JP2002260698A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of recycling exhaust gas by ejectors without causing waste of electric power and noise, at starting of a fuel cell stack. SOLUTION: This fuel cell system is provided with fuel gas supply passages 3 and 8 for supplying pressurized anode gas or cathode gas to the fuel cell stack 1; exhaust gas circulating passages 11 and 12 for supplying the exhaust gas from the fuel cell stack to the fuel gas supply passages; and the ejectors 13 and 14 for introducing the exhaust gas from the exhaust gas circulating passages to a fuel gas passage with fuel gas as a driving fluid. The system is provided further with an insert gas supply passage 15 for supplying pressurized nitrogen gas to the ejectors as the driving fluid, and a gas supply control device for controlling the supply of the fuel gas and inert gas, and starts the circulation of the gas in the exhaust gas circulating passages by supplying the nitrogen gas to the ejectors, at the starting of the fuel cell stack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a fuel cell system in which exhaust gas from a fuel cell stack is recirculated by an ejector.

[0002]

2. Description of the Related Art Fuel cell stacks
Hydrogen as an anode gas and oxygen as a cathode gas as the fuel are supplied to cause an electrochemical reaction to obtain electric energy. Most of both the anode gas and the cathode gas supplied to the fuel cell stack are consumed by the fuel cell stack, but a part of the unconsumed anode gas and cathode gas are respectively discharged as exhaust gas from the fuel cell stack. In order to increase the efficiency of the system, the exhaust gas is supplied again to the fuel cell stack by using an ejector, as proposed in Japanese Patent Publication No. Hei 10-511497.

[0003] Further, in the fuel cell system using the ejector, nitrogen gas, which is an inert gas, is supplied to the ejector in order to purge residual components in the ejector when the ejector is stopped. -54799. Further, Japanese Patent No. 2835181 discloses a system in which nitrogen, which is an inert gas, is supplied as a driving fluid to an ejector for the purpose of inactivating a fuel cell, and the gas supplied to the fuel cell is sucked.

By the way, the ejector has an inexpensive and simple structure, but it is necessary to supply a large amount of gas as a driving fluid to the ejector in order to circulate the gas from the time of startup when no fluid is flowing. For example, if a large amount of anode gas is supplied, a large amount of cathode gas that must be supplied at the same pressure must also be supplied. Need to work with This causes a problem in that electric power is consumed for operating the compressor before power generation in the fuel cell stack, or an expensive and large battery must be used as a separate power supply for driving the compressor. Also, high-speed driving of the compressor is problematic in terms of noise.

The present invention has been made in view of such a conventional problem, and a fuel cell system capable of circulating exhaust gas by an ejector without wasting power or generating noise when starting up a fuel cell stack. It is intended to provide.

[0006]

According to a first aspect of the present invention, a fuel gas supply passage for supplying a pressurized fuel gas to a fuel cell stack, and an exhaust gas from the fuel cell stack are supplied to the fuel gas supply passage. In a fuel cell system including an exhaust gas circulation channel and an ejector that introduces exhaust gas from the exhaust gas circulation channel into the fuel gas channel using the fuel gas as a driving fluid, the pressurized inert gas is used as a driving fluid. An inert gas supply channel for supplying to an ejector; and a gas supply control device for controlling the supply of the fuel gas and the inert gas, wherein the gas supply control device ejects the inert gas when the fuel cell stack is started. To start gas circulation in the exhaust gas circulation channel.

[0007] A second invention is the above-mentioned first invention, wherein:
Nitrogen gas was supplied as an inert gas.

In a third aspect, the gas supply control device according to the first aspect is configured to supply a fuel gas to the fuel cell stack simultaneously with the inert gas.

In a fourth aspect, the gas supply control device according to the first aspect is configured to gradually reduce the flow rate of the inert gas supplied at the time of starting.

According to a fifth aspect of the present invention, the gas supply control device according to the first aspect of the present invention includes a flow sensor for detecting gas circulation in the gas circulation channel, and starts gas circulation based on an output from the sensor. Is determined.

According to a sixth aspect of the present invention, there is provided a gas supply control device according to the fifth aspect, wherein the first valve device for adjusting the flow rate of the fuel gas supplied to the ejector and the flow rate of the inert gas supplied to the ejector are adjusted. And a controller that controls the operation of the first and second valve devices based on a signal from the sensor.

