Modeling studies of fluid flow below flash-smelting burners including transient behavior

Water-model experiments were carried out on 1:14-scale models of venturi, distributor, and jet-flow burners to ascertain flow patterns at varying Reynolds numbers (60,000 to 507,000) using time-lapse streak photography and video streak photography. Digital particle image velocimetry (DPIV) was used to determine the axial and radial velocities and to estimate the turbulence kinetic-energy field beneath the distributor burner. In the DPIV experiments, a temporal instability in the main jet exiting from the burner occurred at a Reynolds number=104,000, a Strouhal number≈3×10⁻³, and a large expansion ratio (shaft/burner-diameter ratio=10). The main jet usually pointed away from the burner inlet but was also observed to fluctuate and precess in a quasi-random fashion. Recom-mendations are made for improving flash-smelting burner performance by promoting conditions to eliminate precessing. The use of higher Reynolds numbers was recommended to improve both the use of shaft volume and the mixing of the concentrate particles and gas stream. A three-dimensional (3-D) mathematical model was used to simulate the water flow through the distributor burner, shaft, and settler. The predicted velocity field consisted of a main jet pointing away from the burner inlet and a large recirculation zone in the center of the shaft. The predicted and measured velocity magnitudes compared well in the recirculation zone, but the steady-state mathematical model predicted higher velocity values in the main jet than were experimentally determined.     

Evaluation of nickel flash smelting through piloting and simulation

An extensive study of the nickel flash smelting process has been undertaken. It is aimed at the optimization of the burner design to improve the smelting performance and to increase the throughput of the rebuilt furnace. A design-based mathematical model was developed to simulate the operation of the four burners and the reaction shaft of the flash furnace at Western Mining Corporation Ltd.’s Kalgoorlie Nickel Smelter. A modified single burner version of the model was validated against data obtained from the pilot plant at the Pyrometallurgical Research Centre (PRC) of the Sumitomo Metal Mining Co.’s Toyo Smelter. The approach taken involved experimental measurements of key process parameters in the pilot plant and detailed numerical simulation of the fluid flow, heat transfer, and combustion in the entire burner-shaft complex. Several burner designs have been tested experimentally at the pilot plant and theoretically through computer simulation. The main outcome of the study was the development of an experimentally validated mathematical model of the flash smelter providing a new powerful design tool. The insight gained about the process from the application of this tool led to the design of a more efficient nickel flash smelting process.     

The trajectories and distribution of particles in a turbulent axisymmetric gas jet injected into a flash furnace shaft

Numerical computations have been performed for the behavior of a vertical turbulent particle-laden gas jet exemplified by the shaft region of a flash-smelting furnace. The two-equation(k-ε) model was used to describe turbulence. Model predictions for the gas and solid flow fields give a satisfactory representation of experimental data taken from the literature. The predictions of flow properties of the two phases under flash-smelting conditions have been obtained for various inlet conditions, particle sizes, particle loading, and oxygen enrichment. Model predictions show that the axial velocity of the particle phase is substantially higher than that of the gas phase. The presence of solid particles causes the axial velocity of the gas phase to be greater near the centerline and lower in the outer region than in a single-phase gas jet. A more uniform distribution of particles was obtained by introducing a strong radial velocity of the distribution air at the inlet. The implications of the behavior of a particle-laden gas jet on flash-smelting processes arc discussed.     

铜闪速熔炼精矿喷嘴性能的数值仿真分析

通过对现有精矿喷嘴工作特性的分析,提出了新喷嘴设计结构,包括精矿喷嘴分散锥曲面及上方吊柱结构的改进和在下料管出口上部增加旋流叶片。以FLUENT 6.3为计算平台,建立了用于分析喷嘴性能的数值模型,在相同条件下对新喷嘴和CJD喷嘴结构下的闪速熔炼过程进行仿真计算。结果表明:新喷嘴结构条件下,反应塔内气粒分散更为均匀,颗粒的反应速度较快,氧气利用率相对更高,反应塔正下方沉淀池气相空间内形成的气流回流强度较小,因而对炉体冲刷较小。     

空燃比对平焰燃烧特性影响的冷态实验

 为研究加热炉内平焰烧嘴下方燃烧速度场的主要机理,采用相似和模化理论建立了冷态实验模型。应用粒子激光测速(PIV)技术对旋流强度为176、空燃比分别为1368、1939、2167的烧嘴下方的湍流速度场进行了测量,得到了主燃烧区域速度场的分布特性,并分析了空燃比对速度场的影响规律,得到了回流区顶部宽度、径向速度最大值出现的位置随空燃比的变化趋势,同时也得知径向速度最大值、轴向速度最大值均随着空燃比的增大而增大。首次得出不同空燃比下速度分量的最大值沿射流长度衰减的无因次曲线。     

