Ore Coal Composite Pellets Research Articles

A kinetic comparison between in situ hybrid microwave and conventional magnetising roasting of low-grade iron ore composite pellet

This article aims to comprehensively summarise the essential aspects of reduction kinetics in magnetising roasting of low-grade iron ore–coal composite pellets in the hybrid microwave and conventional furnace. The influence of crucial process parameters like temperature, time, and heating methods, including traditional and hybrid microwave heating, is explored. Investigating the impact of low-grade iron ore and coal quality on reduction kinetics is conducted to identify optimal heating methods for upgrading low-grade iron ore to blast furnace grade through magnetising roasting. The study uses diverse gas–solid reaction models to assess the reduction mechanism (Fe2O3 to Fe3O4). Results indicate the success of the contracting volume model for microwave heating, while conventional heating transitions from phase-boundary chemical control to diffusion control. XRD confirms magnetite dominance post-reduction, while scanning electron microscopy analysis establishes microwave crack-assisted efficiency over conventional heating for ease of reduction. A comparative study of apparent activation energy reveals the hybrid microwave method's four-fold lower (36.71 kJ/mol) than conventional resistance heating (156.19 kJ/mol). This underscores the potential of microwave heating for enhanced reduction kinetics and low-grade iron ore material processing applications.

Effect of Heating Rate on Carbothermic Reduction and Melting Behavior of Iron Ore-Coal Composite Pellets

In the ironmaking processes via the carbothermic reduction with the tall-bed reactor, the composite pellets are rapidly reduced to highly metallized direct reduced iron (DRI) with high productivity under high temperature. Without coke making and ore sintering process, carbothermic reduction are not only help broaden the selection of raw materials but an environmentally friendly approach for the ironmaking process. In this study, experiments were conducted for iron ore-coal composite pellets under four heating rates. During the reduction, the reaction was quenched at different temperatures by quickly moving the specimens to room temperature. After the experiments, we performed phase analysis by X-ray diffraction, chemical composition analysis by wet method, and microstructure observation and element distribution analysis by scanning electron microscopy with energy dispersive spectrum. The pellet morphology during the experiments was also recorded. The pellets under fast heating rates (80°C/min and 40°C/min) collapsed over 1300°C. The pellets under the slow heating rate (20°C/min) maintained their spherical morphology until 1400°C. We found that the formation and melting of fayalite (2FeO–SiO2 or Fe2SiO4) played a key role in the collapsing behavior of pellets, which can be classified into three different stages, (a) between 1000°C and 1200°C, a large amount of fayalite compound (melting point at 1178°C) was formed. (b) above 1178°C, the fayalite compound started to melt and became a liquid phase. (c) between 1178°C and 1400°C, the pellets lost their strength, and collapsed due to the excess amount of liquid phase present.

Effect of Carbon Addition on Direct Reduction Behavior of Low Quality Magnetite Ore by Reducing Gas Atmosphere

Recently, direct reduced iron (DRI) has been highlighted as a promising iron source for electric arc furnace (EAF)-based steelmaking. The two typical production methods for DRI are gas-based reduction and reduction using carbon composite pellets. While the gas-based reduction is strongly dependent on the reliable supply of hydrocarbon fuel, reduction using ore-coal composite pellets has relatively low productivity due to solid–solid reactions. To overcome the limitations of the above two processes, and to achieve a more efficient direct reduction process of iron ore, the possibility of combining these two methods was investigated. The experiments focused on performing an initial direct reduction using ore-coal composite pellets followed by a second stage gas reduction. It was assumed that the initial reduction of the carbon composite pellets would enhance the efficiency of the subsequent reduction by gas and the total reduction efficiency. The porosity, as well as the carbon efficiency for direct reduction, were measured to determine the optimal conditions for the initial reduction, such as the size ratio of ore and coal particles. Thereafter, further reduction by the reducing gas was carried out to verify the effect of the preliminary reduction. The reduction kinetics of the reducing gas was also discussed.

Reduction Mechanism and Kinetics of a Low Grade Iron Ore-coal Composite Pellets Improved by Sodium Salt

Reduction Mechanism and Kinetics of a Low Grade Iron Ore-coal Composite Pellets Improved by Sodium Salt

A simulation study of reduction kinetics for sponge iron production in a rotary hearth furnace

ABSTRACTA mathematical model has been developed by coupling genetic algorithm (GA) with heat and material balance equations to estimate rate parameters and solid-phase evolution related to the reduction of iron ore-coal composite pellets in a multi-layer bed Rotary hearth Furnace (RHF). The present process involves treating iron ore-coal composite pellets in a crucible over the hearth in RHF. The various solid phases evolved at the end of the process are estimated experimentally, and are used in conjunction with the model to estimate rate parameters. The predicted apparent activation energy for the wustite reduction step is found to be lower than those of the reduction of higher oxides. The thermal efficiency is found to decrease significantly with an increase in the carbon content of the pellet. Thermal efficiency was also found to increase mildly up to three layers. Multilayer bed remains as a potential design parameter to increase thermal efficiency.

