Study of Dispersed Micro-bubbles and Improved Inclusion Removal in Ruhrstahl–Heraeus (RH) Refining With Argon Injection Through Down Leg

The bubble motion behavior and the inclusion removal during the argon injection processing through the down leg of an Ruhrstahl–Heraeus (RH) unit have been investigated using physical modelling, numerical simulating, and theoretical calculations. From the results obtained, it was found that the micro-bubbles generated by argon injection through the down leg can be sent to the ladle below by the downward liquid steel. Increasing the up-leg argon flow rate and decreasing the down-leg argon flow rate as well as the gas nozzle size are beneficial to produce small and dispersed bubbles. Increasing the down-leg argon flow rate would favor an increase of bubble number density. When the up-leg volume argon flow rate is 161 m3/h, the bubbles experience a longer exposure in the vertical direction: for the conditions of the argon nozzle diameter ranging from 0.2 to 0.8 mm and the down-leg argon flow rate from 120 to 1200 mL/min, the largest sinking depth of the bubbles can be controlled to surpass 2.44 m—that is, the lowermost bubbles are close to the bottom of the ladle. The largest spreading length of the bubbles in the horizontal direction is from 0.93 to 2.03 m under all the conditions, corresponding to 32 to 71 pct of the ladle diameter. The down-leg has a large space to set many argon nozzles. Increasing the total down-leg flow rate by the layout of adding the number of the argon nozzles can significantly improve the bubble dispersion and number density. Using the argon injection through down-leg technique can remove nearly all the 50 μm diameters inclusions. The removal efficiency of the inclusions with diameter of 20 μm reaches 55 pct. For the 10 μm diameters inclusions, the removal efficiency is over 10 pct.