Fuel battery system

Abstract

To detect reduction of a flow amount of a modified water at a high speed while suppressing a cost and with high accuracy.SOLUTION: A fuel battery system comprising a fuel battery that generates power by reaction of a fuel gas and an oxidant gas comprises: a modification part that modifies an original fuel gas to the fuel gas by using a moisture vapor; an evaporation part that generates the moisture vapor by evaporating modified water; a modified water supply part that supplies the modified water to the evaporation part; an evaporation part temperature sensor that detects the temperature of the evaporation part; and a determination part that determines that a fluid amount of the modified water supplied to the evaporation part is decreased in the case where an inclination of a temperature change of the evaporation part is calculated on the basis of a temperature detected by the evaporation part temperature sensor, and the inclination of the temperature change of the evaporation part exceeds a predetermined threshold value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] Conventionally, as this type of fuel cell system, a system has been proposed that includes a fuel cell that generates electricity based on fuel gas and oxidant gas, a vaporization section that evaporates reforming water to generate steam, a reforming section that reforms raw fuel into fuel gas using the steam, a water tank that stores the reforming water, and a water pump that supplies the reforming water in the water tank to the vaporization section, and that monitors the flow rate of the reforming water. For example, Patent Document 1 describes a system that includes a flow rate sensor that detects the flow rate of the reforming water, and detects a shortage of the flow rate of the reforming water by comparing the detected flow rate of the flow rate sensor with a threshold value that is set based on a target flow rate of the reforming water corresponding to a target flow rate of the raw fuel.

[0003] Patent document 2 also describes a system that is equipped with a temperature sensor that detects the temperature of the reforming section (evaporation section), and when the temperature detected by the temperature sensor falls below a predetermined threshold, it determines that water has accumulated in the reforming section (evaporation section) and the temperature has dropped, and that an excess of reforming water is being supplied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-77531 A [Patent Document 2] JP 2008-135270 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, if fuel gas is supplied when the reforming water flow rate is reduced and insufficient, carbon may be deposited on the fuel cell or the reforming catalyst in the reforming section, causing deterioration, so it is necessary to quickly detect the reduction in the reforming water flow rate. However, a system equipped with a flow rate sensor as in Patent Document 1 leads to increased costs. Also, as in Patent Document 2, it is possible to detect the reduction in the reforming water flow rate by comparing the detected temperature related to the reforming water flow rate with a predetermined threshold value, but it may take time to reach the threshold value, and detection may be delayed.

[0006] A primary object of the present disclosure is to detect a decrease in the reforming water flow rate accurately and quickly while reducing costs. [Means for solving the problem]

[0007] In order to achieve the above-mentioned main object, the present disclosure has adopted the following means.

[0008] The fuel cell system of the present disclosure comprises: A fuel cell system including a fuel cell that generates electricity by reacting a fuel gas with an oxidant gas, a reforming unit that reforms a raw fuel gas into the fuel gas by using water vapor; a vaporization section that vaporizes the reforming water to generate the water vapor; a reforming water supply unit that supplies the reforming water to the vaporization unit; a vaporizer temperature sensor for detecting a temperature of the vaporizer; a determination unit that obtains a gradient of a temperature change in the vaporizer based on the temperature detected by the vaporizer temperature sensor, and determines that a flow rate of the reforming water supplied to the vaporizer has decreased when the gradient of the temperature change in the vaporizer exceeds a predetermined threshold value; The gist of the invention is to provide the following:

