ReDuce, ReUse, ReCycle, ReThink
The "NoWaste" strategy for steel
Each and every day our steel workers rise to the challenge of further optimising the steel production processes. In their day-to-day work they draw on their knowledge as high-temperature process engineers who control molten material such as steel and slag at temperatures of up to 1,650 °C. This expertise makes it possible to offer new solutions relating to material and thermal recycling for additional materials cycles. Georgsmarienhütte GmbH’s “NoWaste” strategy aims to ensure that, in future, only value-containing materials are transported across the plant boundaries and that they are utilised efficiently internally. Dumping the accumulated slag in landfill, for example, goes against the circulatory principle and should be avoided wherever technically and economically possible. At the same time, Georgsmarienhütte GmbH is working on new recycling routes for other materials and on options for closing the circulation for certain additional products. To date it has been possible to recycle the majority of the residual materials accrued at Georgsmarienhütte GmbH – a significant contribution to resource conservation.
Steel: best practice on three levels
For recycling, scrap steel need simply be collected and sorted. It can then be melted down again in the steel plant to make new steel, this time with very different material characteristics or in a higher quality grade. Scrap steel, which is predominantly utilised in the electric arc furnace process, thereby helps to minimise emissions from primary production via the oxygen steel process, which would otherwise be necessary. Almost half of all steel production in Germany is based on the use of scrap steel – in both routes. Steel thereby ranks among the “best practice” examples both in terms of utilisation and in terms of the circular economy and resource efficiency.
Recycling and reusing waste materials
Steel production via the electric arc furnace process at Georgsmarienhütte GmbH also operates on the principle of “NoWaste” – 100 per cent of the metal used is scrap. Basic thermodynamic and process-related factors unavoidably lead to the production of carbon dioxide and mineral residues. The non-ferrous metal industry would struggle to supply enough zinc without using the zinc-rich dust from the dust collection system of the electric arc furnace. Without it, the predicted shortage of mineable zinc ore would take effect far earlier than currently expected.
The black electric arc furnace slag (EAFS) produced when melting scrap in electric arc furnaces has been successfully used in road construction for many years. Its building physics properties are superior to those of natural materials in many respects. Until now, it has also been possible to use the secondary metallurgical slag (SECS) in road construction. This material is formed in the ladle furnace, which is located downstream of the electric arc furnace to improve the degree of purity. These recovery methods that have been evolved help to avoid the use of primary raw materials. Unfortunately, the potential of this slag in terms of the sustainable contribution it can make to resource conservation is still not sufficiently recognised in the political and social spheres.
In subsequent production processes such as casting and rolling the blooms into round steel, the steel surface reacts with atmospheric oxygen to form iron oxide (known as “scale”), which is mainly used as a replacement for iron ore in the integrated steel plants. Various mineral residues in the form of used refractory materials also occur, and these are needed to line the melting and transport units as protection against the liquid steel.
The steps of our “NoWaste” strategy
When developing our “NoWaste” strategy we first conducted a detailed residual material flow analysis at the steelworks. The priority here was the electric steel plant because that is where the biggest volumes are produced (see Fig. 2). As an initial measure, the residual material flows are carefully separated. Each residual material is, if possible, recorded separately at its place of origin and kept separate from the others. Only then is it possible to make purposeful use of the residual materials in internal processes.
For the filter dust and scale, the recovery methods used successfully to date remain unchanged. The filter dust is passed on to external processors for zinc recycling, and most of the scale is used in the integrated steel works as a replacement for iron ore. Under the “NoWaste” approach, a transformation process into higher-value materials is being developed for the remaining scale, which is currently still disposed of as waste.