Industry - Aluminum

Introduction CO2 emissions of EU industrial sector (2017) Alumina (known as aluminum oxide) is produced from Total CO2 (energy &industry - processes): 3,810 Mt bauxite ore which is the primary source of aluminum. Alumina is extracted from bauxite through the Bayer chemical process in the form of white powder. Alumina is 0.5% the main raw material for primary production of aluminum through the smelting process. In addition, alumina is also used as filler for plastic and production of automotive 76.0% 24.0% 23.5% paint. Large quantities of alumina are also used in refineries for the conversion of dangerous hydrogen sulphide into elemental sulphur. Primary Aluminum is produced through smelting (or reduction) plants, where pure aluminum is extracted from Industry alumina through the Hall-Héroult electrolysis process, Non-industry Non-ferrous metals Other industry whereby the reduction of alumina into liquid aluminum is operated at >950 °C under a high intensity electrical current. For this reason, many aluminum production plants are located near to dedicated, low cost, hydropower supplies to avoid energy losses – the layout and shape of the ‘busbars’ that carry the current is an important factor in reducing energy losses. Secondary Aluminum is produced from re-melting aluminum material recovered from waste streams and recycling process. The collected material is fed into a melting furnace operating at temperatures ranging from 700-760 °C.

Energy and emissions Technology CAPEX TRL Notes reduction

Best Available Techniques - Alumina - Bayer Process

Natural gas has the lowest specific emissions of 5% emissions all types of fossil fuels used in alumina Natural gas reduction No data 9 refineries. The change from oil-fired boilers to as fuel replacing oil (compared to oil-fired gas-powered steam generators can reduce boilers) carbon emissions by 5%.

Circulating fluid bed (CFB) calciners were introduced in 1961 as an alternative to rotary Fluidised bed 15% energy savings kilns. They have much higher energy efficiency calcination/ circulating 20 €/t (compared to rotary 9 than rotary kilns, since the heat recovery is fluid bed kilns) greater. CFB calciners are only applicable to smelter grade alumina.

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Tube digesters can operate at higher temperatures using a molten salt heat transfer medium, enabling plants to operate at lower energy consumption. Specific energy consumption (SEC) can be reduced from 10 GJ/t Tube digesters No data 30% energy savings 8 to below 7 GJ/t. However, tube digesters are unlikely to be compatible with the layout of most existing primary aluminum plants in the EU. Tube digestion is therefore virtually impossible to consider for existing plants for both cost and space reasons. There are many factors, such as the technical configuration of the plant or the quality of alumina they produce, that limit the applicability of such measures. Plate heat exchangers recover heat from the liquor flowing to precipitation. The potential heat recovery is higher than for other techniques such as flash Optimisation of the cooling plants. However, this technology is only refining process (plate Depends on the No data 9 appropriate for cases where energy from the heat exchangers, technique cooling fluid can be reused. The quality of the selection of the bauxite) bauxite ore has impacts on energy consumption. Bauxite with higher moisture content carries more water, which requires evaporation. In addition, bauxites with high mono-hydrate content needs higher pressure and temperature in the digestion process, leading to higher energy demand. In an alumina refinery, cogeneration uses waste heat to produce steam for the refining CHP can save 15% of process and power for all the electricity needed CHP and waste-heat co- primary fuel for the refining process and support systems. In 240 €/t 9 generation consumption of the a combined site with both an alumina and plant aluminium plant, the heat produced can be used in the Bayer process and the electricity for the electrolysis. Best Available Techniques - Electrolysis - Process Optimisation

An improved busbar design can compensate for magnetic fields that destabilise the alumina reduction process and increase electricity consumption. The design of busbar lengths and Magnetic compensation 200 €/t No data 9 cross-sectional areas will balance the magnetic fields, thereby allowing the optimising of the cell performance and the electricity consumption. This technology has no additional OPEX.

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Beneficial for heat balance and energy use. There are no additional operational costs. The exact nature of the upgrades differs by pot-line. These upgrades are typically implemented to Improved hooding 120 €/t No data 9 some extent, and they are almost always ventilation and suction possible. Total costs of optimisation can increase to around 650 €/t capacity, with modest additional operational costs of around 1.8 €/t.

Best Available Techniques - Electrolysis New physical designs for anodes can improve energy efficiency and complement inert materials. - Novel Physical Designs for Anodes

Sloped anodes and 2.0-2.5 kWh/kg Al Allow gaseous bubbles to perforated or “slotted” No data energy savings for 8 safely circulate in the molten cryolite bath. anodes slotted anode

Complementary design for the various Vertical electrode cells No data No data 9 electrode technologies.

