Page 93 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

70 High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications

Figure 3.8 The reversiblefueIcel1-heat engine hybridsystem.

heat consists of the energy from the environment (anergy) and of the exergy
being supplied by the reversible working heat pumps. The fuel cell FC delivers
the fiue gas, the work and the heat as given in Eq. (5). The unmixed product
flue gas is brought from the state T,p of FC to the ambient state T0,po by the
reversible heat engine HEG. The reversible work delivered by HEG is the exergy
of the flue gas with the state T,p. Finally we use the Carnot cycle CC for the heat
management between FC and the environment. FC can exchange heat
reversibly with CC as with the process environment before. CC operates as a
heat engine for ArS < 0.
The fuel cell FC delivers the reversible work wtFCre,,

WtFCrev = ArG = ArH - TFC . ArS (5)

FC is the heat source of the Carnot cycle CC and delivers reversible heat qFCrev.
The reversible work wtCCrev of CC is defined by

and the reversible heat qFCrev

TO
qccrev = qFCrev ' - TO . A'S.
=
TFC
The heat pump HPF has to deliver the reversible heat qHpprev to heat the fuel