The challenge faced by the FEL team was the recovery and containment of sulfur hexafluoride, more commonly referred to as SF6, the most potent of the greenhouse gases in its negative effect on the atmosphere. SF6 is used at JLab to suppress arcing in high-voltage DC electron sources, and is widely used in the commercial power transmission industry in circuit breakers, gas-insulated substations and other switchgear to manage the high voltages carried between generating stations and customer load centers. The power industry uses 80 percent of all SF6 in the U.S. and results for the 2007 reporting year include total reported SF6 emissions of 326,878 pounds (https://www.epa.gov/sites/production/files/2016-02/documents/sf6_2007_ann_report.pdf).
Before its impact to the environment was understood, the gas was vented into the atmosphere. But, early on, in an effort to save time and money, the FEL team designed and built a recovery system to capture and store the gas when the FEL high-voltage system was opened for maintenance. Once evidence was clear that SF6 has a greenhouse gas potential at least 20,000 times greater than carbon dioxide, efforts to capture and store it intensified.
Since 1998, the containment system has been continuously refined, and now includes a remote cesiator - a purification and dehydration component. As a result, the gas is not only safely captured, but it can be conserved and reused rather than being replaced by new product. It's estimated that the program has prevented the release of the equivalent of 900,000 tons of carbon dioxide since its implementation, and saved more than $1.5 million over the past 10 years.
The system was such a success, a new version was assembled for use in the FEL's gun test stand as it was being constructed. The gun test stand model retains the roughly 156 cubic feet of SF6 needed for use in the gun test stand.
The FEL's SF6 recovery system uses readily available hardware and a process that is inexpensive relative to commercially available recovery systems. Bringing accessible components and technologies together in a novel way, the group has devised a capability that has been shared with the Department of Energy's Fugitive Emissions Working Group and other DOE facilities.
The effort also received a "noteworthy practice" commendation by the Department of Energy when it recently announced its annual pollution prevention and environmental sustainability awards. Additionally, the SF6 Fast Recovery System is directly contributing to DOE and JLab's shared site sustainability goals for reducing greenhouse gas emissions.