Numerical Simulation On Oxygen Lance Supersonic Jets Behavior And Their Interaction With Bath In BOF Steelmaking

Supersonic gas jets from convergent-divergent nozzles are employed in many metallurgical processes such as Basic Oxygen Furnace (BOF) and Electric Arc Furnace (EAF) steelmaking. Their interaction with bath plays a significant role in oxygen supply, bath stirring and mixing, cavity formation, emulsification and chemical reactions. So, aiming at the practical condition in convertor a three-dimensional and non-isothermal mathematical model of compressible supersonic free surrounding oxygen jets from an oxygen lance with six convergent-divergent nozzles as well as a CFD-VOF multiphase flow mode is developed. On basis of these models, jets behavior and their interaction with bath are also studied. From current research results, following conclusions can be drawn:(1) Jets turbulent entrainment caused jets pressure difference near the oxygen lance axis and the offside, resulting in the jets coalescence. Along with the increasing distance between the nozzle exit axial distance, jets flows parallel because of their coalescence and almost impact perpendicular to the surface in the molten bath. Along with the increasing distance between the nozzle exit and axial distance, jets velocity decays gradually, radial flow expansion decreases the impact height and enlarges the impact area.(2) The higher ambient temperature, there are the slower jets attenuation, the larger jets velocity when reaching the bath and the more radial expanding of jets. Ambient temperature has no relationship between impact depth and ambient temperature. But, the higher ambient temperature leads to the larger impact area.(3) Shocks are released at the nozzle exits under even the designed operation pressure and repeating expansion and expression waves are observed. The velocity and dynamic pressure of jets increase with increase of operation pressure. But the operation pressure has almost no influence on coalescence behavior of jets.(4) The inclination angle of nozzles makes a significant difference in the coalescence behavior of jets. With nozzle inclination angle decreases from17.5°to10°,the evolution of impinging effect from several scattered small craters to one large integral cavity can be expected for typical lance heights. Different splashing model can be predicted based on the position of jets center. Inward melt splashing with high lance height and outward melt splashing with low lance height can be expected with nozzle inclination angle of10°. With nozzle inclination angle of17.5°, melt splashing pattern opposite to that with nozzle inclination angle of10°can be expected at high blowing lance height.(5) The cavity appears when jets impacts onto the molten bath. Impact depth and diameter are choppy and periodic. When the impact depth increases gradually, the surface of metal fluctuates gently. When the impact depth decreases, the surface fluctuates acutely, and the roughness of surface increases. At the same time, the flow field in the molten bath varies with the cavity periodic oscillation.(6) A quantitative relationship about impact depth and diameter with lance height, inlet velocity and nozzle inclination angle.