Structural and morphological changes during reduction of hematite to magnetite and wustite in hydrogen rich reduction gases under fluidised bed conditions

Abstract

During the reduction of iron ore fines structural changes in particles have a significant influence on the rate of reduction. Investigations regarding porosity, specific surface area and mean pore diameters in the reduction of hematite with hydrogen rich reducing gases were performed by mercury porosimetry. Morphological changes were examined by metallographic analyses of polished sections in reflected light. In the magnetite equilibrium phase, significant influence of temperature on structural parameters and sintering effects were found.

For wustite phases, the influence of temperature was less pronounced. For the reduction of hematite to magnetite and magnetite to wustite topochemical phase growth and microporous product layers were observed. In the single step, reduction of hematite to wustite progressive conversion and significant increase in the mean pore diameter were found. The results presented in this work are of high importance for understanding the reaction kinetics of iron ore fines and essential for modelling heterogeneous reactions.     

Effects of embedding direct reduction followed by magnetic separation on recovering titanium and iron of beach titanomagnetite concentrate

Embedding direct reduction followed by magnetic separation was conducted to fully recover iron and titanium separately from beach titanomagnetite(TTM).The influences of reduction conditions,such as molar ratio of C to Fe,reduction time,and reduction temperature,were studied.The results showed that the TTM concentrate was reduced to iron and iron-titanium oxides,depending on the reduction time,and the reduction sequence at 1 200°C was suggested as follows:Fe_(2.75)Ti_(0.25)O_4→Fe_2TiO_4→FeTiO_3→FeTi_2O_5.The reduction temperature played a considerable role in the reduction of TTM concentrates.Increasing temperature from 1 100 to 1 200°C was beneficial to recovering titanium and iron,whereas the results deteriorated as temperature increased further.The results of X-ray diffraction and scanning electron microscopy analyses showed that low temperature(≤1 100°C)was unfavorable for the gasification of reductant,resulting in insufficient reducing atmosphere in the reduction process.The molten phase was formed at high temperatures of 1 250-1 300°C,which accelerated the migration rate of metallic particles and suppressed the diffusion of reduction gas,resulting in poor reduction.The optimum conditions for reducing TTM concentrate are as follows:molar ratio of C to Fe of 1.68,reduction time of 150 min,and reduction temperature of 1 200°C.Under these conditions,direct reduction iron powder,assaying 90.28 mass%TFe and 1.73 mass% TiO_2 with iron recovery of 90.85%,and titanium concentrate,assaying 46.24mass% TiO_2 with TiO_2 recovery of 91.15%,were obtained.     

Improvement in internal quality of boiler plates at Bhilai Steel Plant

Abstract

Bhilai Steel Plant produces plates of boiler, high tensile and other special quality steels via the basic oxygen furnace–vacuum arc degassing–continuous casting route. These plates need to be ultrasonically sound. However, rejection of plates on account of internal defects was high. Metallurgical investigations of defective plates showed the presence of a martensitic zone associated with cracks around the centreline. The martensitic transformation is favoured by segregation of carbon and other elements. The published literature confirms that, even at a normal cooling rate, martensite formation is possible when the concentration of carbon at the central region is high. Bhilai Steel Plant slab casters have certain inherent deficiencies such as a high roll pitch and low machine rigidity, which lead to strand bulging. High strand bulging causes centreline segregation. Segregation during solidification can be controlled by various techniques including low superheat casting, electromagnetic stirring, mechanical soft reduction, and thermal soft reduction. As a major revamping of the caster and the introduction of additional hardware call for a large capital investment, it was planned to improve the cast product quality using a less capital intensive option, thermal soft reduction. In thermal soft reduction, cooling is intensified close to the final stage of solidification. This creates a thermal compaction which allows the segregated liquid to move upwards and dissipate. The intense cooling also strengthens the solid shell, leading to a significant reduction of bulging and thereby reducing macrosegregation. In the present investigation, the secondary water distribution pattern has been redesigned to incorporate intense cooling close to the final stage of solidification, using a mathematical model developed by Steel Authority of India Ltd (SAIL). The modified water distribution pattern is designed to maintain a high rate of cooling at the outer and inner surfaces of the solidified shell in the strand. Plant trials using the modified water distribution pattern have shown a significant improvement in plate quality, confirmed by macro-and microanalysis of the slabs and plates.     

