Experimental Study on Mixing in Gas-Stirred Ladles with and without the Slag Phase through a Water Physical Model
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Experimental Study on Mixing in Gas-Stirred Ladles with and without the Slag Phase through a Water Physical Model Adrián M. Amaro-Villeda, Jorge A. González Bello, Marco A. Ramírez-Argáez. 1 Facultad de Química, Universidad Nacional Autónoma de México, Mexico City, Mexico [email protected], [email protected] ABSTRACT A 1/6th gas–stirred water physical model of a 140 ton steel ladle is used to evaluate mixing in air–water and air–water–oil systems to model argon–steel and argon–steel–slag systems respectively. Thickness of the slag layer is kept constant at 0.004 m. The effect of the gas flow rate (7, 17, and 37 l/min), plug position (0, 1/3, ½, and 2/3 of the ladle radius, R), and number of plugs (1, 2, and 3) on mixing time is also analyzed in this work. Gas is injected at the bottom of the ladle under several plug configurations varying both position and number of plugs. Chemical uniformity of 95% is selected as mixing criterion. Mixing times are experimentally determined when a tracer is suddenly injected into the ladle and the model is instrumented with a pH meter to track the time evolution of the tracer concentration (NaOH 1 M solution) in a given location inside the ladle. Process conditions for best mixing in both water–gas and water-gas–slag systems are: a single plug located at 2/3 of the ladle radius with a gas flow rate of 17 l/min. INTRODUCTION There is growing interest to improve steel properties through optimization of steelmaking processes. Ladle furnaces play a key role in promoting steel quality where refining operations such as deoxidation, desulphurization, inclusion removal and/or modification, adjustment of the chemical composition, thermal and chemical uniformity are performed. These refining operations are assisted and accelerated by stirring the liquid steel by argon gas injected through porous plugs located at the ladle bottom and in the presence of a slag layer on the top of the steel. Although this process has been widely used in steelmaking for several decades, there are several physical phenomena not fully understood in secondary refining, which drives numerous research efforts currently being developed [1-3]. Research tools include physical and mathematical modeling. Measurements in physical models have characterized the gas-liquid plume structure, gas holdup, bubble frequency, bubble velocity, mixing times, heat and mass transfer. Mathematical models, developed by stating the set of conservation equations involved in the gas-liquid fluid flow problem, have been used to represent hydrodynamics of the ladle, heat and mass transfer as well as mixing and turbulent structure in the ladle. There are many studies in gas-stirred ladles by physical modeling on mixing phenomena which do not present a general agreement about the process conditions required to optimize mixing and these works do not take into account the slag layer [4-9]. Therefore, mixing studies in ladles are still necessary in ladle systems with the presence of the slag.
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