Transformer oil centrifugal separation method

Centrifugal separation of transformer oil is a physical purification technology, which is mainly used to remove moisture, solid particles (such as metal chips, fibers, carbon particles) and some colloidal impurities in the oil, but has limited effect on the removal of dissolved gases (such as acetylene). The following are the centrifugal separation methods and operation points of the system:

1. Principle of centrifugal separation

The centrifugal force generated by the high-speed rotation of the centrifuge (usually thousands of times the acceleration of gravity) is used to separate oil, water and solid impurities into layers according to the density differences:

- Water (density 1.0 g/cm³) → outermost layer

- Solid impurities (density > oil) → middle layer

- Purified oil (density 0.85~0.89 g/cm³) → innermost layer

2. Equipment selection

| Type | Applicable scenarios | Speed range | Separation effect |

|----------------|--------------------------------|-------------------|--------------------------------|

| Disc centrifuge | Efficient separation of water and micron-sized particles | 6000~15000 rpm | Can handle oil with high water content and many impurities |

| Tubular centrifuge | Fine separation of tiny particles and colloids | 15000~30000 rpm | Suitable for high-precision purification, but with small processing volume |

| Horizontal centrifuge | Large flow continuous processing | 3000~8000 rpm | Suitable for industrial site maintenance |

3. Operation steps

(1) Pretreatment

- Filter coarse impurities: First, use a 20~50μm filter to remove large particles to avoid clogging the centrifuge.

- Heating the oil: Raise the oil temperature to 50~60℃ (not exceeding 65℃) to reduce viscosity and improve separation efficiency.

(2) Centrifuge settings

- Speed adjustment: ｓｅｌｅｃｔ the speed according to the degree of oil contamination (such as using a lower speed when the water content is high, and using a higher speed when there are more solid impurities).

- Specific gravity ring selection: Match the density of the oil (such as ring number 1.0 for water-containing oil, 0.9 for dry oil).

- Slag discharge interval: Automatic slag discharge models need to set a cycle (such as every 30 minutes), and manual slag discharge requires regular shutdown and cleaning.

(3) Operation monitoring

- Inspection of export oil quality: visual inspection of transparency, or use of moisture detector (target: moisture <10 ppm), particle counter (NAS 1638 Class 6 or below).

- Temperature control: Maintain stable oil temperature to avoid local overheating and oxidation.

(4) Post-treatment

- Vacuum degassing: If dissolved gases (such as acetylene) need to be removed, it is necessary to combine with vacuum oil filter treatment.

- Adsorption purification: Further remove residual impurities through silica gel or molecular sieve.

4. Precautions

- Safety protection:

- The centrifuge must be loaded evenly to prevent vibration and explosion.

- Open flames are prohibited during heating. There is a risk of explosion when the oil temperature exceeds the flash point (usually above 140°C).

- Efficiency limitation:

- Ineffective for dissolved gases (acetylene, hydrogen), and other technologies must be used.

- Acidic substances cannot be removed, and white clay regeneration or alkaline washing is required.

- Maintenance requirements:

- Clean the drum and disc regularly to prevent sludge accumulation.

- Check bearing wear to avoid high-speed operation failure.

5. Typical parameter reference

| Project | Control range |

|----------------|---------------------------|

| Processing flow | 1000~5000 L/h (depending on the model) |

| Separation factor (G value) | 5000~15000 G |

| Water content in outlet oil | ＜10 ppm (target value) |

| Solid particles | ＜5 μm (more than 90% removal rate) |

7. Common problem solving

- Serious oil emulsification: Add demulsifier (such as 0.01% polyether) and then centrifuge.

- Decreased separation effect: Check whether the specific gravity ring is matched or whether the drum is contaminated.

- Increased oil foam: Reduce the oil inlet speed or vacuum degassing pretreatment.

Centrifugal separation is the core method of mechanical purification of transformer oil, which is suitable for rapid on-site treatment, but it needs to be combined with other processes according to the type of oil pollution to fully restore the oil quality. For gas pollution represented by acetylene, it is still necessary to rely on vacuum degassing or the adsorption method.