大型高炉合理煤气流的分布及控制

合理的煤气流分布是大型高炉实现操作炉型稳定和技术经济指标良好的基础.从太钢5号高炉4年多的生产实践出发,提出在下部通过控制合理的风速和鼓风动能,在上部通过逐步加大矿批,加重焦炭负荷和配以布料档位的及时调整等,煤气利用率50.5%以上和炉顶温度180℃以下.     

折流式移动流化床改质焦炉煤气预还原铁矿粉的数值模拟

 建立了折流式移动流化床内利用改质焦炉煤气进行气基粉铁矿预还原的数学模型。模型求解采用FLUENT和PHOENICS的联合求解。冷态工况的数值模拟结果和试验结果进行了比较。通过比较床层平均压降和分析气固相的流动行为,对提出的数学模型的可靠性进行了验证。利用所建立的数学模型对利用该反应器和采用改质COG(焦炉煤气)对铁矿粉预还原的工艺过程进行了热态模拟。在模拟的工况条件下,指出了反应器内分布板布置上的缺陷;反应器必须采用气体分布板振动才可以保持气固正常流动,同时保持较小的流化气速。还原气温度的整体降幅达到770K,气相还原势的利用率达到35%,矿粉的还原分数达到0.7,反映出该反应器内良好的气固换热和对还原势的利用率。该反应器在一个紧凑的结构下实现了对还原气热能和还原势的梯级利用。     

Model calculations for mass transfer with mixing in ladle metallurgy

It is well known that in secondary metallurgy during gas stirring, zones with differing degrees of homogeneity can occur in the liquid steel. By means of model calculations it will be demonstrated under which conditions mixing has to be considered for mass-transfer phenomena, as for example desulphurization. Under unfavourable conditions, i.e. large regions with low flow velocities – so-called dead zones – and low values for the exchange volume flow between these regions and the bulk volume, the equalization of concentration will become the rate-determining step for the total mass transfer. In order to avoid or minimize dead zones, the general flow pattern in the ladle has to be optimized.     

冶金用喷粉罐喷粉速率控制的冷态模拟试验

 为实现冶金用喷粉罐喷粉速率的稳定控制，通过冷态模拟试验，测定喷粉罐不同喷吹参数对罐内压力和输粉管路压力的影响规律，研究了罐内压力与输粉管路压力的差值Δp对喷粉速率的控制规律。研究结果表明，正常喷粉状态下，罐内压力主要由罐顶充压和流化气压力共同决定。输粉管路压力主要由载气流量决定，其值随载气流量的增大而增大。通过设置罐顶充压、流化气压力和载气流量的不同参数组合来改变Δp，可实现对喷粉速率的稳定控制。在载气流量相同条件下，喷粉速率随Δp的增大而增大；在Δp相同条件下，载气流量值越大，喷粉速率越大。     

Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model

Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm³/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm³/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.     

Influence of bed conditions on gas flow in the COREX shaft furnace by DEM–CFD modelling

The gas flow plays an indispensable part in the production process of direct reduction iron in the COREX shaft furnace. So as to assess the gas flow under different bed conditions which are including shapes of the bed, different particle diameters and particle motion speed, a three-dimensional model has been built. The behaviour of gas flow was investigated by a hybrid model of DEM–CFD coupling. The results show that the bed void differences which is caused by the packing way and particle diameter has an important influence on the gas flow and the shaped bed of ‘V’ is the better choice to provide the optimal gas flow in the packed bed. When the descend velocity is 1 or 2?m?h^?1, it has little impact on the gas flow in the packed bed, and we can think that the bed is static.     

直接碳化法制备碳化钒的热力学分析

对以五氧化二钒为原料制备碳化钒的工艺过程进行热力学分析,分析结果表明:钒氧化物在转化过程中遵循逐级还原理论;钒氧化物在碳化过程中,不转化为金属钒,直接转化为碳化钒;二氧化钒的碳化温度最低,为1018K,因此,在钒氧化物的转化过程中,应尽可能使其转化为二氧化钒。若采用气相还原碳化的方法,则可通过调节气体的流量、配比对还原碳化工艺进行控制。     

