底吹氧气,天然气复吹转炉冶金特点的热模研究

为了开发氧气,天然气作底吹气源,在国内建立顶、底吹氧炼钢法,作者在60 kg热模上进行了50多炉吹炼低碳钢的试验。结果为:喷嘴熔损速度≤1mm/炉,喷嘴畅通,可实现100％的复吹;吹炼特性好,过程平静、无喷溅。试验还比较了顶吹与复吹的脱碳速度变化,观察到复吹前期脱碳速度较大,中期比顶吹略低,变化平稳,持续时间较长。此工艺适合冶炼低碳钢。还对不同底吹氧比对终点氢含量的影响进行了研究,在试验条件下得到的增氢量为0.54 ppm。     

Improvements to Mixing of Natural Gas and Hot-Air Blast in the Air Tuyeres of Blast Furnaces with Thermal Insulation of the Blast Duct

Metallurgist - Using natural gas as an additional fuel in a blast furnace is known to reduce coke consumption during blast-furnace production. In a standard tuyere, the hot blast pushes the natural...     

熔融气化炉风口回旋区冶炼特征的数值模拟研究

相比于高炉风口喷吹富氧热风,熔融气化炉风口采用常温纯氧,使得炉内质量、动量、热量的传输以及煤气流分布等冶炼特征与高炉存在较大差异.通过建立熔融气化炉风口回旋区二维数学模型,系统考察熔融气化炉风口回旋区内速度分布、温度分布及气体组分分布的冶炼特征.结果表明:在气固相热交换及焦炭 (或块煤形成的半焦) 燃烧反应的综合作用下,熔融气化炉风口回旋区内气体温度迅速升高至3 500 K以上;此外,风口前端存在小规模的气体循环流动现象,故风口前端扩孔破损现象严重,进而导致非计划休风率较高;为减少此类休风现象,可适当额外喷吹富氢燃料性气体 (天然气、焦炉煤气),不仅能降低风口回旋区内气体温度,更可替代部分固体燃料,并充分发挥其中H₂的高温还原优势,提升熔融气化炉冶炼效率.      

全氧喷吹高氢燃气高炉风口理论燃烧温度的模拟计算

通过对物料、热量平衡的计算得出全氧高炉喷吹高氢燃气工艺风口理论燃烧温度。从而可知,只要改变不同燃料的配比就能将风口理论燃烧温度控制在保证高炉稳定运行所需要的范围。     

底吹气体参数对透气砖侵蚀速度的影响

为了研究底吹气体喷吹参数(压力、流量、喷孔直径等)对透气砖侵蚀速度的影响,对比了食盐、硼砂、碳酸钠和不同比例的食盐与碳酸钠的混合物在水中的溶解速度,选定天然盐砖来模拟透气砖材质进行侵蚀水模拟试验。以水模拟钢水,在1∶10的有机玻璃模型中喷吹压缩空气,改变喷吹参数(压力、流量和喷吹时间),测量喷吹前后透气砖喷孔尺寸的变化,计算喷孔的侵蚀情况(径向侵蚀速度、轴向侵蚀速度和侵蚀角),构建气体的喷吹参数与透气砖侵蚀速度之间的关系。根据喷孔尺寸、气体的喷吹参数和无量纲数(修正的弗劳德数、雷诺数和表观马赫数等),对喷吹气体进入熔池中的流动状况进行分析,如气流中气泡的当量体积和当量直径、喷吹过程中所形成的气柱高度、气泡流和喷射流的转变等。研究结果表明,透气砖喷孔的轴向侵蚀和径向侵蚀速度均随底吹供气流量提高而增大,侵蚀角受喷孔直径、气体流量的影响很小,采用直径较小的喷孔,可以提高底吹气体对熔池的搅拌效果。研究结果对复吹技术的提高具有参考意义。     

