Reduction Of Iron Oxide Pellets Research Articles

TiO2 and Reducing Gas: Intricate Relationships to Direct Reduction of Iron Oxide Pellets

AbstractIn response to the imperative for sustainable iron production with reduced CO2 emissions, this study delves into the intricate role of TiO2 in the direct reduction of iron oxide pellets. The TiO2-dependent reducibility of iron oxide pellets utilizing H2 and CO gas across varied temperatures and gas compositions is thoroughly investigated. Our findings unveil the nuanced nature of the TiO2 effect, underscored by its concentration-dependent behavior, revealing an optimal range between 1 and 1.5 pct TiO2, where a neutral or positive impact on reduction kinetics and diffusion coefficient is observed. Notably, the synergistic interplay of CO and H2 at 1000 °C emerges as particularly efficacious, suggesting complementary effects on the reduction process. The introduction of H2 into the reducing atmosphere regulated by CO not only extends the transition range but also markedly expedites the rate of reduction. Furthermore, our study highlights the temperature sensitivity of the TiO2 effect, with higher TiO2 content correlating with prolonged reduction time in a 100 pct H2 atmosphere at 900 °C. In a 100 pct H2 atmosphere, the non-contributory role of TiO2 stems from the water-gas shift reaction. Conversely, introducing H2 into a CO-controlled reducing atmosphere with TiO2 enhances the transition range and expedites the reduction rate. Additionally, our findings underscore the role of total iron content, revealing a direct correlation with the reduction process.

Effect of composition and processing conditions on the direct reduction of iron oxide pellets

In this paper, HSC software is used to estimate the effects of composition and processing conditions on the reduction behavior of iron oxide pellets, i.e., hematite (Fe2O3), magnetite (Fe3O4), wustite (FeO), pure iron (Fe), and iron carbide (Fe3C), in a wide temperature range from room temperature (RT) to 1000°C in the presence of H2 and CO mixtures. The reducibility of iron ores, in particular Fe2O3, Fe3O4, FeO, Fe is discussed. The choice of reducing agents CO and H2 is explained, with CO proving to be the more effective reducing agent at high temperatures from a thermodynamic point of view. However, the free Gibbs energy of iron reduction is lowest in the presence of a 100% H2 atmosphere. In addition, H2 reduces tortuosity and increases porosity by reducing it at cooler temperatures and promoting diffusion. In contrast, CO increases tortuosity and reduces initial porosity because it requires higher temperatures for effective reduction and causes structural changes. The presence of impurities other than iron oxides has been shown to impair the activity of reduced pure iron by acting as catalyst poisons or participating in competing reactions. CaO accelerates the reduction of FeO, which is due to the formation of calcium ferrite, but the effect decreases at higher temperatures. MgO can either promote or hinder reduction, depending on its concentration and its influence on pellet porosity. The presence of several non‑iron oxides has been shown to affect the overall direct reduction of iron ore pellets, resulting in a significant impact of the overall process.

Modeling of Gaseous Reduction of Iron Oxide Pellets Using Machine Learning Algorithms, Explainable Artificial Intelligence, and Hyperparameter Optimization Techniques

In this study, a novel application of machine learning (ML) is introduced to pellet modeling in the intricate non‐catalytic gas–solid reaction of direct reduction of iron oxide in the steel industry. Twenty ML models are developed using four algorithms: multilayer perceptron neural networks (MLPNN), radial basis function neural network (RBFNN), support vector regression, and random forest (RF). Hyperparameter optimization is conducted using Bayesian algorithms, random search, and grid search. The optimum model achieves a mean squared error test of 0.0052 with random RF for the larger dataset (872 samples), while smaller datasets (132, 225, and 242 samples) produce optimum models with MLPNN and RBFNN. Hyperparameters vary between the larger datasets and the smaller datasets. The models offer insight into the complex interactions among variables, including time, temperature, gas composition, hematite composition, pellet radius, and initial pellet porosity, influencing the metallization degree. In this study, the significant role of time and temperature is emphasized, as revealed by explainable artificial intelligence using Shapley additive explanation analysis that utilizes the game theory, and the effects of pellet modeling parameters are elucidated through 3D plots, particularly highlighting the impact of changing H2/CO proportion on metallization degree and carbon deposit.

