Research On Fluidization Characterics Inpulsed Fluidized Bed Based On CFD-DEM Electrostatic Model

Fluidized bed reactor is widely used in petrochemical,pharmaceutical,polymer and other industries.Although it provides good solid mixing,the electrostatic interaction between particles will promote the formation of particle agglomeration and reduce the fluidization performance.The performance of fluidized bed is highly dependent on the flow characteristics and bubble characteristics.In order to obtain better performance,the internals are often placed in the fluidized bed.Immersed tube is an internal component of fluidized bed,which can limit the bubble size and promote the gas-solid contact.At the same time,pulsed gas flow is an effective method to enhance particle mixing.Therefore,this paper focuses on the influence of pulse frequency and gas flow ratio on the flow characteristics of fluidized bed under static electricity,which has important guiding significance for production practice.In this paper,computational fluid dynamics and discrete element method are combined.Moreover,a CFD-DEM coupled numerical simulation platform of fluidized bed with pulse flow is established.The main part of the fluidized bed is selected as the calculation area,and the model is simplified as a two-dimensional rectangular bed.The effects of different pulse frequency and gas flow ratio on the flow performance of conventional fluidized bed and immersed tube fluidized bed are investigated in detail,and the optimal pulse gas flow conditions are obtained.In this paper,the influence of different pulse frequency on the fluidization characteristics of fluidized bed under static electricity is studied by numerical simulation.The best pulse frequency is obtained by analyzing the change of voidage,particle and gas velocity distribution and particle diffusion coefficient.At this optimal frequency,the ratio of pulse flow to steady flow is changed.The optimal ratio of pulse flow is obtained by analyzing and comparing the pressure drop of bed and particle flow.At the same time,considering that the immersed tube can limit the bubble size in the bed and enhance the mixing efficiency.The effect of pulsed gas flow on the flow characteristics of the fluidized bed under static electricity is also studied in detail.By comparing the influence of immersed tube,it is found that for the long-term fluidization system,the fluidized bed with immersed tube is conducive to the particles mixing.Then,the influence of the apparent gas velocity on the flow characteristics of the fluidized bed under static electricity is studied,and it is found that the higher apparent gas velocity is more conducive to the particle mixing.Finally,the effects of pulse frequency and gas flow ratio on the flow characteristics are analyzed and compared with the results of steady gas flow.The results show that the pulsed gas flow can improve the particle velocity and the ability of particle diffusion and mixing.For the conventional fluidized bed,the pulse frequency of 2.5 Hz has the most obvious effect on the flow characteristics.Reducing the ratio of pulse flow to steady flow to less than 0.5 can improve the fluidization effect.For the immersed tube fluidized bed,the period of electrostatic force on the particles is consistent with the pulse frequency.When the pulse frequency is 2.5 Hz,the electrostatic force on the particles is the largest and the movement is the most violent.The larger the ratio of pulsed flow,the stronger the particle mixing.In addition,the higher the axial velocity is,the higher the average motion height is.