Estimation and modeling of parameters for direct reduction in iron ore/coal composites: Part II. Kinetic parameters
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I.
INTRODUCTION
Carbon gasification:
The direct reduction of iron ore/coal composites (DRIOCC) is a relatively new coke-free technology which now comprises a small but growing part of the worldwide direct reduction of iron ore industry. Mathematical models are proving useful in understanding the laboratory experiments and in extrapolating these to the pilot and plant scale. Modeling allows the prediction of the time course of the reduction and may suggest strategies for the overall improvement of the process. The validity of these models depends critically on accurate estimates of the kinetic parameters associated with the iron ore reduction process and the production and consumption of reductants. This article gives estimates of the relevant kinetic data and provides a critical analysis of models of the rates of iron ore reduction and the gasification of the carbonaceous material used to supply the reductants, as well as a review of several recent models of pyrolysis. The main reactions for the coal-based direct reduction can be summarized by the following scheme (for details, refer to the article by Donskoi and McElwain[1]): hematite to magnetite: 3Fe2O3 ⫹ CO ⫽ 2Fe3O4 ⫹ CO2
[1]
: 3Fe2O3 ⫹ H2 ⫽ 2Fe3O4 ⫹ H2O
[2]
magnetite to wustite : 1.202Fe3O4 ⫹ CO ⫽ 3.807Fe0.947O ⫹ CO2
wustite to iron
[3]
: 1.202Fe3O4 ⫹ H2 ⫽ 3.807Fe0.947O ⫹ H2O
[4]
: Fe0.947O ⫹ CO ⫽ 0.947Fe ⫹ CO2
[5]
: Fe0.947O ⫹ H2 ⫽ 0.947Fe ⫹ H2O
[6]
E. DONSKOI, QUT Postdoctoral Fellow, and D.L.S. McELWAIN, Professor, are with the Centre in Statistical Science and Industrial Mathematics, School of Mathematical Sciences, Queensland University of Technology, Brisbane, Qld 4001, Australia. Contact e-mail: s.mcelwain @qut.edu.au L.J. WIBBERLEY, Senior Research Associate, is with BHP Billiton Innovation, Wallsend, New South Wales, Australia 2287. Manuscript submitted May 6, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
Boudouard reaction: C ⫹ CO2 ⫽ 2CO Water gas reaction: C ⫹ H2O ⫽ CO ⫹ H2
[7] [8]
Coal devolatilization: Coal to carbon: Coal → C ⫹ volatile matter
[9]
Various different conditions can prevail during the coalbased iron ore reduction: different specimen and particle sizes, ambient atmospheres, heating regimes, geometries, and compositions. This article reviews and analyzes different approaches to the modeling of kinetic parameters in DRIOCC. It is shown that while the modeling may not necessarily involve all the details of the reaction mechanism, it is still able to adequately represent the overall time course of the reduction. II.
RATE OF REDUCTION
A. Integrated Rate of Reduction Here we introduce the term “integrated rate of reduction” (IRoR), by which is meant the total rate of reduction of a whole specimen, which may be, for example, a spherical or cylindrical pellet or packed bed. The IRoR does not carry information about the difference between reduction rates at distinct points in the specimen. In the next section, we discuss modeling of the local rate of reduction (LRoR). We note that the IRoR can be regarded as an LRoR
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