Aluminium smelting is a continuous electrolytic process that requires significant quantities of electrical energy.

Aluminium is highly reactive, which means that it forms very strong chemical bonds with oxygen; thus it takes a lot of energy to separate the two elements present in alumina (Al2O3). Typically, 13 to 15 megawatt hours (DC) is required to produce one metric tonne of molten aluminium.

Aluminium smelters therefore tend to be located close to sources of economical, reliable and plentiful long term power. Thus hydropower makes up a significant share of the industry’s energy consumption – around 40% globally.

The electricity is either purchased from a local, regional or national supplier, with a mix of power sources or a single source power station, or generated by the aluminium producing company itself, usually from a single power source. Around 30% of the industry’s electricity requirements are met by self-generated power.

Power Plants

In thermal power plants, chemical energy in the fuel is converted into heat energy through combustion (or heat energy is directly utilised, in the case of geothermal power). This energy (most often in the form of steam) is transferred to a turbine where it is converted into mechanical/rotational energy which in turn is converted to electrical energy using generators.

The efficiency of a steam turbine is limited by the maximum temperature of the steam produced and is not directly a function of the fuel used. For the same steam conditions, thermal power plants all have the same theoretical efficiency. Overall, if a system is on constantly (base load) it will be more efficient than one that is used intermittently (peak load). Aluminium smelters, which require a constant source of power, play an important role in maintaining base load. Smelters can also modulate their power requirements to a certain degree, thus giving power generators and distributors a base load and allowing them to meet peak demands from other consumers, municipalities and other industries.

Hydroelectric power stations harness the potential energy in a stored body of water by releasing it through one or more water turbines (mechanical energy), connected to electricity generators. While the cost of hydroelectricity generation is relatively low, making it a competitive source of renewable electricity, the capital expenditure required for construction of dams is significant. The presence, or co-development, of an aluminium smelting facility, that can be relied upon to draw a consistent base load of power, is therefore of benefit to both generators and also local communities, providing reliable, low emitting and safe power.

Rectification & Use

Generated power is in the form of alternating current (AC), but the Hall-Héroult process requires direct current (DC); therefore smelters transform AC into DC power using rectifier transformers, located within the smelting facility, for use in the aluminium reduction process. Some AC power is used by other processes and auxiliary services (such as fume treatment or heating & lighting) and the presence and scale of these varies between smelters.