Evaluation of the reduction of iron oxide from liquid slags using a graphite rotating disk
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of new iron smelting technology, socalled reduction smelting, seems to be an irreversible process due to the following three major advantages: (a) use of ordinary noncoking coals, which provides a great economic incentive for implementing such processes; (b) reduction in the number of units from at least three (banks of coke-ovens, sintering plant, and blast furnaces) to one or two units, which constitutes another economic reason for the development of these processes; (c) more effective environmental protection owing to the concentrated production and the capability of implementing ecologically oriented solutions, which should be more economical when compared to the costs of environmental protection associated with the conventional coke plant-sinter plant-blast furnace production line. The iron smelting technologies are not, however, easy for industrial implementation. This results not only from the understandable uncertainty of potential investors about completely new technologies but also from the complexity of the processes involved. In the proposed reduction smelting process,[1–5] the concentration of physicochemical phenomena increases the number of interacting variable factors, thereby, making the evaluation of those phenomena difficult in terms of possible complex thermodynamic equilibria and also the kinetic aspects of those processes. This complexity causes difficulties in the interpretation of experimental results in relation to the reduction mechanism. Nevertheless, the results of numerous studies have shown that the factors that limit the reduction of iron oxides from the liquid phase using a carbon-reduction agent are, above
´ Z, Adjunct Professor, is with the Technical University of JAN MRO Czestochowa, 42-200 Czestochowa, Poland. Manuscript submitted April 18, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
all, FeO diffusion in the slag phase[6–19] and Boudouard’s reaction.[20–25] An effective tool for evaluation of the kinetic aspects of the process involves the rotating disk technique.[26,27] The author has conducted studies on the reduction of iron oxides from liquid CaO-FeO-SiO2 slags using a graphite rotating disk at temperatures of 1350 ⬚C and 1420 ⬚C and at FeO concentrations of 20 and 60 pct. The values of diffusion coefficients and of the limiting, diffusion layer thickness have been determined.[28] Moreover, the rotating disk methodology has made it possible to reveal conditions in which Boudouard’s reaction starts to play a limiting role in the reduction process. The limiting reduction rate at which Boudouard’s reaction begins to be significant is dependent on the temperature, being approximately 10 ⭈ 10⫺6 mole FeOcm⫺2 ⭈ s⫺1 at 1350 ⬚C and approximately 15 ⭈ 10⫺6 mole FeO-cm⫺2 ⭈ s⫺1 at 1420 ⬚C.[28] The purpose of the present study is to evaluate the mass transfer coefficients and to calculate the reduction rate. Comparison of reduction rates obtained experimentally with results obtained by calculations will enable the verification of the calculated kinetic parameters using the rotating
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