JP4857472B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system including a fuel cell that generates electric energy by a chemical reaction between hydrogen and oxygen, and is effective when applied to a moving body such as a vehicle, a ship, and a portable generator.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fuel cell system including a fuel cell that generates power using an electrochemical reaction between hydrogen and oxygen (air) is known. For example, in a polymer electrolyte fuel cell that is considered as a driving source for vehicles and the like, in a low temperature state of 0 ° C. or lower, moisture present in the vicinity of the electrode freezes and inhibits diffusion of reaction gas, There is a problem that the electrical conductivity of the film is lowered.
[0003]
When starting a fuel cell in such a low-temperature environment, the fuel gas may be supplied even if fuel gas is supplied due to clogging of the reaction gas path due to freezing or hindering the progress or arrival of the reaction gas (hydrogen and air) to the electrolyte membrane. There is a problem that the fuel cell cannot be started because the chemical reaction does not proceed. Furthermore, the gas path is also blocked due to the freezing of moisture condensed in the reaction gas path.
[0004]
In order to prevent freezing inside the fuel cell and improve low-temperature startability, it is desirable to previously remove moisture that freezes in a low-temperature environment from the inside of the fuel cell. For this reason, it is conceivable to remove moisture in the fuel cell by supplying air into the fuel cell by an air flow.
[0005]
[Problems to be solved by the invention]
However, when the moisture in the fuel cell is removed by the air flow, heat is taken away by the latent heat of vaporization when the moisture evaporates, and the temperature inside the fuel cell decreases. As a result, there is a problem that the amount of water evaporation decreases and it takes time to remove the water in the fuel cell.
[0006]
In view of the above problems, an object of the present invention is to provide a fuel cell system that can remove moisture inside the fuel cell in a short time when the operation is stopped in a fuel cell system used in a low temperature environment. And
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a fuel cell system including a fuel cell (10) that obtains electric power by electrochemically reacting hydrogen and oxygen, and supplies the fuel cell (10). An air path (20) through which oxygen is passed, a hydrogen path (30) through which hydrogen supplied to the fuel cell (10) passes, a heating means (44) for heating the fuel cell (10), and a fuel cell A temperature sensor (12) for detecting the temperature of (10), a moisture sensor (24, 34) for detecting the water content of the hydrogen electrode and oxygen electrode of the fuel cell (10), an air path (20) and a hydrogen path ( Control means (50) for performing gas supply control to 30) and heating control by the heating means (44) , the control means (50) after stopping the normal operation of the fuel cell (10), the air path (20) And in the hydrogen pathway (30) Supplying a drying gas, if the water content detected by the moisture sensor determines whether or not lower than the less freezing range than the predetermined amount, it is determined to exceed the freezing range, the temperature sensor (12) It is characterized by controlling the heating temperature of the fuel cell that by the heating means (44) based on the detected temperature (10) by.
[0008]
By heating the fuel cell (10) simultaneously with the gas supply in this way, it is possible to prevent the fuel cell temperature from being lowered due to moisture evaporation during the moisture removal operation. As a result, the evaporation of residual moisture inside the fuel cell (10) can be promoted, the moisture inside the fuel cell (10) is removed in a short time, and the fuel cell is prevented from freezing and the fuel cell at a low temperature. The startability of (10) can be improved.
Further, by controlling the heating temperature of the fuel cell (10) by the heating means (44) based on the temperature detected by the temperature sensor (12), the fuel cell temperature does not destroy the electrolyte membrane or the like of the fuel cell (10). It is possible to maintain the temperature at which the residual water can be efficiently evaporated within the range.
[0009]
The invention according to claim 2 is characterized in that the dry gas is air. By using air in this manner, moisture can be removed without providing a special gas supply device. Further, the dried air can be provided by not humidifying the air that is performed during normal operation.
[0010]
Further, in the invention according to claim 3, cooling Mizukei passage for circulating cooling water to the fuel cell (10) and (40), provided in the cooling water passage (40), during normal operation of the fuel cell (10) and a cooling unit for cooling the cooling water (42, 43), heating means, in parallel or serially disposed cooling section (42, 43) in the cooling water passage (40), so as to heat the cooling water is configured to, by the control means (50), the flow path of the cooling water is configured to be switched to the cooling section (42, 43) side or the heating means (44) side, the control means (50), When the fuel cell (10) is heated after the normal operation of the fuel cell (10) is finished, the flow path of the cooling water is switched to the heating means (44) side.
[0011]
With such a configuration, it is possible to heat the fuel cell (10) with a simple configuration using an existing fuel cell cooling system and adding a cooling water heating unit (44) thereto.
[0013]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. In the present embodiment, the fuel cell system is applied to an electric vehicle (fuel cell vehicle) that runs using the fuel cell as a power source.