Steel dissolution in quiescent and gas stirred Fe/C melts

The dissolution rates of commercial black iron rods in iron/carbon melts under isothermal conditions were measured. The effect of melt carbon content, temperature, natural convection, and gas stirred forced convection conditions were investigated. The experimental data under natural convection conditions (no external stirring) were fitted with a dimensionless correlation for vertical cylinders: Sh = 0.13(Gr . Sc)^0.34, representing mass transport control dominated by turbulent natural convection. Under bottom injection gas stirring conditions, it was found that the kinetic power input had little effect on the rod dissolution rates which were controlled by the total gas flow rate. Derived mass transport coefficients under gas stirring conditions were found to have the following dependence on the gas injection rates:k _m ∝Q ^0.21, wherek _m = mass transport coefficient andQ = gas flow rate. A comparison of the experimental results with previously measured mass transfer coefficients under forced convection conditions gave a plume velocity flow rate dependence ofU ∝Q ^0.3. A general discussion of gas stirring fluid dynamics and resulting mass transport effects is presented.     

RH喷吹参数对循环流量和均混时间影响的物理模拟

以某厂300tRH真空精炼装置为研究原型,建立1∶6.5的水力模型对RH喷吹精炼工艺进行物理模拟。研究了喷吹位置、喷吹气量及驱动气体流量对循环流量和均混时间的影响。结果表明:不同喷吹气量、驱动气体流量条件下,获得大循环流量和短均混时间的最优喷吹位置不同。较小的喷吹气量(2.98~3.53m3/h)或者较小的驱动气体流量(0.93~1.02m3/h)时,宜采用低顶枪枪位(153.8mm)喷吹;喷吹气量大于3.91m3/h或者驱动气体流量大于1.12m3/h时,宜采用真空槽底部喷吹角度120°的侧喷嘴喷吹。顶枪与侧喷嘴复合喷吹有利于提高RH喷吹工艺的适应性及循环效率。     

气体雾化制粉工艺中基于气体整流的卫星粉控制技术

金属熔体气体雾化法是制备增材制造专用金属粉末的重要方法。然而,气体雾化工艺制得的粉末中通常混有大量卫星粉,对金属增材制造工艺产生不利影响。本文通过施加辅助气流并采用阶梯状雾化室结构等气体整流措施抑制回流区中的粉尘回旋,进而控制卫星粉的形成。利用计算流体力学软件ANSYS Fluent进行数值模拟,研究施加辅助气流或采用阶梯状雾化室结构时,雾化室内宏观流场特征以及颗粒运动轨迹的变化规律。结果表明,在雾化室顶部距雾化室中心R/2（R为雾化室半径）处施加辅雾比（辅助气流与雾化气流的流量比）大于0.8的辅助气流时能够有效抑制回流区中的粉尘回旋;采用阶梯宽为300 mm、高为575～600 mm的雾化室结构能够有效抑制回流区中的粉尘回旋。根据数值模拟结果,采用气体整流措施制备TC4钛合金粉末,并检测粉末的粒径分布、球形度、赘生物指数等指标,发现与不采用气体整流措施制备的粉末相比,赘生物指数降低约45%。     

高炉中心加焦制度下煤气流速度与压力场模拟

不同的布料制度决定炉料的分布状态与不同部位炉料孔隙度的大小,进而影响煤气流在炉内的速度与压力分布,而煤气流的分布直接影响高炉顺行、煤气流利用率与料柱透气性的优劣.为促进煤气流合理分布,进一步探索高炉在中心加焦条件下炉内不同部位的煤气流速与压力变化规律,借助数值模拟方法,建立二维高炉煤气流流动物理模型,基于多孔介质算法并...     

Prediction of temperature in secondary steelmaking: mathematical modelling of fluid flow and heat transfer in gas purged ladle

As a first step towards prediction of temperatures in secondary steelmaking, mathematical modelling of fluid flow and heat transfer in ladle furnace was undertaken. A two‐dimensional quasi‐single phase model has been developed for turbulent recirculating flow by solving Reynolds averaged Navier‐Stokes equations along with a two‐equation k‐? model. The model was then extended to include thermal transport in a conjugate domain (i.e., molten steel + refractory shell + steel shell). The flow model was validated with water model data reported in literature by different researchers. Good agreement for velocity field and satisfactory agreement for turbulent kinetic energy field were obtained. The thermal model showed good agreement with results predicted in literature. The paper also presents findings of tests for sensitivity of flow on modelling and process parameters. By comparison with water model experiments, it has been demonstrated that the flow field in a ladle with a porous plug can be represented using a gas voidage fraction in the plume obtained from experiments with nozzles for axial gas injection from the bottom. Flow and thermal fields were insensitive to initial turbulence level at nozzle. Maximum temperature inhomogeneity in the melt was 2 °C after 1.5 min and negligible after 3 min of onset of gas purging.     

