Influence of Artificially Induced Porosity on Strength and Reduction Behavior of Hematite Compacts

Higuchi, Kenichi; Heerema, R. H.

doi:10.2355/isijinternational.45.574

Cited by 17 publications

(11 citation statements)

References 18 publications

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“…The effect depended strongly on process parameters such as temperature. Higuchi and Heerema showed that the presence of macropores is more important for improved reducibility than that of micropores (<15 μm) in the case of pellets and sinter reduction.…”

Section: Rate‐limiting Mechanism During Iron Oxide Reductionmentioning

confidence: 99%

Reduction of Iron Oxides with Hydrogen—A Review

Spreitzer

Schenk

2019

steel research int.

385

161

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This review focuses on the reduction of iron oxides using hydrogen as a reducing agent. Due to increasing requirements from environmental issues, a change of process concepts in the iron and steel industry is necessary within the next few years. Currently, crude steel production is mainly based on fossil fuels, and emitting of the climate‐relevant gas carbon dioxide is integral. One opportunity to avoid or reduce greenhouse gas emissions is substituting hydrogen for carbon as an energy source and reducing agent. Hydrogen, produced via renewable energies, allows carbon‐free reduction and avoids forming harmful greenhouse gases during the reduction process. The thermodynamic and kinetic behaviors of reduction with hydrogen are summarized and discussed in this review. The effects of influencing parameters, such as temperature, type of iron oxide, grain size, etc. are shown and compared with the reduction behavior of iron oxides with carbon monoxide. Different methods to describe the kinetics of the reduction progress and the role of the apparent activation energy are shown and proofed regarding their plausibility.

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Section: Rate‐limiting Mechanism During Iron Oxide Reductionmentioning

confidence: 99%

Reduction of Iron Oxides with Hydrogen—A Review

Spreitzer

Schenk

2019

steel research int.

385

161

View full text Add to dashboard Cite

show abstract

“…It was found that the degree of the acquired porosity depends on the reduction boundary conditions, particularly on temperature. Higuchi and Heerema 40,41 suggested that the presence of large pores with sizes above 15 μm enhanced the reduction rate more efficiently than small pores below 15 μm. This finding might be related to the relevance of capillary effects in smaller pores and cracks, as well as connectivity.…”

Section: Structure and Composition Analysis At Macroscopic And Micros...mentioning

confidence: 99%

Influence of Microstructure and Atomic-Scale Chemistry on Iron Ore Reduction with Hydrogen at 700°C

et al. 2020

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With 1.85 billion tons produced per year, steel is the most important material class in terms of volume and environmental impact. While steel is a sustainability enabler, for instance through lightweight design, magnetic devices, and efficient turbines, its primary production is not. For 3000 years, iron has been reduced from ores using carbon. Today 2.1 tons CO2 are produced per ton of steel, causing 30% of the global CO2 emissions in the manufacturing sector, which translates to 6.5% of the global CO2 emissions. These numbers qualify iron-and steel-making as the largest single industrial greenhouse gas emission source. The envisaged future industrial route to mitigate these CO2 emissions targets green hydrogen as a reductant. Although this reaction has been studied for decades, its kinetics is not well understood, particularly during the wüstite reduction step which is dramatically slower than the hematite reduction. Many rate-limiting factors of this reaction are set by the micro-and nanostructure as well as the local chemistry of the ores. Their quantification allows knowledge-driven ore preparation and process optimization to make the hydrogen-based reduction of iron ores commercially viable, enabling the required massive CO2 mitigation to ease global warming. Here, we report on a multi-scale structure and composition analysis of iron reduced from hematite with pure H2, reaching down to near-atomic scale. The microstructure after reduction is an aggregate of nearly pure iron crystals, containing inherited and acquired pores and cracks. Crucial to the reduction kinetics, we observe the formation of several types of lattice defects that accelerate mass transport inbound (hydrogen) and outbound (oxygen) as well as several chemical impurities within the Fe in the form of oxide islands that were not reduced. With this study, we aim to open the perspective in the field of carbon-neutral iron production from macroscopic processing towards a better understanding of the underlying microscopic reduction mechanisms and kinetics.

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“…Young' modulus, E, poisson's ratio, ν and effective surface energy, γ of hematite and magnetite at each temperature were taken from the references [32][33][34][35] and listed in Table 3. γ is expressed by the Griffith's fracture criterion, 36) as shown in Eq.…”

Section: Basic Concept Of Crack Areamentioning

confidence: 99%

Influence of Reducing Gas Composition on Disintegration Behavior of Iron Ore Agglomerates

et al. 2017

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H 2 injection through the shaft into blast furnace (BF) is a potential option for a further reduction of CO 2 emission from BF. H 2 promotes reduction reaction of burden materials, but its influence on their reduction disintegration behavior remains unknown in detail. This study has investigated the influence on the iron ore sinter, self-fluxed and acid pellets and specified essential factors governing the reduction disintegration behavior.Mass ratios of particles below 3 mm in size were measured as an index for reduction disintegration (RDI) after the reduction of burden samples applying the gas mixtures of CO-H 2 -CO 2 -N 2 at 823 K. The reduced samples were observed by an optical-microscope and an electron probe micro-analyzer for evaluation of reaction mode. Further, using the measurement results, stress, strain energy and crack area generated during reduction were calculated and formation mechanism of cracks was examined.RDI value of self-fluxed pellet increased under higher H 2 condition (40%N 2 -20%H 2 -10%CO-30%CO 2 ) and reached to 26 mass%. Such an increase was larger than expected from the standard RDI measure without H 2 . Sample observation revealed a fact that reaction mode governed RDI value, that is, disintegration worsened under the reduction with non-topochemical mode. The fact was explained by the calculation as an influence of crack formation and propagation. In a case of reduction with topochemical reaction, cracks generated in a concentric fashion. Meanwhile, reduction with non-topochemical reaction tended to generate cracks in radial direction, which causes pellet chipping and further degradation. Calculated crack areas showed good correlation with RDI values. The Crack area of non-toochemical reaction was more than double than that of topochemical reaction. This result indicates that disintegration does not much progress when crack area is less than the certain limit value, but it proceeds drastically when it exceeded the limit value.

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Influence of Artificially Induced Porosity on Strength and Reduction Behavior of Hematite Compacts

Cited by 17 publications

References 18 publications

Reduction of Iron Oxides with Hydrogen—A Review

Reduction of Iron Oxides with Hydrogen—A Review

Influence of Microstructure and Atomic-Scale Chemistry on Iron Ore Reduction with Hydrogen at 700°C

Influence of Reducing Gas Composition on Disintegration Behavior of Iron Ore Agglomerates

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