Burning Characteristic of LNG‐Oxygen Mixed Gas used for Vacuum Degassing Process

This study was conducted using LNG (Liquefied Natural Gas) as fuel which has methane gas as its main component, and theoretical and experimental evaluation was made of the burning conditions of LNG‐oxygen mixed gas under atmospheric and subatmospheric pressure in a vacuum chamber used for the RH process. Conclusions reached in this study of the conditions involved in injecting LNG‐oxygen mixed gas in a vacuum chamber of the RH device and burning it near the nozzle outlet to raise the surface temperature of brick were as follows: (1) Laminar burning velocity of mixed gas of LNG and oxygen was fastest when the mixture ratio was 1:2.3, and when the velocity was proportionally related to the square of temperature and 0.5 root of pressure. (2) Turbulent burning velocity u_t was calculated from the research results of Andrews. (3) It is possible to calculate the turbulent burning velocity and to evaluate u_t/u_m which is the index of stability of the burner flame by experimentally obtaining laminar burning velocity.     

节能技术在RH真空精炼工艺中的应用

介绍了MFB顶吹氧枪技术、水环真空泵技术和干式机械泵技术等3种节能技术在RH真空精炼工艺的应用。国内某钢厂300 t RH真空精炼系统的应用表明:应用MFB顶吹氧枪技术,RH处理过程钢液温降可减少15.8℃;应用水环真空泵技术,可降低RH吨钢生产成本约2.25元;应用干式机械泵技术,可降低RH吨钢生产成本约6.05元。     

RH-KTB精炼中钢液溶氧过程动力学的水模拟研究

用顶吹CO2－NaOH溶液体系模拟了RH－KTB顶吹氧溶氧过程。通过对碱液吸收CO2反应动力学的研究,考察了操作参数对RH－KTB顶吹氧脱碳过程中溶氧反应的影响。结果表明：提高气相中氧分压、增加提升氩气流量或采用低枪位喷吹都有利于加速溶氧脱碳。实验中还发现：顶吹氧气流量对容积传质系数影响很小,对熔池内的钢液流动状态影响不大。     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (I) ‐ Decarburization Process and Influences of Some Technological Factors

A novel three‐dimensional mathematical model proposed and developed for the non‐equilibrium decarburization process during the vacuum circulation (RH) refining of molten steel has been applied to the refining process of molten steel in a 90‐t multifunction RH degasser. The decarburization processes of molten steel in the degasser under the conditions of RH and RH‐KTB operations have been modelled and analysed, respectively, using the model. The results demonstrate that the changes in the carbon and oxygen contents of liquid steel with the treatment time during the RH and RH‐KTB refining processes can be precisely modelled and predicted by use of the model. The distribution patterns of the carbon and oxygen concentrations in the steel are governed by the flow characteristics of molten steel in the whole degasser. When the initial carbon concentration in the steel is higher than 400 · 10⁻⁴ mass%, the top oxygen blowing (KTB) operation can supply the oxygen lacking for the decarburization process, and accelerate the carbon removal, thus reaching a specified carbon level in a shorter time. Moreover, a lower oxygen content is attained at the decarburization endpoint. The average contributions at the up‐snorkel zone, the bath bulk and the free surface with the droplets in the vacuum vessel in the refining process are about 11, 46 and 42% of the overall amount of decarburization, respectively. The decarburization roles at the gas bubble‐molten steel interface in the up‐snorkel and the droplets in the vacuum vessel should not be ignored for the RH and RH‐KTB refining processes. For the refining process in the 90‐t RH degasser, a better efficiency of decarburization can be obtained using an argon blow rate of 417 I(STP)/min, and a further increase in the argon blowing rate cannot obviously improve the effectiveness in the RH refining process of molten steel under the conditions of the present work.     

