Study On Charge And Flow Characteristics Of Particles In Spouted Fluidized Bed

Gas-solid fluidization technology has good heat and mass transfer and mixing characteristics,and is widely used in many industries,such as energy,petrochemical,food processing and other industries.However,a significant problem in some gas-solid fluidized beds is that a large amount of static charge is generated due to the continuous contact and collision between particles and between the particles and the wall surface of the fluidized bed reactor.The generation of static charge can cause a series of problems,including the adhesion of fluidized particles to the reactor wall,particle agglomeration and electrostatic discharge.Particle adhesion leads to frequent shutdown of the reactor for cleaning,high production losses and high maintenance costs,resulting in significant economic losses;in severe cases,it can cause explosions and other safety accidents.In this paper,a two-fluid model(TFM)and a discrete element model(CFD-DEM)are used to numerically calculate a three-dimensional rectangular spouted bed.Combined with the experimental results of the spouted bed,the effects of the two calculation models on the flow characteristics of the particles in the spouted bed were compared and analyzed.Based on CFD-DEM and TFM,the effects of four different drag models and two different friction stress models on the flow characteristics of particles in the spouted bed were investigated.It is found that the height of the fountain calculated by CFD-DEM is closer to the experimental results.The height of the fountain calculated by the Gidaspow drag model and the Syammlal-O’Brein drag model is basically the same and is closer to the experimental results.The particle concentration near the bottom wall of the bed calculated by the Srivastava-Sundarasan(S-S)friction stress model is low,and the particles in the bottom area of the bed have obvious downward movement,and the circulation and mixing effect are better.Then based on CFD-DEM,considering the electrostatic force,change the charge of the particles and set the charged particles of different components,and the effects of electrostatic force on particle movement,particle concentration and particle force in spouted bed are analyzed in detail.The results show that for single-charged particles,as the particle charge increases,the height of the fountain in the spouted bed increases significantly;the regular internal circulation motion of the particles in the bottom area of the bed gradually weakens,and the irregular motion is more obvious.Compared with when the particles are not charged,when the particle charge is low,the peak value of the particle concentration in the fountain area along the radial distribution curve is low,and as the particle charge increases,the peak value becomes larger.The drag force on the particles near the jet axis of the annulus is obviously increased.When the particle charge is large,the drag force is greatly increased.For bipolar charged particles with different densities,as the particle charge increases,the number of small density particles in the upper part of the bed increases,and the phenomenon of agglomeration of large and small density particles in the fountain area is more obvious.Compared with when the particles are uncharged or when the particle charge is low,when the particle charge is high,the peak value of the particle concentration in the fountain area along the radial distribution curve is high,and the drag forces experienced by the large and small density particles are similar in the radial distribution,and the values are different.In the annulus area,when the particle charge is low,the drag force on the particles near the injection axis will increase significantly.For bipolar charged particles with different particle sizes,compared with the case of particles with different densities,the range of the annular z one in the spouted bed is significantly larger,and the degree of particle precipitation in the upper part of the bed is more obvious.The drag forces of large and small particles are similar in radial distribution,and the values are different.The drag force on the particles near the jet axis of the annulus is obviously increased,and the increase of the charge is basically the same when the particles are uncharged and the charge is low,and the increase is low when the charge is high.