Simulation And Optimization Of SNG Reactors And Process

By analyzing the methanation system, a three-stage adiabatic fixed-bed methanation process with a loop after the 1st reactor was built. The CO methanation reaction and water gas shift reaction were selected as independent reactions, CH4 and CO2 as key components, a one-dimensional pseudo-homogenous mathematical model of the adiabatic fixed-bed methanation reactor was established. The model was calculated by the method of Runge-Kutta with Matlab. The reactor was simulated under the operating conditions as follows:the feed flow rate 800kmol/h, CH4-0.0149, CO2-0.1010, CO-0.1290, H2-0.7515, H2O-0.0000, N2-0.0036, the recycle ratio 3, the reaction pressure 3MPa and inlet temperature of three reactors 553K. The outlet temperatures of the three reactors are 879K,725K and 611K, and the CO conversions are 86.48%,99.20% and 100%, respectively. The dry molar content of CH4 out of the third reactor is 95.49%. A two-dimensional pseudo-homogenous mathematical model developed showed that the radial difference of temperature and concentration is small, and the one-dimensional model is enough to simulate the reactors.The influences of operating conditions were studied based on the above mathematical model. The results indicate that the methanation location would moves backward with the increase of feed flow. If the inlet temperature was increased, the outlet temperature would rise, and the CO conversion would decrease. Hydrogen-carbon ratio has little effect on the methanation reactor, and the value of H/C between 2.5 to 3.5 can meet production needs. Adding more water in the feed flow would decrease the outlet temperature and CO conversion of the reactor, this is an important method to regulate reactor temperature. Raising the operation pressure is benefit to the methanation reaction. Increasing the recycle ratio can decrease the outlet temperature, increase CO conversion and the dry molar content of CH4.The amount of high-pressure superheated steam, medium-pressure superheated steam, and recycle energy consumption generated in the process was calculated by using RYield with Aspen, the most economical process is feed gas split process, however, the 1st reactor circulation process may produce more high-pressure superheated steam.