The evolution of plant technology
The transformation to a climate-neutral foundry
When the first issue of AluReport was published in 2008, AMAG had already been focused on increasing the energy efficiency of high-temperature processes at its foundries for some time. While the introduction of the ISO 50001 energy management system in 2013 added a further dimension to these efforts, the vision of climate-neutral foundry operations had still not been formed. Nevertheless, AMAG faced up to the challenge of actively shaping this transformation several years ago and is now taking decisive action to prepare itself as effectively as possible.
Legal framework for achieving climate neutrality
The European Union (EU) has set itself the target of becoming climate-neutral by 2050. This means that all EU member states must reduce their net CO2 emissions to zero by the middle of the century. A variety of legal frameworks and initiatives were introduced as a result with the aim of reducing greenhouse gas emissions and promoting the transition to a low-carbon economy. These measures include:
- the European Green Deal [1] with its interim “Fit for 55” proposals [2] and the European Climate Law [3]
- the EU Energy Efficiency Directive (2012/27/EU) [4]
- the EU Emissions Trading System (EU-ETS) [5]
- the Carbon Border Adjustment Mechanism (CBAM) [6]
The Green Deal Industrial Plan [8] was introduced in 2023 as an extension to the European Green Deal of 2019.
It aims to increase the production of green technologies in the EU, ensuring that Europe is well prepared for the transition to clean energy. [9] The drive for decarbonization is supplemented by the long-established EU Emissions Trading System with corresponding carbon pricing and, as of October 1, 2023, the Carbon Border Adjustment Mechanism.Several years ago, as part of its efforts to meet these ambitious legal requirements, AMAG drew up and published a decarbonization roadmap. [7]It continuously updates and adapts this roadmap in light of current developments and changing legal frameworks.
Recycling as a key factor in climate neutrality
The strategy developed by AMAG to achieve climate neutrality and manufacture climate-neutral products examined the company’s activities and derived three pillars [7]:
- Further increase in recyclate content in AMAG alloys
- Further improvements in energy efficiency
- Substitution of fossil fuels with alternative energy vectors
All three points contribute to the manufacture of climate-neutral products. The second and third points, which focus on energy efficiency and replacing fossil fuels, will help make AMAG’s sites climate neutral. Aluminium recycling also represents a direct means of reducing the CO2 intensity of aluminium as it eliminates the need to produce new material.
Climate-neutral plant technology
The transition to climate-neutral technologies in foundries is particularly relevant to energy-intensive smelting and casting furnaces (Figure 1). Natural gas (NG) is the primary energy source used in such systems around the world, with the output of their heating systems typically ranging from 1 MW (in casting furnaces) to the double-digit megawatt range (in large smelting furnaces). The use of hydrogen (H2) represents a promising option for decarbonizing these furnaces, especially given their high power requirements.
Electrical heating systems are not suitable for processing scrap with organic deposits and are only available up to a maximum heating capacity of around 2 MW. Over the medium to long term, plasma torch technologies - which are currently under development - may also represent a suitable alternative for certain applications. There are a number of potential ways to use hydrogen as an alternative fuel:
- Adding hydrogen to the natural gas network, though this would only effect a marginal reduction in CO2 emissions
- Modifying existing natural gas burners to rely on pure hydrogen as the energy vector
- Replacing natural gas burners with specialized hydrogen burners that are optimized for efficient combustion of pure hydrogen
In stoichiometric terms, the combustion of hydrogen leads to significantly higher concentrations of water vapor in the furnace atmosphere and in exhaust gases compared to natural gas. For example, the combustion of H2 (energy vector) with air (oxidizer) almost doubles the H2O content in exhaust gases compared to the combustion of natural gas with air (see Table 1).
