Interfacial reactions occurring between molten iron and carbonaceous materials are of great significance in the steel industry, and specifically, the reaction of iron with metallurgical coke is one of the key phenomena occurring during blast furnace ironmaking. Major operating parameters such as hot metal composition will be directly influenced by the reactions occurring between liquid iron and coke. In the current investigation, the interfacial reactions occurring between coke and liquid iron were studied at a temperature of 1550°C using the sessile drop method to further the understanding of the fundamental reactions occurring at the interface between coke and iron. The formation of interfacial reaction products was observed, and time-dependent reactions were identified. The transfer of elements such as carbon, sulfur, and silicon was determined. The reduction of silica was determined as having a major influence on the transfer of both silicon and carbon into liquid iron.
Carbon-dissolution studies were carried out on four coal-chars (ash content ranging from 9.04 to 12.61 wt pct), using the carburizer-cover method, and the rates of carbon transfer into liquid iron at 1550°C were determined. A theoretical model was developed for estimating the interfacial area of contact between the chars and the liquid iron. Using a force-balance approach, the partial penetration of the particles was calculated numerically and the total solid/liquid contact area was evaluated for a range of system parameters. The wettability was found to have a very significant effect on the area of contact. An improvement in wetting reduced the upward force due to surface tension, thereby increasing the downward penetration of particles in the liquid and the contact area. While two chars showed a monotonic increase in carbon pickup by the liquid iron, a two-stage behavior was observed for the remaining two chars. Stage I, which corresponds to short times of contact, showed a much higher rate of carbon dissolution, as compared to stage II during later times. The slow rate of carbon dissolution in stage II was attributed to high levels of interfacial blockage by reaction products, which resulted in many fewer areas of contact between the carbonaceous material and the liquid iron. Firstorder dissolution rate constants (ϫ10 3 ms Ϫ1 ) were computed for stage I in all chars, and the observed trend was as follows: 0.01795 (Char 1) Ͼ 0.00954 (Char 4) Ͼ 0.0061 (Char 3) Ͼ 0.00274 (Char 2). These results compare well with the dissolution rate constants quoted in the literature. Char 1, which had the highest rate constant, also had the lowest concentration of reducible oxides (e.g., silica) among all chars. The consumption of solute carbon through silica reduction could affect the carbon levels in the liquid iron. Due to reduction reactions, the experimentally measured rates of carbon dissolution are expected to be slower than the inherent rates of carbon dissolution into the liquid metal. This study shows strong evidence that chemical reactions at the interface play an important role in determining the rate of char dissolution into liquid metal.
Using the sessile drop approach, interfacial reactions taking place in the iron/carbon interfacial region were investigated at 1 550°C in a horizontal tube resistance furnace with an argon atmosphere. Two coalchars, labelled as 1 and 2 with respective ash concentrations of 10.88 wt% and 9.04 wt%, and electrolytically pure iron were used in this study. Liquid iron droplets were exposed to chars at high temperatures for times ranging between 1 to 180 min and the assembly was then withdrawn into the colder section quenching the droplet. To examine the time dependant growth of new phases formed in the interfacial region, FESEM and EDS investigations were carried out on the underside of the droplet, which effectively represents the iron/char interface. The transfer of carbon and sulphur into the iron droplet was also determined using a LECO Analyser. Interfacial regions for both chars showed a high occurrence of ash deposits, which were found to increase with time. Al, Ca, S, O, Fe were also detected in EDS analysis of the interface. However very low levels of Si were found in the interfacial region despite high concentrations of silica in the chars initially suggesting chemical reactions involving silica. After three hours of contact, carbon pick-up by liquid iron reached only 0.12 wt% and 0.28 wt% for Char 1 and Char 2 respectively, both of which were much below the saturation level of 5.6 wt%. These results are discussed in terms of the formation of interfacial products, the consumption of solute carbon by reducible oxides and low intrinsic rates of carbon dissolution from non-graphitic Chars.
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