Fuel cell system

Abstract

A fuel cell system comprises: a fuel cell module, which comprises a first fuel cell and a second fuel cell; and an oxidant gas temperature adjustment device, which adjusts the temperature of the oxidant gas supplied to the fuel cell module, at least the first fuel cell is capable of reforming the fuel gas, the fuel cell system also comprises a temperature control unit, the temperature control unit sets a target temperature of the oxidant gas supplied to the fuel cell module in such a way that the temperature of the first fuel cell and the temperature of the second fuel cell do not exceed a prescribed upper limit temperature, and controls the oxidant gas temperature adjustment device based on the target temperature, when the target temperature is set to T, the upper limit temperature is set to Tmax, the difference obtained by subtracting the inlet temperature from the outlet temperature of the first fuel cell is set to ΔT1, and the difference obtained by subtracting the inlet temperature from the outlet temperature of the second fuel cell is set to ΔT2, the temperature control unit calculates the target temperature T as: T=Tmax-ΔT1-ΔT2 (ΔT1>0), T=Tmax-ΔT2 (ΔT1≤0), T=Tmax (ΔT2<0 and ΔT1+ΔT2<0).

Description

Technical Field

[0001] The invention relates to a fuel cell system. Background Art

[0002] US2012 / 0034538A discloses the following structure: in a fuel cell system having a first fuel cell and a second fuel cell arranged in series, when the temperature of the second fuel cell rises, the air flow rate supplied to the cathode is increased; when the temperature of the first fuel cell rises, the air flow rate supplied to the cathode is increased or the air flow rate in a bypass flow path connected to the first fuel cell so as to bypass the second fuel cell is increased, thereby adjusting the temperatures of the first fuel cell and the second fuel cell. Summary of the invention

[0003] However, when the above structure is implemented, it is necessary to detect the temperature of the first fuel cell and the temperature of the second fuel cell. Generally speaking, when detecting the temperature of the fuel cell, the outlet temperature of the cathode of the fuel cell is detected, but arranging a sensor at the outlet of the cathode of the second fuel cell, that is, between the first fuel cell and the second fuel cell, will lead to a larger system or an increase in cost.

[0004] Therefore, an object of the present invention is to provide a fuel cell system including fuel cells arranged in series and capable of adjusting the temperature of the fuel cells with a simple structure.

[0005] According to a certain embodiment of the present invention, a fuel cell system includes: a fuel cell module, which includes a first fuel cell and a second fuel cell arranged in series, and the flow direction of the fuel gas is from the first fuel cell toward the second fuel cell, and the flow direction of the oxidant gas is from the second fuel cell toward the first fuel cell; and an oxidant gas temperature adjustment device, which adjusts the temperature of the oxidant gas supplied to the fuel cell module, at least the first fuel cell can reform the fuel gas, the fuel cell system also includes a temperature control unit, the temperature control unit sets a target temperature of the oxidant gas supplied to the fuel cell module, and controls the oxidant gas temperature adjustment device based on the target temperature so that the temperature of the first fuel cell and the temperature of the second fuel cell do not exceed a specified upper limit temperature. When the target temperature is set to T, the upper limit temperature is set to Tmax, the difference obtained by subtracting the inlet temperature from the outlet temperature of the first fuel cell is set to ΔT1, and the difference obtained by subtracting the inlet temperature from the outlet temperature of the second fuel cell is set to ΔT2, the temperature control unit calculates the target temperature T as: T=Tmax-ΔT1-ΔT2 (ΔT1>0), T=Tmax-ΔT2 (ΔT1≤0), T=Tmax (ΔT2<0 and ΔT1+ΔT2<0). BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a block diagram for simply explaining the present invention and a diagram showing the temperature distribution in the fuel cell stack.

[0007] Figure 2 : is a block diagram showing the main structure of the fuel cell system of this embodiment.

[0008] Figure 3 It is a map showing the relationship between the target air flow rate and the target extracted power.

[0009] Figure 4 It is a map showing the relationship between the target fuel flow rate and the target extracted electric power.

[0010] Figure 5 It is a map showing the relationship between the target partial oxidation reaction air flow rate and the target extracted power.

[0011] Figure 6 It is a control flow chart of the air temperature control unit. DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] <Basic Operation of the Present Invention>

[0014] Figure 1 It is a block diagram for simply explaining the present invention and a diagram showing the temperature distribution in the fuel cell stack.

[0015] like Figure 1 As shown, the fuel cell system of the present invention includes a fuel cell module 1, in which two fuel cell stacks, namely a first fuel cell stack 11 (first fuel cell, STK1) and a second fuel cell stack 12 (second fuel cell, STK2) are arranged in series with respect to a gas flow path, so that the anode gas (fuel gas) flows from the first fuel cell stack 11 to the second fuel cell stack 12, and the cathode gas (oxidant gas) flows from the second fuel cell stack 12 to the first fuel cell stack 11. That is, in the fuel cell module 1, the flow direction of the anode gas and the flow direction of the cathode gas between the first fuel cell stack 11 and the second fuel cell stack 12 as two stacks are opposite to each other.

[0016] In the fuel cell module 1, the inlet of the anode of the first fuel cell stack 11 becomes the inlet of the anode gas, and the inlet of the cathode of the second fuel cell stack 12 becomes the inlet of the cathode gas. The outlet of the anode of the first fuel cell stack 11 is connected to the inlet of the anode of the second fuel cell stack 12, and the outlet of the cathode of the second fuel cell stack 12 is connected to the inlet of the cathode of the first fuel cell stack 11.

[0017] The fuel cell system of the present invention is also provided with a temperature adjustment device 38 (oxidant gas temperature adjustment device) for adjusting the temperature of the cathode gas supplied to the fuel cell module 1, but details will be described later.

[0018] In the fuel cell system of the present invention, a catalyst capable of reforming the fuel gas is arranged in the first fuel cell stack 11 (and the second fuel cell stack 12). The first fuel cell stack 11 reforms the fuel gas into an anode gas (reforming fuel) containing hydrogen, and generates electricity using the reformed anode gas and the cathode gas supplied from the second fuel cell stack 12, and supplies the remaining anode gas to the second fuel cell stack 12. In addition, the cathode gas used for the power generation reaction is discharged as cathode exhaust to the burner 4 constituting the temperature adjustment device 38.

