Reduction Characteristics and Kinetics of Bayanobo Complex Iron Ore Carbon Bearing Pellets

 The kinetics of isothermal reduction of the carbon bearing pellets, which were mainly composed of Bayanobo complex iron ore and pulverized coal, was investigated by thermogravimetry at the temperature of 1273-1673 K. The effects of xC/xO and the atmospheres on the extent of reduction also were investigated. The results indicate that the fractional reaction increased proportionally with temperature increasing and heating temperature is the significant influence factor to the reaction of carbon bearing pellets. The optimum xC/xO is 1. 2 and the effect of atmosphere on the reduction of iron oxides is almost negligible. The results can be interpreted that the reaction was initially controlled by a mixed controlled mechanism of carbon gasification and interface chemical reaction, and in the later stage, interface chemical reaction became the rate-controlling step. Apparent activation energy values of reduction at different levels of fractional reaction were calculated. Before F (fraction of reaction)=0. 5, the apparent activation energy ranges from 66. 39 to 75. 64 kJ/mol, while after F=0. 5, the apparent activation energy is 80. 98 to 85. 37 kJ/mol.     

Reduction Behaviour of Olivine Iron Ore Pellets in the Experimental Blast Furnace

An experimental study was conducted to determine the reduction behaviour of olivine iron ore pellets and associated reduction mechanisms in the experimental blast furnace (EBF) located at Luleå. Two sets of EBF samples, namely slowly annealed excavated samples and rapidly quenched probe samples of olivine bearing iron ore pellets were examined in detail. Pellet samples were analysed using SEM, XRD and SIROQUANT analysis to quantitatively determine iron ore phase transformations during descent in the EBF. In the tested EBF campaign, up to 75% of reduction occurred at less than 1100°C, i.e. before the pellet reached the cohesive zone while rest of 25% reduction was completed when pellets reached a temperature of 1300°C and hence within the cohesive zone. The reduction degree of pellets was found to have a linear correlation with distance from the stock line of the EBF. This study showed that the presence of olivine did not have a significant effect on reduction degree for temperatures less than 1100°C in the upper zone of the EBF. However, olivine increased the reduction rate in the final stage of reduction for temperatures in excess of 1100°C in the cohesive zone, which was attributed to the formation of an increased amount of molten FeO containing slag within the pellet. This study is expected to make important contributions towards further improvements in the pellet design as well as the optimization of blast furnace operation and efficiency.     

Brazilian Iron Ore and Production of Pellets

Brazil is the second-largest producer of iron ore in the world. Brazilian richer superficial deposits are composed of brittle material with fine texture and significant amounts of fines are generated during mining and transport. Another type of ore found in this country is the itabirites that have lower iron contents. Beneficiation and concentration steps are required to prepare these materials for the pelletizing process. A general view of Brazilian types of iron ores, mines, and mining companies is given in this work. Special attention is given to pelletizing and the influence of mineralogical characteristics of different ores on the production and final properties of iron ore pellets.     

Cold Bonding of Iron Ore Concentrate Pellets

Iron ore concentrate pellets are traditionally hardened at high temperatures in horizontal grates and grate-kiln furnaces. However, heat induration requires tremendous quantities of energy to produce high-quality pellets, and is consequently expensive. Cold bonding is a low-temperature alternative to heat induration. Pellets can be cold bonded using lime, cement, sponge iron powder, and organic materials such as starch and flour. Cold bonding consumes less energy than heat induration, and has found favor for bonding self-reducing pellets and for refractory ores that are difficult to heat-treat. Herein, we review the principal cold bonding methods and their fundamentals.     