Investigation of Pellet Shape on the Hydrogen Reduction of Iron Oxide Using Mathematical Modeling and Image Processing

Due to environmental concerns and climate change, the use of hydrogen gas in the reduction of iron oxide has gained more attention recently. Many factors can affect the reduction of iron oxide pellets, and among them, a few studies have considered the shape of iron oxide pellets as a parameter. To evaluate how much the pellets may diverge from their ideal state, the circularity of the pellets is evaluated in this study using an image processing technique. Although this falls to as low as 0.75 in some cases, the computed average circularity of the pellets is 0.96. Afterward, considering that the reaction is non‐catalytic, mathematical modeling is used to develop an unreacted shrinking core model with three interfaces. The examination of the pellet's shape is conducted using this model, resulting in relative errors of 11.13% and 25.02% for the total conversion time at shape factor values of 0.9 and 0.8, respectively. Finally, the impact of the shape factor is demonstrated by varying each of the process parameters, including temperature, pressure, reduction gas composition, and pellet size.

A numerical study on process intensification of hydrogen reduction of iron oxide pellets in a shaft furnace

In this paper, techno-economically feasible technologies for improving the performance of a shaft furnace for hydrogen reduction of iron oxide pellets are explored using a simplified algebraic model in combination with a computational fluid dynamics -based shaft furnace model. The former determines the theoretical maximum gas utilization degree that corresponds to the thermodynamic limit regarding iron ore reduction by hydrogen. The latter clarifies, from a kinetic viewpoint, how the performance indicators respond to variations in the main operating parameters, including iron ore reducibility, top gas pressure and reduction zone length. The results show that an increase in the heat utilization ratio leads to a higher theoretical maximum gas utilization degree and thus, increasing the heat utilization ratio by means for process intensification can give rise to a higher gas utilization degree. An increase in each of those three operating parameters yields a higher heat utilization ratio, but extending the reduction zone lowers furnace productivity. Therefore, enhancing pellet reducibility and increasing the operating pressure are considered effective means for process intensification of the shaft furnace, for which optimal operating parameters are finally determined. The findings of this work may serve as guidelines for the design of more efficient hydrogen shaft furnace operations.

Hydrogen‐Based Direct Reduction of Iron Oxides Pellets Modeling

The present study deals with the analyses of the direct reduction kinetics during the hydrogen reduction of industrial iron oxide pellets. Various types of pellets with different percentage of total iron content and metal oxides are examined. They are reduced at different temperatures and pressure (700–1100 °C and 1–6 bar) in hydrogen atmosphere. The reduction behavior is described in terms of time to reduction, rate of reduction, and kinetics constant. All the obtained results are analyzed through the employment of a commercial multiobjective optimization tool to precisely define the weight that each single parameter has on the reduction behavior. It is shown that from the point of view of the processing conditions, temperature is the main factor influencing the time to total reduction. From the point of view of the pellets properties, it is mainly influenced by the total iron percentage and then by porosity and basicity index. Also, the kinetics behavior is largely influenced by the reduction temperature even if it is mainly governed by the porosity and pores size from the point of view of the reduced pellets. The reduction rate is also mainly influenced by temperature and then by iron percentage, gas pressure, basicity index, and porosity.

