Note: Descriptions are shown in the official language in which they were submitted.
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GR 96 P 3308 P FILE, ~ TIIIS AMr.~t~
~T TI~QNSLATI~!N
Description
Process for operating a high temperature fuel cell
installation, and high temperature fuel cell installation
The invention relates to a process for operating
a high temperature fuel cell installation and to a high
temperature fuel cell installation.
It is known that, during the electrolysiE, of
water, the water molecules are decomposed by electric
current into hydrogen (H2) and oxygen (~2)- In a fuel
cell, this process takes place in reverse. Through the
electrochemical combination of hydrogen (H2) and oxygen
(~2) to form water, electric current is produced with
high efficiency. If pure hydrogen (H2) is u~ed a~ combus-
tion gas, this takes place without the emission of
pollutants and carbon dioxide (C02). Even with a
technical combustion gas, for example natural gas or coal
gaE,, and with air (which may additionally be enriched
with oxygen (~2) ) instead of pure oxygen (~2) ~ a fuel cell
produces conRiderably less pollutants and less carbon
dioxide (C02) than other forms of energy production which
operate using fossil energy sources.
The technical implementation of the fuel cell
principle has given rise to a variety of solutions, and
more precisely with different electrolytes and with
operating temperatures of between 80 ~C and 1000~C.
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Depen~;ng on their operating temperature, fuel
cells are divided into low, medium and high temperature
fuel cells, which in turn differ through various
technical embodiments.
5A high temperature fuel cell block (a fuel cell
block is also referred to a "stack" in the specialist
literature) is generally composed of a multitude of high
temperature fuel cells which are of planar construction
and are stacked on one another. Fuel cell installations
comprising at least one high temperature fuel cell block
are, for example, known from the German Patent Applica-
tions with the official reference nl~hers 195 23 973.3,
195 23 972.5 and 195 14 469.4.
A high temperature fuel cell installation is
operated with a high constant operating temperature of,
for example, in excess of 900~C. For this purpose, in
order to achieve the operating temperature before opera-
tion or to hold the required operating temperature during
brief interruptions to operation, the installation must
be supplied with additional heat.
A further problem is to use the working medium
efficiently during operation of the high temperature fuel
cell block. In order to make it possible to operate the
high temperature fuel cell block with high efficiency,
the working medium needs to be supplied in exceRs. Only
through an excess of working medium is it possible to
guarantee that the active faces of the high temperature
fuel cells are provided with enough working medium. An
unavoidable consequence
. . .
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of operating the high temperature fuel cell block with
excess working medium is that, after the electrochemical
reaction has taken place, there is still some working
medium present in the off-gas at the outlet of the high
temperature fuel cell block. Put another way, the working
medium is not fully consumed in the high temperature fuel
cell block. Some of it emerges unused, and this impairs
efficiency.
Laid-open German Patent Specification 41 37 968
discloses a heat ~YchAnge device in which the off-gas
from a high temperature fuel cell block is fed to an
~YpAn~ion turbine. In this case, the off-gas from the
high temperature fuel cell block contains unconsumed air
from the cathode off-gas and unconsumed hydrogen from the
anode off-gas. In order to heat the off-gas to the input
temperature of the expansion turbine, the off-ga~ is fed
before feeding through a heat eYchAnger integrated in the
high temperature fuel cell block. After having been fed
into the turbine, the off-gas is expanded therein. This
means that only the heat content of the off-gas is used
for the production of energy in the turbine, but not
actually the components of the off-gas, for example
hydrogen.
The object of the invention is to provide a
process for operating a high temperature fuel cell
installation, in which efficient and flexible energy
production is guaranteed. A further object is to provide
a high temperature fuel cell in~tallation having high
efficiency.
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The former object is achieved according to the
invention by a process for operating a high temperature
fuel cell installation comprising at least one high
temperature fuel cell block with an anode part and a
cathode part. In order to increase the energy production,
a gas motor coupled to a generator is provided, the motor
being fed at least a portion of the anode off-gas from
the high temperature fuel cell block.
This process proves efficient since all of the
working medium, unless consumed in the fuel cell block
and therefore not present in the anode off-gas, is
available to the gas motor as working medium for
obtaining further energy. At the same time, the process
proves flexible since the gas motor does not always need
to be provided with the same amount of working medium
from the anode off-gas at every operating time. If, at a
particular operating time, there is not enough working
medium in the anode off-gas to operate the gas motor,
then the missing portion of working medium can be fed
separately to the gas motor.
Preferably, water is withdrawn from the anode
off-gas before feeding into the gas motor. In other
words, the water produced during the electrochemical
reaction in the high temperature fuel cell block is
withdrawn from the anode off-gas, 80 that the working
medium is present in a form which can be exploited by the
gas motor. Together with the water, the anode off-gas
also has some of its heat content withdrawn. The tempera-
ture of the anode off-gas, that is to say the working
medium for the gas
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motor is therefore reduced on the way from the high
temperature fuel cell block to the gas motor.
