(691c) Autothermal Reformer Design for Fuel Cell Applications

Steam reforming of higher hydrocarbons is an attractive route for the production of hydrogen for use in the generation of power from fuel cells for stationary power applications. Power generators based on fuel cells offer advantages including high efficiencies, low emissions, high reliability, quiet operation and easy monitoring when compared to conventional gasoline-powered generators. Such devices can be used in hurricane prone areas where power outages are common or in remote areas (e.g. campsites) where access to the electricity grid is limited. In this research a packed bed reactor is designed and analyzed, in which steam reforming of heptane occurs to produce sufficient hydrogen for generating 1 kW of power. Mass and energy balance equations are developed for each species in the reactor. The pressure drop is modeled via the Ergun equation. Simulations are conducted in MATLAB to determine the effect of process parameters (e.g. steam to heptane ratio, inlet pressure, inlet temperature) on the production of hydrogen. For a range of catalyst particle sizes considered, it is shown that the pressure increase due to the increase in moles in the reactions is roughly balanced by the pressure drop due to flow, resulting in negligible pressure drop. Since the reforming reactions are endothermic, it is necessary to have a source of heat for the reformer. Two different scenarios are analyzed: (1) partial oxidation of heptane in the reformer along with steam reforming and (2) development of an appropriate reactor jacket where heptane is combusted to produce sufficient heat for the steam reforming reaction in the reactor. It is shown that partial oxidation of heptane does not provide sufficient heat for the endothermic reactions. Heat transfer calculations for the jacket show that it is not practical to operate the reactor isothermally. If about 25% of the total heptane is sent to the jacket and the rest is sent to the reformer, sufficient heat is generated for complete conversion of heptane under non-isothermal conditions. Finally, calculations are done for the energy required to bring the fuel processor system from ambient temperature to the operating temperature where fuel cell quality hydrogen can be produced.