JP2013008689A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the performance of a fuel battery cell being degraded by making it possible to check whether a raw fuel and steam are properly mixed in a fuel cell.SOLUTION: A fuel cell system 1 comprises: a fuel battery cell 13 for generating electric power by causing a chemical reaction of an oxidizer and a steam-reformed fuel by interposing a solid electrolyte body; a limiting current type humidity sensor 31 arranged in a fuel supply passage 25 for supplying fuel to an anode of the fuel battery cell 13; and an all region air-fuel ratio sensor 33 arranged in a fuel exhaust passage 27 for exhausting the spent fuel used at the anode of the fuel battery cell 13. Therefore, since the steam amount in the fuel supply passage 25 can be detected by using the limiting current type humidity sensor 31 and the all region air-fuel ratio sensor 33, it can be detected excellently whether steam is properly added to the fuel supplied to the anode of the fuel battery cell 13.

Description

  The present invention relates to a fuel cell including a fuel cell that generates electric power by chemically reacting an oxidant and a steam-reformed fuel through an electrolyte.

  Conventionally, as the fuel cell, there is known a fuel cell that supplies steam-reformed fuel obtained by adding steam to a raw fuel such as hydrocarbon gas or alcohol to the anode (negative electrode) of the fuel cell. (For example, refer to Patent Document 1).

  In addition, the water vapor | steam added to raw fuel is supplied by evaporating water using a vaporizer.

JP-A-9-129256

  By the way, the fuel used in the fuel cell needs to be mixed with an appropriate ratio of raw fuel and water vapor so as not to impair the performance of the fuel cell (power generation efficiency, cell durability, etc.). There is. For this reason, in the conventional fuel cell, for example, the mixing ratio of the raw fuel and the water vapor is adjusted by adjusting the opening of a valve for supplying the raw fuel or a valve for supplying water to the vaporizer.

  However, in the fuel cell, since it is not possible to confirm whether or not the raw fuel and the water vapor supplied from the vaporizer are actually mixed properly, for example, a problem occurs in the vaporizer and the water vapor is appropriately generated. When the fuel cannot be supplied, the supply balance between the raw fuel and the water vapor is lost, and the performance of the fuel cell may be impaired.

  Therefore, in view of such problems, in a fuel cell including a fuel cell that generates electric power by chemically reacting an oxidant and steam-reformed fuel through an electrolyte, raw fuel and steam are It is an object of the present invention to prevent the performance of the fuel cell from being impaired by making it possible to confirm whether or not the fuel cell is properly mixed.

  In order to achieve the above object, a fuel cell according to a first aspect includes a fuel cell that generates electric power by chemically reacting an oxidant and a steam-reformed fuel through an electrolyte, and the fuel cell. And a full-range air-fuel ratio sensor disposed in a fuel discharge path for discharging spent fuel used at the negative electrode of the cell.

  In other words, the full-range air-fuel ratio sensor disposed in the fuel discharge path is configured to detect the amount of water vapor contained in the spent fuel (strictly speaking, the spent oxidant (for example, air) used at the positive electrode of the fuel cell). When oxygen is introduced into the fuel discharge path due to a configuration in which the air discharge path for discharge is joined to the fuel discharge path, a detection signal corresponding to the oxygen partial pressure including oxygen is output. Here, the amount of water vapor contained in the spent fuel is changed depending on the amount of water vapor in the fuel supply path if the fuel cell is operated under a certain condition, and thus is contained in the spent fuel. If the amount of water vapor can be detected, the amount of water vapor in the fuel supply path can be detected.

  Therefore, according to such a fuel cell, the full-range air-fuel ratio sensor disposed in the fuel discharge path is used as a sensor for detecting the amount of water vapor in the fuel supply path for supplying fuel to the negative electrode of the fuel cell. Since it can be used, it can be satisfactorily detected whether or not water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell.

  By the way, in order to achieve the above object, as in the fuel cell of the second aspect, the full-range air-fuel ratio sensors are respectively provided in the fuel supply path and the fuel discharge path for supplying fuel to the negative electrode of the fuel cell. You may have.

  According to such a fuel cell, similarly to the fuel cell of the first aspect, it is possible to satisfactorily detect whether or not water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell. Further, since the change in the water vapor amount can be detected before and after the fuel is used by the fuel battery cell, the failure of the fuel battery cell can be detected.

  In order to achieve the above object, as described in claim 1, a fuel battery cell that generates electric power by chemically reacting an oxidant and a steam-reformed fuel through an electrolyte body; and And a humidity sensor disposed in a fuel supply path for supplying the fuel to the negative electrode of the fuel cell.

