A Study On Gas And Liquid Flow Characteristics In Trickle-bed Reactors At Particle-scale

The trickle-bed reactors(TBRs)are widely used in catalytic hydrogenation and other petroleum processes.A great knowledge of the fluid flow characteristics in the trickle bed is the key to the design of TBRs.The numerical simulation methods with the advantages of simple operation and low cost have been widely employed to study the fluid flow characteristics in TBRs.Besides,the fluid flow characteristics inside the reactor can be obtained by numerical simulation,which are difficult by experimental methods.Numerical simulation study at the catalyst particle-scale ensures that the local fluid flow characteristics in TBRs can be accurately obtained,provides more detailed support for the studies of fluid flow characteristics at bed-and pore-scale,and offers more accurate data for the optimal design of TBRs.Herein,the simulation of the fluid flow characteristics in TBRs at catalyst particle-scale is performed.In this study,a multiphase volume of fluid(VOF)model was adopted to study the fluid flow characteristics of gas and liquid fluids flowing through one-,two-and threeparticles.The results showed that the fluid flow characteristics on the surface of and around the catalyst particles were greatly affected by the adjacent particles.The different number of adjacent particles led to the variation of the fluid flow characteristics on the surface of and around the catalyst particles.For single particle,the effects of gas and liquid velocity and particle size on the fluid flow characteristics on the surface of and around the catalyst particles were investigated,respectively.The results showed that the increase of the gas and liquid velocity resulted in the decrease of the residence time of the liquid fluid on the surface of the catalyst particle and the transitions of the liquid fluid from the film flow to the rivulet on the surface of the particle.The gas velocity and particle size had a great influence on the velocity distribution around the particles and the downstream fluid flow morphology and the former was much stronger.For the two particles,the effects of gas and liquid velocity,particle spacing,and fluid properties were examined,respectively.It was found that the increase of the gas and liquid velocity leaded to clearer transitions of liquid fluid on the upper and lower particles surface from the film flow to the rivulet.And the maximum volume fraction of the liquid on the particle surface was greater than that of the single particle.Besides,with the increase of the spacing between catalyst particles,the variation of liquid volume fraction on the surface of the upper particle was almost consistent with that of the single particle.The maximum value of the volume fraction of the liquid on the lower particle surface gradually decreased and the eddy below the particle shed or even disappeared.The fluid properties had an influence on the liquid distribution on the surface of the particles and the fluid flow patterns around the particles.However,the gas and liquid velocity,the spacing between catalyst particles had a greater effect on the fluid flow characteristics than fluid properties.For the three particles,the effects of the gas and liquid velocity and the particle spacing on the fluid flow characteristics of the surface of and around the middle particle were investigated,respectively.The results showed that with the increase of the gas and liquid phase velocity,the maximum volume fraction of the liquid fluid in the middle particle was between that of the single particle and the two particles and the liquid fluid was more uniformly distributed on the surface of the middle particle.With the increase of the spacing between catalyst particles,the maximum volume fraction of the liquid fluid on the surface of the middle particle gradually decreases,and the eddy below the particle shed or disappeared.A plurality of smaller-sized eddies appeared below the particles in the presence of liquid fluid on the surface of particles.