Fuel operating temperatures

Doppler coefficient (average value within the range of fuel operating temperatures) ( Doppler-, 10 /°C -0.74 -0.77 -0.58 -0.97 -1.1... 

Vessel outside diameter 9.2 m Peak fuel operating temperature 1168 C... 

Al. Data now available on fuel behaviour, coupled with Improved methods of prediction, have shown that fuel operating temperature may be Increased to a level at which the fuel centre is approaching its melting temperature,... 

A large margin should exist between the normal fuel operating temperature and the temperature at which fuel damage occurs. 

The fuel cells are classified based on the fuel, operating temperature, electrolyte type, physical state of fuel cell components and the fabrication technology. The polymer electrolyte membrane fuel cell (PEMFC) operating on a methanol-water mixture as a fuel is called a Direct Methanol Fuel Cell (DMFC). DMFC uses sulphonated fluoropolymer, such as NAFION 117 as the electrolyte membrane. Nafion membranes require high levels of humidification and can operate comfortably only within a narrow temperature range of 25°C... 

Steps such as the substitution of low sulfur fuels or nonvolatile solvents, change of taw materials, lowering of operation temperatures to reduce NO formation or vo1ati1i2ation of process material, and instaHion of weU-designed hoods (31—37) at emission points to effectively reduce the air quantity needed for pollutant capture are illustrations of the above principles. 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

Molten Carbonate Fuel Cell. The electrolyte ia the MCFC is usually a combiaation of alkah (Li, Na, K) carbonates retaiaed ia a ceramic matrix of LiA102 particles. The fuel cell operates at 600 to 700°C where the alkah carbonates form a highly conductive molten salt and carbonate ions provide ionic conduction. At the operating temperatures ia MCFCs, Ni-based materials containing chromium (anode) and nickel oxide (cathode) can function as electrode materials, and noble metals are not required. 

Because of the low operating temperature and ease of fabrication for low power units, PFFCs are the most likely fuel cell to be introduced in portable power packs. PFFCs in sizes of 300—500 W are being considered as a power source, eg, 4-h duration, 300 W, 1.2 kW, for the modem soldier operating in the enclosed environment of a self-contained protective suit, which has faciUties for air conditioning, radio communication, etc. Analytic Power Corp. (Boston) is assessing the use of PFFCs for this appHcation. 

For high temperature fuel ceUs, there is stiU a strong need to develop lower cost materials for ceU components. In the case of SOFCs, improved fabrication processes and materials that permit acceptable performance in fuel ceUs at lower operating temperatures are also highly desirable. 

Another type of combustion unit operates at about 1600°C to produce a molten slag which forms a granular frit on quenching rather than the usual ash. The higher operating temperature is obtained by preheating the combustion air or by burning auxiUary fuel. 

Wall losses through most refractory walls are ca 10% of the heat suppHed by the fuel. Losses increase with rising operating temperature. In special cases, eg, in glass tanks, losses can be as high as 30—35%. In these instances, very high values are requked to maintain the refractory at a temperature below which it does not melt or coUapse. 

The fuels Hsted in Table 2 are generally representative of fuels to be encountered over the range of industrial furnaces and, depending on the type (cooled or refractory wall), exhibit operating temperatures considerably different from adiabatic values. The choice of fuel is dependent upon a number of factors including cost, availabiUty, cleanliness, emissions, reflabiUty, and operations. Small furnaces tend to bum cleaner, easier to use fuels. Large furnaces can more effectively use coal. 

As can be seen from Eigure 11b, the output voltage of a fuel cell decreases as the electrical load is increased. The theoretical polarization voltage of 1.23 V/cell (at no load) is not actually realized owing to various losses. Typically, soHd polymer electrolyte fuel cells operate at 0.75 V/cell under peak load conditions or at about a 60% efficiency. The efficiency of a fuel cell is a function of such variables as catalyst material, operating temperature, reactant pressure, and current density. At low current densities efficiencies as high as 75% are achievable. 

The demonstration unit was later transported to the CECOS faciHty at Niagara Falls, New York. In tests performed in 1985, approximately 3400 L of a mixed waste containing 2-chlorophenol [95-57-8] nitrobenzene [98-95-3] and 1,1,2-trichloroethane [79-00-5] were processed over 145 operating hours 2-propanol was used as a supplemental fuel the temperature was maintained at 615 to 635°C. Another 95-h test was conducted on a PCB containing transformer waste. Very high destmction efficiencies were achieved for all compounds studied (17). A later bench-scale study, conducted at Smith Kline and French Laboratories in conjunction with Modar (18), showed that simulated chemical and biological wastes, a fermentation broth, and extreme thermophilic bacteria were all completely destroyed within detection limits. 

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