[0019] The second fuel cell stack 12 generates electricity using the anode gas supplied from the first fuel cell stack 11 and the cathode gas supplied from the temperature adjustment device 38. The second fuel cell stack 12 supplies the cathode gas used in power generation to the first fuel cell stack 11, and supplies the anode gas used in power generation to the burner 4 as anode exhaust gas.

[0020] In the first fuel cell stack 11 and the second fuel cell stack 12, the higher the temperature, the higher the power generation efficiency. However, an upper limit temperature (eg, 800°C) is set for the first fuel cell stack 11 and the second fuel cell stack 12 for reasons such as heat resistance.

[0021] Therefore, it is necessary to adjust the temperature of the cathode gas in such a manner that the temperature of the first fuel cell stack 11 (the outlet temperature of the cathode of the first fuel cell stack 11) and the temperature of the second fuel cell stack 12 (the outlet temperature of the cathode of the second fuel cell stack 12) do not exceed the upper limit temperature and the power generation reaction can be fully carried out.

[0022] In the invention of the present application, for example, the inlet temperature of the cathode of the second fuel cell stack 12 (the temperature of the cathode gas at the inlet of the cathode) is set as the target temperature, and the temperature adjustment device 38 is controlled in accordance with the target temperature so that the temperature of the first fuel cell stack 11 and the second fuel cell stack 12 does not exceed the upper limit temperature. In this way, the temperature detection unit ( Figure 2 The target temperature is calculated by the target temperature calculation unit 753 ( Figure 2 ) operation.

[0023] In addition, the power generation reaction occurring in the first fuel cell stack 11 and the second fuel cell stack 12 is an exothermic reaction, but the reforming reaction occurring in the first fuel cell stack 11 is an endothermic reaction. In addition, the cathode gas is heated by the temperature adjustment device 38, but depending on the degree of the power generation reaction and the reforming reaction, the cathode gas may be heated in the first fuel cell stack 11 and the second fuel cell stack 12 or cooled in the first fuel cell stack 11 and the second fuel cell stack 12. Therefore, Figure 1 As shown, the temperature distribution of the cathode gas is sometimes as shown in AD below.

[0024] A is the following situation: the load (power generation amount) of the first fuel cell stack 11 and the second fuel cell stack 12 is large, the heat generated by the power generation reaction in the first fuel cell stack 11 becomes sufficiently greater than the heat absorbed by the reforming reaction, and the temperature of the first fuel cell stack 11 and the second fuel cell stack 12 (the outlet temperature of the cathode) becomes higher than the temperature of the cathode gas supplied from the temperature adjustment device 38. In this case, the temperature of the cathode gas supplied from the temperature adjustment device 38 increases as it flows downstream of the cathode gas flow path, and becomes the highest temperature at the outlet of the cathode of the first fuel cell stack 11.

[0025] Here, if the difference obtained by subtracting the inlet temperature from the outlet temperature of the first fuel cell stack 11 is ΔT1, and the difference obtained by subtracting the inlet temperature from the outlet temperature of the second fuel cell stack 12 is ΔT2, then in case A, ΔT1>0, ΔT2>0.

[0026] Therefore, if the target temperature is set to T and the upper limit temperature is set to Tmax, the target temperature calculation unit 753 ( Figure 2 ) The target temperature T is calculated by T=Tmax-ΔT1-ΔT2, thereby setting the outlet temperature of the cathode of the first fuel cell stack 11, which is the highest temperature, as the upper limit temperature Tmax.

[0027] B is the following situation: the load (power generation) for the first fuel cell stack 11 and the second fuel cell stack 12 becomes smaller than that in A, for example, the heat absorption generated by the reforming reaction in the first fuel cell stack 11 becomes the same as the heat generation generated by the power generation reaction. At this time, the temperature of the second fuel cell stack 12 is higher than the temperature of the cathode gas supplied from the temperature adjustment device 38, but the temperature of the first fuel cell stack 11 is lower than the temperature of the cathode gas discharged from the second fuel cell stack 12. As a result, the temperature of the cathode gas becomes the highest temperature at the outlet of the cathode of the second fuel cell stack 12. In addition, in this case, ΔT1≤0, T2>0.

[0028] Therefore, the target temperature calculation unit 753 ( Figure 2) The target temperature T is calculated by T=Tmax-ΔT2, thereby enabling the outlet temperature of the cathode of the second fuel cell stack 12 (i.e., the inlet temperature of the cathode of the first fuel cell stack 11), which will be the highest temperature, to be set as the upper limit temperature Tmax.

[0029] C is the following situation: the load (power generation) for the first fuel cell stack 11 and the second fuel cell stack 12 decreases sharply, and the temperature of the second fuel cell stack 12 becomes lower than the temperature of the cathode gas supplied from the temperature adjustment device 38. At this time, a temperature distribution of ΔT2<0 and ΔT1+ΔT2<0 may be generated. Here, ΔT1 includes the case of ΔT1<0, or the case of ΔT1>0 and its absolute value is less than ΔT2. In this case, the temperature of the cathode gas becomes the highest temperature at the inlet of the cathode of the second fuel cell stack 12.

[0030] Therefore, the target temperature calculation unit 753 ( Figure 2 ) By calculating the target temperature T by T=Tmax, the inlet temperature of the cathode of the second fuel cell stack 12, which is the highest temperature, can be set as the upper limit temperature Tmax.

[0031] D is the same scenario as C, which occurs when, for example, the heat capacity of the first fuel cell stack 11 is greater than the heat capacity of the second fuel cell stack 12, and the degree of temperature reduction of the first fuel cell stack 11 is small. In this case, a temperature distribution is generated such that ΔT2<0 but ΔT1+ΔT2≥0. In this case, the outlet temperature of the cathode of the first fuel cell stack 11 becomes the highest temperature.

[0032] Therefore, the target temperature calculation unit 753 ( Figure 2 ) The target temperature T is calculated by T=Tmax-ΔT1-ΔT2, thereby setting the outlet temperature of the cathode of the first fuel cell stack 11, which is the highest temperature, as the upper limit temperature Tmax. Here, since ΔT1>0, the setting condition of the target temperature T in D is the same as A.

