Fuel flexibility

One of the significant advantages of SOFCs is that they are compatible with many different kinds of fuels, in contrast to other fuel cells. The single cells were evaluated using practical fuels such as LPG and DME that can be easily handled and stored in portable cartridges. 

Cell performance using H2 in N2 (1 1) gas mixture or simulated reformate gas is compared in Fig. 10.11. The composition of simulated reformate was 32% H2, 13% CO, 5% CO2, and 50% N2, based on the preliminary experiment of the catalytic partial oxidation (CPOX) reforming of LPG. As shown in the figure, the differences in cell performance were smaller at lower current densities. However, performance using reformate gas was lower at higher current densities at temperatures of 600° and 700°C. The 

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Fuel Flexible Vehicles. Using dedicated alcohol fuel vehicles pointed to the importance of a wide distribution of fueling stations. Methanol-fueled vehicles require refueling more often than gasoline vehicles. 

Many U.S. and foreign automobile manufacturers are developing a fuel flexible vehicle in the 1990s. Ford has developed FFVs for 5-L engines used... 

Only a small portion of motor fuel needs could be satisfied if truly large-scale alcohol—gasoline blending or fuel switching occurred via transition to fuel-flexible vehicles and ultimately to neat alcohol-fueled vehicles (132). 

The hfe of a gas turbine depends heavily on the type of fuel used. An inherent fuel flexibility is the gas turbines major advantage. Gaseous fuels traditionaUy include natural gas, process gas, and low-Btu gas... 

Molten Carbonate -650 Some fuel flexibility High-grade waste heat Fragile electrolyte matrix Electrode sintering Distribute power Utilities... 

Solid Oxide 800-1000 Maximum fuel flexibility Highest co-generertion efficiency Exotic materials Sealing and cracking issues Distribute power Utilities... 

In contrast with the AFC, the PAFC can demonstrate reliable operation with 40 percent to 50 percent system efficiency even when operating on low quality fuels, such as waste residues. This fuel flexibility is enabled by higher temperature operation (200°C vs. 100°C for the AFC) since this raises electro-catalyst tolerance toward impurities. Flowever, the PAFC is still too heavy and lacks the rapid start-up that is nec-essaiy for vehicle applications because it needs preheating to 100°C before it can draw a current. This is unfortunate because the PAFC s operating temperature would allow it to thermally integrate better with a methanol reformer. 

Coal gasification is fuel flexible so that the process can use the most available feedstock at the best price. Gasifiers have successfully gasified hcar y fuel oil and combinations of oil and waste gas. Other possible gasification feedstock includes petroleum coke, trash, used tires, and sewage sludge. Various combinations of feedstocks and coal have been successfully gasified. 

Kobro, M., and Brereton, L., Control and Fuel Flexibility of Circulation Fluidized Beds, Circ. Fluid. Bed Tech., 263-272 (1986)... 

Schematic diagram of fuel-flexible gasification-combustion process.

Another integrated carbon capture technology is called the fuel-flexible process developed by General Electric (GE). This process takes different feedstocks such as coal and biomass and produces hydrogen and electricity in adjustable ratios (Rizeq et al., 2002). The reaction scheme for this process involves two chemical loops operated using three fluidized-bed reactors as shown in Figure 17.5. 

Heat from all the hot exhaust gas streams is used for steam generation to drive the steam turbine. Thus, the final products from the GE fuel-flexible process are pure hydrogen from the first reactor, C02 from the second reactor, and heat for electricity production from the third reactor. A portion of the solids in the chemical loops needs to be purged to avoid ash accumulation and maintain solid reactivity (Rizeq et al., 2002). The overall energy conversion efficiency for the GE fuel-flexible process is estimated to be 60% (Rizeq et al., 2003). 

Rizeq, R.G. et al., Fuel-Flexible Gasification-Combustion Technology for Production ofH2 and Sequestration-Ready C02, Annual Technical Progress Report to DOE, 2002. 

Liu J, Madsen BD, Ji Z, and Barnett SA. A fuel-flexible ceramic-based anode for SOFCs. Electrochem. Solid State Lett. 2002 5 A122-A124. 

California has more than 1,000 methanol vehicles including cars, trucks, and buses on the road in a state program with auto manufacturers and oil companies. New York City also uses buses that run on methanol. Arizona Checker Leasing uses methanol vehicles with a fleet of 450 M85 fuel flexible vehicles. 

The liquid fuel reformer that has been worked on at Los Alamos and the Argonne National Labs is a fuel-flexible processor which can reform gasoline, natural gas, methanol, or ethanol at the control of a switch. This would also allow the use of the existing fuel infrastructure, but this... 

Early expectations of very low emissions and relatively high efficiencies have been met in power plants with each type of fuel cell. Fuel flexibility has been demonstrated using natural gas, propane, landfill gas, anaerobic digester gas, military logistic fuels, and coal gas, greatly expanding market opportunities. Transportation markets worldwide have shown remarkable interest in fuel cells nearly every major vehicle manufacturer in the U.S., Europe, and the Far East is supporting development. 

Major issues that influence the development of a fuel processor are a) choice of commercially available fuels suitable for specific applications, b) fuel flexibility, c) fuel cell gas reformate requirements, and d) fuel cell unit size. Vaporization of heavier hydrocarbons is another issue. Heavy hydrocarbons, such as diesel, require vaporization temperatures much in excess of 350-400°C where components of these heavier fuels begin to pyrolyze and decompose. 

H2 is preferable for a closed environment such as space vehicle application. There are sources of H2-rich gases, such as an off-gas at a chemical plant, that require only fuel cleaning. Fuel flexibility is not applicable in either case. 

The military will continue with its fuel infrastructure of high sulfur diesel (up to 1,000 ppm sulfur by weight) and jet fuel (JP-8). Sulfur specification will remain high because the military has to consider worldwide fuel sources. High sulfur diesel and JP-8 are close in characteristics so no fuel flexibility is required. However, there is a possibility that some parts of the military or the Coast Guard (a military service within the DOT) could use fuels more compatible to the fuel cell in limited applications. 

Fuel-Flexible Fuel Processor," J. Cuzens, J. Mauzey, and R. Woods, Hydrogen Burner Technology, Pg. 234 Fuel Cell Seminar Abstracts, Courtesy Associates, Inc., November 1998. 

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