Betriebsstrategien für Brenngaserzeugungssysteme zur Anwendung in HT-PEFC-Hilfsstromaggregaten
Jülich / Forschungszentrum Jülich GmbH, Zentralbibliothek (2017) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (IX, 265 Seiten) : Illustrationen, Diagramme
This work set out to develop an operating strategy for fuel processing systems combined with high-temperature polymer electrolyte fuel cells (HT-PEFC). The operating strategy’s focus was to prevent the deactivation of the water-gas shift reactor’s (WGS) noble metal catalyst. The methodical approach undertaken included researching of the subject on two levels. Emphasis was placed on experimental investigation at the system and catalyst levels. This work was supplemented by model calculations. The experimental results identified high gas hourly space velocities of 45,000 1/h and above as a first reason for an accelerated activity drop of the catalyst. Presumably, the degradation was caused by a blockage of the active catalyst centers by reformate components or reaction intermediates like carbonates/ formates. The second reason for deactivation was incomplete fuel conversion in the autothermal reformer (ATR). Higher hydrocarbons caused side reactions on the WGS catalyst and resulted in a higher CO-concentration, as well as accelerated deactivation. The operating strategy comprises new methods to improve the fuel conversion during startup/ shutdown. With the original methods, several thousand ppmv higher hydrocarbons were observed. The new strategies reduced the concentrations up to a factor of 10 during startup and up to a factor of 400 during shutdown. Furthermore, the original catalyst A was displaced by a second catalyst B, which turned out to be much more active and stable. As a third part of the new operating strategy, regeneration methods were developed. A short-term purge (≈5 min) of the WGS-reactor after system shutdown with 80 lN/h air at ≈200 °C was enough to completely regenerate the catalyst activity. The new operating concept was validated by daily load profiles with the fuel HC-kerosene and the CO threshold value of the HT-PEFC of 1.2 vol.-% (dry) was met. With three additional diesel fuels, validation was not possible all of the time. In future, the catalyst volume of the high-temperature shift stage (HTS) must be doubled in order to lower the gas hourly space velocity and decelerate the degradation occurring. Apart from that, catalyst B showed no indication of irreversible deterioration, even after ≈500 h of system operation, including 20 startup/ shutdown cycles, concentrations of higher hydrocarbons up to 3200 ppmv, as well as numerous temperature peaks of up to 763 °C. The integration of the system’s fuel cell and catalytic burner modules into the new operating strategy is unproblematic and can take place without adjustment. Correspondingly, the model calculations could reveal that the energetic utilization of the rejected reactor heat after shutdown is reasonable. With the catalytic burner, a hot water quantity of 10 kg/h can be supplied for 150 minutes. The developed operating strategy constitutes the foundation of long-term operation without a loss of performance, and is an incentive for further work on the fuel processing system.