Numerical Simulation Of Fluid Flow And Inclusion Behavior In RH Vacuum Refining Process

The Rheinsahl–Heraeus(RH)vacuum equipment plays important roles in the removals of carbon,hydrogen,nitrogen,oxygen,and non-metallic inclusions from the steel,which is considered to be one of the most important secondary refining technologies.The achievement of these refining functions is closely related to the fluid flow in the RH degasser.Due to the limitation of high temperature,numerical simulation has been considered as an effective way to study the refining process of RH degasser.In the present work,the fluid flow and inclusion behaviors in the RH degasser were studied by using the numerical simulation method.First,a mathematical model was built to describe the argon–steel two-phase flow in the RH degasser using the Eulerian model,and the effect of bubble expansion and various interphase forces on fluid flow in the RH degasser was investigated.Meanwhile,taking the top gas and slag phases into account,a coupled discrete phase model-volume of fluid(DPM–VOF)approach was developed to investigate the air–argon–steel–slag flow in the RH degasser,and the reasonableness of simplifying the four-phase flow to argon–steel two-phase flow was evaluated and the slag behavior in the vacuum chamber was analyzed.Then,based on the developed Eulerian model,the population balance model(PBM)with inclusion phase was introduced to form a coupled computational fluid dynamics-population balance model(CFD-PBM)approach to simulate the transport,aggregation and removal of inclusions in the RH degasser.Finally,the effect of bottom injection on fluid flow and inclusion behaviors in the RH degasser was investigated by using the above mentioned models.The following conclusions could be drawn:(1)Research on argon–steel two-phase flow shows that bubble expansion has a tremendous impact on fluid flow in the RH degasser,and the calculated circulation flow rate of steel is just half of the measured value if the expansion is not considered;except drag force,the turbulent dispersion force also strongly influences the fluid flow in the RH degasser,and this force is the key to reasonably predict the plume structure in the RH degasser.(2)Study on air–argon–steel–slag flow shows that simplifying the air–argon–steel–slag flow to argon–steel two-phase flow modifies the flow pattern and decreases the mixing time in the RH degasser,while it has an insignificant impact on the circulation flow rate of steel.(3)Research on inclusion behaviors indicates that the evolution of mass fraction,number density and size distribution of inclusions in the RH degasser can be well predicted by the inhomogeneous multiple size group(Inhomogeneous MUSIG)method,while the homogeneous MUSIG method may not be suitable for modeling the inclusion behaviors in steel where large and small inclusions are likely to segregate because of different momentum fields;considering the cluster of Al2O3 inclusions is of great benefit to the aggregation between inclusions,and the calculated value agrees reasonably well with the measurement when the fractal dimension for the aggregation is in the range of 2.4~2.5.(4)Study on bottom injection indicates that bottom injection at X=-0.75 m,-0.35 m,0.0 m or 1.2 m can evidently shorten the mixing time in the RH degasser;when X=-0.35 m,the minimum mass of inclusions in steel can be obtained as well as the minimum size of inclusions,which is considered to be best injection location for inclusion behaviors.