Numerical Simulation And Experimental Study Of An Electric-to-gas Test Reactor

P2G（power-to-gas）is a promising energy conversion and energy storage technology.By electrolyzing water to produce hydrogen from renewable energy,and then converting hydrogen and carbon dioxide into natural gas that can be stored on a large scale,a stable energy supply can be provided,which can effectively overcome the intermittency and volatility of wind power and photovoltaic grid-connection and realize the consumption of large-scale non-water renewable energy by the power grid;it can also convert the surplus hydropower into other energy forms in the southwest of China in the flood season to alleviate the problem of abandoned water in the flood season.Power-to-gas conversion provides a new technical way to make full use of renewable energy and improve the supply capacity of natural gas,which has important engineering application value.Hydrogen methanation is a key technical problem in the whole process of power-to-gas conversion.Fluidized bed reactor is a new methanation reaction device proposed in recent years,but it is still in the theoretical and laboratory research stage at present,and there is a lack of large-scale test system to carry out in-depth research on the reaction process.A test system of fluidized bed methanation reactor with a capacity of 20k W has been set up in this paper;numerical simulation and experimental study were used to study the distribution of parameters such as gas component distribution,solid concentration,temperature and pressure in the reactor,and the influence of key parameters such as reaction temperature,pressure and gas velocity in the methanation process on catalyst performance and methane conversion rate;the optimization method of key design parameters and process parameters of fluidized bed reactor was studied.The results show that:（1）Through comparison and verification,the numerical simulation results are basically consistent with the experimental results under different operating conditions,indicating that the physical model and mathematical model established by numerical simulation in this paper have good rationality and accuracy,and the numerical simulation technology can be applied to carry out the auxiliary research on the scaling-up design of the fluidized bed reactor.（2）Under the condition of not changing the type of catalyst,the influence characteristics of the process parameters on the methanation reaction were obtained:with the increase of reaction temperature,the CO₂ conversion rate increased,but only with the increase of reaction temperature,the methanation reaction rate was not high,the CO₂ conversion rate was not higher than 86%;with the increase of space velocity,the CO₂ conversion rate is reduced,but higher volume space velocity can be obtained,and the amount of catalyst can be reduced;as the pressure increases from 0.3MPa to0.72MPa,the CO₂ conversion rate increases,and the pressure has the most significant effect on the methanation process;both numerical simulation and experimental results show that,in order to achieve a good CO₂ conversion rate,the operation parameters need to be combined and optimized.The optimal parameter combination for the designed 20k W reactor is the reaction temperature of 355℃,space velocity of7000m L·g^-1·h^-1 and pressure of 0.72MPa.（3）Within the range of process parameters selected in this paper,the numerical simulation results show that the temperature and pressure are uniformly distributed in the dense phase zone of the fluidized bed reactor,and the components of CO₂,H₂ and CH₄ are uniformly distributed in each section of the bed;in the actual test,the temperature of each section of the reactor is uniform and no abnormal phenomenon occurs,which indicates that the reactor can realize stable chemical reaction and obtain satisfactory fluidized quality within a wide range of parameters.（4）Within the range of selected parameters,CH₄ selectivity was higher than 99%;after more than 100 hours of various thermal tests,the selectivity is not changed,and the CO₂ conversion rate can reach 93%,which indicates that the catalyst selected in this paper has good stability and wide temperature adaptation range,and can be used in the fluidized bed methanation reactor.（5）In view of the problems existing in the use of single-stage fluidized bed reactor,an improved reactor system using two-stage reaction and two-stage water removal to recover heat is proposed in this paper,which can significantly reduce the pressure of the reactor and the cost of the reactor when the same conversion rate is reached.