Environmental Engineering Reference
In-Depth Information
Cathode interconnection
Electrolyte
Air electrode
(cathode)
Fuel low
Air low
Fuel electrode (anode)
FIGURE 16.3 Schematic view of a tubular SOFC design.
particulates, sulfur compounds, and halides that may be present in the biosyngas.
These contaminants may interact with different anode materials in various ways,
and therefore, the tolerance levels of different anodes for these contaminants may
vary considerably. This, in turn, affects the requirements for gas cleaning systems.
Therefore, selecting suitable anodes, gas cleaning systems, and suitable operating para-
meters is critical for developing feasible and efficient biomass gasifier
SOFC systems.
In the state-of-the-art Ni/YSZ anodes, the electrode performance is most likely
affected by poisoning of the anode as a result of chemical reactions and/or deposition
of contaminant species on the catalyst surface due to preferential adsorption. A proper
understanding of these phenomena enables determination of the cleaning require-
ments for the gas to be fed to the FC.
Once the influence of contaminants on SOFC performance and the effect of the
SOFC operating parameters on these influences are known, the cleaning requirements
and the operating parameters of the system components can be determined. Based on
this information, it will be possible to select suitable cleaning devices and other system
components. Additionally, different types of gasifiers can be compared with respect to
their influence on SOFC operation and durability.
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16.3.1 SOFC Operation with Biosyngas
A summary of possible reactions inside SOFCs when running with syngas is given in
Table 16.1. Hydrogen is one of the main constituents of biosyngas and is the standard
fuel for fuel cells. CO and CH 4 also are fuels for SOFCs, but they can contribute to
carbon deposition (RX. 16.8, 16.9, and 16.10) under certain circumstances. The
carbon deposition tendency is lower when the cell is under an electrical load. This
is because the oxygen ions that pass through can oxidize the deposited carbon. Both
CO 2 and N 2 (from the gasification air) affect the cell voltage. H 2 O assists in the water
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