JP2002352844A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which stably operates a fuel cell stack in spite of water condensation in an off-gas line. SOLUTION: The fuel cell system to generate electricity by reaction of hydrogen and oxygen is equipped with a liquid reservoir (11) to remove the water generated by condensation of water vapor in the off-gas including residual hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system in which unstable fuel supply due to, for example, condensation of water in exhaust hydrogen is suppressed.

[0002]

2. Description of the Related Art First, the structure and operation of a conventional fuel cell (fuel cell system) will be described with reference to FIG.

A fuel cell (fuel cell stack) 1 generates power using hydrogen and oxygen as raw materials. Raw materials such as hydrocarbons react with water vapor in the hydrogen gas generator 2 to become hydrogen-rich gas. At this time, since the reaction in the hydrogen gas generation unit 2 does not occur unless the temperature rises to some extent, the temperature of the hydrogen gas generation unit 2 is increased by the burner 3.

[0004] When water used for the hydrogen generation reaction in the hydrogen gas generation unit 2 contains impurities such as metal ions and organic substances, the water and the catalyst and the electrolyte membrane of the fuel cell stack 1 and the hydrogen gas generation unit 2 are removed. In order to cause the water to degrade, the water once passed through the water purification means 4 and the
Is supplied via

The fuel of the burner 3 is the fuel cell stack 1
Most of the exhaust gas that has not been consumed in the hydrogen gas is supplied to the off-gas supply system 6 through the off-gas supply system 6.
Is supplied by the gas flow control valve 7 so as to raise the temperature to a temperature equal to or higher than the reaction temperature of hydrogen gas generation. The amount of air corresponding to the total amount of the fuel gas is supplied to the combustion fan 8.
Supplied by

[0006] In this manner, the fuel cell generates power by using the hydrogen-rich gas generated by the hydrogen gas generator 2 and the air supplied by the blower 9.

[0007]

However, since the hydrogen discharged from the fuel cell stack 1 has a high temperature and a high humidity, when the temperature of the hydrogen is lowered due to the heat radiation from the pipes, the water is turned off-gas. It condenses in the supply system 6.

When moisture condenses in the off-gas supply system 6,
Since the condensed water stays in the off-gas supply system 6 to form a water phase and a gas phase, the supply of exhaust hydrogen is intermittent or water enters the burner 3, causing the burner 3 to misfire. Sometimes.

As a result, the temperature of the hydrogen gas generator 2 decreases, and it becomes impossible to generate a hydrogen-rich gas. Therefore, the output of the fuel cell stack 1 decreases, or the condensed water re-evaporates in the burner 3. Fluctuation of the pressure in the pipe due to the above causes unstable supply of the raw material gas, which may lead to unstable output of the fuel cell stack 1.

When the off-gas supply system 6 has a downward gradient and an upward gradient with respect to the flow of the exhaust hydrogen and has a possibility of liquid pooling, condensed water is collected. The burner 3 may misfire because the off-gas supply system 6 is blocked and exhaust hydrogen stops flowing. Then, the temperature of the hydrogen gas generation unit 2 decreases, and it becomes impossible to generate a hydrogen-rich gas. Therefore, the output of the fuel cell stack 1 decreases, or the supply of the raw material gas becomes unstable, and the fuel cell stack 1 Output may become unstable.

The present invention provides a fuel cell system capable of stably operating a fuel cell stack even when moisture is condensed in an off-gas supply system in consideration of the above-described conventional problems. The purpose is to:

[0012]

Means for Solving the Problems The first invention (claim 1)
Is a fuel cell system for generating power using a reaction between hydrogen and oxygen, which removes water generated by condensation of water vapor in off-gas containing excess hydrogen from the reaction. Cell system provided with a water removing means for the fuel cell.

A second aspect of the present invention (corresponding to claim 2) is the fuel cell system according to the first aspect of the present invention, comprising a water storing means for storing the removed water.

A third aspect of the present invention (corresponding to claim 3) includes a hydrogen generating means for generating hydrogen used for the reaction, and the stored water is supplied to the hydrogen generating means. It is a fuel cell system of the second invention.