[0033] As described later, ΔT1 and ΔT2 can be calculated. Therefore, the calculation formula for switching the target temperature T makes it possible to determine the position of the first fuel cell stack 11 and the second fuel cell stack 12 where the highest temperature is, by calculating ΔT1 and ΔT2 according to the load on the first fuel cell stack 11 and the second fuel cell stack 12, and set the temperature of the position as the upper limit temperature Tmax. In this way, the first fuel cell stack 11 and the second fuel cell stack 12 can be prevented from being overheated and can be heated to a high temperature.

[0034] As described above, the target temperature calculation unit 753 ( Figure 2 ) The target temperature T can be calculated according to different situations as shown in the following formula 1.

[0035] [Formula 1]

[0036]

[0037] In addition, the target temperature T can also be set to the outlet temperature of the cathode of the first fuel cell stack 11 (the temperature of the cathode gas at the cathode). Figure 1 , then the target temperature calculation unit 753 ( Figure 2 ) The target temperature T can be calculated according to different situations as shown in the following formula 2.

[0038] [Formula 2]

[0039]

[0040] <Structure of this embodiment>

[0041] Figure 2 : is a block diagram showing the main structure of the fuel cell system of this embodiment.

[0042] The fuel cell system of this embodiment is composed of a fuel supply system for supplying anode gas to the fuel cell module 1, an air supply system for supplying air (cathode gas) to the fuel cell module 1, a combustion system for burning the anode exhaust (anode gas) and cathode exhaust (cathode gas) discharged from the fuel cell module 1, a drive system for extracting electricity from the fuel cell module 1 to obtain power, and a control system for controlling the entire system, and is mainly mounted on a vehicle (electric vehicle).

[0043] The fuel supply system includes a tank 21 (TANK), an injector 23 (INJ1), and an injector 24 (INJ2). The air supply system includes a blower 32 (BLW), a bypass valve 33 (BYPVAL), a heat exchanger 35 (HEX), and a variable valve 37 (VAL). The combustion system includes a burner 4 (CMB). Furthermore, the bypass valve 33, the heat exchanger 35, the burner 4, and the injector 24 constitute a temperature adjustment device 38.

[0044] The drive system includes a DC / DC converter 61 (CONV), a battery 62 (BATT), and a drive motor 63 (M). The control system includes a control unit 7 (CONT) that controls the entire system.

[0045] The first fuel cell stack 11 and the second fuel cell stack 12 constituting the fuel cell module 1 are solid oxide fuel cells (SOFC: Solid Oxide Fuel Cell), which are batteries obtained by stacking battery cells, each of which has an electrolyte layer formed of a solid oxide such as ceramics, and the battery cell is obtained by sandwiching the electrolyte layer between an anode (fuel electrode) supplied with an anode gas (reforming gas) and a cathode (air electrode) supplied with air containing oxygen as a cathode gas (oxidant gas).

[0046] Here, a catalyst for reforming the reforming fuel supplied from the injector 23 side into an anode gas (reformed fuel gas) containing hydrogen is arranged in the electrolyte layer of the first fuel cell stack 11 (and the second fuel cell stack 12 ).

[0047] The first fuel cell stack 11 generates electricity by reacting hydrogen contained in the anode gas with oxygen in the cathode gas, supplies the remaining anode gas to the second fuel cell stack 12 , and discharges the cathode exhaust gas to the combustor 4 .

[0048] The second fuel cell stack 12 generates electricity by reacting the anode gas supplied from the first fuel cell stack 11 with the cathode gas supplied from the blower 32 via the temperature adjustment device 38 , and supplies the remaining cathode gas to the first fuel cell stack 11 and discharges the anode exhaust gas to the burner 4 .

[0049] Here, the anode is configured to include not only the anode electrodes in the first fuel cell stack 11 and the second fuel cell stack 12, but also an internal flow path for supplying anode gas to the anode electrode and an internal flow path for discharging anode exhaust after the reaction at the anode electrode. Similarly, the cathode is configured to include not only the cathode electrodes in the first fuel cell stack 11 and the second fuel cell stack 12, but also an internal flow path for supplying cathode gas to the cathode electrode and an internal flow path for discharging cathode exhaust after the reaction at the cathode electrode.

[0050] In the fuel supply system, the tank 21 stores fuel (gas) such as methane or natural gas containing methane as a main component under high pressure, supplies fuel as reforming fuel to the injector 23, and supplies fuel as additional fuel for combustion to the injector 24.

[0051] The fuel supply system includes a fuel flow path 22 (main flow path) that supplies reforming fuel from a tank 21 to the anode of the first fuel cell stack 11 via an injector 23 .

[0052] In addition, a sub-flow path (not shown) branches off from the fuel flow path 22 , and the sub-flow path is connected to the injector 24 .

[0053] The injectors 23 and 24 include: a nozzle body (not shown) into which fuel is pressed; a plunger rod (not shown) which is urged in a direction to close a fuel injection hole (not shown) at the front end of the nozzle body; and a solenoid (not shown) which moves the plunger rod in a direction opposite to the urged direction.

[0054] In the injectors 23 and 24, a command signal (current) is applied to the solenoid, whereby the solenoid drives the plunger rod so as to move the plunger rod in the reverse direction, whereby the plunger rod opens the fuel injection hole to inject fuel. In addition, by stopping the command signal (current), the drive of the solenoid is stopped, the plunger rod moves due to the applied force, and the fuel injection hole is closed to stop the injection of fuel.

[0055] In the injectors 23 and 24, the duty ratio of opening / closing the fuel injection hole depends on the duty ratio of turning on / off the command signal (current). Therefore, the injectors 23 and 24 can adjust the flow rate of the injected fuel by adjusting the duty ratio of the command signal (current).

[0056] The air supply system includes an air flow path 31 for supplying cathode gas (air) to the cathode of the second fuel cell stack 12. In the air flow path 31, a blower 32, a bypass valve 33, and a heat exchanger 35 are arranged from upstream.

[0057] The blower 32 (oxidant gas supply source) takes in external air and supplies air (cathode gas) to the air flow path 31 and the like.

[0058] The heat exchanger 35 communicates with the cathode of the second fuel cell stack 12 via the air flow path 31, exchanges heat (heats) the cathode gas with the combustion gas exhausted from the burner 4, and supplies the cathode gas to the cathode of the second fuel cell stack 12. The combustion gas after heat exchange is exhausted to the outside.

