Estimation and modeling of parameters for direct reduction in iron ore/coal composites: Part I. Physical parameters
- PDF / 175,290 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 84 Downloads / 179 Views
I. INTRODUCTION
Wustite to iron:
DIRECT-REDUCED iron is used as feedstock in iron and steelmaking processes, including electric-arc and blast furnaces. While the majority of the worldwide production uses natural gas as the reductant, there are a significant number of low-reaction-temperature ironmaking processes in which iron ore/coal agglomerates are used to produce iron using the carbon in the coal and the volatiles which evolve from the coal as the reductant. An advantage over the traditional blast-furnace ironmaking technology is that these processes do not require the production of coke, which is expensive and during which the environmentally harmful off-gases are hard to contain. In the direct reduction in iron ore/coal composites (DRIOCC), a mixture consisting of fines of iron-bearing oxide and carbonaceous material (coal, coke, and char) is heated to a temperature below the melting temperature of any of the materials involved. If the process requires the formation of pellets, a small amount of binder is also used. Volatile matter from the coal, carbon monoxide from the Boudouard reaction, and hydrogen and carbon monoxide from the watergas reaction (as detailed subsequently) react with the iron oxide and reduce the iron oxide to iron. The main reactions for the coal-based reduction of hematite can be summarized by the following scheme: Hematite to magnetite: 3Fe2O3 ⫹ CO ⫽ 2Fe3O4 ⫹ CO2
[1]
3Fe2O3 ⫹ H2 ⫽ 2Fe3O4 ⫹ H2O
[2]
Magnetite to wustite: 1.202Fe3O4 ⫹ CO ⫽ 3.807Fe0.947O ⫹ CO2
[3]
1.202Fe3O4 ⫹ H2 ⫽ 3.807Fe0.947O ⫹ H2O
[4]
E. DONSKOI, 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, Queensland, 4007, Australia. Contact e-mail: [email protected] Manuscript submitted May 7, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
Fe0.947O ⫹ CO ⫽ 0.947Fe ⫹ CO2
[5]
Fe0.947O ⫹ H2 ⫽ 0.947Fe ⫹ H2O
[6]
Carbon gasification: Boudouard reaction: C ⫹ CO2 ⫽ 2CO
[7]
Water gas reaction: C ⫹ H2O ⫽ CO ⫹ H2
[8]
Coal devolatilization: Coal to carbon: Coal → C ⫹ volatile matter
[9]
Often, instead of Eqs. [3] through [6], the following equations are used: Magnetite to wustite: Fe3O4 ⫹ CO ⫽ 3FeO ⫹ CO2
[10]
Fe3O4 ⫹ H2 ⫽ 3FeO ⫹ H2O
[11]
Wustite to iron:
[12] FeO ⫹ CO ⫽ Fe ⫹ CO2 FeO ⫹ H2 ⫽ Fe ⫹ H2O
[13]
since it is thought that the stoichiometric difference between FeO and Fe0.947O is small and, so, the difference between the coefficients is also small. However, in reaction [3], for example, 1 mole of CO produces 3.807 moles of wustite instead of the 3 moles predicted by Eq. [10], and this can be quite significant. In section II, we discuss what difference this makes for estimating the heats of reaction. The DRIOCC is a very complex process which includes nonuniform heating and mass transfer and, sometimes, complex geometry. It may, for example, involve two or more layers of pellets and nonisothermal heterogeneous reactions in a porous medium. One of the mo
Data Loading...
