JP6830199B2 - Fuel cell system and its operation method - Google Patents

Description

The present invention relates to a fuel cell system and a method of operating the same.

A fuel cell system is a system for generating electric power by electrochemically reacting a hydrogen-containing gas with an oxidant gas. According to the fuel cell system, highly efficient small-scale power generation is possible.

In conventional fuel cell systems, hydrogen-containing gas (also referred to as "anode-off gas") that was not used for power generation may be returned to the anode gas supply path of the fuel cell and recycled in order to improve hydrogen utilization efficiency. .. However, the anode off gas contains impurities such as nitrogen gas. Therefore, if the anode off-gas is recycled for a long time, the concentration of impurities in the hydrogen-containing gas flowing through the anode gas supply path may increase, and the power generation efficiency may decrease. Therefore, it is necessary to periodically discharge the gas containing impurities from the recycling route for returning the anode off-gas to the anode gas supply route. The gas discharged from the recycling route is called purged gas.

The purge gas contains not only impurities but also flammable hydrogen gas. Therefore, it is important to dilute the purge gas with air to reduce the concentration of hydrogen gas to a safe concentration, and then discharge the diluted purge gas to the outside of the fuel cell system (for example, the outside of the housing). A flammable gas sensor is usually used to detect the concentration of hydrogen gas contained in the purge gas.

Patent Document 1 describes an automobile fuel cell system configured to mix a gas discharged from an anode and a gas discharged from a cathode and then discharge the gas into the atmosphere.

FIG. 7 shows a conventional fuel cell system for automobiles described in Patent Document 1. As shown in FIG. 7, the automobile fuel cell system described in Patent Document 1 includes a fuel cell stack 201, a ventilation pipe 203, an exhaust fuel diluter 205, a relief valve 207, and a hydrogen sensor 209. The hydrogen sensor 209 is arranged inside the exhaust fuel diluter 205. Air is guided from the ventilation pipe 203 to the exhaust fuel diluter 205 through the relief valve 207. In the exhaust fuel diluter 205, the anode off gas is diluted by air.

Japanese Patent No. 4477820

However, flammable gas sensors such as hydrogen sensors are vulnerable to moisture. Therefore, if the combustible gas sensor is arranged in an environment exposed to high humidity purge gas, the combustible gas sensor deteriorates quickly. Therefore, it is necessary to accelerate the inspection and replacement cycle of the combustible gas sensor. This reduces the value of the fuel cell system.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a fuel cell system capable of suppressing deterioration of a combustible gas sensor and maintaining high safety for a long period of time.

In order to solve the above-mentioned conventional problems, the fuel cell system of the present invention is used.
A fuel cell with an anode inlet and an anode outlet,
The anode gas supply path connected to the anode inlet and
A circulation path having one end connected to the anode outlet and the other end connected to the anode gas supply path.
A purge path that has one end connected to the circulation path and extends to a predetermined confluence position,
A housing containing the fuel cell, the anode gas supply path, the circulation path, and the purge path.
A gas merging portion provided inside the housing and merging hydrogen-containing gas discharged from the circulation path through the purging path with the diluted gas at the predetermined merging position.
An exhaust port provided in the housing and for discharging the hydrogen-containing gas diluted by the dilution gas from the gas confluence to the outside of the housing.
With the combustible gas sensor arranged on the upstream side in the flow direction of the diluted gas with reference to the predetermined merging position,
It is equipped with.

Further, the operation method of the fuel cell system of the present invention is the operation method of the fuel cell system described above.
Using a circulation path for returning the unused hydrogen-containing gas discharged from the anode of the fuel cell to the inlet of the anode, the hydrogen-containing gas is returned to the anode for reuse.
When the generated power or voltage of the fuel cell becomes a predetermined value or less during the period when the fuel cell is generating power, the unused hydrogen-containing gas is purged from the circulation path to the purge path.
Diluting the purge gas, which is the unused hydrogen-containing gas discharged from the purge path, with a dilution gas,
To detect the concentration of hydrogen gas in the diluted purge gas,
To measure the elapsed time until the concentration of the hydrogen gas in the diluted purge gas falls below the reference value, and
When the elapsed time exceeds the threshold time, the state or abnormality of the fuel cell system is notified, or the operation of the fuel cell system is stopped.
Is included.

According to the present invention, deterioration of the combustible gas sensor is suppressed, and the safety of the fuel cell system is maintained for a long period of time.

Configuration diagram of the fuel cell system according to the first embodiment of the present invention Detailed configuration diagram of the gas confluence and its surroundings in the fuel cell system of FIG. Graph showing the output voltage of the fuel cell stack Flowchart showing the processing executed in the control Configuration diagram of the fuel cell system according to the second embodiment of the present invention Detailed configuration diagram of the gas confluence and its surroundings in the fuel cell system of FIG. Configuration diagram of a conventional fuel cell system

For example, a semiconductor type combustible gas sensor is used in the fuel cell system. The semiconductor-type combustible gas sensor detects the presence of flammable gas such as hydrogen and hydrocarbon by the change in conductivity of the semiconductor element, and can detect the concentration of combustible gas with high sensitivity.

If the combustible gas sensor is placed in a high humidity environment where dew condensation occurs for a long period of time, the characteristics of the combustible gas sensor may change and the life of the combustible gas sensor may be shortened. Purge gas in fuel cell systems has high humidity and is prone to condensation. Therefore, if the combustible gas sensor is arranged at a position where it is directly exposed to the purge gas, the combustible gas sensor may deteriorate and the concentration of the combustible gas inside the housing may not be detected correctly.