大型蓄热式环形加热炉冷态流场试验分析

 根据模化理论,针对某大型高炉煤气双蓄热式环形加热炉,按照10∶1的比例建立了实物模型。根据二维PIV测试技术的原理,用高速摄像仪对各加热段炉膛进行示踪粒子拍摄和速度分布测量。研究发现从烧嘴喷出的气流,一般不会从正对的第一个吸风口吸出,越靠近均热段的喷口气流越不容易被最近的排烟口排出,从而延长了炉气在炉内的停留时间,避免了烟气短路;炉膛截面速度变化较大,距离烧嘴口越远,截面上速度越平缓;在一定的气流喷射角度下,喷嘴口两侧有气流旋涡产生;流量越大,气流越容易到达对侧炉墙。     

Mathematical modeling of sulfide flash smelting process: Part I. Model development and verification with laboratory and pilot plant measurements for chalcopyrite concentrate smelting

A mathematical model has been developed to describe the various processes occurring in a flash furnace shaft. The model incorporates turbulent fluid dynamics, chemical reaction kinetics, and heat and mass transfer. The key features include the use of thek-ε turbulence model, incorporating the effect of particles on the turbulence, and the four-flux model for radiative heat transfer. The model predictions were compared with measurements obtained in a laboratory flash furnace and a pilot plant flash furnace. Good agreement was obtained between the predicted and measured data in terms of the SO₂ and O₂ concentrations, the amount of sulfur remaining in the particles, and the gas temperature. Model predictions show that the reactions of sulfide particles are mostly completed within about 1 m of the burner, and the double-entry burner system with radial feeding of the concentrate particles gives better performance than the singleentry burner system. The model thus verified was used to further predict various aspects of industrial flash furnace operation. The results indicate that from the viewpoint of sulfide oxidation, smelting rate can be substantially increased in most existing industrial flash furnaces. Formerly Graduate Student, Department of Metallurgical Engineering, University of Utah.     

闪速炉水冷上升烟道的CFD数值仿真

根据闪速炉水冷上升烟道的流动和传热现象,建立三维仿真模型,借助计算流体动力学分析软件FLUENT对其进行数值仿真研究。所得结果对闪速炉水冷上升烟道的设计具有重要的指导意义。     

闪速炉设计优化和改造

为提高闪速炉冶炼能力,金隆公司根据生产实践,结合仿真和模型技术研究成果,对闪速炉反应塔和精矿喷嘴进行了优化设计和改造,取得良好效果,闪速炉生产能力大幅提高。     

Experimental and theoretical study of particle dispersion phenomena in a turbulent gas jet of the flash-smelting process by the image analysis technique

The particle dispersion phenomena in a turbulent gas jet of the flash-smelting process have been investigated. The particle number density in a nonreacting jet was measured experimentally by taking photographs of the particles in flight and counting them using the image analysis technique. Numerical computations were also performed using a mathematical model for a turbulent particle-laden gas jet. The experimental particle number density data were then compared with the predicted results of the model. Good agreement was obtained between the experimental and predicted data. The effects of the parameters such as the injector design, particle loading, and air flow rate are discussed. Optimization of the concentrate burner design can be achieved with the help of experimental and theoretical simulations as performed in this work. YUTAKA YASUDA, formerly Graduate Student, Department of Metallurgical Engineering, University of Utah.     

铜闪速炉悬浮熔炼反应过程机理的研究(Ⅱ)——粒子脉动碰撞模型

在总结前人闪速熔炼反应模型——粒子分裂模型和两粒子碰撞模型的基础上,根据对金隆闪速炉反应塔工艺物料颗粒高温急冷试样的分析结果,通过从微粒运动学、两相流体力学以及统计分析和归纳等方面的论证,提出了闪速熔炼过程反应模型——粒子脉动碰撞模型(简称PPC Model),认为:在闪速炉反应塔不同高度上,精矿粒子的分裂和颗粒群内粒子脉动碰撞过程同时存在;精矿粒子脉动是粒子碰撞聚合主要原因;随着氧化反应的进行,在颗粒中心形成熔融硫化物和SO_2气泡,颗粒外表面是多孔的氧化铁壳;熔融核中气相的生成促使粒子分裂和脉动,当地氧气浓度和温度越高,这一过程越强烈;反应塔中由于粒子的大小、粒子的成分、粒子的周围的氧气浓度和粒子温度的不同,导致各粒子之间的氧化程度差别极大;过氧化粒子在反应塔中下降时,它们彼此之间、或者与反应慢的欠氧化粒子相碰撞,聚合长大,同时过氧化颗粒被欠氧化粒子还原。     

