Discrete Element Method And Computational Fluid Dynamics Coupling Simulation Of A Fixed Bed Reactor

Reactor is a common device in chemical production.According to the flow state of solid particles in the reactor,the reactor can be divided into three types.In fact,fixed bed reactor has been widely used in chemical industry and has been used in most chemical reactions.The flow,heat transfer and mass transfer in fixed bed are complex phenomena.When the catalytic reaction is carried out in fixed bed reactor,the catalytic reaction has multi-scale characteristics in time and space.In the process of the ethylene epoxidation,reactor as the core of the process equipment,inside the reactor have the features of strong exothermic,through the research of characteristic parameters for related inside the reactor can indirectly reflect the reactor bed inside for realizing the optimization of the reactor bed structure has important significance.The experimental measurement method which is limited by the detection instruments cannot directly address the continuous change of the flow field in the reactor bed.On the contrary,the numerical simulation method can accurately and comprehensively obtain internal changes of whole reactor bed.Choosing proper fixed-bed reactor model can replace expensive small-scale experiment to some extent.In the gas-solid two-phase catalytic reaction,the fixed bed is formed by the accumulation of catalyst particles.On the one hand,there is still a lack of research on how the size and shape of the catalyst and the filling mode of the catalyst particle bed affect the mass transfer and heat transfer efficiency inside the fixed bed reactor.On the other hand,due to the limitation of the structure of fixed bed reactor,the catalyst can only be large block catalyst.With the development of advanced material manufacturing technology,many kinds of catalysts,mainly columnar catalyst model,have been widely used in the accumulation of granular bed in fixed bed reactors.This paper studies from the following three aspects:(1)The flow mass transfer in a fixed bed reactor is studied based on the porous media model in computational fluid dynamics.Under the condition of only considering the fluid flow,the porous media simulation method in Fluent software is used to carry out multi-group simulation analysis of industrial grade single-tube fixed bed reactor with different pressures and different pipe diameters.The main research contents include the relationship between pressure drop and porosity at one temperature,two pressures and three sizes of reaction tubes.The velocity variation law at different heights of the center line of fixed bed,Fluid velocity profile of a circular plane cross section in a porous medium region.Based on calculation results of multiple group porous media model,results show that with the increase of catalyst particle fixed bed porosity,the overall bed pressure drop gradually decreases.Especially when the porosity is 0.3,the overall bed pressure drop is consistent with the experimental results.(2)A catalyst particle model is established for particle simulation based on discrete element method simulation EDEM software.Two kinds of catalyst geometry models are designed by using 3D design software,and on this basis,four kinds of catalyst particle models are formed by using basic spherical particle polymerization in EDEM software.A discrete element method is used to study the porosity variation of catalyst particles with different shapes in fixed bed.Discrete element method is used to study the movement of catalyst particles under the action of gravity,the number and porosity of catalysts in the fixed bed formed by catalyst particles at different initial falling velocities are studied,and the porosity of the catalyst bed is increased without changing the overall structure of the catalyst particle model.(3)The CFD coupling DEM method has been widely used to simulate the flow field inside catalyst particle fixed bed.Meanwhile,influence of shapes of catalyst particles model and stacking of fixed height particles bed on the overall pressure drop and velocity distribution inside the field is also studied by the CFD coupling DEM method.EDEM software is used to simulate particle generation and catalyst particle bed accumulation,and Fluent software is used to simulate the results of pressure drop and velocity distribution inside the fixed bed.A series of transfer equations are used to solve the changes of flow field parameters.And the results of velocity change and pressure distribution inside the bed are obtained.