JP2004241183A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain discharge of a non-reacted fuel gas in purge processing. <P>SOLUTION: This fuel cell system is so structured that a pipe 8 used as a combustion fuel supply passage is formed separately from a gas discharge passage 16 communicating with a catalyst combustor 4 from a hydrogen circulation passage 14 of a fuel cell 1; and hydrogen gas having a small flow rate is supplied to the catalyst combustor 4 from the circulation passage 14 in operating the system, and reacted to warm and dry the catalyst combustor 4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system having a hydrogen circulation system for mixing and recycling hydrogen unused in a fuel cell with hydrogen supplied to the fuel cell.
[0002]
[Prior art]
Conventionally, as this kind of technology, for example, a technology described in the following document is known (see Patent Document 1). According to the invention described in this document, hydrogen stored in a hydrogen tank is regulated to a predetermined pressure by a fuel pressure regulating valve, and then mixed with hydrogen circulated and discharged from a fuel cell by an ejector pump. Sent to side water separator. The hydrogen exiting the supply-side water separator passes through a humidifier and is supplied to a fuel electrode of a fuel cell from a fuel inlet. The mixed gas of hydrogen and water vapor that has exited from the fuel outlet of the fuel electrode flows through the discharge-side water separator to the flow path cutoff valve.
[0003]
Thereafter, hydrogen is supplied from the flow path cutoff valve to the ejector pump, mixed with the raw fuel gas supplied through the fuel pressure regulating valve by the ejector pump, and circulated to the fuel cell side. Thus, the unused hydrogen supplied to the fuel cell was circulated.
[0004]
Further, in the fuel cell system having such a hydrogen circulation system, the gas flowing through the pipe downstream of the discharge-side water separator branches off into the purge pipe at the purge branch section, flows through the purge gas cutoff valve, and flows through the purge gas catalytic combustor. Was oxidized and discharged to the outside.
[0005]
[Patent Document 1]
JP 2002-231294 A
[Problems to be solved by the invention]
As described above, in the conventional fuel cell system having the hydrogen circulation system, a large amount of fuel gas is supplied to the catalytic combustor intermittently by the purge process of discharging the impurity gas flowing through the hydrogen circulation system. It was a target. For this reason, the catalyst surface was sometimes wet by the humid air before the purge process was performed. Further, since a large amount of water is contained in the gas supplied to the catalytic combustor, the liquid water has adhered to the surface of the combustion catalyst in the catalytic combustor in the intermittent purging process.
[0007]
As a result, there is a problem that the impurity gas is not ignited when the purging process is performed, the catalytic reaction cannot be performed, and the unreacted fuel gas is discharged outside the system.
[0008]
Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide a fuel cell system that suppresses discharge of unreacted fuel gas during a purge process.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, means for solving the problem of the present invention is a fuel cell system that generates electricity by using a fuel gas supplied from a fuel gas supply device and air supplied from an air supply device. A circulation path for circulating the fuel gas from the downstream to the upstream of the fuel cell, a gas discharge path for discharging gas in the circulation path, and discharged from the circulation path to the gas discharge path. An on-off valve for controlling discharge / cutoff of gas; a combustor provided downstream of the gas discharge flow path, for burning and discharging gas discharged from the circulation flow path via the gas discharge flow path; A combustion fuel supply flow path for supplying a predetermined flow rate of fuel gas to the combustor to make the combustor dry when the battery system is operated.
[0010]
【The invention's effect】
According to the present invention, a combustion fuel supply flow path is provided separately from a gas discharge flow path leading from the fuel gas circulation flow path to the combustor, and a small flow rate of hydrogen gas is supplied to the combustor during operation of the system. Because of the reaction, the combustor can be warmed up and the combustor can be kept dry. Thereby, when performing the purging process of the circulation flow path, the combustor is quickly ignited, and the unreacted fuel gas can be prevented from being discharged to the outside.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a diagram showing the configuration of the fuel cell system according to the first embodiment of the present invention. The fuel cell system according to the first embodiment shown in FIG. 1 includes a fuel cell 1, an air supply device 2 for supplying air to the fuel cell 1, a hydrogen supply device 3 for supplying hydrogen to the fuel cell 1, a catalytic combustor 4, The fuel cell system includes a main mixer 5, a small flow mixer 6, and a controller (not shown) that controls the operation processing of the entire fuel cell system based on a program and the like.
