Power generation system using molten carbonate fuel cells

A reformer includes a reforming chamber for reforming raw material and a heating chamber for heating the reforming chamber. Exhaust gas from a cathode chamber of a fuel cell is directly introduced to the heating chamber such that the exhaust gas is combusted, or the exhaust gas from the cathode chamber is introduced to a catalyst combustor together with exhaust gas discharged from the anode chamber such that these gases undergo combustion. Combustion exhaust gas is introduced to the heating chamber and sensible heat of the cathode exhaust gas is effectively used as heat source for a reforming reaction in the reforming chamber.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to a power generation system for causing a 
reaction of anode gas with cathode gas in a fuel cell for power 
generation. More particularly, the present invention relates to a power 
generation system using molten carbonate fuel cells, in which sensible 
heat of cathode exhaust gas is utilized as part of heat source for a 
reformer when fuel gas is reformed into anode gas. 
2. Background Art 
A molten carbonate fuel cell includes a plurality of cell elements stacked 
with separator plates being interposed between the cell elements. Each 
cell element includes an electrolyte plate (a porous plate soaked with 
molten carbonate), a cathode (oxygen electrode) and an anode (fuel 
electrode). The electrolyte plate is sandwiched by these electrodes. In 
the fuel cell, cathode passages and anode passages are formed to 
respectively feed anode gas to an anode chamber and cathode gas to a 
cathode to perform power generation. 
A conventional molten carbonate fuel cell is illustrated in FIG. 15 of the 
accompanying drawings. In FIG. 15, "I" indicates a fuel cell, and a 
cathode chamber 2 feeds cathode gas CG to a cathode and an anode chamber 3 
feeds anode gas AG to an anode. Numeral 10 designates a reformer which 
reforms fuel gas such as natural gas. The reformer 10 includes a 
combustion chamber 10a and a reforming reaction tube 10b extending through 
the combustion chamber 10a. 
First, feeding of cathode gas to the cathode chamber 2 of the fuel cell I 
will be described. Air A is pressurized by a compressor 4, driven by gas G 
then cooled by a cooling device 5 and compressed again by another 
compressor 6. After that, the air is preheated by an air preheater 7 and 
fed into a cathode chamber 2 through a line 8 with exhaust gas from the 
combustion chamber 10a of the reformer 10 as well as cathode recirculation 
gas from a recirculation line 31. Also, part of the air preheated by the 
air preheater 7 is fed to the combustion chamber 10a of the reformer 10 
through a line 9. Cathode exhaust gas discharged from the cathode chamber 
2 is not only recirculated to the cathode chamber 2 via the recirculation 
line 31 but also introduced to a turbine 12 through a line 11 and then 
expelled to atmosphere via the air preheater 7 and a water heater 21. 
Next, the anode gas fed to the anode chamber 3 will be described. Natural 
gas NG passes through a preheater 14 and a desulfurizer 25 and then enters 
the reforming reaction tube 10b of the reformer 10 with steam supplied 
from a steam line 32. Natural gas is reformed in the reforming tube 10b to 
become the anode gas and then introduced to the anode chamber 3. Anode 
exhaust gas from the anode chamber 3 is cooled through a heat exchanger 13 
and introduced to a cooling device 16 via the preheater 14 and the 
vaporizer 15. In the cooling device 16, the anode exhaust gas is condensed 
and the water thereof is separated from gas by a gas-liquid separator 17. 
Separated gas is sent to the heat exchanger 13 via the line 19 by means of 
the blower 18 driven by motor m and sent to the combustion chamber 10a of 
the reformer 10 in which unreacted H.sub.2 and CO are combusted with air 
fed from the line 9 to maintain a reforming temperature of the reforming 
tube 10b. On the other hand, water separated by the gas-liquid separator 
17 flows through a line 32 to be compressed by a pump 20, to be heated by 
the water heater 21 and to be mixed with natural gas coming from the 
desulfurizer 25 through the line 22, the vaporizer 15 and the steam line 
32. The the water is finally recirculated to the anode chamber 3. 
Combustion exhaust gas of the combustion chamber 10a is fed through the 
line 24 to the cathode chamber 2 as the cathode gas. 
In the power generation system of FIG. 15, the temperature maintenance of 
the reforming reaction tube 10b of the reformer 10 is influenced by an 
amount of heat of air fed into the combustion chamber 10a, an amount of 
heat of the anode exhaust gas which has been separated from the water and 
combustion heat of these gases. However, the anode exhaust gas is cooled 
at the water-gas separation process so that it is necessary to lower a 
fuel utilization factor in order to raise an amount of combustible gas 
among the anode exhaust gas and to increase the combustion heat. An 
example is illustrated in FIG. 17, in which Ti is assigned to an entrance 
temperature of the reformed gas of the reaction tube 10b, To is assigned 
to an exit temperature of the same, T.sub.1 to an entrance temperature of 
the combustion chamber 10b, T.sub.2 to the anode exhaust gas temperature, 
T.sub.3 to a combustion temperature after-the-combustion-temperature), 
T.sub.4 to a temperature at the exit (this temperature is lower than 
T.sub.3 due to the heating of the reforming section). In this case, the 
exit temperature T.sub.4 of the exhaust gas from the combustion chamber 
10a is higher than the air temperature T.sub.1 at the entrance and the 
anode exhaust gas temperature T.sub.2. Therefore, an amount of heat 
required for the combustion includes heat for the reformation and heat for 
raising the air and the anode exhaust gas temperature to the exit 
temperature T.sub.4. In other words, some heat is wasted to raise the air 
temperature and the anode exhaust gas temperature. The same symbols A, G, 
M, AG and CG are utilized in the other figures of drawings herein with the 
same meanings as given hereinabove. 