[0009] The fuel cell system of the present disclosure calculates the slope of the temperature change in the vaporizer based on the temperature detected by the vaporizer temperature sensor, and determines that the flow rate of the reforming water supplied to the vaporizer has decreased when the slope exceeds a predetermined threshold. This makes it possible to determine the decrease in the reforming water flow rate without providing a flow rate sensor, thereby reducing costs. In addition, since the decrease in the reforming water flow rate is determined using the slope of the temperature change in the vaporizer, the decrease in the reforming water flow rate can be detected more accurately and quickly than when the decrease is determined based on the temperature of the reforming water reaching a predetermined temperature. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing an outline of the configuration of a fuel cell system 10. FIG. [Diagram 2] 6 is a flowchart showing an example of a process for determining a decrease in a reforming water flow rate. [Diagram 3] FIG. 4 is an explanatory diagram showing an example of a change in vaporizer temperature Tv. [Figure 4] FIG. 11 is an explanatory diagram showing an example of threshold values ​​Svref1 and Svref2. [Diagram 5] FIG. 4 is an explanatory diagram showing an example of an increase rate ΔQ of the reforming water flow rate. [Figure 6] 10 is a flowchart showing a process for determining a decrease in the reforming water flow rate according to a modified example. [Figure 7] FIG. 4 is an explanatory diagram showing an example of a temperature change when the amount of reforming water is reduced. [Figure 8] FIG. 4 is an explanatory diagram showing an example of a temperature change when an output is reduced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a fuel cell system 10. As shown in Fig. 1, the fuel cell system 10 of this embodiment includes a power generation module 20, a raw fuel gas supply device 30, a reforming water supply device 40, an air supply device 50, an exhaust heat recovery device 60, and a control device 70.

[0012] The power generation module 20 includes a fuel cell stack 21 that generates power through an electrochemical reaction between hydrogen in an anode gas (fuel gas) and oxygen in a cathode gas (oxidant gas), a vaporizer 22 that vaporizes reforming water to generate water vapor, and a reformer 23 that generates fuel gas (reformed gas) from raw fuel gas and water vapor.

[0013] The fuel cell stack 21 is configured as a solid oxide fuel cell in which a plurality of fuel cells are arranged, each of which includes a solid electrolyte made of an oxygen ion conductor, an anode provided on one side of the solid electrolyte, and a cathode provided on the other side of the solid electrolyte. The shape of the fuel cell stack 21 (fuel cell) is not particularly limited, and may be, for example, a cylindrical type or a flat plate type. The output terminal of the fuel cell stack 21 is connected to a power line connecting a commercial power source and a load via a power conditioner (not shown). The DC power output from the fuel cell stack 21 to the output terminal is added to the AC power from the commercial power source after voltage conversion and DC / AC conversion by the power conditioner, and is supplied to the load. A temperature sensor 83 for detecting the temperature (stack temperature Ts) of the fuel cell stack 21 is provided near the fuel cell stack 21.

[0014] The raw fuel gas supplying device 30 includes a gas supply pipe 31 that connects the gas supply source 1 that supplies the raw fuel gas to the vaporizer 22, and a gas supply valve 32 (two-valve), a gas pump 33, and a desulfurizer 34 that are provided in this order on the gas supply pipe 31 from the gas supply source 1 side. The raw fuel gas supplying device 30 supplies the raw fuel gas from the gas supply source 1 to the vaporizer 22 via the desulfurizer 34 by operating the gas pump 33 with the gas supply valve 32 open. The desulfurizer 34 removes sulfur components contained in the raw fuel gas, and may employ, for example, a room temperature desulfurization method. In addition, between the gas pump 33 and the desulfurizer 34 of the gas supply pipe 31, a flow rate sensor 35 that detects the flow rate per unit time of the raw fuel gas flowing through the gas supply pipe 31, a pressure sensor 36 that detects the pressure inside the gas supply pipe 31, and the like are provided.

[0015] The vaporizer 22 evaporates reforming water from the reforming water supply device 40 to generate steam, and preheats the raw fuel gas from the raw fuel gas supply device 30. The reformer 23 is configured by supporting a reforming catalyst (for example, a Ru or Ni-based catalyst) on a support such as ceramic, and reforms a mixed gas of the raw fuel gas and steam supplied from the vaporizer 22 into a fuel gas (reformed gas) by a steam reforming reaction. The reformed fuel gas is supplied to the anode of the fuel cell stack 21 via the manifold 24. A temperature sensor 81 is provided near the outlet of the vaporizer 22 to detect the temperature of the vaporizer 22 (vaporizer temperature Tv). The temperature sensor 81 may be provided in the reformer 23.

