JP2019149271A - Fuel cell system - Google Patents

Abstract

To avoid shortage of water vapor to make operation of a fuel cell continue.SOLUTION: A fuel cell system (100) of the present disclosure comprises: a reformer (11) for making material gas react with water vapor using a reforming catalyst to generate fuel gas including hydrogen gas; a vaporizer (32) for generating water vapor to be supplied to the reformer (11); a fuel cell (13) for generating power using the fuel gas and oxidant gas; detectors (41, 42) for detecting occurrence of shortage of water vapor at the reformer (11); and a controller (50). When shortage of water vapor occurs at the reformer (11), the controller (50) reduces power generation output of the fuel cell (13) from the present power generation output by a first specific value.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a fuel cell system.

  The fuel cell system is a system that generates electric power and heat by an electrochemical reaction between a fuel gas and an oxidant gas. In a general fuel cell system, generated electric power is supplied to an electric power load. Examples of power loads are electrical appliances such as lighting and air conditioners. The generated heat is stored as hot water in a hot water storage tank. Hot water is supplied from the hot water storage tank to the heat load. Examples of the heat load are heat-utilizing equipment such as hot-water supply equipment and floor heating.

  Since an infrastructure for supplying hydrogen gas has not been established, fuel cell systems often include a reformer. The reformer generates a hydrogen-containing gas from the raw material gas and water by a steam reforming reaction using a reforming catalyst. The raw material gas is a gas containing an organic compound, and is typically city gas or liquefied petroleum gas.

JP2013-191320A

  Water is supplied from the water tank to the evaporator by the action of the pump. Steam is generated in the evaporator, and the steam is supplied to the reformer. When water vapor is insufficient for some reason, coking (carbonization of raw material gas) occurs in the reformer. This causes a failure or deterioration of the reformer. Further, when the water vapor is insufficient, the hydrogen gas is insufficient and the operation of the fuel cell system cannot be continued.

  In Patent Document 1, when the rotation speed of the water pump is abnormal with respect to the target rotation speed region during the power generation operation of the fuel cell, the increase / decrease in the rotation speed of the water pump is repeated while continuing the power generation operation of the fuel cell. In other words, it avoids erroneous detection of the amount of water vapor due to resonance of the water pump. However, even if this control is performed, it is not possible to cope with water vapor shortage caused by causes other than the resonance of the water pump.

This disclosure
A reformer that generates a fuel gas containing hydrogen gas by reacting a raw material gas and water vapor using a reforming catalyst;
An evaporator for generating water vapor to be supplied to the reformer;
A fuel cell that generates electric power using the fuel gas and oxidant gas;
A detector for detecting that steam shortage has occurred in the reformer;
A controller;
With
When the steam shortage occurs in the reformer, the controller provides a fuel cell system that reduces the power generation output of the fuel cell by a first specific value from the current power generation output.

  According to the technology of the present disclosure, it is possible to continue the operation of the fuel cell system while avoiding the shortage of hydrogen gas in the fuel cell.

FIG. 1 is a configuration diagram of a fuel cell system according to an embodiment of the present disclosure. FIG. 2 is a trend graph showing an example of changes over time in the temperature of the reformer and the power generation output of the fuel cell. FIG. 3 is a flowchart regarding control for coping with water vapor shortage. FIG. 4 is a flowchart following FIG. FIG. 5 is a flowchart following FIG. FIG. 6 is a trend graph showing an example of a change over time in the detected value of the flow rate of the source gas and the operation amount of the flow rate regulator.

(Knowledge that became the basis of this disclosure)
As a cause of the lack of water vapor in the reformer, for example, foreign substances such as air enter a path for supplying water from the water tank to the evaporator. Further, water does not always evaporate at a constant flow rate in the evaporator, and this is one of the causes of water vapor shortage. For example, bumping of water is thought to cause a lack of water vapor. Furthermore, water vapor shortage can also occur when an abnormality occurs in a flow regulator for adjusting the flow rate of water. It is difficult to remove these causes of water vapor shortage.

  If water vapor necessary for reforming the raw material gas is insufficient, hydrogen gas cannot be generated sufficiently. When the hydrogen gas is insufficient, the voltage of the fuel cell decreases, and it becomes difficult to continue the operation of the fuel cell system. Furthermore, the shortage of water vapor causes deterioration of the reformer and the deterioration of the fuel cell due to the shortage of hydrogen gas.