底吹气体参数对透气砖侵蚀速度的影响

为了研究底吹气体喷吹参数(压力、流量、喷孔直径等)对透气砖侵蚀速度的影响,对比了食盐、硼砂、碳酸钠和不同比例的食盐与碳酸钠的混合物在水中的溶解速度,选定天然盐砖来模拟透气砖材质进行侵蚀水模拟试验。以水模拟钢水,在1∶10的有机玻璃模型中喷吹压缩空气,改变喷吹参数(压力、流量和喷吹时间),测量喷吹前后透气砖喷孔尺寸的变化,计算喷孔的侵蚀情况(径向侵蚀速度、轴向侵蚀速度和侵蚀角),构建气体的喷吹参数与透气砖侵蚀速度之间的关系。根据喷孔尺寸、气体的喷吹参数和无量纲数(修正的弗劳德数、雷诺数和表观马赫数等),对喷吹气体进入熔池中的流动状况进行分析,如气流中气泡的当量体积和当量直径、喷吹过程中所形成的气柱高度、气泡流和喷射流的转变等。研究结果表明,透气砖喷孔的轴向侵蚀和径向侵蚀速度均随底吹供气流量提高而增大,侵蚀角受喷孔直径、气体流量的影响很小,采用直径较小的喷孔,可以提高底吹气体对熔池的搅拌效果。研究结果对复吹技术的提高具有参考意义。     

Mathematical Modeling of Fluid Flow in Bath during Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Application of the Model and Results

The mathematical model developed for the molten steel flow in the combined side and top blowing AOD refining process of stainless steel has been used to compute and analyze the flow fields of the liquid phases in the baths of the 120 t AOD converter and its water model unit with a 1/4 linear scale. The influence of the side tuyere number and the angle between each tuyere on the flows has been examined. The results demonstrate that the mathematical model can quite reliably and well model and predict the fluid flow in an AOD bath with the combined blowing. The liquid flow in an AOD converter bath with the combined blowing is resulted from the gas side blowing streams under the influence of a gas top blowing jet. The streams play a governing role on it; and the liquid in the whole bath is in active agitation and circulatory motion during the gas blowing process. The gas jet from the top lance does not change the essential features of the gas stirring and liquid flow in the bath, but can make the local flow pattern of the bath liquid obviously vary and its turbulent kinetic energy enhance. The changes in the tuyere position and number have similarly not altered the basic characteristics and patterns of the gas agitation and liquid flow and turbulent kinetic energy distribution in the bath. At a given tuyere number and gas side blowing rate or a given angular separation between each tuyere and gas side blowing rate, however, the variation of the angle between each tuyere or the tuyere number can locally change them. Using 6 tuyeres with 27° can reach the more uniform flow field and turbulent energy distribution of the liquid in the bath than taking 7 tuyeres with 18° or 22.5° and 6 tuyeres with 22.5°.     

Making blast-furnace smelting more efficient through the injection of heated natural gas

Subjecting natural gas to multi-stage heating by passing it through the cooled cavities of certain tuyere elements instead of coolant water is technically simple to accomplish and makes it possible to heat the gas to 300°C or more, the exact temperature depending on the amount of gas used. The cost of instituting this technology is an order of magnitude lower than the savings realized by injecting heated natural gas into blast furnaces. The injection of heated natural gas into a blast furnace introduces additional heat into the furnace and makes it possible to use more natural gas in the smelting process without reducing the theoretical combustion temperature. It also increases the value of the coefficient that characterizes the replacement of coke by natural gas, since the gas undergoes more complete combustion in this case. Finally, the injection of heated natural gas results in a more uniform distribution of hydrogen across the furnace and allows fuller use of this element in the smelting operation.     

A Mathematical Model of a Blast Furnace Injection Tuyere

One way to further utilise produced gases in an integrated metallurgical plant is to replace oil with gas as a reducing agent in a modern blast furnace. Accordingly, it is of great interest to study the injection of reducing gas into the blast furnace. Therefore, a three‐dimensional mathematical model has been developed which simulates the injection of the gas by lances into the tuyere. The model includes the coupled solution of the flow field and the chemical reaction of the gases in the tuyere. Two different types of fuel gas, coke oven gas (COG) and basic oxygen furnace gas (BOF) have been modelled using one injection lance. The modelling technique is presented and discussed as well as the implied results. Furthermore, process parameters such as different gas compositions etc. are investigated using the developed model. Not surprisingly, the main results show that the COG is combusted more completely than BOF gas, which leads to higher flame temperature of the blast putting demand forward to lower the heat load of the tuyere. However, the modelling of the raceway is as far not included in the model, hence the influence of the outlet boundary condition at the tuyere is not reflected in the presented results.     

