Fuel cell system

Abstract

A fuel cell system includes a steam generator that heats water to generate water vapor; a reformer that reacts the water vapor and a hydrocarbon to generate a hydrogen-containing reformate; a fuel cell stack that has an anode and a cathode, and generates electric power through electrochemical reactions of the reformate supplied to the anode and an oxidant supplied to the cathode; and an ejector that uses the water vapor as a driving fluid to supply at least one of a raw material containing the hydrocarbon and an anode recycle gas obtained by recovering a portion of an anode exhaust gas discharged from the anode to the reformer. The steam generator has a water flow passage; an anode exhaust gas flow passage that is thermally connected to the water flow passage; and an auxiliary heating device that heats the water, the anode exhaust gas flow passage and the auxiliary heating device being opposed to each other with the water flow passage interposed therebetween.

Description

Technical Field

[0001] This disclosure relates to a fuel cell system equipped with a steam generator. Background Technology

[0002] Patent Document 1 describes an evaporator for a reformer installed in the pre-reformer stage of a fuel cell system. In this evaporator, a burner is provided as a heating element. An evaporator tube is spirally wound around the outer periphery of the heating element. The heat energy generated by combustion in the burner is transferred to the evaporator tube. As a result, the water inside the evaporator tube vaporizes.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2004-14141 Summary of the Invention

[0006] However, in the evaporator for the reformer of Patent Document 1, a continuous supply of combustion gas is required to the burner in order to continuously provide heat of vaporization to the water. Therefore, in the fuel cell system using the evaporator for the reformer of Patent Document 1, there is a problem of reduced energy efficiency.

[0007] This disclosure was made to address the issues described above, with the aim of providing a fuel cell system that achieves higher energy efficiency.

[0008] The fuel cell system disclosed herein comprises: a steam generator for heating water to generate steam; a reforming unit for reacting the steam with hydrocarbons to generate hydrogen-containing reformed gas; a fuel cell stack having an anode and a cathode for generating electrical energy through an electrochemical reaction of the reformed gas supplied to the anode and an oxidant supplied to the cathode; and an injector for using the steam as a driving fluid to supply the reforming unit with at least one of a feedstock containing the hydrocarbons and an anode recycle gas obtained by recovering a portion of the anode exhaust gas discharged from the anode, wherein the steam generator has: an evaporation flow path through which the water flows; an anode exhaust gas flow path thermally connected to the evaporation flow path through which the anode exhaust gas flows; and an auxiliary heating device for heating the water, wherein the anode exhaust gas flow path and the auxiliary heating device are positioned opposite each other, sandwiching the evaporation flow path.

[0009] According to this disclosure, higher energy efficiency can be achieved in fuel cell systems. Attached Figure Description

[0010] Figure 1 This is a system diagram showing the structure of the fuel cell system involved in Embodiment 1.

[0011] Figure 2This is a cross-sectional view showing the internal structure of the steam generator in the fuel cell system according to Embodiment 1.

[0012] Figure 3 This is a cross-sectional view showing the structure of the anode waste gas flow path inlet and its surroundings in the steam generator involved in the variation 1-1 of Embodiment 1.

[0013] Figure 4 This is a cross-sectional view showing the anode waste gas flow path inlet and the surrounding structure in the steam generator involved in variations 1-2 of Embodiment 1.

[0014] Figure 5 This is a cross-sectional view showing the structure of the anode waste gas flow path inlet and its surroundings in the steam generator involved in variations 1-3 of Embodiment 1.

[0015] Figure 6 This is a system diagram showing the structure of the fuel cell system involved in Embodiment 2.

[0016] Figure 7 This is a cross-sectional view showing the internal structure of the steam generator in the fuel cell system according to Embodiment 2.

[0017] Figure 8 This is a system diagram showing the structure of the fuel cell system involved in Embodiment 3.

[0018] Figure 9 This is a cross-sectional view showing the internal structure of the steam generator according to a variation 3-1 of Embodiment 3.

[0019] Figure 10 This is a system diagram showing the structure of the fuel cell system involved in Embodiment 4.

[0020] (Symbol Explanation)

[0021] 1: Fuel cell stack; 1a: Anode; 1c: Cathode; 1e: Electrolyte; 2: Reformer (reforming section); 3: Combustor; 4: Steam generator; 4a: Central shaft; 4b: Outer peripheral wall (flow path wall); 4b1: Inner wall surface; 4c: Inner peripheral wall; 4d: Partition wall; 4e: Upper wall; 4f: Lower wall; 5: Water separator; 6: Water piping; 7: Oxidant heat exchanger; 8: Water pump; 9: Ejector; 10: Heat recovery cooler; 14: Water treatment unit; 18: Blower; 19: Feed pretreatment unit; 20: Steam temperature sensor; 21: Anode exhaust gas temperature sensor; 22: Stack temperature sensor; 23: Circulating heat exchanger; 24: Reformer temperature sensor 41: Outer peripheral space; 42: Inner peripheral space; 50: Auxiliary burner; 90: Control unit; 100: Fuel cell system; 200: Feed system; 201: Reforming feed system; 202: Fuel gas system; 203: Oxidant system; 204: Cathode exhaust gas system; 205: Reforming gas system; 206: Anode exhaust gas system; 207: Anode recovery gas system; 208: Recirculated combustion gas system; 209: Anode recirculated gas system; 210: Circulating water system; 211: Steam system; 214: Heat recovery system; 215: Combustion exhaust gas system; 216: Auxiliary combustion fuel system; 217: Auxiliary combustion fuel system; 218: Auxiliary Combustion fuel system; 221: Recycling branch; 301: Evaporation path; 301a: Heat transfer tube; 301b: Evaporation path inlet; 301c: Evaporation path outlet; 302: Anode waste gas flow path; 303: Auxiliary heating device; 304: Condensation water accumulation space; 305: Condensation water discharge pipe; 305a: Condensation water discharge valve; 306: Heat transfer promoting component; 307: Anode waste gas flow path inlet; 307a: Inflow pipe; 307a1: End face; 308: Anode waste gas flow path outlet; 308a: Outflow pipe; 311: Recirculated combustion gas flow regulating valve (cut-off part); 312: Recirculated combustion gas flow meter; 313: Condensation water guide plate; 313a 313b: One end; 313c: Through hole; 314: Combustion exhaust gas path; 315: Partition wall; 316: First flow path component; 316a: Tank; 317: Second flow path component; F00: Raw material; F01: Raw material; F02: Fuel gas; F03: Oxidant; F04: Cathode exhaust gas; F05: Reforming gas; F06: Anode exhaust gas; F07: Anode recovery gas; F08: Recirculated combustion gas; F09: Anode circulating gas; F10: Circulating water (water); F11: Water vapor; F14: Cooling medium; F15: Combustion exhaust gas; F16: Auxiliary combustion fuel; F17: Auxiliary combustion fuel; F18: Auxiliary combustion fuel. Detailed Implementation

[0022] Implementation method 1.

[0023] This describes the fuel cell system involved in Implementation Method 1. Figure 1 This is a system diagram showing the structure of the fuel cell system according to this embodiment. First, the basic structure of the fuel cell system 100 according to this embodiment will be explained.

[0024] like Figure 1 As shown, the fuel cell system 100 includes a fuel cell stack 1, a reformer 2, a burner 3, a steam generator 4, a water separator 5, a recovery branch 221, an oxidant heat exchanger 7, a water pump 8, an injector 9, a heat recovery cooler 10, a blower 18, a feedstock pretreatment device 19, and a water treatment device 14. Each device processes feedstock, oxidant, water, or fluids originating from these. In this embodiment, air is used as the oxidant.

[0025] The fuel cell system 100 has a control unit 90. The control unit 90 controls the entire fuel cell system 100, including the aforementioned devices. The control unit 90 has a microcomputer equipped with a CPU (Central Processing Unit), ROM (Read-Only Memory), RAM (Random Access Memory), etc.

[0026] The fuel cell system 100 has multiple systems 200-211 and 214-216 that respectively serve as flow paths for fluids. Each system 200-211 and 214-216 is constructed using piping.

[0027] The raw material system 200 is the flow path for raw material F00. The reforming raw material system 201 is the flow path for reforming raw material F01. The fuel gas system 202 is the flow path for fuel gas F02. The oxidant system 203 is the flow path for oxidant F03. The cathode exhaust gas system 204 is the flow path for cathode exhaust gas F04. The reforming gas system 205 is the flow path for reforming gas F05. The anode exhaust gas system 206 is the flow path for anode exhaust gas F06. The anode recovery gas system 207 is the flow path for anode recovery gas F07. The recirculated combustion gas system 208 is the flow path for recirculated combustion gas F08. The anode circulating gas system 209 is the flow path for anode circulating gas F09. The circulating water system 210 is the flow path for circulating water F10. The steam system 211 is the flow path for steam F11. The heat recovery system 214 is the flow path for cooling medium F14. The combustion exhaust gas system 215 is the flow path for combustion exhaust gas F15. The auxiliary combustion fuel system 216 is the flow path for auxiliary combustion fuel F16.

[0028] Raw material F00, such as city gas, is supplied to the raw material system 200 from an external source. A raw material pretreatment device 19 is provided in the raw material system 200. The raw material pretreatment device 19 is configured, for example, to remove unwanted components such as sulfur from the raw material F00. The raw material system 200 is connected to the suction port of the injector 9 via a reformed raw material system 201.

[0029] In this embodiment, the feedstock system 200 branches downstream into a reformed feedstock system 201 and an auxiliary combustion fuel system 216. The downstream end of the auxiliary combustion fuel system 216 is connected to the burner 3. Thus, a portion of the feedstock F00 is supplied to the burner 3 as auxiliary combustion fuel F16 via the auxiliary combustion fuel system 216.

[0030] The ejector 9 is a circulator for circulating fluid. The ejector 9 has an inlet for driving fluid inflow, a suction port for attracting fluid inflow, and an outlet for the outflow of a mixed fluid formed by the mixing of the driving and attracting fluids. Inside the ejector 9, a nozzle is formed for ejecting the driving fluid. The inlet of the ejector 9 is connected to the steam system 211. The suction port of the ejector 9 is connected to the reforming feedstock system 201 and the anode circulating gas system 209. The outlet of the ejector 9 is connected to the fuel gas system 202.

[0031] The injector 9 uses water vapor F11 as the driving fluid and draws in at least one of the feedstock F01 and the anode circulating gas F09 as the attracting fluid. The attracting fluid drawn in by the injector 9, together with the water vapor F11 as the driving fluid, flows out of the injector 9 and is supplied to the reformer 2 through the fuel gas system 202.

[0032] Reformer 2 is configured to react water vapor F11 with hydrocarbons contained in feedstock F01 to generate hydrogen-containing reformed gas F05. Reformer 2 serves as the reforming section in fuel cell system 100. Reformer 2 is thermally connected to or integrated with burner 3. Thus, the heat required for the reforming reaction is supplied to reformer 2 from burner 3. Reformer 2 is connected to the anode 1a of fuel cell stack 1 via reformed gas system 205.

[0033] The burner 3 is configured to burn the cathode exhaust gas F04, the recirculated combustion gas F08, or the auxiliary combustion fuel F16 to generate heat. The burner 3 is connected to the combustion exhaust gas system 215. The gas burned by the burner 3 is discharged to the outside as combustion exhaust gas F15 through the combustion exhaust gas system 215.

[0034] Air, used as oxidant FO3, is supplied to the oxidant system 203 from the outside. A blower 18 is provided in the oxidant system 203. The blower 18 is a fluid machine that pressurizes the oxidant FO3. An oxidant heat exchanger 7 is provided in the oxidant system 203. The downstream end of the oxidant system 203 is connected to the cathode 1c of the fuel cell stack 1.

[0035] The oxidant heat exchanger 7 is thermally connected to the burner 3 or the reformer 2. The oxidant FO3 passing through the oxidant heat exchanger 7 is heated by heat supplied from the burner 3 or the reformer 2. As a result, the temperature of the oxidant FO3 supplied to the fuel cell stack 1 rises.

