integration of solid oxide fuel cells and ... - Ea Energianalyse

Anode recycling (α SPG1 )
5.3. Partial optimization of standard parameters
There are several reasons for using anode recycling. First of all it supplies
water for the pre reformer. But it also means that more the fuel is used,
since some of the fuel that didn’t react the first time through the SOFC
will react next time. This way more of the fuel will be used even though
the fuel utilization factor from the SOFC point of view remains constant
at U f =0,7 (it just means that every time the fuel is sent through the cell
70% of it will be used in the electrochemical reaction).
There is, however, a downside by the anode recycling. The
concentration of the species CO, CO 2 , H 2 , and H 2 O is affected by the
recycling . Generally the concentration of the reaction products are
increased, which makes both the Nernst potential and the cell voltage
decreases when the anode cycling fraction is increased (grey and brown
curve in figure 5.17B).
Figure 5.17: A+B The OC ratio (green) should be above 2 to avoid carbon depositing, so the
recycling fraction should not be below 0,6.
From figure 5.17A it can be seen that the increased use of the fuel in
the SOFC more than compensates for the drop in cell voltages, so elec-
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