LNG cryogenic power generation system using molten carbonate fuel cells

An LNG cryogenic power generation system using a molten carbonate fuel cell is equipped with a CO.sub.2 separator. The CO.sub.2 separator takes advantages of cryogenic LNG in a manner such that CO.sub.2 among gases discharged from an anode chamber of the fuel cell is liquefied with cryogenic LNG and separated from the anode exhaust gas. Cell reactions take place at a cathode chamber and the anode chamber of the fuel cell to cause power generation as the oxidizing gas which contains CO.sub.2 is fed to the cathode chamber and the fuel gas is fed to the anode chamber. LNG is reformed by a reformer of the fuel cell and the reformed gas is fed to the anode chamber. During the cell reaction, CO.sub.2 of the oxidizing gas fed to the cathode chamber is transferred as carbonate ion to the anode chamber and CO.sub.2 is enriched or concentrated before expelled from the anode chamber. This anode gas is introduced to the CO.sub.2 separator. In the CO.sub.2 separator, CO.sub.2 among the anode gas is liquefied by cryogenic LNG and separated from the anode gas. As a result, the power generation and the CO.sub.2 recovery are carried out at the same time, and an amount of CO.sub.2 discharged to atmosphere is remarkably reduced.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to a cryogenic power generation system 
employing fuel cells, and particularly to an LNG cryogenic power 
generation system equipped with a CO.sub.2 separator taking advantages of 
cryogenic LNG. 
2. Background Art 
Power generation systems using fuel cells are known in the art and some 
systems employ molten carbonate fuel cells. A conventional molten 
carbonate fuel cell generally includes an electrolyte plate (tile) soaked 
with carbonate, a cathode chamber (oxygen electrode) and an anode chamber 
(fuel electrode). The electrolyte plate is made from a porous material and 
the carbonate serves as the electrolyte. The electrolyte plate is 
sandwiched by the cathode chamber and the anode chamber. Oxidizing gas is 
introduced to the cathode chamber and fuel gas in introduced to the anode 
chamber to cause the power generation due to an electrical potential 
difference between the cathode chamber and the anode chamber. In a 
conventional power generation system using molten carbonate fuel cells, 
the above-described fuel cells are generally stacked one after another via 
separators to define a multi-layer fuel cell unit or a stack of fuel 
cells. 
One example of such power generation systems is illustrated in FIG. 5 of 
the accompanying drawings. As illustrated in FIG. 5, before air A reaches 
a cathode chamber 102 of a fuel cell 100 via an air feed line 108, the air 
A is compressed by a compressor 104, cooled by a cooling device 105, 
compressed by another compressor 106 and preheated by an air preheater 
107. Part of the air A in the air feed line 108 is branched to a reformer 
110 by a branch line 109. Gases CG discharged from the cathode chamber 102 
(also called "cathode exhaust gas CG") are introduced to a turbine 112 
through an exit line 111 and expelled via the air preheater 107. Gases AG 
discharged from the anode chamber 103 (also called "anode exhaust gas AG") 
contain H.sub.2 O and CO.sub.2. Thus, moisture H.sub.2 O of the anode 
exhaust gas AG is removed and the separated moisture H.sub.2 O is 
recirculated to the system. The anode exhaust gas AG of the fuel cell 100 
is cooled by a heat exchanger 113, heat-exchanged with natural gas NG in a 
preheater 114 and cooled by another cooling device 116. In the cooling 
device 116, the anode exhaust gas AG is condensed, then introduced to a 
gas-liquid separator 117 to separate moisture component from gas 
component. The gas component which contains CO.sub.2 is fed to a 
combustion chamber of the reformer 110 by a blower 118 through a line 119 
extending to the heat exchanger 113. The moisture or water component 
H.sub.2 O is pressurized by a pump 120 and fed to an evaporator 121. In 
the evaporator 121, the water H.sub.2 O is heated to steam, then fed to an 
entrance of the reformer 110 via a superheater 115 through a line 122 such 
that it is mixed with the natural gas NG. Fuel gas produced in the 
reformer 110 is introduced to the anode chamber 103 of the fuel cell 100 
by a piping 123. Gases discharged from the combustion chamber of the 
reformer 110, which contain CO.sub.2, are fed to the cathode chamber 102 
of the fuel cell 100 through a line 124 together with the air of the line 
108. An evaporator 115 is provided between the preheater 114 and the 
cooling device 116 such that the anode exhaust gas AG flows therethrough. 
