Influence of Cohesive Zone Shape on Solid Flow in COREX Melter Gasifier by Discrete Element Method

Based on the principle of discrete element method(DEM),a 2Dslot model of a COREX melter gasifier was established to analyze the influence of cohesive zone shape on solid flow,including mass distribution,velocity distribution,normal force distribution and porosity distribution at a microscopic level.The results show that the cohesive zone shape almost does not affect the particle movement in the upper shaft and deadman shape.The particles in the lower central bottom experience large normal force to support the particles above them,while particles around the raceway and in the fast flow zone exhibit weak force network.The porosity distribution was also examined under three kinds of cohesive zones.Like the velocity distribution,the whole packed bed can be divided into four main regions.With the increase of cohesive zone position,the low porosity region located in the root of cohesive zone increases.And the porosity distribution becomes asymmetric in the case of biased cohesive zone.     

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.     

COREX熔化气化炉物料运动和气流分布

基于离散元数值计算方法(DEM),建立了熔化气化炉模型的离散元数学模型.应用此模型从颗粒尺度对气化炉3种软熔区域形状下的物料质量、运动速度、法向力、空隙度分布进行了研究.利用DEM计算空隙度数值,再结合计算流体力学软件对气化炉气流分布进行了计算.结果表明:软熔区域形状对气化炉料面形状和炉内下部法向力的分布影响很小,炉中...     

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Based on the discrete element method, a 2D slot model of COREX melter gasifier has been established. The solid flow pattern, velocity field and voidage distribution were analyzed by using the proposed model at a particle level. The results show that the solid flow pattern changes from linear mode to curving down on the both sides by means of joining tracer particles. Judging from the velocity field distribution, the solid flow can be divided into several different flow zones including dead zone, the plug flow zone and the channel flow zone. The influence of raceway in the vertical direction is limited to the region of 0. 18m from the hearth bottom level. The decrease of raceway size causes that the region of faster particles becomes small and the height of dead zone increases remarkably. The velocity distribution is asymmetric in the furnace which shows that there exits segregation phenomenon, and the voidage distribution also clarifies this phenomenon. The voidage is 0. 37 in the dead zone, while in the raceway the voidage is about 0. 65, and the voidage in the plug flow is between 0. 37 and 0. 65.     

Mathematical Simulation of Burden Distribution in COREX Melter Gasifier by Discrete Element Method

 COREX process is one of the earliest industrialized smelting reduction ironmaking technology. A numerical simulation model based on discrete element method (DEM) has been developed to analyze the burden distribution in the melter gasifier of COREX process. The DEM considering the collisions between particles can directly reproduce the charging process. The burden trajectory, the location and the burden surface profile are analyzed in melter gasifier with a mixing charging of coal and direct reduction iron (DRI) at the same time. Considering the porosity of packed bed has an important effect on the gas flow distribution of melter gasifier, a method to calculate porosity has been proposed. The distribution of DRI and coal and the porosity in the radial direction are given under different charging patterns, which is necessary to judge the gas flow distribution and provide base data for further researching the melter gasifier for the next work in the future. The research results can be used to guide the operation of adjusting charging and provide important basis for optimizing the charging patterns in order to obtain the reasonable gas distribution.     

加焦方式对气化炉炉料结构和气流分布的影响

装料模式决定了料床的孔隙度结构,进而决定了煤气流的分布信息。建立了气化炉炉料结构的离散单元模型和煤气流动的多孔介质模型,以自编程和软件Fluent为载体,结合两个模型共同描述了不同加焦方式对气化炉的炉料结构和煤气流动带来的变化,获得了炉内炉料结构的孔隙度分布信息和煤气的速度场、流线和质量通量。结果表明：首先,由离散单元模型获得的炉料结构信息可作为气流分布模型的边界条件输入;其次,煤气流模型的模拟结果表明焦柱的加入会在加焦位置处形成煤气发展通路,进而改善气化炉透气性,但应控制焦炭加入量,避免气流过度发展,进而影响煤气利用率。通过模拟计算获得的非均匀床层气体流动规律的认识对气化炉加焦工艺有借鉴意义。     

Mathematical model of COREX melter gasifier: Part I. Steady-state model

The COREX melter gasifier is a countercurrent reactor to produce liquid iron. Directly reduced iron (DRI), noncoking coal, and other additives are charged to the melter gasifier at their respective temperatures, and O₂ is blown through the tuyeres. Functionally, a melter gasifier is divided into three zones: a moving bed, fluidized bed, and free board. A model has been developed for the moving bed, where the tuyere region is two-dimensional (2-D) and the rest is one-dimensional (1-D). It is based on multiphase conservation of mass, momentum, and heat. The fluidized bed has been treated as 1-D. Partial equilibrium is calculated for the free board. The calculated temperature of the hot metal, the top gas, and the chemistry of the top gas agree with the reported plant data. The model has been used to study the effects of bed height, injection of impure O₂, coal chemistry, and reactivity on the process performance.     

