Fuel cell system

Abstract

A fuel cell system comprising: a reformer (2) that reacts hydrocarbons with water to generate reformed gas (F05) containing hydrogen; a fuel cell stack (1) that generates electrical energy through an electrochemical reaction of the reformed gas (F05) and an oxidant (F03); an injector that uses water vapor (F11) as a driving fluid to draw in either a feedstock (F01) containing hydrocarbons or a recycle gas (F07) recovered from the anode exhaust (F06) and supply it to the reformer (2); and a vaporizer (4) that vaporizes water to generate water vapor (F11), wherein the operating temperature of the fuel cell stack (1) is higher than the boiling point of water at the operating pressure, and water vapor (F11) is generated in the vaporizer (4) through heat exchange with the anode exhaust (F06).

Description

Technical Field

[0001] This application relates to fuel cell systems. Background Technology

[0002] Fuel cell systems are widely developed for civilian and industrial power generation due to their low environmental impact and high energy conversion efficiency. A fuel cell stack generates electricity by electrochemically reacting hydrogen-containing reformed gas (obtained from reforming hydrocarbon feedstock) with an oxidant in a state separated by an electrolyte. The remaining reformed gas discharged from the anode (anode exhaust) contains hydrogen, and depending on conditions, may also contain components such as carbon monoxide and methane that can be reused as feedstock. Therefore, by utilizing the remaining reformed gas for the reaction heat of the reformer or circulating it on the feedstock supply side, the energy inherent in the feedstock can be effectively utilized.

[0003] Therefore, it is known that a portion of the anode exhaust gas, after being dehydrated using a gas-liquid separator, is drawn in using a raw material gas pump and mixed with the raw material (for example, see Patent Document 1). Additionally, it is known that an injector, using water vapor generated from the combustion heat of the anode exhaust gas as the driving fluid, draws in the anode exhaust gas and mixes it with the raw material (for example, see Patent Document 2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-198116 (paragraphs 0051-0063) Figure 1 )

[0007] Patent Document 2: Japanese Patent Application Publication No. 7-230816 (paragraphs 0020-0024) Figure 1 ) Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, auxiliary power is required to pump the anode exhaust gas using a feedstock gas pump. Furthermore, when using water vapor generated from the combustion heat of the anode exhaust gas as the driving fluid, the combustion heat of the anode exhaust gas is wasted, reducing the utilization rate of the energy contained in the feedstock. In other words, it is difficult to achieve high-efficiency power generation by effectively utilizing the energy contained in the feedstock.

[0010] This application discloses a technique for solving the above-mentioned problems, the purpose of which is to provide a high-efficiency fuel cell system.

[0011] Methods for solving problems

[0012] The fuel cell system disclosed in this application is characterized by comprising: a reformer that reacts hydrocarbons with water to generate a reformed gas containing hydrogen; a fuel cell stack that generates electrical energy through an electrochemical reaction of the reformed gas and an oxidant separated by an anode and a cathode; an injector that uses water vapor, which is used as the water, as a driving fluid to draw in either a feedstock containing the hydrocarbons or a recycle gas recovered from the anode exhaust, and supplies it to the reformer; and a vaporizer that vaporizes water to generate the water vapor, wherein the operating temperature of the fuel cell stack is higher than the boiling point of water at the operating pressure, and the vaporizer generates the water vapor through heat exchange with the anode exhaust.

[0013] The effects of the invention

[0014] According to the fuel cell system disclosed in this application, water vapor is generated through heat exchange with the anode exhaust, thus effectively utilizing the energy of the fuel and improving efficiency. Attached Figure Description

[0015] Figure 1 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 1.

[0016] Figure 2 A flowchart illustrating the control operation of the fuel cell system according to Embodiment 1 is provided.

[0017] Figure 3 This is a block diagram illustrating the hardware configuration of the control unit or the computation execution unit for performing control in the fuel cell system according to Embodiment 1 and subsequent embodiments.

[0018] Figure 4 A flowchart illustrating the configuration of a fuel cell system according to a variation of Embodiment 1.

[0019] Figure 5 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 2.

[0020] Figure 6 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 3.

[0021] Figure 7 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 4.

[0022] Figure 8 A flowchart illustrating the configuration of a fuel cell system according to a variation of Embodiment 4.

[0023] Figure 9 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 5.

[0024] Figure 10 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 6.

[0025] Figure 11 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 7.

[0026] Figure 12 A flowchart illustrating the configuration of the fuel cell system according to Embodiment 8. Detailed Implementation

[0027] The following detailed description of each embodiment of the fuel cell system disclosed in this application is based on the accompanying drawings. It should be noted that the embodiments shown below are examples, and this application is not limited to these embodiments.

[0028] Implementation Method 1

[0029] Figures 1-3 This diagram illustrates the configuration and control operation of the fuel cell system according to Embodiment 1. Figure 1 To illustrate the schematic flowchart of the fuel cell system configuration, Figure 2 This is a flowchart illustrating the process of changing the operating mode based on fuel utilization rate during control operations. Additionally, Figure 3 This is a block diagram illustrating the hardware configuration of the control unit or the computation execution unit for performing control in the fuel cell system according to Embodiment 1 and subsequent embodiments.

[0030] Before describing the characteristic configuration of the fuel cell system of this application, a configuration and operation common to general fuel cell systems will be described using a diagram showing the configuration of the fuel cell system according to Embodiment 1. Figure 1 As shown, the fuel cell system 100 includes a reformer 2 for reforming raw materials, a fuel cell stack 1 for generating electricity by electrochemically reacting reformed gas with an oxidant, equipment for processing fluids originating from raw materials, oxidant (air), and water, and a control unit 90 for controlling each piece of equipment.

[0031] To receive the heat required for the reforming reaction, the reformer 2 is integrated with the burner 3, which burns a portion of the fuel (recycled combustion gas F08) to generate heat. Additionally, an oxidant heat exchanger 7 is integrated to heat the oxidant F03 supplied to the fuel cell stack 1. Furthermore, the fuel cell stack 1 is assembled using battery components such as flow paths and separators to form an electrochemical device consisting of an anode (negative electrode) 1a, a cathode (positive electrode) 1c, and an electrolyte 1e.

[0032] Oxidant FO3 supplied from air blower 18 flows through oxidant system 203, is heated to a temperature suitable for operation of fuel cell stack 1 via oxidant heat exchanger 7, and is then supplied to cathode 1c. The oxidant FO3 supplied to cathode 1c is configured such that, separated from reformed gas FO5 by electrolyte 1e, a portion of oxygen is consumed through an electrochemical reaction, and the consumed cathode exhaust FO4 is supplied to burner 3 via cathode exhaust system 204.

[0033] Feedstock F01, such as city gas, flows through feedstock system 201 after passing through feedstock pretreatment unit 19 to remove unwanted components such as sulfur. Then, via circulator 9, feedstock F01, together with anode circulating gas F09 (described later) and water vapor F11, is supplied as fuel gas F02 to reformer 2 via fuel gas system 202. Reforming is performed in reformer 2, and reformed gas F05, mainly composed of hydrogen, flows through reformed gas system 205 and is supplied to the anode 1a section of fuel cell stack 1.

