Briquets for washing blast furnaces

Periodic washing of the hearth of a blast furnace by charging hard-to-reduce iron-bearing materials helps form fluid iron-bearing slags whose iron is reduced mainly by coke fines in the coke column. Lump iron ore, specially prepared washing sinters, or welding slag are usually used for this purpose. The washing sinter contains up to 50% ferrous oxide. One alternative to the washing sinter might be briquets made from mill scale. Washing briquets made from mill scale with a cement binder (8–10% Portland cement M500) are made by vibrational compaction. These briquets have good cold strength, remain intact when heated in a reducing atmosphere to 1200°C at a rate of 500°C/h (which corresponds to the rate of heating of the blast-furnace charge), and have low reducibility. Inside the fusion zone, they form primary slags based on iron-calcium olivines with an FeO content on the order of 50%. __________ Translated from Metallurg, No. 5, pp. 46–50, May, 2007.     

Controlling the blast-furnace hearth

At OAO EVRAZ ZSMK, the operation of the blast-furnace hearth is regulated by means of special briquets with good granulometric composition, high iron content, and low impurity content. The briquet charge depends on the total iron-ore consumption, primarily in the intermediate region of the furnace. With steady briquet content (around 2.1% of the charge), the variation in the hearth obstruction is smooth and confined to a narrow range. When the briquets account for 1.0–2.5% of the total charge, the actual mean furnace productivity increases by 6.7%; the adjusted value increases by 3.5%. The actual coke consumption is reduced by 0.5%, and the adjusted value by 0.7%.     

Preparation of iron-bearing wastes for industrial use

To permit the industrial use of sintering and steel-smelting slurries at OAO MMK, laboratory research is undertaken on the formulation of briquets with specified chemical composition and mechanical strength. In the batch for slurry briquetting, it proves expedient to add rolling scale; a binder consisting of ligno-sulfonate powder and portland cement provides the optimum briquet strength.     

Processing of zinc-bearing dust and slurry to obtain crude zinc and iron

Methods for the processing of zinc-bearing dust from steel smelting are briefly reviewed. The system developed at Energoterm-Sistema Development Center is described. This system produces iron and crude zinc by processing dust briquets with carbon reducing agent in a sealed ore furnace. The products are hot metal, zinc and lead captured in the cooling systems, and hot gas that may be used for drying and reduction of the briquets.     

铬粉矿冷压球团的研究

针对铁合金行业在铬粉矿冷压球团生产中存在的问题,进行了探索性研究.在实验室条件下,研究了新型含镁粘结剂对铬粉矿冷压球团常温、高温抗压强度影响,并采用电镜扫描分析了铬粉矿使用新型含镁粘结剂的固结机理.研究结果表明,含镁粘结剂的加入量为5%时,冷压球团的高温强度最高可达到425 N,可满足矿热炉正常冶炼需要;低熔点的钙化合...     

Study of nonisothermal reduction of iron ore-coal/char composite pellet

Cold-bonded composite pellets, consisting of iron ore fines and fines of noncoking coal or char, were prepared by steam curing at high pressure in an autoclave employing inorganic binders. Dry compressive strength ranged from 200 to 1000 N for different pellets. The pellets were heated from room temperature to 1273 K under flowing argon at two heating rates. Rates of evolution of product gases were determined from gas Chromatographie analysis, and the temperature of the sample was monitored by thermocouple as a function of time during heating. Degree of reduction, volume change, and compressive strength of the pellets upon reduction were measured subsequently. Degree of reduction ranged from 46 to 99 pct. Nonisothermal devolatilization of coal by this procedure also was carried out for comparison. It has been shown that a significant quantity (10 to 20 pct of the pellet weight) of extraneous H₂O and CO₂ was retained by dried pellets. This accounted for the generation of additional quantities of H₂ and CO during heating. Carbon was the major reductant, but reduction by H₂ also was significant. Ore-coal and ore-char composites exhibited a comparable degree of reduction. However, the former showed superior postreduction strength due to a smaller amount of swelling upon reduction. Formerly Graduate Student, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India     

