JP4852241B2 - Operation method of fuel cell power generation system - Google Patents

Description

  The present invention relates to a method for operating a fuel cell power generation system and a fuel cell power generation system.

  The fuel cell power generation system supplies fuel such as hydrogen and oxidant such as air to the fuel cell body and reacts them electrochemically, thereby converting the chemical energy of the fuel directly into electrical energy and taking it out. Device. The fuel cell power generation system is characterized by being highly efficient and environmentally friendly despite being relatively small. Moreover, it can be applied as a cogeneration system by collecting heat generated by power generation as hot water or steam. Fuel cell main bodies are classified into various types depending on the difference in electrolyte, etc., but solid polymer fuel cells using a solid polymer electrolyte membrane as the electrolyte are characterized by low temperature operability and high output density. It is suitable for use as a power source for small cogeneration systems and electric vehicles with a view to general household use, and the market size is expected to expand rapidly in the future.

  This polymer electrolyte fuel cell power generation system is, for example, a reformer, a reformer that produces hydrogen-containing gas from hydrocarbon fuels typified by city gas, LPG, etc. The fuel cell stack that generates the electromotive force by supplying the hydrogen-containing gas and air in the atmosphere produced by the gas generator to the fuel electrode and the oxidant electrode, and the electricity that supplies the electric energy generated by the fuel cell stack to the external load It is comprised by the heat utilization system which collect | recovers the heat_generation | fever accompanying a control apparatus and electric power generation. In this way, fuel operation is premised on the operation of the fuel cell power generation system. Therefore, the higher the power generation efficiency defined by the amount of power generated relative to the amount of fuel input, the lower the amount of fuel used and the higher the user merit. Become. Therefore, the power generation efficiency is an index indicating the performance of the fuel cell power generation system.

  By the way, the fuel cell stack that actually has a power generation function in this fuel cell power generation system has a problem that the voltage decreases with time due to various factors associated with the operation, resulting in a decrease in power generation efficiency. That is, suppressing the voltage drop with time of the fuel cell stack is the most important point in providing a fuel cell power generation system with high power generation efficiency.

  The greatest cause of the voltage drop in the fuel cell stack is an increase in activation polarization due to a decrease in the activity of the oxidant electrode catalyst. A carbon-supported platinum catalyst in which platinum particles are supported on carbon particles is generally used for the oxidant electrode of the fuel cell stack. The catalyst of the oxidant electrode represented by a platinum catalyst generates an oxide film with the supply of the oxidant, and the catalytic activity gradually decreases. Accordingly, various methods for suppressing the voltage drop of the fuel cell stack by restoring the catalytic activity of the oxidant electrode have been proposed.

For example, in Japanese Patent Publication No. 8-24050 (Patent Document 1), the supply of the oxidant electrode to be supplied to the fuel cell stack without lowering the load current during power generation of the fuel cell power generation system is reduced. A method for restoring the voltage of a fuel cell stack is described. Patent Document 2 WO 01/0158 (Patent Document 2) describes a method of suppressing voltage drop by intermittently or locally depleting an oxidant during fuel cell power generation. Patent Document 3 Japanese Patent No. 3460793 (Patent Document 3) causes a fuel cell to be short-circuited at start-up to forcibly reduce the battery voltage from 0 V to 0.3 V for 1 to 10 seconds, thereby reducing CO poisoning. The method of solving is described. The method described in Patent Document 3 is to connect a fixed resistor to the fuel cell (short circuit), increase the load current density, and oxidize and remove the adsorbed CO due to an increase in the overvoltage of the fuel electrode. As a result, as the load current density increases, deficiency of the oxidant occurs, so that it is expected that the same effect as the techniques of Patent Document 1 and Patent Document 2 can be obtained. That is, the methods described in Patent Documents 1 to 3 described above are that the potential of the oxidant electrode is temporarily decreased by depleting the oxidant supplied to the oxidant electrode, and the voltage of the fuel cell stack is recovered. It is a common method. In these oxidant-deficient methods, the oxide film of the oxidant electrode catalyst is removed by reduction due to the decrease in the oxidant electrode potential, and the voltage can be recovered as the catalyst activity of the oxidant electrode is improved.
Japanese Patent Publication No. 8-24050 WO / 01/01508 Japanese Patent No. 3460793

  Factors that reduce the catalytic activity of the oxidant electrode, which has a significant effect on the performance of the fuel cell, include not only the formation of an oxide film on the catalyst by the oxidant, but also the presence of impurity molecules in the catalyst caused by the reaction gas and fuel cell components Adsorption is also mentioned. However, when using a voltage recovery method in which the oxidant supplied to the oxidant electrode is depleted, it is limited to the effect obtained by removing the oxide film from the oxidant electrode. There was a problem that the decrease could not be sufficiently suppressed.

