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

5. SIMULATION AND RESULTS
tricity wise it is a good idea to increase the anode recycling 5 . It can also
be seen from the green line in figure 5.17B that the recycling fraction can
not be below 0,6, since the OC ratio at the anode inlet will then fall below
2, which would leat to carbon depositing.
The COP of the absorption unit decreases with increased anode recycling.
This is mainly due to the SOFC using a bigger fraction of the energy
in the fuel to produce electricity, thereby leaving less heat for the absorption
cooling unit. So although the electricity generation raises when
the recycling is increased, the decrease in COP ABS,f uel is about twice as
big. So for each kW electricity gained, 2kW cooling is lost.
SOFC load (i d )
In certain situations, such as during a heat wave, it might be desirable to
generate as much cooling as possible even if it would severely lower the
electricity production. In such cases more of the energy in the fuel could
be used for the absorption unit and less for the SOFC system. Given a
fixed number (and size) of stacks, this can be done in two ways, which
will be compared in the following:
1. Lowering U f : All fuel is still sent through the SOFC. But less
current is drawn, and hence the utilization factor decreases, leaving
more fuel for the burner.
2. Fuel Bypass: Only some of the fuel is sent through the SOFC, while
the rest is fed directly to the burner (completely bypassing the fuel
cell). The utilization factor of the fuel cell remains constant at 0,7.
Figure 5.18 compares the two methods. When Fuel Bypassing (2) is
used, the current density can go all the way from 0 to 3000A/m 2 6 .
But in case (1) where all the fuel has to go through the SOFC, the
current density may not fall below 2100A/m 2 . Because when all the fuel is
sent through the pre reformer and fuel cell, most of it is reformed, which
5 The model does, however, not include blower power for the recycling blower, but
since the anode side volume flow is quite small, it should not consume especially much
power
6 It has been chosen to monitor the current density, since it is easily comparable to
fuel cells of other sizes due to its independence of size
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