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 1 100 ℃. The reduction process can be divided into three steps which correspond to different temperature ranges. Fe2 03 began to transform into Fe304 below 500 ℃, and FeO was reduced into Fe from 900 ℃. At 900 ℃, the reduction product showed a clear porous structure, which promoted the reduction progress. At 1000 ℃, the metallic Fe dominated the sample, and the reduction reached a very high degree.

Reduction–melting behaviors of boron-bearing iron concentrate/carbon composite pellets with addition of CaO

Although the total amount of boron resources in China is high, the grades of these resources are low. The authors have already proposed a new comprehensive utilization process of boron-bearing iron concentrate based on the iron nugget process. The present work describes a further optimization of the conditions used in the previous study. The effects of CaO on the reduction-melting behavior and properties of the boron-rich slag are presented. CaO improved the reduction of boron-bearing iron concentrate/carbon composite pellets when its content was less than lwt%. Melting separation of the composite pellets became difficult with the CaO content increased. The sulfur content of the iron nugget gradually decreased from 0.16wt% to 0.046wt% as the CaO content of the pellets increased from 1wt% to 5wt%. CaO negatively affected the iron yield and boron extraction efficiency of the boron-rich slag. The mineral phase evolution of the boron-rich slag during the reduction-melting separation of the composite pellets with added CaO was also deduced.

Fundamental Study on New Method of Reducing Iron Ore-Coal Pellet in Cocurrent Shaft Furnace

Based on the laboratory experiment of reducing iron ore-coal pellet in oxidizing atmosphere,a new self-heating reduction method of iron ore-coal pellet in the cocurrent shaft furnace(CSF) has been developed.In this process,the pellets and preheated oxygen-enriched air enter the shaft furnace through its top and descend cocurrently in the furnace.Most of the heat required for rising temperature and endothermic reduction of descending pellets is provided by the way that the descending air burns the volatile from pellets and CO from the reduction of iron oxide in pellets.The reduced pellets and high temperature gas are discharged from the lower part.The sensible heat and chemical energy of the off-gas are used to heat the oxygen-enriched air in stove.This process is applicable to the direct reduction of iron pellets and prereduction of iron pellets in smelting reduction with iron bath.

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%.

Reduction and melting separation mechanism of boron-bearing iron concentrate/coal composite pellet

Realizing the boron and iron separation through selective reduction and melting separation of boron-bearing iron con- centrate is of great significance for the utilization of crude ludwigite. The reduction and melting separation mechanism of boron-bearing iron concentrate/coal composite pellet was systematically investigated. The reduction and melting separation test of small size pellet was performed to reveal the evolution of slag and iron in the melting separation process. The isothermal reduction experiment showed the relationship between reduction stage and melting separation stage, and the step reduction and melting separation was perfectly achieved. Coal particles existed through the reduction and melting separation process and finally formed brown residue around the separated product. The pellet could not realize melting separation when the B2O3 content in the concentrate was lower than 6.00 wt%.

Effects of gangue compositions on reduction process of carbonbearing iron ore pellets

The influence of gangue compositions (mainly composed of SiO2,CaO,MgO and Al2O3)on the reduction kinetics of carbon-bearing iron ore pellets was estimated at 1373-1473 K in N2 atmosphere.The results showed that gangue content and each component distribution affected the pellets reduction process.The reduction rate was found to follow a linear correlation with quaternary basicity R4 [mass ratio of (CaO +MgO)to (SIO2 +Al2O3)]of the carbon-beating iron ore pellets;also,the content of SiO2 solid solution in iron oxide had a significant impact on the reduction rate.At the same reduction temperature,a higher R4 resulted in a lower SiO2 free content,weakening its inhibitory effect on the Boudouard reaction.The reduction temperature of Fe2SiO4 could be reduced by increasing the contents of CaO and MgO,improving the iron oxide reduction as well as the precipitation and growth of the iron grains.The g'angue content and .component distribution showed no effect on the rate-controlling step of the reduction;however,the apparent activation energy of reaction decreased with increasing quaternary basicity.When R4 increased from 0.15 to 0.67,the apparent activation energy decreased from 228.51 to 193.66 kJ/mol.

