Study On Spouting And Fluidization Characteristics Of Wet Particles

The wet particles flow system has widely existed in the energy, environment protection,chemical industry, food, pharmaceutical and other fields. In recent years, for the national strategic emerging industries, the wet particles flow technology also has been involved in many new techniques. Such as the generating hydrogen by catalytic reforming in crude oil from biomass pyrolysis in new energy field, the coating of functional granular material in new material field, the coating of targeted drugs in new medical field.As we know, the normal gas-solid two-phase flow for dry particles has been studied in depth, however, the wet particles flow behavior was researched superficially and scatteredly.The wet particles spouting and fluidization behaviors are much more complicated compared to the normal gas-solid two-phase flow, which is the hot spot issue during the development of multiphase flow research. The researches of wet particles spouting and fluidization characteristics can provide basic data and theoretical support for the industrial application and also promote the development of multiphase flow, which has important practical significance and academic value.The present work is devoted to the wet particles flow characteristics in spout bed and bubble fluidized bed with Geldart-D particles by experimental and simulated approaches.A visual wet particles spouted bed (cylindrical and semi-cylindrical spouted bed)experimental system was established. The gas-solid flow characteristics of wet spouted bed were studied systematically with different liquid saturations conditions (S=0?1). The flow patterns for wet particles spouting process were identified. Meanwhile, the flow pattern maps were also plotted for describing the flow patterns transitions of wet spouting process, and the region of liquid saturations for stable spouting were obtained. The relations between important hydrodynamics parameters such as pressure drop, minimum spouting gas velocity,particles circulation rate and the geometrical parameters, operating parameters were presented.Based on the theoretical analysis and experimental data, the correlations of minimum spouting velocity which can be used for wet spouted bed were developed.A visual wet particles fluidized bed (pseudo two-dimensional and three-dimensional fluidized bed) experimental system was established. The fluidization behaviors of wet Geldart D-type particles were studied systematically. The gas-solid flow characteristics of wet particles fluidization were obtained, including flow patterns, pressure drop, minimum fluidization gas velocity and particle mixing characteristic. The differences between dry and wet particles fluidization process were analyzed contrastively. A new particle mixing analysis method was built to study systematically the particle mixing characteristic in the wet fluidized bed. The effects of liquid saturation, particle density, particle size on the mixing behavior were systematically studied. A simple model is proposed to evaluate the initial segregation tendency for wet particles mixture with different densities in a fluidized bed.The repose angle measurement experiments for dry and wet particles were carried out.Based on the experiment, the DEM simulation about wet particles free stacking process was carried out. The shortcomings about traditional cohesive force model for wet particles flow simulation were realized. Based on that, a modified cohesive force model was proposed and applied to DEM simulation for wet particles flow. The simulation results agree well with experiment results.Ultimately,the CFD-DEM numerical simulation models were established which can be used for the cohesive/wet particles gas-solid two phase flow. Based on these models,the 3-D simulation about cohesive/wet particles spouting process was carried out successfully.Meanwhile, the influence of differences cohesive force magnitudes and distances to spouting process were analyzed. The association between the micro force among particles and macroscopic and mesoscopic gas-solid flow phenomenon was realized successfully. The mechanism of cohesive/wet particles dense gas-solid flow was revealed.