Numerical Simulation Of Methanation Process And Reactor Design For Structured Catalysts

The two bed methane process is composed of a conveying bed and a fixed bed,and the methanation reaction is the strong exothermic reaction.The conveying bed has excellent heat transfer performance,and the bed temperature of the methanation reaction is close to isothermal.Most of the material gas is carried out in the conveying bed,and the small part of the reaction gas reacts in the fixed bed.In this process,the problem may be that the particles will bring into the fixed bed when the particles collide with each other,which will cause the blockage of the traditional catalyst and increase the pressure drop of the bed.In order to avoid this problem,we need to study the low pressure methanation fixed bed reactor.We chose the axial flow reactor with structured catalyst.Based on ANSYS workbench,numerical simulation method was used to study four parts.First,a flat plate reactor with the surface reaction also used by the single channel is simulated,and the single channel is simulated by the same method.The regular catalysts were simulated by simulating single channel instead of multi channels,and the regular catalysts for surface reaction and volume reaction were simulated respectively.The second part is changing inlet temperature,pressure,velocity,concentration of operating parameters to study the influence on conversion of the same length and the catalyst length reached the technical requirements of the conversion.The third part studied the bed of methanation catalyst.Study on the pore shape and size effect on the transfer,pressure drop,conversion rate;influence of pore material and catalyst bed distance on methane conversion.The fourth part is to determine the fixed bed process parameters and structure size corresponding to the bed flow velocity of 0.95m/s,1.81m/s,and the fixed bed inlet structure optimization.Then the strength of the reactor is designed and the strength of the designed reactor is checked by the method of thermal fluid solid coupling.The designed reactor meets the need of strength.The results show that:(1)the simulated flat plate methanation reactor can be used to simulate the regular catalysts and the single channel can be used instead of multi channels to simulate the regular catalysts.(2)Regular catalyst conversion decreased with the increase of flow rate;the higher the entrance pressure is,the higher the conversion;the higher the temperature is,the higher the conversion.Entrance temperature required between 260℃-320℃;Fixed bed entrance concentration based on fluidized bed conversion.Fluidized bed conversion efficiency was more than 65%,and he catalyst will not be deactivated in the fixed bed;The concentration and velocity conversion relation were observed.(3)The circular channel has the best transfer effect.The square is second,and the triangle is the worst.But the pressure drop and the conversion rate of the triangular channel are the best,and the circular channel is the worst.The smaller the pore size is,the higher the conversion rate is.For the regular catalyst with large feed concentration,the regular catalyst of metal material can be selected and the outer wall can keep constant temperature in order to avoid deactivation of catalyst.The gap between the catalyst beds has no effect on gas mixing,and it is not necessary to set the segmented catalyst.To achieve the desired rate of conversion,the flow rate has nothing to do with the amount of neat catalyst used to produce the surface reaction.(4)The reactor size of the reactor with flow rate of 0.95m/s and 1.81m/s was determined.Adding the insulation material on the reactor wall achieved the strength requirement.