JP2005317224A - Fuel cell system and scavenging method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing energy consumption when scavenging a fuel cell. When a fuel cell 1 mounted on an automobile as a power source generates electric power, a control unit 40 operates the automobile. In the idling operation state by checking the state, the operation temperature of the refrigerant temperature adjusting valve 19 is controlled, and the inlet temperature of the refrigerant supplied to the fuel cell 1 is raised higher as the load of the fuel cell 1 is smaller. Thereby, when the power generation of the fuel cell 1 is stopped, the temperature of the fuel cell 1 can be increased. Residual water can be effectively removed by warming the scavenging gas inside the fuel cell 1.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system and a scavenging method thereof.

In the fuel cell system, in order to improve the power generation performance particularly when starting at a low temperature (freezing point), so-called scavenging that supplies scavenging gas to the fuel cell and discharges residual water in the fuel cell when power generation stops. Has been done.
As a method for this, for example, in Patent Document 1, a switching valve is provided in a fuel passage for supplying fuel gas to the anode of a fuel cell, and a compressor for supplying air containing oxygen as an oxidant gas to the cathode is provided via the switching valve. Thus, non-humidified air can be supplied to the anode. A technique for scavenging a fuel cell by switching a switching valve when supplying fuel gas to stop power generation and supplying air from a compressor to both an anode and a cathode is disclosed. According to this, outside air can be used as the scavenging gas, and the amount of residual water inside the fuel cell can be set to an appropriate amount in a short time, so that the fuel cell can be stably started at a low temperature. .
JP 2003-331893 A (paragraph numbers 0015, 0016, 0018, FIG. 1)

However, in order to scavenge the fuel cell in the prior art, there is a problem that a great deal of energy is required and energy consumption is large. In a fuel cell system, it is necessary to store a certain amount of energy in an energy storage such as a battery in order to control opening / closing of a valve or supply air as an oxidant gas at the time of startup. If is consumed, the fuel cell may not be started. As a countermeasure, for example, it is conceivable to increase the capacity of a battery or the like and secure energy for starting, but this causes a problem of increasing the weight and volume of the entire fuel cell system and is not an appropriate method.
An object of the present invention is to provide a fuel cell system capable of suppressing energy consumption during scavenging in view of the conventional problems.

  The invention according to claim 1 detects a fuel cell that generates power by a chemical reaction between a fuel gas supplied to the anode and an oxidant gas supplied to the cathode, and detects that the load of the fuel cell is low. A low-load detection means that detects when the load of the fuel cell is low by the low-load detection means, and when the power generation of the fuel cell is stopped And scavenging means for scavenging by supplying a scavenging gas to the fuel cell.

  According to a second aspect of the present invention, the temperature raising means includes a cooling means for cooling the fuel cell, and the temperature of the fuel cell is raised by raising the temperature of the refrigerant supplied from the cooling means to the fuel cell. It was supposed to be

  The invention according to claim 3 is mounted on a vehicle as a power source, and the low load detection means detects that the load of the fuel cell is low when the vehicle is in an idling operation state.

  The invention described in claim 4 is a scavenging method of a fuel cell system having a fuel cell that generates electric power by a chemical reaction between a fuel gas supplied to an anode and an oxidant gas supplied to a cathode. When the load of the fuel cell is low, the temperature of the fuel cell is raised, and when the power generation of the fuel cell is stopped, scavenging gas is supplied to the fuel cell. Supplying and scavenging was performed.

  In the fuel cell system according to claim 1, since the temperature of the fuel cell is increased when the load of the fuel cell is low, the temperature of the fuel cell is increased when the power generation of the fuel cell is stopped. Can do. Therefore, when scavenging is performed, the scavenging gas supplied to the fuel cell 1 is warmed inside the fuel cell, and the amount of gas necessary for scavenging is reduced due to the increase in the volume flow rate of the scavenging gas and the saturated water vapor amount. It is possible to reduce the energy consumed.

  In the fuel cell system according to claim 2, since the temperature of the fuel cell is raised by raising the temperature of the refrigerant for cooling the fuel cell, for example, the capability is limited with respect to the heat radiation of the refrigerant performed by the cooling means. As a result, the temperature of the fuel cell can be raised. Therefore, a means for raising the temperature such as a heater is not necessary, and in addition to the effect of the first aspect, the fuel cell system can be made compact.

  In the fuel cell system according to claim 3, when the fuel cell system is mounted on a vehicle as a power source, the temperature of the fuel cell is raised during the idling operation, so the load of the fuel cell is simply detected. In addition to raising the temperature of the fuel cell, in particular, the temperature of the fuel cell that requires scavenging can be raised, and the certainty of performing scavenging when power generation is stopped increases, and in addition to the effects of claims 1 and 2 , Which prevents unnecessary temperature rise and helps prevent deterioration of the fuel cell.

