Large Stationary Power Plants

In Section 8.2.1 we pointed out that a power plant with a battery of tubular SOFCs had been operated more or less successfiiUy for about 16,000 hours. Apart from the communication cited, very few data can be found in the literature as to the results of long-term testing of soUd-oxide fuel cells. Since this type of high-temperature fuel cell is intended primarily for large stationary power plants and thus has large investment needs, information as to potential lifetimes and reasons for gradual performance degradation or possible cases of sudden failure are extremely important. 

All the advantages of SC-SOFCs mentioned above and the last very serious disadvantage predetermined the main possible fields of application for this fuel cell variety low- and medium-sized portable and mobile powerplants for electronic devices and eleclric vehicles and also small units for individual homes and for backup power. All these application areas are now expanding rapidly and require appropriate new power sources. In contrast to large stationary power plants destined for the production of cheap grid power, for which high fuel utilization is of prime importance, in these application areas Ihe main requirement is the high specific power density of the power unit. 

In this section, large stationary power plants are considered. Small stationary power plants are considered in Section 19.2. 

Solid fuels such as wood, charcoal, coal, and biomass have been used occasionally for motor vehicles at times of scarcity. They are more suitable for large-scale stationary power plants under the watchful eyes of competent engineers, as they are too difficult to feed into the furnaces, and the fuels are too full of sulfur and ash that would corrode and foul the light engines. 

Several processes have been developed for coal liquefaction. Large-scale pilot plants have been in operation for the solvent-refining coal (SRC) process, and a pilot plant is being constructed for the H-Coal process, which is a direct catalytic process. Construction of demonstration plants is under consideration. The coal liquids produced from the current processes contain large amounts of residual fuels. They probably will be used initially as boiler fuels for stationary power plants. However, the nitrogen content of coal liquids is much higher than the petroleum residual fuels. The sulfur contents of coal liquids can vary considerably they depend on the type of coal and the liquefaction process used. Current coal liquefaction processes are capable of produc-... 

In view of their ability to work with different kinds of fuel, MCFCs are of great interest. The electrical and operating parameters of these fuel cells are quite sufficient for building economically justified stationary power plants with a relatively large power output. The only point that, so far, that poses a problem is an insufficiently long trouble-free operation. The minimum length of time a large (and expensive) power plant should work, until it would be replaced, is 40,000 hours (4.5-5 years). 

Today, most large fiiel-cell-based plants are produced and set up in the United States, following active government support. A similar tendency can be seen in South Korea. In Japan, where many large fuel cell-based power plants had been built and operated in earlier years, attention is focused, at present, on the development of small stationary power plants and on power units for electric vehicles. 

In most cases, large fuel cell-based stationary power plants are used for power production and, at the same time, for heat supply to customers in nearby locations (combined heat and power (CHP) systems). This combined use of two different types of energy implies a very considerable increase in the total economic and energetic efficiencies of these plants. 

Fuel cell systems also are easily scaled, allowing them to be used for small applications such as the power source for a personal computer as well as large applications like a stationary power plant. Large or small, all these applications harness the fuel cells inherent efficiency advantages to make better use of a fuel s chemical energy. 

From the energetic point of view all the above-mentioned fields of application can be called small-scale power systems. For each of the devices mentioned self-contained power sources are needed, not depending on large-scale power systems - stationary power plants and power supply lines. In small-scale power systems each individual consumer needs much lower electrical power values and a shorter operation time than one in large-scale power systems (see Figure 2). 

In earlier chapters we pointed out that in Japan in the 1980s and 1990s, a relatively large number of stationary power plants of various sizes, including different fuel cell variants, had been built and operated over extended periods... 

Sales engineering is a very important function that ranges from something that consists of almost pure merchandising for a simple product used in large quantity, to a highly sophisticated technical function involved in the application of complex products such as the selection and specification of stationary power plants, machine tools or other products that are not mass produced, but are made strictly to order. 

We may thus conclude after this short overview on DeNO technologies that NH3-SCR using catalysts based on V-W-oxides supported on titania is a well-established technique for stationary sources of power plants and incinerators, while for other relevant sources of NO, such as nitric acid tail gases, where emissions are characterized from a lower temperature and the presence of large amounts of NOz, alternative catalysts based on transition metal containing microporous materials are possible. Also, for the combined DeNO -deSO, alternative catalysts would be necessary, because they should operate in the presence of large amounts of SO,.. Similarly, there is a need to develop new/improved catalysts for the elimination of NO in FCC emissions, again due to the different characteristics of the feed with respect to emissions from power plants. 

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