Removal of corrosive sulfur from insulating oils by natural sorbent and liquid-liquid extraction

Prevention of energy transformer failures by removing so-called “corrosive sulfur” from insulating oil belongs to the most important tasks. This article is focused on finding a low-cost effective way suitable for decontamination of mineral insulating oils containing sulfur compounds together with regeneration of the insulating oils. Two methods were tested and optimized; sorption technique with new low-cost natural sorbents, bentonites, and a newly suggested liquid-liquid extraction with subsequent sorption. The effectiveness of proposed methods was compared with the common technique of filtration through a layer of commercially available sorbent. The real insulating oil from transformers with a relatively high content of dibenzyl disulfide - 71.6 mg kg-1 was applied in all tests. One of the new low-cost sorbents revealed an excellent efficiency of a corrosive sulfur removal similarly to the combination of liquid-liquid extraction with subsequent sorption. Technological characteristics of all regenerated oils were also measured and met all requirements of the standards no. IEC 62535 and IEC 60422; their properties corresponded to new electro-insulating oils.