Pellets Prepared with Mechanically Activated Iron Ore

This work analyses pellets prepared with iron ore that has been mechanically activated by high energy ball milling. Pellet feed iron ore was submitted to high‐energy ball milling for 60 minutes, and the resulting material was analysed through measurements of particle size and specific surface area, as well as X‐ray diffraction. Pellets were prepared from this material. The pellets were heated at temperatures ranging from 1000 to 1250°C in a muffle furnace, and submitted to the maximum temperature during 10‐12 minutes. The samples were then tested regarding crushing strength, densification and porosity, and were examined in a scanning electronic microscope. The results were compared to those obtained with similar samples made from non‐milled pellet feed. It has been shown that through high‐energy ball milling of iron ore it is possible to achieve pellets presenting high densification and compressive strength at firing temperatures lower than the usual ones.     

链篦机-回转窑铁矿氧化球团焙烧过程的分析

为了降低链-回-环系统球团矿焙烧过程的能耗,对某工业装置进行了平衡测试和分析,得到了流图。分析表明,传热不可逆损和燃烧不可逆损是系统损的主要部分。建立了气体质流量、床层空隙率、床高、球团直径、烟气中氧含量等运行参数与损的关系。结果表明,适当减小气体质流量、床高和球团直径,增大床层空隙率,可以减小损。在其它条件不变的情况下,当烟气中二氧化碳浓度为1.0%～9.0%,将空气消耗系数控制在1.6～2.0,可使损最小。     

添加熔剂对球团矿还原膨胀率的影响

在鞍钢现场的原料条件下,向铁精矿中添加含CaO、MgO等熔剂并研究其对原膨胀率的影响。结果表明:CaO恶化球团的还原膨胀性能,MgO能够很好地降低球团的膨胀率,并随着熔剂配比的增加而降低。当熔剂配比为1%时,镁石球团还原膨胀率指标最低,为11.83%,且比基准球团低1.2%;石灰石球团还原膨胀率指标最高,为14.93%且比基准球团高出1.93%。     

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.     

链-回-环系统铁矿氧化球团焙烧过程的能和(火用)分析

在对铁矿氧化球团链-回-环系统做质能平衡测试的基础上,对其进行了能和火用的分析.能分析表明,系统的排气显热是能损失的主要部分,占29%.火用分析表明,传热不可逆火用损失是火用损失的主要部分,占40%.分析了烟气中氧含量、二氧化碳浓度对系统火用损失的影响.计算结果表明,当烟气中二氧化碳浓度为1.0%～9.0%时,将氧气浓度控制在9.0%～11.0%,可使火用损失最小.通过本研究对链-回-环系统内铁矿氧化球团焙烧过程的能流和火用流有了更进一步的认识.研究结果可以进一步应用于"链-回-环"系统的过程优化,以提高系统的经济效益.     

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.     

含碳球团的还原熔分行为

通过高温电阻炉对含碳球团还原熔分的行为进行热态模拟研究,考察温度、配碳比、化学成分等因素对球团还原熔分的影响程度.结果表明,温度、配碳比和球团传热方向上的尺寸是控制球团还原熔分的关键;化学成分对还原速率影响不明显,但是通过改变渣的组成可对渣铁熔分起促进或抑制作用.     

脉石成分对铁矿球团还原膨胀性能的影响

研究了脉石成分对铁矿球团还原膨胀性能的影响.以纯铁矿物为原料采用压块-焙烧-还原方法进行的研究表明:纯赤铁矿团块的还原膨胀率明显大于纯磁铁矿团块;CaO、SiO2、MgO、Al2O3可显著降低赤铁矿团块的还原膨胀率;SiO2、MgO可在一定程度上降低磁铁矿团块还原膨胀率,CaO、Al2O3则使磁铁矿团块的还原膨胀率增大.在此基础上研究了赤铁精矿为主配加磁铁精矿制备的氧化球团矿的还原膨胀性能,确定了抑制球团矿还原膨胀的适宜添加物及其用量.对CaO导致球团异常膨胀的机理进行了探讨:在浮氏体还原成金属铁的过程中,固溶于铁氧化物晶格中的Ca2 会促进"铁晶须"的生成与发展,导致球团产生异常膨胀.     