[0016] The fuel cell stack 21, the vaporizer 22, and the reformer 23 are housed in a box-shaped module case 28 made of a heat insulating material. A combustion section 25 is provided in the module case 28 to supply heat required for starting the fuel cell stack 21, generating steam in the vaporizer 22, and the steam reforming reaction in the reformer 23. The combustion section 25 is supplied with the fuel off-gas (anode off-gas) and the oxidant off-gas (cathode off-gas) that have passed through the fuel cell stack 21, and supplies combustion heat to the fuel cell stack 21, the vaporizer 22, and the reformer 23 by igniting and burning the mixed gas by the discharge of the ignition heater 26. The combustion exhaust gas generated by the combustion of the fuel off-gas and the oxidant off-gas is supplied to the exhaust heat recovery device 60 (heat exchanger 62) via the combustion catalyst 27. The combustion catalyst 27 is an oxidation catalyst that re-burns the off-gas that remains unburned in the combustion section 25.

[0017] The reforming water supply device 40 includes a reforming water tank 42 that stores reforming water, a reforming water supply pipe 41 that connects the reforming water tank 42 and the vaporizer 22, and a reforming water pump 43 provided in the reforming water supply pipe 41. The reforming water supply device 40 supplies the reforming water in the reforming water tank 42 to the vaporizer 22 by operating the reforming water pump 43.

[0018] The air supply device 50 includes an air supply pipe 51 that connects a filter 53 that communicates with the outside air to the fuel cell stack 21, and an air pump 52 provided in the air supply pipe 51. The air supply device 50 operates the air pump 52 to supply air sucked in through the filter 53 to the cathode of the fuel cell stack 21.

[0019] The exhaust heat recovery device 60 includes a hot water tank 61 for storing hot water, a heat exchanger 62, a circulation pipe 63 for connecting the hot water tank 61 and the heat exchanger 62 to form a circulation path for the hot water, and a circulation pump 64 provided on the circulation pipe 63. The exhaust heat recovery device 60 operates the circulation pump 64 to circulate the hot water, thereby taking out the hot water from the lower part of the hot water tank 61, heating the hot water by heat exchange with the combustion exhaust gas in the heat exchanger 62, and returning the heated hot water to the upper part of the hot water tank 61. The heat exchanger 62 is connected to the reforming water tank 42 via a condensed water supply pipe 65 and is communicated with the outside air via an exhaust pipe 66. The combustion exhaust gas supplied to the heat exchanger 62 is cooled by heat exchange with the hot water, and the water vapor component is condensed and collected in the reforming water tank 42 via the condensed water supply pipe 65 and a water purifier (not shown). The remaining exhaust gas is exhausted to the outside air via the exhaust pipe 66.

[0020] The control device 70 is configured as a microprocessor centered on a CPU 71, and includes, in addition to the CPU 71, a ROM 72 for storing a processing program, a RAM 73 for temporarily storing data, a flash memory 74 as a rewritable non-volatile memory, and an input / output port (not shown). Various detection signals, such as the flow rate sensor 35, the pressure sensor 36, the vaporizer temperature Tv from the temperature sensor 81, and the stack temperature Ts from the temperature sensor 83, are input to the control device 70 via the input port. In addition, the control device 70 outputs various control signals to the solenoid of the gas supply valve 32, the pump motor of the gas pump 33, the pump motor of the reforming water pump 43, the pump motor of the air pump 52, the pump motor of the circulation pump 64, the ignition heater 26, and the like, via the output port.

[0021] In the fuel cell system 10 thus configured, the supply amounts of the raw fuel gas, the reforming water, and the air are controlled so that a target current based on the target output is output from the fuel cell stack 21. The supply amount of the raw fuel gas is controlled by setting a gas flow rate according to the target current to a target gas flow rate so that the fuel utilization rate coincides with the target utilization rate, and controlling the gas pump 33 by feedback control based on the deviation from the flow rate detected by the flow rate sensor 35. The fuel utilization rate is the ratio of the amount of anode gas used for power generation to the amount of anode gas supplied to the anode. The supply amount of the reforming water is controlled by setting a target reforming water flow rate based on the target gas flow rate so that the steam carbon ratio SC in the reformer 23 coincides with the target ratio, and controlling the reforming water pump 43 so that reforming water at the set target reforming water flow rate is supplied. The steam carbon ratio SC is the molar ratio between carbon contained in the hydrocarbons in the raw fuel gas and steam added for steam reforming. The supply amount of air is controlled by setting a target air flow rate so that a predetermined air-fuel ratio is obtained with respect to the target gas flow rate, and controlling the air pump 52 by open control based on the target air flow rate. Of course, an air flow rate sensor may be provided and feedback control may be performed based on the deviation from the flow rate detected thereby.

