| Fluidized dry separation technology is the gas-solid two-phase fluidization technique is applied to an efficient dry separation technology in the field of coal,is a development and innovation in the field of coal preparation with air and the magnet mineral powder composed of particles streaming media can be effective for all types of coal ash fall mass,separation process at the same time does not water,achieved on water saving and protection.With the deepening of coal mining depth,the raw coal moisture content increased,damp raw coal in fluidized bed,the air flow,particle collision,such as complex process,to carry coal surface moisture spread to the whole bed,adhesion between particles under the action of a water Bridges,forming different composition and size of particles.The generation of particle agglomerations changes the fluidization characteristics of the bed,resulting in the instability of the bed and the uneven density distribution within the bed,which deteriorates the sorting process.Based on the wet particle collision adhesion formation of group as the breakthrough point,through theoretical analysis and experimental research,explores the damp conditions increase quality,and the collision between particles and coal surface adhesion characteristics,in order to clear particles adhesion mechanism of group,to achieve the control of the separation in the fluidized bed granular poly group,maintain steady flow,the bed layer provides the theory basis for improve the effect of fluidized bed separation.Using the self-built particle collision adhesion visualization test system,the normal collision process between micron magnetite powder particles and coal surface under different relative humidity conditions is studied,and the influence law of collision speed,particle size and relative humidity on the recovery coefficient is investigated.On the basis of the study of the influence of relative humidity on the collision process of particles and liquid film,the collision adhesion process of particles and liquid film was analyzed,and the influence of collision speed,liquid film thickness and particle size on the collision process was explored.The purpose of this study is to provide basic theoretical support for solving the phenomenon of wet particle agglomeration in gas-solid separation fluidized bed and improving the separation effect of gas-solid separation fluidized bed.The main work of this study is as follows:(1)Through theoretical analysis and numerical calculation,it is determined that the main adhesion forces between particles in the fluidized bed are van der Waals force,electrostatic force and liquid bridge force.By establishing a theoretical adhesion model,it is determined that the liquid bridge force is the dominant adhesion force to promote particle agglomeration.By introducing relative humidity into the calculation model of liquid bridge force,the theoretical model of liquid bridge force between particles under different relative humidity is derived.The Hertz model and JKR model of static contact between particles are described,and it is pointed out that JKR model is more suitable for the actual particle collision process in fluidized bed.Through numerical calculation,it is clear that only elastic deformation occurs in the collision process between particles in the fluidized bed,and no plastic deformation occurs.Based on the energy conservation under dry conditions,the influence of relative humidity on the energy conversion during particle collision is introduced.It is pointed out that the main energy loss of particle collision in fluidized bed under wet conditions is the loss of particle surface viscoelastic energy and the loss of liquid bridge adhesion energy.(2)The effects of different collision velocities,particle size and relative humidity on the collision rebound characteristics of particles were explored by using the selfbuilt particle collision adhesion visual test system.It was found that the normal collision recovery coefficient of particles increased with the increase of collision velocities.Under the same humidity condition,the recovery coefficient of particles with larger particle size at the same collision speed is larger.With the increase of relative humidity,the loss of adhesion energy caused by the liquid bridge force increases,and the particle restitution coefficient decreases.(3)Based on the collision characteristics of particles under different relative humidity conditions,the collision adhesion/rebound characteristics of particles and coal surface covered with liquid film are further studied.The collision process between particles and liquid film can be divided into five stages: immersion into liquid film,contact surface,rebound rise,development of liquid bridge,and fracture of liquid bridge.According to the different experimental conditions,the collision adhesion behavior between particles and liquid film can be divided into direct rebound,direct adhesion and rebound adhesion.The adhesion rate of particles decreases with the increase of collision velocity,and increases with the increase of liquid film thickness.When the liquid film thickness is greater than or equal to the particle size,the particles almost cannot rebound.When the thickness of the liquid film is smaller than the particle size,the adhesion rate decreases in three stages with the increase of particle size.The impact of collision velocity,liquid film thickness and particle size on the recovery coefficient is shown as follows: with the increase of collision velocity,the recovery coefficient increases slowly;With the increase of liquid film thickness,the recovery coefficient decreases at the same velocity,and the critical rebound velocity of particles increases with the increase of liquid film thickness.At the same speed,the coarsegrained particles are easier to get rid of the liquid bridge,have a larger recovery coefficient,and the critical rebound velocity is smaller,so it is more likely to rebound.There are 41 figures,8 tables and 112 references in this thesis. |
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