Effect of Bath Depth and Nozzle Geometry on Spout Height in Submerged Gas Injection at Bottom
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Submerged gas injection is widely utilized in industrial processes, such as steelmaking[1,2] and copper smelting.[3–5] Typically, oxygen-enriched air is injected from the bottom of the vessels into the molten bath. Thus, the gas–liquid mixture is stirred and the oxygen is allowed to participate in the redox reaction and accelerate the smelting process. Bubbles are detached at the nozzle exit and rise upwards, forming a bubble plume or jet depending on the kinetic energy of the injected gas.[6–9] In the vicinity of bath surface, the kinetic energy of the bubbles is reduced, while the potential energy of the liquid is increased. At the bath surface, liquid level is raised above the surrounding surface level, resulting in the so-called spout eye or open eye,[10–15] as shown in Figure 1. The research group of Brimacombe was the first to focus attention into the spout generated during bottom gas injection in ladles.[16,17] They identified four dispersion zones in upwardly injected gas which were primary bubble, free-bubble, plume, and spout. They used an electro-resistivity probe and high-speed photography to
JUNBING XIAO, HONGJIE YAN, LIU LIU, and ZHIWEN HU are with School of Energy Science and Engineering, Central South University, Lushannan Road 932, 410083 Changsha, China. Contact e-mail: [email protected] FELIX MO¨LLER and SEBASTIAN UNGER are with Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany. Manuscript submitted February 18, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
study the characteristics of the spout and showed with gas void fraction, the structure, and height of the spout. Furthermore, cold model experiments have been conducted to investigate the open eye, spout width, and spout height during gas stirring have been conducted.[18–24] They found that the spout height was directly related to the kinetic energy of the injected gas which was represented by the maximum spout elevation. Thus, spout height is an important parameter to quantitatively characterize the gas–liquid flow behavior in submerged gas injection at bottom. In the cold flow model experiments,[10–12,25] water was employed as a working fluid, because the kinematic viscosity of water in room temperature is close to that of molten liquid steel[10,14,15] and molten copper matte.[12,26] Thus, the assumption was made that both fluids have similar momentum transfer ratio. Correlations for spout height were proposed by different groups which are summarized in Table I. Yonezawa and Schwerdtfeger[14,15] presented a nondimensional representation of the spout height h above the surrounding liquid bath. In their equation they neglected the influence of the viscosities and surface tension. ! hg0:2 Q2 ql do ¼f ; ; ; ½1 Q0:4 gd5o qg H where Q is the gas flow rate, qg, ql are the gas and liquid densities, do is the nozzle diameter, H is the bath depth and g is the acceleration due to gravity, Q2 =gd5o is a format of the modified Froude number given by Reference 11.
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