[0059] The bypass valve 33 (flow rate adjustment unit) is arranged at a position upstream of the heat exchanger 35 in the air flow path 31. The upstream side of the bypass valve 33 is connected to the blower 32, and the downstream side is connected to the air flow path 31 (heat exchanger 35) and the bypass flow path 34. The bypass valve 33 adjusts the ratio of the flow rate of the cathode gas (air) in the air flow path 31 and the bypass flow path 34 by adjusting the opening. The bypass flow path 34 bypasses the heat exchanger 35 and merges with the air flow path 31 at a position between the heat exchanger 35 and the cathode of the second fuel cell stack 12 in the air flow path 31.

[0060] A supply path 36 branches off from the air flow path 31 at a position upstream of the bypass valve 33 , and the supply path 36 merges with the fuel flow path 22 at a position in the fuel flow path 22 between the first fuel cell stack 11 and the injector 23 .

[0061] The variable valve 37 is arranged on the supply path 36, and is used to adjust the flow rate of air (oxygen) flowing in the supply path 36. When air (oxygen) is supplied to the anode of the first fuel cell stack 11, the anode gas and oxygen can undergo a partial oxidation reaction (heat-generating reaction) by means of a catalyst arranged on the first fuel cell stack 11 (which may also be the same as the catalyst used for the reforming reaction), so that the temperature of the first fuel cell stack 11 rises. Thus, the partial oxidation reaction air flow control unit 73 described later can avoid lowering the temperature of the first fuel cell stack 11 to a lower limit value below the temperature at which the reforming reaction can be performed. At this time, the blower 32 functions as an oxygen supply source.

[0062] In addition, the supply path 36 may also be connected to the inlet of the anode of the second fuel cell stack 12, so that a partial oxidation reaction can also be performed in the second fuel cell stack 12. In addition, when a partial oxidation reaction is not required, the supply path 36 and the variable valve 37 (and the partial oxidation reaction air flow control unit 73 described later) may be omitted in the first fuel cell stack 11 and the second fuel cell stack 12.

[0063] In the combustion system, the burner 4 is connected to the outlet of the anode of the first fuel cell stack 11 and the outlet of the cathode of the second fuel cell stack 12. A mixed gas of the anode exhaust and the cathode exhaust is introduced into the burner 4. The burner 4 causes catalytic combustion of the mixed gas to generate combustion gas. The burner 4 is provided with a catalyst (not shown) for performing the above-mentioned catalytic combustion and a heater (not shown) for heating the catalyst (not shown) to a temperature at which the fuel can be burned. In addition, additional fuel is supplied to the burner 4 from the injector 24. Thus, the burner 4 burns the mixed gas and the combustion gas while burning the additional fuel, thereby further increasing the temperature of the combustion gas.

[0064] In the temperature adjustment device 38 (bypass valve 33, heat exchanger 35, burner 4, injector 24), the temperature of the combustion gas can be increased by supplying additional fuel to the burner 4, thereby increasing the temperature of the cathode gas passing through the heat exchanger 35, or the temperature of the cathode gas supplied to the fuel cell module 1 can be reduced / increased by increasing / decreasing the flow rate of the cathode gas flowing in the bypass flow path 34.

[0065] The temperature sensor 51 is used to detect the inlet temperature of the cathode of the second fuel cell stack 12. In addition, the temperature sensor 51 may also be arranged at the outlet of the cathode of the first fuel cell stack 11.

[0066] The flow rate sensor 52 is used to detect the flow rate of air (cathode gas) taken in by the blower 32 .

[0067] The first voltage sensor 53 is used to detect the output voltage of the first fuel cell stack 11 .

[0068] The second voltage sensor 54 is used to detect the output voltage of the second fuel cell stack 12 .

[0069] Here, the first fuel cell stack 11 and the second fuel cell stack 12 are also electrically connected in series.

[0070] The current sensor 55 is used to detect the output current flowing between the first fuel cell stack 11 and the second fuel cell stack 12 connected in series and the DC / DC converter 61 .

[0071] The DC / DC converter 61 is connected to the series circuit of the first fuel cell stack 11 and the second fuel cell stack 12 , and boosts the output voltage of the series circuit to supply electric power to the battery 62 or the drive motor 63 .

[0072] The first fuel cell stack 11 and the second fuel cell stack 12 can also extract power independently without being electrically connected. In this case, the following structure can be set: two DC / DC converters 61 are prepared, one DC / DC converter 61 is connected to the first fuel cell stack 11, and the other DC / DC converter 61 is connected to the second fuel cell stack 12, and the two DC / DC converters 61 are connected to the battery 62 and the drive motor 63.

[0073] The battery 62 is charged with the electric power supplied from the DC / DC converter 61 , and can supply the electric power to the drive motor 63 .

[0074] The drive motor 63 is connected to the battery 62 and the DC / DC converter 61 via an inverter (not shown) to serve as a power source for the vehicle. The drive motor 63 generates regenerative power when the vehicle decelerates, and the regenerative power can be charged into the battery 62.

[0075] The control unit 7 is composed of a general-purpose circuit including a microcomputer, a microprocessor, and a CPU, and peripheral devices, and executes a process for controlling the fuel cell system by executing a specific program.

[0076] The control unit 7 includes an extraction power control unit 71 (POWERCONT), an air flow control unit 72 (AIRFLOWCONT), a partial oxidation reaction air flow control unit 73 (POXAIRFLOWCONT), a fuel flow control unit 74 (FUELFLOWCONT), and an air temperature control unit 75 (AIRTEMPCONT). In addition, the control unit 7 includes a calculation unit (not shown) that calculates the target extraction power (POWER) based on the charge rate (SOC) of the battery 62 and the driver's driving request (accelerator pedal opening).

[0077] The control unit 7 can perform start-up control and stop control of the fuel cell system, but these controls are conventional techniques and thus description thereof will be omitted.

[0078] When receiving information on the target power output, the power output control unit 71 outputs a command signal to the DC / DC converter 61 so that the power output from the fuel cell module 1 becomes the target power output. The power output from the fuel cell module 1 is supplied to the battery 62 or the drive motor 63 .

[0079] Figure 3 It is a map showing the relationship between the target air flow rate and the target extracted power. Figure 4 It is a map showing the relationship between the target fuel flow rate and the target extracted electric power. Figure 5 It is a map showing the relationship between the target partial oxidation reaction air flow rate and the target extracted power.