Referring to FIG. 16, there has been proposed a power generation system 
which maintains the reforming temperature of the reformer 28 by the 
sensible heat of the anode exhaust gas. 
In FIG. 16, the natural gas NG is pressurized by the blower 26 and 
introduced to the preheater 26, the desulfurizer 25 and the reformer 28 
(The reformer 28 has the reforming chamber only). After that, the natural 
gas is sent to the preheater 27 and the anode chamber 3 by the blower 29. 
Part of the anode exhaust gas from the anode chamber 3 is mixed with the 
natural gas and then introduced to the reformer 28 as the heat source for 
the reformer 28 whereas the remainder is introduced to the catalyst 
combustor 30. 
Next, the cathode gas to be supplied to the cathode chamber 2 will be 
explained. The air is compressed by the compressor 4, cooled by the 
cooling device 5 and preheated by the air preheater 7. Then, the air is 
led to the catalyst combustor 30 through the line 8 and used to combust 
the combusible components among the anode exhaust gas fed into the 
catalyst combustor 30. Thereafter, the air is sent to the cathode chamber 
2. The cathode exhaust gas from the cathode chamber 2 is partially 
recirculated to the cathode chamber 2 via the recirculation line 31 and 
partially introduced to the turbine 12 via the line 11 to be expelled to 
the atmosphere via the air preheater 7. 
In the power generation system of FIG. 16, since the reforming temperature 
of the reformer 28 is maintained by the sensible heat of the anode exhaust 
gas, it is necessary that a large amount of anode exhaust gas is fed to 
the reformer 28. However, as a amount of anode exhaust gas to be supplied 
increases, the concentration of the fuel gas (H.sub.2 and CO) among the 
anode gas becomes leaner which results in deterioration of fuel 
performances and drop of power generation efficiency. In addition, since 
the reforming temperature of the reformer 28 becomes lower than the anode 
exhaust gas temperature at the anode chamber 3 exit, which is the fuel 
cell system operation temperature, the reforming ratio cannot be set high. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a power generation system 
in which the heat source for maintaining the reforming reaction 
temperature of the reformer, i.e., the sensible heat of the anode exhaust 
gas or the cathode exhaust gas is effectively used in the reforming 
reaction. 
Another object of the present invention is to provide a power generation 
system which mainly utilizes the sensible heat of the cathode exhaust gas 
as the heat source for the maintaining the reforming reaction. 
According to one aspect of the present invention, there is provided a power 
generation system which comprises: molten carbonate fuel cells, each fuel 
cell having an anode chamber and a cathode chamber and power generation 
being caused by the anode gas supplied to the anode chamber and the 
cathode gas supplied to the cathode chamber; a reformer having a reforming 
section and a heating section, raw material such as natural gas being 
reformed to the anode gas by the reforming section and the reforming 
section being heated by the heating section; means for feeding raw 
material to be reformed, to the reforming section of the reformer; means 
for feeding the anode gas, which is the gas reformed by the reformer, into 
the anode chamber; means for feeding the cathode gas into the cathode 
chamber, the cathode gas including air; an anode exhaust gas line for 
discharging the anode exhaust gas from the anode chamber; and a cathode 
exhaust gas line for discharging the cathode exhaust gas from the cathode 
chamber; c h a r a c t e r i z e d in that the reformer has a reforming 
chamber for reforming the raw material and a heating chamber for heating 
the reforming chamber, and the system further comprises: a catalyst 
combustor for combusting combusible components among the anode exhaust 
gas, the combustor being connected with the anode exhaust gasline and the 
cathode exhaust gas line; a line for connecting an exit of the catalyst 
combustor with the heating chamber of the reformer for feeding the exhaust 
gas of the catalyst combustor to the heating chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described with 
reference to the accompanying drawings. 
Referring first to FIG. 1, numeral 40 designates a fuel cell arrangement. 
The fuel cell arrangement 40 includes a molten carbonate fuel cell 41. The 
fuel cell 41 is sandwiched by an anode electrode and a cathode electrode. 
The fuel cell 41 is provided with a cathode chamber 42 at its cathode 41c 
side and an anode chamber 43 at its anode side 41a. The fuel cell 
arrangement 41 is depicted in an illustrative manner, but actually 
includes a plurality of fuel cells 41 stacked via separator plates (not 
shown). The separator plates form anode gas passages and cathode gas 
passages, and anode gas and cathode gas are respectively fed to the anode 
41a and the cathode 41c through the respective passages. Numeral 44 
designates a catalyst combustor which combusts combustible components 
among the anode exhaust gas. Numeral 45 designates a reformer which 
includes reforming chambers 46 and heating chambers 47. The reforming 
chambers 46 and the heating chambers 47 are closely stacked one after 
another. Reforming catalyst is placed in each reforming chamber 46. The 
heating chambers 47 are used to heat the reforming chambers 46. 