According to a seventh aspect, in the first aspect,
An anode gas containing hydrogen is supplied to the fuel gas supply passage as a fuel gas, and anode exhaust gas from a fuel cell stack is circulated as the exhaust gas to the fuel gas supply passage.

According to an eighth aspect, in the first aspect,
A cathode gas containing oxygen is supplied to the fuel gas supply channel as a fuel gas, and a cathode exhaust gas from a fuel cell stack is circulated as the exhaust gas to the fuel gas supply channel.

[0014]

According to the first aspect, since the inert gas is supplied to the ejector as a driving fluid to start the gas circulation when the fuel cell stack is started, the gas circulation is started. There is no need to pressurize and supply only the fuel gas (cathode gas or anode gas) from the beginning of startup. Therefore, when a compressor is provided as the gas pressurizing means, the operation can be minimized, and the generation of useless power and noise can be suppressed. In addition, since the gas can be easily circulated, the gas is not wasted and the power generation efficiency is high.

According to the second invention, a system can be easily constructed by using inexpensive and readily available nitrogen gas as the inert gas.

According to the third invention, at the start of gas circulation,
Since the fuel gas is simultaneously supplied in addition to the inert gas as the driving fluid, the power generation of the fuel cell stack can be started earlier.

According to the fourth aspect, since the supply flow rate of the inert gas is gradually reduced, it is possible to smoothly shift to the fuel gas circulation state without stopping the gas circulation. The reliability of the start of circulation is improved, and power generation by the fuel cell stack can be started more reliably.

According to the fifth or sixth aspect of the invention, the circulation of the gas is detected by the sensor provided in the exhaust gas circulation channel, so that the timing of supplying the fuel gas and the timing of supplying / stopping the inert gas. Can be accurately controlled, the reliability of the circulation start is improved, and the power generation of the fuel cell stack can be reliably performed.

The circulation system via the ejector may be configured to introduce the anode exhaust gas into the anode gas as the fuel gas as described in the seventh invention, or to convert the cathode exhaust gas into the fuel gas as described in the eighth invention. , Or one or both of the configurations for introducing the cathode gas. For example, since the ejector is provided only on the anode side by circulating the gas only on the anode side, the configuration is simplified by reducing the number of ejectors that supply the inert gas to circulate the exhaust gas. In addition, the amount of use of the inert gas as the driving fluid can be reduced.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating the configuration of a fuel cell system according to the present invention. The fuel cell stack 1 receives an anode gas and a cathode gas as fuel gas and generates power by an electrochemical reaction. The anode gas is hydrogen gas stored in the high-pressure hydrogen tank 2 in this embodiment, and is supplied to the fuel cell stack 1 via the fuel gas supply flow path 3. In the middle of the fuel gas supply passage 3, a shutoff valve 5 and a pressure regulating valve 6 are interposed as a first valve device for controlling the flow rate of the anode gas. The cathode gas is air and is pressurized by the compressor 7,
The fuel gas is supplied to the fuel cell stack 1 through the fuel gas supply channel 8. In the middle of the fuel gas supply flow path 8, a shutoff valve 9 and a pressure regulating valve 10 are interposed as a second valve device for controlling the flow rate of the cathode gas.

The anode gas or the cathode gas not consumed in the fuel cell stack 1 is discharged from the fuel cell stack 1 as exhaust gas. The anode exhaust gas is returned to the fuel gas supply channel 3 downstream of the pressure regulating valve 6 via the exhaust gas circulation channel 11. Further, the cathode exhaust gas is returned to the fuel gas supply channel 8 downstream of the pressure regulating valve 10 via the exhaust gas circulation channel 12. Ejectors 13 and 14 are provided at a portion where the anode gas exhaust gas circulation channel 11 is connected to the fuel gas supply channel 3 and at a portion where the cathode gas exhaust gas circulation channel 12 is connected to the fuel gas supply channel 8, respectively. Is provided.

An outlet portion of the exhaust gas circulation passage 11 for the anode exhaust gas is opened to a negative pressure generating portion of the ejector 13, and the anode exhaust gas supplied from the fuel gas supply passage 3 or an inert gas to be described later is used as a driving fluid to drive the anode exhaust gas. Is circulated through the fuel gas supply channel 3. The outlet of the exhaust gas circulation channel 12 for the cathode exhaust gas is opened to a negative pressure generating portion of the ejector 14, and the cathode exhaust gas is supplied from the fuel gas supply channel 8 or an inert gas as a driving fluid to convert the cathode exhaust gas into a fuel gas. Circulate through the supply channel 8.