Numeral 101 designates an electrolyte plate and numeral 125 designates a 
desulfurizer. 
In the above-described power generation system using molten carbonate fuel 
cells, the moisture H.sub.2 O of the anode exhaust gas AG discharged from 
the anode chamber 103 is removed by the gas-liquid separator 117, and the 
CO.sub.2 -containing-gases are combusted in the combustion chamber of the 
reformer 110 before they are fed to the cathode chamber 102. Therefore, a 
CO.sub.2 separation from the gases and a recovery of CO.sub.2 are not 
considered. Consequently, the conventional power generation system is not 
designed to recover CO.sub.2 and CO.sub.2 is expelled to atmosphere. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an LNG cryogenic power 
generation system using molten carbonate fuel cells in which a CO.sub.2 
separator is provided to separate CO.sub.2 contained in the anode exhaust 
gas and cryogenic LNG is used for the CO.sub.2 separation. 
Another object of the present invention is to provide an LNG cryogenic 
power generation system using molten carbonate fuel cells in which 
separated CO.sub.2 is recovered in the form of gas. 
Still another object of the present invention is provide an LNG cryogenic 
power generation system using fuel cells in which the CO.sub.2 recovered 
as gas is fed to cathode chambers of the fuel cells. 
According to one aspect of the present invention, there is provided an LNG 
cryogenic power generation system using molten carbonate fuel cells with 
oxidizing gas being fed to a cathode chamber of the fuel cell and reformed 
gas or LNG being fed to an anode chamber of the fuel cell, characterized 
in that a CO.sub.2 separator is provided and the CO.sub.2 separator takes 
advantages of cryogenic LNG in a manner such that CO.sub.2 among gases 
discharged from the anode chamber is liquefied with cryogenic LNG and 
separated from the anode exhaust gas. Cell reactions take place at the 
cathode chamber and the anode chamber to cause power generation as the 
oxidizing gas which contains CO.sub.2 is fed to the cathode chamber of the 
molten carbonate fuel cell and the fuel gas is fed to the anode chamber. 
At the same time, CO.sub.2 of the oxidizing gas fed to the cathode chamber 
is transferred as carbonate ion to the anode chamber and CO.sub.2 is 
enriched or concentrated before expelled from the anode chamber. This 
anode gas is introduced to the CO.sub.2 separator. In the CO.sub.2 
separator, CO.sub.2 among the anode gas is liquefied by cryogenic LNG and 
separated from the anode gas. As a result, the power generation and the 
CO.sub.2 recovery are carried out at the same time, and an amount of 
CO.sub.2 discharged to atmosphere is remarkably reduced. Further, less 
power is necessary for the CO.sub.2 separation as compared with a 
conventional system since CO.sub.2 is concentrated prior to the 
recovering. Moreover, the very low temperature which cryogenic LNG 
possesses is effectively used for the CO.sub.2 separation so that an 
energy efficiency of the entire system is improved. Conventionally, very 
low temperature LNG is just expelled to atmosphere. Besides, since the 
liquefied and separated CO.sub.2 is recovered as it is, an amount of LNG 
used for the CO.sub.2 liquefaction can be raised and an amount of natural 
gas to be gasified can be raised. This is desirable in a case where the 
system uses a large amount of natural gas. 
