Techn. Hochsch., Diss.--Aachen, 2006.

Zugl.: Hamburg, Helmut-Schmidt-Universiẗat, Diss.

Zugl.: Aachen, Techn. Hochsch., Diss., 2008

Techn. Hochsch., Diss., 2003--Aachen.

A considerable rise in the Electric Arc Furnace steelmaking has taken place in the EU during the last decade. As a result, the amount of steelmaking dust has increased as well. This dust is recycled in order to recover the valuable amount of zinc present in it. In contrast to the increase in dust generation, the capacity of recycling sites has not changed accordingly and there are growing concerns over this imbalance. In the present thesis, logistics and resource allocation of dust recycling in the EU are analysed. Data collected through a questionnaire survey was used to formulate the transportation model of linear programming. The results of the model highlight the location of gaps in recycling capacity and its uneven geographical distribution. The state of the recycling can be improved by research in scrap de-zincing; a process that can recover most of the zinc prior to steelmaking thereby lowering the total amount of dust. To this effect experiments were conducted using electro-galvanized scrap samples in order to study the kinetics of zinc evaporation. Various parameters such as the flow rate of carrier gas, scrap heating rate, packed bed voidage, permeability, and specific surface area were studied with a view of a possible scale-up of the process. The results show that there is a potential of integrating the de-zincing step into high temperature scrap pre-heating processes using shaft type systems that utilize off-gases of steelmaking and auxiliary burners.

A considerable rise in the Electric Arc Furnace steelmaking has taken place in the EU during the last decade. As a result, the amount of steelmaking dust has increased as well. This dust is recycled in order to recover the valuable amount of zinc present in it. In contrast to the increase in dust generation, the capacity of recycling sites has not changed accordingly and there are growing concerns over this imbalance. In the present thesis, logistics and resource allocation of dust recycling in the EU are analysed. Data collected through a questionnaire survey was used to formulate the transportation model of linear programming. The results of the model highlight the location of gaps in recycling capacity and its uneven geographical distribution. The state of the recycling can be improved by research in scrap de-zincing; a process that can recover most of the zinc prior to steelmaking thereby lowering the total amount of dust. To this effect experiments were conducted using electro-galvanized scrap samples in order to study the kinetics of zinc evaporation. Various parameters such as the flow rate of carrier gas, scrap heating rate, packed bed voidage, permeability, and specific surface area were studied with a view of a possible scale-up of the process. The results show that there is a potential of integrating the de-zincing step into high temperature scrap pre-heating processes using shaft type systems that utilize off-gases of steelmaking and auxiliary burners.

Eine umweltverträgliche Methode der Rückgewinnung anorganischer industrieller Abfallprodukte bietet die thermische Behandlung im elektrischen Lichtbogenofen. Hierbei wird der Abfallstoff geschmolzen und die enthaltenen Schwermetalloxide reduziert und von der mineralischen Phase abgetrennt. Der Prozess ist sehr energieaufwändig und noch nicht vollständig verstanden. Die laserinduzierte Plasmaspektroskopie (LIBS) soll als in situ-Messtechnik dabei helfen, das Verständnis zu verbessern und die Methode zu optimieren. In theoretischen Untersuchungen wurde gezeigt, dass die Güte von LIBS-Messungen durch Normierung auch mit einer gesättigten Linie eines Matrixelementes verbessert werden kann. Für LIBS-Messungen im elektrischen Lichtbogenofen wurde ein mobiles Doppelpuls-LIBS-System für industrielle Bedingungen entwickelt, getestet und optimiert. Als Modellsystem für Schlacken wurden dotierte Glasproben verwendet. Für festes und flüssiges Glas wurden Nachweisgrenzen im ppm-Bereich erreicht, was für die Gehalte in Schlackeproben ausreicht. Ferner wurden zwei Methoden entwickelt, Flüssigkeiten mit Hilfe von festen Standards zu quantifizieren. Um die Empfindlichkeit von LIBS zu verbessern, wurde Doppelpuls-LIBS untersucht. Es konnte eine Verstärkung des Signals um das 5,1-fache erreicht werden. Es konnten Emissionen der Moleküle CaCl, MgO, YO und ZrO in LIBS-Plasmen identifiziert und simuliert werden. Eine mögliche Verwendung der Molekülemissionen stellt die Quantifizierung sehr hoher Elementgehalte dar. Trotz der schwierigen experimentellen Bedingungen erwies sich das LIBS-System als empfindlich genug. Es wurde schrittweise Mangan- und Chromoxid zur Schmelze gegeben, was in einen linearen Anstieg der LIBS-Signale resultierte. Die Reduktion und Separation von Chrom gelang und konnte mit LIBS verfolgt werden, was durch die Referenzanalysen bestätigt wurde. / The reduction process in the electric arc furnace offers a sustainable method to recover industrial inorganic waste materials. The material is molten and the containing heavy metals are reduced and separated from the mineral phase. The energy consumption of the process is very high and the detailed reactions and dynamics are not yet fully understood. Laser induced breakdown spectroscopy can provide online-measurements inside a furnace, enabling us to increase understanding and optimize the process. In a theoretical investigation it has been shown that intensity fluctuations of LIBS can be compensated by normalizing the line used for analysis with a saturated line from a matrix element. For LIBS-measurements inside the electric arc furnace, a mobile double pulse LIBS-system designed for an industrial environment was built and tested. Glass was used as a model system for slags due to its lower melting point. Limits of detection in the ppm-region were achieved for solid and liquid glass, which is sufficient sensitivity for recycling slags. Furthermore, two methods were developed to quantify a liquid using solids as standards. To improve the sensitivity of LIBS, double-pulse measurements were conducted. Signal enhancements of up to 5.1 were achieved compared to single pulse. In the LIBS plasma emissions of molucules CaCl, MgO, YO and ZrO were identified and their emissions simulated. These emissions could be used to quantify large element concentrations. Despite the difficult experimental conditions the sensitivity of the LIBS-System has been found to be sufficient for recycling-slags. When stepwise adding manganese and chromium oxide to the melt, the respective LIBS intensity increased linearly. The reduction and separation of chromium was successful, which was confirmed by reference analysis.