Formation mechanism of LaNi5 in the reduction-diffusion process

To clarify the mechanism of the formation of LaNi₅ by the reduction-diffusion (RD) process, two kinds of experiments were carried out: (1) briquets consisting of La₂O₃, CaH₂, and Ni wires were heated at 1300 K in the RD experiment; and (2) Ni wire was immersed into an Ni-La-Ca melt with a composition on the Ni-side liquidus surface at 1300 K. On the surface of Ni, LaNi₅ grew and the formation of CaNi₅ was also observed between the LaNi₅ and Ni in the RD reaction; both layers grew in accordance with a parabolic rate law. Even in the reaction of Ni wire with an Ni-La-Ca ternary melt of low Ca concentrations, CaNi₅ initially grew on the nickel surface before LaNi₅ was formed, and the Ca in CaNi₅ was replaced with La to form LaNi₅. The reason for the initial formation of CaNi₅ was discussed using molecular orbital calculations. These calculations show that the preferential and temporary formation of CaNi₅ and the final production of LaNi₅ can be explained by the electronic structures of Ni alloys containing Ca or La and those of the compounds, CaNi₅ and LaNi₅, respectively.     

微波加热金属液体的实验研究

研究微波加热液态金属的升温特征，在MobileLab-W-R型微波工作站中进行了微波直接加热铜液和铁液的实验研究，实现了微波直接加热铜液和铁液实验，对比研究了微波直接加热和间接加热铜液与铁液的加热效果，并研究了微波功率、金属液质量、温度等对微波直接加热效果的影响，探讨了微波直接加热金属液体的机理。结果表明，微波可以以较快的升温速度直接加热铜液和铁液，且升温速率与微波加热功率呈近似线性递增关系；在相同微波直接加热条件下，同等质量的铜液和铁液的升温速度相近，但不同质量铁液加热时，由于其表面积、微波场强分布等因素的影响，铁液质量对微波加热效果的影响没有明显的线性关系。理论分析认为，铜和铁在熔化后电阻率增大，磁导率明显下降，导致微波在铜液和铁液内部的趋肤深度显著大于固态铜和铁；电导损耗是实现微波直接加热液态金属的主要机制，液态金属可通过电子与原子核碰撞、表面快速更新、内部缺陷阻碍电子运动、原子运动及碰撞等形式吸收微波，将微波能量转化为自身热量。      

Chemical benefication of Rosetta ilmenite by direct reduction leaching

Rosetta ilmenite assaying 40–47% TiO₂ is not suitable for processing to titanium metal or TiO₂ pigment due to its high iron content. The present paper is concerned with studying a rapid and economic process to upgrade Rosetta ilmenite concentrate into synthetic rutile through simultaneous iron removal and titanium insolubilization. This has been possible by using HCl in a low acid/ilmenite mole ratio under reducing conditions created by the addition of metallic iron. A synthetic rutile assaying 89% TiO₂ was prepared from an ilmenite concentrate of about 47% TiO₂. A remaining total iron content of less than 7% Fe₂O₃ is most probably due to complex mineralogical composition resulting from the existence of the three fundamental solid solution series in the FeO–Fe₂O₃–TiO₂ ternary system.     

铁矿石含碳球团中碳的气化反应速度对球团熔融的影响

 利用气化反应速度不同的焦炭和石墨作为还原剂,考察了铁矿石含碳球团在高温加热时还原铁的渗碳、熔融及球团结构的变化规律。根据研究的结果,得到以下结论：①碳的气化反应速度对铁的渗碳及熔融有重要影响;②气化反应速度较快的焦炭混合球团在1 350 ℃加热9 min时球心部首先出现熔融铁粒,而气化反应速度较慢的石墨混合球团在1 250 ℃加热9 min时在球团表面首先出现熔融铁粒;③反应中物料混合状态的变化以及反应后球团内部空洞的大小都受到碳的气化反应速度的影响。     