[0080] When the information of the target power output is input, the air flow control unit 72 outputs a command signal for achieving the target air flow to the blower 32. Here, the target air flow is an air flow that can ensure the amount of oxygen required for the fuel cell module 1 to generate the target power output and the amount of oxygen required for the anode exhaust gas discharged from the fuel cell module 1 to be burned in the burner 4.

[0081] The relationship between the target power output and the target air flow rate is set in advance through experiments and desktop research. Figure 3 As shown, the air flow control unit 72 can include a map having the target power output (POWER) as an input value and the target air flow (AIRFLOW) as an output value. Thus, the air flow control unit 72 can determine the target air flow corresponding to the target power output.

[0082] When receiving information on the target power output, the fuel flow control unit 74 outputs a command signal for achieving the target fuel flow to the injector 23. The target fuel flow is a fuel flow that ensures a fuel utilization rate that enables stable power generation in the fuel cell module 1 and generates the target power output.

[0083] The relationship between the target power output and the target fuel flow rate is set in advance through experiments and desktop studies. Figure 4 As shown, the fuel flow rate control unit 74 can include a map having the target power extraction (POWER) as an input value and the target fuel flow rate (FUELFLOW) as an output value. Thus, the fuel flow rate control unit 74 can determine the target fuel flow rate corresponding to the target power extraction.

[0084] When the information of the target power extraction is input, the partial oxidation reaction air flow control unit 73 outputs a command signal for forming the opening degree of the variable valve 37 for achieving the target partial oxidation reaction air flow to the variable valve 37. The target partial oxidation reaction air flow is an air flow rate supplied to the first fuel cell stack 11 based on the target power extraction in a manner that does not make the temperature of the first fuel cell stack 11 too low (for example, in a manner that the temperature does not fall below the lower limit temperature at which the reforming reaction can be carried out by the catalyst).

[0085] The relationship between the target power extraction and the target partial oxidation reaction air flow rate is set in advance through experiments and desktop studies. Figure 5 As shown, the partial oxidation reaction air flow control unit 73 can include a mapping that sets the target extracted power (POWER) as an input value and the target partial oxidation reaction air flow (POXAIRFLOW) as an output value. Thus, the partial oxidation reaction air flow control unit 73 can determine the target partial oxidation reaction air flow corresponding to the target extracted power.

[0086] The air temperature control unit 75 (temperature control means) includes a first temperature difference calculation unit 751 (STK1ΔT1COMP), a second temperature difference calculation unit 752 (STK2ΔT2COMP), a target temperature calculation unit 753 (AIRTEMPCOMP), and a drive control unit 754 (DRIVECONT).

[0087] When the first temperature difference calculation unit 751 is input with the target fuel flow rate, the target air flow rate for partial oxidation reaction, the air flow rate detected by the flow sensor 52, the voltage detected by the first voltage sensor 53, the voltage detected by the second voltage sensor 54, and the current detected by the current sensor 55, it calculates the difference ΔT1 obtained by subtracting the inlet temperature from the outlet temperature of the cathode of the first fuel cell stack 11 as shown in the following formula 3.

[0088] [Formula 3]

[0089]

[0090] Here, Pp1[W] is the calorific value generated by the power generation of the first fuel cell stack 11. For Pp1, the calorific value corresponding to the power generated by the first fuel cell stack 11 is calculated using the results obtained in advance through experiments and desktop studies (a mapping in which the power generation is set as an input value and the calorific value is set as an output value). In addition, the power generation of the first fuel cell stack 11 can be obtained by multiplying the voltage detected by the first voltage sensor 53 (more precisely, the amount of decrease from the open voltage of the first fuel cell stack 11) by the current detected by the current sensor 55.

[0091] Pr1[W] is the endothermic heat generated by the reforming reaction occurring in the first fuel cell stack 11. The reaction formula of the reforming reaction is CH4+2H2O→4H2+CO2-165[kJ / mol], which is proportional to the flow rate of CH4 [mol / s]. In addition, in the partial oxidation reaction, 2 moles of CH4 are consumed for 1 mole of oxygen. Therefore, the flow rate of CH4 after the partial oxidation reaction is the difference obtained by subtracting the flow rate of 2 times the flow rate of oxygen in the target partial oxidation air flow rate (the flow rate of CH4 consumed in the partial oxidation reaction) from the flow rate of CH4 before the partial oxidation reaction.

[0092] Therefore, the first temperature difference calculation unit 751 calculates Pr1 by, for example, (the amount of heat absorbed by the reforming reaction per 1 mol of the reforming fuel (165 [kJ])) × (target fuel flow rate [mol / s] - the flow rate of oxygen in the target partial oxidation air flow rate [mol / s] × 2). The oxygen flow rate is calculated based on 21% of the air flow rate.

[0093] However, it is not limited to that all the reforming fuel is reformed, and it may vary depending on the reaction speed of the reforming reaction. Therefore, the reforming amount may also vary according to the pressure and flow rate of the reforming fuel, so Pr can also be corrected by detecting these changes and according to these changes, and Pr can also be corrected by detecting the components of the anode gas at the inlet and outlet of the anode of the first fuel cell stack 11 and according to the detection results.

[0094] Pd1 [W] is a fixed amount of heat released to the outside from components other than the anode gas and the cathode gas in the first fuel cell stack 11 , and Pd1 is calculated using results obtained in advance through experiments or desktop studies.

[0095] Po1 is the calorific value when a partial oxidation reaction occurs in the first fuel cell stack 11. The reaction formula of the partial oxidation reaction is 2CH4+O2→CO+4H2+70[kJ / mol], which is proportional to the flow rate [mol / s] of oxygen. Therefore, the first temperature difference calculation unit 751 calculates Po1 by, for example, (the calorific value of the partial oxidation reaction per 1 mole of consumed oxygen (70[kJ]))×(the flow rate of oxygen in the target partial oxidation reaction air flow rate [mol / s]).

[0096] σ[kg / m 3 ] is the density of air, c [kJ / kg·°C] is the specific heat capacity of air, and a fixed value previously determined by experiments or desktop studies is used for the air supplied to the fuel cell module 1. Alternatively, the pressure and temperature of the air may be detected and estimated.

[0097] Q[m 3 / s] is the flow rate of air taken in by the blower 32, and the value detected by the flow rate sensor 52 is used.