Study on Direct Reduction Characteristics of Iron Ore Coal Mixed Pellets

Ｉｒｏｎｏｒｅｃｏａｌｍｉｘｅｄｐｅｌｌｅｔｓａｒｅｃａｐａｂｌｅｏｆｑｕｉｃｋｌｙｓｅｌｆ ｒｅｄｕｃｔｉｏｎ .Ｉｎｔｈｅｙｅａｒｓｏｆｓｉｘｔｉｅｓ ,ｔｈｅＩｎｍｅｔｃｏｐｒｏｃｅｓｓａｎｄＭｉｄｒｅｘＦａｓｔｍｅｔｐｒｏｃｅｓｓｆｏｒｍａｋｉｎｇｃｏａｌｍｉｘｅｄｐｅｌｌｅｔｓｔｏｄｅａｌｗｉｔｈｔｈｅｓｅｃｏｎｄａｒｙｄｕｓｔｉｎｉｒｏｎａｎｄｓｔｅｅｌｐｌａｎｔｏｒｔｏｐｒｏｄｕｃｅＤＲＩ[1- 3] ｗｅｒｅｄｅｖｅｌ ｏｐｅｄ .Ｒｅｃｅｎｔｌｙ ,ａｌｏｔｏｆｂａｓｉｃｒｅｓｅａｒｃｈｅｓｏ…     

铁矿球团复合粘结剂技术经济评价

基于国内外球团矿复合粘结剂研究情况,介绍了球团矿粘结剂的理想模型及复合作用机理,详细论述了复合粘结剂种类、化学成分、基本物性,重点阐述了复合粘结剂对生球质量、成品球团质量、显微组织及其经济性的影响。目前,生产中广泛应用的是由膨润土和有机粘结剂制备的复合粘结剂,而添加镁质复合粘结剂、SF碱性粘结剂和含铁复合粘结剂是改善球团矿品质的重要途径,但其在生产中推广应用还有待进一步研究。     

还原流化床内铁的析出形态与铁矿粉的粘结行为

用电子扫描电镜分析和探讨了铁矿粉在还原流化床中的粘结行为与金属铁析出形态的关系，结果表明，在不同的还原条件下，金属铁将以不同的形态析出，而铁矿粉在还原流化床中的粘结行为又受金属析出形态的影响，在一定温度下，粘结现象主要由铁晶须引起的。最后，为熔融还原流化床提出了一种新的，有效的预防粘结措施。     

球团矿高温还原过程中抗压强度变化及机理

 运用自行设计制造的固态物料高温抗压强度与蠕变在线测试仪,分别测试球团矿在不同温度及还原度状态下的抗压强度及蠕变量,用以表征球团矿在高炉内不同位置的抗压能力。研究发现：未发生还原反应球团矿在中性气氛中,当温度达到1 000 ℃时,球团矿的抗压强度为2 750 N以上,继续升温,球团矿抗压强度下降迅速;球团矿在还原气氛下,还原初期球团矿抗压强度比同温度下中性气氛球团矿抗压强度有较大下降,当温度高于900 ℃时,球团矿抗压强度只有1 250 N,且在抗压试验中形变明显。微观结构分析表明：还原过程中高价铁氧化物到低价铁氧化物变化过程中晶格增大、新生铁相基体孔隙增加、裂纹产生以及颗粒间固相固结减弱是导致强度下降的主要原因。     

高铝铁矿石球团气基还原物相状态研究

在温度为950℃、还原气氛为纯CO条件下,对高铝铁矿石球团进行气基还原,还原时间分别为0、5、10、 20、40、60、80 min以及110 min,以明确各时间段内物相的变化情况。研究结果表明,还原5 min时即出现金属铁、 FeAl 2 O 4 和Fe 2 SiO 4 3种物相,10 min以至更长时间时金属铁峰强度有所增强,而其他2相变化并不明显;另外,该 种铁矿石中氧化铁的逐级还原规律并不明显,当金属铁相过早出现时,Fe 3 O 4 相以及独立存在的浮士体相未检测到。