Fuel cell system

Abstract

This fuel cell system 100 includes: a tank 110 for storing ammonia; a reformer 120 for thermally decomposing ammonia that is supplied from the tank 110 so as to generate hydrogen; a solid oxide fuel cell 150 for generating power using, as a fuel, ammonia that is supplied from the tank 110 or hydrogen that is generated by the reformer 120; a polymer electrolyte fuel cell 130 for generating power using, as a fuel, the hydrogen that is generated by the reformer 120; and an exhaust gas supply flow path 170 for supplying a first exhaust gas that is generated in the solid oxide fuel cell 150 to the reformer 120.

Description

fuel cell system

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-14761, filed February 2, 2024, the contents of which are incorporated herein by reference.

[0002] A fuel cell system has been disclosed that combines a polymer electrolyte fuel cell, which has high responsiveness to load fluctuations, and a solid oxide fuel cell, which has high power generation efficiency (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2019-29051

[0004] Recently, a technology has been studied that uses ammonia, which has a higher energy density than hydrogen, as fuel for fuel cell systems.

[0005] However, due to the temperature constraints imposed by the polymer, polymer electrolyte fuel cells cannot have a mechanism for thermally decomposing ammonia inside. Therefore, even if ammonia is directly supplied to a polymer electrolyte fuel cell, power generation is not possible. For this reason, it is being considered to equip a fuel cell system equipped with a polymer electrolyte fuel cell such as that described in Patent Document 1 with a reformer that thermally decomposes ammonia to produce hydrogen, and a combustor that produces combustion exhaust gas that serves as a heat source for the reformer.

[0006] Such a combustor burns the hydrogen produced by the reformer as fuel, but in this case, the amount of hydrogen supplied to the polymer electrolyte fuel cell is reduced by the amount burned in the combustor, which results in a problem of reduced power generation efficiency of the polymer electrolyte fuel cell.

[0007] Therefore, there is a need to develop a technology that can suppress the decline in power generation efficiency in a fuel cell system that combines a polymer electrolyte fuel cell and a solid oxide fuel cell.

[0008] In view of the above problems, the present disclosure has an object to provide a fuel cell system that can suppress a decrease in power generation efficiency.

[0009] In order to solve the above problems, a fuel cell system according to one embodiment of the present disclosure includes a tank for storing ammonia, a reformer for generating hydrogen by thermally decomposing the ammonia supplied from the tank, a solid oxide fuel cell for generating electricity using the ammonia supplied from the tank or the hydrogen generated by the reformer as fuel, a polymer electrolyte fuel cell for generating electricity using the hydrogen generated by the reformer as fuel, and an exhaust gas supply passage for supplying a first exhaust gas generated in the solid oxide fuel cell to the reformer.

[0010] The fuel cell system may also include a turbine that is rotated by the first exhaust gas discharged from the reformer.

[0011] The fuel cell system may also include a turbine, and a first heat exchanger that exchanges heat between the fluid before being supplied to the turbine and the first exhaust gas discharged from the reformer.

[0012] The turbine may be rotated by a second exhaust gas generated in the polymer electrolyte fuel cell in addition to the first exhaust gas discharged from the reformer.

[0013] The fuel cell system may also include a second heat exchanger that exchanges heat between the hydrogen produced by the reformer and the second exhaust gas.

[0014] According to the present disclosure, it is possible to suppress a decrease in power generation efficiency.

[0015] FIG. 1 is a diagram illustrating an example of a fuel cell system according to a first embodiment. FIG. 2 is a diagram illustrating an example of a fuel cell system according to a second embodiment. FIG. 3 is a diagram illustrating an example of a fuel cell system according to a third embodiment. FIG. 4 is a diagram illustrating an example of a fuel cell system according to a fourth embodiment. FIG. 5 is a diagram illustrating an example of a fuel cell system according to a fifth embodiment. FIG. 6 is a diagram illustrating an example of a fuel cell system according to a sixth embodiment. FIG. 7 is a diagram illustrating an example of a fuel cell system according to a seventh embodiment.

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for ease of understanding and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation. Elements not directly related to the present disclosure are not shown.

