Numerical Simulation Of Slugging Bed Containing Geldart A Particles

Slugging fluidization is a special flow pattern closely related to the diameter of the bed in gas-solid two phases’fluidization.It is easy to occur in a fluidized bed with small diameter and high level.If the superficial gas velocity reaches the minimum slugging velocity,there will be a slugging phenomenon in the bubbling bed.As the superficial gas velocity is further increased,the frequency of the slug rupture is intensified,and the flow pattern gradually transitions from the slugging to the turbulent fluidization.The formation,coalescence and rupture of the slug is one of the main features of the slugging bed,and it is also the main reason for the decrease of the bed contact efficiency and the increase of the fluctuation.Therefore,if the above-mentioned motion characteristics of the slugs are deeply understood,it is helpful to provide reference and guidance for optimizing the design of the bed,or the regulation of the bed operation in the project.Based on the Eulerian-Eulerian two-fluid model which was integrated with the kinetic theory for particle,the numerical simulation of the gas-solid fluidized bed after modifying the drag model showed that the modified drag model can accurately and reasonably simulate the slugging characteristics of fluidized bed through the comparison of experimental results and empirical formulas.In order to ensure the accuracy and computational efficiency of the simulation results,other parameters and equations in the model are determined.In the range of superficial gas velocity 0.09≤U_g≤0.39 m/s,the standard deviation of the differential pressure fluctuation inside the bed increased with the increase of U_g,which corresponded to the change of flow pattern from bubbling to slugging until to the maximum stage of slugging.The gas-solid flow in the bed was mainly affected by the motion characteristics of the axial slug.The pressure drop,the expansion ratio of the bed,the average rising speed of the slug,and the maximum length of axial slug increased with the increase of U_g,and the position of the maximum axial slug decreased as U_g increased.When U_g exceeded 0.39 m/s,the standard deviation of the differential pressure fluctuation inside the bed decreased with the increase of U_g,which corresponded to the change of flow pattern from the weakening of slugging until to the turbulent.The gas-solid flow in the bed was mainly affected by the motion characteristics of the wall slug.The pressure drop,the expansion ratio of the bed,the average rising speed of the slug,and the maximum length of axial slug decreased with the increase of U_g,and the position of the maximum axial slug increased slightly as the U_g increased.In order to understand the spatiotemporal motion characteristics of the slug in the slugging bed,based on the above simulation results,the first slug rise speed,length,slug pressure and standard deviation value were analyzed and correlated,and the relationship between length and the pressure’s standard deviation in side the slug during the first slug motion were found.It is consistent with the analysis of the average characteristics of the slug,and it is verified that U_g=0.39m/s is still the boundary point of the slugging bed.When the superficial gas velocity is 0.09m/s≤U_g≤0.39 m/s,the degree of slugging in the slugging bed is also increased with the increase U_g.The maximum length and average rising velocity of the first slug in the bed are increasing with the increase of U_g.The first slug generating position is decreased by the increase of superficial gas velocity.When U_g>0.39 m/s,the slugging bed has a tendency to change to the turbulent bed.The degree of slugging in the bed gradually decreases.The average rising velocity and initial position of the first slug in the bed increase with the increase of U_g.The maximum length of the first slug and its continuous period decrease with the increase of U_g.