[0013]
The fuel cell 1 generates power using hydrogen supplied from the hydrogen supply device 3 and air supplied from the air supply device 2. The fuel cell 1 is provided with a hydrogen circulation channel 14 so that the hydrogen unused in the fuel cell 1 is mixed with the supplied hydrogen again from the downstream of the fuel cell 1 and recirculated. Unused hydrogen discharged from the fuel cell 1 to the hydrogen circulation channel 14 and circulated is mixed with hydrogen discharged from the hydrogen supply device 3 by the ejector 15 and supplied to the fuel cell 1 again. Note that a pump may be used instead of the ejector 15.
[0014]
The air supplied from the air supply device 2 to the fuel cell 1 is adjusted to an appropriate pressure by the pressure adjusting valve 11 and supplied to the fuel cell 1.
[0015]
The hydrogen circulation flow path 14 is connected to a gas discharge flow path 16 for performing a purge process for discharging gas other than hydrogen accumulated in the hydrogen circulation flow path 14 to the outside of the hydrogen circulation flow path 14. The gas discharge flow path 16 connects the hydrogen circulation flow path 14 and the main mixer 15 and serves as a discharge path for discharging gas in the hydrogen circulation path 14 to the main mixer 5. An on-off valve 10 is provided in the gas discharge channel 16. The on-off valve 10 is normally closed, and is opened as necessary when the hydrogen partial pressure in the hydrogen circulation flow path 14 is reduced or when water is clogged, including when purging the hydrogen circulation flow path 14. Is done.
[0016]
The exhaust air discharged from the fuel cell 1 is supplied to a main mixer 5 serving as a first mixer, mixed with a gas discharged from a hydrogen circulation channel 14 via an on-off valve 10 and a gas discharge channel 16, and mixed. Gas is supplied to the catalytic combustor 4. The mixed gas supplied to the catalytic combustor 4 is subjected to a catalytic reaction by the catalytic combustor 4 to oxidize hydrogen in the mixed gas.
[0017]
Further, the hydrogen circulation flow path 14 is provided with a pipe 8 which constantly discharges the gas in the hydrogen circulation flow path 14 to the catalytic combustor 4 and serves as a combustion fuel supply flow path. The pipe 8 connects the hydrogen circulation channel 14 and the steam separator 7, and discharges the gas in the hydrogen circulation channel 14 to the steam separator 7. The pipe 8 is provided with a flow rate adjusting device 9 that performs a throttle or the like for controlling the flow rate of the released gas. Downstream of the flow control device 9, a steam separator 7 serving as water recovery means is provided. The steam separator 7 removes the liquid water in the release gas discharged from the hydrogen circulation channel 14 via the pipe 8 so that the liquid water does not directly enter the catalytic combustor 4.
[0018]
The steam separator 7 is connected to a small flow rate mixer 6 which is included in the main mixer 5 and serves as a second mixer. The low-flow mixer 6 is supplied with the release gas released from the hydrogen circulation channel 14 via the pipe 8 and a part of the exhaust air discharged from the fuel cell 1 and supplied to the main mixer 5. And the exhaust air, and the mixed gas is supplied to a part of the combustion catalyst of the catalytic combustor 4.
[0019]
In such a configuration, during normal operation of the system, a part of the hydrogen gas circulating in the hydrogen circulation channel 14 is discharged to the pipe 8, and the flow rate of the hydrogen gas discharged to the pipe 8 is controlled by the flow control device. Adjusted at 9. The flow rate of the hydrogen gas on the entire front surface (shown by A in FIG. 1) of the combustion catalyst in the catalytic fuel unit 4 is lower than the heat-resistant temperature of the combustion catalyst and always higher than the temperature of the exhaust air discharged from the fuel cell 1. Is adjusted as follows.
