JPH05251102A - Phospholic acid type fuel cell power generating plant - Google Patents

Abstract

PURPOSE:To provide a phospholic acid type fuel cell power generating plant wherein catalyst deterioration of the fuel cell main body is suppressed to the minimum level during starting and stopping operation. CONSTITUTION:The hydrogen concentration in an anode recycle line 33 is detected by a hydrogen gas detecting means 24 as soon as hydrogen gas is supplied to an anode electrode 2 and the output of the hydrogen gas detecting means 24 is sent to a controlling apparatus 25. Consequently, the controlling apparatus 25 gives an instruction an anode hydrogen gas supplying valve 21 to make the anode electrode 2 maintain a prescribed hydrogen gas concentration (e.g. 2% hydrogen gas concentration). As soon as air is supplied to a cathode electrode 3, the oxygen gas concentration in the cathode recycle line 34 is detected by an oxygen gas detecting means 26 and the output of the oxygen gas detecting means 26 is sent to a controlling apparatus 27. As a result, the controlling apparatus 27 gives an instruction to a cathode oxygen gas supplying valve 23 to make the cathode electrode 3 maintain a prescribed oxygen gas concentration (e.g. 0.5% oxygen gas concentration).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell power generation plant, and more particularly, to a phosphoric acid fuel cell power generation in which means for preventing deterioration of a catalyst of a fuel cell main body during start / stop operations is improved. Related to the plant.

[0002]

2. Description of the Related Art Conventionally, a fuel cell has been known as a device for directly converting the chemical energy of a fuel such as coal or petroleum into a direct electrical energy under isothermal conditions. In this fuel cell, a pair of porous electrodes usually sandwich a matrix containing an electric field, a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidizer such as air is brought into contact with the back surface of the other electrode. Are brought into contact with each other, and the electric energy generated by the electrochemical reaction occurring at this time is extracted from between the electrodes. In this case, hydrogen or a reformed gas obtained by reforming natural gas is used as the fuel gas, and air or oxygen is used as the oxidant. As the electrolyte, a molten carbonate, an alkaline solution, an acidic solution, a solid polymer, a solid oxide, or the like is used. Recently, a phosphoric acid fuel cell using phosphoric acid as an electrolyte has been attracting attention.

FIG. 3 shows a schematic structure of a conventional phosphoric acid fuel cell power plant. In the figure, the unit cell of the fuel cell body 1 is a matrix in which an anode electrode 2 having a back surface in contact with a fuel such as hydrogen and a cathode electrode 3 having a back surface in contact with an oxidant such as oxygen are impregnated with an electrolyte. It is arranged on both sides with a pinch in between. A plurality of these unit cells are alternately stacked via the gas separation plate,
The fuel cell body 1 is configured.

Natural gas 4 and steam 5 in the reformer 6
The mixed gas of and is converted into a hydrogen-rich gas by a steam reforming reaction, the hydrogen-rich gas is supplied to the anode electrode 2, and the compressed air 7 is supplied to the cathode electrode 3. The hydrogen-rich gas supplied to the anode electrode 2 electrochemically reacts with the compressed air 7 supplied to the cathode electrode 3,
It becomes electricity, water and heat.

The gas discharged from the anode electrode 2 is discharged to the atmosphere 11 through the anode outlet phosphoric acid adsorber 8, the anode outlet condenser 9 and the reformer burner 10. The gas discharged from the cathode electrode 3 is fed to the cathode outlet phosphoric acid adsorber 12,
It is discharged to the atmosphere via the cathode outlet condenser 13 and the reformer burner 10. The gas in the anode electrode 2 and the cathode electrode 3 is circulated from the outlet line of each electrode to the inlet line by the anode recycle blower 14 and the cathode recycle blower 15 provided in the anode recycle line 33 and the cathode recycle line 34, respectively, and Used. In addition, 16, 17, and 18 are
They are an anode fuel supply valve, a cathode air supply valve and an atmosphere shutoff valve, respectively.

By the way, in the phosphoric acid fuel cell, when the cell voltage is maintained at 0.8 V or more per unit cell in a high temperature state, the sintering of the cell catalyst is increased and the cell characteristics are deteriorated. On the other hand, the battery voltage is 0 V or less per unit cell,
In other words, it is also known that when a reversal phenomenon occurs, electrolysis occurs and the battery is greatly damaged.