(Outline of one aspect according to the present disclosure)
The fuel cell system of the present disclosure includes:
A reformer that generates a fuel gas containing hydrogen gas by reacting a raw material gas and water vapor using a reforming catalyst;
An evaporator for generating water vapor to be supplied to the reformer;
A fuel cell that generates electric power using the fuel gas and oxidant gas;
A detector for detecting that steam shortage has occurred in the reformer;
A controller;
With
When the steam shortage occurs in the reformer, the controller reduces the power generation output of the fuel cell by a first specific value from the current power generation output.

  According to the first aspect, since the power generation output is reduced when water vapor shortage occurs, the flow rate of hydrogen gas required in the fuel cell is also reduced. As a result, the operation of the fuel cell system can be continued while avoiding the shortage of hydrogen gas in the fuel cell. Degradation of the reformer and the fuel cell can also be suppressed.

  In the second aspect of the present disclosure, for example, in the fuel cell system according to the first aspect, the detector detects a physical quantity reflecting the flow rate of the water vapor at the inlet of the reformer. By referring to the physical quantity reflecting the flow rate of water vapor, it is possible to accurately detect the occurrence of water vapor deficiency.

  In the third aspect of the present disclosure, for example, in the fuel cell system according to the first or second aspect, the detector includes a flow meter that detects a flow rate of the water to be supplied to the evaporator. Since the flow rate of water directly affects the flow rate of water vapor, the occurrence of water vapor deficiency can be accurately detected by measuring the flow rate of water.

  In the fourth aspect of the present disclosure, for example, in the fuel cell system according to the first or second aspect, the detector detects a pressure inside the evaporator or a pressure in a path from the evaporator to the reformer. Includes a pressure sensor to detect. By measuring the pressure of the generated water vapor, it is possible to accurately detect the occurrence of water vapor deficiency.

  In the fifth aspect of the present disclosure, for example, the fuel cell system according to any one of the first to fourth aspects further includes a temperature sensor that detects a temperature of the reformer, and is detected by the temperature sensor. When the temperature of the reformer is equal to or higher than the first threshold temperature, the controller reduces the power generation output of the fuel cell from the current power generation output by a second specific value. By reducing the power generation output, it is possible to prevent the temperature inside the reformer from rising too much.

  In the sixth aspect of the present disclosure, for example, in the fuel cell system according to any one of the first to fourth aspects, the controller controls the fuel cell when the water vapor shortage occurs a plurality of times within a predetermined time. The power generation output is reduced by a second specific value from the current power generation output. If the power generation output is greatly reduced when a shortage of water vapor occurs repeatedly in a short period of time, the reforming catalyst will be damaged greatly, and the fuel cell system will not stop due to an error such as misfiring. You can continue driving.

  In the seventh aspect of the present disclosure, for example, in the fuel cell system according to the fifth aspect, when the temperature of the reformer exceeds a second threshold temperature higher than the first threshold temperature, the controller Stop the fuel cell operation. According to the seventh aspect, it is possible to continue the operation of the fuel cell while avoiding that the reforming catalyst receives great damage or the fuel cell system is stopped due to an error such as misfire.

  In the eighth aspect of the present disclosure, for example, in the fuel cell system according to any one of the fifth to seventh aspects, when the power generation output is reduced by the second specific value, the controller Is set as the upper limit of the power generation output of the fuel cell. By maintaining the power generation output below the upper limit until the temperature of the reformer is sufficiently lowered, the temperature of the reformer can be reliably and rapidly lowered.

  In the ninth aspect of the present disclosure, for example, in the fuel cell system according to the eighth aspect, when the temperature of the reformer falls below a third threshold temperature lower than the first threshold temperature, the controller The upper limit of the power generation output is canceled. According to the ninth aspect, it is possible to continue the efficient operation while avoiding that the reforming catalyst is greatly damaged or the fuel cell system is stopped due to an error such as misfire.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

(Embodiment)
As shown in FIG. 1, a fuel cell system 100 according to an embodiment of the present disclosure includes a reformer 11 and a fuel cell 13. The reformer 11 is a device for generating a hydrogen-containing gas by a reforming reaction such as, for example, a steam reforming reaction (CH ₄ + H ₂ O → 3H ₂ + CO). The reformer 11 contains a reforming catalyst for advancing the reforming reaction. The reformer 11 may contain a catalyst (a CO shift catalyst and a CO selective oxidation removal catalyst) for removing carbon monoxide. The reformer 11 produces | generates hydrogen containing gas using water vapor | steam and raw material gas. The source gas is, for example, a hydrocarbon gas such as city gas or LP gas (liquefied petroleum gas). The hydrogen-containing gas is supplied to the fuel cell 13 as a fuel gas. The fuel cell 13 generates power using oxidant gas and fuel gas. The fuel cell 13 is a solid polymer fuel cell, a solid oxide fuel cell, a phosphoric acid fuel cell, or a molten carbonate fuel cell. Hot water is generated by the exhaust heat of the fuel cell system 100. The generated hot water is stored in a hot water storage tank (not shown).

