The Portland Smelter in south-western Victoria produced its first aluminium in 1986 upon commissioning of the first of two smelting potlines. The second potline, commissioned in 1988, raised the intended production capacity of the plantís 408 smelting pots to about 320,000 tonnes of primary aluminium per annum.
Portland Aluminium is currently a joint venture between Alcoa of Australia, the Victorian State Government, Eastern Aluminium, the Chinese Government and the Japanese trading company Marubeni.
The smelter was designed and built using Alcoa technology. On commissioning, the smelter was placed on a full production setting. However, as might be expected of the plant of the size of Portland, considerable adjustment to design and processes was required in the early stages to achieve satisfactory performance.
During this start-up phase, many of the raw materials used in the aluminium production process ended up in the waste stream, becoming part of over 1,000 cubic metres of waste going to landfill each month during 1989.
Portland Aluminium uses the 'Hall/Heroult' process to convert alumina to aluminium. Alumina ore, (containing aluminium oxide) is subjected to high electric current in smelting pots. The current passes from an anode through a molten bath of cryolite to a cathode, which removes the oxide, leaving a cake of molten aluminium.
Substantial infrastructure surrounds the complex chemical and physical aluminium production process. Alumina, the major component in the process, is produced at the Alcoa refineries in Western Australia and delivered to Portland by sea. Carbon products that are processed to produce 170,000 carbon anodes per annum are also delivered by sea. Electricity is transmitted 700kms from brown coal fired power stations in the Latrobe Valley via a 500KV tower system. Natural gas is supplied by underground pipeline primarily to fuel the anode baking furnaces.
Raw materials are vacuum unloaded at the wharf and conveyed to the plant 4.2km away, via an underground and overland enclosed belt conveyor.
The final product from the process is near-pure aluminium in the form of 22.5kg ingots. The ingots are shipped to various locations throughout South East Asia, China, Korea and Japan.
Cleaner Production Initiative
In 1990, Portland set itself two basic and at the time unique goals. The first objective was to have no process materials going to landfill; the second being to have zero general waste going to landfill by the end of 1995.
At the time that these goals were set, the overall financial loss to landfill was estimated at around $1.3 million per annum.
Cleaner production initiatives were subsequently undertaken in the four key stages of the aluminium production process - raw materials, electrode, smelting, and casting.
The raw material ship unloader at the port uses a vacuum system. During certain weather conditions and 24-hour unloading operations, this system was capable of creating nuisance noise in residential areas around the port. Silencing equipment has now been fitted to alleviate this problem.
Considerable amounts of raw material, mainly carbon and alumina, were lost at the transfer points along the 4.2km belt conveyor from the wharf to the site storage silos. The spills resulted in cross-contamination to the extent that recovery was not possible and landfill the only option. Installation of vacuum duct systems at the conveyor transfer stations and the implementation of a product recovery procedure after each product shipment has allowed raw materials to be returned to the process. A further benefit of the initiative is that system maintenance has been reduced.
Poor handling practices for both anthracite and fluoride resulted in significant material spillage. Ground contamination was a major concern. Handling methods have now been revised using designated bulk handling and storage silos, reducing material loss and minimising environmental risk.
Pencil pitch was formerly used in the aluminium production process as a binding agent in the making of carbon anodes. In its solid form, the material required complicated and stringent materials handling and management practices. It had a further disadvantage in that it needed to be melted before it could be used. Pencil pitch has now been replaced by liquid pitch, resulting in substantial gains in efficiency and improved occupational health and environmental practices.
Installation of a natural gas pipeline to Portland Aluminium has improved process efficiencies, optimised process control and eliminated the need for on-site storage of gas. An assessment of the use of natural gas as a fuel option for vehicles has also been undertaken.
The anode baking furnaces require major maintenance after approximately 100 baking cycles.
Maintenance was traditionally done in-situ. A method has been devised at Portland to allow full units of wall sections to be pre-built off-site, transported and installed with minimal need for people to enter the hot baking furnace.
Bricks from carbon bake furnace re-builds are returned to the manufacturer for re-processing. New products are manufactured from the recycled bricks and sold back to Portland Aluminium or on the open market.
Anodes consumed in the smelting process are removed from the pots after about four weeks. The spent anodes are transported from the pot rooms in purpose built vehicles to reduce the escape of emissions. Anodes are then placed in a cooling tunnel, which allows fluoride-rich gases to be passed through a filter system and recycled.
The aim of the furnace maintenance initiative is to totally recycle all furnace components to the specification standards for new materials.
After smelting pots have been relined, placed in the potline and made ready for commissioning, they are pre-baked using a natural gas fired baking system. This reduces start-up stress, extends pot-life and subsequently reduces the amount of spent potlining material generated.
A specially designed dust and soundproof facility has been constructed where smelting pot shell demolition and maintenance is conducted. Specialised equipment has been developed to allow processing of large aluminium metal pads left in the pots, and to recover for recycling, steel cathode bars, steel vapour barrier, and pot repair steel.