Preparation of blast furnace burdens by composite agglomeration process: effect of distribution of magnetite and hematite concentrates in pelletized and matrix feed

Effect of distribution of iron concentrates between pelletized and matrix feed on the preparation of blast furnace burdens from two different kinds of fine iron concentrates (magnetite and hematite) by composite agglomeration process (CAP) was explored. It was found that when the mass ratio of iron concentrate A (magnetite) to iron concentrate B (hematite) in the mixed feed was constant, the proportion of iron concentrate A in the pelletized and matrix feed significantly affected the quality of CAP products. Particularly, as the proportion of iron concentrate A in the pelletized feed increased from 0 to 100%, the yield decreased from 82.11% to 79.19% and the tumbler index decreased from 71.33% to 68.27%. The mineralization characterization results indicated that when 100% iron concentrate A was used as the pelletized feed, the crystallization styles of the outer layer and the inner layer of the pellet were different, and a lot of pores exist around hematite and magnetite phases in the pelletized part, with the weak connection of pelletized and matrix part, resulting in poor strength of agglomeration product.

铁碳复合球团直接还原试验研究

根据转底炉工艺高温快速还原的特点,在实验室模拟生产条件,以烧结常用铁矿粉和还原剂(焦粉或煤粉)为原料进行了压球直接还原试验研究,讨论了焙烧温度、C/O摩尔比、焙烧时间、球团粒径等工艺参数对球团还原后金属化率和强度指标的影响,并对不同原料条件下焙烧特性进行了基础研究。结果表明,在焙烧温度1 350℃、C/O比1.15、焙烧时间25 m in、球团粒径25 mm条件下金属化率达到85.33%,球团抗压强度达到2 240 N/个。

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。

复合粘结剂球团和氧化球团直接还原对比研究

对复合粘结剂球团和氧化球团微观结构、还原动力学参数、还原后强度进行了试验研究。研究结果表明：复合粘结剂球团中矿物颗粒细小,平均尺寸为59-104μm2,孔隙率高,达到54%-56%,而氧化球团中矿物颗粒粗大,平均尺寸为1 047μm2,孔隙率低,为30%;当还原温度大于900℃时,复合粘结剂球团可快速还原,而氧化球团需要大于1 000℃;800-1 000℃还原过程中,复合粘结球团化学反应速率常数k和扩散系数De明显大于氧化球团;还原后,复合粘结剂球团结构完整,强度远大于氧化球团。研究结果表明,在直接还原工艺中,复合粘结剂球团具有孔隙率高、还原速度快、强度高的优点。

CHARP工艺过程中的硫行为及硫控制

对转底炉煤基热风熔融炼铁工艺(CHARP)含碳球团还原熔分过程中硫的分配、硫的行为以及如何降低或控制珠铁中的硫含量进行了实验研究。结果表明,除了控制原料中以及垫底料中硫含量以外,应尽量缩短珠铁形成以后其在炉内的停留时间,防止液态铁从垫底料中吸硫;垫底料中混合适量的固硫剂有利于降低珠铁中硫含量。含碳球团中碱度对珠铁降硫作用不大,添加适量的Na2CO3和MnO2对珠铁具有较显著的降硫效果。氧化性气氛可促进含碳球团中硫的挥发。

铁矿球团技术进展

本文系统介绍了国内外铁矿球团理论与技术的进展,包括球团矿的产量、生产工艺、球团原料制备、粘结剂及产品品种。球团矿的发展将不仅体现在其产量的进一步增长,而且球团矿品种也将更加丰富,除酸性球团矿外,将生产更多种类的球团矿,如镁质球团矿、自熔性球团矿。此外,原料来源复杂也对球团生产发展带来更大挑战。

低配碳比含碳球团直接还原的实验研究

根据低配碳比含碳球团还原熔分工艺制备粒铁的技术思想,对低配碳比含碳球团的直接还原进行实验研究.结果表明,这种低配碳比的含碳球团还原速度较快,还原反应进行了10 min时表观还原度为84%,20min时表观还原度可达88%;继续延长反应时间,球团表层还原得到的少量金属铁会再次被氧化成FeO.还原反应结束后,球团内仍存在少量尚未还原的FeO,它们与脉石中的SiO2形成低熔点的铁橄榄石,有利于工艺后期渣铁的熔化及分离.