Best Available Techniques - Electrolysis - Heat recovery from H- H off-gases

Retrieving the heat content of the off-gases of the H-H process, and then using it in the Bayer 3-5 GJ/t - 8 GJ/t Al For the Bayer Process No data 9 process to substitute fossil. Applicable when the (long term) smelter and rafinery are both located on the same site.

Use of waste heat in the local environment (e.g. via district heating system). Depends on the Heat recovery and use There is no major technological or scientific No data recovery technique 9 elsewhere hurdle to recovering heat. However, there can and end use be some other commercial or practical barriers affecting the cost-effectiveness of the measure.

Best Available Techniques - Anodes

13 mio €/250kt smelter CO2 and SO2 When natural gas is used to replace fuel oil, Use of natural gas 9 (52 €/t Al capacity) emissions decrease CO2 and SO2 emissions decrease.

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The application of enhanced furnace designs, with recuperative or regenerative burners, may result in fuel savings of 30-50%. Regenerators 30% (recuperative) - Recuperative or typically have a much higher investment cost 4 - 10 €/GJ 50% (regenerative) 8 to 9 regenerative burners and are designed for higher temperature and energy savings 24/7 operations.

OPEX: 0.2 €/GJ

The electrolysis Point Feeder Pre-Bake (PFPB) allows better process has a great control of the electrolysis process and is the potential to reduce most commonly used technology. The use of the emission of PFPB cells with automatic multiple feeding perfluorocarbons points is considered BAT for primary aluminium (PFCs) – potent GHGs Pre-baked Carbon production. Conversion to the state-of-the-art No data – formed during the 9 Anodes PFPB technology is the most accepted route for anode effect, i.e. when increasing operational and environmental the electrolyte efficiency for most systems. Over the past 20 becomes depleted of years, this has been one of the largest alumina. It also leads contributors to reduced GHG emissions from to 10-30% electricity aluminium smelting. consumption reduction Direct casting of the molten metal, with Best Available embodied heat in the aluminium transferred to Techniques - the alloying furnace. Best-practice electricity Downstream 180 mio €/250kt cast Considerable energy 9 use is estimated to be 0.35 GJ/t aluminium Aluminium - Transfer house savings ingot. Hot Metal to Alloying Furnace OPEX: 17.4 mio €/250kt cast house Simple and energy efficient heating process of The combined economic pre-made metal billets, including aluminium Best Available effect of energy savings and copper billets. Billets can be rapidly Techniques - and productivity Considerable energy 8 to 9 brought to a uniform temperature, thus Downstream - Magnetic improvements resulted in savings damage caused by surface overheating is billet heating a payback period of less prevented. Heating costs were reduced by 50% than two years. compared with conventional AC heating. Best Available Techniques - Secondary Gathering and re-melting scrap aluminium. Re-melting Applicable to the secondary aluminum industry 363 MJ/t energy that processes used aluminum, especially savings New de-coating coated aluminium. It uses the energy released 40 €/t Al (saves up to 50% on 9 equipment from volatile organic compounds to pre- heat fuel costs for scrap pre- the scrap to 480 ° C before it goes into the treatment) melting furnace.

Recuperative or In secondary smelters, the application of regenerative burners + enhanced furnace designs, with improved 4-10 €/GJ 30-50% energy savings 8 to 9 improved insulation, gas- insulation, recuperative or regenerative air trim, etc. burners, gas-air trim, etc. can save energy.

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Carbon Capture and Storage Absorbent-based carbon capture is a relatively well-characterized technology for major point sources of carbon emissions such a power plants, but has yet to be applied to an aluminium plant. This route is unlikely to be commercially viable for primary aluminium makers using the H-H process. Due to the inherent features of the effluents produced by Carbon Capture Using primary aluminium smelters, current 90 €/t CO2 + extra energy No data 3 to 4 Absorption Technologies approaches for CCS cannot be applied in a straightforward way. Furthermore, if novel electrolysis routes are implemented which do not emit CO2, CCS will be less viable. The sector specific challenge is to modify the existing process(es) so that one has fewer but larger/ higher concentrated pointsources of CO2, so that capture is both easier and more cost- effective. All on-site fossil-fuel powered plants operating Carbon capture and in the aluminium sector in EU are gas-fired CHP 90% emissions storage (CCS) applied to 425 €/kW capacity 5 to 7 plants. Their exhaust gases can be cleaned with reduction power plants CCS technology, capturing up to 90 % of the CO2 emissions from the gases.