  The present invention has been made to solve the above-described problems, and maintains the voltage recovery effect of the fuel cell stack over a long period of time, and the fuel cell power generation system operating method and fuel cell power generation exhibiting an excellent voltage drop suppression effect. The purpose is to provide a system.

In order to achieve the above object, the invention corresponding to claim 1 is provided with a fuel cell that generates power by supplying fuel and an oxidant to a fuel electrode and an oxidant electrode that are arranged with an electrolyte interposed therebetween, and the power generation output is loaded. In the fuel cell power generation system that can be supplied to the fuel cell, a first operating procedure for setting the output voltage of the fuel cell to less than 0.01 V during power generation of the fuel cell, and the load immediately after the first operating procedure. A method for operating a fuel cell power generation system, comprising: a second operation procedure for reducing a current supplied to the first current operation procedure from a load current before the first operation procedure.

  ADVANTAGE OF THE INVENTION According to this invention, the operating method of a fuel cell power generation system and a fuel cell power generation system which maintain the voltage recovery effect of a fuel cell stack over a long period of time and exhibit the outstanding voltage drop suppression effect can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
(Constitution)
FIG. 1 is a configuration diagram of a fuel cell power generation system showing a first embodiment of a fuel cell power generation system according to the present invention, in which solid lines indicate gas piping, and broken lines indicate connection diagrams of electrical wiring.

  This embodiment includes a fuel cell (fuel cell stack) 1 that generates power by supplying fuel and an oxidant to a fuel electrode 1a and an oxidant electrode 1b arranged with an electrolyte interposed therebetween, and the power generation output is supplied to an electric control device 3. The fuel cell power generation system that can be supplied to the external load 7 via the above has the following configuration.

  Immediately after the potential of the oxidant electrode 1a is first measured, for example, by measuring, for example, the potential detector 8, and immediately after the potential of the oxidant electrode 1b detected by the potential detector 8 is lowered to near the hydrogen standard potential of the fuel electrode 1b. The second controller, for example, the system controller 10 having a so-called voltage recovery operation function for raising the potential of the oxidizer electrode 1b to a potential higher than the potential during normal power generation is provided.

  The system control device 10 is composed of, for example, a microcomputer, and a program necessary for the operation of the fuel cell power generation system is stored in a memory included therein, and control commands are given to the reformer 2 and the air blower 5. It has become. Further, the system control device 10 is given a command for connecting or disconnecting (shut off) the fuel cell 1 with respect to the external load 7.

  As the fuel supplied to the fuel electrode 1a, for example, reformed hydrogen gas obtained by reforming the city gas 4 with the reformer 2 is used. As the oxidant supplied to the oxidant electrode 1b, for example, an oxidant gas composed of air in which air 6 is blown by an air blower 5 is used.

  The potential of the oxidizer electrode 1a may be calculated based on the average cell voltage (output voltage) of the fuel cell 1 without being measured by the potential detector 8.

(Action)
The operation of the fuel cell power generation system configured as described above will be described with reference to the flowchart of FIG. 2 and the time chart of FIG. In this system, the hydrogen concentration in the fuel is, for example, 78% on a dry basis, the average concentration of impurities contained in the air supplied to the oxidizer electrode 1b is, for example, 18 ppb in terms of sulfur oxide, and the nitrogen oxide is, for example, It is 46 ppb.

In such a system, for example, 100 hours have elapsed when power is supplied to the load 7 by the electric control device 3 so that the load current density is kept constant at 0.2 A / cm ² during normal power generation. Every time power generation is interrupted, a voltage recovery operation as shown below is performed. First, in a state where the reformed gas from the reformer 2 is supplied to the fuel electrode 1a, the oxidant (air) to the oxidant electrode 1b is stopped (S1), and the load current density is 0.2 A / cm ^2. Power generation continued under certain conditions. Then whether the potential P of the oxidant electrode is below the standard potential P _L of the fuel electrode is determined arithmetic processing circuit of the microcontroller (S2), when it is determined that satisfies the condition, and shut off the load (S3) Then, the supply of the oxidizing agent is resumed (S4). Thereafter, the arithmetic processing circuit determines whether or not the potential P of the oxidizer electrode becomes equal to or higher than the potential P _H during normal power generation (S5), and gives a connection command to the electric control device 3 when the condition is satisfied. Then, the fuel cell 1 and the load 7 are connected again (S6).

