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

4. SYSTEM DESCRIPTION
which increases system performance and therefore called Additional Air
Preheating.
Afterwards the air is preheated by high temperature exhaust gas by
GGHEX3 to a temperature of 690 ◦ C before it enters the SOFC cathode
inlet point 14.
4.2.3 SOFC stack
The specified cell area of 0,0228 m 2 makes the SOFC the only component
in the model having a physical size. The number of cells per stack has
been set to 60. However these value does not affect system efficiency or
system size - the number of stacks in the system is variable and will depend
on the enthalpy flow of the fuel input 7 . So the cell area and number
of cells are only specified to have some kind of relation to real systems.
The fuel utilization factor (U f ) is set 70% which is a typical value for fuel
cell systems [25]. Together with the fuel input of 100kW and recirculation
factor of 0,62 this gives the current of the system. Instead of the fuel input
of 100kW the current draw could have been specified, but when the fuel
input is kept constant, the cooling and heating powers become easier to
evaluate during the parameter investigations in chapter5.3.
The current density (i d ) is a parameter which determines how much
the SOFC is loaded (regulation). The value of 3000 A/m 2 is an estimate
based on data from TOFC. The fuel input determines the size of the system
(100kW fuel input). These two factors give the number of stacks,
which becomes 20,15. Instead of the current density the number of stacks
n st ack ) could be specified, but it is impractical to have more than one extensive
parameter.
The two inlets at the SOFC are assumed to have equal temperature, and
the two outlets have the same temperature. ∆T min,SOFC determines the
temperature increase from inlet (point 5 and 14) to the outlet (point 6
and 15). ∆T min,SOFC has a value of 90 ◦ C which is a typical value of fuel
cells today [25]. It is important that the limits of minimum temperature
at the inlet and maximum temperature at the outlet are not violated, as
described in section 3.12 page 64.
7 Alternatively the current draw could have be specified or the number of stacks
(since the current density is also given)
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