Treatment methods for lubricating oil dehydration

 Dehydration treatment methods for lubricating oil

Water in lubricating oil will accelerate oil oxidation, reduce lubrication performance, and cause equipment corrosion, wear and even failure. Common dehydration methods include physical separation, vacuum dehydration, adsorption filtration, centrifugal separation, etc. The specific selection depends on water content, oil type and equipment requirements.

 1. Sedimentation separation method (natural dehydration)

Principle: Utilize the density difference between water and oil, and let the water settle to the bottom after standing.

Applicable situations:

- Free water (large amount of visible water)

- Simple treatment, low cost, but low efficiency

Operation steps:

1. Let the lubricating oil stand 24~48 hours (better effect at higher temperature).

2. Release water from the bottom drain valve.

3. The upper oil can continue to be used, but the water content needs to be tested.

Disadvantages:

- Unable to remove dissolved water (<500ppm).

- It takes a long time and is only suitable for preliminary dehydration.

 2. Vacuum dehydration (high-efficiency deep dehydration)

Principle: Under vacuum + heating conditions, lower the boiling point of water to make it evaporate and separate.

Applicable situations:

- Dissolved water (trace water, such as transformer oil, turbine oil)

- Need for rapid and deep dehydration (can be reduced to below 10ppm)

Equipment: Vacuum oil filter (with heating system)

Operation process:

1. Heat the oil (60~70℃, not too high to prevent oxidation).

2. Vacuum (above -0.095 MPa, water can evaporate at 40℃).

3. Condensation drainage (evaporated water vapor is condensed and discharged).

4. Precision filtration (remove residual impurities).

Advantages:

✔ Can remove free water + dissolved water, dehydration is thorough.

✔ Suitable for high-precision oil products (such as transformer oil, turbine oil).

Disadvantages:

❌ The equipment cost is relatively high, suitable for industrial-grade processing.

 3. Centrifugal separation method (mechanical dehydration)

Principle: Use centrifugal force to accelerate the separation of water and oil (water density > oil).

Applicable situations:

- Lubricating oil containing a large amount of free water (such as ship lubricating oil, industrial gear oil).

Equipment: Centrifugal oil filter

Operation steps:

1. The lubricating oil enters the centrifuge with high-speed rotation (5000~15000 RPM).

2. Water and impurities are thrown to the outer wall and discharged through the drain.

3. The purified oil flows out from the center.

Advantages:

✔ Fast processing speed, suitable for a large flow of oil.

✔ Solid particles can be removed at the same time.

Disadvantages:

❌ Limited effect on dissolved water (needs to be combined with vacuum dehydration).

 4. Adsorption filtration method (low-cost dehydration)

Principle: Use water-absorbing materials (silica gel, molecular sieve, coalescing filter element) to absorb water.

Applicable situations:

- Trace moisture (<1000ppm)

- Small equipment or temporary treatment

Common adsorbents:

- Silica gel (can be dried and reused)

- Molecular sieve (efficient water absorption, but high cost)

- Coalescing filter element (makes tiny water droplets gather into large droplets and then separate)

Operation method:

1. Put the adsorbent in the oil or filter it through the oil filter.

2. Regularly ｒｅｐｌａｃｅ or regenerate the adsorbent (such as drying silica gel).

Advantages:

✔ Simple equipment, suitable for on-site emergency treatment.

✔ Can remove some dissolved water.

Disadvantages:

❌ The adsorbent needs to be replaced regularly, and the long-term use cost is high.

 5. Heating evaporation method (simple dehydration)

Principle: Heat the oil (≤80℃) to evaporate the water (ventilation is required).

Applicable situations:

- Lubricating oil with low water content (<0.1%)

- Temporary treatment when there is no professional equipment

Operation steps:

1. Heat the oil to 60~80℃ (avoid high temperature oxidation).

2. Stir or circulate the oil to accelerate the evaporation of water.

3. Purge with dry air or nitrogen to take away water vapor.

Advantages:

✔ No complex equipment is required, suitable for small-scale treatment.

Disadvantages:

❌ Low efficiency, may cause oil oxidation.

6. Coalescing separation method (industrial dehydration)

Principle: Use the coalescing filter element to merge tiny water droplets into large water droplets, and then discharge them through the separation filter element.

Applicable situations:

Emulsified water (water and oil mixed into an emulsion)

Large lubrication systems, such as ships and power plants

Equipment: Coalescing oil filter

Advantages:

✔ Can handle emulsified oil, with high dehydration efficiency.

✔ High degree of automation, suitable for continuous operation.

Disadvantages:

❌ The equipment cost is high, and the filter element needs to be replaced regularly.

Comparison of dehydration methods

Method Applicable water type Dehydration effect (ppm) Advantages Disadvantages

Sedimentation method Free water 500~1000 Low cost, simple Time-consuming, incomplete

Vacuum dehydration: Free water + dissolved water <10 Deep dehydration, high efficiency. Expensive equipment

Centrifugal separation, Free water 100~50,0, Large processing volume, fast.t Ineffective for dissolved water

Adsorption filtration,n Trace water 50~200, Simple operation, Adsorbent needs to be replaced

Heating evaporation Trace water 200~500 No equipment required Low efficiency, may oxidize

Coagulation separation Free water + emulsified water <50 High efficiency, automation High equipment cost

How to choose a dehydration method?

A small amount of free water → sedimentation method/heating evaporation

A small amount of dissolved water → vacuum dehydration/adsorption filtration

A large amount of free water → centrifugal separation/coalescence separation

Emulsified water → coalescence separation/vacuum dehydration

There are various methods for lubricating oil dehydration. Vacuum dehydration (deep dehydration) and coalescence separation (emulsified water treatment) are the best, while the sedimentation method and the adsorption method are suitable for low-cost temporary treatment. When choosing, you need to consider the water content, oil type, and equipment conditions to ensure the best dehydration effect and extend the life of the lubricating oil.