An air feed line 48 is connected to an entrance of the cathode chamber 42, 
and the blower 49 and the air preheater 50 are connected to the air feed 
line 48. A cathode exhaust gas line 51 is connected to the exit of the 
cathode chamber 42, and the catalyst combustor 44 is connected to the 
cathode exhaust gas line 51. A cathode exhaust gas recirculation line 52 
is connected with the cathode exhaust gas line 51. A blower 53 is provided 
on the cathode exhaust gas recirculation line 53. The cathode exhaust gas 
is introduced to the cathode chamber 42 through the air feed line 48 by 
the blower 53. A cathode exhaust gas utilization line 54 is also connected 
to the cathode exhaust gas recirculation line 52 for feeding the cathode 
exhaust gas to the air preheater 50. 
The entrance of the anode chamber 43 and the exit of the reforming chamber 
46 of the reformer 45 are connected with each other by the anode gas feed 
line 55. Natural gas and steam are supplied as the raw material to the 
entrance of the reforming chamber 46 of the reformer 45. The feed line 56 
for the natural gas NG merges with the steam feed line 57 and the raw 
material, which includes natural gas and steam, is supplied to the 
reforming chamber 46 through the line 58. A heat exchanger 59 is provided 
on the line 58 and the anode gas feed line 55. The heat exchanger 59 is 
used for the heat exchange between the raw material and the reformed gas. 
The exit of the anode chamber 43 is connected with the catalyst combustor 
44 via the anode exhaust gas line 60. The exhaust gas exit of the catalyst 
combustor 44 and the heating chamber 47 of the reformer 45 are connected 
with each other via a sensible heat utilization line 61. The exhaust gas 
line 62 is connected with the exit of the heating chamber 47. A group of 
various heat exchangers 63 and a gas-liquid separator 64 are connected 
with the line 62, respectively. Water separated in the gas-liquid 
separator 64 is dehydrated by a line 65, and the gases containing CO.sub.2 
is led by a line 66 to the air feed line 48 which is located on the inlet 
side of the blower 49 so that CO.sub.2 is fed to the cathode chamber 42 
with the air. 
The steam line 57 extends in the system in a manner such that the water 
flows through the heat exchangers 63a and 63b of the above-mentioned group 
of heat exchangers 63. Accordingly, the water is heated to vapor or steam 
of a predetermined temperature before merging with the natural gas line 
56. 
In the foregoing description, the air and CO.sub.2 from the air line 48 and 
the cathode exhaust gas from the cathode exhaust gas recirculation line 
are fed to the cathode chamber 42 of the fuel cell arrangement 40 whereas 
the anode gas (H.sub.2, CO, CO.sub.2, H.sub.2 O and others), which is the 
reformed gas reformed in the reforming chamber 46 of the reformer 45, is 
fed to the anode chamber 43 through the line 55 so that the reaction of 
the anode gas and the cathode gas takes place in the cell 41 to generate 
electricity. Exhaust gases from the anode chamber 43 and the cathode 
chamber 42 are respectively introduced to the catalyst combustor 44 via 
the lines 60 and 51 and the combusible components among the anode exhaust 
gas is combusted with the unreacted oxygen among the cathode exhaust gas. 
By feeding the anode exhaust gas and the cathode exhaust gas into the 
catalyst combustor 44, the anode chamber 43 and the cathode chamber 42 are 
comminicated with each other via the catalyst combustor 44 so that the 
anode chamber 43 and the cathode chamber 42 become equal to each other in 
pressure. Therefore, the differential presure control between the anode 
electrode and the cathode electrode becomes significantly easy. The 
exhaust gas from the catalyst combustor 44 is then supplied to the heating 
chamber 47 of the reformer 45 via the sensible heat utilization line 61. 
As a result, heat required for the reformation of the raw material gas in 
the reforming chamber 46 is provided by the sensible heat of the exhaust 
gas. The gas discharged from the heating chamber 47 is introduced to the 
heat exchanger 63a and 63b through the exhaust gas line 62. The exhaust 
gas is used to generate steam in the heat exchanger 63a and used to 
further heat the steam in the heat exchanger 63b. 
The relation among exit gas temperature of the reforming chamber 46 of the 
reformer 45, the exit gas temperature of the cathode and anode chambers 42 
and 43 and the exit gas temperature of the heating chamber 47 will be 
explained with FIG. 5. 
