Thermodynamic evaluation for reduction of iron oxide ore particles in a high temperature drop tube furnace (original) (raw)
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Journal of Iron and Steel Research International, 2019
HIsarna is a promising ironmaking technology to reduce CO 2 emission. Information of phase transformation is essential for reaction analysis of the cyclone reactor of the HIsarna process. In addition, data of density and volume of the ore particles are necessary for estimation of the residence time of the particles in the cyclone reactor. Phase transformation of iron ore particles was experimentally studied in a drop-tube furnace under simulated cyclone conditions and compared with thermodynamic calculation. During the pre-reduction process inside the reactor, the mineralogy of iron ore particles transforms sequentially from hematite to sub-oxides. The density changes of the particles during the melting and reduction can be predicted based on the phase composition and temperature. Therefore, density models in the studies were evaluated with reported experimental data of slag. As a result, a more reliable density model was developed to calculate the density of the formed slag containing mainly FeO-Fe 2 O 3. The density and volume of the partially reduced ore particles or melt droplets were estimated based on this model. The results show that the density of the ore particles decreases by 15.1% at most along the progressive reduction process. Furthermore, the model results also indicate that heating, melting and reduction of the ore could lead to 6.63-9.37% swelling of the particles, which is mostly contributed by thermal expansion. It would result in corresponding variation in velocity of the ore particles or melt droplets during the flight inside the reactor.
Iron ore Reduction with CO and H 2 Gas Mixtures – Thermodynamic and Kinetic Modelling
The reduction of iron ore pellets has been studied using different techniques. Thermodynamic studies, experi-mental investigations and mathematical modelling have all been undertaken to better understand the behaviour of different pellet types in the new direct reduction process. The mathematical pellet model gives a good fit to most of the experimental conditions used in this work. There are some discrepancies between the experimental and calculated results under certain conditions, which are thought to be due to limitations in the experimental set up rather than fundamental issues in the model. The micromodel indicates that the hematite within the pellets is reduced to magnetite quickly, which in turn is reduced fairly quickly to wüstite. The reduction of wüstite to metallic iron seems to be the limiting stage in the reduction of the pellets, which is in line with what would be expected.
Kinetic Study on Reduction of FeO in a Molten HIsarna Slag by Various Solid Carbon Sources
Metallurgical and Materials Transactions B
To investigate the reduction behaviour of different reductants such as charcoal (CC), thermal coal (TC), and carbon black (CB) with HIsarna slag, a series of isothermal reduction experiments were performed in a vertical tube resistance furnace (VTF), coupled with a Quadrupole mass spectrometer (QMS) at 1450 °C, 1475 °C and 1500 °C. The results confirm that the highest overall reduction rate was achieved by CC, followed by TC and CB. The reduction mechanism between FeO containing molten slag and the selected carbonaceous materials is determined by studying the morphology of the water quenched samples at the intervals of 1.5, 3 and 5 minutes, using optical and scanning electron microscopes. The results reveal that the overall reaction is controlled by two main mechanisms: (1) nucleation and growth of CO bubbles, proceeded by the gaseous intermediates CO and CO2; and (2) diffusion of FeO in the molten slag. The initial reduction period in which chemical reaction control is dominant, ca...
Detailed Modeling of the Direct Reduction of Iron Ore in a Shaft Furnace
This paper addresses the modeling of the iron ore direct reduction process in the context of the reduction in CO2 emissions from the steel industry. The shaft furnace is divided into three sections (reduction, transition, and cooling), and the model is two-dimensional (cylindrical geometry for the upper sections and conical geometry for the lower one) to correctly describe the lateral gas feed and the cooling gas outlet. This model relies on a detailed description of the main physical-chemical and thermal phenomena using a multi-scale approach. The moving bed is assumed to be comprised of pellets of grains and crystallites. Eight heterogeneous and two homogeneous chemical reactions are taken into account. The local mass, energy and momentum balances are numerically solved using the finite volume method. This model was successfully validated by simulating the shaft furnaces of two direct reduction plants of different capacities. The calculated results reveal the detailed interior beh...
