Fundamental Insight into the Dripping Criteria of Slag and Hot Metal in a Coke Bed Using Energy Minimization Model
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DUCTION
THE dripping zone of the iron blast furnace is important as it has a significant effect on the permeability of the bed, furnace productivity, and quality of the product hot metal. Permeability is determined by coke size, and its distribution, as well as liquid holdup in the coke bed at any instant of time. The flooding limit, which is directly a function of permeability of the bed, determines the maximum blast rate that can be purged through the tuyeres, indirectly deciding the furnace’s maximum productivity. On the other hand, it is reported that the various important metalloid reactions, such as reactions of C, Si, Mn, and S, occur in the dripping zone of the blast furnace.[1] Therefore, the quality of the output hot metal is decided by the reactions in this zone. The kinetics of the reactions are dependent on the interfacial area of the liquid–gas, liquid–solid, etc., as well as on the volume of the liquid, and their residence times. Hence, it is important to understand the liquid flow behavior, volume fraction, and shape of the liquid holdup in the packed bed of coke in the dripping zone of the blast furnace.
SNIGDHA GHOSH, N.B. BALLAL, and N.N. VISWANATHAN are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashta 400076, India. Contact email: [email protected]. Manuscript submitted April 30, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
From the fusion zone, the hot metal and slag drip down through the slowly descending coke bed of the blast furnace. During continuous irrigation of a bed, some amount of liquid remains in the bed at any instant due to various resistances; this is known as the total holdup. This total holdup is conceptually divided into two portions: the portion that remains in the bed even after the liquid flow is stopped and the portion that drains away. The first portion is known as the static holdup and the second one is the dynamic holdup. Besides adversely affecting the permeability of the bed, the static holdup and dynamic holdup behave differently in terms of their residence time. This, in turn, has an effect on mass transfer and heat transfer kinetics[2] and, thus, determines the extent of minor reactions in the trickling zone.[3] It is important, therefore, to understand the characteristics of the holdup of hot metal and slag in the packed bed of coke. It is found by predictions from room temperature studies that static holdup of slag and hot metal is significantly greater than the dynamic holdup.[4] Hence, understanding the static shape and volume of the slag and hot metal droplets in the coke bed is important. This article concentrates on developing some fundamental understanding of the static liquid holdup. Various experimental and modeling studies suggest that surface tension, density, contact angle of the liquid, and size of solid particles influence the static liquid holdup in any packed bed. The Bond number, which is the ratio of gravitational force to surface tension force, is used to co
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