[0036] Fuel cell stack 1 is a power generation device comprising multiple stacked fuel cell units. Fuel cell stack 1 has an anode 1a serving as the negative electrode, a cathode 1c serving as the positive electrode, and an electrolyte 1e. The anode 1a and cathode 1c are separated by the electrolyte 1e. In fuel cell stack 1, an electrochemical device consisting of the anode 1a, cathode 1c, and electrolyte 1e is embedded using battery components such as flow paths and spacers. Fuel cell stack 1 is configured to generate electrical energy through an electrochemical reaction between reformed gas FO5 supplied to the anode 1a and oxidant FO3 supplied to the cathode 1c.

[0037] The outlet of anode 1a is connected to the upstream end of anode exhaust gas system 206. Anode exhaust gas system 206 is connected to anode exhaust gas flow path 302 of steam generator 4. In anode exhaust gas system 206, a heat recovery cooler 10 is installed further downstream than anode exhaust gas flow path 302. The downstream end of anode exhaust gas system 206 is connected to the inlet of water separator 5.

[0038] The outlet of cathode 1c is connected to the upstream end of cathode exhaust gas system 204. The downstream end of cathode exhaust gas system 204 is connected to burner 3.

[0039] In the circulating water system 210, circulating water F10 flows. Circulating water F10 is recovered from the water separator 5 using a water pump 8. A water treatment device 14 is installed in the circulating water system 210. The water treatment device 14 is configured to remove unwanted components such as ions from the circulating water F10. In the fuel cell system 100, water is essentially independent, but feedwater can be added from an external source as needed.

[0040] In the circulating water system 210, a water pump 8 is installed downstream of the water treatment device 14. The water pump 8 is a fluid machine that pressurizes the circulating water F10. The downstream end of the circulating water system 210 is connected to one end of the evaporation flow path 301 of the steam generator 4. The other end of the evaporation flow path 301 is connected to the upstream end of the steam system 211. The downstream end of the steam system 211 is connected to the inlet of the ejector 9.

[0041] The steam generator 4 is configured to heat water to vaporize it and generate steam. The steam generator 4 has an evaporation flow path 301, an anode waste gas flow path 302, and an auxiliary heating device 303. In the evaporation flow path 301, circulating water F10 and the steam F11 generated from the vaporization of circulating water F10 flow through. In the anode waste gas flow path 302, anode waste gas F06 flows through. The anode waste gas flow path 302 is thermally connected to the evaporation flow path 301. The auxiliary heating device 303 is configured to heat the circulating water F10 flowing in the evaporation flow path 301.

[0042] The circulating water F10 flowing into the evaporation flow path 301 is heated through heat exchange with the anode waste gas F06 flowing in the anode waste gas flow path 302. Additionally, the circulating water F10 is also heated by an auxiliary heating device 303, which is independently installed from the anode waste gas flow path 302. The heated circulating water F10 evaporates into water vapor F11, which flows out from the evaporation flow path 301 into the water vapor system 211. For a detailed description of the structure of the steam generator 4, please refer to... Figure 2 To be discussed later.

[0043] The heat recovery cooler 10 is a heat exchanger that performs heat exchange between the anode exhaust gas F06 flowing out of the anode exhaust gas path 302 of the steam generator 4 and the cooling medium F14 flowing in the heat recovery system 214.

[0044] Water separator 5 is a gas-liquid separator that separates anode waste gas F06 into gaseous and liquid components. The liquid outlet of water separator 5 is connected to the circulating water system 210 via water piping 6, further upstream than the water treatment unit 14. The gas outlet of water separator 5 is connected to the upstream end of the anode recovery gas system 207.

[0045] The anode recovery gas system 207 branches into a recirculated combustion gas system 208 and an anode recirculated gas system 209 in the recovery branch 221. The downstream end of the anode recirculated gas system 209 is connected to the suction port of the injector 9.

[0046] In the recirculated combustion gas system 208, a recirculated combustion gas flow meter 312 and a recirculated combustion gas flow regulating valve 311 are provided. The recirculated combustion gas flow meter 312 is configured to detect the flow rate of the recirculated combustion gas F08 flowing in the recirculated combustion gas system 208. The recirculated combustion gas flow regulating valve 311 is configured to regulate the flow rate of the recirculated combustion gas F08. The recirculated combustion gas flow regulating valve 311 also functions as a cut-off section to cut off the recirculated combustion gas F08. The downstream end of the recirculated combustion gas system 208 is connected to the burner 3.

[0047] Next, the operation of the fuel cell system 100 according to this embodiment in its basic structure will be explained. The operation described below is based on the operation of the fuel cell system 100 when it is in its rated operating state.

[0048] In the oxidant system 203, oxidant F03 flows through the blower 18. The oxidant F03 is heated to a temperature suitable for the operation of the fuel cell stack 1 in the oxidant heat exchanger 7 and supplied to the cathode 1c of the fuel cell stack 1.

[0049] The oxidant FO3 supplied to cathode 1c is separated from the reformed gas FO5 by electrolyte 1e, and consumes a portion of the oxygen through an electrochemical reaction. The oxidant FO3 after consuming a portion of the oxygen flows out of cathode 1c as cathode exhaust gas FO4. Cathode exhaust gas FO4 is supplied to burner 3 through cathode exhaust gas system 204.

[0050] In the feedstock system 200, feedstock F00, such as city gas, flows. Unwanted components contained in the feedstock F00 are removed by the feedstock pretreatment device 19. The feedstock F00 after passing through the feedstock pretreatment device 19 is drawn into the injector 9 as feedstock F01 for reforming. The feedstock F01 drawn into the injector 9 is mixed with anode circulating gas F09 and water vapor F11, and flows out from the injector 9 as fuel gas F02. The fuel gas F02 is supplied to the reformer 2 through the fuel gas system 202. A portion of the feedstock F00 after passing through the feedstock pretreatment device 19 is supplied to the burner 3 as auxiliary combustion fuel F16 through the auxiliary combustion fuel system 216.

[0051] The fuel gas F02 supplied to the reformer 2 is reformed in the reformer 2 to become reformed gas F05, which contains hydrogen as its main component. The reformed gas F05 flowing out of the reformer 2 is supplied to the anode 1a of the fuel cell stack 1 through the reformed gas system 205.

[0052] The reformed gas F05 supplied to anode 1a, separated from the oxidant F03 by electrolyte 1e, consumes a portion of the fuel through an electrochemical reaction. The reformed gas F05, after consuming a portion of the fuel, is discharged from anode 1a as anode exhaust gas F06. Anode exhaust gas F06 flows through anode exhaust gas system 206 into anode exhaust gas flow path 302 of steam generator 4.

[0053] In the steam generator 4, heat exchange occurs between the anode exhaust gas F06 and the circulating water F10. As a result, the anode exhaust gas F06 is cooled, and the circulating water F10 is heated and vaporized to generate water vapor F11.

[0054] The anode exhaust gas F06 flowing from the steam generator 4 flows into the heat recovery cooler 10. In the heat recovery cooler 10, heat exchange occurs between the anode exhaust gas F06 and the cooling medium F14 flowing in the heat recovery system 214. This further cools the anode exhaust gas F06. The cooled anode exhaust gas F06 then flows into the water separator 5.

[0055] In water separator 5, anode exhaust gas F06 is separated into gaseous and liquid components. The gaseous component, as anode recovery gas F07, flows out of water separator 5 to anode recovery gas system 207. A portion of the anode recovery gas F07 is supplied to burner 3 as recirculated combustion gas F08 through recirculated combustion gas system 208. The remaining anode recovery gas F07 is drawn to ejector 9 as anode recirculated gas F09 through anode recirculated gas system 209. The anode recirculated gas F09 drawn to ejector 9 is mixed with raw material F01 and water vapor F11, and supplied to reformer 2 as fuel gas F02. On the other hand, condensate, as the liquid component, flows out of water separator 5 and is supplied to circulating water system 210 through water piping 6.

[0056] In the circulating water system 210, circulating water F10 recovered from the water separator 5 by the water pump 8 flows. Unwanted components contained in the circulating water F10 are removed by the water treatment device 14. The circulating water F10 after passing through the water treatment device 14 in the circulating water system 210 is supplied to the evaporation path 301 of the steam generator 4. In the fuel cell system 100, water is essentially independent, but feedwater can also be added from the outside as needed.

[0057] In the steam generator 4, the circulating water F10 is heated through heat exchange with the anode exhaust gas F06 or by the auxiliary heating device 303. The heated circulating water F10 evaporates into water vapor F11, which flows out of the steam generator 4.

[0058] Water vapor F11 flowing from steam generator 4 enters ejector 9 via water vapor system 211. The water vapor F11 flowing into ejector 9 is ejected as a driving fluid from nozzles located inside ejector 9. The momentum of the ejected water vapor F11 is supplied to feedstock F01 and anode circulating gas F09. Thus, feedstock F01 and anode circulating gas F09 mix with water vapor F11 to form fuel gas F02, which flows out of ejector 9. The fuel gas F02 flowing out of ejector 9 is supplied to reformer 2.

[0059] The feedstock pretreatment unit 19 uses filters, desulfurizers, etc. The feedstock F00 uses a gas containing hydrocarbons. These hydrocarbon-containing gases include methane, propane, butane, natural gas, city gas, and digester gases primarily composed of methane. Additionally, various alcohols and petroleum-based feedstocks can also be used as feedstock F00. If feedstock F00 is a hydrophilic liquid feedstock, it can be pre-mixed with circulating water. Conversely, if feedstock F00 is a hydrophobic liquid feedstock, it can be preheated and vaporized individually, or it can be mixed with steam F11 and preheated for vaporization.

[0060] In reformer 2, for example, a steam reforming reaction is carried out. Equations (1) and (2) represent a representative reforming reaction using methane as a feedstock. Reformer 2 is filled with a reforming catalyst. An endothermic reaction between methane and steam is initiated by the reforming catalyst. Hydrogen is produced through this reaction. Generally, the flow rate of steam supplied to reformer 2 is expressed using the S / C value. S / C is the mole fraction of steam (S) relative to the carbon (C) contained in the fuel gas. Typically, the flow rate of steam supplied to reformer 2 is set to a fixed value within the range of 2.5 to 3.5 for the S / C. The reforming catalyst, for example, has a structure in which Ni-based, Pt-based, or Ru-based catalysts are supported on a carrier such as Al2O3 or MgO.

[0061]

[0062]

[0063] Furthermore, a steam reforming reaction is illustrated here, but the reforming reaction is not limited to this. Other reforming reactions can also be achieved by introducing air into the reformer 2, by autothermal reforming, or by partial oxidative reforming.

[0064] In a fuel cell stack 1, separated from each other by electrolyte 1e, an electrochemical reaction occurs between reformed gas F05 supplied to anode 1a and oxidant FO3 supplied to cathode 1c. This results in electron exchange within the fuel cell stack 1, thereby generating electrical energy. Specifically, a potential difference is generated within the fuel cell stack 1, simultaneously generating ion exchange via electrolyte 1e and electron exchange within the circuit via the output terminals of both anode 1a and cathode 1c. The direct current generated by the electron movement within the circuit is then output as electrical power.

[0065] The electrode materials and operating temperature of the fuel cell stack 1 vary depending on the type of electrolyte 1e. In addition, the types of ions that move in the electrolyte 1e also vary depending on the type of electrolyte 1e. For example, in the case of a solid oxide fuel cell, the electrode reaction in the anode 1a is represented by equation (3), and the electrode reaction in the cathode 1c is represented by equation (4).

[0066] H2+O 2- →H₂O + 2e - …(3)

[0067] 1 / 2O2+2e - →O 2- …(4)

[0068] In anode 1a, hydrogen equivalent to the amount of electron movement is consumed by the electrode reaction. Therefore, in anode 1a, the hydrogen partial pressure becomes lower the closer to the anode outlet. Additionally, in anode 1a, the same amount of water is generated as the amount of hydrogen consumed. Therefore, in anode 1a, the water vapor partial pressure becomes higher the closer to the anode outlet.

