Reformer-PEFC system

For successful operation a selective CO oxidation catalyst in a reformer-PEFC system must be operated at ca. 353-373 Kin a complex feed consisting of CO, 02, H2, C02, H20 and N2, and be capable of reducing CO concentrations from about 1% to below 50 ppm - this is equivalent to a CO conversion of at least 99.5% [4, 54, 60], In addition, this conversion must be achieved with the addition of equimolar 02 (twice the stoichiometric amount) and the competitive oxidation of H2 must be minimized. This is expressed as selectivity, which is defined as the percentage of the oxygen fed consumed in the oxidation of CO for commercial operation a selectivity of 50% is acceptable, since at this selectivity minimal H2 is oxidized to water. 

A schematic diagram of a methanol-fueled PEFC system is shown in Fig. 27-65. A methanol reformer (to convert CH3OH to H9 and CO9... 

When used in a PEFC system, the reformate must pass through a preferential CO catalytic oxidizer, even after being shifted in a shift reactor. Typically, the PEFC can tolerate a CO level of only 50 ppm. Work is being performed to increase the CO tolerance level in PEFC. At least two competing reactions can occur in the preferential catalytic oxidizer ... 

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

Recupero, V., Pino, L., Vita, A., Cipiti, F., Cordaro, M., and Lagana, M. Development of a LPG fuel processor for PEFC systems Laboratory scale evaluation of autothermal reforming and preferential oxidation subunits. International Journal of Hydrogen Energy, 2005, 30 (9), 963. 

SOFC and PEFC are competing in several stationary markets, with advantages to SOFC technology when reformed hydrocarbon or alcohol fuels are used. PEFC systems however have some distinct advantages in applications where frequent start-stop-cycles and extended periods of standstill are required such as in residential CHP applications. Therefore, more PEFC than SOFC units are ciurently in the field in Japan where market introduction of residential fuel cell systems has already taken place. SOFC systems are in the early phase of deployment. 

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. 

Figure 25.2 Simplified flow sheet for an HT-PEFC system with autothermal reforming, water gas shift reaction,...

Reformate from fuel processing can be directly used in aU fuel cells except PEFCs. In PEFC systems, an additional ZnO adsorbent is required at operating temperatures of 350-400 °C. The sorbent capacity for a threshold of 0.1 ppmv H2S is 9mg of S per gram of ZnO at Ippmv H2S in the reformate [31]. For European gasoHne with 10 ppmv S and a ISkWth fuel processor, an adsorbent mass of 1.3 gh operating time is necessary to decrease the sulfur concentration to 0.1 ppmv H2S. 

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. 

Table 23.3 Comparison of flight endurances with HT-PEFC systems supplied either with pure hydrogen stored in a high-pressure tank or reformate gas from the on-board reforming of methanol...

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