Nitrogen in SL/RN direct reduced iron: origin and effect on nitrogen control in EAF steelmaking

Abstract

In the steel plant considered here, direct reduced iron (DRI), produced by the coal based Stelco–Lurgi/Republic–National (SL/RN) process, makes up 50% or more of the total iron charge. The SL/RN DRI samples from a kiln cooler had high nitrogen contents (50–250 ppm, depending on particle size), contributing to elevated nitrogen levels in liquid steel produced in the electric arc furnaces. The proposed mechanism of nitriding of SL/RN DRI involves gaseous nitrogen (present within the rotary cooler) diffusing into the solid bed and is supported by a simple diffusion model. A strong correlation was found between the melt-in carbon content of the liquid steel and the final tap nitrogen content, with melt-in carbon of 0·3%C or higher resulting in nitrogen levels below 50 ppm at tap, even when charging DRI material that is high in nitrogen.     

Direct Smelting of Metallurgical Dusts and Ore Fines in a 125t DC‐HEP Furnace

In the metallurgical plant of LARCO at Larymna, approximately 200000t/y of nickelferrous dust are collected in the gas cleaning systems of the Rotary Kilns (R/Ks) corresponding to an annual production of 100000t FeNi20%. In addition, a stockpile of one million tons of old R/K dust lies close to the plant and the community of Larymna. A “one‐stage” environmentally friendly process has been developed for the recycling of this dust by direct reduction smelting in a DC arc furnace. The industrial adaptation of this process was tested in the 125t DC‐HEP (Direct Current — Hollow Electrode Powder) furnace at Georgsmarienhütte steelwork (GMH) in Germany. About 70t of dust were directly smelted by injection through the hollow electrode of the furnace. The nickel recovery in the metal bath was 93‐99.9%. Final products were low nickel alloyed steel grades and slag suitable for special cement types production. Main cause of the dust generation in the R/Ks is the disintegration of laterite and the ore fines fraction after the ore crushing. Their separation, collection and metallurgical exploitation prior to their feeding in the R/Ks would significantly reduce the amount of the generated dust. Therefore, the smelting of untreated laterite ore fines in the DC‐HEP furnace was also indicatively tested. Thus, a zero residues industrial production process was developed for the recycling of nickel bearing dust and ore fines by smelting in a DC‐arc furnace, since the finally produced FeNi‐alloy and slag are 100% utilized in the steel and cement industry respectively.     

Nitrogen Removal and Arc Voltage Increase in EAF Steelmaking by Methane Injection into the Arc

Methane injection into the arcs of electric arc furnaces has been shown on pilot scale to lead to a remarkable arc voltage increase at constant arc current and arc length. Recent investigations have been concerned with the associated metallurgical effects making use of a gas‐tight 150‐kg arc furnace operated with two AC plasma torches. A first test with bored graphite electrodes in this furnace confirmed the power increase observed during methane injection. The carburization slowly occurring when 6 % CH₄ were injected into the argon atmosphere of the furnace could be avoided by adding minor amounts of CO₂. A slag layer decreased mass transfer rates without noticeably affecting heat transfer. Manganese loss by evaporation was measured to investigate the influence of power increase and slag layers. From the results, an increase of 200 K was concluded for the melt surface temperature when CH₄ was added to pure argon. Methane injection into the arcs proved to accelerate nitrogen removal considerably. Starting with an intentionally high nitrogen content of about 200 ppm, the nitrogen removal rate was found to be slowest with pure argon plasma arcs, faster with 90 % Ar + 10 % H₂, and fastest with 95 % Ar + 5 % CH₄ reaching final contents of less than 20 ppm of nitrogen. Based on thermodynamic calculations, the denitrogenation reactions appear to take place via atomic nitrogen in pure argon plasma, via NH₃ in Ar + H₂ and via HCN in Ar + CH₄.     