宝钢─炼钢新建2RH真空脱气设施简介

简要说明了宝钢一炼钢新建 2RH真空脱气设施的必要性 ,重点介绍了 2RH采用的顶枪技术、真空系统、纯水闭路循环机械冷却水系统及EIC三电一体化控制系统。新建的 2RH真空脱气设施不仅脱碳、脱氢速度快 ,而且具有化学加热钢水、喷粉脱硫、喂丝吹氩等功能 ,真空槽可保持较高的温度 ,大大减少了槽内结冷钢的可能性     

Dynamic model for on‐line observation of the current process state during RH degassing

Based on the principles of thermodynamics and reaction kinetics, a dynamic model for the vacuum circulation (RH) process was developed. It comprises decarburisation, oxygen removal, dehydrogenation, denitrogenation and the course of steel temperature. The process model was validated by comparison of simulation results with measured process data from the RH/1 plant of Voest Alpine Stahl Linz (VASL). At this plant, it is used for on‐line observation of the contents of carbon, oxygen, hydrogen and nitrogen as well as the steel temperature. Based on cyclically measured values of vessel pressure, lift gas flow rate as well as waste gas flow rate and composition, the current heat status is calculated reliably. The accuracy of the carbon balance with measured waste gas values was improved remarkably by a model‐based correction calculation. The on‐line process observation system provides the operator with valuable information on the progress of vacuum treatment.     

Mathematical Modelling of Molten Steel Flow Process in a Whole RH Degasser during the Vacuum Circulation Refining Process: Application of the Model and Results

A three‐dimensional mathematical model for the molten steel flow during the RH refining process has been applied to the circulatory flow processes in both a practical RH degasser and its water model unit. The model was presented earlier [1] and one of its characteristics is that ladle, snorkels and vacuum vessel are regarded as a whole. Using this model, the fluid flow field and the gas holdups of liquid phases and others have been computed respectively for a 90 t RH degasser and its water model unit with a 1/5 linear scale. The results show that the mathematical model can properly describe the flow pattern of molten steel during the refining process in an RH degasser. Except in the area close to the liquid's free surface and in the zone between the two snorkels in the ladle, a strong mixing of the molten steel occurs, especially in the vacuum vessel. However, there is a boundary layer between the descending liquid stream from the down‐snorkel and its surrounding liquid, which is a typical liquid‐liquid two‐phase flow, and the molten steel in the ladle is not in a perfect mixing state. The lifting gas blown is ascending mostly near the up‐snorkel wall, which is more obvious under the conditions of a practical RH degasser, and the flow pattern of the bubbles and molten steel in the up‐snorkel is closer to an annular flow. The calculated circulation rates for the water model unit at different lifting gas rates are in good agreement with experimentally determined values.     

100t RH顶吹氧去除真空室内壁冷钢的数值模拟和应用

对钢厂100 t RH将原天然气烘烤改为顶吹氧去除真空室内壁冷钢工艺改造进行了研究。对5.5~7.5m氧枪位置及750~1300m³/h氧气流量下的速度场进行了数值模拟,根据计算确定了在枪位为5.5~6.5m,氧气流量为900~1200m³/h时RH顶吹氧去除冷钢是可行的。工业生产应用结果表明,采用该顶吹氧去除冷钢工艺,明显提高了RH的连续处理能力,RH月处理能力由不到28.5%提高到36.0%左右,单月RH处理能力最高比例达到48.8%。     

武钢RH-MFB技术的应用及优化

武钢第二炼钢厂是武钢品种钢生产基地,目前建成两台RH真空处理装置,1#RH真空处理装置设置KTB顶枪装置,WPB喷粉装置;2#RH于2005年三月在对电器,仪表进行改造的同时,新增MFB顶枪装置.RH-MFB顶枪装置具有强制脱碳,处理及非处理在线加热,去除真空室结瘤,加铝升温功能.MFB顶枪运行三个多月来生产品种405炉,厂工程技术人员在设计审查,调试及试生产期间对设备,工艺,操作进行不断完善和优化,取得了满意的效果.     

RH真空精炼过程的动态模拟

建立了描述RH真空精炼装置内钢液动态脱碳（脱气）模型。对RH真空精炼时的脱碳、脱氧、脱氮和脱氢过程进行了动态模拟研究，考察了浸渍管直径、循环流量、吹氩量、氧含量和真空度对脱碳和脱气过程的影响。动态脱碳（脱气）模型考虑了反应机理，认为脱碳是通过上升管中Ar气泡表面、真空室中钢液的自由表面和真空室钢液内部脱碳反应生成的CO气泡表面进行的，并且考虑了精炼处理时的抽真空制度。该模型能全面描述RH精炼过程中不同时刻钢液中碳、氧、氮和氢的含量，能较好预测实际过程，可用于RH真空精炼过程的优化和新工艺开发。     

