Different alloying concepts to trace deoxidation products, mainly aluminium oxides, using rare earth elements (REEs), were tested on the laboratory scale by melting trials with a high-frequency remelting furnace. Lanthanum and Cerium, which belong to the group of light REEs, were used for these experiments. The formed multiphase inclusions were characterized by scanning electron microscopy with energy dispersive spectroscopy. Concerning the higher atomic numbers of REEs, traced non-metallic inclusions (NMIs) seem brighter than the steel matrix compared to deoxidation products. REE-traced aluminium oxides showed a primarily heterogeneous and almost globular morphology. The mean equivalent circle diameter of REE-containing NMIs is for all trials similar and is about 2 µm. The experimental results pointed out that the recovery rates of the various alloying concepts differ only slightly. In contrast, the values mainly depend on the surface-tovolume ratio and the amount of oxygen in the melt.
To meet the target for anthropogenic greenhouse gas (GHG) reduction, the European steel industry is obliged to reduce its emissions. A possible pathway to reach this requirement is through developments of new technologies for a GHG-free steel production. One of these processes is the hydrogen plasma smelting reduction (HPSR) developed since 1992 at the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben in Austria. Based on the already available publication of the methodology in this work, potential process parameters were investigated that influence the reduction kinetics during continuous charging to improve the process further. Preliminary tests with different charging rates and plasma gas compositions were carried out to investigate the impacts on the individual steps of the reduction process. In the main experiments, the obtained parameters were used to determine the effect of the pre-reduction degree on the kinetics and the hydrogen conversion. Finally, the preliminary and main trials were statistically evaluated using the program MODDE® 13 Pro to identify the significant influences on reduction time, oxygen removal rate, and hydrogen conversion. High hydrogen utilization degrees could be achieved with high iron ore feeding rates and low hydrogen concentrations in the plasma gas composition. The subsequent low reduction degree and thus a high proportion of oxide melt leads to a high oxygen removal rate in the post-reduction phase and, consequently, short process times. Calculations of the reduction constant showed an average value of 1.13 × 10−5 kg oxygen/m2 s Pa, which is seven times higher than the value given in literature.
The development of a carbon lean steel production process following the concept of direct carbon avoidance is one of the most challenging tasks the iron and steel industry must tackle in just a few decades. The necessary drastic reduction of 80% of the process’s inherent emissions by 2050 is only possible if a new process concept that uses hydrogen as the primary reductant is developed. The Hydrogen Plasma Smelting Reduction (HPSR) of ultra-fine iron ores is one of those promising concepts. The principle was already proven at a lab scale. The erection of a bench-scale facility followed this, and further scaled-ups are already planned for the upcoming years. For this scale-up, a better understanding of the fundamentals of the process is needed. In particular, knowledge of the kinetics of the process is essential for future economically feasible operations. This investigation shows the principles for evaluating and comparing the process kinetics under varying test setups by defining a representative kinetic parameter. Aside from the fundamentals for this definition, the conducted trials for the first evaluation are shown and explained. Several differences in the reduction behavior of the material at varying parameters of the process have already be shown. However, this investigation focuses on the description and definition of the method. An overall series of trials for detailed investigations will be conducted as a follow-up.
To counteract the rising greenhouse gas emissions, mainly CO2, the European steel industry needs to restructure the current process route for steel production. Globally, the blast furnace and the subsequent basic oxygen furnace are used in 73% of crude steel production, with a CO2 footprint of roughly 1.8 t CO2 per ton of produced steel. Hydrogen Plasma Smelting Reduction (HPSR) utilizes excited hydrogen states with the highest reduction potentials to combine the simultaneous reduction and smelting of iron ore fines. Due to the wide range of iron ore grades available worldwide, a series of hydrogen plasma experiments were conducted to determine how pre-reduced iron ore and iron-containing residues affect reduction behavior, hydrogen consumption, overall process time, and metal phase microstructure. It was discovered that, during the pre-melting phase under pure argon, wet ore increased electrode consumption and hematite achieved higher reduction levels, due to thermal decomposition. The reduction of magnetite ore yielded the highest reduction rate and subsequent hydrogen conversion rates. Both hematite and magnetite exhibited high utilization rates at first, but hematite underwent a kinetic change at a reduction degree of 80–85%, causing the reduction rate to decrease. In comparison to fluidized bed technology, it is possible to use magnetite directly, and the final phase of the reduction can move along more quickly due to higher temperatures, which reduces the overall process time and raises the average hydrogen utilization. A combination of both technologies can be considered advantageous for exhaust gas recycling.
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