  The fuel cell system 100 further includes a combustor 15 and an exhaust path 17. The combustor 15 is a device for heating the reformer 11 by burning fuel. The combustor 15 is adjacent to the reformer 11. The combustor 15 may be disposed inside the reformer 11. The exhaust path 17 is connected to the combustor 15. The exhaust path 17 is a flow path for combustion exhaust gas generated in the combustor 15. The exhaust path 17 extends to the outside of the housing of the fuel cell system 100, for example.

  An air supply path 34 is connected to the combustor 15. The air supply path 34 is a flow path for supplying air to the combustor 15. A flow meter 35 and an air supplier 36 are provided in the air supply path 34. An air supply flow rate is detected by the flow meter 35. Examples of the air supply 36 include a fan and a blower. Using the flow meter 35 and the air supply device 36, the supply flow rate of air to the combustor 15 can be adjusted to a desired supply flow rate. As the flow meter 35, known flow meters such as an electromagnetic flow meter, a Karman vortex flow meter, an impeller flow meter, a thermal flow meter, a diaphragm flow meter, and an ultrasonic flow meter can be used.

  The fuel cell system 100 further includes a fuel gas supply path 12, an oxidant gas supply path 14, an anode offgas path 16, and a cathode offgas path 18. The fuel gas supply path 12 is a flow path for supplying a hydrogen-containing gas from the reformer 11 to the fuel cell 13. The fuel gas supply path 12 connects the reformer 11 and the fuel cell 13. The oxidant gas supply path 14 is a flow path for supplying air as an oxidant gas to the cathode of the fuel cell 13. An air supply unit 23 is provided in the oxidant gas supply path 14. The air supplier 23 is a device for supplying air to the fuel cell 13. Examples of the air supply device 23 include a fan and a blower. By controlling the air supply device 23, the flow rate of air can be adjusted. Other devices such as a humidifier and a valve may be disposed in the oxidant gas supply path 14. The anode off-gas path 16 is a flow path for discharging unreacted hydrogen-containing gas from the anode of the fuel cell 13. The anode off-gas path 16 connects the anode gas outlet of the fuel cell 13 and the combustor 15. Unreacted hydrogen-containing gas is supplied to the combustor 15 through the anode off-gas passage 16. The cathode off-gas path 18 is a flow path for discharging unreacted oxidant gas from the cathode of the fuel cell 13. The cathode offgas path 18 is connected to the cathode gas outlet of the fuel cell 13 and extends, for example, to the outside of the casing of the fuel cell system 100. The cathode offgas path 18 may be connected to the exhaust path 17 or may be connected to the combustor 15.

  The fuel cell system 100 further includes an air path 24, a flow rate regulator 25, and a flow meter 26. The air path 24 is a flow path for supplying air used for CO selective oxidation to the reformer 11. The air path 24 branches from the oxidant gas supply path 14 and is connected to the reformer 11. A flow regulator 25 and a flow meter 26 are provided in the air path 24. As the flow meter 26, the known flow meter exemplified above can be used. The air path 24 may be provided independently of the oxidant gas supply path 14.

  The fuel cell system 100 further includes a source gas supply path 27 and a source gas supplier 28. The raw material gas supply path 27 is a flow path for supplying the raw material gas to the reformer 11 from a raw material supply source (not shown) such as a raw material storage tank or city gas infrastructure. A source gas supply device 28 is provided in the source gas supply path 27. Examples of the source gas supply device 28 include a pump, a flow rate adjustment valve, a flow meter, and a combination thereof. By controlling the source gas supply device 28, the supply flow rate of the source gas can be adjusted. In the raw material gas supply path 27, other devices such as a desulfurizer and a valve may be arranged.

  The fuel cell system 100 further includes a water supply path 30, a water supplier 31 and an evaporator 32. The water supply path 30 is a flow path for supplying water to the reformer 11 from a water source such as a water storage tank. A water supply unit 31 is provided in the water supply path 30. An example of the water supply unit 31 is a pump. By controlling the water supply device 31, the water supply flow rate can be adjusted. The evaporator 32 generates water vapor by evaporating water. In order to evaporate water with the heat of the combustor 15, the evaporator 32 may be adjacent to the reformer 11 or may be integrated with the reformer 11.

