Comparison of steam and autothermal reforming of methanol for fuel cell applications

This proposed study investigates two different reforming methods; autothermal and steam reforming of methanol for fuel cell systems. Generally, the efficiency of the overall fuel cell system can be improved by utilizing thermal waste energy from integrated fuel cell system components. This waste energy typically originates from retentate gas from membrane hydrogen separation units and/or flue gas from anode of the fuel cell. Theoretically, steam-reforming fuel cell systems have higher thermal efficiencies than autothermal reforming fuel cell systems due to the resultant high concentration of hydrogen. Therefore, steam reforming is generally recognized as the more suitable fuel processor for fuel cell applications. However, steam reforming can be adversely affected by mass and heat transfer limitations and catalyst degradation. Heat exchange efficiency with steam reformers has been found in experimental units to be less than 50%. As compared to a steam reformer, an autothermal reformer has internal heat generation which allows for lessened radial temperature gradients and higher resultant heat exchange. Impure methanol streams as found in practice have minute quantities of higher order hydrocarbons which can result in significant catalyst degradation. Due to increased temperature, an autothermal method can reform the small quantities of higher order hydrocarbons and thus increase the effective catalyst lifetime. It is presently unknown if these theoretical and practical benefits of autothermal reformation can balance the entropy increase associated with higher temperature reformation.;It is the goal of this proposed dissertation topic to investigate both steam reformation and autothermal reformation when considering use of methanol for hydrogen fuel cell systems. This will be done with both theory based models and with actual experiments with the available laboratory facilities. Specifically the integration of the reformer system will be considered, the overall fuel cell system will be modeled, and the degradation of the system with typical impurities in the fuel stream will be quantified. In this proposal, a variety of critical factors will be identified and explored in order to increase the overall efficiency of a methanol-fueled fuel cell system.