[0020]
The hydrogen gas of a small flow rate whose flow rate has been adjusted is supplied to the small flow rate mixer 6 after the liquid water contained in the gas is eliminated by the steam separator 7. The small-flow hydrogen gas supplied to the small-flow mixer 6 is mixed with the exhaust air discharged from the fuel cell 1 by the small-flow mixer 6, and the hydrogen gas mixed with the exhaust air is mixed with the combustion catalyst of the catalytic combustor 4. Supplied to some.
[0021]
As described above, the small flow rate of the hydrogen gas whose flow rate is adjusted to be lower than the heat resistant temperature of the combustion catalyst and always higher than the temperature of the exhaust air discharged from the fuel cell 1 is continuously burned by the catalytic fuel unit 4. It is being supplied to the catalyst. Thereby, the state where the combustion catalyst of the catalyst combustor 4 is always dry can be maintained. As a result, when purging the hydrogen circulation flow path 14, the on-off valve 10 is opened, and the gas in the hydrogen circulation flow path 14 is discharged to the main mixer 5 via the gas discharge flow path 16, When the catalyst combustor 4 is mixed with air and supplied to the combustion catalyst of the catalyst combustor 4, the catalyst combustor 4 is immediately ignited, and a catalytic reaction occurs immediately to oxidize the hydrogen gas. Therefore, it is possible to suppress the unreacted fuel gas from being discharged to the outside.
[0022]
Further, since the hydrogen gas supplied from the pipe 8 to the catalytic combustor 4 has a small flow rate, if this small flow rate of the hydrogen gas is mixed with the entire amount of the exhaust air, the hydrogen concentration becomes too low, so that the combustion catalyst cannot be burned. . Therefore, in the present embodiment, by providing the small flow rate mixer 6 suitable for a small flow rate gas, even if the hydrogen gas supplied from the pipe 8 is set to a small flow rate, it is suitable for burning this small flow rate hydrogen gas. It becomes possible to mix with air, and it is possible to reliably burn. Furthermore, since the constantly burning hydrogen can be suppressed to a small flow rate, the twisting cost can be kept from deteriorating.
[0023]
In addition, since the gas in the hydrogen circulation channel 14 is supplied to the catalytic combustor 4 through the pipe 8 as the combustion fuel supply channel, the condensed water in the hydrogen circulation channel 14 is gradually reduced to the outside. It continues to be released to. As a result, water clogging is less likely to occur in the hydrogen circulation flow path 14, and the amount of water discharged when the on-off valve 10 is opened can be reduced.
[0024]
Further, since the steam separator 7 is connected to the pipe 8 through which only a small flow of gas flows, the steam separator 7 is provided in a lower position than the steam separator 7 provided downstream of the on-off valve 10 having a large exhaust gas flow rate. The capacity of the separator 7 can be reduced. For this reason, it is advantageous when mounted in a place where space is limited, such as a vehicle.
[0025]
It should be noted that the on-off valve 10 is always kept open at a very small opening degree without providing the pipe 8, so that a small amount of exhaust gas is always supplied to the catalytic combustor 4 through the gas discharge passage 16. It is also possible to put it. However, the minute opening of the on-off valve 10 at this time is significantly different from the opening required for the purge process, and it is difficult to control any opening with a single valve with high accuracy. Therefore, in the present embodiment, since the pipe 8 is provided separately from the gas discharge flow path 16, the controllability of the on-off valve 10 is not impaired.
[0026]
In addition, although the pipe 8 is branched from the hydrogen circulation flow path 14, it may be branched from the gas discharge flow path 16 upstream of the on-off valve 10.
[0027]
FIG. 2 is a diagram illustrating a configuration of a fuel cell system according to a second embodiment of the present invention. The second embodiment is characterized in that the air supply device 2 and the small flow rate mixer 6 are connected to the configuration shown in FIG. 1 and the fuel cell 1 is not directly passed from the air supply device 2 to the configuration shown in FIG. An air supply pipe 12 serving as a combustion air supply flow path for supplying air to the small flow rate mixer 6 and an on-off valve 13 are provided. Other configurations are the same as those of the embodiment shown in FIG. 1, and the description thereof is omitted.
[0028]
When the fuel cell system is started, air is supplied from the air supply device 3 to the small flow mixer 6 through the air supply pipe 12 according to the procedure shown in the flowchart of FIG. Allow to dry.
