Article pubs.acs.org/IECR
Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Reduction Behavior of Blast Furnace Dust Particles during In-Flight Processes Jin Xu, Nan Wang,* Min Chen, Jianhua Xin, Xiaoao Li, Hui Li, and Ying Wang School of Metallurgy, Northeastern University, Shenyang, Liaoning 110819, China ABSTRACT: Blast furnace (BF) dust can be recycled as one of excellent secondary sources, in view of the valuable amounts of iron and carbon contents, and the in-flight reduction technology is considered to allow processing the fine metallurgical dusts efficiently. In this work, the reduction behavior of BF dust particles during in-flight process was studied using a high-temperature drop-tube furnace in laboratory scale. The effects of temperature and gas composition on the reduction degree were remarkable. Based on the morphological observation and phase diagram analysis, the product layer of the reduced BF dust particle was confirmed in molten state at 1673−1723 K. Kinetic analysis showed that the gas-molten particle reduction during in-flight process was a mixed control of the chemical reaction and diffusion of Fe3+ and O2− ions through the molten product layer, and the corresponding chemical reaction constant (kr) and the diffusion coefficient (D) was also obtained. thought to be lower in RHF.7 In recent years, a novel ironmaking technology called in-flight8,9 or flash reduction technology10−13 has been developed, which is thought to be a flexible technology that can utilize the large quantities of iron ore fines directly to bypass the sintering/pelletization and conventional coke-making steps. The fine iron ores are heated and prereduced rapidly by the high-temperature reduction gas during a very short flight time, and the final reduction is completed in the molten bath. The main product is premiumgrade hot metal, because the gangue materials are separated by density. In addition, the high reactivity gases, such as hydrogen and natural gas, are used as the reducing agent to reduce CO2 emission during the process. Because of the fewer restrictions of the raw material used, the in-flight or flash reduction process can be considered to allow efficient processing of the fine ironbearing waste materials with high level of impurities, in which the iron contained in iron oxides is expected to be prereduced during the in-fight process and extracted to hot metal finally, while the nonvolatile impurities are removed to the molten slag. Besides, other volatile valuable elements such as Zn and alkalis can also be separated. The zinc oxide is reduced by reductive gas and then reoxidized as ZnO into solid particles while K and Na, existing in the form of chloride, are removed by volatilization of KCl and NaCl. All of the Zn, K, and Na products could be collected in the secondary dusts for further use by an exhausted gas treating system simultaneously. Until now, the investigations on in-flight or flash reduction were mainly focused on the reduction behavior of fine iron ore
1. INTRODUCTION The blast furnace (BF) process currently provides more than 90%1 of primary iron with efficient and stable operation. As one of the major solid wastes produced by ironworks, BF dust is discharged with the blast furnace gas and collected from the off-gas treatment system, with an output of ∼4%,2 with much of that iron being produced annually in China. The main components of BF dust are iron oxides, carbon, and a small amount of silicon, aluminum, calcium, magnesium oxides, and so on. In view of the valuable amounts of iron (total Fe of ∼40%3) and carbon contents, BF dust can be regarded as an excellent secondary source and possibly reused as raw material in sintering plants. However, with the characteristics of fine particle size and zinc content, the utilization of BF dust in sintering process has long been difficult, because of the low gas permeability and the low removal efficiency for Zn from BF dust in the sintering process.4 Therefore, it is of significant interest to explore more proper methods for BF dust recycling . Since the dust recycling technology by rotary hearth furnace (RHF) was set up and put into operation at Nippon Steel’s Kimitsu Works in 2000,5 RHF technology has been considered as a reliable and economic way to handle the zinc-bearing metallurgical dusts. In a typical RHF processes, the metallurgical dust, sludge, scale, and pulverized coal are agglomerated into pellets or briquettes to produce direct reduction iron (DRI) after being reduced under a high temperature of 1573−1673 K. Zinc and other volatile impurities in the dust are expelled and exhausted into the off gas and the accumulated zinc can be collected second through the purification process. Nevertheless, the produced DRI has comparatively higher sulfur contents mainly emitted from the coal6 and lower physical strength, and the heat transfer efficiency between the high temperature gas and pellet layers is © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
September 16, 2017 December 13, 2017 December 14, 2017 December 14, 2017 DOI: 10.1021/acs.iecr.7b03849 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
oxide in BF dust is
