Bubbling at high flow rates in inviscid and viscous liquids (slags)
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INTRODUCTION
INDUSTRIAL gas injection into nonferrous slags to recover metal values by slag reduction or fuming is a well-established practice.l-4 Familiar examples include the submerged injection of gas and reductants through multiple tuyeres into lead blast furnace slags and tin bearing slags for the recovery of zinc and tin, respectively. New emerging concentrate smelting processes for lead, copper, and tin have also incorporated submerged gas injection for the treatment of the molten product in oxidizing and reducing cycle. Schematic diagrams of some of the commonly used and developing slag treatment processes are shown in Figure 1. The operating parameters and physical properties of slags in the existing processes are given in Tables I and II. For comparison, physical properties of the modeling liquids are included in Table II. Since the model experiments are performed on vertical flush tuyeres, they apply directly to some of the emerging direct smelting processes. The theory can also be expanded to include blowing horizontally or at an angle. Most slag treatment processes have a low liquid seal depth and shallow tuyere submergence. As a consequence, the large primary bubbles formed at the tuyere tip will not have sufficient rise time to break down into finer bubbles. Hence the primary bubbles play an important role in process kinetics. T. ABEL ENGH is Professor, Metallurgisk Institutt, Technical University of Norway, Trondheim, Norway. M. NILMANI is Lecturer, G. K. Williams Research Laboratory for Extractive Metallurgy Research, Department of Chemical Engineering, University of Melbourne, Parkville, Victoria, 3052, Australia. Manuscript submitted March 4, 1986. METALLURGICALTRANSACTIONS B
In a number of ferro-alloy converter processes the liquid seal depth may be low so that primary bubble volume is important. For this reason bubble volumes in inviscid liquids are included in this work. Furthermore, the inviscid liquids serve as a reference to the work on viscous melts. It is also important to understand and describe the mechanisms and conditions for the transition from bubbling to "jetting". To improve understanding of at least the bubbling regime, the theory of bubbling--valid up to the highest flow rates where bubble volumes have been measured-- is presented in this paper. The mass flow of gas per unit area of nozzle was as high as 180 kg/m 2 s. This loading may be compared with 400 kg/m 2 s where the jet flow regime is dominant. 5 As an introduction, previous papers concerning bubbling, bubble frequency, and penetration are mentioned. 6-9 It seems that the problem of primary bubble volume for high gas momentum blowing has hardly been treated. There is very little information concerning injection into molten slags or viscous liquids, except in a classical paper concerning bubbling at low and intermediate gas flow rates by Davidson and Sch/iler. ~~ They give for vertical injection through a flush tuyere at low Reynolds numbers and low gas flow rates:
Vm =
15 vQ/2g)3/4
[ 1]
The equation is obtained b
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