JP4357306B2 - Fuel reformer and fuel cell system - Google Patents

Description

  The present invention relates to a fuel reformer that generates hydrogen from a reformed fuel containing a hydrocarbon-based compound and a fuel cell system including the fuel reformer.

  Conventionally, various types of fuel reforming apparatuses that generate hydrogen from a reformed fuel containing a hydrocarbon-based compound have been proposed. For example, Patent Document 1 discloses a fuel that supplies a light raw material that is a reformed fuel that is relatively easy to vaporize and a heavy raw material that is a reformed fuel that is relatively difficult to vaporize to a reformer including a reforming catalyst. A reformer is disclosed. Here, by adjusting the amount of steam supplied to the reformer, the ratio of the amount of steam to the amount of reformed fuel supplied to the reformer is set to a predetermined value, and the steam reforming reaction proceeds well. So that it is controlled.

JP 2003-165706 A

  However, in the conventional fuel reformer, when the amount of hydrogen to be generated by the fuel reformer fluctuates, the ratio of the amount of water vapor to the amount of reformed fuel supplied to the reformer is maintained at a predetermined value. Sometimes it was difficult. That is, when the amount of hydrogen to be generated by the fuel reformer fluctuates, it is necessary to vary the amount of reformed fuel and the amount of steam supplied to the reformer, but it is difficult to quickly vary the amount of steam to be supplied. For this reason, it is difficult to maintain the above ratio at a predetermined value. Since the follow-up of the amount of water vapor with respect to fluctuations in the reformed fuel amount (especially increase fluctuations) is insufficient, if the ratio of the amount of water vapor to the reformed fuel amount cannot be maintained at a predetermined value, the reforming efficiency will decrease. Inconvenience such as wrinkle formation may occur.

  The present invention has been made to solve the above-described conventional problems, and provides a technique for ensuring the amount of water vapor used for the steam reforming reaction by quickly changing the amount of water vapor used for the steam reforming reaction. For the purpose.

To achieve the above object, a first fuel reformer of the present invention is a fuel reformer that generates hydrogen from reformed fuel,
A catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
A reformed fuel supply unit for supplying the reformed fuel to the catalyst unit;
A steam supply section for supplying the steam to the catalyst section;
A hydrogen supply unit for supplying hydrogen to the catalyst unit when the amount of the reformed fuel supplied from the reformed fuel supply unit fluctuates;
And an oxygen supply unit that supplies oxygen to the catalyst unit.

  According to the first fuel reforming apparatus of the present invention configured as described above, since hydrogen can be supplied to the catalyst unit by the hydrogen supply unit, hydrogen is oxidized using oxygen supplied by the oxygen supply unit. Thus, water vapor can be generated in the catalyst portion. Therefore, when the amount of reformed fuel increases and fluctuates, the steam generated by the oxidation of hydrogen can be further used as the steam to be used for the steam reforming reaction, and the amount of steam to be used for the steam reforming reaction can be rapidly changed. It can be secured.

  In the catalyst part provided in the fuel reforming apparatus of the present invention, the reforming while producing hydrogen using the oxygen supplied by the oxygen supply part together with the steam reforming reaction for producing hydrogen from the reformed fuel and steam. A partial oxidation reaction for oxidizing the fuel may be allowed to proceed.

The first fuel reformer of the present invention further includes
When the ratio of the water vapor amount to the reformed fuel amount supplied at the time of the increase fluctuation is less than a predetermined value, the amount of hydrogen capable of generating water vapor to bring the ratio close to the predetermined value is supplied to the catalyst unit. It is good also as providing the control part which controls the said hydrogen supply part.

  With such a configuration, the ratio of the amount of water vapor to the amount of reformed fuel can be brought close to a predetermined value in the catalyst unit by oxidizing the hydrogen supplied by the hydrogen supply unit to generate water vapor. In particular, if the hydrogen supply unit is controlled so that a deficient amount of water vapor is generated by oxidation of hydrogen, the ratio of the amount of water vapor to the amount of reformed fuel in the catalyst unit can always be maintained at a predetermined value. Here, a value that sufficiently increases the efficiency of the steam reforming reaction and sufficiently suppresses soot formation on the reforming catalyst is set as the predetermined value, which is a reference value of the ratio of the steam amount to the reformed fuel amount. By doing so, the state of the steam reforming reaction in the catalyst part can be favorably maintained.

In such a first fuel reformer of the present invention,
The control unit may further control the oxygen supply unit so as to supply an oxygen amount corresponding to an amount of hydrogen supplied by the hydrogen supply unit to the catalyst unit.

  With such a configuration, it is possible to make the state of the steam reforming reaction and the oxidation reaction desirable in the catalyst portion and maintain a high reforming efficiency.

In the first fuel reformer of the present invention,
The water vapor supply unit may include an evaporator that vaporizes water.

  When water is vaporized using an evaporator, since the heat of vaporization of water is relatively large, the heating amount for vaporization is increased sufficiently to increase the efficiency as the amount of water to be vaporized increases. It is difficult to increase the amount of vaporization well. Therefore, it is generally difficult to rapidly increase the amount of water vapor generated in the evaporator. With the above configuration, when the amount of reformed fuel supplied to the catalyst section increases rapidly, in addition to the steam that can be generated by the evaporator, the steam obtained by oxidizing the hydrogen supplied by the hydrogen supply section is also steam reformed. It can be utilized in the reaction, and it can be prevented that the amount of water vapor is insufficient.

Alternatively, in the first fuel reformer of the present invention,
The catalyst part further includes an oxidation catalyst,
The hydrogen supply unit and the oxygen supply unit may supply hydrogen and oxygen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst.

  With such a configuration, the hydrogen supplied from the hydrogen supply unit is previously oxidized on the oxidation catalyst to generate steam, and the generated steam is supplied to the reforming catalyst. The ratio of the water vapor amount to the reformed fuel amount can be controlled more reliably.

In the first fuel reformer of the present invention,
The hydrogen supply unit may include a hydrogen tank for storing hydrogen, and supply the hydrogen stored in the hydrogen tank to the catalyst unit.

  In such a case, it is possible to control the generation of water vapor using high purity hydrogen gas, and it becomes easier to control the amount of hydrogen used for generating water vapor.

In the first fuel reformer of the present invention,
The hydrogen supply unit may supply hydrogen generated by the catalyst unit to the catalyst unit.

  In such a case, in the steam reforming reaction that proceeds in the catalyst section, when the amount of steam supplied by the steam supply section is insufficient, steam obtained by oxidizing a part of the hydrogen generated by the catalyst section is used. be able to. When supplying the hydrogen produced in the catalyst part, the reformed gas produced by the reforming reaction and discharged from the catalyst part may be used as it is, or the purity of hydrogen is further increased or reformed. It is good also as supplying to a catalyst part, after removing the impurity in gas. Alternatively, the reformed gas generated in the catalyst unit may be supplied to a predetermined hydrogen consuming device, and the remaining hydrogen that has not been consumed by the hydrogen consuming device may be supplied to the catalyst unit.

A second fuel reformer of the present invention is a fuel reformer that generates hydrogen from a reformed fuel and supplies the generated hydrogen to an anode of a fuel cell,
A catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
A reformed fuel supply unit for supplying the reformed fuel to the catalyst unit;
A cathode off-gas supply unit that contains water vapor and oxygen and is discharged from the cathode of the fuel cell to the catalyst unit;
A hydrogen supply unit for supplying hydrogen to the catalyst unit;
It is a summary to provide.

  According to the second fuel reforming apparatus of the present invention configured as described above, hydrogen is oxidized in the catalyst unit when the cathode offgas whose amount of water vapor contained depends on the amount of power generation is used to supply water vapor. By doing so, further water vapor can be generated. Therefore, it is possible to secure the amount of steam to be used for the steam reforming reaction without being affected by the amount of power generation. In addition, since oxygen in the cathode off-gas can be consumed by oxidizing hydrogen in the catalyst part, the amount of oxygen supplied to the cathode is increased without being limited by the efficiency of the reforming reaction in the catalyst part. It becomes possible to improve the power generation efficiency.

In such a second fuel reformer of the present invention,
The hydrogen supply unit may supply hydrogen to the catalyst unit when the amount of the reformed fuel supplied by the reformed fuel supply unit increases and varies.

