Fuel methane steam reforming

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

In the phosphoric acid fuel cell as currently practiced, a premium (hydrogen rich) hydrocarbon (e.g. methane) fuel is steam reformed to produce a hydrogen feedstock to the cell stack for direct (electrochemical) conversion to electrical energy. At the fuel electrode, hydrogen ionization is accomplished by use of a catalytic material (e.g. Pt, Pd, or Ru) to form solvated protons. 

The number of electrons produced per molecule is an important issue for hydrocarbons. While the addition of H2O to the fuel for steam reforming has no effect on electron production, reforming of hydrocarbons larger than methane is usually accomplished through partial oxidation, with the ideal reaction shown in eq 7... 

One-dimensional models of a solid oxide fuel cell (see Chapter 9) and a methane-steam reformer [19, 20] were incorporated into the ProTRAX programming environment for transient studies. Lumped parameter ProTRAX sub-models were used for the remaining system components (heat exchangers, turbomachinery, valves, etc ). A schematic of the model is provided for reference in Figure 8.21. 

Large-scale production of hydrogen for fuel and chemicals starts from fossil fuels, typically by methane steam reforming (MSR) and WGS processes. 

The production of hydrogen from methane is important because it has a low environmental impact. The production of hydrogen via steam reforming has a H2/C02 ratio of 4 (Table 1), the lowest C02 impact of any fossil fuel source. The dc plasma system produces a H2/C02 ratio of about 1000 in the effluent stream. However, CO is a major product of the system. If the water-gas shift reaction were used to convert all of the produced CO into C02 via reaction [5], the resulting H2/C02 ratio would be approximately 9 for either system. This value is still considerably better than that of other fossil fuels, including steam reforming. 

Achenbach E, Riensche E (1994) Methane steam reforming kinetics for solid oxide fuel-cells. J Power Sources 52 283... 

Figure 2.32. Thermodynamic minimum S/C ratios required to prevent carbon formation in diesel, jet fuel, gasoline, and methane steam reforming.

The carbon deficit observed in methane steam reforming does not occur if naphtha feedstock is converted. In autotheimal processes using fuel oil as a feedstock, sufficient quantities of excess carbon dioxide are available within the installation itself. This gas is recycled from a scrubbing unit. 

Thorium and uranium are used in cotmnercial catalytic systems. Industrially, thorium is used in the catalytic production of hydrocarbons for motor fuel. The direct conversion of synthetic gas to liquid fuel is accomplished by a Ni-Th02/Al203 catalyst that oxidatively cracks hydrocarbons with steam. The primary benefit to the incorporation of thorium is the increased resistance to coke deactivation. Industrially, UsOs also has been shown to be active in the decomposition of organics, including benzene and butanes and as supports for methane steam reforming catalysts. Uranium nitrides have also been used as a catalyst for the cracking of NH3 at 550 °C, which results in high yields of H2. 

R. Peters et al. Kinetics of methane steam reforming . Proceed, of 2000 Fuel Cell seminar, 2000, p. 305-309... 

Fernandez F, Soares A Jr (2006) Methane steam reforming modeling in a palladium membrane reactor. Fuel 85 569-573... 

For a methane steam reforming fuel processor, more than 15% higher fuel processor efficiency was determined experimentally by Heinzel and coworkers [35] when utilizing fuel cell anode off-gas compared with combustion of extra methane... 

Cremers et al. [70] and Pfeifer et al. [71] presented a reactor combining endothermic methane steam reforming with the exothermic combustion of hydrogen stemming from the fuel cell anode off-gas (Figure 24.10). NiCroFer 3220H was... 

K. Schubert, Micro-structured Methane Steam Reformer with Integrated Catalytic Combustor, Fuel Cells 2007, 2,... 

Kusakabe, K., Sotowa, K. I., Eda, T., Iwamoto, Y. (2004). Methane steam reforming over Ce-Zr02-supported noble metal catalysts at low temperature. Fuel Processing Technology, 86, 319—326. Scopus Exact. 

Maluf, S. S., Assaf, E. M. (2009). Ni catalysts with Mo promoter for methane steam reforming. Fuel, 88, 1547—1553. Scopus Exact. 

The process is known as the conventional method of producing hydrogen for meeting the hydrogen demands of the refining and petrochemical industry. The most widely used fuel in steam reforming is natural gas, which is mostly composed of methane ... 

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