[0034] 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 consumed anode exhaust gas F06 flows through anode exhaust system 206, is cooled by heat recovery cooler 10, and is supplied to water separator 5. The gas portion separated by water separator 5 is configured such that it flows as anode recovery gas F07 to anode recovery gas system 207, is split at recovery branch 221 into recirculated combustion gas system 208 toward burner 3, and returns to anode recirculated gas system 209 to reformer 2. On the other hand, the liquid component (water) separated by water separator 5 is returned to water treatment device 14 (described later). It should be noted that the refrigerant F14 flowing in heat recovery cooler 10 is configured to flow within heat recovery system 214.

[0035] Regarding the circulating water F10, the water recovered by the water separator 5 mentioned above is combined with the raw material water. After passing through the water treatment device 14 to remove unwanted components such as ions, it flows through the circulating water system 210 towards the gasifier 4 via the water pump 8. The water vapor F11 vaporized by the gasifier 4 flows towards the circulator 9 in the water vapor system 211, where it acts as a driving fluid, drawing in the raw material F01 and the anode circulating gas F09, and flowing to the fuel gas system 202.

[0036] Here, the raw material pretreatment device 19 is, for example, a filter or a desulfurizer. It should be noted that the raw material F01 can be a hydrocarbon-containing gas such as methane, propane, butane, natural gas, city gas, or digester gas with methane as the main component. Alternatively, various alcohols and petroleum raw materials can also be used. In the case of hydrophilic liquid raw materials, they can be pre-mixed with circulating water. On the other hand, in the case of hydrophobic liquid raw materials, the raw material can be preheated separately to vaporize it; alternatively, it can be preheated while being mixed with steam F11 to vaporize it.

[0037] In reformer 2, for example, a steam reforming reaction is carried out. A representative reforming reaction using methane as feedstock is shown in equations (1) and (2). Using a reforming catalyst packed inside reformer 2, hydrogen is generated through an endothermic reaction between methane and steam. Generally, the steam flow rate supplied to reformer 2 is set constant in the range of approximately 2.5 to 3.5, based on the mole fraction of steam relative to the carbon content in the fuel gas, i.e., S / C. Reforming catalysts include, for example, Ni-based, Pt-based, and Ru-based catalysts supported on Al2O3, MgO, or other carriers.

[0038]

[0039]

[0040] To illustrate, steam reforming is used here as an example, but it is not limited to this. Partial oxidation reforming (not shown) or autothermal reforming can also be used, where air is separately introduced into reformer 2. Furthermore, these reforming reactions can be switched during start-up and shutdown processes.

[0041] On the other hand, in the fuel cell stack 1, an electrochemical reaction occurs between the reformed gas F05 supplied to the anode 1a and the oxidant F03 supplied to the cathode 1c, separated by the electrolyte 1e, resulting in electron transfer and power generation. Specifically, a potential is generated in the fuel cell stack 1, simultaneously generating ion exchange via the electrolyte 1e and electron exchange within the circuit via the output terminals on both sides of the anode 1a and cathode 1c. The movement of electrons within the circuit at this time (direct current) is used as the power output (not shown).

[0042] Regarding the electrochemical reactions in fuel cell stack 1, the types of electrolytes 1e, electrode materials, and operating temperatures vary. Furthermore, the types of ions that move within electrolyte 1e also differ. For example, hydrogen ions move in solid polymer and phosphoric acid fuel cells, carbonate ions move in molten carbonate fuel cells, and oxygen ions move in solid oxide fuel cells. Particularly in molten carbonate fuel cells (approximately 600–700°C) and solid oxide fuel cells (approximately 600–1000°C) operating at high temperatures, water is generated from hydrogen through electrode reactions in anode 1a. Therefore, in anode 1a, the water vapor content increases towards the outlet.

[0043] Taking a solid oxide fuel cell as an example, the electrode reaction at the anode 1a is represented by equation (3), and the electrode reaction at the cathode 1c is represented by equation (4).

[0044] H2+O 2- →H₂O + 2e - (3)

[0045] 1 / 2O2+2e - →O 2- (4)

[0046] In anode 1a, hydrogen, equivalent to the amount of electron movement, is consumed in the electrode reaction. The hydrogen partial pressure decreases towards the anode outlet, but an equal amount of water is generated, increasing the water vapor partial pressure. Conversely, in cathode 1c, oxygen, equivalent to the amount of electron movement, is consumed in the electrode reaction. The gas flow rate and oxygen partial pressure decrease towards the cathode outlet. In the case of a solid oxide fuel cell, internal reforming, where electrode reactions and reforming reactions occur simultaneously, is possible in anode 1a. This allows the reforming reaction of the remaining methane that failed to reform in reformer 2 to proceed in the direction of hydrogen generation.

[0047] Here, in fuel cell stack 1, the hydrogen flow rate consumed in the electrode reaction at anode 1a operates at approximately 0.60 to 0.85 relative to the supplied hydrogen flow rate. Similarly, the oxygen consumption in the electrode reaction at cathode 1c operates at approximately 0.15 to 0.50 relative to the supplied oxygen flow rate. That is, residual fuel is present at the anode outlet, and residual oxygen is present at the cathode outlet. For example, the volume molar fraction of hydrogen in anode exhaust gas F06 is approximately 12%, and water vapor is approximately 60%, while the volume molar fraction of oxygen in cathode exhaust gas F04 is approximately 16%.

[0048] The fuel cell system 100 of this application will be described based on the general configuration and basic operation described above. In the fuel cell system 100 according to Embodiment 1 of this application, as in the fuel cell systems 100 according to subsequent embodiments, the temperature difference between the vaporizer 4 and the anode exhaust gas F06 is used as the heat source. Using the anode exhaust gas F06, details of the configuration and control operation for reliably vaporizing the circulating water F10 will be described.

[0049] In the fuel cell system 100 of this application, the anode exhaust gas F06 discharged from the anode 1a is introduced into the vaporizer 4. The temperature difference between the anode exhaust gas F06 and the vaporizer 4 is used as a driving force and as a heat source for the vaporizer 4. The vaporizer 4 transfers heat energy to the circulating water F10, turning it into water vapor F11. In the heat recovery cooler 10, the anode exhaust gas F06, whose temperature has been reduced by transferring heat energy to the circulating water F10 in the vaporizer 4, further transfers heat energy to the medium (refrigerant F14) flowing in the heat recovery system, reducing its temperature to a predetermined temperature below the dew point, and then introduces it into the water separator 5.

[0050] To achieve the specified temperature, a temperature sensor (not shown) is used to control the flow rate of refrigerant F14. In the water separator 5, water contained in the anode exhaust gas F06 is liquefied and separated as water droplets using the saturated vapor pressure relative to the specified temperature, and stored in the lower part. The stored water is supplied to the vaporizer 4 via the water treatment device 14 and as circulating water F10 from the water pump 8 according to the flow rate required as fuel gas F02. On the other hand, the anode recovery gas F07, from which the specified amount of water has been removed by the water separator 5, flows in the anode recovery gas system 207 and is supplied to the recovery branch 221. The anode recovery gas F07 is split in the recovery branch 221 into recirculated combustion gas F08 and anode circulating gas F09, and the recirculated combustion gas F08 is supplied to the burner 3 through the recirculated combustion gas system 208.

