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The stirring of a molten steel ladle with argon injection through a top submerged lance and a bottom nozzle is numerically studied here through Computational Fluid Dynamics (CFD) simulations. Three lance submergence depths and three injection velocities are considered in the CFD numerical experiments. The turbulent dissipation rate is employed to characterize the stirring phenomenon. The mixing times are determined from the gas flow rate, ladle geometry and bath depth using an empirical correlation.

Nowadays, ladle metallurgy or secondary metallurgy is an important technology to obtain high quality steel products which satisfy strict norms and specifications of mechanical performance [

Commonly, argon is injected into the metal bath through submerged lances or through porous plugs located at the bottom of the ladle. Both procedures have pros and cons, as is reported in the specialized literature. In [

Using Computational Fluid Dynamics (CFD) numerical simulations, in [

In this work, the stirring performance of a molten steel bath in a 150 metric tons ladle with argon injection through a top submerged lance and a bottom nozzle is numerically analyzed using transient 2-D two-phase isothermal CFD numerical simulations. Three lance submergence depths and three injection velocities are considered in the CFD numerical experiments. As in [

For the sake of simplicity, full equations of the mathematical model are not written here given that they can be found elsewhere [

CFD software [_{n} = 0.05 m. The physical properties of molten steel were as follows: density 7100 kg/m^{3}, viscosity 0.0067 kg/(m∙s). The physical properties of argon were as follows: density 1.6228 kg/m^{3}, viscosity 2.125 × 10^{−5} kg/ (m∙s). The PISO (Pressure Implicit with split Operator) algorithm was employed for the pressure-velocity coupling. Boundary conditions for argon injection velocities of 0.1, 0.5 and 1.0 m∙s^{−1} are shown in

Evolution of the phase distribution and streamlines for argon bottom injection are shown in ^{−1}. Argon bubbles ascend from the bottom to the free surface and, as they ascend, the molten bath becomes stirred and mixed. Initially, as is seen in

Argon injection velocity (m∙s^{−1}) | Turbulent kinetic energy (m^{2}∙s^{−2}) | Turbulent dissipation rate (m^{2}∙s^{−3}) |
---|---|---|

0.1 | 1.0 × 10^{−4 } | 4.0 × 10^{−5} |

0.5 | 2.5 × 10^{−3 } | 5.0 × 10^{−3 } |

1.0 | 1.0 × 10^{−}^{2 } | 4.0 × 10^{−2 } |

as time proceeds, the whole volume of the molten metal becomes shaken. In the case of submerged lance injection, argon bubbles ascend from the lance tip to the free surface, as is observed in

The effect of the submergence depth of lance on the phase distribution and bath stirring is shown in

As in [

submergence depth. In ^{−1}, and the considered lance submergence depths are 1.0, 2.0 and 3.0 m. One can observe that the turbulence dissipation rate is increased as the lance submergence depth is increased. However, by comparing ^{−1} the turbulent dissipation rate for the bottom injection is similar than that corresponding to the submerged lance injection with 2.0 m of submergence depth. One would expect that, for the same injection velocity, the results for the bottom injection and the submerged lance injection with 3.0 m of submergence depth would be analogous, however this does not occur. This discrepancy is due to the fact, in the computer simulations, the bottom plug has just one nozzle, whereas the submerged lance has two injection nozzles, therefore the argon flow rates are different when the same injection velocity is considered.

Mixing time (τ_{m}) can be defined as the time (commonly in seconds) required for achieving a certain degree (around 95%) of homogeneity (chemical or thermal) of an injected tracer in a unit operation vessel [_{m}, frequently empirical correlations are used in the literature and at industry. In this work, the following empirical expression reported in [

where Q is the argon injection flow rate (m^{3}∙s^{−1}); R is the mean radius of the ladle = (D1 + D2)/4 (see _{n}vA, where N_{n} is the number of nozzles at the injection point, v is the argon injection velocity and A is the nozzle flow area. A is determined

Argon injection velocity (m∙s^{−1}) | Argon volumetric flow rate for a two nozzles lance (Nm^{3}∙s^{−1}) | Mixing time(s) |
---|---|---|

0.1 | 3.9270 × 10^{−4 } | 296.18 |

0.5 | 1.9635 × 10^{−3 } | 174.14 |

1.0 | 3.9270 × 10^{−3 } | 138.54 |

from the nozzle diameter, D_{n}. Then, ^{−1}. In the cases considered here, for the bottom nozzle N_{n} = 1 and for the submerged lance N_{n} = 2.

The stirring of a 150 metric tons molten steel ladle with argon gas using bottom and top submerged lance injection was numerically studied using a Computational Fluid Dynamics tool. Three injection velocities and three lance submergence depths were considered in the computer simulations. Based on the analysis of the computer results, the following conclusions arise:

1) For the submerged lance injection, the mixing efficiency is increased as the lance submergence depth is increased.

2) For the ladle geometry considered, the mixing time strongly depends on the argon flow rate for the case of submerged lance injection. In fact, an empirical correlation shows that the mixing time decreases as the argon flow rate is increased.

3) During the initial steps of the process, the bottom injection exhibits more mixing efficiency than the submerged lance injection.

Torres, S. and Barron, M.A. (2016) Numerical Simulation of an Argon Stirred Ladle with Top and Bottom Injection. Open Journal of Applied Sciences, 6, 860-867. http://dx.doi.org/10.4236/ojapps.2016.613075