JP4951917B2 - Fuel reforming system - Google Patents

Description

  The present invention relates to a fuel reforming system including a reformer.

  Hydrogen gas used as fuel for a fuel cell can be generated by chemically reacting hydrocarbon fuel and water vapor via a reforming catalyst. In order to efficiently obtain the effect of this reforming catalyst, it is necessary to heat the reforming catalyst to a high temperature of about 600 ° C. to 800 ° C., although it varies depending on the type of the reforming catalyst. Therefore, a technique for increasing the reforming catalyst temperature after the system is stopped in order to improve the restartability of the fuel reforming system is disclosed (for example, see Patent Document 1).

  In the technique of Patent Document 1, air is supplied to a reformer in a state where supply of hydrocarbon fuel and water vapor is stopped, and oxidation is generated by burning combustibles in the reformer using oxygen in the air. By using reaction heat, the temperature of the reforming catalyst is increased.

JP 2002-158027 A

  However, in the technique of Patent Document 1, no endothermic reaction such as a steam reforming reaction occurs in the reformer. Therefore, when there is a large amount of hydrocarbon fuel remaining on the reforming catalyst, the reforming efficiency may deteriorate due to excessive heat of oxidation reaction in the catalyst.

  An object of the present invention is to provide a fuel reforming system that can improve restartability without reducing reforming efficiency.

A fuel reforming system according to the present invention includes a reforming unit that generates hydrogen by a reforming reaction using a reformed fuel, a steam supply unit that supplies steam to the reforming unit, and a reformed fuel that is supplied to the reforming unit. The reformed fuel supply means to be supplied, the oxygen gas supply means for supplying oxygen gas to the reforming means, and the supply of the reformed fuel and water vapor to the reforming means are maintained when the reforming means stops operating. Steam supply means and reformed fuel supply means so that oxygen is supplied to the reforming means more than the amount required for the reforming reaction in the reforming means while the supply amounts of the reformed fuel and the steam are gradually decreased. And a control means for controlling the oxygen gas supply means.

  In the fuel reforming system according to the present invention, the steam is supplied to the reforming means by the steam supply means, the reformed fuel is supplied to the reforming means by the reformed fuel supply means, and the oxygen gas is modified by the oxygen gas supply means. Is supplied to the reforming means, hydrogen is generated by the reforming means, and when the reforming means stops operation, the reforming reaction in the reforming means is performed while the supply amount of reformed fuel and water vapor to the reforming means decreases. The steam supply means, the reformed fuel supply means, and the oxygen gas supply means are controlled by the control means so as to be supplied to the reforming means in a larger amount than is necessary for the control.

  In this case, the ratio of the steam reforming reaction in the reforming means is gradually decreased, and the ratio of the partial oxidation reaction is gradually increased. The steam reforming reaction is an endothermic reaction, and the partial oxidation reaction is an exothermic reaction. Thereby, it is possible to prevent a rapid temperature rise in the reforming unit while preventing a rapid temperature drop in the reforming unit. Further, the temperature of the reforming means can be gradually increased. As a result, the restartability of the fuel reforming system according to the present invention is improved.

  In general, the amount of reformed fuel and the amount of water vapor remaining in the reforming catalyst vary depending on the reforming conditions and the performance of the reforming catalyst at the start of the operation stop process. Therefore, complicated control such as catalyst temperature detection and fine adjustment of the amount of oxygen gas supplied to the reforming means is required. As a result, the cost increases. However, in the present invention, the control law is simplified because only the control for gradually decreasing the steam reforming reaction ratio and gradually increasing the partial oxidation reaction ratio is required. Therefore, the cost can be reduced.

When the reforming unit stops operating , the control unit decreases the supply amount of reformed fuel and steam to the reforming unit until the S / C ratio in the reforming unit exceeds the carbon deposition avoidance limit S / C ratio. As such, the steam supply means and the reformed fuel supply means may be controlled. In this case, carbon deposition in the reforming means can be suppressed. Thereby, the fall of the reforming efficiency of a reforming means can be suppressed.

