JP5352301B2 - FUEL CELL SYSTEM AND FUEL CELL STATE DETECTION METHOD - Google Patents

Description

  The present invention relates to a fuel cell system and a fuel cell state detection method.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of the environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  In a fuel cell system including a fuel cell, a reformer for generating hydrogen from a fuel such as a hydrocarbon may be provided. A technique for detecting deterioration of the reformer by detecting the concentration of hydrocarbons in the fuel gas produced in the reformer is disclosed (for example, see Patent Document 1).

International Publication No. 2005/018035

  By the way, since the fuel cell may deteriorate as the reforming efficiency of the reformer decreases, it is preferable that the reduction in reforming efficiency of the reformer can be detected using the technique of Patent Document 1. However, in the technique of Patent Document 1, it is necessary to provide a hydrocarbon sensor. This costs money.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system and a fuel cell state detection method that can detect the state of a fuel cell without providing a hydrocarbon sensor. To do.

A fuel cell system according to the present invention includes a reforming unit that generates hydrogen from hydrocarbons, a fuel cell that generates power using the hydrogen generated in the reforming unit as fuel, and a combustion chamber that burns anode off-gas of the fuel cell. An oxygen sensor that detects the oxygen concentration in the exhaust gas, a determination unit that determines deterioration of the fuel cell based on fluctuations in the oxygen concentration in the exhaust gas obtained from the detection result of the oxygen sensor, and an excess air ratio in the combustion chamber An excess air ratio control means for controlling, and the excess air ratio control means is characterized in that the excess air ratio is increased when the determination unit acquires a change in the oxygen concentration in the exhaust gas. . In the fuel cell system according to the present invention, the state of the fuel cell can be detected without providing a hydrocarbon sensor.

  The determination unit may determine that the deterioration of the fuel cell is greater as the fluctuation of the oxygen concentration in the exhaust gas is larger with respect to the increase in the excess air ratio in the combustion chamber. In this case, deterioration of the fuel cell can be determined quantitatively.

  The fuel cell system may further include a notification device that notifies the user of the deterioration of the fuel cell when the determination unit determines that the fuel cell is deteriorated. Further, the fluctuation of the oxygen concentration may be a standard deviation calculated from a plurality of detection values detected by the oxygen sensor during a predetermined period. The fuel cell may be a solid oxide fuel cell. The anode of the fuel cell may contain nickel.

The method for detecting a state of a fuel cell according to the present invention includes a method for detecting an oxygen concentration in an exhaust gas from a combustion chamber that burns an anode off-gas of a fuel cell that generates electricity using hydrogen generated from hydrocarbons as fuel in a reforming unit. A concentration detection step; a determination unit step for determining deterioration of the fuel cell based on a variation in oxygen concentration in the exhaust gas obtained in the oxygen concentration detection step; and a step for acquiring a variation in oxygen concentration in the exhaust gas in the determination step And an excess air ratio increasing step for increasing the excess air ratio . In the fuel cell state detection method according to the present invention, the state of the fuel cell can be detected without providing a hydrocarbon sensor.

  In the determination step, it may be determined that the deterioration of the fuel cell is greater as the fluctuation of the oxygen concentration in the exhaust gas is larger with respect to the increase in the excess air ratio in the combustion chamber. In this case, deterioration of the fuel cell can be determined quantitatively.

  The fuel cell state detection method may further include a notification step of notifying the user of the deterioration of the fuel cell when the determination unit determines that the fuel cell is deteriorated. Further, the fluctuation of the oxygen concentration may be a standard deviation calculated from a plurality of detection values detected by the oxygen sensor during a predetermined period. The fuel cell may be a solid oxide fuel cell. The anode of the fuel cell may contain nickel.

  According to the present invention, it is possible to provide a fuel cell system and a fuel cell state detection method that can detect the state of a fuel cell without providing a hydrocarbon sensor.

1 is a schematic diagram showing an overall configuration of a fuel cell system according to Example 1. FIG. It is typical sectional drawing for demonstrating the detail of an oxygen sensor. It is a schematic diagram for demonstrating the detail of a fuel cell. (A) is a figure which shows an example of the flowchart performed in order to acquire oxygen concentration fluctuation | variation, (b) is when determining deterioration of a fuel cell using the oxygen concentration fluctuation | variation memorize | stored in the flowchart of (a). It is a figure which shows an example of the flowchart performed in FIG.