According to another aspect of the present invention, there is provided an 
LNG cryogenic power generation system using fuel cells with oxidizing gas 
being fed to a cathode chamber of the fuel cell and reformed LNG being fed 
to an anode chamber of the fuel cell to cause power generation 
characterized in that CO.sub.2 contained in gases discharged from the 
anode chamber is separated therefrom by liquefying CO.sub.2 with LNG of 
cryogenic temperature. The power generation system is provided with a 
CO.sub.2 separator which performs the CO.sub.2 separation using LNG. The 
CO.sub.2 separator has a gas recovery portion which gasifies the liquefied 
CO.sub.2 and recovers it. Therefore, the CO.sub.2 is recovered in the form 
of gas. 
According to still another aspect of the present invention, there is 
provided an LNG cryogenic power generation system using fuel cells with 
oxidizing gas being fed to a cathode chamber of the fuel cell and reformed 
LNG being fed to an anode chamber of the fuel cell, characterized in that 
there is provided a CO.sub.2 separator which liquefies CO.sub.2 contained 
in gases discharged from the anode chamber of the fuel cell with LNG of 
very low temperature, the CO.sub.2 separator has a gas recovery portion 
which gasifies the liquefied CO.sub.2 and collects it, the gasified 
CO.sub.2 is transferred to the cathode chamber of the fuel cell by a line 
(called "second gas line" in a preferred embodiment), and gases discharged 
from the CO.sub.2 separator which gases no longer contain CO.sub.2 are 
transferred to the anode chamber of the fuel cell by another line (called 
"third gas line" in a preferred embodiment). A power generation efficiency 
is improved since the gasified CO.sub.2 is introduced to the cathode 
chamber and the gases which do not contain CO.sub.2 are introduced as the 
fuel gas to the anode chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, preferred embodiments will be described with the accompanying 
drawings. FIGS. 1 through 4 illustrate preferred embodiments of the 
present invention respectively and same numerals are given to similar 
elements through these Figures. The symbol M is used in the drawings to 
designate a motor in each instance. The abbreviation "ata" is used herein 
as a unit of pressure, 1 ata being equal to 98.07 kPa. 
Referring first to FIG. 1, shown is a fundamental arrangement of an LNG 
cryogenic power generation system I according to the present invention. 
The power generation system I according generally includes a plurality of 
fuel cells 1, but there is shown only one fuel cell 1 for the illustrative 
purpose. 
In the cryogenic power generation system I, gases B containing CO.sub.2 
which are discharged from a natural gas thermal electric power plant 5 are 
introduced to a cathode chamber 3 of a molten carbonate fuel cell 1 
together with fresh air A whereas natural gas (raw material gas to be 
reformed) is reformed and fed to an anode chamber 4 of the fuel cell 1. 
The cryogenic power generation system I is equipped with a CO.sub.2 
separator II which liquefies CO.sub.2 with cryogenic LNG to separate 
CO.sub.2 from the gases. The CO.sub.2 separator II also recovers the 
liquefied CO.sub.2. 
The LNG cryogenic power generation system I includes the molten carbonate 
fuel cell 1 and the fuel cell 1 includes an electrolyte plate 2 sandwiched 
by the cathode chamber 3 and the anode chamber 4. The electrolyte plate 2 
is soaked with carbonate and such a fuel cell 1 is defined as the molten 
carbonate type fuel cell. The fresh air A which has passed through a 
filter 6 is compressed by a compressor 7. The compressed air A flows in an 
air feed line 8 extending to the cathode chamber 3. Gases discharged from 
the cathode chamber 3 (called "cathode exhaust gas") are partially 
transferred to a turbine 10 by a cathode chamber exit line 9 and expelled 
to atmosphere. The remainder of the cathode exhaust gas is introduced to a 
combustion chamber 12b of a reformer 12 by a branch line 11. Gases 
discharged from the combustion chamber 12b of the reformer 12 are 
pressurized by a blower 13 and fed to the cathode chamber 3 by a line 14. 
On the other hand, the natural gas NG is preheated by a preheater 15 and 
introduced to a reforming chamber 12a of the reformer 12 by a natural gas 
feed line 16. In the reforming chamber 12a, the natural gas NG is reformed 
to fuel gas FG and then fed into the anode chamber 4 by a fuel gas feed 
line 17. Gases discharged from the anode chamber 4 (called "anode gas") 
are introduced to a first gas-liquid separator 21 via a heat exchanger 18, 
an evaporator 19 and a condenser 20. In the first gas-liquid separator 21, 
moisture (H.sub.2 O) of the anode gas is separated from the anode gas. 
