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The kinetics of the reduction of magnetite concentrate particles by H2+CO mixtures have been investigated in drop-tube reactors (DTRs) to obtain rate expressions for the design of novel flash ironmaking reactors. The experimental temperature varied from 1423 K (1150°C) to 1873 K (1600°C). The H2/CO ratio was varied from 0.5 to 2, which is the typical composition range of the product gas from the partial oxidation of natural gas. The experimental data were analysed separately in two temperature ranges 1423 K (1150°C)–1623 K (1350°C) and 1623 K (1350°C)–1873 K (1600°C), as the magnetite concentrate particles tend to fuse and melt at temperatures above 1623 K (1350°C) changing the reduction mechanism. CFD (Computational Fluid Dynamics) simulations were used to more accurately account for temperature and concentration variations. Synergistic effects were observed in the reduction by H2+CO mixtures compared with the simple summation of contributions of the individual component gases. [ABSTRACT FROM AUTHOR]

A CDF model for simulating gas dynamics, heat and mass transfer in the freeboard of a pilot-scale Rotary Hearth Furnace (RHF) is developed in conjunction with an independent solid reduction model at the bottom of the hearth. The effect of air-inlet configuration and inlet fuel composition on the fuel requirement, exit gas composition, fluid flow, temperature, and gaseous composition distribution have been investigated using this model. The lower air-inlet tubes orientated at 5° upwards keeping remaining air and fuel tubes horizontal emerged as the most recommended burner configuration. Various alternative fuels categorized in terms of calorific values, demonstrated that the fuel with high calorific value required less fuel and produced less CO2 emission. Interestingly, it was found that for the same calorific value a combination of blast furnace gas and coke oven gas (BF+COG) produced less CO2 emission compared to a combination of COG+BF+NG (Natural gas). [ABSTRACT FROM AUTHOR]

The characteristics and kinetics of iron oxide reduction by carbon in biomass composites were studied. Iron oxide can be reduced by biomass very rapidly, and the degree of metallisation and reduction increases with temperature. Iron oxide reduction by carbon in biomass can be divided into two stages: reduction by volatile carbon followed by reduction by non-volatile carbon. The reduction times of the two stages both decrease with increasing temperature. The first reduction is controlled by gas diffusion, whereas the second stage is dominated by carbon gasification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Non-isothermal reduction kinetics and mechanism of high chromium vanadium-titanium magnetite pellets were studied at 400-1100°C, simulating the lumpy zone of blast furnace conditions. The phase transformation behaviour of valuable elements including Fe, Cr, V and Ti and microstructural changes of reduced pellets were examined by means of X-ray diffraction (XRD) and SEM-EDX. The swelling of reduced pellets was highest at 900°C, while cold crushing strength was highest at 1100°C. Phase transformation behaviour of valuable elements in the lumpy zone is as follows: Fe2O3→Fe3O4→FeO→Fe; Fe2Ti3O9→Fe2TiO4→Fe5TiO8→FeTiO3; V2O3→VO; (Fe0·6Cr0·4)2O3→FeO·Cr2O3→Cr2O3. By analysing the non-isothermal reduction kinetics of high chromium vanadium-titanium magnetite pellets, based on the evaluation of reaction activation energy calculated according to Coats-Redfern method, gaseous internal diffusion through solid product layer and interfacial chemical reaction are most likely to be the main rate controlling steps in the reduction process. [ABSTRACT FROM AUTHOR]

An oolitic iron ore was isothermally reduced by coal at 1423-1573 K, and the reduction kinetics was investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48·26, 69·80 and 127·58 kJ mol−1 respectively. The rate controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction. [ABSTRACT FROM AUTHOR]

In the present study, the reduction kinetics of prefabricated iron ore-graphite/coal composite pellets of different shapes has been studied in a rotary hearth furnace (RHF). Commercial processes involving the RHF such as ITmk3/FASTMET have major problems of low productivity owing to significant heat and mass transfer resistance through the multilayer bed and consequently limited pellet layers over the hearth. In the present investigation, an attempt has been made to improve the heat and mass transfer in such system by increasing the specific surface area of individual pellets. Both the iron ore-graphite and iron ore-coal composite pellets have been reduced in an RHF at a maximum temperature of 1200°C. The ore-coal composite showed much higher degree of reduction (81%) over ore-graphite composite pellets (61%). The tablet shaped pellet with the highest specific surface area displayed a higher degree of reduction than the cylinder or sphere shaped pellets. Although no physical slag metal separation was visible, X-ray diffraction and SEM/EDX of reduced particles indicated separation at the microlevel. Higher amount of reduction and liquid silicate formation for tablet shaped pellets, in comparison with spherical and cylindrical shaped pellets, lay the foundation of a novel process flow scheme involving the use of prefabricated pellets in the RHF. [ABSTRACT FROM AUTHOR]