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

  FIG. 1 is a schematic diagram illustrating an overall configuration of a fuel cell system 100 according to the first embodiment. As shown in FIG. 1, the fuel cell system 100 includes a control unit 10, an anode material supply unit 20, a reformed water supply unit 30, a cathode air supply unit 40, a reformer 50, a fuel cell 60, an oxygen sensor 70, a heat An exchange 80 and a notification device 90 are provided.

  The anode raw material supply unit 20 includes a fuel pump for supplying a fuel gas such as hydrocarbons to the reforming unit 51. The reforming water supply unit 30 supplies the reforming water tank 31 that stores the reforming water necessary for the reforming reaction in the reforming unit 51, and supplies the reforming water stored in the reforming water tank 31 to the reforming unit 51. Including a reforming water pump 32 and the like. The cathode air supply unit 40 includes an air pump for supplying an oxidant gas such as air to the cathode 61.

  The reformer 50 includes a reforming unit 51 and a combustion chamber 52. The fuel cell 60 has a structure in which an electrolyte is sandwiched between a cathode 61 and an anode 62. For example, a solid oxide fuel cell (SOFC) can be used as the fuel cell 60. The notification device 90 is a device for notifying a user or the like of a caution, a warning, or the like. The control unit 10 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like.

  Next, an outline of the operation of the fuel cell system 100 will be described. The anode material supply unit 20 supplies a required amount of fuel gas to the reforming unit 51 in accordance with an instruction from the control unit 10. The reforming water pump 32 supplies a necessary amount of reforming water to the reforming unit 51 in accordance with instructions from the control unit 10. The reforming unit 51 generates a reformed gas containing hydrogen from the fuel gas and the reformed water by a reforming reaction using heat generated in the combustion chamber 52. The generated reformed gas is supplied to the anode 62.

  The cathode air supply unit 40 supplies a necessary amount of cathode air to the cathode 61 in accordance with instructions from the control unit 10. Thereby, power generation is performed in the fuel cell 60. The cathode offgas discharged from the cathode 61 and the anode offgas discharged from the anode 62 flow into the combustion chamber 52. In the combustion chamber 52, combustible components in the anode off gas are burned by oxygen in the cathode off gas. The heat obtained by the combustion is given to the reforming unit 51 and the fuel cell 60.

  Thus, in the fuel cell system 100, combustible components such as hydrogen and carbon monoxide contained in the anode off gas can be burned in the combustion chamber 52. The oxygen sensor 70 detects the oxygen concentration in the exhaust gas discharged from the combustion chamber 52 and gives the detection result to the control unit 10. The heat exchanger 80 exchanges heat between the exhaust gas discharged from the combustion chamber 52 and tap water. Condensed water obtained from the exhaust gas by heat exchange is stored in the reformed water tank 31. The notification device 90 notifies the user or the like of information related to the state of the fuel cell 60.

  FIG. 2 is a schematic cross-sectional view for explaining details of the oxygen sensor 70. As shown in FIG. 2, the oxygen sensor 70 is a limiting current oxygen sensor, and an anode 72 is provided on one surface of the electrolyte 71, and a cathode 73 is provided on the other surface of the electrolyte 71 to form pores. The porous substrate 74 has a structure arranged so as to cover the cathode 73. A heater 75 is disposed on the electrolyte 71.

  The electrolyte 71 is made of an oxygen ion conductive electrolyte, for example, zirconia. The anode 72 and the cathode 73 are made of platinum, for example. The anode 72 and the cathode 73 form an external circuit through wiring. This external circuit is provided with a power source 76 and an ammeter 77. The porous substrate 74 is made of, for example, porous alumina. The heater 75 is made of, for example, a platinum thin film.

