Residence Time Distribution And Mass Transfer Of Droplet Flow In Three-phase Mini-fluidized Bed

Three-phase mini-fluidized bed has wide application prospects in the process industries owing to the advantages of high transfer efficiency,and controllable operation.Therefore,the researchers at domestic and abroad have widely investigated the characteristics such as multiphase flow.However,there are few reports on residence time distribution（RTD）of liquid phase and mass transfer in the three-phase mini-fluidized bed.In this paper,a mini-fluidized bed with 3 mm column diameter and 100 mm column height was designed and processed,the three-phase flow patterns were observed by an industrial camera,and the RTD of liquid phase and mass transfer of three-phase mini-fluidized bed were researched.Firstly,a conductivity method was used to determine the RTD of liquid phase in an air,water and glass beads three-phase flow system,which KCl tracer as an input signal.The results indicate that the RTD curves become significantly smaller,the mean residence time decrease and peclet number（Pe number）increase with the increase of superficial liquid and gas velocities.The mean residence time increases with the addition of solid particles.The flow is close to laminar flow when the superficial liquid velocity is set at 1.96-15.70 mm×s^-1,meanwhile superficial gas velocity 1.18-1.96 mm×s^-1.The mean residence time of liquid phase in the gas-liquid-solid mini-fluidized bed is 19.6±0.4-48.0±0.9 s.A correlation of the Pe number has a relative deviation of ±25%.Secondly,benzoic acid was used as solute,and a water and kerosene two-phase flow mini-system was formed to investigate the liquid-liquid mass transfer under droplet flow pattern.The inpacts of superficial water velocity,viscosity of water and column diameter on the mass transfer performance of two-phase flow were analyzed.The results show that the overall volumetric mass transfer coefficients grow with increasing superficial water velocity.The liquid-liquid extraction efficiency decreases first and then increase with the increase of superficial water velocity.The overall volumetric mass transfer coefficients and extraction efficiency both increases with increasing the viscosity of water or decreasing column diameter.Finally,the mass transfer of liquid-liquid-solid mini-fluidized bed was researched by introducing glass beads into the liquid-liquid flow system.The overall volumetric mass transfer coefficients of three-phase flow significantly enhanced compared to two-phase flow.The overall volumetric mass transfer coefficients and extraction efficiency both increase with the increase of initial height of the particles.When the superficial water velocity is set at 1.96-17.7 mm×s^-1,meanwhile superficial oil velocity 1.96-9.83 mm×s^-1,the overall volumetric mass transfer coefficients and extraction efficiency of three-phase mini-fluidized bed are 0.0451-0.213 s^-1 and 52.4-83.8（4）,respectively.A correlation of overall volumetric mass transfer coefficients in the liquid-liquid-solid mini-fluidized bed has a relative deviation of ±20%.