Therefore, it is necessary to manage the battery voltage not only during power generation but also during start / stop operations.
Therefore, during power generation, the voltage protection control of the inverter keeps the voltage within the allowable value (usually 0.6-0.8V / cell), and if the battery voltage exceeds the allowable value, an emergency stop is performed. Battery protection measures such as are taken.

On the other hand, during the starting / stopping operation, particularly during the stopping operation, since the air supplied during the power generation remains in the cathode electrode 3, the following voltage suppressing means is provided. That is, the cathode supply air is shut off in accordance with the power generation stop command, and at the same time, the supply valves 29 and 32 provided in the cathode nitrogen gas supply line 28 and the anode nitrogen gas supply line 31 are opened, and an inert gas, such as nitrogen, is used as the anode. The oxygen gas in the residual air supplied to the electrode 2 and the cathode electrode 3 is purged.

Further, the inverter reduces the AC output in response to the power generation stop command, and switches to the dummy resistor 30 at the minute output where the operation of the inverter becomes impossible. The dummy resistor 30 has an arbitrary voltage, for example, 0.5 V /
It is controlled to turn on in the cell or higher. The battery voltage is suppressed by the dummy resistor 30 and the nitrogen gas purge of the cathode, and finally the nitrogen gas purge of the anode electrode 2 is performed, and the management of the battery voltage during the stop is completed. Since the voltage suppression control of the dummy resistor is activated during the start / stop, if the battery voltage is generated for some reason and the dummy resistor turning-on condition, for example, battery voltage> 0.5V / cell, is satisfied. , The dummy resistor 30 is turned on and voltage suppression is executed.

[0010]

By the way, in a phosphoric acid fuel cell body, the output voltage of a unit cell composed of a pair of anode electrode and cathode electrode is about 1 V or less.
It is configured by stacking a large number of unit batteries in series. However, when the nitrogen gas purging of the cathode electrode 3 is performed during the stop operation, it is extremely difficult to uniformly supply the nitrogen gas to the individual unit cells. Therefore, the amount of oxygen gas present in the cathode electrodes 3 of the individual unit cells is very large. Will be different.

When the dummy resistor is turned on in this state, the battery voltage is suppressed to a set value, for example, an average cell voltage of 0.5 V / cell, so that the entire battery voltage is suppressed. However, it becomes impossible to uniformly suppress the voltage of each unit battery, and even if the condition that the dummy resistors are cut off due to the voltage variation among the individual unit batteries, a part of the unit battery voltage is high, for example, 0. It is maintained at 8 V / cell or more. Therefore, in this unit cell in which a part of the high voltage is maintained, the sintering phenomenon progresses until the operating temperature of the fuel cell decreases, and the deterioration of the fuel cell characteristics increases. Therefore, there is a big problem that the fuel cell characteristics are greatly deteriorated every time the start / stop operation is performed, and the rated output is not satisfied before the fuel cell guarantee period.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and its object is to minimize the catalyst deterioration of the fuel cell body during the start / stop operation. It is to provide a phosphoric acid fuel cell power generation plant that can be used.

[0013]

In order to achieve the above object, the phosphoric acid fuel cell power plant according to claim 1 introduces a fuel and an oxidant to an anode electrode and a cathode electrode, respectively, and an outlet of the anode electrode. And an anode recycle line and a cathode recycle line, which circulate from the line and the outlet line of the cathode electrode to the inlet line of the anode electrode and the inlet line of the cathode electrode, respectively, and generate electricity by an electrochemical reaction of the fuel and the oxidant. In a phosphoric acid fuel cell power plant,
A hydrogen supply line is connected to the inside of the anode recycle line, and the hydrogen concentration of the anode electrode is controlled to a predetermined value by the output of the hydrogen gas concentration detection means arranged inside the anode recycle line. It is characterized in that a gas supply valve for

According to another aspect of the phosphoric acid fuel cell power generation plant of the present invention, an air supply line is connected to the inside of the cathode recycle line, and the oxygen gas concentration detection is provided inside the cathode recycle line. A gas supply valve for controlling the oxygen concentration of the cathode electrode to a predetermined value by the output of the means is provided. A phosphoric acid fuel cell power plant according to a third aspect of the present invention is characterized in that a resistance is provided between the anode electrode and the cathode electrode that is turned on when a predetermined cell voltage value is exceeded.

