Study On The Gas-liquid Two Phase Flow And Dehydrogenation Behavior In RH Vacuum Refining Process

Due to the market demand for steel quantity and quality becomes more and more largely and strictly,secondary refining has become an essential procedure in the modern steelmaking process.Because of its manifold functions and excellent refining effects,RH vacuum refining has been widely used in the secondary refining process.RH vacuum refining is a very complicated metallurgical process,which involves in multiphase flow,heat and mass transfer,and various chemical reactions.Therefore,in order to take full advantage of the production efficiency and reduce the production costs,it is necessary to have a thoroughly studies on each phenomenon in the RH reactor.In the present study,treating a 210 ton RH reactor as the prototype,a 1:5 scale water model has been developed.The gas-liquid flow behavior and the effect of different operating parameters on the RH refining process were investigated.The results showed that the gas-liquid two phases will maintain the inherent flow mode after the flow field becomes stable in water model.The gas-liquid flow behavior in RH degasser is determined by the gas flow rate,immersion depth and pressure.The circulation flow rate can be increased by the greater gas flow rate,the deeper immersion depth,and the higher liquid level of the vacuum chamber,which also results in the shorter mixing time.The effect of each interphase force and its different combinations on the gas-liquid flow behavior in RH degasser was researched by using ANSYS-CFX commercial software.The results showed that the drag force plays an essential role for RH flow simulation,because it makes a remarkable contribution on circulation flow rate of molten steel.The virtual mass force is the key factor,which avoids the gas-adhering wall effect.Due to the virtual mass force can change the bubble trajectory,the effect of this force on circulation flow rate,and the distribution of gas holdup in the up-snorkel is significant.Although the contribution of the turbulent dispersion force on the circulation flow rate is small,it shows its great effect on the distribution of gas holdup in the up-snorkel.However,the effects of the wall lubrication force,and lift force on these two parameters are negligible.Therefore,the optimal interphase force model for RH flow simulation can be composed of the drag force,virtual mass force and turbulent dispersion force.Based on the optimal interphase force model,the mathematical modelling of gas-liquid flow in RH degasser has been also optimized and validated.The flow field of molten steel,velocity field,the distribution of gas holdup in the up-snorkel and the proper sampling location in the ladle were investigated.The results showed that the optimized mathematical modelling of gas-liquid flow in RH degasser corresponds with the water model results,which prove that the optimized model is robust.The simulation results of the flow field,velocity field,and the distribution of gas holdup are determined by the simulation parameters,geometry size and the interaction between gas and liquid phase.By comparing of the “starting mixing time” of each test point in the ladle and analyzing the flow pattern of molten steel,some proper sampling locations in the ladle can be obtained.The mass transfer processes of dehydrogenation in different RH regions were described using Higbie's penetration model and eddy-cell model,respectively.A new mathematical modelling of dehydrogenation in RH degasser was developed by coupling the 3D optimized RH flow field.The results showed that the present model can not only reflect the two-phase flow behavior in the RH rector,but also predict the actual dehydrogenation process.The dehydrogenation process in RH degasser mainly occurs in the up-snorkel and vacuum chamber.The reaction site in the up-snorkel is determined by the distribution of gas holdup,while the reaction site in the vacuum chamber depends on the distribution of turbulence eddy dissipation.The gas holdup in the up-snorkel and the turbulence eddy dissipation rate in the bath surface of the vacuum chamber can be increased by the larger gas flow rate,which results in the higher dehydrogenation rate in each reaction site.In addition,the flow behavior of molten steel in the ladle has a significant effect on the mixing process of molten steel in the whole RH reactor,which also indirectly affects the dehydrogenation process in the up-snorkel and vacuum chamber.