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2010 Case Study: Project to reduce anode effects eliminates CO2 emissions and reduces costs
 
A focused effort to reduce anode effects at the Portland Aluminium smelter in Australia resulted in an 83%, or 106,000-tonnes, reduction of carbon dioxide equivalent (CO2e) emissions annually and US$135,000 in maintenance savings each year.
 
An anode effect occurs when there is insufficient alumina in the smelting pot. Under normal smelting conditions, alumina is consumed and carbon dioxide (CO2) gas is released. During an anode effect, fluoride material in the pot is consumed, and fluoride gases, known as perfluorocarbons (PFCs), are released. PFCs are greenhouse gases with higher global warming potential than CO2. One PFC unit is considered the equivalent of 6,000 to 9,000 units of CO2, depending on the specific gas.
 
In 2005 Portland Aluminium was experiencing 0.34 minutes of anode effects per smelting pot each day, resulting in 126,000 tonnes of CO2e annually. A global effort to reduce greenhouse gas emissions at Alcoa smelters spurred the location to increase its efforts to identify and eliminate the causes of the anode effects.
 
Since 2005, the location has focused on the following areas:
  • Training operators and supervisors on reducing anode effects and how to properly respond when an effect is occurring;
  • Overhauling the alumina feeders to increase the volume of alumina fed into the pots and reduce the number of feeder failures;
  • Implementing a new design for the pinch valves that control the alumina being dispensed into the pot;
  • Trialling and implementing updates to the computer controls used with the alumina feeding system;
  • Performing accelerated maintenance on the conveyor system that delivers alumina and fluoride from external bins to the pots;
  • Modifying pot start-up techniques to ensure the pots are in control during and following this critical process; and
  • Capturing and disseminating data on anode effects to all smelter employees to ensure the topic remains a high priority.
 
Through these efforts Portland Aluminium reduced the minutes of anode effects per smelting pot each day to 0.07 in 2010—an approximately 80% reduction from 2005 levels. In addition, the improvements to the alumina feeders and pinch valves have resulted in a projected annual maintenance savings of around US$135,000.