  In the scavenging method of the fuel cell system according to claim 4, the power generation of the fuel cell is stopped because the temperature of the fuel cell is increased when the load of the fuel cell is smaller than a predetermined value, as in the invention of claim 1. Sometimes the temperature of the fuel cell can be raised. Therefore, similarly to the first aspect of the invention, the amount of gas required for scavenging can be reduced, and the energy consumed for scavenging can be suppressed. Depending on the fuel cell system, even if sufficient scavenging is performed, there is an effect that the starting energy does not become insufficient.

Embodiments of a fuel cell system according to the present invention will be described below. Here, a fuel cell system mounted on a vehicle as a power source will be described.
FIG. 1 is a diagram showing a configuration of a fuel cell system.
The fuel cell 1 is formed by laminating a single cell in which a membrane electrode structure in which a polymer electrolyte membrane is sandwiched between a cathode and an anode is further sandwiched between separators, and an anode gas inflow passage 2 is connected to the anode side inlet a _1. Are connected, and an anode off gas outflow passage 8 is connected to the anode side outlet a ₂ .
The anode gas inflow passage 2 is provided with a shut-off valve 6, a regulator 5 and an ejector 3 in this order from the hydrogen cylinder 7 connected to the end thereof, and the anode off gas outflow passage 8 is provided with a purge valve 9. .

The shutoff valve 6 controls the hydrogen gas supplied from the hydrogen cylinder 7 to the fuel cell 1. When the valve is opened, the hydrogen gas is supplied to the fuel cell 1. When the valve is closed, the supply of the hydrogen gas is shut off. .
The regulator 5 adjusts the pressure of hydrogen gas supplied to the fuel cell 1.
The ejector 3 is connected to a circulation path 10 branched from the upstream side of the purge valve 9 in the anode off-gas outflow path 8 and circulates the anode off-gas discharged to the anode off-gas outflow path 8 to the fuel cell 1. By this ejector 3, unreacted hydrogen gas discharged as anode off gas can be reused, and the utilization rate of hydrogen gas is improved.
The purge valve 9 controls the flow of anode off gas. When the valve is closed, the anode off gas outflow path 8 is sealed, the anode off gas is circulated from the circulation path 10 to the fuel cell 1, and when the valve is opened, the anode off gas is discharged to the outside. The
The shut-off valve 6, the regulator 5, the ejector 3 and the purge valve 9 are controlled by the control unit 40, respectively.

A cathode gas inlet passage 12 is connected to the cathode side inlet c ₁ of the fuel cell 1, the cathode-side outlet c ₂ cathode off-gas outflow passage 14 is connected.
A compressor 13 for supplying air as an oxidant gas or a scavenging gas is connected to the end of the cathode gas inflow passage 12, and the cathode offgas of the air supplied to the fuel cell 1 by the compressor 13 is externally connected from the cathode offgas outflow passage 14. Is discharged.
A downstream side of the regulator 5 in the anode gas inflow passage 2 and the cathode gas inflow passage 12 are communicated with each other by a communication passage 26, and a shutoff valve 27 is provided in the communication passage 26.
By this communication path 26, when the shut-off valve 27 is opened, air from the compressor 13 can be supplied to the anode of the fuel cell 1 to scavenge the anode.
The shut-off valve 27 and the compressor 13 are controlled by the control unit 40.

A refrigerant inflow path 16 is connected to the refrigerant inlet L ₁ of the fuel cell 1, and a refrigerant outflow path 17 is connected to the refrigerant outlet L ₂ . A refrigerant temperature adjustment valve 19 and a radiator 22 are provided in the refrigerant outflow path 17 in order from the fuel cell 1, and the refrigerant temperature adjustment valve 19 is connected to a communication path 20 branched from the downstream side of the radiator 22. A refrigerant pump 15 is connected between the refrigerant inflow path 16 and the refrigerant outflow path 17, and the refrigerant pump 15 can circulate the refrigerant to the fuel cell 1. The refrigerant temperature adjustment valve 19 operates according to the temperature of the refrigerant circulating in the fuel cell 1 and controls the refrigerant temperature.

That is, when the temperature (outlet temperature) of the refrigerant discharged from the fuel cell 1 is equal to or higher than the operating temperature of the refrigerant temperature adjustment valve 19, the refrigerant temperature adjustment valve 19 operates to switch to the radiator 22 side. Heat is discharged to the outside via the line 22 and circulated to the fuel cell 1.
When the temperature of the discharged refrigerant is lower than the operating temperature of the refrigerant temperature adjustment valve 19, the refrigerant temperature adjustment valve 19 operates so as to switch to the communication path 20 side. The fuel cell 1 is circulated as it is. In this way, the temperature of the refrigerant is controlled by the operation of the refrigerant temperature adjustment valve 19, the temperature of the refrigerant (inlet temperature) supplied to the fuel cell 1 becomes constant, and the operation temperature of the refrigerant temperature adjustment valve 19 is controlled. Thus, the inlet temperature can be changed.
The refrigerant pump 15 and the refrigerant temperature adjustment valve 19 are controlled by the control unit 40.
The fuel cell 1 is connected to an electric device 4 including an auxiliary machine including an automobile drive motor and a battery that supplies power when the fuel cell 1 does not generate power.

