Effect of Slag on Mixing Time in Gas-Stirred Ladles Assisted with a Physical Model
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Effect of Slag on Mixing Time in Gas-Stirred Ladles Assisted with a Physical Model Adrián M. Amaro-Villeda1, A. Conejo2 and Marco A. Ramírez-Argáez1. 1 Facultad de Química, Universidad Nacional Autónoma de México, Mexico City, Mexico [email protected], [email protected] 2 Centro de Graduados, Instituto Tecnológico de Morelia, Avenida Tecnológico 1500, Col Lomas de Santiaguito, Morelia, Michoacán, México. ABSTRACT A 1/6th water physical model of a 140 tons gas-stirred steel ladle is used to evaluate mixing times (m at 95% of chemical uniformity) in a two phase system without slag (air-water) and in a more realistic three phase system (air-water-oil) to simulate the argon-steel-slag system and quantify the effect of the slag layer on the mixing time. Slag layer is kept constant at 0.004 m. Mixing times are estimated through measured changes in pH due to the addition of a tracer (NaOH 1 M). The effect of the following variables on the mixing time is evaluated for a single injector: gas flow rate (7, 17 y 37 l/min) and the injector position (R/r= 0, 1/3, , 2/3 and 4/5). Experimental results obtained in this work show good agreement when compared against mixing time correlations reported by Mazumdar for the two phase air-water case (no slag considered). Another comparison is done using the new concept called “effective bath height” proposed by Barati, where the mixing time is a function of the size of the slag layer since this layer dissipates part of the total amount of stirring energy introduced into the ladle by the injection of gas. Agreement is not good in this case. Finally, an estimation of the percentage of the stirring energy dissipated by the slag is computed, including other factors that govern the dissipation of stirring energy. Percentage of energy dissipated by the slag is found to be between 2.7 to 12 % depending on the process conditions. INTRODUCTION Many research works have been developed on the gas-stirred ladle furnace through physical and mathematical models as presented by the excellent reviews by Mazumdar [1,2]. Most of the models on ladle furnace through physical and/or mathematical models are carried out neglecting the presence of the slag layer. The slag phase plays several roles in the secondary steelmaking: a) to avoid reoxidation of liquid steel, b) to eliminate non-metallic inclusions, c) to eliminate sulphur, d) to prevent radiation losses from the steel to the surroundings. There are only a few works about physical models of the ladle furnace that considered the three phase system gas-steel-slag [3-6]. These works evaluate several issues, being one of the most important to quantify how much is the mixing time increased by the presence of the slag layer. Most of the physical models considering the slag are based on a water-oil system. A great variety of oils have been used as well as other volatile and dangerous organic compounds to simulate the slag. However, usually these substances do not satisfy kinematic similarities or density ratio (steel density/slag density). Despite
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