The fuel cell system of the first invention includes a fuel cell having an anode inlet and an anode outlet, an anode gas supply path connected to the anode inlet, one end connected to the anode outlet, and the anode gas supply path. A circulation path having the other end connected to, a purge path having one end connected to the circulation path and extending to a predetermined merging position, the fuel cell, the anode gas supply path, the circulation path, A gas containing the purge path and a gas provided inside the housing and merging the hydrogen-containing gas discharged from the circulation path through the purge path with the diluted gas at the predetermined merging position. With reference to the merging portion, the exhaust port provided in the housing and for discharging the hydrogen-containing gas diluted by the diluting gas from the gas merging portion to the outside of the housing, and the predetermined merging position. By providing the combustible gas sensor arranged on the upstream side in the flow direction of the diluted gas, it is possible to prevent the combustible gas sensor from being directly exposed to the hot and humid purge gas discharged from the purge path. Condensation can also be prevented from forming on the combustible gas sensor. Therefore, deterioration of the combustible gas sensor is suppressed, and the life of the combustible gas sensor can be extended. In addition, the measurement error of the combustible gas sensor is reduced. As a result, the safety and reliability of the fuel cell system can be ensured for a long period of time.

In a second aspect of the invention, in particular, the purge path of the fuel cell system of the second invention includes an opening that opens toward the predetermined confluence position, and the dilution from the combustible gas sensor to the exhaust port. Since the opening of the purge path is present on the gas flow path, the purge gas can be reliably diluted with air, and the diluted purge gas can be reliably guided to the exhaust port.

The third invention is based on the fact that the distance from the predetermined confluence position of the fuel cell system of the first or second invention to the exhaust port is shorter than the distance from the combustible gas sensor to the exhaust port. It is possible to prevent the moisture contained in the purge gas from reaching the combustible gas sensor as much as possible.

In the fourth invention, in particular, the gas merging portion of the fuel cell system of any one of the first to third inventions has a partition wall surrounding the predetermined merging position, so that the merging position is from the purge path. It is possible to effectively control the diffusion of the purge gas discharged toward.

In a fifth aspect of the invention, in particular, the partition wall of the fuel cell system of the fourth invention constitutes a wind tunnel having one end and the other end open, and the one end of the wind tunnel and the other end of the wind tunnel. By connecting the purge path to the partition wall between the two, the diffusion of the purge gas can be controlled more effectively.

The sixth invention ensures that the moisture contained in the purge gas does not reach the combustible gas sensor, in particular, by disposing the combustible gas sensor outside the wind tunnel of the fuel cell system of the fifth invention. At the same time, the concentration of hydrogen gas in the purge gas diluted with air can be detected.

In a seventh invention, in particular, the fuel cell of the fuel cell system of any one of the first to sixth aspects further has a cathode outlet, and the fuel cell system has a cathode connected to the cathode outlet. An off-gas mixer further provided with an off-gas path, an off-gas mixer that communicates the cathode off-gas path and the purge path to mix the oxidizing agent gas in the cathode off-gas path and the hydrogen-containing gas in the purge path. Therefore, the hydrogen concentration (hydrogen gas concentration) in the purge gas can be efficiently lowered.

The eighth invention, in particular, is due to dew condensation because the off-gas mixer of the fuel cell system of the seventh invention includes a gas-liquid separator to remove water from the mixed gas of the cathode off-gas and the purge gas. Deterioration of the combustible gas sensor can be suppressed more effectively.

A ninth aspect of the invention is that the housing of the fuel cell system of any one of the first to eighth aspects has an intake port for taking in air as a diluting gas from the outside of the housing. Therefore, the air taken into the inside of the housing from the intake port can be used as the oxidant gas of the fuel cell. The air taken into the housing from the intake port can also be used as a diluting gas for the hydrogen-containing gas discharged from the fuel cell.

In the tenth invention, in particular, since the exhaust port of the fuel cell system of the ninth invention is provided on the upper side in the vertical direction with respect to the intake port, hydrogen gas is likely to be discharged to the outside of the housing. ..

In the eleventh invention, in particular, the fuel cell system of any one of the first to tenth inventions operates the exhaust fan by further including an exhaust fan arranged at a position facing the exhaust port. When this is done, the inside of the housing becomes negative pressure. Since the air flow direction in the internal space of the housing is determined in a fixed direction, it is possible to reliably measure the concentration of hydrogen gas with one combustible gas sensor.

A twelfth invention, in particular, the fuel cell system of any one of the first to eleventh inventions further comprises an air-cooled radiator for removing heat from the fuel cell coolant, by the diluent gas. By further diluting the diluted hydrogen-containing gas with the air that has passed through the radiator, the concentration of the hydrogen gas in the purge gas can be further reduced and discharged to the outside of the housing.

A thirteenth invention, in particular, the fuel cell system of any one of the first to tenth inventions further comprises a purge valve arranged in the purge path and a controller for controlling the opening and closing of the purge valve. By providing the fuel cell, the output voltage of the fuel cell can be kept high at all times.

In the fourteenth invention, in particular, the controller of the fuel cell system of the thirteenth invention is controlled to open the purge valve at a predetermined timing during a period in which the fuel cell is generating electricity. The output voltage of the fuel cell can be kept high at all times.

