Reduction Behaviour of Iron Ore–Coal Composite Pellets in Rotary Hearth Furnace (RHF): Effect of Pellet Shape,Size, and Bed Packing Material

Reduction of iron ore–coal composite pellets in multi-layers at rotary hearth furnace (RHF) is limited by heat and mass transfer. Effect of various parameters like pellet shape, size, and bed packing material that are supposed to influence the heat and mass transfer in the pellet bed, have been investigated, on the reduction behaviour of iron ore–coal composite pellets at 1250 °C for 20 min in a laboratory scale RHF. Reduced pellets have been characterised through weight loss measurement, estimation of shrinkage, porosity, and qualitative, quantitative phase analysis by XRD. A significant difference in the degree of reduction is observed layer-wise in the pellet bed with the variation in pellet shape and size. Pellet bed without any packing material or packed with coal have demonstrated higher degrees of reduction compared to the pellet bed packed with graphite and sand.     

含锌粉尘内配碳球团还原模型

以转底炉处理钢铁厂含锌粉尘为背景,结合转底炉实际生产工艺条件,建立了含锌粉尘内配碳球团直接还原一维非稳态数学模型.模型不仅考虑了铁氧化物的还原反应和碳的气化反应,还加入了氧化锌的还原反应,并通过实验验证了模型的准确性.利用计算结果分析讨论了炉温、球团半径及孔隙率对球团还原的影响.炉温对球团的金属化率和脱锌率均有显著影响,孔隙率和球团半径仅对球团的金属化率影响较小,而对脱锌率基本没有影响.      

含碳球团低温熔分过程中硫的行为

 根据低配碳比含碳球团还原低温熔分制备粒铁的技术思想,对含碳球团还原熔分过程中硫的分配及硫的行为进行了试验研究。结果表明,影响产品铁粒中硫质量分数的主要因素为碳质垫料、球团原料中硫量以及熔分后铁粒在炉内的停留时间。为了降低铁粒中硫质量分数,应尽量限制煤粉、铁矿带入的硫量。要选择硫量较低的碳质垫料,尽量缩短熔分后铁粒在炉内停留时间。垫料中混和适量的固硫剂有利于降低铁粒中硫质量分数。球团中添加CaO未见有脱硫作用,铁粒中硫质量分数反而稍有增加。球团中配碳比的增加会导致含碳球团中煤粉带入的硫量的增加,因此配碳比的增加会稍微提高铁粒中硫质量分数。     

Beneficiation of Titanium Oxides From Ilmenite by Self-Reduction of Coal Bearing Pellets

The study on the beneficiation of titanium oxides from Panzhihua ilmenites by reduction of coal bearing pellets was carried out. The iron oxides in pellets were efficiently reduced to metal iron, and titanium oxide slag beneficiated was separated from metal iron. The effect of temperature, flux and coal blending ratio on the reduction and separation was investigated, and rational parameters were determined. A new process for the beneficiation of titanium oxides by rotary hearth furnace （RHF） was proposed.     

以转底炉技术利用钛资源的基础研究

提出了一种以转底炉煤基直接还原技术利用钛资源的新工艺及两个不同的方案。该工艺以攀枝花钒钛磁铁精矿或钛精矿粉、煤粉和少量添加剂组成的复合球团为原料,在高温加热条件下将含钛矿中的氧化铁还原为铁,经渣铁分离后获得生铁和富集了的钛渣。第一方案以钒钛磁铁精矿配20%钛精矿为原料,还原后渣铁自然分离,得到块铁和品位为50%左右的钛渣;第二方案以钛精矿为原料,还原后经破碎磁选分离得到粒铁和TiO2富集率为～75%的钛渣。对这两种方案均进行了初步试验,确定了合理的工艺条件。     

CFD Modeling of Flow,Temperature, and Concentration Fields in a Pilot-Scale Rotary Hearth Furnace

A three-dimensional mathematical model for simulation of flow, temperature, and concentration fields in a pilot-scale rotary hearth furnace (RHF) has been developed using a commercial computational fluid dynamics software, FLUENT. The layer of composite pellets under the hearth is assumed to be a porous media layer with CO source and energy sink calculated by an independent mathematical model. User-defined functions are developed and linked to FLUENT to process the reduction process of the layer of composite pellets. The standard k–ε turbulence model in combination with standard wall functions is used for modeling of gas flow. Turbulence-chemistry interaction is taken into account through the eddy-dissipation model. The discrete ordinates model is used for modeling of radiative heat transfer. A comparison is made between the predictions of the present model and the data from a test of the pilot-scale RHF, and a reasonable agreement is found. Finally, flow field, temperature, and CO concentration fields in the furnace are investigated by the model.     

A Computational Study on the Reduction Behavior of Iron Ore/Carbon Composite Pellets in Both Single and Multi-layer Bed Rotary Hearth Furnace

Metallurgical and Materials Transactions B - A phenomenological model for the reduction of iron ore/carbon composite pellets in a multi-layer bed rotary hearth furnace has been developed. A single...     