[0098] When calculating ΔT1, the first temperature difference calculation unit 751 outputs the calculated ΔT1 to the target temperature calculation unit 753 .

[0099] When the second temperature difference calculation unit 752 receives the same information as the first temperature difference calculation unit 751 , it calculates the difference ΔT2 obtained by subtracting the inlet temperature from the outlet temperature of the cathode of the second fuel cell stack 12 as shown in the following equation 4, similarly to ΔT1 .

[0100] [Formula 4]

[0101]

[0102] Here, Pp2[W] is the heat generated by the power generation of the second fuel cell stack 12, and Pp2 is calculated in the same way as Pp1. In addition, Pd2[W] is the fixed heat released to the outside from the components other than the anode gas and the cathode gas in the second fuel cell stack 12, and Pd2 is calculated in the same way as Pd1.

[0103] When no reforming reaction is performed in the second fuel cell stack 12, Pr2[W] is zero, but when a reforming reaction is performed, Pr2 is calculated in the same way as Pr1. When no partial oxidation reaction is performed in the second fuel cell stack 12, Po2[W] is zero, but when a partial oxidation reaction is performed, Po2 is calculated in the same way as Po1.

[0104] When calculating ΔT2, the second temperature difference calculation unit 752 outputs it to the target temperature calculation unit 753.

[0105] In addition, the above-mentioned formula 3 and formula 4 depend on the target power extraction. Therefore, the first temperature difference calculation unit 751 may also have a mapping in which the target power extraction is set as an input value and ΔT1 is set as an output value, and ΔT1 corresponding to the target power extraction may be calculated based on this. Similarly, the second temperature difference calculation unit 752 may also have a mapping in which the target power extraction is set as an input value and ΔT2 is set as an output value, and ΔT2 corresponding to the target power extraction may be calculated based on this.

[0106] When the information of ΔT1 and ΔT2 is input, the target temperature calculation unit 753 calculates the target temperature T of the air (cathode gas) according to the above-mentioned Expression 1 (or Expression 2), and outputs it to the drive control unit 754 .

[0107] The information of the target temperature T and the information of the temperature detected by the temperature sensor 51 are input to the drive control unit 754. Then, the drive control unit 754 uses the difference obtained by subtracting the detected temperature from the target temperature T, and outputs a command signal to the injector 24 and the bypass valve 33 through, for example, PI control so that the temperature of the cathode gas becomes the target temperature T. For example, when the detected temperature is lower than the target temperature T, a command signal for increasing the additional fuel amount (for increasing the duty cycle) is output to the injector 24 (additional fuel supply unit) in order to increase the temperature of the cathode gas. On the contrary, when the detected temperature is higher than the target temperature T, a command signal for controlling the opening is output to the bypass valve 33 in order to increase the flow rate of the cathode gas bypassing the heat exchanger 35 to reduce the temperature of the cathode gas. Regarding the command signal for the injector 24 and the command signal for the bypass valve 33, there is a case where only one of them is output, and there is a case where both are output at the same time.

[0108] <Control Flow>

[0109] Figure 6 : is a control flow chart of the air temperature control unit 75. Next, the control flow in the air temperature control unit 75 will be described.

[0110] First, in step S1 , the first temperature difference calculation unit 751 calculates a difference ΔT1 obtained by subtracting an inlet temperature from an outlet temperature of the cathode of the first fuel cell stack 11 .

[0111] In step S2, the second temperature difference calculation unit 752 calculates a difference ΔT2 obtained by subtracting the inlet temperature from the outlet temperature of the cathode of the second fuel cell stack 12. The steps S1 and S2 may be performed in reverse order or simultaneously.

[0112] In step S3 , the target temperature calculation unit 753 determines whether ΔT2<0 and ΔT1+ΔT2<0. If yes, the process proceeds to step S4 , and if no, the process proceeds to step S5 .

[0113] In step S4 , the target temperature calculation unit 753 determines that the cathode inlet of the second fuel cell stack 12 in the fuel cell module 1 (the temperature of the cathode gas at the inlet) is the position with the highest temperature, calculates the target temperature T by T=Tmax and outputs it to the drive control unit 754 .

[0114] In step S5 , the target temperature calculation unit 753 determines whether ΔT1>0, and if so, the process proceeds to step S6 , and if so, the process proceeds to step S7 .

[0115] In step S6, the target temperature calculation unit 753 determines that the outlet of the cathode of the first fuel cell stack 11 in the fuel cell module 1 (the temperature of the cathode gas at the outlet) is the location of the highest temperature, calculates the target temperature T by T=Tmax-ΔT1-ΔT2 and outputs it to the drive control unit 754.

[0116] In step S7, the target temperature calculation unit 753 determines that the outlet of the cathode of the second fuel cell stack 12 in the fuel cell module 1 (the temperature of the cathode gas at the outlet) is the location of the highest temperature, calculates the target temperature T by T=Tmax-ΔT2 and outputs it to the drive control unit 754.

[0117] As long as the fuel cell module 1 continues to generate power, the air temperature control unit 75 repeats the above-described process of steps S1 to S7 .

[0118] As described above, when the temperature sensor 51 is disposed at the cathode outlet of the first fuel cell stack 11 and the cathode outlet temperature is set as the target temperature, the target temperature can be calculated by the same control flow as described above. However, the target temperature calculation unit 753 calculates the target temperature according to Formula 2.

[0119] That is, in step S4, the target temperature calculation unit 753 calculates the target temperature T by T=Tmax+ΔT1+ΔT2. In step S6, the target temperature calculation unit 753 calculates the target temperature T by T=Tmax. Furthermore, in step S7, the target temperature calculation unit 753 calculates the target temperature T by T=Tmax+ΔT1.

