Iron Ore Pellet Dustiness Part I: Factors Affecting Dust Generation

Iron ore pellets abrade during handling and produce dust. This study was conducted to determine what factors affect pellet dustiness, and whether dustiness can be related to the abrasion index. Factors studied included bed depth within a straight grate furnace; pellet chemistry; firing temperature; coke breeze addition; and tumble index. Abrasion indices for all pellet samples ranged from 1.9–5.0% (20 samples) and from 7.1–27.5% (5 samples). Pellets were dropped in an enclosed tower, which enabled the collection of airborne particles generated during pellet breakdown. The quantity of airborne particles generated by each pellet type was 10–100 mg/kg-drop, or 50–500 mg/kg over five drops through the tower. Pellet dustiness was predominantly affected by pellet chemistry and by pellet firing temperature. Results showed a nearly 21% increase in dustiness for every percent decrease in firing temperature – this was based on a typical firing temperature of 1280°C. Pellet dustiness was regressed to the pellet abrasion index (for AI < 5%), which yielded a correlation coefficient of 0.22. These results show that, although AI is one of the best indicators of fired pellet quality and can indicate high levels of dust, it could not explain the dustiness of good quality pellets.

The second paper (Iron Ore Pellet Dustiness Part II) explains the relationship between AI and dust for good-quality pellets; and compares fines generation between pellets fired in Straight-Grate (Traveling Grate) and Grate-Kiln furnaces.     

Effect of the firing temperature and the added MgO on the reduction swelling index of the pellet with low SiO2 content

The use of pellet with low SiO₂ content in blast furnace (BF) will reduce the slag amount as well as fuel rate and increase the productivity. In this paper, the effect of the firing temperature and the added MgO on the reduction swelling index (RSI) and the compressive strength of the reduced pellet with low SiO₂ content was investigated, and the microstructure of the fired and reduced pellets was analysed by means of the electron microscopy. It was found that the decrease of SiO₂ content will raise the RSI and reduce the compressive strength of reduced pellet. When the SiO₂ content of pellet is 4.8%, the RSI is 16.5% and compressive strength of reduced pellet is 423 N/P. When the SiO₂ content is 2.8 and 1.8% fired at 1280°C, the RSI of the reduced pellet will increase to 34.5 and 55.8% and the compressive strength is reduced to less than 200 and 80 N/P. However, if some MgO was added, the RSI and the compressive strength of the reduced pellet could be improved significantly. When pellet’s MgO content was over 1.7% and SiO₂ content was 2.8% or MgO content was 2.5% and SiO₂ content was 1.8% fired at 1280°C, the RSI of the two pellets could drop to less than 20% and the compressive strength could increase to more than 300 N/P. Then, the technical index of pellet will meet the requirement of the charging in large BF. The added MgO pellet with low SiO₂ content have been used in 5500?m³ BF in Shougang Jingtang Corporation and delivered sustainable improvement of cost reduction.     

STUDIES ON THE REDUCTION KINETICS OF HEMATITE IRON ORE PELLETS WITH NONCOKING COALS FOR SPONGE IRON PLANTS

In the present investigation, fired pellets were made by mixing hematite iron ore fines of ?100, ?16 + 18, and ?8 + 10 mesh size in different ratios and studies on their reduction kinetics in Lakhanpur, Orient OC-2 and Belpahar coals were carried out at temperatures ranging from 850°C to 1000°C with a view toward promoting the massive utilization of fines in ironmaking. The rate of reduction in all the fired iron ore pellets increased markedly with an increase in temperature up to 1000°C, and it was more intense in the first 30 min. The values of activation energy, calculated from integral and differential approaches, for the reduction of fired pellets (prepared from iron ore fines of ?100 mesh size) in coals were found to be in the range 131–148 and 130–181 kJ mol^?1 (for α = 0.2 to 0.8), indicating the process is controlled by a carbon gasification reaction. The addition of selected larger size particles in the matrix of ?100 mesh size fines up to the extent studied decreased the activation energy and slightly increased the reduction rates of resultant fired pellets. In comparison to coal, the reduction of fired pellets in char was characterized by significantly lower reduction rates and higher activation energy.     

