Study On The Process Intensification Of Mixing And Separation In A Novel External Loop Slurry Reactor

The gas-liquid-solid slurry reactor,taking the liquid phase as the continuous phase,has the advantages of large production capacity,simple structure,low energy consumption,good dispersion effect,excellent mass and heat transfer performance,and easy online addition and replacement of the catalyst,leading to a wide employment in the industrial production.Although the slurry reactor has so many advantages,there are still some difficulties for its industrialization.Among these difficulties,the fundamental one is the high cost and poor continuity for the separation of the clean liquid products from the solid catalyst,which is not conducive to industrial production.Additionally,the slurry pump,which is applied in the solid catalyst recirculation,is expensive and fragile.In view of the above problems,this project combines the directional flow in an external loop airlift reactor with the efficient liquid-solid separation in the hydrocyclone,and a new pilot-scale external loop airlift slurry reactor was first designed and built to realize the process intensification of the mixing and separation.In this topic,the hydrodynamics and mass transfer characteristics under different solid concentrations and operating conditions are explored experimentally and systematically,which could provide a theoretical basis for the designing,optimization,scaling-up,and evenly industrial applications of this kind of slurry reactor in the future.The main contents of this topic include the following parts.Firstly,the performances of separation and circulation in the new external loop airlift slurry reactor were qualitatively tested.Two kinds of brown corundum with different particle sizes(d₅₀= 66.11 μm and d₅₀= 109.7 μm)were employed.The superficial gas velocity was taken to be 0.068 m/s,and the circulation was kept for 4hours.It is found that the solid particles can be retained for a long time in the new slurry reactor,and the minimum particle sizes of solid particles in the slurry reactor were 6.82μm and 10.57 μm,respectively.Then,on the basis of qualitative analysis aforementioned,the hydrodynamic properties and mass transfer characteristics at the solid phase fraction of 0.3%,0.6%,0.9% were investigated.The results show that the gas holdup,circulating liquid velocity,and volumetric mass transfer coefficient increase with the increase of superficial gas velocity.Additionally,the higher the solid concentration,the smaller the gas holdup,the circulating liquid velocity,and the volumetric mass transfer coefficient are at the same superficial gas velocity.Finally,the influences of two critical operating parameters,i.e.,the top clearance and the liquid throughput on the hydrodynamics and mass transfer in the slurry reactor with a high solid concentration of 3% and free of solid particles are investigated to promote the mixing and yield.The results show that the gas holdup and volumetric mass transfer coefficient were reduced markedly when the top clearance and the liquid throughput increase at high superficial gas velocity.Additionally,the circulating liquid velocity can be promoted by 14.0% at most when the top clearance increases from 7cm to 22 cm,while the circulating liquid velocity can be increased by 97.3% at most when the liquid throughput increased by 3.3 times.Moreover,it was found that the flow in the riser changes from the homogeneous regime to the heterogeneous regime at the superficial gas velocity of 0.047 m/s.For the typical low solid concentration of 0.3%,the axial solid concentration distribution tends to be more uniform with the increase of superficial gas velocity.However,the uniformity of solid particles in the axial direction increases at first and then decreases for the solid concentrations of 0.6% and 0.9% when the superficial gas velocity increases.