About UsOur productThe smelting process

To make aluminium, large blocks of carbon called ‘anodes’ are placed into a special bath material containing alumina. An electrical current is passed through, leaving behind molten aluminium. This is then cast into different shapes, ready to be sold on to customers.

This process is called an electrolytic reduction reaction, and is known as the Hall-Heroult process.

BSL obtains its alumina from QAL, transporting it direct via a conveyor 10 kilometres long. Around 3,000 tonnes of alumina is consumed daily to make 1,560 tonnes of aluminium.

BSL has three major sections:

  • carbon plant, which make the carbon ‘anodes’ crucial to the process
  • reduction lines, where the electrolytic reduction reaction occurs
  • metal products, where molten aluminium is cast into its final product, ready to leave the smelter.

Carbon

Carbon anodes are made from petroleum coke, liquid pitch and recycled carbon from ‘spent’ anodes. They resemble large black bricks, each weighing up to 1.4 tonnes. They are baked for 18 days in large furnaces in an ongoing production line at finely controlled temperatures increasing to 1250 degrees Celsius. The baking process makes them conductive, meaning that when electricity is applied, the vital electrolytic reduction reaction will take place.                        

When the carbon anodes have finished baking, they are attached to aluminium rods which conduct electricity and support the anode in the reduction cell. They are taken to the reduction lines, where they are lifted into cells where they become part of the electrical circuit and ultimately make aluminium.

BSL has two carbon bake furnaces, one of which was recently upgraded and the other was brand new in 2012, costing $330 million alone. The new carbon bake is a cleaner technology, dramatically reducing greenhouse gas emissions while also producing better quality anodes with less gas.

The new carbon bake furnace and upgrades to the existing bake allowed for the decommissioning  and demolition of BSL’s original carbon bake furnaces 1 and 2.

Reduction

Reduction cells, which contain the carbon anodes, are filled with a special bath of molten cryolite. Alumina is fed into the reduction cells, where it dissolves in the bath.

A strong electrical current is then passed through the reduction cells. The current causes oxygen in the alumina to react with the carbon anodes, creating carbon dioxide. At the same time, hot liquid aluminium is separated from the oxygen and sinks to the bottom of the reduction cell.

Around 230,000 amps are used for Reduction Lines 1 and 2, and around 360,000 for Line 3.

Carbon anodes have a life cycle of around 26 days in a reduction cell before needing to be replaced. The remaining carbon is recycled to make new carbon anodes.

Metal products

Hot liquid aluminium is siphoned from the reduction cell into pre-heated containers called ‘crucibles’. The crucibles, which carry ten tonnes of molten aluminium at a time, transfer the aluminium to holding furnaces. The metal cools in a controlled environment  in the holding furnace from more than 950 degrees Celsius to a little over 700 degrees Celsius. It is then poured into moulds and cast into various products.

Smelting

Carbon anodes being  attached to aluminium rods

anodes

Reduction cells

reduction

Molten aluminium

molten aluminium