JPS60177565A - Operation method of fuel cell power generating system - Google Patents

Abstract

PURPOSE:To prevent deterioration, caused by aggregation, of noble metal catalyst by controlling cell operation so as not to exceed a setting voltage of unit cell at which a noble metal catalyst is deteriorated by aggregation in low load operation. CONSTITUTION:An electric signal sent from an output detector 11 mounted in a cell main body 1 is inputted into a computing element 13, and an instruction is sent from the computing element 13 to a rotating controller 12 of a compressor 2c in an air supply line 2b by pressure pattern corresponding to a setting load. A setting pressure signal is sent to a cell inlet pressure controller 14 and a pressure control valve 15 is controlled so that setting pressure is kept. Operating pressure is controlled in low load operation so that unit cell voltage is made small by decreasing pressure. Thereby, cell voltage in low load operation can be decreased, and deterioration, caused by aggregation, of a noble metal catalyst in low load operation can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of operating a fuel cell power generation system.

[Background of the invention]

FIG. 1 shows a conventional example of a general fuel cell power generation system. As shown in the figure, the fuel cell power generation system includes a battery body 1, a reaction gas supply system 2 that supplies and discharges reaction gas to and from the battery body 1, that is, a fuel reforming supply system 2a that supplies and discharges fuel, and a fuel reforming supply system 2a that supplies and discharges air. Exhaust air supply system 2b
, a temperature control system 3 for controlling the temperature of the battery body 1, and the like. The battery body 1 is composed of a single cell (none of which is shown) in which an electrolyte (acidic electrolyte) is held between a pair of gas diffusion electrodes having a noble metal catalyst (platinum or a platinum-based alloy). In the figure, 4.5 is a steam separator, 6 is a water treatment device, 7 is an air supply line, 8 is a fuel supply line, 9 is a fuel reformer, and 10 is a shift converter.

Examples of general current density-voltage characteristics and corresponding current density-output characteristics of a fuel cell in a fuel cell power generation system configured as described above are shown in FIGS. 2 and 3. Figure 2 shows the change characteristics of the single cell voltage due to current density, with the vertical axis representing the single cell voltage and the horizontal axis representing the current density. The output of a single cell is taken, and the horizontal axis represents the current density to show the change characteristics of the output of the single cell depending on the current density.

As shown in both of these figures, in a fuel cell, the single cell voltage is high when the load is low, and the voltage is low when the load is high. In addition, in FIG. 2, S is the rated point.

By the way, it is known that noble metal catalysts used in electrode catalysts, which are catalysts for gas diffusion electrodes, aggregate in the high temperature and high potential atmosphere of acidic electrolytes, causing deterioration of catalytic activity. In the case of 0.79V/
The cell is said to have an allowable voltage V1 of a single cell. Therefore, as is clear from the figure, when the output is under low load (01 or less), the allowable voltage v1 may be exceeded, but the allowable voltage v1
If this value is exceeded, the noble metal catalyst will coagulate and deteriorate.

In order to solve this problem, in conventional fuel cell power generation systems, a dummy load is installed on the DC or AC side, and the single cell output is generated at 01 or higher, which reaches the cell allowable voltage v1, regardless of the required load of the system. This was to prevent the battery voltage from becoming too high. For this reason, if the required load is lower than the single cell output 01, power generation will be wasted by the difference υ, resulting in a decrease in thermal efficiency. Furthermore, even when this difference, that is, surplus, is consumed within the fuel cell power generation system, there are applications in which it does not contribute to thermal efficiency, resulting in poor efficiency at low loads. In addition, in the event of an accident on the grid side, the DC side remains ready to transmit power at any time, in what is called a hot standby mode, and the fuel cell is operated with a protective dummy load, that is, the lowest load. There was a problem that the load resistance value was large.

[Purpose of the invention]

The present invention has been made in view of the above points, and is a fuel that makes it possible to prevent cohesive deterioration of precious metal catalysts at low loads. The purpose of this invention is to provide a method for operating a battery power generation system.

