There are several methods of regeneration of used transformer oil. One of these is dehydration by zeolite, purification in a filter press, purification and dehydration in a centrifuge (purification, clarification and vacuum drying), there are also processes based on adsorption.
Adsorption is the most efficient and the least complicated method of complete purification and regeneration of transformer oil. The process involves passing the oil through a layer of sorbent, which captures moisture and contaminating particles in just one processing cycle. Sorbents used for this purpose should have excellent filtration qualities and be capable to capture the molecules of the various contaminants. One of the advantages of Fuller’s earth is that it can be reactivated multiple times, making this sorbent very efficient and cost-effective.
Fuller’s earth is a clay with the ability to capture contaminants from mineral or vegetable oils and fats. Fuller’s earth has become the quality standard in oil regeneration and purification processes.
Fuller’s earth is widely used in the petrochemical industry worldwide. And although it is quite successfully used in the construction and pharmaceutical industries, due to the specific properties of its main use in modern
In the past, the purpose of Fuller’s earth was very different from the modern times. Initially, itt was used for extraction of oil and other fat from wool fabrics in the process of finishing, which gave it its name. It is also considered one of the clays that can absorb harmful particles, serve as an antiseptic or bleach fabric.
According to a 1913 document, Fuller’s earth was used for the first time in the United States for purification of vegetable oils, in 1878-1880.
Now, this substance is often used to purify new transformer oil before use, removing contaminants, or to restore used transformer oil to its initial performance quality.
Transformer oil accumulates many contaminants during use, apart from moisture and gases. Some of the contaminants dissolved in the oil are the products of the oil’s use. Solid particles, which originate from the solid insulation of the transformer, turn into sediment. The microscopic particles, which promote oxidation of oil, are also hazardous for the transformer’s cellulose insulation, and can pass through various filters. The use of adsorbents, such as Fuller’s earth, allows to capture these contaminants and completely purity and restore the oil. Due to large pores, Fuller’s earth can capture sulfonates, tar and asphaltenes with high molecular mass.
The process of oil regeneration involves pumping the oil directly from the transformer into a regeneration unit, where the oil is filtered and clarified, passing through Fuller’s earth.
Color alone is not necessarily an indication of the oil’s condition, however, it can indicate undesired processes in the oil. For instance, if the oil’s color changes from yellow to orange or red, this means that internals of the transformer may have suffered damage.
Contaminants formed in the process of using the oil influence the color. When the contaminants are dissolved in the oil, the color of the oil gradually changes to red. The contaminants continue to oxidize, damaging the transformer in the long run.
Therefore, while the color is not the one essential indication of oil quality, clarification of the oil by Fuller’s earth indicates the removal of the harmful substances from the oil and restoration of the oil’s performance quality. Also, practical use of the product has demonstrated its viability and efficiency. The benefits of using Fuller’s earth as a sorbent for oil reclamation are quite obvious.