Thermodynamic analysis of ATR-based PEM fuel cell system with hydrogen membrane separation

In this work we present a simulative energy efficiency analysis on innovative fuel processor - PEM fuel cell systems in which hydrogen is produced via methane autothermal reforming (ATR), separated with a membrane unit coupled with a water gas shift (WGS) reactor and then converted into electric energy in a PEM fuel cell. The simulations were performed in stationary conditions, by using the commercial package Aspen Plus®. Fuel processors based on ATR process represent a promising technology to develop small scale hydrogen production units for stand-alone and portable power generation, due to their compactness and to fast response to load changes. These advantages are enhanced when a highly selective hydrogen separation unit is introduced in the system for pure hydrogen generation. However, the global energy efficiency of these systems and, thus, their feasibility strictly depends on fuel processor configuration and on operating parameters; therefore, a comprehensive simulative analysis on membrane-based fuel processors coupled with a PEM fuel cell will allow to identify the conditions that maximize system performance. Two system configurations are investigated: one with the membrane unit placed downstream the WGS reactor and another one with the membrane unit embedded into the WGS reactor. The results are discussed and compared with the case of a fuel processor constituted by an ATR reactor followed by two WGS reactors and a preferential CO-oxidation reactor (conventional fuel processor). Operating parameters such as steam to methane and oxygen to methane inlet ratios, as well as pressure, are screened to identify the conditions that maximize global energy efficiency. The effect of the addition of steam as sweep gas in the permeate side of the membrane unit is also presented and discussed.