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.

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%.

Effect of Na_2CO_3 on reduction and melting separation of ludwigite/coal composite pellet and property of boron-rich slag

The effects of Na_2CO_3 on the reduction and melting separation behavior of ludwigite/coal composite pellet, the desulfurization ratio and the property of the separated boron-rich slag were investigated at laboratory scale in the present work. Na_2CO_3 could improve the reduction rate of the composite pellet to some extent. The melting separation of the composite pellet became increasingly difficult with the increase of Na_2CO_3 in the pellet due to the sharply increasing of the melting point of slag. The sulfur content of the iron nugget gradually decreased from 0.27% to 0.084%（mass fraction） with the Na_2CO_3 content in the pellet increasing from 0 to 6%. The efficiency of extraction of boron（EEB） of the slow cooled boron-rich slag decreased from 86.46% to 59.52% synchronously. Na_2CO_3 had obviously negative effect on melting separation of the composite pellet and boron extraction of the boron-rich slag.

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.

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.

Reduction behaviour of Odisha Sands Complex,India ilmenite-coke composite pellets

Presently,ilmenite concentrates from Odisha Sands Complex at Chhatrapur,India are utilized to produce TiO2 slag by direct smelting in an electric arc furnace.However,the process involves the consumption of excess electrical energy and difficulty in handling the arc furnace due to frothing effects.A more efficient process of pre-reducing the ilmenite before smelting has been proposed in the present communication.In particular,studies have been undertaken on the reduction process of ilmenite-coke composite pellets.The difference in the reduction behaviour of raw ilmenite and ilmenite-coke composite pellets has been established and compared with that of the pre-oxidized raw pellets.The effects of various processing parameters like temperature,residence time,and reductant percentage on the metallization of composite pellets in a static bed have been investigated.Metallization of about 90%has been achieved at 1250°C for a reduction period of 360 min with a 4%coke composition.Furthermore,the reduced pellets have been characterized through chemical analysis,optical microscopy,field emission scanning electron microscopy and X-ray diffraction analysis.The reduction behaviour of composite pellets has also been found better than that of pre-oxidized pellets indicating the former to be more efficient.

Exploring a new path of green and efficient utilization of sinter return fine to produce composite pellets

Efficient utilization of sinter return fine is an important measure to reduce cost,increase efficiency,save energy and reduce emission.A new path of green and efficient utilization of return fine was proposed to produce composite pellets.The metallurgical properties of composite pellets under the condition of hydrogen-rich blast furnace were studied.The experimental results indicate that the coated concentrate was consolidated for the composite pellets through normal Fe_(2)O_(3) recrystallization.Near the surface of core return fine,the liquid phase formed due to its low-melting point,assimilated the adjacent concentrate,and then consolidated with the temperature decreasing.Compared with regular pellets,the com-pressive strength and reduction swelling index of composite pellets were decreased,but the reducibility index and softening-melting properties were improved.In addition,the reduction degradation index of composite pellets was sig-nificantly higher than that of sinter.Therefore,adding composite pellets was conducive to indirect reduction in blast furnace,reducing fuel ratio and improving production efficiency.According to the effect of the roasting system on the metallurgical properties,the roasting temperature and time were determined as 1250℃and 30 min,respectively.The composite pellets can be produced under the traditional pelletizing process.

Effect of organic binders on the activation and properties of indurated magnetite pellets

In the ironmaking process,the addition of an organic binder to replace a portion of bentonite has the potential to improve the per-formance of pellets.The interaction between original bentonite(OB)and organic binder was investigated.Results indicated that the micromor-phology of organic composite bentonite(OCB)became porous and the infrared difference spectrum exhibited a curved shape.In addition,the residual burning rates of OB and organic binder were determined to be 82.72%and 2.30%,respectively.Finally,the influence of OCB on the properties of pellets was investigated.The compressive strength of OCB-added green pellets(14.7 N per pellet)was better than that of OB-ad-ded pellets(10.3 N per pellet).Moreover,the range of melting temperature of OCB-added green pellets(173℃)was narrower than that of OB-added pellets(198℃).The compressive strength of OCB-added green pellets increased from 2156 to 3156 N per pellet with the increase in roasting temperature from 1200 to 1250℃.