  According to such a fuel cell, since the amount of water vapor in the fuel supply path can be detected using a humidity sensor, whether or not water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell. Can be detected satisfactorily.

  Furthermore, in order to achieve the above object, instead of the full-range air-fuel ratio sensor provided in the fuel cell of the first aspect or the fuel cell of the second aspect, as described in claim 2 and claim 3, A humidity sensor may be provided.

  According to such a fuel cell, since the amount of water vapor in the fuel supply path can be detected using a humidity sensor, whether or not water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell. Can be detected satisfactorily.

  In particular, in the description of claims 1 to 3, any type of humidity sensor may be adopted as the humidity sensor as long as the sensor can output a detection signal corresponding to the humidity. For example, if a limiting current humidity sensor is used, the humidity can be measured with higher accuracy than when other types of humidity sensors (for example, a polymer film humidity sensor or the like) are used.

  In order to achieve the above object, the fuel cell used in the fuel supply path for supplying fuel to the negative electrode of the fuel cell and the negative electrode of the fuel cell as in the fuel cell of the third aspect A full-range air-fuel ratio sensor disposed in one of the fuel discharge passages for discharging the spent fuel, and a humidity sensor disposed in the other of the fuel supply passage and the fuel discharge passage. May be.

  According to such a fuel cell, it is possible to satisfactorily detect whether or not water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell, similarly to the fuel cells described above. Further, since the change in the water vapor amount can be detected before and after the fuel is used by the fuel battery cell, the failure of the fuel battery cell can be detected.

Furthermore, in the fuel cell according to any one of claims 1 to 3, the electrolyte body constituting the fuel cell may be a solid electrolyte body as described in claim 4.
In such a fuel cell, it is possible to satisfactorily detect whether or not water vapor is appropriately added to the fuel using each of the sensors. Therefore, cell cracks that occur when water vapor is not appropriately added to the fuel. It is possible to prevent peculiar problems occurring in the solid electrolyte body such as internal damage.

  By the way, in a fuel cell that uses a raw fuel (fuel before steam reforming) generally containing carbon atoms, the reaction temperature between the fuel and the oxidant in the fuel cell is abnormally high, It is known that if the amount of water vapor contained in the fuel is abnormally reduced, carbon may be deposited on the negative electrode, and if this is the case, the performance of the fuel cell will be significantly reduced.

  Accordingly, the invention of the fourth aspect provides a fuel cell that generates electric power by chemically reacting an oxidant and steam-reformed fuel through an electrolyte, and supplies the fuel to the negative electrode of the fuel cell. And a water vapor sensor that is disposed in the fuel flow passage for discharging and detects the amount of water vapor in the fuel flow passage, and controls the mixing ratio of raw fuel and water vapor contained in the fuel A control method for a fuel cell, wherein a mixing ratio of raw fuel and water vapor contained in the fuel is calculated based on a detection signal from the water vapor sensor, and water vapor relative to the amount of carbon contained in the fuel is calculated according to the calculation result It is characterized in that at least the amount of water vapor mixed into the raw fuel is controlled so that the molar ratio of the amount is 1.5 or more.

  According to such a fuel cell control method, since the fuel cell has a characteristic configuration according to any one of the above, water vapor is appropriately added to the fuel supplied to the negative electrode of the fuel cell. It is possible to detect well whether or not.

  Further, according to this fuel cell control method, the amount of water vapor contained in the fuel can be controlled to be equal to or greater than a certain value (water vapor amount (mol) / carbon amount (mol) ≧ 1.5). It is possible to prevent the reaction temperature between the fuel and the oxidant in the inside from becoming abnormally high or the amount of water vapor contained in the fuel from being abnormally reduced. Therefore, it is possible to prevent carbon from being deposited on the negative electrode of the fuel cell.

In addition, as a water vapor sensor in this invention, various sensors, such as a full range air-fuel ratio sensor and a humidity sensor (a limit current type humidity sensor is included), can be used.
Further, in the control method for the fuel cell according to the fourth aspect, the mixing ratio of the raw fuel and the water vapor supplied as fuel is controlled based on the detection result from the sensor, as in the control method for the fuel cell according to the fifth aspect. Whether or not there is an abnormality in the control system, and if it is detected that there is an abnormality in the control system, a partial reforming operation in which air is mixed with the fuel and sent to the negative electrode of the fuel cell, or the fuel Alternatively, a purge operation in which only air is sent to the negative electrode of the fuel cell may be performed.