A fifteenth aspect of the present invention is particularly, the controller of the 14 fuel cell system of the present invention the output of the combustible gas sensor monitors the period from the time of opening the purge valve until a predetermined time elapses, the combustible When the output of the gas sensor exceeds the threshold value, an electric process for notifying the state of the fuel cell system or an abnormality of the fuel cell system is executed, or the operation of the fuel cell system is stopped. The fuel cell system can be operated more safely.

The method for operating the fuel cell system of the sixteenth invention is, in particular, the method for operating the fuel cell system of the first invention, in which unused hydrogen-containing gas discharged from the fuel cell anode is used at the inlet of the anode. The hydrogen-containing gas is returned to the anode and reused by using the circulation path for returning, and the generated power or voltage of the fuel cell becomes a predetermined value or less during the period during which the fuel cell is generating power. In this case, purging the unused hydrogen-containing gas from the circulation path to the purge path, diluting the purge gas which is the unused hydrogen-containing gas discharged from the purge path with a diluting gas, and the above. Detecting the concentration of hydrogen gas in the diluted purge gas, measuring the elapsed time until the concentration of the hydrogen gas in the diluted purge gas falls below the reference value, and determining the elapsed time as the threshold time. When it exceeds, the concentration of hydrogen gas in the diluted purge gas becomes the flammable limit (combustion) by notifying the state or abnormality of the fuel cell system or stopping the operation of the fuel cell system. Can be prevented from reaching a possible concentration). In addition, it is possible to prevent the state in which the concentration of hydrogen gas in the purge gas is equal to or higher than the reference value continues beyond the threshold time. Therefore, the fuel cell system can be operated safely.

The seventeenth invention, in particular, the method of operating the fuel cell system of the sixteenth invention is to increase the flow rate of the diluted gas when the concentration of the hydrogen gas in the diluted purge gas is equal to or higher than the reference value. The fuel cell system can be operated more safely because the elapsed time is the elapsed time from the time when the flow rate of the diluted gas is increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 shows a configuration diagram of a fuel cell system according to the first embodiment of the present invention. As shown in FIG. 1, the fuel cell system 100 of the present embodiment includes a housing 10 and a fuel cell 20. The fuel cell 20 (fuel cell stack) is arranged inside the housing 10. Other components of the fuel cell system 100 are also arranged inside the housing 10 like the fuel cell 20. The fuel cell 20 has an anode 21 (fuel electrode), a cathode 22 (air electrode), and an electrolyte layer 23. The fuel cell 20 is, for example, a solid polymer fuel cell, a solid oxide fuel cell, a phosphoric acid fuel cell, or a molten carbonate fuel cell.

The housing 10 has, for example, the shape of a hollow rectangular parallelepiped. The housing 10 is provided with an intake port 11 and an exhaust port 12. The intake port 11 is an opening for taking in air from the outside of the housing 10 to the inside of the housing 10. The air taken into the inside of the housing 10 from the intake port 11 can be used as an oxidant gas for the fuel cell 20. The air taken into the housing 10 from the intake port 11 can also be used as a diluting gas for the hydrogen-containing gas discharged from the fuel cell 20. The exhaust port 12 is an opening for discharging gas from the inside of the housing 10 to the outside of the housing 10. The unreacted hydrogen-containing gas discharged from the fuel cell 20 is diluted inside the housing 10 and discharged to the outside of the housing 10 through the exhaust port 12. The intake port 11 is provided, for example, on only one side surface of the housing 10. According to the present embodiment, the installation method of the fuel cell system 100 can be diversified as compared with the case where the intake ports are provided on a plurality of side surfaces. The exhaust port 12 is provided on an upper portion of a side surface different from the side surface on which the intake port 11 is provided. However, the exhaust port 12 may be provided on the same side surface as the side surface on which the intake port 11 is provided. A plurality of intake ports 11 may be provided in the housing 10. A plurality of exhaust ports 12 may be provided in the housing 10.

In the present embodiment, the exhaust port 12 is provided above the intake port 11 in the vertical direction. The intake port 11 is provided at the lower part of the housing 10, for example. The exhaust port 12 is provided, for example, in the upper part of the housing 10. According to such a configuration, hydrogen gas is easily discharged to the outside of the housing 10. Further, the air taken into the inside of the housing 10 from the intake port 11 acts as a ventilation wind (broken line arrow) in the internal space of the housing 10. In this case, the air warmed by the components such as the fuel cell 20 is likely to be discharged to the outside of the housing 10 during the operation of the fuel cell system 100. When the housing 10 is divided into three equal parts in the height direction, the portion located at the top can be defined as the "upper portion", and the portion located at the bottom can be defined as the "lower portion".

The anode 21 of the fuel cell 20 includes an anode inlet and an anode outlet. The cathode 22 of the fuel cell 20 includes a cathode inlet and a cathode outlet. The anode gas supply path 31 is connected to the anode inlet. A circulation path 33 is connected to the anode outlet. A cathode gas supply path 41 is connected to the cathode inlet. A cathode off gas path 42 is connected to the cathode outlet. Each path shown in FIG. 1 is composed of at least one pipe made of metal or resin.

The anode gas supply path 31 is a path for supplying fuel gas to the anode 21. The anodic gas supply path 31 extends outside the housing 10 and may be connected to a fuel supply source (not shown). The fuel supply source is an infrastructure for supplying fuel gas to the anode 21 of the fuel cell 20. The fuel gas is typically hydrogen gas. The fuel source is, for example, a storage tank for liquefied hydrogen. Other equipment such as a humidifier may be provided in the anode gas supply path 31.