  With such a configuration, even when the amount of reformed fuel supplied to the catalyst section rapidly increases due to a rapid increase in the amount of power generated in the fuel cell, even if the amount of steam in the cathode offgas is insufficient, the steam reforming reaction is performed. The amount of water vapor to be provided can be ensured.

In such a second fuel reformer of the present invention, further,
The amount of reformed fuel supplied to the catalyst unit is the amount of reformed fuel required to generate hydrogen in the catalyst unit in an amount corresponding to the required power generation amount for the fuel cell. A reformed fuel control unit for controlling the reformed fuel supply unit,
When the ratio of the steam amount supplied by the steam supply unit to the required reformed fuel amount is less than a predetermined value when the required reformed fuel amount increases and fluctuates, the ratio is brought close to the predetermined value. It is good also as providing the hydrogen control part which controls the said hydrogen supply part so that the amount of hydrogen which can produce | generate water vapor | steam is supplied to the said catalyst part.

  With such a configuration, the ratio of the amount of water vapor to the amount of reformed fuel can be brought close to a predetermined value in the catalyst unit by oxidizing the hydrogen supplied by the hydrogen supply unit to generate water vapor. Therefore, the efficiency of the reforming reaction can be stably maintained in the catalyst portion, and a desired amount of hydrogen can be stably supplied to the fuel cell.

In the second fuel reformer of the present invention, further,
An oxidizing gas supply unit for supplying an oxidizing gas containing oxygen to the cathode of the fuel cell;
An oxidizing gas control unit that controls the amount of oxidizing gas supplied by the oxidizing gas supply unit based on the power generation amount to be generated by the fuel cell and the power generation efficiency in the fuel cell;
The steam and oxygen are supplied to the catalyst unit by the cathode offgas supply unit, and in the catalyst unit, partial oxidation which is an oxidation reaction accompanied by the generation of hydrogen using the reformed fuel together with the steam reforming reaction A hydrogen control unit that controls the hydrogen supply unit to supply the hydrogen to the catalyst unit when the reaction proceeds may be provided.

  With such a configuration, even if the amount of oxidizing gas supplied to the cathode is increased in order to improve the power generation efficiency in the fuel cell, oxygen in the cathode off-gas is consumed in the catalyst unit to oxidize hydrogen. . Therefore, when the partial oxidation reaction proceeds together with the steam reforming reaction, it is possible to suppress an excessive amount of oxygen in the catalyst portion, and it is possible to prevent the efficiency of hydrogen generation from decreasing.

A third fuel reformer of the present invention is a fuel reformer that generates hydrogen from a reformed fuel and supplies the generated hydrogen to an anode of a fuel cell,
A catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
A reformed fuel supply unit for supplying the reformed fuel to the catalyst unit;
A steam supply section for supplying the steam to the catalyst section;
When the amount of the reformed fuel supplied from the reformed fuel supply section increases and fluctuates, a hydrogen supply section that supplies hydrogen to the catalyst section and anode offgas discharged from the anode of the fuel cell to the catalyst section When,
And an oxygen supply unit that supplies oxygen to the catalyst unit.

  According to the third fuel reformer of the present invention configured as described above, since hydrogen in the anode off-gas is used to supplement the steam used in the reforming reaction, it is necessary to prepare a separate hydrogen source. In addition, the energy efficiency of the entire system is not lowered because hydrogen is oxidized to obtain water vapor.

A fourth fuel reformer of the present invention is a fuel reformer that generates hydrogen from the reformed fuel and supplies the generated hydrogen to the anode of the fuel cell,
A catalyst unit including an oxidation catalyst together with a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam,
A part of the reformed fuel is supplied to the catalyst unit so as to reach the reformed catalyst after passing through the oxidation catalyst, and the rest of the reformed fuel is supplied to the reformed catalyst. A supply section;
A steam supply section for supplying the steam to the catalyst section;
A hydrogen supply unit that supplies hydrogen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst, the anode off-gas containing hydrogen and discharged from the anode of the fuel cell;
And an oxygen supply unit that supplies oxygen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst.

  According to the fourth fuel reformer of the present invention configured as described above, when the steam reforming reaction proceeds with the reforming catalyst, the steam supplied by the steam supply unit and the hydrogen in the anode off-gas In addition to the steam obtained by oxidizing the catalyst on the oxidation catalyst, the steam obtained by oxidizing a part of the reformed fuel on the oxidation catalyst can also be used. Therefore, even if the water vapor obtained by oxidizing hydrogen in the anode off-gas is added to the water vapor supplied by the water vapor supply unit, even if the water vapor amount cannot be sufficiently secured, the ratio of the water vapor amount to the reformed fuel amount The steam reforming reaction can be performed while maintaining the above.

The fuel cell system of the present invention comprises:
A fuel cell; and a fuel reformer according to any one of claims 1 to 13,
The gist is to generate electricity by supplying hydrogen generated by the fuel reformer to the anode of the fuel cell.

  According to the fuel cell system of the present invention configured as described above, the state of the steam reforming reaction in the fuel reformer can be satisfactorily maintained, so that hydrogen can be stably supplied to the fuel cell. it can.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of an operation method of a fuel reformer, an operation method of a fuel cell system, and the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Overall configuration of the fuel reformer of the first embodiment:
B. Control for reforming reaction:
C. Second Embodiment D. Third embodiment:
E. Fourth embodiment:
F. Variations:

A. Overall configuration of the fuel reformer of the first embodiment:
FIG. 1 is a block diagram showing an outline of the configuration of the fuel cell system 20 of the first embodiment. The fuel cell system 20 includes a reformer 30 and uses the hydrogen generated by the reformer 30 to generate power in the fuel cell 40.

  The reformer 30 is supplied with reformed fuel, oxygen, and steam in order to generate hydrogen by a reforming reaction. The reformer 30 is provided with a mixer 32, and the reformed fuel, oxygen and water vapor are mixed in the mixer 32 before being supplied to the reformer 30.

  The reformed fuel is supplied to the mixer 32 while the flow rate is adjusted by the pump 34. As the reformed fuel used for the reforming reaction, various hydrocarbon compounds such as hydrocarbons such as gasoline and natural gas, alcohols such as methanol, and aldehydes can be used. Further, oxygen and water vapor are supplied to the reformer 30 by supplying a cathode off gas, which is a gas containing oxygen and water vapor, and is discharged from the cathode of the fuel cell 40 to the mixer 32. In the fuel cell system 20, a cathode offgas supply path 60 that connects the cathode offgas outlet portion of the fuel cell 40 and the mixer 32 is provided, and the cathode offgas is supplied to the mixer 32 via the cathode offgas supply path 60. Is supplied.

  In this embodiment, the reformed fuel is supplied to the mixer 32 while the flow rate is adjusted by the pump 34. However, the reformed fuel supply unit that supplies the reformed fuel to the reformer 30 has a different configuration. Also good. For example, when gaseous fuel is used as the reformed fuel, a flow rate adjusting valve may be provided in place of the pump 34. In the case where liquid fuel is used as the reformed fuel, a heating device for vaporizing the liquid fuel is further provided in the mixer 32. In the mixer 32, in addition to the operation of mixing the reformer and the cathode offgas. The reformed fuel may be vaporized. Alternatively, the liquid fuel may be vaporized prior to supply to the mixer 32 using a predetermined vaporizer.

  In this embodiment, hydrogen can be further supplied to the reformer 30. Specifically, the gas containing hydrogen and the anode off gas discharged from the anode of the fuel cell 40 can be supplied to the mixer 32. In the fuel cell system 20, an anode offgas supply path 64 that connects the anode offgas flow path discharged from the fuel cell 40 and the mixer 32 is provided, and the mixer 32 is connected via the anode offgas supply path 64. Anode off gas is supplied to The configuration for supplying the anode off-gas and the cathode off-gas to the reformer 30 will be further described later.