[0051] In burner 3, recirculated combustion gas F08 and cathode exhaust gas F04, which exits from cathode 1c and flows through cathode exhaust system 204, are combusted. The combusted gas provides the heat energy required for the reforming reaction in reformer 2, for example, to raise the reforming reaction temperature to 600°C. Furthermore, in oxidant heat exchanger 7, heat energy is provided to oxidant F03, raising it to the temperature at which cathode 1c of fuel cell stack 1 can operate, for example, from 25°C to 550°C. After providing heat energy to reformer 2 and oxidant heat exchanger 7, the combusted gas is discharged from combustion exhaust system 215 as combustion exhaust gas F15.

[0052] Anode circulating gas F09 flows through anode circulating gas system 209 and is supplied to circulator 9. Circulator 9 is, for example, an ejector with water vapor F11 as the driving fluid, which ejects water vapor F11 from a nozzle located inside the ejector and draws them in by imparting the momentum of the ejected water vapor F11 to the raw material F01 and anode circulating gas F09.

[0053] The success of the above work is investigated based on the output enthalpy (hereinafter referred to as output enthalpy) of the fuel cell stack 1. As an example of the fuel cell system 100, a solid oxide fuel cell using city gas as feedstock is operated at a fuel utilization rate of 75%, a single cell voltage of 0.84V, and a current of 24A. Under these conditions, the output enthalpy of the anode exhaust gas F06 at the anode outlet is -3081 J / s·kW. The heat of vaporization required to convert circulating water F10 into water vapor F11 is estimated to be 247 J / s·kW; therefore, the anode exhaust gas F06, after being heated by the vaporizer 4, exceeds 150°C using thermal balance calculations. That is, through heat exchange with the anode exhaust gas F06, the heat energy required for the generation (evaporation) of water vapor F11 in the vaporizer 4 can be provided.

[0054] Here, the establishment of thermal energy balance is illustrated by the case where the fuel utilization rate is typically 75%, which is the operating condition for fuel cell stack 1. However, when operating at a high fuel utilization rate, the heat energy contained in the anode exhaust gas F06 discharged from fuel cell stack 1 decreases, and the required heat of vaporization may not be obtained. For example, if the fuel utilization rate is 80%, the temperature of the anode exhaust gas F06 discharged from vaporizer 4 is assumed to be 100°C, and if the fuel utilization rate is 83%, the temperature of the anode exhaust gas F06 discharged from vaporizer 4 is assumed to be 60°C.

[0055] Therefore, assuming that the thermal energy required for steam generation is insufficient when operating at a fuel utilization rate of 80% or higher, it is preferable to additionally heat the circulating water F10 introduced into the gasifier 4. Therefore, for example, the control unit 90 is designed to perform operation control that changes the operating mode based on the fuel utilization rate.

[0056] Specifically, such as Figure 2 As shown, fuel cell operating data, such as the flow rate of reformed gas F05 flowing into fuel cell stack 1 and the DC current output from fuel cell stack, are periodically read in (step S10). Fuel utilization rate is calculated from the read data (step S20), and it is determined whether the calculated fuel utilization rate Uf is within the threshold Th (step S30).

[0057] If the fuel utilization rate Uf is within the threshold Th ("Yes" in step S30), the normal heat exchange mode, which utilizes only the heat energy of the anode exhaust F06 for vaporization, is maintained (step S40). On the other hand, if the fuel utilization rate Uf exceeds the threshold Th ("No" in step S30), it is determined that the heat is insufficient when using only heat exchange, and the mode is changed to supplementary heating mode (step S50). In supplementary heating mode, heating can be performed by auxiliary burner 4a, etc., as described later, or by using a separately installed heater. In either case, compared to responding after detecting insufficient water vapor F11 flow or a drop in the temperature of vaporizer 4, countermeasures against insufficient heat can be implemented quickly, thus achieving stable operation.

[0058] To clarify, in the fuel cell system 100 according to Embodiment 1 and subsequent embodiments, when the control unit 90 is referred to as hardware 900, for example, as follows: Figure 3 As shown, the hardware 900 comprises a processor 901 and a storage device 902. The storage device 902 includes a volatile storage device such as random access memory (not shown) and a non-volatile auxiliary storage device such as flash memory. Alternatively, a hard disk drive may be used as an auxiliary storage device instead of flash memory. The processor 901 executes a program input from the storage device 902. In this case, the program is input to the processor 901 from the auxiliary storage device via the volatile storage device. Furthermore, the processor 901 can output data such as calculation results to the volatile storage device of the storage device 902, or it can store data in the auxiliary storage device via the volatile storage device.

[0059] The temperature below the dew point in the water separator 5 is set, for example, to be about 60°C. In this case, the saturated vapor pressure is about 0.025 MPa. As a result, the volume molar fraction of water vapor contained in the anode exhaust gas F06 is about 60%, which condenses into water, the flow rate is halved, and the volume molar fraction of water vapor is reduced to about 20%, becoming the anode recovery gas F07. Furthermore, in the recovery branch 221, the anode recovery gas F07 is distributed at approximately the same flow rate as the recirculated combustion gas F08 and the anode recirculation gas F09.

[0060] Therefore, the flow rate of the anode circulating gas F09 is approximately 1 / 4 of the flow rate of the anode exhaust gas F06. Furthermore, the water vapor flow rate contained in the anode circulating gas F09 is approximately 8% of the water vapor flow rate contained in the anode exhaust gas F06. Compared to the water vapor flow rate required by the reformer 2 or fuel cell stack 1, the water vapor flow rate contained in the anode exhaust gas F06 is only about 15%, therefore the remainder is vaporized from the circulating water F10 in the vaporizer 4, becoming water vapor F11 at approximately 0.5 MPa.

[0061] According to this disclosure, in the anode exhaust system 206, there is no phase change caused by condensation up to the heat recovery cooler 10, therefore the fluctuation of gas flow through the fuel cell stack 1 is small, and the output from the fuel cell stack 1 is stabilized. Furthermore, since no excess energy is used to generate water vapor F11, a high-efficiency and stable-output fuel cell system 100 can be achieved. This can be easily implemented in molten carbonate fuel cells operating at temperatures above 600°C, in addition to the solid oxide fuel cell used in this example. Furthermore, in a phosphoric acid fuel cell, although the operating temperature is lower than that of the aforementioned fuel cells, it still operates at approximately 200°C higher than the boiling point of water at the operating pressure, thus enabling the generation of water vapor F11. Additionally, even if the total heat required for generating water vapor F11 is not reached, it can at least be used for preheating the circulating water F10.

[0062] In the fuel cell system 100, water vapor F11 is supplied to the reformer 2, and then to the anode 1a of the fuel cell stack 1, and discharged from the anode 1a after an electrochemical reaction. Unaffected by the gas conditions at the cathode 1c, water vapor can be generated by utilizing the thermal energy from the gas flowing in the anode 1a (anode exhaust F06), thus enabling control of the fuel cell system 100 in accordance with the operating state of the fuel cell stack 1.

