Reduction Kinetics of Iron Ore-Graphite Composite Pellets in a Packed-Bed Reactor under Inert and Reactive Atmospheres
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INTRODUCTION
THE depletion of coking coal reserves and growing environmental concerns have motivated researchers to search for a coke-free and environmentally friendly ironmaking process. Furthermore, large amounts of iron ore fines and coal fines are generated during mining and a large fraction of these particles remains unused. The fines cannot be used as charge materials in a conventional blast furnace because fines will either be fluidized or hamper the permeability of the countercurrent gassolid reaction severely, and, consequently, affect the productivity of the blast furnace. Therefore, several attempts have been made to find alternative routes of iron making where noncoking coal and ore fines could be used. Although several alternative routes have already been developed which could use ore and coal fines fully/partially (Fior, Corex, Fastmelt, ITmk3, etc.), it appears that there is still a need for further studies on the possible process development, which can use both iron ore and coal fines for the production of iron. Generation of composite pellets by using these fines, and subsequently their reduction in a shaft furnace/retorts could produce excellent product for feeding blast G.M. CHOWDHURY, formerly SRF, Department of Metallurgical & Materials Engineering, Indian Institute of Technology, is Assistant Manager, RDCIS, SAIL, Ranchi, India. G.G. ROY, Associate Professor, and S.K. ROY, Full Professor, are with the Department of Metallurgical & Materials Engineering, Indian Institute of Technology, Kharagpur, India, 721 302. Contact e-mail: [email protected] Manuscript submitted July 18, 2007. Article published online March 20, 2008. 160—VOLUME 39B, APRIL 2008
furnaces or even Electric Arc Furnace (EAF) depending on the degree of metallization. This process could be a possible alternative to use the fines effectively. Several fundamental studies[1–15] have been carried out on the reduction kinetics of composite pellets. Several authors[1–8] have demonstrated that increasing the amount of carbonaceous materials relative to iron-oxide content in an iron-ore-coal composite pellet/mixture increases the rate of reduction. A few reports[1,9,10] have also mentioned the effect of type and size of carbonaceous materials on the reduction kinetics. Both Rao[1] and Fruehan[9] have reported that the rate of reduction increases with decreasing carbon particle size. Some researchers[2,3,11] have studied the dependence of rate of reduction on the specimen size. Although Srinivasan et al.[2] and Basu et al.[3] did not observe any effect of specimen size on the rate of reduction in the size range of 9 to 12 mm, Nacimento et al.[11] demonstrated that the pellet size in the range 9.1 to 15.3 mm does affect the kinetics of reduction process. Seaton et al.[12] have also indicated that the reduction of higher size pellet (14 mm) comes to a halt at the later stage of reduction due to inadequate heat transfer from the furnace atmosphere to pellet interior. It is further reported[5,13] that different additives, such as Li2O, Na2CO3, K2CO
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