Reformer-Based PEFC Systems

FIG. 24-52 System diagram for reformer-based PEFC system. 

Reformer-based PEFC systems avoid the complexities and compromises of hydrogen storage, but instead the system must be designed to handle hydrocarbon fuels (similar considerations apply for alcohol fiaels). This requires four major additional unit operations (Figure 3-11), collectively referred to as fuel processing ... 

The choice between a direct hydrogen and a reformate-based system depend on the application. For light duty vehicles, most experts now prefer direct hydrogen systems (hence the focus of the U.S. DOE program), while for stationary applications natural gas reformer-based PEFC systems are favored. 

In the following example, the use of a fractional factorial design will be explained. This time, the design will not be applied to an experiment. Instead, it will be used to analyze a fuel cell system. For this purpose, a polymer electrolyte fuel ceU (PEFC) system based on the autothermal reforming of kerosene was designed. The effects of different parameters, such as system pressure, cathode air ratio, ceU voltage. 

Fig. 30 Scheme of a power system based on a PEFC stack operating on reformed carbonaceous fuel (eg., natural gas) and air [63]. 

Minor species, such as CO, result from subsequent dissociation reactions governed by thermodynamics. Of the various fuels involved, methanol is the simplest liquid-based fuel to reform due to the lack of carbon-carbon bond and low reformation temperature of only around 200°C [21]. This temperature can easily be coupled to low-temperature systems. The PAFC is almost perfectly thermally matched to the methanol reformation temperature, so that waste heat from the fuel cell can be used to drive the process. For PEFCs, some additional input heat is needed for methanol and other fuel reformation. For high-temperature fuel cells, methanol (and other fuel) reformation can be accomplished internally or externally, as discussed in Chapter 7. The reformation temperature of other fuels can be several hundreds of degrees higher than that of methanol, depending on the complexity and strength of the chemical bonds as well as the catalyst used to promote the reaction. 

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