Optimization and improvement of a conventional tri-reforming reactor to an energy efficient membrane reactor for hydrogen production

This study represents a numerical investigation of methane tri-reforming process with full computational fluid dynamics (CFD) in a conventional and a novel membrane fixed-bed reactor. A 2-D non-isothermal axisymmetric model is stablished to analyze the influence of relevant parameters. Three single objective optimization are conducted to maximize the H-2 purity, energy efficiency and CO2 conversion, individually. The decision variables are the molar ratios of CO2/CH4, H2O/CH4 and O-2/CH4 and the reactor inlet temperature. The optimization results indicate that the maximum value of energy efficiency in the conventional reactor is 73.29%. Moreover, when the H-2 purity is maximum, the energy efficiency is almost 2% lower than its maximum value. Therefore, the novel membrane reactor is simulated using the first optimal conditions to achieve an energy efficient process for H-2 production. A "hot-spot ", which is beneficial for the high endothermic reactions, is observed near the reactor entrance. It is proved that the hotter and greater "hot-spot " is in favor of the H-2 production and energy efficiency. The counter-current configuration is more efficient due to its higher "hot-spot ". Finally, it is found that as the sweep gas velocity increases, the H-2 purity and H-2 recovery increase due to the "hot-spot " increment.