[0069] On the other hand, in cathode 1c, oxygen equivalent to the amount of electron movement is consumed by the electrode reaction. Therefore, in cathode 1c, the closer to the cathode outlet, the smaller the gas flow rate and the lower the oxygen partial pressure. In the case of a solid oxide fuel cell, internal reforming that allows the electrode reaction and the reforming reaction to occur simultaneously can be achieved in anode 1a. In this case, in anode 1a, the reforming reaction of the remaining methane that cannot be reformed in reformer 2 can be carried out in the direction of hydrogen production.

[0070] The fuel cell stack 1 operates such that the amount of hydrogen consumed in the electrode reaction at the anode 1a is greater than the flow rate of hydrogen supplied from the reformer 2 or generated through internal reforming, at a ratio of approximately 0.60 to 0.85. That is, the anode exhaust gas F06 at the anode outlet contains residual fuel. For example, the volume molar fraction of hydrogen contained in the anode exhaust gas F06 at the anode outlet is approximately 12%. Additionally, for example, the volume molar fraction of water vapor contained in the anode exhaust gas F06 at the anode outlet is approximately 60%.

[0071] Furthermore, the fuel cell stack 1 operates in such a manner that the ratio of the amount of oxygen consumed in the electrode reaction at the cathode 1c to the oxygen flow rate supplied via the oxidant system 203 is approximately 0.15 to 0.50. That is, the cathode exhaust gas F04 at the cathode outlet contains residual oxygen. For example, the volume molar fraction of oxygen contained in the cathode exhaust gas F04 at the cathode outlet is approximately 16%.

[0072] Based on the basic structure and operation of the fuel cell system 100 described above, the detailed structure of the fuel cell system 100 involved in this embodiment will be explained.

[0073] In the fuel cell system 100 according to this embodiment, the temperature difference and enthalpy difference between the anode exhaust gas F06 and the circulating water F10, as well as the auxiliary heating device 303, are used as the heat source for the steam generator 4. This point is also the same in the fuel cell system 100 described in Embodiment 2 and later.

[0074] Figure 2 This is a cross-sectional view showing the internal structure of the steam generator of the fuel cell system according to this embodiment. Figure 2 The vertical direction indicates the vertical direction. Figure 2 The thick arrow in the image indicates the direction of fluid flow.

[0075] like Figure 2 As shown, the steam generator 4 has a cylindrical shape as a whole. The central axis 4a of the steam generator 4 runs along the vertical direction. The steam generator 4 has an outer peripheral wall 4b and an inner peripheral wall 4c located on the inner periphery side of the outer peripheral wall 4b. Both the outer peripheral wall 4b and the inner peripheral wall 4c are formed in a cylindrical shape centered on the central axis 4a and extend along the vertical direction. An annular space is formed between the outer peripheral wall 4b and the inner peripheral wall 4c.

[0076] A partition wall 4d is formed between the outer peripheral wall 4b and the inner peripheral wall 4c, that is, further inside the periphery than the outer peripheral wall 4b and further outside the periphery than the inner peripheral wall 4c. The partition wall 4d is formed in a cylindrical shape coaxial with the outer peripheral wall 4b and the inner peripheral wall 4c, extending in the vertical direction. The space formed between the outer peripheral wall 4b and the inner peripheral wall 4c is divided by the partition wall 4d into an outer peripheral space 41 and an inner peripheral space 42. Both the outer peripheral space 41 and the inner peripheral space 42 are annular spaces. The upper ends of the outer peripheral space 41 and the inner peripheral space 42 are closed by the upper wall 4e. The lower ends of the outer peripheral space 41 and the inner peripheral space 42 are closed by the lower wall 4f. Both the upper wall 4e and the lower wall 4f are formed in annular shape.

[0077] An evaporation flow path 301 is disposed in the inner peripheral space 42. A heat transfer tube 301a with a helical structure is formed in the inner peripheral space 42. The heat transfer tube 301a extends spirally along the partition wall 4d with the central axis 4a as the helical axis. An evaporation flow path inlet 301b, which serves as the inlet of the evaporation flow path 301, is provided at the upper end of the heat transfer tube 301a. An evaporation flow path outlet 301c, which serves as the outlet of the evaporation flow path 301, is provided at the lower end of the heat transfer tube 301a. The height of the heat transfer tube 301a from the lower wall 4f decreases monotonically from the evaporation flow path inlet 301b toward the evaporation flow path outlet 301c. The heat transfer tube 301a is in close contact with the inner peripheral surface of the partition wall 4d. As a result, heat energy can easily move between the heat transfer tube 301a and the partition wall 4d.

[0078] An evaporation flow path 301 is formed inside the heat transfer tube 301a. That is, the evaporation flow path 301 is formed in a spiral shape with the central axis 4a as the spiral axis. The evaporation flow path 301 extends at an angle relative to the vertical direction. In the evaporation flow path 301, a downward slope is created from the upstream side to the downstream side. The circulating water F10 flowing into the evaporation flow path 301 from the inlet 301b gradually evaporates as it flows downward along the evaporation flow path 301, exiting as water vapor F11 from the outlet 301c.

[0079] The auxiliary heating device 303 is a heating device for heating the circulating water F10 flowing in the evaporation flow path 301. The auxiliary heating device 303 is disposed in the inner peripheral space 42. The auxiliary heating device 303 is disposed on the inner peripheral side of the evaporation flow path 301, that is, between the evaporation flow path 301 and the central axis 4a. The auxiliary heating device 303 is controlled by the control unit 90.

[0080] As an auxiliary heating device 303, an electric heater or the like is used. For example, the auxiliary heating device 303 has multiple electric heaters formed in a straight tube shape. In this case, the multiple electric heaters are arranged on a circumference centered on the central axis 4a. Each of the multiple electric heaters is arranged parallel to the central axis 4a. The auxiliary heating device 303 may also be formed in a cylindrical shape centered on the central axis 4a.

[0081] A heat transfer promoting component 306 is filled around the evaporation flow path 301 and the auxiliary heating device 303 in the inner peripheral space 42. This facilitates the movement of heat energy between the evaporation flow path 301 and the auxiliary heating device 303. The evaporation flow path 301 and the auxiliary heating device 303 are thermally connected to each other via the heat transfer promoting component 306. The heat transfer promoting component 306 can be, for example, made of metal particles, metal mesh, or heat-transfer cement.

[0082] The anode waste gas flow path 302 is disposed in the outer peripheral space 41. In this embodiment, the entire outer peripheral space 41 constitutes the anode waste gas flow path 302. The anode waste gas flow path 302 is defined by the outer peripheral wall 4b, the partition wall 4d, the upper wall 4e, and the lower wall 4f. That is, the outer peripheral wall 4b, the partition wall 4d, the upper wall 4e, and the lower wall 4f constitute the flow path walls of the anode waste gas flow path 302.

[0083] The anode exhaust gas flow path 302 is thermally connected to the evaporation flow path 301 via the partition wall 4d and the heat transfer tube 301a. In the anode exhaust gas flow path 302, heat transfer fins, such as offset fins, are provided and thermally connected to the partition wall 4d. This improves the heat transfer performance between the anode exhaust gas F06 and the partition wall 4d, thus enabling miniaturization of the steam generator 4.

[0084] The steam generator 4 has an inlet pipe 307a that forms the inlet 307 of the anode waste gas flow path and an outlet pipe 308a that forms the outlet 308 of the anode waste gas flow path. The anode waste gas F06 flows into the anode waste gas flow path 302 via the inlet pipe 307a and flows out of the anode waste gas flow path 302 via the outlet pipe 308a.

[0085] The inlet pipe 307a is connected to the lower part of the anode waste gas flow path 302. The inlet pipe 307a penetrates the outer peripheral wall 4b and extends radially along the steam generator 4. Here, the radial direction of the steam generator 4 refers to the direction along the radius of the steam generator 4 centered on the central axis 4a.

[0086] The outlet pipe 308a is connected to the upper end of the anode waste gas flow path 302. The outlet pipe 308a penetrates the outer peripheral wall 4b and extends radially along the steam generator 4. When viewed along the central axis 4a, the outlet pipe 308a is positioned symmetrically to the inlet pipe 307a with the central axis 4a as the center.

[0087] Anode exhaust gas F06 flows from the anode exhaust gas flow path inlet 307 to the anode exhaust gas flow path outlet 308 in the anode exhaust gas flow path 302. Circulating water F10 and water vapor F11 flow downwards, while anode exhaust gas F06 flows upwards. That is, the flow of anode exhaust gas F06 is counter-current relative to the flow of circulating water F10 and water vapor F11.

[0088] Between the anode waste gas flow path 302 and the evaporation flow path 301, heat exchange occurs between the anode waste gas F06 and the circulating water F10. As a result, the circulating water F10 is heated and vaporized to generate water vapor F11.

[0089] The anode waste gas flow path 302 and the auxiliary heating device 303 are positioned opposite each other, sandwiching the evaporation flow path 301. That is, the evaporation flow path 301 is sandwiched between the anode waste gas flow path 302 and the auxiliary heating device 303. Thus, the circulating water F10 flowing in the evaporation flow path 301 is heated from both sides using the anode waste gas F06 and the auxiliary heating device 303.

[0090] A condensation water accumulation space 304 is provided in the anode waste gas flow path 302, positioned below both the inlet pipe 307a and the outlet pipe 308a. Specifically, the condensation water accumulation space 304 is located below both the anode waste gas flow path inlet 307 and the anode waste gas flow path outlet 308. A condensation water discharge pipe 305 is connected to the bottom of the condensation water accumulation space 304. The condensation water discharge pipe 305 extends downwards through the lower wall 4f. A condensation water discharge valve 305a is provided in the condensation water discharge pipe 305.

[0091] A water vapor temperature sensor 20 is provided in the water vapor system 211 located downstream of the evaporation flow path 301. The water vapor temperature sensor 20 is configured to detect the temperature of the water vapor F11 flowing out of the evaporation flow path 301 and output the detection signal to the control unit 90.

[0092] In the anode exhaust gas system 206, an anode exhaust gas temperature sensor 21 is installed downstream of the anode exhaust gas flow path 302. The anode exhaust gas temperature sensor 21 is configured to detect the temperature of the anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302 and output the detection signal to the control unit 90.

[0093] Next, the operation of the fuel cell system 100, centered on the detailed structure described above, will be explained. Circulating water F10 is supplied to the evaporation path 301 of the steam generator 4 by a water pump 8. The circulating water F10 flows through the evaporation path 301 from the inlet 301b to the outlet 301c using the discharge pressure of the water pump 8 and gravity.

[0094] Anode exhaust gas F06, discharged from anode 1a, is supplied to the anode exhaust gas flow path 302 of the steam generator 4. The anode exhaust gas F06 flowing through the anode exhaust gas flow path 302 transfers heat energy to the circulating water F10 flowing in the evaporation flow path 301 via the partition wall 4d and heat transfer tube 301a. As a result, the circulating water F10 vaporizes into water vapor F11. The anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302 flows into the heat recovery cooler 10 through the anode exhaust gas system 206.

[0095] The control unit 90 obtains information about the temperature of the anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302 based on the detection signal from the anode exhaust gas temperature sensor 21. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302. Specifically, the control unit 90 activates the auxiliary heating device 303 when the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21 is below a lower threshold. The control unit 90 stops the auxiliary heating device 303 when the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21 exceeds an upper threshold.

[0096] The auxiliary heating device 303 can be controlled by either on / off control or by phased or continuous phase control. For example, the control unit 90 can also control the output of the auxiliary heating device 303 in stages or continuously based on the temperature when the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21 is between the lower and upper threshold values.

[0097] When the auxiliary heating device 303 is operating, the circulating water F10 flowing in the evaporation flow path 301 is heated by the anode exhaust gas F06 and also by the auxiliary heating device 303. That is, the circulating water F10 flowing in the evaporation flow path 301 is heated from both sides using the anode exhaust gas F06 flowing in the anode exhaust flow path 302 and the auxiliary heating device 303. This provides sufficient heat of vaporization to the circulating water F10.

[0098] The anode exhaust gas temperature sensor 21 can also be installed at or near the anode exhaust gas outlet 308. Even in this case, the control unit 90 controls the auxiliary heating device 303 in the same way as described above, based on the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21.