  The reformer 30 is configured as a catalyst unit including a reforming catalyst. When the mixed gas containing the reformed fuel, oxygen, and water vapor generated in the mixer 32 is supplied to the reformer 30, the reformer 30 is reformed. The reaction proceeds to produce hydrogen-rich reformed gas. That is, in the reformer 30, the steam reforming reaction proceeds using the steam in the cathode offgas, and the partial oxidation reaction that is an oxidation reaction accompanied by the generation of hydrogen proceeds using the oxygen in the cathode offgas. Thus, hydrogen is generated from the reformed fuel by these reactions. In the reformer 30, the steam reforming reaction may be advanced using heat generated in the partial oxidation reaction, or an external heating device is further provided in the reformer 30, and the heat required for the steam reforming reaction is provided. It is good also as supplementing by the heating from the outside. As the reforming catalyst for promoting the reforming reaction, for example, a copper-zinc base metal catalyst or a noble metal catalyst such as platinum is known, and may be appropriately selected according to the reformed fuel to be used. The reforming catalyst can be constituted, for example, by supporting a catalytic metal on a honeycomb carrier made of metal or ceramics. Alternatively, the catalyst metal may be supported on a pellet-shaped carrier, or the reforming catalyst may be formed into a pellet. As described above, the reformer 30 can also be supplied with an anode off gas containing hydrogen. When hydrogen is further supplied to the reformer 30 in a state where oxygen is supplied, the hydrogen is rapidly oxidized on the reforming catalyst to generate steam. In this embodiment, a hydrogen oxidation reaction is used to adjust the amount of water vapor provided for the reforming reaction, but detailed operations relating to hydrogen oxidation will be described in detail later. Further, by supplying the anode off gas to the reformer 30 in this way, water vapor in the anode off gas can also be used in the reforming reaction. In other words, the anode off-gas is produced by back diffusion (generated in the electrolyte layer from the cathode side to the anode side), which is generated at the cathode of the fuel cell, and is included in the reforming reaction. Is done.

  The hydrogen-rich reformed gas generated in the reformer 30 is guided to the anode of the fuel cell 40 and is subjected to an electrochemical reaction as a fuel gas. The fuel cell system 20 includes a blower 44, and the blower 44 supplies air as an oxidizing gas to the cathode of the fuel cell 40. Here, the fuel cell 40 is provided with a heat exchanger 42 to which the heat of the fuel cell 40 is transmitted, and the air supplied from the blower 44 cools the fuel cell 40 through the heat exchanger 42. After that, it is supplied to the cathode. In addition, as a refrigerant used for heat exchange with the fuel cell 40, a liquid refrigerant such as water or oil is used instead of the air supplied from the blower 44 or in addition to the air supplied from the blower 44. It is also good.

  The fuel cell 40 of the present embodiment has an electrolyte layer having proton conductivity, and is constituted by, for example, a phosphoric acid fuel cell or a solid polymer fuel cell. Although FIG. 1 schematically illustrates a state in which the fuel cell 40 includes an anode and a cathode, the actual fuel cell 40 has a stack structure in which single cells are stacked. In such a fuel cell cathode, water is generated by an electrochemical reaction. Therefore, the air (cathode off-gas) discharged after being subjected to the electrochemical reaction at the cathode is left as a residual remaining without being consumed in the electrochemical reaction. A predetermined amount of water vapor is contained together with oxygen. This cathode off gas is guided to the cathode off gas supply path 60 described above, and is supplied to the reformer 30 via the mixer 32.

  After the fuel gas supplied to the anode is used for power generation, it is led to the outside through the pipe 62 as an anode off gas. The aforementioned anode off-gas supply path 64 that branches from the pipe 62 and is connected to the mixer 32 is further provided. A switching valve 38 is provided at a branch portion where the pipe 62 branches to the anode off-gas supply path 64. By controlling the switching valve 38, the amount of anode off-gas supplied to the reformer 30 via the mixer 32 is determined. The amount of anode off-gas exhausted to the outside can be adjusted.

A purifier 46 is provided downstream of the switching valve 38 in the pipe 62. Since the anode off gas contains residual hydrogen that has not been used in power generation, and combustible components such as CO and CH ₄ , the purifier 46 has a hydrogen concentration and a combustible component concentration prior to exhausting the anode off gas to the outside. To reduce the anode off-gas. The purifier 46 includes an oxidation catalyst. By passing through the purifier 46, residual hydrogen and combustible components in the anode off-gas are burned and removed. Air used for combustion is supplied from the blower 45 via the pipe 63. The pipe 63 is disposed so as to pass through the heat exchanger 42, and joins the pipe 62 downstream of the switching valve 38. As a result, the anode off gas and air are mixed, and a fuel reaction is performed in the purifier 46.

  The fuel cell system 20 further includes a control unit 50 for controlling the operating state of each part of the fuel cell system 20. Information related to the operating state of each part of the fuel cell system 20 such as the fuel cell 40 and the reformer 30 is input to the control unit 50, and a pump 34, blowers 44 and 45, and a switching valve are input from the control unit 50. A drive signal is output to each unit such as 38.

  Although omitted from FIG. 1, a carbon monoxide reducing device is further provided between the reformer 30 and the fuel cell 40 to reduce the carbon monoxide concentration in the reformed gas and then reforming. Gas may be supplied to the fuel cell 40. As a carbon monoxide reduction apparatus, it can be set as a shift part provided with the shift catalyst which advances the shift reaction which produces a carbon dioxide and hydrogen from carbon monoxide and water vapor | steam, for example. Or it can be set as the carbon monoxide selective oxidation part provided with the selective oxidation catalyst which advances the carbon monoxide selective oxidation reaction which preferentially oxidizes carbon monoxide in preference to the hydrogen which exists excessively.

  The fuel cell system 20 can be mounted on a mobile body such as an electric vehicle and used as a power source for driving the mobile body. Alternatively, the fuel cell system 20 may be used as a stationary power generator.

B. Control for reforming reaction:
Hereinafter, an outline of control performed in the fuel cell system 20 for the reforming reaction that proceeds in the reformer 30 will be described. FIG. 2 is a flowchart showing a reformer control processing routine executed by the control unit 50. This routine is repeatedly executed by the control unit 50 at predetermined intervals while the fuel cell system 20 is activated and power generation is performed in the fuel cell 40 using the fuel gas generated in the reformer 30.

  When this routine is executed, the control unit 50 first acquires the target power generation amount to be generated by the fuel cell 40, the current power generation amount, and the reformed fuel amount supplied to the reformer 30 (step). S100). For example, when the fuel cell system 20 is used as a power source for driving a vehicle, the target power generation amount is set based on the accelerator opening and the vehicle speed of the vehicle. The current power generation amount of the fuel cell 40 can be obtained from the detected value of the ammeter by providing an ammeter in a circuit to which the fuel cell 40 is connected. The amount of the reformed fuel supplied to the reformer 30 may be obtained based on the drive signal output from the control unit 50 to the pump 34, or a flow meter is provided in the reformed fuel flow path to May be actually detected.

  Next, the control unit 50 calculates the amount of water vapor in the cathode offgas and the amount of hydrogen in the anode offgas based on the current power generation amount and reformed fuel amount acquired in step S100 (step S110). In this embodiment, the amount of water vapor in the cathode off gas is handled as the amount of water generated by the electrochemical reaction, and can be theoretically calculated from the amount of power generation. Below, the formula showing the electrochemical reaction that proceeds in the fuel cell is shown. Formula (1) represents the reaction that proceeds at the anode, Formula (2) represents the reaction that proceeds at the cathode, and the reaction shown in Formula (3) proceeds throughout the battery.

_{^{H 2 → 2H + + 2e -}} ... (1)
2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The control unit 50 calculates the amount of water generated by the electrochemical reaction based on the current power generation amount acquired in step S100 and the above formulas (1) to (3). The amount of hydrogen in the anode off gas is obtained by subtracting the amount of hydrogen consumed in the electrochemical reaction from the amount of hydrogen generated in the reformer 30. The amount of hydrogen generated in the reformer 30 is determined by the reformed fuel amount acquired in step S100 and the conversion rate in the reformer 30 (the reformed fuel supplied to the reformer 30 is actually converted by the reforming reaction). And the ratio of the reformed fuel that produces hydrogen). The conversion rate in the reformer 30 may be obtained experimentally in advance. The amount of hydrogen consumed in the electrochemical reaction can be calculated based on the current power generation amount acquired in step S100 and the above formulas (1) to (3).

  Next, the control unit 50 calculates the amount of reformed fuel to be supplied to the reformer 30 based on the target power generation amount acquired in step S100 (step S120). In order to calculate the amount of reformed fuel to be supplied to the reformer 30, first, it is necessary to obtain the target power generation amount based on the target power generation amount and the equations (1) to (3) described above. What is necessary is just to calculate the amount of hydrogen. Thereafter, the amount of reformed fuel to be supplied to the reformer 30 can be calculated based on the necessary hydrogen amount and the conversion rate in the reformer 30 described above.

