Study On Fluidization And Bond Characteristics Of Coarse Cohesive Particles In Fluidized Process

Fluidization reactor has been widely used in many fields as an importantequipment. The characterstic of fluidized particles has a great influence on its normaloperation. Coarse cohesive particles can easily cause the unbalance of the heat and masstransfer and the particle bond behavior blocks the reactor frequently, so it is difficult tostabilize normal operations in fluidized bed, even shut-down accident happens in theactual industry. The study on the fluidization and bond process for coarse cohesiveparticles is rather less than that for fine particles and further research should beconcentrated on the fluidization and bond characteristic of coarse cohesive particles. Itis of great theoretical and practical significance for the research on the fluidization andbond characteristic of coarse cohesive particles in fluidized process.Conventional drag force models can not accurately consider the effect ofnonuniform particle distributions which limits their applicability in fluidized processsimulation. To improve the existing drag force models, a meshless method(Element-Free Galerkin method) was used for direct numerical simulations to simulatereal particle collisions and investigate the drag coefficient variations in various uniformand nonuniform particle distributions. Nonuniformity coefficients were used toquantitatively represent the nonuniform particle distributions and the classical dragforce model was improved using nonuniformity coefficients based on variousnonuniform particle distributions. Then the application of nonuniformity coefficientsand modified drag force model in the fluidized process has been investigated. It is foundthat nonuniformity coefficients and modified drag force model can more accuratelyreflect the dynamic effect of the drag coefficient and have good application prospect.The fluidization and bond behavior of coarse cohesive particles was investigatedvisually using paraffin particles and the corresponding fluidization and bond laws havebeen obtained. S attractor comparison method was adopted to monitor the dynamicparticle bond process. It is found that S value reflected the bond effect and bondevolution well in various cases, so it could be used as a criterion of fluidization qualityin fluidized process and be effectively applied to bond extent monitor of coarsecohesive particles in various bond processes. The high viscosity particle bond process resulting from solid-bridge force wasinvestigated. Experimental observation on the neck growth of single particle indicatedthat the neck growth process could be well predicted by the sintering theory. The effectof bond time on the neck was less than that of surface rheological property. Theexperimental system for measuring the solid-bridge force of high viscosity material wasdesigned and constructed. The dimensionless neck strength formula for viscous materialwas proposed based on penetration which can evaluate the rheological property ofmaterial. Then the experimental method and device for measuring the penetration ofhigh viscosity fly ash was proposed, and it established the foundation for developingquantitative fly ash bond model.