Power increase and metallurgical effects during arc heating of liquid steel due to the addition of molecular gases

Molecular gases were laterally injected into the gas atmosphere of a pilot furnace containing 200 kg of steel melt and heated by two AC argon plasma arcs. The power increase in the arcs obtained by the injection was 12 % for 20 % N₂, 70 % for 20 % CO₂, 32 % for 3 % CH₄, and 62 % for 3 % C₃H₈. Mixtures of CO₂ and hydrocarbons were also tested. CO₂ acted as an oxidizing agent for steel components with oxygen transfer efficiencies of 28 % in the case of slag-free steel melts and of 10 % in the presence of slag, while the addition of CH₄ did not cause any noticeable carbon transfer to the melt.     

Power increase of plasma heating systems by CO2 addition into the furnace atmosphere: Investigations in view of the plasma ladle furnace

For certain steel grades the treatment in conventional ladle furnaces equipped with graphite electrodes may not be advisable because of the risk of carbon pick-up. In these cases metallic plasma torch systems operated with argon as plasma gas may be preferable. However, the maximum active power available from a 3 torch AC argon plasma system is at present limited to about 4 MW. Tests were carried out with 200 kg heats in a pilot furnace equipped with 2 AC argon plasma torches to investigate the arc voltage increase by adding CO₂ to the furnace atmosphere. With 20% CO₂, the voltage of a 30 cm arc was raised from 100 to 173 V. The transfer rate of oxygen from the CO₂ in the atmosphere via the plasma arc to the steel melt was measured by means of steel and off-gas analyses. After formation of a slag layer, about 10% of the oxygen supply injected into the furnace as CO₂ was transferred to the melt. The measured values concerning power increase and oxygen transfer were extrapolated to ladle capacities of 50 to 150 t and 3-torch 12 kA AC plasma heating systems. In a furnace atmosphere containing 60% CO₂, the active power available from a plasma system would be 10 MW as compared to 3.5 MW in pure argon. The oxygen transfer rates proved to be relatively small due to the low gas flow rates of such systems and to the low mass transfer efficiency. The addition of 40% CO₂ would raise the power to heat 110 t of steel at a heating rate of 3 K/min, while the oxygen level would increase within 30 min by less than 10 ppm. The specific CO₂ demand would in that case be 0.12 m³(STP)/t.     

Metallurgical results from a 30-t AC plasma ladle furnace

In a 30-t ladle furnace equipped with three A.C. transferred arc-plasma torches for a power input of 6 MW, the influence of argon plasma heating on the chemical composition of a number of steel grades from carbon to chromium-nickel steels was investigated. The concentrations of carbon, manganese, chromium and nickel remained virtually constant even for extra-long heating periods of 2 hours. Silicon melting loss was appr. 0.03%/h, comparable to conventional ladle furnaces. Nitrogen pickup proved to be negligibly small, although the N₂ partial pressure in the furnace was about 0.5 bar. Since the slag is well heated up by the plasma flames, a metal desulphurization is noticed, the extent of which depends on the basicity of the slag. At the slag/gas interface, equilibrium is established with the slightly oxidizing furnace atmosphere, leading to sulphur transfer from slag to gas via SO₂.     

Metallurgical value of converter slag

The characteristics of OAO ZSMK converter slag are investigated, including a series of experimental melts in a laboratory arc furnace. The losses of iron with converter tailings slag at OAO ZSMK after primary magnetic separation in the slag fields amount to 22.7%, on average (9.0% metallic iron + 13.7% iron oxides). In sorting the slag, the large fractions are enriched with iron oxides—primarily FeO and Fe₃O₄; Fe₂O₃ passes to the small fractions. In melting converter slag, some of the iron is recovered, with increase in the content of metallic iron to 11.7%, on average. Most of the metallic iron is concentrated in the large fractions (more than 40 mm), where its content is 18%, on average, as against 5–6% in the smaller fractions.     