  A temperature sensor 40 is attached to the reformer 11. The temperature sensor 40 detects the temperature inside the reformer 11 (for example, the temperature of the catalyst or the outlet temperature of the catalyst layer). A temperature sensor 40 may be attached to each of the plurality of positions of the reformer 11.

  The fuel cell system 100 further includes a flow meter 41 and a pressure sensor 42. Each of the flow meter 41 and the pressure sensor 42 is an example of a detector that detects that steam shortage has occurred in the reformer 11, and detects a physical quantity that reflects the flow rate of water vapor at the inlet of the reformer 11. . The flow meter 41 detects the flow rate of water as a physical quantity reflecting the flow rate of water vapor at the inlet of the reformer 11. The pressure sensor 42 detects the pressure inside the evaporator 32 as a physical quantity reflecting the flow rate of water vapor at the inlet of the reformer 11. By referring to the physical quantity reflecting the flow rate of water vapor, it is possible to accurately detect the occurrence of water vapor deficiency. However, as will be described later, it is also possible to detect the occurrence of water vapor shortage by a method that does not directly refer to physical quantities such as flow rate and pressure.

  The flow meter 41 is disposed in the water supply path 30. Specifically, the flow meter 41 is located upstream of the evaporator 32 in the water supply path 30. The flow meter 41 detects the flow rate of water to be supplied to the evaporator 32. One cause of water vapor shortage is that foreign substances such as air enter the water supply path 30. When the water vapor shortage is a foreign matter that has entered the water supply path 30, it is impossible to determine whether the water vapor shortage has occurred or not only by referring to the rotation speed of the pump. On the other hand, the flow rate of water in the water supply path 30 directly affects the flow rate of water vapor, so that the occurrence of water vapor deficiency can be accurately detected by measuring the flow rate of water. As the flow meter 41, the known flow meter exemplified above can be used.

  The pressure sensor 42 is attached to the evaporator 32. The pressure sensor 42 detects the pressure inside the evaporator 32. Specifically, the pressure sensor 42 is disposed at a position where the pressure of water vapor generated by the evaporation of water can be detected. The pressure sensor 42 may be disposed in a path from the evaporator 32 to the reformer 11 in order to detect the pressure of the water vapor. One cause of the lack of water vapor is a change in the evaporation flow rate of water in the evaporator 32. Since there is a phase change from liquid water to water vapor, water vapor may not be generated at a constant flow rate even if the flow rate of water is constant. For example, when a sudden boiling of water occurs, water vapor shortage may occur even if the water supply flow rate to the evaporator 32 is sufficient. On the other hand, if the pressure of the generated water vapor is measured, the occurrence of water vapor deficiency can be accurately detected. The type of the pressure sensor 42 is not particularly limited. As the pressure sensor 42, a known pressure sensor such as a capacitance pressure sensor, a resistance wire pressure sensor, or a piezoresistive pressure sensor can be used.

  In the present specification, the phrase “steam-deficient” means a situation where steam necessary for reforming the raw material gas is not supplied to the reformer 11 at a necessary flow rate.

  The fuel cell system 100 further includes a controller 50. The controller 50 controls objects to be controlled such as the fuel cell 13, the air supply unit 23, the flow rate regulator 25, the raw material gas supply unit 28, the water supply unit 31, the air supply unit 36, and various auxiliary devices. Auxiliary equipment includes valves (including on-off valves, switching valves, and flow rate adjustment valves), pumps, electric heaters, and the like. Detection signals are input to the controller 50 from the flow meter 26, the flow meter 35, the temperature sensor 40, the flow meter 41, the pressure sensor 42, and other various sensors. As the controller 50, a DSP (Digital Signal Processor) including an A / D conversion circuit, an input / output circuit, an arithmetic circuit, a storage device, and the like can be used. The controller 50 stores a program for properly operating the fuel cell system 100.

  In the fuel cell system 100, each path can be configured by one or a plurality of pipes.

  Next, the operation of the fuel cell system 100 will be described.

  FIG. 2 is a trend graph showing an example of changes over time in the temperature of the reformer and the power generation output of the fuel cell. Time t1 is the time when occurrence of water vapor shortage is detected. Time t2 is the time when the temperature of the reformer 11 exceeds the first threshold temperature. Time t3 is the time when the process of reducing the power generation output by the second specific value is completed. Time t4 is the time when the temperature of the reformer 11 decreases to the third threshold temperature.