[0015]
FIG. 1 shows the overall configuration of the fuel cell system of the present embodiment. As shown in FIG. 1, the fuel cell system of the present embodiment includes a fuel cell (FC stack) 10 that generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen. The FC stack 10 is configured to supply electric power to an electric device (load) 11 for running the vehicle and an electric device such as a secondary battery (not shown).
[0016]
In the FC stack 10, the following electrochemical reaction between hydrogen and oxygen occurs to generate electric energy.
(Negative electrode side) H ₂ → 2H ⁺ + 2e ⁻
(Positive electrode side) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O
In this embodiment, a solid polymer electrolyte fuel cell is used as the FC stack 10, and a plurality of cells serving as basic units are stacked. Each cell has a configuration in which an electrolyte membrane is sandwiched between a pair of electrodes. The FC stack 10 is provided with a temperature sensor 12 for detecting the temperature of the FC stack body.
[0017]
In the fuel cell system, an air path 20 for supplying air (oxygen) to the oxygen electrode (positive electrode) 10a side of the FC stack 10 and hydrogen for supplying hydrogen to the hydrogen electrode (negative electrode) 10b side of the FC stack 10 are provided. A hydrogen path 30 is provided. The air path 20 is provided with a blower (gas compressor) 21 for air supply for supplying air. Hydrogen is supplied to the hydrogen path 30 from a hydrogen supply device 31.
[0018]
For the electrochemical reaction during power generation, the electrolyte membrane in the FC stack 10 needs to be in a wet state containing moisture. Therefore, during normal operation, humidification is performed on the air in the air path 20 and the hydrogen in the hydrogen path 30 by a humidifier (not shown), and the humidified air and hydrogen are supplied to the FC stack 10. As a result, the inside of the FC stack 10 operates in a wet state. Further, moisture is generated by the electrochemical reaction on the oxygen electrode 10a side.
[0019]
In addition, during the moisture removal operation described later, dry air that is not humidified and dry hydrogen that is not humidified are supplied to the FC stack 10. In order to remove moisture remaining in the FC stack 10, it is desirable that these dry gases have as low a humidity as possible, and at least lower than the humidity in the FC stack 10.
[0020]
Shut valves 22 and 23 for blocking the air path 20 are provided at both ends of the air path 20. By closing these shut valves 22, 23, the inside of the FC stack 10 and the inside of the air path 20 can be shut off from the outside air. Similar shut valves 32 and 33 are provided at both ends of the hydrogen passage 30.
[0021]
The air path 20 and the hydrogen path 30 are connected on the upstream side of the FC stack 10. A hydrogen path switching valve 35 is provided at a connection portion in the hydrogen path 30. By switching the hydrogen path switching valve 35, hydrogen from the hydrogen supply device 31 can flow through the hydrogen path 30 during normal operation, and air from the air path 20 can flow through the hydrogen path 30 during moisture removal operation.
[0022]
The FC stack 10 is provided with moisture sensors 24 and 34 for detecting residual moisture present in the oxygen electrode 10a and the hydrogen electrode 10b inside the FC stack 10. In the present embodiment, humidity sensors are used as the moisture sensors 24 and 34. The humidity sensors 24 and 34 are desirably provided near the outlet of the FC stack 10 in the oxygen electrode 10a and the hydrogen electrode 10b in order to appropriately detect the humidity inside the FC stack 10.
[0023]
The FC stack 10 generates heat with power generation. For this reason, the fuel cell system is provided with cooling systems 40 to 45 so that the FC stack 10 is cooled and the operating temperature becomes an appropriate temperature (about 80 ° C.) for the electrochemical reaction.
[0024]
The cooling system is provided with a cooling water path 40 that circulates cooling water (heat medium) through the FC stack 10, a water pump 41 that circulates the cooling water, and a radiator 42 that includes a fan 43. The radiator 42 and the fan 43 constitute a cooling unit.
[0025]
The heat generated in the FC stack 10 is discharged out of the system by the radiator 42 through the cooling water. With such a cooling system, the cooling amount control of the FC stack 10 can be performed by the flow rate control by the water pump 41 and the air volume control by the radiator 42 and the fan 43.
[0026]
In the cooling system of the present embodiment, a heating unit (heating unit) 44 for heating the cooling water is provided in parallel with the radiator 43. As the heating unit 43, for example, an electric heater, a combustion heater, a catalyst heater, or the like can be used. With such a configuration, the heating amount control of the FC stack 10 can be performed by the heating amount control of the cooling water by the heating unit 44 and the flow rate control by the water pump 41.
