Documents, Tools and Resources
Chose from the items below for additional information about VAIP and primary aluminum production.
- PFCs and Primary Aluminum Production
- Inventory Tools
- Sites related to PFCs and Aluminum Smelting
PFCs and Primary Aluminum Production
Primary aluminum is produced using the Hall-Héroult electrolytic process. In this process, aluminum production is carried out in a semi-batch manner in large electrolytic cells called pots with a direct electric current input of up to 280,000 amperes and about 5 volts. The pot is a rectangular steel shell typically 8 to 13 meters long, and 2.5 to 3 meters wide, and 0.75 to 1 meters high, and is lined with a refractory insulating shell on which carbon blocks are placed to form a cathode. Steel collector bars are inserted into the cathode blocks to carry current away from the pot.
Molten cryolite (sodium-aluminum fluoride) is placed in the cavity formed by the cathode blocks. Anodes, also of baked carbon, are immersed in the cryolite to complete the electric path. Anodes may be either pre-baked in a separate process and attached to connecting rods for immersion in the bath (termed prebake design cells), or may be formed through self-baking from coal-tar and petroleum coke paste that is fed into the top of a steel casing above the cell (termed Soderberg design cells). Alumina (Al2O3) is fed in powder form into the pots and is dissolved in the cryolite bath. Molten aluminum is evolved while the anode is consumed:
Al2O3 + 3/2C => 2Al +3/2 CO2
Production of Primary Aluminum
Source: IPAI, 1996
When the alumina ore content of the electrolytic bath falls below critical levels optimal for the above chemical reaction to take place, rapid voltage increases occur, termed “anode effects”. During an anode effect, carbon from the anode and fluorine from the dissociated molten cryolite bath combine, producing CF4 and C2F6. These gases are emitted from the exhaust ducting system or other pathways from the cell (e.g., the hood of the cell).
Two of the Four Primary Production Cell Technology Types
Source: IPAI, 1996
Anode effects occur both periodically and randomly in aluminum reduction cells. The frequency, duration, and voltage profile of anode effects depend primarily on the cell technology and operational procedures, in particular the alumina feed strategy. Because PFC emissions are associated with anode effects, total emissions are also driven by these characteristics. The magnitude of PFC emissions for a given level of aluminum production depends on the frequency and duration of anode effects.
You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA’s PDF page to learn more about PDF, and for a link to the free Acrobat Reader.
Measures undertaken by partners to reduce PFC emissions include:
- Improving alumina feeding techniques by installing point feeders and regulating feed with computer control;
- Training operators on methods and practices to minimize the frequency and duration of anode effects (e.g., providing employees with measurement devices to monitor alumina feed rates and anode effects);
- Using improved computer controls to optimize cell performance; and
- Measuring PFC emissions (PDF) (42 pp, 318K) and monitoring cell operating parameters to determine relationships between them.
A long-term industry initiative which has significant potential to reduce emissions, is the development of non-consumable inert anodes. These inert anodes do not utilize carbon, thereby eliminating the source of carbon for PFC and process-related CO2 generation. This technology is being pursued aggressively through a joint R&D program that has been established between the aluminum industry and the U.S. Department of Energy in its Industrial Technologies Program . These efforts are expected to result in a commercially viable anode design in about 10 to 15 years. Information on the costs of reducing PFC emissions from primary aluminum is available at EPA’s High GWP Home Page.
Protocol for Measurement of CF4 and C2F6 from Primary Aluminum Production (PDF) (5 pp, 82K)
This article, published in Light Metals 2003, describes a measurement protocol to assist with developing accurate PFC inventories based on the Intergovernmental Panel on climate Change (IPCC) Tier 3b method. The protocol was produced with the aim to foster consistency in smelter-specific sampling programs.
Factors Affecting PFC Emissions from Commercial Aluminum Reduction Cells (PDF) (8 pp, 304K)
This article, published in Light Metals 2001, presents the results of the first set of PFC measurements sponsored by the VAIP Program at individual aluminum smelters. The paper reviews the data, and provides recommendations for predicting PFC emissions based on time reduction cells or on anode effect.
PFC Emissions and Reductions: The Domestic and International Perspective (PDF) (7 pp, 524K)
This article, published in the February 1999 issue of Light Metal Age. It outlines current U.S. and international activities by industry to reduce emissions and opportunities for further action.
International Efforts to Reduce Perfluorocarbon Emissions from Primary Aluminum Production (PDF) (58 pp, 1.3MB)
This report summarizes international efforts to reduce PFC emissions through government-industry initiatives. It describes each producer nation’s PFC reduction efforts, accomplishments, and challenges. Future options for reducing PFC emissions from primary aluminum production are also discussed.
Perfluorocarbon (PFC) Generation at Primary Aluminum Smelters (PDF) (7 pp, 320K)
This paper, published in Light Metals, February 1998, presents the results of the first set of PFC measurements sponsored by the VAIP Program at individual aluminum smelters. The paper reviews the data, and provides recommendations for predicting PFC emissions based on time reduction cells or on anode effect.
Aluminum Industry Technology Roadmap (PDF) (60 pp, 1MB)
The industry, in cooperation with the Aluminum Association and the Department of Energy, has published the “Aluminum Industry Technology Roadmap” in February 2003. The Roadmap presents industry-wide performance targets for energy, environment, and market share, and describes the research and development strategy for achieving those targets. One goal, pursued aggressively by industry, is the development of the advance cell technology, with inert anode and wettable cathode components. An advanced cell will not only reduce the energy requirements, but will also eliminate the carbon anode thereby removing the source of carbon for PFC generation.
The Aluminium Sector Greenhouse Gas Protocol (PDF) (64 pp, 1.3MB)
The International Aluminium Institute (IAI), in collaboration with the global aluminum industry, has developed an addendum to the WBCSD/WRI Greenhouse Gas Protocol. This Addendum provides additional interpretation, guidance and examples tailored to the international aluminum industry.
PFC Emissions Measurement Protocol for Primary Aluminum (PDF) (42 pp, 318K)
EPA is working with the IAI to improve global emissions data. EPA and IAI have completed a standard measurement protocol for PFCs. This is the 2008 version, which replaces the May 2003 document.
IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories
See Chapter 3 - Industrial Processes - discusses PFC Emissions from the Aluminum Industry.
- The Aluminum Association
- International Aluminium Association
- Australian Aluminum Council
- Aluminum Association of Canada
- European Aluminum Association
- The Minerals, Metals, and Materials Society
- USGS Minerals Information: Aluminum
- U.S. Department of Energy Industries for the Future: Aluminum