A fourth aspect of the present invention (corresponding to claim 4) is the fuel cell system according to the second aspect of the present invention, wherein the water storage means is a condensed water reservoir provided in a pipe along which the off-gas flows. is there.

According to a fifth aspect of the present invention (corresponding to claim 5), the flow direction of the off-gas flow downstream of the condensed water reservoir in the pipe is substantially downward with respect to the vertical direction. It is a fuel cell system according to a fourth aspect of the present invention.

According to a sixth aspect of the present invention (corresponding to claim 6), a predetermined portion of the pipe downstream of the condensed water reservoir in the flow of the off-gas and a predetermined portion of the condensed water reservoir are communicated. A condensed water return pipe for returning the condensed water to the condensed water reservoir, wherein a predetermined portion of the pipe on the downstream side of the flow of the off-gas from the condensed water reservoir is higher than a liquid level of the condensed water reservoir. The fuel cell according to the fifth aspect of the present invention, which is substantially above the vertical direction and the predetermined portion of the condensed water reservoir is substantially lower than the liquid level of the condensed water reservoir with respect to the vertical direction. System.

In a seventh aspect of the present invention (corresponding to claim 7), the direction of the flow of the off-gas downstream of the condensed water reservoir in the pipe is substantially upward with respect to the vertical direction. It is a fuel cell system according to a fourth aspect of the present invention.

According to an eighth aspect of the present invention (corresponding to claim 8), the inside diameter of a portion of the pipe downstream of the condensed water reservoir in the flow of the off gas is larger than a predetermined value based on the flow rate of the flow It is a large seventh fuel cell system of the present invention.

[0020]

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

(Embodiment 1) First, the configuration of a fuel cell according to the present embodiment will be described with reference to FIG. 1, which is a configuration diagram of a fuel cell (fuel cell system) according to the present embodiment. The same means as those in the conventional fuel cell (see FIG. 3) are denoted by the same reference numerals.

Reference numeral 10 denotes an off-gas supply system including a battery-side off-gas supply system 10a and a burner-side off-gas supply system 10b. The battery-side off-gas supply system 10a has a downward gradient with respect to the flow of the exhausted hydrogen (that is, based on the vertical direction). Substantially downward) or vertically downward, and the burner-side off-gas supply system 10b has a downward gradient with respect to the flow of the exhaust hydrogen.

Reference numeral 11 denotes a liquid reservoir provided between the battery-side off-gas supply system 10a and the burner-side off-gas supply system 10b, and communicates the fuel cell stack 1 with the burner 3.

Reference numeral 12 denotes a condensed water return pipe, which communicates a portion of the burner side off-gas supply system 10b above the liquid surface of the liquid reservoir 11 with a portion below the liquid surface of the liquid reservoir 11 (liquid reservoir). It is necessary to communicate with the part below the liquid level of 11,
Not necessarily. However, the liquid level must be below the burner 3 to prevent backflow from the liquid reservoir 11).

Reference numeral 13 denotes condensed water stored in the liquid reservoir 11,
The water supply system supplies the hydrogen gas generation unit 2 with the water supply pump 14.

Reference numeral 15 denotes a water supply system for supplying water to the liquid reservoir 11 from outside (for supplying the hydrogen gas to the hydrogen gas generator 2).
Communicates with 1.

Reference numeral 17 denotes a reservoir water level detecting means for opening and closing the water supply valve 16 according to the level of condensed water in the reservoir 11.

The liquid reservoir 11 corresponds to the means including the water removing means and the water storing means of the present invention,
Corresponds to the hydrogen generating means of the present invention, and the offgas supply system 10
Corresponds to the means including the piping of the present invention.

Next, the operation of the fuel cell according to the present embodiment will be described.

During operation of the fuel cell 1, the fuel cell 1
Excess hydrogen not consumed in the above is supplied to the burner 3 through the off-gas supply system 10.

At this time, when the high-temperature and high-humidity excess hydrogen is cooled in the off-gas supply system 10, the water in the hydrogen condenses. The condensed water turns into a liquid and flows through the pipe of the off-gas supply system 10.

