C

methanol combustor, recompression, high-temp turbo-expander

38.2 kW

-11.4 kW

23.2 kW

149.2 kW

+10.7 %

To compare the efficiencies of the hydrogen and methanol systems we take cases that are likely to approximate the optimal designs. For hydrogen, this might be the 37% efficient system with single stage expansion of fuel cell exhaust and compressed hydrogen. For methanol, a compromise might be struck between methanol-fueled systems A and B (which would satisfy heat requirements with combustion of anode exhaust in addition to some methanol, with the relative amounts determined in part by performace of expander technologies) that would have an efficiency of roughly 31%. The methanol-fueled system then has an efficiency relative to the hydrogen system of 84%. (As far as the full fuel cycle, this difference is widened by the lower efficiency with which natural gas or biomass is converted to methanol compared to hydrogen, roughly 92% in relative terms including hydrogen compression at the refilling station(5).) On the other hand, there are the obvious benefits of a less dramatic change in fuel infrastructure required by methanol compared to hydrogen.

1. The simulations were carried out using Aspen Plus, a software package for simulating chemical and industrial processes.

2. This is consistent with typical figures in the literature, for example, James, Brian D„ George N. Baum, and Ira Kuhn, 'Technology Development Goals for Automotive Fuel Cell Power Systems." Final Report, Contract No. 22822402,1994, Argonne National Laboratory.

3. This is consistent with typical figures in the literature, for example, Arthur D. Little, "Multi-Fuel Reformers for Fuel Cells Used in Transportation." Final Report, 1994, USDoE, Office of Transportation Technologies.

4. Weisbrod, K. and N. Vanderborgh, "Effect of perating Parameters and Anode Gas Impurities Upon Polymer Electrolyte Fuel Cells." 29th IECEC, 1994, American Institute of Aeronautics and Astronautics, also, personal communication, S. Gottesfeld, Los Alamos National Laboratory, 1996.

5. Derived from R. Williams, E. Larson, R. Katofsky, and J. Chen, "Methanol and Hydrogen from biomass for Transportation" Energy for Sustainable Development, January, 1995.

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