  After calculating the amount of reformed fuel to be supplied, the control unit 50 calculates the amount of steam to be supplied to the reformer 30 based on the calculated amount of reformed fuel and the S / C ratio (step S130). . Here, the “S / C ratio” means “water molecules constituting water vapor supplied to the reformer 30 relative to“ number of moles of carbon atoms contained in the reformed fuel supplied to the reformer 30 ”. Is the value of the ratio of “number of moles of”. In this embodiment, the S / C ratio is set to a predetermined value so that the reforming efficiency in the reformer 30 is sufficiently secured and soot formation in the reformer 30 can be sufficiently suppressed. . The value of such S / C ratio can be set to 1.5-2, for example. In step S130, the amount of water vapor to be supplied to the reformer 30 is calculated based on the previously determined S / C ratio and the reformed fuel amount calculated in step S120.

  After calculating the amount of water vapor to be supplied, the control unit 50 next determines whether or not the amount of water vapor in the cathode off-gas calculated in step S110 is sufficient for the amount of water vapor to be supplied (step S140). ). When the amount of water vapor in the cathode off gas is sufficient, that is, when the amount of water vapor in the cathode off gas is equal to or greater than the amount of water vapor to be supplied, the control unit 50 determines the drive amount of the blower 44 and the drive amount of the pump 34. Setting is made (step S150). In order to set the drive amount of the blower 44, that is, the amount of air supplied to the cathode, first, based on the target power generation amount acquired in step S100 and the above-described equations (1) to (3), the target power generation The amount of oxygen required to generate electricity is theoretically determined. Thereafter, the amount of air supplied to the cathode is set so that the amount of supplied air becomes a predetermined excess rate (excess air rate) with respect to the theoretically determined oxygen amount. The excess air ratio is a value set in advance as a value at which the power generation efficiency in the fuel cell 40 becomes sufficiently high. The drive amount of the pump 34 is a control value for actually supplying the reformer 30 with the reformed fuel amount to be supplied calculated in step S120.

  Thereafter, the control unit 50 outputs a drive signal to the blower 44 and the pump 34 based on the result of step S150, and switches the switching valve 38 so that all the anode off-gas is exhausted (step S160), and ends this routine. To do. Here, it is determined that the amount of water vapor in the cathode off-gas is sufficient in step S140, and it is not necessary to oxidize hydrogen in the anode off-gas in the reformer 30 to generate further water vapor. Exhaust to the outside. As a result, the reformer 30 uses the steam and oxygen in the cathode off-gas to progress the steam reforming reaction and the partial oxidation reaction under a sufficiently high S / C ratio, thereby obtaining the target power generation amount. The required amount of hydrogen is produced.

  In Step S140, when the amount of water vapor in the cathode off gas is insufficient, that is, even if all the water vapor in the cathode off gas is used, the desired S / C ratio cannot be achieved in the reformer 30. The amount of anode off gas required to generate the insufficient water vapor by the oxidation reaction is calculated (step S170). The insufficient amount of water vapor is obtained as the difference between the amount of water vapor to be supplied calculated in step S130 and the amount of water vapor in the cathode off-gas calculated in step S110. The amount of hydrogen necessary for generating this insufficient water vapor by the oxidation reaction of hydrogen can be calculated theoretically. Therefore, in step S170, in order to obtain the necessary amount of hydrogen calculated theoretically, how much anode off-gas containing the amount of hydrogen calculated in step S110 is required.

  In addition, the control unit 50 separately supplies the amount of air supplied to the cathode of the fuel cell 40, that is, the driving amount of the blower 44 that supplies air to the cathode, the driving amount of the pump 34, and the driving amount of the switching valve 38. Are set (step S180). The amount of air supplied to the cathode is set based on the theoretically required required oxygen amount and a predetermined excess air ratio in the same manner as step S150 described above, and the theoretically required amount. An excess of oxygen is supplied to the cathode. Here, step S180 is a process performed when the amount of water vapor in the cathode off gas is insufficient. Therefore, the cathode offgas supplied to the reformer 30 needs to include oxygen required for hydrogen oxidation in addition to oxygen required for the partial oxidation reaction. As described above, the cathode is supplied with oxygen in excess of the amount theoretically necessary for power generation. Therefore, the amount of oxygen that can sufficiently cover both the partial oxidation reaction and the hydrogen oxidation reaction is usually provided. Oxygen will be included in the cathode offgas. However, when oxygen is consumed by oxidizing hydrogen in the reformer 30 and oxygen for the partial oxidation reaction is insufficient, control for further increasing the amount of air supplied to the cathode may be performed. That is, in step S180, the amount of oxygen gas consumed in the oxidation of hydrogen is further taken into account, and the amount of supplied oxidizing gas is further corrected to set the driving amount of the blower 44 to ensure the amount of oxygen in the cathode off-gas. The driving amount of the pump 34 set in step S180 is the driving amount of the pump 34 for actually supplying the reformed fuel amount to be supplied calculated in step S120 to the reformer 30. The driving amount of the switching valve 38 set in step S180 is the driving amount of the switching valve 38 for supplying the amount of anode off gas calculated in step S170 to the mixer 32 via the anode off gas supply path 64. is there.

  Thereafter, the control unit 50 outputs a drive signal to the blower 44 and the pump 34 based on the result of step S180, and the switching valve 38 so that the amount of anode off-gas calculated in step S170 is supplied to the reformer 30. Is switched (step S190), and this routine is terminated. As a result, the reformer 30 uses the water vapor generated by oxidizing the hydrogen in the anode off gas together with the water vapor in the cathode off gas, and the steam reforming reaction proceeds under a desired S / C ratio and the partial oxidation reaction. The amount of hydrogen necessary to obtain the target power generation amount is generated. As described above, the anode off-gas contains part of the generated water that has moved to the anode side due to the back diffusion of the fuel cell as water vapor, and this water vapor can also be used in the reforming reaction. Therefore, in step S170, when calculating the amount of anode off gas required to generate the insufficient amount of water vapor, the amount of water vapor in the anode off gas may be further taken into consideration.

  According to the fuel cell system 20 of the present embodiment configured as described above, the steam reforming reaction can be performed using the steam generated by oxidizing the hydrogen in the anode off gas in the reformer 30. Therefore, even when the amount of steam that can be supplied to the reformer 30 becomes insufficient, the amount of steam that can be used in the reforming reaction is quickly increased to achieve the desired S / C ratio and perform the reforming reaction. Can be done. Accordingly, even when the amount of hydrogen to be supplied by the reformer 30 increases suddenly, such as when the load connected to the fuel cell 40 increases rapidly, a desired S / C ratio can be obtained when performing the steam reforming reaction. And the state of the steam reforming reaction can be kept good. In particular, when the reforming reaction is performed using water vapor in the cathode offgas, the amount of water vapor depends on the amount of power generation. Therefore, when the amount of power generation increases rapidly from a small state, the amount of water vapor in the cathode offgas is insufficient. Probability is high. By generating hydrogen vapor by oxidizing hydrogen in the reformer 30 as in this embodiment, the S / C ratio can be maintained without being affected by the amount of power generation. In addition, when the amount of hydrogen to be generated in the reformer 30 is drastically reduced, when the anode off gas is supplied to the reformer 30, if the supply amount is reduced or the supply is stopped, the reforming reaction is performed. The amount of water vapor provided can be quickly reduced.

  In addition, according to the fuel cell system 20 of the present embodiment, the oxygen in the cathode offgas is consumed to oxidize the hydrogen in the anode offgas, thereby optimizing the O / C ratio when the oxidation reaction proceeds. It becomes possible. The “O / C ratio” is the ratio of the “number of moles of oxygen atoms supplied to the reformer 30” to the “number of moles of carbon atoms contained in the reformed fuel supplied to the reformer 30”. Value. In a fuel cell, it is desirable to set a large excess air ratio in order to ensure power generation efficiency. However, in this embodiment, by setting a large excess air ratio, the amount of oxygen remaining in the cathode offgas is reduced by the partial oxidation reaction. Even when the amount exceeds the optimum value, hydrogen is consumed in order to produce steam in the reformer. Therefore, the O / C ratio in the reformer 30 can be made smaller and close to the optimum value, and when the partial oxidation reaction is performed together with the steam reforming reaction in the reformer 30, the reforming is performed while suppressing the generation of soot. The efficiency of the quality reaction can be kept high.