| Energieträger | Oxidationsmittel | H2O [vol.%] | CO2 [vol.%] | N2 [vol.%] |
|---|---|---|---|---|
| NG | Luft | 19 | 9 | 72 |
| NG | O2 | 33 | 67 | - |
| H2 | Luft | 35 | - | 65 |
| H2 | O2 | 100 | - | - |
The industrial use of hydrogen as an energy vector can also result in a variety of metallurgical and process-related changes due to the elevated water vapor levels in the furnace:
- Hydrogen absorption by the melt
- Dross formation during smelting and hot-holding processes
- Altered pyrolysis reactions and kinetics when smelting scrap with organic deposits
- Reduced durability of refractory materials
- Emissions
AMAG has initiated research projects in collaboration with the Montanuniversität Leoben to investigate these aspects in detail. This research includes both fundamental tests and industry-focused experiments. The insights gained from this collaborative endeavor formed the basis for industrial trials with hydrogen as an energy vector in 2023. The hydrogen content of the melt is a decisive factor in determining the quality of the produced metal. Due to its high reactivity, contact between liquid aluminium and H2O can result in the immediate formation of H2. The resulting hydrogen is then available for potential absorption into the melt. Increased water vapor partial pressures p(H2O) are therefore accompanied by an increase in hydrogen partial pressure p(H2), which is a decisive factor in theoretical hydrogen solubility. Figure 3 shows the influence of the smelting bath temperature and p(H2O) on the hydrogen solubility of a 5xxx alloy. These calculations were carried out using FactSage 8.1. An increase in the theoretical hydrogen content of the melt with elevated water vapor partial pressures in the furnace is evident. The rising equilibrium concentrations in Figure 3 very clearly demonstrate > the increased need for degassing units for hydrogen removal. In certain established process routes, however, such units fail to remove sufficient amounts of hydrogen from the melt. At present, degassing units are usually dimensioned for currently prevailing hydrogen concentrations. Particular attention has been devoted to this topic in industrial trials to date due to its significant influence on metal quality. The quantitative formation of dross is dependent on a number of factors. In addition to the type of furnace used, decisive factors include the level of organic impurities in the scrap and the size and shape of the material for smelting. Moreover, the influence of the furnace atmosphere on dross formation should not be underestimated. In principle, the findings of the basic research do not indicate increased oxidation due to elevated water vapor levels. [10] However, as these laboratory experiments relied on “static melts”, they should be considered in isolation from actual, observed behavior on an industrial scale. This is because experience has shown that bath movement and atmospheric turbulence from the gas burners can contribute significantly to an increase in dross formation. Furthermore, hydrogen burners may also influence the resulting emissions. In addition to pyrolosis emissions, it is important to pay particular attention to NOX formation.
AMAG conducts industrial trials as optimal preparation for the transformation
In 2023, AMAG conducted industrial trials in an effort to provide greater clarity into the questions outlined above, installing hydrogen burners in a rotary tilt furnace and a single-chamber holding furnace. Figures 4 and 5 depict the systems used in these trials, while (Figure 6) shows the gas supply from trailer-mounted hydrogen canisters. This is the only way to ensure a sufficient supply of hydrogen. Depending on the heating capacity of the furnace in question, the hydrogen required to smelt a batch within six hours can require six of the trailers shown here (Figure 6). This emphatically demonstrates that the only way to ensure a sufficient supply of hydrogen for industrial-scale production is with a suitable pipeline network. If European and Austrian policymakers hope to meet the proposed time frames for achieving climate neutrality, they must work swiftly to implement the requisite infrastructure and supply networks.
Industrial trials focused on the production routes for cast and wrought alloys. An examination of installed degassing capacity found that AMAG’s existing plant is capable of producing metal with a consistently high melt quality, even with higher hydrogen content in the melt. Elevated aluminium oxide levels were observed in the smelting process. Laboratory-scale investigations suggest that it is not the elevated water vapor content but rather the lack of CO2 that increases the melt’s tendency to oxidize in the altered furnace atmosphere. [13, 14] Although these tests found no significant effects on metal quality, it presents an economic issue in terms of metal yield. As for changes in process emissions, the experiments confirmed an increase in the NOX concentrations in dry exhaust gases.Further evaluation and discussion is required in conjunction with the manufacturers of burner systems to determine whether adapting these systems can achieve sufficient reductions in NOX concentrations and comply with current legal requirements.
