Fuel Cell Networks

The cell and stacks that compose the power section have been discussed extensively in the previous sections of this handbook. Section 9.1 addresses system processes such as fuel processors, rejected heat utilization, the power conditioner, and equipment performance guidelines. System optimization issues are addressed in Section 9.2. System design examples for present day and future applications are presented in Sections 9.3 and 9.4 respectively. Section 9.5 discusses research and development areas that are required for the future system designs to be developed. Section 9.5 presents some advanced fuel cell network designs, and Section 9.6 introduces hybrid systems that combine fuel cells with other generating technologies in integrated systems. 

Molten Carbonate Fuel Cell Networks Principles, Analysis and Performance... 

In an improved design, called an MCFC network, reactant streams are ducted such that they are fed and recycled among multiple MCFC stacks in series. Figure 9-19b illustrates how the reactant streams in a fuel cell network flow in series from stack to stack. By networking fuel cell stacks, increased efficiency, improved thermal balance, and higher total reactant utilizations can be achieved. Networking also allows reactant streams to be conditioned at different stages of utilization. Between stacks, heat can be removed, streams can be mixed, and additional streams can be injected. 

The fuel cell network which was simulated was not fully optimized. Optimization of flow geometry, operating pressure, stack fuel utilization and current, reactant conditioning, and other parameters would be expected to yield further significant increases in total system efficiency. 

Key to the concept of networking is the arrangement of multiple fuel cell stacks relative to the flow of reactant streams. Conventional fuel cells systems have been designed such that reactant streams flow in parallel through fuel cell stacks. In a fuel cell network, however, reactant streams are ducted such that they are fed and recycled through stacks in series. 

Nordic and Baltic Applied Fuel cell network (Technical University of Denmark (DK), IFE (N), Statkraft (N), Kgl.Tekniska Hogskolan (S)). 

Three specific associations for hydrogen and fuel cells have been established the Spanish Hydrogen Association, the High Council for Scientific Research Fuel Cells Network and the Spanish Association for Fuel Cells. 

FCTESTNET. Fuel Cells Network for Tests and Standardization. 

Virtual fairground Hessen www.brennstofkeiie-hessen.de Fuel Cell Network NRW www.fueiceii-nrw.de... 

Figure 17.4 Cartoon representation of strategies for studying and exploiting enzymes on electrodes that have been used in electrocatalysis for fuel cells, (a) Attachment or physisorption of an enzyme on an electrode such that redox centers in the protein are in direct electronic contact with the surface, (b) Specific attachment of an enzyme to an electrode modified with a substrate, cofactor, or analog that contacts the protein close to a redox center. Examples include attachment of the modifier via a conductive linker, (c) Entrapment of an enzyme within a polymer containing redox mediator molecules that transfer electrons to/from centers in the protein, (d) Attachment of an enzyme onto carbon nanotubes prepared on an electrode, giving a large surface area conducting network with direct electron transfer to each enzyme molecule.

Bridged polysilsesquioxanes having covalently bound acidic groups, introduced via modification of the disulfide linkages within the network, were studied as solid-state electrolytes for proton-exchange fuel cell applications.473 Also, short-chain polysiloxanes with oligoethylene glycol side chains, doped with lithium salts, were studied as polymer electrolytes for lithium batteries. 

The beginning of the possible market introduction of hydrogen passenger cars in the most optimistic scenarios is around 2015, which is also in line with the implementation plan of the European Hydrogen and Fuel Cell Technology Platform (HFP, 2007). The Reference scenario features high policy support, fast learning, concentrated users, early network and no country-specific bounds. 

In addition to the chapters discussing the various aspects of bio-energy, two chapters are dedicated to hydrogen production and fuel cells. A second book in this series, based on a second workshop, Catalysis for Sustainable Energy Production (organized by IDECAT - the European Network of Excellence on catalysis, see Preface), will discuss these aspects in more detail. 

Fuel Cell technology is a great technology but it has been designed mostly for a mature market, since it requires that a pervasive refueling station network be available before the market can accept the technology. 

Connection to the utility grid provides many advantages to on-site power producers such as reliability improvement and increase of load factor, as well as giving the electric utilities a chance to improve the supply capability. When a fuel cell power plant is used for electric utility applications, the inverter is the interface equipment between the fuel cell and the electrical network. The inverter acts as the voltage and frequency adjuster to the final load. The interface conditions require the following characteristics for the inverter ... 

Network voltage imbalance will not be a concern while the fuel cell is connected to the grid. 

Two ASPEN (Advanced System for Process Engineering, public version) simulations compare the performance of conventional and networked fuel cell systems having identical recycle schemes and steam bottoming cycles. Each simulated system was composed of three MCFC stacks operating at the same temperature and pressure. The Nemst potential of each MCFC in both systems was reduced by 0.3 volts due to activation, concentration and ohmic voltage... 

When the total fuel utilization of each system was optimized for maximum efficiency, the efficiency of the fuel cell stacks networked in series was nearly 10% greater than that of the stacks arranged in parallel (44.9% vs. 35.4%, LHV). When the power generated by each system s steam bottoming cycle was considered in addition to its fuel cell power, the gap in efficiency narrowed to 5.5%. The efficiency of the total networked system is 56.8%, while that of the total conventional system was 51.3%. 

This oversimplified random network model proved to be rather useful for understanding water fluxes and proton transport properties of PEMs in fuel cells. - - - It helped rationalize the percolation transition in proton conductivity upon water uptake as a continuous reorganization of the cluster network due to swelling and merging of individual clusters and the emergence of new necks linking them. ... 

An external gas pressure gradient applied between anode and cathode sides of the fuel cell may be superimposed on the internal gradient in liquid pressure. This provides a means to control the water distribution in PEMs under fuel cell operation. This picture forms the basis for the hydraulic permeation model of membrane operation that has been proposed by Eikerling et al. This basic structural approach can be rationalized on the basis of the cluster network model. It can also be adapted to include the pertinent structural pictures of Gebel et and Schmidt-Rohr et al. ... 

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