However, in the present embodiment, since the battery-side off-gas supply system 10a has a downward gradient with respect to the flow of the exhaust hydrogen, all the water condensed in the battery-side off-gas supply system 10a flows into the liquid reservoir 11. There is no possibility that the path will be blocked (if the battery-side off-gas supply system 10a has an upward gradient with respect to the flow of exhaust hydrogen, the battery-side off-gas supply system 1
The water condensed at 0a flows back to the fuel cell stack 1 and the path may be blocked by the condensed water.)

In the present embodiment, the burner-side off-gas supply system 10b is inclined downward with respect to the flow of the discharged hydrogen, and a portion above the liquid surface of the liquid reservoir 11 in the middle thereof is taken as the liquid surface of the liquid reservoir 11. Since the lower portion communicates with the condensed water return pipe 12, almost all the water condensed in the burner side off-gas supply system 10b returns to the liquid reservoir 11 (condensed water in the liquid reservoir 11 decreases. In this case, the water supply valve 16 is opened by the liquid reservoir level detecting means 17 and purified water is supplied from the water supply system 15 to the liquid reservoir 11 through the water purification means 4).

Thus, the clogging of the off-gas supply system 10 by the condensed water is eliminated, and the supply of the exhaust hydrogen and the raw material gas is hardly unstable. Therefore, a stable operation of the fuel cell can be realized by stable supply of the exhaust hydrogen and the source gas.

The water in the liquid reservoir 11 is (1) water purified by the water purifying means 4 and supplied to the hydrogen gas generator 2 but not used for the reaction, and (2) water in the fuel cell 1. This is water that is a mixture of water generated by the reaction of hydrogen and oxygen during power generation, and can be supplied to the hydrogen gas generation unit 2 and reused. However, water purification means (not shown)
It is preferable to supply the hydrogen gas to the hydrogen gas generator 2 after purification (because the catalyst and the electrolyte membrane in the fuel cell 1 and the hydrogen gas generator 2 are less likely to deteriorate).

(Embodiment 2) Next, the configuration of the fuel cell according to the present embodiment will be described with reference to FIG. 2, which is a configuration diagram of the fuel cell according to the present embodiment. In addition,
The same units as those in the above-described fuel cell of the first embodiment (see FIG. 1) are denoted by the same reference numerals.

Reference numeral 18 denotes an off-gas supply system comprising a battery-side off-gas supply system 18a and a burner-side off-gas supply system 18b. The battery-side off-gas supply system 18a has a downward gradient (or a vertical downward gradient), and The side off-gas supply system 18b has a vertical upward gradient. The burner-side off-gas supply system 18b has an inner diameter equal to or greater than a predetermined value determined by the flow rate of the exhaust hydrogen flowing through the inside.

Reference numeral 11 denotes a liquid reservoir provided between the cell-side off-gas supply system 18a and the burner-side off-gas supply system 18b, and communicates the fuel cell stack 1 with the burner 3.

The off-gas supply system 18 corresponds to a means including the piping of the present invention.

Next, the operation of the fuel cell according to the present embodiment will be described.

The high-temperature and high-humidity exhaust hydrogen is cooled in the off-gas supply system 18 and water condenses.

The water condensed in the battery-side off-gas supply system 18a all flows into the liquid reservoir 11 because the direction of the flow of exhaust hydrogen in the battery-side off-gas supply system 18a is downward.

On the other hand, the water condensed in the burner-side off-gas supply system 18b is supplied to the burner-side off-gas supply system 1b.
Since the direction of the flow of the exhaust hydrogen in 8b is vertically upward,
It is indeterminate whether to flow in the direction of the burner 3 or in the direction of the reservoir 11.

Therefore, the burner-side off-gas supply system 18b
The flow of water condensed in the interior will be described in detail.

The water condensed in the burner-side off-gas supply system 18b first adheres to the tube wall of the burner-side off-gas supply system 18b.

The water adhering to the pipe wall is expressed by (a) due to the magnitude of three forces: a vertical force due to gravity, a frictional force with the pipe wall, and a vertical force generated by friction with the discharged hydrogen. ) Either stay in that location, (b) flow out in the direction of the burner 3 or (c) flow out in the direction of the reservoir 11.