In this context, it is important to note that statutory emissions regulations (on the use of best available techniques - BATs) will require adaptation to accommodate hydrogen as an energy vector.
Literaturverzeichnis:
[1] Communication from the Commission to the European Parliament, the European Council, the Council, the European Economic and Social Committee and the Committee of the Regions: The European Green Deal, Document 52019DC0640, https://eur-lex.europa.eu/resource.html?uri=cellar:b828d165-1c22-11ea-8c1f-01aa75ed71a1.0002.02/DOC_1&format=PDF[2] Communication from the Commission to the European Parliament, the European Council, the Council, the European Economic and Social Committee and the Committee of the Regions: ‘Fit for 55’: delivering the EU’s 2030 Climate Target on the way to climate neutrality, Document 52021DC0550, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52021DC0550 [3] Regulation (EU) 2021/1119 of the European Parliament and of the Council of 30 June 2021 establishing the framework for achieving climate neutrality and amending Regulations (EC) No 401/2009 and (EU) 2018/1999 (‘European Climate Law’), Document 32021R1119, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32021R1119 [4] Directive 2012/27/EU of the European Parliament of 25 October 2012 on energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC, Document 32012L0027, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32012L0027 [5] Directive 2003/87/EC of the European Parliament and of the Council of 13 October 2003 establishing a scheme for greenhouse gas emission allowance trading within the Community and amending Council Directive 96/61/EC (Text with EEA relevance), Document 32003L0087, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32003L0087 [6] Regulation (EU) 2023/956 of the European Parliament and of the Council of 10 May 2023 establishing a carbon border adjustment mechanism (Text with EEA relevance), Document 32023R0956, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32023R0956 [7] European Parliament, Carbon leakage: preventing firms from avoiding emissions rules, 30-06-2023, https://www.europarl.europa.eu/topics/en/article/20210303STO99110/carbon-leakage-preventing-firms-from-avoiding-emissions-rules [8] Pfeifer H. et al.: Energieeffizienz und Minderung des CO2-Ausstoßes durch Sauerstoffverbrennung. Stahl und Eisen 129, 2009, 51-62.[9] Kwaschny P. and H.-J. Meißner: Der Einsatz von Wasserstoff in Gießerein. Gießerei, 2021 (2021), 44-51.[10] Tichy, S., Pucher, P., Prillhofer, B., Wibner, S., Antrekowitsch, H. (2023). Hydrogen Absorption of Aluminum-Magnesium Melts from Humid Atmospheres. In: Broek, S. (eds) Light Metals 2023. TMS 2023. The Minerals, Metals & Materials Series. Springer, Cham. https://doi.org/10.1007/978-3-031-22532-1_122[11] Krone K.: Aluminiumrecycling. Vereinigung Deutscher Schmelzhütten, Düsseldorf (2000). [12] Bateman W., G. Guest und R. Evans: Decoating of Aluminium Products and the Environment. In: Eckert, E. C. (ed): Light metals 1999. Proceedings of the technical sessions presented by the TMS Aluminium Committee at the 128th TMS annual meeting, San Diego, California, February 28 - March 4, 1999. Warrendale, Pa.: Minerals Metals and Materials Society, 1099-1106. [13] Tichy, S., Doppermann, S., Pucher, P., Prillhofer, B., Wibner, S., & Antrekowitsch, H. (2024). Influence of Water Vapor on the Oxidation Behavior of Molten Aluminum Magnesium Alloys. In Light Metals 2024 (pp. 890-896). Springer Nature Switzerland.[14] Doppermann, S. (2023). Untersuchung des Oxidationsverhaltens von Aluminiumlegierungsschmelzen unter verschiedenen Atmosphären. Master’s Thesis, Montanuniversitaet Leoben.