[0063] Specifically, when the fuel cell system 100 operates under partial load depending on the load, the operating temperature of the fuel cell stack 1 remains approximately constant, while the gas flow rate increases or decreases according to the load (current). That is, the amount of water vapor supplied along with the feedstock is approximately proportional to the anode exhaust flow rate. Furthermore, by arranging a vaporizer 4 downstream of the anode outlet without installing other equipment, the heat energy required for vaporization can be obtained from the anode exhaust F06 according to the operating state of the fuel cell stack 1, simplifying the controllability of the system.

[0064] Furthermore, the flow ratio of anode circulating gas F09 to water vapor F11 can be reduced, allowing the application of an injector using water vapor F11 as the driving fluid in the circulator 9. The injector utilizes the momentum of the driving fluid to draw in other fluids. Therefore, since no power is required, the auxiliary power of the system can be reduced, resulting in virtually maintenance-free operation and enabling a highly efficient and reliable fuel cell system 100.

[0065] Furthermore, the momentum of water vapor F11 can draw in not only the anode circulating gas F09 but also the feedstock F01. Therefore, auxiliary equipment such as blowers for pressurizing the feedstock is unnecessary, enabling a highly efficient and reliable fuel cell system. Additionally, for example, the flow rate of anode exhaust F06 is approximately one-quarter that of combustion exhaust F15, resulting in a smaller gas flow rate in the vaporizer 4. This allows for a more compact vaporizer 4, leading to increased efficiency and reduced costs due to decreased heat dissipation.

[0066] Variations

[0067] In this variation, an example of providing an auxiliary burner to compensate for insufficient heat in the gasifier will be described. Figure 4 This is a schematic flowchart illustrating the configuration of the fuel cell system involved in the modified example. Except for the configuration of the gasifier equipped with an auxiliary burner, it is the same as the example above; descriptions of identical parts are omitted.

[0068] Regarding the modified fuel cell system 100, such as Figure 4 As shown, a thermoelectric auxiliary burner 4a is provided in the gasifier 4. For example, a burner or a catalytic burner can be used as the auxiliary burner 4a. Therefore, in Figure 2 In the case where the fuel utilization rate becomes higher than specified and additional heating is required (step S50), the heat generated by the auxiliary burner can be used to ensure the necessary amount of water vapor.

[0069] Furthermore, when starting the fuel cell system 100, there are times when operations differ from those during stable operation, such as replenishing water from the external source when the water level in the water separator 5 is insufficient. Therefore, by utilizing the auxiliary burner 4a regardless of fuel utilization, a smooth start-up can sometimes be achieved.

[0070] Specifically, oxidant F03 from air blower 18 is supplied to burner 3 via cathode 1c of fuel cell stack 1, and feedstock is supplied to burner 3 via a system not shown, where it is combusted with oxidant F03. The combustion gases transfer heat to reformer 2 and oxidant heat exchanger 7, and are discharged from combustion exhaust system 215 as combustion exhaust F15. In oxidant heat exchanger 7, oxidant F03 is heated, and the heated oxidant F03 transfers heat to fuel cell stack 1, thus heating fuel cell stack 1.

[0071] During the heating process, the temperature conditions for the reforming reaction in reformer 2 are met. At the moment when the anode 1a of fuel cell stack 1 becomes a reducing atmosphere, steam F11 is supplied from steam system 211, and feedstock F01 is supplied from feedstock system 201. At this time, since no heat energy is available for vaporizing water in vaporizer 4, heat energy is supplied to vaporizer 4 using auxiliary burner 4a to generate steam. Then, at the moment when the prescribed heat energy is obtained from anode exhaust F06, heating using auxiliary burner 4a is stopped, and the energy source for vaporizing circulating water F10 is switched from auxiliary burner 4a to anode exhaust F06.

[0072] Furthermore, in the above example, an example of operation of the auxiliary burner 4a during heating is shown. However, under other conditions such as cooling of the fuel cell system 100, when the heat energy is insufficient relative to the water vapor generated in the gasifier 4, the auxiliary burner 4a may also operate intermittently or continuously.

[0073] According to this disclosure, even under operating conditions where the thermal energy required by the vaporizer 4 is temporarily insufficient due to the anode exhaust F06 alone, stable water vapor F11 can be generated, enabling the high-efficiency fuel cell system 100 to operate more stably.

[0074] Implementation Method 2

[0075] In Embodiment 1 described above, the anode circulating gas, after water droplets have been removed by the water separator, is directed toward the circulator as before. In Embodiment 2, an example is described where the gas is preheated after water droplet removal and then directed toward the circulator. Figure 5 A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 2 is provided. The figures are explained in connection with the description of the fuel cell system according to a variation of Embodiment 1. Figure 4 An example is given of the configuration required to add waste heat to the anode circulating gas. Apart from the configuration related to the waste heat of the anode circulating gas, the configuration used in Embodiment 1 is the same as in Embodiment 1 regarding control operations, etc. Figure 2 , 3 The description of the parts that are the same as those in Implementation Method 1 is omitted.

[0076] Regarding the fuel cell system 100 according to Embodiment 2, as follows Figure 5As shown, circulating heat exchangers 13 are provided between the vaporizer 4 and the heat recovery cooler 10 in the anode exhaust system 206, and between the recovery branch 221 and the circulator 9 in the anode circulating gas system 209. With this configuration, the anode exhaust gas F06 discharged from the vaporizer 4 transfers heat energy to the anode circulating gas F09 via the circulating heat exchanger 13. As a result, the temperature of the anode exhaust gas F06 is further reduced compared to the temperature reduced by the vaporizer 4, and conversely, the temperature of the anode exhaust gas F09 can be increased from the temperature cooled by the heat recovery cooler 10.

[0077] According to this disclosure, by supplying heat energy from the anode exhaust gas F06 to the anode circulating gas F09, which is in a saturated vapor state in the water separator 5, via the circulating heat exchanger 13, the temperature of the anode circulating gas F09 is made higher than the dew point, and the relative humidity is reduced. As a result, it is possible to prevent water vapor contained in the anode circulating gas F09 flowing between the circulating heat exchanger 13 and the circulator 9 from condensing in the piping. Therefore, the flow rate of the anode circulating gas F09 can be stabilized, and the accuracy of the water vapor flow rate in the anode circulating gas F09 can be improved, thus enabling a fuel cell system with higher performance and more stable output.

[0078] Implementation Method 3

[0079] In embodiments 1 and 2 described above, only configurations that simply supply cathode exhaust to the burner were illustrated. In this embodiment 3, an example configured to distribute cathode exhaust according to its function will be described. Figure 6 A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 3 is provided. The figures are explained in connection with the description of the fuel cell system according to Embodiment 2. Figure 5 An example is given of a configuration required for additional cathode exhaust distribution. Furthermore, aside from the configuration related to cathode exhaust distribution, the same configuration as in Embodiments 1 and 2 can be used; regarding control operations, the configuration used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 and 2 is omitted.

