w(MgO)对熔剂性球团矿冶金性能的影响

 为了研究添加高镁粉时w(MgO)对熔剂性球团矿冶金性能的影响。考察了w(MgO)为1.6%～2.4%时,其对球团矿抗压强度、RI(还原性指数)、RDI(低温还原粉化指数)和RSI(还原膨胀指数)的影响。采用光学显微镜和X射线衍射仪对球团矿微观结构和矿物组成进行了分析。结果表明,随着MgO质量分数的增加,抗压强度呈先升高后降低的趋势,w(MgO)为2.0%时,抗压强度最大,为3 533 N;随着w(MgO)由1.6%增加到2.4%,球团矿RI、RDI和RSI得到改善;w(MgO)为1.8%～2.0%时,球团矿微观形貌和矿物组成较好,赤铁矿成片结晶,球团矿强度良好。在用高镁粉和研山精粉造球时,w(MgO)控制为1.8%～2.0%,以期得到较低的还原膨胀指数和较好的冶金性能。     

Effects of MgO Containing Additive on Low-Temperature Metallurgical Properties of Oxidized Pellet

 As a main charging form of BF (blast furnace), pellets play an important role in blast furnace process. However, comparing with sinters, pellets have many disadvantages, such as reduction swelling, low softening and melting temperature and so on. Therefore, the flux pellets have been applied in blast furnace widely, especially MgO containing pellets. The light burned magnesite is applied as MgO containing additive in pellet production. The characters of light burned magnesite are explored. Meanwhile, the effects of it on low-temperature metallurgical properties are investigated such as low-temperature reduction degradation index (RDI), compressive strength (CS) and the reduction swelling index (RSI). The light burned magnesite calcined at 850 ℃ manifests better grindability, larger specific surface area, and higher hydration activity. It is found that the addition of light burned magnesite can improve low-temperature metallurgical properties (RDI, RSI) of the pellets. With the increase of light burned magnesite in pellets, the RSI and RDI decrease gradually; when the proportion of light burned magnesite does not exceed 2. 0% in pellets, the CS decreases slightly, but it still surpasses 2689 N, which can still meet the demand of BF.     

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.     

MgO含量和来源对球团焙烧特性及冶金性能的影响

分别以5种不同的含镁添加剂（高镁磁铁矿、镁橄榄石、白云石、菱镁石和氧化镁粉）制备镁质球团,阐述MgO含量和来源对磁铁矿球团焙烧特性及冶金性能的影响。研究结果表明:不同的含镁添加剂对于生球的落下强度有着一定影响,其中氧化镁粉与高镁磁铁矿均能够提高球团的落下强度。相同的预热焙烧制度下,提高MgO含量会增加球团孔隙率,降低预热和焙烧球团的抗压强度,其中白云石对焙烧球团强度的不利影响最小。增加预热球团的氧化度有利于促进镁质焙烧球团固结,提高其抗压强度。在MgO来源相同的情况下,MgO含量的增加会导致球团孔隙的增减,降低了球团强度,而配加不同种类的含镁添加剂,均能不同程度改善球团的还原膨胀性、低温还原粉化性和还原性,其中配加高镁磁铁矿的球团的还原膨胀性和低温还原粉化性均优于于其他含镁球团。      

Chemistry,microstructure, and reduction characteristics of dolomite-fluxed magnetite pellets

The addition of dolomite to iron ore pellets improves high temperature reduction properties, primarily by increasing their softening point and reducibility. This study was made to ascertain the compositional ranges within which dolomite fluxed magnetite pellets show such an improvement over good acid pellets. A variety of compositions with MgO levels from 1 to 2 wt pct and CaO/SiO₂ ratios of 0.6 to 1.8 were prepared using Hibbing magnetic concentrate. These compositions were balled and then pot-grate fired to various temperatures. Petrographic examination and electron microprobe analyses were used to characterize the phase assemblages. Reduction characteristics were also evaluated. As evidenced by the following petrographically observed relationships, the CaO/SiO₂ ratio (c/S) was found to be the controlling factor for pellet microstructure: a) The low c/S (< 0.8) pellets were predominantly oxide-bonded, b) the intermediate c/S (0.8 to 1.3) pellets were slag- and oxide-bonded, and c) the high C/S (> 1.3) pellets were mostly calcium ferrite-bonded. Intermediate c/S compositions contain more magnesioferrite than do either low or high basicity compositions. Pellets must be fired to a high enough temperature to generate sufficient liquid for ion transport but not so high as to cause pellets to stick together. Well-fired pellets with a c/S of 1.3 or less performed adequately in low temperature degradation tests. Pellets with a c/S of 0.8 or greater displayed satisfactory swelling behavior. Therefore, we determined that pellets within a c/S range of 0.8 to 1.3 are technically acceptable. Pellets containing 1.5 wt pct MgO had the best reduction characteristics, but all fluxed compositions reduced faster and more completely than did acid pellets. Increasing MgO content up to 2.0 pct increased the softening temperature by 165‡C over acid pellets. On the basis of pellet test results and taking into consideration the auxiliary influence of economic and operating considerations, we determined the optimum composition of dolomite fluxed Hibbing pellets to be 1.5 pct MgO and a C/S of 0.8.     