(effect)
By performing the voltage recovery operation as described above, the voltage drop rate of the fuel cell 1 can be reduced, so that a reduction in power generation efficiency of the fuel cell power generation system can be suppressed. As a result, it is possible to provide a fuel cell power generation system operating method and a fuel cell power generation system that maintain the voltage recovery effect of the fuel cell stack for a long period of time and exhibit an excellent voltage drop suppression effect.

(Second Embodiment)
(Constitution)
FIG. 4 is a configuration diagram of a fuel cell power generation system showing a second embodiment of the fuel cell power generation system according to the present invention, in which a solid line indicates a gas piping and a broken line indicates a connection diagram of electric wiring. This embodiment is provided with voltage detection means, for example, a voltage detector 9 for detecting the output voltage of the fuel cell (fuel cell stack) 1 shown in FIG. 1, and the detected value of the voltage detector 9 is, for example, a microcomputer as shown in FIG. Is input to the system control device 10a, and a predetermined calculation process is performed in the system control device 10a. A command is given to the reformer 2 and the air blower 5 according to the calculation processing result, or the electric control device 3 is It is configured to give a command.
The system control device 10a reduces or stops the flow rate of the oxidant supplied to the oxidant electrode 1 during power generation of the fuel cell 1, thereby setting the output voltage of the fuel cell detected by the voltage detector 9 to around 0V. Immediately after this, the oxidant is restored and the load 7 is shut off to thereby make the fuel cell voltage variable means for making the output voltage of the fuel cell 1 equal to or higher than a predetermined voltage.

(Action)
The operation of the fuel cell power generation system configured as described above will be described with reference to the flowchart of FIG. 5, the time chart of FIG. 6, and the characteristic diagrams of FIGS. Here, the hydrogen concentration in the fuel was 78% on a dry basis, and the average concentration of impurities contained in the air supplied to the oxidant electrode was 18 ppb in terms of volume for sulfur oxide and 46 ppb for nitrogen oxide.
In the fuel cell power generation system configured as described above, when the electric power supplied to the load 7 is controlled by the electric control device 3 so that the load current density is kept constant at 0.2 A / cm ² during normal power generation, The power generation is interrupted every time and a voltage recovery operation as shown below is performed. First, in a state where fuel (reformed gas) is supplied to the fuel cell 1 to the fuel electrode 1, the supply of oxidant to the oxidant electrode 1b is stopped (S1), and the load current density is constant at 0.2 A / cm ^2. Continued power generation. Next, the arithmetic circuit in the personal computer determines whether the average cell voltage of the fuel cell 1 is equal to or lower than the minimum voltage setting value V _L (= 0.01 V) (S7). If it is determined that the condition is satisfied, a command is given to the electric control device 3 to cut off the load from the fuel cell 1 (S3), and the supply of the oxidant is resumed (S4). Thereafter, it is determined whether the average cell voltage of the fuel cell 1 is equal to or higher than the maximum voltage setting value V _H (= 0.96 V) (S8). When this condition is satisfied, power generation is resumed, a command is given to the electric control device 3, a load is connected to the fuel cell 1, and the current density is controlled to be constant at 0.2A / cm ² (S6). .

Next, normal operation of the fuel cell power generation system configured as described above will be described. The fuel cell 1 is in a power generation state, that is, during power generation (in the fuel cell power generation state, hydrogen-rich reformed gas is supplied to the fuel electrode 1a, oxidant is supplied to the oxidant electrode 1b, and power is supplied to the load 7. When the oxidant supplied to the oxidant electrode 1b is stopped, the average cell voltage of the fuel cell 1 decreases. After the average cell voltage drops below the minimum voltage setting value V _L (= 0.01 V), when the load 7 is shut off and the supply of the oxidizing agent is restarted, the maximum voltage setting value V _H (= 0) near the open circuit voltage. .96V), the supply of power to the load 7 is waited until the average cell voltage of the fuel cell 1 rises to 0.96V. That is, in this embodiment, the voltage of the fuel cell 1 after the reduction operation before the voltage _{V R} to 0.01 V, rises to 0.96 V.

