SF₆ is one of the gases set for reduction in usage in the Kyoto Protocol. Recovery work was started in 2002, and requests for this work from heavy electric machinery manufacturers have increased annually.

SF₆ has exceptional electric insulation properties, it can be easily injected into and discharged from insulation equipment, and it is very safe. In comparison with other insulation methods, such as air or oil insulation, it enables downsizing of power receiving and transforming facilities. It is therefore a gas that industry wants to continue using, but it has a global warming potential (GWP) 23,900 times that of carbon dioxide (CO₂). Therefore, reducing its release into the atmosphere is required to protect the global environment. So to find out how SF₆ can be recovered and reused, The Gas Review talked to Taiyo Nippon Sanso Higashikanto. They have around 15 years of experience in SF₆ recovery work.

The handling standards for SF₆ Gas in Electric Power Applications issued by the Electric Technology Research Association, an association of power companies and insulation equipment manufacturers that investigates, researches and provides information on electric technologies, stipulated SF₆ recovery rates of 97% minimum for testing and inspection and 99% minimum for equipment removal and disposal. The Act on Promotion of Global Warming Countermeasures requires “enterprises that consume 125kg equivalent of SF₆ gas to take measures to suppress SF₆ discharge” along with “the obligation to report discharge,” and fines imposed for failure to file reports. Therefore, if devices charged with SF₆ are used, the charged amounts must be calculate, and proof of recovery of equivalent amounts must be maintained.

Increased momentum in reducing environmental footprint leads to new business

Since the time when Taiyo Nippon Sanso Higashikanto was Hitachi Oxygen, they have designed and manufactured gas-related equipment for Hitachi electrical power facilities, allowing them to accumulate knowhow on controlling fluids. Junichi Terakado, Director in charge of sales of gas systems for the Gas Business Division, said, “For approximately 45 years we have manufactured SF₆ recovery equipment for Hitachi. At first, the goal was not to reduce the environmental footprint, but rather in response to the demand for recovery systems for SF₆ because of its high price.”

Since the Kyoto Protocol was adopted, inquiries from heavy electric machinery on SF₆ recovery methods when updating and removing equipment increased. SF₆ recovery as a business was started in 2002. Presently, the business of gas systems for gas supply, and maintenance, including SF₆ recovery business, accounts for 25% of the company sales of about ¥8bn.

Although it depends on the state of the gas, the equipment used in SF₆ recovery work includes mainly recovery equipment, decomposition gas and water removal refining equipment, recovery containers, and SF₆ charging/recharging facilities. For recovery containers, Taiyo Nippon Sanso Higashikanto has 500 lightweight seamless 47 litter cylinders and several liquid recovery tanks. The procedure includes a liquid recovery system that consists of a vacuum pump and compressor which is used to recover SF₆ from a SF₆-filled device into a cylinder or tank.

The quality of the recovered gas is analysed onsite and in advance and the analysis data is used to remove impurities and water, which can lower insulating properties, with refining and water removal equipment. Also, if electrical discharge or arcs have decomposed the gas into hydrogen fluoride, sulfer dioxide, or other components, a decomposition gas removal tube developed in-house is used to remove them. The SF₆ is purified to 98% to 99% and then recharged into the SF₆-filled device. If the SF₆-filled device is being removed, destructive processing is performed in response to a processing evidence submission request from owner of the equipment.

The recovery work is preformed by a worker qualified under the High Pressure Gas Safety Act. Normally, two workers work on the same site, but three to five workers may be involved depending on the work procedures and onsite conditions. After the work is completed, a recovery report is submitted.

The gas is recovered, for example, from power stations and sub stations of power companies, and power receiving and transforming facilities, accelerators, and other equipment in factories, large buildings and bullet trains. Recovery work is perfomed during disassembly and removal of old equipment when equipment is being inspected, repaired and updated. Around 60% of recovery requests come from seven large heavy electric machinery manufacturers, 30% from power companies and factories, and the remaining 10% from other customers.

Technical development based on accumulated knowledge

Taiyo Nippon Sanso Higashikanto used knowhow gained through previous recovery work to reduce the recovery cost and to develop and sell peripheral devices that increase the efficiency of recovery work.

Their in-house developed Conbas Recovery System, which recovers gas into unique gas bags, is used for small recovery jobs of 40kg or less or for emergency recovery work. Gas bags are available in 100 litre, 300 litre and 1,000 litre sizes. The bags can be folded to make them compact, enabling easily transporting the to the work site. They can therefore be used when sufficient work space is not available, such as for installations underground for transportation infrastructure or building electrical substation equipment. According to Taiyo Nippon Sanso Higashikanto, the Conbas recovery method has been praised as compact method for its wide range of applicability and high convenience. SF₆ gas is liquefied for recovery onsite if there is sufficient space, or if it is liquefied and recovered at Taiyo Nippon Sanso Higashikanto.

Also, a purity management and calculation system is being developed to manage the purity of liquefied gas when there are impurities in the SF₆. It is essential to be able to ensure the purity of the recovered gas when recharging it. However, managing the purity of recovered liquefied gas was previously thought impossible due to the complex factors involved, such as the recovered gas amount, amount of impurities in the gas, and the gas temperature.

Based on purity date for both the gas and liquid phases that were collected in liquefied recovery work in the past, relationships between the recovered gas amount and impurity quantities were analysed to develop the management system. According to Terakado, “Successful development of the system led to expanded application of recovered gas quality assurances. This technology has gained the trust of the customer, which gave momentum to expanding our recovery business.”

Gaining new customers with many recovery methods and response capability

In FY2016 alone, Taiyo Nippon Sanso Higashikanto recovered 69 tonnes of SF₆ for either recharging or destruction to make a large contribution to reducing the environmental footprint. The amount of SF₆ that they recover is increasing every year. Terakado explained, “The reason is an increase in requests from heavy electric machinery manufacturers.”

“One of our strengths is the ability to identify problems and improvements and make an appropriate judgement based on the extensive recovery work that we’ve performed in the past. This provides the basis to ensure speed in recovery work and maintain high quality in the recovered gas. I believe this has led to more orders. What’s important is the ability to analyse the status of the gas and process it correctly according to the analytical results.

Terakado is enthusiastic about the future. “It will become more challenging for heavy electric machinery manufacturers to dispatch workers for recovery work. For this reason, we would like to continue focusing on recovered gas quality management and cost performance,” he concluded.

Source: The Gas Review, issue no.442

*Original article online at https://www.gasworld.com/recovery-of-sf6-in-focus-for-taiyo-nippon-sanso-/2013705.article