Investigations On Flow Characteristics And Scaling Of Spouted Beds With Non-spherical Particles

Spouted bed,as one of the typical fluidization reactors,has been widely used in agriculture,food,pharmacy,energy,environment,chemical industry and many other fields,showing the commercial successes in a variety of physical operations such as drying,blending,granulation,cooling,coating,as well as the attractive prospects in the thermochemical processes including coal gasification,resource utilization of biomass,oil shale pyrolysis,petroleum catalytic cracking,etc.Nevertheless,up to today,our knowledge on spouted bed is still very limited,especially in the aspects on the spouting dynamics of non-spherical particles and the scale-up of reactors,leading to numerous difficulties in the design,operation or optimization of spouted beds.The present work is devoted to revealing the complex spouting characteristics of non-spherical particles and the scaling relationships of spouted beds by experimental and simulated approaches.The spouted bed experimental system was established and the spouting behaviors of the mixtures of cylindroid particles and spherical bed materials were investigated.Results found that in the spouted bed with two particles,the spouting process and mixing process usually synchronously develop.Once the spouting is well established,two particles in the bed will easily achieve the fulling mixing.The detailed relationships between spouting characteristics and the operating conditions were also obtained.Based on such relationships,two different non-spherical particle spouting systems,i.e.,the spouting system dominated by the non-spherical particles and that dominated by bed materials were proposed.The CFD-DEM model of spouting cylindroid particles was improved in the current dissertation.The particle with perfect cylindroid shape was represented with the combined geometric elements method.With fully analyzing the various contact criterions between cylindrical surface,flats and edges and improving the syamlal-O'brien drag model,and thus calculating the contact forces between cylinders and interaction forces between cylinders and fluid more accurately,the CFD-DEM simulations on "turbulent gas phase + real cylinders + spouting" was achieved.Based on the CFD-DEM simulations,the effects of particle shape on the spouting characteristics were investigated in the particle scale.The numerical scale-up and design method were developed.By directly predicting the gas-solid flow behaviors in large-scale spouted bed with the CFD approach,the relationships between the minimum spouting velocity and the particle properties,bed structures and operating conditions were systematically studied and a new correlation was proposed.Lastly,the numerical scale-up method was used to design an industrial scale biomass-carrier mixer.