Preliminary Investigation of Fluid Mixing Characteristics during Side and Top Combined Blowing AOD Refining Process of Stainless Steel

The fluid mixing characteristics in the bath during the side and top combined blowing AOD (argon‐oxygen decarburization) refining process of stainless steel were preliminarily investigated on a water model unit of a 120 t AOD converter. The geometric similarity ratio between the model and its prototype (including the side tuyeres and the top lances) was 1:4. On the basis of the theoretical calculations for the parameters of the gas streams in the side tuyeres and the top lances, the gas blowing rates used for the model were more reasonably determined. The influence of the tuyere number and position arrangement, and the gas flow rates for side and top blowing on the characteristics was examined. The results demonstrated that the liquid in the bath underwent vigorous circulatory motion during gas blowing, without obvious dead zone in the bath, resulting in a high mixing effectiveness. The gas flow rate of the main tuyere had a governing role on the characteristics, a suitable increase in the gas flow rate of the subtuyere could improve mixing efficiency, and the gas jet from the top lance made the mixing time prolong. Corresponding to the oxygen top blowing rate specified by the technology, a roughly equivalent and good mixing effectiveness could be reached by using six side tuyeres with an angle of 27 degrees between each tuyere, and five side tuyeres with an angular separation of 22.5 or 27 degrees between each tuyere. The relationships of the mixing time with the gas blowing rates of main‐tuyeres and sub‐tuyeres and top lance, the angle between each tuyere, and the tuyere number were evaluated.     

Combustion of coke and natural gas in blast furnaces with hybrid blast

The interrelated redox processes in the high-temperature lower region of a blast furnace with a hybrid blast are analyzed. Particular attention is paid to the gas composition, the thermal effects of the reactions, and the motion of solids, liquids, and gases in the hearth’s tuyere region. The rate of moisture formation from the injected natural gas and also its decomposition rate in the lower part of the furnace are studied. The composition of elementary oxygen in coke combustion is determined as a function of the degree of oxygen enrichment of the blast.     

Design and calculation of gas property parameters for constant area lance under conditions of friction flow with heating

Abstract

Formulae for calculating the outlet property parameters of gas heating and friction streams in tubular and annular type lances with constant area (tuyeres) are given, and have been applied to the case of an annular type used for an AOD (argon–oxygen decarburisation) vessel of 18 t capacity. The distributions of both the inner wall temperatures of the tuyere and the gas stagnation temperatures along its length have been more reasonably fixed. The friction factors for the gas flows through the main and subtuyeres during blowing refining have been determined by comparison of the practically measured P–Q relationships with the results from trial calculations. The outlet parameters of the gas streams for the central tube (main tuyere) and annular slit pipe (subtuyere) of the tuyere have been calculated. The influences of the gas supply pressure, the length and diameter of the tuyere, and the type and composition of the gases, as well as the heating effect, on the gas outlet parameters have been considered. The results obtained may be expected to offer useful information and a reliable basis for tuyere design and determination, control, and optimisation of the gas blowing parameters and technology, as well as for the investigation of hydraulic modelling of the blowing processes.     