Definition of Raceway Boundary Using Fractal Theory

The particle velocity contours were obtained by tracking the tracer particles in the raceway region of the COREX melter gasifier model and the contours were irregular.According to the fractal theory,the fractal dimensions of different particle velocity contours were determined.Through the analysis of the fractal dimensions,a new method for precise determination of the raceway boundary was proposed.The results show that,when the velocity is less than 0.18m/s,the particles are located in the stagnant zone and the fractal dimensions of particle velocity contours are almost constant as 1.41;when the velocity increases from 0.18 to 0.83m/s,the particles are located in the rapid movement zone and the fractal dimensions decrease gradually from 1.41 to 1.05;when the velocity is greater than 0.83m/s,the particles are located in the cavity zone and the fractal dimensions are again almost constant as approaching to 1.00.Therefore,the velocity contour of 0.18m/s,which is critical to distinguish the rapid movement zone and stagnant zone,can be used to define the raceway boundary.Based on this method,the effect of blowing rate on raceway size was calculated and the results show that the penetration depth and height of the raceway increase with the increase of blowing rate.     

COREX熔化气化炉区域模型及其理论燃烧温度

把熔化气化炉划分为炉缸区、风口区、填充床、流化床和自由空间5个区域。在已开发的COREX工艺整体静态模型的基础上,对各区域分别建立了物料平衡热平衡模型并联立求解。根据各区域内的物理化学进程设定各区域间边界的条件,模型计算可给出熔化气化炉内各区域的能量分布和物料流状况。利用区域模型还可计算喷煤对理论燃烧温度、炉缸渣铁温度、煤气量等的影响。     

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.      

加焦方式对气化炉内气流分布的影响

布料模式决定了料床的空隙度,而料床的空隙度分布决定了煤气流的二次分布.本文建立了研究三维气化炉炉料结构和煤气流分布的物理模型和数学模型,物理模型采用热电偶测温的方法,从炉内气体温度分布信息考察了气体的流动情况,由于物理实验无法获得内部空隙度分布信息,故基于离散单元法模型,以Fluent软件为载体,利用多孔介质模型并加入用户自定义函数,通过数学模型进一步研究了不同加焦方式下气化炉内煤气流分布的影响机理,获得了气化炉内煤气的速度场和流线.物理模拟与数值模拟结果相吻合.通过模拟计算获得的非均匀床层内气体流动规律的认识对COREX气化炉加焦工艺有借鉴意义.     

气固流化床内锂颗粒停留时间影响因素研究

为提高锂精渣颗粒在气固流化床中的燃烧效率及延长颗粒的停留时间,基于CPFD理论详细研究了气流速度、质量流和压力等对颗粒在流化床中停留时间的影响,并分析锂精渣颗粒在流化床提升管内轴向高度颗粒浓度的分布情况。结果表明,在质量流一定的情况下可以通过增加气流速度来提高颗粒的停留时间;在相同气流速度下可以通过降低质量流来提高颗粒停留时间;进气压力对颗粒的停留时间影响很小;通过提高气流速度可以显著提高颗粒在密相区的停留时间。     

Transport phenomena and penetrability of solid particles in hot metal during lance injection

Abstract

The transport phenomena in injection lance and the penetrability of solid particles into liquid metal at the lance tip during injection treatment was analysed by a one-dimensional mathematical model developed in this work. Mechanic interactions and heat transfers between a solid particle, carrier gas, lance and/or hot metal have been incorporated in the model. Temperatures and velocities of carrier gas and solid particles were examined for a typical hot metal desulphurisation process by granulated magnesium injection. The temperature of gas increases by several hundred degrees, while that of solid magnesium particles only by several degrees in the lance. The gas velocity is increased by thermal expansion in lance. At the lance tip, the magnesium particle velocity is slower than the gas velocity. The penetrability of a magnesium particle into the hot metal at the lance tip was analysed.     

