Fig. 12 Conceptual Drawing of Fuel/Air System in Methane Fuel Experiment
Fig. 13 Cell Power Generation Characteristics with Methane Used as Fuel
Also the measurement is performed, for comparison, by bypassing the humidifier. In the experiment, the temperature was measured near the outlet of the flask and the degree of humidification was adjusted. The fuel gas is reformed by Ni catalyst immediately before the cell, and hydrogen and carbon monoxide generated are fed to the cell. In principle, the power generating section of the cell is the same in construction as that used in the previous chapter. Also the surface roughness of the cell electrolyte used in the experiment was sufficiently high.
4.2 Results and Discussion
Figure 13 shows the power generation characteristics obtained by using natural gas as fuel. The values of an open circuit voltage for natural gas are slightly higher than those for hydrogen. On the other hand, in those areas where current is extracted to the outside, the voltage obtained by natural gas shows a value lower slightly than that obtained by hydrogen.
The acceleration of the reforming reaction of methane by Ni catalyst depends on the steam partial pressure contained in the fuel and, therefore, the power generation performance is considered also to be affected by it. However, any remarkable difference was not found between the results obtained by using the humidifier, by not using it, and by varying the temperature in humidification. This is considered because steam produced by the bonding with oxygen ion and steam remaining on the fuel electrode side are re-used for reforming reaction, or methane is oxidized directly on the cell electrode. For the latter, in actual, the possibility of direct oxidation of methane on the surfaces of the electrode is reported recently.5)6)
This will be the subject to be solved in the future.
5. Conclusion
As those problems which can be expected when the SOFC is used for marine power, improvements of the power generation performance and load change characteristics of a unit cell and the applicability of the SOFC to natrural gas fuel were studied experimentally.