[0022] Next, the operation of the fuel cell system 10 thus configured, particularly the operation for determining the reduction in the supplied reforming water flow rate with respect to the target reforming water flow rate, will be described. FIG. 2 is a flow chart showing an example of a process for determining a reduction in the reforming water flow rate. This process is executed by the CPU 71 of the control device 70 at predetermined time intervals while the fuel cell system 10 is in operation. In the process for determining a reduction in the reforming water flow rate, the CPU 71 first acquires the vaporizer temperature Tv and calculates the amount of temperature change ΔTv (S100). The CPU 71 calculates the amount of temperature change ΔTv by subtracting the vaporizer temperature Tv acquired in the previous process from the vaporizer temperature Tv acquired in the current process.

[0023] Next, the CPU 71 calculates a gradient Sv of the temperature change (temperature rise) of the vaporizer temperature Tv (S110). The CPU 71 calculates the gradient Sv (ΔTv / t) by dividing the temperature change amount ΔTv by a unit time t (control period). Next, the CPU 71 sets a first threshold value Svref1 and a second threshold value Svref2 based on the vaporizer temperature Tv (also called the pre-change temperature Tv) before the temperature change (before the temperature rise) (S120).

[0024] Fig. 3 is an explanatory diagram showing an example of a change in the vaporizer temperature Tv. Fig. 3 illustrates an example in which the reforming water flow rate (shown by a dashed line) decreases and the vaporizer temperature Tv (shown by a solid line) increases. Also, an example is shown in which the output of the fuel cell stack 21 (shown by a two-dot dashed line) does not change and remains substantially constant. Note that the vaporizer temperature Tv before the temperature change (temperature before change Tv) may be, for example, the vaporizer temperature Tv obtained in the previous process, or may be an average temperature of the vaporizer temperatures Tv obtained in multiple processes including the previous one.

[0025] FIG. 4 is an explanatory diagram showing an example of the threshold values ​​Svref1 and Svref2. When the vaporizer temperature Tv (temperature before change Tv) is less than a predetermined temperature Tvref (for example, 300° C.), the first threshold value Svref1 is set to a value of 0.3, and the second threshold value Svref2 is set to a value of 0.8. When the vaporizer temperature Tv is equal to or higher than the predetermined temperature Tvref, the first threshold value Svref1 is set to a value of 0.2, and the second threshold value Svref2 is set to a value of 0.5. That is, the second threshold value Svref2 is set to a value larger than the first threshold value Svref1. Also, the higher the vaporizer temperature Tv is, the smaller the values ​​set for the threshold values ​​Svref1 and Svref2 are. Note that the predetermined temperature Tvref and the threshold values ​​Svref1 and Svref2 are only examples, and are not limited to these values. Also, the threshold values ​​Svref1 and Svref2 are not limited to being switched in two stages, and may be switched in multiple stages of three or more stages. Alternatively, the threshold value is not limited to being switched in stages, so long as the higher the vaporizer temperature Tv, the smaller the threshold value is set.