Characteristics of coal required for superior performance of Corex ironmaking

Abstract

The Corex smelting reduction process was developed as an alternative to the blast furnace and consists of two reactors: the reduction shaft and the melter gasifier. Coal rather than coke is used for heat generation, production of reducing gases and to maintain adequate bed permeability; hence, coals have to meet certain physical, chemical and especially high temperature properties for stable process operation and high iron outputs. Statistical analysis was employed to investigate the influence of coal properties on Corex performance, and laboratory coal characterisation studies were correlated with plant performance. This paper details these coal characteristic studies and highlights the coal blend properties required for superior plant performance.     

The Removal of Finely-divided Particles by Liquid Beds

Abstract

The removal of finely-divided prticles in alumina, silica and coal particles of average size of 5 microns in diameter has been investigated utilizing liquid fluidized and packed beds. The bed particles used included 40×100, 100×150 and 150×200 mesh silica and corundum particles. Important variables examined included surface charge, flow rate, pH and amount of bed particles

A mathematical model describing the concentration profile of fine particles in the axial direction in liquid fluidized beds has also been developed. The equation of continuity was solved using a forward finite differentiation technique. The application of this model to the scale-up investigation was discussed

The recovery of silica and coat fines was possible on corundum bed particles, while alumina fines was possible on silica beds as well as corundum bed particles due to electrostatic and van der Waals attractive forces. Fine particle recovery wasdirectly proportional to the total surface area of bed particles. The possibility of recycling bed particles after desorption of adsorbed fine particles was also studied.     

移动床固体颗粒绕流顺排圆管的过程

工业中常用带埋管的移动床来加热或冷却固体颗粒物料,其过程涉及颗粒流与管壁间的复杂传热,而颗粒绕流圆管的流动过程对其传热效果起着决定性作用.为简化描述颗粒的流动过程,通过分析颗粒绕流圆管的特性,建立了拟漏斗流模型,并给出了模型所需颗粒绕流圆管描述参数的取值范围,模型可用以求取颗粒绕流圆管的速度场和时长等参数.建立了埋管移动床实验系统,考察了颗粒绕流顺排管束的过程;同时利用离散单元法(DEM)对该过程进行数值模拟,获得了颗粒绕流圆管的流动过程,并利用移动床实验结果对比验证了离散单元法数值模拟结果;最后,对比了基于拟漏斗流模型的计算结果和离散单元法数值模拟结果,并根据此结果对拟漏斗流模型的描述参数进行了确定.      

Flow Behavior in Z-Path Fluidized-Moving Bed with Inclined Perforated Plate

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Influence of post-combustion heat transfer efficiency on fuel reduction in COREX process

Abstract

The influence of post-combustion, heat transfer efficiency, and the degree of metallisation is studied with regard to coal saving and export gas in the COREX process using a thermochemical model. An increase in post-combustion ratio decreases the coal rate and the amount of reduction gas, which influences the achievable degree of metallisation, when no additional reduction gas is added to the system. Further post-combustion with oxygen generates a higher temperature than that with air at all post-combustion ratios. A higher heat transfer rate is necessary to keep the temperature of the gas within the refractoriness limits of the lining material. It is asserted that the post-combustion ratio, the degree of metallisation, and the medium for post-combustion must be adjusted according to the refractoriness of the lining material of the melter–gasifier, the efficiency of heat transfer mechanisms from the post-combustion zone to the bath, the gas handling efficiency, and the thermal energy requirement of the surplus gas, when considering the use of post-combustion in the COREX process.     

Residence time distribution of solid particles in liquid fluidised bed separator

Abstract

Residence time distribution (RTD) of coal particles in a floatex density separator (FDS) was investigated using stimulus response technique. The mean residence time of the underflow particles was observed to increase with a decrease in the particle size as well as density. The resistance to settling is enhanced at higher bed pressure and the residence time of the particles increases. A linear correlation of the mean residence time with the terminal settling velocity of the particles was observed. The mixing behaviour in the FDS was neither plug flow type nor fully mixed type. The n-tank in series model described the mixing pattern in the FDS well with ‘n’ values in the range of 3–5. The relatively low values of ‘n’ indicated that the flow behaviour in the FDS was closer to the well mixed state.     

风口回旋区的数字图像处理方法

风口回旋区对高炉及COREX熔化气化炉冶炼过程起着十分重要的作用,人们对风口回旋区进行了大量的试验与模拟研究.目前通过试验方法得到的风口回旋区仅仅是由若干个测量点确定.物理参数场可以用来准确确定回旋区边界,但是目前为止所有的研究风口回旋区的物理参数场都是由数值模拟确定,并且没有明确的回旋区的定义标准.在本研究中利用CO...