Intraparticle Heat And Mass Transfer And Synergistic Mechanism In A Water Gas Shift Reaction Fixed-bed Reactor

The water gas shift reaction(WGSR)plays a crucial role in the process of reforming hydrogen production.Water gas shift reaction reactors are generally particle-filled fixed-bed tubular reactors.There are two common simulation methods today: Particle-resolved CFD(PRCFD)and pseudo continuum model(PCM).However,the particle analytical model is difficult to apply to large-scale actual production due to the high computational cost,and the accuracy of the PCM is not good.In this research,an anisotropic continuum model(ACM)with suitable computational cost and accuracy is proposed based on PRCFD and PCM,and a numerical simulation of the heat transfer process in the water-steam fixed-bed reactor is carried out,revealing its synergistic mechanism.First,we reconstructed the bed topography using discrete element methods and reconstructed the bed geometry filled with cylindrical and spherical particles.Next,we applied different physical equations to the PRCFD,PCM and ACM.After that,we processed the simulation results to obtain flow,heat transfer,mass transfer and reaction distribution cloud diagrams,and statistically obtained the axial and radial average results.Second,we investigated the reactors filled with spherical and cylindrical particles for different particle diameters and reactor diameters.When the diameter of the reactor remained unchanged and the particle diameter changed from 5 mm to 7 mm,the pressure drop decreased by 50%-70%,which was caused by the larger gap between the particles,the decrease in the flow rate,and the decrease in the specific surface area.In addition,the average age of the gas has increased;the maximum temperature rise of spherical particles decreased by 7%,and the average temperature rise of cylinders increased by 8%,indicating that the increase in the diameter of spherical particles is conducive to reducing the temperature;the average reaction rate decreased by 20%,the reactor The outlet conversion rate dropped by 27%,indicating that increasing the particle diameter still significantly hindered the reaction.When the particle diameter remains unchanged and the reactor diameter decreases from 20 mm to 14 mm,the pressure drop in the reactor decreases by 20%-40%,and the gas age also increases;the average temperature rise of spherical particles decreases by 20%,while the average temperature of the cylindrical particles varied less;the overall conversion was reduced by 11% due to the reduction in particle volume.It shows that reducing the diameter of the reactor can effectively reduce the temperature of the reactor and improve the utilization efficiency of the catalyst.Finally,we analyze the characteristics of the two mainstream methods,PRCFD and PCM,and propose ACM based on the conclusions of Chapter 3 and their advantages.We found that the accuracy of PRCFD lies in the analysis of the complete geometry,so we compress the 3D geometric information into 2D information for radial porosity;in addition,we use the analytical simulation of a single particle to obtain an effective factor that varies with temperature and mole fraction.Finally,the PRCFD results were used as the benchmark to compare the ACM and PCM results,and it was found that ACM improved the conversion rate accuracy by 20% and the temperature accuracy rate by 70%,which was two orders of magnitude lower than the calculation time of PRCFD.Furthermore,it is proved that the radial geometry of the particle bed,the heat and mass transfer within the particle and the interaction between the physical fields lead to the special radial distribution of the physical field,while the axial geometry has little effect on the physical field.