[0017] [First Embodiment: Fuel Cell System 100] FIG. 1 is a diagram illustrating an example of a fuel cell system 100 according to a first embodiment. As shown in FIG. 1, the fuel cell system 100 according to the first embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell (hereinafter sometimes referred to as a "PEFC") 130, a compressor 140, a solid oxide fuel cell (hereinafter sometimes referred to as an "SOFC") 150, a compressor 160, and an exhaust gas supply passage 170. In FIGS. 1 to 7, solid arrows indicate the flow of ammonia and hydrogen. Furthermore, dashed arrows indicate the flow of an oxygen-containing gas. Dot-dash arrows indicate the flow of a first exhaust gas and a second exhaust gas.

[0018] The tank 110 stores either or both of liquid ammonia and gaseous ammonia.

[0019] The reformer 120 is connected to the tank 110 via an ammonia flow path 112. The ammonia stored in the tank 110 is supplied to the reformer 120 through the ammonia flow path 112. The reformer 120 thermally decomposes the ammonia supplied from the tank 110 to generate hydrogen. The reformer 120 is, for example, a heat exchanger that exchanges heat between the ammonia and a first exhaust gas generated in the SOFC 150 (described later). The reformer 120 transfers heat contained in the first exhaust gas to the ammonia, thereby thermally decomposing the ammonia. The reformer 120 has, for example, an ammonia passage and an exhaust gas passage. Ammonia is supplied to the ammonia passage from the tank 110. For example, the ammonia passage is filled with a catalyst that promotes the thermal decomposition of ammonia. The catalyst is, for example, either one or both of a ruthenium (Ru) catalyst and a nickel (Ni) catalyst. The first exhaust gas is supplied from the SOFC 150 to the exhaust gas passage.

[0020] The anode (fuel electrode) of the PEFC 130 is connected to the reformer 120 via a hydrogen flow path 122. Hydrogen generated by the reformer 120 is supplied to the anode of the PEFC 130 through the hydrogen flow path 122. In addition, an oxygen-containing gas is supplied to the PEFC 130 from a compressor 140, which will be described later. The oxygen-containing gas is, for example, air or oxygen-enriched air. The PEFC 130 generates power using the hydrogen generated by the reformer 120 as fuel. The power generated by the PEFC 130 is output to a load after its voltage is converted, for example, by a DC / DC converter.

[0021] The compressor 140 compresses the oxygen-containing gas. In this embodiment, the compressor 140 is connected to the cathode (air electrode) of the PEFC 130 via an oxygen-containing gas flow path 132. Therefore, the oxygen-containing gas compressed by the compressor 140 is supplied to the cathode of the PEFC 130 through the oxygen-containing gas flow path 132.

[0022] An anode (fuel electrode) of the SOFC 150 is connected to the tank 110 via an ammonia flow path 112 and an ammonia flow path 114. The ammonia flow path 114 branches off from the ammonia flow path 112 and is connected to the anode of the SOFC 150. The ammonia stored in the tank 110 is supplied to the anode of the SOFC 150 via the ammonia flow path 112 and the ammonia flow path 114. An oxygen-containing gas is also supplied to the SOFC 150 from a compressor 160, which will be described later. The SOFC 150 generates power using ammonia as fuel. The power generated by the SOFC 150 is output to a load after voltage conversion by, for example, a DC / DC converter.

[0023] In the fuel cell system 100, for example, the SOFC 150 may be operated at all times, and the PEFC 130 may generate power to compensate for load fluctuations.

[0024] The compressor 160 compresses the oxygen-containing gas. In this embodiment, the compressor 160 is connected to the cathode (air electrode) of the SOFC 150 via the oxygen-containing gas flow path 152. Therefore, the oxygen-containing gas compressed by the compressor 160 is supplied to the cathode of the SOFC 150 through the oxygen-containing gas flow path 152.

[0025] The exhaust gas supply passage 170 connects an off-gas exhaust port of the SOFC 150 and an inlet of an exhaust gas passage of the reformer 120. Therefore, the first exhaust gas generated in the SOFC 150 is supplied to the reformer 120 through the exhaust gas supply passage 170. The first exhaust gas generated in the SOFC 150 is, for example, either or both of an anode off-gas and a cathode off-gas.

