Electrostatic Characteristics Of Particles In Fluidized Bed And Its Effect On Flow Characteristics

Due to continually contact,collision and friction among particle-particle and particle-wall during the fluidization process,the accumulation of electrostatics charges is almost unavoidable.The particles electrostatics not only causes particles cohesion,particle-wall adhesion,affecting the fluidization state in the whole reactors,but also result in serious economic losses in production accidents.The effect of electrostatic characteristics on dynamic behavior is not fully understanding because of the complexity of dynamic characteristics and electrostatic mechanisms in fluidized beds.Then the experimental studies were carried out to further explore the electrostatic characteristics and the influence mechanism on the flow characteristics.On the two dimensional fluidized bed electrostatic system,glass beads,polyethylene and corn powder were used to examine the influences of operating parameters such as fluidization time,fluidization velocity,sampling height and initial bed height on particles electrostatic characteristics in fluidized bed.The results showed that with the increase of fluidization time,the charge-mass ratio of the particles increased.And it reached the electrostatic saturation state within 90 minutes.Increasing the fluidized velocity,along with the stronger turbulence in the bed,the particle charge-mass ratio increased.When the initial bed height was 50 cm,at the lower fluidization velocity,the charge-mass ratio of the particles from the lowest sample port was greater than that from the sampling port farther from the air distribution plate.As fluidizations velocity increased,the latter gradually became greater than the former.When the initial bed height was set as 80 cm,the particle charge-mass ratio at the lowest sampling port was always highest for the three sample ports.To investigate the effects of material properties such as particle size and type on particle electrostatics,corn powders,glass beads,and polyethylene were used,respectively.The results showed that corn powders and glass beads carried positive charge,while polyethylene particles carried negative charge.With the similar fluidization number,it was found that the absolute value of the charge-mass ratio of polyethylene particles was always higher than that of corn powders and glass beads.The charge-mass ratio of corn particles was higher than that of glass beads.For the same material,smaller particle particles carried more static charge than larger particles.Based on experimental data,the particle electrostatics models were fitted and analyzed using dimensional analysis.The fitting formulas for the static change of glass beads and polyethylene particles were obtained.Based on bubble injection and digital image analysis methods,the effects of particle electrostatics on the bubbles characteristics in the fluidized bed were investigated.The bubble rise velocity,circularity,aspect ratio,and bubble area at different electrostatic characteristics were systematically studied.The particles charge-mass ratio was adjusted by fluidization velocity.The bubble parameters were extracted using the MATLAB image processing program.The results showed that with the increase of the particles charge-mass ratio in the bed,the particles movements around the bubble led to the bubble deformation.The rising speed of individual bubble markedly increased.Particle electrostatics had a significant effect on the bubble aspect ratio,circularity,and area during rise process.The height at which the bubble first split linearly decreased with the increase in the particles electrostatic.Since the electrostatic repulsion between charged particles,the distance between particles increased.The void ratio of the emulsified phase increased and the bubble size decreased slightly.The bubble aspect ratio and circularity were closely related to the phenomenon of splitting and polymerization with bubble rise.In order to obtain the effect of the particles electrostatic characteristics on the bubble splitting and polymerization process,the bubble images treated were used to qualitatively compare the bubble shape at different heights with different particles charge-mass ratio.The quantitative analysis of the height of the single bubble at the first split with different electrostatic characteristics was performed.It was found that as the particles charge-mass ratio increased,the degree of particle movement around the bubbles was affected.And the height of the bubble at the first split was linearly reduced.