Numerical Simulation of Nonmetallic Inclusions Behaviour in Gas‐Stirred Ladles

Abstract

The secondary refining of molten steel in gas-stirred ladle has played a more and more important role in the production of high quality steel. In the present work, a mathematical model of the fluid flow and inclusions behaviour in a 150t gas-stirred ladle was presented, and the variations in concentration, size and density for non-metallic inclusions in the ladle during the refining process were predicted. The results show that during the refining process, the variations in the number density of the inclusions differed depending on size. The inclusions with a diameter less than 25 urn decrease during the whole period, while inclusions with diameter larger than 25 urn increase in the first stage of the treatment and gradually decrease during the later stage. After 15 minutes, all inclusions show a tendency to decrease, but the removal rate for inclusions of smaller size becomes slower. After treatment in the ladle, inclusions with a diameter larger than 50 urn were removed, the number of inclusions with a size between 30-40 urn was not high, while inclusions that were smaller than 25 urn still remained in the molten steel. Two-jet bubbling demonstrated an advantage over one-jet for inclusion removal. The practice of bubbling argon with a higher gas flowrate initially, followed by a lower flowrate in the ladle was found to be beneficial for inclusions removal.

Numerical Simulations of Inclusion Behavior and Mixing Phenomena in Gas-stirred Ladles with Different Arrangement of Tuyeres

“…It is well known that gas blowing has been widely applied in metallurgical processes to enhance the inclusion removal and metallurgical reaction rates and to homogenize the temperature and composition of the melt, and the number, arrangement and gas flow rate of bottom blowing have a great impact on these transport phenomena. Hence, the study of inclusions removal behavior and mixing phenomena under different arrangement of gas blowing in gas-stirred system is necessary and has received considerable attention [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] over the years. Inclusion behavior in gas-stirred system involves complex phenomena, such as inclusion transport due to liquid flow, inclusion growth due to inclusion-inclusion collision and inclusion removal due to flotation and attachment to bubbles, and some models have been proposed to describe these behaviors.…”

“…Inclusion behavior in gas-stirred system involves complex phenomena, such as inclusion transport due to liquid flow, inclusion growth due to inclusion-inclusion collision and inclusion removal due to flotation and attachment to bubbles, and some models have been proposed to describe these behaviors. [1][2][3][4][5][6][7][8][9][10] Miki and Thomas et al 4) predicted the inclusion removal in RH degassing vessel with PBM by taking into account inclusions growth due to turbulent shear collision and inclusions removal due to Stokes flotation and bubble-inclusion buoyancy collision. Söder et al 5) adopted similar models to study the growth and removal of inclusions in gas-stirring ladle, and considered inclusion flotation by spherical-cap bubbles.…”

“…Söder et al 5) adopted similar models to study the growth and removal of inclusions in gas-stirring ladle, and considered inclusion flotation by spherical-cap bubbles. Furthermore, some researchers [6][7][8][9][10] developed CFD-based models considering not only inclusions growth and removal, but also their transport carried by fluid flow and spatial distribution, to simulate inclusion behavior in a gas-stirred ladles, and the effect of bottom tuyere configurations on inclusion removal in the ladle were also investigated by Zhu et al, 7) Wang et al 8) and Geng et al 9) To some extent, the existing models had succeeded in predicting the inclusion removal efficiency in gas-stirred systems. However, some important phenomena and mechanisms were still not taken into account in these models, such as inclusion turbulent random motion, bubble wake and slag eye on the liquid surface and so on, as shown in Fig.…”

Numerical Simulation for Collision and Growth of Inclusions in Ladles Stirred with Different Porous Plug Configurations

“…The inclusion transport equations which describe collision and aggregation among inclusions can be expressed as follows [16][17][18] : The inclusions have a constant floatation velocity in vertical direction since the density of liquid steel is larger than that of the inclusion. So the convection velocities in Eq.…”

“…[16][17][18][19] By solving the transport equations of the inclusion characteristic number density and concentration, the number and mass conservation model can consider the effect of fluid flow on inclusion agglomeration process. Although the number and mass conservation model has been applied to the inclusion removal in the case of gas injection by some researchers, but the current model did not take the effect of injected gas bubbles on the inclusion removal into account, 17,18) and ignored the Stokes collisions among inclusions which has been proved to be significant if the difference in inclusion radius is large. 7,13,20,21) Thus, the purpose of the present work is to develop an inclusion number and mass conservation model in which the Stokes collision and bubble adhesion are taken into account.…”