When the reforming unit stops operating and the S / C ratio in the reforming unit exceeds the carbon deposition avoidance limit S / C ratio, the control unit is configured to supply steam to the reforming unit after a predetermined time has elapsed. The steam supply means, the reformed fuel supply means, and the oxygen gas supply means may be controlled so that the supply of the reformed fuel and oxygen gas is stopped. In this case, temperature reduction of the reforming unit can be prevented while suppressing carbon deposition in the reforming unit.

  The fuel cell may further include a fuel cell that generates water vapor at the cathode accompanying power generation, and the water vapor supply unit may supply the water vapor generated in the fuel cell to the reforming unit. In this case, it is not necessary to newly provide a device for generating water vapor. Thereby, the fuel reforming system according to the present invention can be reduced in size and the cost can be reduced. Further, the amount of power generation generated water in the fuel cell is reduced by reducing the amount of reformed fuel supplied to the reforming means. Therefore, the effect of the present invention can be obtained without introducing a special control law.

  Current detection means for detecting the power generation current of the fuel cell may be further provided, and the control means may acquire the amount of steam supplied to the reforming means by the steam supply means based on the detection result of the current detection means. In this case, the amount of water vapor supplied to the reforming means can be acquired without providing a device for detecting the amount of water vapor. Therefore, cost can be reduced.

  The oxygen gas supply means may supply oxygen gas to the reforming means via the cathode of the fuel cell. In this case, the oxygen gas supply means necessary for the operation of the fuel cell can be used as the oxygen gas supply means of the present invention. Thereby, it is not necessary to newly provide oxygen gas supply means. As a result, the fuel reforming system according to the present invention can be reduced in size. Further, by reducing the amount of reformed fuel supplied to the reforming means, the amount of water generated by power generation decreases, and the amount of oxygen consumed at the cathode also decreases. As a result, the ratio of the partial oxidation reaction in the reforming means increases. Therefore, the effect of the present invention can be obtained without introducing a special control law.

  ADVANTAGE OF THE INVENTION According to this invention, the rapid temperature rise in a reforming means can be prevented, preventing the rapid temperature fall in a reforming means. Further, the temperature of the reforming means can be gradually increased. As a result, the restartability of the fuel reforming system according to the present invention is improved. Further, since only the control for gradually decreasing the ratio of the steam reforming reaction and gradually increasing the ratio of the partial oxidation reaction is required, the control law is simplified. Therefore, the cost can be reduced.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram showing an overall configuration of a fuel reforming system 100 according to a first embodiment of the present invention. As shown in FIG. 1, the fuel reforming system 100 includes a control unit 10, a reformed fuel tank 20, a fuel pump 30, a metering valve 40, a reformer 50, a fuel cell 60, and air pumps 70 and 80.

  The reformer 50 includes a reforming unit 51, a heating unit 52, a temperature sensor 53, and an excess air ratio λ sensor 54. The temperature sensor 53 is provided in the reforming unit 51. The excess air ratio λ sensor 54 is provided in an exhaust system that leads from the heating unit 52 to the outside. Here, the excess air ratio λ indicates the ratio of the amount of oxygen supplied to the heating unit 52 to the amount of oxygen necessary for complete combustion in the heating unit 52. The fuel cell 60 includes a cathode 61, an anode 62, a cooling unit 63, a voltmeter 64, and an ammeter 65.

  In this example, a hydrogen separation membrane battery was used as the fuel cell 60. Here, the hydrogen separation membrane battery is a fuel cell provided with a hydrogen separation membrane layer. The hydrogen separation membrane layer is a layer formed of a metal having hydrogen permeability. The hydrogen separation membrane battery has a structure in which the hydrogen separation membrane layer and an electrolyte having proton conductivity are laminated. Hydrogen supplied to the anode of the hydrogen separation membrane battery is converted into protons via the catalyst, moves through the proton conductive electrolyte, and combines with oxygen at the cathode to become water. The water generated at the cathode is converted into water vapor by heat generated during power generation of the hydrogen separation membrane battery.

  The control unit 10 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. In addition, the control unit 10 is provided with a start switch 11. The control unit 10 controls each part of the fuel reforming system 100 based on the detection results given from the temperature sensor 53, the excess air ratio λ sensor 54, the voltmeter 64 and the ammeter 65 and the operation of the start switch 11. Details will be described later.