Which of these three cases occurs depends on the relationship between the amount of condensed water, the flow rate of exhaust hydrogen, the temperature, and the like.
It becomes easier to flow in the direction of 1, and it becomes easier to flow in the direction of the burner 3 as the flow rate of the discharged hydrogen, which determines the flow rate of the discharged hydrogen, becomes larger. (It is noted that the stay at that place is when the three forces are balanced. Since the downward force due to gravity increases as the amount of condensed water increases, in this case, the water eventually flows toward the reservoir 11).

Therefore, in consideration of the fact that the flow rate and temperature of the discharged hydrogen vary depending on the operating conditions, the water condensed on the tube wall is not practically allowed to flow in the direction of the burner 3 under any operating conditions. Thus, the inner diameter of the burner-side off-gas supply system 18b is increased so as to reduce the flow rate of the exhaust hydrogen.

When the burner-side off-gas supply system 10b (see FIG. 1) has a downward slope as in Embodiment 1 described above, the burner-side off-gas supply system 10b
To prevent condensed water from accumulating in b,
A portion of the burner-side off-gas supply system 10b above the liquid surface of the liquid reservoir 11 and a portion of the liquid reservoir 11 below the liquid surface must be communicated by the condensed water return pipe 12. Furthermore, in order to make the burner-side off-gas supply system 10b have a downward gradient with respect to the flow of the discharged hydrogen, the portion above the liquid surface of the liquid reservoir 11 (that is, the portion without liquid) needs to be sufficiently wide. . Therefore, in the above-described fuel cell according to the first embodiment, the size of the liquid reservoir 11 may be increased to increase the size of the device.

In the fuel cell of this embodiment, the liquid reservoir 11
It is not necessary to widen a portion where there is no liquid above the liquid level, so that a compact fuel cell capable of stably supplying exhaust hydrogen and source gas can be realized without increasing the size of the apparatus. .

In the above, the first and second embodiments have been described in detail.

The water generated by the condensation of the water vapor in the off-gas of the present invention is water generated by the natural cooling of the pipes of the off-gas supply systems 10 and 18 in the above-described embodiment. However, the present invention is not limited to this. For example, water condensed by forcibly cooling the off-gas supply system with a fan or cold water may be used.

In the present embodiment, the surplus hydrogen in the reaction of the present invention is used to raise the temperature of the hydrogen generator 2, but the present invention is not limited to this. It may be used in other applications such as.

In the first embodiment described above, the condensed water return pipe of the present invention has a portion above the liquid surface of the liquid reservoir 11 of the burner-side off-gas supply system 10b and a portion below the liquid surface of the liquid reservoir 11. However, the present invention is not limited to this. For example, when the piping of the burner-side off-gas supply system 10b is extremely short, or when the accuracy of removing the condensed water may be slightly poor, there is no problem. May not be provided.

In the present embodiment, the removed water of the present invention is supplied to the hydrogen gas generator 2 after being stored in the liquid reservoir 11, but is not limited to this. It may be used as drinking water (after being purified) or may be discarded.

In short, the fuel cell system of the present invention
A fuel cell system for generating power using a reaction between hydrogen and oxygen, comprising a water removing unit for removing water generated by condensation of water vapor in off-gas containing excess hydrogen from the reaction. It is a fuel cell system provided.

As described above, the present invention provides a hydrogen gas generating section for generating a hydrogen-rich gas from a raw material such as a hydrocarbon,
A fuel cell stack that generates electric power using the hydrogen-rich gas and oxygen generated in the hydrogen gas generation unit as raw materials, and exhaust gas discharged from the fuel cell stack flows from the upstream side of the exhaust hydrogen flow to a cell-side off-gas supply system, A liquid reservoir for storing water in the condensed exhaust hydrogen, an off-gas supply system composed of a burner-side off-gas supply system, and a burner that burns the exhaust hydrogen flowing through the off-gas supply system and uses heat to supply battery-side off-gas The system is inclined downward or vertically downward with respect to the flow of exhaust hydrogen, and the burner-side off-gas supply system is inclined downward with respect to the flow of exhaust hydrogen, and is disposed above the liquid level in the reservoir, and the burner-side off-gas supply system And a condensed water return pipe that communicates the vicinity of the burner with a portion below the liquid level of the liquid reservoir. Thereby, it is possible to prevent the flow of the exhaust hydrogen and the raw material from becoming unstable due to the condensation of water in the off-gas supply system, and to provide a fuel cell that can be operated stably.

