Effect of CaO and CaCO3 on Reduction Rate of Iron Ore Pellets Containing Carbon

The effect of metallurgical fluxes CaO and CaCO3 on the reduction rate of iron ore pellets containing carbon in nitrogen atmosphere has been studied by a weight-loss thermal balance. The experimental results showed that adding CaO or CaCO3 can promote reduction reaction as the added CaO or CaCO3 probably decrease the apparent activation energy of iron ore concentrate-carbon-CaO or CaCO3 reaction, and the reduction rate constant changes with mass percent of CaO and CaCO3. The kinetic analysis also showed that the rate-controlling step of the reaction is inner gas diffusion.

Reduction of 1-3 mm iron ore by H_2 in a fluidized bed

The reduction of 1-3 mm fine powder of iron ore by H2 was conducted in a lab-fabricated kg class high temperature fluidized bed. The results show that the differential pressure in the fluidized bed, which has small fluctuation with time, increases with the increase of gas flowing velocity. The utilization ratio of gas decreases when the reaction lasts longer time indicating that the reaction is faster at the beginning of reduction and becomes slower in the latter process. The higher the reaction temperature is, the higher the utilization ratio of gas is, but the difference of utilization ratio among the different temperatures becomes smaller with time. The utilization ratio of gas and the metallization ratio can reach 9% and 84% respectively at 750℃ for 20 min, which shows the reduction reaction by H2 is very fast. The increase of metallization ratio with gas velocity performs quite good linearity, which shows that a higher velocity of reducing gas can be used to improve the productivity of the reactor when H2 is used as reducing gas. With the increase of charge height, the metallization ratio decreases, but the utilization ratio of gas increases. The reaction temperature can be reduced to 700-750℃ from 800-850℃ when H2 is used as reducing gas.

Application of Different Models for the Prediction of the Kinetics of Direct Reduction of Natural Iron Ores

Simulation of the direct reduction conditions was performed in a laboratory furnace. Lump samples from natural hematite iron ore were reduced by a gas mixture of H2 and CO (H2/CO =1.5) at temperatures of 700°C, 800°C and 900°C. The effect of reduction temperature on the reduction degree, reduction rate of samples and carbon deposition were investigated and discussed in this study. The thermo-gravimetric data obtained from the reduction experiments was run in a programme that calculates the solid conversion rate. Also, three models: 1) Grain Model (GM), 2) Volumetric Model (VM), and 3) the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. It was found that the RPM model result agreed best with the obtained experimental results. Furthermore, it gave better predictions of the natural iron oxide conversion and thereby the reduction kinetics.

Model for Reduction of Iron Oxide Pellet with a C-O-H-N Gas Mixture Considering Water Gas Shift Equilibrium in the Gas While It Diffuses through the Product Layer

In metallurgical processes, more and more usage of hydrocarbons is encouraged to bring down the carbon emissions. In this regard, numerous investigations on reduction of oxides by C-O-H-N gas mixture have been reported. Attempts to simulate these reduction processes using shrinking core model, one of the common models used for such studies, have under predicted the reduction rates. This may be owing to the fact that the homogeneous reaction in the gas phase is not being considered. If the reaction temperatures are above 1,000 K, generally so for many reduction processes, the homogeneous gas reaction rates are expected to be high enough that local equilibrium in the gas phase can be assumed. In the present study, reduction of wustite in a C-O-H-N gas mixture has been modeled using shrinking core model considering the water gas shift equilibrium in the gas while it diffuses through the product layer.

Effect of temperature and reaction path interaction on fluidization reduction kinetics of iron ore powder

Due to the instability of FeO at temperatures below 843 K,the fuidization reduction pathway of iron ore powder changes with the reduction temperature.Thus,the effect of temperature and reaction pathway interaction on the kinetics of fuidization reduction of iron ore powder under low-temperature conditions ranging from 783 to 903 K was investigated to describe the fluidization reduction rate of iron ore powder from three aspects:microstructure change,reaction limiting link,and apparent activation energy of the reaction,exploring their internal correlation.The experimental results revealed that in a temperature range of 783-813 K,the formation of a dense iron layer hindered the internal diffusion of reducing gas,resulting in relatively high gas diffusion resistance.In addition,due to the differences in limiting links and reaction pathways in the intermediate stage of reduction,the apparent activation energy of the reaction varied.The apparent activation energy of the reaction ranged from 23.36 to 89.13 kJ/mol at temperature ranging from 783 to 813 K,while it ranged from 14.30 to 68.34 kJ/mol at temperature ranging from 873 to 903 K.

