Study On Flow Characteristics Of Intermittent Liquid-solid Fluidized Bed With Stepped Flow Velocity And Fluctuation

Biological fluidized bed technology is a new and efficient wastewater treatment technology.Because of its good mixing,heat and mass transfer characteristics,simple structure,convenient operation,and low cost,the technology has received increasing attention in the field of wastewater treatment and has become a research hotspot and direction in this field.Under the driving force of liquid flow or airflow,the carrier particles in the biological fluidized bed mostly move in the same direction with the liquid,and the relative speed between the liquid and the solid phase and the transfer strength between the phases is restricted,which makes it difficult to further improve the efficiency of wastewater treatment,and the applicability of fluidized bed to particle types is weak.Therefore,this paper proposes to build a step velocity pulsating intermittent liquid-solid fluidized bed to make the liquid flow rate change periodically,to further improve the efficiency of wastewater treatment.Based on this,a pulsating batch liquid-solid fluidized bed was designed and built,and the flow characteristics of the pulsating batch liquid-solid fluidized bed were explored through the combination of experiment and numerical simulation.On the pulsating fluidized bed test bench,using polypropylene spherical particles as the carrier,the flow pattern of the fluidized bed was obtained by continuously changing the pulsation amplitude and pulsation period of the liquid velocity.The experimental results show that the experimental data and numerical simulation data of the average axial solid hold-up and the average radial solid hold-up of the fluidized bed tend to be consistent with the deviation within 15%,which verifies the accuracy of the numerical simulation results.In this paper,the Euler-Euler double fluid model and particle kinetics method were used to study the flow characteristics of pulsating fluidized beds,such as mean axial solid holdup,mean radial solid holdup,radial particle velocity,and liquid-solid phase relative velocity.The simulation results show that: In a complete fluid velocity change period,the whole bed of average axial distribution of solid holdup is relatively uniform,along with the pulse amplitude,pulse cycle,with the increase of particle size and the central axial solid holdup increases gradually,at the top and bottom of the shaft to reduce solid holdup,when pulsation amplitude increasing,the average axial solid holdup and present the phenomenon of evenly in the bed,particle and the liquid density difference,the greater the average axial solid holdup distribution of the whole bed is more uneven.Due to the sidewall effect,the average radial solid holdup at the bed height H=1m shows a distribution pattern of low in the middle and high near the sidewall.With the increase of liquid velocity pulsation amplitude,pulsation period,liquid-solid density difference,and particle size,the relative velocity of the liquid-solid phase in the whole bed increases first and then decreases slowly.