Computational analysis of hydrogen reduction of iron oxide pellets in a shaft furnace process

To gain a better understanding of the performance characteristics of a shaft furnace for hydrogen reduction of iron oxide pellets under operation with top gas recycling (TGR), a kinetic model was applied to investigate the coupled phenomena of gas-solid countercurrent reactive flow and heat transfer. The effects of operating parameters were studied for scenarios where the furnace is equipped with a single-row injection TGR system. The potential of a new TGR system featuring dual-row injection was also assessed preliminarily. The results showed that the productivity of the shaft furnace is much higher than in a syngas-based shaft furnace provided that a high mass flow of feed gas can be ensured to introduce adequate sensible heat. Hot charging of the pellets yielded an increase in the total energy consumption so the scope to reduce the gas mass flow by this method was found to be limited due to the poor heat utilization. By contrast, using a dual-row gas injection system was found to improve the performance, especially with respect to gas utilization and total energy consumption. This is chiefly attributed to a clear improvement in the thermochemical state of the furnace, which leads to a better utilization of the furnace volume.

A Review on the Modeling of Gaseous Reduction of Iron Oxide Pellets

The investigations on direct reduced iron (DRI) have commonly been made at two different scales: the pellet scale and the macroscopic or reactor scale. The reduction of a single pellet is typically investigated for developing kinetics of chemical reactions accompanied by heat and mass transport, whereas in the macroscopic view, the reduction process is investigated in the reactor scale. However, these two aspects are not independent of each other and usually the kinetic parameters that are used in the reactor modeling come from the single pellet study. This article reviews the most relevant models in the literature with regard to direct reduction reactions in the pellet scale together with more recently developed new approaches. This review also presents a critical assessment of the previously proposed models in terms of which models are applicable under what conditions and to what types of the solid structure. The flaws and pitfalls in some of these models are also pointed out with cautions. The present article is broadly divided into experimental and mathematical sections.

Reduction kinetics of iron oxide pellets with H2 and CO mixtures

Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar (1:0, 3:1, 1:1, 1:3, and 0:1) at different reducing temperatures (1073, 1173, and 1273 K) was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.

Effect of Different PCI Practice on the Texture Obtained during Reduction of Iron Oxide Pellets

In modern blast furnace ironmaking, producers continuously strive to reduce coke consumption by replacing coke with e.g., an increased amount of injected pulverized coal. A change in pulverized coal injection rate (PCR) and injection coal type will influence the in-furnace conditions and thus the reduction of iron oxides. In the present study, the reduction behaviour of olivine pellets and textures formed were investigated in the LKAB Experimental Blast Furnace (EBF) and in laboratory scale. In the EBF, effects of injection of an low-volatile (LV) and an high-volatile (HV) coal type at different PCR while two types of oxygen supply methods were employed were investigated. The choice of injection coal type was conclusive for the Femet texture formed during reduction, extent of Femet carburization and K distribution in the pellets. The amount of volatile matters in the coal type had a greater effect on the reduction properties than the PCR and oxygen supply method. Laboratory experiments simulating PCR, based on measurements in the EBF, showed that the initial reduction conditions, in terms of temperature level and reduction gas composition, determined the pellet texture up to a reduction degree of at least 60%. The tests carried out in the EBF showed that the pellets were well suited for blast furnace reduction under all the investigated process conditions. The laboratory tests supported this conclusion.

The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part III. The simulation of volatile reduction in a multi-layer rotary hearth furnace process

For reduction of iron oxides by volatiles from coal, the major reductant was found to be H2, and it can affect the overall reduction of iron oxides. In this study, the reduction by actual volatiles of composite pellets at 1000 °C was studied. The volatile reduction of the hand-packed Fe2O3/coal composite pellet as it is devolatilizing out of the pellet was found to be negligible. However, the reduction of iron oxide pellets at the top layer by volatiles from the bottom layers of a three-layer pellet geometry was observed to be about 15 pct. From the morphological observations of partially reduced pellets and the computed rates of bulk mass transfer, volatile reduction appears to be controlled by a mixed-controlled mechanism of bulk gas mass transfer and the limited-mixed control reduction kinetics. Using the reduction rate obtained from the single pellet experiments with pure hydrogen and extrapolating this rate to an H2 partial pressure corresponding to the H2 from the volatiles, an empirical relationship was obtained to approximately predict the amount of volatile reduction up to 20 pct.