Role of Direct Reduced Iron Fines in Nitrogen Removal from Electric Arc Furnace Steel

Electric arc furnace steel contains about 70‐120 ppm nitrogen. There is no suitable method for nitrogen removal from electric arc furnace steel up to the level desired for good quality bars and flat rolled products (30 ppm max). The existing process based on vacuum degassing can remove only up to 20% of nitrogen in steel. In the present study DRI fines have been injected into a steel bath which can drift out nitrogen in steel through production of fine CO bubbles in‐situ on reaction with residual FeO in DRI fines and C in bath. For high and medium carbon steel, nitrogen got reduced to 30 ppm and 60 ppm respectively where initial nitrogen was 150 – 200 ppm in steel. Nitrogen removal also depends upon bath depth and addition level of DRI.     

Electric Melting of Iron-Ore Prereduced Pellets in an Electric Arc Furnace

This article discusses the aspects of the melting loss in electric steelmaking during continuous feeding of prereduced pellets into the bath of an electric arc furnace via hollow electrodes. It is shown that adjustment of the melting loss and the dust discharge from electric arcs by changing the pellet consumption and accounting for the heat parameters of furnace operation makes it possible to significantly increase the ingot-to-product yield during electric steelmaking.     

Mechanism of Desulfurization from Liquid Iron by Hydrogen Plasma Arc Melting

In this study, desulfurization from liquid iron by Ar and (10 to 40 pct)H₂?+?Ar plasma arc melting (HPAM) was examined. The experimental results show that the rate of desulfurization increases as hydrogen is added proportionally to plasma gas. The thermodynamic analysis suggests that the interaction of activated atomic hydrogen and dissolved sulfur in liquid iron, \( \left[ {\text{S}} \right] + 2{\text{H}} = {\text{H}}_{ 2} {\text{S}}, \) could be taking place. The kinetic analysis confirms that the desulfurization from liquid iron obeys a first-order rate law.     

Analisys of Electric Arc Furnace Slag

The black slag produced during the melting process in electric arc furnace can be used as adjunct in the operation of land filling, building operation of road grounds, and production of concrete. Their use limitation is due to the presence of polluting chemical elements, including Cr, Ba, V, Mo, etc, that can be dangerous for human and environment, resulting by using of polluted scraps (i.e., painted, lubricated, or polymeric compound scraps). The release extent of polluting elements appears to behave as a function of the constituent phases, i.e., CaO, SiO₂, Al₂O₃, MgO, etc. The main tools employed in the characterization of the black slag consists in optical basicity calculation, SEM‐EBS and SEM‐EDS analysis. The combination of the data coming from chemical analysis, micro‐structural examination and releasing tests allows to identify the correct chemical range avoiding dangerous chemical release and to develop a working disposal procedure for the investigated slag.     

Arc Distribution During the Vacuum Arc Remelting of Ti-6Al-4V

Currently, the temporal distribution of electric arcs across the ingot during vacuum arc remelting (VAR) is not a known or monitored process parameter. Previous studies indicate that the distribution of arcs can be neither diffuse nor axisymmetric about the center of the furnace. Correct accounting for the heat flux, electric current flux, and mass flux into the ingot is critical to achieving realistic solidification models of the VAR process. The National Energy Technology Laboratory has developed an arc position measurement system capable of locating arcs and determining the arc distribution within an industrial VAR furnace. The system is based on noninvasive magnetic field measurements and a VAR specific form of the Biot–Savart law. The system was installed on a coaxial industrial VAR furnace at ATI Albany Operations in Albany, OR. This article reports on the different arc distributions observed during production of Ti-6Al-4V. It is shown that several characteristic arc distribution modes can develop. This behavior is not apparent in the existing signals used to control the furnace, indicating the measurement system is providing new information. It is also shown that the different arc distribution modes observed may impact local solidification times, particularly at the side wall.     

