Three-Dimensional Cfd Simulation Of Gas-Liquid Two-Phase Flow On Particles Near The Wall Of The Trickle Bed Reactors

The Trickle-bed reactor is an important gas-liquid-solid three-phase catalytic reactor widely used in petroleum refining,petrochemical and other industries,especially in the hydrotreating of diesel and gasoline.In recent years,researchers have conducted a large number of studies on the parameters of gas-liquid two-phase flow in the trickle bed reactor on a macro scale,but there are few reports on the local flow behavior in the trickle bed.The local flow state in the trickle bed,such as the uneven distribution of liquid on the catalyst or the formation of short circuit,channel flow in the catalyst bed,causes the performance of the reactor to decrease.A full understanding of the hydrodynamic properties of the catalyst bed is important for the design and optimization of the trickle bed reactor.In this paper,the VOF volume model built into the CFD software is used to simulate the surface flow phenomenon of gas-liquid two-phase flow catalyst particles.It is observed that the flow of liquid on the surface of the particles during the trickle located at the intermediate position and the near wall position of the bed of the trickle bed in this chapter.For the particles at the middle of the bed,the uniformity of liquid distribution on the surface of the particles has a strong correlation with the gas velocity and liquid velocity,and the single particle flow pattern is also consistent with the macroscopic flow pattern.For the particles near the wall position,the gas and the liquid velocity have a greater influence on the surface liquid distribution.The near-wall particle flow transition curve shifts to the left compared with the macroscopic flow pattern.Three functions are defined to quantify the uniformity of the liquid phase distribution on the surface of the particles.Combined with the above factors leading to the change of flow pattern and liquid film distribution,the local channel phenomenon of the catalyst bed is avoided,and the reference operation range is provided.The effects of gas velocity,liquid phase velocity,particle size and other factors on the distribution of liquid film on the surface of the particles at the intermediate and near-wall positions and the size of the gas phase vortex at the lower end of the particles were investigated.The results show that the radius of the gas phase vortex increases with the increase of the gas phase velocity and decreases with the increase of the liquid phase velocity.When the liquid phase velocity is larger,the gas phase vortex radius decreases at the lower end of the particle;The speed or liquid velocity will increase the surface wetting rate of the particles.The change of droplet size within a certain range has no obvious effect on the gas vortex radius and surface liquid film distribution at the lower end of the particle.The vortex radius at the lower end of the particle located near the wall is lower than the vortex radius of the particle at the middle position,and the wall effect also causes a large difference in the size of the two vortices at the lower end of the particle.When the distance between the near walls is small,the droplets tend to accumulate between the particles and the wall voids,and the gas vortex radius at the lower end of the particles becomes smaller.The liquid film on the surface of the particles is unevenly distributed.The effect of gas velocity and liquid velocity on the vortex radius at the lower end of the near-wall position is the same as that particles at the middle position.Only the left vortex appears at the lower end of the particle at low gas velocity and liquid velocity.The liquid film on the surface of the particle is shifted to the near wall side and it can results an uneven distribution of liquid film.