Then, gases which do not contain the moisture but contain CO.sub.2 are 
introduced to the CO.sub.2 separator II. In the CO.sub.2 separator II, the 
gases are cooled such that the CO.sub.2 component is liquefied and the 
CO.sub.2 component is separated from the gas component. After that, the 
liquefied CO.sub.2 is recovered. H.sub.2 O separated by the first 
gas-liquid separator 21 is pressurized by a pump 22 and transferred to a 
liquid pool device (container) 23. Then, the water H.sub.2 O is vaporized 
by the evaporator 19 to steam and the steam is introduced to the natural 
gas feed line 16. The gases B from the thermal electric power plant 5 are 
led into the filter 6 by a line 24 and then into the air feed line 8. 
The CO.sub.2 separator device II includes a cooling device 33, a second 
gas-liquid separator 25, a gas heat exchanger 26, an indirect heating type 
heat exchanger 27, a CO.sub.2 gas-liquid separation drum 28, a liquid 
recovery portion 43, an open-rack vaporizer and a heater 41. The liquid 
recovery portion 43 includes a storage tank 29 and a pump 30. The pump 30 
is used to pump the liquid CO.sub.2. The heat exchanger 27 is used for the 
CO.sub.2 liquefaction. The anode gas which contains CO.sub.2 discharged 
from the first gas-liquid separator 21 is forced into the line 42 and 
cooled by the cooling device 33. If the anode gas contains moisture, the 
moisture is removed at the second gas-liquid separator 25 before the anode 
gas is fed to the gas heat exchanger 26. This is because the moisture 
would condense in the heat exchangers 26 and/or 27 and cause the clogging 
or closing of the heat exchanger(s). The anode gas cooled in the heat 
exchanger 26 is transferred to the indirect-heat-exchanging type heat 
exchanger 27. This heat exchanger 27 is used for the CO.sub.2 
liquefaction. In the heat exchanger 27, CO.sub.2 contained in the anode 
gas is cooled to liquid with LNG of cryogenic temperature. The liquefied 
CO.sub.2 is removed by the CO.sub.2 separating drum 28. The pressure of 
the anode gas coming from the anode chamber 4 is generally about 7 ata. 
However, since CO.sub.2 is not condensed until the partial pressure of 
CO.sub.2 reaches a value below 5.2 ata, the gas pressure in the CO.sub.2 
separator device II is maintained to or above 5.2 ata and the anode gas is 
cooled enough to condense CO.sub.2 of the anode gas completely in the heat 
exchanger 27. 
The liquefied CO.sub.2 is transferred to the liquid CO.sub.2 treating 
device 34. Therefore, the liquid CO.sub.2 flows into the liquid CO.sub.2 
treating device 34 from the gas-liquid separating drum 28 via the storage 
tank 29, the pump 30 and a first CO.sub.2 recovery line 32. On the other 
hand, LNG which is used to liquefy CO.sub.2 at the heat exchanger 27 is 
gasified in the heat exchanger 27 and becomes natural gas NG. Part of the 
natural gas NG flows into the natural gas feed line 16 via the line 51 and 
the open-rack vaporizer 31. Gases (H.sub.2 O and CO) going out of the heat 
exchanger 27 are introduced to a residual gas line 44 from the gas-liquid 
separating drum 28, then introduced to the heat exchanger 26 to cool the 
anode gas. After that, these gases are heated by the heater 41 and 
transferred to the first gas line 35 from the CO.sub.2 separator unit II. 
H.sub.2 O and CO are then compressed by the blower 36 and fed back to the 
cathode chamber 3 via the combustion chamber 12b. 