Reduction and Swelling of Fired Hematite Iron Ore Pellets by Non-coking Coal Fines for Application in Sponge Ironmaking

In the present investigation, the reduction and swelling behaviors (in low grade coal) of fired iron ore pellets, prepared by blending hematite iron ore fines of ?100, ?18 + 25, and ?10 + 16 mesh sizes in different proportions, have been studied in the temperature range of 850–1000°C with an objective to promote massive utilization of fines in sponge ironmaking. An increase in temperature up to the range studied (850–1000°C) substantially enhanced the reduction rate and the rate was found to be highest in the first 15–30 min at all these temperatures. All the fired pellets, made by mixing iron ore particles of ± 100 mesh size, have shown approximately the same reduction rates and slightly higher swelling indices than those made from fines of ?100 mesh size only. In all the fired pellets reduced at temperatures of 850°C and 900°C, the results indicated an increase in the extent of swelling with reduction time. Reduction of fired pellets at temperatures of 950°C and 1000°C exhibited shrinkage in their reduced products, and the extent of this shrinkage increased with increase in exposure time.     

Phase Transformation of Andalusite-Mullite and Its Roles in the Microstructure and Sinterability of Refractory Ceramic

Andalusite has been realized as a special mineral for the production of refractory ceramics due to its unique property to automatically decompose into mullite and silica during heating at high temperature. The phase transformation from andalusite to mullite plays a critical role for the effective applications of andalusite. This study investigated the microstructural characteristics and sinterability of andalusite powder during high-temperature decomposition. The andalusite powder was bonded with kaolin and prepared as a cylinder green body at 20 MPa; it was then fired at 1423 K to 1723 K (1150 °C to 1450 °C). The microstructures and mechanical strengths of the sintered ceramics were studied by the compressive test, X-ray diffraction, and scanning electron microscopy. The results showed that newly born mullite appeared as rodlike microcrystals and dispersed around the initial andalusite. At 1423 K (1150 °C), the mullitization of andalusite was started, but the complete mullitization was not found until firing at 1723 K (1450 °C). The compressive strength of the ceramics increased from 93.7 to 294.6 MPa while increasing the fire temperature from 1423 K to 1723 K (1150 °C to 1450 °C). Meanwhile, the bulk density of the ceramics was only slightly changed from 2.15 to 2.19 g/cm³.     

Studies on the Reduction–Swelling Behaviors of Hematite Iron Ore Pellets with Noncoking Coal

Studies on the reduction and swelling behaviors of fired pellets, made by mixing hematite iron ore fines of ?100, ?18 + 25, and ?10 + 16 mesh sizes in different proportions, were carried out with low-grade coal in the temperature range of 850–1000°C with an aim to promote the massive utilization of fines in ironmaking. The rate of reduction in all the fired iron ore pellets increased markedly with an increase in temperature up to 1000°C and it was more intense in the first 15-min soak time. Relatively higher reduction rates and swellings/shrinkage were observed in the pellets made by the addition of larger size (+100 mesh) particles in the matrix of ?100 mesh size fines. In general, highest swelling was observed in the fired pellets at a reduction temperature of 850°C, followed by a decrease at 900°C. At both these temperatures, the percentage of swelling increased with reduction time up to the range studied (120 min). The fired pellets reduced at temperatures of 950°C and 1000°C, showed shrinkage, and the extent of this shrinkage increased with increase in exposure time at 950°C. The percentage swelling/shrinkage in the fired pellets was found to be related to their crushing strengths and porosities.     

Iron Ore Pellet Dustiness Part II: Effects of Firing Route and Abrasion Resistance on Fines and Dust Generation

Iron ore pellets abrade during their production and handling, which lowers product quality and leads to dustiness issues. Pellets were collected from a variety of plants (operating either Straight-Grate (SG) or Grate-Kiln (GK) furnaces) to understand whether furnace type affects fines and dust formation. Results showed that pellets fired in SG furnaces were less abrasion-resistant (3.5 × lower) than pellets fired in GK furnaces. Concurrently, laboratory pellets were prepared using various ores, binders, and firing temperatures. These were tested to understand the relationship between abrasion index and dustiness. AI was observed to range from 1 to 14%. Dustiness, determined via AI and size distributions of abrasion progeny, ranged from 0.2 to 1.6%. For AI greater than 5%, AI can be used to indicate potentially high levels of dust. For AI less than 5%, there was a poor correlation between AI and dustiness. This was explained by the observation that as AI decreased, the abrasion product fineness increased. The results from parts I and II of this investigation suggest that material loss and levels of pellet dustiness may be significantly affected by pellet quality up to a certain point. Poorly fired pellets will be dusty during handling and transportation, while well-fired pellets will generate less – but finer – material as their quality improves. This could lead to little observed changes in dust generation over a wide range of pellet quality. Dust generation at each site would then depend on the quantity of material produced and their extent of handling.     

