JPH0652876A - Fuel cell power generating plant - Google Patents

Abstract

PURPOSE:To extend the life of a fuel cell by measuring the amount of electrolyte held in the fuel cell, and determining the proper time and amount of supply of electrolyte when necessary. CONSTITUTION:The fuel supply line and oxidizer discharge line of a cell main body 1 are provided with respective condensors 13, 17. An anode drain tank 31 and a cathode drain tank 41 are connected to the respective condensors 13, 17. Mounted in both the anode drain tank 31 and the cathode drain tank 41 are level gauges 32, 42 for measuring the amount of drain remaining in the tanks 31, 41 and phosphoric acid concentration meters 33, 43 for measuring the concentration of phosphoric acid in the drain. Further, an arithmetic unit 39 is provided for computing the amount of conveyed phosphoric acid from the output values of the level gauges 32, 42 and the phosphoric acid concentration meters 33, 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power plant using a fuel cell, and more particularly to a fuel cell power plant for determining when and how much electrolyte is replenished to a fuel cell. .

[0002]

2. Description of the Related Art Generally, a fuel cell is a device for directly converting the energy released by an oxidation reaction into electrical energy by oxidizing the chemical energy of the fuel in a gas chemical process. The thermal efficiency of power generation of this fuel cell reaches 40 to 50% even on a relatively small scale. Therefore, the thermal efficiency of a fuel cell power plant using a fuel cell is expected to be far higher than that of a new thermal power plant, and it has attracted much attention.

Further, the fuel cell power plant does not need a large amount of cooling water because it emits very little SO _x and NO _x which are environmental factors and does not include a fuel cycle in the power plant. Moreover, since the vibration is small, there is little noise. Furthermore, it is suitable for a cogeneration system that has good responsiveness to load fluctuations, can theoretically expect high conversion efficiency, and uses heat as well as power generation. Due to the advantages described above, fuel cell power generation plants have been increasingly researched in recent years.

The structure and operating principle of the fuel cell will be described below. A fuel cell is configured by stacking a plurality of unit cells each having a pair of porous electrodes forming a catalyst layer and an electrolyte layer arranged between the porous electrodes with a separator interposed therebetween. Among them, the porous electrode forming the catalyst layer is composed of an anode electrode (fuel electrode) and a cathode electrode (oxidizer electrode), and an electrolyte is stored in a porous body (substrate). A fuel gas such as hydrogen is brought into contact with the back surface of the anode electrode, and an oxidant gas such as oxygen is brought into contact with the back surface of the cathode electrode, and electric energy generated by an electrochemical reaction occurring at this time is applied to the pair of electrodes. Can be taken from.

On the other hand, the electrolyte layer is formed by impregnating a porous layer containing electrolyte-resistant fine particles as a main raw material with an electrolyte.
Further, the electrolyte layer plays a role of ion transfer between the anode electrode and the cathode electrode, which accompanies the electrochemical reaction. At the same time, it also has a function of separating the two reaction gases from each other so that the fuel gas and the oxidant gas do not come into contact with each other.

In the fuel cell, if the electrolyte layer is sufficiently impregnated with the electrolyte, there is no problem in the above function of the electrolyte layer. However, when the amount of the impregnated electrolyte decreases, the resistance of ion transfer (battery internal resistance) increases. In addition, a leak (cross leak) of the reaction gas to the counter electrode occurs, and the cell voltage greatly decreases. In the worst case, it may cause an explosion. For this reason, the management of the remaining amount of the electrolyte in the electrolyte layer is extremely important for maintaining the high performance of the fuel cell and ensuring the safe operation of the cell.

It is also known that when the fuel cell is operated, the electrolyte impregnated in the electrolyte layer evaporates into the reaction gas, though in a small amount, and is carried out to the outside of the cell body. Even if the amount of the electrolyte evaporated in such a reaction gas is very small, the amount of the electrolyte in the electrolyte layer gradually decreases when the fuel cell is operated for a long period of time. The reduction of the electrolyte in the electrolyte layer causes an increase in the internal resistance of the battery and the occurrence of cross leak, and the performance of the battery is significantly reduced. As a result, the life of the fuel cell is shortened.

FIG. 2 shows the result of a life test conducted by the applicant. The internal resistance of the battery gradually increases with the lapse of operating time, and sharply increases after a certain period. It is also clear that the voltage of the fuel cell drops sharply at this time.

However, even if the battery characteristics are drastically lowered as shown in FIG. 2, the battery characteristics can be recovered by supplying an appropriate amount of electrolyte. An example thereof is shown in FIG. That is, in the fuel cell, as long as the fuel gas, the oxidant gas and the electrolyte are supplied in appropriate amounts, the electric energy can be continuously extracted with high conversion efficiency. Therefore, in the fuel cell power plant, a supply / discharge line for supplying / discharging the fuel gas and the oxidant gas to the cell body and an electrolyte replenishing structure are arranged.

