Smart scrap sorting for green steel

In high demand

There are many different sources for these enormous quantities of scrap: the scrap iron container at the building yard, disused railroad wheels, end-of-life vehicle bodies or carrier scrap. Our own scrap is also generated during production. However, not all scrap can simply be used as it is classified and only certain types may be used. In order to produce high-quality steel, the scrap must also be of a correspondingly high quality. One of the quality factors is the amount of trace elements in the scrap. The limits for trace elements in the product standards or specifications are sometimes very low, which also limits the usability of individual scrap grades. It is therefore an important goal to increase the quality of the scrap with regard to the contained but sometimes undesirable by-elements.

Recyclable material re-sorted

In a research project, voestalpine Stahl Donawitz therefore initially tested laser-based real-time analysis for scrap sorting with a partner company at a pilot plant. The aim of smart scrap sorting was to get the best out of the recyclable material and make new scrap grades accessible in order to achieve a high-quality product. As part of the project, the accuracy of the steel analysis was increased and adapted to the purposes of voestalpine. The results were verified and further optimized in melting tests in the Technical Metallurgy Laboratory (TechMet) and Metallurgy Laboratory (MetLab) at voestalpine Stahl Donawitz. Around forty tons of scrap were precisely analyzed and melted down for research purposes.

Scrap analyzed with laser sharpness

In practice, the smart scrap sorting system works as follows: Shredded, cut or shredded scrap is mechanically separated on a vibrating chute and fed onto a conveyor belt running at a speed of up to 3 m/sec. A laser cutting process is then used to determine the position of the parts to be analyzed on the measuring belt and the "landing point" for the analysis. To do this, the surface is first cleaned of coatings, etc. with a large number of individual laser pulses. With a second burst of laser pulses, plasma is generated from a small volume of the sample, the emitted light of which is used for the actual chemical analysis. This process is called LIBS (laser induced breakdown spectroscopy). A targeted jet of compressed air then sorts and separates the parts according to the previously programmed specifications. After around one and a half years of project work, during which the analytical concept was tested in practice on the test facility, the project team was finally satisfied with the results.

EU-weit geforscht: Projekt PURESCRAP

It was clear to the project team from the outset that the technology and the concept should nevertheless be continuously developed and that potential applications should be defined even more precisely. At one of our cooperation partners, two processes are currently being examined on the smart sorting system implemented there: LIBS and X-ray fluorescence analysis (XRF). voestalpine Stahl Donawitz is now also part of the EU project PURESCRAP - Purity improvement of scrap metal. The aim of the project is to increase the utilization of low-quality scrap (post-consumer scrap) through the use and application of innovative sensor combinations and analyses - supported by artificial intelligence. A pan-European consortium of twelve companies - from Sweden to Belgium and Italy - is working intensively on the various aspects of the process in order to further develop the steel cycle as one of the key factors of industrial sustainability.

• What significance does smart scrap sorting have for sustainability?

  Scrap is a major issue when it comes to reducing emissions and sustainability in steel production. The more scrap is used, the lower the CO₂ emissions. Reusing the recyclable material therefore conserves resources and is precisely the step we need to take to mitigate the increasingly noticeable consequences of climate change. Technology and metallurgy make a valuable contribution to manufacturing high-quality products and protecting the environment at the same time.

• A lot is happening in the smart scrap sorting project. What insights have you gained from the latest activities

  We can already see that multi-stage sorting offers great potential. The scrap is first cleaned using conventional methods such as magnetic separation. Only in the final step do LIBS or XRF separate the wheat from the chaff.

• Where do the impurities in recyclable scrap actually come from?

  It is impossible to imagine modern cars without features such as electric windows or electric seat adjustment. Numerous electric motors are required for these functions and one of the main components of these motors is copper wire. During conventional processing, the steel scrap is contaminated with copper, for example, and the content of this disruptive element in the scrap as a raw material is therefore constantly increasing. These interfering elements can no longer or only partially be removed from the steel production process, which limits the amount of valuable raw material that can be recycled.

• What challenges in the project are you particularly concerned with?

  Linking all the sensors and systems is very complex. In addition, there are several methods for analyzing the scrap that are currently being tested. Adapting the measurement technology to the specific voestalpine purposes and integrating and linking all systems is one of the major challenges of this project.

• Can voestalpine Stahl Donawitz manage smart scrap sorting on its own?

  We work closely with our cooperation partners to obtain the enormous quantities of good primary material we need for sustainable steel production. The limited space available would not allow us to process such huge quantities of steel in Donawitz.