A cold model study of raceway hysteresis
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INTRODUCTION
I N ironmaking blast furnaces, hot air is introduced through the tuyere, in the bottom part of the furnace, at a high velocity, which creates a void space in front of the tuyere called a “raceway.” Due to the combustion of coke in the raceway region, a high-temperature region exists in the lower part of the blast furnace called the “bosh region,” also known as the “dropping zone.” The high thermal and chemical efficiency of the process are due to the intimate contact of the gas and solid. The aim of the process operation is to control the flow dynamics of the gas, solids, and liquids generated in the high-temperature zone of the furnace, so that reducing and heat-transfer potential of the gases are best used. The flow of gases from the raceway also causes the maldistribution of the flow of liquid metal in the lower part of the blast furnace.[1] It has been shown [2] that, as the raceway size increases, productivity of the furnace also increases. Due to the direct relevance of the raceway and dropping zones with the smooth and stable operation of the blast furnace, attention has been paid to understanding the physicochemical phenomenon occurring in these zones through experimental and theoretical studies.[3–13] First, physical study of raceway was done by Elliot et al.,[3] who used a real blast furnace and pointed out that raceway is basically a fluid flow problem. Subsequently, Wagstaff[4] and Wagstaff and Holman[5] provided the basic predictive correlation for raceway depth Dr as a function of particle S. SARKAR, Graduate Student, and G.S. GUPTA, Assistant Professor, are with the Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India. J.D. LITSTER, V. RUDOLPH, and E.T. WHITE, Professors, are with the Department of Chemical Engineering, The University of Queensland, St. Lucia, Queensland 4072, Australia. S.K. CHOUDHARY, Manager, is with the Research & Development Division, Tata Steel, Jamshedpur 831 007, India. Contact e-mail: [email protected] Manuscript submitted April 1, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
properties by performing the experiments. Since then, various correlations to predict the raceway size and shape have been proposed by various authors. The important correlations are summarized in Table I. From Table I, it is clear that each of the correlations shows a different dependence of Dr (raceway penetration depth) on the bed height (H ), particle size (dp), solid density (rs), blast velocity (Vb), tuyere opening (dt) and bed voidage (). The terms rg, S, AJ, and Am are gas density, particle surface area, tuyere area, and hearth area of the furnace, respectively. A few of these correlations[6,7] are based on theory that is based on the force balance between the momentum energy of the gas and the total weight of solids above the raceway. Other correlations are based on experimental results. The wide variation in these correlations indicates that the theory of this region is not yet understood. In most of these correlations, raceway shape ha
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