  That is, in this control method, the partial reforming operation or the purge operation is performed when an abnormality is detected in the control system, such as when the mixing ratio of the raw fuel and the steam supplied as fuel cannot be controlled. Accordingly, the operation is performed with the power generation performance lowered (partial reforming operation), or the power generation function itself is stopped (purge operation).

  Therefore, according to such a control method of the fuel cell, it is possible to prevent the fuel cell from being damaged even when an abnormality is detected in the control system.

It is explanatory drawing which shows typically schematic structure of a fuel cell system. It is a flowchart which shows the fuel cell power generation control process in this embodiment. It is a flowchart which shows the fuel cell power generation control process in other embodiment. It is a flowchart which shows the fuel cell power generation control process in other embodiment.

Embodiments according to the present invention will be described below with reference to the drawings.
[Configuration of this embodiment]
FIG. 1 is an explanatory diagram schematically showing a schematic configuration of a fuel cell system 1 to which the present invention is applied.

As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 13, a large number of pipes connected to the fuel battery cell 13, and a large number of devices connected to these pipes.
The fuel cell 13 has a structure in which a number of well-known solid oxide fuel cells (SOFC) are stacked, for example, and a fuel and an oxidant are contained therein, and a solid made of a compound such as a platinum electrode and zirconia, for example. Electric power is generated between the cathode (positive electrode terminal) and the anode (negative electrode terminal) by a chemical reaction through a cell made of an electrolyte. The cathode and the anode are connected to wiring (not shown) for energization from these terminals to the driven object.

  An air supply path 21, an air discharge path 23, a fuel supply path 25, and a fuel discharge path 27 are connected to the fuel battery cell 13. In addition, each supply path 21 and 25 and each discharge path 23 and 27 (the same also about the switching path 79 and the mixing path 77 mentioned later) are comprised as a metal pipe, for example.

  The air supply path 21 is a path for supplying air to the cathode of the fuel cell 13, and the air three-way valve 71, the air branching portion 81, and the air mass flow 51 are sequentially from the upstream side of air (the right side in FIG. 1). It has. The air mass flow 51 and various mass flows 53, 55, and 57, which will be described later, are configured as well-known mass flow controllers that control the flow rate of the fluid to a set flow rate (that is, a constant flow rate). These mass flows 51, 53, 55, and 57 are driven and controlled by a control unit 11 to be described later.

  The opening direction of the air three-way valve 71 is switched when the drive unit 61 is driven. That is, the air three-way valve 71 is switched by the drive unit 61 to send the air flowing from the upstream side to the cathode side of the fuel cell 13 or to the switching path 79 side.

The air branch portion 81 branches the air flowing from the air three-way valve 71 side to the cathode side of the fuel cell 13 and the mixing path 77 side.
Here, the mixing path 77 is connected to the fuel supply path 25, and the mixing path 77 is provided with a two-way valve 75 and a partially oxidized air mass flow 57 in order from the air supply path 21 side.

The two-way valve 75 is switched between open and closed states by the drive unit 65.
The partially oxidized air mass flow 57 is driven when the two-way valve 75 is in an open state. When the partially oxidized air mass flow 57 is driven, air is mixed into the fuel supply path 25 to the anode side of the fuel cell 13. Can be sent to.

The air mass flow 51 controls the flow rate of air supplied to the cathode side of the fuel cell 13.
Next, the air discharge path 23 is configured as a path for discharging the air supplied to the cathode of the fuel cell 13.

  The fuel supply path 25 is a path for supplying fuel to the assortment of the fuel cells 13, and the raw fuel three-way valve 73, in order from the upstream side of the city gas (mainly methane) as the raw fuel, A fuel mass flow 53, a fuel branch 83, a vaporizer 41, a limiting current humidity sensor 31, and a reformer 43 are provided.

  The opening direction of the raw fuel three-way valve 73 is switched by the drive unit 63. That is, the raw fuel three-way valve 73 is switched by the driving unit 63 to send the fuel flowing from the upstream side or the air flowing from the switching path 79 side to the anode side of the fuel cell 13.

The fuel mass flow 53 controls the flow rate of fuel or air supplied to the anode side of the fuel cell 13.
In the fuel branch portion 83, the air flowing from the air three-way valve 71 side is merged with the fuel flowing from the fuel mass flow 53 side.

  The vaporizer 41 is connected to a water supply path 29 for introducing water whose flow rate is controlled to a predetermined amount by the water liquid mass flow 55. The vaporizer 41 evaporates the introduced water to form water vapor, This water vapor is mixed with the city gas flowing through the supply path 25.