Confinement Effects in Shallow-Water Jets

This paper documents measurements of the mean velocity field and turbulence statistics of an isothermal, round jet entering a shallow layer of water. The lower boundary of the jet was a solid wall and the upper boundary a free surface. The jet axis was midway between the solid wall and the free surface in all cases. Experiments were performed at a Reynolds number of 22,500 for water layer depths 15, 10, and 5?times the jet exit diameter (9?mm). Particle image velocimetry measurements were made on vertical and horizontal planes—both containing the axis of the jet. The measurements were taken from 10 to 80 jet diameters downstream. Results showed that, for the highly confined cases at downstream locations, the axial velocity was quite uniform over the depth, with a mild peak below the jet axis. In the horizontal plane, the velocity profiles were slightly narrower than the free jet profile, but in the vertical plane, they were wider. The mean vertical velocity profiles showed that entrainment was suppressed in the vertical direction. At the same time, the lateral velocity profiles indicate that fluid flows from the sides toward the jet centerline. For the shallow cases, the mean vertical velocity becomes negative over most of the depth at downstream locations, indicating that this inflow from the sides is directed downward toward the solid wall. The relative turbulence intensity results were suppressed in the axial and vertical directions and mildly enhanced in the lateral direction. As well, the Reynolds shear stress in the vertical plane was significantly reduced by the vertical confinement, while in the horizontal plane it was only slightly affected by the confinement.     

Experiments on Vertical Turbulent Plane Jets in Water of Finite Depth

Detailed experiments on vertical turbulent plane jets in water of finite depth were carried out in a two-dimensional water tank. The jet velocities were measured with a laser Doppler velocimeter (LDV). The LDV measurement covers the entire flow regime: the zone of flow establishment (ZFE), the zone of established flow (ZEF), the zone of surface impingement (ZSI), and the zone of horizontal jets (ZHJ). From the experimental results, the following conclusions are reached. First, the jet flow is independent of the Reynolds number if the Reynolds number is sufficiently large to produce a turbulent jet. Second, in the initial ZFE, the jet flow is nonsimilar and is characterized by the two free shear layers along the two edges of the jet orifice. Third, the jet flow in ZEF is self-similar. Both mean and fluctuation velocities are scaled with the mean jet centerline velocity. The turbulent shear stress is predictable by Prandtl's third eddy viscosity model. The spreading of the confined vertical jets is larger than that of a free jet, so is the faster decay of jet centerline velocity. Fourth, in ZSI the jet flow is nonsimilar and high turbulent intensities were found. The vertical turbulent jet transforms into two opposite horizontal surface jets after the impingement. And finally, the maximum velocity of the horizontal surface jet in ZHJ decays according to a power law.     

Dynamics of Air Flow in Sewer Conduit Headspace

Pressurization in sanitary sewer conduit atmosphere is modeled using computational fluid dynamics techniques. The modeling approach considers both turbulent and laminar flow regimes. The turbulent model takes into consideration the turbulence-driven secondary currents associated with the sewer headspace and hence the Reynolds equations governing the air flow field are closed with an anisotropic closure model which comprises the use of the eddy viscosity concept for the turbulent shear stresses and semiempirical relations for the turbulent normal stresses. The resulting formulations are numerically integrated. The turbulent model outputs are verified with experimental data reported in the literature. Satisfactory agreement is obtained between numerical simulations and experimental data. Mathematical formulas and curves as functions of longitudinal pressure gradient, wastewater velocity, and sewer headspace geometry are developed for the cross-sectional average streamwise velocity.     

Mathematical simulation and physical modeling of unsteady fluid flows in a water model of a slab mold

Fluid flow of water in a model of a slab caster has been simulated using the large eddy simulation (LES) computational approach, and the simulated results are compared with experimental measurements performed using digital particle image velocimetry (DPIV) techniques. Simulation results agree acceptably well with the experimental measurements of instantaneous velocity fields. Flow patterns change with time as a consequence of the vertical oscillation of the jet core. These oscillations are originated by the residual Reynolds stresses that characterize turbulent flows. The asymmetry of fluid flows caused by these stresses provides biased flows. Thus, turbulence originates natural biasing effects without the influence of other operating factors such as the slide gate opening, gas bubbling, or inclusions clogging of the submerged entry nozzle (SEN). Instantaneous velocities follow periodical behaviors with time whose frequencies increase with increases of flow rate of liquid. Periodical flow changes originate velocity spikes, at some given casting speed, which are physically and mathematically identified. These sudden changes of fluid velocities are responsible of unsteady phenomena associated with fluid dynamics during steady operations of the mold.     