An inert gas supply passage 15 is connected to the fuel gas supply passages 3 and 8 so as to be connected to intermediate portions between the respective pressure regulating valves 6 and 10 and the ejectors 13 and 14. The inert gas supply channel 15 supplies nitrogen gas from a high-pressure nitrogen gas tank 16 as an inert gas. The inert gas supply passage 15 is provided with a pressure reducing valve 17 and a shutoff valve 18 as valve devices for controlling the flow rate of the nitrogen gas. ,
8 is connected. As shown in FIG. 2, the high-pressure nitrogen tank 16 may be connected to the inert gas supply flow path 15 via the joint connector 19 only when used.

FIG. 3 shows the supply timing of the inert gas and the fuel gas under the above configuration. As shown in the figure, when the fuel cell system is started, the shut-off valves 5 and 9 are closed, the shut-off valve 18 is opened in a state where the supply of the anode gas and the cathode gas is stopped, and the nitrogen gas adjusted to a predetermined pressure by the pressure reducing valve 17. Through the inert gas supply channel 15 to the ejector 13,
14. As a result, the ejectors 13 and 14 respectively use the nitrogen gas as a driving fluid and
2, the shutoff valves 5 and 9 are opened, and the anode gas and the cathode gas adjusted to a predetermined pressure or flow rate by the pressure adjusting valves 6 and 10 are supplied through the fuel gas supply channels 3 and 8. To the fuel cell stack 1. After the supply of the fuel gas, the fuel gas continues to circulate the exhaust gas by the ejectors 13 and 14 as a driving fluid. Thereafter, the shutoff valve 18 is closed and the supply of the nitrogen gas is terminated.

In this way, the exhaust gas circulation is started by supplying the nitrogen gas as a driving fluid to the ejector at the beginning of the startup to start the exhaust gas circulation, without operating the starting device such as the compressor which consumes a large amount of electric power. Therefore, it is possible to suppress wasteful power consumption before the startup when the fuel cell is not generating power and generation of the compressor noise at the startup. As described above, the gas supply control at the time of startup is performed by a gas supply control device (not shown) in which each valve device is configured by an electromagnetic valve, and is controlled to be opened and closed by a controller including a microcomputer and its peripheral devices. ) Can be realized.

FIGS. 4 and 5 show another embodiment relating to the supply control of the inert gas and the fuel gas. In the embodiment shown in FIG. 4, at the start of circulation, in addition to the nitrogen gas used as the driving fluid for the ejectors 13 and 14 #, the anode side simultaneously supplies reduced-pressure hydrogen from the high-pressure tank 2 to the fuel cell stack 1. Supplies a mixed gas of nitrogen gas and hydrogen gas as an anode gas. The cathode side operates the compressor 7 to supply air, thereby supplying the fuel cell stack 1 with a mixed gas of nitrogen gas and air as a cathode gas. According to this method, the flow rate of the driving fluid necessary for the circulation of the exhaust gas can be supplemented with the nitrogen gas, and a certain amount of the anode gas and the cathode gas are also supplied to the fuel cell stack 1 from the beginning, so that the fuel cell stack Power generation can be started.

In the embodiment shown in FIG. 5, the supply of nitrogen gas is gradually reduced at the end of the starting process. If the supply of nitrogen gas is suddenly stopped at the end of the process, the circulation of the exhaust gas may be stopped. However, such a gradual stop can avoid the disadvantage of stopping the exhaust gas circulation. In this case, as shown in the figure, by gradually increasing the flow rates of the anode gas and the cathode gas in accordance with the decrease in the flow rate of the nitrogen gas, a smooth transition to the ejector drive by the fuel gas is made.

