Small Stationary Power Generation

There are numerous future mass markets for fuel cells with power outputs between 0.1 and 10 kW. These include electronic communications equipment. 

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As stated earlier, fuel processing technology from large chemical installations has been successfully transferred to small compact fuel cell units to convert pipeline natural gas, the fuel of choice for small stationary power generators. The technology for converting natural gas is described later in this section. 

The fuel cell is an electrochemical reactor, the required output of which is the energy released rather than the reaction product. The main fields of its application include transport systems, stationary power generation, and combined heat and power sources. What emerges from the specialist literature is that, despite the innovations and improvements made in recent years, there is still much room for further developments. " Central to the success of fuel-cell technology are the catalyst systems. This is where bi- and multi-metallic nanostructured colloids, especially those of small particle size (1-2.5 nm), scattering as nearly perfect single crystals , are important. They offer improved efficiency and tolerance against CO-... 

Figure 1.17 presents some examples of stationary power generators Figure 1.17(a) shows small-seale systems and Figures 1.17(b) to 1.17(e) show large-scale utility plants. 

Fuel cells can be classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide full cells, polymer electrolyte membrane fuel cells, and alkaline full cells according to the type of electrolyte used (150). All these fuel cells operate on the same principle, but the t) e of fuel used, operating speed, the catalyst used and the electrolyte used are different. In particular, pol5mier electrolyte membrane fuel cells can be used in small-sized stationary power generation equipment or transportation systems due to their high reaction speed, low operating temperature, high output density, rapid startup, and variation in the requested output. 

The PEMFC has been under development for the last two decades primarily as a potential replacement for internal combustion engines in electric passenger vehicles with power needs of 50-100 kW. However, PEMFCs have also been considered for larger vehicles of few hundred kilowatts for buses and trucks, as auxiliary power units, for small-scale stationary power generations of few kilowatts for combined heat and power of residential buildings, and even in smaller units of few watts for portable power electronics applications (Li, 2008 O Hayre et al, 2006). 

Polymer electrolyte membrane or proton exchange membrane fuel cells (PEMFC) use a thin (s50 im) proton conductive polymer membrane (such as perfluorosulfonated acid polymer) as the electrolyte. The catalyst is typically platinum supported on carbon with loadings of about 0.3mg/cm, or, if the hydrogen feed contains minute amounts of CO, Pt-Ru alloys are used. Operating temperature is typically between 60 and 80°C. PEM fuel cells are a serious candidate for automotive applications, but also for small-scale distributed stationary power generation, and for portable power applications as well. 

PAFC systems are commercially available from the ONSI Corporation as 200-kW stationary power sources operating on natural gas. The stack cross sec tion is 1 m- (10.8 ft"). It is about 2.5 m (8.2 ft) tall and rated for a 40,000-h life. It is cooled with water/steam in a closed loop with secondary heat exchangers. The photograph of a unit is shown in Fig. 27-66. These systems are intended for on-site power and heat generation for hospitals, hotels, and small businesses. Another apphcation, however, is as dispersed 5- to 10-MW power plants in metropolitan areas. Such units would be located at elec tric utihty distribution centers, bypassing the high-voltage transmission system. The market entiy price of the system is 3000/kW. As production volumes increase, the price is projec ted to dechne to 1000 to 1500/kW. 

As stationary fuel cells reduce their costs with continuing R D, they will be able to compete with other small- to medium-sized power generation sources for on-site generation, particularly cogeneration for factories and commercial buildings. The installed cost for fuel cell generation systems is expected to reach 800/ kW. 

The potential of stationary fuel cells for distributed generation depends on feed-in tariff policies and electricity and gas prices, as well as on market competition from gas engines and small turbines. SOFCs and MCFCs, mostly fuelled by natural gas, are likely to play an important role for combined heat and power generation in buildings. 

If renewable targets are set, biomass gasification is the cheapest renewable hydrogen supply option however biomass has restricted potential and competition of end-use, for instance, with other biofuels or stationary heat and power generation. Biomass gasification is applied in small decentral plants during the early phase of an infrastructure roll-out and in central plants in later periods. 

Proton exchange membrane fuel cells (PEMFCs) work with a polymer electrolyte in the form of a thin, permeable sheet. The PEMFCs, otherwise known as polymer electrolyte fuel cells (PEFC), are of particular importance for the use in mobile and small/medium-sized stationary applications (Pehnt, 2001). The PEM fuel cells are considered to be the most promising fuel cell for power generation (Kazim, 2000). 

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