填充床中气体流动特性的数值研究

以SIMPLE算法编制了数值求解描述填充床内气体运动规律的Ergun方程的程序,就不同的气体入口设置高度、不同的气体流入床层方式、不同床层结构计算了填充床内的速度场和压力场。结果表明：只要入口距出口足够远,出口及与其相连的床层内大部分区域的流场在不同气体流入方式下是相同的,通过模拟计算获得的对进风口设置高度的认识、非均匀床层中气体流动规律的认识对高炉工艺有借鉴意义。     

A cold model study of raceway hysteresis

The effect of a gas flow field on the size of raceway has been studied experimentally using a two-dimensional (2-D) cold model. It is observed that as the blast velocity from the tuyere increases, raceway size increases, and when the blast velocity is decreased from its highest value, raceway size does not change much until the velocity reaches a critical velocity. Below the critical velocity, raceway size decreases with decreasing velocity but is always larger than that for the same velocity when the velocity increased. This phenomenon is called “raceway hysteresis.” Raceway hysteresis has been studied in the presence of different gas flow rates and different particle densities. Raceway hysteresis has been observed in all the experiments. The effect of liquid flow, with various superficial velocities, on raceway hysteresis has also been studied. A study of raceway size hysteresis shows that interparticle and particle-wall friction have a very large effect on raceway size. A hypothesis has been proposed to describe the hysteresis phenomenon in the packed beds. The releance of hysteresis to blast furnace raceways has been discussed. Existing literature correlations of raceway size ignore the frictional effects. Therefore, their applicability to the ironmaking blast furnace is questionable.     

高炉内渣铁焦界面润湿行为研究现状及展望

 高炉作为目前世界上最大的移动床式冶金反应器,保持高炉内良好的透气透液性是保证高炉稳定顺行的关键。高炉内部被软熔带分割开来,分为上部固体散料区和下部固液共存区,下部的固液共存区是决定高炉透气透液性和煤气流分布的重要区域,因此若想明晰高炉影响透气透液性的关键,必须对高炉下部固液共存区的反应进行全面研究。高炉高温区焦炭床与渣铁的相互作用行为是决定铁-焦-渣交互作用及高炉透气透液性的重要因素,调控好液态渣铁与焦炭床的润湿性变化,可以有效改善高炉内部的透气透液性,最终会影响高炉生产效率和稳定性。因此,明晰高炉内渣铁焦的界面润湿行为显得尤为重要。首先对界面润湿现象进行了概述;然后详细从铁水成分以及焦炭性质对铁-焦界面润湿行为的影响进行了总结;其次详细分析了炉渣温度、炉渣成分以及焦炭自身性质对渣-焦界面润湿行为的影响。结果表明,目前高炉内渣铁焦界面润湿行为的研究已经从实验室试验以及基础模拟方面进行了研究,研究结果可为高炉操作者理解高炉内渣铁焦界面润湿行为提供初步理论指导,但仍需在可反映高炉内实际复杂情况的润湿行为变化方面进行深入研究。     

Numerical Study of Gas‐Solid Flow in the Raceway of a Blast Furnace

This paper presents a numerical study of gas‐solid flow in a blast furnace raceway using a 2D slot cold model. Numerical experiments are conducted by combining the discrete element method for the solid phase with computational fluid dynamics for the gas phase. The motion of particles caused by lateral gas blasting under conditions similar to that in the blast furnace process is examined at a particle scale. Combustion and associated solids movement around the raceway are simulated by extraction of particles from the bottom of the bed. The effect of bed height or solid pressure is considered by imposing a downward force on the top layers of particles in the bed. It is shown that depending on the gas velocity, the bed can transit from a fixed bed to a fluidized bed or vice versa. Two zones can be identified in such a bed: a stagnant zone in which the particles remain at their initial positions, and a moving zone in which particles can move in various flow patterns. In particular, if the gas velocity is in a certain range, the moving zone is formed just in front of the gas inlet, giving the so‐called raceway in which the particles can circulate. The effects of gas velocity, solid pressure and solid extraction are quantified. The fundamentals governing the gas‐solid flow and the formation mechanisms of a raceway are discussed in terms of particle‐particle and particle‐fluid interaction forces.     

Modeling the discontinuous liquid flow in a blast furnace

This article presents a mathematical model to describe the discontinuous flow of an isothermal liquid in packed beds, simulating in part the flow condition in and below the blast furnace cohesive zone. The model is developed based on a force balance approach to describe the discrete liquid flow and a stochastic treatment to take into account the complex packing structure. The interaction between gas and liquid flows has also been included in the governing equations, so that the localized liquid flow in a packed bed can be modeled with or without gas flow. The difference between the microscopic and macroscopic approaches is discussed, and it is argued that at this stage of development, liquid flow modeling should be conducted at the macroscopic level. Techniques for numerical solution are provided. The validity of the proposed model is demonstrated by comparing model predictions with measurements obtained using a two-dimensional cold model apparatus under different gas and/or liquid flow conditions.     