ASSESSMENT OF REDUCTION BEHAVIOR OF HEMATITE IRON ORE PELLETS IN COAL FINES FOR APPLICATION IN SPONGE IRONMAKING

Studies on isothermal reduction kinetics (with F grade coal) in fired pellets of hematite iron ores, procured from four different mines of Orissa, were carried out in the temperature range of 850–1000°C to provide information for the Indian sponge iron plants. The rate of reduction in all the fired iron ore pellets increased markedly with a rise of temperature up to 950°C, and thereafter it decreased at 1000°C. The rate was more intense in the first 30 minutes. All iron ores exhibited almost complete reduction in their pellets at temperatures of 900 and 950°C in < 2 hours' heating time duration, and the final product morphologies consisted of prominent cracks. The kinetic model equation 1 ? (1 ? α)^1/3 = kt was found to fit best to the experimental data, and the values of apparent activation energy were evaluated. Reductions of D. R. Pattnaik and M. G. Mohanty iron ore pellets were characterized by higher activation energies (183 and 150 kJ mol^?1), indicating carbon gasification reaction to be the rate-controlling step. The results established lower values of activation energy (83 and 84 kJ mol^?1) for the reduction of G. M. OMC Ltd. and Sakaruddin iron ore pellets, proposing their overall rates to be controlled by indirect reduction reactions.     

Effect of Annealing on Properties of Carbonaceous Materials. Part II: Porosity and Pore Geometry

The pore structure of carbonaceous materials was studied using image analysis. The effect of annealing on the porosity and pore geometry of cokes, chars, and pyrolyzed coals (laboratory chars) was examined in the temperature range of 973 K to 1773 K (700 °C to 1500 °C). The porosity of chars and pyrolyzed coals significantly increased during annealing at temperatures below 1373 K (1100 °C) due to volatile matter release. Further increasing of the annealing temperature from 1373 K to 1773 K (1100 °C to 1500 °C) caused marginal porosity evolution. The porosity of cokes was not affected by annealing at temperatures below 1573 K (1300 °C) and slightly increased in the temperature range 1573 to 1773 K (1300 °C to 1500 °C). The increase in the porosity of chars and pyrolyzed coals during annealing at temperatures 1373 K to 1773 K (1100 °C to 1500 °C), and cokes at 1573 K to 1773 K (1300 °C to 1500 °C), was a result of reactions with oxides of their mineral phases. Annealing had a marginal effect on the pore shape (Feret ratio) of carbonaceous materials, but enlarged the pore size of chars and pyrolyzed coals and decreased their pore density.     

Replacement of bentonite in hematite ore pelletisation using a combination of sodium lignosulphonate and copper smelting slag

Bentonite is the most common binder used in iron ore pelletisation owing to its good bonding properties in green and dry pellets at both ambient and elevated temperatures. However, due to its high alumina and silica content, it increases the slag volume and energy consumption in downstream processes. Organic binders may be used to replace bentonite; however, they fail to provide strength at a high temperature (700–900°C) due to poor thermal stability during pellet induration. In the present study, an organic binder Na lignosulphonate (NLS) has been used along with copper smelting slag (Cu-SS). FeO in Cu-SS provides diffusion bonding at high temperature and maintains the strength of pellets even after evaporation/burning of NLS. It also enhances recrystallisation bonding at relatively lower temperature to provide good strength. The study has been carried out with hematite ore and varying amounts of NLS and Cu-SS. Copper smelting slag (1.0%) addition with 0.5%NLS has been found to be optimum to provide very good green properties and ～300?kg/pellet cold crushing strength (CCS) at 1250°C induration temperature. However, hematite pellets of similar basicity with 0.5% bentonite requires higher induration temperature (1300°C) to achieve a similar CCS. The developed pellet also shows better reducibility (80%), similar reduction degradation index (18%) and swelling index (10%) to the usual bentonite pellet. Thus, the induration temperature of hematite pellet has been lowered by 50°C using a combination of NLS and Cu-SS eliminating bentonite completely, which can provide a considerable energy and cost saving.     

Physicochemical properties of nickel electrolytes

The density, electrical conductivity, viscosity, and surface tension of nickel electrolytes containing sodium, chloride, and sulfate ions, as well as boric acid, were determined. This investigation was carried out over the temperature range of 30 °C to 70 °C. Based upon the experimental data, regression equations were developed for calculating these properties as a function of electrolyte composition and temperature.     