[0015]

In the phosphoric acid fuel cell power plant of the present invention having the above-mentioned structure, during the start-up / shutdown operation, the circulation operation by nitrogen gas is carried out in the anode recycle line and the cathode recycle line. According to claim 1, hydrogen gas is supplied to the anode electrode to maintain a predetermined hydrogen gas concentration, and the cathode electrode is
According to the second aspect, by supplying the air and maintaining the predetermined oxygen gas concentration, the predetermined battery voltage can be maintained. Furthermore, when the predetermined battery voltage is exceeded, claim 3
As described above, the resistance is applied between the anode electrode and the cathode electrode to suppress and control the battery voltage to a predetermined value.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to FIG. The same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

(1) Structure of the embodiment ... FIG. 1 In this embodiment, 20 is an anode hydrogen gas supply line connected to the inside of the anode recycle line on the inlet side of the anode electrode 2, where the anode is The hydrogen gas supply valve 21 is connected. Reference numeral 22 denotes a cathode air (oxygen gas) supply line connected to the inside of the cathode recycle line on the inlet side of the cathode electrode 3, to which a cathode oxygen gas supply valve 23 is connected.

The anode electrode 2 is provided with hydrogen gas detecting means 24 such as a gas detector for detecting the gas concentration inside the anode electrode 2, and the output end of the hydrogen gas detecting means 24 is the anode hydrogen depending on the detected concentration. It is connected to a control device 25 that controls the valve opening of the gas supply valve 21. The cathode electrode 3 is also provided with an oxygen gas detection means 26 for detecting the gas concentration therein, and the output end of the oxygen gas detection means 26 has a valve opening degree of the cathode oxygen gas supply valve 23 according to the detected concentration. Is connected to a control device 27 that controls the.

(2) Operation and effect of the embodiment In the phosphoric acid fuel cell power generation plant of the present embodiment having the above-described structure, first, in the case of the starting operation, the cell is in the process of increasing the temperature of the fuel cell. A predetermined temperature (a temperature at which the cell catalyst promotes sintering, for example, 10
(0 ° C.), the anode recycle blower 14 and the cathode recycle blower 15 are driven. At this time, since the anode recycle line 33 and the cathode recycle line 34 are in a pressure-holding state of nitrogen gas, the nitrogen gas is uniformly supplied to the anode electrode 2 and the cathode electrode 3 of the unit cells stacked on the fuel cell body 1, The stirring circulation operation is carried out. At this time, the anode hydrogen gas supply valve 21 and the cathode oxygen gas supply valve 23 are simultaneously opened, and hydrogen gas and air are supplied to the anode electrode 2 and the cathode electrode 3, respectively.

At the same time when the hydrogen gas is supplied to the anode electrode 2, the hydrogen gas concentration in the anode recycle line 33 is detected by the hydrogen gas detecting means 24.
Is input to the control device 25. Thereby, the control device 25 gives a command to the anode hydrogen gas supply valve 21 so that the anode electrode 2 maintains a predetermined hydrogen gas concentration (below the explosion limit of hydrogen gas, for example, 2% hydrogen gas concentration). The above-mentioned control for maintaining the anode electrode 2 at a predetermined hydrogen gas concentration at the time of startup is carried out until just before the introduction of the cathode reformed gas in the standby state shown in FIG.

Simultaneously with the supply of air to the cathode electrode 3, the oxygen gas concentration in the cathode recycle line 34 is detected by the oxygen gas detecting means 26, and the output of this oxygen gas detecting means 26 is input to the control device 27. Thereby, the control device 27 gives a command to the cathode oxygen gas supply valve 23 so that the cathode electrode 3 maintains a predetermined oxygen gas concentration (for example, 0.5% oxygen gas concentration). The above-mentioned control for maintaining the cathode electrode 3 at a predetermined oxygen gas concentration at the time of startup is carried out until just before the introduction of cathode air in the standby state shown in FIG.

