Step-wise reduction kinetics of Fe 2 O 3 by CO/CO 2 mixtures for chemical looping hydrogen generation

Wang, Y.D.; Hua, Xiuning; Zhao, Chaofan; Fu, Tiantian; Li, W.; Wang, W.

doi:10.1016/j.ijhydene.2017.01.159

Cited by 53 publications

(28 citation statements)

References 19 publications

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“…The kinetic models which can describe these reaction mechanisms to determine the reaction rate are categorized into random nucleation and subsequent growth (A), diffusion (D), geometric contraction (R), and chemical reaction-order models (F). [44,46,47] Dickinson and Heal [43] reported 27 kinetic models in total and those well-established models are listed in Table III.…”

Section: Reaction Mechanismmentioning

confidence: 99%

Reduction of FeO in Molten Slag by Solid Carbonaceous Materials for HIsarna Alternative Ironmaking Process

Khasraw

Yan

Hage

et al. 2022

Metall Mater Trans B

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To investigate the use of biomass in the novel HIsarna technology, the reduction of FeO in the slag by chars produced from thermal coal (TC), charcoal (CC), and Bana grass char (BGC) was studied. A drop tube furnace coupled with a quadrupole mass spectrometer (DTF-QMS) was employed to study the injection of chars into pre-melted slag in the temperature range between 1450 °C and 1525 °C. The reduction rate was calculated from evolved gases and the extent of FeO reduction was confirmed by wavelength-dispersive X-ray fluorescence (WDXRF). The FeO reduction proceeds through two stages, starting with a rapid reduction, which is dependent on the carbon type, and followed by gradual leveling off. The reduction rate with the charcoal char (CC) was the highest, over 60 pct reduction was achieved in the first 500 seconds at 1500 °C, while ~ 50 and 40 pct achieved with TC and BGC chars, respectively, for the same reaction time. The kinetic analysis suggests that the first and second stages of the reaction can be described by the second-order (F2) and three-dimensional diffusion (D3) models, respectively. The apparent activation energy values for the first stage were 290, 229 and 267 kJ/mol for reactions with TC, CC and BGC chars, while 265, 369, and 282 kJ/mol were obtained for the second stage. Based on the experimental data and kinetic results, it can be concluded that the first stage is controlled by chemical reactions on the carbon surface, and the second stage is influenced by a mixed-controlling mechanism.

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Section: Reaction Mechanismmentioning

confidence: 99%

Reduction of FeO in Molten Slag by Solid Carbonaceous Materials for HIsarna Alternative Ironmaking Process

Khasraw

Yan

Hage

et al. 2022

Metall Mater Trans B

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“…Since the development of gas-based DR processes, kinetic analysis has been conducted for the reduction of many conventional non-titaniferous iron ores [65]- [113]. Such studies have simulated reductions in industrial shaft furnaces [72], [76], [79], [101], [114], as well as the Fluidized Bed system and Flash Reduction [84], [102], [115], [116]. For all these processes, CO, methane (CH4) and H2, were the most commonly studied reducing gases [65]- [113].…”

Section: Summary Of the Kinetic Analysismentioning

confidence: 99%

“…Models based on either mathematical equations or numerical simulation methods have been applied to determine the kinetic behaviour [106], [117]. Some studies developed a multi-stage mechanism that accounted for all of the separate reaction steps participating in the process [72], [81]. However, many other works have assumed a single overall reaction step which describes the whole process.…”

Section: Summary Of the Kinetic Analysismentioning

confidence: 99%

Reduction of New Zealand Titanomagnetite Ironsand pellets in H2 Gas at High Temperatures

