Study On Triboelectric Charging And Adhesion Characteristics Of Fine Particles In Gas-solid Fluidized Bed

The fine particles in the fluidized bed can provide better contact efficiency and higher reaction rate than traditional materials in the gas-solid and solid-solid reaction processes,and have received more and more attention in recent years.Different from the coarse particles,the fluidization of fine particles is affected by adhesion.In dry environment,the particles adhere to each other mainly through electrostatic force and van der Waals force,forming loose aggregates,which affect the fluidization state of particles,bubble size,bed pressure drop,bed height and other parameters.The coupling of the two adhesion forces is the main reason for particle agglomeration and complex particle behavior in the fluidization process.The study of the effect of triboelectric charging and van der Waals force on fluidization of fine particles under different conditions and the interaction of two kinds of adhesion are of guiding significance for deepening the understanding of fluid-fine particle two-phase flow,the regulation and optimization design of related reactors.Based on CFD-DEM,a gas-solid two-dimensional fluidized bed model considering triboelectric charging phenomenon and Van der Waals force is established and numerical simulation work is carried out.This work discusses the influence of the triboelectric charging phenomenon and van der Waals force on the particle fluidization state and the mutual influence of the two adhesion forces under the conditions of different fluidization speed and particle size.The study on the effect of triboelectric charging on particle fluidization shows that with the increase of fluidization velocity,the electrostatic interaction and agglomeration phenomenon weaken,the average coordination number of particles decreases,the effect of particlewall collision on triboelectric charging increases,and the negative net charge of the bed particles increases.With the decrease of particle size,the electrostatic interaction and agglomeration phenomenon increase,and the electrostatic force gradually occupies the dominant position of particle force.The mean coordination number of particles increases,the pseudo-temperature of particles decreases,the effect of particle-wall collision on triboelectric charging weakens,and the net charge of particle bed decreases relatively.The study on the effect of van der Waals force on particle fluidization shows that as the particle size decreases,under the action of van der Waals force,particles will adhere to the wall and agglomerate,which affects the distribution of bubbles and weakens the vortex motion of particles.The increasing trend of the average coordination number increases;the influence of van der Waals force on particle fluidization changes more drastically with the particle size,and the van der Waals force quickly surpasses the effect of triboelectric charging as the particle size decreases.The results show that the effects of the two adhesions on the fluidization of particles are superposition and mutual promotion,in which the frictional charge phenomenon dominates the formation of the agglomeration structure of particles,and the van der Waals force makes the particles in the agglomeration adhere to each other more firmly.The van der Waals force accelerates the accumulation of particle charge and increases the net charge accumulation.Van der Waals force and electrostatic force are greater than that of single adhesion,and the resultant force of the two adhesion forces is further increased,and the two forces promote each other.With the increase of fluidization velocity,the two adhesion forces and the total adhesion effect weaken,and the promotion effect of van der Waals force on the static force weakens slowly,while the promotion effect of van der Waals force on the static force weakens faster.