Further, according to the present invention, the off-gas supply system on the battery side is inclined downward or vertically downward with respect to the flow of waste hydrogen,
A fuel cell characterized in that the burner-side off-gas supply system has an upward gradient, and the inner diameter thereof is determined by the maximum exhaust hydrogen flow rate flowing through the off-gas supply system. As a result, the size of the liquid reservoir can be reduced, and a compact and stable fuel cell can be provided.

That is, according to the present invention, all the water condensed in the battery-side off-gas supply system flows to the reservoir, all the water condensed in the burner-side off-gas supply system returns to the reservoir, and the water stays in the off-gas supply system. However, the off-gas supply system does not block. Therefore, a fuel cell that can operate stably can be obtained.

Further, water condensed in the burner-side off-gas supply system can be returned to the liquid reservoir without increasing the size of the liquid reservoir. Therefore, a fuel cell which is compact and can be operated stably can be obtained.

[0061]

As is apparent from the above description,
The present invention has an advantage that the fuel cell stack can be operated stably even when water condenses in the off-gas supply system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a fuel cell according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram of a fuel cell according to Embodiment 2 of the present invention.

FIG. 3 is a configuration diagram of a conventional fuel cell.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 Fuel cell (fuel cell stack) 2 Hydrogen gas generator 3 Burner 4 Water purifying means 10 Off gas supply system 10a Battery side off gas supply system 10b Burner side off gas supply system 11 Liquid reservoir 12 Condensed water return pipe 13 Water supply system 14 Water supply Pump 15 Water replenishment system 16 Water replenishment valve 17 Reservoir water level detecting means 18 Off gas supply system 18a Battery side off gas supply system 18b Burner side off gas supply system

Continued on the front page (72) Inventor Masataka Ozeki 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Reference) 5H027 AA02 BA01 BA05

Claims (8)

[Claims] 1. A fuel cell system for generating electricity by utilizing a reaction between hydrogen and oxygen, wherein water generated by condensation of water vapor in off-gas containing excess hydrogen from the reaction is removed. Cell system provided with a water removing means for the fuel cell. 2. The fuel cell system according to claim 1, further comprising a water storage unit for storing the removed water. 3. The fuel cell system according to claim 2, further comprising a hydrogen generator for generating hydrogen used for the reaction, wherein the stored water is supplied to the hydrogen generator. 4. The water storage means is a condensed water reservoir provided in a pipe along which the off-gas flows.
The fuel cell system as described. 5. The fuel cell system according to claim 4, wherein a direction of the flow of the off-gas downstream of the condensed water reservoir in the pipe is substantially downward with respect to a vertical direction. 6. A method for returning the condensed water to the condensed water reservoir, which communicates a predetermined portion of the pipe downstream of the condensed water reservoir with respect to the flow of the off gas and a predetermined portion of the condensed water reservoir. A condensed water return pipe, a predetermined portion of the pipe downstream of the condensed water reservoir in the flow of the off-gas is substantially above a liquid surface of the condensed water reservoir with respect to a vertical direction, 6. The fuel cell system according to claim 5, wherein the predetermined portion of the condensed water reservoir is substantially lower than a liquid level of the condensed water reservoir with respect to a vertical direction. 7. The fuel cell system according to claim 4, wherein a direction of the flow of the off-gas downstream of the condensed water reservoir in the pipe is substantially upward with respect to a vertical direction. 8. The fuel cell system according to claim 7, wherein an inner diameter of a portion of the pipe downstream of the condensed water reservoir with respect to the flow of the off gas is larger than a predetermined value based on a flow rate of the flow.