Investigating the Effect of Water Gas Shift Reaction and Other Parameters on the Direct Reduction of Iron Ore Pellets (original) (raw)
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International Journal of Engineering Research and Technology (IJERT), 2015
https://www.ijert.org/investigating-the-effect-of-water-gas-shift-reaction-and-other-parameters-on-the-direct-reduction-of-iron-ore-pellets https://www.ijert.org/research/investigating-the-effect-of-water-gas-shift-reaction-and-other-parameters-on-the-direct-reduction-of-iron-ore-pellets-IJERTV4IS020311.pdf The enormous production cost associated with the use of the conventional route for steel making has necessitated the need to explore more economically viable routes. In this study we examined how the water gas shift reaction, reducing temperature, iron ore pellet type and gas composition (CO-H 2) influences the direct reduction of the iron ore pellets. Different iron ore pellets were reduced in a thermo gravimetric analysis (TGA) equipment using a reducing gas with different composition of CO and H 2 and at different temperatures. As the H 2 content in the gas increased, the reduction process became rapid while a much slower reduction process was observed for increased CO content in the reducing gas. The reducing temperature affected the reduction process such that higher reduction degrees were observed at higher temperatures. Two different pellet types; KPRS and CVRD were used in this study. By comparison, the KPRS pellets gave the highest degree of reduction at all the experimental conditions examined and this observation can be related to the relatively smaller size of the KPRS pellets. In general the water gas shift reaction impacted the reduction process in a positive manner as a result of the additional reducing gasses from the water gas shift reaction contributing to the kinetics of the reduction process.
Effect of H2/CO Ratios on the Reduction Kinetics and Mechanism of Iron Ore Pellets
The H2/CO ratio in the reducing gas is one of the most important factors that affect the reduction rate of iron ore pellets in the direct reduction processes. The present study is focusing on the effect ofH2/CO gas ratio on kinetics of direct reduction of iron ore pellets. The H2/CO ratio was in the range of 1 .0-2.6 which simulates the reducing gas composition in different direct reduction technologies (Midrex, HyL, and Syngas based direct reduction). The reaction rate constants and the apparent activation energy of the reduction process were calculated for both of the experimental and mathematical regression model. The unreacted core shrinkage mathematical formulations are applied to determine the rate controlling mechanism. The highest regressions and the lowest deviations from straight lines were obtained by the application of the mathematical formulations that corresponded to the interfacial chemical reaction mechanism and mixed control of chemical reaction with gaseous diffusion mechanism. The comparison between the calculated apparent activation energy and the standard ranges indicated that the rate controlling mechanism is mixed of the interfacial chemical reaction and gaseous diffusion. The contribution of chemical reaction in the rate controlling mechanism increased as the H2/CO ratio increased. The reaction rate constants and the apparent activation energy values were found to increase as H2/CO ratio increased due to the higher diffusivity ofH2 compared to that ofCO gas.
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.
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.
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.
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.
Kinetics of reduction of iron ore—coal pellets
Journal of Thermal Analysis, 1989
Kinetic data on the reduction of iron ore-coal pellets are compared with similar data for lump ore. It is shown that, when ore and coal are mixed intimately, the reduction reactions are accelerated considerably. Ore-coal pellets offer some additional advantages, as discussed in the text. It is shown that the kinetics of ore-coal reduction can be studied by using a pseudo kinetic parameter, f (fraction of reaction), defined as the instantaneous weight loss divided by the maximum possible weight loss. Plots off versus t have been analysed to establish the kinetic equations and evaluate the kinetic parameters.
Metals
Iron ore pellet reduction experiments were performed with pure hydrogen (H2) and mixtures with carbon monoxide (CO) at different ratios. For direct reduction processes that switch dynamically between reformed natural gas and hydrogen as the reductant, it is important to understand the effects of the transition on the oxide reduction kinetics to optimize the residence time of iron ore pellets in a shaft reactor. Hence, the reduction rates were studied by varying experimental parameters such as the temperature (800, 850 & 900 °C), reactant gas flow rate (100, 150 & 200 cm3/min), pellet size and composition of the reactant gas mixture. The rate of reduction was observed to increase with an increase in temperature and reactant gas flow rate, but it decreased with an increase in pellet size. SEM greyscale analysis was performed to analyze the porosity and phase composition of partially reduced pellets. The porosity of the pellets was observed to increase from 0.3 for unreacted pellet to ...
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.