Validation of CFD-DEM model for iron ore reduction at particle level and parametric study

Iron ore reduction is a primary unit operation in current metallurgy processes and dominates the energy consumption and greenhouse gas(GHG)emissions of the iron-making process,Therefore,even a slight improvement of the energy efficiency or GHG emissions of iron ore reduction would yield considerable benefits to the cost of pig iron and,more importantly,to mitigation of the associated carbon footprint.The current study presents a discrete model that describes the iron ore reduction process for a single pellet.The transient reaction progress can be predicted and is validated against experimental measurements under various operating conditions,including different reducing gases and temperatures.The effects of pressure,isothermality,gas composition,and flow rate on reduction are investigated.The reduction rate increases significantly with increasing pressure until 5 atm,and the entire reduction process occurs more slowly under non-isothermal conditions than under isothermal conditions.This work provides a solid foundation for the development of a comprehensive particulate system model that considers both heat and mass transfer.

Reaction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in a static magnetic field

The use of low-grade,refractory and composite paragenetic mineral resources is necessary for overcoming the shortage of iron ore resources in China.As a solution to the treatment of such iron ores,the direct reduction of carbon-bearing pellets can ensure complete iron removal and the effective enrichment of other high-value elements.Thus,this technology enjoys a broad application prospect.However,there are several problems with low-temperature reduction,such as low iron ore reaction efficiency,long reaction time,and high energy consumption.To improve the low-temperature carbothermic reduction efficiency of iron ores,a static magnetic field with magnetic induction intensity of 1.0 T was introduced.An isothermal reduction experiment was conducted at 1223 K to study the low-temperature self-reduction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in the static magnetic field.Also,the acting mechanism of the magnetic field was explored from the perspective of the reduction process,reaction efficiency,phase composition,microstructure changes,and dynamic behavior of iron ores.The results showed that the magnetic field can increase the low-temperature reduction rate of carbon-bearing pellets of Bayan Obo lean iron ores.Under the conditions of reduction temperature of 1223 K,magnetic induction intensity of 1.0 T,and reduction time of 60 min,the reduction degree was 92.42%,1.65 times that without a magnetic field.The magnetic field promoted the replacement of Ca^(2+)and Fe^(2+),so that the hard-to-reduce iron-bearing silicates were reduced in the order of Fe2SiO_(4)→(Ca,Na)FeSiO_(4)→FeO→Fe.The magnetic field enabled loose minerals,more pores and cracks,and changes in the growth morphology and distribution position of metallic iron.Compared with the case under the non-magnetic condition,the metallic iron precipitated from the slag phase in a foliated shape,separated from the matrix iron oxides,and grew up at the junction of the slag phase and coke.The magnetic field significantly increased the interfacial chemical reaction rate of the carbothermic reduction of iron ores and reduced the internal diffusion resistance of gas in the product layer.Specifically,the interfacial chemical reaction rate increased by 138%and the internal diffusion coefficient increased by 309%.Therefore,the effect of the magnetic field on the internal diffusion resistance was the main cause for strengthening the low-temperature reduction of iron ores.

武钢高炉直接还原度及碳熔损率的计算与分析

对武钢7座高炉的直接还原度、碳熔损量、焦炭起始反应温度进行了研究,结果表明：武钢高炉直接还原度偏高且波动范围宽,为了降低焦比,需要发展间接还原;高炉碳熔损量在20%-25%之间,为了能够更加准确地指导高炉生产,需要进行恒定反应性的焦炭热性能实验;随着直接还原度降低,高炉煤气利用率呈线性升高,焦比呈线性降低;焦炭的起始反应温度受配煤比、工艺条件、炉型等因素的影响,其中工艺条件的影响最大。

铁矿石还原过程速率探讨

定义了还原反应率的计算式，依据矿石失重实验数据可计算反应率的大小及其变化关系，可分析矿石还原过程速率的限制性环节。

含铌铁矿粉氢气选择性还原实验研究

实验在自制底供气扩散床管式电阻炉内,研究不同还原时间（30～180 min）和温度（800～1 050℃）下,H2选择性还原含铌铁矿粉中铁氧化物的规律。得到950℃为最佳还原温度,还原2 h还原度达到90.98%,金属化率为86.47%,还原3 h还原度达到94.07%,金属化率为91.11%,而低于这一温度或高于这一温度时,还原度和金属化率在同样还原时间下都有所降低。

