Aluminium is among the most sought-after materials, valued for its unique combination of strength, versatility, and lightness. Its value also lies in its resistance to corrosion and its electrical conductivity. For this reason, industrial sectors such as electronics, transportation, and construction require a continuous supply of aluminium.
At the same time, it is a highly energy-intensive industry that depends on stable and uninterrupted operations: its production relies on both energy efficiency and the reliability
of the power supply. In this context, power converters play a crucial role in ensuring grid stability and preventing disruptions in the production process.
Understanding the aluminium refining process
Aluminium derives from bauxite and its production require multiple stages: from the refining of the raw material, up to the refinement into pure metal. The production process of aluminium begins with bauxite mining, which is usually done via open-cut mining or simply removing the surface to reach the deposits. It is the main source of aluminum oxides. The next step is to extract alumina from refined bauxite, which must be smelted to produce aluminium metal. Refining typically involves the Bayer method, while smelting employs an electrolytic process called Hall-Héroult.
The Bayer method uses a high-temperature caustic soda solution to dissolve aluminium oxide. This process is called “digestion,” carried on in a pressure vessel to create a sodium aluminate solution. The clarification step removes impurities from that solution, resulting in aluminium hydroxide. This process produces a “red mud” as a byproduct, which must be carefully disposed of, given its toxicity.
After the clarification process, the aluminate solution forms alumina hydroxide crystals at the bottom of the tank. In the final step, called “calcination,” these crystals are washed to remove the remaining traces of sodium hydroxide, using a kiln to heat them up to above 1000ºC to eliminate water molecules, leaving a white powder of pure alumina.
The smelting process gives an electrolytic treatment to alumina in Hall-Héroult cells, diluting it in molten cryolite, using an electric current to separate the elements. The Hall-Heroult method was developed in 1886 by Charles Martin Hall and Paul Héroult, and it’s still dominant in the aluminium industry, delivering purity up to 99.8%.
Electrolysis is vital to this process, producing oxygen gas at the carbon rods (anodes) and reducing aluminium at the carbon lining (cathode). Since the molten aluminium is much heavier than the cryolite, it sinks to the bottom of the tanks, ready to be cast into ingots. This process requires a lot of electrical power, which is why power converters are crucial.
The role of electrolysis in aluminium production
The Hall-Heroult process is crucial for the efficiency and reliability of the entire production, ensuring high-purity aluminium as a result. Additionally, the Hall-Heroult process uses cathodes to extract and reduce aluminium ions, later forming molten aluminium. It also removes oxygen from the mix, turning oxygen ions into gas, producing carbon dioxide, and preventing oxidation.
The molten cryolite and aluminium oxide mixture then goes to a steel container with graphite, which provides the negative electrodes (cathodes). Positive electrodes (carbon anodes) are later added to the mix. This steel container is called an “electrolytic cell,” since it’s where the electrolysis occurs. The process results in reduced aluminium, and, as it’s heavier than the rest of the mixture, it decants to the bottom of the cell.
Albeit efficient, this method is very energy-demanding, meaning industries using it should have a reliable backup power supply and watch out for their carbon footprints. Since the chemical bond between aluminium and oxygen is very strong, much DC energy is required to set them apart during electrolysis.
Why power converters are essential in aluminium refining
Aluminium refining requires between 14,000 kWh and 17,000 kWh of electricity for each ton of aluminium (consider that energy consumption per capita in Italy is around 5,000 kWh). Indeed, it’s one of the most energy-intensive industries worldwide, and the Hall-Héroult process is responsible for much of this consumption.
To prevent any interruptions in productivity, often aluminium production factories need to combine different sources of power, not only to cope with the high energy demand but also to create a backup power in times of instability.
Within this scenario, the reliability of the power converters deployed to supply the electrolysis process is crucial to assure the continuity of production.
In this context, aluminium recycling represents a strategic alternative, capable of reducing costs by up to 95% compared to production from raw materials.
Benefits of high-efficiency power converters
Highly efficient power converters are vital in aluminium production: the more efficient they are, the lower the production cost will be.
Indeed, the benefits are many. For instance, a 5% increase in the efficiency of power converters can result in savings of up to 25%.
Key technologies in power conversion for aluminium smelting
Separating aluminium ions from oxygen isn’t an easy task, requiring advanced technologies for enhanced efficiency, reliability, accuracy, and sustainability. AC/DC rectifiers (diode or thyristor based) are so used to convert the oscillating AC to stable DC currents, required for the supply of the electrolysis process.
The main typologies for the rectifier are two: half-wave and full-wave rectifiers. The first type creates pulsating DC electricity by allowing only one AC half-cycle waveform to pass, while the second rectifies both halves.
Looking at the semiconductors, diodes allow a smooth energy flow in one direction while cutting currents that come in the opposite direction, blocking AC negative currents.
On the other side, Thyristor-based rectifiers use controlled switches to convert AC (alternating current) into DC (direct current), allowing to simplify the design of other critical components within the system (e.g. rectifier transformer). Such rectifiers are also called SCR or silicon-controlled rectifiers.
Additionally, modern digital control systems optimize rectifier performance by dynamically adjusting phase angles in real time, minimizing energy waste. These innovations are critical for operations where even minor efficiency gains translate to significant cost savings and lower carbon emissions.
FRIEM has been supplying high-quality power converters since 1950, consistently using the most advanced proprietary technologies. FRIEM understands that the majority of CO₂ emissions generated over the lifecycle of these systems occur not during manufacturing, but during operation. That’s why all supplied equipment undergoes Life Cycle Assessment (LCA), ensuring efficiency and a reduced environmental impact.
Moreover, FRIEM provides reliable technology to boost aluminium production, which is essential for the energy transition. FRIEM’s rectifiers are designed to ensure long-lasting efficiency and high reliability, even under the most demanding conditions, and are optimized for use with thyristors and diodes. In addition, the company offers lifetime after-sales support, further extending the lifespan of its products.