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

Abstract

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 H2 purity, energy efficiency and CO2 conversion, individually. The decision variables are the molar ratios of CO2/CH4, H2O/CH4 and O2/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 H2 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 H2 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 H2 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 H2 purity and H2 recovery increase due to the “hot-spot” increment.