[0099] In this embodiment, the auxiliary heating device 303 is controlled based on the temperature of the anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302, but the control of the auxiliary heating device 303 is not limited to this. The control unit 90 may also control the auxiliary heating device 303 based on the temperature detected by the water vapor temperature sensor 20, that is, the temperature of the water vapor F11 flowing out of the evaporation flow path 301. In addition, the control unit 90 may also control the auxiliary heating device 303 based on both the temperature of the anode exhaust gas F06 flowing out of the anode exhaust gas flow path 302 and the temperature of the water vapor F11 flowing out of the evaporation flow path 301.

[0100] Alternatively, the anode exhaust gas temperature sensor 21 can also be installed upstream of the anode exhaust gas flow path 302 in the anode exhaust gas system 206. In this case, the control unit 90 calculates the thermal energy of the anode exhaust gas F06 based on the detection signal from the anode exhaust gas temperature sensor 21 and the operating condition signal of the fuel cell system 100 input to the control unit 90. The control unit 90 compares the thermal energy of the anode exhaust gas F06 with the thermal energy required for the vaporization of the circulating water F10. If the thermal energy required for the vaporization of the circulating water F10 is insufficient, the control unit 90 controls the output of the auxiliary heating device 303 based on the deviation.

[0101] In the fuel cell system 100, when the heat energy required for the vaporization of circulating water F10 can be obtained from the anode exhaust gas F06, the control unit 90 does not need to operate the auxiliary heating device 303. On the other hand, when the heat energy required for the vaporization of circulating water F10 cannot be obtained from the anode exhaust gas F06 due to fluctuations in the output of the fuel cell system 100, the control unit 90 operates the auxiliary heating device 303.

[0102] In the anode waste gas flow path 302, when heat energy is supplied from the anode waste gas F06 to the circulating water F10, and the temperature of the anode waste gas F06 drops below the dew point, condensation occurs in the anode waste gas F06. In this embodiment, the condensate generated by the condensation of the anode waste gas F06 is accumulated in a condensate accumulation space 304 located below the anode waste gas flow path inlet 307. The condensate accumulated in the condensate accumulation space 304 is appropriately discharged via the condensate discharge valve 305a. This prevents the anode waste gas flow path 302 from being blocked by condensate, thus suppressing pulsations in the anode waste gas F06.

[0103] Preferably, the condensate is automatically discharged based on the amount of condensate in the condensate storage space 304. For example, the condensate discharge valve 305a can also be configured to open using the weight of the condensate in the condensate storage space 304. Alternatively, a U-shaped pipe can be provided in the condensate discharge pipe 305 to discharge the condensate based on the head difference of the condensate. Of course, the condensate discharge valve 305a can also be configured to periodically discharge condensate by opening and closing a timer.

[0104] The anode exhaust gas F06 flowing out of the anode exhaust gas path 302 further provides heat energy to the cooling medium F14 in the heat recovery cooler 10, and then flows into the water separator 5. The temperature of the anode exhaust gas F06 flowing into the water separator 5 is a predetermined temperature below the dew point. In order to make the temperature of the anode exhaust gas F06 in the water separator 5 close to the target temperature, the control unit 90 controls the flow rate of the cooling medium F14 based on the temperature of the anode exhaust gas F06 after passing through the heat recovery cooler 10 or the temperature of the anode exhaust gas F06 in the water separator 5. The temperature of the anode exhaust gas F06 after passing through the heat recovery cooler 10 or the temperature of the anode exhaust gas F06 in the water separator 5 is detected using a temperature sensor (not shown).

[0105] In water separator 5, the moisture contained in anode exhaust gas F06 is liquefied based on the saturated vapor pressure at the temperature of the anode exhaust gas F06. The liquefied moisture forms droplets and separates from the anode exhaust gas F06, accumulating as condensate in the lower part of water separator 5. The condensate accumulated in water separator 5 is supplied to circulating water system 210 as circulating water F10 through water pipe 6. Circulating water F10 is supplied to steam generator 4 by water pump 8 according to the required flow rate of water vapor F11 for fuel gas F02.

[0106] On the other hand, the anode exhaust gas F06, after moisture removal by the water separator 5, flows out of the water separator 5 as the anode recovery gas F07 and reaches the recovery branch 221 through the anode recovery gas system 207. In the recovery branch 221, the anode recovery gas F07 is divided into recirculated combustion gas F08 flowing in the recirculated combustion gas system 208 and anode recirculated gas F09 flowing in the anode recirculated gas system 209. The recirculated combustion gas F08 is supplied to the burner 3 through the recirculated combustion gas flow meter 312 and the recirculated combustion gas flow regulating valve 311.

[0107] For example, based on the flow signal from the recirculated combustion gas flow meter 312, the control unit 90 controls the opening of the recirculated combustion gas flow regulating valve 311. As a result, in the recovery branch 221, the recirculated combustion gas F08 and the anode recirculation gas F09 are distributed at an appropriate flow ratio based on the operating conditions of the fuel cell system 100. Therefore, the high efficiency of the fuel cell system 100 is achieved.

[0108] Burner 3 is supplied with recirculated combustion gas F08, cathode exhaust gas F04 discharged from cathode 1c, and auxiliary combustion fuel F16. These gases are combusted in burner 3. A portion of the heat energy from the combusted gases is supplied to reformer 2 as heat energy required for the reforming reaction. As a result, the temperature of reformer 2 rises to the temperature required for the reforming reaction. The temperature required for the reforming reaction in reformer 2 is, for example, 600°C.

[0109] Another portion of the thermal energy from the combustion gases is supplied to the oxidant FO3 in the oxidant heat exchanger 7. As a result, the temperature of the oxidant FO3 rises to the operating temperature of the cathode 1c of the fuel cell stack 1. For example, the temperature of the oxidant FO3 rises from 25°C (the temperature of the outside air) to 600°C.

[0110] After the gas is burned in the burner 3, it provides heat energy to the reformer 2 and the oxidant heat exchanger 7, and is discharged to the outside as combustion exhaust gas F15 through the combustion exhaust gas system 215.

[0111] Anode circulating gas F09 is drawn into ejector 9 via anode circulating gas system 209. The anode circulating gas F09 drawn into ejector 9 mixes with water vapor F11 and feedstock F01, and flows out of ejector 9 as fuel gas F02. Fuel gas F02 is supplied to reformer 2 via fuel gas system 202.

[0112] Based on the enthalpy per output of fuel cell stack 1, we investigate whether the above work holds true. As an example, fuel cell system 100 includes a solid oxide fuel cell using city gas as fuel, configured to operate at a fuel utilization rate of 75%, a cell voltage of 0.84V, and a current of 24A. Under these conditions, the enthalpy per output of fuel cell stack 1 in the anode exhaust gas F06 at the anode outlet is -3081J / s·kW.

[0113] On the other hand, the heat of vaporization required for circulating water F10 to become steam F11 is estimated to be 247 J / s·kW. Therefore, the temperature of the anode exhaust gas F06 after providing heat energy to the circulating water F10 in the steam generator 4 exceeds 150°C according to the heat balance calculation. That is, the heat energy required for the circulating water F10 to become steam F11 in the steam generator 4 can be supplied through heat exchange between the circulating water F10 and the anode exhaust gas F06.

[0114] The temperature of the anode exhaust gas F06 within water separator 5 is set, for example, to 60°C. The saturated vapor pressure at this temperature is approximately 0.025 MPa. The volume mole fraction of water vapor contained in the anode exhaust gas F06 at the anode outlet is approximately 60%. In contrast, regarding the volume mole fraction of water vapor contained in the anode exhaust gas F06 within water separator 5, the flow rate of water vapor decreases to approximately 20% due to condensation, which reduces the flow rate to about half. The anode exhaust gas F06 exits from water separator 5 as anode recovery gas F07.

[0115] The anode recovery gas F07 flowing out from the water separator 5 is distributed in the recovery branch 221 as recirculated combustion gas F08 and anode recirculated gas F09 at approximately the same flow rate.

[0116] Therefore, the flow rate of the anode circulating gas F09 is approximately one-quarter of the flow rate of the anode exhaust gas F06 at the anode outlet. Furthermore, the flow rate of water vapor contained in the anode circulating gas F09 is approximately 8% of the flow rate of water vapor contained in the anode exhaust gas F06 at the anode outlet. The flow rate of water vapor contained in the anode exhaust gas F06 at the anode outlet is only about 15% of the water vapor required by the reformer 2 or the fuel cell stack 1. To supplement the insufficient water vapor, approximately 0.5 MPa of water vapor F11 is generated in the steam generator 4 by vaporizing the circulating water F10.

[0117] Next, the operation of the fuel cell system 100 when the output of the fuel cell stack 1 is increased will be explained. When the output of the fuel cell stack 1 is increased, the flow rates of the oxidant F03, the feedstock F01, and the water vapor F11, which are gases required for the battery reaction, are increased according to the output load conditions under the control of the control unit 90.

[0118] At this time, regarding the raw material F01 and water vapor F11, if the S / C value in the reforming catalyst filling section inside the reformer 2 is less than a certain value, there is a possibility that carbon (C) will be produced instead of the reforming reaction shown in equations (1) and (2). As a result, the produced C sometimes causes problems such as flow path blockage. To avoid this problem, the control unit 90 increases the flow rate of water vapor F11 before increasing the flow rate of raw material F01. That is, in order to increase the output of fuel cell stack 1, it is necessary to first increase the flow rate of water vapor F11, i.e., the flow rate of circulating water F10. Along with this, in the steam generator 4, a heat of vaporization equivalent to the increase in the flow rate of circulating water F10 is required.

[0119] In this embodiment, as the flow rate of circulating water F10 increases, the temperature of anode exhaust gas F06, detected by anode exhaust gas temperature sensor 21, decreases, thus activating the auxiliary heating device 303. That is, the auxiliary heating device 303 provides additional heat energy to the circulating water F10 within the evaporation path 301. Therefore, the auxiliary heating device 303 supplements the heat of vaporization equivalent to the increase in the flow rate of circulating water F10.

[0120] After the transition of the fuel cell system 100's operating state, which accompanies the increase in output of the fuel cell stack 1, is completed, the heat energy from the anode exhaust gas F06 can be used to supply the heat of vaporization of the circulating water F10. In this case, the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21 rises, so the auxiliary heating device 303 stops. After the auxiliary heating device 303 stops, the circulating water F10 flowing in the evaporation flow path 301 is heated from one side using only the anode exhaust gas F06 flowing in the anode exhaust gas flow path 302.

[0121] Thus, according to this embodiment, water vapor can be stably supplied based on the operating state of the fuel cell system 100.

[0122] The operation of the fuel cell system 100 when increasing the output of the fuel cell stack 1 is not limited to the examples described above. If the heat of vaporization of the circulating water F10 is insufficient due to the operating conditions of the fuel cell system 100, the auxiliary heating device 303 may operate continuously or intermittently. Furthermore, if the increase in the output of the fuel cell stack 1 is small and the heat energy from the anode exhaust gas F06 can be used to supply the increase in the heat of vaporization of the circulating water F10, the auxiliary heating device 303 may not need to operate.

[0123] In this embodiment, the thermal energy of the anode exhaust gas F06 flowing in the anode exhaust gas system 206 can be used to convert the circulating water F10 into water vapor F11. Therefore, the flow rate of the recirculated combustion gas F08 supplied to the burner 3 can be reduced, while the flow rate of the anode circulating gas F09 returning to the reformer 2 via the injector 9 can be increased. Therefore, according to this embodiment, a fuel cell system 100 with high energy efficiency can be achieved.

[0124] Furthermore, in this embodiment, in the steam generator 4, the anode waste gas flow path 302 and the auxiliary heating device 303 are positioned opposite each other, sandwiching the evaporation flow path 301. Therefore, the circulating water F10 flowing in the evaporation flow path 301 can be heated from both sides. Thus, according to this embodiment, heat loss can be reduced, and a fuel cell system 100 with higher energy efficiency can be achieved.

[0125] Furthermore, in this embodiment, a highly responsive and stable supply of steam can be provided according to the operating conditions of the fuel cell system 100. Therefore, according to this embodiment, miniaturization of the fuel cell system 100 can be achieved.

