Dissolution kinetics of particulate graphite injected into iron/carbon melts
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I.
INTRODUCTION
TURBULENTmolten iron/carbon alloys are highly reducing and provide effective heat and mass transfer media. If air or oxygen are blown onto or into an iron/carbon melt an exothermic reaction occurs in which the oxidation of dissolved carbon to carbon monoxide is extremely rapid at temperatures in excess of 1300 ~ If coal or other carbonaceous material is added to the melt the strong affinity of molten iron for carbon ensures efficient solubilization. The simultaneous dissolution of carbon and the oxidation of the dissolved carbon by oxygen injection forms the basis of a number of proposed iron bath coal gasification and ferrous smelting processes. [~'21The addition of auxiliary fuel in the form of solid carbonaceous materials to oxygen steelmaking converters to increase scrap melting capacity is also being actively pursued. [3.4] The most appropriate carburizing agent is, of course, coal, added either as lumps or injected as fines. The dissolution behavior of coal is highly complex, involving the rapid evolution of volatiles under flash heating conditions, perhaps particle breakup and the dissolution of the remaining pyrolyzed char. In order to avoid these complications, the present work considered the dissolution kinetics of nonvolatile particulate graphite injected into iron/carbon baths. The reaction and dissolution of coals is being assessed in continuing work.
II. PREVIOUS G R A P H I T E DISSOLUTION STUDIES The majority of previous experimental graphite dissolution investigations have concentrated on the use of stationary or rotating graphite rods immersed in Fe/C melts, tS-~~ All these studies concluded that graphite dissolution is governed by mass transfer in which diffusion of carbon in a J. K. WRIGHT is Senior Principal Research Scientist, CSIRO, Division of Mineral Engineering, Melbourne, Australia. B.R. BALDOCK, formerly Experimental Scientist, CSIRO, Division of Mineral Engineering, is Development Metallurgist, AUSMELT Pry. Ltd., Melbourne, Australia. Manuscript submitted January 2, 1987. METALLURGICALTRANSACTIONSB
liquid boundary layer at the graphite surface is rate controlling. It is also generally agreed that sulfur in molten iron, even at relatively low levels, depresses graphite dissolution rates. There is some disagreement, however, as to whether the retarding effect of dissolved sulfur is due to mass transfer or chemical limitations. Little work has been done on the dissolution kinetics of particulate carbon in Fe/C melts. Wright and Denholm t2'"] investigated the dissolution rates of batch additions of particulate graphite, petroleum coke, and brown coal char to gas stirred Fe/C melts. It was found that the rates were mass transfer controlled, and increased with increase in the gas stirring power input. This work also showed the retarding effect of bath sulfur on the carbon dissolution rates. Lehner ]~21injected carbon powder into 6 tonne steel melts and found that mass transport under the conditions used is so fast that carbon assimilation matched the feed rate.
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