Fuel Cell Subsystems

In order to simplify the process of modeling, the properties of the three control volumes, or sections, of the fuel cell—anode, cathode, and membrane— will be considered to be uniform. In other words, the model will not describe what happens at an exact point along the membrane but will attempt to analyze the overall effects and the average values. In addition, several 

The fundamental governing equations for a control volume are the continuity equation, based on the conservation of mass, the energy equation, and the momentum equation. Because this study considers the overall effects, the 

These two basic governing equations can be applied to the three control volumes of the fuel cell, but they are very abstract and generic. A more detailed discussion of what occurs in each of the control volumes continues below. 

The mass flow in the anode and cathode consists of mass entering at the inlet, mass exiting at the outlet, and mass crossing the membrane. The inlet and outlet mass flow can be simplified using the nozzle flow rate equation as 

The consumption of hydrogen and oxygen is directly related to the electrical current, as shown in the equation 

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Over the last year, we retrofitted the existing fuel processor sub-system, designed the fuel cell subsystem, and integrated the two units. The integrated power plant was delivered to ANL in June 2002. Figure 9 shows typical performance of the integrated system on gasoline. 

The analysis is based on the assumption of a 50 kW system with an annual production of500 000 units. Under these conditions the total cost was estimated at 325/kW. The fuel cell subsystem was responsible for 67 % of this cost. 

Selected methodologies for fuel cell process engineering were introduced in this chapter. The use of the DOE theory was discussed as a powerfiil tool for system verification using examples from fuel cell subsystems. Measurement uncertainty... 

Of interest is the view that the majority of the cost is dominated by the fuel cell stack and the fuel processing subsystems. Further, the primary cost reduction for smaller SOFC units will stem from improvements to the fuel cell subsystem, whilst cost reductions for the fuel processing system will be difficult balance of plant component costs reduction opportunities, such as compressors, pumps, sensors and heat exchangers, are considered to be fairly small. Similarly, other subsystems such as power electronics are considered fairly stable cost wise. 

A fuel cell system also needs ancillaries to support the stack, just as an IC engine has many of the same type of ancillary subsystems. Major subsystems are needed for providing adequate humidification and cooling, and for supplying fuel and oxidant (air) with the correct purity and appropriate c uantity. 

These subsystems profoundly affect the fuel cell system performance. As an example, the inherently slow air (oxygen) electrode reaction must be acceler-... 

Electric Power System Design For specific applications, fuel cells can be used to supply DC power distribution systems designed to feed DC drives such as motors or solenoids, controls, and other auxiliary system equipment. The goal of the commercial fuel cell power plant is to deliver usable AC power to an electrical distribution system. This goal is accomplished through a subsystem that has the capability to deliver the real power (watts) and reactive power (VARS) to a facility s internal power distribution system or to a utility s grid. The power conditioning... 

Numerous other unit operations and subsystems can be found in fuel cell systems. It is not however the intent of this handbook to review all of these operations and subsystems that are well documented in many other references [e g., (2,8,9,10)]. For convenience, the unit operations that are commonly found within fuel cell power system are listed below ... 

High temperature fuel cell stacks and materials Currently, UK companies are active at the short stack and subsystem level. For the longer term the industry expects to build on this materials research strength to provide competitive advantage through enhanced performance and lower costs. 

The critical technology development areas are advanced materials, manufacturing techniques, and other advancements that will lower costs, increase durability, and improve reliability and performance for all fuel cell systems and applications. These activities need to address not only core fuel cell stack issues but also balance of plant (BOP) subsystems such as fuel processors hydrogen production, delivery, and storage power electronics sensors and controls air handling equipment and heat exchangers. Research and development areas include ... 

A process flow schematic of the demonstration unit1 installed at the Tokyo Electric Power facility at Goi. Japan and in operation since 1983 is shown in Fig. 4, Fuel cell generalors have three unique major subsystems that are unfamiliar to electric utilities (1) A fuel processing subsystem, (2) a fuel cell power section, and (3) a power conditioning subsystem. Sec Fig. 5. 

Various combinations of applications, including different choices of photovoltaic panels and electrolysers were tested. The cumulative operating times logged for the various plant subsystems differed considerably according to the test programs run, ranging from 6000 h for the alkaline low-pressure electrolyser, to 2000 h for the membrane electrolyser, 5200 h for the catalytic heater, 3900 h for the PAFC fuel cell plant and 900 h for the LH2 filling station. 

The committee believes that PEM electrolysis is subject to the same basic cost reduction drivers as those for fuel cells. Cost breakthroughs in (1) catalyst formulation and loading, (2) bipolar plate/flow field, (3) membrane expense and durability, (4) volume manufacturing of subsystems and modules by third parties, (5) overall design simplifications, and (6) scale economies (within limits) all promise to lower... 

Importantly, hydrogen fuel cell vehicles provide special attractions to automakers. By eliminating most mechanical and hydraulic subsystems, they provide greater design flexibility and the potential for using fewer vehicle platforms and therefore more efficient manufacturing approaches. As a result, the automotive industry, or at least an important slice of it, sees fuel cells as its inevitable and desired future. As noted by Jim Boyd in Chapter 10, automaker support was not evident in other movements to promote alternative fuels. 

Among the dozens of demonstration plants, subsystems, test facilities, and other related hardware constructed or planned in the United States, Europe, and Japan in those years, three examples stand out. The first was the first megawatt-class fuel cell power plant the PC-19 phosphoric acid plant, built by United Technologies in South Windsor, Connecticut and tested during the first half of 1977. 

The first Goi plant had been built within its budget of about 25 million—about 60 percent of the cost of the New York plant—and only 38 months after the order was signed. Considering the problems that had occurred with similar subsystems in New York, Appleby and Foulkes wrote, completion of the experiment in Goi must be regarded as a remarkable achievement, which leaves in no doubt the possibilities of properly designed fuel cells operating in a utility context. ... 

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