Experimental And CFD-DEM Numerical Study On The Fluidization Characteristics In A Liquid-Containing Gas-Solid Fluidized Bed

From the development of gas-solid fluidization,there have been some characteristic gas-solid fluidized bed reactors to meet different requirements,such as liquid-containing gas-solid fluidized bed reactors.The liquid phase addition increases the inhomogeneity of flow field and the complexity of hydrodynamics,and it also increases the contacting areas between different phases.Therefore,these liquidcontaining gas-solid fluidized beds are commonly used in olefin polymerization,fluid coking,fluid catalytic cracking,spray granulation and other processes.However,the liquid addition causes the formation of the inter-particle liquid bridge force and makes particles sticky,which could cause particle agglomerations form and then affect the fluidization behaviors.Therefore,it is of great significance to study the fluidization characteristics under liquid to the industrial production processes.This work focuses on the effect of liquid content on fluidization characteristics,the effect of liquid properties on the fluidization characteristics,the effect of fluidizing gas temperature on the fluidization characteristics and heat transfer characteristics in a liquid-containing gas-solid fluidized bed.It is studied to provide theoretical guidance for the regulation and application of liquid-containing gas-solid fluidized beds in the actual industrial production processes.1.The study mainly investigates the fluidization characteristics of dry particles under different gas velocities and the fluidization characteristics of liquid-containing particles under different liquid content in a pseudo 2D fluidized bed using camera and acoustic emission techniques.For liquid-containing particles,as the liquid content increasing,the bubble changes from a regular circular shape to a narrow shape and the gas channeling happens.In the axial radial distribution of acoustic energy of liquid-containing particles,as the liquid content increasing,the acoustic energy tends to decrease in most region,especially in the lower bed region.It can be obtained that the increase of liquid content reduces the collision frequency of liquid-containing particles.Compared with the acoustic energy distribution of dry particles with gas velocity,the distribution of acoustic energy of liquid-containing particles with the increase of liquid content is more complicated and variable.Thus,the increase of liquid makes the fluidization characteristics more complicated.2.The study mainly investigates the fluidization characteristics in a liquid-containing fluidized bed as increasing liquid content V* and surface tension Bog are simulated using CFD-DEM with liquid bridge force model.Through the comparison of fluidization process,bed expansion ratio,particle concentration and particle velocity,the influence of liquid surface tension on fluidization characteristics is more significant.The particle agglomerations behavior under different V* and Bog are compared.The results show that at lower V* small particle agglomerations occur only when Bog is higher while at higher V* obvious particle agglomerations occur even when Bog is lower.The stagnant height reflected from the distribution of particle velocity increases with V* and Bog and then the stagnant region expands.The increase in stagnant height under the effect of surface tension is more pronounced than the liquid content.In the whole bed,the size of the spout region,annulus region and fountain region decreases with the increase of liquid content,which shows a good regularity.While,the distribution of these regions under the influence of surface tension is more complicated and variable.Above all,it can be obtained that the liquid surface tension has more significant influence on the fluidization characteristics.3.Based on the above study of the effects of liquid content on fluidization characteristics using CFD-DEM,the effects of gas temperature on the fluidization and heat transfer characteristics are studied by changing gas temperature.The results show that the fluidization characteristics are similar under different gas temperatures.However,as the gas temperature increasing,the agglomeration phenomenon becomes more obvious and the size of particle agglomerations increases.The fluidizing gas temperature has different effects on the distribution of particle concentration under different liquid contents,mainly in the surface of the initial bed and in the higher region of the bed.An increase in the fluidizing gas temperature reduces the velocity of the particles,especially in higher region of bed.The particle temperature,Rep and Nup of particles have larger values in the middle spouting region and the non-fluidizing region on both sides of the bottom of bed.Thus,the heat transfers in these region is well.However,due to the assumption of numerical model,there are still some differences between the fluidization characteristics under liquid in high temperature environment and the actual production process,and thus further research is needed.