Decarbonisation with Novel Techniques

Alumina generation from bauxite creates large quantities of a hazardous solid waste - red mud - with correspondingly high disposal costs. With some grades of bauxite, 2.5 t bauxite is needed to make 1 t Al + 1.5 t red-mud. A novel EAF The process converts a technology, Advanced Mineral Recovery hazardous waste into Technology (AMRT), can smelt red mud without Bauxite: Red mud two viable co- any pre-treatment, producing pig iron and treatment with novel products, also viscous slag suitable for industrial mineral wool. EAF technology and preventing accidental No data 3 to 4 The solid charge is fed into the ‘arc zones’ of Advanced Mineral discharge into rivers/ each electrode, where flash smelting takes Recovery Technology marine or water table. place. The red mud, with chemical exergy of (AMRT) It also offers a route 0.49 GJ/t Al, is replaced by saleable pig iron and for cleaning-up legacy mineral wool products, with total chemical red-mud. exergy 6.32 GJ/t Al. In total, the new proposed process for complete bauxite exploitation (for alumina, pig iron and mineral wool production) could increase the exergy efficiency from 3% in the conventional Bayer Process to 9-13%.

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High temperature carbo-thermic reduction of alumina is the only non-electrochemical process that has shown potential for aluminium production to date. Carbo-thermic reduction reacts alumina with carbon at high Alumina reduction: Technology not mature/ 20-30% energy savings 2 to 3 temperatures (>2000 ° C) to form aluminium Carbo-thermic Reduction No data and CO. Cost: 3000 €/t Al (-50% OPEX compared to conventional H-H smelting)

Market entry: 2050+ Kaolin is an alumina-silicate clay. Kaolin reduction for aluminium production pre-dates Aluminium reduction the H-H process. However, the process is still at from other raw Technology not mature/ 12-46% energy savings 1 to 2 R&D stage. This process could be good for the materials: Kaolinite No data EU as the EU has plentiful supply of kaolin, Reduction rather than relying on imported bauxite or aluminium metal.

Eliminates GHGs (HFC, PFC, CO2) produced by Inert electrodes would replace the energy- electrolysis with intense-to-make (and direct CO2 emitting) carbon anodes. 10%-30% lower carbon electrodes (anodes). Materials that have Electrolysis: Inert Instead, inert anodes (compared to 5 been considered for inert anodes include electrodes produce oxygen. For conventional anodes) metals, ceramics, and cermets. inert anodes with zirconia tubes, cell Market entry: 2030 energy losses reduced by over 60%.

"Wetting" refers to improved electrical contact between molten aluminium and the carbon cathode. A completely wetted cell lining that 20% energy savings Electrolysis: Wettable was also inert to the cell bath would allow the No data (for TiB2 composite 5 Cathodes anode to be brought closer to molten Al cathodes) without high magneto hydrodynamic (MHD) instability and molten aluminium to be drained out of the anode-cathode spacing. Removes the H-H process emissions. Instead of 55-72% emissions Electrolysis: The Elysis CO2, the process emits oxygen and replaces all reduction process (combination of point-source greenhouse gas emissions – CO2, No data (if electrolysis process 6 inert electrodes and PFCs and HFCs. is powered through wetted cathodes) renewable means) Market enry: 2025

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In the H-H cell, one needs to maintain a minimum distance between anode and cathode to avoid short-circuiting. However, the greater the electrode separation, the greater the cell Electrolysis: Application 20 mio €/250kt smelter resistance, which in turn consumes more of a dynamic AC 5-20% energy savings 3 to 4 (80 €/t Al capacity) electricity. The application of a dynamic AC magnetic field magnetic field significantly suppresses ripples in the molten aluminium, enabling smaller electrode separation and therefore reduce electricity use.

