Study On Flow Field Characteristics Of Double-Ring Radial Reactor And Simulation Of Methanation Process

The methanation reaction is a strong exothermic reaction,which is often carried out in a fixed bed.If the heat generated cannot be removed in time,catalyst deactivation will occur,which will seriously affect the methane production rate and reactor performance.The double-ring radial reactor has the advantages of large flow area,small pressure drop and fast heat dissipation,and is suitable for strong exothermic reactions such as methanation reactions.Therefore,it is necessary to study the double-ring radial methanation reactor.This paper takes the double-ring radial reactor as the research object,and uses the PFC-CFD method to study the flow field characteristics and simulate the methanation process.First,after the numerical model of the double-ring radial reactor was established using SCDM software,spherical catalyst particles were filled in the inner and outer beds using PFC-3D software.Secondly,FLUENT software was used to simulate the cold flow field of the reactor.This paper explores the influence of reactor structure parameters such as particle size,open porosity and flow channel cross-sectional ratio on the flow field.The optimal reactor structure was obtained based on the principle of optimal flow field distribution in the inner and outer bed layers.Finally,based on the optimal structure of the reactor,the thermal simulation of methanation was carried out to explore the influence of the three operating conditions of inlet temperature,gas velocity and feed gas hydrogen-carbon ratio on the methanation process.Using the orthogonal experiment method to obtain the optimal parameter combination that can maximize the methane yield.The research results show that:（1）In the cold simulation,the fluid diffuses mainly in the radial direction on the upper part of the catalyst bed,and the flow field is relatively uniform.The fluid flows both radially and axially at the lower end of the catalyst bed,and the flow field is chaotic.（2）When exploring the influence of particle size on the flow field,two situations were discussed,namely,the accumulation of particles of the same size in the inner and outer beds(d_{p inner}=d_{p outer}=10,12,16,20mm)and the accumulation of different particles in the inner and outer beds(d_{p inner}=10mm,d_{p outer}=20mm;d_{p inner}=20mm,d_{p outer}=10mm).Comprehensive analysis found that when the particle size of the bed layer is 12mm,the bed uniformity is the highest,but the maximum difference in uniformity is 0.171,indicating that the particle size has a small effect on the flow field.（3）The flow field changes when the flow channel cross-sectional ratio is 1.44,2.85,4.33,5.84 and 7.39.When the cross-sectional ratio is 2.85,the uniformity of the inner and outer beds differs by 0.056,and the overall uniformity is higher.（4）When exploring the influence of the opening rate of the distribution cylinder on the flow field,two situations were discussed,namely,the inner and outer bed distribution cylinders use the same opening rate(φ_inner=φ_outer=0.044,0.087 and 0.121)and the inner and outer beds distribution cylinders use the different opening rate(φ_inner=0.087,φ_outer=0.044;φ_inner=0.044,φ_outer=0.087).Comprehensive comparison shows that whenφ_inner=0.044 andφ_outer=0.087,the uniformity of the flow field between the inner and outer beds differs by 0.001,and the overall uniformity of the reactor flow field is the best under this structure.（5）In the thermal simulation,the reaction at the top of the reactor is more complete and the temperature is the highest.Using orthogonal simulation,it is found that the inlet gas velocity has the greatest influence on methanation.When the temperature is 538.15 K,the inlet gas velocity is13 m·s^-1,and the feed gas hydrogen to carbon ratio is 3.5,the methanation yield is the highest.