Influence of CaO-SiO 2 -Al 2 O 3 Ternary Oxide System on the Reduction Behavior of Carbon Composite Pellet: Part I. Reac
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CURRENTLY, many ironmaking operations have facilities that make iron ore more usable for the blast furnace operation by improving its physical properties (e.g., pelletizing or sintering). The agglomerating process is well known to be indispensable as the burden acts as a spacer for maintaining the bed permeability. However, during the process, a large amount of fuel is supplied to indurated materials which consequently produce large CO2 emissions.[1] Along with the increased interests in environmental issues and energy usage, extensive research regarding the direct utilization of iron ore fines and non-coking coal in the ironmaking process has been conducted. There are several examples of direct reduction processes, such as rotary hearth furnace (FASTMET, ITmk3), fluidized bed process (FIOR), and rotary kiln process (SL/RN).[1] However, the advantages of these technologies are limited by low productivity combined with a high energy consumption rate, whereas direct reduction processes are usually considered as recycling process for treatment of secondary materials from iron and steel works.[2] For these reasons, the direct use of raw materials in the form of a carbon composite pellet is considered to be more HYUNSIK PARK, Graduate Student, and VEENA SAHAJWALLA, Scientia Professor, are with the Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia. Contact e-mail: [email protected] Manuscript submitted August 7, 2012. Article published online October 11, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
appropriate for the conventional blast furnace process in terms of energy efficiency and cost effectiveness. Due to its advantages of fast reaction rates resulting from the close proximity of reactants, the application of carbon composite iron ore pellet (or briquette) in the blast furnace has been reported by several researchers.[3–6] Nevertheless, there are still plenty of practical challenges in the self-reducing pellet because of the physical property requirements. As the gasification of carbon and the reduction of iron oxide occur simultaneously among the constituents, rapid gas generation of CO and CO2 is clearly expected in the carbon composite pellet that may adversely affect their mechanical integrity. Previous work has developed a kinetic model which is suitable for self-reducing iron oxide pellet.[7] More recently the authors have examined the role of the Boudouard reaction in iron oxide and carbon briquettes[8] with respect to various carbonaceous materials (coal-char, coke, and graphite) on the reactivity of pellets. Although those previous studies established fundamental understanding about the reaction kinetics in carbon composite pellets, there has been limited understanding of the role of mineral binders from the view point of their oxide chemistry. Kang et al.[9] studied the coal-char/slag interactions during pulverized coal injection in a blast furnace. They measured wetting character
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