Effect of carbonaceous particles on slag foaming
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I.
INTRODUCTION
CONTROL of slag foaming is very important in bath smelting as well as in other steelmaking processes. The bath-smelting process is designed to produce hot metal at a high specific productivity without metallurgical coke. The process uses prereduced ore fines or pellets as the raw material, coal as the fuel and reductant, and oxygen or air for combustion. In this process, a large quantity of gas is evolved due to the intense reaction in the vessel. As a result, the volume of the slag expands extensively due to foaming. Therefore, slag foaming has to be controlled to prevent the slag from slopping out of the vessel. Foaming of the slag can be found to limit productivity in bath smelting. Hence, control of foaming is one of the key issues for achieving the optimum production rate. On the other hand, a certain amount of foamed slag in the vessel is considered to be useful for promoting the transfer of heat generated by post-combustion to the bulk slag. A dynamic measurement of foam stability, the foam index,t~J is a method to quantitatively describe slag foaming. The foam index, E, is defined as the ratio of the foam height, H~ to the superficial gas velocity, vs: =H---Z [1] v, In this case, the foam height is defined as the difference between the level of the surface of the foamed slag and that of the slag at rest. The superficial gas velocity is the volumetric gas flow rate (Q) per unit area of the cross section
Y. ZHANG, formerly Graduate Student and Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University, is with Armco Advanced Materials Co., Butler, PA 16003-0832. R.J. FRUEHAN, Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted February 9, 1993. METALLURGICALAND MATERIALSTRANSACTIONS B
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In the studies by Ito and Fruehan,tq Jiang and Fruehan, t2] and Roth et aL,t3] slag foams were generated by argon gas bubbling through injection nozzles, and the foam indexes of many slag systems have been examined. As a result, the foam index has been correlated as a function of the physical properties such as the density, viscosity, and surface tension of the liquid slag. Recently, Zhang and Fruehan[4] have demonstrated that the foam index is also inversely proportional to the gas bubble size. It is known that coke can reduce slag foaming in steelmaking processes. Matsuo [51have reported that top injection of coke was very effective in controlling excess foaming during the smelting reduction of iron chrome ore. Iso et al. t61 have also found that slopping in an oxygen converter was totally suppressed after injection of 200 kg/min coke breeze into the foamed slag for only 1 - 2 min. Recently, the use of carbonaceous particles in controlling foaming has been investigated in pilot-scale bath-smelting experiments by several authors. [7,s,9] The foam height was found to decrease significantly with the increase of the ratio of the weight of the c
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