High-Temperature Compression Behavior of Cast and Homogenized IN939 Superalloy

Hot deformation behavior of IN-939 superalloy was investigated in this work. Hot compression experiments were performed at temperatures of 1273 K, 1323 K, 1373 K, and 1423 K (1000 °C, 1050 °C, 1100 °C, and 1150 °C) at strain rates of 0.001, 0.01, 0.1, and 1 s^?1 up to a true strain of 0.8. Then variations in stress-strain curves as well as changes in microstructures of various hot-deformed samples were studied. At 1273 K to 1323 K (1000 °C to 1050 °C), dynamic recovery (DRV), and at 1373 K to 1423 K (1100 °C to 1150 °C), dynamic recrystallization (DRX), were recognized to be the main mechanisms of the alloy softening during hot compression tests. The relationships between flow stress, strain rate, and temperature were mathematically modeled with three well-known equations, and on the basis of those equations, the activation energy of hot deformation was calculated. For improvement of the proposed models, it was necessary to conduct the investigation at two temperature ranges: 1373 K to 1423 K (1100 °C to 1150 °C), in which DRX occurred, and 1273 K to 1323 K (1000 °C to 1050 °C), where DRV as well as γ′ precipitation happened. For each of the temperature ranges, a different value for activation energy was obtained, which in conjunction with the related model, can be used for simulating the deformation behavior of the alloy.     

A New On-Line Method for Predicting Iron Ore Pellet Quality

The Abrasion Index (AI) describes fines generation from iron ore pellets, and is one of the most common indicators of pellet quality. In a typical pellet plant, dust is generated during the process and then captured. Can the dust be measured and used to predict AI? In this paper, the feasibility of using airborne dust measurements as an indicator of AI is investigated through laboratory tests and using data from a pellet plant. Bentonite clay, polyacrylamide and pregelled cornstarch contents, and induration temperature were adjusted to control the abrasion resistance of laboratory iron ore pellets. AI were observed to range from approximately 1% to 12%. Size distributions of the abrasion progeny were measured and used to estimate quantities of PM₁₀ (particulate matter with aerodynamic diameter less than 10 µm) produced during abrasion. A very good correlation between AI and PM₁₀ (R² = 0.90) was observed using the laboratory pellets. Similarly, a correlation was observed between AI and PM measured in the screening chimney at a straight-grate pelletization plant in Brazil, with an R² value of 0.65. Thus, the laboratory and industry data suggest that measuring dust generation from fired pellets may be an effective on-line measurement of pellet quality. The data also showed that particulate emissions from pelletization plants may be directly affected by AI.     

Investigation of factors affecting pellet strength in straight grate induration machine

Abstract

During induration in a straight grate machine, the green pellets pass through four different thermal treatments, namely drying, preheating, heating and cooling. The pellet bed is fired with downdraught firing leading to thermal gradients through the bed. Corex sludge, which is used as fuel in the pellet mix, supplies the necessary energy for uniform heating of the pellet. The physicochemical conditions, e.g. the temperature and oxygen partial pressure mainly depend on the amount of fuel incorporated in the pellet mix. As a result the percentage and the distribution of various phases in the pellets vary, leading to deviation in quality. To study the distribution of phases and their impact on cold crushing strength at different carbon levels (1·20 and 1·35%), pellets from different layers of the induration bed in an industrial straight grate were characterised. It was observed that the strength of the pellets varied from 142 to 268 kg/pellet and 128 to 245 kg/pellet across bed, with carbon 1·20 and 1·35% respectively. It was found that middle layer pellets had higher strength compared to top and bottom layers. It was observed that amount of hematite, magnetite, porosity and the pore size plays a significant role on the pellet strength. Pellets with 1·20% carbon showed better physical and microstructural properties across the pellet bed compared to pellets with 1·35% carbon.     

Use of Iron Ore Fines in Cold-Bonded Self-Reducing Composite Pellets

The feasibility of producing direct reduced iron from cold-bonded, self-reducing composite pellets, constituted from beneficiated iron ore slime, coke, and different binders (dextrin, bentonite, calcium lignosulfonate, and carboxymethyl-cellulose [CMC]) was studied. This was done using a design of experiments approach. It was found that as-received beneficiated iron ore slime is suitable as a raw material for the production of self-reducing composite pellets with carboxymethylcellulose as the most suitable binder. Dry strengths in excess of 300 N/pellet were attained by curing the pellets under ambient conditions. The composite pellets reduced within 20 min to degrees of metallization in excess of 90% at 1100°C, with decrepitation indices significantly below 5%. The degree of metallization of composite pellets increased with an increase in reduction temperature (from 1000 to 1100°C), reduction time (20 min. vs. 40 min), and coke quantity (15% vs. 20%). CMC was identified as the most economical and suitable binder for the Sishen concentrate.     