In FIG. 5, T.sub.5 are assigned to the exit temperature of the cathode 42 
and that of the anode chamber 43. The anode exhaust gas and the cathode 
exhaust gas are brought into the catalyst combustor 44 with the 
temperature of T.sub.5 and combusted in the combustor 44 whereby its 
temperature is raised to T.sub.3. After that, the gases enter the heating 
chamber 47 to give the heat (the heat required for the reformation) to the 
reforming chamber 46. In other words, the gases gives off their sensible 
heat and the temperature thereof drops to T.sub.4 at the exit. On the 
other hand, Ti is assigned to the entrance temperature of the raw material 
gas to be supplied to the reforming chamber 46 and To is assigned to the 
exit temperature of the same. As seen from FIG. 5, the exit temperature of 
the heating chamber 47 is higher than the entrance temperature Ti of the 
raw material gas and considerably lower than the anode and cathode exhaust 
gas temperature T.sub.5. This means that the sensible heat of the anode 
exhaust gas and the cathode exhaust gas, i.e., the sensible heat 
corresponding to the temperature drop of T.sub.5 - T.sub.4 is utilized to 
heat the raw material gas, in addition to the heat (T.sub.3 -T.sub.5) 
combusted in the catalyst combustor 44. 
With FIG. 5 being compared with FIG. 17 which shows the temperature 
variations at the entrance and the exit of the reformer of the 
conventional system illustrated in FIG. 15, followings become is clear: In 
the conventional system, the anode exit gas is cooled due to water removal 
and heated again before introduced to the catalys combustor 10. The anode 
exit gas is mixed with the low temperature air in the catalyst combustor 
10. Therefore, these temperatures T.sub.1 and T.sub.2 become lower than 
the exit temperature T.sub.4 of the combustion chamber 10a of the reformer 
10. Consequently, additional heat is required in the combustion chamber 
10a to raise the air temperature T.sub.1 and the anode exhaust gas 
temperature T.sub.2 (Part of heat of the anode exhaust gas has been used 
before.) to the exit temperature of T.sub.4. Therefore, a corresponding 
amount of natural gas should be increased. In the first embodiment of the 
present invention, on the other hand, the high temperature anode exhaust 
gas and the high temperature cathode exhaust gas are directly introduced 
to the catalyst combustor 44 and combusted therein. Accordingly, the 
entire combustion heat can be used to maintain the temperature of the 
reforming reaction. In addition, the sensible heat of the anode exhaust 
gas and the cathode exhaust gas can be used to heat the reforming chamber 
46. Furthermore, the exhaust gas entering the heating chamber 46 from the 
catalyst combustor 44 is the mixture of the anode exhaust gas and the 
cathode exhaust gas. Thus, the flow rate of the gas to be introduced to 
the heating chamber 47 can be set to an arbitrary value with the power 
generation efficiency of the fuel cell arrangement 40 being maintained at 
a high level by appropriately adjusting an amount or flow rate of the 
cathode exhaust gas discharged from the line 54. Tables below show 
temperature, pressure and flow rate of the respective gases picked up at 
locations to of the system of FIG. 1. 
TABLE I 
__________________________________________________________________________ 
REFORMER REFORMER ANODE 
NG ENTRANCE EXIT ENTRANCE ANODE EXIT 
1 2 3 4 5 
__________________________________________________________________________ 
FLUID STATE G G G G G 
TEMPERATURE [.degree.C.] 
15 449 750 570 680 
PRESSURE [Kg/cm.sup.2 A] 
1.24 1.22 1.18 1.16 1.14 
AV. MOLECULAR. WT. 
Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ 
& M.W. Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
H.sub.2 30.3940 30.3940 2.8988 
CO 5.8356 5.8356 1.6299 
CO.sub.2 3.6198 3.6198 39.5263 
O.sub.2 
N.sub.2 
Ar 
CH.sub.4 7.056 7.056 0.1366 0.1366 0.1366 
C.sub.2 H.sub.6 
0.416 0.416 
C.sub.3 H.sub.8 
0.408 0.408 
.eta.-C.sub.4 H.sub.10 
0.120 0.120 
H.sub.2 O (V) 28.776 15.7008 15.7008 43.1960 
H.sub.2 O (L) 
TOTAL 8.0 36.776 55.6869 55.6869 87.3876 
TOTAL Kg/Hr 
TOTAL M.sup.3 /Hr 
OR (GPM) 
LIQUID S.G. @ O.T. 
OR (*API) 
LIQUID VISC. @ O.T. 
[CST] 
ENTHALPY 
[MM-Kcal/Hr] 
__________________________________________________________________________ 
TABLE II 
__________________________________________________________________________ 
AIR PRE- CATHODE CATHODE REFORMER 
AIR HEATER EXIT 
ENTRANCE EXIT ENTRANCE 
6 7 8 9 10 
__________________________________________________________________________ 
FLUID STATE G G G G G 
TEMPERATURE [.degree.C.] 
18 334 570 680 838 
PRESSURE [Kg/cm.sup.2 A] 
1.03 1.16 1.16 1.14 1.12 
AV. MOLECULAR. WT. 
Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ 
& M.W. Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
H.sub.2 
CO 
CO.sub.2 0.0422 48.5606 91.9142 60.2134 48.5184 
O.sub.2 29.0107 34.4402 82.2425 66.3921 5.4295 
N.sub.2 108.2524 189.4416 676.5762 676.5762 81.1892 
Ar 1.3078 2.2887 8.1738 8.1738 0.9809 
CH.sub.4 
C.sub.2 H.sub.6 
C.sub.3 H.sub.8 
.eta.-C.sub.4 H.sub.10 
H.sub.2 O (V) 
2.0109 20.9513 74.8260 74.8260 55.3471 
H.sub.2 O (L) 
TOTAL 140.6240 295.6821 933.7324 886.1809 191.4651 
TOTAL Kg/Hr 
TOTAL M.sup.3 /Hr 
OR (GPM) 
LIQUID S.G. @ O.T. 
OR (*API) 
LIQUID VISC. @ O.T. 
[CST] 
ENTHALPY 
[MM-Kcal/Hr] 
__________________________________________________________________________ 
TABLE III 
__________________________________________________________________________ 
REFORMER KO DRUM STEAM SUPER- 
EXIT EXIT HEATER EXIT 
STEAM 
11 12 13 14 
__________________________________________________________________________ 
FLUID STATE G G G G 
TEMPERATURE [.degree.C.] 
515 50 300 175 
PRESSURE [Kg/cm.sup.2 A] 
1.10 1.03 1.24 9.03 
AV. MOLECULAR. WT. 
Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ Kg-mol/ 
& M.W. Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
Hr Mol.Fr. 
H.sub.2 
CO 
CO.sub.2 48.5184 48.5184 
O.sub.2 5.4295 5.4295 
N.sub.2 81.1892 81.1892 
Ar 0.9809 0.9809 
CH.sub.4 
C.sub.2 H.sub.6 
C.sub.3 H.sub.8 
.eta.-C.sub.4 H.sub.10 
H.sub.2 O (V) 
55.3471 18.9404 28.7760 26.944 
H.sub.2 O (L) 
TOTAL 191.4651 155.0584 28.7760 26.944 
TOTAL Kg/Hr 
TOTAL M.sup.3 /Hr 
OR (GPM) 
LIQUID S.G. @ O.T. 
OR (*API) 
LIQUID VISC. @ O.T. 
[CST] 
ENTHALPY 
[MM-Kcal/Hr] 
__________________________________________________________________________ 
FIG. 2 shows a second embodiment of the present invention. In this figure, 
same numerals are give to the same elements as those of FIG. 1 and the 
explanation of these elements will be omitted. Such is the case with 
following embodiments. 
The air is pressurized by a low pressure side compressor 70, cooled by an 
intercooler 71, pressurized by a high pressure side compressor 72, 
introduced to the air preheater 50 and fed to the cathode chamber 42 
through the air feed line 48. The cathode exhaust gas from the cathode 
chamber 42 is fed to a turbine 62 via a line 79 branched from the cathode 
exhaust gas line 51 and then used to drive a turbine 73. After that, the 
cathode exhaust gas preheats the air of the air feed line 48 in the air 
preheater 50 and further gives its heat to the water such that the water 
becomes steam in the vaporizer 48 before going out of the system. The 
turbine 73, the low pressure side compressor 70, the high pressure side 
compressor 72 and a generator are connected with each other by a shaft 174 
and the compressors 70 and 72 and the generator are driven by the rotation 
of the turbine 73. 
Branched from the cathode exhaust gas line 51 is a cathode exhaust gas 
sensible heat utilization line 74. The line 74 is used to feed the cathode 
exhaust gas to the heating chamber 47 of the reformer 45. The exit of the 
heating chamber 47 is connected to the combustor 44 via the line 75. The 
anode exhaust gas line 60 is also connected to the combustor 44. In the 
combustor 44, combusible components among the anode exhaust gas is 
combusted with the air contained in the cathode exhaust gas from the 
heating chamber 47. The combustion exhaust gas at the exit of the 
combustor 44 is led into the cathode exhaust gas recirculation line 76 
connecting the combustor exit with the air feed line 48. A blower 53 is 
disposed on the line 76. 
Downstream of the air preheater 50, there is provided a steam generator 78 
and the water is heated to steam in the steam generator 78. The steam line 
57 merges with the natural gas feed line 56 so that the steam and the 
natural gas NG are fed to the reforming chamber 46 through the line 58 as 
the raw material for the reformation. The natural gas feed line 56 is 
equipped with the blower 77 and the blower 77 pressurizes the natural gas. 
The blower 77 also raises the pressure of the anode gas from the reformer 
46 to a value equal to the pressure of the cathode gas which has been 
compressed by the compressors 70 and 72. 
The anode gas, which has undergone the reformation at the reforming chamber 
46, is introduced to the anode gas feed line 55 to reach the heat 
exchanger 59. In the exchanger 59, heat exchange takes place between the 
anode gas and the raw material gas, and thereafter the anode gas is led to 
the anode chamber 43. 
In the second embodiment, the heat required for the reforming reaction at 
the reforming chamber 46 entirely depends on the sensible heat of the 
cathode exhaust gas fed into the heating chamber 47 from the cathode 
exhaust gas sensible heat utilization line 74. The temperature of the 
cathode exhaust gas has been dropped at the fuel cell exit since the 
cathode exhaust gas gives its heat to the reforming reaction in the 
reformer 45, but its temperature is raised again by the heating in the 
catalyst combustor 44, before returning to the cathode chamber entrance. 