[0027]
The flow path of the cooling water is switched to the radiator 43 side and the heating unit 44 side by the cooling water switching valve 45. During normal operation of the FC stack 10, the cooling water switching valve 45 is switched to the radiator 43 side, and the FC stack 10 is cooled. On the other hand, during the water removal operation of the FC stack 10 in the present embodiment, the cooling water switching valve 45 is switched to the heating unit 44 side, and the FC stack 10 is heated.
[0028]
The fuel cell system of this embodiment is provided with a control unit (ECU) 50 that performs various controls. The control unit 50 receives a required power signal from the load 11, a temperature signal from the temperature sensor 12, a residual moisture amount signal from the moisture sensors 24 and 34, and the like. The control unit 50 is configured to output control signals to the secondary battery, the blower 21, the water pump 41, the radiator fan 43, the heating unit 44, the cooling water switching valve 45, and the like.
[0029]
Next, moisture removal control in the fuel cell system having the above-described configuration will be described with reference to FIG. FIG. 2 is a flowchart showing water removal control of the fuel cell system.
[0030]
First, it is determined whether or not moisture removal (moisture purge) in the FC stack 10 is necessary after the normal operation is stopped (step S10). The determination of whether or not to remove moisture is performed in consideration of the environmental temperature (outside temperature) at the time of operation stop, seasonal information, and the like. That is, the necessity for the water removal operation is determined based on the condition that the environmental temperature is 0 ° C. or lower, or that the temperature is predicted to decrease in winter. Naturally, moisture operation is not necessary because there is no risk of freezing in conditions such as summer.
[0031]
Further, when the operation of the FC stack 10 is stopped, an expected time of the FC stack 10 stop time by the driver may be input. This is because even if the environmental temperature is below the freezing point when the FC stack 10 is stopped, the FC stack 10 does not immediately drop below the freezing point because the FC stack 10 is sufficiently preheated, and the high temperature is maintained for a while. It is to be done. Therefore, it is not necessary to remove the residual water when the operation is stopped within the stop time of about 10 hours (all day and night).
[0032]
When it is determined in step S10 that the water removal operation is necessary, the cooling water switching valve 45 is switched to the heating unit 44 side (step S11). As a result, the cooling water is heated by the heating unit 44. Since the FC stack 10 has already stopped generating power, the cooling water switching valve 45 and the like are operated by supplying power from the secondary battery.
[0033]
Next, the hydrogen path switching valve 35 is switched to the air path 20 side (step S12), and air blowing control by the blower 21 is performed (step S13). As a result, air is supplied to the air path 20 and the hydrogen path 30. At this time, the air is not humidified, and dry air is supplied to the oxygen electrode 10a and the hydrogen electrode 10b of the FC stack 10. As a result, moisture present as droplets in the FC stack 10 is blown out of the FC stack 10 by the air flow.
[0034]
Next, the moisture sensors 24 and 34 detect the residual moisture amount in the FC stack 10 (step S14), and determine whether the residual moisture amount is less than the predetermined amount and below the freezing range (step S15).
[0035]
If the residual water content in the FC stack 10 is below the freezing range, the shut valves 22, 23, 32, 33 provided at both ends of the air path 20 and the hydrogen path 30 are closed (step S16). As a result, the inside of the FC stack 10, the inside of the air path 20, and the inside of the hydrogen path 30 are blocked from the outside air, and moisture intrusion from the external environment can be prevented.
[0036]
As a result, when the residual moisture amount in the FC stack 10 exceeds the freezing range, the FC stack temperature control in the following steps S17 to S21 is performed, and the FC stack 10 is heated to evaporate and remove the residual moisture.
[0037]
First, the temperature sensor 12 detects the temperature T of the main body of the FC stack 10 (step S17), and determines whether or not the FC stack temperature T exceeds the target temperature Tr (step S18). The target temperature Tr is preferably as high as possible in order to evaporate the water in the FC stack 10. However, if the target temperature Tr is set too high, the size of the heating unit 44 is increased and the electrolyte membrane inside the FC stack 10 is destroyed. Therefore, in order to prevent these problems, the target temperature Tr is set to 80 to 100 ° C.
[0038]
When the FC stack temperature T is higher than the target temperature Tr, the cooling water heating amount by the heating unit 44 is set to zero (step S19), and when the FC stack temperature T is lower than the target temperature, heating is performed. The cooling water heating amount by the unit 44 is set to K (Tr-T) [K: proportionality constant] (step S20). Next, the circulating amount of the cooling water is controlled by the water pump 41 (step S21). Thereby, temperature control is performed so that the FC stack temperature T becomes the target temperature Tr. After the above temperature control, the process returns to step S14.