In particular, a working medium for the anode
part may be supplied with water in the form of water
5 vapor before the feeding.
In a further refinement, a portion of the
electric current produced with the generator is used to
heat a working medium when the high temperature fuel cell
block is being started up. For example, the working
medium provided for the high temperature fuel cell block
in normal operation may at the start be fed directly via
a bypass to the gas motor, the energy of which is there-
fore used for electrically heating the high temperature
fuel cell block. The high temperature fuel cell block may
15 consequently be started up with the gas motor, which
forms part of the overall high temperature fuel cell
installation.
In particular, a working medium for the anode
part and/or cathode part of the high temperature fuel
cell block may be heated with the heat dissipated by the
gas motor.
The latter object is achieved according to the
invention by a high temperature fuel cell installation
having at least one high temperature fuel cell block
comprising an anode part and a cathode part. In order to
increase the energy production, a gas motor coupled to a
generator is provided, the gas motor being connected to
the discharge path of the anode part of the high tempera-
ture fuel cell block.
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Preferably, at least one water precipitator is
provided in the discharge path of the anode part. The
water removed from the anode off-gas by at least one
water precipitator may, for example, be fed via a feed
water tank to a steam generator, the water subsequently
evaporated being fed back to the working medium for the
anode part of the high temperature fuel cell block. ~y
virtue of this, even the water from the anode off-gas can
be fed for reuse in the high temperature fuel cell block.
In particular, at least one heat e~ch~nger may be
arranged in the discharge line of the gas motor.
In a further refinement, a steam generator i8
provided in the discharge line of the gas motor. Using
the ~team generator, the water from the off-gas of the
anode part of the high temperature fuel cell block is
evaporated for reuse in the cathode part.
Preferably, the generator is connected to a
heating device arranged in the feed path of the cathode
part. A fraction of the electric current produced in the
generator is used to heat the working medium for the
cathode part.
In particular, the generator may be connected to
an electrical network in order to feed it with electric
current. The current may be fed to a load via the
electrical network.
For further explanation of the invention,
reference will be made to the illustrative embodiment in
the drawing, the single
, .
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figure of which schematically represents a high tempera-
ture fuel cell installation.
According to the figure, a high temperature fuel
cell installation 2 comprises a high temperature fuel
cell block 4 which is divided into an anode part 6 with
anode gas spaces (not shown in detail) and a cathode part
8 with cathode gas spaces (not further shown). The high
temperature fuel cell block 4 is preferably composed of
a multitude of high temperature fuel cells (not further
shown) of planar design.
An invertor 10, which converts the direct current
produced by the high temperature fuel cell block 4 into
alternating current for an electrical network 18, is
connected to the high temperature fuel cell block 4.
The anode part 6 is assigned an anode path 12 for
supplying it with a working medium, for example hydrogen
(H2) or a mixture of combustion gas and reaction vapor,
this anode path 12 comprising a feed path 14 and a
discharge path 16. Before feeding into the anode part 6,
the working medium is referred to as "working medium for
the anode part 6", and after it has left the anode part
6, it is referred to as "anode off-gas of the anode part
6".
A gas splitter 20, a mixing chamber 22 and a heat
eYchAnger 24 are successively arranged, in that order in
the flow direction, in the feed path 14 of the anode
part 6 of the high temperature fuel cell block 4. A gas
motor 26 is connected to the discharge path 16 of the
anode part 6 of the
, .
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high temperature fuel cell block 4. The term "gas motor"
is in this context intended to mean a device for
converting the chemical energy contained in the working
medium (anode off-gas) into mechanical energy. A
generator 50, which converts the mechanical energy
produced in the gas motor 26 into alternating current, i8
coupled to the gas motor 26. The alternating current is
delivered to an electrical network 54 via a line 52.
The off-gas from the gas motor 26 is discharged
by a discharge line 17 from the high temperature fuel
cell installation 2. A heat ~Yrhanger 36, a steam
generator 38 and a further heat ~X~hAnger 40 are
successively arranged, in that order in the flow
direction, in the discharge line 17.
Two water precipitators 30, 32 and a mixing
chamber 34 are successively arranged, in that order in
the flow direction, in the discharge path 16 of the anode
part 6.
The working medium for the anode part 6 is fed
into the anode part 6 of the high temperature fuel cell
block 4 via the feed path 14. This being the case, the
working medium firstly flows through the ga~ splitter 20,
in which a fraction of the working medium is diverted
from the feed path 14 via a line 44 and fed directly into
the mixing chamber 34 arranged upstream of the gas motor
26 in the discharge path 16 of the anode part 6.