Modeling of Thermochemical Behavior in an Industrial-Scale Rotary Hearth Furnace for Metallurgical Dust Recycling

Metallurgical dusts can be recycled through direct reduction in rotary hearth furnaces (RHFs) via addition into carbon-based composite pellets. While iron in the dust is recycled, several heavy and alkali metal elements harmful for blast furnace operation, including Zn, Pb, K, and Na, can also be separated and then recycled. However, there is a lack of understanding on thermochemical behavior related to direct reduction in an industrial-scale RHF, especially removal behavior of Zn, Pb, K, and Na, leading to technical issues in industrial practice. In this work, an integrated model of the direct reduction process in an industrial-scale RHF is described. The integrated model includes three mathematical submodels and one physical model, specifically, a three-dimensional (3-D) CFD model of gas flow and heat transfer in an RHF chamber, a one-dimensional (1-D) CFD model of direct reduction inside a pellet, an energy/mass equilibrium model, and a reduction physical experiment using a Si-Mo furnace. The model is validated by comparing the simulation results with measurements in terms of furnace temperature, furnace pressure, and pellet indexes. The model is then used for describing in-furnace phenomena and pellet behavior in terms of heat transfer, direct reduction, and removal of a range of heavy and alkali metal elements under industrial-scale RHF conditions. The results show that the furnace temperature in the preheating section should be kept at a higher level in an industrial-scale RHF compared with that in a pilot-scale RHF. The removal rates of heavy and alkali metal elements inside the composite pellet are all faster than iron metallization, specifically in the order of Pb, Zn, K, and Na.     

钒钛矿转底炉直接还原炉底上涨成因及对策

针对钒钛磁铁矿转底炉直接还原过程中炉底上涨的原因进行了分析研究,并在实验室开展了相关试验。通过分析黏结物化学组成和物相组成,得出转底炉炉底上涨为玻璃质液相黏结高熔点橄榄石和铁氧化物累积导致炉底上涨;通过实验室试验研究表明,物料粒度是影响转底炉炉底上涨的关键因素,其次是还原温度和还原时间。根据上述研究结果,结合资源综合利用中试线现场条件,优化了原料转底炉系统的工艺参数,改进了干球技术指标,转底炉炉底上涨基本得到抑制,实现了试验生产顺行。     

现代炼铁技术进展

评述了国际上发展较快的几种主要非高炉炼铁工艺流程.COREX、FINEX和HISMELT等熔融还原流程可以避免炼焦工艺引发的环境污染.成熟的竖炉气基还原工艺是COREX流程工业化的重要保障,粉体流化床由于粘结等问题尚未完全解决和铁浴炉二次燃烧与炉衬侵蚀之间的固有矛盾注定了FINEX和HISMELT实现的难度远高于COREX流程.气基还原流程(MIDREX、HYL-Ⅲ、FINMET)目前都要使用天然气资源,很难在我国得到发展.转底炉可使用低强度的含碳球团,给煤基直接还原流程注入新的活力,但其能耗高、生产效率低、产品质量差将会制约它的发展.我国自主研发的炼铁新工艺,即低温快速还原工艺,目前仍处于研究开发阶段,它能够实现低温快速还原反应,是一种能耗低、污染少、资源利用率高的新型绿色冶金工艺流程,具有良好的发展前景.     

转底炉直接还原铜渣回收铁、锌技术

采用转底炉直接还原工艺,将铜渣含碳球团在高温条件下直接还原得到金属化球团和高品位氧化锌粉尘,再通过熔分或磨矿磁选方式将铁回收,得到的铁产品可作为冶炼含铜钢的原料.转底炉中试结果表明:采用"转底炉直接还原—燃气熔分"流程处理铜渣,可获得TFe品位94%以上、铁回收率93%以上的熔分铁水;采用"转底炉直接还原—磨矿磁选"流程处理铜渣,可获得TFe品位90%以上、铁回收率85%以上的金属铁粉;采用两种流程处理铜渣,均可获得锌品位60.02%的ZnO粉尘.结果表明,经过转底炉直接还原,铜渣中的铁橄榄石Fe_2SiO_4和磁铁矿Fe_3O_4相转变为含有金属铁Fe、二氧化硅SiO_2和少量辉石相Ca(Fe,Mg)Si_2O_6的金属化球团,具备通过磨选或熔分进行进一步富集的条件.     

Estimation of rate parameters for reduction of iron ore–graphite composite pellets in packed bed reactor using genetic algorithm

Abstract

A semiempirical kinetic model has been developed to determine the course of reduction of iron ore–graphite composite pellets over time in a laboratory scale side heated packed bed reactor attached with a tailor made bottom hanging thermogravimetric set-up. The rate parameters in the model, especially the three sets of apparent activation energy values and frequency factors associated with the reduction of iron oxides in three elementary steps, namely hematite to magnetite, magnetite to wustite and wustite to iron, have been estimated based on experimental data by employing an optimisation tool, the genetic algorithm (GA). The difference between the predicted and experimental degree of reduction is minimised to obtain the rate parameters. The experimental degree of reduction is calculated based on mass loss data during reduction and the exit gas analysis. Estimated values of apparent rate parameters were found to be of the same order of magnitude to their intrinsic counterparts reported in literature. Finally, by using the predicted rate parameters the temporal evolution of various oxide phases as well as pure iron has been evaluated.     