  In the present embodiment, since all the cathode off-gas is supplied to the reformer 30, when the target power generation amount decreases, the value of the S / C ratio becomes higher than a predetermined value. Even if the S / C ratio is set higher, there is usually no problem because the degree of reduction in reforming efficiency is small, but when the amount of water vapor in the cathode offgas is sufficient, part of the cathode offgas is exhausted to the outside, Control for maintaining the S / C ratio at a desired value may be performed. Thus, if the S / C ratio is prevented from excessively increasing, it is possible to suppress the generation of condensed water due to an excessive amount of water vapor in the fuel gas flow path in the fuel cell 40.

  In the present embodiment, the steam reforming reaction is performed using the steam in the cathode off gas. Further, since steam is generated by the oxidation reaction in the reformer 30, it is specially used for vaporizing water. There is no need to consume energy, and the energy efficiency of the entire system is not lowered to obtain water vapor. Further, in this embodiment, since the steam is generated using hydrogen in the anode off-gas discharged to the outside when not required, the system efficiency is not lowered in order to obtain insufficient steam.

C. Second embodiment:
Since the reforming catalyst provided in the reformer 30 has the activity of promoting the oxidation reaction, in the first embodiment, hydrogen in the anode off-gas is oxidized using the reforming catalyst. An oxidation catalyst for oxidizing may be further provided. Such a configuration will be described below as a second embodiment.

  FIG. 3 is an explanatory diagram showing an outline of the configuration of the reformer 130 of the second embodiment. The reformer 130 of the second embodiment is used in place of the mixer 32 and the reformer 30 in the fuel cell system 20 of the first embodiment. The control of each part is performed according to the process of FIG. 2 described in the first embodiment. In the following description, parts that are the same as those in the first embodiment will be given the same reference numerals, and the description will focus on a configuration that is different from the first embodiment.

  The reformer 130 of the second embodiment includes a reforming catalyst 138 similar to the reforming catalyst provided in the reformer 30 of the first embodiment, and further includes an oxidation catalyst 137 upstream of the reforming catalyst 138. . As the oxidation catalyst, a noble metal catalyst such as platinum (Pt) can be used. The oxidation catalyst 137 and the reforming catalyst 138 can be configured by supporting a catalytic metal on a honeycomb-like or pellet-like carrier, similarly to the reforming catalyst of the first embodiment.

  Similarly to the reformer 30 of the first embodiment, the reformer 130 is supplied with the cathode offgas via the cathode offgas supply path 60 and is supplied with the anode offgas via the anode offgas supply path 64. These cathode offgas and anode offgas first pass through the oxidation catalyst 137, and in the oxidation catalyst 137, hydrogen in the anode offgas is oxidized to generate water vapor.

  In the reformer 130, a mixing unit 139 that is a space having a predetermined size is formed between the oxidation catalyst 137 and the reforming catalyst 138. The reforming fuel is supplied to the mixing unit 139 as in the mixer 32 of the first embodiment. The reformed fuel supplied to the mixing unit 139 is mixed with the water vapor generated by the oxidation catalyst 137, the water vapor in the cathode off-gas that has passed through the oxidation catalyst 137, and the remaining oxygen (oxygen not used for hydrogen oxidation). And flows into the reforming catalyst 138. In the reforming catalyst 138, the reformed fuel is reformed to generate hydrogen. That is, the steam reforming reaction is performed using the steam generated by the oxidation catalyst 137 and the steam in the cathode offgas, and the partial oxidation reaction is performed using the remaining oxygen in the cathode offgas. In addition, when the anode off gas is supplied to the reformer 130 and the steam reforming reaction is performed, the steam contained in the anode off gas (product water moved to the anode side by back diffusion in the fuel cell) can also be used. It becomes. Therefore, the anode off-gas amount supplied to the reformer 130 may be set in consideration of the amount of water vapor in the anode off-gas as in the first embodiment.

  According to the reformer 130 of the second embodiment configured as described above, in addition to the same effects as those of the first embodiment, the effect that the S / C ratio in the reforming reaction can be more reliably controlled. Play. That is, since hydrogen in the anode off-gas supplied to the reformer 130 to make up for the insufficient steam is oxidized by the oxidation catalyst 137 prior to being supplied to the reforming catalyst 138, steam is generated. The water vapor can be reliably used for the reforming reaction. In addition, since the reformed fuel is supplied to the mixing unit 139 downstream of the oxidation catalyst 137, the reformed fuel is not completely oxidized by the oxidation catalyst 137, and the reformed fuel supplied to the reformer 130 can be surely supplied. Can be subjected to a reforming reaction. Since hydrogen is much easier to oxidize than reformed fuel, even if the reformed fuel is supplied from upstream of the oxidation catalyst 137, the amount of reformed fuel oxidized by the oxidation catalyst 137 is kept within an allowable range. It is possible.

D. Third embodiment:
Hereinafter, as a third embodiment, a fuel cell system having a configuration for generating water vapor by oxidizing reformed fuel in addition to the configuration for generating water vapor by oxidizing hydrogen in the anode off-gas will be described.

  FIG. 4 is a block diagram showing an outline of the configuration of the fuel cell system 220 of the third embodiment. In the fuel cell system 220, parts common to the fuel cell system 20 of the first embodiment are denoted by the same reference numerals, and here, differences from the fuel cell system 20 will be mainly described. The fuel cell system 220 includes a reformer 130 similar to that of the second embodiment, instead of the mixer 32 and the reformer 30. As in the second embodiment, the cathode offgas supplied from the cathode offgas supply path 60 and the anode offgas supplied from the anode offgas supply path 64 are supplied from the upstream side of the oxidation catalyst 137 included in the reformer 130. The flow path of the reformed fuel supplied by the pump 34 is branched into two flow paths at the switching valve 235. The first reformed fuel path 265 that is one flow path is connected to the reformer 130 in the mixing unit 139, and the second reformed fuel path 266 that is the other flow path is upstream of the oxidation catalyst 137. To the reformer 130. By switching the switching valve 235, the amount of reformed fuel supplied to the upstream side of the oxidation catalyst 137 and the amount of reformed fuel supplied to the downstream side of the oxidation catalyst can be adjusted.

  FIG. 5 is a flowchart showing a reformer control processing routine executed by the control unit 50 provided in the fuel cell system 220 of the third embodiment. This routine is repeatedly executed at predetermined intervals by the control unit 50 while the fuel cell system 220 is activated and power generation is performed by the fuel cell 40 using the fuel gas generated by the reformer 130.

  When this routine is started, the control unit 50 executes the same processing as steps S100 to S130 in the reformer control processing routine of FIG. 2, and the amount of water vapor in the cathode offgas is sufficient as in step S140. It is determined whether or not there is (step S200). When it is determined in step S200 that the amount of water vapor in the cathode off-gas is sufficient, the control unit 50 reforms the reformer 130 and the blower 44 that supplies the oxidizing gas to the fuel cell 40 as in step S150. The drive amount of the pump 34 for supplying fuel is set. Further, the control unit 50 sets the drive amount of the switching valve 235 so that all the reformed fuel supplied via the pump 34 flows into the mixing unit 139 via the first reformed fuel path 265 ( Step S210). Thereafter, the control unit 50 drives the blower 44, the pump 34, and the switching valve 38 based on the result of Step S210 (Step S220), and ends this routine. As a result, the reforming reaction proceeds satisfactorily at the reforming catalyst 138 of the reformer 130 and a desired amount of hydrogen is generated. At this time, the reformed fuel is not supplied via the second reformed fuel path 266.

  When it is determined in step S200 that the amount of water vapor in the cathode off-gas is insufficient, the control unit 50 calculates the amount of hydrogen required to generate the insufficient water vapor (step S230). Thereafter, the control unit 50 determines whether or not the amount of hydrogen in the anode offgas can cover the amount of hydrogen required to generate the insufficient water vapor, based on the amount of hydrogen in the anode offgas calculated in step S110. Judgment is made (step S240).