  As the limit current type humidity sensor 31, for example, a limit current type sensor as disclosed in Japanese Patent Laid-Open No. 62-150151 can be employed. Japanese Patent Laid-Open No. Sho 62-150151 discloses a method for measuring the water vapor concentration in a gas containing oxygen and water vapor, but almost no oxygen is contained in the fuel supply path 25 in this embodiment. Since such a limiting current sensor is used, only the water vapor concentration can be measured satisfactorily.

  In such a limit current type humidity sensor 31, the limit current when water vapor is dissociated is detected when the voltage applied to the cell functioning as the oxygen pump is about 1V or more. Therefore, in this embodiment, for example, a voltage of 1.5 V is applied to a cell that functions as an oxygen pump.

  Next, the reformer 43 performs steam reforming of the city gas. That is, in the reformer 43, a chemical reaction is performed in which the mixed gas in a state where the city gas and the steam are mixed is changed to a steam-reformed fuel.

More specifically, in the reformer 43,
CH4 + H2O → CO + 3H2 (steam reforming reaction)
and,
CO + H2O → CO2 + H2 (shift reaction)
These chemical reactions are allowed to proceed simultaneously. As a result, 4 mol of hydrogen can be obtained by adding 2 mol of water vapor to 1 mol of city gas (methane).

Next, the fuel discharge path 27 is a path for discharging spent fuel supplied to the anode of the fuel battery cell 13, and an all-range air-fuel ratio sensor 33 is provided therein.
Here, as the full-range air-fuel ratio sensor 33, for example, a full-range air-fuel ratio sensor as disclosed in JP-A-62-148849 can be employed. When such a full-range air-fuel ratio sensor 33 is used, if the oxygen concentration contained in the spent fuel flowing through the fuel discharge path 27 is constant, the detection signal from the full-range air-fuel ratio sensor 33 is a change in the water vapor concentration. It changes according to. Therefore, the water vapor concentration can be detected using the full-range air-fuel ratio sensor 33.

  The reformer 43 is provided with a temperature sensor 35. The temperature sensor 35 outputs a detection signal corresponding to the temperature. When this detection signal is received by the control unit 11 described later, the temperature inside the reformer 43 is monitored by the control unit 11.

  By the way, in the fuel cell system 1, the control unit 11 which performs operation control of each mass flow 51-57 and the drive parts 61-65 is provided. The control unit 11 is configured as a well-known microcomputer including a CPU, ROM, RAM, etc., and inputs detection signals from various sensors 31 to 35 provided in the fuel cell system 1. Processing according to the detection signal (for example, fuel cell power generation control processing described later) is executed.

  The limit current type humidity sensor 31 and the full-range air-fuel ratio sensor 33 in the present embodiment correspond to the water vapor sensor referred to in the present invention. The fuel supply passage 25 and the fuel discharge passage 27 correspond to the fuel flow passage in the present invention.

[Processes implemented in this embodiment]
Next, the operation control method of the fuel cell system 1 will be described with reference to FIG. FIG. 2 is a flowchart showing a fuel cell power generation control process executed by the control unit 11.

  This fuel cell power generation control process is started when the power of the control unit 11 is turned on. First, the carburetor 41 is operated, and the air (air) mass flow 51, the raw fuel mass flow 53, and the water The liquid mass flow 55 is controlled so that each gas or liquid flows at a predetermined flow rate (initial flow rate: stored in the ROM) (S110).

  At this time, the air (Air) three-way valve 71 is opened in the cathode direction, and the raw fuel three-way valve 73 is opened in the anode direction. In addition, the two-way valve 75 is closed, and the partially oxidized air (Air) mass flow 57 is turned OFF.

  Subsequently, it is determined whether or not the detection result (output value indicating the absolute humidity) by the limit current humidity sensor 31 (inlet sensor) is within a predetermined inlet humidity allowable range set in advance (S120). If the detection result by the limit current type humidity sensor 31 is outside the allowable inlet humidity range (S120: No), depending on whether the detection result by the limit current type humidity sensor 31 is larger or smaller than the allowable range of the inlet humidity, The flow rates of the city gas and water controlled by the raw fuel mass flow 53 and the water-liquid mass flow 55 are adjusted so that the detection result by the limit current type humidity sensor 31 falls within the allowable inlet humidity range (S130).

  That is, in the process of S130, the mixing ratio of city gas and water vapor contained in the fuel is calculated based on the detection signal from the limit current humidity sensor 31, and the amount of water vapor relative to the amount of carbon contained in the fuel is calculated according to the calculation result. The amount of water vapor mixed into the city gas is controlled so that the molar ratio is in the range of 2.5 to 3.5 (at least 1.5 or more).

