Mathematical Modelling and Experimental Investigation of Coke Reduction of FeO in Slag

Mathematic model development and experimental investigations were carried out for the reduction of FeO in slag by coke. Rate expressions for the reduction limited by the different steps and through different reaction routes were proposed. In the experimental investigation, the FeO reduction was found to be a first order and irreversible reaction; the reduction rate increased with increasing temperature and the FeO content in slag, and decreased with increasing ash content in the coke. Low CO₂/CO ratio in the product gas and preferential reduction of FeO over SiO₂ in slag were observed in the reaction system. The proposed reaction mechanisms were discussed with the observed kinetic phenomena. The reduction of FeO in slag by coke was found most likely to be jointly dominated by the mass transfer of FeO in slag and the chemical reactions at slag‐coke, slag‐gas or slag‐metal interfaces.     

Recycling Waste Plastics in EAF Steelmaking: Carbon/Slag Interactions of HDPE‐Coke Blends

Due to the inherent limitations of current methods of plastic waste disposal, there have been concerted efforts worldwide towards developing alternative, environment friendly and economic recycling processes. With an aim to recycle waste plastics in EAF steelmaking, carbon/slag interactions for a number of blends made of metallurgical coke and HDPE (high density polyethylene) and an EAF slag (34.8 mass‐% Fe₂O₃) have been investigated at 1550°C using a sessile drop arrangement. The rate of gas generation showed an increase with increasing HDPE concentration, reaching a maximum for blend #3 (with appr. 30 % HDPE) and decreasing thereafter. Among all the blends investigated, blend #3 showed significantly higher levels of slag foaming as compared to metallurgical coke. HDPE‐coke blends also showed better wetting compared to metallurgical coke with contact angles in some cases improving from 140° to 70° after 10 minutes of contact. These results have been discussed in terms of ash and sulphur contents of carbonaceous residues and dynamic changes in slag composition. Industrial trials on blend #3 showed a good agreement with laboratory results. This work opens novel avenues for the utilisation of plastics wastes as a valuable carbon resource in EAF steelmaking.     

Investigation of Reduction and Smelting Mechanism in the Hi‐QIP Process

A new coal‐based reduction and smelting process for production of high quality iron pebbles in a rotary hearth furnace (Hi‐QIP Process) was developed. The reduction, carburization, smelting, and separating mechanism of the Hi‐QIP process were investigated. The experiments were carried out in a graphite heater furnace under rapidly heating up to 1773 K. A mixture of coal and ore produced molten metal and slag, which were held on the coal and did not come into contact with the refractory located under the coal layer. It is confirmed that the reduction of wettability between the iron and slag promotes the separation of them, when the content of FeO slag decreases. High productivity of the process is expected when using iron ore with small particle diameter and low gangue content. Favourable operating results were obtained in a pilot test using a rotary hearth furnace with a diameter of 7 m and a width of 1.5 m. This test demonstrated the possibility of continuous production of iron pebbles with high productivity (15t‐iron/d).     

New Methods for In‐Situ Determination of Iron Oxide in Steelmaking Slags

Although iron oxide is the most important component of steelmaking slags, no reliable technique for its in‐situ determination has been established yet. This paper however, presents data on the effect of iron oxide on the electrical conductivity of CaO‐SiO₂‐FeO‐Fe₂O₃ melts, and on limiting current and impedance in direct current or alternating current charge transfer at iron electrodes. The strong influence of iron oxide content can be utilized for in‐situ determination of total iron oxide content and Fe³⁺/Fe²⁺ ratio. The possible probe designs are presented and the principles and procedures of the measurement are explained.     

Plasma Reduction of Iron Oxide by Methane Gas and its Process Up‐scaling

This paper investigates the characteristics of the methane plasma reduction of iron ore in comparison to that of the hydrogen plasma reduction process. Although hydrogen plasma smelting reduction (HPSR) has potential advantages as a steelmaking alternative in terms of simplicity (less operation units) and less harmful detrimental environmental implications, its high cost has a negative influence on its usage. In this regard, natural gas (> 96 % methane) could be adopted in the field of plasma smelting reduction. A brief comparison between hydrogen and methane options has been carried out experimentally. Heat and mass balance models were conducted to explore the features of up‐scaled processes with respect to consumption figures and CO₂ emissions. It was found that the methane plasma is a good alternative iron oxide smelting process.     

Adhesion and Thermal Shock Resistance of Al2O3 Thin Films Deposited by PACVD for Die Protection in Semi‐solid Processing of Steel

In this work thin Al₂O₃ films were deposited on hot working steel AISI H11 by plasma assisted chemical vapour deposition (PACVD). The effect of the AlCl₃/O₂ ratio in the gas mixture and the substrate temperature on the film hardness and constitution of the deposited films was investigated by nanoindentation and X‐ray diffraction, respectively. Within the investigated process parameter window thin films containing either the γ‐Al₂O₃ or the α‐Al₂O₃ phase were grown. The performance of these Al₂O₃ coatings for the semi‐solid processing of steel was studied with respect to hardness, adhesion and resistance to thermal shock. The maximum critical load of 50 N as determined by scratch testing was achieved after plasma nitriding of the substrate. No cohesive or adhesive coating failure could be detected after 1000 thermal shock cycles at a contact temperature of 1170±30 °C. Based on the here presented adhesion and thermal shock data it can be concluded that the Al₂O₃ thin films are suitable candidates for the die protection during semi‐solid processing of steel.