Thermodynamic analysis of fuel processors based on catalytic-wall reactors and membrane systems for ethanol steam reforming

The integration of membranes into fuel processors to obtain hydrogen that meets the purity requirements of polymer electrolyte membrane fuel cells (PEMFC) was studied. Different configurations of systems that combined a fuel processor and a PEMFC were developed, considering low-temperature membranes to extract hydrogen from the cold reformate gas, or high-temperature membranes integrated into the water shift and reformer reactors. Detailed mass and energy balances were carried out for each configuration to establish the combinations of reforming temperature, pressure, and steam-to-carbon ratio enabling a self-sustainable operation of the fuel processor, and the efficiency of the integrated system was calculated. In all cases the thermal energy demand was supplied by a catalytic combustor directly coupled to the reformer, and effective heat recovery among streams was implemented to improve the thermal efficiency of the system. The catalytic combustor used the reject gas from the membrane and the FC anode spent gas as the sole fuel source. Results show that self-sustainable operation is feasible for most configurations, achieving power production efficiencies equivalent to that of a conventional fuel processor (reformer, shift reactor and COPROX reactor). The configurations that use high-temperature membranes – especially the membrane reformer – provide better process integration, but their feasibility appears uncertain because of membrane cost and useful lifetime issues under the harsh reaction conditions. Configurations based on low temperature membranes appear more feasible in practice.

► Use of membranes to purify hydrogen in ethanol fuel processors coupled to PEMFCs.
► Low-temperature inert membranes vs. high-temperature membrane reactors.
► Membrane reject and PEMFC anode off-gas as sole fuel. Optimized heat recovery.
► Electrical efficiency (LHV) of 0.40–0.42 possible for several configurations.