CFD Simulation on The Effect of Impeller Immersion Depth and Impeller Rotational Speed on The Flow Pattern and Temperature Drop of Molten Ferronickel During Desulphurization Process

Abstract

Desulphurization is the purifying process of molten ferronickel from sulphur impurity. During the desulphurization process using a ladle furnace equipped with an impeller, the fluid flow characteristics and the temperature drop of molten ferronickel are important things that must be observed. One approach that can be done to find out the fluid flow characteristics and temperature drops is through Computational Fluid Dynamics (CFD) simulation. The limitation of the simulation in the previous study did not simulate the effect of operating parameters such as impeller immersion depth and impeller rotational speed on the temperature drop of molten metal. Therefore, the simulation carried out in this study was a CFD simulation on the effect of impeller immersion depth and impeller rotational speed on the temperature drop of molten ferronickel during the desulphurization process. This study began by comparing the initial simulation results with a prototype experiment and simulation that another researcher conducted to validate the simulation model. After the selected model had been validated, the main simulations were carried out with variations in the immersion depth and impeller rotation speed. Variations in impeller immersion depth were 700 mm and 900 mm, while variations in impeller rotational speed were 30 rpm, 40 rpm, 50 rpm, and 60 rpm. The simulation began with creating a 3D design of an impeller and 2236 mm high ladle furnace using Ansys SpaceClaim. Then, the meshing and setup process was carried out using Ansys Fluent. The simulation was set by activating the Volume of the Fluid model, the Multiple Reference Frame model, the energy model, and the Renormalization Group (RNG) k-ɛ turbulent model. Based on the simulation results, the impeller immersion depth affects the size of the recirculation flow pattern and the characteristics of the molten ferronickel temperature profile. The impeller rotational speed affects molten ferronickel's vortex depth, velocity, and temperature drop. If the impeller is immersed deeper, the upper recirculation zone will be larger than the lower recirculation zone and the molten ferronickel temperature in the upper area will be hotter, while the bottom area will be colder. The faster the rotation of the impeller is the deeper the vortex, the higher the velocity of molten ferronickel, and the greater the temperature drop of molten ferronickel. The desulfurization process is influenced by a combination of mechanical operating parameters, such as the depth of immersion and impeller rotational speed, which result in ideal mixing characteristics. Impeller immersion depth of 900 mm and impeller rotational speed of 50 rpm are the ideal operational parameters for the desulfurization process in this study. A more uniform distribution of temperature profiles in the ladle's top and lower zones is produced by this parameter. There is slight difference in the size of the upper and lower recirculation flow zones when the impeller immersion depth is 900 mm. With an impeller rotating at 50 rpm, there is a temperature decrease of roughly 24 °C and a vortex depth that is almost at the top of the impeller.