Next, control of the oxygen sensor 70 by the control unit 10 will be described. The controller 10 heats the electrolyte 71 by supplying power to the heater 75. After the temperature of the electrolyte 71 reaches a predetermined value, the control unit 10 controls the power supply 76 so that a positive voltage is applied to the anode 72. When a voltage is applied to the anode 72 by the power source 76, oxygen becomes oxygen ions at the cathode 73 and conducts through the electrolyte 71 according to the following formula (1). In the anode 72, oxygen ions become oxygen molecules according to the following formula (2).
O ₂ + 4e ⁻ → 2O ²⁻ (1)
2O ²⁻ → O ₂ + 4e ⁻ (2)

  Since the amount of oxygen transported to the cathode 73 is governed by the pores of the porous substrate 74, the current (limit current) generated by the reaction of the formulas (1) and (2) is in the pores of the porous substrate 74. It is determined by the amount of oxygen gas diffusion. This oxygen gas diffusion amount is determined by the oxygen concentration outside the porous substrate 74.

  The control unit 10 acquires the output current of the oxygen sensor 70 according to the detection value of the ammeter 77. The output current of the oxygen sensor 70 is proportional to the oxygen concentration. Based on this proportional relationship, the controller 10 detects the oxygen concentration of the atmosphere to which the oxygen sensor 70 is exposed.

  FIG. 3 is a schematic diagram for explaining details of the fuel cell 60. As shown in FIG. 3, the fuel cell 60 has a structure in which an electrolyte 63 is sandwiched between a cathode 61 and an anode 62. The cathode 61 is made of, for example, lanthanum manganite. The anode 62 is made of, for example, nickel. The electrolyte 63 is made of, for example, zirconia.

  Hydrogen and carbon monoxide in the reformed gas supplied to the anode 62 emit electrons to the anode 62. Electrons emitted to the anode 62 are supplied to the cathode 61 after performing electrical work through an external circuit. Oxygen in the cathode air supplied to the cathode 61 receives electrons supplied to the cathode 61 and becomes oxygen ions. The oxygen ions move through the electrolyte 63 and reach the anode 62. At the anode 62, hydrogen and carbon monoxide from which electrons have been released react with oxygen ions to produce water and carbon dioxide gas.

When the reforming efficiency in the reformer 50 decreases due to a decrease in catalyst function or the like, the concentration of hydrocarbon fuel in the reformed gas supplied from the reformer 50 to the anode 62 increases. In this case, the hydrocarbon fuel reacts with steam by the steam reforming reaction of the following formula (3) using nickel of the anode 62 as a catalyst. Thereby, hydrogen and carbon monoxide are produced. In formula (3), methane was used as an example of the hydrocarbon fuel. Hydrogen and carbon monoxide produced by the following formula (3) are subjected to the above power generation reaction.
_{CH 4 + H 2 O → CO} + 3H 2 (3)

  However, when the hydrocarbon fuel is supplied to the anode 62, carbon in the hydrocarbon fuel may be deposited on the surface of the anode 62. The catalytic function of the anode 62 decreases with carbon deposition. As a result, the power generation performance of the fuel cell 60 is lowered, and the hydrocarbon concentration in the anode off-gas is increased. From the above, it can be determined that the fuel cell 60 has deteriorated by detecting an increase in the hydrocarbon concentration in the anode off-gas. Note that the catalytic function of the anode 62 is also reduced by oxidation of the anode 62 and the like.

  For example, when the catalytic function of the anode 62 is lowered, the ratio between the hydrogen concentration and the hydrocarbon concentration in the anode off gas varies. Since the specific combustibility of hydrocarbon and hydrogen is different from each other, the combustion state in the combustion chamber 52 varies with variation in the ratio between the hydrogen concentration and the hydrocarbon concentration. Therefore, in the present embodiment, an increase in the hydrocarbon concentration in the anode off-gas is detected based on the fluctuation of the combustion state in the combustion chamber 52.

  Specifically, since the specific flammability of hydrocarbons is lower than the specific flammability of hydrogen, when the concentration of hydrocarbons relative to hydrogen in the anode offgas increases, the specific flammability of the anode offgas decreases. Thereby, the combustion in the combustion chamber 52 becomes unstable, and the oxygen concentration in the exhaust gas varies. On the other hand, when the hydrocarbon concentration with respect to hydrogen in the anode off gas decreases, the specific combustibility of the anode off gas improves. Thereby, the combustion in the combustion chamber 52 is stabilized, and the fluctuation of the oxygen concentration in the exhaust gas is suppressed. From the above, based on the detection result of the oxygen sensor 70, it can be determined whether or not the hydrocarbon concentration in the anode off-gas is increasing.