  The reformed fuel tank 20 stores hydrocarbon fuel used as the reformed fuel. The fuel pump 30 supplies hydrocarbon fuel stored in the reformed fuel tank 20 to the metering valve 40 in accordance with instructions from the control unit 10. The metering valve 40 supplies an amount of hydrocarbon fuel necessary for the reforming reaction in the reforming unit 51 to the reforming unit 51 in accordance with an instruction from the control unit 10.

  In the reforming unit 51, a reformed gas containing hydrogen is generated from a hydrocarbon fuel and a cathode off gas described later. First, a steam reforming reaction is caused by methane in the hydrocarbon fuel and steam in the cathode offgas, and hydrogen and carbon monoxide are generated. Next, a part of the generated carbon monoxide reacts with the water vapor in the cathode offgas, and hydrogen and carbon dioxide are generated. When the steam required for the steam reforming reaction is insufficient, oxygen and methane in the cathode offgas undergo a partial oxidation reaction, and hydrogen and carbon monoxide are generated.

  The reformed gas generated in the reforming unit 51 is supplied to the anode 62. At the anode 62, hydrogen in the reformed gas is converted into protons. Hydrogen that has not been converted into protons at the anode 62 and methane, carbon monoxide, and water vapor that have not reacted in the reforming unit 51 are supplied to the heating unit 52 as anode offgas.

  The air pump 70 supplies a necessary amount of air to the cooling unit 63 in accordance with instructions from the control unit 10. The air supplied to the cooling unit 63 cools the fuel cell 60 and is supplied to the heating unit 52. In the heating unit 52, a combustion reaction occurs due to the anode off gas and the air supplied from the cooling unit 63. Exhaust gas generated by the combustion reaction in the heating unit 52 is discharged to the outside of the fuel reforming system 100. Further, the combustion heat generated by the combustion reaction in the heating unit 52 is used for the steam reforming reaction in the reforming unit 51.

  The temperature sensor 53 detects the temperature of the reforming catalyst in the reforming unit 51 and gives the detection result to the control unit 10. The excess air ratio λ sensor 54 detects the excess air ratio λ in the heating unit 52 from the exhaust gas discharged from the heating unit 52 and gives the detection result to the control unit 10.

  The air pump 80 supplies a necessary amount of oxygen to the cathode 61 in accordance with an instruction from the control unit 10. In the cathode 61, water is generated and electric power is generated from the protons converted in the anode 62 and oxygen in the air supplied to the cathode 61. The generated electric power is stored in a storage battery (not shown) or used for a load such as a motor. The generated water becomes water vapor by the heat generated in the fuel cell 60. The air that has not reacted with the water vapor and protons generated at the cathode 61 is supplied to the reforming section 51 as a cathode off-gas and used for the steam reforming reaction and the partial oxidation reaction, respectively.

  The voltmeter 64 detects the voltage generated by the power generation in the fuel cell 60 and gives the detection result to the control unit 10. The ammeter 65 detects the current generated by the power generation reaction in the fuel cell 60 and gives the detection result to the control unit 10. The start switch 11 is a switch for starting the fuel reforming system 100. The controller 10 starts the fuel reforming system 100 when the start switch 11 is turned on by an operator, and stops the fuel reforming system 100 when the start switch is turned off by the operator. Perform stop processing. Hereinafter, the operation stop process by the control unit 10 when the fuel reforming system 100 is stopped will be described.

  First, the control unit 10 determines whether or not an instruction to stop the operation of the fuel reforming system 100 has been made. In this embodiment, it is determined that an instruction to stop the operation of the fuel reforming system 100 has been made when the start switch 11 is turned off by the operator. The control unit 10 may determine that an operation stop instruction has been issued when the temperature of the fuel cell 60 falls below a predetermined value. This is because it is determined that the power generation of the fuel cell 60 has been completed. Moreover, the control part 10 may determine with the driving | operation stop instruction | indication being made when the electrical storage amount of a storage battery exceeds predetermined amount. This is because if the amount of electricity stored in the storage battery increases, the power generation of the fuel cell 60 becomes unnecessary.