  If it is determined in step S240 that the amount of hydrogen in the anode off-gas is sufficient, the control unit 50 sets the drive amounts of the blower 44, the pump 34, and the switching valve 38 as in step S180 of FIG. The driving amount of the switching valve 235 is set so that all the reformed fuel flows into the mixing unit 139 (step S250). Thereafter, the control unit 50 drives the blower 44, the pump 34, and the switching valves 235 and 38 based on the result of Step S250 (Step S260), and ends this routine. As a result, the insufficient steam is obtained by oxidizing hydrogen in the anode offgas, and the reformed fuel is controlled to be used only for the reforming reaction. When the reforming reaction proceeds in the reformer 130, as described above, the water vapor contained in the anode off-gas by back diffusion can also be used. Therefore, when executing this routine, the amount of water vapor in the anode off gas may be further taken into consideration.

  If it is determined in step S240 that the amount of hydrogen in the anode off-gas is insufficient, the control unit 50 sets the drive amount of the blower 44 as in step S180. Further, the drive amount of the switching valve 38 is set so that all the anode off gas is supplied to the reformer 130. Further, the control unit 50 sets the drive amounts of the pump 34 and the switching valve 235 so that an insufficient amount of water vapor is obtained by oxidation of the reformed fuel (step S270). That is, the control unit 50 sets the drive amount of the pump 34 so that the total amount of reformed fuel required for the reforming reaction and the reformed fuel required for generating a desired amount of water vapor is supplied. Further, the control unit 50 supplies the reformed fuel required for the reforming reaction from the first reformed fuel path 265, and the reformed fuel required for steam generation passes through the second reformed fuel path 266 to the oxidation catalyst 137. The driving amount of the switching valve 235 is set so as to be supplied to the upstream side. If the oxygen required to oxidize the reformed fuel and generate water vapor is insufficient, the amount of air supplied to the cathode is increased by correcting the drive amount of the blower 44, and the amount of oxygen in the cathode off-gas is reduced. What is necessary is just to secure. Thereafter, the control unit 50 drives the blower 44, the pump 34, and the switching valves 235 and 38 based on the result of step S270 (step S280), and ends this routine. Thereby, the deficient water vapor is generated by both oxidation of hydrogen in the anode off-gas and oxidation of the reformed fuel.

  According to the fuel cell system 220 of the third embodiment, in addition to the water vapor in the cathode off gas, the reformer can be used by using the water vapor in the anode off gas and the water vapor obtained by oxidizing hydrogen in the anode off gas. Even in the case where the desired S / C ratio cannot be achieved, the water vapor obtained by oxidizing the reformed fuel can be used to achieve the desired S / C ratio. That is, even when the amount of power generation in the fuel cell increases rapidly and the amount of hydrogen in the anode offgas is insufficient together with the amount of water vapor in the anode offgas, the reformer is used by using the steam obtained by oxidizing the reformed fuel. Thus, the required amount of water vapor can be ensured.

E. Fourth embodiment:
In the first to third embodiments, the water vapor in the cathode off-gas is used as the water vapor used in the water vapor reforming reaction. However, in order to obtain the water vapor used in the water vapor reforming reaction, a separate evaporator may be provided. . Such a configuration will be described below as a fourth embodiment.

  FIG. 6 is a block diagram showing an outline of the configuration of the fuel cell system 320 of the fourth embodiment. In the fuel cell system 320, the same reference numerals are assigned to portions common to the first and second embodiments. The fuel cell system 320 of the fourth embodiment includes an evaporator 333 together with the reformer 130 similar to that of the second embodiment. Water is supplied to the evaporator 333 via a pump 349, and water is vaporized in the evaporator 333. The evaporator 333 includes a burner, a heater, or a combustor including an oxidation catalyst (not shown) as a heat source for vaporizing water. The water vapor evaporated by the evaporator 333 and the reformed fuel supplied via the pump 34 are introduced into the mixing unit 139 of the reformer 130 and used for the reforming reaction that proceeds in the reforming catalyst 138. The In FIG. 6, the reformed fuel is supplied to the evaporator 333. However, when the reformed fuel is a gaseous fuel, the reformed fuel may be mixed with water vapor downstream of the evaporator 333. .

  The fuel cell system 320 also includes a blower 347 that takes in air from the outside. The flow path of the air taken into the blower 347 communicates with the upstream side of the oxidation catalyst 137 of the reformer 130. Further, the anode off gas supply path 64 is connected to the reformer 130 as in the first embodiment, and the anode off gas can be supplied to the upstream side of the oxidation catalyst 137. Therefore, oxygen in the air supplied from the blower 347 to the reformer 130 is used for oxidation of hydrogen in the oxidation catalyst 137 when the anode off-gas is supplied to the oxidation catalyst 137. Used for partial oxidation reaction of quality fuel. In the fuel cell system 320, the cathode offgas is led to the cathode offgas discharge path 61 and exhausted to the outside.

  FIG. 7 is a flowchart showing a reformer control processing routine executed in control unit 50 of fuel cell system 320. This routine is repeatedly executed by the control unit 50 at predetermined intervals while the fuel cell system 320 is activated and power generation is performed in the fuel cell 40 using the fuel gas generated by the reformer 130.

  When this routine is started, the control unit 50 first supplies the target power generation amount to be generated by the fuel cell 40, the current power generation amount, and the reformer 130 in the same manner as in step S100 of FIG. The reformed fuel amount is acquired (step S300). Next, the control unit 50 calculates the amount of hydrogen in the anode off-gas based on the current power generation amount and reformed fuel amount acquired in step S300, similarly to step S110 in FIG. 2 (step S310). Thereafter, the controller 50 further calculates the amount of reformed fuel to be supplied to the reformer 130 based on the target power generation amount acquired in step S300, similarly to step S120 in FIG. 2 (step S320).

  After calculating the amount of reformed fuel to be supplied, the control unit 50 determines the amount of steam to be supplied to the reformer 130 based on the calculated amount of reformed fuel, the S / C ratio, and the O / C ratio. The amount of oxygen is calculated (step S330). The calculation of the supplied water vapor amount is performed in the same manner as in step S130 in FIG. In this embodiment, the target value of the O / C ratio is also set in advance. In step S330, the reformer 130 is based on the predetermined O / C ratio and the reformed fuel amount calculated in step S320. The amount of oxygen to be supplied to the battery is also calculated. As the O / C ratio increases, soot formation in the reformer is suppressed. However, as the O / C ratio increases, reforming efficiency (utilization rate of reformed fuel) decreases, so reforming while suppressing soot formation. In order to ensure efficiency, it is necessary to maintain the O / C ratio within a predetermined range. The value of such O / C ratio can be set to 0.1 to 0.3, for example.

  After calculating the amount of water vapor to be supplied in step S330, the control unit 50 next determines whether or not the evaporator 333 can supply the amount of water vapor to be supplied (step S340). In the evaporator 333, an amount of water corresponding to the current power generation amount is supplied to vaporize the water. However, if the amount of water supplied to the evaporator 333 is rapidly increased, the amount of water increases. However, the heating cannot catch up, and the temperature of the evaporator 333 decreases, making it impossible to obtain a desired amount of water vapor. The amount of water vapor that can be generated by the evaporator 333 depends on the properties of the evaporator 333, such as the heating capacity and heat capacity of the evaporator 333, and the current throughput in the evaporator 333, that is, the current power generation. It depends on the amount. In this embodiment, for the evaporator 333, the relationship between the power generation amount and the amount of water vapor that can be generated is examined in advance and stored in the control unit 50. In step S340, referring to the relationship between the power generation amount and the amount of water vapor that can be generated, whether or not the water vapor amount to be supplied can be supplied when the current power generation amount is the value acquired in step S300. Judgment is made. Note that the amount of water vapor that can be generated by the evaporator 333 referred to in step S340 may be corrected by measuring the amount of water vapor actually generated by the evaporator 333 and feeding back the measured value.

  When it is determined that the amount of water vapor to be supplied can be supplied, that is, the amount of water vapor to be supplied can be obtained by vaporizing water with the evaporator 333, the control unit 50 determines the drive amount of the pumps 34 and 349 and the blower The drive amount of 347 is set (step S350). The drive amount of the pump 34 is a drive amount for actually supplying the reformed fuel amount to be supplied calculated in step S320 to the reformer 130. The drive amount of the pump 349 is a drive amount for supplying the evaporator 333 with an amount of water necessary for obtaining the amount of water vapor to be supplied calculated in step S330. The driving amount of the blower 347 is a driving amount for supplying the mixing unit 139 with the amount of oxygen to be supplied calculated in step S330.