Operation of the gas motor 26 is therefore guaranteed
even if not enough working medium is present in the anode
off-gas of the anode part 6 of the high temperature fuel
cell block 4. In the heat eYc-h~nger 24, the working
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medium for the anode part 6 i~ heated by the anode off-
gas.
After the electrochemical reaction has taken
place in the high temperature fuel cell block 4, the
anode off-gas is discharged from the high temperature
fuel cell block 4 via the discharge path 16. In the water
precipitators 30 and 32, a large portion of the process
water produced during the reaction in the high tempera-
ture fuel cell block 4 is removed together with a
fraction of the heat content of the anode off-gas.
After the procens water has been removed from the
anode off-gas, the cooled anode off-gas passes as working
medium via the ~;Y; ng chamber 34 into the gas motor 26.
In the latter, the working medium, i.e. the anode off-
gas, is burnt to produce mechanical energy.
In the steam generator 38, the process waterremoved by the water precipitators 30, 32 from the anode
off-gas is evaporated. For this purpose, the process
water from the water precipitators 30, 32 is fed to the
steam generator 38 via a line 60, in which a feed water
tank 62 and a pump 64 are arranged. The feed water tank
62 is in this case used as a reservoir for the process
water. The latter is fed in the required quantity to the
steam generator 38 by the pump 64.
The water vapor produced in the steam generator
38 is fed via a line 68 to the mixing chamber 22 which is
arranged in the feed path 14 of the anode part 6. The
water
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vapor is therefore mixed with the working medium for the
anode part 6 in order to heat this medium.
The heat obtained in the water precipitator 30
and in the further heat eYchAnger 40 can be fed via a
line 120 carrying a heat-exchange medium into a local hot
water network 122 (not shown in detail).
The cathode part 8 of the high temperature fuel
cell block 4 is assigned a cathode path 80 which
comprise~ a feed path 82 and a discharge path 84. A
compressor 86, a gas splitter 88, a ~iY;ng chamber 90, a
heat ~YchAnger 92 and an electrical heating device 94 are
succes~ively arranged, in that order in the flow
direction, in the feed path 82 of the cathode part 8.
The working medium for the cathode part 8 is fed
to the cathode part 8 via the feed path 82. This being
the case, the working medium, for example air or air
enriched with oxygen (~2) ~ i8 fed into the gas splitter
88 via the compre~or 86.
In the gas splitter 88, at lea~t a fraction of
the working medium for the cathode part 8 is diverted
from the feed path 82 of the cathode part 8 and fed via
a line 100 through the heat ~YchAnger 36. It i8 then fed
back via the mixing chamber 90 to the feed path 82. Since
the heat exchanger 36 is connected downstream of the gas
motor 26 in the discharge line 17 for the off-gas from
the gas motor 26, the working medium for the cathode part
8 diverted from the feed path 82 is heated by the off-gas
from the gas motor 26. The waste heat of the off-gas
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from the gas motor 26 i~ therefore advantageously used to
heat the working medium for the cathode part 8.
The undiverted fraction of the working medium
passes directly via the line 82 into the ;Y; ng chamber
90, where it is recombined with the diverted fraction.
The working medium for the cathode part 8 is then heated
in the heat exchanger 92 and in the electrical heating
device 94. In the heat exchanger 92, the working medium
for the cathode part 8 is heated by the cathode off-gas,
and in the electrical heating device 94 it is
electrically heated for starting up the high temperature
fuel cell block 4. In this case, the electrical heating
device 94 is supplied with current from the generator 50
assigned to the gas motor 26. The electrical heating
device 94 is in this case supplied with current via a
line 102 from the line 52.
The cathode off-gas i8 firstly fed via the
discharge path 84 of the cathode path 8 through the heat
~YrhAnger 92, where it heats the working medium for the
cathode part 8. It i8 then fed to a local heat-using
system 110 (not shown in detail).
On the one hand, therefore, the gas motor 26 is
operated using the anode off-ga~ from the high
temperature fuel cell block 4 and on the other hand the
gas motor 26 is used for starting up the high temperature
fuel cell block 4. The process water obtained during the
electrochemical reaction in the high temperature fuel
cell block 4 is fed in the form of water vapor to the
.
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working medium for the anode part 6 in order to heat it.
Further, the current produced by the gas motor 26 and the
generator 50 is used to operate the electrical heating
device 94 for heating the working medium for the cathode
part 8 of the high temperature fuel cell block 4. In
addition, the heat of the off-gas from the gas motor 26
preheats the working medium for the cathode part 8 of the
high temperature fuel cell block 4.
It i8 therefore possible for the etart-up process
of the high temperature fuel cell installation 2 to be
carried out merely using components which are provided in
the high temperature fuel cell installation 2.