Here, since the average cell voltage of the fuel cell 1 is equivalent to the average value of the difference between the potential of the oxidant electrode 1b and the potential of the fuel electrode 1a, the potential of the oxidant electrode 1b subtracts the fuel electrode potential from the average cell voltage. Value. In the above operation, since sufficient hydrogen is supplied to the fuel electrode 1a, the fuel electrode potential is approximately 0 V in terms of the hydrogen reference potential. Therefore, if the oxidizer electrode potential was hydrogenated reference potential translation substantially equal to the change in the average cell voltage, varies from 0.96V vicinity After reduction operation from the previous V _R to 0.01V vicinity. FIG. 6 shows a timing chart of the potential change of the oxidizer electrode and various operations.

  Here, paying attention to the potential change amount of the oxidant electrode 1a of the fuel cell 1, it was found that the impurity molecules adsorbed to the oxidant electrode 1b of the fuel cell 1 can be desorbed by increasing the potential change amount. An example is shown in FIG. FIG. 7 shows the relationship between the amount of change in cell voltage and the catalyst coverage during the recovery operation after supplying sulfur dioxide containing air, which has a great influence on the battery characteristics among impurity molecules, to the oxidizer electrode for 200 hours of power generation. Is shown. For acceleration evaluation, the sulfur dioxide concentration in the air was set to 40 ppb on a dry basis in consideration of the environmental standard value of the sulfur oxide concentration contained in the air (daily average 40 ppb). As shown in FIG. 7, the greater the amount of change in the cell voltage in the state in which the hydrogen-rich gas is supplied to the fuel electrode, that is, the greater the change in the oxidant electrode potential, the more the impurity molecules adsorbed on the oxidant electrode catalyst are oxidized. It can be seen that the catalyst activity is restored.

  Here, the action has been described with sulfur dioxide as a representative, but the same effect can be obtained with other sulfur compounds, nitrogen oxides, ammonia, organic solvents, and the like.

  Therefore, according to the present embodiment, since the potential change amount of the oxidant electrode during the recovery operation can be increased to about 0.95 V per cell, the desorption of impurity molecules adsorbed on the oxidant electrode is promoted, The catalytic activity of the oxidizer electrode can be recovered.

(effect)
FIG. 8 is a diagram showing the effect of the present embodiment, and shows the time variation of the average cell voltage of the fuel cell 1. In addition, as a conventional example, the time variation of the average cell voltage when the oxidant is stopped during the power generation of the fuel cell 1 and the voltage is lowered to around 0 V and then immediately shifted to the normal power generation is also shown. In the case of the conventional example, the amount of voltage change due to the recovery operation was about 0.8 V per cell. As apparent from FIG. 8, the voltage drop rate of the conventional example (shown by a broken line) is 17.0 μV per hour, whereas the voltage drop rate of the present embodiment (example: shown by a solid line) is 1 hour. It was 8.94 μV per unit, and could be reduced to 53% compared to the conventional example. That is, according to the present embodiment, the voltage drop rate of the fuel cell 1 can be reduced, so that a reduction in power generation efficiency of the fuel cell power generation system can be suppressed.

  In the present embodiment, an example in which the load current density is made constant in order to compare the voltage drop speed under the same condition is shown, but it is not always necessary to make the load current density constant, and in the fuel cell system in which the load current fluctuates. The same effect can be obtained.

(Modification of the second embodiment)
FIG. 9 is a flowchart for explaining a modified example of the above-described second embodiment, and is a driving method including the following two operation procedures. That is, the first operating procedure for setting the output voltage of the fuel cell 1 to around 0 V during power generation of the fuel cell 1 and the current supplied to the load immediately after the first operating procedure are the load currents before the first operating procedure. It is the operating method of a fuel cell power generation system including the 2nd operation procedure to reduce more.

This will be specifically described with reference to FIG. With the fuel (reformed gas) supplied to the fuel cell 1 to the fuel cell 1, the oxidant (air) of the oxidant electrode 1b is stopped (S1), and the load current density is constant at 0.2 A / cm ^2. Continued power generation. Next, it is determined whether or not the average cell voltage of the fuel cell 1 is below the minimum voltage setting value V _L (= 0.01 V) (S7). The operation procedure so far is the same as FIG. In S7, after the battery voltage falls below the minimum voltage setting value V _L , the load current is reduced to 0.01 A / cm ² and then the oxidant supply is resumed (S7a). Thereafter, it is determined whether or not the average cell voltage of the fuel cell 1 exceeds the maximum voltage setting value V _H (= 0.90 V) (S8). After the average cell voltage exceeds the maximum voltage setting value V _{H, the} load current is set by the electric control device 3. In this case, the current density is controlled to be constant at 0.2 A / cm ² (S8a).