The circulation path 33 is a path for returning the anode off-gas discharged from the anode 21 to the anode gas supply path 31. The anode off gas is a hydrogen-containing gas that has not been used for power generation. The circulation path 33 has one end connected to the anode outlet and the other end connected to the anode gas supply path 31. In this embodiment, the circulation path 33 includes a first portion 33a, a second portion 33b and an anode condensed water tank 33c. The first portion 33a is a portion connecting the anode outlet and the anode condensed water tank 33c. The second portion 33b is a portion connecting the anode condensed water tank 33c and the anode gas supply path 31. The anode off gas is guided from the anode 21 of the fuel cell 20 to the anode condensed water tank 33c through the first portion 33a. The condensed water contained in the anode off-gas is stored in the anode condensed water tank 33c. The anode off-gas is guided from the anode condensed water tank 33c to the anode gas supply path 31 through the second portion 33b.

The cathode gas supply path 41 is a path for supplying the oxidant gas to the cathode 22. The oxidant gas is typically air. The cathode gas supply path 41 may extend to the outside of the housing 10 or may have an opening located inside the housing 10. According to the former, air is taken into the cathode gas supply path 41 from the outside of the housing 10, and according to the latter, air is taken into the cathode gas supply path 41 from the inside of the housing 10. Other equipment such as a blower and a fan may be provided in the cathode gas supply path 41.

The cathode off gas path 42 is a path for discharging the cathode off gas discharged from the cathode 22 to the outside of the fuel cell 20. Cathode-off gas is air that has not been used for power generation. In the present embodiment, the cathode off-gas path 42 connects the cathode outlet and the off-gas mixer 50 described later. The cathode off gas is guided from the cathode 22 of the fuel cell 20 to the off gas mixer 50 through the cathode off gas path 42.

Further, the fuel cell system 100 includes a purge path 52, an off-gas mixer 50, a gas confluence 53, and a combustible gas sensor 54.

The purge path 52 is a path for purging the hydrogen-containing gas from the circulation path 33 to the inside of the housing 10. The purge path 52 has one end connected to the circulation path 33 and extends to a predetermined confluence position inside the housing 10. In other words, the purge path 52 branches off from the circulation path 33 (specifically, the second portion 33b). A purge valve 35 is arranged in the purge path 52. The purge valve 35 is typically an on-off valve. In this embodiment, the purge path 52 includes a first portion 52a and a second portion 52b. The first portion 52a is a portion connecting the circulation path 33 and the off-gas mixer 50. The second portion 52b is a portion that is connected to the off-gas mixer 50 and extends to a predetermined confluence position. The predetermined merging position is the position where the gas merging portion 53 is provided. The purge valve 35 is arranged in the first portion 52a.

The off-gas mixer 50 communicates the cathode off-gas path 42 and the purge path 52. The role of the off-gas mixer 50 is to mix the oxidant gas (cathode-off gas) in the cathode-off-gas path 42 with the hydrogen-containing gas (purge gas) in the purge path 52. As a result, the hydrogen concentration (hydrogen gas concentration) in the purge gas can be efficiently lowered. A mixed gas of the cathode off gas and the purge gas is sent to the gas confluence portion 53 through the second portion 52b of the purge path 52.

In the off-gas mixer 50, the cathode off-gas and the purge gas are mixed, and the condensed water is separated from the mixed gas. That is, the off-gas mixer 50 also plays the role of a gas-liquid separator. Since water is removed from the mixed gas, deterioration of the combustible gas sensor 54 due to dew condensation can be suppressed more effectively.

One end of the condensed water path 43 is connected to the off-gas mixer 50. The other end of the condensed water path 43 is connected to the cathode condensed water tank 44. The condensed water recovered by the off-gas mixer 50 is guided from the off-gas mixer 50 to the cathode condensed water tank 44 through the condensed water path 43. The condensed water contained in the cathode off gas is stored in the cathode condensed water tank 44.

The gas merging portion 53 is a portion provided inside the housing 10 and is a portion for merging the purge gas discharged from the circulation path 33 through the purge path 52 with the diluted gas at a predetermined merging position. The diluent gas is air. The diluted purge gas proceeds from the gas confluence 53 toward the exhaust port 12, and is discharged to the outside of the housing 10 through the exhaust port 12. In the present embodiment, the gas merging portion 53 is arranged in the upper part of the housing 10. Specifically, the gas confluence 53 is located above the fuel cell 20.

The combustible gas sensor 54 detects the hydrogen gas concentration in the diluted purge gas. The flammable gas sensor 54 is typically a semiconductor hydrogen gas sensor.

The fuel cell system 100 further includes an exhaust fan 55. The exhaust fan 55 is arranged at a position facing the exhaust port 12. The exhaust fan 55 is arranged inside the housing 10. When the exhaust fan 55 is operated, the inside of the housing 10 is in a negative pressure state. Since the air flow direction in the internal space of the housing 10 is determined in a fixed direction, it is possible to reliably measure the concentration of hydrogen gas with one combustible gas sensor 54. As a result, the manufacturing cost of the fuel cell system 100 can be reduced without impairing the safety of the fuel cell system 100.

Further, the fuel cell system 100 includes a controller 62. The controller 62 is, for example, a DSP (Digital Signal Processor) including an A / D conversion circuit, an input / output circuit, an arithmetic circuit, a storage device, and the like. The controller 62 stores a program for properly operating the fuel cell system 100. In this embodiment, the controller 62 is arranged on the upper part of the housing 10.

