Analysis of the Reduction Rate of Hematite Concentrate Particles in the Solid State by H 2 or CO in a Drop-Tube Reactor
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INTRODUCTION
THE blast furnace process has produced more than 90 pct of the primary iron until 2014, according to the World Steel Association, with the balance by alternative processes such as direct reduction and smelting reduction. However, the blast furnace process suffers from problems like high energy consumption, high level of pollution, and CO2 emissions, although it has a high production rate and other advantages. A novel flash reduction process has been under development at the University of Utah as a high-throughput industrial manufacturing process, attracting much global interest.[1–13] In this process, iron is produced from fine iron oxide concentrate in a flash process, utilizing hydrogen, natural gas, or coal gas as the reducing agent as well as the fuel. Flash ironmaking allows the direct use of iron oxide concentrate to bypass the pelletization/sintering and cokemaking steps in the blast furnace process, which will significantly reduce the CO2 emission as well as the energy consumption.[4–8] Further, there is an abundance of hematite ores in the global market, which adds to the significance of the information presented here to be highly relevant to potential industrial application. The reduction of hematite by H2 or CO has been investigated widely.[14–20] However, most of the previous work has been focused on pellets, briquettes, or particles much larger than concentrate particles. Moreover, the
DE-QIU FAN, H. Y. SOHN, and MOHAMED ELZOHIERY are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112. Contact e-mail: [email protected] Manuscript submitted February 21, 2017. Article published online July 27, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
temperatures used in their work have been lower than 1423 K (1150 C). The experimental work of the reduction of hematite concentrate particles by H2 or CO in the temperature range of 1423 K to 1623 K (1150 C to 1350 C) in a drop-tube reactor (DTR) has been reported.[10,12] However, a uniform temperature along the reactor length with a correction at the end of the isothermal zone was used in the kinetic analysis. The present paper summarizes the results of the kinetic analysis of hematite concentrate reduction based on a CFD approach, following a similar approach applied to H2 reduction of magnetite concentrate.[11] This approach eliminates the error associated with the assumptions of an isothermal temperature and constant velocity in the region close to the tip of the cooling tube where the carrier gas and concentrate particles are injected at room temperature and in the bottom part of the reactor where temperature starts to decrease gradually.
II.
EXPERIMENTAL WORK
The relevant experimental work has been detailed in previous work,[10–12] and thus only the salient information will be given here. The high temperature drop-tube reactor is schematically shown in Figure 1, which consisted of a pneumatic powder feeding system, a gas delivery unit, a cooling device, and a powder collection system. An alumina tube
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