Effect of gangue composition on iron nugget production from iron ore–coal composite pellet

The rotary hearth furnace iron nugget process has advantages of short reaction time, high-quality reduced product and wide adaptability of raw materials and meets the trend in ecofriendly development of iron and steel industry. Although the rotary hearth furnace iron nugget process cannot replace blast furnace process, which is affected by production scale, thermal efficiency and technical maturity, it is still a feasible technology for iron production. In order to realize the efficient utilization of high Al2O3 iron ore resources, preparation of iron nuggets with high Al2O3 iron ore was studied. Using iron concentrate as raw material, the effects of slag basicity, Al2O3 and MgO on melting separation of iron ore–coal composite pellets, such as the melting separation temperature, the melting separation time, the morphology of melting separated product, and the recovery rate of iron nugget, were studied. The results showed that relatively low or high liquidus temperature of slag had a negative effect on reduction and melting separation of iron ore–coal composite pellets. The increase in fluidity index of slag resulted in a decline in the melting separation temperature and time of iron ore–coal composite pellets. Optimum basicity to produce iron nuggets using iron ore–coal composite pellets was 0.8–1.0, 0.4 and 0.8 for iron concentrate containing 2, 4 and 6–10 wt.% Al2O3, respectively. Corresponding liquidus temperature and fluidity index of slag were 1300–1475 °C and above 4.5, respectively. Under this condition, the lowest melting separation temperature and the shortest melting separation time of iron ore–coal composite pellets were 1375 °C and 7 min, respectively. The recovery rate of metallic iron in the form of iron nugget could reach about 94%.

Carbothermic Reduction of Ore-Coal Composite Pellets in a Tall Pellets Bed

Recently, increasing attention has been paid to alternative ironmaking processes due to the desire for sustainable development. Aiming to develop a new direct reduction technology, the paired straight hearth (PSH) furnace process, the carbothermic reduction of ore-coal composite pellets in a tall pellets bed was investigated at the lab-scale in the present work. The experimental results show that, under the present experimental conditions, when the height of the pellets bed is 80 mm (16–18 mm each layer, and 5 layers), the optimal amount of carbon to add is C/O = 0.95. Addition of either more or less carbon does not benefit the production of high quality direct reduced iron (DRI). The longer reduction time (60 min) may result in more molten slag in the top layer of DRI, which does not benefit the actual operation. At 50 min, the metallization degree could be up to 85.24%. When the experiment was performed using 5 layers of pellets (about 80 mm in height) and at 50 min duration, the productivity of metallic iron could reach 55.41 kg-MFe/m2·h (or 75.26 kg-DRI/m2·h). Therefore, compared with a traditional shallow bed (one or two layers), the metallization degree and productivity of DRI can be effectively increased in a tall pellets bed. It should be pointed out that the pellets bed and the temperature should be increased simultaneously. The present investigation may give some guidance for the commercial development of the PSH process in the future.

Effect of CaO on the reduction behaviour of iron ore–coal composite pellets in multi-layer bed rotary hearth furnace

ABSTRACTThe effect of CaO on the reduction behaviour of iron ore–coal composite pellets has been studied in a laboratory scale multi-layer bed rotary hearth furnace at 1250°C for 20 min. Reduced pellets have been characterised through weight loss, porosity measurement, phase analysis by XRD, and morphology study by SEM. The addition of CaO to the composite pellets showed different effects at different carbon levels. For higher carbon-containing pellets (C/Fe2O3 molar ratio at the upper stoichiometric level of 3), the addition of CaO increased the extent of reduction for all three layers significantly up to a certain limit (4 wt-%); and thereafter the degree of reduction is decreased with a further increase in CaO percentage in the pellets. For low carbon-containing pellets (C/Fe2O3 molar ratio of 1.66), the addition of CaO to the pellets did not show any beneficial effect.

Reduction Behaviour of Iron Ore–Coal Composite Pellets in Rotary Hearth Furnace (RHF): Effect of Pellet Shape, Size, and Bed Packing Material

Reduction of iron ore–coal composite pellets in multi-layers at rotary hearth furnace (RHF) is limited by heat and mass transfer. Effect of various parameters like pellet shape, size, and bed packing material that are supposed to influence the heat and mass transfer in the pellet bed, have been investigated, on the reduction behaviour of iron ore–coal composite pellets at 1250 °C for 20 min in a laboratory scale RHF. Reduced pellets have been characterised through weight loss measurement, estimation of shrinkage, porosity, and qualitative, quantitative phase analysis by XRD. A significant difference in the degree of reduction is observed layer-wise in the pellet bed with the variation in pellet shape and size. Pellet bed without any packing material or packed with coal have demonstrated higher degrees of reduction compared to the pellet bed packed with graphite and sand.

