A DEM Numerical Investigation On Dry And Wet Particles Mixing In Rectangular Spouted Bed

Spouted beds have been extensively used in various industrial processes such as drying,granulation, combustion, coating, coal gasification, chemical vapor deposition, etc., in orderto provide good mixing and large gas-solid contact area for dry and wet granular materials.The Discrete Element Method (DEM) resolves particle flow behaviors at an individualparticle level, and it can provide a wealth of information of the particle’s force and motion.Therefore, it has been widely used for studying the particle behavior of spouted bed. The aimof the present paper is to investigate the mixing mechanism and flow behavior of dry and wetparticles in spouted bed by using DEM. In particular, the standard k-ε two-equation model,the Beer&Johnson equation and the Mikami model are adopted to investigate the influenceof turbulence, rolling friction and liquid bridge force.This thesis presents three main parts as follows:In part one, the research on choosing drag model of rectangle spouted bed is done withDEM. Firstly, the Arastoopour, Di Felice, Syamlal&O’Brien and Gidaspow model, areadopted in DEM simulations to obtain the distributions of particles’ voidage, velocity andgranular temperature in spouted bed. Then, the applicability of different drag models isverified by comparing results between simulation and experiment. The results indicated thatthe Arastoopour, Di Felice, Syamlal&O’Brien and Gidaspow models are able to predict theflow pattern, while the Gidaspow model has the best agreement to the experimental data.In part two, numerical simulation of dry particle mixing process in rectangular spoutedbed is carried out with three dimensional discrete element method, and an Ashton&Valentinmixing index is introduced to investigate the characteristics of dynamic mixing process.Firstly, in simulation of the axial and the lateral mixing process, the relationship between theparticle flow behavior and the mixing process, and the mixing rate relationship between thedifferent regions and the whole bed are investigated. Then, the effect of the spouting gasvelocity and the density ratio are discussed. The results indicate that the near tapered wallregion has the slowest mixing rate in the spouted bed. Thus, the mixing rate of annulus plays acritical role in the mixing rate of spouted bed. Increasing spouting gas velocity will increasemixing rate of the whole bed. Furthermore, increasing density ratio will decrease the maximum mixing index.In part three, the mixing characteristics and the flow behavior of wet particles in arectangular spouted bed is simulated with a three-dimensional discrete element method. Theinfluence of liquid bridge force is investigated using the Mikami model. First, thecharacteristics and relationship between particle flow behavior and mixing process areinvestigated by simulating the axial and the lateral mixing process. After that, the effect of themoisture content is discussed. The result indicated that the wet particle’s mixing rate inspouted bed is also depends on the mixing rate of the annulus. Moreover, increasing moisturecontent will decrease the mixing rate of spouted bed and the maximum of mixing index.It is expected that the investigations on mixing characteristics of dry and wet particle inspouted bed can provide some references for the project designing, manufacture andapplication of the rectangular spouted bed.