Cold Briquetting of DRI Fines for Use in Steel Making Process

DRI fines, generated during its manufacture and handling, generate high content of fines in the size fraction less than 2 mm. It has iron content above 80%. It is difficult to directly use such iron-rich material in the primary steel making process, without agglomeration. At JSW Steel Vijayanagar, around 50 to 70 tons per day of DRI fines with < 2 mm size fraction get generated. The fines are used in base sinter mix or it may be agglomerated suitably to use it as a coolant in the primary steel making process. Since the fines are extremely reactive, they are susceptible to oxidation if it is not agglomerated as soon as it is generated. The present study brings out the development of an agglomeration process for the DRI fines to a dense metallized briquette, for use as a coolant in basic oxygen furnace. Initially, the conditions for briquetting such as use of binder, hardener, lime, dust, moisture, briquetting and curing conditions were established in a 10 kg batch size. This was followed by industrial-scale processing, at 500 kg batch size. The physical and chemical characteristics of the fines and briquettes were assessed at different stages. The cold compressive strength of the cured briquette was found to be a function of moisture content. The handling parameters in the production condition, for long-term pile-up of briquettes against oxidation, were brought out. The successful use of the briquettes in basic oxygen process was demonstrated.     

直接还原铁在我厂电弧炉炼钢中的应用及效果分析

概述了直接还原铁的特性及在我厂电弧炉炼钢中的使用情况，并将其效果作了进一步分析。     

Effect of Direct Reduced Iron (DRI) on Dephosphorization of Molten Steel by Electric Arc Furnace Slag

Metallurgical and Materials Transactions B - We investigated the effect&nbsp;of direct reduced iron (DRI) addition on dephosphorization of molten steel by electric arc furnace (EAF) slag at...     

电弧炉炼钢中碳氧二次燃烧的影响因素和应用

电弧炉炼钢时，废气与熔池和渣子接触，CO气体的温度接近钢水温度，整个过程基本由反应动力学条件控制，凭借吹氧可以在熔池上方进行二次燃烧。1台60t电弧炉2000多炉的二次燃烧的应用结果表明，当吹入氧气操作得当，二次燃烧对水冷炉壁、炉顶、电极寿命、3角区耐火材料寿命、金属烧损率均无影响，氧耗增加7．93m^3/t，电耗降低38kWh/t，冶炼周期可稳定缩短4min。     

钢中残余有害元素对油井管质量的影响

钢中的残余有害元素致使钢材产生红脆性表面裂纹和具有回火脆性倾向，并使耐热钢的热强性降低。因废钢中残余有害元素含量较高，为降低油井用钢的残余元素含量，应在电弧炉炉料中加入一定比例的生铁(铁水)或直接还原铁。     

Control and Engineering of Non‐metallic Inclusions belonging to xSiO2‐yCaO‐zAl2O3 System in Ca‐treated Al‐killed and Al‐Si‐killed Steel

A model based on the fundamental principles of thermodynamics has been applied to forecast and control the precipitation of non‐metallic inclusions in Ca‐treated Al‐killed or Al‐Si‐killed steels. The engineering of the non‐metallic inclusions takes place during the period just after the tapping from the electric arc furnace until the beginning of the casting period. The construction of the model and its validation have been accomplished through a precise monitoring of the treatment of several steel grades characterized by different oxygen contents after tapping. The oxygen killing of the steel melt with an oxygen content between 750‐1200 ppm is performed by the addition of Si and Al, which produces the formation of pure Al₂O₃ but not always the formation of pure SiO₂. This is a fundamental hypothesis of the model confirmed by experimental observations. The other fundamental aspect is related to the determination of the oxygen activity in the steel bath, which is defined from experimental measurements by an electrochemical concentration cell and through the computation of the equilibrium between the steel bath and the ladle slag. The comparison between the experimental data and the non‐metallic evolution forecast by the model on the basis of the minimization of the oxygen potentials has shown very interesting performances, which makes the model a suitable and very stable tool for industrial application.     

