Simulation Of Liquid Phase Flow On Spherical Particle Surface Of Hydrogenation Catalysts

The combustion emission standards of fossil fuels are becoming more and more strict.For example,the national Ⅵ standard of diesel fuel clearly stipulated that the sulfur content should not exceed 10 μg/g.Trickle bed reactors(TBRs)hydrotreating technology is commonly used for diesel desulfurization,but the problem of poor liquid distribution is common.Therefore,it is still necessary to further study the liquid flow behavior in trickle bed reactors which commonly used in industry,to analyze the mechanism of the liquid phase distribution,and propose optimization countermeasures of improving the uniform distribution of liquids.In this work,computational fluid dynamics(CFD)method is used as the research method for the liquid-phase flow process on a single catalyst particle.After constructing the geometric model of the catalyst particle,the structured mesh of multi-layer O-Block is generated,and only the grid close to the surface of the particle encrypted,which can not only accurately capture the behavior characteristics of the liquid phase but also help to reduce the amount of calculation.VOF(Volume of Fluid)two-fluid model is selected for simulation,comparing with the image results obtained by high-speed camera in the control experiment shows that the model can accurately describe the liquid phase flow characteristics.The simulation results show that there is a suitable range for the effect of material physical properties on the distribution uniformity of the liquid phase.For the water-rigid spherical particles in this work,when the liquid surface tension is less than or equal to0.08 N/m,the viscosity is less than or equal to 0.0010 kg/(m·s),and the contact angle is less than or equal to 60°,the liquid phase can form a uniform liquid film.However,with the increase of each parameter,it will change to the flow state of maintaining a complete droplet.The contact angle is an important parameter to measure the wettability,and it has significant impact on the liquid phase flow state.When physical parameters are in the appropriate range,whether the liquid phase can form a uniform liquid film is also affected by the operating conditions.For the object in this work,droplet-particle size ratio of 1:3,initial droplet impact velocity of 0.8 m/s,and gas-phase inlet velocity of 1.0 m/s are the optimal operating parameters.In terms of increasing the gas-liquid interface area,reducing the thickness of the liquid film or the mass transfer resistance,and prolonging the residence time of the liquid phase,dividing the same amount of liquid into multiple parts and hitting the particle surface intermittently is better than impacting all the liquid at one time,which can enhance the mass transfer between the gas and liquid phases.After the droplet feeding is changed to hollow droplet or bubble,the liquid phase tends to aggregate into a complete droplet due to the increase of the liquid surface energy,which makes the liquid phase dispersion even worse.The flow form of the liquid phase after impacting the particle mainly depends on whether the liquid phase has enough kinetic energy to overcome surface tension,solid-liquid interface adhesion,and intermolecular friction in the initial tens of milliseconds of impact.If a uniform liquid film cannot be formed at the initial stage of the impact,the surface energy will re-aggregate the liquid phase into a complete droplet through surface tension work,then lack of power to redisperse the liquid phase,so the liquid phase maintains the droplet state and quickly slides down from the particle surface.This paper studied the effect of material properties,operating conditions,etc.on distribution of liquid phase on spherical particle surface,deepened the cognition of liquid phase flow characteristics in trickle bed,which provides basic information for optimizing designing of the trickle bed.