Since the cathode exhaust gas at the fuel cell exit reaches a considerably 
high temperature due to the fuel reaction and its flow rate is 
sufficiently high, the sensible heat of the cathode exhaust gas includes 
enough heat to maintain the reforming reaction. 
Temperature variations at the entrance and the exit of the cathode exhaust 
gas and the raw material for the reformer 45 of the second embodiment is 
shown in FIG. 6. In the illustration, "Y" indicates the distance between 
the entrance and the exit of the heating chamber 47 and the reforming 
chamber 46, T.sub.6 indicates the entrance temperature of the cathode 
exhaust gas entering the heating chamber 47, T.sub.4 indicates the exit 
temperature of the same, Ti indicates the entrance temperature of the raw 
material gas entering the reforming chamber 46 and To indicates the exit 
temperature of the same. 
FIG. 3 depicts a third embodiment of the present invention. The reformer 45 
includes the reforming chamber 46 and two heating chambers 47a and 47b. 
These heating chambers 47a and 47b extend along the reforming chamber 46, 
but the first heating chamber 47a is separated from the second heating 
chamber 47b. The former heating chamber 47a extends from one end 
(entrance) of the reforming chamber 46 and the latter heating chamber 47b 
terminates at the other end (exit) of the reforming chamber 46. This 
arrangement is just for the illustrative purpose. In an actual system, the 
first heating chamber 47a and the second heating chamber 47b may be 
continuous and define in combination a separate gas passage. 
The cathode exhasut gas line 51 of the cathode chamber 42 and the anode 
exhaust gas line 60 of the anode chamber 43 are connected to the catalyst 
combustor 44. A first sensible utilization line 80 is branched from the 
line 51 to introduce the cathode exhaust gas to the first heating chamber. 
The exit of the first heating chamber 47a is connected to the line 81 and 
the line 81 is connected to the turbine 73 to drive the turbine 73. The 
exit of the catalyst combustor 44 is connected to the second heating 
chamber 47b via a second sensible heat utilization line and the cathode 
exhaust gas recirculation line 52 is connected to the exit of the second 
heating chamber 47b. The cathode exhaust gas recirculation line 52 is also 
connected to the air feed line 48. 
The way of vaporizing the water by the cathode exhaust gas and the feeding 
of the raw material gas (steam and natural gas) are same as those 
described with FIG. 2. Thus, the explanation will be omitted. 
In the third embodiment, the heating chamber 47 is divided into the 
separate heating chambers 47a and 47b. Therefore, the raw material gas at 
the entrance side of the reforming chamber 46 is heated by the cathode 
exhaust gas coming from the first sensible heat utilization line 80 into 
the first heating chamber 47a whereas the raw material gas at the exit 
side of the reforming chamber is heated by the high temperature combustion 
exhaust gas coming from the exit of the catalyst combustor 44 into the 
second heating chamber 47b through the second sensible heat utilization 
line 82. In this embodiment, the reformer 45 is illustrated as one unit, 
but the reformer 45 may comprise two sections: a first reformer section 
having a first heating chamber 47a and a second reformer section having a 
second heating chamber 47b. 
FIG. 7 shows temperature changes of the entrance gas and the exit gas of 
the combustor 44 and the reformer 45 of the third embodiment. In this 
figure, Y.sub.1 and Y.sub.2 represent the distances between the entrances 
and the exits of the first heating chamber 47a and the second heating 
chamber 47b, respectively. "P" represents a contact point of the first 
heating chamber 47a and the second heating chamber 47b. 
The anode exhaust gas of temperature T.sub.2 and the cathode exhaust gas of 
temperature T.sub.2 reach the entrance of the combustor 44 and these gases 
are combusted in the combustor 44. Upon the combustion, the temperature of 
the gases is raised to T.sub.3 and fed to the second heating chamber 47b 
(Y.sub.2). On the other hand, the cathode exhaust gas of temperature 
T.sub.2 is fed to the first heating chamber 47a. The raw material gas 
whose temperature is Ti at the entrance of the reformer 46 is heated by 
the cathode exhaust gas in the first heating chamber 47a and its 
temperature is raised to Tm at the contacting point P as the reforming 
reaction proceeds. Then, the raw material gas is heated from Tm to To by 
the combustion exhaust gas in the second heating chamber 47b. After that, 
the raw material gas flows as the-anode-gas-to-be-gas. 
FIG. 4 illustrates a fourth embodiment of the present invention. This 
embodiment is a modified version of the system of FIG. 2 (second 
embodiment). 
The second embodiment shows an example that the combustion exhaust gas of 
the combustor 44 is recirculated to the cathode chamber 42. On the other 
hand, the fourth embodiment shows a following example: the cathode exhaust 
gas line 51 and the anode exhaust gas line 60 are connected with the 
combustor 44 and the combustion exhaust gas from the combustor 44 is fed 
to the heating chamber 47 via the sensible heat utilization line 61. The 
exhaust gas of the heating chamber 47 is fed to the air feed line 48 via a 
recirculation line 85 and the blower 53. 