  When it is determined that the operation stop instruction has been issued, the control unit 10 performs an operation stop process for the fuel reforming system 100. First, the control unit 10 acquires a carbon deposition avoidance limit S / C ratio. Here, the S / C ratio indicates the molar ratio between the steam supplied to the reforming unit 51 and the carbon in the hydrocarbon fuel supplied to the reforming unit 51. Therefore, the S / C ratio can be obtained from the amount of water vapor generated in the fuel cell 60 and the amount of hydrocarbon fuel supplied to the reforming unit 51 by the metering valve 40. The carbon deposition avoidance limit S / C ratio is an S / C ratio necessary for preventing carbon deposition from occurring in the reforming portion 51.

  The carbon deposition avoidance limit S / C ratio is a function of the type of catalyst, the catalyst temperature, and the O / C ratio. Here, the O / C ratio indicates a molar ratio between oxygen supplied to the reforming unit 51 and carbon in the hydrocarbon fuel supplied to the reforming unit 51. Therefore, the O / C ratio can be obtained from the amount of air supplied from the cathode 61 to the reforming unit 51 and the amount of hydrocarbon fuel supplied to the reforming unit 51 by the metering valve 40. The type of catalyst is fixed because it does not change during operation of the fuel reforming system 100. Therefore, the carbon deposition avoidance limit S / C ratio can be obtained from the catalyst temperature and the O / C ratio.

  FIG. 2 is a diagram showing an example of the relationship between the carbon deposition avoidance limit S / C ratio, the catalyst temperature, and the O / C ratio. 2 indicates the carbon deposition avoidance limit S / C ratio, and the horizontal axis in FIG. 2 indicates the catalyst temperature of the reforming unit 51. As shown in FIG. 2, the carbon deposition avoidance limit S / C ratio increases as the catalyst temperature decreases and as the O / C ratio decreases. Therefore, the lower the catalyst temperature and the smaller the O / C ratio, the easier it is for carbon to precipitate in the reforming section 51.

Next, the control unit 10 determines whether or not the current S / C ratio exceeds the carbon deposition avoidance limit S / C ratio. The current S / C ratio can be obtained from the amount of water generated by the power generation of the fuel cell 60 and the amount of hydrocarbon fuel supplied to the reforming unit 51. Therefore, it is not necessary to newly provide a device for detecting the amount of water vapor. The amount of water generated by the fuel cell 60 can be obtained from the following equation (1). The generated current in the formula (1) is obtained from the detection result of the ammeter 65. The number of stacked cells is the number of stacked cells in the fuel cell 60.
Power generation volume (mol / sec)
= (Generated current x Number of stacked cells) / (2 x Faraday constant) (1)
Faraday constant: 96485

  When the current S / C ratio is equal to or less than the carbon deposition avoidance limit S / C ratio, the control unit 10 gradually decreases the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 and Gradually increase the / C ratio. In this case, the control unit 10 determines the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 by the product of the current amount of hydrocarbon fuel and a predetermined fuel attenuation coefficient (<1). It can also be determined by subtracting a predetermined amount of fuel attenuation from the current amount of hydrocarbon fuel. However, it is preferable that the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 is determined using the fuel attenuation coefficient. This is because the overheat damage period of the reforming catalyst at the time of control failure such as excessive air supply by the air pump 80 can be shortened and the time required for gas purging of the reforming catalyst can be realized with easy logic. is there.

  Further, the control unit 10 can determine the target O / C ratio by the product of the current O / C ratio and a predetermined O / C ratio increase coefficient (> 1). It can also be determined by adding a predetermined amount of increase in O / C ratio. The control unit 10 can achieve the target O / C ratio by controlling the amount of air supplied from the air pump 80 to the reforming unit 51. The control unit 10 gradually decreases the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 until the S / C ratio exceeds the carbon deposition avoidance limit S / C ratio, and the O / C ratio. Increase gradually. In this case, carbon deposition in the reforming part 51 can be suppressed.