Calculation and Analysis of Liquid Holdup in Lower Blast Furnace by Model Experiments

A hydromechanics experiment on the countercurrent flow of gas and liquid simulating the flow conditions in the lower blast furnace was carried out. A cold model of a packed bed with various packing materials and liquids was used to study the holdup of liquid. Correlations for static holdup, dynamic holdup, and total holdup were obtained. A good agreement was found between the calculated and experimental data. A mathematical model simulating the flow fields was applied to study the effect of liquid holdup in blast furnace. The results of the model calculation show that static holdup is the determinant of the total holdup of molten materials when the blast furnace works in stable condition. The slag phase generally reaches flooding holdup ahead of the hot metal. The radial distribution of gas flow is almost not influenced by the holdup of molten materials, but it has a greater influence on the pressure drop. The size of coke has far greater influence on static holdup than liquid properties does. The study is useful for acquiring a deeper understanding of the complex phenomena in the blast furnace and for determining appropriate operational actions under different production conditions.     

可描述高炉内液流分布的数学模型

 高炉内液体流动现象的研究对控制高炉工艺过程具有重要意义。针对液流由非润湿液滴组成、惯性力对运动方向影响可忽略、垂直运动方向上有质量交换等高炉内液体运动的特点,采用合适的假设,建立了一个可描述高炉内液流分布的数学模型。该数学模型以整个填充床区域为求解范围,其数值求解网格尺度仅满足数值精度即可,不必和床层填充颗粒尺寸相一致。模型预测结果和实验数据有较好的一致性。高炉模拟中本模型是一个可供选择的模型。     

Modelling of Gas‐Powder Flow in a Blast Furnace

This paper presents a study of the gas‐powder flow in a slot type packed bed in order to investigate the distribution of powder flow and accumulation in an ironmaking blast furnace. The effects of operational parameters such as gas flow rate, and cohesive zone shape are examined. It is shown that a distinct and stable accumulation region can be formed in the low gas‐powder velocity zone in a bed with a lateral gas inlet. Also, the existence of a cohesive zone changes the powder accumulation pattern significantly. The inverse‐V cohesive zone leads to low accumulation in the bed compared to other cohesive zone shapes. A mathematical model is developed to describe the gas‐powder flow and powder accumulation. Its validity is verified by comparing the predicted and measured distributions of powder accumulation under various flow conditions.     

Numerical Simulation of Fluid Flow in Blast Furnace Hearth

SymbolList C———Coefficient,1inthepackedbedand0inother place; C1,C2,Cμ,σκ,σε———Empiricalconstant; d———Diameterofcokeparticle; H———Heightofpackedbed,m; P———Pressure,Pa; ui,uj———Velocityalongdirectioni,jrespectively,m·s-1; vA———Vel     

Experimental Studies of Gas‐Liquid‐Powder Flow in Moving Particles

An experimental study has been carried out of gas‐liquid‐powder flow in moving particles in one‐ and two‐dimensional packed beds, simulating the complex four‐fluid flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that the contacts between packed particles are important for powder entrapment, and the presence of a liquid phase can significantly increase the powder hold‐up and gas pressure drop. Only when the packed particles have significant downward velocity can the flow of powder and liquid be maintained without flooding. Depending on the flowing conditions, both steady and unsteady flows can be observed, giving the so‐called operational and non‐operational regimes. For the gas‐glass powder‐water system considered, the effects of solid, liquid, powder and gas flow rates on the two regimes have been quantified. The non‐operational regime stems from the flooding caused by high gas and liquid flowrates and/or hanging caused by high powder and low gas flow rates. The operational regime expands with solid flow rate, and contracts with an increase in gas, liquid and/or powder flow rates. Implications of the findings to blast furnace operations are also discussed.     

Analysis on Non‐Uniform Gas Flow in Blast Furnace Based on DEM‐CFD Combined Model

Blast furnace technology is currently aiming at low reducing agent operation so as to decrease CO₂ emissions. At the same time, the inner volume of blast furnaces has frequently been enlarged so as to increase production rate in some countries, including Japan. Operating conditions designed for low reducing agent in a large blast furnace tend to cause unfavorable phenomena such as slipping of the burden and gas channeling due to the decrease in coke rate. Mathematical models help to clarify the in‐furnace phenomena under these situations. From the above backgrounds, a new model has been developed that combines Discrete Element Method with Computational Fluid Dynamics (DEM‐CFD) to simulate precisely the gas flow and solid motion in a blast furnace. The present study aimed to develop a three‐dimensional mathematical model based on DEM‐CFD for simultaneous analysis of gas and solid flow in the whole blast furnace. The unbalanced gas flow in the case of clogging of the particular tuyere was analyzed to clarify the circumferential unevenness in the lower part of the blast furnace. Based on the combined DEM with CFD model, the non‐uniform gas flow in the lower part of the blast furnace was precisely evaluated.     