[0029]
In FIG. 3, when the system is started (step S30), the on-off valve 13 is opened (step S31), and the pressure regulating valve 11 provided at the outlet of the exhaust air of the fuel cell 1 is closed (step S32). In such a state, the air supply device 2 is started, and the supply of air to the small flow rate mixer 6 via the air supply flow path 12 and the on-off valve 13 is started (step S33). After the supply of air is started, it is determined whether or not a predetermined time has elapsed (step S34). When the predetermined time has elapsed, the hydrogen supply device 3 is started to supply hydrogen to the fuel cell 1 (step S34). Step S35).
[0030]
Dry air is supplied from the air supply device 2 to the combustion catalyst of the catalytic combustor 4 via the air supply passage 12 and the small flow rate mixer 6, so that the temperature of the combustion catalyst rises (step S36). When the warming-up of the combustion catalyst is completed in this way (step S37), the pressure regulating valve 11 is opened, the on-off valve 13 is closed (step S38), and power generation is started in the combustion battery 1.
[0031]
It should be noted that whether or not the combustion catalyst in the catalytic combustor 4 downstream of the small flow mixer 6 has dried can be grasped by a predetermined time after the supply of air (the processing in step S34 in FIG. 3). This predetermined time may be set as a value confirmed in advance by an experiment or the like. Further, whether or not the combustion catalyst has increased to a temperature at which the exhaust hydrogen gas can be processed can be determined based on the temperature measured by a temperature sensor (not shown). can do.
[0032]
Since the exhaust air of the fuel cell 1 is humid air, after the combustion cell system is stopped, moisture remains in the catalytic combustor 4, and the temperature of the catalytic combustor 4 decreases, and the moisture adheres to the catalyst surface. Therefore, at the time of starting the system, the catalytic reaction cannot occur unless the water on the catalyst surface is removed.
[0033]
However, in the present embodiment, since the air supply pipe 12 for supplying air to the small flow rate mixer 6 bypassing the fuel cell 1 is provided, dried and heated air can be introduced into the combustion catalyst. Thereby, the front surface (shown by A in FIG. 2) of the combustion catalyst can be dried.
[0034]
Here, in order to dry the entire combustion catalyst, it is necessary to supply a large amount of air to the combustion catalyst. In this case, the power consumed by the air supply device 2 increases, and it is necessary to increase the capacity of a power source such as a secondary battery that supplies power to the air supply device 2.
[0035]
However, in the present embodiment, only a part of the combustion catalyst downstream of the small flow rate mixer 6 is dried when the system is started. Therefore, only a small amount of air needs to be supplied, the power required to supply the air is reduced, and the power source such as a secondary battery can be downsized. Further, the diameter of the air supply pipe 12 can also be reduced in accordance with the small flow rate of air, and the space required for mounting on a vehicle or the like is small.
[0036]
FIG. 4 is a diagram showing a configuration of a fuel cell system according to the third embodiment of the present invention. The third embodiment is characterized in that an air flow adjusting device 17 such as a throttle that adjusts the flow rate of air downstream of the air supply pipe 12 is used instead of the on-off valve 13 in the configuration shown in FIG. Has been established. Further, instead of the pipe 8, the hydrogen supply device 3 and the small flow rate mixer 6 are connected, and a pipe 18 serving as a combustion fuel supply path for directly supplying hydrogen from the hydrogen supply apparatus 3 to the small flow rate mixer 6 is provided. is there. The small flow mixer 6 has a structure in which the exhaust air of the fuel cell 1 supplied to the main mixer 5 and the hydrogen gas in the hydrogen circulation channel 14 do not flow. Other configurations are the same as those of the embodiment shown in FIG. 2, and the description thereof is omitted.
[0037]
In such a configuration, during startup and during operation of the fuel cell system, the air whose flow rate has been adjusted by the air flow rate adjusting device 17 from the air supply device 2 to the small flow rate mixer 6 via the air supply pipe 17 at all times. Supplied. Further, during startup and operation of the fuel cell system, hydrogen whose flow rate has been adjusted by the flow rate adjusting device 9 is constantly supplied from the hydrogen supply device 3 to the small flow rate mixer 6 via the pipe 18.
