carbonaceous material with iron ore during agglomeration has definite advantages. The reduction kinetics is expected There is a need for the development of efficient to be enhanced owing to the presence of reductants in situ, industrial processes to use iron ore fines of high leading to shorter diffusion distances of the reductant, and grade. Attention is particularly drawn to rotary kiln also because a large number of reaction sites are available sponge ironmaking technology using lump iron ore, simultaneously. These agglomerates must be cold bonded where productivity is low and energy consumption since the carbonaceous material is to be retained for reduction. high compared with gas based processes.Any attempt to heat harden would result in premature Fundamental studies carried out elsewhere indicate consumption of in situ reductants. that the reduction of lump iron is accelerated if aThe reduction of iron oxides mixed with carbonaceous limited amount of carbonaceous material is material has been an interesting area of research for many incorporated in the agglomerate of iron ore fines.years. Most investigations have been of a fundamental Based on these considerations, cold bonded nature, studying the kinetics and reaction mechanisms of ore-coal composite pellets have been developed carbothermic reduction.3-8 These studies have been confor sponge ironmaking in a rotary kiln. These ducted on either single particles or handmade agglomerates. composite pellets were tested in the laboratory andIn a few cases, a commercial process has been developed to found to reduce very quickly, compared with lump produce ore-coal agglomerates, with subsequent reduction iron ore. Composite pellets were also tested in an studies. In a programme started at Michigan Technological 8 t/day rotary kiln sponge iron plant giving University (MTU) in 1966, a cold bonded pelletisation enhanced productivity and lower coal consumption, process termed 'MTU Pelletech' was developed,1 but low and these results will be presented in Part 2 of this temperature, high pressure autoclaving was needed to paper (next issue).I&S/1494a harden the green pellets. Another process termed 'Inmetco' produced green pellets without any heat hardening step2At the time the work was carried out, Dr Agrawal and Dr Prasad but the pellets were so weak that they had to be charged were at the R&D Centre for Iron and Steel, Steel

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Cold bonded ore-coal composite pellets developed on a laboratory scale (Part 1 of this two part paper) were tested in a rotary kiln sponge iron plant. This plant had a 12 m length refractory lined rotary kiln of 8 t/day iron ore throughput capacity. Kiln operation was optimised to achieve more than 90% metallisation of sponge iron using ore-coal composite pellets. The kiln productivity increased and energy consumption decreased, compared with levels obtained when sized lump ore was used as iron oxide feed material. The plant trials established the suitability of composite pellets for sponge ironmaking with enhanced kiln productivity.I&S/1494b

Kinetic studies on smelting reduction of unreduced fluxed composite pellets (FCP) and fluxed composite pre‐reduced iron ore pellets (FCRIP) have been carried out in an induction furnace. The pellets are charged into the slag layer floating on the carbon saturated molten iron bath in a graphite crucible. The slag basicity was however varied such that it has the same value as that of the pellets charged. The temperature of the slag is varied within the range of 1623K to 1823K for the pellets of basicity 2.0. Kinetic studies show a mixed kinetic model of both diffusion and chemical reaction controlled. While the smelting of FCRIP follows the model expressed as G(or) = 1‐(2/3)(α) ‐(1‐α)2/3, the unreduced FCP pellets initially follow the diffusion controlled model of G(α) = α2 followed by a chemical reaction controlled first order model of ‐ln(1‐α) at the latter stages of smelting reduction, where α denotes the degree of reduction. The basicity dependence on the kinetics is not very significant. Comparison of the activation energy values explains that the smelting reduction with pre‐reduced pellets seems to be a rather less energy intensive process.

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Johnson-Mehl equation is written as da.~. = kn tn_ 1 (1 -a ) where a is the degree of reaction, t time and n a constant. Use of this equation in kinetic analysis present problems because of the presence of a 't' term on the right hand side. The equation is not a true -kinetic equation and k is not a true rate constant.This paper presents a brief discussion on the use of this equation as such or in a modified form and also indicates the proper procedure for evaluating kinetic parameters correctly. Some experimental data on the reduction of Fe203 to Fe304 have been used to test the mathematical procedure proposed. This reaction is known to follow the typical trend described by Johnson-Mehl equation.

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