[0010]

By the way, in the electrolyte replenishment structure arranged in the fuel cell power generation plant, particularly problematic is the electrolyte replenishment timing and the amount of electrolyte replenishment. Considering the replenishment timing, the crossover has already occurred in the unit cell after the time when the amount of the electrolyte affects the voltage of the fuel cell has passed. Therefore, the pair of porous electrodes forming the dissolution medium layer are considerably damaged. In this case, the voltage of the fuel cell cannot be sufficiently recovered even if an appropriate amount of electrolyte is replenished.

On the other hand, considering the amount of electrolyte replenishment,
If a necessary and sufficient amount is not supplied, problems such as blocking will occur. In the past, the amount of replenishment was determined by the operating time of the fuel cell, but the amount of electrolyte in the electrolyte layer differs depending on the operating conditions, etc., so the amount of replenishment may be too small or conversely too large. . When the replenishment amount is small, the time until the next replenishment becomes short and the number of replenishment times increases. On the other hand, when the amount of the electrolyte is too much, the gas diffusivity in the porous body (substrate) of the catalyst layer is lowered and the diffusion polarization becomes large, so that the voltage of the fuel cell cannot be sufficiently recovered.

As described above, although it is extremely important to control the electrolytic mass of the electrolyte layer, the conventional fuel cell power plant accurately measures the amount of electrolyte impregnated in the electrolyte layer. There was no means to do so, and it was not possible to determine the appropriate electrolyte replenishment timing / replenishment amount.

The present invention has been made to solve the above-mentioned problems, and its purpose is to measure the amount of electrolyte retained in a fuel cell and appropriately determine the time and amount of electrolyte replenishment. It is an object of the present invention to provide a fuel cell power plant that can determine and prolong the life of the fuel cell significantly.

[0014]

In order to achieve the above object, a fuel cell power plant of the present invention comprises a pair of porous electrodes forming a catalyst layer and an electrolyte layer arranged between them. A fuel cell power plant comprising a fuel cell main body formed by stacking a plurality of cells, and arranging a supply / exhaust line for supplying / exhausting a fuel gas and an oxidant gas to the cell main body and a structure for replenishing the electrolyte. , A condenser is arranged in each of the fuel gas and oxidant gas discharge lines,
An anode drain tank and a cathode drain tank are connected to the condenser and arranged, and a sensor for measuring the amount of drain staying in the anode drain tank and the cathode drain tank and the electrolyte concentration in the drain is provided, and the output value of the sensor is also provided. It is characterized by further comprising an arithmetic unit for calculating the amount of electrolyte carried out.

[0015]

In the fuel cell power plant of the present invention, the condenser disposed in the discharge line is provided with a sensor for measuring the amount of drain and the concentration of the electrolyte contained in the drain, and the amount of the electrolyte discharged to the outside of the cell by the exhaust gas. The residual electrolytic mass in the fuel cell can be continuously measured and monitored by detecting Therefore, it is possible to grasp the state of the residual electrolytic mass in the predetermined battery in which the battery performance can be recovered by carrying out the electrolyte replenishment, and to know the electrolyte replenishment timing. In addition, since the amount to be carried out to the outside of the battery is clear, it is possible to accurately know the appropriate amount of electrolyte replenishment.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to FIG. FIG. 1 shows a system diagram of a fuel cell power plant according to an embodiment of the present invention. The fuel cell in this example uses phosphoric acid as the electrolyte. Fuel cells that use phosphoric acid operate at high temperatures, which is advantageous for electrode reactions and has the advantage of low reaction resistance. On the other hand, phosphoric acid is easily evaporated and reduced, and the amount of phosphoric acid carried out to the outside of the cell can be detected. Is required. Therefore, the effects of the present invention are extremely effective.

As shown in the figure, the fuel cell main body 1 is a unit cell in which an anode electrode 2 and a cathode electrode 3 are arranged on both sides of a matrix layer impregnated with phosphoric acid so as to form a unit cell. It is configured by stacking a plurality of layers. A fuel gas supply line is arranged in the anode electrode 2. The fuel gas supply line includes the reformer 10 and the anode gas supply valve 2.
0 and anode cycle blower 18. The reformer 10 is a device that converts a mixed gas of natural gas 8 and steam 9 into a hydrogen-rich gas 22 by a steam reforming reaction. The anode gas supply valve 20 is installed between the reformer 10 and the gas inlet side of the anode electrode 2 so as to control the fuel. The anode cycle blower 18 circulates the gas inside the anode electrode 2.