  Thereafter, the control unit 50 outputs drive signals to the pumps 34 and 349 and the blower 347 based on the result of step S350, and switches the switching valve 38 so that all anode off-gas is exhausted (step S360). Exit. Thus, the reformer 130 uses the steam generated in the evaporator 333 and the oxygen supplied by the blower 347 to perform the steam reforming reaction and partial reaction under a desired S / C ratio and O / C ratio. The oxidation reaction proceeds and an amount of hydrogen necessary to obtain the target power generation amount is generated.

  In step S340, when it is determined that the amount of water vapor to be supplied cannot be generated by the evaporator 333, the control unit 50 is an anode required for generating water vapor that is insufficient from the water vapor obtained from the evaporator 333 by the oxidation reaction. An off gas amount is calculated (step S370). The amount of water vapor that is insufficient is obtained as the difference between the amount of water vapor that should be supplied calculated in step S330 and the amount of water vapor that can be generated by the evaporator 333 under the current power generation amount referenced in step S340. The amount of hydrogen necessary for generating this insufficient water vapor by the oxidation reaction of hydrogen can be calculated theoretically. Therefore, in step S370, in order to obtain the necessary amount of hydrogen calculated theoretically, how much anode off-gas containing the amount of hydrogen calculated in step S310 is required.

  Apart from this, the control unit 50 sets the drive amount of the pumps 34 and 349 and the drive amount of the switching valve 38 together with the drive amount of the blower 347 (step S380). The drive amount of the blower 347 is to supply the reformer 130 with the total amount of oxygen required for oxidizing the hydrogen in the anode offgas calculated in step S370 together with the amount of oxygen supplied in step S330. This is the drive amount of the blower 347. The drive amount of the pump 34 is the drive amount of the pump 34 for actually supplying the reformed fuel amount to be supplied calculated in step S320 to the reformer 30. The driving amount of the pump 349 is a driving amount for supplying the evaporator 333 with an amount of water required for the evaporator 333 to generate the maximum amount of water vapor under the current power generation amount. The driving amount of the switching valve 38 is the driving amount of the switching valve 38 for supplying the amount of anode off gas calculated in step S370 to the reformer 130 via the anode off gas supply path 64.

  Thereafter, the control unit 50 drives the blower 347, the pumps 34 and 349, and the switching valve 38 based on the result of step S380 (step S390), and ends this routine. As a result, in the reformer 130, the steam reforming reaction proceeds under a desired S / C ratio using the steam generated by oxidizing the hydrogen in the anode off-gas with the steam supplied from the evaporator 333. The partial oxidation reaction also proceeds under a desired O / C ratio, and an amount of hydrogen necessary to obtain a target power generation amount is generated.

  According to the fuel cell system 320 of the fourth embodiment configured as described above, the steam reforming reaction can be performed using the steam generated by oxidizing the hydrogen in the anode off-gas in the reformer 130. Therefore, even when the amount of water vapor that can be supplied from the evaporator 333 to the reformer 130 becomes insufficient, the amount of water vapor that can be used in the reforming reaction is quickly increased to achieve a desired S / C ratio. Thus, the reforming reaction can be performed.

  Further, in the fuel cell system 320 of the fourth embodiment, oxygen required for the partial oxidation reaction proceeding in the reformer 130 is supplied by the blower 347 and is not affected by the power generation amount as in the case of using the cathode offgas. The O / C ratio in the reformer can be optimized more easily. The excess air ratio when supplying the oxidizing gas to the fuel cell 40 using the blower 44 gives priority to the efficiency of the fuel cell 40 independently of the reforming reaction without considering the efficiency of the reforming reaction. Can be set to the optimum value. Note that the fuel cell system 320 of the fourth embodiment does not use cathode off-gas for supplying water vapor to the reformer 130, and therefore does not generate water on the cathode side (for example, has oxide ion conductivity). The present invention can also be favorably applied to a solid oxide fuel cell having an electrolyte layer. Further, by not supplying the cathode off gas to the reformer 130, poisoning of the reforming catalyst due to impurities discharged from the fuel cell can be suppressed. Further, in the fuel cell system 320 of the fourth embodiment, similarly to the third embodiment, the reformed fuel may be further oxidized in order to generate water vapor in the reformer.

F. Variations:
The present invention is not limited to the above examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

F1. Modification 1:
In the first to fourth embodiments described above, the anode off gas is used as the hydrogen source for generating water vapor in the reformer. However, a different hydrogen source may be used. For example, a separate hydrogen tank may be provided in the fuel cell system, and a necessary amount of hydrogen may be supplied from the hydrogen tank to the reformer. In this case, unlike the case where anode off gas is used, the amount of hydrogen that can be supplied is not limited by the amount of power generation.

  Alternatively, instead of the anode off gas, a gas containing hydrogen generated in the reformer and upstream of the anode off gas, for example, a reformed gas discharged from the reformer may be used. Thus, when using the reformed gas before being supplied to the fuel cell, when setting the amount of hydrogen to be generated in the reformer, the amount of hydrogen used for steam generation and the amount of steam to be circulated are set. Correction may be performed with further consideration.

F2. Modification 2:
In the first to fourth embodiments, all of the insufficient steam is generated by oxidizing hydrogen in the reformer, but part of the insufficient steam may be generated by oxidation of hydrogen. Even when only a part of the deficient steam is generated by the oxidation reaction, an effect can be obtained by bringing the S / C ratio during the reforming reaction closer to the optimum value. Alternatively, when a part of the steam that is insufficient to achieve the desired S / C ratio is generated by oxidation of hydrogen, the target value of the hydrogen generation amount in the reformer is set lower, and the S / C May be maintained at a desired value.

F3. Modification 3:
Alternatively, the reformer does not perform the partial oxidation reaction, and the reformer may be provided with an external heating device to generate hydrogen only by the steam reforming reaction. In this case, oxygen is not normally supplied to the reformer, and oxygen may be supplied to the reformer only when hydrogen is oxidized for steam generation in the reformer. Even in such a configuration, the present invention is applied, and if necessary, the oxidation reaction of hydrogen proceeds in the reformer, so that steam shortage during the reforming reaction is prevented and the S / C ratio is set to a desired value. The value can be maintained. In such a case, while a sufficient amount of water vapor is secured in the reformer, air or cathode off-gas as an oxygen source is not supplied to the reformer. Non-contributing components (such as nitrogen) are not mixed into the fuel gas supplied to the fuel cell. Therefore, in the fuel cell, the hydrogen partial pressure in the fuel gas can be kept high, and the power generation efficiency can be improved.

F4. Modification 4:
In the first to third embodiments, the cathode offgas is supplied to the reformer, and the steam and oxygen in the cathode offgas are used in the reforming reaction. Hydrogen is being supplied to the mass device. Thus, in the fuel cell system that supplies the cathode offgas to the reformer, the operation is controlled by supplying hydrogen to the reformer during normal operation (when the amount of water vapor in the cathode offgas is not insufficient). Quality efficiency and power generation efficiency can be improved.

In order to improve the power generation efficiency in the fuel cell, it is desirable to increase the excess air ratio when supplying the oxidizing gas to the fuel cell. However, in the system that supplies the cathode off-gas to the reformer, if the excess air ratio is increased, the amount of oxygen supplied to the reformer increases, so the O / C ratio in the reformer becomes too high, and the reformer reforms. Efficiency can be reduced. Therefore, when supplying the cathode off-gas to the reformer, it is necessary to set the amount of oxidizing gas supplied to the fuel cell so that the power generation efficiency becomes higher within a range in which the reforming efficiency can be sufficiently secured. . When the amount of oxidizing gas supplied to the fuel cell is set in this way, the O / C ratio in the reformer is usually higher than the optimum value. Here, if hydrogen is supplied to the reformer using an anode off gas or the like even during normal operation, oxygen is consumed in the reformer to oxidize hydrogen, resulting in an O / C ratio. Decreases, and the O / C ratio can be made closer to the optimum value. In addition, if oxygen is consumed in the reformer in this way, the amount of oxidizing gas supplied to the fuel cell can be set without being restricted by the reforming efficiency, and the power generation efficiency becomes higher. As described above, the excess air ratio can be set higher.