  By carrying out the operation method as described above, the amount of change in the oxidant potential is about 0.9 V, which is slightly smaller than that of the second embodiment, but has the same effect as that of the second embodiment. It is done. The modification shown here is an operation method that does not cut off the load current during the voltage recovery operation, and it goes without saying that this modification is also included in the present invention.

(Third embodiment)
(Constitution)
As shown in FIG. 10, the second embodiment includes the fixed resistor 11 and the switches 12a and 12b, and the system controller 10a can switch between the load 7 and the fixed resistor 11 by opening and closing the switches 12a and 12b. It is a thing.

With this configuration, as in the second embodiment, the electric power supplied to the load 7 is controlled by the electric control device 3 so that the load current density is constant at 0.2 A / cm ² during normal power generation. During the operation, the normal power generation was interrupted every 100 hours and a voltage recovery operation as shown below was performed.

(Action)
As shown in FIG. 11, with the fuel cell 1 supplied with fuel (reformed gas) to the fuel electrode 1a and oxidant (air) to the oxidant electrode 1a, the external load 7 is shut off (S9), and the fixed resistance 8 is connected (S10). Next, the oxidant to the oxidant electrode 1b is stopped (S1), and then the system controller 10a determines whether the average cell voltage of the fuel cell 1 is below the minimum voltage set value V _L (= 0.01V). Is determined (S7).

After the average cell voltage falls below the minimum voltage set value _VL , the fixed resistor 11 is shut off (S11), and the oxidant supply is resumed (S4). Thereafter, the arithmetic circuit determines whether or not the average cell voltage of the fuel cell 1 exceeds the maximum voltage setting value V _H (= 0.96 V) (S8). When it is determined that the average cell voltage exceeds the maximum voltage setting value V _H , the power generation of the fuel cell 1 is resumed, and the electric control device 3 controls the current density to be constant at 0.2 A / cm ^2. .

(effect)
When the voltage recovery operation procedure as described above is performed, the load current is naturally reduced as the electromotive force of the fuel cell 1 is reduced when the residual oxygen in the oxidant electrode 1b is consumed by connecting to the fixed resistor 11. In addition, the control of the load current becomes unnecessary, and the control of the electric control device 3 can be simplified. Other functions and effects are the same as those of the second embodiment.

(Fourth embodiment)
(Constitution)
The present embodiment is similar to the above-described second embodiment. The difference is the configuration of the electric control device 3a shown in FIG. 12, and the other points are the same as those of the second embodiment. The electric control device 3a is an electric control device with a forced current mode having a function of forcing a predetermined current to flow even when the electromotive force of the fuel cell 1 is low.

(Action)
FIG. 13 is a diagram for explaining the operation. When the system controller 10a shown in FIG. 12 performs the voltage recovery operation procedure in the same manner as in the previous embodiment, after the oxidant is stopped to the oxidant electrode 1b (S1), the constant load current is maintained regardless of the electromotive force of the fuel cell. It becomes possible to flow.

(effect)
Therefore, the rate of consumption of residual oxygen in the oxidizer electrode 1b is increased, and as a result, the time required for operation can be shortened.

  Note that the average cell voltage of the fuel cell when the residual oxygen is consumed is maintained at a voltage lower than 0 V by an amount corresponding to the overvoltage of the fuel electrode determined by the load current at that time.

(Fifth embodiment)
(Constitution)
FIG. 14 is a block diagram showing a fifth embodiment of the fuel cell power generation system according to the present invention, in which solid lines indicate gas piping, and broken lines indicate connection diagrams of electrical wiring. In the fuel cell power generation system of the second embodiment described above, the DC voltage generator 13 and the switch 14 are provided,
The negative electrode 13a and the positive electrode 13b of the DC voltage generator 13 can be connected to the fuel electrode 1a and the oxidant electrode 1b of the fuel cell 1, respectively, and the switch 14 is opened and closed by the system controller 10a. .