Phase equilibria in the Fe-Ti-Cl-H-O system

Conclusions In the Fe-Ti-O system at 1373°K only Ti₂O₃ is stable, and iron is reduced from oxides and passes into solution. At practically all compositions of the solid solution preferential chlorination of titanium takes place, together with its transport to iron. During the chlorination of an iron-titanium alloy only gaseous chlorides are formed (T = 1373°K) because under these conditions equilibrium between the solid solution and liquid chlorides is not attained. Chlorination of titania in the presence of hydrogen as a reducing agent is impractical owing to difficulties in ensuring the required composition of the gaseous phase. The results obtained can be utilized for developing technological processes for the surface alloying of iron parts through a chloride phase and producing iron-titanium alloy powders.Translated from Poroshkovaya Metallurgiya, No. 1(265), pp. 52–55, January, 1985.     

Analysis of the efficiency of alternative methods for recycling iron-bearing metallic wastes

This article compares the total amount of fuel used in making steel from dispersed iron-bearing metallurgical wastes by different alternative technologies. Recycling such wastes by briquetting them and then smelting the briquets in blast furnaces is shown to be clearly more advantageous from an economic and environmental standpoint. The availability of excess pig-iron production capacity at a metallurgical plant allows the plant to recycle the given type of wastes by the most cost-effective means while also reducing emissions of greenhouse gases. Similar results can be obtained by smelting the briquets in cupolas.     

Sticking behaviour and mechanism of iron ore pellets in COREX pre-reduction shaft furnace

COREX is a clean process releasing lower pollution and consuming fewer cokes than the blast furnace process. However, serious sticking phenomenon often occurs in COREX shaft furnace, causing many problems to the normal operation. In this study, the loading reduction experiments of iron ore pellets were carried out under the simulating COREX reducing conditions. The influence of temperature and H₂ content in the syngas on the sticking behaviour of the pellets was observed by scanning electron microscope, energy-dispersive spectrometer and X-ray diffraction. The results indicated that the sticking index increased from 6.7 to 90.43%, when the temperature increased from 750 to 950°C. The main composition of sticking material was metallic iron, and the sticking behaviour depended upon the amount and morphology of precipitated iron on the pellets’ surface. The sticking mechanism was the interpenetrating diffusion mechanism of iron atoms between the adjacent pellets.     

Effects of the Composition of Residual Materials from Steelwork on the Crushing Strength of DRI

The goal of this study is to investigate the effects of the composition of residual materials, such as the basicity and (C/O_red)_mol, as well as the reduction temperature and time, on the crushing strength of direct reduced iron (DRI) under the carbothermic reduction through the rotary hearth furnace (RHF) process. Laboratory‐ scale experiments were executed to examine the DRI quality in the RHF operation. It is observed that when the composition of residual materials varies or the reduction temperature and time decrease, DRI crushing strength becomes lower than the 60 kg/piece requirement for blast furnace feed stock. Both basicity and (C/O_red)_mol of the residual materials would affect the crushing strength of DRI. As B₂ increase, the crushing strength of DRI also rises, and the maximum value is when the basicity is 1.4. The result shows that as the value of (C/O_red)_mol rose above 1.20, the DRI strength declined.     

Effect of magnetic field on reduction of magnetite

The reduction behaviour of magnetite oxide by hydrogen below Curie temperature was investigated in the presence of external magnetic field by thermogravimetric analysis. The reduction rate of magnetite powder increased with increasing external magnetic field strength below Curie temperature of magnetite. In order to figure out the effect of external magnetic field on reduction of magnetite, two types of magnetite, powder and pellet, were studied. It was possible to enhance the reduction rate of magnetite powder, because the particles of magnetite in the presence of an external magnetic field exposed more surface to the reducing gas. The effects of reduction temperature, reducing agent, iron oxide type, particle size and specimen shape on the metallisation behaviour of magnetite were visually clarified below the Curie temperature under the influence of external magnetic field. Despite of the increase in reduction degree by applied magnetic field, the rate controlling step was not changed due to the formation of porous metallic iron layer that keeps the path for reducing agent to approach the unreduced iron oxide in the core of magnetite particle.     