Physical modeling of liquid/liquid mass transfer in gas stirred ladles

Several of the metallurgical reactions occurring in gas stirred steel ladles are controlled by liquid phase mass transfer between the metal and slag. In order to calculate the rate of these reactions, information about the two phase mass transfer parameter is necessary. The mass transfer between two immiscible liquids, oil and water simulating slag and steel, respectively, was measured in a scale model of a ladle. The mass transferred species was thymol which has an equilibrium partition ratio between oil and water similar to that for sulfur between slag and metal. The mass transfer rate was measured as a function of gas flow rate, tuyere position and size, method of injection, oil viscosity, and oil/water volume ratio. In addition, mixing times in the presence of the oil layer and mass transfer coefficient for the dissolution of solid benzoic acid rods were measured. The results show that there are three gas flow rate regimes in which the dependence of mass transfer on gas flow rate is different. At a critical gas flow rate, the oil layer breaks into droplets which are entrained into the water, resulting in an increase in the two phase interfacial area. This critical gas flow rate was found to be a function of tuyere position, oil volume, densities of two phases, and interfacial tension. Two phase mass transfer for a lance and a tuyere was found to be the same for the same stirring energy in low energy regions regardless of lance depth. Mass transfer is faster for a center tuyere as compared to an offcenter tuyere, but mixing times are smaller for the offcenter tuyere. From the results obtained, the optimum stirring conditions for metallurgical reactions are qualitatively discussed. SEON-HYO Kim, formerly Graduate Student in the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University.     

Study of solid mushroom formation in direct iron ore smelting reduction process using low temperature water model

Abstract

In the direct iron ore smelting reduction process, molten iron near the bottom blowing gas tuyere is cooled by low temperature/endothermic gas and forms a mushroom shaped solid on top of the tuyere. The formation of an appropriate solid mushroom, which covers the tuyere, can protect the tuyere and the surrounding refractory. In the present study, a water model with a low temperature gas system was established to investigate formation of the solid mushroom and the effects of operating conditions on its shape and dimensions. Transparent acrylic was used to construct the water model, which was 40% of the size of the actual furnace. Water was used to simulate the molten iron. Low temperature air, obtained by passing air through a heat exchanger cooled by liquid nitrogen, was blown into the water bath through a bottom tuyere. The air temperature was able to reach-188±1°C. In the water model experiments, water near the tuyere was cooled, and formed an ice mushroom surrounding the tuyere. The effects of operating conditions, mainly gas flowrate and mould material surrounding the tuyere, on the parameters of the solid mushroom were investigated. The parameters of the solid mushroom included whether it could be formed and duration of the solid mushroom, as well as the shape, dimensions, and weight of the solid mushroom. Attempts were also made to relate the temperature-time and pressure-time relationships of the blown gas to the parameters of the solid mushroom. With copper used as mould material surrounding the tuyere, the water model experiments were conducted with flowrate of the bottom blown gas set in the range 30-90 NL min^-1. The results show that as the gas flowrate was increased, the highest water temperature which allowed the solid mushroom to form in the water model was increased. Three different types of pressure-time curve were obtained under different gas flowrates in the present study. They also corresponded to different forms of solid mushroom. As peaks appeared in the pressure-time curve, they revealed ice capsulation and subsequent bursting to release the pressure. A gas flowrate of 80 NL min^-1 and water temperature of 19·2°C with copper plate as the bottom material are considered to be optimal conditions of the water model for growth of the appropriate ice mushroom. These data are rather consistent with the gas flowrate and superheat for the actual direct iron ore smelting reduction unit, which are 2700 NL min^-1 and 120°C (equivalent to 70 NL min^-1 and 22·7°C in the water model).     

氧气高炉炉身喷吹煤气在炉内的分布

通过二维冷态物理模型对氧气高炉炉身喷吹煤气在炉内分布进行了实验研究,分别研究了炉身煤气总量、辅助风口直径以及炉身喷吹煤气量与炉身煤气总量之比对炉身喷吹煤气在炉内分布的影响.结果表明,炉身喷吹煤气量与炉身煤气总量之比对炉身喷吹煤气在炉身分布起决定性作用,而炉身煤气总量和辅助风口直径的影响较小.同时,在炉身煤气上升过程中涡流扩散效应的影响也较小.通过对根据实验数据绘制的炉身等浓度分布图进行研究发现,炉身煤气分布主要分为两个不同的区域,一个是炉身喷吹煤气主流区,另一个是从高炉下部产生的上升煤气主流区.在炉身等浓度分布图的基础上通过回归分析的方法推导出炉身喷吹水平喷吹煤气的渗透公式.此外,辅助风口被安装在炉身下部有利于铁矿石在炉身的间接还原.      

