Characterization of Slag Flow in Fixed Packed Bed of Coke Particles
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DUCTION
THE blast furnace (BF) is a counter-current and co-current flow reactor that involves many complex processes. The coexistence of several phases (solids like coke and iron ore, liquids like slag and metal melts, gases like CO, CO2, H2, H2O, and N2, and char and coal powders) makes the processes complicated.[1] These different phases interact and undergo chemical and physical changes as they are exposed to very high temperatures and pressures.[2] Owing to the very slow descent of the coke bed in the dripping zone of the BF, it is usually considered as a fixed (stationary) packed bed.[3] One of the important processes that occurs in the dripping zone of the BF is the mass transfer between gas, metal, slag, and coke, which depends on the flow phenomena of the liquids and gases in the packed coke bed.[4,5] The flow behaviors of the liquids and gases are strongly influenced by their physical properties and the packing structure of the coke bed. Additionally, factors like the contact angle of the slag on the coke, the surface tension of the slag, and the slag density significantly affect the slag holdup in the packed coke bed.[6]
DEREJE DEGEFA GELETA, MD IRFANUL HAQUE SIDDIQUI, and JOONHO LEE are with the Department of Materials Science and Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Korea. Contact e-mail: joonholee@ korea.ac.kr Manuscript submitted 9 May 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
In the BF, iron ore and coke particles are charged alternately from the top; thus, stratified descending layers are formed.[7] The iron ore starts softening and melting in the cohesive zone. Below this, coke—the only solid material at a temperature around 2273 K (2000 °C) in the dripping zone of the BF—provides a mechanical support for the burden above it. To allow the downward flow of molten iron and slag and the upward flow of blast air, the coke bed must be permeable. The permeability is strongly affected by liquid holdups in the coke bed, which are affected by the packing density and structure of the packed bed.[8,9] Numerous researches in different engineering disciplines have investigated the liquid holdup for liquid flow through packed-bed particles. Most of the previous studies were based on a cold model[3,10–15] in which tap water was used as the liquid and stainless steel or alumina balls were used as the packed-bed material. However, the flow of slag and metal melts in the BF is different from the flow of water of a cold model: molten slag and metal have a higher density than solid coke particles, and molten slag exhibits greater nonwetting behavior on the packed coke particles. In recent years, fascinating research has been performed on the slag holdup and the dripping flow at high temperatures.[9,16–23] Saito et al.[18] studied the density, surface tension, and contact angle of the molten slag for carbonaceous materials in the temperature range of 1673 to 1773 K by using the sessile drop method and found that at a temperature of less than 1773 K, the aforementioned slag properties essentially
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