Scrap Dissolution in Molten Iron Containing Carbon for the Case of Coupled Heat and Mass Transfer Control
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ION THROUGH SIMULTANEOUS HEAT AND MASS TRANSFER
SEVERAL investigations have been done where the problem of scrap dissolution is solved by considering simultaneous heat and mass transfer[1–19] (of carbon). The special problems in this category include the case of scrap melting in the BOF steelmaking process. Asai and Muchi[1] presented a detailed model for dissolution of scrap in the BOF. Temperature and carbon concentration of the melt were considered as important variables and their influence on the progress of melting of the scrap was investigated for different operating conditions. The temperature and carbon concentration profiles were assumed to exist only inside the liquid close to the interface. As a simplification, the composition of the solidified shell formed on the scrap was assumed to be the same as that of the scrap. The temperature inside the scrap was considered to be uniform and the velocity of the moving interface was considered to be constant. It AJAY KUMAR SHUKLA, Assistant Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Madras, Chennai 600036, India. Contact e-mail: [email protected] BRAHMA DEO, Professor, is with the Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, Kanpur 208016, India. D.G.C. ROBERTSON, Professor, is with the Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO. Manuscript submitted May 12, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
may be noted that such approximations are, however, valid only for the case of thin-sized scraps. Hartog et al.[2] developed an interesting numerical procedure based on the solution of simultaneous, unsteady-state heat transfer and mass transfer of carbon equations solved at the bath–scrap interface. They considered a moving boundary layer approach to estimate the heat transfer coefficient and used the Chilton–Colburn analogy to estimate the mass transfer coefficient. The value of the heat transfer coefficient was estimated as 47,500 W/m2/K. The temperature of the scrap–melt interface and the carbon composition at the interface was deduced from the Fe-C phase diagram. The rates of energy generation due to chemical reactions were calculated from off-gas analysis and bath sampling. The heat losses from the BOF were calculated by a posteriori calculations in real heats. Solutions were thus obtained for different sizes of scrap and carbon contents. The results showed that the evolution of temperature of the bath and complete dissolution of the scrap depended upon the scrap size distribution. For example, in the presence of a higher proportion of light scrap, the temperature of the bath was predicted to be almost near the liquidus temperature, while the dissolution of the colder heavy scrap had to wait until the light scrap dissolved. The diffusion of carbon inside the solid scrap was ignored. In another parallel approach, Gaye et al.[3] expressed heat transfer coefficient as a function of input energy to the sy
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