Factors influencing dissolution of carbonaceous materials in liquid iron
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km rm [C] 100 kr f C* km rm Kr 100
kr a solid [C]*
Factors Influencing Dissolution of Carbonaceous Materials in Liquid Iron
Replacing [C]* in Eq. [4] with Eq. [6], the carbon dissolution rate is given by rd Ak t aasolid
HAIPING SUN Carbon dissolution into liquid iron was investigated by a kinetic model assuming the rate is limited by interfacial carbon dissociation and mass transfer in the liquid iron. The rate influencing factors and the inter-relations among them were discussed with the aid of the kinetic model.
Carbon dissolution into liquid iron has been intensively studied with various carbonaceous materials due to its importance in future blast furnace ironmaking and alternative iron smelting processes. The rate of this reaction was conventionally considered to be limited by the mass transfer in liquid iron.[1–6] In the recent studies with various carbonaceous materials, the interfacial dissociation reaction was suggested to be slow for the materials with complex structure, such as coal.[7,8,9] This requires a kinetic treatment of observed rates that includes interfacial reaction and mass transfer. In this study, a kinetic model is presented and the rate influencing factors are discussed with the aid of the kinetic model. When a solid carbon material contacts with liquid iron, the dissolution of carbon occurs through two elementary steps: the first step is the dissociation of carbon atoms from solid structure into the liquid at the solid-liquid interface, as shown by Eq. [1], and its rate is written as Eq. [2] for a reversible reaction: C(solid) → [C]* rr Akr aasolid
a C* b Kr
[1] [2]
The second step is the mass transfer of carbon from the interface into liquid bulk, as shown by Eq. [3], and its rate is given by Eq. [4] for a diffusion process: [C]* → [C] rm
Ak m rm ([C]* [C]) 100
[3] [4]
Since two steps occur in series, the dissolution rate is rd rr rm
[5]
Equating Eq. [2] with Eq. [4] and using the activity relation at the interface, aC* f C* [C]*, the carbon content at the interface can be obtained as HAIPING SUN, Lecturer, is with the CRC for Coal in Sustainable Development, School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia. Contact e-mail: h.sun@ unsw.edu.au Manuscript submitted October 4, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
[6]
f C* [C] b Kr
[7]
where 100 f C* 1 1 kt kr k m rm Kr
[8]
Equation [7] involves interfacial reaction and mass transfer. The driving force is a solid f C* [C]/Kr. There is no integration form of Eq. [7] because kt and f C* vary with [C]* and the latter varies with [C]. When the carbon dissolution is limited by mass transfer, i.e., 100 f C* /k m rm Kr 1/kr, the equilibrium of Reaction [1] will be achieved at the interface. It gives [C]* [C]sat, f C* fCsat, and a*C asat C . The rate equation becomes rd
Ak m rm ([C]sat [C]) 100
[9]
The driving force is [C]sat [C]. The rate is dictated by km and [C]sat: the former varies with temperature, liquid composit
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