  Here, when changing the flow rate of each mass flow 51, 53, 55, 57, the control unit 11 stores the value of the flow rate after the change in a memory such as a RAM, and during the processing of S130, The amount of carbon contained in the fuel can be calculated by reading the value of the flow rate.

  In the process of S130, the molar ratio of the water vapor amount to the carbon amount contained in the fuel is controlled to be 2.5 or more even when the water vapor amount contained in the fuel changes due to some factor. This is because carbon is not immediately deposited on the anode (specifically, the molar ratio of the water vapor amount to the carbon amount is prevented from being less than 1.5).

  In addition, controlling the molar ratio of the amount of water vapor to the amount of carbon contained in the fuel to be less than 3.5 prevents a decrease in power generation efficiency due to an excessive increase in the amount of water vapor (ie, oxygen partial pressure) in the fuel. It is to do.

When S130 processing ends in this way, the processing returns to S120.
On the other hand, if the detection result by the limit current type humidity sensor 31 is within the allowable range of the inlet humidity (S120: Yes), the detection result (output value indicating the absolute humidity) by the entire region air-fuel ratio sensor 33 (exit sensor) is It is determined whether or not it is within a set predetermined outlet humidity allowable range (S140). If the detection result by the full-range air-fuel ratio sensor 33 is within the allowable range of the outlet humidity (S140: Yes), the current condition is maintained (in particular, the two-way valve 75 is closed) for a predetermined time (for example, about 1 second). ) Is carried out (S170), and the fuel cell power generation control process is repeated from the beginning.

  Further, if the detection result by the full-range air-fuel ratio sensor 33 is outside the allowable range of the outlet humidity (S140: No), the flow rate of water controlled by the water / liquid mass flow 55 is detected, and the detection result by the full-range air-fuel ratio sensor 33 is the outlet humidity. Adjustment is made so as to be within the allowable range (S150). That is, in the process of S150, as in the process of S130, the mixing ratio of the city gas and water vapor contained in the fuel is calculated based on the detection signal from the full-range air-fuel ratio sensor 33, and the fuel is determined according to the calculation result. The amount of water vapor mixed into the city gas is controlled so that the molar ratio of the amount of water vapor to the amount of carbon contained in the gas is in the range of 2.5 to 3.5 (at least 1.5).

  Note that the control unit 11 responds to the detection signal from the full-range air-fuel ratio sensor 33 and the operating state of the fuel cell (for example, the output from the fuel cell 13, the flow rate of raw fuel, whether or not normal operation is performed, etc.). In addition, a map in which the ratio of the amount of water vapor contained in the fuel can be calculated uniquely is stored in the ROM, and in the processing of S150, the above calculation is performed using this map.

Subsequently, it is determined again whether or not the detection result by the full-range air-fuel ratio sensor 33 (exit sensor) is within a preset outlet humidity allowable range (S160).
Since the process of S160 is already performed after adjusting the flow rates of the city gas and water, the mixing ratio (flow rate) of the city gas and water vapor supplied as fuel is determined according to the detection result by the all-region air-fuel ratio sensor 33. It is possible to detect whether there is an abnormality in the control system to be controlled.

  In other words, if the detection result by the full-range air-fuel ratio sensor 33 is within the allowable range of the outlet humidity (S160: Yes), it is assumed that there is no abnormality in this control system, and a normal operation is performed for a predetermined time (S170). Repeat the power generation control process from the beginning.

  On the other hand, if the detection result by the full-range air-fuel ratio sensor 33 is outside the allowable range of the outlet humidity (S160: No), an operation in which air is mixed with fuel (partial oxidation operation) is performed assuming that the control system is abnormal. (S180). That is, the two-way valve 75 is opened, and the partially oxidized air (Air) mass flow 57 is operated. As a result, air is supplied to the cathode of the fuel cell 13 and is also mixed with city gas and supplied to the anode. As a result, the oxygen partial pressure is increased inside the fuel battery cell 13, so that damage to the cell and carbon deposition can be prevented.

  Subsequently, it is determined again whether or not the detection result by the full-range air-fuel ratio sensor 33 (exit sensor) is within the allowable range of the outlet humidity (S190). That is, in the process of S190, it is determined whether or not the control system abnormality has been improved by performing the partial oxidation operation. Note that the allowable outlet humidity range in the process of S190 is set to an allowable range corresponding to the amount of air mixed in the fuel.

