Mixing of concentric gas jets issuing vertically into a liquid
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I.
INTRODUCTION
BOTTOM-blowing o f oxygen to refine hot metal into steel has been made possible with the advent of Maxhfitte tuyeres, and many commercial processes such as OBM/Q-BOP, SIP, etc. have emerged in the seventies utilizing this invention. In these tuyeres, oxygen gas blown through a central pipe is shrouded by a hydrocarbon gas, which is blown through a coaxial annular pipe around the central one. Shrouding has also been achieved by a liquid hydrocarbon like fuel oil, as in the LWS process. These processes show many metallurgical advantages over the top-blown oxygen steelmaking process due to improved stirring of the metal bath and injection o f powdered lime through the bottom tuyeres. This has led to the introduction of bottom-blowing facility in many steelmelting shops.1 It has been reported that the shrouding o f the oxygen jet makes the wear of the bottom lining uniform and almost completely eliminates the localized wear around tuyeres.2'3 The shrouding fluid, upon emerging from the tuyere, is supposed to protect the lining from excessive rise of temperature and consequent localized wear. As the cost of petroleum products has escalated, it is imperative that alternative shrouding fluids be explored. Understanding of the mechanism of protection of lining from this as well as other points of view is important. The protection of the lining may be attributed to the following three mechanisms: (i) Physical shielding, whereby the shrouding fluid physically surrounds the oxygen jet from the metal near the tuyere exit and thus takes the zone of oxidation away from the bottom lining. This would decrease the temperature and wear rate of the bottom lining. (ii) Thermal shielding, whereby the endothermal cracking of the hydrocarbon cools the region around the tuyere exit and thus slows down the wear rate. (iii) Chemical shielding, whereby the hydrocarbon maintains a reducing condition around the tuyere exit, thus shifting the oxidation zone away from the lining. The cracking of the hydrocarbon may even result in the deposition of carbon on the lining. N.B. BALLAL, formerly a Graduate Student at Indian Institute of Technology, Kanpur, is presently Assistant Professor, Department of Metallurgical Engineering, Indian Institute of Technology, Bombay 400076, India. A. GHOSH is Professor, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur 208016, India. Manuscript submittedAugust 2 3 , 1982. METALLURGICAL
TRANSACTIONS B
The generally accepted view is that the thermal shielding mechanism plays a majorrole.2'3 It is, however, worthwhile to know the effectiveness of the other mechanisms. The present investigation was undertaken with a view to ascertain the effectiveness of physical shielding. Mixing o f two concentric jets of dissimilar gases (air and carbon dioxide) issuing vertically upward into a water bath in a cold model has been studied. Measurements consisted o f determining the concentration profiles for the gases at various locations downstream from the tuyere exit.
II.
EXPERIM
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