The smelting pot reline facility allows several pot shells to be re-built at once. Part of this operation is to prepare new cathodes for pot installation. The cathodes have a steel electrode glued into them. In heating up the pots, the glue gives off solvent gases into the working area of the pot rooms. Now, prior to pot start-up, the cathodes are baked in a special purpose, EPA-licensed furnace. Volatile gases are collected and scrubbed within the furnace prior to atmospheric discharge.
A process has been developed in conjunction with Ausmelt, an Australian furnace development company, which is unique to the world aluminium smelting industry. It is projected that the process, once in full operation, will allow the old linings from smelting pots to be heat treated to remove residual cyanide and to recover the valuable fluorides. These will then be recycled back into the smelting process. Preliminary trials show that by-products from the process have the potential to be used in various civil industries applications. In the meantime, spent potlining material destined to be recycled is being stored in special containers and buildings.
Major up-grades of the bath handling facility have reduced both occupational health and environmental risks. Bath products are recovered during the recycling of spent anodes from the smelting pots. Traditionally, this caused an extremely dusty work environment. Dust has now been greatly reduced and contained.
The quality and presentation of aluminium ingots is important to market acceptance. A continual effort is being made to reduce the level of impurities in metal during smelting. The installation of robots to skim ingots during casting has complemented these efforts. Skimming improves surface quality, reduces the risk of moisture ingress during storage and transport, and the subsequent dangers during ingot re-melting. This task was previously performed manually with operators exposed to risk of both hot metal splashes and fumes.
Advantages of the Process
All the above process improvements are aimed at increasing commercial returns to the plant.
The cost of material loss and waste disposal has been reduced from over $1.3 million in 1990 to less than $200,000 in 1997, increasing revenue by more than $1 million per annum.
Minimising raw material loss and substituting pencil pitch for liquid pitch have both led to significant energy savings and have improved process control and anode performance. The use of natural gas has improved baking efficiencies and reduced gaseous emissions from scrubbers.
The goals that Portland Aluminium set itself in 1990 in relation to landfill have largely been achieved. Through the pursuit of efficiencies and implementation of waste reduction initiatives, waste going to landfill in 1992 had fallen to 1,100 cubic metres. In 1997, the amount of landfill waste was only 21 cubic metres.
Off-site maintenance of the anode baking furnaces minimises health and safety risks, increases furnace life, and reduces the generation of refactory waste. Furthermore, by improving the quality of anode, smelting pot processing performance is enhanced.
The initiative cost $9 million and has an estimated payback period of 6-8 years. Emissions have been substantially reduced as a result of the initiative.
The cost of refurbishing each smelting pot is between $80,000 and $100,000. In the process, around 100 tonnes of spent potlining is generated, which requires treatment at a cost of $200 to $250 per tonne. Considerable savings are derived by extending pot life beyond the normal production period of 5,000 days.
The smelting pot maintenance processes developed by Portland Aluminium were designed to minimise downtime and increase productivity. Portland Aluminiumís methods are now used by other smelters to obtain improved performance, reduce emissions, and lessen health and safety risks.
Cleaner Production Incentive
With so much raw material being wasted and going to landfill in the early years of smelter operations, there was strong incentive to recover as much raw material as possible to increase production revenue.
Waste minimisation has thus become, since the early 1990s, an integral part of Portland Aluminiumís operations. The company now actively embraces cleaner production practices as a means of achieving improved process performance in all aspects of its operations.
Process changes reflect the companyís commitment to its environmental, health and safety policies.
The Portland smelter has set many process benchmarks, strengthening its competitive position in the world aluminium market.
Waste management and cleaner production tools have provided the vehicle for competitive change, impacting strongly on the economic viability of the plant while reducing environmental risk and creating a healthier and safer working environment.
Many cleaner production initiatives, both large and small, continue to be undertaken as part of Portland Aluminiumís commitment to commercial sustainability, without compromise to the environment, health and safety of employees and the surrounding community.
Portland Aluminium has sound corporate policies and objectives that sponsor and promote management initiatives built on cleaner production principles. Some of these are set out in Alcoa Corporate Environment Report on Cleaner Production of 2 May 1995.
Alcoa supports the concept of cleaner production for existing, as well as new products and processes. It recognises that there are significant benefits to be gained in all aspects of the business by carefully considering raw materials, conversion processes, product design, waste production, product distribution/reuse/recycling, and ultimate product disposal as product decisions are made. Alcoa will continue to utilise a multi-dimensional approach, 'Early Environmental Involvement' for design, 'Pollution Prevention' for existing facilities, and 'Life Cycle Analysis' for products, to assist in the cost effective implementation of cleaner production concepts for all Alcoa businesses.
Although extensive research and planning, followed by careful implementation, was required for the initiatives, no major barriers were encountered.
Case study coordinated by the Environment Management Industry Association of Australia (EMIAA), June 1998.