Next, the detailed structure of the gas confluence 53 and its surroundings will be described. In FIG. 2, the flow of air G1 as a diluting gas, the flow of purge gas G2, and the flow of purge gas G3 diluted with air are indicated by arrows.

As shown in FIG. 2, the gas merging portion 53 has a partition wall 53k surrounding a predetermined merging position 57. In other words, a part or all of the space surrounded by the partition wall 53k is a predetermined confluence position 57. According to the partition wall 53k, the diffusion of the purge gas discharged from the purge path 52 toward the merging position 57 can be effectively controlled. Therefore, in order to accurately detect the concentration of hydrogen gas in the purge gas diluted with air, the positional relationship between the combustible gas sensor 54, the gas confluence 53, and the exhaust port 12 can be determined relatively easily.

The combustible gas sensor 54 is arranged on the upstream side in the air flow direction with reference to the predetermined merging position 57. In other words, there is a predetermined merging position 57 on the air flow path from the combustible gas sensor 54 to the exhaust port 12. According to such a positional relationship, it is possible to reliably prevent the combustible gas sensor 54 from being directly exposed to the hot and humid purge gas. In addition, the phrase "distance" in this specification means the shortest distance.

The partition wall 53k has, for example, the shape of a cylinder having both ends open. That is, the partition wall 53k constitutes a wind tunnel in which one end 53p and the other end 53q are open. A purge path 52 is connected to the partition wall 53k between one end 53p of the wind tunnel and the other end 53q of the wind tunnel. The one end 53p and the other end 53q are also the inlet 53p and the outlet 53q of the gas confluence 53, respectively. According to such a structure, the diffusion of the purge gas can be controlled more effectively. In the present embodiment, a straight line connecting the center of the exhaust fan 55 and the flammable gas sensor 54 passes through the wind tunnel formed by the partition wall 53k. According to such a structure, the purge gas diluted with air is quickly guided to the exhaust port 12 and discharged to the outside of the housing 10.

The purge path 52 includes an opening 52p that opens toward a predetermined confluence position 57. The opening 52p of the purge path 52 exists on the air flow path from the combustible gas sensor 54 to the exhaust port 12. According to such a structure, the purge gas can be reliably diluted with air, and the diluted purge gas can be reliably guided to the exhaust port 12.

The combustible gas sensor 54 is arranged on the same side as the inlet 53p (one end 53p of the wind tunnel) of the gas confluence 53 with reference to the opening 52p of the purge path 52. The distance from the combustible gas sensor 54 to the inlet 53p of the gas confluence 53 is shorter than the distance from the combustible gas sensor 54 to the opening 52p of the purge path 52. According to such a positional relationship, it is possible to reliably prevent the combustible gas sensor 54 from being directly exposed to the hot and humid purge gas.

Further, the distance from the predetermined merging position 57 to the exhaust port 12 is shorter than the distance from the combustible gas sensor 54 to the exhaust port 12. According to such a positional relationship, it is possible to prevent the moisture (water vapor) contained in the purge gas from reaching the combustible gas sensor 54 as much as possible. Since the diffusion rate of hydrogen gas is much faster than that of water vapor, the concentration of hydrogen gas can be detected even if the combustible gas sensor 54 is arranged on the upstream side in the air flow direction. Each of the above distances is set so that the concentration of hydrogen gas can be reliably detected by the combustible gas sensor 54, and the diluted purge gas can be efficiently discharged to the outside of the housing 10.

In this embodiment, the combustible gas sensor 54 is arranged outside the wind tunnel. That is, the combustible gas sensor 54 is arranged outside the space surrounded by the partition wall 53k. Specifically, the combustible gas sensor 54 is arranged at a position facing one end 53p of the wind tunnel (the inlet 53p of the gas confluence portion 53). When the flammable gas sensor 54 is arranged at such a position, the concentration of hydrogen gas in the purge gas diluted with air is detected while surely preventing the moisture contained in the purge gas from reaching the flammable gas sensor 54. can do. Of course, the combustible gas sensor 54 may be arranged in the wind tunnel. In this case, the concentration of hydrogen gas in the purge gas diluted with air can be detected more accurately.

In the fuel cell system 100 of the present embodiment, the hydrogen-containing gas is supplied from the fuel supply source to the anode 21 of the fuel cell 20 through the anode gas supply path 31. Air is introduced into the cathode gas supply path 41 by an air pump (not shown) from the intake port 11 of the housing 10. Air passes through the cathode gas supply path 41 and is supplied to the cathode 22 of the fuel cell 20. In the fuel cell 20, electric power is generated using hydrogen-containing gas and air.

The anode off gas that was not used for power generation is in a humid state. Therefore, the anode off-gas is sent from the anode 21 of the fuel cell 20 to the anode condensed water tank 33c through the first portion 33a of the circulation path 33. In the anode condensed water tank 33c, the condensed water is removed from the anode off-gas. The anode off-gas is returned from the anode condensed water tank 33c to the anode gas supply path 31 through the second portion 33b of the circulation path 33, and is reused for power generation in the fuel cell 20.

The cathode off gas that was not used for power generation is also in a humid state. The cathode-off gas is sent to the gas-liquid separator 50 through the cathode-off gas path 42, mixed with the purge gas in the gas-liquid separator 50, and guided to the gas confluence portion 53. That is, the cathode off gas is used as a diluting gas for the purge gas. The condensed water contained in the cathode off gas is separated from the gas component in the gas-liquid separator 50 and sent to the cathode condensed water tank 44 through the condensed water path 43.