[Summary of the invention]

That is, the present invention provides a battery main body composed of a single cell that holds an electrolyte between a pair of gas diffusion electrodes having a noble metal catalyst, a reaction gas supply system for supplying and discharging reaction gases of an oxidizer and fuel to and from the battery main body, respectively, and the above-mentioned. A specific fuel cell power generation system equipped with a temperature control system that controls the temperature of the battery body,
The fuel cell power generation system is characterized in that during low load operation, the fuel cell power generation system is operated with a control means that does not exceed the permissible voltage of the single cell at which the precious metal catalyst starts coagulating and deteriorating. The noble metal catalyst can now be operated at a battery voltage that does not cause agglomeration degradation.

The inventor investigated what kind of control means would be effective, and focused on operating pressure, reaction gas partial pressure, gas flow rate (gas utilization rate), operating temperature, etc. Fuel cell power generation systems generally operate at higher pressures (4 to 6 Kf/i) than normal pressure.
An example of the pressure dependence of the single cell voltage when the current density is constant is when the single cell voltage is varied vertically and horizontally.
This is shown in FIG. 4, where the rollover is plotted as a logarithm of the pressure.

As shown in the figure, when the current density is constant, the single cell voltage increases in proportion to the logarithm of the pressure. Therefore, when the current density-voltage characteristics and current density-output characteristics of a cell are shown using pressure as a parameter as shown in FIGS. 2 and 3 above, they are shown in FIGS. 5 and 6. Figure 5 shows the single cell voltage in the vertical and horizontal directions using pressure as a parameter, and the current density on the horizontal axis to show the pressure dependence of the current density-voltage characteristic. Figure 6 shows the pressure dependence of the current density-voltage characteristic with pressure as a parameter and the vertical axis shows the output. υ, current density is plotted on the horizontal axis, and the current density-output pressure dependence corresponding to FIG. 5 is shown. As is clear from these two figures, the rated pressure curve pi is 25 cm (
When operating at a low load at point B in FIG. 6, the single cell voltage becomes the voltage at point A on the rated pressure curve p1 in FIG. 5, exceeding the cell allowable voltage ■1. Therefore, we set a pressure (point D on the pressure curve p2 in Figure 6) that does not exceed the allowable voltage Vs of the single cell at a low load of 25 cm, and if we operate below this pressure, the single cell voltage will be the pressure shown in Figure 5. Since the voltage is below the 0 point of the curve p2 and does not exceed the allowable voltage Vl even under low load, agglomeration and deterioration of the noble metal catalyst can be prevented.

Next, we investigated the partial pressure of the reaction gas. In general, phosphoric acid fuel cells use air as the oxidant and hydrogen-rich reformed gas obtained by reforming natural gas whose main component is methane as the fuel.The cell voltage is shown in Figure 7. It changes depending on the oxygen concentration in the air and the hydrogen concentration in the fuel. FIG. 7 shows the change characteristics of the single cell voltage depending on the oxygen and hydrogen concentrations when the current density is constant, with the vertical axis representing the single cell voltage and the horizontal axis representing the logarithm of the oxygen and hydrogen concentrations.

As is clear from the figure, the single cell voltage is proportional to the logarithm of the oxygen and hydrogen concentrations, and increases along the straight line G for oxygen and the straight line H for hydrogen. Therefore, as in the case of pressure, a relationship characteristic curve (not shown) similar to that shown in Figs. The optimal hydrogen concentration, oxygen concentration, or a combination thereof at low loads can be determined.

Furthermore, we investigated the gas flow rate. In fuel cells, reactant gases such as oxygen and hydrogen are supplied into the cell, which is greater than the theoretical amount of gas calculated from Faraday's law required to draw an actual current. The ratio between this theoretical value and the actual gas supply amount is called the gas utilization rate, and the relationship between this gas utilization rate and the single cell pressure is shown in FIG. This shows the change characteristics of the single cell voltage depending on the gas utilization rate or gas flow rate when the current density is constant, with the cell voltage on the vertical axis and the gas utilization rate and gas flow rate on the horizontal axis. However, the gas utilization rate increases as it goes to the right in the diagram, and the gas flow rate decreases as it goes to the right in the diagram. As is clear from the figure, the single cell voltage decreases as the gas flow decreases, as shown by curve GO1 for oxygen and curve H6 for hydrogen, and also decreases as the gas utilization rate increases. Therefore, in this case as well, the same relational characteristic curves (not shown) as in Figs. 5 and 6 above can be obtained using these gas flow rates or gas utilization rates as parameters, as in the case of pressure. Similar techniques can be used to determine optimal air utilization, fuel utilization, or a combination thereof at low loads.

