Effect of Coating Mg(OH)&lt;sub&gt;2&lt;/sub&gt; with Heterogeneous Deposition Method on Sticking during Fluidized Bed Reduction of Iron Ore

Guo, Lei; Yang, Zerong; Gao, Jintao; Zhong, Yiwei; Guo, Zhen

doi:10.2355/isijinternational.isijint-2015-370

Cited by 11 publications

(4 citation statements)

References 35 publications

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“…The low-temperature direct reduction process avoids the melting of the particles, but there are also problems like particle agglomeration and long reduction period. According to previous studies [11], iron whiskers produced on the surface of the particles during the low-temperature gas-based reduction of iron ore fines cause the sticking problem of the material bed. Therefore, in-depth analysis of iron whisker generation and the microscopic reduction process of iron ore particles has far-reaching significance for solving the problems of sticking and low efficiency during low-temperature gas-based reduction of iron ore fines.…”

Section: Introductionmentioning

confidence: 94%

Nucleation and Growth of Iron Whiskers during Gaseous Reduction of Hematite Iron Ore Fines

Guo

Zhong

Bao

et al. 2019

Metals

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A high-temperature confocal scanning laser microscope and an online reduction–water quenching experiment system were used to systematically study the generation of iron whiskers during the reduction of hematite ore particles with CO/CO2 gas. The "blooming" phenomenon of the surface during the reduction of iron ore particles was found in this experiment. The orientation of the grain on the longitudinal section of an iron whisker was measured to be uniform by applying the electron back-scattered diffraction technique, which proved that the iron whiskers are most likely to exist in single crystal form. According to the in-situ online experimental video, the average diffusion flux of iron atoms when the layered iron completely covers the surface of the ore particle is about 0.0072 mol/(m2·s). While the iron atom diffusion flux at the root of the iron whisker during the pre-growth process is much larger than the flux when the layered iron is produced, which are defined to be 0.081 mol/(m2·s), 0.045 mol/(m2·s), 0.013 mol/(m2· s), and 0.0046 mol/(m2·s), respectively during the four stages of the growth of an iron whisker. The quantitative relationship between the chemical driving force and the whisker growth is established as Δ G θ + R T ln p CO 2 p CO + 2 n 0.056 r ρ E s T = 0 .

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Section: Introductionmentioning

confidence: 94%

Nucleation and Growth of Iron Whiskers during Gaseous Reduction of Hematite Iron Ore Fines

Guo

Zhong

Bao

et al. 2019

Metals

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“…Adsorption forms of coating particles on the surface of ore fines: bc: physical adsorption; d: chemical adsorption. 115) L. Guo 117,118) tried some coating methods such as the powder method, the slurry method, the on-line coating method, and the co-deposition method. If the metallization ratio of the obtained product is used as the criterion, it is found that the order of several coating methods from good to bad is: the co-deposition method, the online method, the powder method and the slurry method.…”

Section: Coating Treatment and Isolation Treatmentmentioning

confidence: 99%

A Review on Prevention of Sticking during Fluidized Bed Reduction of Fine Iron Ore

et al. 2020

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The fluidized bed ironmaking technology has attracted the attention of many researchers for decades as a direct reduction ironmaking method with many advantages. This process has been applied as a pretreatment method in many non-blast furnace ironmaking processes. However, the sticking problem hindered its development greatly. Defining the essential cause of sticking, and fundamentally solving this problem are the key steps encountered by this process. The research works related to the prevention of sticking problem during fluidized bed reduction of fine iron ore are comprehensively summarized in this article. The causes of sticking, the influencing factors of sticking and the solution of sticking are firstly discussed, followed by the analysis on the possible development direction of future fluidized bed ironmaking technology.