  In order to deal with the occurrence of water vapor deficiency, the controller 50 periodically executes each process shown in the flowchart of FIG. 3 (for example, every control cycle). In addition, the controller 50 periodically executes each process shown in the flowcharts of FIGS. 4 and 5. Each process shown in the flowcharts of FIGS. 4 and 5 can be executed not only in a certain period after the shortage of water vapor occurs but also in a period in which the shortage of water vapor does not occur. However, each process shown in the flowcharts of FIGS. 4 and 5 may be executed only for a certain period after the water vapor shortage occurs.

  As shown in FIG. 3, in step S1, the current power generation output is stored. The power generation output to be stored may be a control target value or an actually measured value by a sensor. Prior to time t1, the power generation output of the fuel cell 13 is controlled to follow the power load. Next, in step S2, it is determined whether or not the occurrence of water vapor shortage is detected. Specifically, it is determined whether or not the detection value of the flow meter 41 indicates the occurrence of water vapor shortage. Alternatively, it is determined whether or not the detection value of the pressure sensor 42 indicates the occurrence of water vapor shortage.

  Whether or not water vapor shortage has occurred can be determined, for example, by the following method. The power generation output of the fuel cell 13 follows the power load. Specifically, the target value of the power generation output is set according to the power load, and the inverter is controlled so that the power generation output converges to the target value. When the target value of power generation output is determined, the required flow rate of hydrogen gas is also determined. When the flow rate of hydrogen gas is determined, the raw material gas flow rate, the water flow rate, and the water vapor flow rate are also determined. The flow rate of water vapor corresponds to the pressure. Therefore, when there is a certain difference (difference exceeding the allowable limit) between the detected value of the flow meter 41 and the flow rate of water calculated from the target value of the current power generation output, water vapor shortage has occurred. It can be judged. Or, when there is a certain difference (difference exceeding the allowable limit) between the detected value of the pressure sensor 42 and the pressure calculated from the target value of the current power generation output, water vapor shortage has occurred. I can judge.

  If the occurrence of water vapor shortage is detected in step S2, the power generation output is lowered from the current power generation output by a first specific value in step S3. The first specific value may be a constant value experimentally determined in advance. The first specific value is a reduction amount of the power generation output necessary for avoiding a temporary shortage of hydrogen gas. For example, assuming that the first specific value is 100 W, in step S3, the power generation output (for example, target value) of the fuel cell 13 is reduced to a power generation output that is 100 W lower than the current power generation output. The first specific value being a constant value is advantageous from the viewpoint of ease of control. Alternatively, the first specific value may be a value calculated from the current power generation output based on a predetermined arithmetic expression. For example, an output of 20 to 30% of the current power generation output can be set as the first specific value.

  According to this embodiment, since the power generation output is reduced when water vapor shortage occurs, the flow rate of hydrogen gas required in the fuel cell 13 is also reduced. As a result, the operation of the fuel cell 13 can be continued while avoiding the shortage of water vapor. Degradation of the reformer 11 and the fuel cell 13 can also be suppressed.

  In the present embodiment, the rate of decrease in power generation output when the occurrence of water vapor shortage is detected is faster than the rate of change in power generation output when water vapor shortage does not occur. For example, when the maximum value of the change rate of the power generation output when steam shortage does not occur is 1 W per control cycle, in this embodiment, a faster speed (for example, 10 W or more per control cycle). Reduce the power output. “Control cycle” represents the control cycle of the inverter circuit for converging the power generation output to the target value. An example of “when water vapor shortage does not occur” is when the power generation output of the fuel cell 13 is changed according to the power load. If the power generation output is changed rapidly when there is no shortage of water vapor, the flow rate of hydrogen gas consumed in the fuel cell 13 changes rapidly. Then, the flow rate of the hydrogen-containing gas introduced into the combustor 15 changes, and the temperature of the reformer 11 changes greatly, or the operating point of the fuel cell system 100 changes significantly. These should be avoided because they cause failure. However, when water vapor shortage occurs, hydrogen gas cannot be sufficiently supplied to the fuel cell 13, and the fuel cell 13 may deteriorate. Therefore, for the fuel cell system 100, the shortage of hydrogen gas due to the shortage of water vapor needs to be avoided more than the rapid change of the power generation output. Therefore, if the power generation output of the fuel cell 13 is deliberately accepted and priority is given to avoiding the shortage of hydrogen gas, damage to the fuel cell 13 can be minimized.

