Reduction Of Iron Ore Fines Research Articles

Kinetic Analysis of Isothermal and Non-Isothermal Reduction of Iron Ore Fines in Hydrogen Atmosphere

Direct reduction of iron ore with H2 has become an alternative technology for iron production that reduces pollutant emissions. The reduction kinetics of iron ore fines in an H2 atmosphere under isothermal and non-isothermal conditions were studied by thermogravimetric analysis. X-ray diffraction and scanning electron microscopy were used to measure the mineral composition and analyse the morphology of the reduced fines, respectively. In the isothermal reduction experiment, it was found that the final reduction time was shorter, the higher the temperature, and the metallic iron particles formed a dense matrix structure. It is likely that the initial stages reduction process is the result of a combination of gaseous diffusion and interfacial chemical reaction mechanisms, and that the later stages a combination of interfacial chemical reaction and solid diffusion is the rate control mechanism. In the non-isothermal experiment, the heating rate had a significant effect on the reaction rate. The results show that the non-isothermal reduction proceeded through three stages: mixing control model, two-dimensional diffusion, and three-dimensional diffusion.

Numerical Simulation of the Operating Conditions for the Reduction of Iron Ore Powder in a Fluidized Bed Based on the CPFD Method

In this work, the computational particle fluid dynamics (CPFD) method is used to simulate the high-pressure visual fluidized bed experimental equipment independently designed and developed by the experimentation of the fluidized reduction process of iron ore powder. A numerical model for reducing iron ore fines in a three-dimensional fluidized bed is established, and the model is verified by combining numerical simulation and experimental testing. Moreover, the influences of different reducing factors on the reduction effect in the process of the fluidized reduction of iron ore fines are simulated in detail. Via the CPFD simulation of the fluidized reduction of iron ore fines, the optimal reduction pressure is found to be 0.2 MPa, and the optimal reducing gas is found to be H2. Moreover, the optimal gas velocity is 0.6 m/s, and the optimal reduction temperature is 923 K. This conclusion is consistent with the experimental measurements, so the simulation results can be used to verify the reliability of the optimal operating conditions.

Substitution of coking coal with biochar for thermal and metallurgical utilisation

ABSTRACT To meet the global demand for energy, biochar can be a substitute and a green source of energy for fossil fuels and their derivatives. Biochar has its own supremacy to meet the requirements of the energy sector and replace coking coal for metallurgical purposes, and the mitigation of CO2 emissions from the Iron and Steel industry. This study includes the characterisation and comparative study of the reduction of iron ore pellets and iron ore fines using saw dust char (SDC) as one of the biomass wastes. The results show that the reduction of iron ore fines with comparable ratios with SDC gives the maximum degree of reduction than that of iron ore pellets. Thus, SDC can play an important role in the premium quality of coking coal reserves.

Effect of different modification methods on fluidized bed hydrogen reduction of cohesive iron ore fines

To develop breakthrough technologies that enable a drastic reduction in CO2 emissions from the ironmaking industry, the direct reduction of iron ore fines by H2–N2 in a fluidized bed with different modification methods was investigated. The results show that powder coating could prevent the defluidization of cohesive iron ore fines through the physical spacer effect, while granulation modification with cheap cement as the binder not only inhibits the occurrence of sticking, but also greatly accelerates the reduction rate. Microstructure observations indicate that granulation modification has reconstructed the irregularly shaped iron ore fines to be spherical, consisting of small grains, and created porous channels for gas diffusion, thereby increasing the reduction rate. In addition, structure reorganization constructs nonsticking barriers on the surface using native gangue and cement, and the occurrence of defluidization is avoided. Moreover, granulation modification has been demonstrated to be an effective and general solution for efficient and stable fluidized bed reduction of iron ore fines. This makes hydrogen ironmaking through fluidized bed direct reduction technically attractive.

Non-Isothermal Reduction Kinetics of Iron Ore Fines with Carbon-Bearing Materials

This study investigates the non-isothermal reduction of iron ore fines with two different carbon-bearing materials using the thermogravimetric technique. The iron ore fines/carbon composites were heated from room temperature up to 1100 °C with different heating rates (5, 10, 15, and 20 °C/min) under an argon atmosphere. The effect of heating rates and carbon sources on the reduction rate was intensively investigated. Reflected light and scanning electron microscopes were used to examine the morphological structure of the reduced composite. The results showed that the heating rates affected the reduction extent and the reduction rate. Under the same heating rate, the rates of reduction were relatively higher by using charcoal than coal. The reduction behavior of iron ore-coal was proceeded step wisely as follows: Fe2O3 → Fe3O4 → FeO → Fe. The reduction of iron ore/charcoal was proceeded from Fe2O3 to FeO and finally from FeO to metallic iron. The reduction kinetics was deduced by applying two different methods (model-free and model-fitting). The calculated activation energies of Fe2O3/charcoal and of Fe2O3/coal are 40.50–190.12 kJ/mol and 55.02–220.12 kJ/mol, respectively. These indicated that the reduction is controlled by gas diffusion at the initial stages and by nucleation reaction at the final stages.