[0080] Regarding the fuel cell system 100 according to Embodiment 3, as follows: Figure 6 As shown, the cathode exhaust system 204 through which the cathode exhaust F04 flows is provided with an air branch 222. Thus, the cathode exhaust system 204 branches into a preheating combustion gas system 212 connected to the reformer 2 and a combustion gas system 213 connected to the burner 3. That is, the cathode exhaust F04 is used respectively as preheating combustion gas F12 supplied to the reformer 2 and combustion gas F13 supplied to the burner 3.

[0081] The heat energy of the preheated combustion-supporting gas F12, branched through air branch 222, is used as part of the reforming reaction in reformer 2 and as part of the heating of oxidant FO3 in oxidant heat exchanger 7. Meanwhile, the combustion-supporting gas F13 supplied to burner 3 is combusted with recirculated combustion gas F08. The remaining heat energy generated from combustion, used for the reforming reaction in reformer 2 and the heating of oxidant FO3, is discharged from combustion exhaust system 215 as combustion exhaust F15 along with the preheated combustion-supporting gas F12.

[0082] According to this disclosure, the cathode exhaust gas F04 discharged from the cathode 1c of the fuel cell stack 1 can be branched at the air branch 222 in a manner that ensures stable combustion in the burner 3, thereby stabilizing the combustibility of the burner 3. Furthermore, the thermal energy supplied to the reformer 2 can be effectively utilized. Therefore, the composition of the reformed gas F05 discharged from the reformer 2 is stabilized, and the thermal efficiency of the reformer 2 is improved, thus enabling a high-performance fuel cell system with stable electrical output.

[0083] Implementation 4

[0084] In embodiments 1 to 3 described above, only a configuration where circulating water is simply supplied to the vaporizer is illustrated. In this embodiment 4, an example is described where heat from the anode exhaust gas is received before being supplied to the vaporizer. Figure 7 This is a schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 4. The diagram is explained for use in the description of the fuel cell system according to Embodiment 3. Figure 6 An example is given of the configuration required for adding heat exchange between circulating water and anode exhaust. Furthermore, aside from the configuration related to the heat exchange between circulating water and anode exhaust, the same configuration as in Embodiments 1-3 can be used. Regarding control operations, the configuration used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 to 3 is omitted.

[0085] Regarding the fuel cell system 100 according to Embodiment 4, as follows Figure 7 As shown, a water heat exchanger 11 is provided for heat exchange between circulating water F10 flowing in the circulating water system 210 and anode exhaust gas F06 flowing in the anode exhaust system 206. The water heat exchanger 11 is provided between the circulating heat exchanger 13 and the heat recovery cooler 10 in the anode exhaust system 206, and between the water pump 8 and the vaporizer 4 in the circulating water system 210.

[0086] The anode exhaust gas F06 discharged from the circulating heat exchanger 13 transfers heat energy to the circulating water F10 flowing from the water pump 8 through the water heat exchanger 11. As a result, the temperature of the anode exhaust gas F06 decreases, while the temperature of the circulating water F10 increases. At this time, since the water heat exchanger 11 is not located upstream of the circulating heat exchanger 13 in the anode exhaust system 206, but downstream, the temperature of the anode circulating gas F09 can be reliably raised.

[0087] According to this disclosure, the circulating water F10 is preheated from the anode exhaust gas F06 via the water heat exchanger 11, thereby reducing the heat energy required for generating water vapor in the gasifier 4 by approximately 10% in terms of the unit output of the fuel cell stack 1. Therefore, the surplus relative to the utilization of the heat energy possessed by the anode exhaust gas F06 is increased, the required operating range of the auxiliary burner 4a is narrowed, and thus a high-performance fuel cell system can be achieved. It should be noted that this configuration can also be applied to the fuel cell system 100 described in Embodiment 1 or 2, which does not include the circulating heat exchanger 13.

[0088] Variations

[0089] In this variation, an example of using a heat recovery cooler that integrates a heat recovery exchanger and a water heat exchanger is illustrated. Figure 8 This is a schematic flowchart illustrating the configuration of the fuel cell system involved in the modified example. Except for the integration of the heat exchanger, the description of the same parts is omitted as in the example above.

[0090] In the fuel cell system 100 involved in this modification, such as Figure 8 As shown, a heat recovery heat exchanger 12 is provided that integrates the heat recovery cooler 10 and the water heat exchanger 11. The anode exhaust gas F06 flowing in the anode exhaust system 206 provides heat energy to the circulating water F10 flowing in the circulating water system 210 and the refrigerant F14 flowing in the heat recovery system 214 via the integrated heat recovery heat exchanger 12.

[0091] According to this disclosure, compactness is achieved by reducing the number of heat exchangers, thereby enabling a reduction in heat dissipation at a lower cost and enabling a higher performance fuel cell system.

[0092] Implementation Method 5

[0093] In embodiments 1 to 4 described above, the control of the distribution from the anode recovered gas to the recirculated combustion gas and the anode cycle gas was not addressed. In this embodiment 5, an example in which the distribution to the recirculated combustion gas and the anode cycle gas is controlled will be described. Figure 9A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 5 is provided. The figures are explained in connection with the description of the fuel cell system according to Embodiment 4. Figure 7 An example is given of the configuration required for the distribution control of the anode recovery gas. Furthermore, apart from the configuration related to the distribution control of the anode recovery gas, the same configuration as in Embodiments 1-4 can be used. Regarding control operations, the configuration used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 to 4 is omitted.

[0094] In the fuel cell system 100 according to Embodiment 5, such as Figure 9 As shown, a circulating gas flow regulating valve 21 is provided in the anode circulating gas system 209 to adjust the flow ratio of recirculated combustion gas F08 to anode circulating gas F09. Furthermore, a combustion gas flow meter 31 for measuring the flow rate of recirculated combustion gas F08 is provided between the recovery branch 221 and the burner 3, and a circulating gas flow meter 32 for measuring the flow rate of anode circulating gas F09 is provided between the recovery branch 221 and the circulating gas flow regulating valve 21. The combustion gas flow meter 31 and the circulating gas flow meter 32 are each, for example, composed of a combination of an orifice and a differential pressure gauge, and output an electrical signal corresponding to the pressure difference generated at the orifice portion as a signal indicating the flow rate to the control unit 90.

[0095] The control unit 90 maintains data on the target flow distribution ratio of recirculated combustion gas F08 and anode circulating gas F09 corresponding to the operating state. Therefore, the control unit 90 calculates the flow distribution ratio based on the differential pressure signals output from the combustion gas flow meter 31 and the circulating gas flow meter 32, and controls the circulating gas flow regulating valve 21 in a manner that is appropriate for the current operating state. For example, if the power generation load of the fuel cell stack 1 is low, the heat dissipation of the reformer 2 increases relatively, and the thermal energy required by the reformer 2 is insufficient. Therefore, by selecting the target flow distribution ratio corresponding to the power generation load, the control unit operates in the direction of closing the circulating gas flow regulating valve 21, thereby increasing the flow rate of recirculated combustion gas F08. Alternatively, even without maintaining the data, if a decrease in the temperature of the reformer 2 or a deficiency in the thermal energy required by the reformer 2 is detected, the control unit can also operate in the direction of closing the circulating gas flow regulating valve 21, thereby increasing the flow rate of recirculated combustion gas F08.

