Thesis for degree: Licentiate of Engineering

H 2 O. Both CO and H 2 are initially set to small values to enable the numerical calculations, but
CO 2 and H 2 O are decided in accordance with the chosen methane content and SF.
Figure 4.11: Reaction rate distribution in the middle of the anode for 45% CH 4 (left) and 75% CH 4
(right).
The reaction rates for 45% and 60% methane contents are rather similarly distributed, but in
the case of 75 % methane the steam reforming reaction rate has initially higher values and
much lower values at the outlet of the cell. Also, the water-gas-shift reaction rate for high CH 4
content increases to the maximum value closer to the inlet of the cell than it does for the other
two cases. For the situations 45% and 75% content of methane shown in Figure 4.11, the
steam reforming reaction rate (within the anode) is high as long as a high concentration of
methane is available. The reaction rate increases as the temperature and concentration of
steam increase, and decreases as the concentration of methane decreases. Note that there is a
difference in scale between the x- and y-axes. It is possible to change the reaction rate, either
by changing the particle size of the active catalyst, catalytic material composition or the
porous structure, i.e., the active catalytic area. The limitation to be considered is that the
probability of carbon deposition increases where there is almost no hydrogen present. A
higher risk for carbon deposition occurs when there is a high temperature gradient close to the
cell inlet. This is not the case here as the gradients are not so high.
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