[0126] In this embodiment, even if condensation occurs in the anode exhaust gas F06 in the anode exhaust gas flow path 302 due to the transitional operating state of the fuel cell system 100, the condensate can be stored in the condensate storage space 304. This prevents the flow of the anode exhaust gas F06 from being obstructed by the condensate, thus suppressing pulsation in the anode exhaust gas F06.

[0127] In this embodiment, the waste heat from the anode exhaust gas F06 can be used to convert the circulating water F10 into water vapor F11. Therefore, according to this embodiment, the thermal energy of the fuel cell system 100 can be effectively utilized, thus achieving a fuel cell system 100 with high energy efficiency.

[0128] During the transitional operating conditions of the fuel cell system 100, the heat energy obtainable from the anode exhaust gas F06 is sometimes insufficient relative to the heat energy required as the heat of vaporization of the circulating water F10. In this embodiment, even under such conditions, the auxiliary heating device 303 can responsively supplement the heat energy. Therefore, in this embodiment, a wide range of operating conditions of the fuel cell system 100 can be met.

[0129] Furthermore, in this embodiment, the auxiliary heating device 303 can be stopped when the thermal energy required for the gasification heat of the circulating water F10 can be obtained from the anode exhaust gas F06. Therefore, it is not necessary to continuously supply energy to the auxiliary heating device 303. Thus, according to this embodiment, a fuel cell system 100 with high energy efficiency can be realized.

[0130] Figure 3 This is a cross-sectional view showing the anode waste gas flow path inlet and its surrounding structure in the steam generator according to Variation 1-1 of this embodiment. Figure 3 As shown, the inflow pipe 307a has an end face 307a1. The end face 307a1 faces the anode waste gas flow path 302. The end face 307a1 is formed perpendicular to the pipe axis of the inflow pipe 307a. The end face 307a1 is formed on a surface different from the inner wall surface 4b1 of the outer peripheral wall 4b. In this modified example, the inflow pipe 307a is inserted into the interior of the anode waste gas flow path 302, so the end face 307a1 protrudes towards the interior side of the anode waste gas flow path 302 relative to the inner wall surface 4b1. However, the end face 307a1 is away from the partition wall 4d.

[0131] Anode exhaust gas F06 flows into anode exhaust gas flow path 302 via inlet pipe 307a, flows upward in anode exhaust gas flow path 302, and flows out to the outside of steam generator 4. When condensation occurs in anode exhaust gas F06, the condensate mainly flows down along the inner wall surface 4b1 of the outer peripheral wall 4b and moves to the condensate accumulation space 304.

[0132] In this modified example, the end face 307a1 of the inflow pipe 307a is formed on a different surface from the inner wall surface 4b1, so the condensed water flowing down along the inner wall surface 4b1 is difficult to penetrate into the interior of the inflow pipe 307a. Therefore, the flow of the anode exhaust gas F06 can be prevented from being obstructed by the condensed water, and thus the generation of pulsations in the anode exhaust gas F06 can be suppressed.

[0133] In particular, in this modified example, the end face 307a1 of the inflow pipe 307a protrudes towards the inner side of the anode waste gas flow path 302 relative to the inner wall surface 4b1, thus more reliably preventing condensation water from seeping into the interior of the inflow pipe 307a. Therefore, it is more reliable to prevent pulsation in the anode waste gas F06.

[0134] Figure 4This is a cross-sectional view showing the anode waste gas flow path inlet and its surrounding structure in the steam generator according to variations 1-2 of this embodiment. Figure 4 As shown, the end face 307a1 of the inflow pipe 307a is formed at an angle relative to the pipe axis of the inflow pipe 307a, except that it is formed on a surface different from the inner wall surface 4b1. The end face 307a1 is inclined relative to the inner wall surface 4b1 in such a way that the higher it is, the further away it is from the inner wall surface 4b1. Therefore, in this modified example, compared with the structure of modified example 1-1, condensate is less likely to penetrate into the interior of the inflow pipe 307a. Therefore, according to this modified example, the flow of anode exhaust gas F06 can be more reliably prevented from being obstructed by condensate, and thus the generation of pulsations in the anode exhaust gas F06 can be more reliably prevented.

[0135] Figure 5 This is a cross-sectional view showing the anode waste gas flow path inlet and its surrounding structure in the steam generator according to variations 1-3 of this embodiment. Figure 5 As shown, in this modified example, a condensation guide plate 313 is formed above the anode waste gas flow path inlet 307 within the anode waste gas flow path 302. One end 313a of the condensation guide plate 313 engages with the inner wall surface 4b1 at a position higher than the anode waste gas flow path inlet 307. The condensation guide plate 313 is inclined such that its height decreases the further away from the inner wall surface 4b1, i.e., the closer to the other end 313b of the condensation guide plate 313. A gap is formed between the other end 313b of the condensation guide plate 313 and the partition wall 4d. The other end 313b may also engage with the partition wall 4d. In this modified example, the inflow pipe 307a and the anode waste gas flow path inlet 307 have a connection with... Figure 2 The structure shown is the same as the structure shown.

[0136] The condensed water flowing down the inner wall surface 4b1 of the outer peripheral wall 4b is guided by the condensed water guide plate 313 to the other end 313b after reaching one end 313a. The condensed water flows towards the other end 313b according to the inclination of the condensed water guide plate 313 and drips downwards from the other end 313b. The dripping condensed water is accumulated in the condensed water storage space 304. Therefore, according to this modified example, the flow of the anode exhaust gas F06 can be prevented from being obstructed by the condensed water, thus preventing pulsation in the anode exhaust gas F06.

[0137] In this modified example, at least one through hole 313c is formed in the condensation guide plate 313. Each through hole 313c extends through the condensation guide plate 313 along its thickness direction. Thus, the through hole 313c becomes part of the flow path of the anode exhaust gas F06, allowing the anode exhaust gas F06 flowing into the anode exhaust gas flow path 302 to easily flow upwards. Alternatively, if the flow path of the anode exhaust gas F06 is sufficiently ensured, the through hole 313c may not be formed in the condensation guide plate 313.

[0138] As explained above, the fuel cell system 100 according to this embodiment includes a steam generator 4, a reformer 2, a fuel cell stack 1, and an injector 9. The steam generator 4 is configured to heat circulating water F10 to generate water vapor F11. The reformer 2 is configured to react the water vapor F11 with hydrocarbons to generate hydrogen-containing reformed gas F05. The fuel cell stack 1 has an anode 1a and a cathode 1c. The fuel cell stack 1 is configured to generate electrical energy through an electrochemical reaction between the reformed gas F05 supplied to the anode 1a and the oxidant F03 supplied to the cathode 1c. The injector 9 is configured to use the water vapor F11 as a driving fluid to supply at least one of a feedstock F01 containing hydrocarbons and anode circulating gas F09 obtained by recovering a portion of the anode exhaust gas F06 discharged from the anode 1a to the reformer 2. The steam generator 4 includes: an evaporation flow path 301 through which circulating water F10 flows; an anode waste gas flow path 302, thermally connected to the evaporation flow path 301 through which anode waste gas F06 flows; and an auxiliary heating device 303 for heating the circulating water F10. The anode waste gas flow path 302 and the auxiliary heating device 303 are positioned opposite each other, sandwiching the evaporation flow path 301. Here, the reformer 2 is an example of a reforming unit. The circulating water F10 is an example of water.

[0139] According to this structure, the circulating water F10 flowing in the evaporation flow path 301 can be heated from both sides using the anode waste gas flow path 302 and the auxiliary heating device 303. Therefore, according to this embodiment, heat loss can be reduced, thus enabling a fuel cell system 100 with higher energy efficiency.

[0140] In the fuel cell system 100 of this embodiment, the evaporation flow path 301 extends at an incline relative to the vertical direction. The evaporation flow path 301 slopes downwards from the upstream side to the downstream side. According to this structure, circulating water F10 can be circulated in the evaporation flow path 301 using gravity.

[0141] In the fuel cell system 100 according to this embodiment, the anode waste gas flow path 302 extends vertically. The steam generator 4 has an outer peripheral wall 4b, an inlet pipe 307a, and an outlet pipe 308a. The outer peripheral wall 4b extends vertically and defines the anode waste gas flow path 302. The inlet pipe 307a passes through the outer peripheral wall 4b and connects to the anode waste gas flow path 302. Anode waste gas F06 flows in from the inlet pipe 307a. The outlet pipe 308a connects to the anode waste gas flow path 302 above the inlet pipe 307a. Anode waste gas F06 flows out from the outlet pipe 308a. In the anode waste gas flow path 302, a condensation water accumulation space 304 is provided below the inlet pipe 307a to accumulate condensate water. Here, the outer peripheral wall 4b is an example of a flow path wall.

[0142] Based on this structure, the blockage of the anode exhaust gas flow path 302 by condensation water can be prevented, thus suppressing the generation of pulsations in the anode exhaust gas F06.

[0143] In the fuel cell system 100 according to this embodiment, the inlet pipe 307a has an end face 307a1 facing the anode exhaust gas flow path 302. The end face 307a1 protrudes further into the anode exhaust gas flow path 302 than the inner wall face 4b1 of the outer peripheral wall 4b. According to this structure, condensation water can be prevented from entering the interior of the inlet pipe 307a, thus preventing pulsation in the anode exhaust gas F06.

[0144] In the fuel cell system 100 of this embodiment, a condensation guide plate 313 is provided above the inlet pipe 307a in the anode exhaust gas flow path 302 to guide condensation water. According to this structure, condensation water can be prevented from entering the interior of the inlet pipe 307a, thus preventing pulsation in the anode exhaust gas F06.

[0145] In the fuel cell system 100 according to this embodiment, the auxiliary heating device 303 includes an electric heater. With this structure, the output of the auxiliary heating device 303 can be easily adjusted.

[0146] The fuel cell system 100 according to this embodiment also includes an anode exhaust gas temperature sensor 21 for detecting the temperature of the anode exhaust gas F06 and a control unit 90. The control unit 90 controls the auxiliary heating device 303 according to the temperature of the anode exhaust gas F06.

[0147] According to this structure, even if the heat energy that can be obtained from the anode exhaust gas F06 is insufficient relative to the heat energy required as the heat of vaporization of the circulating water F10, the heat energy can be supplemented by the auxiliary heating device 303.

[0148] The fuel cell system 100 according to this embodiment also includes a water vapor temperature sensor 20 for detecting the temperature of water vapor F11 and a control unit 90. The control unit 90 controls the auxiliary heating device 303 according to the temperature of water vapor F11.

[0149] According to this structure, even if the heat energy obtained from the anode exhaust gas F06 is insufficient relative to the heat energy required as the heat of vaporization of the circulating water F10, the heat energy can be supplemented by the auxiliary heating device 303.

[0150] Implementation method 2.

[0151] This describes the fuel cell system involved in Implementation Method 2. Figure 6 This is a system diagram showing the structure of the fuel cell system involved in this embodiment. Figure 7 This is a cross-sectional view showing the internal structure of the steam generator in the fuel cell system according to this embodiment. This embodiment differs from Embodiment 1 in that the auxiliary heating device 303 includes an auxiliary burner 50 and a combustion exhaust gas path 314. Furthermore, components having the same functions and effects as those in Embodiment 1 are given the same reference numerals and their descriptions are omitted.

[0152] like Figure 6 as well as Figure 7 As shown, an auxiliary burner 50 is provided on the upper part of the steam generator 4. The auxiliary burner 50 is part of the auxiliary heating device 303. The auxiliary burner 50 is disposed on the central axis 4a of the steam generator 4. The auxiliary burner 50 sandwiches the evaporation flow path 301 and is opposite to the anode waste gas flow path 302.

[0153] The auxiliary combustion fuel system 216 branches into auxiliary combustion fuel systems 217 and 218. Auxiliary combustion fuel system 217 is connected to burner 3. Auxiliary combustion fuel system 218 is connected to auxiliary burner 50. Auxiliary combustion fuel F16 flowing in auxiliary combustion fuel system 216 is split into auxiliary combustion fuel F17 and auxiliary combustion fuel F18. Auxiliary combustion fuel F17 flows through auxiliary combustion fuel system 217 and is supplied to burner 3. Auxiliary combustion fuel F18 flows through auxiliary combustion fuel system 218 and is supplied to auxiliary burner 50.