[0120] <Effects of the present embodiment>

[0121] As described above, according to the fuel cell system of the present embodiment, the fuel cell system includes: a fuel cell module 1, which includes a first fuel cell (a first fuel cell stack 11) and a second fuel cell (a second fuel cell stack 12) arranged in series, and the flow direction of the fuel gas (anode gas) is from the first fuel cell toward the second fuel cell, and the flow direction of the oxidant gas (cathode gas) is from the second fuel cell (the second fuel cell stack 12) toward the first fuel cell (the first fuel cell stack 11); and an oxidant gas temperature adjustment device (temperature adjustment device 38), which adjusts the temperature of the oxidant gas (cathode gas) supplied to the fuel cell module 1, at least the first fuel cell (the first fuel cell stack 11) can reform the fuel gas (anode gas), and the fuel cell system also includes a temperature control unit (air temperature control unit 75), which temperature control unit allows the first fuel cell to The target temperature of the oxidant gas (cathode gas) supplied to the fuel cell module 1 is set in such a way that the temperature of the material cell (the first fuel cell stack 11) and the temperature of the second fuel cell (the second fuel cell stack 12) do not exceed the prescribed upper limit temperature, and the oxidant gas temperature adjustment device (temperature adjustment device 38) is controlled based on the target temperature. When the target temperature is set to T, the upper limit temperature is set to Tmax, the difference obtained by subtracting the inlet temperature from the outlet temperature of the first fuel cell (the first fuel cell stack 11) is set to ΔT1, and the difference obtained by subtracting the inlet temperature from the outlet temperature of the second fuel cell (the second fuel cell stack 12) is set to ΔT2, the temperature control unit (air temperature control unit 75) calculates the target temperature T as: T=Tmax-ΔT1-ΔT2 (ΔT1>0), T=Tmax-ΔT2 (ΔT1≤0), T=Tmax (ΔT2<0 and ΔT1+ΔT2<0).

[0122] According to the above structure, even when the position of the highest temperature in the fuel cell module 1 is the outlet of the cathode of the first fuel cell (first fuel cell stack 11) or the outlet of the cathode of the second fuel cell (second fuel cell stack 12), the position of the highest temperature can be determined by calculating ΔT1 and ΔT2, and the target temperature T can be calculated accordingly. Therefore, even in the fuel cell module 1 including at least the first fuel cell (first fuel cell stack 11) in which the reforming reaction occurs, control of power generation without exceeding the upper limit temperature and maintaining a high temperature can be achieved with a simple structure.

[0123] Furthermore, according to the above structure, when the position of the highest temperature in the fuel cell module 1 is the inlet of the cathode of the second fuel cell (the second fuel cell stack 12), it is also possible to determine that the position of the highest temperature is the inlet by calculating ΔT1 and ΔT2, and calculate the target temperature T accordingly. Therefore, even in the fuel cell module 1 including at least the first fuel cell (the first fuel cell stack 11) in which the reforming reaction occurs, it is possible to achieve control of power generation without exceeding the upper limit temperature and maintaining a high temperature with a simple structure.

[0124] In the present embodiment, the temperature control unit (air temperature control unit 75) calculates ΔT1 based on the amount of heat generated accompanying the power generation of the first fuel cell (first fuel cell stack 11), the amount of heat absorbed in the reforming reaction of the fuel gas (anode gas) supplied to the first fuel cell (first fuel cell stack 11), the amount of heat dissipated to the outside of the first fuel cell (first fuel cell stack 11), and the flow rate of the oxidant gas (cathode gas) supplied to the first fuel cell (first fuel cell stack 11). The temperature control unit calculates ΔT2 based on the amount of heat generated accompanying the power generation of the second fuel cell (second fuel cell stack 12), the amount of heat dissipated to the outside of the second fuel cell (second fuel cell stack 12), and the flow rate of the oxidant gas (cathode gas) supplied to the second fuel cell (second fuel cell stack 12).

[0125] According to the above configuration, ΔT1 and ΔT2 can be calculated without actually detecting the temperature.

[0126] In the present embodiment, an oxygen supply source (blower 32) for supplying oxygen to the anode of the first fuel cell (first fuel cell stack 11) is further provided. At least in the first fuel cell (first fuel cell stack 11), a partial oxidation reaction can occur between oxygen and the fuel gas (anode gas). The temperature control unit (air temperature control unit 75) controls the temperature of the anode gas to be heated based on the heat generated by the power generation of the first fuel cell (first fuel cell stack 11), the heat generated by the partial oxidation reaction, and the heat generated by the partial oxidation reaction. ΔT1 is calculated based on the endothermic amount generated in the differential reforming reaction obtained by the flow rate of the feed gas (anode gas), the heat dissipated to the outside of the first fuel cell (first fuel cell stack 11), and the flow rate of the oxidant gas (cathode gas) supplied to the first fuel cell (first fuel cell stack 11). The temperature control unit calculates ΔT2 based on the heat generated by the power generation of the second fuel cell (second fuel cell stack 12), the heat dissipated to the outside of the second fuel cell (second fuel cell stack 12), and the flow rate of the oxidant gas (cathode gas) supplied to the second fuel cell (second fuel cell stack 12).

[0127] According to the above configuration, even when the partial oxidation reaction is performed in the first fuel cell (first fuel cell stack 11 ), ΔT1 and ΔT2 can be calculated without actually detecting the temperature.

[0128] In the present embodiment, the oxidant gas temperature adjustment device (temperature adjustment device 38) comprises: a burner 4, which mixes and burns the fuel exhaust (anode exhaust) discharged from the fuel cell module 1 and the oxidant exhaust (cathode exhaust); a heat exchanger 35, which performs heat exchange between the combustion gas discharged from the burner 4 and the oxidant gas (cathode gas) supplied to the fuel cell module 1; and an additional fuel supply unit (injector 24), which supplies additional fuel to the burner 4, and the temperature control unit (air temperature control unit 75) controls the additional fuel supply unit (injector 24) so ​​that the oxidant gas (cathode gas) reaches the target temperature.

[0129] The temperature of the air taken in from the outside is equivalent to the outside air temperature. Since it is so low that directly supplying it to the fuel cell module 1 (SOFC) will hinder power generation, it needs to be heated. On the other hand, it is necessary to input fuel cell module 1 in an excess of fuel than the fuel required for power generation, which will cause a surplus. Therefore, the oxidant gas temperature adjustment device (temperature adjustment device 38) causes the high-temperature air (cathode exhaust) discharged from the fuel cell module 1 and the high-temperature combustion gas obtained by burning the remaining fuel (anode exhaust) in the burner 4 to exchange heat with the air (cathode gas) supplied to the fuel cell module 1. Then, the oxidant gas temperature adjustment device (temperature adjustment device 38) supplies the air (cathode gas) heated by the heat exchange to the fuel cell module 1, thereby forming a highly efficient fuel cell system.

