Numerical analysis of output characteristics of tubular
SOFC with internal reformer
, Akihiko Momma, Tohru Kato, Yasuhiro Kasuga
Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305-8568, Japan
Received 5 June 2000; received in revised form 6 November 2000; accepted 17 January 2001
In the solid oxide fuel cell (SOFC) system, the internal reforming of raw fuel will act as an ef®cient cooling system. To realize this
cooling system, a special design of the internal reformer is required to avoid the inhomogeneous temperature distribution caused by the
strong endothermic reforming reaction at the entrance of the internal reformer. For this purpose, a tubular internal reformer with adjusted
catalyst density can be inserted into the tubular SOFC stack. By arranging this, the raw fuel ¯ows along the axis of the internal reformer to
be moderately reformed and returns at the end of the internal reformer as a suf®ciently reformed fuel.
In this paper, the output characteristics of this con®guration are simulated using mathematical models, in which one-dimensional
temperature and molar distributions are computed along the ¯ow direction. By properly mounting the catalyst density in the internal
reformer, the temperature distribution of the cell stack becomes moderate, and the power generation ef®ciency and the exhaust gas
temperature are higher. Effects of other operating conditions such as fuel recirculation, fuel inlet temperature, air recirculation and air inlet
temperature are also examined under the condition where the maximum temperature of the stack is kept at 1300 K by adjusting the air ¯ow
rate. Under this condition, these operating conditions exert a considerable effect on the exhaust temperature but have a slight effect on the
ef®ciency. # 2001 Elsevier Science B.V. All rights reserved.
Keywords: Solid oxide fuel cell (SOFC); Tubular SOFC; Internal reform; Simulation
Tubular solid oxide fuel cells (SOFCs) have been pointed
out to have advantages with respect to mechanical stresses
developed by seals and thermal stresses caused by the
temperature distribution along the cell axis, in comparison
with planar SOFCs . However, leveling of the tempera-
ture distribution is still required to avoid cell deterioration
due to the higher local temperature. The higher temperature
may lead to electrode sintering and chemical reaction
between the electrode and the electrolyte. Therefore, the
temperature distribution has to be restricted in a narrow
The reforming of raw fuel is an endothermic reaction.
Therefore, the internal reforming can be used to cool the cell
stack, only if some design is contrived to avoid the inho-
mogeneous temperature distribution caused by the strong
reforming reaction at the inlet of the internal reformer.
To ®ll this requirement, the internal reformer should be
separated from the fuel electrode to adjust the catalyst
density. For this purpose, a tubular internal reformer with
a thin or graded catalyst density can be inserted into the
tubular cell. The raw fuel will ¯ow then along the axis of
the reformer to be reformed moderately and will change
its ¯ow direction as a suf®ciently reformed fuel at the end
of the internal reformer.
There is also another advantage of the internal reforming
avoiding the heat loss that cannot be avoided in the external
In this paper, the schematic structure of the tubular SOFC
equipped with an internal reformer is presented, and the
effects of the internal reforming and other operating con-
ditions are discussed by numerical simulations.
2. SOFC system equipped with internal reformer
A schematic structure of the SOFC system having both a
pre-reformer and an internal reformer is shown in Fig. 1. In
this ®gure, one cell stack with an internal reformer and two
air supply tubes are shown. In a real system, many stacks,
internal reformers and air tubes have to be arranged. The
enlarged drawing of the stack will be shown later in Fig. 3.
Journal of Power Sources 101 (2001) 60±71
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E-mail address: email@example.com (S. Nagata).
0378-7753/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
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