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Page Line 20, " • • . where Z > 0 fluid a and Z < 0 outside fluid a -American Iron and Steel Institute and to the National Research Council for the award of an N.R.C. Scholarship. Grateful acknowledgments are due to the technical staff and graduate students of the Department of Metallurgy and Material Science at McMaster whose help has been invaluable. Many thanks are given to Mrs. Barbara O'Connor for the excellent typing of this thesis and to Mr. Martin van Costen and Mr. Don Wilson for their capable assistance with the technical drawings and photographs.

The present work is a fundamental study of

The kinetics of the carbothermic reduction of iron oxides in a composite pellet made of taconite concentrate and high-volatility coal has been studied by means of mathematical modeling that simultaneously takes into account the transfer rates of both the mass and the heat, and the rates of chemical reactions. The computational results, which have been validated with experimental data in the literature, confirm that the overall rate of the carbothermic reduction, which is strongly endothermic, is limited by heat-transfer steps. From a kinetics viewpoint, the optimum composition of the composite pellet is approximately in accordance with the stoichiometry, when CO is assumed to be the sole oxide of carbon in the gas. To raise the temperature of the pellet from its ambient value to furnace temperature, the heat required is greater than that needed for sustaining all chemical reactions, including the Boudouard reaction. The gaseous product consists mainly of CO and H 2 , except in the very initial stage. The overall observable reaction rate, in terms of the volumetric rate of the generation of gases, peaks at approximately 30 seconds of reaction time.

Fundamentals of kinetics and mechanisms of iron oxide reduction of indurated pellets by reducing gases and of coal-containing iron ore composites, are reviewed. The gaseous products of the latter can be used to protect sponge iron from re-oxidation by a fully oxidized flame, provided the bed height of coal-containing iron ore agglomerates and the flame temperature are sufficiently high. Potential operational problems in RHF (Rotary Hearth Furnace) for tall beds and high flame temperature are discussed and a new hearth furnace, the Paired Straight Hearth (PSH) Furnace, is proposed.

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