When CO.sub.2 among the gases B discharged from the electric power plant 5 
is desired to be recovered, the gases B are led into the gas line 24 and 
the air feed line 8 such that the gases B are compressed by the compressor 
7 with the air A before they are introduced to the cathode chamber 3. On 
the other hand, part of natural gas NG gasified at the CO.sub.2 separator 
unit II is introduced to the natural gas feed line 16 so as to reform that 
part of natural gas NG and then it is fed as the fuel gas FG into the 
anode chamber 4 to cause cell reactions at the cathode chamber 3 and the 
anode chamber 4. CO.sub.2 is therefore concentrated when it is expelled 
from the anode chamber 4. In the cathode chamber, on the other hand, a 
following reaction takes place: 
EQU CO.sub.2 +1/2O.sub.2 +2e.sup.-.fwdarw.CO.sub.3.sup.-- 
Therefore, CO.sub.2 is transformed to carbonate ion CO.sub.3.sup.--. The 
carbonate ion CO.sub.3.sup.-- migrates within the electrolyte plate 2 and 
reaches the anode chamber 4. In the anode chamber 4, a following reaction 
takes place: 
EQU CO.sub.3.sup.-- +H.sub.2 .fwdarw.H.sub.2 O+CO.sub.3 +2e.sup.- 
Power generation proceeds as the cell reactions advance in the cathode 
chamber 3 and the anode chamber 4. At the same time, CO.sub.2 is 
transferred to the anode chamber 4 from the cathode chamber 3. The gas 
flow rate across the anode chamber 4 is smaller than that across the 
cathode chamber 3, namely between one ninth and one second that at the 
cathode chamber 3. Thus, CO.sub.2 transferred to the anode chamber 4 is 
enriched due to the flow rate difference. The CO.sub.2 concentration in 
the anode chamber 4 is several times that in the cathode chamber 3. This 
means that the power generation takes place in the fuel cell 1 and at the 
same time CO.sub.2 is enriched or concentrated in the fuel cell 1. 
The anode gas whose CO.sub.2 is enriched at the anode chamber 4 is 
introduced to the heat exchanger 18, the evaporator 19, the condenser 20 
and the first gas-liquid separator 21. In the first gas-liquid separator 
21, the mositure (H.sub.2 O) is removed from the anode gas, and then the 
anode gas is led into the CO.sub.2 separation unit II. After passing 
through the CO.sub.2 separation unit II, the anode gas is led into the 
cooling device 33 and the second gas-liquid separator 25. In the second 
gas-liquid separator 25, another moisture removal is carried out. Then, 
the anode gas is heat exchanged with the low temperature gas in the heat 
exchanger 26. The anode gas is cooled due to this heat exchange and 
CO.sub.2 contained in the anode gas is then cooled with very low 
temperature LNG in the indirect heating type heat exchanger 27 so that the 
liquefied CO.sub.2 is obtained. The liquefied CO.sub.2 is separated from 
the gaseous component in the gas-liquid separating drum 28 and introduced 
to the storage tank 29 for an equalization of loads on the CO.sub.2 
treating device 34. CO.sub.2 is then pumped up by the pump 30 to the 
CO.sub.2 treating device 34 via the first recovery line 32. This reduces 
an amount of CO.sub.2 to be expelled to atmosphere which contributes to 
the suppression of the greenhouse effect of the earth. 
In this embodiment, since CO.sub.2 is recovered in the form of liquid, it 
is possible to design a system in which a large amount of LNG is used to 
liquefy CO.sub.2 at the indirect heating type heat exchanger 27. 
Consequently, a large amount of natural gas NG can be used in the system. 
This is desirable in a certain case since some systems require a large 
amount of natural gas for the power generation. 