高 炉 内 的 液 体 流 动 现 象

 高炉内液体流动现象的研究对控制高炉工艺过程具有重要意义。介绍了目前可描述高炉内液体流动规律各模型的内容、局限性和在高炉工艺上的应用特点。通过对比可知,在填充床层区域大小尺度上,笔者前期建立的模型更全面地描述了填充床层对运动液体的作用。并以此认识为基础,给出了确定该模型参数的实验方法。另外,在填充颗粒大小尺度上,给出了计算机模拟床层内非润湿液流分布的做法,进而据此给出了该模型参数的预测方法。     

料床充填结构对高炉内气体流动的影响

用有限差分法对高炉内气体流动行为进行了数值解析，并系统地分析了不同料床结构对气体流动行为的影响。结果表明，Ｖ形层状料床横截面上气体的流速呈矩形波状分布。在高炉边缘加小粒焦炭可抑制边缘气流，可提高炉衬寿命。     

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...     

高炉喷煤直吹管内气粉两相流的流场

在高炉富氧喷煤过程中 ,直吹管使喷入的煤粉与氧气预混、预热 ,并促使煤粉的热解和部分煤的燃烧。运用多相流的拟流体模型建立了高炉局部富氧喷煤直吹管内气粉两相流动的数学模型 ,对气粉两相流场进行了数值研究 ,探讨了气相和煤粉的速度分布规律及其影响因素 ,其中包括氧 -煤喷枪的结构、漩流数和富氧率等。结果表明 ,氧 -煤喷枪的漩流、富氧率等仅在氧枪出口的有限区域内对流场有较大的影响 ;喷煤对整个直吹管内的流场影响较小 ,但在氧 -煤喷枪出口附近区域会促使气相和煤粉激烈混合 ,动量和质量传输较强烈     

Numerical Simulation of Gas and Liquid Two-Phase Flow in Gas-Stirred Systems Based on Euler–Euler Approach

Based on the Euler–Euler approach, a mathematical model is established to describe gas and liquid two-phase flow in the gas-stirred system for steelmaking, and the influences of the interphase force including turbulent dispersion force, drag force, and lift force are investigated. The modified k–ε model with extra source terms to account for the bubble-induced turbulence is adopted to model the turbulence in the system, and the simulation results of gas volume fraction, liquid velocity, and turbulent kinetic energy are compared with the measured data. The results show that the turbulent dispersion force dominates the bubbly plume shape and is responsible for successful prediction of the gas volume fraction. The bubble-induced turbulence has a significant influence on the liquid turbulence, and the conversion coefficient C _b, which denotes the fraction of bubble-induced energy converted into liquid turbulence, should be in the range of 0.8 and 0.9. The drag force also strongly influences the bubbly plume dynamics, and the coefficient model proposed by Kolev performs the best for determining the drag force; however, the lift force and bubble diameter do not have much effect on the current bubbly plume system. For different gas flow rates, the current Euler–Euler approach predictions are more consistent with the measured data than the Euler–Lagrange approach and the early Euler–Euler model.     

Modeling of Blast Furnace with Layered Cohesive Zone

An ironmaking blast furnace (BF) is a moving bed reactor involving counter-, co-, and cross-current flows of gas, powder, liquids, and solids, coupled with heat exchange and chemical reactions. The behavior of multiple phases directly affects the stability and productivity of the furnace. In the present study, a mathematical model is proposed to describe the behavior of fluid flow, heat and mass transfer, as well as chemical reactions in a BF, in which gas, solid, and liquid phases affect each other through interaction forces, and their flows are competing for the space available. Process variables that characterize the internal furnace state, such as reduction degree, reducing gas and burden concentrations, as well as gas and condensed phase temperatures, have been described quantitatively. In particular, different treatments of the cohesive zone (CZ), i.e., layered, isotropic, and anisotropic nonlayered, are discussed, and their influence on simulation results is compared. The results show that predicted fluid flow and thermochemical phenomena within and around the CZ and in the lower part of the BF are different for different treatments. The layered CZ treatment corresponds to the layered charging of burden and naturally can predict the CZ as a gas distributor and liquid generator.     

底吹氩过程LF炉盖内气体流动的数值模拟

基于流体模型和湍流修正模型,借助流体工程模拟软件Fluent 6.3.26对吹氩过程中210 t LF精炼炉盖内气体的流动、混合和质量、动量传输进行了计算模拟,分析了其流动行为和分布状态。结果表明,随钢包净空高度增加,液面上部氩气回旋区扩大,"死区"减小;当氩气流量增至500 L/min时,吹氩孔位于0.68 R的盖内流动效果优于0.3 R的效果;正常工作状态下的合理抽气压力为-150 Pa;在合理的抽气压力和吹氩孔位置的情况下,300 L/min的氩气流量基本可以满足要求,强搅拌时可增至500 L/min。