络合铁-多酚类液相脱硫催化剂氧化-还原行为研究

通过化学实验,研究了络合铁多酚类液相脱硫催化剂的脱硫—再生反应行为和热力学趋势,结果表明,脱硫反应和再生反应都属于氧化还原反应,反应进程中电势—pH的变化规律反映了氧化还原反应的反应速度和反应程度;催化剂溶液较适宜酸碱度为8.2 5≤pH≤8.5 0。

内配煤团块高温自还原特性研究

通过对内配煤团块高温自还原过程中的直接还原和间接还原反应的研究,定义了内配煤团块自还原反应的间接还原指数(α),并建立了间接还原指数(α)与直接还原度(γd)之间的关系.结果表明,内配煤团块在高温下的自还原反应并不是100%的直接还原反应.内配煤团块自还原反应的直接还原度随团块内脉石(或渣相)含量升高而降低;直接还原度越高,还原产物的残碳含量也就越低.内配煤团块自还原反应氧化铁的还原率随含铁品位升高而增加.内配煤团块自还原过程中的气化脱硫率可达到25%~28%.

铁矿石固态还原过程中吸硫的反应动力学

研究了铁矿石固态还原条件下，矿石吸硫动力学．用电子探针（ＥＰＭＡ）研究了硫在矿内的分布．结果表明，硫化氢与矿内金属铁的界面反应为吸硫反应的限制步骤．

CO还原含Fe_tO二元炉渣反应速率研究(Ⅱ)

温度为1450℃时；进行了CO气体还原FetO－TiO2、FetO－V2O5PetO－CaF2和FetO－Al2O3四个二元渣系的试验，根据CO2红外分析仪测定的出口气体中CO2含量计算了还原的反应速率．结果表明，FetO－TiO2渣系的反应速率随TiO2含量的增加而减小；FetO－V2O5渣系的反应速率随V2O5含量的增加而增加；Al203对FetO-Al2O3的反应速率影响不大；CaF2对FetO－CaF2渣系的反应速率有增加作用。

装填方式对矿焦耦合反应中焦炭溶损特性的影响

采用两种不同热态性能的焦炭与烧结矿进行矿焦耦合反应,探究了不同装填方式(分层填装和混合填装)下焦炭溶损与烧结矿还原的关系.结果表明:与分层装填方式相比,炉料的混合装填更能促进矿焦耦合反应,矿焦耦合反应过程中焦炭的溶损率与矿石还原度成线性关系,提炼线性方程参数斜率k和截距b分别来表征焦炭还原矿石的夺氧能力和初始状态;当由分层装填改变至混合装填时,矿焦耦合参数k值增加而b值降低,低反应性焦炭的k值增加了45.0%,高反应性焦炭的k值增加了7.8%,混合装填对低反应性焦炭夺取含铁炉料中氧原子能力的促进作用更强;改变炉料装填方式对低反应性焦炭的溶损行为影响较大,但对高反应性焦炭的溶损行为影响有限.

甲烷气氛中铁精矿粉闪速还原行为研究

高炉炼铁工艺存在流程长、能耗高以及强烈依赖冶金焦等问题,发展绿色低碳的非高炉炼铁工艺对钢铁生产具有重大意义。本文采用超级铁精矿粉进行了甲烷闪速还原试验,考察还原温度及甲烷体积分数对金属化率的影响,研究铁精矿粉在试验条件下的闪速还原行为,并对还原产物微观形貌进行观察,分析闪速还原机理。结果表明:还原温度为1550 K、甲烷体积分数7.5%、还原时间为5.49 s时,矿粉金属化率可达90.0%;还原温度的升高及甲烷体积分数的增加提高了矿粉的金属化率;甲烷在还原过程中发生裂解,生成的固体碳在还原产物表面沉积,促进铁氧化物的还原和金属铁的渗碳;渗碳过程降低了金属铁的熔点,还原产物由不规则形状向球型转变;矿粉内部为致密的铁层包裹着未反应的铁氧化物的结构,在FeO/Fe界面处FeO的还原主要是由铁中的固溶碳[C]完成。