FIG. 2 shows another LNG cryogenic power generation system according to the 
present invention. In this embodiment, the CO.sub.2 separator unit II is 
also provided with a gas recovery portion 45 which gasifies the liquefied 
CO.sub.2 and recovers the gaseous CO.sub.2. More specifically, instead of 
the gas heat exchanger 26 of the foregoing embodiment, there is provided a 
low temperature heat recovering, multi-fluid type heat exchanger 37. In 
addition, a compressor 38 is provided to compress gases discharged from 
the second gas-liquid separator 25 before these gases are introduced to 
the heat exchanger 27, a third gas-liquid separator 39 is provided on a 
line 42 extending between the heat exchangers 37 and 27 and a second 
recovery line 40 is provided to transfer part of the liquid CO.sub.2 into 
the multi-fluid heat exchanger 37 from the gas-liquid separator drum 28 
such that the heat exchange at the multi-fluid heat exchanger 37 takes 
advantages of low temperature liquid CO.sub.2 as well as non-CO.sub.2 
containing gases of the line 44 (called "residual gas") and such that the 
CO.sub.2 containing gases of the line 42 are cooled by this heat exchange 
in the multi-fluid heat exchanger 37. CO.sub.2 used for the heat exchange 
is gasified and recovered through the second recovery line 40. Further, a 
branch line 46 is provided to introduce the remaining liquid CO.sub.2 to 
the storage tank 29 from the gas-liquid separator drum 28 and the liquid 
CO.sub.2 in the storage tank 29 is recirculated to the second recovery 
line 40 via the pump 29 and the recirculation line 47 such that it merges 
with the liquid flowing into the multi-fluid heat exchanger 37. Other 
arrangements are similar to those illustrated in FIG. 1. 
In the embodiment shown in FIG. 2, the anode gas introduced to the CO.sub.2 
separator unit II is transferred to the multi-fluid heat exchanger 37 via 
the cooling device 33, the first gas-liquid separator 35 and the 
compressor 38. In the multi-fluid heat exchanger 37, the anode gas is heat 
exchanged with the non-liquid-containing gases and the liquid so that part 
of CO.sub.2 is liquefied. CO.sub.2 is further liquefied with LNG of low 
temperature in the indirect heating type heat exchanger 27. The liquefied 
CO.sub.2 is introduced to the storage tank 29 via the CO.sub.2 gas-liquid 
separation drum 28. In this case, part of the liquid CO.sub.2 is directly 
fed to the multi-fluid heat exchanger by the second recovery line 40 so 
that low temperature thereof is used to cool the anode gas and 
consequently that part of CO.sub.2 is gasified again. The gasified 
CO.sub.2 is taken out of the multi-fluid heat exchanger 37 and transferred 
to the CO.sub.2 treating device 34. Therefore, the gasified CO.sub.2 is 
not discharged to atmosphere. Gases which are not condensed in the 
indirect heating type heat exchanger 27 are introduced to the multi-fluid 
heat exchanger 37 by the residual gas line 44 from the CO.sub.2 gas-liquid 
separator drum 28. Then, these residual gases flow through the heater 41, 
the blower 36 of the power generation system I, the heat exchanger 18 and 
the combustion chamber 12b of the reformer 12. This means that the 
residual gases are recirculated to the cathode chamber 3. 
In this system, since the compressor 38 pressurizes the gases discharged 
from the first gas-liquid separator 25, the gas pressure in the CO.sub.2 
separator unit II can be maintained at or above 5.2 ata. In addition, 
raising the gas pressure results in the improvement of the CO.sub.2 
liquefaction efficiency at the CO.sub.2 liquefaction indirect heating type 
heat exchanger 27. As a result, the blower 36 may not be required if the 
gas pressure allows it. 
FIG. 3 shows another embodiment of the present invention. This cryogenic 
power generation system includes a molten carbonate type fuel cell 50 
which has a reforming chamber 12c to reform natural gas with heat produced 
upon the cell reaction of the fuel cell. In addition, a second gas line 48 
is provided to feed all or part of CO.sub.2 gas separated and recovered by 
the CO.sub.2 separating unit II of FIG. 2 as part of the oxidizing gas to 
be fed to the cathode chamber 3 of the fuel cell 50. Further, a third gas 
line 49 is provided to feed to the inlet of the reforming chamber gases 
which remain in the CO.sub.2 separating unit II after the CO.sub.2 
recovery. This arrangement improves the power generation efficiency. More 
specifically, CO.sub.2 contained in the gases is liquefied and separated 
from the gases with LNG of low temperature. The second recovery line 40 of 
the CO.sub.2 separating unit II of FIG. 2, which gasifies the liquefied 
CO.sub.2 again and recovers it, and the air feed line 8, which feed the 
air A to the cathode chamber 3 of the fuel cell 1, are connected with each 
other by the second gas line 48 so that CO.sub.2 is recirculated to the 
cathode chamber 3 together with the air A. Gases which remains, after the 
CO.sub. 2 recovery, in the CO.sub.2 separating unit II are recirculated to 
the inlet of the reforming chamber 12c by the third gas line 49. 
