In-depth characterization through dimensional analysis of the performance of a membrane-integrated fuel processor for high purity hydrogen generation

Abstract

Efficient production of high purity hydrogen from reforming of natural or synthetic hydrocarbons is an enabling technology for the competitiveness of hydrogen-based systems. Specifically, fuel processors based on membrane-integrated reformers are one of the most promising technologies being potentially more efficient than state-of-the-art fuel processors. The effects of the operating parameters on the performance of the complete membrane-integrated fuel processor are relevant and have not been properly investigated, especially in terms of mutual interactions. Therefore, we analyze the effects of the pressure and temperature of the steam reforming reactor as well as of the steam to fuel and air to fuel ratios, on the system efficiency. To this aim, we use a steady state model developed in Aspen Plus® that implements a hybrid lumped-distributed parameter approach. To generalize our results to diverse system sizes and fuel compositions we conduct a dimensional analysis to express all the parameters in non-dimensional form. The results show that the fuel processor efficiency based on lower heating value varies between 75% and 84% as a function of the operating parameters. Notably, it always exceeds 75% that is the reference value for a state-of-the-art fuel processor based on pressure swing adsorption purification. We also note that the retentate composition has a relevant impact on the fuel processor operation. Specifically, when the retentate is rich in fuel content the fuel processor can turn in exothermic regime or can suffer oxygen starvation in the catalytic oxidation reaction. However, when the fuel processor operates in regular conditions the only relevant mutual interaction is between the steam to fuel and air to fuel ratios. Also, the fuel processor efficiency is mostly sensitive to the operating temperature and to the steam to fuel ratio. The 770 °C optimal temperature implies that only dense ceramic membranes can be used to build a fuel processor that operates at the maximum possible efficiency. Finally, leveraging on such results we evaluate the preliminary design of an innovative tubular plug flow reactor with layer catalysts.