Study of nonisothermal reduction of iron ore-coal/char composite pellet
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I.
INTRODUCTION
THE term "composite pellet" describes a pellet consisting of a mixture of fines of iron-beating oxide and carbonaceous material (coal, coke, char), to which coldbonding techniques have imparted sufficient green strength for subsequent handling. The pellet should have sufficient strength to withstand high temperature and stresses during reduction in a furnace. Recent studies by various researchers have demonstrated that cold-bonded composite pellets can be charged as burden material in cupolas, l~-SJ rotary kiln, 15,6,71and even in blast furnaces. E5,8,91Advantages of processing composite pellets are: (a) utilization of fines without high-temperature burden preparation, such as sintering, heat hardening of pellets, and cokemaking; (b) use of noncoking coal as reductant; and (c) enhancement of productivity in ironmaking processes such as sponge ironmaking in rotary kiln, due to higher rates of reduction as a consequence of intimate mixing of fines of iron ore and reductant. The principal technological barrier to utilization of composite pellets on a large scale is the high cost of effective cold-bonding techniques. However, the composite pellet route of ironmaking seems to have commercial potential for the future. Indian iron ore deposits are partly soft and friable in nature, so they contain quite a good amount of superfines ( - 1 0 0 mesh) rich in iron content (65 pct and S.K. DUTTA, formerly Graduate Student, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India, is Senior Lecturer, Department of Metallurgical Engineering, Faculty of Technology and Engineering, Maharaja Shyaji Rao University of Baroda, Baroda-390 001, India. A. GHOSH, Professor, is with the Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur-208 016, India. Manuscript submitted August 20, 1992. METALLURGICAL AND MATERIALS TRANSACTIONS B
above). These are known as "blue dust." Ore and iron oxide fines are generated during processing as well. India also has a large deposit of noncoking coal. Again, significant quantities of coal fines and coke breeze also are produced during coal mining and coking of coal, respectively. In view of the commercial prospects of composite pellets, it was decided to carry out some laboratory investigations. The present article reports the findings of some fundamental studies on reduction of composite pellets consisting of blue dust, noncoking coal or char fines. The mixture was cold bonded with inorganic binders by steam curing in an autoclave. Reduction was carried out nonisothermally. Reduction of iron oxide or ore by carbon is a key metallurgical reaction in ironmaking. Several laboratory investigations tl~ have been carried out on kinetics of this reaction. Most of them t~~ employed mixtures of iron oxide or iron ore powder with carbon powder. Sometimes the oxide was agglomerated into micropellets b e f o r e u s e . 113.14] In a way, these also were investigations on composite pellets. However, in the context of the present study these w
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