In the gas merging portion 53, the air inside the housing 10 passes through the combustible gas sensor 54 and is drawn into the gas merging portion 53 by the action of the exhaust fan 55. The purge gas released from the purge path 52 is further diluted by air at the confluence position 57 of the gas confluence portion 53. The diluted purge gas flows out of the gas confluence portion 53 and is discharged to the outside of the housing 10 through the discharge port 12.

The diffusion rate of hydrogen gas is faster than the diffusion rate of air. Therefore, even if the combustible gas sensor 54 exists on the upstream side in the air flow direction with reference to the merging position 57, hydrogen gas can reach the combustible gas sensor 54. As a result, the combustible gas sensor 54 can detect the hydrogen gas in the diluted purge gas. The reachable range of hydrogen gas and the reachable concentration of hydrogen gas are determined according to the flow velocity of air, the size of the space surrounded by the partition wall 53k, and the like. Therefore, the flow rate of air and the cross-sectional area of the wind tunnel by the partition wall 53k are appropriately designed so that hydrogen gas reaches the combustible gas sensor 54.

According to the present embodiment, it is possible to prevent the combustible gas sensor 54 from being directly exposed to the hot and humid purge gas discharged from the purge path 52. It is also possible to prevent dew condensation from forming on the combustible gas sensor 54. Therefore, deterioration of the combustible gas sensor 54 is suppressed, and the life of the combustible gas sensor 54 can be extended. In addition, the measurement error of the combustible gas sensor 54 is also reduced. As a result, the safety and reliability of the fuel cell system 100 can be ensured for a long period of time.

Next, the control of the purge valve 35 will be described.

In the fuel cell 20, hydrogen-containing gas is supplied to the anode 21, air is supplied to the cathode 22, and electric power is generated by an electrochemical reaction. When the anode off gas is recycled by utilizing the circulation path 33 during the operation of the fuel cell system 100, the concentration of impurities in the hydrogen-containing gas of the anode gas supply path 31 increases with the passage of time. As a result, the output voltage of the fuel cell 20 decreases with the passage of time.

As shown in Graph B of FIG. 3, when the anode off-gas is not purged at all, the output voltage of the fuel cell 20 drops sharply from a certain point in time. On the other hand, if the purge valve 35 is opened when a predetermined condition is satisfied and hydrogen-containing gas is flowed from the circulation path 33 to the purge path 52 to remove impurities such as nitrogen gas, the hydrogen-containing gas supplied to the anode 21 The concentration of hydrogen gas in the water increases. As a result, as shown in Graph A of FIG. 3, the output voltage of the fuel cell 20 can be recovered. The above-mentioned predetermined condition is, for example, that the operation of the fuel cell system 100 is continuously operated for a predetermined time with the purge valve 35 closed. In other words, the controller 62 controls to open the purge valve at a predetermined timing during the period during which the fuel cell 20 is generating power. The purge valve 35 is opened every time a predetermined time (for example, 30 minutes) elapses. According to such control, the output voltage of the fuel cell 20 can always be maintained in a high state. Graph A in FIG. 3 shows the change in voltage when the purge valve 35 is controlled to be opened at the timings of time t1, t2 and t3. The voltage of the fuel cell 20 always exceeds the threshold voltage Vth.

Next, an example of operation of the fuel cell system 100 will be described with reference to FIG. The flowchart of FIG. 4 shows the process executed by the controller 62. The controller 62 executes the following processes from the start of power generation to the end of power generation. The fuel cell system 100 generates electric power by electrochemically reacting the hydrogen-containing gas supplied to the anode 21 of the fuel cell 20 with the oxidant gas supplied to the cathode 22 of the fuel cell 20.

In step S101, it is confirmed whether or not there is an instruction to stop power generation of the fuel cell system 100, and it is determined whether or not power generation should be continued. If there is an instruction to stop power generation, the operation of the fuel cell system 100 is stopped (step S112). When the power generation should be continued, the generated power of the fuel cell 20 is measured (step S102). Then, it is determined whether or not the measured generated power is equal to or less than a predetermined value (step S103). In the present embodiment, 90% of the generated power instructed by the controller 62 is a "predetermined value". If the measured generated power is larger than the predetermined value, the process returns to step S101. When the measured generated power is equal to or less than a predetermined value, the anode off gas is purged from the circulation path 33 to the purge path 52 (step S104). Specifically, the purge valve 35 is opened. The purge gas, which is the gas guided from the circulation path 33 to the purge path 52, is discharged from the purge path 52 to the gas confluence 53. At the gas confluence 53, the purge gas is diluted with air. Then, the concentration of hydrogen gas in the purge gas diluted with air is detected by the combustible gas sensor 54 (step S105).

In addition, instead of the "generated power", as described with reference to FIG. 3, the "voltage" is measured, and the purge is performed according to the comparison result between the measured voltage and the predetermined threshold voltage (predetermined value). The valve 35 may be controlled. Further, as described with reference to FIG. 3, the purge valve 35 may be controlled to be opened at predetermined time intervals.

