Effect of Contact Resistance on Bulk Resistivity of Dry Coke Beds
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THE electrical resistivity of the coke bed is of great interest when producing FeMn, SiMn, or FeCr in a submerged arc furnace. A coke-enriched area has been found around and beneath the electrode tip in several digouts of industrial furnaces of such processes.[1–4] In this article, this coke-enriched area between the electrode tip and the metal bath is refered to as the coke bed. The shape and size of the coke bed may vary from a cylinder of approximately the same diameter as the electrode, extending from the electrode tip to the metal,[3] to a wide coke bed stretching between the electrodes.[4] The energy necessary for the reduction of the ore is supplied by P.A. EIDEM, formerly with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway, is Researcher, with Eramet Norway AS, c/o SINTEF Materials and Chemistry, Alfred Getz vei 2, N-7465 Trondheim, Norway. Contact e-mail: per-anders.eidem@ erametgroup.com M. RUNDE, Senior Researcher, is with Electric Power Technology, SINTEF Energy Research, NO-7465 Trondheim, Norway, and Adjunct Professor, Department of Electrical Power Engineering, NTNU. M. TANGSTAD, Professor, and J.A. BAKKEN, Professor Emeritus, are with the Department of Materials Science and Engineering, NTNU. Z.Y. ZHOU, Postdoctoral Student, and A.B. YU, Professor, are with the Lab for Simulation and Modelling of Particulate Systems, School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. Manuscript submitted April 9, 2008. Article published online April 15, 2009. 388—VOLUME 40B, JUNE 2009
ohmic heating from the current flowing through the coke bed, as described by, e.g., Olsen et al.[5] The coke bed resistance Rtot of a dry coke bed with no slag (Figure 1(a)) is dependent on the geometry and the bulk resistivity of the coke bed qbulk. The bulk resistivity is dependent on the contact resistance Rc, the material resistivity qm of the material the particles are made of, and how the particles are electrically connected to each other. The geometry of the coke particles together with the material resistivity of the coke define the resistance of a particle Rm. An aim of this work has been to obtain empirical data that may be used in a model of the coke bed. Several investigations have been done on the electrical resistivity of both dry coke beds,[6–18] charge mixes,[6,9,10,13,15–17,19] and of the related slags.[6,20–22] These investigations have been valuable in understanding how the bulk resistivity of the coke bed is affected by various factors such as the temperature, type of carbonaceous material, and particle size. At a particle level, i.e., when considering one or two particles or pieces of coke, measurements have been done on material resistivity, i.e., the resistivity of the uncrushed material that makes up the coke particles[23,24] and contact resistance, i.e., the resistance between two particles in contact[24] (Figure 1(a)). The link between these two levels has to some exte
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