Simulation Study Of The Methanation Shaped Catalyst

Through the analysis of the syngas methanation system,a reasonable physical and geometric model was established by multiphysics simulation software COMSOL Multiphysics.From the two scales of single particle and particle group,five irregular shaped catalysts were modeled respectively,and the simulation result were carried out to verify the reliability of the model.The effects of catalyst structure changes on fluid flow,mass transfer,heat transfer and reaction rate were investigated.The calculation results of single-particle show that under the condition of laminar flow,increasing the diameter of the hole has a greater effect on the flow than increasing the number of holes.At this time,the order of promoting the reaction for the five catalysts is as follows:4-hole>3-hole>7-hole>1-big-hole>1-small-hole.Under the condition of turbulent,increasing the number of holes provides more effective contact area and enhances mass transfer,which is much better than increasing the aperture.At this time,the effective utilization rate for 1-small-hole cylindrical catalyst is 20%～25%,1-big-hole is 30%～40%,3-hole is 45%～50%,4-hole is 65%～70%,7-hole is 80%～85%.Through the calculation of the reaction and transfer in the particle group,the fluid will shift radially when passing through the small hole or the group of particles with a small number of holes,which is favorable for heat transfer,but the hole will restrict the flow path and produce the radial flow.The average reaction rate in the seven-hole catalyst was the maximum,0.6656 mol·kg-1·s-1,Based on the best performance of seven-hole structure catalyst among the five kinds of irregular-shaped catalysts,an optimized plum-shaped catalyst is proposed.The highest temperature on the plum-shaped catalyst is 608K,which is lower than the maximum temperature of 630K on the seven-hole catalyst and help to enhance heat transfer and overcome the disadvantages of higher temperature rise in the seven-hole structure.At the same time,the calculation method was improved.The diffusion resistance in the methanation reaction is large,and the diffusion rate of H2 and CO is different,which result in a high ratio of hydrogen to carbon inside the catalyst.At the same time,the internal reaction conditions are changed compared to the surface of the catalyst.Therefore,according to the change of CO concentration in the catalyst,two different kinetic equations are applied to different regions of the catalyst.Under the control of two kinetics,the average reaction rate of methanation have been accelerated,which is closer to the actual process and show that the new model is more accurate.