Dr Stephen Spooner – Senior Research Officer, Swansea University, provides us with his reasons why the automotive recycling industry needs to focus on understanding the value of material retention and the processing potential of the cleaner products produced in order to move to a more sustainable future.
End of life automotive treatment is driven through multiple competing requirements; these include the safe disposal of potentially toxic, carcinogenic, and flammable materials, as well as the minimisation of loss to both value and material.
Historically, automobiles have been designed to be faster, safer, and more efficient, all of which are important in terms of advancement of the respective fields of engineering. However, these drivers have increased the complexity of vehicles in assembly, the variety of materials used and the requirements of their specification.
The largest material by mass used within the average automobile is steel, with almost a tonne used within the average family car. Let us take steel as a case study of the potential for improved end of life vehicle treatment: Steel application in automobiles is split between long, strip and speciality products, each part with its own requirements in strength, corrosivity resistance, ware, and fatigue performance.
The performance is dictated by a multitude of factors including the composition, the physical structure the atoms are arranged in and the fraction of entrained non-metallics captured in a separate phase during production processes.
With steel being such a major component within automotive manufacturing, it is quickly becoming a crux of transformation for the industry to reach environmental/sustainability performance targets. For several years, in-life CO2 emissions have been a factor in the design of automobiles, leading to efforts in light-weighting of vehicles. This understanding is quickly becoming obsolete as full life-cycle-assessment of products is developed as we see the vastly higher production emissions for materials such as aluminium and CCFP’s. With this in mind, there is an aim to produce more and more material through manufacturing routes based on circularity and where materials are both used less and kept in use for longer. Also, when the time comes for recycling, this is performed in a manner that allows the material to be reused within the same application.
With the drive to emission reduction, more and more steel is produced via scrap production routes such as the melting of scrap and reprocessing possible through the electric arc furnace (EAF). This production method can use almost 100% steel scrap as opposed to the currently dominant integrated blast furnace route, which must use a majority of iron ore and thus has higher emissions due to the need to react the ore with carbon to remove oxygen. This shift in focus has led to an international interest to improve both the productivity and the product quality manufactured via the EAF.
EAF has historically seen its major product as reinforcing bar. This steel functions as a vibration distributor within construction application, as such, it has product specifications that have been more than achievable with current practices around both production and scrap quality. However, with the drive for emission reduction, the EAF is quickly becoming the focus for future innovations in a diverse range of steel products that enable the semi-downcycling of scrap steel into reinforcing bar but also enable high specification, high-value product production. Thin strip steel is used for automotive body panellings amongst other applications. It has some of the highest constraints of steel application in both processability (given the thin gage that must be attained) as well as product performance as a customer-facing and safety-critical material.
Thus, thin strip steel products have tight constraints on the compositions tolerable for their manufacture, with elements such as copper, tin, chromium, nickel, and molybdenum (known as residual elements) all requiring tight constraints on acceptable levels. Standard strip production currently allows for around a cumulative 0.2 wt.% fraction of these residuals. When virgin iron ore is used in steel production, it has extremely low levels of these residuals. Thus, production methods have been able to meet requirements, however with the progressive switch to high percentage scrap-based EAF manufacture the content of these contaminants must be controlled to much higher degrees.
Figure 1 presents a potential future of how cumulative residual levels are expected to rise within steel scrap over iterative production cycles of steel within the UK based on a distribution of BF and EAF production with current practices around steel scrap quality. We can see that a shift beyond 40% production via the EAF is currently inhibited due to levels surpassing the 0.2 maximum value with any greater ratio of EAF use.
This current inhibition to further EAF production is a particular issue to the decarbonisation of both the steel industry and the life-cycle emissions of the automotive industry and its viability as a mass consumer market in a sustainable community.
Approximately 20% (2850 Kt) of ferrous scrap in the UK is produced from the UK’s automotive industry and is currently sold mostly as fragmentised scrap with a cumulative residual equivalence of 3.8. The typical quality of this scrap currently can be seen in figure 2, where there are visible levels of contamination such as copper wires, stainless steel, tin cans, and dirt. If this scrap can be brought to the level of quality similar to prompt scraps (those produced during manufacturing processes with low contamination), it would facilitate up to a 70% production of steel within the UK via the EAF. This would look like the shredded scrap shown in figure 3, which was produced by applying advanced shredding and sorting technology. This is a major shift in materials quality potential, and a significant reduction in CO2 emissions, with each tonne of steel produced in the EAF as opposed to the BF saving around 1.3 tonnes of CO2 generation.
Automotive steel scrap is only likely to increase in contamination if no intervention is made, reducing the potential of EAF steel production from where it is today. However, with a better understanding of material retention value and the processing potential of the cleaner products produced, end-of-life vehicles present a deliverable pathway to make significant step changes towards a more sustainable future across multiple sectors and industries.
The concepts discussed above sit within the wider research area my team are currently active in. Our focus is on zero waste circularity of materials, with a lilt towards the foundation industries as a major intervention point for the rapid impact we need in a time frame to make systemic changes before issues such as global temperatures and pollution go even further. Key to these initiatives is a quantifiable measurement, both of the materials themselves which I employ both standard and advanced characterisation tools, but also in the improvements to sustainability that are being generated. I believe dynamic measurable evolution of our understanding as to what a sustainable society will be, is key to enabling the long-term change and stability our world needs.
Acknowledgements:
The team would like to thank GB recycling, Tata Steel UK and Celsa Steel UK, for providing images. The team would also like to acknowledge funding from the EPSRC SUSTAIN steel research hub reference number: EP/S018107/1 for their support through ECR funding.
If you would like to contact Dr Spooner, please email him at s.r.a.spooner@swansea.ac.uk
