Recycling technology of transformer oil aiming to achieve carbon neutrality

Passion for practical application of recycled oil

KitamuraOur company manufactures and sells pole-mounted transformers mounted on the utility poles. Pole-mounted transformers are filled with transformer oil, which provides electrical insulation and cooling. The pole-mounted transformer is often repaired approximately every 10 years. In the repair process, a tank and a transformer core are collected and recycled if at all possible, but the transformer oil is replaced with new oil each time. I was wondering why the collected transformer oil could not be recycled as transformer oil, though it was thermally recycled as fuel in thermal power plants.

Therefore, I asked a person who was familiar with the transformer oil, and I learned that although the transformer oil was recycled in Japan, the used transformer oil had not been used as transformer oil again since the 1990s because PCBs, which are hazardous to humans and the environment, was detected in the recycled oil. However, because of the worldwide trend of environmental consciousness and the fact that all PCB contaminants must be disposed of in Japan by 2027, I feel that in the future, there is a high possibility that recycled oil will be able to be used domestically without having to worry about PCB contamination.

I was working in the electric equipment design department and then posted to the material technology group three years ago. I was happy to handle chemical materials in which I was originally interested because I graduated from the chemistry department at university. In the material technology group, I take charge of evaluating the compatibility of the transformer oil and equipment and analyzing the materials.

On the occasion of starting the research into recycled oil, I first deepened my knowledge of transformer oil. Whenever I had problems, I counted on an environment where I was free to consult my supervisors, including the material technology manager and the group manager (Ms. Otake), who were familiar with research in the recycled oil and environment-conscious materials.

OtakeI am the group manager in the material technology group and manage the research and development of members, including Ms. Kitamura. Since I used to research plant-derived resin materials and recycling, we have something in common, such as the approach to environmentally conscious materials research, and I sometimes discuss these issues together with Kitamura. Ms. Kitamura is a reliable person who has reliably conducted experiments herself and reported the result even without my detailed instructions.

Confrontation of various problems with team members toward practical application

KitamuraIn the research, we used the transformer oil which deterioration had been accelerated in a simulation of the environment of the pole-mounted transformer. Among some methods for recycling the transformer oil, we focused on the adsorption method by which recovery and improvement can be performed to a level that meets the quality requirements for transformer oil characteristics, using relatively simplified facilities. We treated the transformer oil for which deterioration had been accelerated by using five adsorbents with different characteristics. As a result, we found that activated clay used as an adsorbent in the recycling of edible oil was the most effective for recycling transformer oil.

In addition, we measured conductivity to determine the situation of recycling treatment. Since there was no precedent where a conductivity sensor was used in the verification of recycled oil, and the sensor itself had broad utility, we had a lot of trouble interpreting the measurements. In our interpretation of the results, it is important to understand not only the value itself but also the principle and mechanism in which the value was derived. After receiving advice from the material technology manager, supervisors, and senior staff and after surveying the previous literature and documents, I was able to fully understand the principles and mechanisms, which enabled me to successfully proceed with verification of the recycling treatment.

As an issue for commercialization, we also found that oxidation degradation was likely to occur in the recycled oil as recycling was repeated. Since the cause was that an original antioxidant component contained in the transformer oil decreased from the recycling treatment, a significant improvement could be expected by adding an antioxidant or an additive. From now on, it will be necessary to conduct experiments aiming to shorten the recycling treatment time and increase the recyclable number of times for commercialization and application to products in the recycled oil.

Approach to problems in environments and resources via Research and Development of recycled oil

KitamuraThe research results were presented at The Japan Petroleum Institute in 2022 and 2023. With many questions asked at the site, I knew much again about the attention brought to recycled oil in the industry.

I think my job is worthwhile when I get to know a verification result before everyone else. Since the recycled oil is not often researched by other researchers, I feel special pleasure in seeing the result.

In the future, with an eye toward realization of more advanced cyclic use of recycled oil, we will research and develop the appropriate recycling treatment technology to allow semi-permanent repetitive use.