Process Simulation Of Methanation In Fixed-bed And Structural Strength Analysis Of Reactor

By using ANSYS-Workbench software and combining with the data of the reactor structure, import and export parameters of 5000 m³ /h methanation demonstration unit, the self-heating methanation fixed-bed reactor has been studied. Firstly, the catalytic bed voidage distribution and its links with the flow characteristics were analyzed, and then the flow pattern of the entire reactor has also been studied. Structural parameters were optimized for uniform flow distribution. Secondly, methanation kinetics equation was added into the existing fluid model by writing the source term with CEL language. The internal field distributions were extracted and the influence factors of temperature distribution and methane yield were studied. Finally, based on the temperature field and using "thermal- mechanical coupling" method the structural strength of the reactor has been evaluated.The results show that:?1? combining PFC-3D with ANSYS-APDL stochastic spheric packed-bed model with variable diameter was constructed. The voidage fluctuates according to the distance from wall and near the wall remarkable "wall effect" is existed. The speed fluctuation is consistent with the voidage. The fluctuation of pressure drop decrease gradually with the decreasing diameter.?2? The flow pattern inside the reactor is laminar flow. With the comprehensive influence of voidage and boundary layer, the extremum of speed appears in the center and the position that is 250 mm from center. There is non-ideal flow in annular space and then adding turbulence ring board at outer cylinder wall got uniform flow distribution.?3? In catalytic zone, temperature rises up quickly before slow affected by the concentration of reactants in axial direction. In radial direction, temperature distribution appears " high at both sides, low at intermediate " and temperature wave within the range of 5K to 30K. Methane yield and temperature field are influenced by the inlet temperature, flow rate, the ratio of H₂/CO and the structure. The operation scopes of inlet parameters were determined through the numerical simulation and analysis.?4? The temperature in axial and radial direction changed greatly at the wall of inner cylinder, which results in high thermal stress. The axial temperature gradient brings larger secondly stress and the radial temperature gradient cause larger peak stress which may cause fatigue.