[0026] When the thresholds Svref1 and Svref2 are set in this way, the CPU 71 judges whether the slope Sv is equal to or smaller than the first threshold Svref1 (S130), and ends this process if it judges that the slope Sv is equal to or smaller than the first threshold Svref1. That is, even if the vaporizer temperature Tv rises, if the slope Sv is small and equal to or smaller than the first threshold Svref1, the CPU 71 judges that the temperature rise is within an allowable range and that no problematic decrease in the reforming water flow rate has occurred, and ends this process. On the other hand, if the CPU 71 judges in S130 that the slope Sv is not equal to or smaller than the first threshold Svref1 but exceeds the first threshold Svref1, it judges that the reforming water flow rate has decreased (S140). In this way, in this embodiment, the decrease in the reforming water flow rate is judged based on the slope Sv of the temperature change of the vaporizer temperature Tv, and therefore, it is possible to make a quicker judgment (detection) than, for example, a judgment based on the vaporizer temperature Tv reaching a predetermined temperature. Next, the CPU 71 determines whether the slope Sv is equal to or smaller than the second threshold value Svref2, i.e., whether the slope Sv exceeds the first threshold value Svref1 and is equal to or smaller than the second threshold value Svref2 (S150). If the CPU 71 determines that the slope Sv is equal to or smaller than the second threshold value Svref2, it sets the increase rate ΔQ and controls the reforming water supply device 40 so as to increase the reforming water flow rate (S160), and ends this process.

[0027] FIG. 5 is an explanatory diagram showing an example of the increase rate ΔQ of the reforming water flow rate. As shown in the figure, the increase rate ΔQ is set so that it increases as the slope Sv increases. Specifically, the increase rate ΔQ is set so that it is a first increase rate ΔQ1 (e.g., 10%) when the slope Sv is a first threshold value Svref1, and a second increase rate ΔQ2 (e.g., 30%) when the slope Sv is a second threshold value Svref2, and increases linearly from the first increase rate ΔQ1 to the second increase rate ΔQ2. This makes it possible to appropriately set the increase rate ΔQ required to compensate for the decrease in the reforming water flow rate, and to appropriately increase the amount of reforming water. Here, if fuel gas is supplied in a state where there is a shortage of reforming water, there is a risk that carbon will be deposited on the fuel cell stack 21, the reforming catalyst of the reformer 23, and the like. In this embodiment, the decrease in the reforming water flow rate is promptly determined based on the slope Sv of the vaporizer temperature Tv, and the reforming water flow rate is increased, so that carbon deposition can be suppressed. Note that the increase rates ΔQ1 and ΔQ2 are merely examples and are not limited to these values. Even if the slope Sv does not immediately become equal to or less than the threshold value Svref1 after the process of S160 is performed, as long as it is equal to or less than the threshold value Svref2, the process of S160 is repeatedly performed, so that the reforming water shortage can be resolved by repeatedly increasing the reforming water flow rate.

[0028] Furthermore, when the CPU 71 determines that the slope Sv is not equal to or less than the second threshold Svref2 but exceeds the second threshold Svref2, it determines that the vaporizer temperature Tv has risen significantly, and suppresses the output of the fuel cell stack 21 or stops the fuel cell system 10 (system stop) (S170), and ends this process. For example, the CPU 71 suppresses the output when the process of S170 is executed in a state where the process of S170 is not executed, and stops the system when the process of S170 is executed in a state where the output of the fuel cell stack 21 has already been suppressed. This makes it possible to appropriately protect the fuel cell system 10. When the system is stopped, the CPU 71 adjusts the supply amounts of the raw fuel gas, the reforming water, and the air so that the fuel cell stack 21 and the like are cooled and the anode of the fuel cell stack 21 does not oxidize and deteriorate in a high-temperature atmosphere, and when the cooling of the fuel cell stack 21 and the like is completed, performs a process to stop the supply of the raw fuel gas, the reforming water, and the air. In S170, a message indicating that output will be suppressed or the system will be stopped due to a decrease in the reforming water flow rate may be displayed on the screen of an operation panel (not shown), and an abnormality alarm lamp on the operation panel may be turned on.

[0029] In the fuel cell system 10 described above, the CPU 71 of the control device 70 obtains the gradient Sv of the temperature change of the vaporizer 22 based on the vaporizer temperature Tv, and determines that the reforming water flow rate has decreased when the gradient Sv exceeds a determination threshold (first threshold Svref1). This allows the decrease in the reforming water flow rate to be determined without providing a flow rate sensor for the reforming water, thereby reducing costs. In addition, since the decrease in the reforming water flow rate is determined based on the gradient of the temperature change of the reforming water, the decrease in the reforming water flow rate can be detected more accurately and quickly than when the decrease is determined based on the temperature of the reforming water reaching a predetermined temperature.