Next, it is determined whether or not the detected hydrogen gas concentration is less than the reference value (step S106). In the present embodiment, the "reference value" is 2% (volume%). When the concentration of hydrogen gas in the diluted purge gas is 2% or more, the air volume of the exhaust fan 55 is increased to promote the dilution of the purge gas with air (step S107). Specifically, the rotation speed of the exhaust fan 55 is increased to increase the air flow rate. Next, the elapsed time from the time when the air volume of the exhaust fan 55 is first increased is measured (step S108). In other words, the elapsed time from the time when the air flow rate is increased to the present is measured. The elapsed time can be the time until the concentration of hydrogen gas in the diluted purge gas falls below the reference value.

Next, it is determined whether the elapsed time is equal to or less than the threshold time (for example, 1 minute) (step S109). When the elapsed time exceeds the threshold time, the operation of the fuel cell system 100 is stopped (step S112). That is, when the hydrogen gas concentration of 2% or more continues for more than 1 minute, the operation of the fuel cell system 100 is stopped and the power generation is stopped. When the elapsed time is equal to or less than the threshold time, the concentration of hydrogen gas in the purge gas diluted with air is detected again (step S110), and it is determined whether the concentration of hydrogen gas is less than 2% (step S111). When the hydrogen gas concentration is 2% or more, the process returns to step S107, and the air volume of the exhaust fan 55 is maintained (maintaining the rotation speed of the exhaust fan 55) until the hydrogen gas concentration drops to less than 2%. Alternatively, the air volume of the exhaust fan 55 may be gradually increased. In other words, the rotation speed of the exhaust fan 55 may be gradually increased.

If the concentration of hydrogen gas is less than 2% in step S106, and if the concentration of hydrogen gas is less than 2% in step S111, the process returns to step S101. After the processing of each step is completed, the processing of the next step may be performed instantly without providing a waiting time.

By executing each process shown in the flowchart of FIG. 4, it is possible to prevent the concentration of hydrogen gas in the diluted purge gas from reaching the flammable limit (for example, 4%). In addition, it is possible to prevent the state in which the concentration of hydrogen gas in the purge gas is equal to or higher than the reference value continues beyond the threshold time. Therefore, the fuel cell system 100 can be operated safely.

The purge valve 35 opened in step S104 is closed after a predetermined time (for example, after 2 minutes have elapsed). According to the process of step S105, the concentration of hydrogen gas in the diluted purge gas is detected while the purge valve 35 is open. That is, the controller 62 monitors the output of the combustible gas sensor 54 during a period from the time when the purge valve 35 is opened until a predetermined time (2 minutes) elapses. Then, when the output of the combustible gas sensor 54 exceeds the threshold value, an electric process for notifying the state of the fuel cell system 100 or the abnormality of the fuel cell system 100 is executed. Alternatively, the controller 62 stops the operation of the fuel cell system 100 when the output of the combustible gas sensor 54 exceeds the threshold value. In this way, the fuel cell system 100 can be operated more safely. "When the output of the combustible gas sensor 54 exceeds the threshold value" means a case where the output of the combustible gas sensor 54 shows a flammable limit or a concentration close to it.

In step S112, instead of stopping the operation of the fuel cell system 100, an electric process for notifying the state of the fuel cell system 100 or the abnormality of the fuel cell system 100 may be executed. For example, an electric process for notifying the power generation state of the fuel cell system 100, the detected value of the hydrogen gas concentration, the hydrogen gas concentration exceeding 2%, or the like is executed. This information may be displayed on a monitor connected to the controller 62, or may be transmitted to a terminal of a user or an administrator via a communication network such as the Internet and displayed.

(Embodiment 2)
As shown in FIG. 5, the fuel cell system 200 of the present embodiment includes a radiator 63 and a cooling fan 64. Elements common to the fuel cell system 100 of the first embodiment and the fuel cell system 200 of the present embodiment are designated by the same reference numerals, and the description thereof may be omitted. That is, the description of each embodiment can be applied to each other as long as there is no technical conflict. Moreover, the embodiments may be combined with each other as long as they are not technically inconsistent.

The radiator 63 is a device for removing heat from the coolant of the fuel cell 20. The coolant is a coolant such as water. The radiator 63 is composed of, for example, a fin tube heat exchanger. The radiator 63 is connected to the fuel cell 20 by a cooling path 65. The coolant circulates between the radiator 63 and the fuel cell 20. A pump (not shown) is provided in the cooling path 65. During operation of the fuel cell system 200, the fuel cell 20 is cooled by the coolant. When the cooling fan 64 is operated, air (outside air) is supplied to the radiator 63, and heat exchange is performed between the coolant and the air in the radiator 63.

In the present embodiment, the radiator 63 is an air-cooled type. The housing 10 is provided with a second intake port 13. The second intake port 13 is adjacent to, for example, the exhaust port 12. A duct 67 is provided inside the housing 10, and the exhaust port 12 and the second intake port are surrounded by the duct 67. A radiator 63 and a cooling fan 64 are arranged inside the duct 67. The cooling fan 64 is arranged at a position where an air flow (arrow) is generated from the outside of the housing 10 toward the radiator 63 through the second intake port 13. In FIG. 6, only one cooling fan 64 is shown. However, a plurality of fans may be arranged inside the duct 67 so that the air flows in the order of the second intake port 13, the radiator 63, and the exhaust port 12. A component such as a straightening vane that adjusts the air flow direction may be arranged inside the duct 67.