  Further, since the hydrocarbon combustion limit mixing ratio (about 2.5 in the case of methane) is larger than the hydrogen combustion limit mixing ratio (about 10), by increasing the excess air ratio λ in the combustion chamber 52, The amount of fluctuation in the combustion state can be increased. Therefore, the detection accuracy of the combustion state is improved by increasing the excess air ratio λ. The excess air ratio λ can be controlled by controlling the anode material supply amount from the anode material supply unit 20 and the cathode air supply amount from the cathode air supply unit 40.

  In this embodiment, when it is determined that the fuel cell 60 has deteriorated, the notification device 90 notifies the user of an alarm or the like according to the instruction of the control unit 10. Thereby, the user or the like can inspect the fuel cell 60 or the like. Hereinafter, specific control for detecting the state of the fuel cell 60 will be described.

FIG. 4A is a diagram illustrating an example of a flowchart executed to acquire oxygen concentration fluctuations. The flowchart of FIG. 4A is executed periodically (for example, every 100 ms). As shown in FIG. 4A, the control unit 10 measures the oxygen concentration CNC_O ₂ in the exhaust gas from the combustion chamber 52 based on the detection result of the oxygen sensor 70 (step S1). Next, the control unit 10 adds “1” to the counter N (step S2).

Next, the control unit 10 determines whether or not the counter N is less than the calculated data number N_ref (for example, “120”) (step S3). When it is determined in step S3 that the counter N is less than the calculated data number N_ref, the control unit 10 ends the execution of the flowchart. Thereby, the oxygen concentration CNC_O ₂ is measured “N_ref” times. When it is not determined in step S3 that the counter N is less than the calculated data number N_ref, the control unit 10 calculates and stores the oxygen concentration fluctuation σ_O ₂ from “N_ref” oxygen concentrations CNC_O ₂ (step S4). . The oxygen concentration fluctuation σ_O ₂ is a standard deviation calculated from “N_ref” oxygen concentrations CNC_O ₂ .

FIG. 4B is a diagram illustrating an example of a flowchart executed when the deterioration of the fuel cell 60 is determined using the oxygen concentration fluctuation σ_O ₂ stored in the flowchart of FIG. As shown in FIG. 4B, the control unit 10 determines whether or not the oxygen concentration fluctuation σ_O ₂ exceeds the allowable upper limit σ_O ₂ _ref (for example, “0.2”) (step S11). The allowable upper limit σ_O ₂ _ref is a threshold value for determining a change in the combustion state in the combustion chamber 52.

If it is not determined in step S11 that the oxygen concentration fluctuation σ_O ₂ exceeds the allowable upper limit σ_O ₂ _ref, the control unit 10 determines whether or not the excess air ratio λ exceeds the excess ratio upper limit λ_max (for example, “8”). Is determined (step S12). Here, the excess ratio upper limit λ_max is the maximum value of the excess air ratio allowed in the combustion chamber 52.

When it is determined in step S12 that the excess air ratio λ exceeds the excess ratio upper limit λ_max, the control unit 10 ends the execution of the flowchart. If it is not determined in step S12 that the excess air ratio λ exceeds the excess ratio upper limit λ_max, the control unit 10 increases the excess air ratio λ by “0.1” (step S13). Note that the air excess ratio λ is increased or decreased by repeating step S13. Thereby, the detection accuracy of the oxygen concentration fluctuation σ_O ₂ is improved.

When it is determined in step S11 that the oxygen concentration fluctuation σ_O ₂ exceeds the allowable upper limit σ_O ₂ _ref, the control unit 10 controls the excess air ratio λ to the normal control value λ_bse (eg, “2.5”) ( Step S14). The normal control value λ_bse is an excess air ratio that is controlled during normal power generation of the fuel cell 60.

Next, the control unit 10 selects a control value corresponding to the oxygen concentration fluctuation σ_O ₂ (step S15). For example, the control unit 10 performs control for stabilizing combustion in the combustion chamber 52. Specifically, the control unit 10 performs control to increase the anode material supply amount from the anode material supply unit 20.

