A Computational Study on the Reduction Behavior of Iron Ore/Carbon Composite Pellets in Both Single and Multi-layer Bed
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NTRODUCTION
DEPLETION of high grade ore, the demand for utilizing low grade iron ore and coal fines, iron bearing steel plant solid waste, and environmental concerns[1] have lead researchers to look for alternative routes of iron making. One such route involves RHF (rotary hearth furnace), where iron ore and coal fines in the form of cold bonded composite pellets/ briquettes are converted to direct reduced iron (DRI) nuggets for subsequent melting in the electric arc furnace. RHF is a donut shaped furnace where a rotating hearth carries the pellets/briquettes through various temperature regimes to produce DRI. Some of the successful commercial processes based of RHF are Inmetco, FASTMELT and ITmk3.[2,3] The major advantages of RHF lie in the flexibility of the input material. Iron bearing steel plant solid waste, low grade iron ore fines cold bonded with
SOUMYADEEP DASGUPTA, SOORAJ SALEEM, and GOUR G. ROY are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721302, India. PRAKASH SRIRANGAM and MICHAEL AUINGER are with the Warwick Manufacturing Group, University of Warwick, Coventry CV4 7AL, UK. Contact e-mail: [email protected] Manuscript submitted July 17, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
low grade carbonaceous material in the form of pellets and briquettes, could be utilized and thereby they are more eco-friendly reducing the solid waste disposal. Extensive research work has been carried out to understand the reduction of iron ore coal composite pellets, which are mostly limited to experimental investigations for single pellets. The amount of carbon inside the pellet as well as the effects of pellet size, shape, additives, heating rates, and compactness of the pellets have been studied in detail.[4–8] However, very few studies have been reported on multi-layer bed pellet reduction. Sohn and Fruehan[9] investigated the role of coal volatiles on the kinetics of the composite pellet reduction in an infra-red heated laboratory scale multi-layer RHF. For a single pellet, the volatiles come out fast and thereby do not contribute much to its reduction. However, for a multi-layer system, volatiles coming out from the bottom layers participate in the reduction of upper layers pellets during their ascent. Huang et al.[10] studied the reduction of iron ore–coal composite pellets in a tall bed hearth furnace and reported higher metallization at the top of the bed compared to the bottom layer, in the presence of coal with a low content of volatiles. A higher degree of metallization at the bottom of the bed compared to the topmost zone was found in the case of coal with higher volatile content. It is apparent that there have been very few investigations on the multi-layer bed RHF, and particularly no attempts have been made to simulate the RHF using mathematical models on the continuum
level. Although few semi-empirical models[6,11–14] have been reported to estimate rate parameters and to predict the phase evolution during the
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