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.
Capralís Kurri Kurri Smelter
The Companyís 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 Capralís 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 ëanode effectí. 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 ëanode effectí results in the generation of PFCs.
During the period 1990-1996 Capralís Kurri Smelter went through major organisational change. The smelterís 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.
In addition, technical improvements were made in two areas:
- Process control, including the introduction of individual computer based control systems for each pot which enhanced energy efficiency and process stability through increased automation; and
- Control of alumina feed was upgraded to ensure smoother, more stable operation of the pots.
The measures undertaken achieved a 13.9 % reduction in the amount of CO2 equivalent emitted per tonne of aluminium between 1990-96. This resulted in a total reduction of 492,500 tonnes per annum of CO2 equivalent. This reduction was broken down as follows:
- 375,000 tpa CO2 equivalent from reduced PFC emissions;
- 111,000 tpa CO2 equivalent from efficiency improvements implemented by the power generators (this reduction was not a result of Capral initiatives, but is incorporated into reporting on energy efficiency by the aluminium industry); and
- 5,700 tpa CO2 equivalent from combustion efficiency improvements implemented by Capral.
The future action plan for the period 1997 - 2000 focuses on two major equipment modifications:
- The process for bonding anode rods to anode blocks is to be upgraded by changing the material which forms the bond from rammed carbonaceous paste to cast iron; and
- The ring furnace, in which carbon anodes are baked before being used in the smelting process, will be rebuilt to a superior design.
It is anticipated these projects will further improve the energy efficiency of the smelter operation.
The expected reduction in greenhouse gas emissions is summarised below, using 1990 as a base year.
|
1990 |
1996 |
2000 |
|
|
Tonnes (CO2) equivalent per tonne of metal produced |
1 |
0.86 |
0.77ñ0.82 |
Long before the greenhouse effect was identified as a major global issue, Capral and all other members of the Australian aluminium industry were addressing ways of increasing energy efficiency to reduce costs. Recognition of the greenhouse effect has reinforced the need for energy efficient practices.
There are significant operational benefits in reducing anode effects and PFC emissions. The occurrence of anode effects diverts energy away from aluminium production, thereby reducing the overall production efficiency. Reducing PFC emissions has the dual effect of reducing direct emission of a greenhouse gas and increasing energy efficiency.
There have been no significant barriers to reducing greenhouse gas emissions. This reflects the importance of energy related costs to the aluminium smelting business.
Mr Paul Jones
Manager Environment, Occupational Health & Safety
Capral Aluminium Limited
PO Box 12
Granville NSW 2142
Ph: 02 9682 0937
Fax: 02 9682 0067
Case Study Prepared:
May 1997 by ACCP
The Cleaner Production Case Studies Directory is part of EnviroNET Australia.
- For more information contact:
Environment Australia
Environment Protection Group
PO Box E305
KINGSTON ACT 2604
AUSTRALIA
Email: cproduction@ea.gov.au
URL: http://www.environment.gov.au/net/environet.html