  When the current S / C ratio exceeds the carbon deposition avoidance limit S / C ratio, the control unit 10 realizes the amount of hydrocarbon fuel supplied to the reforming unit 51 by the metering valve 40. Control to the minimum amount possible. Further, the control unit 10 determines the amount of air supplied from the air pump 80 to the cathode 61 by the product of the excess air ratio λ and the amount of hydrocarbon fuel supplied to the reforming unit 51. Thereafter, the control unit 10 stands by until a predetermined time (for example, 5 seconds) elapses. Thereafter, the control unit 10 stops the supply of hydrocarbon fuel from the metering valve 40 to the reforming unit 51, the supply of air from the air pump 80 to the cathode 61, and the supply of air from the air pump 70 to the cooling unit 63. . Thereby, the operation of the fuel reforming system 100 is completely stopped.

  The control unit 10 also supplies the reforming unit 51 to the reforming unit 51 from the metering valve 40 even when the current reformed fuel supply amount is below the minimum amount that the metering valve 40 can realize. The supply of hydrocarbon fuel, the supply of air from the air pump 80 to the cathode 61, and the supply of air from the air pump 70 to the cooling unit 63 are stopped.

  FIG. 3 is a diagram illustrating an example of a result of the operation stop process performed by the control unit 10. The horizontal axis of FIG. 3 indicates time, and the vertical axis of FIG. 3 indicates the reforming catalyst temperature, the excess air ratio λ, the S / C ratio, and the amount of power generated by the fuel cell 60. As shown in FIG. 3, after the operation stop process is started, the S / C ratio decreases and the excess air ratio λ increases. Along with this, the reforming catalyst temperature gradually increases. Further, the power generation of the fuel cell 60 decreases.

  Thus, in the present embodiment, the steam supply amount and the hydrocarbon fuel supply amount to the reforming unit 51 gradually decrease. Further, the O / C ratio in the reforming section 51 gradually increases. Thereby, the ratio of the steam reforming reaction in the reforming section 51 is gradually decreased, and the ratio of the partial oxidation reaction is gradually increased. The steam reforming reaction is an endothermic reaction, and the partial oxidation reaction is an exothermic reaction. In this case, it is possible to prevent a rapid temperature rise in the reforming unit 51 while preventing a rapid temperature drop in the reforming unit 51. Further, the temperature of the reforming unit 51 can be gradually increased. As a result, the restartability of the fuel reforming system 100 is improved.

  In general, the amount of hydrocarbon fuel and the amount of steam remaining in the reforming catalyst vary depending on the reforming conditions and the reforming catalyst performance at the start of the operation stop process. Therefore, complicated control such as catalyst temperature detection and fine adjustment of the amount of air supplied to the reforming unit is necessary. As a result, the device cost increases. However, in this embodiment, since only the control for gradually decreasing the ratio of the steam reforming reaction and gradually increasing the ratio of the partial oxidation reaction is required, the control law is simplified. Therefore, the device cost can be reduced.

  In particular, when the power generation product water is used for the steam reforming reaction as in the fuel reforming system 100 according to the present embodiment, the power generation product water amount is reduced by reducing the reformed fuel amount and further consumed at the cathode 61. Since the amount of oxygen also decreases, as a result, the ratio of the partial oxidation reaction increases. Therefore, the effect of the present invention can be obtained without introducing a special control law.

  In the case of the present embodiment, there is no need to newly provide a device for generating water vapor. Thereby, the fuel reforming system 100 can be reduced in size and the cost can be reduced. Further, the air pump 80 necessary for the operation of the fuel cell 60 can be used as oxygen supply means to the reforming unit 51. Thereby, it is not necessary to newly provide oxygen supply means. As a result, the fuel reforming system 100 can be reduced in size.

  In this embodiment, the minimum amount of hydrocarbon fuel that can be realized by the metering valve 40 when the current S / C ratio exceeds the carbon deposition avoidance limit S / C ratio is supplied to the reforming unit 51. As a result, the partial oxidation reaction continues. Thereby, the temperature fall of the modification part 51 can be prevented, suppressing the carbon precipitation in the modification part 51. FIG. In this embodiment, the cathode off gas is supplied to the reforming unit 51, but a steam supply unit and an oxygen supply unit may be newly provided.