  The system controller 10a of this embodiment reduces the output of the fuel cell detected by the voltage detector 9 by reducing or stopping the flow rate of the oxidant supplied to the oxidant electrode 1b during power generation of the fuel cell 1. Is a fuel cell voltage varying means that cuts off the load immediately after this, and connects the DC voltage generator 13 to the fuel cell 1 to make the output voltage of the fuel cell 1 higher than a predetermined voltage.

(Action)
The operation of the fifth embodiment configured as described above will be described with reference to the flowchart of FIG. 15, the time chart of FIG. 16, and the characteristic diagram of FIG. In the fuel cell power generation system having the configuration shown in FIG. 14, during normal power generation, electric power supplied to the load 7 is controlled and controlled by the electric control device 3 so that the load current density is constant at 0.2 A / cm ^2. During the operation, the normal power generation was interrupted every 100 hours and the voltage recovery operation procedure as shown below was performed. First, in a state where fuel is supplied to the fuel electrode 1a of the fuel cell 1, the supply of the oxidant is stopped (S1), and the power generation is continued under the condition that the load current density is constant at 0.2 A / cm ² . Next, the arithmetic circuit described above determines whether or not the average cell voltage of the fuel cell 1 is equal to or lower than the minimum voltage setting value V _L (= 0.01 V) (S12). After determining the average cell voltage is equal to or less than the lowest voltage setting value V _L, and blocks the load 7 (S13), then advance the highest voltage DC power supply set voltage of the unit cell number per set to a voltage higher than the set value V _H A DC power supply applied to V _S (= 0.97 V) is connected (S14). Thereafter, the arithmetic circuit determines whether or not the average cell voltage of the fuel cell 1 exceeds the maximum voltage setting value V _H (= 0.96 V) (S15). It is determined whether or not 5 seconds have elapsed after the average cell voltage exceeds the maximum voltage setting value V _H (S16). After 5 seconds, the DC voltage generator 13 is shut off and oxidation is performed in the same manner as in the previous embodiment. The agent is supplied (S4), and the load (rated load) 7 is connected (S6). In this way, the fuel cell 1 is restarted, and the electric control device 3 controls the current density to be constant at 0.2 A / cm ² .

Next, normal operation of the fuel cell power generation system configured as described above will be described. When the fuel cell stack is in a power generation state, that is, when the hydrogen-rich reformed gas is supplied to the fuel electrode 1a, the oxidant is supplied to the oxidant electrode 1b, and power is supplied to the load 7, When the oxidant supplied to the oxidant electrode 1b is stopped, residual oxygen in the oxidant electrode 1b is consumed, and the potential of the oxidant electrode 1b is eventually lowered to the hydrogen reference potential. At this time, the average cell voltage of the fuel cell 1 decreases until it falls below 0.01 V, which is the minimum voltage setting value _VL . Thereafter, the negative electrode 13a and the positive electrode 13b of the DC voltage generator 13 having the average cell voltage set so that the DC power supply setting voltage V _S per unit cell number is 0.96 V are used as the fuel electrode 1a and the oxidant electrode of the fuel cell 1. By connecting each to 1b, applying a DC voltage to the fuel cell 1 and waiting for a holding time T (= 5 seconds) after the average voltage of the fuel cell 1 exceeds 0.95V which is the maximum voltage setting value V _H The oxidant electrode potential varies from 0.01V to 0.96V. FIG. 16 shows the time change of the potential of the oxidizer electrode.

(effect)
According to this embodiment, since the voltage drop rate of the fuel cell stack can be reduced as in the second embodiment, a reduction in system efficiency of the fuel cell power generation system can be suppressed.

Furthermore, in this embodiment, the oxidant electrode potential can be arbitrarily set by changing the DC power supply setting voltage V _S and the maximum voltage setting value V _H per unit cell number in FIGS. Therefore, it is possible to maintain a high potential of 1 V or higher, which is an oxidizer electrode potential in a general open circuit.

FIG. 17 shows the voltage change of the embodiment shown in FIG. 7 and the change of the catalyst coverage when _VH is changed using the DC voltage generator 13 of this embodiment. As a result, even when poisoning of impurities such as sulfur oxides becomes a problem, it can be understood that the problem can be almost eliminated by setting V _H in FIG. 15 to 1.2 V or more. In the usual range, the catalyst coverage by the impurity molecules on the oxidizer electrode is preferably 20% or less, and is preferably 0.9 V or more. Further, if it is 1.6 V or more, the activity of the catalyst is lowered by sintering of the catalyst, so it is preferable to set it to 1.6 V or less. Therefore, the optimum setting voltage of the DC voltage generator is 0.9V or more and 1.6V or less.