Experimental studies on the bath oscillation during gas blowing into liquids,part 2: measurements in a converter model

Experimental studies on the wave motion during gas blowing into liquid iron in a converter model were carried out on the systems water/air and Wood's alloy/nitrogen under various blowing conditions. Variables of the measurement were the gas flow rate and the configuration of nozzles. The measured results showed that a wave motion appears only if the gas flow rate exceeds a critical value which depends on the nozzle configuration. The blowing conditions for wave formation can be characterized by the relation of the bath depth to the vessel diameter and by the gas flow rate. The frequency or the oscillation period of the wave is independent of the gas flow rate. The amplitude of the wave follows a logarithmic function of gas flow rate.     

Bubble Formation at a Submerged Orifice for Aluminum Foams Produced by Gas Injection Method

The bubble formation at a submerged orifice in the process of aluminum foams produced by gas injection method is investigated. The experimental results show that the increase of the gas flow rate and the orifice diameter can lead to increasing of the bubble size. The large orifice can make the frequency of bubble formation decrease by slowing down the increase of the gas chamber pressure when the gas flow rate increases. The effect of the gas chamber volume on the bubble size can be ignored in the experiment when it expands from 1 to 125 cm³. A theoretical model of bubble formation, expansion, and detachment under constant flow conditions is established to predict the bubble size. The theoretical predictions for air-aluminum melt systems are consistent with the experimental results.     

碳热FeO反应过程的控速环节分析

为了探讨煤基还原FeO在试验过程可能出现的控速环节,分多种条件进行了理论计算及分析。在不考虑传热条件下(加热方向物料很薄时),同一种还原剂在不同的温度段表现出不同的控速环节。气煤作为还原剂时,1 273 K以下碳的气化反应为控速环节,1 273~1 523 K为混合控速;温度超过1 523 K,则CO还原FeO转为反应的控速环节。不同煤种在同一温度下,可能表现出不同的控速环节。如1 373 K,气煤作为还原剂时,碳气化与FeO间接还原混合控速,而兰炭作为还原剂时,碳气化为控速环节。煤粉粒度与FeO粒度之比不同会使控速环节发生变化。如果物料厚度小于1 mm,则可忽略传热影响;如果物料厚度不小于4 mm,则传热将成为限制性环节;如果试验时的物料厚度介于两者之间,就有可能出现传热与反应混合控速情况。     

Reduction of Iron Oxide Fines to Wustite with CO/CO<Subscript>2</Subscript> Gas of Low Reducing Potential

The reduction of iron oxide fines to wustite between 590 °C and 1000 °C with a CO–CO₂ gas mixture of low reducing potential was studied. The reduction kinetics and the dominating reaction mechanism varied with the temperature, extent of reduction, and type of iron oxide. Reduction from hematite to wustite proceeded in two consecutive reaction steps with magnetite as an intermediate oxide. The first reduction step (hematite to magnetite) was fast and controlled by external gas mass transfer independently of the oxide type and the temperature employed. The second reduction step (magnetite to wustite) was the overall reaction-controlling step, and the reduction mechanism varied with the temperature and the oxide type. Moderately porous oxide fines followed the uniform internal reaction for the temperature range studied. For highly porous oxides, the second reduction step was controlled by external gas mass transfer above 700 °C. Below that temperature, a mixed regime that involves external gas mass transfer and limited mixed control, which comprises pore diffusion and chemical reaction, takes place. The rate equations for this mixed control reaction mechanism were developed, and the limited mixed control rate constant (k_lm) was computed. For denser oxides under uniform internal reaction, the product of the rate constant and pore surface area (k·S) was calculated.     

