Calculation of the energy efficiency of fuel processor PEM (proton exchange membrane) fuel cell systems from fuel elementar composition and heating value

This simulative work analyzes the impact of fuel type on the energy efficiency of systems composed by a fuel processor for hydrogen production and a PEM (proton exchange membrane) fuel cell. Two fuel processors are simulated, one employs steam reforming to produce hydrogen, the other one autothermal reforming. In both cases, fuel processing is completed by two water gas shift units and one preferential CO oxidation unit. Five classes of fuels are considered, i.e. alkanes, alkenes and alkynes, alcohols and aromatics and steam to carbon and oxygen to carbon inlet ratios, reforming temperature, fuel cell split fraction and exhaust gas temperature are explored as operative parameters. For each fuel considered, Aspen Plus was used to calculate the operative conditions that maximize the energy efficiency of the systems. For each system, the data were employed to identify an analytic expression to calculate the best possible energy efficiency given the elementar composition of the fuel and its lower heating value. The expressions proved to hold true for a broad range of fuel types