There are two main types of aluminium smelting technology - Söderberg and Pre-bake. The principal difference between the two is the type of anode used.

Söderberg Cell:

Söderberg technology uses a continuous anode which is delivered to the cell (pot) in the form of a paste, and which bakes in the cell itself.

Prebake Cell:

Pre-bake technology uses multiple anodes in each cell, which are pre-baked in a separate facility and attached to rods that suspend the anodes in the cell. New anodes are exchanged for spent anodes - anode butts - being recycled into new anodes. The newest primary aluminium production facilities use a variant on pre-bake technology called Centre Worked Pre-bake Technology (CWPB). This technology provides uses multiple point feeders and other computerised controls for precise alumina feeding.

A key feature of CWPB plants is the enclosed nature of the process. Fugitive emissions from these cells are very low, less than 2% of the generated emissions. The balance of the emissions is collected inside the cell itself and carried away to very efficient scrubbing systems, which remove particulates and gases. Computer technology controls the process down to the finest detail, which means that occurrence of the anode effect - the condition that causes small quantities of perfluorocarbons (PFCs) to be produced - can be minimised. All new plants and most plant expansions are based on pre-bake technology.

Breakdown of technology types

Horizontal Stud Söderberg	4%
Vertical Stud Söderberg	13%
Side Worked Pre-bake	3%
Centre Worked Pre-bake	80%

Many IAI Members carry out continuous research into process improvements, particularly energy efficiency and emission levels, and some market their smelting technology.

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