[0154] A combustion exhaust gas flow path 314 is provided between the auxiliary burner 50 and the exterior of the steam generator 4. The combustion exhaust gas flow path 314 is located further inward than the inner circumference of the inner circumference space 42. The combustion exhaust gas flow path 314 and the inner circumference space 42 are divided by a partition wall 315. The partition wall 315 is formed in a cylindrical shape centered on the central axis 4a. The combustion exhaust gas flow path 314 is thermally connected to the evaporation flow path 301 via the partition wall 315, the heat transfer promoting component 306, and the heat transfer tube 301a.

[0155] The combustion exhaust gas flow path 314 forms part of the auxiliary heating device 303. The combustion exhaust gas flow path 314 is positioned opposite the evaporation flow path 301 and the anode exhaust gas flow path 302.

[0156] In the auxiliary burner 50, auxiliary combustion fuel F18 and combustion-supporting gases such as air are ignited and burned by an igniter, producing high-temperature combustion exhaust gas. This high-temperature combustion exhaust gas passes through the combustion exhaust gas flow path 314, providing heat energy to the circulating water F10 flowing in the evaporation flow path 301. After providing heat energy to the circulating water F10, the combustion exhaust gas is discharged to the outside of the steam generator 4. The heat of the combustion exhaust gas is controlled by adjusting the flow rate of the auxiliary combustion fuel F18. Other operations are the same as in Embodiment 1.

[0157] Regarding the supply of combustion-supporting gas to the auxiliary burner 50, the auxiliary burner 50 can also be configured to introduce air into the atmosphere via natural intake. In this case, although it is difficult to change the combustion air ratio, the structure of the auxiliary burner 50 becomes simplified. Alternatively, air can be supplied to the auxiliary burner 50 via a separately provided air supply system. In this case, any combustion air ratio can be obtained by controlling the flow ratio of the auxiliary combustion fuel F18 and air. As a result, the temperature of the adiabatic flame can be controlled, and therefore the amount of heat energy moving to the circulating water F10 can be controlled more reliably.

[0158] According to this embodiment, in addition to the effects obtainable by embodiment 1, the following effects are also obtained. That is, in this embodiment, an auxiliary burner 50 is used in the auxiliary heating device 303, so the heat energy required for the steam generator 4 can be generated using the raw material F00 required for the fuel cell stack 1. Therefore, the fuel cell system 100 can be made more efficient.

[0159] Furthermore, in this embodiment, an auxiliary burner 50 is used in the auxiliary heating device 303, so compared to a structure that uses an electric heater in the auxiliary heating device 303, the power consumption during startup of the fuel cell system 100 is particularly suppressed. Therefore, the fuel cell system 100 can also be used as an emergency power source. Moreover, the operation of the fuel cell system 100 during startup will be described in Embodiment 3 below.

[0160] As explained above, in the fuel cell system 100 according to this embodiment, the auxiliary heating device 303 includes an auxiliary burner 50 and a combustion exhaust gas flow path 314 through which combustion exhaust gas generated by the auxiliary burner 50 flows. With this structure, power consumption in the auxiliary heating device 303 can be suppressed.

[0161] Implementation method 3.

[0162] This describes the fuel cell system and its operation method according to Embodiment 3. This embodiment mainly relates to the operation of the fuel cell system 100 during startup. Figure 8 This is a system diagram showing the structure of the fuel cell system involved in this embodiment.

[0163] like Figure 8 As shown, a stack temperature sensor 22 is installed in the fuel cell stack 1. The stack temperature sensor 22 is configured to detect the representative temperature of the fuel cell stack 1. A reformer temperature sensor 24 is installed in the reformer 2. The reformer temperature sensor 24 is configured to detect the representative temperature of the reformer 2. Other structures are similar to those shown. Figure 1 as well as Figure 2 The structure of Embodiment 1 shown is the same.

[0164] This describes the operation of the fuel cell system 100 during startup, controlled by the control unit 90. First, oxidant F03 discharged from the blower 18 flows through the oxidant system 203, passes through the oxidant heat exchanger 7 and the cathode 1c, and is supplied to the burner 3 as cathode exhaust gas F04. Additionally, a portion of the feedstock F00 flows through the auxiliary combustion fuel system 216 and is supplied to the burner 3 as auxiliary combustion fuel F16. In the burner 3, the cathode exhaust gas F04 and the auxiliary combustion fuel F16 are ignited and burned by an igniter, producing combustion gases.

[0165] The combustion gases generated by the burner 3 heat up the reformer 2 and the oxidant heat exchanger 7, and are discharged as combustion exhaust gas F15 through the combustion exhaust gas system 215. The oxidant FO3 heated in the oxidant heat exchanger 7 is supplied to the cathode 1c, and the sensible heat of the oxidant FO3 itself heats up the fuel cell stack 1.

[0166] In parallel with the above process, power is supplied to the auxiliary heating device 303. Here, the auxiliary heating device 303 in this embodiment is assumed to be an electric heater. By energizing the auxiliary heating device 303, the steam generator 4 heats up.

[0167] When the temperatures of the fuel cell stack 1 and the reformer 2 rise to a temperature at which water vapor does not condense, for example, 150°C, the water pump 8 is started to supply circulating water F10 to the steam generator 4. The circulating water F10 flows from top to bottom in the evaporation path 301 using the discharge pressure of the water pump 8 and gravity. The circulating water F10 flowing in the evaporation path 301 absorbs heat from the auxiliary heating device 303 and evaporates into water vapor F11. The water vapor F11 is then supplied to the reformer 2 and the anode 1a via the injector 9 as fuel gas FO2 during startup.

[0168] The anode exhaust gas F06 discharged from anode 1a flows from bottom to top in the anode exhaust gas flow path 302 of steam generator 4 and flows out from the anode exhaust gas flow path outlet 308.

[0169] During the heating process of the steam generator 4, the anode exhaust gas F06 is in a state rich in water vapor. When a low-temperature section exists in the anode exhaust gas flow path 302, the water vapor in the anode exhaust gas F06 condenses. However, even when water vapor in the anode exhaust gas F06 condenses, the condensate is accumulated in the condensate storage space 304 located at the bottom of the anode exhaust gas flow path 302 and discharged via the condensate discharge pipe 305.

[0170] Furthermore, when the temperature of reformer 2 rises to a temperature sufficient to produce hydrogen through the reforming reaction generated by the reforming catalyst packed inside, such as 450°C, feedstock F01 is supplied using feedstock system 200 and reforming feedstock system 201. The flow rate of feedstock F01 at the start of supply is controlled considering the S / C ratio. The S / C value under rated operating conditions is, for example, in the range of 2.5 to 3.5. In contrast, the flow rate of feedstock F01 at the start of supply is set such that the S / C value is greater than the S / C value under rated operating conditions. During startup, a transitional temperature distribution is formed in reformer 2. To prevent carbon (C) precipitation in reformer 2 due to this temperature distribution, the flow rate of feedstock F01 at the start of supply is set with an S / C value of, for example, around 8.0. Subsequently, the flow rates of steam F11 and feedstock F01 are appropriately controlled.

[0171] Feedstock F01 is supplied before the temperature of the fuel cell stack 1 rises to the temperature at which the oxidation reaction of the components constituting the fuel cell stack 1 takes place, for example, 300°C. That is, feedstock F01 is supplied when the temperature of the reformer 2 is above 450°C and the temperature of the fuel cell stack 1 is below 300°C. To achieve this temperature condition, the combustion temperature of the burner 3 and the input energy of the burner 3 are controlled by adjusting the flow rate of the auxiliary combustion fuel F16 supplied to the burner 3 and the flow rate of the oxidant F03 supplied to the burner 3 as cathode exhaust gas F04.

[0172] The flow rates of the oxidant F03, feedstock F01, and water vapor F11, which are gases required for the battery reaction, are each set to predetermined flow rates. The fuel cell stack 1 is heated to a temperature capable of generating electricity, for example, 600°C. After the temperature of the fuel cell stack 1 reaches the temperature capable of generating electricity, the flow rates of the oxidant F03, feedstock F01, and water vapor F11 are controlled to predetermined flow rates. Simultaneously, electricity generation begins in the fuel cell stack 1 using methods such as current control or electrical control, and the fuel cell system 100 transitions to a predetermined rated operating state.

[0173] As the fuel cell stack 1 heats up, the flow rate of the anode exhaust gas F06 increases, and the temperature of the anode exhaust gas F06 rises. Consequently, the enthalpy of the anode exhaust gas F06 increases. Therefore, the thermal energy supplied from the anode exhaust gas F06 to the circulating water F10 in the steam generator 4 increases.

[0174] The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode exhaust gas F06 detected by the anode exhaust gas temperature sensor 21. Specifically, the control unit 90 controls the auxiliary heating device 303 in a manner that the heat generated by the auxiliary heating device 303 decreases as the temperature of the anode exhaust gas F06 rises. Therefore, as the temperature of the anode exhaust gas F06 rises, the heat generated by the auxiliary heating device 303 decreases. This prevents the supply of more heat energy than necessary to the circulating water F10. In this way, the heat energy supplied to the circulating water F10 is adjusted.

[0175] Alternatively, the control unit 90 can control the auxiliary heating device 303 based on the temperature of the water vapor F11 detected by the water vapor temperature sensor 20. Specifically, the control unit 90 controls the auxiliary heating device 303 in such a way that the higher the temperature of the water vapor F11, the less heat is generated by the auxiliary heating device 303. In this way, it is also possible to prevent the supply of more than necessary heat energy to the circulating water F10.

[0176] The anode exhaust gas F06 after passing through the steam generator 4 then provides heat energy to the cooling medium F14 flowing in the heat recovery system 214 in the heat recovery cooler 10. As a result, the temperature of the anode exhaust gas F06 flowing into the water separator 5 is reduced to a predetermined temperature below the dew point.

[0177] In water separator 5, the moisture contained in anode exhaust gas F06 is liquefied based on the saturated vapor pressure at the temperature of the anode exhaust gas F06. The liquefied moisture forms water droplets and separates from the anode exhaust gas F06, accumulating in the lower part of water separator 5.

[0178] On the other hand, the anode exhaust gas F06, after moisture removal by the water separator 5, flows out of the water separator 5 as the anode recovery gas F07, passes through the anode recovery gas system 207, and reaches the recovery branch 221. In the recovery branch 221, the anode recovery gas F07 is divided into recirculated combustion gas F08, which flows through the recirculated combustion gas system 208, and anode recirculated gas F09, which flows through the anode recirculated gas system 209. The recirculated combustion gas F08 is supplied to the burner 3 through the recirculated combustion gas system 208.

[0179] When the fuel cell system 100 starts up, in the burner 3, auxiliary combustion fuel F16 supplied by the auxiliary combustion fuel system 216 and cathode exhaust gas F04 supplied by the cathode exhaust gas system 204 are mainly combusted. When the feedstock F01 is supplied and its flow rate increases, the flow rate of recirculated combustion gas F08 increases, thus increasing the amount of combustion fuel supplied to the burner 3. Therefore, after the feedstock F01 is supplied, the flow rate of auxiliary combustion fuel F16, the flow distribution ratio of recirculated combustion gas F08 in the recovery branch 221, and the flow rate of oxidant F03 are appropriately controlled.

[0180] In this embodiment, the anode recovery gas F07 flowing in the anode recovery gas system 207 is split into recirculated combustion gas F08 and anode recirculated gas F09 in the recovery branch 221, but it is not limited to this. For example, when the fuel cell system 100 is started, the entire amount of anode recovery gas F07 flowing in the anode recovery gas system 207 may be used as recirculated combustion gas F08 to flow in the recirculated combustion gas system 208.

[0181] In this embodiment, the auxiliary heating device 303 is controlled by the control unit 90 to supply water vapor F11 to the reformer 2 and the anode 1a at a specific period. This specific period is the time between when the temperature of the fuel cell stack 1 rises to a first temperature and before it rises to a second temperature. The first temperature is the temperature at which water vapor does not condense inside the fuel cell stack 1, for example, 150°C. The second temperature is the temperature at which the oxidation reaction of the components constituting the fuel cell stack 1 takes place, for example, 300°C.