Effect of Amount of Carbon on the Reduction Efficiency of Iron Ore-Coal Composite Pellets in Multi-layer Bed Rotary Hearth Furnace (RHF)

The effect of carbon-to-hematite molar ratio has been studied on the reduction efficiency of iron ore-coal composite pellet reduced at 1523 K (1250 °C) for 20 minutes in a laboratory scale multi-layer bed rotary hearth furnace (RHF). Reduced pellets have been characterized through weight loss measurement, estimation of porosity, shrinkage, qualitative and quantitative phase analysis by XRD. Performance parameters such as the degree of reduction, metallization, carbon efficiency, productivity, and compressive strength have been calculated to compare the process efficacy at different carbon levels in the pellets. Pellets with optimum carbon-to-hematite ratio (C/Fe2O3 molar ratio = 1.66) that is much below the stoichiometric carbon required for direct reduction of hematite yielded maximum reduction, better carbon utilization, and productivity for all three layers. Top layer exhibited maximum reduction at comparatively lower carbon level (C/Fe2O3 molar ratio 2.33). Correlation between degree of reduction and metallization indicated non-isothermal kinetics influenced by heat and mass transfer in multi-layer bed RHF. Compressive strength of the partially reduced pellet with optimum carbon content (C/Fe2O3 molar ratio = 1.66) showed that they could be potentially used as an alternate feed in a blast furnace or any other smelting reactor.

Reduction Efficiency of Iron Ore–Coal Composite Pellets in Tunnel Kiln For Sponge Iron Production

In order to explore the efficacy of iron ore–coal composite pellets over ordinary green pellets, indurated pellets, briquettes as well as standard charging of material in the form of concentric layers of iron ore and coal fines, or their mixture, these pellets were tested at 1,150 °C in a 7 tons per day (7 tpd) pilot tunnel kiln. Reduction of iron ore coal composite pellets in tunnel kiln emerges with an edge over all other systems studied. Performance parameters like percentage metallic iron formed, percentage metallization, reduction efficiency, carbon utilization efficiency, energy efficiency have been calculated and found to be significantly higher for composite pellets than the other systems studied. The materials of the container are found to have significant effect on the reduction kinetics. Energy and carbon efficiency have also been observed to be higher for higher capacity kiln. Significant amount of energy (25 % of total loss) is found to escape through exit gas.

Mass Loss and Direct Reduction Characteristics of Iron Ore-coal Composite Pellets

Mass loss and direct reduction characteristics of iron ore-coal composite pellets under different technological parameters were investigated. Meanwhile, changes of iron phase at different temperatures were analyzed by using X-ray diffraction (XRD), and characteristics of crushed products were studied by using a scanning electron microscope (SEM). The results showed that heating rate had little influence on the reduction, but the temperature played an important role in the reduction process. The mass loss rate increased rapidly from 800 to 1100 °C. The reduction process can be divided into three steps which correspond to different temperature ranges. Fe2 O3 began to transform into Fe3O4 below 500 °C, and FeO was reduced into Fe from 900 °C. At 900 °C, the reduction product showed a clear porous structure, which promoted the reduction progress. At 1000 °C, the metallic Fe dominated the sample, and the reduction reached a very high degree.

Mathematical Model to Estimate the Rate Parameters and Thermal Efficiency for the Reduction of Iron Ore–Coal Composite Pellets in Multi-layer Bed at Rotary Hearth Furnace

Reduction of iron ore–coal composite pellets at a rotary hearth furnace (RHF) could be an energy efficient process under optimized design and operating conditions. The present study aims to analyze such process through process models for optimization of thermal efficiency. In the present article, a mathematical model has been described to calculate the rate parameters, evolution of various phases, temperature profile, and thermal efficiency of the process. Experiments have been carried out for reduction of iron ore–coal composite pellets in multi-layers at laboratory scale RHF. It has been observed that while the total average time of reduction for three layer bed at 1,200 °C is 48 min, the average time of reduction at 1,300 °C is estimated as 11 min only. The thermal efficiency of the process is found to be maximum for three layer bed and least for the single layer bed. Extra fuel in terms of carbon equivalent has also been reported.

Influence of temperature and time on reduction behavior in iron ore–coal composite pellets

In this study, the kinetics of reduction in iron ore–coal composite pellets has been investigated. Kinetic parameters were estimated from thermogravimetric data. X-ray diffraction was used to identify the products obtained after heating the composite pellet to different temperatures. Experimental results indicate that the reduction process is diffusion controlled below 900°C. There is a change in reduction mechanism above this temperature and mixed control is observed up to 1100°C above which reduction is phase-boundary controlled. The reduction rate has also been observed to decrease with progress in reduction.

