Page 91 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

68 High Temperature Solid Oxide Fuel CelIs: Fundamentals, Design and Applications

These equations are sufficient to calculate the necessary excess air h for a given
heat extraction -QFc of the module, or vice versa to calculate the necessary SOFC
cooling by the heat extraction -& for a defined excess air has shown below.
The consideration of the stacks only allows a more detailed modelling and the
energy balance delivers

fiH + fiAI = QFC + pel + fiAn0 + fiCa0. (56)
This equation is identical with Eq. (53) if all the fuel is used in the stacks. The
enthalpy flow of the incoming fuel is

kF1 = hFI * (LHV f hi1) (5 7)

and the enthalpy flow of the incoming air is

fiA1 = mAI ?& = rizp~ . h . /-LAO . hir.

The stoichiometric specific air demand pAo is defined by the relation of the
stoichiometric air mass flow and the corresponding fuel mass flow. The relation
of all terms of the energy balance on the mass flow rizFl of the incoming fuel allows
a generalised consideration. The generated heat is

QFC = hFI . qFC. (59)
The produced power is

pel = PI . Pel.

With the fuel utilisation Uf

uj=1-- mFAnO
mF1

the enthalpy flow at the anode outlet is

The flow of the reaction product gas RG is

kRG = kFI ' uf + m02 = kF1 * uf ' (1 + /-L020),
with
h02 = uf . mF1 ' /-L020.

The mass flow at the outlet of the anode side consists of the not utilised fuel and
of RG. RG consists of the reaction products GO2 and H2O. Its mass flow is equal to