Modeling the discontinuous liquid flow in a blast furnace
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I.
INTRODUCTION
AN ironmaking blast furnace is a complex reaction vessel involving counter-, co- and/or cross-current flows of gas, liquid, and solids. It is important to understand the multiphase flow phenomena involved in order to better describe the chemical reactions and heat and mass transfer between different phases and, therefore, to develop effective methods for process control. In the past, many efforts have been made in this direction. Yagi[1] recently presented a comprehensive review of the previous work in this area, which can well be used as the basis for further development. The particular interest here is the transport phenomena in the cohesive zone of a blast furnace. It is known that the cohesive zone plays an important role in achieving stable and efficient blast furnace operation. Through this zone, gas is redistributed for the prereduction of iron ore in the stack zone, where counter-current flow of gas and solids occurs. It is also within this zone that the liquid phase (liquid iron and slag) is generated and the complex multiphase flow in the lower part of a blast furnace starts. It is extremely difficult, if not impossible, to measure the internal gas-liquid flow through packed coke beds, and, as such, mathematical modeling, often coupled with physical modeling, has been widely used to describe this complex flow system. A number of liquid flow models have been proposed to simulate the liquid flow below the blast furnace cohesive zone. The potential flow model, in which continuous flow is assumed for both gas and liquid phases, was mainly used by early investigators.[2–5] However, to obtain predictions comparable to experimental measurements, the liquid flow region for a given condition had to be determined a priori. Consequently, the general and effective use of this model is difficult. Moreover, evidence points to the fact that liquid flow in the lower part of a blast furnace, particularly within G.X. WANG, Research Fellow, S.J. CHEW, Research Student, and A.B. YU, Senior Lecturer, are with the School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia. P. ZULLI, Principal Research Engineer, is with BHP ResearchPort Kembla Laboratories, NSW 2505, Australia. Manuscript submitted January 30, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
the cohesive zone where the liquid is generated, is not continuous.[6,7] The discontinuous flow feature was first taken into account by Ohno and Schneider in their so-called probability model.[8] In contrast to the continuum approach, this model can predict the liquid flow region in addition to the liquid flow distribution. However, the computational grids generated for the numerical calculation of this model should correspond to the size of packed particles, which would increase the numerical effort considerably. To overcome this deficiency, Wang et al.[9] proposed a combined probability-continuous model to simulate the liquid flow. In this model, the probability model of Ohno and Schneider is used to determin
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