Kinetic Analysis of the Iron Oxide Reduction Using Hydrogen-Carbon Monoxide Mixtures as Reducing Agent

The kinetics of the reduction of hematite pellets using hydrogen-carbon monoxide mixtures as reducing agent was described by using the grain model. This model involves the particle size and the porosity of the pellet asmain structural parameters which affect directly the kinetics of the hematite pellets during the reduction process. The predictions of the model were compared with the experimental results. Fired hematite pellets were reduced at 850°C using hydrogen, carbon monoxide and Midrex gas. The weight loss technique was used to follow the reduction process. The reduction of iron oxide pellets using hydrogen or carbon monoxide is a mixed controlled system, where chemical reaction and internal gas diffusion are competing processes during the first stage of the reduction, while internal gas diffusion becomes controlling step at the last stage of the process. The reduction of iron oxide pellets using Midrex gas is a mixed controlled system throughout the whole reduction process.

00/01540 Furnace process for carbothermic reduction of iron-oxide pellets or briquets, and melting of the metalized hot product to obtain pig iron for steelmaking

00/01540 Furnace process for carbothermic reduction of iron-oxide pellets or briquets, and melting of the metalized hot product to obtain pig iron for steelmaking

Heat transfer and chemical reaction models for reduction of iron oxide pellets in countercurrent moving bed reactors

Mass, energy and pressure balances are performed in a volume slice of a HyL III reactor in order to build a mathematical simulator for the different reduction steps. Three iron ore feed mixtures were simulated finding, in general, good agreement between plant data for metallization of DRI and the corresponding mathematical simulations. The main differences between these two types of data are explained as a consequence of the low efficiency of the contact between the reducing gases, H2 and CO, and the bed of solids due to the formation of clusters in the different ore feeds. This tendency observes a remarkable increase with rise of the total iron content in the ore feed. The existence of clusters promotes fluid flow malfunctions affecting the uniformity of the DRI quality expressed as it final metallization. This leads to the need of a 3D simulator which should be able to quantify this effect. Finally it was found, in the present research, that carbon monoxide plays a minor role in the dynamic behaviour of the reduction for the feed mixtures analyzed with the mathematical simulator. Um die verschiedenen Reduktionsschritte mathematisch simulieren zu können, wurden die Massen-, Energie- und Druckbilanzen in einem Volumenelement eines HyL-III-Reaktors betrachtet. Drei Erzaufgabemischungen wurden simuliert. Im Allgemeinen zeigten die so ermittelten Werte gute Übereinstimmung mit Betriebsdaten, wie z.B. dem Metallisationsgrad. Die gravierenden Unterschiede zwischen beiden Datengruppen beruhen auf der geringen Durchgasung des Feststoffbettes mit den Reduktionsgasen H2 und CO aufgrund von Clusterbildung in den jeweiligen Erzmischungen. Diese Tendenz wird mit zunehmendem Fetot-Gehalt in der Erzmischung deutlich verstärkt. Das Vorhandensein von Clustern begünstigt Strömungsfehler, die eine gleichmäßige DRI-Qualität-ausgedrückt durch den Endmetallisationsgrad- beeinträchtigen. Mit einer dreidimensionalen Simulation könnte dieser Effekt quantifiziert werden. Schließlich führte die vorliegende Untersuchung für die analysierten Aufgabemischungen zu dem Ergebnis, daß Kohlenmonoxid für das dynamische Reduktionsverhalten eine untergeordnete Rolle spielt.

Ishida-Wen's Model for Non-spherical Particle.

Thiele's modulus for non-spherical particle is assumed by introducing the concept of non-spherical radius. Based on this modulus, Ishida–Wen's model for non-spherical particle considering the shape effect is presented. An example of the application of this model to the analysis of gaseous reduction of iron oxide pellets of various shapes is illustrated. According to the analysis result, Thiele's modulus for non-spherical particle is proportional to non-spherical radius as assumed while the rate parameters included in this model are independent of the size and shape of the iron oxide particle.