预造球强化难制粒精矿烧结工艺

随着进口铁矿石价格的增长,充分利用廉价的难处理铁矿资源成为钢铁企业降本增效的关键。本文针对难制粒精矿在烧结中利用率低的问题,在复合造块法的基础上开发了预造球工艺,显著提高了难制粒精矿的配入量,有效改善了制粒效果与烧结产、质量指标。研究表明,在难制粒精矿配比达到36%时,采用预造球制粒可以使准颗粒平均粒径提高1.53 mm,透气性指数提高0.17。在此基础上,垂直烧结速度提高13.97 mm/min,利用系数提高0.815 t/(m^(2)·h),转鼓强度提高3.39%。预造球烧结中,由于难制粒精矿的分离,常规制粒料部分的制粒性能得到优化,局部碱度得到提高,形成大量的针柱状铁酸钙。在常规制粒料与球团料交界处固相固结与液相固结同时存在,铁酸钙与铁氧化物相互交织,形成球团嵌入式分布的成品矿结构,具有良好的成矿效果和强度性能。

氧气体积分数对钒钛磁铁矿球团氧化过程的影响

提高高炉球团配比有利于降低钢铁行业的污染物和碳排放,为了使钒钛磁铁矿球团在高炉中得到更好的应用,本文研究了氧气体积分数对钒钛球团氧化速率的影响,利用动力学模型分析了其氧化反应的控速环节,分析了钒钛球团氧化过程物相组成、矿相结构等演变规律。结果表明:富氧能促进钒钛磁铁矿球团的氧化,钒钛磁铁矿球团的氧化过程符合未反应核模型,氧化过程前期以界面化学反应控速为主,后期以内扩散控速为主,内扩散阻力大于界面化学反应时的氧化度随着氧气体积分数的增加而降低。钒钛磁铁矿球团的氧化伴随着Fe_(3)O_(4)→Fe_(2)O_(3)、Fe_(2.75)Ti_(0.25)O_(4)→Fe_(2)TiO_(4)/FeTiO_(3)→Fe_(9)TiO_(15)的物相转变过程,在预热氧化过程会出现赤铁矿连晶,致使矿物间的孔隙率降低,氧气内扩散的阻力增大,氧化反应的速率降低。

复合黏结剂对铁精矿球团质量的影响

为充分发掘有机黏结剂对铁精矿球团质量提升的优点,同时弥补有机复合黏结剂削弱成品球抗压强度的不足,本文将蛭石、羧甲基纤维素钠(有机黏结剂)、膨润土进行复配,探究复合黏结剂对铁精矿球团质量的影响,并借助SEM和热重分析探索蛭石改善成品球强度的机理。试验结果表明:在不复配有机黏结剂,仅仅添加1%的膨润土时,球团的落下强度只有1.5次/(0.5 m),抗压强度为8.2 N/P,爆裂温度为550℃,在预热温度为950℃、焙烧温度为1200℃时成品球的强度为3121 N/P;固定膨润土用量,随着有机黏结剂复配比例增加到0.12%,生球落下强度可提升到8.0次/(0.5 m),抗压强度提升到11.3 N/P,但生球的爆裂温度下降到395℃,成品球强度下降到2465 N/P;加入0.03%蛭石+0.12%有机黏结剂+1%膨润土的复合黏结剂后,球团的质量指标最好,球团落下强度可达到6.5次/(0.5 m),抗压强度为13.4 N/P,爆裂温度为362℃,成品球强度在相同条件下可以提升至2764 N/P。SEM和热重分析结果表明:蛭石膨胀能不断填充球团中的孔隙,在焙烧过程中生成液相,有利于固相扩散晶体长大,降低球团孔隙率,从而提升成品球的抗压强度。

Reduction Kinetics of Vanadium Titano-Magnetite Carbon Composite Pellets Adding Catalysts Under High Temperature

Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope （SEM） was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.

