1992 1993 1994 1995 1996

Figure Is PC25 Power Plant Weight and Volume Improvement

The advances in the PC25 design resulted from improvements in each of the major components; cell stack, fuel processor, power conditioner and ancillary systems. Figure 2 compares the PC25A and PC25 C cell stacks. The height of the stack has been reduced by 20 percent contributing together with processing improvements to a dramatic reduction in stack manufacturing cost. Even further reductions in stack cost and size have been defined under a recent cell component development program sponsored through the Defense Advanced Research. Projects Agency (DARPA) and administrated by the U.S. Army Construction Engineering Research Laboratories and parallel efforts funded by IFC and Toshiba. These programs focused on reducing the manufactured cost of the cell stack assembly and resulted in thinner, lower-cost cathode substrate, separator plate and cooler configurations. Incorporation of these advanced components will lead to an additional 12-inch reduction in stack height and significant cost reduction.

Figure 2: PC2S C Cell Stack Improvement

The fuel processing system has been simplified and its size has been reduced. The capability for operation on propane has been developed. The combination of the reformer size reduction with the reduced stack height provides an overall reduction of 18 inches in power plant height for the PC25 C. Further reformer improvements are being developed in other programs discussed below.

The advent of high capacity Insulated Gate Bipolar Transistors (IGBT) has simplified the power conditioner. Figure 3 compares the electrical system of the PC25 A and PC25 C power plants. The electrical system for the PC25 C is only one third the size of that for the PC25 A. Alternative topologies combined with higher rated IGBT's, presently becoming commercially available, are anticipated to lead to further cost reductions.

Figure 3: PC2S C Electrical System Improvement

Figure 4: Improved Component Accessibility

The ancillary components also represent a significant power plant cost element. Reductions in their cost have been ad-; dressed through value engineering, including supplier participation, to identify integration opportunities which eliminate components or reduce their size. Figure 4 shows the improved component accessibility designed into the PC25C.

Figure 4: Improved Component Accessibility

Application Expansion Combined With Technology Extension

Specific application improvements in phosphoric acid fuel cells are illustrated by two on-going development programs; a program sponsored by Georgetown University through the, U.S. Department of Transportation to develop a 100-kW power system for a transit bus and a DARPA funded program to develop a 100-kW Mobile Electric Power (MEP) system operational on logistics fuel.

The Georgetown University bus application has specific weight and volume requirements for a dc system that are one-fourth those of the PC25 C and requires multiple start-stop cycles. Methanol is the specified fuel. Significant advances in cell stack and fuel processing technologies are necessary to meet these requirements. A conceptual power plant design is shown in Figure 5. Using the technology base from the PC25, IFC has designed an advanced cell configuration of small planform area with increased performance. An advanced 32-cell stack under test is shown in Figure 6. This cell stack operates at higher power density and and has lower weight per unit area than the PC25 C cell stack. Figure 7 compares the 100-kW compact methanol reformer with the PC25 natural gas reformer. This compact reformer has been tested on methanol and natural gas and scales to less than 50 percent of the PC25 reformer at a 200-kW rating.

Figure 5: 100 kW Bus Power Plant Concept Figure 6: Advanced Cell Stack

Although some of the advancement in characteristics are associated with the transportation design requirements, significant portions of this technology improvement are readily transferable to the PC25 leading to future cost reduction.

The 100-kW MEP power plant concept is shown in Figure 8. The broader military application requires use of logistic fuels. The MEP program is focused on j developing a fuel processing system with logistics fuel capability including JP-8 and DF-2. An advanced, auto-thermal reformer has been designed. A full-size wcn-isbo module of this design was successfully tested with 200 kW 100 kW

over 3500 hours of stable operation demonstrating Figure 7: PC25 C Reformer Compared

greater than 98 percent conversion on JP-8 fuels containing 100,800 and 3000 ppm sulfur. Figure 9 shows the module mounted in the test stand. Post-test tear-down and inspection showed no evidence of carbon deposits. A complete 100-kW assembly will be built and tested early in 1997.

To Advanced Bus Design

Figure 8: Diesel Fueled MEP100 kW Power Plant Concept

Figure 9: Logistics Fuel

Reformer Under Test

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