Some Studies to Establish the Reaction Mechanism for the Reduction of Iron Ore‐Graphite Composite Pellets in a Packed Bed Reactor

In this article an attempt has been made to propose a reaction mechanism for the reduction of iron ore‐graphite composite pellets in a packed bed reactor through experiments and mathematical models developed by the authors previously, along with some new supportive experimental data. A tailor made thermo‐gravimetric setup with a provision of packed bed has been developed to carry out isothermal experiments at elevated temperature and in controlled atmosphere. A kinetic model that calculates the evolution of various phases of iron oxides and a thermal model that calculates the temperature at the surface and centre of the cylindrical packed bed have been used along with experimental data under different operating conditions to formulate the reaction mechanism. It is proposed that reduction of iron ore‐graphite composite pellets in packed bed is initially heat transfer controlled and become mass transfer controlled at the later stage of reduction. The role of heat and mass transfer has been ascertained by observing the effect of C/Fe₂O₃ molar ratios, size of pellets, and CO gas in reactive atmosphere on the extent of reduction and the predicted temperature gradient, carbon consumption rate within the packed bed during the course of reduction.     

新型有机黏结剂HC用于制备冷压球团的研究

采用新型有机黏结剂(HC)代替膨润土制备冷压球团的方法,得到高冶金性能的入炉原料.随着HC和膨润土用量(质量分数,下同)的增加,铁矿球团和含碳球团生球的抗压强度均呈逐渐升高的趋势,当黏结剂用量为1.5%时,抗压强度分别为5264,2012N/个;生球落下强度随着HC用量的增加而增加,但随着膨润土用量的增加变化趋势不明显.通过研究生球微观结构发现,膨润土附在铁矿颗粒表面且成片聚集,而HC能完全浸润在铁矿颗粒附近且大部分嵌入矿粉颗粒内部,显著提高了生球的落下强度.添加0.3%的HC与添加0.6%~1.2%的膨润土相比生球性能相近,同时球团铁品位较高,因此HC有望部分或全部代替膨润土.     

Evaluation of a New Process for Ironmaking: a Productivity Model for the Rotary Hearth Furnace

In order to address the key issues of capital costs and CO₂ emissions in ironmaking operations, a new process was proposed combining a Rotary Hearth Furnace (RHF) and a Bath Smelter. This paper describes the construction of a productivity model for the RHF based on previous studies concerning the reduction behaviour of pellets of carbon and iron oxides. The model was used to estimate changes in RHF productivity according to the type of carbon used in the RHF pellets, numbers of layers of pellets, final metallization degree of the direct reduced iron (DRI) produced, and initial sizes of the pellets. The results indicate that productivity gains between 33 and 46% can be achieved replacing coal with wood charcoal, a carbon source virtually free of net CO₂ emissions. Also, the productivity of the RHF can be doubled by reducing the charge only up to 70% metallization. The model allows the study of changes in overall energy consumption due to changes in the extent of primary oxidation of the gas at the pellet level showing that the use of wood charcoal increases the total amount of carbon consumed by less than five percent relative to operations with coal.     

转底炉直接还原工艺综合数学模型

为发展和深入认识转底炉直接还原工艺技术,建立了转底炉综合数学模型,该模型由转底炉本体热化学平衡、转底炉区域热平衡计算模型、余热回收模型、生球干燥模型、炉膛温度校核与尾气露点校核模型和转底炉流程模型组成.采用综合模型计算了该工艺流程的基本工艺参数.计算结果表明:煤气热值、废气排放温度和余热回收利用方案对整体能量消耗有不同程度影响,煤气发热值每增加50kJ·m-3,理论燃烧温度提高22~25℃,煤气用量减少41~47m3·t-1;空气预热温度平均每增加100℃,理论燃烧温度提高35~40℃,煤气用量减少90~103m3·t-1.此外,应用此模型还可以计算任何原料和燃料等条件下的直接还原工艺参数,研究不同余热回收方案条件下的各个工艺参数的变化规律.      

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.     

Morphology and reduction kinetics of fluxed iron ore pellets

Abstract

The present paper describes studies of the reduction and sintering behaviour, followed by examination of the structural changes taking place, during direct reduction of fluxed composite (ore plus coal) pellets. The kinetics and morphological aspects of the direct reduction of fluxed composite pellets are compared with those for the gaseous reduction of fluxed ore pellets without carbon addition. It is shown that the chemical reaction is the rate limiting factor for fluxed composite pellets, and the mass transport of reactant gas through the reaction product iron layer governs the overall reduction process in the case of fluxed ore pellets. Microscopic analysis of the fluxed composite pellets has indicated no tendency to form a reduction inhibition iron shell towards the end of the reduction, as found in the case of gaseous reduction of fluxed ore pellets under identical reduction process conditions. The effects of basicity, Fe/C, temperature, and other variables on morphological and microstructural changes in the directly reduced fluxed composite pellets have been experimentally investigated in the present work.