[0030] Furthermore, the CPU 71 uses, as the thresholds for judgment (first threshold Svref1, second threshold Svref2), thresholds that are set so that they become smaller as the vaporizer temperature Tv before the temperature change is higher. Here, even if the reforming water flow rate is reduced to the same extent, the temperature change amount ΔTv will be different if the vaporizer temperature Tv is different, for example, the lower the vaporizer temperature Tv, the more likely the vaporizer temperature Tv is to rise due to a reduction in the reforming water flow rate. For this reason, by using thresholds that are set so that they become smaller as the vaporizer temperature Tv is higher, the reduction in the reforming water flow rate can be more accurately judged.

[0031] The CPU 71 uses a first threshold Svref1 and a second threshold Svref2 larger than the first threshold Svref1 as thresholds for judgment, and compares the gradient Sv of the temperature change of the vaporizer 22 with the gradient Sv, and judges that the reforming water has decreased when the gradient Sv exceeds the first threshold Svref1. If the gradient Sv exceeds the first threshold Svref1 and is equal to or smaller than the second threshold Svref2, the CPU 71 executes a response process to increase the reforming water supplied by the reforming water supply device 40. Therefore, when a decrease in the reforming water flow rate is judged, the reforming water flow rate is increased, so that carbon deposition can be suppressed. Furthermore, if the gradient Sv exceeds the second threshold Svref2, the CPU 71 executes a response process to reduce the output of the fuel cell stack 21 or stop the fuel cell system 10. Therefore, when the decrease in the reforming water flow rate cannot be resolved even if the reforming water flow rate is increased, or when the reforming water flow rate is greatly decreased and there is a high possibility of a breakdown, the fuel cell system 10 can be appropriately protected and a breakdown can be prevented.

[0032] In the embodiment, the decrease in the reforming water flow rate is determined based on the vaporizer temperature Tv (gradient Sv), but the decrease may be determined based on the vaporizer temperature Tv and another temperature. Fig. 6 is a flowchart showing a process for determining the decrease in the reforming water flow rate according to a modified example. In the modified example, the same processes as those in the embodiment are assigned the same step numbers, and the description thereof will be omitted.

[0033] In FIG. 6, when the CPU 71 determines in S130 that the slope Sv exceeds the first threshold Svref1, it acquires the stack temperature Ts and calculates the temperature change amount ΔTs (S132). The CPU 71 calculates the temperature change amount ΔTs by subtracting the stack temperature Ts acquired in the previous process from the stack temperature Ts acquired in the current process. Next, the CPU 71 calculates the slope Ss of the temperature change of the stack temperature Ts (S134). The CPU 71 calculates the slope Ss by dividing the temperature change amount ΔTs by the unit time t. Next, the CPU 71 determines whether the absolute value of the slope Ss is equal to or less than the threshold Ssref, that is, whether the slope Ss is within the range of ±Ssref (S136). When the CPU 71 determines that the absolute value of the slope Ss is not equal to or less than the threshold Ssref but exceeds the threshold Ssref, it ends this process. Furthermore, when the CPU 71 determines that the absolute value of the gradient Ss is equal to or smaller than the threshold value Ssref, it determines in S140 that the reforming water flow rate has decreased, and executes the subsequent processes.

[0034] FIG. 7 is an explanatory diagram showing an example of temperature change when the amount of reforming water decreases. FIG. 8 is an explanatory diagram showing an example of temperature change when the output decreases. FIGS. 7 and 8 show an example of temperature change of the vaporizer temperature Tv and the stack temperature Ts. As shown in FIG. 7, when the reforming water flow rate decreases while the output of the fuel cell stack 21 is substantially constant, the vaporizer temperature Tv increases without the stack temperature Ts changing (decreasing) significantly. In this case, the CPU 71 determines in S136 that the absolute value of the gradient Ss of the temperature change of the stack temperature Ts is equal to or less than the threshold value Ssref, that is, the gradient Ss is within the range of ±Ssref, and determines that the reforming water flow rate has decreased. Also, as shown in FIG. 8, when the output of the fuel cell stack 21 decreases while the reforming water flow rate is substantially constant, the stack temperature Ts decreases and the vaporizer temperature Tv increases. In this case, the CPU 71 determines in S136 that the absolute value of the gradient Ss of the temperature change in the stack temperature Ts exceeds the threshold value Ssref, ie, that the gradient Ss is not within the range of ±Ssref, and does not determine that the reforming water flow rate has decreased.

