Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters
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I.
THE top and bottom blowing processes imply different oxygen transfer mechanisms to metal and slag. Consequently the main steel-making reactions taking place in bottom blown converters seem to differ widely in a kinetic sense to those of top blown processes. Investigations have revealed that these differences are due to the much stronger stirring action provided in Q-BOP baths as compared to those of LD fumaces. Metallurgists 1-~'6have observed these facts through qualitative studies while quantitative evaluations are very few. A quantitative interpretation of these differences has been attempted in this paper on the basis of cold model experiments. Three types of experiments have been conducted. Firstly, the mixing time has been determined in a model vessel. Secondly, the amount of bath agitation has been studied through measurement of splashing and spitting as one of the criteria. Finally, overall mass transfer coefficient between slag-metal has been evaluated. The variable parameters for all sets have been gas flow-rate, bath depth, and tuyere configurations. II.
TRACER INJECTION
INTRODUCTION m
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Fig. 1--Experimental apparatus of water model and set-up for measurement of tracer dispersion.
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A. Measurement of Mixing Time
S. PAUL is Research Scientist with Usha Martin Black, Ranchi, India. D.N. GHOSH is Professor, Department of Metallurgical Engineering, Indian Institute of Technology, Kharagpur 721 302, India. Manuscript submitted October 16, 1984.
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EXPERIMENTAL
The mixing time was measured with a conductimetric probe located on one side of the vessel (Figure 1). The probe was employed to monitor local changes in the conductivity of water after 10 ml of 20 pct KC1 solution was added, as a pulse of input on the other side of the vessel. The probe was made of two platinum electrodes (0.1 cm ~b x 1.0 cm) separated by a distance of 1.0 cm. Mixing time was defined as the time beyond which changes in the conductivity are less than 5 pct of the steady-state. The time was recorded on an X-Y recorder (Figure 2). Three experiments per operat-
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Mixing Time 5 secs . . . . TIME, SECONDS
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SCALE X = 0.5 sec/cm Y = 10 mv/cm
Fig. 2--Graphical representation of measurement of time of mixing in an X-Y recorder.
ing condition were conducted and the mean value was taken as mixing time. The standard deviation of (mixing time) under any operating condition was below 0.10 second. VOLUME 17B, SEPTEMBER 1986--461
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B. Mass Transfer between Slag and Metal
SCALE X = 0 5 sec/cm Y = 100 mv/cm
In our work, the analogy of pure water to liquid steel and liquid benzene to that of slag was used. Iodine as a tracer was dissolved in the benzene in advance. Benzene was poured onto the surface of pure water and then gas was injected subsurface so as to stir both phases. Iodine transferred continuously into the water. Samples of w
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