还原气氛对流态化还原铁矿粉黏结失流的影响

采用热态可视流化床装置研究了973~1173 K不同气氛条件对流态化还原铁矿粉黏结失流的影响.研究发现,一定表观气速条件下温度和还原气氛组成对失流时铁矿粉的金属化率影响不大,而失流时颗粒微观形态受还原气种类和温度的影响较显著,但还原气体积分数对形态的影响较小.此外,流化时间随着还原气体积分数的增大而逐渐缩矩,并通过线性拟合得到了不同温度时二者间的数学关系式.      

Positron annihilation study of dislocations produced by polishing in the surface of iron single crystals: Part I. Density profile and removal by annealing

The trap concentration as a function of the depth from the abraded surface of iron single crystals was investigated by means of positron Doppler broadening. The deformation depth was about 40 μm from the surface when the specimen was mechanically polished on 240-grit SiC paper. The depth of the damaged region is less than 15 μm from the surface when a slurry of 0.3 /xm A1"₂O₃ particles is used. A mixture of edge and screw dislocations was found in the deformed layer. The two stages in recovery observed upon annealing mechanically polished iron are interpreted as being due to the disappearance of screw components during lower temperature anneals (273 to 473 K). When the number of screw dislocations has fallen considerably, the edge-dislocation dipoles begin to disappear. The activation energies for recovery of screw and edge dislocations are estimated at 30.5 and 103.2 kJ/mol, respectively, using the second-order Li model. Based on these small energies, dislocation dipoles disappear by glide rather than by climb in pure iron. Migration of monovacancies and climb are apparently important with impure iron, since the activation energy is similar to that for vacancy migration. Formerly Postdoctoral Fellow, Physics Department, Michigan Technological University     

A Study of Surface Reactions on Steel Samples Using a Mass Spectrometer Probe

This study presents a new probe to analyse the gas composition near a metal surface. The probe uses a mass spectrometric detector and is incorporated in an experimental reactor for the thermal treatment and surface formation of steel sheet samples. Steel samples were exposed to various oxidizing and reducing gas flows at pressures between ambient and 3 bar. The reaction product H₂O was measured with the MS‐probe while reducing oxidized steel surfaces with H₂ as well as the consumption of H₂ as a function of the sample temperature. Similarly, the reaction products CO and H₂ were monitored during the oxidation of the bulk carbon with H₂O. The sample temperature was ramped linearly from ambient to 900 °C. From these measurements it was possible to evaluate the onset temperatures and the activation energies for the respective reactions. The in‐situ monitoring of the gas phase near the steel surface within the experimental reactor allows controlling the formation of a layer of iron as a result of the iron oxide reduction. Similarly, the decarburization of steel can be followed up by measuring the time course of the CO concentration. It is expected that the MS‐probe will become an efficient tool for the understanding and optimization of the annealing and formation processes during strip annealing before hot dipping.     

Entrained-flow chlorination of ilmenite to produce titanium tetrachloride and metallic iron

The reaction of FeCl₂ vapor with TiO₂ in ilmenite to yield TiCl₄ and metallic iron was studied at 1523 to 1723 K in an entrained-flow reactor. Ilmenite/carbon mixtures containing carbons with internal surface areas from 1 to 600 m²/g were milled to various average particle diameters ranging from 6 to 65 μm. Up to 44 pct of the stoichiometric FeCl₂ reacted at the highest retention time of 34 seconds when a sixfold excess of FeCl₂ vapor was used. Maximum ex-perimental reaction yields were only about two thirds of the theoretical yield calculated for equilibrium conditions. For large particles, a negative effect of temperature on reaction rate indicated that the reaction rate was controlled by ash layer diffusion resistance. For small par-ticles, under the higher turbulence conditions, the early stages of reaction appear to be influ-enced by film mass transfer.