Reduction Study of Iron Ore Pellets with Wooden Bark Char

In the process of iron making reduction of iron ores to metallic iron is done by coke which acts as a reluctant. As, both the reduction process, conventional blast furnace and DRI technologies are driven by the Boudouard reaction, so there is a probability for substituting of coal/coke with biochars, which could provide a good source of carbon and energy for the reduction. Hence, the utilization of bio char can become an emerging technology and better option for replacing coking coal for metallurgical purposes. This study includes characterization and comparative study of reduction of Iron ore pellets and fines using Wooden Bark Char (WBC) as one of the biomass waste. From the results, reduction of iron-ore fines with comparable ratios with WBC gives the maximum degree of reduction than reduction of iron-ore pellets. Thus, WBC can play an important role in behind the premium quality of coking coal reserves.

Sticking-Free Reduction of Titanomagnetite Ironsand in a Fluidized Bed Reactor

Fluidized bed reduction of iron ore fines is typically inhibited by the onset of “sticking” at temperatures above 973 K, which leads to particle agglomeration and defluidization of the bed. Here, we report the sticking-free fluidized bed reduction of titanomagnetite (TTM) ironsand at 1223 K in Ar-H2 gas mixtures. We show that sticking is prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. This protective shell prevents iron-iron contact between particles throughout the reduction process, enabling metallization degrees of 93 pct to be attained without sticking occurring. Phase evolution during the reaction has also been analyzed using q-X-ray diffraction and scanning electron microscope/energy dispersed spectroscopy. We find that the reduction proceeds through four separate stages. During the initial stage, approximately half of the initial TTM phase is converted to wustite, forming a network of sub-micron wustite channels which interlace the TTM matrix. During this stage, Ti and Al are enriched within the TTM matrix, due to the low solubility of both species in wustite. This enrichment stabilizes the remaining TTM, meaning that wustite is then preferentially reduced to metallic iron in stage 2 of the reduction. In stage 3, the remaining Ti-enriched TTM is reduced directly to metallic iron and ilmenite. The final stage of reduction involves the conversion of ilmenite into rutile and pseudobrookite. Our findings clarify the important role played by titanium species during the reduction of TTM and suggest that New Zealand ironsand can offer significant advantages over conventional hematite ores when used as a feedstock for fluidized bed direct-reduced iron processes.

Fluidization state monitoring using electric current during fluidized bed reduction of iron ore

It was found that the real-time fluidization state can be monitored with the help of electric current acquisition during a fluidized bed reduction of iron ore fines, which might be used to the prediction of de-fluidization and localized fluidization state monitoring in a plant-scale fluidized bed. All Fe, FeO, and Fe3O4 phases have been proven to be conductive at high temperatures. In addition, the electric current detected in a fluidized bed under a normal fluidized state is virtually zero even for conductive bed materials. The solid bridges that emerged between these conductive particles were proved to be the cause of conductivity in a fluidized bed.

Evolution of deposited carbon during multi-stage fluidized-bed reduction of iron ore fines

The influence of reduction conditions on carbon deposition during fluidized-bed pre-reduction of iron ore fines was investigated experimentally. The results showed that reduction temperature and the composition of reducing gases had a significant effect on the rate of carbon deposition and the type of carbon deposits (graphite and Fe3C). Low reduction temperature, high CO content, and addition of H2 favored the deposition of carbon, especially graphite. The reduction conditions also significantly affected the surface morphology of the as-reduced iron ore fines. As the amount of deposited graphite increased, the formation of fibrous iron disappeared and graphite filaments were observed. The pre-reduced iron ore fines were further fluidized in pure CO at 850°C for final reduction. The results showed that graphite could suppress the formation of fibrous iron and decrease the surface viscosity, thereby inhibiting agglomeration during the final high-temperature reduction stage. Reactions that consume the deposited carbon during the final high-temperature reduction were identified and graphite was shown to be more reactive than Fe3C. To enhance the application of fluidization technology in producing sponge iron, a novel solid-state high-temperature reduction method via deposited carbon was proposed and demonstrated to be feasible.