[0035] Here, when the output of the fuel cell stack 21 decreases, the fuel utilization rate decreases, the amount of off-gas supplied to the combustion section 25 increases, and the temperature of the combustion section 25 increases due to the combustion of the off-gas. Depending on the state of the output decrease, such an increase in the vaporizer temperature Tv may be erroneously determined as a decrease in the reforming water flow rate. In contrast, in the modified example, when the gradient Sv of the temperature change of the vaporizer temperature Tv exceeds the threshold value Svref1, if the gradient Ss of the temperature change of the stack temperature Ts is within the range of ±Ssref, it is determined that the stack temperature Ts has hardly changed (decreased) and there is no decrease in the output of the fuel cell stack 21, and the reforming water flow rate has decreased. Also, if the gradient Ss is not within the range of ±Ssref, it is determined that the stack temperature Ts has changed (decreased) and the vaporizer temperature Tv has increased due to the decrease in the output of the fuel cell stack 21, and it is not determined that the reforming water flow rate has decreased. This prevents the increase in the vaporizer temperature Tv due to the decrease in the output of the fuel cell stack 21 from being erroneously determined as a decrease in the reforming water flow rate, and it is possible to more accurately determine the decrease in the reforming water flow rate. The threshold value Ssref is also referred to as a threshold value for preventing erroneous judgment, and the range of ±Ssref is also referred to as a predetermined range for preventing erroneous judgment. The threshold value Ssref is set to, for example, 0.5, but is not limited to this value.

[0036] In the embodiment, the first threshold value Svref1 and the second threshold value Svref2 are used, and if the slope Sv exceeds the first threshold value Svref1 and is equal to or smaller than the second threshold value Svref2, a process for increasing the reforming water flow rate is executed, and if the slope Sv exceeds the second threshold value Svref2, a process for reducing the output of the fuel cell stack 21 or stopping the system is executed, but this is not limited to the above. The determination threshold is not limited to using two threshold values, and at least a reduction in the reforming water flow rate may be determined using one threshold value. In addition, when a reduction in the reforming water flow rate is determined based on one threshold value, a process for increasing the reforming water flow rate may be executed first, and when the reduction in the reforming water flow rate is determined based on the threshold value thereafter, a process for reducing the output of the fuel cell stack 21 or stopping the system may be executed. Alternatively, the process for increasing the reforming water flow rate and the process for reducing the output of the fuel cell stack 21 or stopping the system are examples of response processes when the reforming water flow rate is reduced, and the process is not limited to performing all of these.

[0037] In the embodiment, the first threshold value Svref1 and the second threshold value Svref2 are set so as to become smaller as the temperature of the vaporizer 22 increases, but this is not limited thereto. One or both of the first threshold value Svref1 and the second threshold value Svref2 may be set to a constant value regardless of the temperature of the vaporizer 22. In addition, as described above, the present invention is not limited to using two threshold values ​​for determination, and only one threshold value set to a constant value regardless of the temperature of the vaporizer 22 may be used.

[0038] The correspondence between the main elements of the embodiment and the main elements of the present disclosure described in the section on means for solving the problems will be described below. The reformer 23 of the embodiment corresponds to the "reforming section" of the present disclosure, the vaporizer 22 corresponds to the "vaporization section", the reforming water supply device 40 corresponds to the "reforming water supply section", the temperature sensor 81 corresponds to the "vaporization section temperature sensor", and the control device 70 (CPU 71) that executes S100 to S140 of the process for determining whether the reforming water flow rate has decreased corresponds to the "determination section". The temperature sensor 83 corresponds to the "fuel cell temperature sensor". The control device 70 (CPU 71) that executes S150 to S170 of the process for determining whether the reforming water flow rate has decreased corresponds to the "control section".

