Numerical study on flow characteristics of multi-shape particles mixed in blast furnace raceway
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 mecha-nism 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 vol-ume 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 par-ticles,and by analyzing the bed pressure drop under different gas flow rates.Furthermore,the study explored the effects of dif-ferent 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 vol-ume 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 nor-malized 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 micro-structure 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 rota-tional energy.Furthermore,considering the microstructure,the drag force on particles increased as the volume fraction of non-spherical 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.
computational fluid dynamicsdiscrete element methodraceway of blast furnacemulti-shape particlesnumeri-cal simulation
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