A novel ironmaking technology is under development at the University of Utah. The purpose of this research was to determine comprehensive kinetics of the flash reduction reaction of magnetite concentrate particles by hydrogen. Experiments were carried out in the temperature range of 1423 K to 1673 K (1150 °C to 1400 °C) with the other experimental variables being hydrogen partial pressure and particle size. The nucleation and growth kinetics expression was found to describe the reduction rate of fine concentrate particles and the reduction kinetics had a 1/2-order dependence on hydrogen partial pressure and an activation energy of 463 kJ/mol. Unexpectedly, large concentrate particles reacted faster at 1423 K and 1473 K (1150 °C and 1200 °C), but the effect of particle size was negligible when the reduction temperature was above 1573 K (1300 °C). A complete reaction rate expression incorporating all these factors was formulated.

Hydrogen Reduction Kinetics of Magnetite Concentrate Particles Relevant to a Novel Flash Ironmaking Process

Despite the dominance of the blast furnace ironmaking process, increasing attention is being paid to the development of new technologies with lower energy consumption and CO2 emissions. At the University of Utah, a novel flash ironmaking technology to meet these demands is under development. This technology eliminates the highly problematic cokemaking and pelletization/sintering steps by directly utilizing iron ore concentrate, which is currently produced in large quantities in North America and elsewhere. This transformative technology is expected to allow significant energy saving and reduced CO2 emissions compared with the blast furnace process. It has been demonstrated that iron of more than 95 % metallization can be obtained by reduction with hydrogen or a mixture of carbon monoxide and hydrogen in 2–7 s at temperatures of 1473–1823 K. The development of the technology has gone through the stages of proof-of-concept and small laboratory flash reactor tests. A large prototype bench reactor that has most of the features of an eventual industrial reactor has been commissioned. In this paper, some details of advances made in the development are discussed.

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Development of a Novel Flash Ironmaking Technology with Greatly Reduced Energy Consumption and CO2 Emissions

During the reduction of iron ore fines structural changes in particles have a significant influence on the rate of reduction. Investigations regarding porosity, specific surface area and mean pore diameters in the reduction of hematite with hydrogen rich reducing gases were performed by mercury porosimetry. Morphological changes were examined by metallographic analyses of polished sections in reflected light. In the magnetite equilibrium phase, significant influence of temperature on structural parameters and sintering effects were found.For wustite phases, the influence of temperature was less pronounced. For the reduction of hematite to magnetite and magnetite to wustite topochemical phase growth and microporous product layers were observed. In the single step, reduction of hematite to wustite progressive conversion and significant increase in the mean pore diameter were found. The results presented in this work are of high importance for understanding the reaction kinetics of iron ore fines and...

Structural and morphological changes during reduction of hematite to magnetite and wustite in hydrogen rich reduction gases under fluidised bed conditions

Utilization and impacts of hydrogen in the ironmaking processes: A review from lab-scale basics to industrial practices

Particles (approximately 180 to 250 Μm across) were reduced by CO-CO2, by H2-H2O, and by CO-CO2-H2-H2O in a small fluidized bed, with facilities for automatic sampling of off-gas. Structural changes in the preheating period and during reduction were followed by surface area measurements and by microscopy. During reduction, surface areas increased initially and then decreased, as porosity created by chemical reaction was reduced by sintering; ‘uniform internal reduction’ was observed from magnetite to wustite. Although the bed was operated under vigorously bubbling conditions, with flow rates 7 to 15 times the minimum fluidization velocity at temperature, gas utilization was high for abstraction of about two-thirds of the maximum amount of oxygen removable by the inlet gas. The utilization fell sufficiently in the remaining stages of the reaction for approximate rate constants to be estimated. The rate increased (a) with increasing temperature, (b) with increasing gas flow, (c) with increasing reducing potential of the inlet gas, and (d) with increasing hydrogen content of inlet gas. The off-gas analyses showed the importance of the water gas shift reaction within the pores of the fluidized particles.

The reduction of hematite to wustite in a laboratory fluidized bed

Batches hematite particles were reduced to magnetite by hydrogen in small scale fluidized bed, from which samples of partially reduced ore could be extracted for metallographic studies or surface area measurements. A stabilized zirconia cell was used to monitor the gas phase composition at eight locations in the bed. With this device a complete picture of the consumption of hydrogen was established that could detect small changes in the efficiency of the reduction reaction. Approximate rates of reduction could also be calculated. Hematite reduction took place in three stages; an initial period in which the efficiency of the reaction increased with time, followed by a period of relatively constant reduction efficiency, and finally after about 85 to 90 pct transformation a period of falling efficiency. Wustite did not form while hematite was present. The efficiency of the reaction increased when the hematite particles were coated with platinum and decreased when the particles were coated either with silica or with a naturally occurring dirt film. A kinetic and morphological analysis indicated that the reaction was rate controlled by a surface reaction at the bottom of pores in the magnetite. These pores do not appear to penetrate to the receding hematite interface. The initial increase in the efficiency of the reaction was attributed to the developing pore structure of the magnetite which increased the area for reaction.

M. V. Srinivasan

Papers

A study of the reduction of hematite to magnetite using a stabilized zirconia cell