[0096] According to this disclosure, the circulating gas flow regulating valve 21 can operate in an environment of approximately 60°C, for example. Therefore, a flow regulating valve with special high-temperature specifications is not required, and a standard-specification flow regulating valve can be used. Thus, a fuel cell system 100 with excellent controllability and high reliability can be easily provided. Furthermore, since the flow rate of gases with the same physical properties is measured, the configuration is such that the distribution ratio is determined solely based on the ratio of the pressure difference when flowing through the orifice.

[0097] Therefore, compared to measuring the absolute values ​​of the flow rates of the anode circulating gas F09 and the recirculated combustion gas F08, the distribution ratio can be determined using a simple measuring instrument regardless of changes in gas composition, temperature, etc. Thus, for example, even if the moisture content of the anode recovery gas F07 varies due to condensation, the anode circulating gas F09 and the recirculated combustion gas F08 can be appropriately branched by the recovery branch 221, thereby achieving high efficiency in the fuel cell system 100.

[0098] To clarify, this disclosure shows an example where the circulating gas flow regulating valve 21 is positioned between the circulating gas flow meter 32 and the circulating heat exchanger 13 in the anode circulating gas system 209, but it is not limited to this. For example, the same effect can be achieved even if the valve is positioned between the combustion gas flow meter 31 and the burner 3 in the recirculating combustion gas system 208.

[0099] Implementation Method 6

[0100] In embodiments 1 to 5 described above, adjusting the pressure difference between the anode and cathode was not described. In this embodiment 6, an example configured to adjust the pressure of the anode recovery gas in order to reduce the pressure difference between the anode and cathode will be described. Figure 10 A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 6 is provided. The figures are explained in connection with the description of the fuel cell system according to Embodiment 5. Figure 9 An example is given of the configuration required for adjusting the pressure of the anode recovery gas. Apart from the configuration related to the pressure adjustment of the anode recovery gas, the same configuration as in Embodiments 1-5 can be used. Regarding control operations, the configuration used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 to 5 is omitted.

[0101] Regarding the fuel cell system 100 according to Embodiment 6, as follows Figure 10 As shown, a pressure equalizing blower 17 is installed between the combustion gas flow meter 31 and the burner 3 in the recirculated combustion gas system 208 to reduce the pressure of the anode recovery gas F07.

[0102] The recirculated combustion gas F08, which is part of the anode exhaust gas F06 of the fuel cell stack 1, and the combustion-supporting gas F13, which is part of the cathode exhaust gas F04, are combusted and then discharged as combustion exhaust gas F15. Although the gas flow rate in the anode system is significantly reduced midway, the pressure loss is greater compared to the gas flowing in the cathode system due to the presence of the vaporizer 4, circulating heat exchanger 13, water heat exchanger 11, heat recovery cooler 10, and water separator 5 in the system. The equalizing blower 17 operates by drawing in the recirculated combustion gas F08 to reduce the static pressure of the gas flowing in the anode system, bringing the gas pressure in the anode 1a of the fuel cell stack 1 closer to the gas pressure in the cathode 1c.

[0103] According to this disclosure, the equalizing blower 17 can operate in an environment of approximately 60°C, thus eliminating the need for a blower with special high-temperature specifications. By using the equalizing blower 17, the pressure difference between the anode 1a and the cathode 1c can be reduced, thereby suppressing gas leakage (crossing) via the electrolyte 1e, inhibiting the deterioration of the fuel cell stack 1, and providing a high-performance fuel cell system 100. It should be noted that the equalizing blower 17 can be installed, for example, within the anode recovery gas system 207 to draw anode recovery gas F07, provided it can reduce the static pressure of the anode exhaust gas F06 to be close to that of the cathode exhaust gas F04. Even in this case, as long as it is located downstream of the water separator 5, the impact of condensation on the equalizing blower 17 can be reduced, stabilizing the pressure.

[0104] Implementation Method 7

[0105] In the embodiments 1 to 6 described above, an example was shown in which water vapor was used as the driving fluid and the anode circulating gas was drawn in using an ejector constituting a circulator, but this is not the only example. In this embodiment 7, an example configured to mix the anode circulating gas with the raw material even when the momentum of the driving fluid is small will be described. Figure 11 A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 7 is provided. The figures are explained in relation to the fuel cell system used in the description of Embodiment 5. Figure 9 An example was illustrated by replacing the circulating gas flow regulating valve with a circulating blower for mixing the anode circulating gas and the raw material. Furthermore, aside from the configuration for mixing the anode circulating gas and the raw material gas, the same method as in Embodiments 1 to 6 can be used. Regarding control operations, the method used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 to 6 is omitted.

[0106] Regarding the fuel cell system 100 according to Embodiment 7, as follows Figure 11As shown, a circulating blower 16 is provided between the recovery branch 221 of the anode circulating gas system 209 and the circulating heat exchanger 13. Furthermore, the anode circulating gas system 209 is not connected to the circulator 9, but is connected to the mixing section 223 located downstream of the circulator 9 in the fuel gas system 202. Therefore, in the circulator 9, water vapor F11 merges with the raw material F01, and in the mixing section 223 located downstream of the circulator 9, it merges with the anode circulating gas F09.

[0107] Unlike embodiments 1 to 6 described above, in the circulator 9 of embodiment 7, water vapor F11 is used as the driving fluid to draw in only the raw material F01. Then, in the mixing section 223 located downstream of the circulator 9, the anode circulating gas F09 flowing from the anode circulating gas system 209, which is pressurized by the circulating blower 16, is combined and supplied to the reformer 2. To explain, the anode circulating gas F09 is supplied to the mixing section 223 in a state where it is heated by the heat energy from the anode exhaust gas F06 in the circulating heat exchanger 13 located downstream of the circulating blower 16.

[0108] This configuration is suitable for use in fuel cell systems 100 where, for example, the absolute flow rate of water vapor F11 is low. If the absolute flow rate of water vapor F11 is low, the momentum of the water vapor F11, which becomes the driving fluid for the injector, decreases, and therefore only the feedstock F01 is drawn into the circulator 9. On the other hand, the anode circulating gas F09 is pressurized using the circulating blower 16.

[0109] According to this disclosure, the circulating blower 16 can operate in an environment of approximately 60°C, thus eliminating the need for a blower with special high-temperature specifications. Furthermore, the flow rate of the anode circulating gas F09 is lower than that of the anode exhaust gas F06, allowing for miniaturization of the circulating blower 16 and reducing power consumption. Therefore, although auxiliary power to the circulating blower 16 is required, the increase in power consumption can be significantly suppressed, enabling a highly efficient fuel cell system.

[0110] To clarify, this disclosure illustrates an example of using a circulator 9 to draw anode circulating gas F09 and feedstock F01, but it is not limited to this. For example, when feedstock F01 is city gas, it is generally supplied at a pressure of about 2 kPa. Therefore, the feedstock system 201 can be connected to the mixing unit 223, and the anode circulating gas system 209 can be connected to the circulator 9 without the circulating blower 16. That is, the circulator 9 can also be used to draw anode circulating gas F09 and feedstock F01. In this case, it can be appropriately applied to a fuel cell system 100 with a low absolute flow rate of water vapor F11 without the need for additional auxiliary equipment and auxiliary equipment power.