  If the detection result by the all-range air-fuel ratio sensor 33 is within the allowable range of the outlet humidity (S190: Yes), it is assumed that the abnormality of the control system has been improved and the current time is set for a predetermined time (for example, about 1 second). A partial oxidation operation is performed under the conditions (particularly, the two-way valve 75 is open) (S200), and the fuel cell power generation control process is repeated from the beginning.

  On the other hand, if the detection result by the full-range air-fuel ratio sensor 33 is outside the allowable range of the outlet humidity (S190: No), it is determined that the abnormality of the control system has not been improved, the city gas is shut off, and the air is fuel cell. Each valve and the mass flow are controlled so as to be fed into the 13 anodes (S210). That is, the air three-way valve 71 is switched to the switching path 79 (anode) side, the two-way valve 75 is closed, and the raw fuel three-way valve 73 is switched to the switching path 79 side. Further, the raw fuel mass flow 53 is fully opened, and the air mass flow 51, the water liquid mass flow 55, and the partially oxidized air mass flow 57 are turned off.

  Subsequently, a purge operation is performed in which the operation is performed under a current condition (a state in which air is sent to the anode of the fuel cell 13) for a predetermined time (for example, about 10 seconds) set in advance (S220), and fuel cell power generation is performed. The control process ends.

[Operations and effects in this embodiment]
In the fuel cell system 1 described in detail above, the fuel cell 13 that generates electric power by chemically reacting air and steam-reformed fuel through a solid electrolyte body, and the anode of the fuel cell 13 A limit current type humidity sensor 31 disposed in a fuel supply path 25 for supplying fuel to the fuel cell and a fuel discharge path 27 for discharging spent fuel used at the anode of the fuel cell 13. The full-range air-fuel ratio sensor 33 is provided.

  In other words, the full-range air-fuel ratio sensor 33 disposed in the fuel discharge path 27 corresponds to the amount of water vapor contained in the spent fuel (strictly speaking, the oxygen partial pressure including oxygen introduced through the solid electrolyte body). The detected signal is output. Here, since the amount of water vapor contained in the spent fuel changes according to the amount of water vapor in the fuel supply path 25, if the amount of water vapor contained in the spent fuel can be detected, the amount of water vapor in the fuel supply path 25 Can be detected.

Further, the limit current humidity sensor 31 detects the amount of water vapor in the fuel supply path 25.
Therefore, according to such a fuel cell system 1, the amount of water vapor in the fuel supply path 25 can be detected using the limit current type humidity sensor 31 and the full-range air-fuel ratio sensor 33, so that the fuel cell 13 It is possible to satisfactorily detect whether or not water vapor is appropriately added to the fuel supplied to the anode.

In addition, since the change in the water vapor amount can be detected before and after the fuel is used by the fuel battery cell 13, a failure of the fuel battery cell 13 can be detected.
In particular, since the limiting current humidity sensor 31 is used in the fuel cell system 1 of the present embodiment, the humidity is higher than when using other types of humidity sensors (for example, a polymer film humidity sensor). It can measure with high accuracy.

  Further, since the solid electrolyte body constituting the fuel battery cell 13 is composed of the solid electrolyte body, the solid electrolyte body generates cracks and internal damage caused by the water vapor not being appropriately added to the fuel. A peculiar malfunction can be prevented.

  In addition, in the fuel cell system 1 of the present embodiment, the control unit 11 performs a fuel cell power generation control process (FIG. 2) for controlling the mixing ratio of city gas (raw fuel) and water vapor contained in the fuel. In this process, the control unit 11 calculates the mixing ratio of city gas and water vapor contained in the fuel based on the detection signals from the limit current type humidity sensor 31 and the full-range air-fuel ratio sensor 33, and the fuel is determined according to the calculation result. The flow rate of the city gas (flow rate by the raw fuel mass flow 53) and the flow rate of water affecting the water vapor amount (flow rate by the water liquid mass flow 55) are set so that the molar ratio of the water vapor amount to the carbon amount contained in the gas is 1.5 or more. Control.

  Therefore, according to such a fuel cell system 1, the amount of water vapor contained in the fuel can be controlled to be equal to or greater than a certain value (water vapor amount (mol) / carbon amount (mol) ≧ 1.5). It is possible to prevent the reaction temperature between the fuel and air in the cell 13 from becoming abnormally high or the amount of water vapor contained in the fuel from being abnormally reduced. Therefore, it is possible to prevent carbon from being deposited at the anode of the fuel battery cell 13.