Reduction Behavior With CO Under Micro-Fluidized Bed Conditions

To process optimization and improve the degree of reduction, a two-step experiment was designed. The experiment was carried out in the micro-fluidized bed. The reactor in the micro-fluidized bed is operated as a differential reactor to ensure an equal temperature and residence time with the reactor volume. The experiment used Brazilian iron ore and reducing gas of CO. The operating temperature was 400 to 800 ℃ and the residence time was between 10 and 60 min. In correspondence with experiment, microscopic technique was applied too. The test shows that temperature and residence time of the pre-reduction stage have an important effect on the degree of reduction. By using two-step experiment, the maximum value of reduction degree increases by 44.1% compared with the maximum value of traditional reduction experiment. Microscopic analysis shows that the specific surface area, surface morphology and texture of reduced iron ore after pre-reduction stage have an important effect on the degree of final reduction too.

钒钛铁精矿竖炉预还原的热力学计算和试验研究

采用热力学计算软件HSC对攀枝花钒钛铁精矿内配碳球团竖炉预还原进行了平衡组分、金属化率和还原度的计算;试验研究了内配碳球团不同的竖炉预还原工艺下的金属化率和还原度。研究结果表明:随着反应温度升高,内配碳球团的金属化率和还原度呈现升高的趋势,当温度达到800℃左右,体系中金属化率达到最大值为99.2%;温度升高到1 000℃,还原度达到最大值87.2%;试验得到的金属化率和还原度变化规律与理论相符。在1 200℃时,获得最大金属化率和还原度分别为:85.23%和80.15%。当底部吹入还原性气氛(10%N2+30%H2+60%CO)时, 1 200℃达到的最大金属化率和还原度分别为:88.43%和90.42%。因此,在体系中通入还原性气体,还原过程被明显强化。

焦炭与烧结矿在耦合反应过程中的溶损特性

为了研究高炉冶炼中焦炭的溶损行为,选用2种不同反应性的焦炭考察焦炭与烧结矿在不同温度下的耦合反应,研究不同温度下焦炭溶损与烧结矿还原的关系。研究结果表明,焦炭溶损和烧结矿还原的耦合反应随着反应温度的升高逐渐加剧,且焦炭反应性提高有利于烧结矿的还原。焦炭溶损率与烧结矿还原度呈正线性相关性,焦炭反应性(CRI)与拟合曲线的斜率k呈反比,而与截距b呈正比,截距可以表征焦炭对烧结矿的初始还原能力。耦合反应后焦炭的光学各向异性指数OTI增大、平均孔径和气孔率大幅增大,反应性较大的焦炭易于在焦炭表面溶损,反应后的孔径较大;而反应性较小的焦炭在反应过程中CO_(2)气体易于扩散至焦炭内部均匀溶蚀各级气孔。

铁精粉通过掺煤提高还原性的研究

随着近年环保和节能降耗政策的逐渐收紧,高炉炉料结构变化较大,主要是球团和烧结矿冶金性能相差较大,对高炉稳定性以及经济技术指标造成一定影响。实验研究了铁精粉和煤粉的配比及不同气氛、不同温度铁精粉所达到还原度,结果表明,铁精粉掺煤颗粒试样在还原温度和还原气氛相同的条件下,试样的还原度、金属化率都是随着掺煤量的增加而升高,说明煤中的C对铁精粉的还原性影响较大,当掺煤量为15%时,还原后试样的还原度、金属化率达到97%以上,继续添加煤粉对结果的影响不明显。还原后试样的Fe^(2+)含量随着掺煤量的增加而减少;在还原气氛和掺煤量相同、还原温度不同时,还原度、金属化率随着温度的升高而提高。在900℃进行冶金性能测试,还原度未能达到97%;在还原温度和掺煤量相同时,还原度、金属化率随着CO浓度的提高而升高;还原后试样表面出现孔洞和凹坑,表面形成致密铁层,有柱状铁晶须。试样能够打出主要成分是C的点,原因可能是高温还原过程中,煤粉从铁矿粉上脱落,结合不够紧密。实验为实际生产工艺过程中提供了准确的还原温度、还原气氛、掺煤量等数据,可节省能源、降低成本。