Optimisation of the MgO/Al2O3 ratio of high-alumina BF slag based on MOPSO algorithm

To reduce the content of MgO in the slag, which helps in lowering production costs, the chemical components of a SiO₂–CaO–MgO–Al₂O₃–TiO₂ blast furnace (BF) slag system with high Al₂O₃ content were optimised using the multi-objective particle swarm optimisation (MOPSO) algorithm. First, models for predicting the metallurgical properties of BF slag were established and verified, based on mixture experimental designs and the ion and molecule coexistence theory. Second, the problem was solved by MOPSO using the MATLAB software package. Optimisation results show that the appropriate content of MgO in the slag should be 4–7%, and the MgO/Al₂O₃ ratio should be 0.2–0.6. Finally, optimised solutions were used in the 3200?m³ BF of a steel company in China. MgO in the slag was reduced to less than 5%, the MgO/Al₂O₃ ratio was controlled at 0.3–0.4, and the fuel ratio remained at 515?kg?t^?1.     

优化配矿强化西澳超细粒磁铁精矿球团焙烧研究

进行了西澳超细粒磁铁精矿分别配加国产磁铁精矿和巴西赤铁精矿制备氧化球团矿的实验研究.结果表明,以100%西澳超细磁铁精矿为原料制备氧化球团矿时,球团预热及焙烧性能较差,在预热温度为1050℃、预热时间20 min及焙烧温度1300℃、焙烧时间40 min的条件下,预热球团和焙烧球团矿抗压强度分别为每个502和2313 N.西澳超细粒磁铁精矿配加40%国产磁铁精矿或20%巴西赤铁精矿时,球团适宜预热温度由1050℃分别降低到950和975℃,适宜的焙烧温度由1300℃分别降低到1250和1280℃;而且焙烧球团矿的抗压强度分别提高到每个2746 N和每个2630 N.焙烧球团矿的微观结构研究表明：配加国产磁铁精矿后,焙烧球团矿中Fe₂O₃晶粒发育优良,晶粒间互联程度提高,晶粒粗大,孔隙率低,固结更加紧密.配加20%巴西赤铁精矿时,焙烧球团矿中Fe₂O₃晶粒基本连接成片,Fe₂O₃晶体发育良好.优化配矿是改善西澳超细粒磁铁精矿球团矿预热及焙烧性能的有效途径.     

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。     

低硅含镁球团矿抗压强度及冶金性能

提高入炉原料品位降低硅含量,改善冶金性能是高炉精料的主要方向。研究了低硅球团矿的还原膨胀率及MgO对低硅球团矿抗压强度和冶金性能的影响。研究结果显示,低硅球团矿虽然具有品位高,脉石含量低等优点,但随着SiO2含量的降低球团矿还原膨胀率恶化,影响高炉冶炼。低硅球团配加含镁添加剂可以有效控制还原膨胀率,同时改善球团矿的还原度和熔滴性能。球团矿SiO2的质量分数低于2%时,还原膨胀率在60%以上;当MgO的质量分数提高到2.15%以上时,还原膨胀率能降到20%以下,但随着MgO含量的增加低硅球团矿抗压强度下降,需要提高焙烧温度,才能形成稳定的铁酸镁,改善抗压强度。MgO的质量分数为2.15%时,焙烧温度要提高到1 270℃,MgO的质量分数超过2.8%以上时,焙烧温度需要提高到1 300℃。     