The mitigation of CO2 emissions has become a global priority in the iron and steel industry. One promising solution to decrease CO2 emissions is recycling of the blast furnace top gas to be reused in the reduction of iron oxide. In this study, iron oxide compacts were reduced isothermally with simulated conventional blast furnace top gas (BFTG: 20%CO, 20%CO2, 5%H2, 55%N2) at 700-900°C using a thermogravimetric technique. The reduction reached 30-34% depending on the applied temperature. The compacts were reduced completely to wüstite (Fe0·925O or Fe0·971O) with a few grains of metallic iron, which appeared only at 900°C. To investigate the reduction behaviour at the later stages, the compacts reduced with BFTG at 900°C were followed by isothermal reduction with simulated blast furnace shaft gas (BFSG: 30%CO, 5%CO2, 10%H2, 55%N2) at 950-1100°C. The total reduction extents were increased to 66-90% at 950-1100°C respectively. The remaining unreduced wüstite (Fe0·974O) has a higher Fe/O ratio compared with that formed by reduction with BFTG. At the initial stages of reduction, the rate controlling mechanism was interfacial chemical reaction, while at the later stages, solid state diffusion was the rate controlling mechanism. Reflected light microscope, scanning electron microscope, X-ray diffraction and Poresizer techniques are used to estimate the reduction kinetic and mechanisms. [ABSTRACT FROM AUTHOR]

Reduction experiments of carbon containing pellets made from metallurgical dust were conducted under a weak oxidising atmosphere in the temperature range of 1348-1573 K. Analysis of kinetics and the reduction mechanism revealed that the rate determining step of the reduction of the pellets is the interfacial or local reaction with the activation energy 111·66 kJ mol-1. The reduction rate can be expressed by the McKewan equation 1-(1-R)1/3 = kt. In addition, temperature is an important factor influencing the reaction rate as dezincification and metallisation increase with the increased temperature. The amount of dezincification and metallisation could be up to 97·8 and 79·9% respectively at 1573 K compared to a minimum of 75·3 and 60·2% at 1348 K. [ABSTRACT FROM AUTHOR]

The effect of basicity on the metallic iron whisker growth during wüstite reduction was studied in the present investigation. Compacts of pure and CaO/SiO2 doped wüstite were synthesised. The annealed compacts were isothermally reduced in thermogravimetric apparatus with CO gas at 800–1100°C. The course of reduction was followed by measuring the weight loss as a function of time. X-ray diffraction (XRD), scanning electron microscope (SEM), optical microscope and porosity measurements were used to characterise the annealed and reduced samples. The influence of temperature and basicity (CaO/SiO2) on the reduction behaviour and the morphology of the annealed samples were investigated. The reduction rate increased with temperature but decreased by increasing basicity value. Metallic iron whisker shape structure was detected in the pure wüstite samples after reduction at high temperatures while in basic wüstite samples, whiskers were formed at the surface of the compacts. From the activation energy values, the reduction of pure wüstite is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. The reduction of basic wüstite compacts with 0·2 and 0·5 basicity ratios are most likely controlled by chemical reaction mechanism while for 0·8 basicity ratio, the reduction rate is most likely controlled by solid state reaction mechanism. [ABSTRACT FROM AUTHOR]

An attempt has been made to clarify metallic iron whisker growth and swelling behaviour during iron oxide reduction in the presence of K2O alkali. Annealed pure and K2O doped wüstite compacts were isothermally reduced in a thermogravimetric apparatus with CO gas at 800–1100°C. The reduction rate increased with temperature but decreased with increasing K2O content. Morphologically, by increasing reduction temperature, porosity and whisker growth of the metallic iron produced increased, which in turn leads to the apparent swelling and compact disintegration. The reduction of pure wüstite at both the initial and final stages is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. For K2O doped wüstite samples, the reduction at the initial stages is most likely controlled by gaseous diffusion mechanism, while in the final stages, it is most likely controlled by a chemical reaction mechanism. [ABSTRACT FROM AUTHOR]