[0026] As described above, the fuel cell system 100 according to the first embodiment includes a tank 110 for storing ammonia, a reformer 120 for generating hydrogen by thermally decomposing the ammonia supplied from the tank 110, a solid oxide fuel cell 150 for generating electricity using the ammonia supplied from the tank 110 as fuel, a polymer electrolyte fuel cell 130 for generating electricity using the hydrogen generated by the reformer 120 as fuel, and an exhaust gas supply passage 170 for supplying the first exhaust gas generated in the solid oxide fuel cell 150 to the reformer 120.

[0027] As a result, the fuel cell system 100 according to the first embodiment can thermally decompose ammonia using the high-temperature first exhaust gas generated in the solid oxide fuel cell 150. Therefore, unlike the comparative example in which ammonia is thermally decomposed using the combustion exhaust gas obtained by burning hydrogen produced by the reformer 120, it is possible to avoid a situation in which the amount of hydrogen supplied to the polymer electrolyte fuel cell 130 decreases. Therefore, the fuel cell system 100 according to the first embodiment can suppress a decrease in the power generation efficiency of the polymer electrolyte fuel cell 130.

[0028] [Second Embodiment: Fuel Cell System 200] Figure 2 is a diagram illustrating an example of a fuel cell system 200 according to a second embodiment. As shown in Figure 2, the fuel cell system 200 according to the second embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a compressor 140, a solid oxide fuel cell 250, a compressor 160, and an exhaust gas supply passage 170. Note that components that are substantially the same as those in the fuel cell system 100 described above are denoted by the same reference numerals, and description thereof will be omitted. The fuel cell system 200 according to this embodiment differs from the fuel cell system 100 in that it includes a hydrogen passage 222 instead of the ammonia passage 114, but is otherwise the same.

[0029] In this embodiment, the SOFC 250 is connected to the reformer 120 via the hydrogen flow path 122 and the hydrogen flow path 222. The hydrogen flow path 222 branches off from the hydrogen flow path 122 and is connected to the anode of the SOFC 250. The hydrogen generated by the reformer 120 is supplied to the anode of the SOFC 250 via the hydrogen flow path 122 and the hydrogen flow path 222. The SOFC 250 generates power using the hydrogen generated by the reformer 120 as fuel.

[0030] As described above, the fuel cell system 200 according to the second embodiment includes a tank 110 for storing ammonia, a reformer 120 for generating hydrogen by thermally decomposing the ammonia supplied from the tank 110, a solid oxide fuel cell 250 for generating electricity using the hydrogen generated by the reformer 120 as fuel, a polymer electrolyte fuel cell 130 for generating electricity using the hydrogen generated by the reformer 120 as fuel, and an exhaust gas supply passage 170 for supplying the first exhaust gas generated in the solid oxide fuel cell 250 to the reformer 120.

[0031] As a result, the fuel cell system 200 according to the second embodiment can thermally decompose ammonia using the high-temperature first exhaust gas generated in the solid oxide fuel cell 250. Therefore, unlike the comparative example in which ammonia is thermally decomposed using the combustion exhaust gas obtained by burning hydrogen produced by the reformer 120, it is possible to avoid a situation in which the amount of hydrogen supplied to the polymer electrolyte fuel cell 130 and the solid oxide fuel cell 150 decreases. Therefore, the fuel cell system 200 according to the second embodiment can suppress a decrease in the power generation efficiency of the polymer electrolyte fuel cell 130 and the solid oxide fuel cell 150.

[0032] Third Embodiment: Fuel Cell System 300 In the fuel cell system 100 according to the first embodiment, no mention is made of how the energy contained in the first exhaust gas discharged from the reformer 120 is utilized. In the third embodiment, how the energy contained in the first exhaust gas discharged from the reformer 120 is utilized will be described. FIG. 3 is a diagram illustrating an example of a fuel cell system 300 according to the third embodiment. As shown in FIG. 3, the fuel cell system 300 according to the third embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a compressor 140, a solid oxide fuel cell 150, a compressor 160, an exhaust gas supply passage 170, a turbine 310, and a generator 320. Note that components that are substantially the same as those in the fuel cell system 100 are denoted by the same reference numerals and will not be described again. The fuel cell system 300 according to this embodiment is the same as the fuel cell system 100 except for the addition of a turbine 310 and a generator 320.