  According to the example shown in FIG. 2, at the time t1, the power generation output rapidly decreases to the power generation output obtained by subtracting the first specific value from the most recent power generation output. For example, the target value of the power generation output may be lowered from the current target value by the first specific value in one control cycle.

  If water vapor shortage is not detected in step S2, the process returns to the original control loop while maintaining the current power generation output.

  In FIG. 2, a period between time t1 and time t2 is a period in which the power generation output is changed so that the power load follows the power generation output.

  Next, each process of the flowchart of FIG. 4 will be described.

  In step S <b> 11 of FIG. 4, the temperature of the reformer 11 is detected using the temperature sensor 40. In step S12, it is determined whether the temperature of the reformer 11 is equal to or higher than the first threshold temperature. When the temperature of the reformer 11 is equal to or higher than the first threshold temperature, in step S13, the power generation output (target value) is gradually reduced to the power generation output obtained by subtracting the second specific value from the current power generation output. The second specific value may be a constant value experimentally determined in advance. The second specific value is a reduction amount of the power generation output necessary for lowering the temperature of the reformer 11. For example, assuming that the second specific value is 100 W, in step S13, the power generation output of the fuel cell 13 is gradually reduced to a power generation output that is 100 W lower than the current power generation output. The second specific value is a constant value, which is advantageous from the viewpoint of ease of control. Alternatively, the second specific value may be a value calculated from the current power generation output based on a predetermined arithmetic expression. For example, an output of 20 to 30% of the current power generation output can be set as the second specific value.

  When the occurrence of water vapor shortage is detected and the power generation output is lowered, the fuel consumption in the fuel cell 13 decreases, and the flow rate of the hydrogen-containing gas introduced into the combustor 15 increases. Then, the amount of heat generated in the combustor 15 increases, and the temperature inside the reformer 11 rises. If the temperature inside the reformer 11 rises too much, the durability of the reforming catalyst will be adversely affected, and other errors such as misfire may occur and the fuel cell system 100 must be stopped. .

  As shown in the flowchart of FIG. 4, if the temperature inside the reformer 11 is equal to or higher than the first threshold temperature, it is possible to prevent the temperature inside the reformer 11 from rising excessively by reducing the power generation output. As a result, it is possible to avoid the fuel cell system 100 from being damaged due to large damage to the reforming catalyst or from an error such as misfire.

  The “first threshold temperature” is a temperature that is appropriately determined according to the composition of the reforming catalyst, the structure of the reformer 11, the position of the temperature sensor 40, and the like. In one example, the first threshold temperature is a temperature in the range of 650 to 700 ° C.

  The decrease rate when the power generation output is decreased by the second specific value in step S13 is slower than the decrease rate when the power generation output is decreased by the first specific value in step S3 (FIG. 3). In the example shown in FIG. 2, the power generation output gradually decreases at a constant speed (slope) during the period from time t2 to time t3. The length of the period from time t2 to time t3 is, for example, in the range of 50 to 350 seconds.

  When the power generation output is decreased by the second specific value in step S13, next, the process of step S14 is executed. In step S <b> 14, the power generation output when the power generation output is reduced by the second specific value is set as the upper limit of the power generation output of the fuel cell 13.

  In the example shown in FIG. 2, the upper limit L1 of the power generation output is set at time t3, and the power generation output is maintained at the upper limit L1 during the period from time t3 to time t4. Even if the power generation output starts to decrease from time t2, the temperature of the reformer 11 may overshoot and exceed the first threshold temperature. By maintaining the power generation output below the upper limit L1 until the temperature of the reformer 11 is sufficiently lowered, the temperature of the reformer 11 can be reliably and rapidly lowered.

  According to this embodiment, even if the power load exceeds the upper limit L1 after time t3, the load following operation is not performed exceeding the upper limit L1, and the power generation output is maintained at the upper limit L1. After the time t3, when the power load is lower than the upper limit L1, the load following operation is performed. Thereby, not only can the temperature of the reformer 11 be surely and quickly lowered, but also a reduction in energy saving performance of the fuel cell system 100 can be suppressed.

  Next, each process of the flowchart of FIG. 5 will be described.

  In step S <b> 21 of FIG. 5, the temperature of the reformer 11 is detected using the temperature sensor 40. In step S22, it is determined whether or not the temperature of the reformer 11 is lower than the third threshold temperature. When the temperature of the reformer 11 falls below the third threshold temperature, the setting of the upper limit L1 of the power generation output is canceled in step S23. Thereby, the load following operation exceeding the upper limit L1 is permitted. Efficient operation can be continued while avoiding the fuel cell system 100 from being stopped due to an error such as misfiring or the reforming catalyst being heavily damaged.