In current practice, electrolysis is performed at Electrolysis: Lower about 950 ° C, far above the melting point of temperature, while aluminium (680 ° C). No data 5% electricity savings 7 maintaining stable Extra operational cost: 75 €/t (cost of operations decreasing the electrolyte temperature by optimising its composition)

Offer energy savings of Existing Hall-Héroult (H-H) cells can have around 40% by: multiple anodes but only one horizontal operating at lower cathode, which is both capital and energy temperatures (around intensive. Multipolar cells offer benefits. They Electrolysis: Multipolar No data 700°C), 2 only work with inert anodes, due to the need Cells working at higher for a stable ACD, which in turn offer longevity (3 current densities, and y rather than 1 month for C electrodes), plus allowing better control emits O2 rather than CO2 (and other GHGs) as of heat loss part of the process. Ionic liquids are a range of non-conventional organic solvents, electrolytes and molten salts that have low melt temperatures, which could 15-85% energy savings replace H-H electrolysis, allowing the (compared to H-H electrolysis to happen closer to room smelting), reduces Electrolysis: Ionic Liquids No data 1 to 2 temperature rather than 1000 ° C. It Increases polluting gases (CO), bauxite-to-alumina conversion efficiency. It reduces solid wastes appears that ionic liquids could be more from spent linings suitable for electroplating products with Al rather than producing large quantities of primary Al.

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Secondary Al from recycled sources consumes only about 6% of the energy compared to primary Al. However, aluminum comes in a variety of different grades and quality (as well as impurities), which act as a major cost and implementation barrier. Economic scrap collection and sorting is key. Nowadays, physical sorting of scrap metal is more 94% emissions economical than melt refining technology. Any Potential life cycle cost reduction, successful, cost-effective technology would help Aluminium recycling: savings due to improved 12% energy savings improve overall recovery, plus act as a 5 Emerging Technologies secondary aluminium over current disincentive for EU to export > 1 Mt/y quality secondary production aluminium scrap to emerging economies, where techniques labour sorting predominates. Potential low-cost techniques for economic aluminium sorting include: - Fluidized bed sinks float technology - Colour etching then sorting - Laser induced breakdown spectroscopy (LIBS). LIBS appears as the most promising high volume/ high speed process, it is currently at demo stage. Most secondary aluminum is produced in ingots that are then shipped to rolling mills to be 84% energy savings made into final products. Mini mills are an (compared to current integrated design that eliminates several scrap-to-product Aluminum Mini Mills No data 6 energy-intensive re-heating/cooling steps. They recycling processing), can be located nearer population centres – substantial raw making better use of the scrap source material material savings – rather than shipping to developing countries for physical sorting.

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Complementary Tables

Table 1: General technology Efficiency Efficiency CAPEX 2020 CAPEX 2030 CAPEX 2050 prediction of costs and efficiency improvement 2030 improvement 2050 of typical alumina and aluminium- ( €/kW) ( €/kW) ( €/kW) (%) (%) making pocesses.

Alumina

Digestion 575 915 824 9 14 Source: Advanced System Studies for Energy Transition Project, Cyclones 280 927 678 11 17 PRIMES Model Technology Data (2018). Technology pathways in Precipitation 225 386 280 10 14 decarbonisation scenarios. Calcination 175 330 275 10 13

Primary Aluminium

Alumina refining 391 716 549 9 14

Smelting 534 1978 1875 15 21

Casting and Rolling 670 750 660 6 9

Secondary Aluminium

Srap processing 293 654 545 9 13

Melting Refining 567 945 859 9 13

Casting and Rolling 421 571 548 6 9

References

[1] Friedrichsen, N., Erdogmus, G. and Duscha, V. (2018). CLIMATE CHANGE Comparative analysis of options and potential for emission abatement in industry – summary of study. [online] Umweltbundesamt. Available at: https://www.umweltbundesamt.de/sites/default/files/medien/1410/publikationen/2018-07-16_climate-change_19- 2018_ets-7_analyse-minderungspotenzialstudien_fin.pdf [Accessed 25 Sep. 2019]. [2] Fraunhofer Institute for Systems and Innovation Research (ISI), ICF Consulting Services Limited (2019). Industrial Innovation: Pathways to dep decarbonisation of Industry. Part 1: Technology Analysis. [online] Available at: https://ec.europa.eu/clima/sites/clima/files/strategies/2050/docs/industrial_innovation_part_1_en.pdf [Accessed 7 Oct. 2019]. [3] Fraunhofer Institute for Systems and Innovation Research (ISI), ICF Consulting Services Limited (2019). Industrial Innovation: Pathways to dep decarbonisation of Industry. Part 2: Scenario analysis and pathways to deep decarbonisation. [online] Available at: https://ec.europa.eu/clima/sites/clima/files/strategies/2050/docs/industrial_innovation_part_2_en.pdf [Accessed 7 Oct. 2019].

[4] Advanced System Studies for Energy Transition Project, PRIMES Model Technology Data (2018). Technology pathways in decarbonisation scenarios. [5] United Nations Framework Convention on Climate Change (UNFCCC). “GHG Emissions Inventories 1990-2017, National Submissions,” 2019.

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