Zhang¹

2021

Preprint

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To reduce the emission of carbon dioxide (CO2) from industrial ironmaking in New Zealand (NZ), it is proposed to perform direct reduction (DR) of NZ titanomagnetite ironsand pellets using H2 gas. In this thesis, the H2 reduction behaviour of pellets made from the NZ ironsand are examined. The aim of the thesis is to understand the reduction mechanism, and develop an analytical kinetic model to describe the reduction progress with time. This has been addressed through a series of reduction experiments in H2 gas. The overall reduction kinetics are examined in a Thermogravimetric analysis system (TGA); the phase evolution during reduction is measured by an in-situ neutron diffraction (ND) method; and the evolution of pellet- and particle-scale morphologies are analysed by scanning electron microscopy (SEM) of quenched samples. Based on the analysis of results from these experiments, the mechanism of the reduction is found to be adequately described by a single interface shrinking core model (SCM). Two different types of pellet are considered in this work: Ar-sintered pellets were sintered in an inert atmosphere to produce pellets containing mainly titanomagnetite (TTM). Pre-oxidised pellets were sintered in air to produce pellets containing mainly titanohematite (TTH). The reduction rate of both types of pellets is found to increase with reduction temperature, H2 gas flow rate, and H2 gas concentration. Above 1143 K, it is found that both types of pellets present a similar reduction rate, while below 1143 K, the reduction of pre-oxidised pellets is much faster than that of Ar-sintered pellets. For both pellets, the maximum reduction degree can reach ~97%. After complete reduction, metallic Fe coexists with other unreduced Fe-Ti-O phases (FeTiO3, TiO2 or pseudobrookite (PSB)/ferro-PSB), which is consistent with the observed reduction degree of < 100%. During reduction of both types of pellets, any TTH present is rapidly reduced first. After this step, TTM is then reduced to FeO, with Ti becoming enriched in the remaining unreduced TTM. FeO is further reduced to metallic Fe, which makes up to ~90% reduction degree. Eventually Ti-enrichment of the TTM leads to a change in the reduction pathway and it instead directly converts to metallic Fe and FeTiO3. Above ~90% reduction degree, reduction of the remaining Fe-Ti-O phases occurs (leading to the formation of TiO2 or PSB/ferro-PSB). The enrichment of Ti in TTM which accompanies the generation of FeO is substantially different from conventional non-titaniferous ores. This enrichment is confirmed by EDS-maps of the particles and stoichiometric calculations of the molar fraction Ti within the TTM phase. This enrichment effect changes the morphology of FeO in the particles, leading to the formation of FeO channels surrounded by Ti-enriched TTM. At the pellet-scale, both types of pellets present a single interface shrinking core phenomenon at higher temperatures. Metallic Fe is generated from pellet surface with a reaction interface moving inwards. However, at lower temperatures this pellet-scale interface becomes less defined in the pellets. Instead, particle-scale reaction fronts are observed. A single interface shrinking core model (SCM) is shown to successfully describe the reduction of pellets for reduction degrees < ~90% at all temperatures studied. However, at reduction degrees > ~90% this model fails. This is attributed to the change in reaction mechanism required to reduce the residual Fe-Ti-O phases that remain dispersed throughout the whole pellet at this stage of the reaction. The single interface SCM indicates that the reduction rate of the Ar-sintered pellets is controlled by the interfacial chemical reaction rate. However, two different temperature regimes are identified. Above 1193 K, the activation energy is calculated to be 41 ± 1 kJ/mol, but below 1193 K the calculated activation energy increases to 89 ± 5 kJ/mol. This change in activation energy appears to be associated with the change of the rate-limiting reaction from FeO → metallic Fe to TTM → FeO. By contrast, the pre-oxidised pellets exhibit mixed control at 1043 K, where a role is played by both the interfacial chemical reaction rate and the diffusion rate through the outer product layer. However, at temperatures of 1143 K and above, the pre-oxidised pellets also exhibit interfacial chemical reaction control, with a single activation energy of 31 ± 1 kJ/mol, which again seems to be consistent the rate-limiting reaction being FeO → metallic Fe. In summary, the findings in this thesis contribute to understanding of the reduction of NZ ironsand pellets in H2 gas, and establish a kinetic model to describe this process. In the future, this information will be applied to develop a prototype H2-DRI shaft reactor for NZ ironsand pellets.

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“…They derived a multistep kinetic model based on the Johnson–Mehl–Avrami (JMA) approach − that was a combination of two parallel reaction steps. From the JMA constant, the mechanism, activation energies, and free exponential constants were found with the help of experimental results. − Recently, Wang et al proposed a three-step reduction kinetics for the reduction of pure Fe 2 O 3 to Fe by mixtures of CO/CO 2 using the JMA approach.…”

Section: Introductionmentioning

confidence: 99%

“…From the JMA constant, the mechanism, activation energies, and free exponential constants were found with the help of experimental results. 30−34 Recently, Wang et al 35 proposed a three-step reduction kinetics for the reduction of pure Fe 2 O 3 to Fe by mixtures of CO/CO 2 using the JMA approach.…”

Section: Introductionmentioning

confidence: 99%

Complete Reduction of Ilmenite by CO in Chemical Looping Combustion—Multistep Kinetic Model Approach

Prabakaran

Jayanti

2019

Energy Fuels

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The complete reduction behavior of iron oxide to iron in ilmenite ore was studied thermogravimetrically in the temperature range of 900−1100 °C by 30% CO concentration over 200 min. The rate of reduction curves moved from deceleratory to sigmoidal-shape (knee shape) behavior after about one-third of conversion. Analysis of data reveals that the reduction of ilmenite ore occurs by three independent parallel reduction steps, namely, Fe 2 O 3 → Fe 3 O 4 , Fe 3 O 4 → FeO, and FeO → Fe. The conversion data have been correlated for the first time using a multistep kinetic model derived from the Johnson−Mehl−Avrami approach. The apparent activation energies of these three steps have been estimated to be 46.32, 63.14, and 46.07 kJ/mol. The model is able to predict reduction data of complete conversion of ilmenite ore.

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Step-wise reduction kinetics of Fe 2 O 3 by CO/CO 2 mixtures for chemical looping hydrogen generation

Cited by 53 publications

References 19 publications

Reduction of FeO in Molten Slag by Solid Carbonaceous Materials for HIsarna Alternative Ironmaking Process

Reduction of FeO in Molten Slag by Solid Carbonaceous Materials for HIsarna Alternative Ironmaking Process

Reduction of New Zealand Titanomagnetite Ironsand pellets in H2 Gas at High Temperatures

Complete Reduction of Ilmenite by CO in Chemical Looping Combustion—Multistep Kinetic Model Approach

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