- What is sulfur hexafluoride (SF6) and why is EPA concerned?
- How is SF6 used in the magnesium industry?
- What are the potential abatement strategies available to the magnesium industry?
- What was the goal of this partnership?
- What are EPA’s plans to work with the magnesium industry in the future?
- Will SF6 emissions from the magnesium industry grow in the future?
- Will Partners continue to report data on GHG emissions to EPA?
1. What is sulfur hexafluoride (SF6) and why is EPA concerned?
SF6 is a highly potent greenhouse gas (GHG). Over a 100-year period, SF6 is 22,800 times more effective at trapping infrared radiation than an equivalent amount of carbon dioxide (CO2). SF6 is also a very stable chemical, with an atmospheric lifetime of 3,200 years. Consequently, it will accumulate in the atmosphere and its effect on the climate will be felt by many future generations. For more information on Climate Change proceed to EPA’s Climate Change Web site.
2. How is SF6 used in the magnesium industry?
SF6 is a non-hazardous, inert gas that is used to prevent the oxidation of molten magnesium during production and processing operations. Approximately 0.2% to 0.5% by volume of SF6 is used in gaseous mixtures containing air and/or CO2. The mixture is supplied to the molten magnesium surface, where SF6, in particular the fluorine component, forms a protective film of fluorine-containing magnesium oxides (MgO). Without an effective cover gas, molten magnesium oxidizes with atmospheric oxygen, producing a lower quality product and a potentially violent fire. Any SF6 that is not consumed in the cover gas process is typically emitted directly to the atmosphere.
The use of SF6 mixtures has been the predominant method for protecting molten magnesium surfaces for several decades. It replaced the use of more toxic and corrosive compounds, such as solid salt fluxes and sulfur dioxide (SO2), as the primary cover gas mechanism.
3. What are the potential abatement strategies available to the magnesium industry?
There are several pollution prevention options available to reduce and eliminate SF6 emissions from the magnesium industry. Over the last decade, the International Magnesium Association (IMA) and EPA have studied alternate cover gas compounds. Initial studies identified compounds such as boron trifluoride (BF3), sulphuryl fluoride (SO2F2), 1,1,1,2-tetrafluoroethane (HFC-134a), hydrofluoroethers (HFE 7100 and HFE 7200), and a fluoroketone (FK) Novec™612. AMCover™ (HFC-134a blend) and 3M’s Novec™612 (FK) are commercially available cover gas alternatives for SF6 that have been tested and in some instances, adopted by facilities in the United States. For those companies still using SF6, research is also being conducted into advanced recycle/capture techniques. These devices collect the process exhaust gases, and filter the SF6 component for reuse on site. On another level, research has also been conducted into innovative equipment designs. Brochot, a casting equipment manufacturer, developed a magnesium ingot casting machine. The machine reportedly uses two innovative processes (a new casting wheel design, and patented inert cover gas containing a mixture of xenon, argon, and CO2) to reduce the impact of melt surface oxidation on casting productivity and operational costs (Brochot 2006).
4. What was the goal of this Partnership?
The goal of the Partnership was to reduce emissions of SF6 from magnesium production and processing through a voluntary collaborative approach. In February 2003, EPA’s partner companies and the IMA committed to eliminate SF6 emissions by year-end 2010. At the end of 2010, while not all Partners eliminated SF6 emissions, EPA’s partners in the magnesium industry made significant progress in improving their operational efficiencies and environmental performance by optimizing SF6 cover gas concentrations, flow rates, and delivery mechanisms, as well as identifying and repairing leaks in SF6 gas distribution systems. Notably, as a result of the Partnership, multiple technically proven alternative climate friendly cover gases were identified and in some instances, deployed.
5. What are EPA’s plans to work with the magnesium industry in the future?
At this time, EPA does not plan to establish a new emissions reduction goal post- 2010; however, EPA will continue to support the industry’s full transition away from SF6 by maintaining its technical expertise and leadership.
6. Will SF6 emissions from the magnesium industry grow in the future?
Estimated emissions of SF6 by the U.S. magnesium industry have declined from nearly 6 MMTCO2e (million metric tons of carbon dioxide equivalent) in 1999 at the outset of the Partnership to roughly 1.3 MMTCO2e in 2010 (USEPA, 2012). Despite industry contraction within the U.S., the decrease in total U.S. emissions was enabled by transitions to alternative cover gas options and optimized cover gas usage. Growing demand for lightweight magnesium automotive parts and components of hand-held electronic devices is expected to support strong future growth in the magnesium casting sector both in the U.S. and internationally. When considering business-as-usual (BAU) practices before the Partnership, overall U.S. industry emissions reported are estimated to have been cumulatively reduced by 5.7 MMTCO2e since 1999. With more environmentally friendly cover gas technologies such as 3M’s Novec™ 612 (FK) and AMCover™ (HFC-134a blend) available in the marketplace, it is unlikely the industry’s SF6 emissions will grow significantly in the future. However, it will continue to be important to share information with growing international magnesium industry to assure they have access to and implement the most environmentally friendly production and casting technologies.
7. Will Partners continue to report data on GHG emissions to EPA?
Under subpart T of EPA’s Greenhouse Gas Reporting Program (40 CFR Part 98), owners or operators of facilities that contain magnesium production processes are required to annually report emissions from use of cover or carrier gases as well as for all other source categories located at the facility for which methods are defined in the rule. Facilities covered by subpart T are those that have emissions equal to or greater than 25,000 MTCO2e per year in combined emissions from stationary fuel combustion and all other source categories identified by the rule. Covered facilities were required to begin monitoring GHG emissions on January 1, 2011 in accordance with the methods specified in the rule. The first report was due to EPA by September 28, 2012; subsequent report are due annually thereafter by March 31. Reporters will report their data to EPA electronically through EPA’s Electronic Greenhouse Gas Reporting Tool (e-GGRT). For more information about EPA’s Greenhouse Gas Reporting Program, please see: http://www.epa.gov/ghgreporting/index.html.