复合有机膨润土用于鄂州球团生产实践

武钢资源集团鄂钢球团有限公司球团生产以1.1%配比辽宁科技大学托田炉料有限公司研制的复合有机膨润土替代1.5%配比的印度膨润土后,生球质量指标改善,成球率提高,吨球膨润土消耗降低,成品球团矿品位升高,SiO_(2)含量下降,物理指标改善。降低膨润土消耗和球团矿品位提高折算每吨铁带来经济效益2.51元。

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.

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%.

转炉炼钢用球团复合结合剂的开发

为对钢厂除尘灰等二次资源进行绿色、循环再利用,根据转炉炼钢工艺要求,需将炼钢除尘灰等二次资源配加适量造渣材料制成转炉炼钢用冷固球团。采用传统工艺生产的结合剂制备球团,冷固球团强度约100 N、粉面率在20%以上,强度低,粉面率高,使用过程中利用效率较低。通过对结合剂机理进行系统分析,认为可以在复合剂中配加大量有机物的前提下,加入适量分散剂,提高其使用效果;并确定在工业淀粉50%、钠盐25%、硅微粉25%的配比下,固定混合料、结合剂添加比例不变,复合结合剂的成球效果最好。工业试验证明,结合剂添加比例1.5a%、搅拌时间210 s/缸、压球机压力4~8 MPa、辊坯线速度0.35~0.45 m/s时,制备的复合结合剂用于炼钢用球团,冷固球团的初始强度提高到200 N以上,最终强度达到800 N以上,粉面率降低至5%以下,可满足用户使用要求,提高使用效率。

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。

生物质颗粒燃料特性及其对燃烧的影响分析

采用欧盟生物质固体成型燃料标准(CEN/TC 335)试验检测了中国和瑞典典型的10种生物质颗粒燃料,重点对中国的秸秆类颗粒燃料与瑞典的木质颗粒进行了对比,并分析其对燃烧特性的影响。结果表明中瑞两国的生物质颗粒燃料都能满足技术标准要求,瑞典木质颗粒具有较高的性能参数;中国的玉米秸秆颗粒燃料发热量比瑞典木质颗粒低20.9%,挥发分低,燃烧后灰渣中的硅含量高20%,灰熔点低,燃烧后灰分多,易结渣,对燃烧设备有较高的要求。

增加球团矿用量以优化高炉炉料结构

阐述了武钢高炉炉料结构中球团矿配比的变化情况,在一定范围内增加进口球团矿配比可优化高炉技术经济指标.当球团矿配比＜12%时,高炉装料制度无须调整.当球团矿配比＞20%时,则需预防中心堵塞.球团矿质量决定其配比,质优的球团矿利于高炉顺行.经比较分析得出武钢高炉较合理的炉料结构为:(65%～70%)烧结矿+(20%～25%)球团矿+高铁块矿.

硫酸渣复合球团还原焙烧法制备高品位磁铁精矿

进行了硫酸渣复合球团还原焙烧-磁选实验。研究结果表明:以铁品位低(TFe 45.56%)、铜和硫含量高(Cu 0.19%,S 1.45%)的某硫酸渣为原料,添加复合添加剂5%,在圆盘造球机上制备复合球团,将生球干燥后进回转窑还原焙烧,往每吨复合球团中喷入煤300 kg,在700～800℃还原焙烧20 min,将还原焙烧后产物通过两段球磨、四段磁选工艺,可得到铁品位高(总铁含量为66.23%),Cu和S含量低(Cu 0.048%,S 0.053%)的优质磁铁精矿,其铁回收率达73.32%,铜脱除率达74.73%,硫脱除率达96.34%。实验的关键技术是复合粘结剂促进铁氧化物的还原及铜、硫等杂质的转化,在磁选分离过程中脱除杂质。使用此新工艺,能综合利用硫酸渣中铁资源,扩大钢铁工业原料来源。