The benefits of using aluminium may more than offset the impacts of extraction and production. These are the main steps in primary aluminium production:
The production of primary aluminium takes place in large production lines. The primary smelter is where it happens.
Here, the smelting process transforms refined alumina into aluminium. To do this, three different raw materials are required:
- Aluminium oxide (alumina)
The aluminium atom in alumina is bonded to oxygen. These bonds have to be broken by electrolysis to produce aluminium metal.
- Alumina is transported to the plants and into a pot (large container). Here the alumina is dissolved in an electrolytic bath.
- Alumina has a high melting point and is converted through an electrolytic process. In the electrolytic cells, a very high direct current is run between a negative cathode and a positive anode, both made of carbon. The anode is consumed in the process, as it reacts with the oxygen in the alumina to form CO2.
- Liquid aluminium is drawn from the cells using specialized vehicles and is cast into extrusion ingots, sheet ingots or other ingots, depending on how it will be processed further.
How much aluminium does a smelter make?
The capacity of Hydro’s fully owned and part-owned smelters varies between 60,000 and 600,000 metric tons of aluminium per year. The largest smelters in the world can produce up to 1 million metric tons per year.
Better potlines = less energy spend
Making aluminium is an energy-intensive process. Hydro is continuously working to further develop our potlines to improve:
- Energy efficiency
- Economic performance
- Environmental effect
- Working environment
Hydro is proud to be in the forefront among aluminium producers in developing and implementing energy-efficient cells with low emissions.
The technology Hydro has developed is becoming more and more energy efficient and help to reduce climate gas emissions per ton aluminium produced.
China is by far the world’s largest aluminium producer, and also has the highest growth rate.
How much aluminium is being produced?
In 2011, global production of primary aluminium reached about 44 million metric tons. Hydro’s primary production in 2011 was close to 2 million metric tons, which is 4.5 percent of the world’s production.
What are the environmental challenges when producing primary aluminium?
- Energy production and transmission – including greenhouse gas emissions
- Greenhouse gas emissions from the production process
- Emissions of fluoride, SO2, dust and PAH
- Liquid effluents
- Waste disposal
Energy supply issues
Because it takes a lot of energy to produce aluminium, energy costs constitutes a big part (20-40 percent) of aluminium production.
Development of a smelter has often been a trigger for developing a local power source, and vice versa. This is why most of the Norwegian smelters are located close to waterfalls, used to develop hydropower.
As several aluminium smelters are struggling to survive because of increasing power prices, it is a big challenge for policy makers to create regulations that make the best plants able to survive.
What impacts does energy production have on the environment?
Even though the power used to make aluminium is purchased in the market, our industry also has responsibility for the environmental footprint of power sources.
Hydro has an energy sourcing strategy with these priorities:
- Renewable power (in practice, hydropower)
- Gas power with high efficiency
If new plants should be built with coal as power base, we would like the geological conditions to enable carbon capture in the longer term.
How we plan to use less energy
Roughly 14 kilowatt hours of electricity are required to produce 1 kilogram of aluminium. That’s as much power as 30 TV sets use in one hour.
Thanks to its efficient production, Hydro currently makes primary aluminium at a lower cost than most other producers and is a leading supplier of refined casthouse products.
Improvements have reduced the worldwide consumption of electricity in smelters by 70 percent, compared to 100 years ago.
Hydro has ambitious plans to reduce energy consumption even more. In Årdal, Norway, we achieve 12.5 MWh/metric ton of aluminium produced, and the technology used is now ready for a full-scale smelter project.
Hydro is also exploring the opportunities to use heat recovery.
The aluminium plants in Sunndal, Høyanger and Årdal in Norway all deliver hot water for heating of public buildings and sport facilities.
Sunndal plant, Norway
Greenhouse gas emissions
The main greenhouse gases emitted from modern smelters is CO2, and the main source of this is the consumption of the anodes that are used in the production. In addition, small amounts of the highly potent greenhouse gases perfluorocarbons (PFCs) are produced through process disturbances called the anode effect. Hydro is minimizing the anode effect, mainly through good production systems and highly skilled operators.
Electricity to the smelter is nearly 60 percent of the overall CO2 emissions made by aluminium production (this number reflects world average emissions, except emissions from China), from the mine to metal.
Other air emissions
In addition to greenhouse gases, smelters also emit other gases.
In a modern smelter, the level of these emissions may be controlled to very low levels per metric ton of aluminium produced. Still, some smelters are so large that there may be some local impacts.
Fluorides are mainly emitted from the pots during interventions in the pots (like anode changing). Hydro’s smelters in Norway are in the world’s top league when it comes to low fluoride emissions. Fluoride emissions from modern smelters are not considered a health hazard to humans.
Sulfur dioxide (SO2) is emitted mainly from oxidation of the sulfur content in the anodes. The SO2 is often removed by wet scrubbing (such as with seawater). All of Hydro's Norwegian smelters, as well as the joint-venture aluminium plant in Qatar, Qatalum, have such scrubbers, removing 90-99 percent of the SO2.
Dust is mainly emitted from potlines and material handling systems. The finest dust particles may contribute to respiratory disorders, particularly in the work environment. Better dust control systems have reduced these problems significantly at most smelters in recent years.
PAH is a group of tar compounds that may cause cancer. Older potline technology causing PAH emissions has mostly been eliminated. Anode production is also a source of PAH, but more efficient systems have reduced these emissions to a minimum.
The Sunndal, Årdal and Qatalum plants use special oxidizers (RTO) to eliminate PAH in an energy-efficient way.
Water use in smelters
In many geographical areas, use of freshwater is constrained. To meet this challenge, water treatment systems that allow re-use of water have been developed. New smelters are often built with zero discharge of fresh process water; they only purchase the water they need to replace evaporation and other small losses. Qatalum has such a design.
Most of the Norwegian smelters are located in areas with lots of fresh water. These smelters are therefore using once-through cooling systems.
Waste from smelters
- Aluminium smelters generate solid wastes.
- Every 5-8 years, relining of the pots is necessary.
The carbon part of the spent potlining is considered a hazardous waste because of its content of fluoride, cyanide, PAH and reactive metals.
To minimize this waste, Hydro is working to make the pots last longer. Other industries can also use some of the spent potlining in their production.
The cement industry can use the carbon from spent potlines (SPL) as an energy source. At our joint venture at Albras in Brazil we deliver all the SPL to local cement plants, to be used as an alternative fuel and raw material.
Hydro’s objective is to eliminate landfilling of SPL within 2020.
Dross is residue removed from the casting process. The dross has a high content of aluminium, which is recovered in specialized recycling plants. This recovery process creates residue that contains aluminium oxide, salts and traces of metal. This waste is supplied as a raw material for different operators who makes product out of the residue after processing it.
In addition to the SPL and dross, aluminium production creates a number of other wastes.
Strict controls in the plants aim to reduce these wastes, make them useable in production, or make them useful in other industries.