In the fourth embodiment, the entrance temperature change and the exit 
temperature change of the gases of the reformer 45 and the combustor 44 
have the same patterns as the patterns of FIG. 5. 
FIGS. 8 to 11 respectively depict fifth to the eighth embodiments. 
Specifically, the reforming chamber 46 of the reformer 45 is modified. 
The reforming chamber 46 of FIGS. 8 to 11 includes a self sensible heat 
consumption section 46X and a main reforming section 46Y (or 46Y.sub.1 and 
Y.sub.2). The section 46X has a self sensible heat consumption zone X. At 
the entrance of this zone X, the raw material gas and the anode exhaust 
gas are mixed with each other, and then the reforming reaction proceeds 
using the sensible heat of the anode exhaust gas. The main reforming 
section 46Y has a sensible heat absorption zone Y (or Y.sub.1 and 
Y.sub.2). The zone Y contacts the heating chamber 47 and is heated by the 
heating chamber 47. 
The fifth embodiment of FIG. 8 shows a modified system of FIG. 2 and uses 
the above-described reformer 45. The way of feeding and discharging the 
cathode gas is same as the example of FIG. 2. 
In other words, the air is pressurized by the relatively low pressure 
compressor 70, cooled by the intercooler 71, pressurized by the relatively 
high pressure compressor 72, introduced to the air preheater 50 and fed to 
the cathode chamber 42 through the air feed line 48. The cathode exhaust 
gas of the cathode chamber 42 is fed to the turbine 72 via the line 79 
branched from the cathode exhaust gas line 51 and drives the turbine 73. 
Then, the cathode exhaust gas preheats the air in the air feed line 48 at 
the air preheater 50 before expelled to the atmosphere. 
The cathode exhaust gas is not only fed to the turbine 73 but also fed to 
the heating chamber 47 of the reformer 45 through the cathode exhaust gas 
sensible heat utilization line 74 and then to the combustor 44 through the 
line 75. In the combustor 44, the combusible contents of the anode exhaust 
gas introduced from the anode exhaust gas line 60 is combusted with air 
contained in the cathode exhaust gas. The combustion exhaust gas of the 
combustor 44 is recirculated to the cathode chamber 42 through the cathode 
gas recirculation line 76, the blower 53 and the air line 48. 
The way of feeding and discharging the anode gas of this example is same as 
the way of FIG. 2. 
The natural gas NG is heated by the preheater 59 after it is pressurized by 
the blower 77. Then, the natural gas NG is fed to the reforming chamber 
46. An anode exhaust gas recirculation line 90 branched from the anode 
exhaust gas line 60 is connected to the line 58, and the raw material gas 
and the anode exhaust gas flow into the self sensible heat consumption 
section 46X of the reforming chamber 46 from the line 58. In the self 
sensible heat consumption section 46X, the temperature of the mixture of 
the raw material gas and the anode exhaust gas drops to Ti due to the 
reforming reaction, as shown in FIG. 12. After that, the mixture is heated 
at the main reforming section 46Y by the cathode exhaust gas fed from the 
cathode exhaust gas sensible heat utilization line 74 passing through the 
heating chamber 47 and the temperature of the mixture is raised to To as 
the reforming reaction further proceeds. The heating temperature patterns 
in the zone Y is the same patterns of FIG. 6. In this particular 
embodiment, since the anode exhaust gas is directly fed to the reforming 
chamber 46, the steam required for the reforming reaction is given by 
steam produced in the cell reaction. 
The anode gas reformed through the main reforming section 46Y of the 
reforming chamber 46 flows in the anode gas feed line 91 and heats the 
natural gas at the heat exchanger 59. Thereafter, the anode gas flows in 
the line 91 to be pressurized by the blower 92 and to be introduced to the 
anode chamber 43. 
In the fourth embodiment, the anode exhaust gas and the raw material gas 
may be directly mixed with each other and the mixture may be heated above 
the reforming temperature such that the reforming reaction takes place in 
the self sensible heat consumption zone X, in addition to the embodiment 
of FIG. 2. In such a case, not only the sensible heat of the cathode 
exhaust gas but also the sensible heat of the anode exhaust gas can be 
effectively used in the reforming reaction. 
Referring now to FIG. 9 showing the fifth embodiment of the present 
invention, which is the modified embodiment of the embodiment of FIG. 3, 
the fundamental way of gas flow is same as FIG. 3. The anode exhaust gas 
flows from the anode gas recirculation line 90 branched from the anode 
exhaust gas line 60, into the line 58, and the natural gas and the anode 
exhaust gas are mixed with each other therein. Then, the mixture is 
introduced to the self sensible heat consumption zone 46X of the reforming 
chamber 46. On the other hand, the anode gas reformed through the main 
reforming sections 46Y.sub.1 and 46Y.sub.2 flows in the anode gas feed 
line 91 and heats the natural gas at the heat exchanger 59. Then, the 
anode gas is pressurized by the blower 92 as it flows through the line 91 
and then introduced to the anode chamber 43. Other structure of the system 
is same as FIG. 3. 