Study on Direct Reduction Characteristics of Iron Ore Coal Mixed Pellets

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

Effect of CaO on the reduction behaviour of iron ore–coal composite pellets in multi-layer bed rotary hearth furnace

The effect of CaO on the reduction behaviour of iron ore–coal composite pellets has been studied in a laboratory scale multi-layer bed rotary hearth furnace at 1250°C for 20?min. Reduced pellets have been characterised through weight loss, porosity measurement, phase analysis by XRD, and morphology study by SEM. The addition of CaO to the composite pellets showed different effects at different carbon levels. For higher carbon-containing pellets (C/Fe₂O₃ molar ratio at the upper stoichiometric level of 3), the addition of CaO increased the extent of reduction for all three layers significantly up to a certain limit (4?wt-%); and thereafter the degree of reduction is decreased with a further increase in CaO percentage in the pellets. For low carbon-containing pellets (C/Fe₂O₃ molar ratio of 1.66), the addition of CaO to the pellets did not show any beneficial effect.     

微波加热还原含碳铁矿粉试验研究

微波是一种清洁能源,可以对冶金粉料进行选择性体加热。利用含碳铁矿粉自还原性和对微波的吸收性,采用微波加热,可以直接进行碳热还原。微波加热可以快速提高含碳铁矿粉的金属化率,降低还原反应温度,对原料有广泛的适应性,并可以取消球团的制备工艺,对“绿色”钢铁冶金流程具有深远的意义。     

煤种对含煤球团还原速度的影响

研究了在１２２３￣１４７３Ｋ的氮气氛中３种不同挥发分煤粉的粒度、铁精矿粉粒度、温度及碳－氧摩尔比对含煤球团还原速度的影响。发现降低煤粉或铁精矿粉粒度，提高温度或碳－氧摩尔比可提高含煤球团的还原速度，且这４种因素对还原速度的影响程度随煤种挥发分的降低而增大。分别采用以碳气化反应、气相内扩散、界面反应为控制环节而得出的表达含煤球团反应过程的速度方程处理本研究数据，发现３种速度方程（４种表达形式）均能较     

转底炉工艺的发展与实践

论文介绍了转底炉炼铁工艺在国内外的发展概况,重点阐述北京科技大学研究和开发转底炉炼铁技术所取得的经验与成果.结合国情和政策,认为我国当前应把\     

Novelty on reduction of raw and pre-oxidised titaniferous magnetite ore with boiler grade coal

Pre-oxidation of fines of magnetite containing materials is usually carried out to get better yield of metals. Titaniferous magnetite ore (TMO) is one kind of low-grade iron ore (around 45–50% of total Fe) with a significant amount of TiO₂ (23.23%) and V₂O₅ (0.403%). TMO fines have been pre-oxidised at 973?K (700°C) for 9?h under air atmosphere. The effect of reduction of raw TMO fines as well as the pre-oxidised TMO fines using boiler grade coal in the form of cylindrical briquettes has been studied in the temperature range of 1273?K (1000°C) to 1473?K (1200°C) for periods of 10, 20, 30, 40 and 60?min to estimate the relative yield of iron. The influence of temperature and time on reduction experiments has also been investigated with XRD, FESEM analyses along with chemical analysis of the reduced samples. The most novel result is that the yield of Fe by direct reduction of raw TMO (92.42%) is even marginally better than that of reduction of pre-oxidised TMO (90.89%) at 1473?K (1200°C) for 60?min. Thus the single-step reduction of raw TMO is techno-economically more viable than the pre-oxidation followed by reduction technique.     

煤基处理硫酸渣制备含硫钢原料的实验研究

以含有低熔点FeS₂的硫酸渣和烟煤为原料,对硫酸渣含碳球团进行还原熔分,考察了碱度、焙烧温度、焙烧时间和C/O摩尔比对铁回收率的影响,确定了最佳工艺参数.在碱度R=1.0、焙烧温度1450℃、焙烧时间20 min以及配煤量C/O=1.2的条件下还原熔分硫酸渣,可以获得93.1%铁回收率的珠铁.对尾渣的X射线衍射分析可知,硫酸渣中铁氧化物及含铁硫化物被还原,铁回收率较高,且熔分时间短造成大量铁以金属态滞留于渣中;还原熔分硫酸渣所得珠铁因其较高硫含量,可用于冶炼硫系易切削钢.     

