The process of Reclaiming Transformer Oil involves the removal of Partials, Moisture, Gases, Acidity and other Oxidation Decay Products, polishing the oil and restores oil to like-new quality.
This process of Regeneration is simply the passing of Badly Deteriorated Transformer Oil through an Absorbent Bed. Several types of absorbents are available but the most common are Fuller’s Earth, Activated Alumina, Trisodium Phosphate and Activated Carbon.
The FILTERALL REGENERATION process utilises a blend of such Absorbents which is formulated and structured in order to provide the most efficient Absorbent Bed, whilst retaining an ability to be Reactivated once they become no longer active, due to the volume of Decaying Products which have been retained during the oil Reclaiming process.
The Temperature achieved during the REACTIVATION of the Clay Beds determines the degree of Internal Porosity and the High Surface Area of the Absorbent Beds determines its ability to absorb polar compounds & lighten the colour of service-aged oil. The unique crystalline structure or the bed material is thus very important and during extraction, the Absorbents are crushed, mixed and heat activated before being loaded into the Regeneration Columns.
Activated Regeneration Beds can absorb large quantities of acid. The amount of acid removed depends on many factors since absorption is a dynamic equilibrium process. Temperature, Flow Rates, Oil Viscosity, Residence Time and Initial Acid Level all affect the rate and capacity for Absorption.
While Transformer Oil can be Regenerated in just one pass of the oil through the rig, it takes more passes to sufficiently clean the Transformer Internals. In most cases, this work can be done safely and more efficiently while the Transformer being processed is Energised. The cleaning is more efficient because the 100/120 cycle coursed through an energised transformer, causes the laminations to vibrate, thus helping to loosen sludge from the transformer internals. The heat produced in an energised transformer will also aid in getting the oil temperature to the aniline point in a more timely manner.
The following graph, which plots Initial Neutralization value against Clay Required, offers a useful reference in order to determine the Regeneration Ability of the Filterall Beds for Initial Acidity Levels when processing Transformer Oil. This assumes a Tank to Tank processing arrangement and that the Processed Oil is required to be “as new” after a single pass. When processing (circulating) on a Transformer or Tank, although multi passes are required, the volume of oil which can be treated between Bed Reactivation will increase since the “feed” acidity level will be reduced with each pass.
**e.g. Oil with Initial Acidity of say 1.0 mg KOH/gram requires some 2lb of Clay to treat 1 gallon down to 0.05 mg KOH/gram in a single pass.
In order that this detail can be related to existing National Grid Operated Regeneration Plant, we advise the Regeneration Bed Absorbent Capacities of each below:
MRP2 offers 2 Regeneration Columns Sets and each set of 9 Columns (1 set) holds some 1,000 kg ( 2,200 lbs) of Absorbent.
MDD3 and MDD4 both have 1 set of Regeneration Columns containing some 1,200 kg (2,700lbs) of Absorbent.
** So using basis as above ** with MDD3 or MDD4 you can treat 2,700/2 = 1,350 gallons (5,000 litres) between Bed reactivations in order to achieve required product in a single pass.
In practice however, when circulating on a Transformer, you can assume some 3 or 4 passes would be required & some 10,000 L processed per cycle initially building up to 20,000 L for the final polishing pass. Required Contact Time between the Oil & the Clay Bed material will depend on total contamination of the initial oil (colour a good indication), so the flow rate at which MDD3 or MDD4 should be run during Regeneration will vary; 2,000 L/H is suggested as a start point & then it can be adjusted according to performance. In practice, it is best to adjust flow so that you can process the required litres & reactivate the columns on a 24-hour cycle.
Factors to Consider when Regenerating in Service Transformer Oil in order to achieve best performance:
- Advantageous to Dehydrate the oil before it contacts the Absorbent in order to prevent water from wetting the Bed Material. It is considered an advantage if Initial Processing is carried out without going through the Clay Beds in order to ensure the oil is as dry as possible prior to carrying out Regeneration via the Clay Beds.
Also, Purification (filtration, dehydration & degassing) & Heating should be continued when the columns are Reactivating.
2. Ensure that the Oil coming out of the columns is dehydrated and degassed via
Vacuum Chamber before being returned to the transformer or clean oil tank.
The Clay beds can hold up to 10% moisture, which can be passed on to the treated oil.
This is Particularly applicable when recalculating oil in a transformer.
3. Regeneration of oil can remove added Oxidation Inhibitor left, as well as contaminates existing in oil prior to treatment. Oxidised oil will have had its inhibitor consumed during the Deteriorating Process.
