Steel scrap decarbonising cement
Dr Luis Escott is coordinating research at SaMI to gain a better understanding of scrap as a vital step in creating a circular economy within the steel industry.
The steel and cement industries are together responsible for almost a fifth of global carbon emissions.
Luis’ is working on the RECTIFI project which is bringing together the steel, cement, and recycling industries to significantly reduce these carbon emissions. RECTIFI stands for Reducing Embedded Carbon Through Transformation of Foundation Industries and the aim of the research is to avoid almost 5 million tonnes of CO2 from entering the earth’s atmosphere a year.
Materials analysis for industry
SaMI’s role is developing and implementing improved sorting processes to reduce enrichment of problematic residuals associated with melting scrap material. We will sort and characterise 3B scrap to improve our understanding of the scrap material, its sources, and contaminants.
From this we can identify, implement, and develop scrap sorting processes to improve the quality of scrap for steelmaking. This will help industry partners develop rigorous and objective material specifications for the new recycled material grades. It provides independently verified, fully transparent bulk materials analysis for those materials, together with life-cycle assessment of emissions saved during the project.
Decarbonising cement and steel
The UK consumes approximately 12 million tonnes of semi-finished steel and generates around 11 million tonnes of recycled steel per year. Currently, 80 percent of this recycled material is exported, with millions of tonnes of virgin iron ore imported in its place. Recycled material offers 85% lower embedded carbon when compared with steel production from virgin iron ore.
However, the percentage of recycled metal that major UK steelmakers like Tata Steel UK can add during steelmaking is limited. This is due to process technology and the presence of contaminating elements in end-of-life steel scrap which can restrict steel production. This is because tailored steel compositions often require high quality raw materials that can generally only be produced via primary steel production.
Therefore, better control of residual elements would improve scrap quality which would enable higher recycling rates and reduce the reliance and use of raw materials – a vital step in reducing carbon emissions during steelmaking.
Alternatively, by-products produced during metal recycling can also be utilized to decarbonise cement production through the development and use of mineral-rich products that can be used as an alternative raw material during the cement production process.
Improving scrap quality
At SaMI we are performing extensive sorting and characterisation of the scrap material to identify high residual material and determine the weight percentage of that material within the overall mass of scrap. We have melted large volumes of material using our Vacuum Induction Melting (VIM) furnace to gain a better understanding of the bulk chemistry of the scrap.
The VIM is unique in that it melts under vacuum or argon atmosphere which has the benefit of reducing slag formation during the melting process. This allows for a cleaner melting process which gives a better compositional representation of the melted scrap material and prevents key elements of interest from being oxidised and leaving the steel. Using optical emission spectroscopy (OES) we provide an accurate compositional analysis of the assay melt chemistry.
We are also developing a sampling method to determine whether a small volume of scrap material can accurately characterise a larger volume of material. In this case, taking a 60kg sample from a 6-tonne batch of scrap. This has the benefit of reducing the cost, time and energy currently used to determine bulk scrap chemistry.
By characterising the scrap, we have identified high residual material that is undesirable for increased scrap use for steelmaking. From this knowledge we have successfully implemented an improved sorting process to demonstrate that the quality of scrap can be significantly improved. This has the potential for allowing for larger volumes of scrap to be used.
This will help advance the steel industry in their decarbonisation challenge.
Contributor Luis Escott