Further, a fuel gas discharge line is arranged on the gas outlet side of the anode electrode 2. The fuel gas discharge line comprises an anode outlet flow meter 12 and an anode outlet condenser 13. Temperature sensors 35 and 36 are installed at the inlet and outlet of the anode outlet condenser 13, respectively. Temperature sensor 3
The outputs of 5, 36 and the output of the anode outlet flow meter 12 are connected to the arithmetic unit 39 and arranged.

Further, a drain tank 31 for storing the generated drain is connected to the anode outlet condenser 13. A liquid level meter 32 for measuring the drain liquid level and a phosphoric acid concentration meter 33 for measuring the concentration of phosphoric acid contained in the drain are installed in the drain tank 31. Further, an arithmetic unit 39 is connected to the output side of the liquid level meter 32 and the phosphoric acid concentration meter 33.

On the other hand, the cathode electrode 3 is provided with an oxidant gas supply line. The oxidant gas supply line includes a cathode air supply valve 21 for supplying compressed air 11 as an oxidant,
It is composed of a cathode recycle blower 19 that circulates the gas inside the cathode electrode 3. Further, an oxidant gas discharge line is connected to the gas outlet side of the cathode electrode 3. The oxidant gas discharge line includes a cathode outlet flow meter 16 and a cathode outlet condenser 17. Further, a reformer burner 14 is connected to the anode outlet condenser 13 and the cathode outlet condenser 17, and the exhaust gas is fed to the reformer burner 14 to the atmosphere 1
The atmosphere shutoff valve 22 for discharging to 5 is connected.

Temperature sensors 45 and 46 are installed at the inlet and outlet of the cathode outlet condenser 17, respectively. The outputs of the temperature sensors 45 and 46 are connected to the arithmetic unit 39 together with the output of the cathode outlet flow meter 16. Further, the cathode outlet condenser 17 has a drain tank 41 for storing the generated drain.
Connect and place. A liquid level gauge 42 for measuring the drain liquid level and a phosphoric acid concentration meter 43 for measuring the concentration of phosphoric acid contained in the drain are installed in the drain tank 41. Further, the arithmetic unit 39 is connected to the output side of the liquid level meter 42 and the phosphoric acid concentration meter 43.

Next, the operation of this embodiment having the above construction will be described.

In the operating state of the phosphoric acid fuel cell power plant, the reformer 10 reforms the mixed gas of the natural gas 8 and the steam 9 through the anode gas supply valve 20 to obtain the hydrogen rich gas 22 (about 75%) is supplied to the anode electrode 2. On the other hand, the cathode air supply valve 21 is compressed air 1
1 is supplied to the cathode electrode 3. Then, the hydrogen-rich gas 22 supplied to the anode electrode 2 and the cathode electrode 3
A predetermined electric power can be obtained by electrochemically reacting with the compressed air 11 supplied to the.

By the way, since the operating temperature of the fuel cell main body 1 using phosphoric acid as an electrolyte is usually around 200 ° C., the hydrogen-rich gas 22 and the compressed air 1 which are reaction gases.
During 1 the phosphoric acid evaporates. As a result, the hydrogen-rich gas 22 supplied to the anode electrode 2 consumes hydrogen by a power generation reaction and takes in phosphoric acid, and discharges it as an anode exhaust gas to the anode outlet condenser 13 provided at the outlet of the anode electrode 2. The anode outlet condenser 13 condenses the vapor component in the anode exhaust gas by the heat exchanger structure and also condenses the phosphoric acid evaporated in the anode exhaust gas. Further, the anode outlet condenser 13 discharges the condensed drain water containing phosphoric acid to the anode drain tank 31, and the anode drain tank 31 holds it.

Here, the liquid level meter 32 and the phosphoric acid concentration meter 33 installed in the anode drain tank 31 respectively detect the liquid level of the anode drain tank and the phosphoric acid concentration in the anode drain tank, and calculate the output values thereof. To the device 39. The arithmetic unit 39 calculates the drain amount from the anode drain tank liquid level output value, and also obtains the total phosphoric acid amount “X” recovered in the anode drain tank from the relationship of the obtained drain concentration. On the other hand, the anode outlet flow meter 1
2 and the outlet temperature sensor 35 entering the anode outlet condenser,
36 transmits the detected output value to the arithmetic unit 39, and the arithmetic unit 39 calculates the anode condenser drain recovery rate "r1" from the relation of these detected values.

On the other hand, the compressed air 11 supplied to the cathode electrode 3 consumes oxygen by the power generation reaction and takes in phosphoric acid, and discharges it as cathode exhaust gas to the cathode outlet condenser 17 provided at the outlet of the cathode electrode 3. . The cathode outlet condenser 17 condenses the vapor component in the cathode exhaust gas by the heat exchanger structure and also condenses the phosphoric acid generated in the cathode exhaust gas. Further, the cathode outlet condenser 17 discharges the condensed drain water containing phosphoric acid to the cathode drain tank 41, and the cathode drain tank 41 holds it.