Numerical Analysis of Pulverized Coal Combustion inside Tuyere and Raceway

The process of pulverized coal combustion inside the tuyere and raceway plays a very important role in the performance of a blast furnace. A three‐dimensional multiphase CFD model using Eulerian approach has been developed to simulate the coal devolatilization and combustion process inside tuyere and raceway. The velocity field, temperature distribution, and combustion characteristics have been determined in details and the effect of tuyere diameter on the pulverized coal combustion process has been predicted. Numerical results show that the pulverized coal combustion process displays different characteristics when the tuyere diameter changes. For a bigger diameter tuyere, there is more coal devolatilization, and combustion occurs inside the tuyere, which results in a better combustion condition compared to smaller tuyere diameters. The gas temperature distributions inside the raceway are dependent on the tuyure diameter; the temperature for the large size tuyere is higher than that of the small one. The coal burnout changes from 85.3% to 60.0% when the tuyere diameter reduces from 0.165m to 0.146 m.     

高炉风口焦炭的形貌与冶金行为

 为了研究焦炭在风口区域的劣化过程,获取高炉风口区及风口区边缘焦炭样品,利用显微分光光度计和扫描电镜对焦炭与氧化性气体、炉渣和铁水的反应界面形貌与生成物进行了检测,分析了焦炭在风口区的冶金行为。研究结果表明,氧化性气体会以消耗碳元素方式侵蚀焦炭基质,炉渣则会进入焦炭气孔和裂纹中,通过反应、冲蚀和挤压气孔壁的方式瓦解焦炭。铁水主要通过渗碳作用侵蚀焦炭,残留的灰分会覆盖气孔壁表面,阻碍化学反应进行。风口区的焦炭已经高度石墨化,呈现大量片状石墨结构,微观结构的改变导致焦炭强度降低,最终瓦解粉化。焦炭内部的灰分、炉渣颗粒会与炉渣融合,形成终渣。     

Characteristics and analyses of COG injection from tuyere in COREX melter gasifier

Coke oven gas (COG), as an environment-friendly source, is projected to be introduced into the COREX process to reduce solid fuel consumption. In this paper, a static model has been developed based on mass and heat balance, which can calculate characteristics of melter gasifier, such as the raceway adiabatic flame temperature (RAFT), volume and component of bosh gas. The results showed that compared with N2, the COG injection from tuyere is more effective on reducing the RAFT and improving the bosh gas volume. The quantity of COG injected is limited for the RAFT, and without other thermal compensation, the largest injection quantity is about 150 Nm³ t^?1. The quantity of COG injection can be increased by preheating tuyere oxygen, adjustment of fuel structure and addition of tuyere oxygen. COG injection can promote the reduction and hearth permeability, decrease the RAFT and protect the tuyere, which is beneficial to COREX operation.     

一种新型高炉风口中套压紧装置的设计与应用

针对天钢3 200 m~3高炉风口大套前端锥面与风口中套上端锥面之间煤气泄漏的问题,通过对风口装置进行结构分析和现场跟踪实测,在风口中套的另一端设计安装了一套中套压紧装置。该新型压紧装置投入使用后,保证了高炉风口装置的安全稳定运行,减少了设备损失,创造了较高的经济效益。     

COREX-3000风口破损的原因分析和对策

宝钢1#COREX-3000投产以来,风口破损较为频繁,对COREX-3000生产的稳定及产量带来了很大的影响。从COREX纯氧鼓风工艺特点、风口氧气流速、单风口熔炼率、风口通氮、出铁制度、焦炭比例和生产工况等方面进行了分析,分析结果显示,COREX风口破损的主要原因是由于风口理论燃烧温度高,风口前端焦炭和半焦粒度小,透气透液性能较差,导致风口前端氧气孔道高温熔化或磨损扩孔,出现漏水现象而破损。通过适度降低风口氧气流速和单风口熔炼率、风口添加氮气、稳定炉况和优化出铁制度可以有效减少风口破损数。