[0039]
By performing the FC stack temperature control in steps S17 to S21 described above, the inside of the FC stack 10 can be kept at a high temperature without decreasing the temperature due to moisture evaporation. Thereby, evaporation of residual water is promoted inside the FC stack 10. The evaporated residual water is discharged to the outside of the FC stack 10 while being contained in the air supplied from the air path 20 and the hydrogen path 30. At this time, since dry air is supplied from the air path 20 and the hydrogen path 30, the inside of the FC stack 10 can be efficiently dried.
[0040]
(Other embodiments)
In the above embodiment, the humidity sensors are used as the moisture sensors 24 and 34 for detecting the residual moisture amount in the FC stack 10. However, the present invention is not limited to this. For example, the electrical resistance of the electrolyte membrane in the FC stack 10 as a moisture sensor. The residual moisture content inside the FC stack 10 can also be detected by measuring this change.
[0041]
Further, it is sufficient that at least a part of the water is removed from each cell constituting the FC stack 10. If a part of the cell is dry, power generation can be started by supplying hydrogen and air to the dry part. If power generation is started in a part of the cell, the temperature of the other part can be raised by heat generated by the power generation, and power generation can be performed in the entire cell.
[0042]
Moreover, in the said embodiment, although dry air was supplied from the air path 20 and the hydrogen path | route 30 at the time of a water | moisture-content removal driving | operation, you may comprise not only this but arbitrary gas, such as nitrogen, for example.
[0043]
If the FC stack temperature T detected in step S16 is higher than the temperature at which the electrolyte membrane is destroyed (for example, 150 ° C.), the cooling water switching valve 45 is switched to the radiator side to actively cool the cooling water. The FC stack 10 may be cooled.
[0044]
Moreover, in the said embodiment, although the heating part 44 which heats cooling water was provided in parallel with the radiator 43, you may provide not only this but the heating part 44 in series with the radiator 43 in the cooling water path 40. . In this case, in the configuration of the fuel cell system of FIG. 1, the heating unit 44 may be moved to the upstream side of the branch point between the heating unit 44 side and the radiator side and to the downstream side of the water pump 41. In the case of such a configuration, the path where the heating unit 44 is provided is a bypass path for bypassing the cooling water to the radiator 42. With such a configuration, when performing moisture removal control after the end of normal operation, the cooling water heated through the heating unit 44 passes through the bypass passage and bypasses the radiator 42.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a schematic configuration of a fuel cell system according to the embodiment.
FIG. 2 is a flowchart showing water removal control of the fuel cell system of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell (FC stack), 10a ... Oxygen electrode, 10b ... Hydrogen electrode, 12 ... Temperature sensor, 20 ... Air path, 22, 23 ... Shut valve, 30 ... Hydrogen path, 32, 33 ... Shut valve, 35 ... Hydrogen path switching valve, 42, 43 ... cooling unit, 44 ... heating unit (heating means), 50 ... control unit (ECU).

Claims (3)

A fuel cell system comprising a fuel cell (10) for obtaining electric power by electrochemical reaction of hydrogen and oxygen,
An air path (20) through which oxygen supplied to the fuel cell (10) passes;
A hydrogen path (30) through which hydrogen supplied to the fuel cell (10) passes;
Heating means (44) for heating the fuel cell (10) ;
A temperature sensor (12) for detecting the temperature of the fuel cell (10);
Moisture sensors (24, 34) for detecting the moisture content of the hydrogen electrode and oxygen electrode of the fuel cell (10);
Control means (50) for performing gas supply control to the air path (20) and the hydrogen path (30) and heating control by the heating means (44) ,
The control means (50) supplies a predetermined dry gas to the air path (20) and the hydrogen path (30) after the normal operation of the fuel cell (10) is stopped, and the amount of moisture detected by the moisture sensor. Is less than a predetermined amount and below the freezing range, and if it is determined that the freezing range is exceeded, the heating means (44 ) is based on the temperature detected by the temperature sensor (12). fuel cell system and controls the heating temperature of the fuel cell (10) that by the).   The fuel cell system according to claim 1, wherein the dry gas is air. The cooling Mizukei passage for circulating cooling water to the fuel cell (10) and (40),
A cooling section (42, 43) provided in the cooling water path (40), for cooling the cooling water during normal operation of the fuel cell (10),
The heating means is provided in parallel or in series with the cooling units (42, 43) in the cooling water path (40), and is configured to heat the cooling water,
Wherein with said cooling section the flow path of the cooling water (42, 43) side or the heating means (44) Ru switched to side cooling water switching means (45),
When the fuel cell (10) is heated after the normal operation of the fuel cell (10 ) is completed, the control means (50) heats the flow path of the cooling water by the cooling water switching means (45). 3. The fuel cell system according to claim 1, wherein the fuel cell system is switched to the means (44) side.

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