  That is, according to the present embodiment, the voltage drop rate of the fuel cell stack can be effectively reduced even when the influence of impurities is large, so that a reduction in system efficiency of the fuel cell power generation system can be suppressed.

(Sixth embodiment)
(Constitution)
This embodiment is configured as shown in FIG. 18, and the difference from the second embodiment is a system control apparatus 10b. Specifically, the system control device 10b supplies the fuel electrode 1a with fuel and connects the fuel cell 1 with a load 7 at the start of power generation (starting up) of the fuel cell 1, thereby adjusting the voltage of the fuel cell 1. This is a fuel cell voltage variable means for setting the voltage of the fuel cell 1 to a predetermined voltage or higher by supplying the oxidant to the oxidant electrode 1b immediately thereafter and cutting off the load 7 at around 0V. Except for the points described above, the second embodiment is the same as the second embodiment.

(Function)
Hereinafter, an operation procedure when the system is started will be described with reference to FIG. The arithmetic circuit included in the system controller 10b described above confirms the supply stop of the oxidant (S18). When the supply stop confirmation of the oxidant is performed, a supply command for the reformed gas as a fuel is given (S19), and a load connection is made (S21). In S18, when the supply of oxidant is not confirmed to be stopped, the supply of oxidant is stopped (S20).

After connecting the load to the fuel cell 1 in this way, it is determined by the arithmetic circuit whether the average cell voltage of the fuel cell 1 is equal to or lower than 0 V which is the minimum voltage setting value _VL (S22). When it is determined that the average cell voltage has become equal to or lower than the minimum voltage set value V _L , the load is cut off (S23), the oxidizing agent is supplied (S24), and then the average cell voltage is set to the maximum voltage set value V _H (= 0. It is judged whether it exceeds (95V) (S25). If it is determined that the average cell voltage has exceeded the maximum voltage setting value V _H, connects the rated load in the fuel cell 1 (S26).

(effect)
As described above, even when this operation is performed at the time of starting the system, the same effect as in the second embodiment can be obtained.

  FIG. 20 shows the relationship between the carry-out speed of fluoride ions released from the system together with the reaction gas due to deterioration of the fluorine-based electrolyte membrane (normal power generation is 1) and the battery temperature during the recovery operation. . Therefore, when durability of the electrolyte membrane is required, it is preferable that the temperature of the fuel cell stack at the time of the recovery operation is low. By performing the operation at a fuel cell stack temperature of 25 ° C. or less during the operation, the membrane is deteriorated. Is suppressed. That is, it is optimal to perform the recovery operation before the temperature of the fuel cell 1 is raised.

(Seventh embodiment)
This embodiment is an example when the operation procedure is performed at the time of system startup as shown in the flowchart of FIG. 21. The difference from FIG. 19 is that the following is performed after the load is interrupted (S23) in FIG. The operation procedures S27 to S31 are performed. That is, after S23, a DC voltage generator is connected to the fuel cell 1 (S27), and the average cell voltage exceeds the maximum voltage setting value V _H (= 0.95V), as in the embodiment of FIG. 14 described above. Whether or not (S28). If it is determined that the average cell voltage has exceeded the maximum voltage setting value V _H, the DC voltage generator to shut off (S29), it performs oxidant supply (S30), connects the rated load (S31).

    According to the present embodiment, the same effects as those of the sixth embodiment described above can be obtained.

(Eighth embodiment)
This embodiment is an example when the operation procedure is performed at the start of the system stop operation as shown in the flowchart of FIG. First, the arithmetic circuit confirms fuel supply (reformed gas supply) or load connection (S32). When this is confirmed, the oxidant is stopped (S33), and then the average cell voltage becomes the lowest voltage setting value V. It is determined whether or not _L is 0 V or less (S35). If it is determined that this condition is satisfied, the load is cut off (S36), the oxidizing agent is supplied (S37), and then the average cell voltage is set to the maximum voltage setting value _VH (= 0.95V). It is determined whether it exceeds (S38). If it is determined that the average cell voltage exceeds the maximum voltage setting value _VH , the supply of oxidant is stopped (S39), and the fuel supply (reformed gas supply) is stopped (S40). Note that when the fuel supply or the load connection is not confirmed in S32, the stop operation is terminated (S34).