RH处理超低碳钢中总氧含量预报模型

根据300 t钢包RH真空处理超低碳铝镇静钢工业生产数据,建立了RH处理过程钢中总氧含量(氧化物夹杂含量)的预报模型。模型综合考虑了RH脱碳结束时钢中的初始氧[O]0及钢包渣中(FeO+MnO)的质量分数、吹氩流量、真空度、处理时间等因素的影响。模型计算值与实测值误差为±(3.5~8.0)%,说明该模型是可信的;利用模型分析讨论了RH操作过程的工艺因素对钢水总氧含量的影响。     

Behaviour of Argon Gas Bubbles in an Electromagnetic Driven Swirling Flow

An innovative steelmaking process is suggested using an electromagnetic driven swirling flow in the up‐leg of an RH vacuum degassing vessel. The effectiveness of this new process depends on the two‐phase flow behaviour of molten steel and argon gas. A physical and a mathematical model are developed to understand the effect of electromagnetic driven swirling flows on the behaviour of gas bubbles in the up‐leg of an RH vessel. Both water model experiments and numerical simulation show the distribution and trajectories of the gas bubbles. The gas bubbles’ trajectories are spiral and move towards the centre of the up‐leg in the swirling flow field. The accumulation of gas bubbles depends on the swirling number. At the same time, the swirling flow can prolong the residence time and trajectories of non‐metal inclusions in the vessel. The viscous drag force becomes important for small bubbles in the RH degassing vessel, and small bubbles have the trend to rotate with the swirling flow.     

Mathematical modelling of molten steel flow in a whole degasser during RH refining process

Abstract

A three-dimensional mathematical model for molten steel flow in a whole degasser during the RH (Ruhrstahl–Heraeus) refining process is proposed. The model has been developed considering the physical characteristics of the process, particularly the behaviour of gas–liquid two phase flow in the up snorkel and the momentum exchange between the two phases. The fluid flow fields and gas holdups of liquid phases, among other parameters, in a 90 t RH degasser and a water model unit of one-fifth linear scale have been computed using this mathematical model. The results show that the flow pattern of molten steel in a whole RH degasser can be well represented by the mathematical model. Apart from the area close to the free surface and the zone between the two snorkels in the ladle, the molten steel in an RH degasser, especially in the vacuum vessel, is reasonably fully mixed during the refining process. However, there is a boundary layer between the descending liquid stream from the down snorkel and the surrounding liquid, which is typical liquid–liquid two phase flow, and the molten steel in the ladle is not perfectly mixed. The blown lifting gas ascends mostly near the up snorkel wall, which is more obvious under the conditions of an actual RH degasser, and the flow pattern of bubbles and molten steel in the up snorkel is closer to annular flow. Calculated circulation rates for the water model unit at various lifting gas rates are in good agreement with values determined by means of water modelling experiments.     

唐钢RH钢包混匀时间及流场模拟计算与分析

研究了真空度、提升气体量和吹气孔位置对RH钢水混匀时间的影响,模拟了钢包流场情况。试验结果表明:提高RH系统真空度、增加RH提升气体量或增大气体的吹入深度均可减小混匀时间;唐钢RH精炼过程中无死区存在,在相应的混匀时间内可以实现整包钢水成分和温度的均匀;合理控制真空度、提升气体量和浸渍管插入深度有利于稳定出站钢水碳含量,提高Al2O3夹杂物的去除率。     

气泡搅拌和炉渣成分对低碳钢水洁净度的影响

在80t氧气转炉、钢包吹氩和RH真空处理工序进行净化钢水的试验,考察反应器内氩气流量、真空脱气操作和顶渣成分对低碳钢水全氧含量的影响以及夹杂物的尺寸分布和全氧的排除速率,改进操作的结果表明,二次精炼后低碳钢水全氧w[T.O]降低到0.001%。     

RH真空冶炼过程中锰损

为了减少RH真空冶炼过程中钢水锰元素偏差和提高最终产品性能的稳定性,采用直读光谱仪对不同条件下RH真空冶炼镇静钢与非镇静钢锰损情况开展研究。结果表明,RH真空冶炼过程中锰损存在4种形式,与钢水中自由氧反应烧损、钢渣界面反应、合金粉末抽吸、真空锰挥发;随着钢水中锰含量增加、真空时间延长,钢水温度和氧化性提高,RH真空锰损逐渐增加;真空度小于1 000 Pa时,RH真空锰损随真空度的降低而降低,而当真空度大于1 000 Pa时,继续降低真空度,RH真空锰损几乎不变。通过降低RH真空度、进站锰含量和温度、减少RH真空处理时间等措施,RH结束目标锰的质量分数±0.01%命中率接近100%。     

