Experimental And Computational Study On The Motion Behavior Of Special-shape Large Particles In A Fluidized Bed

In the actual application of fluidized bed engineering,particles in fluidized bed are often not homogeneous.Especially in the use of solid waste,biomass combustion,coal particles drying and sorting and other production process,differences in the size,density,and shape of each components of the fuel particles,differences between the physical properties of fuel particles and bed material,which are easy to cause unstable fluidization in the multi-component fluidization system,large particles in the fluidized bed increase the wear of the furnace combustion system,and more easy to block the air distribution device.Therefore,it is necessary to further study the movement law of large particles in the fluidized bed to discharge non-flammable heavy particles as soon as possible.One of the most important indexes for the performance of fluidized bed discharge large particles is the residence time of large particles in fluidized bed.Based on the cold fluidized bed with 15°∧ air distributor,residence time distribution(RTD)of large particles in fluidized bed,effects of fluidization velocity,shape characteristics and property of large particles on residence time,trajectory characteristics of large particles in the fluidized bed were experimental studied repeatedly,and the three-dimensional numerical simulation of the force law of large particles in fluidized bed was carried out.The results show that the density shape characteristics of the particles have significant effect on the mean residence time(MRT),the influence of shape characteristics is the second and the fluidization velocity and the particle size are relative small.With the increase of particle density,the mean residence time of large particle are decreased.For the sheet cylinder large particle,the mean residence time synchronous increases with the increase of large particle size,but the residence time of square cylinder and long cylindrical particles decreases with the increase of large particle size,and the more increase in the size,the faster decrease in residence time.When the fluidization velocity was smaller,the large particle movement speed and range are smaller,which causes the particles were prone to stagnation.When the fluidization velocity is higher than the movement critical transformation speed,the residence time of particles decrease rapidly,the residence time of large particles tends to a fixed value with the increase of fluidization velocity.The mean residence time of cylindrical particles is obviously larger than that of sheet cylindrical particle.The movement trajectories of the particles were tracked and displayed that the motion range and the movement continuity of the large particles enhance in the case of large fluidization velocity or low particle density.For sheet cylinder large particle,the direction of movement shows irregularity,but movement range of the particle on the air distributor is relatively large compared to two other cylinder large particles,the square cylinder particle is more prone to radial(z direction)movement along the air distributor.Numerical simulations show that the force Fbd acted on the large particles in the fluidized bed show near-cyclical fluctuations in a certain range,where exist the maximum and minimum of force.The force Fbdx that toward in direction of the air distributor low-side and the axial force Fbdy of the sheet particles are larger than the cylindrical particles.With the increase of fluidization velocity,the force Fbdx and the axial force Fbdy of three kind of large particles with different shapes increase,and the fluctuation amplitude and frequency of the force Fbd in three directions showed an increase trend.