In this case, since hydrogen gas and oxygen gas are supplied to the anode electrode 2 and the cathode electrode 3, respectively, a battery voltage is generated and the cathode electrode potential becomes a predetermined value (0.8 V / cell) or more. Therefore, by inserting the dummy resistor 30 between the anode electrode 2 and the cathode electrode 3 of the fuel cell, the cathode electrode potential is set to a predetermined value (0.8 V).
/ Cell or less). in this case,
Since the circulation operation by the anode recycle blower 4 and the cathode recycle blower 15 is carried out, the gas is uniformly supplied to the individual unit cells that are stacked, so that the voltage of each individual unit cell can be controlled uniformly. Also,
Since the hydrogen gas and the oxygen gas supplied to the anode electrode 2 and the cathode electrode 3 have very small concentrations, sufficient voltage suppression control can be achieved without using a large resistance capacity itself. FIG. 4 is a measurement example showing current-voltage characteristics in a small phosphoric acid fuel cell under a low concentration of supplied oxygen gas. At each current, the following relationship was obtained. V = V0 + k * Log (PO2) where k is a function of the current I: k = f (I), and PO2 is the oxygen gas concentration.

From this relationship, the cathode oxygen gas concentration and the dummy resistance value required for the predetermined battery voltage control are determined.
Actually, the smaller the dummy resistance value is, the more realistic it is, but the smaller the cathode oxygen gas concentration is, the better the facility efficiency is. Further, in this case, since the battery voltage is expected to increase as the temperature increases, the supply gas condition becomes a substantially constant value.

Next, in the case of stopping operation, the cathode electrode 3
As shown in FIG. 2, the cathode supply air 7 is shut off as the power generation state shifts to the standby state, and at the same time, the cathode nitrogen gas supply valve 29 is opened and oxygen gas in the air remaining in the cathode electrode 3 is discharged. Is purged with nitrogen gas. During this standby state, the reformed gas is still supplied to the anode electrode 2 and the residual oxygen gas is present on the cathode side, so that the battery voltage is generated. Therefore, the operation of controlling the cathode potential to a predetermined value (0.8 V / cell or less) is performed by turning on the dummy resistor 30 between the anode electrode 2 and the cathode electrode 3.

Since the voltage suppression implemented by turning on the dummy resistor 30 controls the total voltage of the fuel cell main body 1 within a predetermined voltage range, pay attention to the individual unit cells stacked. As described in the related art, the unit cell voltage may vary, and some unit cells may remain in a state where the voltage of 0.8 V / cell or more promoted by catalyst sintering is maintained for a long time. However, in the present embodiment, the cathode recycle blower 15 is circulated even during the stop operation so that the gas is uniformly supplied to the cathode electrodes 3 of the individual unit cells that are stacked. As a result, in the present embodiment, the purging of air (oxygen) by the nitrogen gas in the cathode electrode 3 is carried out uniformly,
The dummy resistor 30 also suppresses the battery voltage for each unit battery without variation.

At this time, the oxygen gas concentration in the cathode recycle line 34 is detected by the oxygen gas detection means 26, and the output of this oxygen gas detection means 26 is input to the control device 27. As a result, the controller 27 causes the cathode electrode 3 to have a predetermined oxygen gas concentration (for example, 2
%) Is issued to the cathode oxygen gas supply valve 23. Therefore, even after the nitrogen gas purging of the cathode electrode 3 immediately after the stop of power generation, the control for maintaining the predetermined oxygen gas concentration is lowered to the predetermined temperature (the temperature at which the battery catalyst promotes sintering, for example, about 100 ° C.). Will be implemented until.

On the other hand, as shown in FIG. 2, the anode electrode 2 in the stopped state is supplied with the anode nitrogen gas in the anode nitrogen gas supply line 31 after the reformed gas supplied to the anode is cut off in accordance with the transition from the standby state to the stopped state. The valve 32 is opened and the hydrogen gas remaining in the anode electrode 2 is purged with nitrogen gas. Although the hydrogen gas concentration in the anode electrode 2 is lowered by this operation, the gas detection means 24 detects the hydrogen gas concentration and sends a signal to the control means 25. The control device 25
A command is given to the anode hydrogen gas supply valve 21 so that the anode recycle line maintains a predetermined hydrogen gas concentration. Anode electrode 2 implemented during such stop operation
The hydrogen gas concentration control in the inside is also performed until the cell temperature drops to a predetermined temperature.