Furthermore, we investigated the battery temperature, which is the operating temperature.

The electrochemical reaction in a fuel cell is an exothermic reaction, and a cooling system is provided to keep the cell temperature constant. Figure 9 shows the relationship between cell voltage and cell temperature. . Figure 9 shows the relationship between battery temperature and voltage, with battery voltage on the vertical axis and battery temperature on the horizontal axis.As is clear from the figure, the battery voltage varies within a certain temperature range. Increases in proportion to battery temperature. Therefore, in this case as well, the battery temperature is used as a parameter as in the case of the above-mentioned pressure.
A relationship characteristic curve (not shown) similar to that shown in FIG. 6 and FIG. 6 is obtained, and the battery temperature that suppresses the rise in battery voltage at low loads can be determined using the same method as in the case of pressure.

For these reasons, control means for controlling pressure, reaction gas partial pressure, gas flow rate, operating temperature, etc. are effective as control means to prevent the noble metal catalyst from exceeding the permissible voltage of the cell, which causes coagulation deterioration during low-load operation. It has been confirmed that if the system is operated with this control means, the system can be operated efficiently even during low load operation without coagulating and deteriorating the precious metal catalyst. Therefore, in the present invention, the fuel cell power generation system is operated with a control means that does not exceed the permissible voltage of the single cell at which the noble metal catalyst starts to coagulate and deteriorate during low load operation. By doing so, it is possible to obtain a method of operating a fuel cell starting system that makes it possible to prevent cohesive deterioration of the precious metal catalyst during low load conditions.

[Embodiments of the invention]

The present invention will be explained below based on the illustrated embodiments. FIG. 10 shows a control means according to an embodiment of the present invention. Note that parts that are the same as those in the prior art are designated by the same reference numerals, and explanations thereof will be omitted. In this embodiment, the above operating pressure is used for the control means and the pressure of the air supply system 2b is reduced by □.

That is, an output detector 11 was provided in the battery body 1, a rotation speed control device 12 was provided in the compressor 2C of the air supply system 2b, and an arithmetic unit 13 was provided between the rotation speed control device 12 and the output detector 11. . By doing this, the electrical signal from the output detector 11 attached to the battery body 1 is inputted to the computing unit 13 by the electrical signal circuit indicated by the dotted line in the figure, and the above-mentioned method is received from the computing unit 13 in advance. (Method when considering pressure as a control means) A pressure pattern corresponding to the set load is used to issue a rotation speed command to the rotation speed control device 12 of the compressor 2C, and to the battery inlet pressure control device 14. A signal of the set pressure is output, and the pressure adjustment valve 15
The pressure is controlled to the set pressure by Further, when a pre-scheduled low-load operation command is input from the central control system 16 to the computing unit 13, the operating pressure is similarly controlled by controlling the rotational speed of the compressor 2C.

An example of the input/output characteristics of this arithmetic unit 13 is shown in FIG. This shows the change characteristics of battery pressure and single cell voltage due to battery output, with battery pressure and single cell voltage plotted on the vertical axis and battery output plotted on the horizontal axis. As shown in the single cell voltage curve iL on the battery pressure curve, the battery pressure is set to be low and the single cell voltage is set to be low during low load. By controlling the operating pressure in this way, it is possible to lower the cell voltage during low loads on p1, and this fuel cell power generation system has made it possible to prevent cohesive deterioration of precious metal catalysts during low loads. You can learn how to drive.

Although there is no compressor in the fuel reforming supply system of a general fuel cell power generation system, it is synchronized with the air supply system,
Pressure control can be performed by controlling the source pressure of input raw material gas depending on the load. In addition, the fuel reforming supply system has the effect of increasing the efficiency of hydrogen generation at low pressure, allowing low-load operation while maintaining high efficiency while preventing deterioration of the precious metal catalyst.