煤中氢对含碳球团还原的影响

针对含碳球团还原过程中的煤种选择问题,研究了烟煤和无烟煤挥发分中氢对含碳球团还原的作用以及温度、加热速度对氢还原过程的影响。结果表明,含碳球团中煤热解产生的氢对铁氧化物有还原作用。由于煤中挥发分的热解析出温度与氢还原铁氧化物的还原温度不一致,氢在还原初期迅速放出,导致氢的还原作用率低;提高温度和加热速度可提高煤中氢的还原作用率和挥发分的利用率。综合考虑,含碳球团实际生产选择煤种时,应选择反应性好的无烟煤。     

微波加热含碳氧化锰矿粉体还原过程中磷的迁移行为

通过电子探针面扫描成分分析,研究了微波加热含碳锰矿粉体还原过程中磷的迁移行为。在rc：ro原子摩尔比为1．06、rcao：rsio2分子摩尔比为1．27的条件下,将含碳锰矿粉放入微波,冶金炉中进行加热还原并保温一段时间。结果表明：固相还原时,有53％～67％的磷分布于气相中,高于常规冶炼的气化脱磷率。温度高于1000℃后,部分磷以锰、铁磷化物的形式迁移进入金属化物中。随着温度的提高和保温时间的增加,锰铁金属化物中的含磷量随之增加。将微波加热温度控制在1100℃以内,并缩短保温时间,有利于获得低磷海绵锰铁。     

高铁锰矿粉熔融还原生产富锰渣新技术

富锰渣是电炉冶炼硅锰合金的原料,而高炉法是冶炼富锰渣的主要方法,但该方法存在工艺流程长,焦炭消耗量大,铅、锌等易挥发金属影响冶炼等问题。提出了高铁锰矿熔融还原冶炼富锰渣新技术,该技术具有工艺流程短,不需要消耗焦炭,铅、锌等金属可以综合回收等优点。试验研究结果表明,高铁锰矿熔融还原生产富锰渣工艺是可行的,在还原温度为1 400 ℃、还原时间为20 min的条件下,渣铁可以完全分离,铁、锰回收率高。     

Research and development of the intelligent control of iron ore sintering process based on fan frequency conversion

The process state of iron ore sintering is characterised via the bed permeability, the temperature rising point, the burn rising point and the burn through point. The intelligent control strategy of sintering process based on fan frequency conversion is put forward. The stability of process state is firstly evaluated based on the knowledge of domain experts. If process state is fluctuating, an expert controller is activated to realise a normal production. If process state becomes steady, then a fuzzy controller is activated to obtain the optimisation of process state and reduce the power consumption of main exhaust fan. The closed-loop control of sintering production showed that the system can realise the optimisation of sintering process state, and reduce the energy consumption of sintering production while ensure the stability of sinter quality indices, it theoretically saves power consumption of 1×10⁴?kWh every day.     

天津钢管公司DRC直接还原厂生产工艺与自动控制

天津钢管公司DRC直接还原厂将采用英国戴维国际工程公司的DRC煤基直接还原技术,以铁矿石、煤、石灰石为原燃料,用回转窑来生产直接还原铁(DRI)。该厂将由两条回转窑生产线组成,每条生产线的生产能力为15万tDRI/年,回转窑规格为φ5.0m×80m。工厂生产主线将采用计算机集散控制系统(DCS)以实现对生产过程的自动控制。     

LiCl催化剂对含铌铁矿粉氢气选择性还原的影响

在自制的扩散床底供气管式电阻炉内进行实验,研究了添加LiCl催化剂对H2选择性还原白云鄂博含铌铁矿粉中铁氧化物的影响。发现含铌铁矿粉中加入LiCl催化剂后对还原反应有促进作用,还原度和金属化率明显提高,铁氧化物几乎全部被还原为金属铁。改变催化剂的加入比率（质量分数）分别为2.14%、1.71%、1.43%、1.00%、0.71%、0.43%,结果表明,70g含铌铁矿粉中添加质量分数为0.71%的LiCl催化剂的催化效果最好,且杂质含量相对较少,其还原度达到95.82%,金属化率达93.73%。     

