Kinetics of the reaction of CH 4 gas with liquid iron
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kc-
Ksask
r
+
1 +Ksas
1 +Ksas
where k ~ , kr, K s , and as are the bare surface rate constant, residual rate constant, adsorption coefficient for sulfur, and activity of sulfur in the metal, respectively. The second term in the rate equation represents the rate of dissociation on the adsorbed sulfur. The rate constants and adsorption coefficient were determined as functions of temperature to be -
12,000
log k ~ - -
+ 2.95
( m o l e / c m 2 s atm)
- 14,000 log k~ - - + 3.45 T
( m o l e / c m 2 s atm)
log Ks -
I.
-
T
1800 T
+ 1.04
INTRODUCTION
T h e r e is a worldwide effort to develop an iron-making process that uses coal directly rather than coke for reduction and energy. For example, in bath smelting, coal is used, eliminating the need for a coke plant. In addition, coal is used in oxygen steelmaking and the electric arc furnace (EAF) to increase scrap melting or reduce the electrical energy required. However, coal contains considerable volatile matter (10 to 45 pct), and a considerable amount of hydrocarbon gas is generated. C H 4 gas represents from 65 to 85 wt. pct of the hydrocarbon gas. Therefore, it is important to clarify the reaction mechanism between CH4 gas and liquid iron. In spite of this importance, little information is available on the interfacial chemical kinetics of this reaction, tl,21 Grabke IEl measured the rate of carburization of y-Fe in CH4-H 2 mixtures. He concluded that the rate of carburization was controlled by the dissociation of C H 4 on the surface of the iron and the dissociation of the activated complex
K. SEKINO, formerly Research Associate, Department of Materials and Engineering, Carnegie Mellon University, is Research Associate, Sumitomo Metal Industries, Ltd., Ibaraki, Japan. T. NAGASAKA, formerly Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University, is Associate Professor, Tohoku University, Sendai, Japan. R.J. FRUEHAN, Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh,-PA 15213. Manuscript submitted February 22, 1994. METALLURGICALAND MATERIALSTRANSACTIONSB
(CH3) was the rate-determining step of this reaction. In addition, Grabke t3J and Fruehan and Martonik t4'SJ measured the reverse reaction, the formation of CH4, on solid iron and concluded that the formation of the activated complex (CH3) controlled the rate of this reverse reaction. However, these measurements were limited to lower temperatures (
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