2 is a block diagram illustrating a schematic configuration of a fuel cell system 20. FIG. It is a flowchart showing a reformer control processing routine. FIG. 3 is an explanatory diagram illustrating an outline of a configuration of a reformer 130. 2 is a block diagram illustrating an outline of a configuration of a fuel cell system 220. FIG. It is a flowchart showing a reformer control processing routine. 2 is a block diagram illustrating an outline of a configuration of a fuel cell system 320. FIG. It is a flowchart showing a reformer control processing routine.

Explanation of symbols

20, 220, 320 ... Fuel cell system 30, 130 ... Reformer 32 ... Mixer 34, 349 ... Pump 38 ... Switching valve 40 ... Fuel cell 42 ... Heat exchanger 44, 45 ... Blower 46 ... Purifier 50 ... Control Portion 61 ... Cathode off-gas discharge passage 62, 63 ... Piping 60 ... Cathode off-gas supply passage 64 ... Anode off-gas supply passage 137 ... Oxidation catalyst 138 ... Reforming catalyst 139 ... Mixing portion 235 ... Switching valve 265 ... First reforming fuel passage 266 ... Second reformed fuel path 333 ... Evaporator 347 ... Blower 349 ... Pump

Claims (15)

A fuel reformer that generates hydrogen from reformed fuel,
A catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
A reformed fuel supply unit for supplying the reformed fuel to the catalyst unit;
A steam supply section for supplying the steam to the catalyst section;
A hydrogen supply unit for supplying hydrogen to the catalyst unit when the amount of the reformed fuel supplied from the reformed fuel supply unit fluctuates;
An oxygen supply unit for supplying oxygen to the catalyst unit;
When the ratio of the water vapor amount to the reformed fuel amount supplied at the time of the increase fluctuation is less than a predetermined value, the amount of hydrogen capable of generating water vapor to bring the ratio close to the predetermined value is supplied to the catalyst unit. And a control unit that controls the hydrogen supply unit and controls the oxygen supply unit so as to supply the catalyst unit with an oxygen amount corresponding to the amount of hydrogen supplied by the hydrogen supply unit. apparatus. A fuel reforming apparatus according to claim 1 Symbol placement,
The water vapor supply unit is a fuel reformer including an evaporator that vaporizes water. The fuel reformer according to claim 1 or 2 , wherein
The catalyst part further includes an oxidation catalyst,
The fuel reformer, wherein the hydrogen supply unit and the oxygen supply unit respectively supply hydrogen and oxygen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst. The fuel reformer according to any one of claims 1 to 3 ,
The hydrogen supply unit includes a hydrogen tank that stores hydrogen, and supplies the hydrogen stored in the hydrogen tank to the catalyst unit. The fuel reformer according to any one of claims 1 to 3 ,
The hydrogen supply unit supplies the hydrogen generated in the catalyst unit to the catalyst unit. The fuel reformer according to claim 1, wherein
The fuel reformer is a device for supplying the produced hydrogen to the anode of the fuel cell,
Wherein A steam supply unit and the oxygen supply unit, a cathode off-gas discharged from the cathode of the previous SL fuel cell you containing water vapor and oxygen, a fuel reforming constituted by supplying the cathode offgas supply unit in the catalytic section apparatus. The fuel reformer according to claim 6 , wherein
The controller is
The amount of reformed fuel supplied to the catalyst unit is the amount of reformed fuel required to generate hydrogen in the catalyst unit in an amount corresponding to the required power generation amount for the fuel cell. A reformed fuel control unit for controlling the reformed fuel supply unit,
When the ratio of the steam amount supplied by the steam supply unit to the required reformed fuel amount is less than a predetermined value when the required reformed fuel amount increases and fluctuates, the ratio is brought close to the predetermined value. A fuel reformer comprising: a hydrogen control unit that controls the hydrogen supply unit so as to supply a hydrogen amount capable of generating water vapor to the catalyst unit. The fuel reformer according to claim 6 , further comprising:
An oxidizing gas supply unit for supplying an oxidizing gas containing oxygen to the cathode of the fuel cell;
An oxidizing gas control unit that controls the amount of oxidizing gas supplied by the oxidizing gas supply unit based on the power generation amount to be generated by the fuel cell and the power generation efficiency in the fuel cell;
The steam and oxygen are supplied to the catalyst unit by the cathode offgas supply unit, and in the catalyst unit, partial oxidation which is an oxidation reaction accompanied by the generation of hydrogen using the reformed fuel together with the steam reforming reaction And a hydrogen control unit that controls the hydrogen supply unit to supply the hydrogen to the catalyst unit when the reaction proceeds. The fuel reformer according to claim 1 , wherein
The fuel reformer is a device for supplying the produced hydrogen to the anode of the fuel cell,
The hydrogen supply unit, an anode off-gas discharged from the anode of the previous SL fuel cell you containing hydrogen, the fuel reformer is supplied to the catalytic section. The fuel reformer according to claim 1 , wherein
The fuel reformer is a device for supplying the produced hydrogen to the anode of the fuel cell,
The catalyst part includes an oxidation catalyst together with the reforming catalyst,
The reformed fuel supply unit supplies a part of the reformed fuel to the catalyst unit so as to reach the reformed catalyst after passing through the oxidation catalyst, and the rest of the reformed fuel is supplied to the reformed fuel. Supply to the reforming catalyst,
The hydrogen supply unit, an anode off-gas discharged from the anode of the previous SL fuel cell you containing hydrogen is supplied to the catalytic section to reach the reforming catalyst after passing through the oxidation catalyst,
The oxygen supply unit supplies oxygen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst. A fuel reformer that generates hydrogen from reformed fuel,
A catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
A reformed fuel supply unit for supplying the reformed fuel to the catalyst unit;
A steam supply section for supplying the steam to the catalyst section;
A hydrogen supply unit for supplying hydrogen to the catalyst unit when the amount of the reformed fuel supplied from the reformed fuel supply unit fluctuates;
An oxygen supply unit for supplying oxygen to the catalyst unit ;
A control unit for controlling the oxygen supply unit so as to supply the catalyst unit with an amount of oxygen corresponding to the amount of hydrogen supplied by the hydrogen supply unit ,
The catalyst part further includes an oxidation catalyst,
The fuel reformer, wherein the hydrogen supply unit and the oxygen supply unit respectively supply hydrogen and oxygen to the catalyst unit so as to reach the reforming catalyst after passing through the oxidation catalyst. A fuel cell system,
A fuel cell; and a fuel reformer according to any one of claims 1 to 11 ,
A fuel cell system for generating electricity by supplying hydrogen generated by the fuel reformer to an anode of the fuel cell. A fuel reforming method for generating hydrogen from a reformed fuel,
(A) supplying hydrogen together with the reformed fuel and the steam to a catalyst unit including a reforming catalyst that promotes a steam reforming reaction that generates hydrogen using the reformed fuel and steam;
(B) When the amount of the reformed fuel supplied in the step (a) fluctuates and increases, in addition to the steam supplied to the catalyst part, steam generated by oxidation of the hydrogen in the catalyst part is used. And a step of causing the steam reforming reaction to proceed,
In the step (a), when the ratio of the water vapor amount to the reformed fuel amount is lower than a predetermined value, an amount of hydrogen capable of generating water vapor to bring the ratio close to the predetermined value is supplied to the catalyst unit. ,
The step (b)
(B-1) A fuel reforming method comprising a step of oxidizing the hydrogen by supplying an oxygen amount corresponding to the hydrogen amount supplied in the step (a) to the catalyst unit . A fuel reforming method according to claim 13 , wherein
The fuel reforming method is a method of generating hydrogen to be supplied to an anode of a fuel cell,
In the step (a), water vapor in the cathode off-gas discharged from the cathode of the fuel cell is used as the water vapor to be supplied to the catalyst unit.
The step (b) uses a water vapor generated by oxidizing hydrogen using the oxygen in the cathode offgas as the water vapor generated by the oxidation of the hydrogen. A fuel reforming method according to claim 13 , wherein
The fuel reforming method is a method of generating hydrogen to be supplied to an anode of a fuel cell, and
(C) oxidizing the reformed fuel to generate water vapor,
In the step (a), hydrogen in the anode off-gas discharged from the anode of the fuel cell is used as hydrogen to be supplied to the catalyst unit.
The step (b) uses the water vapor generated in the step (c) in addition to the water vapor generated by the oxidation of hydrogen in the anode offgas as part of the water vapor used in the steam reforming reaction. Quality method.

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