Abstract
The combination of gasification and solid oxide fuel cells (SOFCs) has the potential to improve efficiency and reduce emissions for fuels, such as coal and biomass. Gasification syngas is a mix of fuel gases containing contaminants, such as sulfur and tar, which have the potential to cause degradation of the materials used in the anode of the SOFC. In this study, nickelgadolinium-doped ceria (NiCGO) composites are exposed to syngas and toluene- and sulfur- (as CS2) contaminated syngas at temperatures from 600 to 765 °C to investigate the effects of the feed gases and contaminants on their reforming activity and the amount and type of carbon deposited. Under conditions favoring carbon deposition, a two-stage deactivation of the reforming activity is observed, with this being largely the same whether the syngas is pure or contaminated. Toluene- contaminated syngas does not increase the amount of carbon deposited or make it more difficult to remove graphitic carbon compared to uncontaminated syngas below 700 °C, but at 700 °C and above, it does increase the amount of carbon and produce more graphitic carbon. Syngas and toluene appear to compete for active sites, suggesting that the effects of tars and model tars on SOFCs need to be investigated under syngas rather than under hydrogen. Sulfur contamination reduces the amount of carbon deposition above 11 ppm of H2S.
Highlights
As part of the energy mix in society, it may be necessary to use fuels, such as coal and biomass, which are cheap and widely available, in a way that minimizes their environmental impact. Gasification of these fuels and feeding of the product gas into a solid oxide fuel cell (SOFC) has the potential of high efficiency and low emissions of carbon dioxide and other pollutants compared to their use in conventional power stations.[1−4] The use of gasification products as SOFC fuel has been tested experimentally.[5−7] One of the main issues with the use of gasification feed streams in SOFCs is the detrimental effect that some components of the gas have on the materials used in the anode of the SOFC.[8−10] Gasification feed streams are composed of a mix of hydrogen, carbon monoxide, carbon dioxide, methane, water vapor, and nitrogen as major components, along with contaminants, such as tars and sulfides.[11]
One further feature was the return of the very low temperature peak, with increasing size as the sulfur content increased. This may result from carbon deposition starting on the metal particles but failing to spread. These results indicate that, under conditions where carbon deposition would be expected to occur, the deposition is not worsened by toluene as a model tar
In regimes where carbon deposition does not occur under pure syngas, carbon deposition is still observed with toluene
Summary
As part of the energy mix in society, it may be necessary to use fuels, such as coal and biomass, which are cheap and widely available, in a way that minimizes their environmental impact. Carbon monoxide itself can cause carbon deposition in certain conditions.[19,20] Mitigation strategies for carbon deposition at the fuel cell itself include a high concentration of steam[21,22] to promote tar reforming or avoiding low current density[23] to maintain high oxygen fluxes These strategies seek to maintain the SOFC anodes in a thermodynamic regime, where carbon deposition should not occur, albeit previous experiments have shown that tars can cause the formation of carbon deposits even outside the envelope of operating conditions, where it would be favored.[24−26]. The effect of aromatic compounds, including tars, on operating SOFCs has recently been comprehensively reviewed.[27] In general, these studies run the SOFC under conditions where carbon deposition is not predicted thermodynamically, for example, at high temperature and under load. Once the temperature dropped below 200 °C, the gas was changed to 100 mL min−1 2% O2 in Ar and the reactor was heated to 1000 °C at 5 °C min−1, again using mass spectrometry to measure the gas composition
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