[0033] The turbine 310 is connected to the outlet of the exhaust gas passage of the reformer 120 via an exhaust gas exhaust passage 312. The first exhaust gas exhausted from the reformer 120 is supplied to the turbine 310 through the exhaust gas exhaust passage 312. The turbine 310 is rotated by the first exhaust gas exhausted from the reformer 120.

[0034] The generator 320 is connected to the turbine 310. The generator 320 generates electricity by the rotation of the turbine 310. The generated power of the generator 320 is output to the compressors 140 and 160, for example, or is output to the outside together with the generated power of the PEFC 130 and the SOFC 150.

[0035] As described above, the fuel cell system 300 according to the third embodiment includes the turbine 310 in addition to the fuel cell system 100. This allows the fuel cell system 300 according to the third embodiment to recover energy contained in the first exhaust gas discharged from the reformer 120. Furthermore, the fuel cell system 300 according to the third embodiment includes the generator 320, allowing the energy recovered by the turbine 310 to be converted into electric power.

[0036] [Fourth Embodiment: Fuel Cell System 400] In the fuel cell system 300 according to the third embodiment, the first exhaust gas discharged from the reformer 120 is directly supplied to the turbine 310. However, the turbine may be rotated by thermal energy contained in the first exhaust gas discharged from the reformer 120. FIG. 4 is a diagram illustrating an example of a fuel cell system 400 according to a fourth embodiment. As shown in FIG. 4, the fuel cell system 400 according to the fourth embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a compressor 140, a solid oxide fuel cell 150, a compressor 160, an exhaust gas supply passage 170, and a binary generator 410. Note that components that are substantially the same as those in the fuel cell system 300 are denoted by the same reference numerals and will not be described again. The fuel cell system 400 according to this embodiment is the same as the fuel cell system 300 except that it includes a binary generator 410 instead of the turbine 310 and the generator 320.

[0037] The binary generator 410 includes a circulation path 412, a compressor 414, a turbine 416, a generator 418, and a first heat exchanger 420. The circulation path 412 is a flow path through which a fluid circulates. The compressor 414 is provided in the circulation path 412 and compresses the fluid.

[0038] The turbine 416 is provided in the circulation path 412 and is rotated by the fluid compressed by the compressor 414. The generator 418 is connected to the turbine 416. The generator 418 generates electricity by the rotation of the turbine 416. The generated power of the generator 418 is output to the compressors 140 and 160, or is output to the outside together with the generated power of the PEFC 130 and the SOFC 150, for example.

[0039] The first heat exchanger 420 exchanges heat between the fluid before being supplied to the turbine 416 and the first exhaust gas discharged from the reformer 120. In this embodiment, the first heat exchanger 420 exchanges heat between the fluid flowing between the compressor 414 and the turbine 416 in the circulation path 412 and the first exhaust gas flowing through the exhaust gas discharge path 312. This allows the heat of the first exhaust gas discharged from the reformer 120 to be transferred to the fluid, heating the fluid and cooling the first exhaust gas.

[0040] Therefore, in this embodiment, the turbine 416 is rotated by the fluid after heat exchange by the first heat exchanger 420 .

[0041] As described above, the fuel cell system 400 according to the fourth embodiment includes a turbine 416 and a first heat exchanger 420 in addition to the components of the fuel cell system 100. This allows the fuel cell system 400 according to the fourth embodiment to recover thermal energy contained in the first exhaust gas discharged from the reformer 120. Furthermore, the fuel cell system 400 according to the fourth embodiment includes a generator 418, allowing the energy recovered by the turbine 416 to be converted into electric power.

[0042] Furthermore, the fuel cell system 400 according to the fourth embodiment supplies the first exhaust gas discharged from the reformer 120 to the first heat exchanger 420. The pressure loss occurring in the first heat exchanger 420 is smaller than the pressure loss occurring in the turbine 310 of the fuel cell system 300. Therefore, the fuel cell system 400 according to the fourth embodiment can discharge the first exhaust gas from the reformer 120 more efficiently than the fuel cell system 300, and can avoid malfunctions of the SOFC 150.

