PS22
ガスジェット浮遊炉による溶融酸化鉄の水素還元速度測定手法の開発
Development of a Measurement Method for Assessing
the Hydrogen Reduction Rate of Molten Iron Oxide
using Aerodynamic Levitation Furnace
川島匠生 1，高橋駿介 1，清宮優作 1，守田祐哉 2，小澤俊平 1
Takumi KAWASHIMA, Shunsuke TAKAHASHI, Yusaku SEIMIYA, Yuya MORITA, Shumpei
OZAWA
千葉工業大学, Dept. of Advanced Materials Science and Engineering, Chiba Institute of Technology, Chiba Japan#1,
JFE スチール, Dept. of Ironmaking Research Laboratory, JFE Steel Corporation, Chiba Japan#2,121.

Introduction
The operation of blast furnaces significantly contributes to CO2 emissions, primarily due to the use of carbonaceous

materials as reducing agents for iron ore. To reduce these emissions, efforts have been made to replace carbon-based
reducing agents with hydrogen-based alternatives. However, the reported hydrogen reduction rate of molten iron oxide isinconsistent1-3), potentially due to chemical reactions between the sample and its container at high temperatures.
In this study, molten iron oxide was maintained under a flowing hydrogen-mixed gas in a containerless state using an
aerodynamic levitation (ADL) technique. The purpose of this study was to investigate the possibility of accurately
measuring the hydrogen reduction rate of molten iron oxide using ADL.

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Experimental procedure
Electrolytic iron with a mass purity of 99.99%, weighing between 35-40 mg, was chemically cleaned in a nitric acid-ethanol solution using an ultrasonic cleaner, followed by a cleaning in acetone. The cleaned iron was then melted in air
on a copper hearth using a semiconductor laser beam and maintained at 2000 K for 45 seconds before being rapidly
solidified into a spherical Fe-14.8%O sample. This sample was placed on the nozzle of the ADL and levitated by a jet of
Ar-H2 gas mixture, injected from the bottom at a flow rate of approximately 1.4 L·min-1. The oxygen partial pressure of
the gas was confirmed by a zirconia-type oxygen sensor, operating at 1008 K at the inlet. The levitated sample wasirradiated with a semiconductor laser beam, melted, and maintained at 1960 K for a certain period of time before rapid
solidification. The reduction behavior of the molten iron oxide sample was monitored at 6000 frames·sec-1 using a highspeed video camera, in conjunction with the temperature measured by a monochromatic pyrometer The oxygen content
of the solidified sample was analyzed using the inert gas fusion-infrared absorption method to calculate the hydrogen
reduction rate r [kg-O·m⁻²·s⁻¹].

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3.

Result and discussion
Figure 1 shows typical time-lapse images of molten ironoxide being reduced at 1960 K under a flow of Ar-5%H2 mixedgas, observed from above. The oxygen partial pressure (Po2)of the gas was estimated to be ~10-23 atm, derived from thestandard Gibbs energy of the formation of H2O(g). Thisestimation was based on the measured Po2 value from azirconia-type oxygen sensor, assuming that the ratio of partialpressures of H2O(g) to H2(g) remains constant regardless oftemperature. Under this gas flow condition, the molten ironFig.1. Typical time-lapse images of molten iron oxide

oxide gradually reduced, resulting in the formation of a low-being reduced at 1960 K under a flow of Ar-5%H2

emissivity liquid iron phase at around 45 seconds.

mixed gas.

Subsequently, the levitated molten iron oxide was completely reduced by the 58-second mark. In addition, the volume ofthe droplet decreased as the reduction progressed.

Figure 2 illustrates the oxygen concentration in thesolidified sample as a function of the exposure time of thelevitated droplet to the Ar-5%H2 gas mixture. For comparison,
it also depicts results obtained under high-purity Ar gas, where
the oxygen partial pressure is maintained at 10-7 atm. While theoxygen content of the molten sample maintained under highpurity Ar gas remains nearly constant even after 90 seconds, itdecreases linearly under the Ar-5%H2 gas mixture with time.
This confirms that the levitated molten iron oxide was reduced

Fig.2. Time dependence of oxygen concentration in aunder the flow of Ar-5%H2 mixed gas. Moreover, an increasemolten sample maintained at approximately 1960 K

in hydrogen concentration of the gas enhances the reduction ofunder an Ar-H2 gas flow of 1.4 L/min.

the sample.

Figure 3 displays the time-dependent changes in the surface
area of the levitated droplet during the hydrogen reduction
reaction. These changes were estimated from the droplet
images observed from above, under the assumption that thedroplet retains a spherical shape. Based on these droplet
images, the molten iron oxide covered the sample surface until
the liquid iron phase appeared. From the observed changes inthe surface area prior to the formation of liquid iron phase andthe corresponding amounts of reduced oxygen, the hydrogen
reduction rate of molten iron oxide sample was calculated tobe 0.10 kg-O·m-2·s-1. Thus, the ADL technique enabled theFig.3. Typical time dependence of the surface area inthe levitated droplet of molten iron oxide during its
reduction under an Ar-H2 gas flow of 1.4 L·min-1.

accurate measurement of the reduction rate of molten ironoxide, unaffected by any sample contamination from the container, even at elevated temperatures. At this stage of theresearch, however, the possibility that hydrogen supply might be the rate-determining step in the reduction process cannot
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be dismissed. Further studies involving increased hydrogen gas concentration and flow rate are essential for advancing
our understanding in future work.
4.

Summary
Using the ADL technique, the Fe-14.8%O sample was levitated and melted under a flow of Ar-5%H2 mixed gas, withthe objective of developing an accurate method for measuring the hydrogen reduction rate of molten iron oxide withoutsample contamination from the container at high temperatures. The results clearly showed the reduction of the molten
sample, as evidenced by a marked transition from molten iron oxide to a liquid iron phase, coupled with a noticeable
decrease in sample volume. In our experimental setup, which maintained an Ar-5%H2 gas flow rate of 1.4 L·min-1, wetentatively determined the hydrogen reduction rate of molten iron oxide to be 0.10 kg-O·m²·s⁻¹.

References
1) S. Ban-ya, Y. Iguchi, and T. Nagasaka：Rate of Reduction of Liquid Wustite with Hydrogen.
Tetsu-to-Hagane, 70 (1984) 14, DOI: 10.2355/tetsutohagane1955.70.14_1689
2) S. Hayashi and Y. Iguchi: Hydrogen Reduction of Liquid Iron Oxide Fine in Gas-conveyed
Systems. ISIJ International, 34 (1994) 7, DOI: 10.2355/isijinternational.34.555
3) J. Wegrzyn and L. Krol: Reduction of Fe1-xO in liquid state by H2+Ar mixtures. Steel Research,69 (2016) 2, DOI: 10.1002/srin.199801340© 2024 by the authors. Submitted for possible open access publication under the terms and conditions of theCreative Commons Attribution (CC BY) license (http://creativecommons.org/li censes/by/4.0/).

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