(3) Effects of the embodiment In the embodiment constructed as described above, in the starting / stopping process, particularly when the fuel cell is in a high temperature state, the anode electrode and the cathode electrode are each filled with a minute hydrogen gas concentration atmosphere. Also, by controlling the atmosphere to have a slight oxygen gas concentration and further inserting a dummy resistor between the anode electrode and the like, the battery voltage can be continuously and stably controlled to a predetermined value. As a result, it is possible that some of the unit batteries generated during the start-up / shutdown process due to the locally remaining oxygen gas.
It is possible to avoid a high potential state of 8 V / cell or more, prevent the sintering phenomenon of the catalyst due to it, and prolong the life of the fuel cell characteristics.

(4) Other Embodiments The present invention is not limited to the above-mentioned embodiments, and the fuel or the oxidant gas in the electrode can be protected by only carrying out either claim 1 or claim 2. The concentration can be controlled to prevent sintering of the catalyst.

[0030]

As described above, according to the present invention, the cell voltage of the fuel cell can be controlled to a predetermined value under the condition that the cell temperature is high during the start-up / shut-down operation, so that the high residual oxygen gas It is possible to prevent sintering of the electrode catalyst caused by the electrode potential, and to obtain an excellent phosphoric acid fuel cell power plant capable of extending the life of the fuel cell characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a phosphoric acid fuel cell power generation plant of the present invention.

FIG. 2 is a time chart explaining the operation of FIG.

FIG. 3 is a block diagram showing an example of a conventional phosphoric acid fuel cell power generation plant.

FIG. 4 is a graph showing hydrogen gas and oxygen gas concentration characteristics of a fuel cell.

[Explanation of symbols]

 1; Fuel cell main body 2; Anode electrode 3; Cathode electrode 4; Natural gas 5; Water vapor 7; Compressed air 11; Atmosphere 14; Anode recycle blower 15; Cathode recycle blower 20; Anode hydrogen gas supply line 21; Anode hydrogen gas supply Valve 22; Cathode oxygen gas supply line 23; Cathode oxygen gas supply valve 24, 26; Gas detection means 25, 27; Valve control means 33; Anode recycle line 34; Cathode recycle line

Claims (3)

[Claims] 1. A fuel and an oxidant are introduced to an anode electrode and a cathode electrode, respectively, and circulated from an outlet line of the anode electrode and an outlet line of the cathode electrode to an inlet line of the anode electrode and an inlet line of the cathode electrode, respectively. In a phosphoric acid fuel cell power plant having an anode recycle line and a cathode recycle line and generating electricity by an electrochemical reaction of the fuel and the oxidant, a hydrogen supply line is connected to the inside of the anode recycle line and the hydrogen supply is performed. The line is equipped with a gas supply valve for controlling the hydrogen concentration of the anode electrode to a predetermined value by the output of a hydrogen gas concentration detecting means arranged inside the anode recycle line. Battery power plant. 2. A fuel and an oxidant are introduced to an anode electrode and a cathode electrode, respectively, and circulated from an outlet line of the anode electrode and an outlet line of the cathode electrode to an inlet line of the anode electrode and an inlet line of the cathode electrode, respectively. In a phosphoric acid fuel cell power plant having an anode recycle line and a cathode recycle line and generating electricity by an electrochemical reaction of the fuel and the oxidant, an air supply line is connected to the inside of the cathode recycle line and the air supply is performed. The line is equipped with a gas supply valve for controlling the oxygen concentration of the cathode electrode to a predetermined value by the output of the oxygen gas concentration detecting means arranged inside the cathode recycle line. Battery power plant. 3. The phosphoric acid fuel cell according to claim 1, further comprising a resistor provided between the anode electrode and the cathode electrode, the resistor being turned on when a predetermined cell voltage value is exceeded. Power plant.