[0043] Fifth Embodiment: Fuel Cell System 500 In the fuel cell system 400 according to the fourth embodiment, thermal energy contained in the first exhaust gas discharged from the reformer 120 is supplied to the turbine 416 connected to the generator 418. However, the thermal energy contained in the first exhaust gas discharged from the reformer 120 may be supplied to another turbine. FIG. 5 is a diagram illustrating an example of a fuel cell system 500 according to the fifth embodiment. As shown in FIG. 5, the fuel cell system 500 according to the fifth embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a solid oxide fuel cell 150, a compressor 160, an exhaust gas supply passage 170, a turbocharger 510, and a first heat exchanger 520. Note that components that are substantially the same as those in the fuel cell system 400 are denoted by the same reference numerals, and description thereof will be omitted. The fuel cell system 500 according to this embodiment differs from the fuel cell system 400 in that it includes a supercharger 510 instead of the binary generator 410, but is otherwise the same.

[0044] The supercharger 510 has a turbine 512 and a compressor 514. In the present embodiment, the supercharger 510 is, for example, an electric turbocharger that has, in addition to the turbine 512 and the compressor 514, a motor 516 that rotates the compressor 514.

[0045] The turbine 512 is connected to the exhaust port of the PEFC 130 via a second exhaust gas passage 134. The second exhaust gas (e.g., cathode off-gas) exhausted from the exhaust port of the PEFC 130 is supplied to the turbine 512 through the second exhaust gas passage 134. The turbine 512 is rotated by the second exhaust gas generated in the PEFC 130.

[0046] The compressor 514 is connected to the turbine 512. The compressor 514 is rotated by the rotation of the turbine 512. In this embodiment, the compressor 514 is rotated by the motor 516 in addition to the rotation of the turbine 512. The compressor 514 compresses an oxygen-containing gas. In this embodiment, the compressor 514 is connected to the cathode of the PEFC 130 via the oxygen-containing gas flow path 132. Therefore, the oxygen-containing gas compressed by the compressor 514 is supplied to the cathode of the PEFC 130 through the oxygen-containing gas flow path 132.

[0047] The first heat exchanger 520 exchanges heat between the first exhaust gas discharged from the reformer 120 and the second exhaust gas (fluid) before being supplied to the turbine 512. In this embodiment, the first heat exchanger 520 exchanges heat between the first exhaust gas flowing through the exhaust gas discharge passage 312 and the second exhaust gas flowing through the second exhaust gas passage 134. This allows the heat of the first exhaust gas discharged from the reformer 120 to be transferred to the second exhaust gas discharged from the PEFC 130. Therefore, the second exhaust gas discharged from the PEFC 130 is heated, and the first exhaust gas discharged from the reformer 120 is cooled.

[0048] Therefore, in this embodiment, the turbine 512 is rotated by the second exhaust gas after heat exchange by the first heat exchanger 520 .

[0049] As described above, the fuel cell system 500 according to the fifth embodiment includes the turbine 512 and the first heat exchanger 520 in addition to the components of the fuel cell system 100 .

[0050] As a result, the fuel cell system 500 according to the fifth embodiment can rotate the turbine 512 using the second exhaust gas generated in the PEFC 130. Therefore, the fuel cell system 500 according to the fifth embodiment can obtain the power required for the compressor 514 from the rotation of the turbine 512, thereby reducing the power consumption of the motor 516. Furthermore, the fuel cell system 500 according to the fifth embodiment can heat the second exhaust gas using the high-temperature first exhaust gas and then supply the second exhaust gas to the turbine 512. Therefore, the fuel cell system 500 according to the fifth embodiment can rotate the turbine 512 using the thermal energy of the first exhaust gas in addition to the energy of the second exhaust gas. Therefore, the fuel cell system 500 according to the fifth embodiment can increase the power supplied from the turbine 512 to the compressor 514. Therefore, the fuel cell system 500 according to the fifth embodiment can further reduce the power consumption of the motor 146.

[0051] Furthermore, the fuel cell system 500 according to the fifth embodiment can prevent the first exhaust gas discharged from the reformer 120 from being directly supplied to the turbine 512. This makes it possible for the fuel cell system 500 according to the fifth embodiment to prevent a malfunction of the turbine 512 due to dust or the like contained in the first exhaust gas discharged from the reformer 120.