FIGS. 6 and 7 show second and third embodiments of the fuel cell system according to the present invention, respectively. In each figure, the same parts as those in FIG. 1 are denoted by the same reference numerals. In the second embodiment shown in FIG. 6, the ejector 13 is provided only in the fuel gas supply channel 3 for the anode gas, and the exhaust gas circulation channel 11 circulates the anode exhaust gas and the inert gas supply channel 15 at the time of startup. The exhaust gas is supplied to the cathode electrode side, and the exhaust gas is not circulated on the cathode electrode side. Excess air is discharged to the atmosphere via an exhaust gas passage 21 provided with a pressure regulating valve 20. According to this embodiment, since the ejector and the inert gas are supplied to only one system on the anode electrode side, the amount of nitrogen gas used can be reduced and the cost of the apparatus can be reduced.

In the third embodiment shown in FIG. 7, a flow sensor 23 is provided in each of the exhaust gas circulation channels 11 and 12, and after detecting that gas circulation has actually started, the anode gas and the cathode gas are detected. The timing at which the gas is supplied and the timing at which the nitrogen gas is stopped are controlled. The first and second embodiments are configured to control the gas supply / stop by estimating the timing at which the gas circulation starts, but in this embodiment, the actual gas circulation can be detected, so that the accuracy is higher and the gas utilization is higher. Efficient control can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a fuel cell system according to the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment relating to a connection portion of the high-pressure nitrogen tank in FIG. 1;

FIG. 3 is a timing chart of control of supply of an inert gas and a fuel gas in the first embodiment.

FIG. 4 is a timing chart of another embodiment relating to supply control of an inert gas and a fuel gas.

FIG. 5 is a timing chart of another embodiment relating to supply control of an inert gas and a fuel gas.

FIG. 6 is a schematic configuration diagram of a second embodiment of the fuel cell system according to the present invention.

FIG. 7 is a schematic configuration diagram of a third embodiment of the fuel cell system according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 High-pressure hydrogen tank 3 Fuel gas supply flow path 5 Shutoff valve 6 Pressure control valve 7 Compressor 8 Fuel gas supply flow path 9 Shutoff valve 10 Pressure control valve 11 Exhaust gas circulation path 12 Exhaust gas circulation path 13 Ejector 14 Ejector Reference Signs List 15 inert gas supply flow path 16 high-pressure nitrogen tank 17 pressure reducing valve 18 shutoff valve 19 joint connector 20 pressure regulating valve 21 exhaust gas flow path 23 flow sensor

Claims (8)

[Claims] A fuel gas supply passage for supplying pressurized fuel gas to the fuel cell stack; an exhaust gas circulation passage for supplying exhaust gas from the fuel cell stack to the fuel gas supply passage; An ejector for introducing exhaust gas from the exhaust gas circulation channel into the fuel gas channel as a driving fluid, wherein the inert gas supply channel supplies pressurized inert gas to the ejector as a driving fluid. And a gas supply control device that controls the supply of the fuel gas and the inert gas. The gas supply control device supplies the inert gas to the ejector when the fuel cell stack is started, and supplies the inert gas to the ejector in the exhaust gas circulation flow path. A fuel cell system configured to start gas circulation. 2. The fuel cell system according to claim 1, wherein nitrogen gas is supplied as said inert gas. 3. The fuel cell system according to claim 1, wherein the gas supply control device is configured to supply a fuel gas to the fuel cell stack simultaneously with the inert gas. 4. The fuel cell system according to claim 1, wherein the gas supply control device is configured to gradually reduce the flow rate of the inert gas supplied at the time of starting. 5. The fuel cell system according to claim 1, wherein the gas supply control device includes a flow sensor for detecting gas circulation in the gas circulation flow path, and the gas circulation control is performed based on an output from the sensor. Fuel cell system configured to determine the start of fuel cell. 6. A fuel cell system according to claim 5, wherein said gas supply control device includes a first valve device for adjusting a flow rate of a fuel gas supplied to an ejector, and a flow rate of an inert gas supplied to the ejector. And a controller for controlling the operation of the first and second valve devices based on a signal from the sensor. 7. The fuel cell system according to claim 1, wherein an anode gas containing hydrogen is supplied as fuel gas to the fuel gas supply passage, and an anode exhaust gas from a fuel cell stack is used as the exhaust gas. A fuel cell system that circulates through a supply channel. 8. The fuel cell system according to claim 1, wherein a cathode gas containing oxygen is supplied as a fuel gas to the fuel gas supply passage, and a cathode exhaust gas from a fuel cell stack is used as the exhaust gas. A fuel cell system that circulates through a supply channel.