[0111] Implementation Method 8

[0112] In embodiments 3 to 7 described above, the control of distributing cathode exhaust gas into preheating combustion gas and combustion gas was not addressed. In this embodiment 8, an example of controlling the distribution of preheating combustion gas and combustion gas will be described. Figure 12 A schematic flowchart illustrating the configuration of the fuel cell system according to Embodiment 8 is provided. It should be noted that the figures used in the description of the fuel cell system according to Embodiment 5 are... Figure 9 An example is given of the configuration required for adding cathode exhaust distribution control. Furthermore, apart from the configuration related to cathode exhaust distribution control, the same configuration as in Embodiments 1-7 can be used; regarding control operations, the configuration used in Embodiment 1 is adopted. Figure 2 , 3 The description of the parts that are the same as those in embodiments 1 to 7 is omitted.

[0113] Regarding the fuel cell system 100 according to Embodiment 8, as follows: Figure 12 As shown, in order to adjust the flow ratio of preheating combustion gas F12 to combustion combustion gas F13, a combustion gas flow regulating valve 22 is provided between the air branch 222 and the reformer 2 in the preheating combustion gas system 212. Furthermore, a combustion combustion gas flow meter 33 for measuring the flow rate of combustion combustion gas F13 is provided between the air branch 222 and the burner 3, and a preheating combustion gas flow meter 34 for measuring the flow rate of preheating combustion gas F12 is provided between the air branch 222 and the combustion gas flow regulating valve 22. The combustion combustion gas flow meter 33 and the preheating combustion gas flow meter 34 are each, for example, composed of a combination of an orifice and a differential pressure gauge, and output an electrical signal corresponding to the pressure difference generated by the orifice portion as a signal indicating the flow rate to the control unit 90.

[0114] The control unit 90 maintains data on the target flow distribution ratio of preheating combustion gas F12 and combustion gas F13. Therefore, the control unit 90 calculates the flow distribution ratio based on the differential pressure signals output from the combustion gas flow meter 33 and the preheating gas flow meter 34, respectively, and controls the combustion gas flow regulating valve 22 in a manner that corresponds to the current operating state. It should be noted that the target flow distribution ratio of preheating combustion gas F12 and combustion gas F13 can be set to a constant value independent of the operating state. Therefore, the combustion gas flow regulating valve 22 can also calculate the flow distribution ratio based on the signals obtained from the combustion gas flow meter 33 and the preheating gas flow meter 34, respectively, and perform self-control in a predetermined flow distribution manner.

[0115] According to this disclosure, since the flow rate measurement is of gases with the same physical properties, the distribution ratio is determined solely based on the ratio of pressure differences as the gases flow through the orifice. Therefore, compared to measuring the absolute values ​​of the flow rates of the preheating combustion-supporting gas F12 and the combustion-supporting gas F13, the distribution ratio can be determined using a simple measuring instrument regardless of changes in gas composition, temperature, etc.

[0116] On the other hand, a high-temperature valve is required in the combustion gas flow regulating valve 22. By controlling the flow rate of the combustion gas F13, the ratio of combustible gas to combustion gas in the burner 3 can be adjusted. This makes it easier to control the temperature of the reformer 2 by varying the flame temperature. Therefore, stable hydrogen generation is achieved, the output of the fuel cell stack 1 is stabilized, and a highly reliable fuel cell system 100 can be provided.

[0117] It should be noted that this disclosure shows an example of installing the combustion-supporting gas flow regulating valve 22 in the preheating combustion-supporting gas system 212, but it is not limited to this. Even if it is installed in the combustion-supporting gas system 213, it will have the same effect.

[0118] In each of the above embodiments 1 to 8, the medium flowing in the heat recovery system 214 is typically a refrigerant F14 such as water, but it is not limited to this. Other refrigerants or heat storage materials can also be used, as long as they can accept heat energy. In addition, the water treatment device 14 can be, for example, an ion exchange resin, but a permeable membrane can also be used. Depending on the specifications, only a filter may be provided, or it may not be provided if it is not needed.

[0119] Furthermore, the condensation temperature in the water separator 5 is shown as an example of approximately 60°C, but it is not limited to this. Preferably, the condensate volume per unit time 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, there is no need to replenish water from outside the system, enabling the system to achieve water self-sufficiency and reducing system operating costs.

[0120] It should be noted that this application describes various exemplary embodiments and examples, but the various features, methods, and functions described in one or more embodiments are not limited to the application of the configuration disclosed in a specific embodiment, and can be applied to the embodiments individually or in various combinations. Therefore, numerous variations not illustrated are contemplated within the scope of the technology disclosed in this application. For example, variations, additions, or omissions of at least one constituent element may be included, further encompassing the extraction of at least one constituent element (e.g., differences between embodiments) and combination with constituent elements disclosed in other embodiments.

[0121] As described above, the fuel cell system 100 according to various embodiments includes: a reformer 2 that reacts hydrocarbons with water to generate reformed gas F05 containing hydrogen; a fuel cell stack 1 that generates electrical energy through an electrochemical reaction between the reformed gas F05 and the oxidant F03 separated by an anode 1a and a cathode 1c; and an injector (circulator 9) that uses water vapor F11, used as water, as a driving fluid to draw in feedstock F01 containing hydrocarbons and recirculated gas (anode recovery gas) recovered from the anode exhaust F06. F07: Strictly speaking, any of the anode recycle gas F09 distributed from the anode recovery gas F07 and supplied to the reformer 2; and the vaporizer 4, which vaporizes water to produce water vapor F11, wherein the operating temperature of the fuel cell stack 1 is higher than the boiling point of water at the operating pressure, and the vaporizer 4 is configured to produce water vapor F11 by heat exchange with the anode exhaust gas F06, thus using the heat of the anode exhaust gas F06 to produce water vapor F11, thereby effectively utilizing the energy of the feedstock F01 and improving efficiency.

[0122] Furthermore, if an auxiliary burner 4a is provided for heating the gasifier 4 or for adding water vapor F11, and a control unit 90 is provided to adjust the start-up and stop times of the auxiliary burner 4a according to the operating state of the reformer 2 and the fuel cell stack 1, then even when the generation of water vapor F11 in the gasifier 4 is insufficient during start-up, stop-up, or according to operating conditions such as fuel utilization rate, a suitable amount of water vapor F11 can be ensured with minimal energy.

[0123] Furthermore, if the configuration includes: a cooler (heat recovery cooler 10 or heat recovery heat exchanger 12) that further cools the anode exhaust gas F06, which has absorbed heat from the vaporizer 4, to a temperature below the dew point; a water separator 5 that removes water droplets from the anode exhaust gas F06 cooled to below the dew point and recovers them as recirculated gas (anode recovery gas F07); and a heat exchanger (circulating heat exchanger 13) that heats the recirculated gas (anode recovery gas F07: strictly speaking, anode circulating gas F09 distributed from anode recovery gas F07) by exchanging heat with the anode exhaust gas F06 before it is cooled by the cooler, then the residual heat of the anode exhaust gas F06 can be effectively utilized, and condensation can be prevented until the anode circulating gas F09 is supplied to the reformer 2.