真空感应熔炼含铝钢的脱氧规律

 通过热力学分析研究了用氧化钙坩埚熔炼含铝钢时熔炼温度、真空度和钢液铝含量与氧化钙分解向钢液增氧的关系。在25 kg真空感应炉中分别用电熔镁砂和氧化钙砂捣打坩埚熔炼含铝钢,在10~50 Pa真空度下,镁砂坩埚表现出强烈的供氧倾向,全氧含量随着钢中铝烧损量的增加而增加;而氧化钙坩埚不向钢液供氧。随着钢液中Al2O3夹杂被氧化钙坩埚吸收同化,全氧的质量分数逐渐下降至3×10-6。     

超低碳钢RH混合喷吹Ar-CO2冶金反应特性

 钢铁生产过程CO₂的资源化利用对中国“碳达峰,碳中和”目标的实现起着重要作用。氩气驱动的RH(ruhrstahl-heraeus)真空装置是超低碳钢精炼的关键设备,利用高真空下钢水循环流动可有效脱碳、脱气和去除夹杂物。由于真空条件下CO₂可直接与钢水中碳反应生成CO,在实现脱碳的同时可促进熔池搅拌。因此,尝试将Ar-CO₂混合气体作为提升气体引入超低碳钢RH脱碳过程。首先,针对CO₂在RH脱碳条件下的冶金反应行为,通过热力学理论分析了不同压力下Fe-C-O熔体与Ar-CO₂的反应特性。其次,搭建了Ar-CO₂混合气体作为RH提升气体的工业试验平台,通过工业性试验研究了超低碳钢RH脱碳过程混合喷吹Ar-CO₂对钢水脱碳、脱氮和温降的影响。Fe-C-O熔体与Ar-CO₂反应热力学表明,在低于100 kPa和超低碳条件下,Ar-CO₂混合气体中的CO₂仍可能与钢水中碳反应,从而促进RH脱碳和脱气。工业性试验表明,喷吹100% CO₂、50% Ar+50% CO₂和100% Ar炉次出站平均碳质量分数分别为0.001 50%、0.001 57%和0.001 19%,因而混合喷吹Ar-CO₂并不会显著影响RH脱碳效率。同时,由于CO₂与钢水中碳反应十分有限,与喷吹100% Ar相比,喷吹100% CO₂和50% Ar+50% CO₂对RH脱氮效率和钢水温降没有明显影响。因此,超低碳钢RH脱碳时,完全可采用CO₂取代部分或全部氩气作为提升气体,尽管无法提高精炼效率,但仍具有显著的经济价值和环保优势。     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (II) ‐ Non‐equilibrium Factors and their Influences on the Decarburization Process

The results, which were obtained by applying the novel three‐dimensional mathematical model proposed and developed earlier [1] to model and analyse the decarburization process of molten steel during the RH and RH‐KTB refining in a 90‐t multifunction RH degasser, showed that under the conditions of the present work, the contributions of the flow, mass diffusion and chemical reactions and other non‐equilibrium processes to the Raleigh‐Onsager dissipation function are not large throughout vacuum circulation refining of molten steel. Thus, it is held everywhere in the whole flow field of the system that the value of the non‐linear dissipation factor is approximately equal to one. The entropy generation and energy dissipation in the system rapidly decrease with increasing refining time. Compared to the work done by the drag force while the bubbles passing through the liquid phase as well as by the viscous and turbulent flow and diffusion processes, the carbon‐oxygen reaction itself plays a more governing role to the entropy production and energy dissipation in the system. The RH refining process of low and ultra‐low carbon steels seems to be close to the linear zone of the non‐equilibrium state. The influences of the viscous and turbulent flow dissipation as well as diffusion processes on the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel may almost be neglected. Except in the regions where the chemical C‐O reaction takes place (the up‐snorkel zone and the bath in the vacuum vessel), the non‐equilibrium components of the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel at the other places in the degasser are all tending towards one. The non‐equilibrium effects (mainly, the C‐O reaction itself) give a restraining role on the decarburization of liquid steel in the RH refining process. This model is able to model more reasonably and precisely the non‐equilibrium decarburization process during the vacuum circulation refining of molten steel in comparison to a model without considering the non‐equilibrium effects.