Next, the control unit 10 determines whether or not the oxygen concentration fluctuation σ_O ₂ exceeds a warning determination value σ_O ₂ _max (for example, “0.5”) (step S16). The warning determination value σ_O _{2 —} max is a threshold value for determining whether or not the fuel cell 60 has deteriorated. If the oxygen concentration variation Shiguma_O ₂ is determined to exceed the warning judgment value σ_O ₂ _max In step S16, the control unit 10 controls the notifying unit 90 to display an alarm (step S16). Thereafter, the control unit 10 ends the execution of the flowchart. If it is not determined in step S16 that the oxygen concentration variation σ_O ₂ exceeds the warning determination value σ_O ₂ _max, the control unit 10 ends the flowchart.

  According to the flowcharts of FIGS. 4A and 4B, it is possible to detect combustion fluctuations in the combustion chamber 52 using the oxygen sensor 70. Thereby, deterioration of the fuel cell 60 can be detected.

When the excess air ratio λ is increased or decreased, it can be determined that the deterioration of the fuel cell 60 is more advanced as the oxygen concentration fluctuation σ_O ₂ is larger than the increase in the excess air ratio λ. In this case, deterioration of the fuel cell 60 can be determined quantitatively.

  In the present embodiment, the control unit 10 functions as a determination unit, and the cathode air supply unit 40 functions as an excess air ratio control unit.

DESCRIPTION OF SYMBOLS 10 Control part 20 Anode raw material supply part 30 Reformed water supply part 31 Reformed water tank 32 Reformed water pump 40 Cathode air supply part 50 Reformer 51 Reformer 52 Combustion chamber 60 Fuel cell 61 Cathode 62 Anode 63 Electrolyte 70 Oxygen sensor 100 Fuel cell system

Claims (12)

A reformer that produces hydrogen from hydrocarbons;
A fuel cell for generating electricity using the hydrogen produced in the reforming section, and
An oxygen sensor for detecting the oxygen concentration in the exhaust gas from the combustion chamber for burning the anode off-gas of the fuel cell;
A determination unit that determines deterioration of the fuel cell based on a change in oxygen concentration in the exhaust gas obtained from a detection result of the oxygen sensor;
An excess air ratio control means for controlling an excess air ratio in the combustion chamber,
The excess air ratio control means increases the excess air ratio when the determination unit acquires a change in oxygen concentration in the exhaust gas . The determination unit, according to claim 1 larger the variation in the oxygen concentration in the exhaust gas with an increase in the excess air ratio in the combustion chamber, deterioration of the fuel cell and judging that the large The fuel cell system described . 3. The fuel cell system according to claim 1 , further comprising a notification device that notifies the user of the deterioration of the fuel cell when the determination unit determines that the fuel cell is deteriorated. 4. . The fuel cell system according to any one of claims 1 to 3 , wherein the fluctuation of the oxygen concentration is a standard deviation calculated from a plurality of detection values detected by the oxygen sensor during a predetermined period. The fuel cell system according to claim 1 , wherein the fuel cell is a solid oxide fuel cell. The fuel cell system according to claim 5 , wherein the anode of the fuel cell contains nickel. An oxygen concentration detection step for detecting the oxygen concentration in the exhaust gas from the combustion chamber for burning the anode off-gas of a fuel cell that generates electricity using hydrogen generated from hydrocarbons as fuel in the reforming section;
A determination step of determining deterioration of the fuel cell based on a change in oxygen concentration in the exhaust gas obtained in the oxygen concentration detection step;
A method for detecting a state of a fuel cell, comprising: an excess air ratio increasing step for increasing the excess air ratio when acquiring a change in oxygen concentration in the exhaust gas in the determination step . In the determination step, according to claim 7 larger the variation in the oxygen concentration in the exhaust gas with an increase in the excess air ratio in the combustion chamber, deterioration of the fuel cell and judging that the large The state detection method of the fuel cell as described . The fuel cell according to claim 7 , further comprising a notification step of notifying the user of the deterioration of the fuel cell when the determination unit determines that the fuel cell is deteriorated. State detection method. The state detection of a fuel cell according to any one of claims 7 to 9 , wherein the fluctuation of the oxygen concentration is a standard deviation calculated from a plurality of detection values detected by the oxygen sensor during a predetermined period. Method. The fuel cell state detection method according to claim 7, wherein the fuel cell is a solid oxide fuel cell. The method of claim 11 , wherein the anode of the fuel cell contains nickel.

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