[0130] On this basis, when the temperature of the heated air (cathode gas) does not reach the target temperature, additional fuel is supplied to the burner 4 to increase the temperature of the combustion gas and thereby increase the heat exchange amount of the air (cathode gas), thereby enabling the temperature of the air (cathode gas) to reach the target temperature.

[0131] In the present embodiment, an oxidant gas supply source (blower 32) for supplying oxidant gas (cathode gas) to the fuel cell module 1 is included, and an oxidant gas temperature control device (temperature control device 38) is provided with: a burner 4, which mixes and burns the fuel exhaust gas (anode exhaust) discharged from the fuel cell module 1 and the oxidant exhaust gas (cathode exhaust); a heat exchanger 35, which connects the oxidant gas supply source (blower 32) to the fuel cell module 1 and performs heat exchange between the combustion gas discharged from the burner 4 and the oxidant gas (cathode gas) supplied to the fuel cell module 1; and a bypass flow path. 34, supplies oxidant gas (cathode gas) to the fuel cell module 1 from an oxidant gas supply source (blower 32) bypassing the heat exchanger 35; a flow regulating unit (bypass valve 33), which adjusts the ratio of the flow of the oxidant gas (cathode gas) in the heat exchanger 35 and the bypass flow path 34; and an additional fuel supply unit (injector 24), which supplies additional fuel to the burner 4, and a temperature control unit (air temperature control unit 75) controls the flow regulating unit (bypass valve 33) and / or the additional fuel supply unit (injector 24) so ​​that the oxidant gas (cathode gas) reaches the target temperature.

[0132] According to the above configuration, when the temperature of the heated air (cathode gas) is higher than the target temperature, the flow rate of the air flowing through the bypass flow path 34 is increased to reduce the amount of heat exchange with the heat exchanger 35, so that the temperature of the air (cathode gas) can be quickly reduced to the target temperature. Conversely, when the temperature of the heated air (cathode gas) is lower than the target temperature, the flow rate of the air flowing through the bypass flow path 34 is reduced to increase the amount of heat exchange with the heat exchanger 35, so that the temperature of the air (cathode gas) can be quickly increased to the target temperature.

Claims

1. A fuel cell system, comprising: A fuel cell module comprising a first fuel cell and a second fuel cell arranged in series, wherein a fuel gas flows in a direction from the first fuel cell toward the second fuel cell, and an oxidant gas flows in a direction from the second fuel cell toward the first fuel cell; and an oxidant gas temperature regulating device for regulating the temperature of the oxidant gas supplied to the fuel cell module, at least the first fuel cell is capable of reforming the fuel gas, The fuel cell system further includes a temperature control unit that sets a target temperature of the oxidant gas supplied to the fuel cell module in such a manner that the temperature of the first fuel cell and the temperature of the second fuel cell do not exceed a prescribed upper limit temperature, and controls the oxidant gas temperature adjustment device based on the target temperature. When the target temperature is set to T, the upper limit temperature is set to Tmax, the difference obtained by subtracting the inlet temperature of the cathode of the first fuel cell from the outlet temperature of the cathode of the first fuel cell is set to ΔT1, and the difference obtained by subtracting the inlet temperature of the cathode of the second fuel cell from the outlet temperature of the cathode of the second fuel cell is set to ΔT2, the temperature control unit calculates the target temperature T as: T=Tmax-ΔT1-ΔT2, where ΔT1>0, T=Tmax-ΔT2, where ΔT1≤0, T=Tmax, where ΔT2<0 and ΔT1+ΔT2<0.

2. The fuel cell system according to claim 1, wherein: The temperature control unit calculates ΔT1 based on a heat amount generated by power generation of the first fuel cell, an amount of heat absorbed during a reforming reaction of the fuel gas supplied to the first fuel cell, an amount of heat dissipated to the outside of the first fuel cell, and a flow rate of the oxidant gas supplied to the first fuel cell. The temperature control unit calculates ΔT2 based on a heat amount generated by power generation of the second fuel cell, a heat amount dissipated to the outside of the second fuel cell, and a flow rate of the oxidant gas supplied to the second fuel cell.

3. The fuel cell system according to claim 1, wherein: further comprising an oxygen supply source for supplying oxygen to the anode of the first fuel cell, At least in the first fuel cell, a partial oxidation reaction can occur between the oxygen and the fuel gas. The temperature control unit calculates ΔT1 based on a heat amount generated accompanying power generation of the first fuel cell, a heat amount generated by the partial oxidation reaction, an endothermic amount generated in a reforming reaction based on a difference obtained by subtracting a flow rate of the fuel gas lost due to the partial oxidation reaction from a flow rate of the fuel gas supplied to the first fuel cell, an amount of heat dissipated to the outside of the first fuel cell, and a flow rate of the oxidant gas supplied to the first fuel cell. The temperature control unit calculates ΔT2 based on a heat amount generated by power generation of the second fuel cell, a heat amount dissipated to the outside of the second fuel cell, and a flow rate of the oxidant gas supplied to the second fuel cell.

4. The fuel cell system according to any one of claims 1 to 3, wherein: The oxidant gas temperature adjustment device comprises: a burner that mixes and burns the fuel exhaust gas and the oxidant exhaust gas exhausted from the fuel cell module; a heat exchanger that performs heat exchange between the combustion gas exhausted from the burner and the oxidant gas supplied to the fuel cell module; and an additional fuel supply unit for supplying additional fuel to the burner, The temperature control unit controls the additional fuel supply unit so that the oxidant gas reaches the target temperature.

5. The fuel cell system according to any one of claims 1 to 3, wherein: comprising an oxidant gas supply source for supplying the oxidant gas to the fuel cell module, The oxidant gas temperature adjustment device comprises: a burner that mixes and burns the fuel exhaust gas and the oxidant exhaust gas exhausted from the fuel cell module; a heat exchanger that connects the oxidant gas supply source to the fuel cell module and exchanges heat between the combustion gas exhausted from the burner and the oxidant gas supplied to the fuel cell module; a bypass flow path for supplying the oxidant gas from the oxidant gas supply source to the fuel cell module by bypassing the heat exchanger; a flow rate adjusting unit that adjusts a ratio of a flow rate of the oxidant gas in the heat exchanger and in the bypass flow path; and an additional fuel supply unit for supplying additional fuel to the burner, The temperature control unit controls the flow rate adjustment unit and / or the additional fuel supply unit so that the oxidant gas reaches the target temperature.

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