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.     

A Comparison of Pellet Quality from Straight-grate and Grate-kiln Furnaces

Both straight-grate and grate-kiln furnaces have been accepted in the iron ore industry. Both are considered to be roughly equal when comparing overall costs and expenses versus the final product production rate. However, the product quality of these two systems is not equal. This is shown by critically examining the dust generation of pellets from several facilities. The dustiness of pellets is associated with overall pellet strength, and is an important quality measure of fired pellets on its own. A clear distinction between the dustiness of grate-kiln and straight-grate fired pellets is established. We conclude that grate-kiln-cooler systems provide superior pellet quality, but at the cost of some pellet production rate.     

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.     

A case study of pellet size fraction influence on pelletizing operation

Pellet production is constantly optimized considering different aspects of the production chain from run of mining (ROM) to metallic iron. Industrially, the trade-off between an optimum pellet-size-ratio and the maximum performance in the steel production chain is a relevant subject. The present case study at a Brazilian operation shows the impact of different pellet size fractions on performance of operation, improvements on the fired pellets, less fine generation during handling, and superior metallurgical behavior during the reduction process, resulting in the production of direct reduction iron (DRI) that add more value to the economic performance of the electric arc furnaces (EAF).     

The Effect of Calcined Colemanite Addition on the Mechanical Strength of Magnetite Pellets Produced with Organic Binders

Iron ore pellets must have sufficient mechanical strengths against degradation in all stages of pellet production. Low strength is also a problem for product pellets since they abrade during transportation to the reduction furnaces. The use of a binder is necessary to provide sufficient strength to the pellets and for better operation and handling of pellets. Bentonite is the standard binder in the industry; however, it is considered an impurity due to its acid oxide contents. Organic binders have been tested for many years as alternative binder to bentonite. They have been found to give sufficient wet pellet properties. However, they failed to provide sufficient strength to the preheated and fired pellets due to lack of slag bonding. It has been assumed that one possible effective method to improve the preheated and fired pellet strengths is addition of a slag-bonding constituent. In this study, calcined colemanite was added to the pellet feed to overcome the lower strength problem encountered with organic binder use. The strength of pellets produced with organic binders and calcined colemanite alone and in combination was comparatively studied against the strength of pellets made with standard bentonite binder in magnetite concentrate pelletizing. The results showed that addition of calcined colemanite into the pellet mixture improved the preheated and fired pellet strengths of pellets produced with organic binders.     

Compressive Strength of Fired Pellets Using Organic Binder: Response Surface Approach for Analyzing the Performance

In the present investigation, boric acid was used in the ball formation of iron ore fines to improve the compressive strength (CS) of fired pellet. Boric acid was used in combination with carboxymethyl cellulose (CMC) and saw dust and the pellets were fired at different firing temperatures from 1000 to 1300 °C. Box–Behnken statistical design was followed for analyzing the CS at different levels of boric acid, CMC and firing temperature. Results were discussed using 2D surface plots. Response function predictions determined by the regression analysis showed coefficient of correlation (R²) for CS as 0.96. Highest CS of 450 kg/pellet was obtained with addition of 1% boric acid, 0.1% CMC and a temperature of 1300 °C within the range of parameters under investigation.     

利用神经网络模型预测球团矿的冷压强度(英文)

建立了一个神经网络模型来预测球团矿的冷压强度,该网络模型采用三层前向BP神经网络,网络结构为12-12-1,12个输入变量分别为给料率、料层高度、焙烧温度、干透点温度、COREX煤气单耗、膨润土的添加量、生球水分、生球碳含量以及成品球的FeO、MgO、Al2O3含量和碱度;隐层含有12个神经元;输出为成品球团冷压强度;神经元激活函数选择双曲正切函数;神经网络学习算法使用的是带惯量项的误差反向传播学习算法(BP学习算法)。选取353组数据来训练和测试神经网络,其中247组数据用于训练网络,其余数据用于测试网络。测试结果表明,该网络的预测结果与实际结果的误差在3%以内,同时通过敏感性分析得出以下结论:①膨润土添加量、生球碳含量以及成品球的FeO、MgO、Al2O3含量和碱度对球团矿的冷压强度有重要影响;②增加膨润土添加量、成品球碱度、MgO含量、焙烧温度、干透点温度、COREX煤气单耗有助于改善球团矿的冷压强度;③增加FeO含量、生球碳含量、Al2O3含量、料层高度、给料率将使球团矿的冷压强度迅速下降;④增加生球水分会降低冷压强度;⑤提高球团矿冷压强度的参数设置(膨润土的添加量:0.86%～0.92%;wFeO<0.5%;生球碳含量:1.00%～1.10%;MgO含量:0.39%～0.44%);⑥在0.3～0.7范围内增加碱度不能显著改善球团矿的冷压强度。     

含锌粉尘内配碳球团还原模型

以转底炉处理钢铁厂含锌粉尘为背景,结合转底炉实际生产工艺条件,建立了含锌粉尘内配碳球团直接还原一维非稳态数学模型.模型不仅考虑了铁氧化物的还原反应和碳的气化反应,还加入了氧化锌的还原反应,并通过实验验证了模型的准确性.利用计算结果分析讨论了炉温、球团半径及孔隙率对球团还原的影响.炉温对球团的金属化率和脱锌率均有显著影响,孔隙率和球团半径仅对球团的金属化率影响较小,而对脱锌率基本没有影响.      

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.     

