高炉风口回旋区多形貌颗粒混合流动特性数值模拟

Numerical study on flow characteristics of multi-shape particles mixed in blast furnace raceway

【目的】高炉的稳定运行和能耗控制受制于风口回旋区内复杂的物理化学行为,因此对回旋区内混合多形貌颗粒的气固相互作用机制进行研究。【方法】采用计算流体力学-离散单元法耦合方法对高炉风口回旋区内混合多形貌焦炭颗粒的流动行为和动力学特性进行数值模拟;系统地研究和分析4种不同的混合非球形颗粒体积分数对风口回旋区演化形貌和微观结构等的影响。【结果】随着非球形颗粒的体积分数从0增至9%,回旋区的宽度和高度分别增加96%和67%,转动能则增加3.53倍;颗粒所受曳力随非球形颗粒混合体积分数的增大而增大,颗粒间接触法向力概率密度函数分布也会向左偏移且峰值随之减小,而混合非球形颗粒时配位数概率密度函数分布峰值均小于不混合时的工况。【结论】混合非球形颗粒体积分数对高炉风口回旋区形貌和曳力分布、颗粒配位数概率分布等产生显著影响。

Objective Stable operation and energy consumption control of the blast furnace are subject to the complex physical and chemical behavior within the raceway.However,there is still a lack of research on the gas-solid flow characteristics and interaction mechanisms of non-spherical particles in the raceway.Fundamental dynamical problems,such as elucidating the motion mechanism of non-spherical particles and assessing the effect of the mixing ratio of various multi-shape particles on raceway evolution,remain largely unaddressed.This study systematically investigates the effects of four different mixed non-spherical particle volume fractions on raceway evolution morphology and microstructure.The developed model provides fundamental insights into the complex transport phenomena in the raceway zone to achieve better understanding and optimization in operation.Methods The study began by addressing the fluid flow using the Navier-Stokes equations,alongside particle motion modeled via the Discrete Element Method(DEM),which includes both translation and rotation equations governed by Newton's second law.To couple the gas and solid phases,the well-established Di Felice model for drag force was employed.The drag coefficient for non-spherical particles was calculated using the Holzer-Sommerfeld approach.Validation of the developed model was conducted by examining the particle flow patterns in a bubbling fluidized bed,which were moving at 2 m/s comprising disc-shaped particles,and by analyzing the bed pressure drop under different gas flow rates.Furthermore,the study explored the effects of different non-spherical particle volume fractions on the evolution process and microstructure of the raceway.Results and Discussion The study analyzed the impact of non-spherical particle volume fractions on raceway zone profiles and microscopic characteristics.Findings revealed a significant effect of non-spherical particle volume fraction on the upper sections of the raceway,with a distinct decrease observed as the volume fraction increased from 0 to 9%.However,no visible difference was observed for the lower parts of the raceway.Simultaneously,an increase in volume fraction facilitated gas movement in the counterclockwise direction.With the gradual increase in volume fraction,the gyratory region expanded.Specifically,the width of the raceway increased by 96%,from 46 to 70 mm,while its height grew by 67%,from 45 to 75 mm.Rotational energy increased by a factor of 3.53.Notably,the mixed particle system exhibited the largest fluctuation amplitude,with the average value of the rotational kinetic energy peaking at φ=9%.Additionally,as the volume fraction of non-spherical particles rose,the drag force in the stable stage gradually increased.The upper region of the raceway experienced stronger drag force when the volume fraction of non-spherical particles was low,whereas it weakened with higher volume fraction.Furthermore,the probability density function(PDF)of the coordination number(CN)followed a normal distribution across all cases,showing a prominent peak of 25 at φ=0.At CN=5,the operation condition exhibited a 15% decrease compared to the other three.Additionally,an increase in volume fraction of non-spherical particles in the mixed particle system resulted in a leftward shift in the PDF of normalized contact normal force.The lower right part of the multi-shape particle mixed bed exhibited a large contact force.Conclusion This study investigated the effects of non-spherical particles volume fraction on the evolution process and microstructure of the raceway.Through kinetics analysis,it was observed that increasing the volume fraction of mixed non-spherical particles from 0 to 9%yielded a 96%increase in the raceway width,a 67% increase in height,and a 3.53-fold increase in rotational energy.Furthermore,considering the microstructure,the drag force on particles increased as the volume fraction of nonspherical particles in the mixture increased.Additionally,the probability density function distribution of the normal contact forces between particles shifted leftward,accompanied by a decrease in peak magnitude.Moreover,the peak of the coordination probability density function distribution diminished when non-spherical particles were mixed,compared to the condition with only spherical particles.