In this embodiment, the CO.sub.2 separator unit II takes advantages of the 
cryogenic temperature of LNG to liquefy and separate CO.sub.2, and the 
liquefied CO.sub.2 is gasified when recovered. The recovered gaseous 
CO.sub.2 returns to the cathode chamber 3 of the fuel cell 50 whereas the 
residual gases (H.sub.2 and CO) after the CO.sub.2 separation at the 
CO.sub.2 separator unit II return to the inlet of the reforming chamber. 
Thus, it is possible to improve the power generation efficiency of the 
fuel cell 50. 
In the cryogenic power generation system shown in FIG. 3, like those 
illustrated in FIGS. 1 and 2, CO.sub.2 contained in the gases discharged 
from the thermal electric power plant may be introduced into the air feed 
line 8 and in turn into the cathode chamber 3. In addition, the CO.sub.2 
separator unit II may send out CO.sub.2 in the form of liquid although the 
unit II of FIG. 3 sends out CO.sub.2 in the form of gas. 
As to the fuel cell 50, the foregoing description deals with the fuel cell 
50 which has the reforming chamber 12c that reforms natural gas with heat 
generated upon the cell reaction of the fuel cell 50. In other words, the 
reforming chamber 12c is located in the fuel cell 50. However, the 
embodiment of FIG. 3 may be also applied to the systems of FIGS. 1 and 2, 
respectively. More specifically, this embodiment is applicable to cases 
where part of the cathode gas and anode gas discharged from the fuel cell 
are respectively introduced to the combustion chamber 12b of the reformer 
12. In such a case, like the system of FIG. 3, there may be provided a 
second gas line 48 and a third gas line 49, and there may be provided a 
fourth gas line 52 and a fifth gas line 53 for introducing part of the 
anode gas discharged from the anode chamber 4 and part of the cathode gas 
discharged from the cathode chamber 3 to the combustion chamber 12b of the 
reformer 12. 
In the systems of FIGS. 3 and 4, even if an excessive amount of H.sub.2 and 
CO are fed into the anode chambers 4 of the fuel cells 1 and 50, these 
gases (H.sub.2 and CO) are recirculated in the systems via the separator 
unit II so that the fuel utilization factor of the entire system is not 
deteriorated and the "one-pass" fuel utilization factor at the anode 
chamber 4 can be set low. This raises the cell voltage. In addition, 
according to the system of FIG. 4, even if the reforming rate at the 
reformer 12 is not set to high, non-reformed CH.sub.4 circulates in the 
system and the system efficiency is not lowered. 
The present invention is not limited to the above-described embodiments. 
For example, FIGS. 1 and 2 show the systems for the thermal electric power 
plant 5. However, the present invention can be applied to other type of 
power plants. In addition, the gases discharged from the power plant are 
mixed with the air before they are introduced to the cathode chamber of 
the fuel cell in the illustrated embodiments. However, the recirculation 
gas line 24 may be omitted if CO.sub.2 produced in the system is liquefied 
and separated from the gases by the cryogenic LNG and fed to the cathode 
chamber of the fuel cell. Furthermore, although part of natural gas NG 
gasified by the CO.sub.2 separator unit II is introduced to the entrance 
of the reformer in the illustrated embodiments, this is not a requisite. 
Moreover, another fuel cell may be provided downstream of the turbine 10 
and the gases passing through the turbine 10 may be introduced to a 
cathode chamber of this fuel cell.