The contrast is impressive: While the primary production of aluminum from bauxite requires about 14,000 kWh per ton, recycling needs only a fraction of this energy.

“Reprocessing secondary aluminum saves up to 95% of the energy that would be required for new production,” explains Dr. Michael Weber from the Institute for Metallurgy and Energy Systems. This efficiency makes the material an exemplary material for the circular economy.

The figures prove the growing success of secondary aluminum in industry:

• 59% of aluminum used in Europe already comes from recycling sources
• In the second quarter of 2024 alone, over 725,000 tons of recycled aluminum were produced in Germany
• Recycling rates of 90% in the automotive sector demonstrate the potential achieved

The market value for recycled aluminum is expected to grow to over 42 billion euros by 2028 – with annual growth rates of more than 8%.

“Aluminum can be recycled any number of times without loss of quality. This property makes it the ideal material for closed production cycles,” says Julia Berger from Aluminum Germany e.V.

Heat Management in the Recycling Process

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1. Thermal Pre-treatment

Before aluminum scrap can be melted, it undergoes several thermal pre-treatment steps. These begin with the removal of organic residues and coatings, which typically takes place in pyrolysis plants at temperatures between 400°C and 550°C.

“Purposefully utilizing the process heat from this phase was long a neglected aspect,” reports engineer Thomas Müller from Aachen Technical University. “Today’s modern plants recover up to 40% of this heat and use it to preheat the subsequent scrap material.”

In the decontamination of coated products such as window frames or facade elements, innovative processes are increasingly being implemented:

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• Low-temperature pyrolysis with precise temperature control to preserve the aluminum substance
• Catalytic oxidation of emissions for heat recovery
• Integrated heat exchanger systems for direct energy recirculation

2. Melting Process and Digital Optimization

The heart of the recycling process is the melting phase. In modern recycling plants, different furnace systems are used, whose efficiency significantly determines energy consumption:

“Digitalization has revolutionized the melting processes,” explains Dr. Sandra Klein from Speira Recycling GmbH. “Our AI-supported control systems adjust energy supply and process parameters to the respective scrap composition on a second-by-second basis.” This precision leads to energy savings of 15-22% compared to conventional plants.

A key element of modern melting plants is heat recovery from exhaust gases. Recuperative burners and heat exchanger systems recover up to 60% of the waste heat and feed it back into the process.

(Source: Adobe Stock)

3. Innovative Concepts for Waste Heat Utilization

Beyond the actual recycling process, leading companies are increasingly developing cascading heat utilization concepts:

Example: Integrated Energy System at Hydro Aluminum Recycling

1. Primary waste heat (>450°C) is used for steam generation
2. Medium temperature levels (200-450°C) serve to preheat raw material
3. Low-temperature heat (<200°C) is used for drying processes and building heating

This multiple use of process heat has reduced the Norwegian company’s total energy consumption by 34% and is considered a blueprint for the industry.

Technological Challenges and Solution Approaches

Alloy Diversity and Thermal Precision

A central challenge in aluminum recycling is the great variety of alloys in the source material. Depending on the application, aluminum scrap contains different amounts of silicon, magnesium, copper, or zinc. This variance requires precisely controlled thermal processes.

“The melting temperatures of different alloys can vary by up to 150°C,” explains Prof. Dr. Martina Weber from the Institute for Materials Research. “To avoid energy waste, we need to treat each batch individually.”

Advanced solution approaches include:

• Real-time spectral analysis to determine the alloy composition before melting
• Zone-tempered melting furnaces for different material classes
• Adaptive temperature control through self-learning control systems

Hybrid Energy Systems for Melting Processes

The decarbonization of heat generation is the focus of current developments. “We are increasingly implementing hybrid energy systems that can switch between different energy sources depending on availability,” reports energy manager Markus Schmidt from Recycling Technologies GmbH.

Particularly promising are:

• Electric-fossil hybrid solutions as transitional technology
• Power-to-heat systems for integrating volatile renewable energies
• First pilot plants with direct hydrogen firing

International Best Practices and Future Trends

Internationally, different approaches to energy-efficient recycling processes are evident:

Japan has established a closed “Can-to-Can” system for beverage cans that optimizes thermal processes for minimal energy consumption. Within 60 days, used cans are processed into new cans, with a sophisticated heat management system reducing energy consumption to 465 kWh per ton.

In Norway, aluminum manufacturer Hydro takes advantage of the country’s geographical benefits: Waste heat from recycling plants is coupled into fjord-water heat pumps and used for heating industrial plants and residential areas. With its “Circal” program, the company produces aluminum with at least 75% recycled consumer scrap and a CO₂ footprint that is 84% below the global average.

Germany is leading in the development of digital twins for thermal recycling processes. The virtual mapping and continuous optimization of the melting processes enables precise control of energy supply and reduces fluctuations in the production process.

Outlook: Complete Decarbonization of Thermal Processes

The future of aluminum recycling will be significantly shaped by the decarbonization of heat generation. Three key technologies are in focus:

1. Electrification of melting processes with electricity from renewable sources
2. Direct reduction with green hydrogen for specific applications
3. Biomass-based heat generation as a complement in integrated systems

“Complete climate neutrality of aluminum recycling is a realistic goal by 2040,” predicts climate researcher Dr. Elena Schmidt. “The technological foundations are in place; now it’s about widespread implementation and scaling.”

For process heat utilization, this means an increasing interconnection of industrial and municipal heat networks, in which aluminum recycling plants can function as central energy suppliers.

Conclusion: Thermal Efficiency as a Competitive Advantage

The optimized use of thermal energy in aluminum recycling is much more than an ecological contribution – it is developing into a decisive economic factor. Companies that consistently optimize their heat processes benefit from:

• Significant cost savings with rising energy prices
• Reduced dependence on volatile raw material and energy markets
• Competitive advantages through lower CO₂ balances and ESG conformity
• Development of new business fields in the area of thermal services

The example of aluminum impressively demonstrates how intelligent control of thermal processes and closed material cycles form the basis for a sustainable and competitive process industry. The insights gained can be applied to many other energy-intensive industries – an opportunity that we should use in the interest of both the economy and the environment.

Further Information and Sources

• Speira Recycling Services
• Aluminum Germany e.V.
• German Raw Materials Agency