Study of reduction behaviour of prefabricated iron ore–graphite/coal composite pellets in rotary hearth furnace

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.

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.

Kinetic Studies of Iron Ore–Coal Composite Pellet Reduction by TG–DTA

An attempt has been made to study the effect of coal quality on the reduction kinetics of iron ore–coal composite pellets under non-isothermal condition in inert atmosphere. During non-isothermal reduction of composite pellets, it is observed that (i) reduction rate of iron oxide increases with increasing temperature, (ii) reduction rate increases with increase in porosity of pellets and (iii) the computed values of activation energy (E) are lower during the initial stage of reduction (0.86–8.82 kJ mol−1) than those in the later stages of reduction (12.37–38.32 kJ mol−1). These values indicate that the initial stage reduction is controlled by gaseous diffusion mechanism and at final stage, mixed control reaction mechanism (i.e., both gaseous-diffusion and chemical reaction) is the rate controlling step. The present investigation aims at to assess the effect of Fetot/Cfix ratio in pellet, volatile matter in coal, and temperature on the reduction kinetics of iron ore–coal composite pellets using simultaneous thermogravimetric and differential thermal analyser (TG–DTA).

Effects of Binder on the Properties of Iron Ore-Coal Composite Pellets

Large amounts of fines and superfines are generated in Indian iron ore and coal mines due to mechanized mining and mineral dressing operations. Utilization of these fines for extracting metal is of vital concern for resource utilization and pollution control. For agglomeration of these fines, a suitable binder is required. Iron ore-coal composite pellets were prepared by cold bonding. Various binders such as lime, Ca(OH)2, slaked lime, dextrose, molasses, and sodium polyacrylate (SPA), alone or in combination, were employed for making composite briquettes. The slaked lime–dextrose combination produced the highest strength among the various binders employed for producing composite briquettes and was therefore selected for producing composite pellets for the smelting reduction. In cold bonding, the composite pellets attain the requisite properties due to physico-chemical changes of the binder in ambient conditions. It was possible to obtain a dry strength of more than 300 N per pellet in some cases and more than 200 N per pellet in many trials. Drop strength and shatter index values of composite pellets were also measured. In the present paper an attempt has been made to evaluate the mechanical properties of cold-bonded composite pellets so as to throw some light on the capacity of these pellets to withstand stresses during handling and transportation.

Mathematical Modeling of the Kinetics of Carbothermic Reduction of Iron Oxides in Ore-Coal Composite Pellets

The kinetics of the carbothermic reduction of iron oxides in a composite pellet made of taconite concentrate and high-volatility coal has been studied by means of mathematical modeling that simultaneously takes into account the transfer rates of both the mass and the heat, and the rates of chemical reactions. The computational results, which have been validated with experimental data in the literature, confirm that the overall rate of the carbothermic reduction, which is strongly endothermic, is limited by heat-transfer steps. From a kinetics viewpoint, the optimum composition of the composite pellet is approximately in accordance with the stoichiometry, when CO is assumed to be the sole oxide of carbon in the gas. To raise the temperature of the pellet from its ambient value to furnace temperature, the heat required is greater than that needed for sustaining all chemical reactions, including the Boudouard reaction. The gaseous product consists mainly of CO and H2, except in the very initial stage. The overall observable reaction rate, in terms of the volumetric rate of the generation of gases, peaks at approximately 30 seconds of reaction time.

Localized Heating and Reduction of Magnetite Ore with Coal in Composite Pellets Using Microwave Irradiation

Magnetite iron ore-coal composite pellets were microwave irradiated in N2 atmosphere with a power supply gradually increased in 2 min intervals from 0.2 up to 2 kW at 2.45 GHz. Electron probe microanalysis (EPMA), X-ray image of SEM micrographs, back scattered electron image (BSE) and Fe, O, S and C mappings of composite pellets irradiated up to different temperatures were obtained. Under the present experimental conditions, pellets heated up to about 800°C without reduction. Above this temperature the reduction occurred stepwise; Fe3O4 reduced to FeO between about 800°C and 1000°C and then FeO reduced to Fe from about 1000 to 1250°C average temperatures. The measured temperature appears to reasonable represent the average temperature of the pellet. However inside of the reacting mass localized slightly different temperatures may exist. Point carbon contents of reduced iron inside the composite pellet irradiated up to 1150°C were from almost 0% to 2% with no correlation between with their spatial location inside the pellet. It is concluded that carbon in the microwave irradiated pellet acting as a reducing and heating agent at the same time generates localized reduction microenvironments.