Enhanced effect and mechanism of Fe2O3 on CaO for defluidization inhibition during fluidized bed reduction of iron ore fines

Brazilian iron ore fines were reduced in a laboratory fluidized bed with different Ca-based additives at 800°C using 0.5L/min H2–0.5L/min N2. The fluidization results show that pure CaO and Ca(NO3)2·4H2O only slightly prolong the fluidization time, with defluidization occurring eventually. However, mixtures of Ca(NO3)2·4H2O and Fe(NO3)3·9H2O could effectively inhibit defluidization. Reduction results of CaO/Fe2O3 suggest that Ca-based additives mainly inhibit defluidization through the physical spacer effect. Microstructure observations indicate that 2CaO·Fe2O3 could suppress the growth of sharp-pointed whisker, and the introduction of Fe2O3 allows the Ca species to adhere tightly to the surface of the sticky iron, thereby decreasing its adhesiveness. Moreover, Fe2O3 is demonstrated to be a general binder capable of enhancing the ability of ineffective additives to prevent defluidization.

Reduction Behavior and Structural Evolution of Iron Ores in Fluidized Bed Technologies—Part 2: Characterization and Evaluation of Worldwide Traded Fine Iron Ore Brands

The reduction of iron ore fines by means of fluidized bed technology has become an alternative route of ironmaking. To investigate the reduction behavior of fine ores and to improve fluidized bed processes, a lab scale fluidized bed facility is installed. The reactor is charged with different kinds of fine ores. The reactors get fluidized by a reducing gas mixture containing H2, H2O, CO, CO2, CH4, and N2 in variable range. Additionally, a sampling system is installed, which enables the sampling of bed material during reduction. All samples are analyzed regarding their grain size distribution, chemistry, and morphology. The comparison of the raw input ore with the reduced ore—bed samples during the tests and final material—leads to a new way of fine ore characterization. After the determination of a standardized process, globally traded iron ore fines are tested under the same process conditions. The results enable the validation of the morphological evolution of different iron ore types and brands (hematitic, magnetitic, and limonitic) during the reduction with CO‐rich reducing gas in fluidized bed processes. Further investigation on the structure and porosity of the different phases is done to evaluate the relation to reduction rate and final reduction degree.

Kinetic study on gas molten particle reduction of iron ore fines at high temperature

A kinetic study of gas molten particle reduction has been carried out using a high temperature drop tube furnace at the typical conditions of the smelting cyclone of the HIsarna ironmaking process. The results demonstrated that particle size has a significant effect on the reduction rate of fine iron ore particles and that the reduction ability of H2 is two to three times higher than that of CO at high temperature. It was found that almost all of the Fe2O3 in the iron ore particles was reduced to Fe3O4 and FeO in the first 210 ms. The morphology images of the partially reduced spherical particles showed that a liquid FeO product layer was formed outside the solid Fe3O4 unreacted core. The kinetic analysis revealed that the rate controlling step of the gas molten particle reduction was the diffusion of Fe3+ in the liquid product layer and that the activation energy was ∼156 kJ mol − 1.

Investigation on the Kinetics of Iron Ore Fines Reduction by CO in a Micro-fluidized Bed

Kinetics of Brazilian iron ore fines reduction was investigated in a micro fluidized bed, a newly developed kinetics analyzer for gas-solid reactions, where the effects of external and internal diffusion were significantly reduced by modifying the operation conditions. The reducing gas was a mixture of CO and N2 and the temperature ranged from 973K to 1123K. The experimental data was analyzed with respect to the reduction mechanism of iron oxides, and the feasibility of the segment treatment on the experimental data was discussed. The kinetics parameters were determined by the iso-reduction degree method as well as models matching method, and compared with available data in the literature. Moreover, a reduction model for iron ore fines was hence established in terms of piecewise differential rate function, and the reduction stage FexO→Fe is considered as the most likely limit step during the reduction of iron ore fines.

Effect of Coating MgO on Sticking Behavior during Reduction of Iron Ore Concentrate Fines in Fluidized Bed

AbstractThe effect of coating MgO with different methods on sticking behavior during the reduction of iron ore fines was investigated, at 1073 K with 70%CO–30%H2 gas mixture in a visualization fluidized bed. It was found that coating MgO on particle surface could extend fluidization time from 12 min to more than 80 min, and improve the degree of metallization from 22% to more than 80%. The expansion level of bed after defluidization could also be obviously decreased. To achieve a similar effect, the initial coating content with solution method was less than that with powder method. The reason was that coating MgO could effectively insulate the contact of metallic iron on particle, which provided the reaction time for carbon deposition and the production of Fe3C with low stickiness. Therefore, the decrease of metallic iron on particle surface led to the decrease of particle stickiness at high temperature.