直接还原铁作为废钢替代品在电弧炉中的应用

为了满足用户对优质钢和纯净钢的要求,直接还原铁作为废钢的替代品用于电弧炉炼钢应是一种可行的选择。概述了直接还原铁的特点,指出高比例使用DRI可以得到N、Cu、Cr、Ni、As、Sn等含量低的钢,直接还原铁可认为是一种较好的电弧炉炼钢原料。     

Development of Non‐coke Ironmaking Processes in China

Development of non‐coke ironmaking process in China is presented. It is concluded that coal‐based rotary kiln is still the main process for direct reduced iron (DRI) production in the near future in China. The most important problems of DRI production in China are small production scale and heavy environment pollution. Now the gas‐based shaft furnace process has become one of the significant processes of DRI production in China. The market demand for DRI production in China is continuously increasing. Due to the tense supply of coking coal and its heavy environmental load, more steel plants in China will use smelting reduction (SR) technology.     

炼钢电弧炉工艺过程的仿真,预测,诊断与优化

介绍了以计算机为工具，对炼钢电弧炉工艺过程进行仿真与优化的一些应用，包括：炼钢电弧炉工艺指标预测，诊断和优化，竖式电弧炉废钢预热过程仿真，钢液中磷，硫浓度的预测，直流电弧炉电磁偏弧和控制弧仿真以及电弧炉操作监控仿真等。     

Cost and Life Cycle Analysis for Deep CO2 Emissions Reduction for Steel Making: Direct Reduced Iron Technologies

Among heavy industrial sectors worldwide, the steel industry ranks first in carbon dioxide (CO₂) emissions. Technologies that produce direct reduced iron (DRI) enable the industry to reduce emissions or even approach net-zero CO₂ emissions for steel production. Herein, comprehensive cradle-to-gate (CTG) life cycle analysis (LCA) and techno-economic analysis (TEA) are used to evaluate the CO₂ emissions of three DRI technologies. Compared to the baseline of blast furnace and basic oxygen furnace (BF–BOF) technology for steel making, using natural gas (NG) to produce DRI has the potential to reduce CTG CO₂ emissions by 33%. When 83% or 100% renewable H₂ is used for DRI production, DRI technologies can potentially reduce CO₂ emissions by 57% and 67%, respectively, compared to baseline BF–BOF technology. However, the renewable H₂ application for DRI increases the levelized cost of steel (LCOS). When renewable natural gas (RNG) and clean electricity are used for steel production, the CTG CO₂ emissions of all the DRI technologies can potentially be reduced by more than 90% compared to the baseline BF–BOF technology, although the LCOS depends largely on the cost of RNG and clean electricity.     

走向21世纪的炼铁技术

本文介绍一种通过磁场换各来取代原有的直流电机中电刷换向，从而获直流电机特性的新型电机。     

直接还原铁生产技术的现状及展望

 分析了世界及中国直接还原铁的技术现状。直接还原工艺可以摆脱焦煤资源短缺的束缚,降低CO2排放,促进资源综合利用,且高品质的直接还原铁是生产洁净钢不可缺少的原材料,是钢铁工业发展不可缺少的组成部分。随着铁矿精选技术、煤制气技术的成熟,从及气基竖炉生产规模的不断增大,煤制气→竖炉将成为中国主要的直接还原生产工艺。高温高料层PSH工艺应当具有良好的应用前景。回转窑、隧道窑等工艺在特定地区可适当发展,但不会成为直接还原铁生产的主流。     

CONARC 2000—最灵活的炼钢方法

CONARC炉将传统转炉工艺与电炉炼钢法溶于同一炉体 ,即可作为转炉炼钢又可作电炉使用。该炉对入炉料的适应性极好 ,即可是铁水也可是一定比例的海棉铁、生铁,还包括废钢,炉子灵活性更大,并可满足不同钢种和品种的要求,出钢周期缩短,生产成本降低.     

