Numerical Simulation Of Gas-Solid Flow Characteristics And Methanation Process In High-flux Circulating Fluidized Bed

The methanation reaction characteristics with rapid and strong heat release have always been an inevitable problem in the research of its reactor.The circulating fluidized bed reactor with raw gas as solid catalyst particle fluidization medium has better mass and heat transfer efficiency and is an ideal methanation reactor.However,the gas-solid two-phase flow in the reactor and the methanation process are not well understood.In this paper,based on the establishment of three-dimensional model of circulating fluidized bed reactor,the MP-PIC model was introduced to analyze the distribution pattern of catalyst particles and the methanation reaction process in the high flux circulating fluidized bed reactor by numerical simulation in CPFD software.Firstly,a full-loop geometric model of the same scale size was established with reference to the cold test device in the literature.Numerical modeling was carried out for the gas-solid flow characteristics in the high-flux circulating fluidized bed riser,and the influence of operating conditions?gas velocity U_g,initial material quantity M_p,operating pressure P?on the axial and radial flow characteristics?volume distribution,velocity distribution?of catalyst particles in the riser was analyzed.Then,on the basis of gas-solid two-phase flow,the methanation reaction kinetic model is coupled to carry out the thermal simulation,and the simulation results are verified by the experimental data reported in the literature.The internal flow field,temperature field and component concentration distribution of methanation circulating fluidized bed reactor were extracted,and the influence of catalyst flow characteristics on methanation yield was analyzed.The methane-forming process in the reactor was numerically studied under different temperatures,inlet velocity,pressure and raw gas H₂/CO ratio.The combination of operation conditions with the highest methanation yield was explored by orthogonal experiment.Finally,the structure of the return valve was optimized by taking the maximum particle circulation rate G_s and the minimum gas backflow as the target.The results show that:?1?By comparing the simulated value of riser pressure drop with the cold state experimental data in the literature,the curve is in good agreement,and the feasibility of the simulation method is confirmed.?2?The catalyst particles in the reactor were distributed in the axial direction with more lower part and less upper part,and in the radial direction with the distribution of"low center,high side wall",and determine the influence of operating conditions on gas-solid flow characteristics.?3?Through the methanation reaction simulation,the temperature field cloud chart,component concentration distribution cloud chart and data in the circulating fluidized bed were obtained.It was found that when the proportion of H₂/CO in the syngas was lower than 3,and the inlet temperature was lower than 460K,the lower CO conversion rate and CH4 yield would be obtained.Through the orthogonal experiment,it is found that the inlet velocity is the main influencing factor of the methanation process,and the combination of operating conditions with the highest methanation yield is the inlet temperature of 500K,the inlet velocity of 4m/s,and the H₂/CO ratio of 3.5.?4?Compared with the conventional U-type return valve,the N-type return valve with a 45°return inclined pipe has the best working performance under the same working conditions.