CHARACTERIZATION OF PROPERTIES AND REDUCTION BEHAVIOR OF IRON ORES FOR APPLICATION IN SPONGE IRONMAKING

Studies on the chemical and physical properties, and the reduction behavior (in coal) of hematite iron ores procured from 10 different mines of Orissa, were undertaken to provide information for the iron and steel industries (sponge iron plants in particular). The majority of the iron ores were found to have high iron and low alumina and silica contents. All these iron ores were free from the deleterious elements (S, P, As, Pb, alkalies, etc.). The results indicated lower values of shatter and abrasion indices, and higher values of tumbler index in all the iron ore lumps except Serazuddin (previous) and Khanda Bandha OMC Ltd. For all the fired iron ore pellets, the degree of reduction in coal was more intense in the first 30 min, after which it became small. Slow heating led to higher degree of reduction in fired pellets than rapid heating. All the iron ores exhibited more than a 90% reduction in their fired pellets in 2-h time interval at a temperature of 900°C. Iron ore lumps showed a lower degree of reduction than the corresponding fired pellets.     

马钢链箅机-回转窑氧化球团试验研究

基于马钢球团原料条件,在模拟试验装置中研究了链箅机-回转窑氧化球团生产的料层高度、鼓风干燥热风温度、抽风干燥热风温度、预热热风温度和回转窑焙烧等工艺参数。在配用40%(质量分数)赤铁精矿时,采用最佳链箅机-回转窑工艺参数条件下,获得了冶金性能良好的成品球团矿,主要指标为:单球抗压强度3 113 N,转鼓强度93.16%,抗磨指数2.00%,w(TFe)63.64%,w(FeO)1.62%。     

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.     

Characterisation studies on swelling behaviour of iron ore pellets

At JSW Steel Limited (JSWSL), pellets form the major part of the iron-bearing feed to corex and blast furnace. JSWSL produces low-basicity pellets ((CaO/SiO₂) – 0.40 to 0.50). The quality of the pellet is affected by the raw material chemistry (gangue content), flux proportion and their subsequent heat treatment to produce the fired pellets. The raw material silica, limestone addition, i.e. basicity – CaO/SiO₂ of pellet decides the mode, temperature and the amount of melt formed. The properties of the pellets are, therefore, largely governed by the form and degree of bonding achieved between ore particles and also by the stability of these bonding phases during the reduction of iron oxides. In the present study, laboratory pelletisation experiments have been carried out to know the effects of silica and basicity on the microstructure and swelling behaviour of pellets during reduction. Phase analysis was carried out using image analyser, and chemical analysis of oxide and slag phases was carried out using SEM–EDS. From the laboratory studies, it was observed that the swelling index of the pellets decreased with an increase in silica content due to the decrease in porosity. The presence of higher silica in pellet hinders the reduction step of haematite to magnetite at lower temperatures. Pellets with basicity range 0 to 0.1 exhibited lower swelling index due to the formation of high melting point fayalite phase and also at this basicity range the structure is held together by the seam-like compounds between Fe₂O₃ and SiO₂ primarily at high silica content. Higher swelling index was observed at the basicity range 0.3 to 0.7 due to the presence of low melting point calcium olivines (1115°C) between fayalite (FeSiO₄) and dicalcium silicate (Ca₂SiO₄). Low melting point slag phase enhances the swelling index of the pellets. Swelling index of the pellets considerably dropped between the basicity range 0.9 to 1.1 due to the formation of calcium ferrite phases with a close pore structure.     

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.     

高配比镜铁矿的生产实践

为了降低漓铁8 m2竖炉生产成本,配加30%(质量分数)的镜铁矿进行球团生产。针对镜铁矿焙烧温度高的特点,为了有效提高成品球的抗压强度,对漓铁竖炉球团生产线的燃烧室及水梁等进行了改造,在配加镜铁矿的情况下使成品球能够满足高炉的要求。在焙烧温度为1 250℃的条件下,成品球团矿抗压强度可达到2 741 N/个,表明添加了镜铁矿后的球团矿指标仍然达到了国家标准。     

Utilization of High Sulfur Raw Materials in Iron Ore Pellets

Pyrite cinder and high sulfur magnetite were used as raw materials to produce iron ore pellets. Good qualities of green balls and fired pellets were obtained from the feed comprising 50% pyrite cinder and 50% high sulfur magnetite concentrate at a small scale. Small-scale tests were proven by pilot-scale tests. The high grade fired pellets, assaying 63.22% Fe, were analyzed, and the compressive strength of fired pellets was over 2500 N/pellet. The fired pellets possessed excellent metallurgical performances, such as reducibility index higher than 67%, reduction swelling index lower than 15% and low temperature reduction degradation index (+ 3.15 mm) higher than 1%, which can be used as the burden for blast furnace.     

带式机镁质球团热工制度仿真及优化

镁质球团矿冶金性能好,是一种优质炼铁炉料,其生产最适宜的设备是带式焙烧机,但镁质球团对焙烧均匀性要求高.针对带式机生产镁质球团,采用Fluent工具对焙烧过程进行了模拟仿真,以获得均匀的温度场.建模考虑了碳酸镁的分解、氧化镁含量对磁铁矿氧化的影响,仿真结果通过链篦杯实验进行了验证,模型模拟的温度准确率大于90％.随后利...     

Application of artificial neural network model to predict reduction degradation index of iron oxide pellets

Abstract

The reduction degradation index (RDI) is an important metallurgical property of iron ore pellets used for the production of RDI from shaft furnace or for use in blast furnaces. In order to develop a control strategy, a neural network model has been developed to predict the RDI of pellets from 13 input variables, namely feedrate of green pellets, bed height, burn through temperature, firing temperature, specific corex gas consumption, bentonite, moisture and carbon content in green pellets and Al₂O₃, SiO₂, CaO, MgO and FeO in fired pellets. The RDI of pellets was more sensitive to variation in MgO, CaO, bentonite and green pellet carbon content. The predicted results were in good agreement with the actual data.     

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.     

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.