Symmetry of Arc Furnace Operation

The electrical asymmetry in the operation of arc furnace with an asymmetric triangular configuration of the electrodes is noted. Experimental data from the DSP-100 furnace permit analysis of how the electrical parameters affect the arc characteristics. Nonuniform power distribution over the phases of the electrofurnace decreases the component of the useful power consumed in heating the metal and slag. The power consumption by the furnace may potentially be reduced by 7.4% and the electrode consumption by 9%. The results confirm the need for research on phase-by-phase regulation of the power of ac arc furnaces.     

火焰原子吸收光谱法测定火法冶炼镍基体料矿热炉渣中镍

通过对火法冶炼镍基体料矿热炉渣化学组成和性质的研究,确定了测定微、痕量镍的实验方法。由于样品中二氧化硅含量在40%～65%,样品的分解难度很大,且对镍的测定存在严重的负干扰,因此需在样品分解过程中加入足量氢氟酸与之反应生成SiF₄挥发除去。溶液中其余共存离子主要有Mg²⁺、Ca²⁺、Fe³⁺、Al³⁺、Cr⁶⁺等,其中Ca²⁺对测定存在严重的正干扰,通过向空白溶液中加入同量的钙可消除此干扰。高氯酸是最佳的分析介质,其浓度控制在3%～5%即可达到稳定分析。方法的检出限为0.001 2 mg/L。对4个火法冶炼镍基体料矿热炉渣实际样品中镍进行分析,回收率为99%～102%,相对标准偏差处于1.3%～2.9%范围内,与ICP-AES的分析结果相一致。     

On the smelting reduction of iron ores with hydrogen-argon plasma

Investigations of the plasma smelting reduction of iron ore have been carried out on a laboratory scale using a transferred argon-hydrogen plasma arc. Pyrometric measurements show that the surface temperature near the arc foot is about 2600 K when the hydrogen is mixed with the plasma-gas in front of the cathode, about 2250 K when the hydrogen is introduced laterally into the arc and ca. 2150 K when a pure argon plasma is used. With the help of thermodynamic plasma data the corresponding arc temperatures have been estimated to be 13 000 K, 11000 K and 9500 K. It has been shown that the reduction rate after the smelting phase remains constant and is practically independent of the manner of addition of the hydrogen. The measured efficiencies of utilization of hydrogen were 43% and 50% and thus correspond closely to the equilibrium FeO + H₂ = Fe + H₂O. A combination of the rate constants obtained for the plasma smelting reduction with those found in literature for lower temperatures leads to an activation energy of approximately 67 kJ/mol. This value lies in the range of energies reported for the reduction of wustite after precipitation of the iron phase. It is therefore not unlikely, that in the case of plasma smelting reduction also, the rate determining step is the reaction H^ad+OH^ad → H₂O^ad.     

不锈钢渣资源化研究现状

不锈钢渣是不锈钢生产过程中产生的有毒废渣,包括初炼渣和精炼渣,其特殊性在于其含有水溶性致癌物质Cr6+,并且在渣的堆放过程中一直持续着Cr3+向Cr6+的转化,严重污染环境。介绍了高温硅铁熔融还原法、湿法及固化法对不锈钢渣脱毒原理,分析了不锈钢渣在烧结、返回炼钢、制备微晶玻璃及烧制水泥等方面的资源化利用现状。     

电弧炉直接用煤氧的节能技术

本文叙述了电弧炉炼钢直接用煤氧技术,总结了煤气枪助熔技术、K-ES电炉新工艺和喷煤氧造泡沫渣操作工艺。结合长期从事煤氧枪研究的经验,从理论上分析了“煤氧电炉”的可行性,并阐明了煤氧推广的意义和煤氧炼钢的发展前景。     

Development of Deep Desulphurization Process for X65 HIC Resistant Pipeline Steel

The effect of ladle slag composition, bottom stirring intensity, and refining duration on desulphurization (De-S hereafter) behavior was investigated in ladle furnace (180t) through production data analysis and plant scale experiments. The results show that the ladle slag composition for deep De-S is w(CaO): 50%-55%, w(CaF2): 3%-7%, w(Al2O3): 20%-25%, w (SiO2) <10%, w (MgO) <10%, and w(FeO) <0.5%; De-S ratio doubled from around 10% to around 20%, within the selected period of 8 min with the increase of Ar flowrate of bottom blowing from 400 L/min to 600 L/min; sulfur can be reduced to less than 10 ppm from around 35 ppm within 20 min if the Ar flowrate is kept at 600 L/min; during steelmaking trial of X65 HIC resistant steel, the sulfur content of final product was controlled to be below 10 ppm when sulfur content of the melt at BOF blowing end was kept below 60 ppm, De-S was carried out with the above mentioned slag, and 600 L/min Ar stirring for more than 20 min.     