FIG. 12 shows control means of another embodiment of the invention. This example uses the above-mentioned reactive gas partial pressure as the control means, and the gas discharged from the battery body 1 is recycled again to the inlet of the battery body 1 to reduce the concentration of the reactive gas components. It is.

That is, an output detector 11 and a calculator 13a are connected in series to the battery body 1, a stop pulp 17 is connected in series between the calculator 13a and the steam/water separator 4, and a stop pulp 17 is connected in series between the stop pulp 17 and the air supply line 7. Recycle blower 18,
The flow meter 19 and the flow control pulp 20 are connected to this flow meter 1.
9 and the computing unit 13a, a flow rate control device 21 was provided, respectively.

By doing this, the air normally supplied from the air supply line 7 leaves the battery body 1 by the electrical signal circuit indicated by the dotted line in the figure, and after the generated water is removed by the steam/water separator 4, the fuel is reformed. However, when the output detector 11 detects that the battery main body 1 is in low-load operation, or a preliminary command to reduce the load is sent from the central control system 16 to the calculator 13a, the power supply is stopped. The pulp 17 opens, the recycle blower 18 operates, and the flow meter 19 and flow control device 21 operate according to the recycle gas amount command from the computing unit 13H according to the load.
The amount of recycle, that is, the oxygen concentration, is automatically controlled by the flow rate control pulp 20.

FIG. 13 shows an example of the input/output of the arithmetic unit 13a, and FIG. 14 shows the corresponding oxygen concentration in the supplied air. In other words, in Figure 13, the vertical axis represents the recycle ratio of the reactant gas, and 9.
The horizontal axis shows the battery output and the relationship between the battery output and the recycling ratio of the reaction gas. Figure 14 shows the relationship between the battery output and the reaction gas recycling ratio, with the vertical axis representing the oxygen concentration in the supplied air and the horizontal axis representing the battery output. This figure shows the change characteristics of oxygen concentration depending on battery output.

As shown in the figure, the exhaust gas is recycled to reduce the concentration of oxygen, which is a reactive gas, at low loads. In this way, by recycling the exhaust gas and lowering the concentration of reaction gas at low loads, it becomes possible to lower the battery voltage at low loads, producing the same effect as in the case described above. be able to.

In this embodiment, the case of the air supply line has been described, but the fuel supply line can also be subjected to recycling control in the same manner.

FIG. 15 shows control means of still another embodiment of the present invention. In this example, the partial pressure of the reactant gas is used as the control means as in the case described above, but the concentration of the components of the reactant gas is lowered without recycling. In the fuel supply system shown in the same figure, in the fuel supply line 8, raw material gas such as natural gas is reformed by adding steam in the fuel reformer 9, and becomes a hydrogen-rich gas. Further, the gas is supplied to the battery main body 1 through a shift converter 10 for removing carbon oxide, a heat exchanger 22, and a steam separator 5 for increasing the hydrogen concentration by removing water from the gas. The gas temperature in this steam-water separator 5 is controlled by the amount of cooling water 23 supplied to the heat exchanger 22,
The lower the gas temperature in the steam/water separator 5 is, the higher the hydrogen concentration can be obtained. By increasing the temperature in the steam separator 5, the water vapor concentration in the fuel can be kept high and the hydrogen concentration can be lowered. Now, since the output detector 11 and the arithmetic unit 13b are installed in series with the battery body 1, how can the output detector 11 detect that the battery body 1 is in low-load operation using the electrical signal circuit indicated by the dotted line in the figure? When the advance command for load reduction is sent from the central control system 16 to the computing unit 13b, the temperature controller 24 and The temperature of the steam water separator 5 is raised by the cooling water flow rate regulating pulp 25.

An example of the input and output of this arithmetic unit 13b is shown in FIG.
This shows the temperature change of the steam/water separator depending on the battery output, with the vertical axis representing the temperature of the steam/water separator and the horizontal axis representing the battery output. As is clear from the figure, the temperature of the steam/water separator is set to be high when the load is low. In this way, by controlling the temperature of the steam-water separator at the fuel inlet and lowering the hydrogen concentration in the fuel, the battery voltage at low loads can be lowered, which is different from the case described above. Similar effects can be achieved.