[0124] At this time, if the configuration includes a water heat exchanger 11, which is located downstream of the heat exchanger (circulating heat exchanger 13) in the flow path (anode exhaust system 206) of the anode exhaust F06, and heats the water (circulating water F10) supplied to the gasifier 4 by exchanging heat with the anode exhaust F06 before it is cooled by the cooler (heat recovery cooler 10), the heat required in the gasifier 4 is reduced, the range of operating conditions that require auxiliary burner 4a or additional heating is narrowed, and more efficient operation can be performed.

[0125] If the system is configured to include: a gas distribution system (recovery branch 221, recirculated combustion gas system 208, anode recirculated gas system 209) that divides the recirculated gas (anode recovered gas F07: strictly speaking, anode recirculated gas F09 distributed from anode recovered gas F07) into a supply to the reformer 2 and a supply to the burner 3 used to heat the reformer 2; a flow regulator (e.g., combustion gas flow meter 31, recirculated gas flow meter 32, recirculated gas flow regulating valve 21) that adjusts the supply flow to the reformer 2 and the supply flow to the burner 3 to a set ratio; and a control unit 90 that sets the ratio according to the operating state of the fuel cell stack 1, then the distribution ratio can be appropriated, and the reformer 2, which is accompanied by an endothermic reaction, can operate stably.

[0126] If the configuration includes a pressure equalizing blower 17 that draws in recirculated gas (anode recovery gas F07) to reduce the static pressure of anode exhaust F06, then even when the pressure loss is high when passing through the gasifier 4, the static pressure of anode exhaust F06 can be made close to the static pressure of cathode exhaust F04 and thus equalized, thereby suppressing the deterioration of fuel cell stack 1 and increasing reliability.

[0127] Because it is configured to include: a blower (circulating blower 16) that pressurizes the recirculated gas (anode recovery gas F07: strictly speaking, anode circulating gas F09 distributed from anode recovery gas F07); and a mixing unit 223 that is provided between the ejector (circulator 9) and the reformer 2 to mix the recirculated gas (the anode circulating gas F09) with the gas containing the raw material F01, it can operate stably and efficiently even in systems with a low absolute flow rate of water vapor F11.

[0128] Explanation of reference numerals in the attached figures

[0129] 1: Fuel cell stack; 1a: Anode; 1c: Cathode; 1e: Electrolyte; 2: Reformer; 3: Combustor; 4: Gasifier; 4a: Auxiliary Combustor; 5: Water separator; 7: Oxidant heat exchanger; 8: Water pump; 9: Circulator (ejector); 10: Heat recovery cooler; 11: Water heat exchanger; 12: Heat recovery heat exchanger; 13: Circulating heat exchanger; 14: Water treatment unit; 16: Circulating blower (blower); 17: Fuel cell stack; 18: Anode; 19: Cathode; 20: Electrolyte; 20: Electrolyte; 21: Electrolyte; 22: Anode; 23: Electrolyte; 24: Anode; 25: Electrolyte; 20: Electrolyte; 20: Electrolyte; 21: Electrolyte; 22: Anode; 23: Electrolyte; 24: Electrolyte; 25: Electrolyte; 26: Electrolyte; 27: Electrolyte; 28: Electrolyte; 29: Electrolyte; 20 ... 18: Equalizing blower; 19: Air blower; 200: Raw material pretreatment device; 21: Circulating gas flow regulating valve; 22: Combustion gas flow regulating valve; 31: Combustion gas flow meter; 32: Circulating gas flow meter; 33: Combustion gas flow meter; 34: Preheating gas flow meter; 90: Control unit; 100: Fuel cell system; 201: Raw material system; 202: Fuel gas system; 203: Oxidant system; 204: 205: Cathode exhaust system; 206: Reforming gas system; 207: Anode exhaust system; 208: Anode recovery gas system; 209: Anode circulating gas system; 210: Circulating water system; 211: Steam system; 212: Preheating combustion gas system; 213: Combustion combustion gas system; 214: Heat recovery system; 215: Combustion exhaust system; 221: Recovery branch; 222: Air branch; 223: Mixing section; F01: Raw material; F02: Fuel gas; F03: Oxidant; F04: Cathode exhaust; F05: Reforming gas; F06: Anode exhaust; F07: Anode recovery gas; F08: Recirculating combustion gas; F09: Anode circulating gas; F10: Circulating water; F11: Steam; F12: Preheating combustion gas; F13: Combustion combustion gas; F14: Refrigerant; F15: Combustion exhaust.

Claims

1. A fuel cell system, characterized in that, have: A reformer is a device that reacts hydrocarbons with water to produce reformed gas containing hydrogen. A fuel cell stack that generates electrical energy through an electrochemical reaction of reformed gas and oxidant separated by an anode and a cathode; An injector, using water vapor as the driving fluid (for the moisture content), draws in either the feedstock containing the hydrocarbons or the recycle gas recovered from the anode exhaust, and supplies it to the reformer; and A vaporizer that vaporizes water to produce the water vapor, wherein, The operating temperature of the fuel cell stack is higher than the boiling point of water at the operating pressure. The vaporizer generates the water vapor by exchanging heat with the anode exhaust gas prior to the recovery of the recirculated gas.

2. The fuel cell system according to claim 1, characterized in that, have: An auxiliary burner for heating the gasifier or for adding heating to the steam; and The control unit adjusts the start-up and stop times of the auxiliary burner based on the operating status of the reformer and the fuel cell stack.

3. The fuel cell system according to claim 1 or 2, characterized in that, have: A cooler that further cools the anode exhaust gas, which has absorbed heat from the vaporizer, to a temperature below the dew point; A water separator that removes water droplets from the anode exhaust cooled below the dew point, recovering them as the recirculated gas; and A heat exchanger heats the recirculated gas by exchanging heat with the anode exhaust gas before it is cooled by the cooler.

4. The fuel cell system according to claim 3, characterized in that, It includes: a water heat exchanger disposed downstream of the heat exchanger in the flow path of the anode exhaust gas, which heats the water supplied to the gasifier by heat exchange with the anode exhaust gas before it is cooled by the cooler.

5. The fuel cell system according to claim 1 or 2, characterized in that, have: A gas distribution system that divides the recirculated gas into a supply for the reformer and a supply for a burner used to heat the reformer; A flow regulator that adjusts the supply flow to the reformer and the supply flow to the burner to a set ratio; as well as The control unit sets the ratio based on the operating status of the fuel cell stack.

6. The fuel cell system according to claim 1 or 2, characterized in that, It includes: a pressure equalizing blower that draws in the recirculated gas to reduce the static pressure of the anode exhaust.

7. The fuel cell system according to claim 1 or 2, characterized in that, It comprises: a blower that pressurizes the recirculated gas; and a mixing unit disposed between the ejector and the reformer to mix the recirculated gas with the gas containing the raw material.

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