[0052] Sixth Embodiment: Fuel Cell System 600 In the fuel cell system 500 according to the fifth embodiment, the thermal energy of the first exhaust gas discharged from the reformer 120 is supplied to the turbine 512. However, the first exhaust gas discharged from the reformer 120 may be directly supplied to the turbine 512. FIG. 6 is a diagram illustrating an example of a fuel cell system 600 according to the sixth embodiment. As shown in FIG. 6, the fuel cell system 600 according to the sixth embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a solid oxide fuel cell 150, a compressor 160, an exhaust gas supply passage 170, a turbocharger 510, and an exhaust gas exhaust passage 612. Note that components that are substantially the same as those in the fuel cell system 500 are denoted by the same reference numerals and will not be described again. The fuel cell system 600 according to this embodiment is the same as the fuel cell system 500 except that the first heat exchanger 520 is omitted.

[0053] The exhaust gas exhaust passage 612 merges the first exhaust gas exhausted from the reformer 120 with the second exhaust gas generated in the PEFC 130. The exhaust gas exhaust passage 612 connects, for example, an outlet of the exhaust gas passage of the reformer 120 and the second exhaust gas passage 134.

[0054] Therefore, the turbine 512 is rotated by the second exhaust gas generated in the PEFC 130 in addition to the first exhaust gas discharged from the reformer 120 .

[0055] As described above, the fuel cell system 600 according to the sixth embodiment includes, in addition to the components of the fuel cell system 100, a turbine 512 and an exhaust gas discharge passage 612.

[0056] As a result, the fuel cell system 600 according to the sixth embodiment supplies the second exhaust gas generated in the PEFC 130 to the turbine 512 in addition to the first exhaust gas discharged from the reformer 120. Therefore, the fuel cell system 600 according to the sixth embodiment can rotate the turbine 512 using the first exhaust gas and the second exhaust gas. Therefore, the fuel cell system 600 according to the sixth embodiment can increase the power supplied from the turbine 512 to the compressor 514. Therefore, the fuel cell system 600 according to the sixth embodiment can further reduce the power consumption of the motor 516.

[0057] [Seventh Embodiment: Fuel Cell System 700] In the fuel cell system 500 according to the fifth embodiment, the thermal energy of the first exhaust gas discharged from the reformer 120 is supplied to the turbine 512. However, in addition to the thermal energy of the first exhaust gas discharged from the reformer 120, other thermal energy may be supplied to the turbine 512. FIG. 7 is a diagram illustrating an example of a fuel cell system 700 according to the seventh embodiment. As shown in FIG. 7, the fuel cell system 700 according to the seventh embodiment includes a tank 110, a reformer 120, a polymer electrolyte fuel cell 130, a solid oxide fuel cell 150, a compressor 160, an exhaust gas supply passage 170, a turbocharger 510, a first heat exchanger 520, and a second heat exchanger 710. Note that components that are substantially the same as those in the fuel cell system 500 are denoted by the same reference numerals, and description thereof will be omitted. The fuel cell system 700 according to this embodiment differs from the fuel cell system 500 in that a second heat exchanger 710 is added, but is otherwise the same.

[0058] The second heat exchanger 710 exchanges heat between the hydrogen generated by the reformer 120 and the second exhaust gas generated in the PEFC 130. In this embodiment, the second heat exchanger 710 exchanges heat between the hydrogen passing through the hydrogen flow path 122 and the second exhaust gas passing through the second exhaust gas flow path 134. This allows the heat of the hydrogen generated by the reformer 120 to be transferred to the second exhaust gas, heating the second exhaust gas and cooling the hydrogen.

[0059] Furthermore, in this embodiment, the first heat exchanger 520 exchanges heat between the first exhaust gas discharged from the reformer 120 and the second exhaust gas that has been heat exchanged by the second heat exchanger 710 and has not yet been supplied to the turbine 512. In this embodiment, the first heat exchanger 520 exchanges heat between the first exhaust gas flowing through the exhaust gas discharge passage 312 and the second exhaust gas that flows between the turbine 512 and a location in the second exhaust gas passage 134 where the second heat exchanger 710 is provided. This allows the heat of the first exhaust gas discharged from the reformer 120 to be transferred to the second exhaust gas after heat exchange. Therefore, the second exhaust gas generated in the PEFC 130 is further heated, and the first exhaust gas discharged from the reformer 120 is cooled.