FIG. 17 shows control means of still another embodiment of the present invention. This example is a case where the above-mentioned gas flow rate (gas utilization rate) is used. Air from the air supply line 7 is supplied to the battery body 1 through a gas flow meter 26 and a flow rate adjustment valve 27, and fuel from the fuel supply line 8 is similarly supplied through a gas flow meter 28 and a flow rate adjustment valve 29. However, in this embodiment, since the output detector 11 and the arithmetic unit 13C are provided in series with the battery body 1, the electric signal circuit indicated by the dotted line in the figure allows the battery body 1 to operate under low load. When the output detector 11 detects that the load has become low, or when a preliminary load reduction command is sent from the central control system 16 to the computing unit 13C, the gas is The gas flow rate is controlled by flow controllers 30, 31, gas flow meters 26.28, and flow control valves 27.29.

An example of the input/output of this arithmetic unit 13C is shown in FIG.
This graph shows the gas utilization rate and gas supply amount on the vertical axis, and the battery output on the horizontal axis, showing changes in the gas utilization rate and gas supply amount depending on the battery output. As is clear from the gas utilization rate curve N1 and the gas supply amount curve M in the figure, the gas supply rate is set to be low during low load to increase the gas utilization rate. By controlling the amount of gas supplied to the battery body in this way and increasing the gas utilization rate during low loads, it is now possible to suppress the rise in battery voltage during low loads. The same effect as in the case described above can be achieved.

FIG. 19 shows control means of still another embodiment of the present invention. This example is a case where the above-mentioned battery temperature (operating temperature) is used. The battery cooling system is composed of a cooler 32, a cooling water temperature detector 33, a cooling water temperature control device 34, a cooling water flow rate regulating pulp 35, a cooling water circulation pump 36, a steam separator 37, etc., which are stacked inside the battery body 1. The steam generated in the steam separator 37 is used for steam reforming of fuel. In this embodiment, the output detector 11 and the arithmetic unit 13d are provided in series with the battery body 1 of the battery cooling system configured as described above, so that the battery body 1 can be operated under low load by the electric signal circuit indicated by the dotted line in the figure. When the output detector 11 detects that this has occurred, or when a preliminary load reduction command is sent from the central control system 16 to the computing unit 13d, the cooling water is turned off according to the relationship between the load and battery temperature set in advance in the computing unit 13d. The temperature detector 33, the cooling water temperature control device 34, and the cooling water flow rate adjustment valve 35 increase the cooling water flow rate to lower the battery temperature.

An example of the input/output of this arithmetic unit 13d is shown in FIG.
This shows battery temperature and cooling water flow rate on the vertical axis and battery output on the horizontal axis, showing changes in battery temperature and cooling water flow rate due to battery output. Battery temperature curve P in the same figure
1. As is clear from the cooling water flow rate curve Q, the cooling water flow rate is set to be large during low load to lower the battery temperature. In this way, by controlling the cooling water flow rate and lowering the battery temperature at low loads, it is possible to not only lower the battery voltage at low loads, but also to reduce the amount of steam generated in the steam separator. This can reduce the amount of excess steam.