腐植酸改性膨润土在铁矿球团中的应用效果

课题组在前期研究中,以腐植酸和钙基膨润土为原料采用半干法制备了腐植酸改性膨润土复合粘结剂。本文通过造球试验、红外光谱分析、接触角测定等方法研究了该复合粘结剂在铁矿球团中的应用效果,探讨了复合粘结剂提高生球强度的内在原因。造球试验表明,相对于单一使用膨润土或腐植酸,使用腐植酸改性膨润土可以显著提高生球强度,在复合粘结剂用量0.5%的条件下,生球落下强度达到3.5次/(0.5 m)。红外分析表明,腐植酸通过羟基、羧基等官能团吸附在膨润土表面,粘结剂中的有机组分使铁矿表面接触角减小,亲水性增强,并且改善了粘结剂在铁矿颗粒间的分散性,有利于生球强度的提高。

铁矿球团复合粘结剂的试验研究

针对有机粘结剂SN与膨润土复合而成的粘结剂,研究了其对球团生产指标的影响。试验结果表明:该复合粘结剂是一种成球性能良好的粘结剂,能有效地提高生球强度;同时,具有较好的抗爆裂性能,当复合粘结剂E、F添加量为0.8%,动爆温度由500℃升至700℃时,其生球无爆裂发生;而且它对成品球抗压强度的影响并不明显,可大大降低膨润土用量,提高球团矿品位。

配矿对改善昆钢球团质量的影响

在综合考虑昆钢10种单一铁精矿成球性能以及球团预热、焙烧性能的互补性、铁精矿TFe品位、原料成本、矿石供应量等因素影响的前提下,对10种配矿方案的造球性能以及球团预热、焙烧性能进行了研究。结果表明,与昆钢生产使用的配矿结构相比,通过对铁精矿进行优化配矿,采用C矿∶E矿∶H矿=30%∶40%∶30%的配矿结构,能最大幅度地降低膨润土用量,提高生球质量和球团矿强度,保障球团有效TFe品位,降低原料成本。

含铁尘泥在转炉中的利用

为实现含铁尘泥有效成分的资源化利用——用于转炉炼钢,考察铁碳球的使用对炼钢指标的影响以及经济效益。理论和试验分析表明,含铁尘泥制备成铁碳复合球团后完全可应用于转炉冶炼,并能促进化渣脱磷;也可作为炼钢终点的降温剂。铁碳复合球团的使用可以替代部分废钢,在适量使用的情况下,对工序的最终成本几乎无影响。

含碳球团的低温熔分

根据低nC/nO含碳球团直接还原-低温熔分工艺制备粒铁的技术思想,进行了低nC/nO含碳球团低温条件下的熔分实验研究.实验结果表明,1 300℃,nC/nO为0.8的含碳球团,还原熔分时间为55 min时,得到的铁粒中存有少量熔渣2FeO.SiO2;60 min时渣铁则完全分离,铁粒中几乎没有熔渣存在.nC/nO为0.8和0.85的含碳球团还原后渣相FeO质量分数较高,熔点较低,易于渣铁熔化分离.nC/nO为0.9的含碳球团渣相FeO的质量分数较低,熔点较高,需要较长时间或在较高温度下才能进行渣铁分离.在1 320℃,nC/nO为0.8,还原熔分时间为60 min时,铁的收得率可达86.1%以上,铁粒中金属铁的质量分数约为94.8%.

铁碳复合球团在转炉炼钢中的应用

为了实现铁碳复合球团在转炉炼钢中的应用,研究了铁碳复合球团的加入方式、加入量对冶炼结果的影响。结果表明,铁碳复合球团可作为化渣剂或降温剂使用,可使转炉回硫量稳定。铁碳复合球团作为化渣剂使用时,可缩短成渣时间,提高转炉炉渣的去磷能力,且可回收部分铁元素;作为降温剂使用时,可以替代部分矿石等降温剂。

提高球团矿品位的工业试验及生产

鞍钢矿业弓长岭矿业公司为解决高品位铁精矿未能生产出高品位球团矿的问题,在对铁精矿造球性能进行研究的基础上,改造选矿工艺,使精矿中的微细粒级含量增加(但铁精矿品位有所降低);而后,进行了配加新型复合膨润土和降低粘结剂配比的工业试验,同时配合造球操作和热工参数的调整,使球团矿品位达到65.4%,且各项质量指标良好,生产稳定顺行,既满足了高炉生产要求,企业也获得了良好的经济效益。