Numerical Simulation Study Of Fixed Bed Reactor For Sng Methanation

Natural gas becomes an attractive choice in the transformation of energy industry development due to the safe and clean characteristics of low carbon quality. The process of synthesis gas methanation is the most important technology. Application CFD method to learn the complex physical and chemical changes in methanation process and the large exothermic properties related to synthesis gas reactor can provide the basis for the development of traditional reactor and further industrialization.The system for methanation of syngas was simulated in this paper. The two dimensional pseudo-homogenous mathematical model of methanation fixed bed reactor was established with taking methanation of CO and water gas shift reaction as the independent reactions. Using Fluent software to simulate the reaction system with the improved kinetic equation model and numerical method. First, verifiy the reaction under the experimental conditions and the simulation results agree well with the experimental values, indicating that the mathematical models and calculation methods are effective. Based on this, simulated different processes (reaction temperature, the partial pressure of CO、H2, volumetric flow rate) and the feed gas composition (contained CO2、H2O、CH4) and actual gas methanation reaction conditions, analysed the impact of these factors on the reaction system. By simulation methods, we can understand the distribution of gas composition along the axial in the reactor and the mass fraction distribution contours intuitively and clearly.Numerical results show that:in the investigated temperature range (553K-613K), when the gas volume flow is 0.30L/min and the operating pressure is 2atm as well the feed conditions are Ar:0.40, H2:0.50, CO:0.10, CO2:0, CH4:0, H2O:0, CO is completely conversed substantially. When the temperature increases from 553K to 613K, the chemical reaction rate becomes faster and the outlet volume fraction of methane has a small increase but not significantly, from 10.27% to 12.76%. The stable segment becomes long, the gas distribution in the reactor from unstable to reaching stable at 0.075m, 0.055m and 0.045m positions. For this paper, increasing the feed gas partial pressure of CO and H2 contributes to generating methane and the outlet volume fraction of CH4 increased accordingly at different temperatures. At 553K, the impact of flow rate on the gas composition is greater, when the flow rate increases from 0.20L/min to 0.60L/min, the outlet CH4 concentration decreases from 11.59% to 5.02%; when the reaction temperature is 573K, mainly affecting the gas distribution.CO2、CH4、H2O impact the outlet gas composition and the distribution of gas in the reactor at different temperature. CO2 participated in the water gas shift reaction to promote the methanation reaction, so the volume fraction of CH4 increases gradually under the above temperature. CH4 and H2O have effect on the export volume fraction of CH4, but the change is not obvious. The common phenomenon is that the gas distribution doesn’t reach to stability at 553K and 573K and reach to stability in different locations at 593Kand613K.