  As in the embodiment described above, even when this operation is performed when the system is stopped, the same effects as those of the first embodiment can be obtained. Furthermore, in the case of a power generation system equipped with a reformer, the power supplied to the load changes greatly during voltage recovery operation, so the reformer may go out of the predetermined temperature range and the CO concentration may increase. It is necessary to control the device. However, since the increase in CO does not become a problem during the stop operation, the control can be simplified.

(Ninth embodiment)
In the present embodiment, when the operation procedure shown in FIG. 23 is performed in the fuel cell power generation system of the second embodiment described above, the oxygen partial pressure of the oxidant electrode is reduced when the stop operation is completed as shown in FIG. This lowers the oxidant electrode potential, which is more preferable because sintering of the catalyst during storage at rest is suppressed.

23 differs from FIG. 22 in that after S38, load connection is performed (S42), oxidant supply is stopped (S43), and then the average cell voltage becomes 0 V or less, which is the lowest voltage setting value V _L. Is determined (S44). If it is determined that this condition is satisfied, the load is cut off (S45), and the fuel supply (reformed gas supply) is stopped (S46). As described above, even when this operation is performed when the system is stopped, the same effects as those of the second embodiment can be obtained.

(Tenth embodiment)
In this embodiment, in the second fuel cell power generation system described above, an operation procedure was performed when the system was stopped as shown in the flowchart of FIG. 25 differs from FIG. 22 in that a direct current voltage generator is connected to the fuel cell 1 after S36 (S47), and whether the average cell voltage exceeds the maximum voltage setting value V _H (= 0.95V). Is determined (S48). If it is determined that the average cell voltage has exceeded the maximum voltage setting value V _H, the DC voltage generator to shut off (S49), a fuel supply (reformed gas supply) performs stop (S50). As described above, even when this operation is performed when the system is stopped, the same effects as those of the second embodiment can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram for demonstrating 1st Embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating operation | movement of embodiment of FIG. The timing chart for demonstrating operation | movement of embodiment of FIG. The schematic block diagram for describing 2nd Embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating operation | movement of embodiment of FIG. The timing chart for demonstrating operation | movement of embodiment of FIG. The figure for demonstrating the effect of embodiment of FIG. The figure for demonstrating the effect of embodiment of FIG. The flowchart for demonstrating the modification of 2nd Embodiment. The schematic block diagram for demonstrating 3rd Embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating operation | movement of embodiment of FIG. The schematic block diagram for demonstrating 4th Embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating the operation | movement of embodiment of FIG. The schematic block diagram for demonstrating 5th Embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating operation | movement of embodiment of FIG. The timing chart for demonstrating the operation | movement of embodiment of FIG. The figure for demonstrating the effect of embodiment of FIG. The schematic block diagram for demonstrating 6th, 7, 8, 9, 10 embodiment of the fuel cell power generation system of this invention. The flowchart for demonstrating the operation | movement of 6th Embodiment. The figure for demonstrating the effect of embodiment of FIG. The flowchart for demonstrating operation | movement of 7th Embodiment. The flowchart for demonstrating the operation | movement of 8th Embodiment. 10 is a flowchart for explaining the operation of the ninth embodiment. The timing chart for demonstrating the operation | movement of embodiment of FIG. The flowchart for demonstrating operation | movement of 10th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack, 1a ... Fuel electrode, 1b ... Oxidant electrode, 2 ... Reformer 3, 3a ... Electric control device, 4 ... City gas, 5 ... Air, 6 ... Air blower, 7 ... External load, DESCRIPTION OF SYMBOLS 8 ... Potential detector 9 ... Voltage detector 10, 10a, 10b ... System controller, 11 ... Fixed resistance, 12a, 12b ... Switch, 13 ... DC voltage generator, 13a ... DC voltage generator negative electrode 13b ... DC Voltage generator positive electrode, 14 ... switch.

Claims (1)

A fuel cell power generation system comprising a fuel cell that generates power by supplying fuel and an oxidant to a fuel electrode and an oxidant electrode arranged with an electrolyte interposed therebetween, and capable of supplying the power generation output to a load,
A first operating procedure for setting the output voltage of the fuel cell to less than 0.01 V during power generation of the fuel cell, and a current supplied to the load immediately after the first operating procedure before the first operating procedure. A method for operating a fuel cell power generation system, comprising a second operation procedure for reducing the load current from the load current of the fuel cell.

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