Capral Aluminium Limited has operations in Australia and New Zealand and is a producer of refined aluminium ingots and supplier of semi-fabricated and fabricated products. Capral is a major exporter of primary aluminium and sheet products to Asia. Capral also runs two aluminium recycling facilities with a total capacity of 70,000 tonnes per year.
The Company's vision is to maintain a sustainable competitive position as a producer of primary aluminium, and supplier of rolled and extruded product in the Australian/New Zealand region and to export ingot and semi-fabricated products into the Asian market.
In March 1995, the Commonwealth Government announced its Greenhouse Challenge initiative, a programme of co-operative agreements with industry aimed at reducing greenhouse gas emissions. Capral has participated in this programme and has worked with the Commonwealth to develop cost-effective voluntary measures to reduce greenhouse gas emissions through improving energy and process efficiencies.
This case study describes the energy efficiency improvements at Capral's Kurri Kurri Smelter. This smelter commenced production in 1969 and has grown from an initial production of 45,000 tonnes per year to the current rate of 150,000 tonnes per year. Today the smelter is an important part of the regional Hunter Valley and national economies, with approximately 650 employees.
At the Kurri Smelter aluminium is produced in a series of cells or pots. The process involves the electrolytic reduction of alumina (aluminium oxide) dissolved in a molten cryolite (a sodium-aluminium fluoride mineral) and aluminium fluoride bath. The reduction is achieved by a carbon anode that is immersed in the molten bath.
The aluminium industry is Australiaís largest industrial electricity user and demands a substantial base load from the electricity generation industry. Electricity in NSW is largely produced from fossil fuels (mainly coal), so gains in energy efficiency at smelters such as Capralís have major benefits in terms of reducing greenhouse gas emissions.
In addition to greenhouse gas emissions resulting from electricity generation and the consumption of carbon anodes, aluminium smelters also generate a type of greenhouse gas called perfluorocarbons (PFCs). These PFCs are very damaging greenhouse gases and are thousands of times more damaging than carbon dioxide (CO2).
PFCs are generated during aluminium smelting, through a phenomenon known as the 'anode effect'. Under normal smelter operation, pot voltage is stable and there is no appreciable formation of PFCs. However, if the feed alumina concentration drops the voltage will rapidly rise and reduction of the cryolite occurs. This 'anode effect' results in the generation of PFCs.
Cleaner Production Initiative
During the period 1990-1996 Capral's Kurri Smelter went through major organisational change. The smelter's employees undertook significant training which enabled them to operate in smaller multi-skilled teams. A substantial part of this training focused on environmental controls and practices which enhance the stability and energy efficiency of the smelting process.