[0038]
In the third embodiment, air and hydrogen are always directly supplied from the air supply device 2 and the hydrogen supply device 3 to the small flow rate mixer 6. Therefore, even after the fuel cell 1 is stopped, the surface of the combustion catalyst downstream of the small flow rate mixer 6 can be kept in a dry state. Therefore, the time required for drying the combustion catalyst at the time of starting the system is not required, so that the starting time of the system can be shortened and the power consumption at the time of starting the system can be reduced.
[0039]
Further, even during the operation of the fuel cell system, the exhaust air of the fuel cell 1 and the exhaust hydrogen gas from the hydrogen circulation channel 14 are not supplied to the small flow rate mixer 6. For this reason, even when the liquid water condensed and accumulated in the pipes and the fuel cell 1 enters the catalytic combustor 4, the combustion catalyst in the entered portion is prevented from misfiring. As a result, the temperature in the area in front of the combustion catalyst (indicated by A in FIG. 4) can be increased, and the area in front of the combustion catalyst can be dried again.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a fuel cell system according to a second embodiment of the present invention.
FIG. 3 is a flowchart showing a processing operation of a fuel cell system according to a second embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of a fuel cell system according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Air supply device 3 ... Hydrogen supply device 4 ... Catalytic combustor 5 ... Main mixer 6 ... Small flow rate mixer 7 ... Steam / water separator 8, 18 ... Piping 9 ... Flow control device 10, 13 ... On-off valve 11 ... Pressure adjusting valve 12 ... Air supply pipe 14 ... Hydrogen circulation channel 15 ... Ejector 16 ... Gas discharge channel 17 ... Air flow control device

Claims (11)

In a fuel cell system that generates power by using fuel gas supplied from a fuel gas supply device and air supplied from an air supply device,
A circulation flow path that circulates fuel gas unused in the fuel cell from downstream to upstream of the fuel cell,
A gas discharge channel for discharging gas in the circulation channel,
An on-off valve for controlling discharge / cutoff of gas discharged from the circulation flow path to the gas discharge flow path;
A combustor that is provided downstream of the gas discharge flow path and burns and discharges gas discharged from the circulation flow path via the gas discharge flow path,
A fuel supply system for supplying a predetermined flow rate of fuel gas to the combustor during operation of the fuel cell system. The fuel cell system according to claim 1, wherein a predetermined flow rate of fuel gas that causes the combustor to be in a dry state is supplied to the combustor during operation of the fuel cell system. The fuel cell system according to claim 1, wherein the combustion fuel supply passage supplies gas in the circulation passage to the combustor. 2. The fuel cell system according to claim 1, wherein the combustion fuel supply passage directly supplies the fuel gas from the fuel gas supply device to the combustor without passing through the fuel cell. 3. During operation of the fuel cell system, a fuel gas is continuously supplied to the combustor from the combustion fuel supply passage.
The fuel cell system according to any one of claims 1, 2, 3, and 4, wherein: A first mixer that mixes gas and air provided from the gas discharge channel and provides the mixed gas to the combustor;
The gas supplied from the combustion fuel supply channel and air are mixed, and the mixed gas is supplied to the combustor, and a second mixer having a smaller capacity than the first mixer is provided. The fuel cell system according to any one of claims 1, 2, 3, 4, and 5. The fuel cell system according to any one of claims 1, 2, 3, 4, 5, and 6, wherein the combustor is provided with an exhaust air supply passage that supplies exhaust air of the fuel cell. . 8. A combustion air supply flow path for supplying air from the air supply device to the combustor without passing through the fuel cell. The fuel cell system according to claim 1. 4. A water recovery means for removing water contained in gas supplied to the combustor is provided in a path from the circulation flow path to the combustor via the combustion fuel supply flow path. A fuel cell system as described. A combustion air supply channel is provided for supplying air from the air supply device to the combustor without passing through the fuel cell, and the combustion air supply channel supplies air to the combustor via the second mixer. 7. The fuel cell system according to claim 6, wherein: The fuel cell system according to claim 10, wherein air is supplied to the second mixer via the combustion air supply passage when the fuel cell system is started.

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