〔Effect of the invention〕

As described above, the present invention enables operation at a battery voltage that does not cause agglomeration deterioration of the precious metal catalyst even under low load, and prevents agglomeration deterioration of the noble metal catalyst during low load. It is possible to obtain a method for operating a fuel cell power generation system that makes it possible to prevent agglomeration and deterioration of precious metal catalysts at low loads.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a power generation system according to a conventional fuel cell power generation system operation method, and Figure 2 is a fuel cell current density-direct pressure characteristic diagram according to a conventional fuel cell power generation system operation method.
Figure 3 is a current density-output characteristic diagram corresponding to Figure 2;
The figure is a characteristic diagram showing the relationship between cell pressure and battery voltage in the operating method of the fuel cell power generation system. FIG. 6 is an explanatory diagram showing the pressure dependence of the reflux density-output characteristic corresponding to FIG. The figure is a characteristic diagram showing the relationship between gas flow rate, gas utilization rate, and battery voltage depending on the operating method of the fuel cell power generation system, and Figure 9 is the characteristic diagram showing the relationship between battery temperature and battery voltage depending on the operating method of the fuel cell power generation system. 10 is an air pressure control system diagram showing operation by air pressure control in an embodiment of the operating method of the fuel cell power generation system of the present invention, and FIG. 11 is the input/output characteristics of the computing unit corresponding to FIG. 10. Figure 12 is an air supply control system diagram showing operation by air supply control in another embodiment of the operating method of the fuel cell power generation system of the present invention, and Figure 13 is the input/output of the computing unit corresponding to Figure 12. A characteristic diagram, FIG. 14 is a cell output-oxygen concentration characteristic diagram showing the concentration control results corresponding to FIG. 13, and FIG. 15 is a fuel supply control of still another embodiment of the operating method of the fuel cell power generation system of the present invention. 16 is an input/output characteristic diagram of the computing unit corresponding to FIG. 15, and FIG. 17 is a fuel supply control system diagram showing the operation according to the present invention. and an air and fuel supply control system diagram showing operation by fuel supply control.
FIG. 9 is a battery cooling control system diagram showing operation by battery cooling control in still another embodiment of the operating method of the fuel cell power generation system of the present invention, and FIG. 20 is a diagram showing the input/output characteristics of the computing unit and FIG. 3 is a characteristic diagram showing control results. 1... Battery body, 2... Reaction gas supply and exhaust system, 2a.
...Fuel reforming supply system, 2b...Air supply system, 3.
...Temperature control system, 4, 5...Steam water separator, 6...
Water treatment device, 7... Air supply line, 8... Fuel supply line, 9... Fuel reformer, 10... Shift converter, 11... Output detector, 12... Rotation speed Control device, 13, 13a. 13b, 13C, 13d... Arithmetic unit, 16... Central control system, 17... Stop valve, 18... Recycle blower-119... Flow meter, 20... Flow rate control valve, 21... ...Flow rate control device, 23...Cooling water, 25...Cooling water flow rate adjustment valve, 26.28...
Gas flow meter, 30.31... Gas flow controller, 32.
...Cooler, 34...Cooling water temperature control device, 35...
・Cooling water flow rate adjustment valve, 37...Steam separator. Agent Patent Attorney Akio Takahashi active? Kasumi Den IJ, hoe height 70 Den flood return high lO mouth? C Live! 1 mist electric power self 2 power (begging) erase 13I2]; Ko right / 412] electric grip power (ye> ji 1S (2) γ also 160 electric power (z) me11 J 18 X electrician Power(%)

Claims (1)

[Scope of Claims] 1. A battery body consisting of a unit cell that holds an electrolyte between a pair of gas diffusion electrodes having a noble metal catalyst, and a reaction gas for supplying and exhausting reactive gases of an oxidizer and fuel to and from the battery body, respectively. A fuel cell power generation system equipped with a temperature control system for controlling the temperature of a supply system and the battery body is operated with a control means that does not exceed the permissible voltage of the single cell at which the precious metal catalyst starts coagulating and deteriorating during low load operation. A method of operating a fuel cell power generation system, characterized in that: 2. The method of operating a fuel cell power generation system according to claim 1, wherein the control means lowers the gas pressure of the reaction gas supply system. 3. The control means lowers the concentration of the reaction gas by recycling the reaction gas discharged from the reaction gas supply system to the reaction gas supply system, or by mixing an inert gas into the reaction gas supply system. 2. A method of operating a fuel cell power generation system according to claim 1, which comprises: 4. Operation of the fuel cell power generation system according to claim 1, wherein the control means increases the utilization rate of the reaction gas by reducing the amount of the reaction gas supplied from the reaction gas supply system. Method. 5. Claim 1, wherein the control means lowers the operating temperature of the battery main body of the temperature control system.
Method of operating the fuel cell power generation system described in Section 1. 6. The fuel according to any one of claims 1 to 5, wherein the noble metal catalyst is platinum or a platinum-based alloy! How to operate a pond power generation system. 7. The method of operating a fuel cell power generation system according to any one of claims 1 to 5, wherein the electrolyte is an acidic electrolyte.