Influence of sinter grate suction pressure (flame front speed) on microstructure,productivity and quality of iron ore sinter

Abstract

From a sinter production point of view, it is important to optimise the sintering process with regard to both sinter quality and production rate. In sintering, airflow rate within the sinter bed decides the production rate and its physical and metallurgical properties. To study the influence of airflow rate (flame front speed) on sinter production and sinter quality, pot grate sintering experiments were conducted at sinter grate suction pressures ranging from 900 to 1700 mm water column over the sinter bed. During sintering, time–temperature data were recorded, and mineralogical studies were carried out. This study reveals that increase in sinter grate suction pressure through the sinter bed from 900 to 1700 mm water column significantly improved the sinter productivity from 34·37 to 48·90 t/m²/day; however, the physical and metallurgical properties of the sinter at higher suction pressure were not optimum with respect to blast furnace requirements. The maximum sinter productivity with desired physical and metallurgical properties was obtained at suction pressure 1300 mm water column. At this pressure, improvement in sinter quality was due to optimum firing temperature and enough retention time available for formation of mineral phases. At an airflow rate 1300 mm water column, sinter productivity was 41·0 t/m²/day, sinter strength (TI) was 73·10%, reduction degradation index was 25·0 and reducibility was 71·50%.     

Microstructure of Solid Phase Reduction on Manganese Oxide Ore Fines Containing Coal by Microwave Heating

Microstructure of solid phase reduction on manganese oxide ore fines containing coal (MOOFCC) is one of important kinetics conditions of influencing microwave heating. On condition that an atomic molar ratio of rO∶rC in MOOFCC is 1∶1.06 as well as a molecular molar ratio of rSiO2∶rCaO is 1∶1.28,1 kg of MOOFCC is heated by microwave to reach 1000-1300℃ and hold different time respectively. Experiments show that the metal phase takes the iron-based metal compounds containing manganese as the main content. The manganese content of metal phase increases with the rise of temperature. The particle size of the metal phase is within the range from 0.01 to 0.05mm. MO2 phase in the stuff is entirely changed into MnO phase and the slag phase is mainly composed of wollastonite and manganese olivine. The stuff reduced is loose and massive as a whole and its porosity is from 30% to 45%. The low softening-melting property and the low density of the stuff impact,to some degree,the solid phase reduction of powder by microwave heating.     

铁精矿粉粒度对精控还原工艺的影响

本文以河北承德地区的铁精矿粉为原料,选用模拟隧道窑还原工艺制备海绵铁粉,研究了铁精矿粉粒度对精控还原工艺的影响。结果表明:铁精矿粉粒度对其还原工艺影响很大,并直接影响海绵铁粉的产品性能。在既定试验条件下,随着铁精矿粉粒度的增大,其精控还原所需最优还原温度随着增加,最佳配碳量先减少后增大,而最佳还原时间随粒度的增大呈现出先增大后减小的变化趋势。究其原因为粒度过小导致的粉体烧结和粒度过大导致的粉体芯部不易还原均会阻碍还原过程的进行。45~75μm粒度区间铁精矿粉最适合作为制备优质海绵铁粉原料,其在配碳量0.8、还原温度1150℃、还原时间4.5 h的精控还原工艺下可制得的海绵铁粉的铁含量高达97.88%。     

不同反应性炭的气化差异及对铁矿还原的影响

纯氧高炉和煤气化耦合联产是降低炼铁和煤气化工艺能耗和碳排放的重要手段,而研究不同反应性炭的气化差异及其对铁矿石还原影响是实现煤气调质与降低焦比的关键.在模拟纯氧高炉与煤气化耦合联产工艺条件下进行了木炭、兰炭、焦炭的气化和烧结矿、球团矿的还原试验研究.研究结果表明,3种炭与CO2和水蒸气的反应性由强到弱的顺序为木炭＞兰炭...