Numerical Simulation On Flow Field,Electromagnetic Field,Temperature Field In DC Ladle Furnaces And Process Optimization

As an important secondary refining method,LF refining technology can improve the purity of molten steel,adjust the composition and temperature,optimize the process between converter and continuous casting,it has been widely used all over the world with the advantages of simple operation,powerful functions and less investment,etc.The ladle furnace usually use the arc for temperature compensation,compared with three-phase alternating current,direct current ladle furnace(DCLF)can reduce the consumption of electrode and refractory material greatly,improving arc stability,strengthening the metallurgical effect,so more and more people pay attention to it in recent years.However,the underlying physical mechanism of current-coupled argon-blowing process in DCLF was not understood until now.Based on the 3t ladle furnace,the flow field,the electromagnetic field,temperature field in different conditions was numerically simulates with the help of the computational fluid dynamics,electromagnetism,thermodynamics,and the complete mixing time of the molten steel was calculated.The simulated results presented a theory support for the optimal design and controlling.A numerical study was performed at first for the three-dimensional turbulent fluid and mixing characteristics in gas-stirred ladles with off-center single injection.The effect of gas flow rate,positions of nozzle on the flow pattern and mixing were investigated.According to the calculated results,the optimum operation process is obtained.The electric field,magnetic field,the Lorentz force and the flow field in the molten steel formed by the DC current were analyzed later.The results show that the current density,Lorentz force and magnetic flux in the molten pool were mainly concentrated in the upper electrode.The electromagnetic field had strong stirring effect on the molten steel,and created a circulating vortex which flow down in the center and upward in the wall,the maximum speed appeared in the below of the electrode.Moreover,the numerical simulation coupled the flow field and the electromagnetic field.The results show that the flows changed significantly,three circulating vortices are formed between the wall,the nozzle,and the electrode.compared to bottom blowing or DC electromagnetic stirring,the average turbulent kinetic energy increased,the weak flow region and mixing time reduced,which means the stirring and refining were strengthened.At last,the temperature field of the molten steel under heating and soft blowing conditions is simulated.The results show that there is a large temperature gradient under the electrode when the ladle is heated,the high-temperature molten steel flow to the low-temperature zone due to the electromagnetic and argon blowing and the heat exchange become faster.The heating rate of molten steel is 2.2 K·min-1,which is correspond to the experimental data.The temperature distribution of molten steel during soft blowing is more uniform and the temperature difference is very small.