Influence of MgO Additive on Fluidized Bed Reduction of Iron Ore Fines under Simulate COREX Reducing Gas

Influence of mixing MgO additive on fluidized bed reduction of iron ore fines using simulate COREX reducing gas was investigated. Experiments were conducted at 1073 K in a visualization fluidized bed. Mixing MgO additive was carried out using powder method and solution method. It was found that mixing MgO into ore fines using solution method could increase fluidization time from 12 to 80 minutes, and improve the metallization ratio from 22% to 81%. Reason was that coating MgO could effectively insulate the contact of metallic iron on particles, which provided the reaction time for carbon deposition and the production of Fe3C with low stickiness. Therefore, the decrease of metallic iron on particle surface led to the decrease of particle stickiness in fluidized bed reduction

Effects of alkaline earth oxides on precipitation behavior of metallic iron under CO atmosphere

In gaseous reduction of iron ore fines, alkaline earth oxides have profound effects on the precipitation behavior of fresh metallic iron on the particle surface. In this work, in situ observation was performed to reveal the influence of alkaline earth oxides on the precipitation morphology and micro-structure variation of fresh metallic iron from microscopic level by simulation of the gas-solid reaction condition on the surface of ore particles. Experimental results indicate that doping MgO in the particle surface can inhibit the reduction of iron oxide and however doping CaO, SrO and BaO promote; all alkaline earth oxides tested in this study can change the precipitation morphology of fresh metallic iron; minimum doping mole fraction of one oxide to inhibit iron whiskers growth (NAO) is related to its cation radius \(\left( {r_{A^{2 + } } } \right)\) and its extranuclear electronic layers \(\left( {n_{A^{2 + } } } \right)\), which can be expressed as \(N_{AO} = 1.3 \times 10^{ - 5} r_{A^{2 + } }^2 \sqrt {n_{A^{2 + } } }\).

Kinetics of Reduction Reaction in Micro-Fluidized Bed

Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is operated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume. In order to understand the dynamic process of the reduction reaction in micro-fluidized bed, a series of kinetic experiments were designed. In the micro-fluidized bed, the use of shrinking core model describes the dynamic behavior of reduction of iron ore. And the apparent activation energy is calculated in the range of 700–850 °C while the initial atmosphere is 100% content of CO.

Simulation Study on Performance of Z-path Moving-fluidized Bed for Gaseous Reduction of Iron Ore Fines

Simulation Study on Performance of Z-path Moving-fluidized Bed for Gaseous Reduction of Iron Ore Fines

Evaluation of the Limiting Regime in Iron Ore Fines Reduction with H2‐Rich Gases in Fluidized Beds: Fe2O3 to Fe3O4

AbstractIn metallurgical processes, fluidized‐bed technology is gaining more importance because of its advantages. Processes with H2‐rich and CO‐rich reducing gases were developed for the reduction of iron ore fines (e.g. FINEX®). For improvement of these new technologies, greater knowledge about the chemical kinetics of iron ore reduction in fluidized beds is necessary. The scope of this work is to evaluate the limiting regime of the iron ore fines reduction. Therefore, experimental results of reduction tests were compared with theoretically investigated reduction rates. These reduction rates were based on a limitation either of mass transfer through the external gas film to the particle surface, diffusion in a porous product layer (pore diffusion and Knudsen diffusion), diffusion in a dense product layer (solid diffusion) or the phase boundary reaction. The phase boundary reaction was found to be the most likely limiting reaction regime.

Reduction of Iron Ore Fines with CO-rich Gases under Pressurized Fluidized Bed Conditions

Pressurized fluidized bed processes for the reduction of iron ore fines using CO-rich reducing gas formed by coal gasification are an upcoming ironmaking technology. They operate in a continuous multi-staged countercurrent mode at an absolute pressure of 4 bar.For process optimization, a laboratory-scale pressurized fluidized bed reactor was built to perform experiments similar to industrial conditions. The reactor is operated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume.Three-stage experiments with three different iron ores were carried out at an absolute pressure of 4 bar in batch-wise operation. The reducing gas consisted of a mixture of H2, H2O, CH4, CO2 and CO. The CO-concentration was varied in a range between 30% and 50%, the residence time in pre-reduction between 30 and 60 min and the operating temperature from 400°C to 850°C. In correspondence to the tests, microscopic techniques were applied to determine the importance of morphological properties of the ores on their reduction behavior.A higher temperature in the pre-reduction stage causes an increase of porosity as well as an increase of the final reduction degree. Comparing different ore types, a significant correlation between the morphology of the employed ores and the final reduction degree was found.