  Furthermore, in the fuel cell system 1 of the present embodiment, the control unit 11 is based on the detection results from the limit current type humidity sensor 31 and the full-range air-fuel ratio sensor 33, and the mixing ratio of city gas and water vapor supplied as fuel When it is detected whether or not there is an abnormality in the control system that controls the fuel, and when it is detected that there is an abnormality in the control system, a partial reforming operation in which air is mixed with the fuel and sent to the anode of the fuel cell 13 is performed. If the control system abnormality is not improved, a purge operation is performed in which only air is supplied to the anode of the fuel cell 13 instead of the fuel.

  In other words, in this control method, when an abnormality is detected in the control system, such as when the mixing ratio of city gas and water vapor supplied as fuel cannot be controlled, partial reforming operation and purge operation are performed. Accordingly, the operation is performed with the power generation performance lowered (partial reforming operation), or the power generation function itself is stopped (purge operation).

Therefore, according to such a fuel cell system 1, even if abnormality is detected in the control system, it is possible to prevent the fuel cell 13 from being damaged.
[Other Embodiments]
Embodiments of the present invention are not limited to the above-described embodiments, and can take various forms as long as they belong to the technical scope of the present invention.

  For example, in the present embodiment, the fuel cell 13 is configured as a solid electrolyte fuel cell (SOFC). However, for example, the fuel cell 13 may be configured as a polymer electrolyte fuel cell (PEFC). Similar effects can be obtained.

Further, in the present embodiment, the limit current type humidity sensor 31 is disposed on the upstream side of the reformer 43 in the fuel supply pipe 25, but may be disposed on the downstream side of the reformer 43.
In the fuel cell system 1 of the present embodiment, the limit current type humidity sensor 31 is disposed in the fuel supply path 25 and the full-range air-fuel ratio sensor 33 is disposed in the fuel discharge path 27. As the sensor disposed in the discharge path 27, the limit current type humidity sensor 31 and the full-range air-fuel ratio sensor 33 can be disposed in any combination.

  That is, the limit current type humidity sensor 31 or the full-range air-fuel ratio sensor 33 may be arranged in both the fuel supply path 25 and the fuel discharge path 27, or the full-range air-fuel ratio sensor 33 is arranged in the fuel supply path 25, A limit current type humidity sensor 31 may be disposed in the fuel discharge path 27.

Furthermore, the limit current type humidity sensor 31 or the full-range air-fuel ratio sensor 33 may be disposed only in the fuel supply path 25 or the fuel discharge path 27.
For example, when the limiting current humidity sensor 31 or the full-range air-fuel ratio sensor 33 is disposed only in the fuel supply path 25, the control unit 11 replaces the fuel cell power generation control process shown in FIG. 2 with the fuel shown in FIG. Battery power generation control processing is executed.

  In the fuel cell power generation control process shown in FIG. 3, only portions different from the power generation control process shown in FIG. 2 will be described. Further, in this process, a description will be given assuming that the limit current type humidity sensor 31 is disposed in the fuel supply path 25.

  In the fuel cell power generation control process shown in FIG. 3, if the detection result by the limit current humidity sensor 31 (inlet sensor) is within the allowable inlet humidity range (S120: Yes), the output (for example, voltage) from the fuel cell 13 is It is determined whether or not the output is within a preset allowable range (S310). If the output from the fuel cell 13 is within the allowable output range (S310: Yes), the processing from S170 onward is executed.

  If the output from the fuel cell 13 is outside the allowable output range (S310: No), readjustment to increase or decrease the flow rate of the water-liquid mass flow 55 is performed (S320), and the output (for example, voltage) from the fuel cell 13 again. Is within the allowable output range (S330). If the output from the fuel cell 13 is within the allowable output range (S330: Yes), the processing from S170 is executed.

  If the output from the fuel cell 13 is outside the allowable output range (S330: No), the process of S180 (adjustment for performing the partial oxidation operation) is performed. Then, when the processing of S180 is completed, it is determined again whether or not the output (for example, voltage) by the fuel cell 13 is within the output allowable range (S340).

  If the output from the fuel cell 13 is within the allowable output range (S340: Yes), the processing from S200 is executed. If the output from the fuel cell 13 is outside the allowable output range (S340: No), the processing from S210 onward is executed.

  Next, for example, when the limit current type humidity sensor 31 or the full-range air-fuel ratio sensor 33 is arranged only in the fuel discharge path 27, the control unit 11 replaces the fuel cell power generation control process shown in FIG. The fuel cell power generation control process shown in FIG.

