Study on jet characteristics of a new dual Mach number oxygen lance for 200t converter

In the converter steelmaking process, the shape of the supersonic jet of the oxygen lance has an important influence on the smelting process. Based on the isentropic flow theory, this study developed a 6-hole staggered double Mach oxygen lance. Through numerical simulation, the effects of variable pressure operation and oxygen lance structural parameters on the jet shape and the impact area of the molten pool were explored. The results show that under low pressure conditions (0.78MPa), the subcritical operation of the main nozzle (P/Pcr = 0.78) produces a delayed coalescence effect, which makes the jet coverage area larger. At the same time, the average velocity in the negative pressure zone is reduced by 50%, and the proportion of low velocity gradient zone is increased to 75%, which can effectively reduce the occurrence of splashing behavior during the blowing process. Under high pressure conditions (0.9MPa), the secondary nozzle reaches the supercritical pressure ratio (P/Pcr = 1.28). At this time, the main nozzle hole is in normal working state, and the momentum of the auxiliary nozzle hole increases due to the expansion effect outside the tube. Compared with the supersonic length at low pressure, it is increased by 38% and 41% respectively, which provides an energy basis for deep stirring of the molten pool. Under different parameter schemes, when the inclination angles of the inner and outer holes of the oxygen lance are 13°and 17° respectively, the axial velocity and effective impact area are larger when the flow ratios are 65% and 35%. The impact depth and the stirring kinetic energy of the molten pool at high pressure are increased by 14% and 35.2%, respectively, compared with those at low pressure, which is beneficial to strengthen the stirring of the molten pool and shorten the mixing time of the molten pool.