Modeling of Liquid Flow in a Packed Bed in the Presence of Gas Flow
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BLAST furnace technology for the production of molten iron has been in use for over a century, but the actual physics behind the fluid flow phenomena is still not well understood. In an iron making blast furnace, the material is charged from the top, and high temperature/pressure blast is given at the bottom of the furnace through the tuyeres. This high pressure gas blast creates a gas cavity in front of the furnace that is known as the raceway. The lower part of the blast furnace is very important because most of the reducing gases are generated in this zone, and the conditions over there dictate the chemical processes occurring elsewhere in the furnace. Coke particles are burnt in the raceway region and become replenished by fresh coke particles from the surrounding of the raceway. Therefore, the entire burden descends downward very slowly. Molten metal and slag also descend through the coke matrix. Gas rises cross-current (in front of the raceway) and countercurrent to this descending molten material. Determination of optimum operating conditions for the furnace necessitates a sound knowledge of the flow phenomena there. The size of the raceway plays an important role in this entire process. A recent development in the blast furnace theory is the recognition of raceway hysteresis.[1,2,3] In raceway hysteresis phenomena, one can obtain two raceway sizes at the same gas velocity depending on whether the measurement is made in the increasing or V. SINGH, Graduate Student, and G.S. GUPTA, Associate Professor, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012, India. Contact e-mail: [email protected] S. SARKAR, formerly Graduate Student, Department of Materials Engineering, Indian Institute of Science, is Postdoctoral Fellow, Fundamentals of Chemical Reaction Engineering, Faculty of Science and Technology, University of Twente, Twente, The Netherlands. Manuscript submitted July 21, 2006. Article published online April 28, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
decreasing gas velocity. It has been shown experimentally that the decreasing gas velocity conditions are applicable to a moving bed.[4] Gupta et al.[5] successfully predicted cavity size and cavity size hysteresis in a packed bed on increasing and decreasing gas flow rate through a simplified two-dimensional (2-D) model. Subsequently, the same authors developed a correlation for raceway size, applicable to the blast furnace conditions. Comparison with the plant data was good. The main aim of the current study is to develop a model for liquid flow that is applicable to blast furnace conditions and to study the effect of the raceway size hysteresis on it. The molten metal and slag are nonwetting to the coke matrix through which they descend. Experiments have shown that the nonwetting liquid in a packed bed flows in the form of droplet and rivulets.[6,7,8] Most of the early studies aimed at the modeling of liquid flow in the lower part of a blast furnace were based on the continuum assumption for t
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