Numerical simulation of the effects of lance velocity and immersion depth on slag-iron flow in the flash ironmaking pool

Flash ironmaking is an emerging non-blast furnace ironmaking technology that has attracted the attention of metallurgical researchers due to its high efficiency, low energy consumption, and low pollution. While many studies have focused on the flash reduction section, research on the molten reduction reactor-a key component of the flash ironmaking remains limited. This study utilized CFD software with the VOF model to investigate the flow field and phase distribution of the molten pool under varying lance injection velocities (175–250 m · s −1 ) and immersion depths (0–350 mm). Key results show that: (1) The molten pool reaches a dynamic balance state after approximately 2.8 s of gas injection, with a stable turbulent kinetic energy of ∼0.9 m 2 · s −1 for non-immersed lances and ∼1.39 m 2 · s −1 for immersed lances. (2) A lance velocity of 225 m · s −1 is optimal, reducing the dead zone ratio from 34.58% to 27.42% and expanding the active zone ratio to 47.25%. (3) A lance immersion depth of 250 mm eliminates gas polymerization, redirects high-velocity gas away from furnace walls, and boosts the active zone ratio to 61.05%, while increasing slag-iron average velocity to >0.25 m · s −1 . These findings provide quantitative operational guidelines for industrial flash ironmaking furnaces, supporting improved molten pool mixing efficiency and reduced energy loss.