Study On The Effect Of Impurity Particles On Fluidization Characteristics Of Gas-solid Fluidized Bed

A large number of fluidized bed studies have proved that the addition of a small amount of impurity particles in a single component fluidized bed has a great influence on fluidization characteristics of fluidized bed.According to the different gather location of impurity particles during fluidization process,impurity particles can be divided into floating particles accumulated at the top of the bed layer and sinking particles accumulated at the bottom of the bed layer.Because different kinds of impurity have different particle distribution in fluidized bed,this will lead to different impurity particles have different effects on fluidization characteristics of fluidized bed,the fluidization characteristics mainly include bubble size,particle velocity distribution and granular temperature.Therefore,it is of great importance to study the effect of different kinds of impurity particles on fluidization characteristics of gas-solid fluidized bed.At present,the numerical simulation methods of gas-solid fluidized bed are mainly TFM method and CFD-DEM method.The difference between the two methods is mainly reflected in the treatment of solid particle phase,in the TFM method,the particle phase is regarded as a quasi-fluid with continuity,CFD-DEM method can obtain discrete phase information by tracking the motion of each particle in the flow field.Based on the respective characteristics of the two simulation methods,the TFM method has a small amount of calculation and can obtain the macroscopic trend of motion in fluidized bed,the CFD-DEM method has a large amount of calculation and can obtain the detailed information of each particle,which is suitable for the study of particle motion mechanism.Based on the TFM method and CFD-DEM method,a two-component gas-solid fluidized bed calculation model with Geldart B particle as the main particle and Geldart D particle as the main particle was established in this thesis,and the influence of impurity particle type,impurity particle concentration and inlet velocity on fluidization characteristics of main particle was studied.The results show that the two-component gas-solid fluidized bed with sinking particles has smaller bubbles,better particle flow trend and more uniform granular temperature distribution than the fluidized bed with floating particles in the fluidized bed where Geldart B particle acts as main particle.In the fluidized bed where Geldart D particle acts as main particle,whether the fluidized bed contains impurity particles has little effect on particle velocity distribution,but the addition of impurity particles in the fluidized can significantly increase the main particle granular temperature,and sinking particle has more advantages in increase the main particle granular temperature comparing with the floating particle at the bottom of bed.At the same time,in the study of mixing characteristics of impurity particles and main particles,the results showed that the concentration of impurity particles had no effect on the mixing property of two-component particles,and the inlet gas velocity is the main factor that affects the mixing property of particles.The higher the inlet velocity,the better the particle mixing property.Some working conditions were studied using TFM method and CFD-DEM method respectively,the simulation results of the two methods agree well with each other on the distribution of particle in the bed,height of fluidized bed particles and mixing index of two-component particles.