Hot Deformation Behavior and Microstructural Evolution of a Nickel-Free Austenitic Steel with High Nitrogen Content

In current study, the effect of microstructure on hot ductility of nickel-free austenitic high nitrogen steel DIN EN 1.4452 was investigated. Phase transformations and precipitation were modeled as well as experimentally determined via microstructural evaluation. Hot tensile and compression tests were used to simulate the hot deformation behavior at temperatures between 1173 K and 1573 K (900 °C and 1300 °C). Hot tensile test determined the high-temperature properties. The effect of temperature on cracking sensibility during hot deformation was investigated using hot compression test. The results showed that better hot ductility is observed at temperatures ranging from 1423 K to 1523 K (1150 °C to 1250 °C). The increase of hot ductility depends on grain refinement due to dynamic recrystallization at this temperature range.     

Powder injection moulding of Inconel 713C alloy

ABSTRACT

To find a proper super alloy applied to gasoline engine turbochargers which demand a high operating temperature over 950°C, the IN713C super alloy was investigated in this study. The rheological properties of feedstock, density, microstructure and mechanical properties were measured. The proper powder loading was 61?vol.-%. Through the analysis of viscosity, 160°C was supposed to be more suitable for the injection. After debinding, most binder components were removed. A reasonable debinding process was formulated. Two pre-sintering temperature (850, 950°C) were investigated, then 850°C was considered to be more proper relatively. The samples were sintered at different temperatures for various time. The best properties of sintered parts were obtained when sintered at 1300°C for 3?h, the density of sintered parts was 7.83?g?cm^?3 while the hardness was 43.6 HRC and tensile strength was 1216.9?MPa.     

Hydrogen Reduction Kinetics of Magnetite Concentrate Particles Relevant to a Novel Flash Ironmaking Process

A novel ironmaking technology is under development at the University of Utah. The purpose of this research was to determine comprehensive kinetics of the flash reduction reaction of magnetite concentrate particles by hydrogen. Experiments were carried out in the temperature range of 1423 K to 1673 K (1150 °C to 1400 °C) with the other experimental variables being hydrogen partial pressure and particle size. The nucleation and growth kinetics expression was found to describe the reduction rate of fine concentrate particles and the reduction kinetics had a 1/2-order dependence on hydrogen partial pressure and an activation energy of 463 kJ/mol. Unexpectedly, large concentrate particles reacted faster at 1423 K and 1473 K (1150 °C and 1200 °C), but the effect of particle size was negligible when the reduction temperature was above 1573 K (1300 °C). A complete reaction rate expression incorporating all these factors was formulated.     

Recovery of Manganese Ferrite in Nanoform from the Metallurgical Slags

The present work investigates the formation of manganese ferrite of nanosize by oxidation of MnO- and FeO-containing slag. A horizontal resistance furnace was used as an experimental setup. The experiment was conducted in the temperature range of 1573 K to 1673 K (1300 °C to 1400 °C) in an oxidizing atmosphere. The samples were quenched to the cold end of the furnace and were analyzed by X-ray diffraction (XRD). The XRD patterns of the products showed the presence of two phases??manganese ferrite and calcium silicate. The particle size of the manganese ferrite was estimated by the Scherrer formula to be in the range of nanometers.     

Dielectric and microstructural properties of YAG:Dy3+ ceramics

Yttrium aluminium garnet(Y_3 Al_5 O_(12):YAG) singly doped with Dy3+ at different concentrations was prepared by solid state reactions using repeated heating cycles over the temperature range of 1300-1600 ℃. X-ray powder diffraction analysis confirms the presence of a well-crystallized YAG perovskite phase with cubic structure(by Rietveld refinement). The rare earth dopant is successfully integrated into the YAG host lattice without any major changes in the original structure. The temperature dependence,up to 250 ℃, of the conductivity, dielectric constant, dielectric loss, and loss tangent, at various frequencies of up to 5.0 MHz for undoped and doped crystals is compared to understand the electrical and structural characteristics. The experimental results reveal that Dy3+ dopants in YAG crystal significantly influence the conductivity, dielectric constant, and lossy mechanisms, which is probably due to the 3 d-AI ions and 4 f-Dy ions incorporated at different positions of both tetrahedral and octahedral symmetries in YAG:xDy3+ ceramics.