Several technologies (multipolar cells, novel physical designs for anodes, wetted cathodes, carbothermic reduction of alumina, and kaolinite reduction) offer energy efficiency potential, but many are still in relatively early stages of development.

Other areas for innovation are electrolysis demand-response, which could help with integrating variable renewable energy by providing flexibility services to the grid, and new physical recycling techniques that could increase scrap availability for secondary production.

Inert anodes for primary aluminium production

Using inert anodes would substantially reduce process emissions from primary aluminium production.

Technology principles: Primary aluminium smelting currently relies largely on carbon anodes, which produce CO2 as they degrade. Inert anodes made from alternative materials instead produce pure oxygen and do not degrade.

Multipolar cells

While conventional Hall-Héroult cells have a single-pole arrangement, multipolar cells could be produced with bipolar electrodes or with multiple anode-cathode pairs in the same cell. They could reduce energy consumption by 40%, owing to lower operating temperatures and higher current densities. Since the cells require inert anodes, process emissions from the use of carbon anodes would also decrease.

Technology principles: The Hall-Héroult method is currently the main commercial process for primary aluminium smelting. It uses electrolysis to separate aluminium from aluminium oxide (alumina) within a cell. The carbon-lined cell acts as a cathode, and an anode is dipped into the electrolyte bath contained within the cell. A current is passed from the anode to the cathode to separate the aluminium.

Novel physical designs for anodes

The physical design of anodes can be altered to improve the energy efficiency of Hall-Héroult cells. For example, sloped and perforated anodes make electrolysis more efficient by allowing better circulation within the electrolyte bath, while vertical electrode cells save energy by reducing heat loss and improving electrical conductivity. Energy savings can be considerable, with one source estimating that slotted anodes can reduce energy consumption by 2 kWh to 2.5 kWh per kg of aluminium.

Technology principles: The Hall-Héroult method is currently the main commercial process for primary aluminium smelting. It uses electrolysis to separate aluminium from aluminium oxide (alumina) within a cell. The carbon-lined cell acts as a cathode, and an anode is dipped into the electrolyte bath contained within the cell. A current is passed from the anode to the cathode to separate the aluminium.

Pulp & paper

Fuel switching and energy efficiency will be the primary mechanisms to cut CO2 emissions in the pulp and paper subsector. Innovation is also important, however.

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