[0060] Therefore, in this embodiment, the turbine 512 is rotated by the second exhaust gas after heat exchange by the second heat exchanger 710 and the first heat exchanger 520 .

[0061] As described above, the fuel cell system 700 according to the seventh embodiment includes the first heat exchanger 520 and the second heat exchanger 710 .

[0062] As a result, the fuel cell system 700 according to the seventh embodiment can heat the second exhaust gas with the high-temperature hydrogen and high-temperature first exhaust gas produced in the reformer 120, and then supply the heated second exhaust gas to the turbine 512. Therefore, the fuel cell system 700 according to the seventh embodiment can rotate the turbine 512 with the thermal energy of the hydrogen and the thermal energy of the first exhaust gas, in addition to the energy of the second exhaust gas. Therefore, the fuel cell system 700 according to the seventh embodiment can further increase the power supplied from the turbine 512 to the compressor 514. As a result, the fuel cell system 700 according to the seventh embodiment can further reduce the power consumption of the motor 516.

[0063] Furthermore, the fuel cell system 700 according to the seventh embodiment can use the second heat exchanger 710 to lower the temperature of the hydrogen before it is supplied to the PEFC 130. This makes it possible to prevent the PEFC 130 from being deteriorated by heat.

[0064] Although the embodiments have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to the above-described embodiments. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0065] For example, in the fuel cell system 700 according to the seventh embodiment, the first heat exchanger 520 is provided between the second heat exchanger 710 and the turbine 512 in the second exhaust gas passage 134. However, the first heat exchanger 520 may be provided between the PEFC 130 and the second heat exchanger 710 in the second exhaust gas passage 134.

[0066] The fuel cell system 600 according to the sixth embodiment may also include a second heat exchanger 710 .

[0067] Furthermore, the fuel cell systems 100, 200, 300, 400, 500, 600, and 700 according to the first to seventh embodiments may include a combustor that combusts the first exhaust gas generated in the solid oxide fuel cell 150. The combustor may be provided between the solid oxide fuel cell 150 and the reformer 120. In this case, the efficiency of ammonia decomposition by the reformer 120 can be improved. The combustor may also combust the first exhaust gas exhausted from the reformer 120. In this case, the energy recovered in the turbine 310, the turbine 416, and the turbine 512 can be increased.

[0068] 100: Fuel cell system 110: Tank 120: Reformer 130: Polymer electrolyte fuel cell (PEFC) 150: Solid oxide fuel cell (SOFC) 170: Exhaust gas supply passage 200: Fuel cell system 250: Solid oxide fuel cell (SOFC) 300: Fuel cell system 310: Turbine 400: Fuel cell system 416: Turbine 420: First heat exchanger 500: Fuel cell system 512: Turbine 520: First heat exchanger 600: Fuel cell system 700: Fuel cell system 710: Second heat exchanger

Claims

1. A fuel cell system comprising: a tank for storing ammonia; a reformer for generating hydrogen by thermal decomposition of the ammonia supplied from the tank; a solid oxide fuel cell for generating electricity using as fuel the ammonia supplied from the tank or the hydrogen generated by the reformer; a polymer electrolyte fuel cell for generating electricity using as fuel the hydrogen generated by the reformer; and an exhaust gas supply passage for supplying a first exhaust gas generated in the solid oxide fuel cell to the reformer.

2. The fuel cell system according to claim 1, further comprising a turbine rotated by the first exhaust gas discharged from the reformer.

3. The fuel cell system according to claim 1, comprising: a turbine; and a first heat exchanger that exchanges heat between a fluid before being supplied to the turbine and the first exhaust gas discharged from the reformer.

4. The fuel cell system according to claim 2 or 3, wherein the turbine is rotated by a second exhaust gas generated in the polymer electrolyte fuel cell in addition to the first exhaust gas discharged from the reformer.

5. The fuel cell system according to claim 4, further comprising a second heat exchanger for exchanging heat between the hydrogen produced by the reformer and the second exhaust gas.

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