Reduction Behaviour of Iron Ore Fluxed Pellets under Load at 1023-1273 K
ISIJ International, 2004
Commercially, high grade acidic and basic fluxed iron ore pellets were isothermally reduced at 1 023-1 273 K under different load values ranging from 0.0 up to 0.0559 MPa. The reduction was carried out with synthetic gas mixture containing 55 vol% H 2 , 36 vol% CO, 5 vol% H 2 O, 3 vol% CO 2 and 1 vol% N 2. The oxygen weight loss resulted from the reduction of Fe 2 O 3 to lower oxides or to metallic iron was continuously recorded as function of time. X-ray phase analysis, optical microscope, high-pressure mercury porosimeter were used to characterise fluxed and reduced pellets. The different parameters affecting the reduction of these pellets were studied and correlated. It was found that the basicity of pellets (CaOϩMgO)/(SiO 2 ϩ Al 2 O 3) is 0.37 and 1.62. At early and intermediate stages, the reduction increased gradually with temperature showing a significant increase in the rate at Ͼ1 173 K. At later reduction stages, the load had a measurable effect on the reduction due to the sintering of freshly reduced metallic iron that increased with temperature and reduction extent. The internal structure was correlated with the reduction kinetics to predict the corresponding mechanism. The interrelating effect of temperature and load on the reduction kinetics of fluxed pellets was also given.
Kinetics of Direct Iron Ore Reduction with CO-H2 Gas Mixtures
International Journal of Engineering Research and, 2015
Though the reduction of iron oxide pellets by reducing gases is a well-studied phenomenon that has found a wide technological application, many poorly understood factors such as the effect of the water gas shift reaction on the reduction process and whether the reduction process is diffusion or interfacial chemical reaction controlled or mixed controlled still exist. The effect of diffusion and interfacial chemical reaction on the reduction of CVRD and KPRS pellets were investigated by varying the process temperature, and gas composition (H2-CO mixture), and using diffusion and chemical reaction models to calculate the effective diffusion coefficient (De) and the chemical rate constant (Kr). The results from the study showed that the reduction process is both diffusion and interfacial reaction controlled. That is the initial stage of the reduction process is interfacial chemical reaction controlled while the later stage is diffusion controlled. By examining the phases present after the reduction process with optical microscope, it was observed that the phases present were mainly metallic Iron and Wustite since all the experiments recorded a reduction degree greater than 35%. The presence of cracks especially in the pellets reduced with H2 was observed and it was attributed to the rapid diffusion of H2 through the pellets during the reduction process.
IJERT-Kinetics of Direct Iron Ore Reduction with CO-H2 Gas Mixtures
International Journal of Engineering Research and Technology (IJERT), 2015
https://www.ijert.org/kinetics-of-direct-iron-ore-reduction-with-co-h2-gas-mixtures https://www.ijert.org/research/kinetics-of-direct-iron-ore-reduction-with-co-h2-gas-mixtures-IJERTV4IS040955.pdf Though the reduction of iron oxide pellets by reducing gases is a well-studied phenomenon that has found a wide technological application, many poorly understood factors such as the effect of the water gas shift reaction on the reduction process and whether the reduction process is diffusion or interfacial chemical reaction controlled or mixed controlled still exist. The effect of diffusion and interfacial chemical reaction on the reduction of CVRD and KPRS pellets were investigated by varying the process temperature, and gas composition (H2-CO mixture), and using diffusion and chemical reaction models to calculate the effective diffusion coefficient (De) and the chemical rate constant (Kr). The results from the study showed that the reduction process is both diffusion and interfacial reaction controlled. That is the initial stage of the reduction process is interfacial chemical reaction controlled while the later stage is diffusion controlled. By examining the phases present after the reduction process with optical microscope, it was observed that the phases present were mainly metallic Iron and Wustite since all the experiments recorded a reduction degree greater than 35%. The presence of cracks especially in the pellets reduced with H2 was observed and it was attributed to the rapid diffusion of H2 through the pellets during the reduction process.