Here, the liquid level meter 42 and the phosphoric acid concentration meter 43 installed in the cathode drain tank 41 detect the cathode drain tank liquid level and the phosphoric acid concentration in the cathode drain tank, respectively, and calculate the output values thereof. To the device 39. The arithmetic unit 39 calculates the drain amount from the cathode drain tank liquid level output value, and also obtains the total phosphoric acid amount “Y” recovered in the cathode drain tank from the relationship of the obtained drain concentration. On the other hand, cathode outlet flow meter 1
6 and an outlet temperature sensor 45 for entering the cathode outlet condenser,
46 transmits the detected output value to the arithmetic unit 39, and the arithmetic unit 39 calculates the cathode condenser drain recovery rate "r2" from the relation of these detected values.

As a result of the above, the arithmetic unit 39 calculates the residual amount of phosphoric acid in the cell using the following formula from the obtained calculation result. Here, the calculated phosphoric acid residual amount in the cell is “Z”, and the phosphoric acid charging amount for the fuel cell body 1 is “W”.

[0029]

## EQU1 ## Z = W- (X * 1 / r1-Y * 1 / r2) When the above equation satisfies the condition "replenishable limit phosphoric acid residual amount <calculated phosphoric acid residual amount in battery", Arithmetic unit 3
9 can judge the phosphoric acid replenishment timing and issue an appropriate phosphoric acid replenishment timing signal to the operator.

As described above, according to this embodiment, the phosphoric acid carried out to the outside of the fuel cell body 1 generated during the power generation operation is recovered as drain in the condensers 13 and 17 provided at the anode outlet and the cathode outlet. In addition, since the amount of phosphoric acid in the drain is continuously measured and monitored, the residual amount of phosphoric acid in the battery can be calculated by the arithmetic unit 39, and at the same time, this value reaches the replenishable limit phosphoric acid residual amount. Since a signal is issued to the operator as soon as possible, the operator can automatically know the proper phosphoric acid supply timing. Moreover, since the residual amount of phosphoric acid is also calculated, it is possible to supply a sufficient amount of supplemented phosphoric acid.

As a result, it is possible to determine an appropriate replenishment timing without causing damage such as crossover to the unit cells in the fuel cell main body 1, and to make sure that the replenishment amount of phosphoric acid that causes blocking or the like does not occur. It is possible to determine the exact replenishment amount. Therefore, the life of the fuel cell can be significantly extended.

[0032]

As described above, according to the fuel cell power generation plant of the present invention, the amount of drain staying in the drain tank connected to the condenser installed in the exhaust gas line at the outlet of the cell body and the electrolyte concentration in the drain can be determined. Since the amount of electrolyte carried out by the exhaust gas is calculated and calculated, the mass of electrolysis remaining in the fuel cell can be continuously measured and monitored, so damage to the cells in the cell body such as crossover can be prevented. Therefore, it is possible to determine an appropriate replenishment timing, and also to determine an appropriate replenishment amount without causing an error in the replenishment amount that causes blocking or the like. Therefore, the life of the fuel cell can be significantly extended.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fuel cell power plant showing an embodiment of the present invention.

FIG. 2 is a graph showing an example of battery life characteristics when electrolyte is not replenished.

FIG. 3 is a graph showing an example of changes in battery characteristics when electrolyte is replenished.

[Explanation of reference numerals] 1 battery main body 2 anode electrode 3 cathode electrode 13 anode outlet condenser 17 cathode outlet condenser 31 anode drain tank 32 anode drain liquid level meter 33 anode drain phosphoric acid concentration meter 39 arithmetic unit 41 cathode drain tank 42 cathode Drain liquid level meter 43 Cathode drain phosphoric acid concentration meter

Claims (1)

[Claims] 1. A pair of porous electrodes forming a catalyst layer,
A supply / exhaust line for supplying / discharging fuel gas and oxidant gas to / from the fuel cell main body, which is formed by stacking a plurality of unit cells each having an electrolyte layer disposed therebetween with a separator interposed therebetween. And a fuel cell power plant comprising the electrolyte replenishment structure, wherein condensers are respectively arranged in the discharge lines of the fuel gas and the oxidant gas, and an anode drain tank and a cathode drain tank are connected to the condenser. A sensor for measuring the amount of drain staying in the anode drain tank and the cathode drain tank and the electrolyte concentration in the drain is provided, and an arithmetic unit for calculating the amount of electrolyte carried out from the output value of the sensor is provided. A fuel cell power plant characterized by the above.