  Next, an example of a flowchart when the control unit 10 performs the operation stop process of the fuel reforming system 100 will be described. FIG. 4 is a diagram showing an example of the flowchart. The control unit 10 executes the flowchart of FIG. 4 every 100 ms, for example. First, as shown in FIG. 4, the control unit 10 determines whether or not an operation stop instruction has been issued (step S1). In this case, the control unit 10 determines that the operation stop instruction has been given because the start switch 11 is turned off.

  If it is not determined in step S1 that the operation stop instruction has been issued, the control unit 10 ends the process. When it is determined in step S1 that the operation stop instruction has been issued, the control unit 10 determines whether an accumulated combustion time described later is longer than 0 (step S2). If it is not determined in step S2 that the accumulated combustion time is greater than 0, the control unit 10 determines that the current supply amount of hydrocarbon fuel to the reforming unit 51 is less than the minimum amount that the metering valve 40 can realize. It is determined whether or not there is (step S3).

  In Step S3, when it is not determined that the current supply amount of hydrocarbon fuel to the reforming unit 51 is equal to or less than the minimum amount that can be realized by the metering valve 40, the control unit 10 determines that the carbon deposition avoidance limit S / C ratio is acquired (step S4). In this case, the control unit 10 can obtain the carbon deposition avoidance limit S / C ratio using the detection result of the temperature sensor 53, the current O / C ratio, and FIG.

  Next, the control unit 10 determines whether or not the current S / C ratio is equal to or less than the carbon deposition avoidance limit S / C ratio (step S5). When it is determined in step S5 that the current S / C ratio is equal to or less than the carbon deposition avoidance limit S / C ratio, the control unit 10 determines the amount of hydrocarbon fuel supplied to the reforming unit 51 by the metering valve 40. (Step S6). In this case, the control unit 10 determines whether the product of the amount of hydrocarbon fuel supplied from the current metering valve 40 to the reforming unit 51 and the fuel attenuation coefficient (for example, 0.5) or the metering valve 40 can be realized. The larger one of the amounts is set as the amount of hydrocarbon fuel supplied to the reforming unit 51 by the metering valve 40.

  Next, the control unit 10 determines a target O / C ratio (step S7). In this case, the control unit 10 calculates the product of the current O / C ratio and the O / C ratio increase coefficient (for example, 1.5) or the O / C ratio at which the reforming reaction in the reforming unit 51 can be maintained. The smaller one of the upper limit values is set as the target O / C ratio. Next, the control unit 10 obtains the amount of air supplied to the cathode 61 by the air pump 80 from the hydrocarbon fuel supply amount obtained in step S6 and the target O / C ratio obtained in step S7 (step S8).

  In this case, the control unit 10 corrects the amount of oxygen used when generating power in the fuel cell 60. This correction amount can be obtained based on the generated current of the fuel cell 60. The control unit 10 can learn the correction amount based on the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 and the generated current of the fuel cell 60. In this case, the air amount can be accurately obtained in step S8. Thereafter, the control unit 10 ends the process.

  If it is not determined in step S5 that the current S / C ratio is less than or equal to the carbon deposition avoidance limit S / C ratio, the control unit 10 sets the accumulated combustion time to 0 (step S9). Next, the control unit 10 sets the amount of hydrocarbon fuel supplied from the metering valve 40 to the reforming unit 51 to the minimum amount that can be realized by the metering valve 40 (step S10). Next, the control unit 10 sets the amount of air supplied to the cathode 61 by the air pump 80 to the product of the amount of hydrocarbon fuel obtained in step S10 and the excess air ratio λ (for example, 3.5) (step S11). .

  Next, the control unit 10 increases the accumulated combustion time by 0.1 seconds (step S12). Next, the control unit 10 determines whether or not the accumulated combustion time is less than or equal to the maximum accumulated combustion time (for example, 5 seconds) (step S13). When it determines with integrated combustion time being below the maximum integrated combustion time in step S13, the control part 10 complete | finishes a process. When it is not determined in step S13 that the accumulated combustion time is less than or equal to the maximum accumulated combustion time, the control unit 10 supplies hydrocarbon fuel from the metering valve 40 to the reforming unit 51, and from the air pump 80 to the cathode 61. The supply of air and the supply of air from the air pump 70 to the cooling unit 63 are stopped (step S14).