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。     

中关铁矿制备熔剂性球团生球性能试验

 通过增加熔剂性球团矿的入炉比例,能够改善炉料结构,降低炼铁系统能耗,并且通过“源头减量”的途径可以降低炼铁过程中污染物的排放。实现高球比冶炼的核心环节是制备熔剂性球团,而熔剂性球团质量取决于生球的性能,因此,保证生球质量是探究熔剂性球团制备工艺较为重要的环节。由于中关铁矿硅含量较低、镁含量适宜,适合作为低硅熔剂性球团的原料。以中关铁矿为原料探究熔剂性球团的制备工艺,并在此基础上分析了影响熔剂性球团生球质量的因素(粒度、时间、水分、膨润土、SiO₂含量、碱度和MgO含量)。试验结果表明,生球的抗压强度、落下强度及爆裂温度受碱度、SiO₂和MgO含量变化的影响不大;生球的抗压强度、落下强度及爆裂温度主要受造球时间、水分、黏结剂用量、铁矿粉及熔剂的理化性能影响,并在造球时间维持为12 min、水分维持为8%～9%、膨润土用量为2%时,生球抗压强度、落下强度及爆裂温度较优且满足运输与入炉要求。     

高硅镁质熔剂性球团成球过程及冷态性能实验

生球质量的好坏是直接关系到企业是否顺利生产高质量熔剂性球团的前提。为探明SiO₂、碱度及MgO含量对生球性能的影响规律,以唐钢生产所用3种磁铁矿为原料,通过添加生石灰调节碱度,添加白云石调节MgO含量,配比3种铁矿粉调节SiO₂含量,进行了造球及生球冷态性能的试验。研究发现,无论是改变SiO₂、碱度还是MgO含量,其生球适宜水分基本都保持在8%～9%(质量分数)之间。生球的成球率维持在90%以上,成球率良好。生球的抗压强度、落下强度的大小以及爆裂温度的高低,主要受铁矿粉及熔剂的粒度组成、物理性能以及生球适宜水分大小的影响。     

MgO质量分数对氧化球团性能的影响

 为了改善澳洲某磁铁矿氧化球团的冶金性能,研究了MgO质量分数对其质量的影响。研究结果表明,随着MgO质量分数的提高,生球落下强度和爆裂温度提高,MgO质量分数对生球抗压强度影响较小。随着MgO质量分数提高,预热球团和焙烧球团抗压强度降低,还原度有所改善;提高MgO质量分数可以有效抑制球团的低温还原粉化和球团的还原膨胀,软化开始温度、软化结束温度和滴落温度均有所提高,软熔性能得以改善。这主要是由于提高MgO质量分数,渣相中铁酸镁和钙镁橄榄石质量分数升高,在还原过程中Mg2+与Fe2+发生晶格取代,生成FeO与MgO的固溶体,具有稳定晶格的作用,从而抑制还原膨胀和低温还原粉化。     

MgO添加方式对镁质球团矿的影响

 为了获得优质镁质球团矿,在添加0.7%新型复合黏结剂的条件下进行了MgO添加方式(菱镁石粉、轻烧镁粉)对造球过程、氧化焙烧及冶金性能影响的试验研究。结果表明,复合黏结剂改善了生球指标、提高了球团矿铁品位,球团矿中w(TFe+MgO)质量分数提高0.65%;当w(MgO)/w(SiO₂)为0.14～0.24时,球团矿添加菱镁石粉改善了生球落下强度、提高了球团矿还原性,MgO添加方式对抗压强度的影响很小,球团矿添加菱镁石粉、轻烧镁粉都降低了还原膨胀率,改善了低温还原粉化指标、熔滴性能。     

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.     

Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂?=?1.1–1.4, 6–12?mass% MgO and 10–16?mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.     

改善鞍钢球团矿冶金性能的研究

对带式机酸性球团矿添加含MgO添加剂的造球、焙烧和冶金性能研究表明,在带式机目前焙烧工艺制度条件下,MgO／SiO2比值在0．45～0．6时,球团矿抗压强度高于2500N／个,还原膨胀率大幅度降低;随着MgO／SiO2比值的升高,低温还原粉化率RDI＋3.15、RDI＋6.3提高;900℃还原度提高。当MgO／SiO2比值为0．45时,球团矿的综合冶金性能较好。     

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.     

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.     

复合镁质添加剂对球团生产影响的试验分析

球团矿作为一种优质的高炉炼铁原料,其配比不断增加.试验采用复合镁质添加剂代替膨润土,提高球团矿中的MgO含量,考察其对生球质量和球团冶金性能的影响规律和作用机理.试验结果表明,采用复合镁质添加剂代替膨润土后,生球抗压强度略有降低,落下次数变化不大,爆裂温度均高于600℃;球团矿的低温还原粉化指数(RDI+3.15)变化...