Studying On Cluster Behaviors In The Circulating Fluidized Bed With Binary Particles

Because of highly efficient and bubble-free gas-solid contact characteristics,the circulating fluidized bed(CFB)is an important chemical reactor and it has been widely used in energy,chemicals,metallurgy,materials,environmental and other industries;Cluster is one of the most important phenomenon,which affects the mixing and reaction efficiency in CFB.And it is of great significance to optimum design for the CFB reactor to obtain the characteristics of the clusters in the CFB.Experimental was carried out in a 2-D CFB,which is made of Perspex with dimensions equal to150mm×15mm×2400mm.A digital camera was set nearby 2D CFB and 100 W halogen bulbs were used as the light source to illuminate the back side of the bed.Air was used as the fluidizing gas,sand particles were used as the heavy component and silica gel particles were used as the light component.Digital image analysis technique was employed and the program was developed with Matlab in this work.The program could get the cluster information,such as cluster distribution and cluster velocity.Experimental results show that the content of the heavy components in the bottom is more than that in the top of the bed.The content of the heavy component increases in the top and decreases in the bottom of the bed with increasing the superficial gas velocity.The number and its distribution of the clusters have been investigated in both the mono-particles and binary particles systems in this work.Number of clusters in the heavy particles CFB is more than that in the light particles CFB.The number of the cluster in the peripheral region is greater than that in the central region of the CFB,and it in the bottom region is greater than that in the top region.The number of clusters increases with the increase of the solid flux and gas velocity.The cluster diameter in the binary particles CFB is larger than that in the mono-particles system,and the cluster in the peripheral region is larger than the diameter in the central region.The cluster diameter presents an “S” type distribution along the bed height and it increases with the increase of gas velocity and solid flux.The cluster velocity is suitable for the normal distribution and increases with increasing gas velocity.The clusters in the peripheral region mainly move downward,whereas the clusters in the central region flow upward.The velocity of the cluster in the top region is greater than that in the bottom region.However,the lateral velocity of the cluster in the bottom region is greater than that in the top region of the CFB.The duration time of the cluster in the binary particles fluidized bed is less than that in the mono-particle fluidized bed and decreases with the increase of the gas velocity.The more clusters in the light particles fluidized bed exhibit elliptical and the clusters in the heavy particles CFB mainly show parabolic.The more elongated clusters are observed in the binary particles CFB.