  If it is determined in step S2 that the accumulated combustion time is longer than 0, the control unit 10 performs the operation of step 12. Further, when it is determined in step S3 that the current supply amount of hydrocarbon fuel to the reforming unit 51 is equal to or less than the minimum amount that can be realized by the metering valve 40, the control unit 10 performs the operation of step S14. .

  Thus, by performing the operation stop process according to the flowchart of FIG. 4, it is possible to prevent a rapid temperature rise in the reforming unit 51 while preventing a rapid temperature drop in the reforming unit 51. Further, the temperature of the reforming unit 51 can be gradually increased. As a result, the restartability of the fuel reforming system 100 is improved. In addition, when the current S / C ratio exceeds the carbon deposition avoidance limit S / C ratio, a partial amount of hydrocarbon fuel that can be realized by the metering valve 40 is supplied to the reforming unit 51, thereby causing a partial oxidation reaction. continue. Thereby, the temperature fall of the modification part 51 can be prevented, suppressing the carbon precipitation in the modification part 51. FIG.

  In this embodiment, the reforming unit 51 corresponds to the reforming means, the fuel cell 60 and the air pump 80 correspond to the water vapor supply means, the air pump 80 corresponds to the oxygen gas supply means, and the metering valve 40 reforms. The control unit 10 corresponds to the fuel supply means, the control unit 10 corresponds to the control means, and the ammeter 64 corresponds to the current detection means.

1 is a schematic diagram showing an overall configuration of a fuel reforming system according to a first embodiment of the present invention. It is a figure which shows an example of the relationship of carbon precipitation avoidance limit S / C ratio, catalyst temperature, and O / C ratio. It is a figure which shows an example of the result of the operation stop process by a control part. It is a figure which shows one example of the said flowchart.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control part 20 Reformed fuel tank 40 Metering valve 50 Reformer 51 Reformer 52 Temperature sensor 53
54 Air excess ratio λ sensor 60 Fuel cell 61 Cathode 62 Anode 64 Voltmeter 65 Ammeter 70, 80 Air pump 100 Fuel reforming system

Claims (6)

Reforming means for generating hydrogen by a reforming reaction using the reformed fuel;
Steam supply means for supplying steam to the reforming means;
Reformed fuel supply means for supplying reformed fuel to the reforming means;
Oxygen gas supply means for supplying oxygen gas to the reforming means;
When the reforming unit stops operating, the supply of reformed fuel and steam to the reforming unit is maintained, while the supply amounts of the reformed fuel and steam gradually decrease, and oxygen is improved. Control means for controlling the steam supply means, the reformed fuel supply means, and the oxygen gas supply means so as to be supplied to the reforming means in an amount larger than that required for the reforming reaction in the quality means. A fuel reforming system characterized by   The control means supplies the reformed fuel and steam to the reforming means until the S / C ratio in the reforming means exceeds the carbon deposition avoidance limit S / C ratio when the reforming means stops operating. 2. The fuel reforming system according to claim 1, wherein the steam supply means and the reformed fuel supply means are controlled so that the amount decreases.   When the reforming unit stops operating, and the S / C ratio in the reforming unit exceeds the carbon deposition avoidance limit S / C ratio, the control unit is configured to perform the reforming unit after a predetermined time has elapsed. 3. The water vapor supply means, the reformed fuel supply means, and the oxygen gas supply means are controlled so that the supply of water vapor, reformed fuel, and oxygen gas to is stopped. Fuel reforming system. It further comprises a fuel cell in which water vapor is generated at the cathode along with power generation,
The fuel reforming system according to any one of claims 1 to 3, wherein the steam supply means supplies the steam generated in the fuel cell to the reforming means. Further comprising current detection means for detecting the generated current of the fuel cell;
5. The fuel reforming system according to claim 4, wherein the control unit obtains a steam supply amount to the reforming unit by the steam supply unit based on a detection result of the current detection unit.   6. The fuel reforming system according to claim 4, wherein the oxygen gas supply means supplies oxygen gas to the reforming means via a cathode of the fuel cell.

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