康斯迪电弧炉连续炼钢技术

康斯迪技术采用泡沫渣埋弧冶炼，留钢留渣操作，用钢水直接加热炉料，连续运行，同时对预热炉料后的烟气进行处理。采用康斯迪工艺可以减少设备配置，节约投资，提高生产率，大幅度降低２生产成本，且该工艺适应的炉料范围较广，是一种适于在我国推广应用的电炉炼钢技术。     

电弧炉脱[S][P]和[Pb][Zn] 的操作实践

控制电弧炉[P][S]含量和[Pb][Zn]总量,为生产洁净钢创造了基本条件,防止炉渣回磷和无渣出钢操作是获得低[P][S]电弧炉钢水的关键操作。应控制炉料中[Pb][Zn]含量,当熔清时,[Pb]等成分超出标准要求的情况下,首先停止喷碳操作,增大吹氧强度和角度,将[C]降至0.10%以下,钢水经搅拌和升温,促使沉降在炉底[Pb]通过钢水的溶解、氧化被炉渣捕集,2～6min后,喷入发泡剂碳粉,使Pb氧化物还原成Pb蒸发排出,脱[Pb]率为19.0%～46.4%。脱[Zn]操作与脱[Pb]相同。     

Kinetics of chromium oxide reduction from a basic steelmaking slag by silicon dissolved in liquid iron

The reduction of chromium oxide from a basic steelmaking slag (45 wt pct CaO, 35 wt pct SiO₂, 10 wt pct MgO, 10 wt pct A1₂O₃) by silicon dissolved in liquid iron at steelmaking temperatures was studied to determine the rate-limiting steps. The reduction is described by the reactions: (Cr₂O₃) + Si = (SiO₂) + (CrO) + Cr [1] and 2 (CrO) +Si = (SiO₂) + 2 Cr [2] The experiments were carried out under an argon atmosphere in a vertical resistance-heated tube furnace. The slag and metal phases were held in zirconia crucibles. The course of the reactions was followed by periodically sampling the slag phase and analyzing for total chromium, divalent chromium, and iron. Results obtained by varying stirring rate, temperature, and composition defined the rate-limiting mechanism for each reaction. The rate of reduction of trivalent chromium (reaction [1] above) increases with moderate increases in stirring of the slag, and increases markedly with increases in temperature. The effects of changes in composition identified the rate-limiting step for Cr⁺³ reduction as diffusion of Cr⁺³ from the bulk slag to the slag-metal interface. The rate of reduction of divalent chromium does not vary with changes in stirring of the slag, but increases in temperature markedly increase the reaction rate. Thus, this reaction is limited by the rate of an interfacial chemical reaction. The reduction of divalent chromium is linearly dependent on concentration of divalent chromium, but is independent of silicon content of the metal phase.     

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。     

Sustainability–steel and the environment

Abstract

A two-dimensional heat and fluid flow model was used to simulate the plasma arc furnace, where the flow is governed by the steady state incompressible Navier–Stokes equations. The flow has been taken as turbulent and the standard k-epsilon model was used to simulate the turbulence in the flow. The coupled non-linear differential equations were solved with suitable boundary conditions and temperature dependent plasma properties at atmospheric pressure by employing an efficient finite volume method. The calculations and heat transfer to various parts of the furnace were calculated for argon, nitrogen and hydrogen plasmas. The voltage–current characteristic for the different types of plasma and the effect of other process parameters on heat transfer are discussed.