Behavior of Powder in Ladle Impinged upon Molten Steel through Top Lance of Vacuum Vessel in RH Degasser

Synopsis : A numerical analysis and an experiment were carried out in order to make clear the effects of operational factors on the behaviors of powder in a ladle impinged upon molten steel in a vacuum vessel and the penetration ratio of the powder into molten steel blasted through a top lance in an RH degasser. The powder behavior in the ladle was numerically calculated by the equation of motion of the powder in the field of fluid flow given by numerical analysis of Navier-Stokes equation, and was compared with the results of a cold experiment of the RH degasser. Penetration ratio was estimated from the velocity profile of a free jet of gas and powder blasted through the top lance and verified by the hydrogen behavior of molten steel on which pulverized Ca(OH)2 was blasted in the RH degasser. The resident times of powder in the ladle decrease as the circulating flow rate and the powder size increase. The floating powders are found near down-leg for larger powder size, whereas they are sucked through up-leg when powder size becomes smaller. Therefore, optimal powder size exists to spread powders in the whole free surface of molten steel in the ladle. The yields of powder into molten steel increase with hard blow of gas and by increasing powder size. It is necessary to design the procedure of powder blasting in an RH degasser by considering the effects of cutoff of molten slag on molten steel and the yield of powder as well as the reaction rate between powder and molten steel.