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“…After agglomeration, fluidisation is lost, and the process operation stops. This results in a stuck bed which cannot be conveyed between reactors (Hayashi and Iguchi, 1992;Zhong et al, 2011;Guo et al, 2016). In the FB reduction of conventional hematite and magnetite ores by hydrogen gas, particle sticking has been reported to occur at high temperatures (≳ 800°C) (Gransden and Sheasby, 1974;Zhang, Lei and Zhu, 2014).…”

Section: Problem Statementmentioning

confidence: 99%

Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

Prabowo¹

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<p>Titanomagnetite (TTM) ironsand has been used to produce steel in New Zealand (NZ) for about 40 years. However, the current steelmaking process in NZ produces high emissions of CO2 because it uses coal as a primary reducing agent. The fluidised bed (FB) process allows the use of pure hydrogen gas to reduce ironsand, and as a result, does not produce CO2 gas. However, for conventional hematite ores, reduction in a FB system is usually limited by the onset of particle sticking at temperatures ≳ 800°C. This thesis investigates the reduction of NZ TTM ironsand by hydrogen gas in the FB system with a key focus on ore sticking behaviour. Initially, this thesis reports preliminary fluidisation tests by nitrogen and helium gases at room temperature, carried out to determine key fluidisation parameters for ironsand powder. From these results, a laboratory-scale experimental FB reactor has been designed and built for the hydrogen reduction study at high temperatures. A key feature of the reactor is a novel in-situ sampling system, which enables extraction of multiple samples during a single experimental run without interrupting operation of the FB. Quantitative X-ray diffraction (q-XRD) has been used to determine the metallisation degree of partially reduced samples. Phase evolution during the reaction has also been analysed using q-XRD alongside scanning electron microscopy/energy dispersed spectroscopy (SEM/EDS). Additionally, the water vapour compositions in the exhaust gas were calculated from the q-XRD data and also measured in real-time using a high-temperature humidity sensor. The effect of various parameters has been investigated within the FB reduction experiments: hydrogen gas concentrations, hydrogen gas flow rate, bed mass, particle size, and temperature. The results indicate that across the entire range of controlled studied, the FB reduction rate of TTM ironsand is simply controlled by the rate of hydrogen gas supply. Interestingly, there were no occurrences of the sticking phenomenon at any point during the reduction by hydrogen gas at high temperatures of up to 1000°C. Sticking appears to be prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. Importantly, this shell remains present throughout the reduction process, and as a result, the reduction reaction proceeds rapidly to completion with a metallisation degree of ~93%. The influence of temperature on the reaction progress has also been investigated. The reduction pathway appears to vary within different temperature regimes. At low temperatures (750°C-800°C), TTM is directly reduced to metallic iron and ilmenite without any evidence of wüstite phase. At ‘intermediate temperatures’ (850°C-900°C) small amount of short-lived wüstite is observed. Some of the amount of TTM appears to be reduced to wüstite, and some is directly reduced to metallic iron. At high temperatures (≥ 950°C), approximately half of the initial TTM phase is quickly reduced to wüstite. After that point, wüstite is then reduced to metallic iron whilst the reduction of TTM stops. This is due to the enrichment of Ti species in TTM phase, which stabilises TTM crystal. Once wüstite has been fully reduced, the reduction of TTM then resumes. Throughout the entire experimental program for this thesis, particle sticking was observed to occur only under two specific sets of experimental conditions. These were: reduction by 100% H2 gas at 1050°C (case A) and reduction by 7.5 mol.% H2O – 92.5 mol.% H2 at 950°C (case B). In both cases, sticking occurred as a sinter which nucleated at the reactor wall surface, while most particles remained fluidised as loose powder. The mechanism of these sticking cases has been analysed by XRD and SEM. The results suggest that silica from the quartz reactor wall reacted and bonded with Fe from particles to nucleate the initial sinter. In summary, the findings in this thesis show that the hydrogen-FB process is highly effective in reducing NZ ironsand to a direct reduced iron (DRI) product. These findings open up the possibility of developing a new industrial FB technology for the direct reduction of NZ TTM ironsand, with extremely low CO2 emissions.</p>

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Effect of Coating Mg(OH)<sub>2</sub> with Heterogeneous Deposition Method on Sticking during Fluidized Bed Reduction of Iron Ore

Cited by 11 publications

References 35 publications

Nucleation and Growth of Iron Whiskers during Gaseous Reduction of Hematite Iron Ore Fines

Nucleation and Growth of Iron Whiskers during Gaseous Reduction of Hematite Iron Ore Fines

A Review on Prevention of Sticking during Fluidized Bed Reduction of Fine Iron Ore

Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

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