Numerical Simulation of Fluid Flow and Mixing in Gas-Stirred Ladle

Ladle metallurgy is one of the most important stages for producing high quality and clean steel in the secondary steelmaking process. It is not only used for transporting molten steel coming from primary steelmaking processes, but also for desulfurization, de-oxidation, chemical and temperature adjustment, and refining of metals prior to continuous casting. During the refining process, it is essential to maintain the liquid steel in a homogenized condition. One of the most effective flow control methods to mix and homogenize liquid steel is a gas-stirred system. The bottom-stirring ladle is the most common system, and it has been most widely studied. Due to the complexity of the ladle refining process, it is almost impossible to observe the hydrodynamics within the refining ladle. CFD technology with more and more physically based numerical models have been developed to simulate the turbulent multiphase flows with a high accuracy. In this study, a three-dimensional CFD gas-stirred ladle model is developed to simulate the transient multiphase flow and mixing process based on VOF-Lagrangian approaches. The model is first validated against with experimental data by using water model. Then, the model is validated industrial measurement data. Average percentage of 6.67% different compared with water model experimental measurement data of slag eye size from previous literature. The good model performance has been observed over the water model validation, which shows that the current modeling method can be trusted enough to simulate the practical ladle geometry for design and process optimization of industrial gas-stirred ladle in steelmaking process. A baseline case is first investigated to analyze the flow field of multiphase in ladle, then the results of slag eye size is validated against with industrial measurement data of slag eye size. An average percent difference is about 8.71%, which shows a good agreement with industrial measurement data. In addition, six tracers are introduced in ladle to analyze the mixing efficiency of ladle; volume percentage of turbulence intensity over 2% is defined and calculated to explain the mixing time in baseline case. Parametric studies on argon flow rate, slag thickness, and plug positions are conducted. The effect of different plugs locations on the flow field and mixing efficiency are studied. Results shown that for different refining purposes, different argon gas flow rates are needed. Increasing the slag thickness would increase the slag eye size based on gas flow rate of 30 SCFM. Moreover, thinner slag thickness promotes the mixing process. For current simulation, each ladle with plugs’ distance ratio of 0.8 and separation angle of 60° show less mixing time and better mixing. Considering the effect of slag eye formation and mixing efficiency, higher ladle aspect ratio always gives the better result. So, a ladle aspect ratio of 1.2 is recommended in this study