The temperature patterns of the fifth embodiment is shown in FIG. 13. The 
temperature patterns are same as FIG. 7 except that the raw material gas 
is reformed by the sensible heat of the anode exhaust gas at the self 
sensible heat consumption zone X and its temperature is lowered to Ti from 
Tx. 
FIG. 10 illustrates a fixth embodiment of the present invention. This is 
the modified version of the system of FIG. 4 and the basic manner of flow 
is same as FIG. 4. The anode exhaust gas flows in the line 58 from the 
anode gas recirculation line 90 branched from the anode exhaust gas line 
60 and the natural gas and the anode exhaust gas are mixed with each 
othere therein. The mixture flows in the self sensible heat consumption 
section 46X of the reforming chamber 46. On the other hand, the anode gas 
reformed through the main reforming section 46Y of the reforming chamber 
46 flows in the anode gas feed line 91 and heats the steam and the natural 
gas at the heat exchanger 59. Then, the anode gas is pressurized by the 
blower 92 as it proceeds in the line 91, and then it is introduced to the 
anode chamber 43. Other structure is same as FIG. 4. 
The temperature patterns of the sixth embodiment is shown in FIG. 14 and 
the temperature patterns is same as FIG. 5 except for the self sensible 
heat consumption zone X. 
FIG. 11 illustrates a seventh embodiment of the present invention. The way 
of feeding and discharging the cathode gas is same as the system of FIG. 8 
(the fourth embodiment). This embodiment differs from the embodiment of 
FIG. 8 in that the anode exhaust gas from the anode exhaust gas line 60 is 
not directly fed to the combustor and the raw material gas feed line 58, 
but gas component and moisture component among the anode exhaust gas are 
separated from each other at a liquid-gas separator 100 (the separator 100 
includes a vaporizer 101, a condenser 102 and a gas-liquid separating drum 
103), in that the moisture component is changed to steam by the vaporizer 
102 prior to flowing into the natural gas feed line 56, in that the raw 
material gas containing the natural gas and the steam is fed to the 
reforming chamber 46 from the line 58, and in that the separated gas 
component is fed to the combustor 44. 
The gas-liquid separator 100 will be now explained. The anode exhaust gas 
of the anode chamber 43 is cooled by the vaporizer 101 connected with the 
anode exhaust gas line 60 and then condensed by the condenser 102. After 
that, the anode exhaust gas is introduced to the gas-liquid separating 
drum 103 and the gas component and the moisture component thereof are 
separated from each other. The gas component is fed to the combustor 44 
via a blower 105 from a gas line 104 extending from a top of the drum 103 
(The gas line 104 is a line downstream of the drum 103). On the other 
hand, the moisture component is led into a water line 106 extending from a 
bottom of the drum 103, and then into the steam generator 101 via a pump 
107. The moisture component is converted to the steam by the anode exhaust 
gas and introduced to the line 58 via the steam line 108. 
Apparent from the above description, the present invention has following 
advantages: 
(1) Fuel used to heat the reformer is remarkably reduced since the high 
temperature cathode exit gas discharged from the cathode is fed as the 
heat source to the heating chamber of the reformer; 
(2) Consequently, it is possible to raise the fuel utilization ratio of the 
fuel cell and in turn the power generation efficienty of the system; 
(3) The anode exit gas and the cathode exit gas are directly introduced to 
the catalyst combustor and the combusible component of the anode exit gas 
is combusted with oxygen of the cathode exit gas, and accordingly 
following merits arise: (a) The oxygen concentration of the cathode exit 
gas is low as compared with the air so that an amount of gas to be fed 
increases to ensure the oxygen required for the combustion of the fuel. 
This means that a large amount of the sensible heat of the cathode exhaust 
gas is brought into the reformer and that the combustion temperature is 
lowered. Thus, longevities of the combustion catalyst and metallic 
partitions are prolonged and the reliability of the system is improved. 
The longevity of the combustion catalyst becomes shorter considerably if 
the operation temperature is unduly high; (b) The combusible component of 
the anode exit gas and the oxygen concentration of the cathode exit gas 
are relatively low. In such a case, various values of these gases are 
below the explosion limits so that no explosion would occur even if 
combustion did not take place in the catalyst combustor due to the 
deterioration of the catalyst or other reasons. Thus, safety is ensured. 
In addition, if the combustion takes place in the catalyst combustor in a 
normal manner, the oxygen concentration at the catalyst combustor exit is 
extremely low. Therefore, even if the partitions of the reformer are 
broken and the fuel of high concentration flows into the heating chamber, 
the explosion does not occur since the oxygen concetration is sufficiently 
low; and (c) Control of differential pressure between the anode electrode 
and the cathode electrode is not necessary. As a result, valves for 
adjusting the differential pressure, which are otherwise provided at the 
high temperature section, are not necessary; and 
(4) In the system having the self sensible heat consumption zone and the 
heating zone, the sensible heat of gas can be effectively used in the 
reformation so that the fuel for the heating is further reduced. 
In the foregoing embodiments, the catalyst combustor and the reformer are 
illustrated as separate devices. However, the catalyst combustor may be 
incorporated in the reformer to provide a single element.