92 t EAF-LF冶炼20G钢液的氮含量控制

攀成钢公司采用92 t EBT(偏心底)UHP EAF-LF(钢包炉)工艺冶炼成分(%)为0.17~0.23C-≤0.15Mo的高压锅炉钢20G。操作实践表明,在EAF(电弧炉)炉料中配加35%的生铁,并通过添加3~10 mm的碳粒和强化供氧,形成500~750 mm的泡沫渣,以利去除钢液中的部分氮,使EAF出钢时钢中氮含量平均达到45×10^-6。LF精炼时采用大渣量埋弧操作,氩气弱搅拌和缩短加热时间,以便控制精炼时钢液增氮量不超过10×10^-6,并使LF精炼后钢中氮含量达(60~66)×10^-6,有效地防止钢材产生时效脆性。     

粗煤气铁矿颗粒床高温除尘联产直接还原铁工艺及估算

在煤灰熔点高于直接还原铁还原温度200℃的条件下,以直接还原竖炉作为移动颗粒床除尘器为核心技术的3段连续除尘,以铁矿煤球团为直接还原铁原料和移动颗粒床除尘颗粒,粗煤气显热可以直接用于生产直接还原铁。粗煤气显热约占煤炭气化热值的13%,估算联产直接还原铁显热利用效率可达70%以上,与现有的粗煤气废锅发电比,综合热效率提高约2倍,直接还原铁能耗303kg（C）/t.Fe,可以实现温室气体近零排放,减排CO₂约1.7t/t.Fe。可以在不减少粗煤气化学热能（H₂+CO）,联产直接还原铁的同时解决粗煤气的高温除尘与净化问题。     

Removal of hydrogen in the vacuum treatment of steel

The degassing of 09Г2C steel produced in an arc furnace and treated in a ladle–furnace unit at AO Uralskaya Stal is analyzed. The vacuum-treatment parameters that determine the effectiveness of hydrogen removal from the steel are identified: the depth and duration of vacuum treatment; the argon flow rate; the steel temperature; the thickness of the slag layer; and the free board in the vacuum chamber. The hydrogen content changes most significantly when the degassing time is increased to 20 min. Longer treatment is not recommended. The greatest effect of the residual pressure in degassing is observed with simultaneous decrease in the minimum pressure to 2 mbar. Vacuum treatment of the steel is considerably impaired with increase in the residual pressure. Hydrogen removal is improved with increase in the steel temperature to 1600–1620°C, but slows considerably at higher temperatures. The influence of the vacuum-treatment parameters is established quantitatively, and a regression equation is derived for predicting the results of hydrogen removal and selecting the parameter values corresponding to specified hydrogen content in the steel. Vacuum-treatment parameters that permit the economical production of steel with 2.1 ppm are determined: steel heating before vacuum treatment by 100–110°C; vacuum treatment for 20 min at a pressure no higher than 1.5 mbar in the vacuum chamber; argon flow rate 0.05 m³/t. The temperature losses of the metal are determined by the total treatment time, consisting of the active degassing time and the auxiliary time (the preliminary evacuation time), which depends on the capabilities of the equipment and the organization of the process. The minimum residual hydrogen content in the steel for the given equipment (1.6 ppm) is ensured by vacuum treatment for 40 min at a pressure no higher than 1 mbar in the vacuum chamber, with preliminary heating of the steel by 120–125 °C and with an argon flow rate up to 0.072 m³/t.     

Laboratory investigation of denitrogenation of low carbon steel by gas generation in situ

Abstract

Denitrogenation of low carbon steel with carbon monoxide generated in situ by the reaction of carburised iron /graphite with dissolved oxygen in the bath has been investigated in an air induction furnace. A melt size of 50 kg was used. Experimental parameters, namely nature and size of the deoxidising reactants and bath parameters, such as dissolved carbon, nitrogen and oxygen levels in the bath and temperature of the bath, were varied to investigate effects on the extent of denitrogenation. A trend of increasing denitrogenation with increasing gas evolution in the bath was observed. The extent of denitrogenation showed a decreasing trend with increasing temperature and oxygen level in the bath. Thermodynamic consistency was checked by calculating the average partial pressure of desorbed nitrogen from the total gas generated and the total volume of nitrogen liberated at the reaction site.