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

3. COMPONENT DESCRIPTION
3.12 Solid Oxide Fuel Cell - SOFC
Figure 3.15: SOFC component
The SOFC is modeled as a number of stacks (n st ack ) each consisting of
a number of cells (n cell ). Electricity wise the cells are connected in series.
This means that the voltage of the stack will be n cell times bigger than
the cell voltage. The total power of the SOFC is just the number of stacks
times the power of each stack:
Ẇ SOFC = n st ack ·Ẇ st ack (3.73)
Ẇ st ack = n cell I cell V cell (3.74)
Gas flow wise the stacks can be connected in parallel or in series. If
the stacks are in series, they can use a higher percentage of the fuel,
since cell number two will be fed with the exhaust from the first cell.
In parallel connection, however, the power will be bigger, since each cell
gets its own gas. And since SOFCs are still quite expensive, the extra fuel
utilization of the series connection is probably not enough to compensate
for the lower electricity generation per kg fuel cell. So in the model the
stacks are coupled in parallel.
The model has an anode side, where all the fuel, water and CO 2 is
sent in, and a cathode side, where the air is sent in. The air is modeled as
consisting of 79% Nitrogen and 21% Oxygen (volume fraction).
Some of the heat generated by the chemical reactions in the SOFC can
be set to be lost to the surroundings ( ˙Q loss ), whereas the rest will lead
to a temperature increase of the gasses at the outlet. In reality the outlet
temperature of the anode side is different from that of the cathode side,
but since the model is zero dimensional the temperature distribution in
the cell has not been calculated, and the outlet temperatures have instead
been set equal to each other.
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