[0182] In this embodiment, when the fuel cell system 100 starts up, the auxiliary heating device 303 provides the heat energy required to generate the necessary flow rate of water vapor F11 to the evaporation flow path 301. As the fuel cell system 100 heats up, the heat energy provided to the evaporation flow path 301 from the anode exhaust gas path 302 increases. Therefore, under the control of the control unit 90, the heat output of the auxiliary heating device 303 decreases. Thus, the heat energy required to generate water vapor F11 is provided to the evaporation flow path 301 from both the auxiliary heating device 303 and the anode exhaust gas path 302. When the fuel cell system 100 reaches its rated operating state, the heat energy provided to the evaporation flow path 301 from the anode exhaust gas path 302 further increases. Therefore, under the control of the control unit 90, the auxiliary heating device 303 stops. Thus, the heat energy required to generate water vapor F11 is provided to the evaporation flow path 301 from the anode exhaust gas path 302.

[0183] Thus, in this embodiment, the fuel cell system 100 can be continuously heated while simultaneously forming the necessary gas atmosphere during startup. Therefore, according to this embodiment, stable water vapor generation with minimal pulsation can be achieved based on the heating conditions of the fuel cell system 100. Furthermore, according to this embodiment, a fuel cell system 100 with high degree of freedom and high energy efficiency can be realized.

[0184] Figure 9 This is a cross-sectional view showing the internal structure of the steam generator according to Variation 3-1 of this embodiment. Figure 9 As shown, the steam generator 4 has a first flow path component 316 and a second flow path component 317.

[0185] The first flow path component 316 is formed in a cylindrical shape centered on the central axis 4a. A groove 316a is formed on the outer peripheral surface of the first flow path component 316. The groove 316a extends in a spiral shape with the central axis 4a as the spiral axis.

[0186] The second flow path component 317 is formed in a cylindrical shape centered on the central axis 4a. The second flow path component 317 has an inner diameter equal to the outer diameter of the first flow path component 316. The inner circumferential surface of the second flow path component 317 is engaged with the outer circumferential surface of the first flow path component 316.

[0187] An evaporation flow path 301 is formed inside the tank 316a. An evaporation flow path inlet 301b is provided at the upper end of the evaporation flow path 301. An evaporation flow path outlet 301c is provided at the lower end of the evaporation flow path 301.

[0188] The first flow path component 316 and the second flow path component 317 are disposed further outward than the combustion exhaust gas flow path 314 and further inward than the anode exhaust gas flow path 302. The inner peripheral surface of the first flow path component 316 faces the combustion exhaust gas flow path 314. The evaporation flow path 301 is thermally connected to the combustion exhaust gas flow path 314 via the first flow path component 316. The outer peripheral surface of the second flow path component 317 faces the anode exhaust gas flow path 302. The evaporation flow path 301 is thermally connected to the anode exhaust gas flow path 302 via the second flow path component 317.

[0189] Combustion exhaust gas flowing in combustion exhaust gas path 314 provides heat energy to circulating water F10 flowing in evaporation path 301 via first flow path component 316. In addition, anode exhaust gas F06 flowing in anode exhaust gas path 302 provides heat energy to circulating water F10 via second flow path component 317.

[0190] According to this embodiment, both the combustion exhaust gas flowing in the combustion exhaust gas path 314 and the anode exhaust gas F06 flowing in the anode exhaust gas path 302 transfer heat energy to the circulating water F10 via a single component. As a result, the thermal resistance is reduced in any heat transfer path, thus improving the heat transfer characteristics of the steam generator 4. Therefore, a compact and highly responsive steam generator 4 can be realized, enabling a high-performance fuel cell system 100.

[0191] As explained above, the fuel cell system 100 according to this embodiment also includes a stack temperature sensor 22 for detecting the temperature of the fuel cell stack 1 and a control unit 90. When starting the fuel cell system 100, the control unit 90 controls the auxiliary heating device 303 to start supplying steam F11 to the reformer 2 during a specific period. The specific period is after the temperature of the fuel cell stack 1 rises to a first temperature and before the temperature of the fuel cell stack 1 rises to a second temperature higher than the first temperature.

[0192] In the fuel cell system 100 of this embodiment, the first temperature is 150°C and the second temperature is 300°C.

[0193] According to the above structure, condensation can be prevented from forming inside the fuel cell stack 1. Furthermore, according to the above structure, water vapor F11 can be supplied before the oxidation reaction of the components constituting the fuel cell stack 1 takes place.

[0194] Implementation method 4.

[0195] This describes the fuel cell system and its operation method according to Embodiment 4. This embodiment mainly relates to the operation of the fuel cell system 100 when it is stopped. The structure of the fuel cell system 100 according to this embodiment is similar to... Figure 8 The fuel cell system 100 shown in Embodiment 3 has the same structure. That is, the fuel cell system 100 in this embodiment has the same stack temperature sensor 22 and reformer temperature sensor 24 as the fuel cell system 100 in Embodiment 3.

[0196] This describes the operation of the fuel cell system 100 under the control of the control unit 90 when the fuel cell system 100 is stopped. When the fuel cell system 100 is stopped, the control unit 90 reduces the output of the fuel cell stack 1, stopping the power generation of the fuel cell stack 1. Additionally, in parallel with the reduction of the output of the fuel cell stack 1, or after the power generation of the fuel cell stack 1 stops, the control unit 90 reduces the supply of feedstock F01, stopping the supply of feedstock F01. The control unit 90 activates the auxiliary heating device 303 simultaneously with the reduction of the feedstock F01 supply. Here, the auxiliary heating device 303 in this embodiment is assumed to be an electric heater. When the flow rate of feedstock F01 is less than a threshold, the control unit 90 completely closes the recirculated combustion gas flow regulating valve 311. This cuts off the supply of recirculated combustion gas F08 to the burner 3, stopping combustion in the burner 3.

[0197] Pump 8 remains operational. Circulating water F10 is supplied to the evaporation path 301 of the steam generator 4 via pump 8. Anode exhaust gas F06 is supplied to the anode exhaust gas path 302 of the steam generator 4 via the anode exhaust gas path 302. Heat energy is provided to the circulating water F10 in the evaporation path 301 from the anode exhaust gas path 302 and the auxiliary heating device 303. Thus, water vapor F11 is stably generated in the steam generator 4.

[0198] At this time, the fuel gas F02 flowing in the fuel gas system 202 consists of water vapor F11 and anode recirculation gas F09. This fuel gas F02 undergoes a slight CH4 generation reaction in the reformer 2 and fuel cell stack 1 as the temperature decreases, but most of the H2 component remains unchanged and becomes anode exhaust gas F06, which is supplied to the steam generator 4. The anode exhaust gas F06 flowing out of the steam generator 4 is cooled in the heat recovery cooler 10 and flows into the water separator 5. In the water separator 5, the water vapor in the anode exhaust gas F06 condenses into condensate, separating from the gaseous components of the anode exhaust gas F06.

[0199] The gas components of the anode exhaust gas F06 flow out from the water separator 5 and flow into the anode recovery gas system 207 as the anode recovery gas F07. The recirculation combustion gas flow regulating valve 311 is completely closed, so the entire amount of the anode recovery gas F07 becomes the anode circulating gas F09 as is.

[0200] In injector 9, water vapor F11 generated by steam generator 4 becomes the driving fluid, attracting anode circulating gas F09. Water vapor F11 and anode circulating gas F09 flow out of injector 9 as fuel gas F02, and are supplied to reformer 2 and fuel cell stack 1 through fuel gas system 202. That is, in fuel cell system 100 at this point in time, the gas circulation of the anode system occurs simultaneously with the repeated generation, supply, and condensation of water vapor.

[0201] Based on conditions such as the cooling rate of fuel cell stack 1 and reformer 2, the flow rate of oxidant FO3 supplied to cathode 1c is set to an appropriate flow rate. Through the movement of sensible heat caused by the flow of oxidant FO3, the temperatures of both fuel cell stack 1 and reformer 2 decrease.

[0202] After the temperature of fuel cell stack 1 drops to a temperature at which anode 1a does not oxidize and the temperature of reformer 2 drops to a temperature at which reforming catalyst does not oxidize, the anode system is cleaned using oxidant FO3 or the closed-loop anode system is opened to the atmosphere. The temperature of fuel cell stack 1 is obtained based on the detection signal from stack temperature sensor 22. The temperature of reformer 2 is obtained based on the detection signal from reformer temperature sensor 24. Oxidant FO3 is introduced into fuel gas system 202 under the control of control unit 90, thereby cleaning the anode system. Furthermore, in Figure 8 The path for introducing oxidant FO3 into the fuel gas system 202 is not shown. Under the control of the control unit 90, the recirculated combustion gas flow regulating valve 311 is opened, thereby opening the anode system to the atmosphere in a closed loop.

[0203] Provided that the feedstock F00 does not adversely affect the reforming catalyst of reformer 2 or the anode 1a, the feedstock F00 can also be introduced into the fuel gas system 202 for cleaning. Alternatively, the anode system can be cleaned with oxidant F03 or feedstock F00 and then disconnected from the atmosphere to form a closed loop.

[0204] At this point, the control unit 90 stops the auxiliary heating device 303 and the water pump 8. This stops the generation of water vapor. Through the above process, the fuel cell system 100 stops.

[0205] In this embodiment, when the fuel cell system 100 is stopped, it is not necessary to start the burner 3; instead, the necessary flow rate of water vapor can be generated using the steam generator 4. The generated water vapor circulates in the anode system under the driving force of the injector 9. That is, the water vapor becomes the medium, substantially maintaining the gas composition immediately after the fuel cell system 100 is stopped. Therefore, the reformer 2 and the fuel cell stack 1 can be cooled in a reducing atmosphere using the fuel gas F02 and the reforming gas F05. As a result, the gas atmosphere in each system of the fuel cell system 100 can be maintained as is, thereby enabling efficient cooling of each component of the fuel cell system 100.

[0206] As explained above, the fuel cell system 100 according to this embodiment further includes a water separator 5, a recovery branch 221, and a recirculated combustion gas flow rate regulating valve 311. The water separator 5 is configured to separate anode exhaust gas F06 into condensate and anode recovery gas F07. The recovery branch 221 is configured to divert the anode recovery gas F07 into recirculated combustion gas F08, which is supplied to the burner 3, which is thermally connected to the reformer 2, and anode recirculated gas F09. The recirculated combustion gas flow rate regulating valve 311 is configured to cut off the supply of recirculated combustion gas F08 to the burner 3. When the fuel cell system 100 is stopped, the control unit 90 stops generating electrical energy in the fuel cell stack 1, closes the recirculated combustion gas flow rate regulating valve 311, and controls the auxiliary heating device 303 to ensure the flow rate of water vapor F11, thereby cooling the reformer 2 and the fuel cell stack 1. Here, the recirculated combustion gas flow rate regulating valve 311 is an example of a cut-off mechanism.

[0207] According to this structure, the gas atmosphere in each system of the fuel cell system 100 can be maintained as is, thereby enabling efficient cooling of each device in the fuel cell system 100.

[0208] The fuel cell system 100 according to this embodiment also includes an anode exhaust gas temperature sensor 21 for detecting the temperature of the anode exhaust gas F06. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode exhaust gas F06. With this structure, it is possible to prevent the supply of more than necessary heat energy to the circulating water F10.

[0209] The fuel cell system 100 according to this embodiment also includes a water vapor temperature sensor 20 for detecting the temperature of water vapor F11. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the water vapor F11. With this structure, it is possible to prevent the supply of more than necessary heat energy to the circulating water F10.

[0210] In the fuel cell system 100 according to this embodiment, the control unit 90 may also open the recirculated combustion gas flow regulating valve 311 after the temperature of the fuel cell stack 1 drops to the second temperature mentioned above. In addition, the control unit 90 may also introduce oxidant FO3 or feedstock FO0 into the anode system, such as the fuel gas system 202, through the reformer 2 and the anode 1a after the temperature of the fuel cell stack 1 drops to the second temperature mentioned above.