[0039] This specification also discloses the technical idea of ​​changing "a fuel cell system according to claim 1 or 2" in claim 4 originally filed to "a fuel cell system according to any one of claims 1 to 3."

[0040] In addition, the correspondence between the main elements of the embodiment and the main elements of the present disclosure described in the Means for Solving the Problem column does not limit the elements of the present disclosure described in the Means for Solving the Problem column, since the embodiment is an example for specifically explaining the form for implementing the present disclosure described in the Means for Solving the Problem column. In other words, the interpretation of the present disclosure described in the Means for Solving the Problem column should be made based on the description in that column, and the embodiment is merely a specific example of the present disclosure described in the Means for Solving the Problem column.

[0041] The above describes the form for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms without departing from the gist of the present disclosure. [Industrial Applicability]

[0042] The present disclosure is applicable to the fuel cell system manufacturing industry and the like. [Explanation of symbols]

[0043] 1 gas supply source, 10 fuel cell system, 20 power generation module, 21 fuel cell stack, 22 vaporizer, 23 reformer, 24 manifold, 25 combustion section, 26 ignition heater, 27 combustion catalyst, 28 module case, 30 raw fuel gas supply device, 31 gas supply pipe, 32 gas supply valve, 33 gas pump, 34 desulfurizer, 35 flow sensor, 36 pressure sensor, 40 reforming water supply device, 41 reforming water supply pipe, 42 reforming water tank, 43 reforming water pump, 50 air supply device, 51 air supply pipe, 52 air pump, 53 filter, 60 exhaust heat recovery device, 61 hot water tank, 62 heat exchanger, 63 circulation pipe, 64 circulation pump, 65 condensed water supply pipe, 66 exhaust pipe, 70 control device, 71 CPU, 72 ROM, 73 RAM, 74 Flash memory, 81 temperature sensor (evaporator temperature sensor), 83 temperature sensor (fuel cell temperature sensor).

Claims

1. A fuel cell system including a fuel cell that generates electricity by reacting a fuel gas with an oxidant gas, a reforming unit that reforms a raw fuel gas into the fuel gas by using water vapor; a vaporization section that vaporizes the reforming water to generate the water vapor; a reforming water supply unit that supplies the reforming water to the vaporization unit; a vaporizer temperature sensor for detecting a temperature of the vaporizer; a determination unit that obtains a gradient of a temperature change in the vaporizer based on the temperature detected by the vaporizer temperature sensor, and determines that a flow rate of the reforming water supplied to the vaporizer has decreased when the gradient of the temperature change in the vaporizer exceeds a predetermined threshold value; A fuel cell system comprising:

2. The determination unit uses, as the predetermined threshold value, a threshold value that is set to be smaller as the temperature of the vaporization unit before the temperature change is higher. The fuel cell system according to claim 1 .

3. a fuel cell temperature sensor for detecting a temperature of the fuel cell; the determination unit determines a gradient of temperature change of the fuel cell based on the temperature detected by the fuel cell temperature sensor, and determines that the flow rate of the reforming water supplied to the vaporization unit has decreased when the gradient of temperature change of the vaporization unit exceeds the predetermined threshold value and is within a predetermined range.

3. The fuel cell system according to claim 1 or 2.

4. The determination unit uses a first threshold value and a second threshold value greater than the first threshold value as the predetermined threshold value, and determines that the amount of the reforming water has decreased when a gradient of the temperature change of the vaporization unit exceeds the first threshold value; a control unit which, when it is determined that the flow rate of the reforming water has decreased, executes a corresponding process to increase the amount of the reforming water supplied by the reforming water supply unit if the gradient of the temperature change of the vaporization unit exceeds the first threshold value and is equal to or smaller than the second threshold value, and executes a corresponding process to reduce the output of the fuel cell or stop the fuel cell system if the gradient of the temperature change of the vaporization unit exceeds the second threshold value.

3. The fuel cell system according to claim 1 or 2.

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