Alcoa Renewable Powered Electric Calcination Pilot

Summary

Need

Alumina is produced from bauxite in a two-step process. Firstly, bauxite is digested in the Bayer process to produce alumina hydrate. Secondly, alumina hydrate is calcined to produce alumina. The calcination process uses high temperatures to remove chemically bound water from the hydrate. Conventional calcination combusts natural gas to achieve the high temperatures required. Much of the energy used in calcination is exhausted as water vapour (i.e. steam), which results in a low process efficiency. The steam is not recycled in the conventional alumina refining process because it is contaminated with exhaust gasses from the combustion of natural gas.

Electric pressure calcination could potentially eliminate fossil fuels in the calcination process by using renewable electricity to heat the hydrate under pressure. Since there is no combustion of natural gas, electric calcination produces pure, uncontaminated steam exhaust, which can be captured, recycled and utilised in the Bayer process, reducing demand for steam from natural gas boilers. Alcoa estimates that electric calcination by itself could potentially reduce Australian alumina refining emissions by 40% when powered by 100% renewable electricity.

Action

The Alcoa Calcination Pilot will be delivered in two stages. Stage 1 will investigate the techno-economic feasibility of integrating electric calcination powered by renewable energy in Australian alumina refining processes and consider the commercialisation pathway under retrofit and growth scenarios. Stage 1 includes design and construction of a Stage 1 Field Pilot at Alcoa’s Pinjarra Alumina Refinery and preliminary engineering for a Stage 2 Field Pilot. The Stage 1 Field Pilot will have the following characteristics:

• a small electric heating vessel including a steam fluidised bed
• the capacity to calcine approximately 200 kg/h of alumina
• power demand of up to 140kW
• operate at a temperature range up to approximately 850°C.

Stage 2 involves the detailed design, procurement, construction, operation and performance testing of the Stage 2 Field Pilot at the Pinjarra Alumina Refinery in Western Australia. The findings will inform the commercialisation pathway and technology development for the technology. The Stage 2 Field Pilot will have the following characteristics:

• the capacity to calcine approximately 2000 kg/h of alumina
• power demand of up to 1400 kW
• electrically heated molten salt to supply indirect heat for the calciner
• operate at a temperature range up to approximately 850°C.

Outcome

The project aims to:

1. Improve understanding of the techno-economic feasibility of electric calcination powered by renewable energy as a low emissions technology under growth and retrofit scenarios in Australia.
2. Improve understanding of the economic benefits that electric calcination powered by renewable energy can achieve through increased load flexibility and the provision of Western Australian South-West Interconnected System Essential System Services.
3. Demonstrate techno-economic performance of electric calcination powered by renewable energy at pilot scale within an operational alumina refinery to de-risk technology development.