[0211] Implementation method 5.

[0212] This describes the fuel cell system and its operation method involved in Implementation Method 5. Figure 10 This is a system diagram showing the structure of the fuel cell system involved in this embodiment.

[0213] like Figure 10As shown, a circulating heat exchanger 23 is provided in the fuel cell stack 1. The circulating heat exchanger 23 is configured between the steam generator 4 of the anode exhaust gas system 206 and the heat recovery cooler 10, and between the recovery branch 221 of the anode circulating gas system 209 and the injector 9. Other structures are similar to... Figure 6 The structure of Embodiment 2 shown is the same.

[0214] In the circulating heat exchanger 23, heat exchange occurs between the anode exhaust gas F06 flowing in the anode exhaust gas system 206 and the anode circulating gas F09 flowing in the anode circulating gas system 209. The anode circulating gas F09 gains heat energy from the anode exhaust gas F06 flowing out of the steam generator 4 in the circulating heat exchanger 23. As a result, the temperature of the anode circulating gas F09 rises.

[0215] In this embodiment, the anode recovery gas F07 immediately after exiting the water separator 5 is saturated vapor, while the anode recirculation gas F09 after passing through the recirculation heat exchanger 23 becomes superheated vapor due to the heat energy obtained from the anode exhaust gas F06. Therefore, condensation can be prevented in the piping from the recirculation heat exchanger 23 to the ejector 9 in the anode recirculation gas system 209. Consequently, pulsation of the anode recirculation gas F09 flowing in the anode recirculation gas system 209 is suppressed, enabling a stable fuel cell system 100.

[0216] In all the above embodiments, each structural component of the fuel cell system 100 is surrounded by heat-insulating material. This suppresses heat loss from each structural component to the outside.

[0217] In all the above embodiments, it is described that the entire amount of cathode exhaust gas FO4 is supplied to the burner 3 to become combustion-supporting gas, but this is not a limitation. Alternatively, the cathode exhaust gas FO4 may be branched upstream of the burner 3, supplying a portion of the cathode exhaust gas FO4 to the burner 3, with the remaining cathode exhaust gas heating at least one of the reformer 2 or the oxidant heat exchanger 7. Furthermore, the cathode exhaust gas FO4 may be branched inside the burner 3, dividing it into a gas that burns together with the recirculated combustion gas F08 or the auxiliary combustion fuel F16, and a non-combustible gas. Furthermore, they may be combined. This allows for combustion conditions at a suitable air-to-fuel ratio.

[0218] In all the above embodiments, the timing of the auxiliary heating device 303 starting operation and the timing of the water pump 8 operation are not limited to those described above. For example, the auxiliary heating device 303 may be activated based on the respective heat capacities of the fuel cell stack 1, the reformer 2, and the steam generator 4, and the respective temperature rise states of the reformer 2 and the fuel cell stack 1 using the burner 3.

[0219] In all the above embodiments, water can be used as the cooling medium F14 circulating in the heat recovery system 214. However, as the cooling medium F14, it can also be a refrigerant or a heat storage material, as long as it is an example that can extract heat energy from the anode exhaust gas F06.

[0220] In all the embodiments described above, the water treatment device 14 can be, for example, an ion exchange device utilizing ion exchange resin. However, the water treatment device 14 can utilize a transmissive membrane, or it can be simply a filter depending on the necessary specifications. Furthermore, if it is not necessary, the water treatment device 14 may not be provided.

[0221] In all the above embodiments, the evaporation flow path 301 is formed in a spiral shape with intervals of one revolution. However, the evaporation flow path 301 can also be formed in a tightly closed spiral shape without gaps. In this case, the heat transfer area per unit length in the axial direction of the steam generator 4 becomes larger, so the heat transfer performance of the steam generator 4 is improved.

[0222] In all the above embodiments, the condensation temperature of the anode exhaust gas F06 in the water separator 5 is approximately 60°C. However, the condensation temperature of the anode exhaust gas F06 in the water separator 5 is not limited to this and can be other temperatures. However, the condensation temperature of the anode exhaust gas F06 in the water separator 5 is preferably set such that the hourly condensate flow rate of the anode exhaust gas F06 in the water separator 5 is equal to or greater than the flow rate of the circulating water F10. In this case, after the fuel cell system 100 is started, it is not necessary to replenish water to the fuel cell system 100 from the outside. Therefore, the fuel cell system 100 can be water-independent, which can reduce the operating cost of the fuel cell system 100.

[0223] The above-described embodiments and variations can be combined and implemented together.

Claims

1. A fuel cell system comprising: A steam generator heats water to produce steam. The reforming section reacts the water vapor with hydrocarbons to generate hydrogen-containing reformed gas; A fuel cell stack, having an anode and a cathode, generates electrical energy through an electrochemical reaction of a reformed gas supplied to the anode and an oxidant supplied to the cathode; and An injector, using the water vapor as a driving fluid, supplies at least one of the feedstock containing the hydrocarbons and the anode recycle gas obtained by recovering a portion of the anode exhaust gas discharged from the anode to the reforming unit. The steam generator has: Evaporation flow path, through which the water flows; The anode waste gas flow path is thermally connected to the evaporation flow path, allowing the anode waste gas to circulate; and An auxiliary heating device heats the water. The inlet of the evaporation flow path where water flows in and the outlet of the evaporation flow path where water vapor flows out are positioned vertically. The anode waste gas inlet and the anode waste gas outlet are arranged vertically in the vertical direction. The anode waste gas flow path and the auxiliary heating device are positioned opposite each other, sandwiching the evaporation flow path.

2. The fuel cell system according to claim 1, wherein, The evaporation flow path extends at an angle relative to the vertical direction. In the evaporation flow path, a downward slope is generated from the upstream side to the downstream side.

3. The fuel cell system according to claim 1, wherein, The anode waste gas flow path extends in the vertical direction. The steam generator has: The flow path wall extends along the vertical direction, defining the anode waste gas flow path; An inflow pipe is inserted through the flow path wall and connected to the anode waste gas flow path, through which the anode waste gas flows in; as well as The outflow pipe is connected to the anode waste gas flow path above the inflow pipe, through which the anode waste gas flows out. In the anode waste gas flow path, a condensate storage space is provided below the inflow pipe to collect condensate.

4. The fuel cell system according to claim 3, wherein, The inflow pipe has an end face facing the anode waste gas flow path. The end face protrudes further into the inner side of the anode waste gas flow path than the inner wall surface of the flow path wall.

5. The fuel cell system according to claim 3, wherein, In the anode waste gas flow path, above the inflow pipe, there is a condensation guide plate to guide the condensation water.

6. The fuel cell system according to any one of claims 1 to 5, wherein, The auxiliary heating device includes an electric heater.

7. The fuel cell system according to any one of claims 1 to 5, wherein, The auxiliary heating device has an auxiliary burner and a combustion exhaust gas flow path through which the combustion exhaust gas generated by the auxiliary burner flows.

8. The fuel cell system according to any one of claims 1 to 5, wherein, It also has: An anode exhaust gas temperature sensor detects the temperature of the anode exhaust gas; and Control Department The control unit controls the auxiliary heating device based on the temperature of the anode exhaust gas.

9. The fuel cell system according to any one of claims 1 to 5, wherein, It also has: A water vapor temperature sensor detects the temperature of the water vapor; and Control Department The control unit controls the auxiliary heating device based on the temperature of the water vapor.

10. The fuel cell system according to claim 8, wherein, It also includes a stack temperature sensor for detecting the temperature of the fuel cell stack. The control unit controls the auxiliary heating device to begin supplying steam to the reforming unit at a specific time when the fuel cell system is started. The specific period is after the temperature of the fuel cell stack rises to a first temperature and before the temperature of the fuel cell stack rises to a second temperature that is higher than the first temperature.

11. The fuel cell system according to any one of claims 1 to 5, wherein, It also has: A stack temperature sensor detects the temperature of the fuel cell stack; and Control Department The control unit controls the auxiliary heating device to begin supplying steam to the reforming unit at a specific time when the fuel cell system is started. The specific period is after the temperature of the fuel cell stack rises to a first temperature and before the temperature of the fuel cell stack rises to a second temperature that is higher than the first temperature.

12. The fuel cell system according to claim 10, wherein, The first temperature is 150°C, and the second temperature is 300°C.

13. The fuel cell system according to claim 10 or 12, wherein, It also has: A water separator separates the anode waste gas into condensate and anode recovery gas. The recovery branch section splits the anode recovered gas into recirculated combustion gas supplied to a burner thermally connected to the reforming section and the anode recirculated gas; and The cut-off section cuts off the supply of the recirculated combustion gas to the burner. When the fuel cell system is stopped, the control unit stops generating electrical energy in the fuel cell stack, shuts off the cut-off unit, controls the auxiliary heating device to ensure the flow rate of water vapor, and cools down the reforming unit and the fuel cell stack.

14. The fuel cell system according to claim 13, wherein, The control unit opens the cut-off section after the temperature of the fuel cell stack drops to the second temperature.

15. The fuel cell system according to claim 13, wherein, After the temperature of the fuel cell stack decreases to the second temperature, the control unit introduces the oxidant or the raw material into the anode system through the reforming unit and the anode.

16. A fuel cell system comprising: A steam generator heats water to produce steam. The reforming section reacts the water vapor with hydrocarbons to generate hydrogen-containing reformed gas; A fuel cell stack having an anode and a cathode generates electrical energy through an electrochemical reaction of a reforming gas supplied to the anode and an oxidant supplied to the cathode. as well as An injector, using the water vapor as a driving fluid, supplies at least one of the feedstock containing the hydrocarbons and the anode recycle gas obtained by recovering a portion of the anode exhaust gas discharged from the anode to the reforming unit. The steam generator has: Evaporation flow path, through which the water flows; The anode waste gas flow path is thermally connected to the evaporation flow path, allowing the anode waste gas to circulate; and An auxiliary heating device heats the water. The anode waste gas flow path and the auxiliary heating device are positioned opposite each other, sandwiching the evaporation flow path. The anode waste gas flow path extends in the vertical direction. The steam generator has: The flow path wall extends along the vertical direction, defining the anode waste gas flow path; An inflow pipe is inserted through the flow path wall and connected to the anode waste gas flow path, through which the anode waste gas flows in; as well as The outflow pipe is connected to the anode waste gas flow path above the inflow pipe, through which the anode waste gas flows out. In the anode waste gas flow path, a condensate storage space is provided below the inflow pipe to collect condensate.

17. A fuel cell system comprising: A steam generator heats water to produce steam. The reforming section reacts the water vapor with hydrocarbons to generate hydrogen-containing reformed gas; A fuel cell stack having an anode and a cathode generates electrical energy through an electrochemical reaction of a reforming gas supplied to the anode and an oxidant supplied to the cathode. as well as An injector, using the water vapor as a driving fluid, supplies at least one of the feedstock containing the hydrocarbons and the anode recycle gas obtained by recovering a portion of the anode exhaust gas discharged from the anode to the reforming unit. A stack temperature sensor detects the temperature of the fuel cell stack. A water separator separates the anode waste gas into condensate and anode recovery gas. The recovery branch section splits the anode recovered gas into recirculated combustion gas supplied to a burner thermally connected to the reforming section and the anode recirculated gas; and The cut-off section cuts off the supply of the recirculated combustion gas to the burner; and Control Department The steam generator has: Evaporation flow path, through which the water flows; The anode waste gas flow path is thermally connected to the evaporation flow path, allowing the anode waste gas to circulate; and An auxiliary heating device heats the water. The anode waste gas flow path and the auxiliary heating device are positioned opposite each other, sandwiching the evaporation flow path. The control unit controls the auxiliary heating device to begin supplying steam to the reforming unit at a specific time when the fuel cell system is started. The specific period is after the temperature of the fuel cell stack rises to a first temperature and before the temperature of the fuel cell stack rises to a second temperature higher than the first temperature. When the fuel cell system is stopped, the control unit stops generating electrical energy in the fuel cell stack, shuts off the cut-off unit, controls the auxiliary heating device to ensure the flow rate of water vapor, and cools down the reforming unit and the fuel cell stack.

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