水口结构对连铸结晶器内钢水流动的影响

采用雷诺平均（RANS）数学模拟方法,研究波浪形和山形水口底部结构对结晶器内钢水湍流现象及表面流速的影响。通过1∶1结晶器模型水模拟进行了验证,表明采用OA光纤测速仪对结晶器表面流速测量的结果和数值模拟结果吻合较好。研究表明波浪形水口可以抑制水口流出钢水的射流,改善结晶器内钢水流场,降低表面流速稳定液面,进而改善铸坯表面质量。     

Transient Turbulent Flow in a Liquid-Metal Model of Continuous Casting,Including Comparison of Six Different Methods

Computational modeling is an important tool to understand and stabilize transient turbulent fluid flow in the continuous casting of steel to minimize defects. The current work combines the predictions of two steady Reynolds-averaged Navier–Stokes (RANS) models, a “filtered” unsteady RANS model, and two large eddy simulation (LES) models with ultrasonic Doppler velocimetry (UDV) measurements in a small-scale liquid GaInSn model of the continuous casting mold region fed by a bifurcated well-bottom nozzle with horizontal ports. Both mean and transient features of the turbulent flow are investigated. LES outperformed all models while matching the measurements, except in locations where measurement problems are suspected. The LES model also captured high-frequency fluctuations, which the measurements could not detect. Steady RANS models were the least accurate methods. Turbulent velocity variation frequencies and energies decreased with distance from the nozzle port regions. Proper orthogonal decomposition analysis, instantaneous velocity patterns, and Reynolds stresses reveal that velocity fluctuations and flow structures associated with the alternating-direction swirl in the nozzle bottom lead to a wobbling jet exiting the ports into the mold. These turbulent flow structures are responsible for patterns observed in both the time average flow and the statistics of their fluctuations.     

Characteristics of Shear Layer Structure in Skimming Flow over a Vertical Drop Pool

The characteristics of shear layer structure between the sliding jet and the pool for skimming flows over a vertical drop pool were investigated experimentally, using flow visualization technique and high speed particle image velocimetry. Four series of experiments having different end sill ratios (h/H = 0.12, 0.43, 0.71 and 1.0, where h=end sill height and H=drop height) with various approaching flow discharges were performed to measure the detailed quantitative velocity fields of the shear layer. The mean velocities and turbulence properties were obtained by ensemble averaging the repeated measurements. From the velocity profiles, it is found that the growth of the shear layer in the downward direction as the jet slides down the pool represents the momentum exchange. Analyzing the distribution of measured velocity, the similarity profile of the mean velocity at different cross sections along the shear layer was obtained. The proposed characteristic scales provided unique similarity profiles having promising regression coefficient. The selection of these characteristic scales is also discussed. Further, the spatial variations of mean velocity profiles, turbulence intensities, in-plane turbulent kinetic energy, and Reynolds shear stress were also elucidated in detail. The imperative observation is that the Reynolds shear stress dominates the major part along the shear layer as compared to the viscous shear stress. The study also provides an insight into the flow phenomena through the velocity and turbulent characteristics.     

聚合射流流场的仿真模拟

 为研究有低密度伴随的聚合射流氧枪射流流场,利用氧枪射流检测系统,对常温下(冷态)以空气模拟的射流进行了物理模拟。结合数值模拟结果,分析了传统无伴随流射流以及带有副孔氦气低密度伴随情况下射流流场的流动状态,讨论了在不同的滞止压力和环境温度时有、无伴随射流流场特性。结果表明,修正的k ε双方程模型能较好地预测实验结果,伴随流的存在减缓了中心射流的沿程衰减,环境温度的变化影响射流在径向和轴向的流动状态。     

Computational Fluid Dynamics Simulation of Supersonic Oxygen Jet Behavior at Steelmaking Temperature

Supersonic oxygen jets are used in steelmaking and other different metal refining processes, and therefore, the behavior of supersonic jets inside a high temperature field is important for understanding these processes. In this study, a computational fluid dynamics (CFD) model was developed to investigate the effect of a high ambient temperature field on supersonic oxygen jet behavior. The results were compared with available experimental data by Sumi et al. and with a jet model proposed by Ito and Muchi. At high ambient temperatures, the density of the ambient fluid is low. Therefore, the mass addition to the jet from the surrounding medium is low, which reduces the growth rate of the turbulent mixing region. As a result, the velocity decreases more slowly, and the potential core length of the jet increases at high ambient temperatures. But CFD simulation of the supersonic jet using the k−ε turbulence model, including compressibility terms, was found to underpredict the potential flow core length at higher ambient temperatures. A modified k-ε turbulence model is presented that modifies the turbulent viscosity in order to reduce the growth rate of turbulent mixing at high ambient temperatures. The results obtained by using the modified turbulence model were found to be in good agreement with the experimental data. The CFD simulation showed that the potential flow core length at steelmaking temperatures (1800 K) is 2.5 times as long as that at room temperature. The simulation results then were used to investigate the effect of ambient temperature on the droplet generation rate using a dimensionless blowing number.