Study on the foaming of CaO-SiO 2 -FeO slags: Part I. Foaming parameters and experimental results
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In order to understand the effect of slag composition on foaming in iron and steelmaking processes, slag foaming was quantitatively studied for CaO-SiO2-FeO slags in the temperature range of 1250 ~ to 1400 ~ It was found that slag foaming could be characterized by a foaming index (~), which is equal to the retention or traveling time of the gas in the slag, and the average foam life (q-). The effects of P2Os, S, MgO, and CaF2 on foaming were studied. As expected, slag foaming increased with increasing viscosity and decreasing surface tension. It was found that suspended second-phase solid particles such as CaO, 2CaO. SIO2, and MgO stabilized the foam and had a larger effect on foaming than changes in viscosity and surface tension for the slags studied.
I.
INTRODUCTION
THE foaming
phenomenon of molten slags in metallurgical processes has been observed and studied for a long time. Most of the early practical work on slag foaming was carried out to reduce or eliminate the foam in oxygen steelmaking furnaces, because the foamed slag prevents proper operation. On the other hand, the basic research on foaming was limited to a qualitative understanding of this complex phenomenon. Recently, slag foaming has become important not only for basic oxygen furnace (BOF) steelmaking but also for the modern electric arc furnace (EAF) and the new ironmaking processes ( i . e . , bath smelting). In modern electric furnace steelmaking, foaming practices are being widely used to shield the refractories from the arc. The foamed slag also stabilizes the arc and shields the metal from the atmosphere. The control of foaming height is required to maintain a steady operation. In the bath-smelting process currently being developed (smelting reduction), coal and iron oxide are injected into an iron bath; the main reactions are the cracking of the coal and the reduction of iron oxide in slag by solid carbon and carbon dissolved in metal. Therefore, a large amount of CO and H, gas is evolved when a high production rate is maintained, and violent foaming will be inevitable. On the other hand, the foamed slag plays an important role in heat transfer from the post-combustion flame to the metal in the process reactor. Therefore, the control of foaming is critical for these new processes. Since the prediction and control of slag foaming are required for current and future iron and steelmaking processes, a quantitative study of foaming is important. However, in previous work, It-41 foaming was described in terms of the surface chemistry, whereas foaming is a
KIMIHISA ITO, Research Associate, formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is with the Research Instxtute of Mineral Dressing and Metallurgy, Tohoku University, Sendai, Japan. R.J. FRUEHAN, Professor, is with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submttted May 19, 1988. METALLURGICAL TRANSACTIONS B
dynamic phenomenon of a special case o
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