Influence of the Stirring Gas in a 170‐t Ladle on Mixing Phenomena – Formation and On‐line Control of Open‐Eye at an Industrial LD Steel Plant

3D calculations with Computational Fluid Dynamics were carried out to evaluate the flow pattern under industrial conditions with different gas flow rates at the steel plant of Saarstahl AG. The generated flow pattern consists of a circulating loop characterised by an upward flow driven by the argon gas and a downward flow close to the wall on the opposite side of the porous plug in the case of a gas flow rate of 27 STP m³/h. When this high gas flow rate is used, the gas bubbles are taking a straight way from the inlet, but further up the momentum from the circulating steel is affecting the path of the gas bubbles followed by a breakthrough zone at the top surface. Intensive experiments with the 170‐t ladle of Saarstahl AG revealed typical open‐eyes. Large open‐eyes coupled with turbulences in the surface were generated in the case of gas flow rates between 20 and 30 STP m³/h. Intensive turbulences and even smoke formation were identified when a gas flow rate of > 30 STP m³/h was applied. For the investigation of the influence of gas stirring processes on the mixing phenomena samples were taken from the melt immediately after alloying. It could be seen that the analyses of Al, C, Mn and Si increased to the target analyses due to alloying and introduction of Ar through the porous plug. The total time for complete alloying depended on the elements within these experiments. It seemed to be that the alloying time increased in the order of Al, C, Mn and Si. For on‐line control and analysis of open‐eyes in the melt surface during ladle stirring, a BFI image processing system was installed at the steel plant of Saarstahl. It consisted of a conventional digital camera equipped with an infrared filter and coupled to an image processing software. Primary tests showed a slight influence of the open‐eye diameter at the end of the ladle treatment on inclusion densities in the liquid steel and oxidic K0 values of the finished wire rod. Additional experiments were performed but only a small correlation existed between the stirring energy at the end of ladle treatment and the inclusion length index of the applied blue brittle tests. But as soon as an open‐eye came into existence, the inclusion length was higher compared to those heats produced under a closed top slag.     

5kA级惰性阳极铝电解槽流场仿真研究

针对铝电解槽流场计算方法的不足,率先提出一种用于铝电解槽流场仿真计算的间接耦合方法,并使用此方法对5 kA级惰性阳极铝电解槽分别在电磁力、阳极气体、电磁力和阳极气体共同作用下的电解质和铝液流场分布情况进行了仿真计算。计算表明,计算方法能够合理计算出电解质和铝液在任一体积力作用下的流场分布。5 kA级惰性阳极铝电解槽电解质流动主要受阳极气体控制,铝液流动主要受电磁力控制。电解质在仅电磁力作用、仅阳极气体作用、电磁力和阳极气体共同作用下的平均流速分别为1.784 cm/s、3.657 cm/s、3.814 cm/s,铝液平均流速分别为1.295 cm/s、3.509 cm/s、3.696 cm/s。     

Kinetics of oxidation of carbon in liquid iron-carbon-silicon-manganese-sulfur alloys by carbon dioxide in nitrogen

The oxidation of carbon with the simultaneous oxidation of silicon, manganese, and iron of liquid alloys by carbon dioxide in nitrogen and the absorption of oxygen by the alloys from the gas were studied using 1-g liquid iron droplets levitated in a stream of the gas at 1575 °C to 1715 °C. Oxidation of carbon was favored over oxidation of silicon and manganese when cast iron (3.35 pct C, 2.0 pct Si, 0.36 pct Mn, and 0.05 pct S) reacted with CO₂/N₂ gas at 1635 °C. An increase in the flow rate of CO₂/N₂ gas increased the decarburization rate of cast iron. The rate of carbon oxidation by this gas mixture was found to be independent of temperature and alloying element concentrations (in the range of silicon = 0 to 2.0 pct manganese = 0 to 0.36 pct and sulfur = 0 to 0.5 pct) within the temperature range of the present study. Based on the results of a kinetic analysis, diffusion of CO₂ in the boundary layer of the gas phase was found to be the rate-limiting step for the reactions during the earlier period of the reaction when the contents of carbon, silicon, and manganese are higher. However, the limiting step changed to diffusion of the elements in the metal phase during the middle period of the reaction and then to the diffusion of CO in the gas phase during the later period of the reaction when the content of the elements in the metal were relatively low. For the simultaneous oxidation reactions of several elements in the metal, however, the diffusion of CO₂ in the gas phase is the primary limiting step of the reaction rate for the oxidation of carbon during the later period of reaction. Formerly Visiting Assistant Research Scientist, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109