Aluminium smelting is the process of extracting aluminium from its oxide, alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery.
This is an electrolytic process, so an aluminium smelter uses huge amounts of electricity; smelters tend to be located close to large power stations, often hydro-electric ones, in order to reduce the overall carbon footprint. Smelters are often located near ports, since many smelters use imported alumina.
"Final energy consumption in the global aluminium industry in 2007 was estimated to be 93 Mtoe. The industry is highly electricity-intensive. Primary aluminium smelters used just over 50 Mtoe of electricity in 2007, equivalent to about 4% of global electricity consumption. In total, the aluminium industry emits 0.4 Gt CO2-equivalent of greenhouse gases, including process emissions and indirect emissions from electricity production, equivalent to just under 1% of total global greenhouse-gas emissions (IEA, 2010)."
Given that primary aluminium production consumes about 20 times more energy as recycled aluminium and given that electricity consumption constitutes roughly one-third of the production costs, reducing electricity consumption is one of the industries R&D priorities. Aside recycling, several technologies to improve the performance of the aluminium production process are available, such as the use of inert anodes (instead of the conventional carbon anode). Inert anode technology is seen as one of the more promising options for the industry for the years to come.
There are three principal potential advantages in favour of developing a new cell technology with inert anodes:
- Cost reduction. All costs directly associated with the consumable carbon anode will then be eliminated, including the capital saving and raw materials costs by eliminating the need for the carbon anode fabrication, baking, and also the anode rodding plant. These cost savings may be significant. It has been indicated that there might be 25% to 30% lower capital costs for a new potline with inert anode cell technology.
- Environmental friendliness. Inert anodes would eliminate all greenhouse gas generation and emissions from the electrolysis cells. Smelters would no longer generate CO2, carbon monoxide, or perfluorocarbon gases (CF4 and C2F6), because carbon would no longer be used as anode material. Carbon residues (butts) will of course disappear. In addition, the fluoride and dust emissions during anode change will also be eliminated.
- Improved occupational health issues. Inert anodes would reduce the work practices associated with the present prebaked carbon anode change. The frequency of anode changes will certainly be drastically reduced with inert anodes. Working conditions in the pot-rooms would also be improved by avoiding all anode effects.
Aside from the anode, a basic Hall-Heroult electrolytic cell also comprises a cathode and electrolyte. So-called development and use of wetted cathodes in combination with inert anodes allows for lower anode-cathode distances. This in turn is accompanied by reduced voltages and lower energy consumption (estimates are in the range of 20-30% reduced energy consumption). The wetted drained cathodes is another advanced technology that would significantly improve the aluminium smelting process in the coming years.
Finally, carbothermic production of aluminium is one more advanced research which is currently underway which will revolutionize the smelting of aluminium. All these researches and technologies are more directed towards reducing the power consumption in smelting and impact on environment. Energy efficient process and impact on socio-economic development and environment protection are the primary objective in today’s world.
