Modeling Of Gas-Slag-Metal Multiphase Fluid During Basic Oxygen Steelmaking Process

Currently,Basic Oxygen Furnace(BOF)steelmaking is the predominant steelmaking process around the world.The multiphase fluid behavior in the converter is of great significance to a high-efficiency and smooth steelmaking.The multiphase transport phenomena in the molten bath are fairly sophisticated,involving many complicated aspects such as gas,liquid and solid flow,mass transfer,heat transfer,melting,dissolution and chemical reaction between molten steel,slag and gas phase.The fluid behavior of the multiphase is the fundamental of the abovementioned complex phenomena.Therefore,revealing the multiphase behavior in the converter is conducive to uncover the multiphase transfer mechanism during BOF steelmaking and provide proofs and guidance for optimal design of the reactor and optimization of converter steelmaking process.The modeling work can be an important component to the realization of real-time data-driven intelligent manufacturing in converter steelmaking.The objective of the present study is giving an illustration of the multiphase fluid behavior in an 80 t converter using physical and mathematical modeling methods.The modeling contains the stirring and mixing behavior in the liquid bath,the scrap behavior,the interacted cavity shape behavior,the multiphase interaction behavior and the slag splashing towards the mechanical erosion caused by multiphase interaction.The obtained results can provide optimal operating parameters with better mixing effect,"visualize" the instantaneous scrap behavior,clarify the relationship between cavity shape and metallurgical characteristics,expound the multiphase fluid behavior,and acquire the splashing scheme for refractory abrasion area.The complex modeling includes the fluid flow,scrap movement and melting,gas-liquid fluid,gas-slag-metal multiphase fluid,and slag splashing movement.The stirring and mixing behavior in the liquid bath were systematically studied by water model experiments.It was found that the effects of oxygen lance height,bottom nozzles configurations,gas flow rate of bottom nozzles and oxygen lance on the stirring and mixing behavior in the converter are significant.Furthermore,through variance analysis,the optimal operating parameters of the 80 t combined blown converter were obtained as follows:lance height 950 mm,oxygen flow rate 14000 Nm3/h,five nozzles oxygen lance,bottom nozzle configuration B and bottom gas flow rate 100 Nm3/h.In addition,the agitation energy generated from top blowing,bottom blowing and combined blowing and its effect on bath mixing were analyzed,and then the estimation model for the mixing time in the converter was proposed using nonlinear curve fitting method,and its expression is τ= 169.72εA-0.35.A physical modeling based on the similarity principle were established for the study of the scrap behavior during converter steelmaking process.Specially-made ice pieces with different shapes and sizes were used to simulate the scrap,and its motion and melting were visualized in a transparent scaled-down model.It has been indicated that the scrap behavior is closely related to the fluid characteristics in the converter.The enhancement of stirring and mixing can be of importance to the scrap controlling.The scrap with small size is more favorable for the actual production.As for the scrap melting,the shape of scrap is a crucial parameter.Large-sized scrap with small specific surface area should be avoided during converter steelmaking process.It is also found that increasing the fluid temperature and accelerating the fluid flow rate are beneficial to the melting of scrap by numerical simulation of the dynamic melting characteristics of a given ice piece,and increasing the fluid flow rate of the surrounding liquid presences a more significant effect.The interacted cavity shape behavior was investigated by water modeling experiments.To clearly describe the cavity appearance,the cavity shape index(IC)was put forward,which is a dimensionless factor to demonstrate the cavity shape related to cavity depth and cavity width.It was obtained that cavity shape index and blowing number(NB)present significant exponential relationship,and the functional expression is IC = 1.0205-0.2428NB + 0.0228NB2-0.0005NB3.Moreover,the effect of cavity shape on the stirring characteristics and the mixing effect in the converter were investigated.The results show that lower and higher cavity shape index may lead to longer mixing time in smelting process.For the 80 t converter,the penetration depth and impact width should be controlled approximately equal(IC fluctuates around 1)to obtain better mixing effect.A three-dimensional,compressible and non-isothermal model was established to simulate the gas-slag-metal multiphase interaction between the high pressure jet and the molten bath in the converter.The time-dependent movement of the multiphase interface shows great instability in both vertical and horizontal directions.Oxygen lance parameters have an important influence on the multiphase interaction.The variation of oxygen lance height can significantly affect the shape of the cavity,and it is also closely related to the splashing and droplet generation in the liquid bath.However,the slag viscosity and surface tension have little effect on the momentum transfer of multiphase interaction,especially for the area away from the interaction zone under the present simulation conditions.According to the results of numerical simulation,the main area of the refractory abrasion caused by the multiphase interaction in the converter lies in the slag line region and the part below the trunnion.The area needs to be specially protected through slag splashing.Physical modeling experiments were conducted to investigate the influence of oxygen lance height,oxygen flow rate,density of splashed slag,the holes of oxygen lance,bottom nozzles configuration and bottom gas flow rate on the slag splashing behavior.The results showed that the lance height significantly affects the slag splashing behavior,and it is an important parameter to control the slag splashing area.Furthermore,the optimal operating parameters for protecting the refractory abrasion region were acquired as follows:lance height 960 mm,top gas flow rate 18000 Nm3/h,four-nozzle oxygen lance,bottom nozzles configuration D4,bottom blowing flow rate 100 Nm3/h and amount of remained slag 10%.