Mass transfer characteristics between molten steel and particles in RH–PTB refining

Abstract

The mass transfer characteristics between powder particles and liquid steel in RH–PTB (powder top blowing) refining have been investigated on a ⅕ scale water model of a 90 t RH degasser. Sodium chloride powder of analytical purity has been used as the flux for blowing, and the mass transfer coefficient of solute (NaCl) in the liquid has been determined under the conditions of the RH–PTB process. The influence of the main technological and structural parameters on the mass transfer rate has been examined. The results have shown that, under the conditions of the present work, the mass transfer coefficient in the liquid increases with increasing lifting gas flowrate, with increasing inner diameter of the upsnorkel, with increasing circulation rate of the liquid, and with increasing particle size of powdered flux. On the other hand, mass transfer in the liquid decreases with an increase in the inner diameter of the downsnorkel. Its value is in the range (1·36–7·30) × 10−4 m s−1. The following dimensionless relationships, correspondingly, have been obtained for the mass transfer coefficient in the range:Sh = 2 + 0·073Re0·777s Sc1/3Sh = 2 + 0·073(ϵ1sd4p/ν3l)0·259 Sc1/3When the mass transfer is treated as that between rigid bubbles and molten steel, it may be characterised bySh = 2 + 0·026[Re0·48s Sc0·339(g1/3dp/D2/3p)0·072]1·455