Heat Generation by Oxygen Injection during Reduction of Iron Ores in the Fluidized State by Hydrogen
jim.or.jp
Problems relating to the oxygen injection through the Electrogen Furnace shaft were studied to meet some of the heat requirements during reduction. Reduction was performed mainly in a small silica fluidized bed reactor with Aswan iron ore using pure hydrogen or hydrogen mixed with either steam or oxygen or both. Preliminary work using a tube furnace arrangement was useful in understanding the process and determining the working conditions in the fluidized bed reactor. The rate of reduction increased with temperature and hydrogen flow rate, but was retarded by the addition of steam and oxygen. However, in case of oxygen addition, the heat generated due to hydrogen-oxygen reaction counteracted the retarding effect. The rate of the hydrogen-oxygen reaction was found to increase with the O2 content but was retarded with the increase in the amount of steam present. The latter has a moderating effect on the explosion tendency of the hydrogen-oxygen mixture. This tendency increased with the oxygen content in the gas mixture and under the present experimental conditions no explosions occurred as long as the oxygen content was less than 15% of the hydrogen content. Heat generated was calculated theoretically and determined experimentally.
Mathematical Analysis of the Parameters Affecting the Direct Reduction of Iron Ore Pellets
The H2/CO ratio in the reducing gas of iron ore pellets is one of the most important factors that affect the efficiency of the direct reduction processes. The magnitude effect of this ratio on the reduction is still not clear compared with the reduction time and temperature. In the current study, a 2 3 factorial design was used to elucidate the reduction potential of different ratios of H2/CO in the reduction process at different temperatures and time. A regression model has been developed based on the experimental data of iron ore pellets that reduced with simulated Midrex, Hyl, and Syngas at 850 o C and 1050 o C. The reduction time was selected at 1.0 and 15 minutes in all trails. The H2/CO ratios in the applied reducing gas were equal to 0.4, 1.0, 1.6, and 2.6. The results showed that the reduction time has the highest positive effect followed by the applied temperature and then H2/CO ratio. The mutual interaction combination between time and temperature was higher than that between H2/CO ratio with either time or temperature. The lowest positive effect on the reduction processes was exhibited by the mutual interaction between all of operational parameters which are represented in H2/CO ratio, temperature, and time. The developed mathematical model was tested against various experimental data to estimate its efficiency in the prediction of the reduction degree. The predicted values of the reduction process by the current mathematical model were found in a good agreement with experimental results in many cases. The Matlab program was used to carry out the required calculations.
ISIJ International
Using hydrogen as a reducing agent for iron production has been the focus of several studies due to its environmental potential. The aim of this work is to study the influence of H 2-H 2 O content in the gas phase on the reduction of acid iron ore pellets under simulated blast furnace conditions. Temperature and gas compositions for the experiments were determined with multi-point vertical probes in an industrial blast furnace. The results of the reduction tests show that higher temperatures and H 2 content increase the rate and extent of reduction. For all the gas and temperature combinations, morphological, mineralogical, and microstructure changes were observed using different characterization techniques. Microscopy images reveal that H 2-H 2 O, in the gas phase, has a positive influence on reduction, with metallic iron forming at the pellet's periphery and core at lower temperatures compared to CO-CO 2-N 2 reducing gas. Porosity and surface area changes were determined using a gas pycnometer and the BET method. The results indicate that increasing the reduction temperatures and H 2 content results in greater porosity and a larger surface area. Moreover, carbon deposition did not take place, even at lower temperatures. A rate minimum was detected for pellets reduced at 800°C, probably due to metallic iron formation, hindering the diffusion of reducing gases through the product iron layer.