LAUSR

To meet the demands for high-quality steel, ladle refining is performed widely, which is used for temperature and composition homogenization, decarburization, desulphurization, and inclusion removal. In a typical secondary refining technique, argon gas is blown into the molten steel from the bottom of the ladle furnace through purging plugs. Bubbles are successively formed at the exit of the purging plugs, rise upward entraining the surrounding molten steel into their wakes, turn horizontally at the bath surface, push the slag layer to the periphery of the ladle, and escape from the bath surface into the atmosphere. Meanwhile, the inclusions are attached to the rising bubbles and come up to the slag layer with the bubbles. Nevertheless, the rising bubbles form a turbulent bubble plume, and the resulting slag eye causes the reoxidation of liquid steel. Intense interactions occur between the slag and molten steel because the overlying slag is pushed to the side. It is widely known that the bubble size and its motion affect momentum, heat, and mass transfer in gas–liquid bubble flow. In addition, finer bubbles have a high probability for inclusions attachment due to their larger gas/liquid interfacial area, which is determinant to the quality of steel. Therefore, bubbles play an important role in the flow field, which affects not only the mixing time that was usually applied for representing the chemical efficiency, but also inclusion removal rate that determines the cleanliness of steel liquid, and slag eye where slag entrapment and mass transfer always occurs. Major process variables, such as gas flow rate, plug position, bath height, and slag layer, relevant to gas stirred ladle metallurgy, have been deeply studied, and their influences are now known with a considerable level of accuracy. For instance, Conejo et al. explored the influences of the slag thickness, nozzle position, and the number of nozzles on mixing time. The effect of the nozzle diameter on the mixing has also been investigated. These results indicate the effect of the nozzle on mixing time. Moreover, to model the inclusion removal, a criterion applicable for a water model has been suggested, based on which different sizes of inclusions can be represented by the particle-to-liquid density ratio. After that, certain studies have established computational approaches and water model systems to investigate the inclusion removal mechanism. It has been shown that the bubble size can be controlled by optimized structural of purging plug for higher inclusion removal rate and lower entrapment rate. In addition, to investigate the behavior of the slag layer, the relations between the slag eye area and operating conditions were explored using a physical model. Cao and Nastac developed a transient numerical model to simulate slag entrapment in a bottom gas stirring ladle. It can be concluded that the variations in the main controlling parameters (bubble size and gas flow rate) and their potential impact on the multiphase fluid flow and mass transfer characteristics (turbulent intensity, mass transfer rate, slag eye area, flow patterns, and so on) in gas-stirred ladles were quantitatively determined to ensure the proper increase in the ladle refining efficiency. Dr. F. Tan, Prof. Z. He, L. Pan, Prof. Y. Li The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and Technology Wuhan 430081, China E-mail: [email protected] Dr. F. Tan, Prof. Z. He, L. Pan, Prof. Y. Li National-Provincial Joint Engineering Research Center of High Temperature Materials and Lining Technology Wuhan University of Science and Technology Wuhan 430081, China Dr. S. Jin Chair of Ceramics Montanuniversität Leoben A-8700 Leoben, Austria Prof. B. Li School of Metallurgy Northeastern University Shenyang 110819, China