  As shown in FIG. 2, the third threshold temperature is a temperature lower than the first threshold temperature. Similar to the first threshold temperature, the third threshold temperature is also appropriately determined according to the composition of the reforming catalyst, the structure of the reformer 11, the position of the temperature sensor 40, and the like. In one example, the third threshold temperature is a temperature in the range of 550 to 650 ° C.

  The following processing that is not shown in the flowcharts of FIGS. 3, 4, and 5 may be further executed.

  For example, when water vapor shortage occurs a plurality of times within a predetermined time, the power generation output of the fuel cell 13 is decreased from the current power generation output by a second specific value. Specifically, when the occurrence of water vapor shortage is detected, first, the power generation output is reduced by a first specific value from the current power generation output. The rate of decrease when the power generation output is decreased by the first specific value is as described in step S3 of the flowchart of FIG. After the power generation output is decreased by the first specific value, the power generation output is further decreased without increasing the power generation output. The rate of decrease when the power generation output is decreased by the second specific value is as described in step S13 of the flowchart of FIG.

  The temperature sensor 40 is often disposed at a position where a typical temperature of the reforming catalyst can be detected. Typical positions where the temperature can be detected include a position where the average temperature of the reforming catalyst can be detected, a position where the highest temperature of the reforming catalyst can be detected, and a position where the lowest temperature of the reforming catalyst can be detected. Can be mentioned. When the shortage of water vapor occurs repeatedly in a short time, the temperature distribution of the reforming catalyst varies greatly, and heat is stored in the reforming catalyst. In this case, there is a possibility that the reforming catalyst may be damaged greatly or the fuel cell system 100 may be stopped due to an error such as misfire. If the power generation output is greatly reduced when a shortage of water vapor occurs repeatedly in a short time, the operation of the fuel cell 13 can be continued while avoiding those disadvantages.

  The “predetermined time” is appropriately determined according to the composition of the reforming catalyst, the structure of the reformer 11, the position of the temperature sensor 40, and the like. In one example, the predetermined time is in the range of 30 to 90 minutes. The number of occurrences of water vapor shortage within a predetermined time is not particularly limited. The number of occurrences of water vapor shortage within a predetermined time is, for example, in the range of 5 to 15 times.

  Further, when the temperature of the reformer 11 exceeds the second threshold temperature (FIG. 2) higher than the first threshold temperature, the operation of the fuel cell 13 may be stopped. In this way, it is possible to continue the operation of the fuel cell 13 while avoiding that the reforming catalyst is greatly damaged or the fuel cell system 100 is stopped due to an error such as misfire.

  Similar to the first threshold temperature and the third threshold temperature, the second threshold temperature is also appropriately determined according to the composition of the reforming catalyst, the structure of the reformer 11, the position of the temperature sensor 40, and the like. In one example, the second threshold temperature is a temperature in the range of 700-750 ° C.

  The method of detecting the occurrence of water vapor shortage is not limited to the method of referring to the detection value of the flow meter 41 or the detection value of the pressure sensor 42. For example, the occurrence of water vapor shortage can be detected from the flow rate of the source gas. When the raw material gas supply device 28 includes a flow meter and a flow rate regulator, it is possible to detect that steam shortage has occurred in the reformer 11 from the operation amount of the flow rate regulator and the detected value of the flow meter.

  FIG. 6 is a trend graph showing an example of a change over time in the detected value of the flow rate of the source gas and the operation amount of the flow rate regulator. As shown in FIG. 6, when the water vapor shortage occurs, the pressure inside the reformer 11 decreases, so the flow rate of the raw material gas introduced into the reformer 11 through the raw material gas supply path 27 increases from Q1 to Q2. To do. When the flow meter and the flow rate regulator of the source gas supply unit 28 constitute a feedback system, the operation amount of the flow rate regulator decreases (60% → 40%) so as to suppress an increase in the source gas flow rate. Thereby, the flow volume of source gas returns to Q1. When the shortage of water vapor is resolved for a while, the flow rate of the raw material gas decreases from Q1 to Q3. The operation amount of the flow regulator increases (40% → 60%) so as to suppress the decrease in the flow rate. As a result, the flow rate of the source gas increases from Q3 to Q1. According to such knowledge, it is possible to detect that steam shortage has occurred in the reformer 11 from the operation amount of the flow rate regulator constituting the source gas supply device 28 and the detected value of the flow meter.