The purge gas diluted with air in the gas confluence 53 flows toward the exhaust port 12 by the action of the cooling fan 64. On the path from the gas confluence 53 to the exhaust port 12, the purge gas is sucked into the duct 67, further diluted by the air passing through the radiator 63 inside the duct 67, and outside the housing 10 through the exhaust port 12. Is discharged to. According to such a configuration, the concentration of hydrogen gas in the purge gas can be further reduced and discharged to the outside of the housing 10. Further, according to the present embodiment, the cooling fan 64 also plays the role of the exhaust fan 55 described in the first embodiment. Since the exhaust fan 55 can be omitted, the fuel cell system 200 can be simplified.

Other configurations of the fuel cell system 200, such as the structure of the gas confluence 53 and the arrangement of the combustible gas sensor 54, are as described in the first embodiment. Therefore, the same effect as that of the first embodiment can be obtained in the present embodiment as well.

The present invention is useful for fuel cell systems.

10 Housing 11 Intake port 12 Exhaust port 20 Fuel cell 31 Anode gas supply path 33 Circulation path 35 Purge valve 42 Cathode off gas path 50 Off gas mixer 52 Purge path 52p Opening 53 Gas confluence 53k Partition 54 Combustible gas sensor 55 Exhaust fan 57 Confluence position 63 Dissipator 100,200 Fuel cell system

Claims (17)

A fuel cell with an anode inlet and an anode outlet,
The anode gas supply path connected to the anode inlet and
A circulation path having one end connected to the anode outlet and the other end connected to the anode gas supply path.
A purge path that has one end connected to the circulation path and extends to a predetermined confluence position,
A housing containing the fuel cell, the anode gas supply path, the circulation path, and the purge path.
A gas merging portion provided inside the housing and merging hydrogen-containing gas discharged from the circulation path through the purging path with the diluted gas at the predetermined merging position.
An exhaust port provided in the housing and for discharging the hydrogen-containing gas diluted by the dilution gas from the gas confluence to the outside of the housing.
With the combustible gas sensor arranged on the upstream side in the flow direction of the diluted gas with reference to the predetermined merging position,
A fuel cell system equipped with. The purge path includes an opening that opens toward the predetermined confluence position.
The fuel cell system according to claim 1, wherein the opening of the purge path exists on the flow path of the diluted gas from the combustible gas sensor to the exhaust port. The fuel cell system according to claim 1 or 2, wherein the distance from the predetermined merging position to the exhaust port is shorter than the distance from the combustible gas sensor to the exhaust port. The fuel cell system according to any one of claims 1 to 3, wherein the gas merging portion has a partition wall surrounding the predetermined merging position. The partition wall constitutes a wind tunnel with one end and the other end open.
The fuel cell system according to claim 4, wherein the purge path is connected to the partition wall between the one end of the wind tunnel and the other end of the wind tunnel. The fuel cell system according to claim 5, wherein the combustible gas sensor is arranged outside the wind tunnel. The fuel cell further has a cathode outlet.
The fuel cell system
The cathode off gas path connected to the cathode outlet and
Claimed to further include an off-gas mixer that communicates the cathode off-gas path with the purge path to mix the oxidant gas in the cathode off-gas path with the hydrogen-containing gas in the purge path. Item 6. The fuel cell system according to any one of Items 1 to 6. The fuel cell system according to claim 7, wherein the off-gas mixer includes a gas-liquid separator. The fuel cell system according to any one of claims 1 to 8, wherein the housing has an intake port for taking in air as a diluent gas from the outside of the housing. The fuel cell system according to claim 9, wherein the exhaust port is provided on the upper side in the vertical direction with respect to the intake port. The fuel cell system according to any one of claims 1 to 10, further comprising an exhaust fan arranged at a position facing the exhaust port. Further equipped with an air-cooled radiator for removing heat from the fuel cell coolant,
The fuel cell system according to any one of claims 1 to 11, wherein the hydrogen-containing gas diluted with the diluting gas is further diluted with air passing through the radiator. The purge valve arranged in the purge path and
A controller that controls the opening and closing of the purge valve,
The fuel cell system according to any one of claims 1 to 12, further comprising. The fuel cell system according to claim 13, wherein the controller controls the purge valve to be opened at a predetermined timing during a period in which the fuel cell is generating power. Wherein the controller, the output of the combustible gas sensor monitors the period from the time of opening the purge valve until a predetermined time elapses, if the output of the combustible gas sensor exceeds a threshold value, in the fuel cell system The fuel cell system according to claim 14, wherein an electric process for notifying an abnormality of the fuel cell system is executed, or the operation of the fuel cell system is stopped. The method of operating the fuel cell system according to claim 1 .
Using a circulation path for returning the unused hydrogen-containing gas discharged from the anode of the fuel cell to the inlet of the anode, the hydrogen-containing gas is returned to the anode for reuse.
When the generated power or voltage of the fuel cell becomes a predetermined value or less during the period when the fuel cell is generating power, the unused hydrogen-containing gas is purged from the circulation path to the purge path.
Diluting the purge gas, which is the unused hydrogen-containing gas discharged from the purge path, with a dilution gas,
To detect the concentration of hydrogen gas in the diluted purge gas,
To measure the elapsed time until the concentration of the hydrogen gas in the diluted purge gas falls below the reference value, and
When the elapsed time exceeds the threshold time, the state or abnormality of the fuel cell system is notified, or the operation of the fuel cell system is stopped.
How to operate a fuel cell system, including. When the concentration of the hydrogen gas in the diluted purge gas is equal to or higher than the reference value, the flow rate of the diluted gas is further increased.
The method for operating a fuel cell system according to claim 16, wherein the elapsed time is an elapsed time from the time when the flow rate of the diluted gas is increased.

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