Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

Abstract

A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO 2 and wu¨stite reduction by CO by isolating them from the influence of heat-and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wu¨stite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coalchar. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wu¨stite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wu¨stite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

Reduction of Iron-Oxide-Carbon Composites: Part II. Rates of Reduction of Composite Pellets in a Rotary Hearth Furnace Simulator

“…It is important to note that the same coal was used for making both the composite pellets and the powder mixtures that were used, in turn, to determine the reaction-rate constants. [5] The eucalyptus wood charcoal (Vallourec & Mannesmann Tubes, Belo Horizonte, MG, Brazil) contained 71.49 mass pct fixed carbon, 24.67 mass pct volatiles, 0.85 mass pct ash, and 2.99 mass pct moisture. After mixing, the constituents were emptied into a quartz bowl and mixed with the appropriate amounts of distilled water.…”

“…This is because of the higher rate of the carbon gasification reaction by CO 2 (higher intrinsic reactivity) for wood charcoal, as reported elsewhere. [5] Figure 6 shows the mass-loss curves for three layers of taconite-coal-char composite pellets. It may be noticed that the relative proportion of CO to CO 2 generated in this case is higher than the scenario (Figure 3) in which three layers of PAH (Fe 2 O 3 )-coal-char pellets were reduced.…”

“…Previously, [5] the reaction-rate constants for the chemical reactions, namely, the carbon gasification by CO 2 and the wu¨stite reduction by CO were determined. Two different carbonaceous reductants, coal char and devolatilized wood charcoal, and two kinds of ferric oxide, an artificial highly porous hematite and naturally occurring hematite ore tailings, were the subjects of the investigation for the rate constants.…”

Scale Recycling Through Self-Reducing Briquettes to Use in EAF

“…This reasoning applies well for the agglomerates small in weight and size (briquettes, pellets, powder poured into a crucible) used in the studies of self-reduction by thermogravimetry [3][4][5][6][7] or chemical analysis of evolving gas 8,9) at laboratory scale. In these cases, it is implicitly admitted (and sometime experimentally proved) that there is not a significant temperature gradient inside the sample.…”

The Strength and Density of Green and Reduced Briquettes Made with Iron Ore and Charcoal

“…Fortini and Fruehan [16] and Halder and Fruehan [17] reported on the reduction of composite pellets made with charcoal. They showed that the reduction rate of composite pellets made with charcoal is higher than that of comparable pellets made using coal.…”