  In the fuel cell power generation control process shown in FIG. 4, only portions different from the power generation control process shown in FIG. 2 will be described. Further, in this processing, the description will be made assuming that the entire region air-fuel ratio sensor 33 is disposed in the fuel discharge path 27.

  In the fuel cell power generation control process shown in FIG. 4, the processes of S120 and S130 are not performed, and when the process of S110 ends, the process proceeds to S140. In S140, if the detection result by the full-range air-fuel ratio sensor 33 is outside the outlet humidity allowable range (S140: No), the detection result by the limit current humidity sensor 31 is larger than the outlet humidity allowable range, or Depending on whether it is small, the flow rates of the city gas and water controlled by the raw fuel mass flow 53 and the water liquid mass flow 55 are adjusted so that the detection result by the limit current type humidity sensor 31 falls within the allowable range of the outlet humidity (S410). ).

Then, when the process of S410 ends, the processes of S160 and subsequent steps are executed.
As described above, even when the limiting current humidity sensor 31 or the full-range air-fuel ratio sensor 33 is disposed only in the fuel supply path 25 or the fuel discharge path 27, the fuel cell power generation control process shown in FIG. By carrying out, the same effect as this embodiment can be obtained.

  Moreover, in the said embodiment, although it was set as the structure which discharges used air and a spent fuel, without making the air exhaust path 24 and the fuel exhaust path 27 merge, the air exhaust path 24 and the fuel exhaust path 27 join. After that, the configuration may be such that spent air and spent fuel are discharged.

  As such a fuel cell system, for example, as shown in FIG. 1, the air discharge path 24 is discharged from the air upstream of the sensor disposed in the fuel discharge path 27 (in the above embodiment, the full-range air-fuel ratio sensor 33). A first combined flow path 85 connected to the path 27 may be provided, or a second combined flow path 87 connecting the air discharge path 24 to the fuel discharge path 27 on the downstream side of the sensor disposed in the fuel discharge path 27. You may have.

  Here, in the fuel cell system provided with the first combined flow path 85, the oxygen concentration (oxygen partial pressure) is relatively high in the vicinity of the sensor disposed in the fuel discharge path 27. As the sensor to be disposed in the air-fuel ratio sensor, it is desirable to employ the full-range air-fuel ratio sensor 33 that measures the oxygen concentration rather than the humidity sensor and obtains the humidity from the decrease amount.

  Further, in the fuel cell system 1 and the fuel cell system including the second combined flow path 87 in the present embodiment, the oxygen concentration (oxygen partial pressure) is extremely low near the sensor disposed in the fuel discharge path 27. Therefore, even if the limiting current humidity sensor 31 is employed as the sensor disposed in the fuel discharge path 27, the water vapor amount can be measured with high accuracy.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 11 ... Control unit, 13 ... Fuel cell, 21 ... Air supply path, 23 ... Air discharge path, 25 ... Fuel supply path, 27 ... Fuel discharge path, 29 ... Water supply path, 31 ... Limit Current humidity sensor 33 ... Air-fuel ratio sensor, 41 ... Vaporizer, 43 ... Reformer, 51 ... Air mass flow, 53 ... Raw fuel mass flow, 55 ... Water liquid mass flow, 57 ... Partial oxidation air mass flow, 61 ... Drive part 63 ... Drive part 65 ... Drive part 71 ... Air three-way valve 73 ... Raw fuel three-way valve 75 ... Two-way valve 77 ... Mixing path 79 ... Switching path 81 ... Air branching part 83 ... Fuel branching portion, 85... First joint channel, 87.

Claims (4)

A fuel cell for generating electric power by chemically reacting an oxidant and steam-reformed fuel through an electrolyte body;
A humidity sensor disposed in a fuel supply path for supplying the fuel to the negative electrode of the fuel battery cell;
A fuel cell comprising: A fuel cell for generating electric power by chemically reacting an oxidant and steam-reformed fuel through an electrolyte body;
A humidity sensor disposed in a fuel discharge path for discharging spent fuel used in the negative electrode of the fuel cell;
A fuel cell comprising: A fuel cell for generating electric power by chemically reacting an oxidant and steam-reformed fuel through an electrolyte body;
A first humidity sensor disposed in a fuel supply path for supplying the fuel to the negative electrode of the fuel cell;
A second humidity sensor disposed in a fuel discharge path for discharging spent fuel used in the negative electrode of the fuel cell;
A fuel cell comprising:   The fuel cell according to any one of claims 1 to 3, wherein the electrolyte body constituting the fuel cell is a solid electrolyte body.

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