On the Polygeneration of Electricity, Heat and Hydrogen with High Temperature Fuel Cells

The use of a high-temperature fuel cell (HTFC) to continuously and simultaneously polygenerate hydrogen in combination with electricity and heat represents a promising technology as a source of fuel for fuel cell vehicles. Different configurations of polygenerating HTFC, including different SOFC designs with internal and external reforming, are options to polygenerate electricity, hydrogen and heat. To establish the most effective strategy, the following three methodologies are developed and applied: (1) the State-of-the-art method; (2) the Ideal Polygeneration method; and (3) the Supplemental Inputs method. The overall efficiency and the efficiency in the generation of each product are used as the basis for comparison.;A detailed chemical engineering model of a polygenerating HTFC is developed with Aspen PlusRTM. The model includes an internal reforming SOFC and a HSU block based pressure swing adsorption technology. Results from the model indicate that the highest performance configuration is achieved by operating the SOFC at 60% fuel utilization and extracting 95% of the H 2 of the anode-off-gas. In this case, 144.2 kW of net power is produced at 53.2% efficiency and 148.8 kg of H2 per day is produced at 82.8% efficiency. The relatively high overall and component efficiencies associated with a polygenerating HTFC are associated with the following synergistic attributes: (1) higher fuel concentrations along the anode compartment increases the fuel cell operating voltage, (2) the additional endothermic reformation cools the fuel cell and reduces auxiliary power associated with forced cathodic air, and (3) less electrochemical heat generated per mol of fuel in, associated with the higher voltages, further reduces the auxiliary power associated with forced cathodic air.;The first synergy is estimated to increase the electrochemical efficiency by 6.4%. To evaluate the second and third synergies, an optimization strategy is required to minimize air input flow. The overall efficiency is 76.7% and the corresponding electricity and hydrogen product efficiencies are 55.5% and 85.7% respectively.;The best polygenerating HTFC configuration is compared on a well-to-tank efficiency basis to a conventional means of producing hydrogen. Results show a well-to-tank efficiency for a polygenerating HTFC and distributed SMR plant of 76% and ∼60% respectively.