Relation between sulfur pressure and sticking of fine lron ores in fluidized bed reduction.

Fourteen kinds of iron ore fines (0.015-0.021 cm diameter) were reduced to iron in a laboratory batch fluidized bed with a 90%CO-10%CO2 mixture (flow rate: 8 times the minimum fluidization velocity Umf) at 700-900°C to investigate the relation between sticking behavior and sulfur activity in gas phase of bed during metallization (aS), which could be evaluated from chemical analysis of sulfur species in exhausted gas, relative to iron/iron sulfide equilibrium.Values of aS obtained in all of tests were in the range of 0.01-1. The tests showing middle sulfur activities around 0.1, fell into sticking state soon after initial metallization, accompanied with long iron whiskers at higher temperatures. The tests showing activities other than the above conditions, induced short iron whiskers and porous or plain irons, indicating fluidized state until higher reduction degrees at lower temperatures. These temperature and sulfur activity dependences of product morphologies, which were in nearly agreement with authors' previous researches about abnormal swelling during reduction of iron oxide pellets prepared from reagent, corresponded to a sticking tendency of bed. These results give one reasonable idea by which the ore kind dependence of sticking can be interpreted.

酸化鉄ペレットのガス還元の速度解析への未反応核モデルの適用性

酸化鉄ペレットのガス還元の速度解析への未反応核モデルの適用性

Rate Enhancement of the Gaseous Reduction of Iron Oxide Pellets by Pressure Cycling

The effect of carrying out gaseous reduction of iron oxide under external pressure cycling has been investigated. When the reduction is carried out at 800°C with pellets of 30% porosity, relatively moderate pressure cycling with an amplitude of 0.5atm and frequency of 0.5cps can lead to about 25% higher reduction within 20min from the start of reaction. A threefold improvement in initial conversion rate can be obtained if higher amplitude and frequency of cycling are used. Computation shows that, for pellets and naturally occurring hematite ore, viscous flow effects can be neglected.The results of the investigation provide justification for further research in the use of external pressure cycling to overcome diffusional resistances in gas-solid reaction systems.

Effects of Gaseous Sulfide on the Reduction of Iron Oxide Pellets

Effects of addition of 5% of gaseous sulfide on the rate of reduction of iron oxide pellets were studied in temperature range of 800 to 1000°C with the following results:(1) The reduction rate was greatly decreased with the additon of COS and H2S respectively to CO and H2.(2) Analysis of the reduction rate based on the unreacted-core model and observation of the fractured surface of partially reduced pellets by using a scanning electron microscope and an electron probe microanalyzer demonstrated that the formation of dense FeS shells offered great resistance to the intraparticle diffusion of reducing gas toward the oxide core, thus greatly retarding the reduction of pellets, and that the partial penetration of the sulfide gas into the oxide core was also responsible to the decrease of reduction rate.

Mathematical simulation of direct reduction

A finite element analysis is developed for nontopochemical reduction of a porous iron oxide pellet. The reduction kinetics are essentially the same as those used by Trushenski, Li and Philbrook. However, several novel features arise in the present analysis. The computational technique used in this analysis provides an explicit way of calculating gas profiles for each step of the computations. To a limited extent multicomponent gas mixtures (either carbon monoxide, carbon dioxide and inert gases; or hydrogen, steam and inert gases) can be accomodated as the reducing agent. A corresponding analysis for direct reduction of iron oxide in a countercurrent shaft furnace assumes adiabatic conditions to prevail in the furnace as opposed to the usual isothermal assumption. The analysis assumes steady-state operation of the furnace, and plug flow of gas and solid. Profiles of gas and solid temperatures, degree of reduction of iron oxide pellets, bulk gas and solid compositions are calculated.