  A feedback system including a flow rate regulator and a flow meter serves as a detector that detects that steam shortage has occurred in the reformer 11. That is, it is possible to configure a part of the detector that detects the occurrence of water vapor shortage with software. The controller 50 may have a detector function, and another controller may have the detector function.

  The pressure sensor 42 may be disposed in a position other than the inside of the evaporator 32 and the path from the evaporator 32 to the reformer 11. The pressure sensor 42 may be disposed at any position as long as the pressure change caused by the water vapor shortage propagates. For example, even if the pressure sensor 42 is disposed in the fuel gas supply path 12 or the exhaust path 17, it is possible to detect the occurrence of water vapor shortage from the detection value of the pressure sensor 42.

  It is also possible to detect the occurrence of water vapor deficiency from the air flow rate for CO selective oxidation. The flow rate of air for CO selective oxidation can be detected by the flow meter 26. When water vapor shortage occurs in the reformer 11, the internal pressure of the reformer 11 decreases, and the flow rate of air introduced into the reformer 11 through the air path 24 increases from Q1 to Q2 (FIG. 6). When the flow rate regulator 25 and the flow meter 26 constitute a feedback system, the operation amount of the flow rate regulator 25 decreases so as to suppress an increase in the air flow rate (60% → 40%). Thereby, the flow rate of air returns to Q1. When the shortage of water vapor is resolved after a while, the air flow rate decreases from Q1 to Q3. The operation amount of the flow rate regulator 25 is increased so as to suppress the decrease in the flow rate (40% → 60%). This increases the air flow rate from Q3 to Q1. According to such knowledge, it is possible to detect that steam shortage has occurred in the reformer 11 from the operation amount of the flow regulator 25 and the detected value of the flow meter 26.

  The technology disclosed in this specification is useful for a fuel cell system.

DESCRIPTION OF SYMBOLS 11 Reformer 12 Fuel gas supply path 13 Fuel cell 14 Oxidant gas supply path 15 Combustor 16 Anode off-gas path 17 Exhaust path 18 Cathode off-gas paths 23 and 36 Air supply 24 Air path 25 Flow rate regulators 26, 35, and 41 Flow meter 27 Raw material gas supply path 28 Raw material gas supply apparatus 30 Water supply path 31 Water supply apparatus 32 Evaporator 34 Air supply path 40 Temperature sensor 42 Pressure sensor 50 Controller 100 Fuel cell system

Claims (9)

A reformer that generates a fuel gas containing hydrogen gas by reacting a raw material gas and water vapor using a reforming catalyst;
An evaporator for generating water vapor to be supplied to the reformer;
A fuel cell that generates electric power using the fuel gas and oxidant gas;
A detector for detecting that steam shortage has occurred in the reformer;
A controller;
With
When the steam shortage occurs in the reformer, the controller reduces the power generation output of the fuel cell by a first specific value from the current power generation output.   The fuel cell system according to claim 1, wherein the detector detects a physical quantity reflecting a flow rate of the water vapor at an inlet of the reformer.   The fuel cell system according to claim 1, wherein the detector includes a flow meter that detects a flow rate of the water to be supplied to the evaporator.   The fuel cell system according to claim 1 or 2, wherein the detector includes a pressure sensor that detects a pressure inside the evaporator or a pressure in a path from the evaporator to the reformer. A temperature sensor for detecting the temperature of the reformer;
When the temperature of the reformer detected by the temperature sensor is equal to or higher than a first threshold temperature, the controller reduces the power generation output of the fuel cell by a second specific value from the current power generation output. Item 5. The fuel cell system according to any one of Items 1 to 4.   5. The controller according to claim 1, wherein when the water vapor shortage occurs a plurality of times within a predetermined time, the controller reduces the power generation output of the fuel cell by a second specific value from the current power generation output. The fuel cell system described in 1.   The fuel cell system according to claim 5, wherein when the temperature of the reformer exceeds a second threshold temperature higher than the first threshold temperature, the controller stops the operation of the fuel cell.   When the power generation output is decreased by the second specific value, the controller sets the power generation output at the time when the power generation output is decreased by the second specific value as an upper limit of the power generation output of the fuel cell. The fuel cell system according to any one of claims 5 to 7.   The fuel cell system according to claim 8, wherein when the temperature of the reformer falls below a third threshold temperature lower than the first threshold temperature, the controller releases the upper limit of the power generation output.

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