3. Water Concentration Reduction

The progressive visible changes in the appearance of Mobilgear SHC 320 before, during and after dehydration with the Oil Dehydrator are shown in Figure 4. The initial water concentration in the lubricant before dehydration was 1160 ppm. The final water concentration when the dehydration process was stopped was 25 ppm.

Figure 4. Typical Water Removal Performance (8 liter, Mobilgear SHC 320 Lubricating Fluid)

The heart of the Oil Dehydrator is CMS’s chemically inert membrane with very high water vapor transport. The membrane works by a molecular sieving mechanism. Small molecules such as water and oxygen easily permeate through the membrane. The larger hydrocarbons or esters and additives that are present will not pass through the membrane. The Dehydrator can remove free, dispersed and dissolved water. The driving force for water permeation is provided by the integral vacuum pump. The permeated water vapor is discharged to the atmosphere. The chemical inertness of the membrane means that it is able to withstand the relatively harsh thermal and chemical environment associated with lubricating fluids.

The system can be used to remove water from gearboxes for a wide range of equipment using low to high viscosity grades of lubricating oils. A few examples of applications are: wind turbines, coal crushers, cooling towers, and paper mills. The Oil Dehydrator is used during normal operation of the lubrication system to continuously maintain low water concentrations in the oil, improving the reliability and life of gearboxes, reducing maintenance costs, and increasing uptime.

The target for commercial introduction of the Oil Dehydrator is the fourth quarter of 2011. Check our website over the coming months for updates.

To read the article about the oil dehydrator in Tribology & Lubrication Technology magazine click here.

Click here for more general information on membrane gas/liquid contactors.

Click here to learn more about CMS gas/liquid contactors.