  In the present embodiment, when the automobile stops and the power generation of the fuel cell 1 stops, scavenging is performed in preparation for restart. At this time, the temperature of the fuel cell 1 is raised so as to increase the scavenging efficiency. That is, by scavenging the fuel cell 1, the scavenging gas is warmed inside the fuel cell 1 during scavenging, and the residual water removal capability can be improved by increasing the volume flow rate. Moreover, since the amount of saturated water vapor increases as the scavenging gas is warmed, in other words, the relative humidity of the scavenging gas decreases, the amount of residual water that is taken away increases even at the same volume flow rate. As a result, the amount of gas necessary for scavenging is reduced, and the energy consumed for scavenging can be suppressed. Depending on the fuel cell system, scavenging and starting energy can be secured simultaneously without changing the battery.

Next, control of the fuel cell 1 will be described based on a flowchart. FIG. 2 is a flowchart showing the flow of fuel cell control.
When the control unit 40 receives an ignition switch ON signal (IGN ON) from the vehicle side (S1), the control unit 40 opens the shut-off valve 6 and activates the compressor 13. As a result, hydrogen gas and air are respectively supplied to the fuel cell 1, and the power generation of the fuel cell 1 is started. At this time, the shutoff valve 27 in the communication passage 26 that communicates the anode and the cathode is in a closed state, and hydrogen gas and air as an oxidant gas do not flow to the other side. While the fuel cell 1 is generating power, the control unit 40 performs power generation control of the fuel cell 1 through control of the regulator 5, the purge valve 9, and the like according to the load of the fuel cell 1, that is, the electric power supplied to the electric device 4. The power generation of the fuel cell 1 enables the automobile to travel with power.
As the power is generated, the temperature of the fuel cell 1 rises, and the control unit 40 inputs the detection value of the temperature sensor T provided in the cathode offgas outflow passage 14 to confirm the temperature of the fuel cell 1. When the temperature of the fuel cell 1 reaches a predetermined temperature, the control unit 40 activates the refrigerant pump 15 assuming that the warm-up is completed (S2). As a result, the refrigerant is supplied to the fuel cell 1 and cooling of the fuel cell 1 is started.

The control unit 40 detects the load of the fuel cell 1 so as to control the refrigerant flow rate to the fuel cell 1 (S3), and controls the refrigerant pump 15 based on the load (S4).
That is, the control unit 40 is provided with a refrigerant flow rate corresponding to the load indicated by the line 3 in FIG. 3 as a map so that the fuel cell 1 is supplied with a flow rate according to the load, and according to the detected load. Using the refrigerant flow rate read from the map as a target value, the flow rate of the refrigerant supplied to the fuel cell 1 is controlled by controlling the refrigerant pump 15. In line 3 of FIG. 3, the larger the load, the larger the refrigerant flow rate. For this reason, the cooling capacity increases in the high load region c where heat generation is large, and the power consumption for driving the refrigerant pump 15 can be suppressed in the medium load region b and low load region a where heat generation is relatively low.

The control unit 40 checks whether or not the vehicle is idling (S5). This can be done, for example, by checking whether the shift position is parked or neutral. Alternatively, it can be performed by checking whether or not the vehicle speed is zero when the accelerator opening is zero.
When not in the idling operation state (S5, NO), the control unit 40 controls the temperature of the refrigerant supplied to the fuel cell 1, that is, the refrigerant inlet temperature, assuming that the automobile is running.
That is, the control unit 40 includes an inlet temperature corresponding to the load indicated by the line 1 in FIG. 3 as a map, and the inlet temperature read from the map according to the detected load is supplied to the fuel cell 1 as a refrigerant. The operating temperature of the refrigerant temperature adjustment valve 19 is controlled as a target value for the inlet temperature of the refrigerant.
In a fuel cell, it is necessary to keep the outlet temperature of the refrigerant below a heat-resistant temperature in accordance with the durability requirement of the fuel cell. For this reason, when setting the inlet temperature, it is assumed that the outlet temperature is kept below the heat-resistant temperature of the fuel cell 1 in the high load region c where the calorific value is large as shown by the line 4 in FIG. Is set to the inlet temperature indicated by line 1.
Therefore, even if the fuel cell 1 enters the high load region c by controlling the inlet temperature of the refrigerant during traveling, the outlet temperature of the fuel cell 1 can be suppressed to a heat resistant temperature or less, and the fuel cell 1 is caused by excessive temperature rise. Will not deteriorate.

The control unit 40 checks whether or not the ignition switch signal from the vehicle side has become an off signal (S8), and if it is not an off signal (S8, NO), it returns to step S3 because it is running, and a new fuel is generated. The load of the battery 1 is detected, and the control of the refrigerant flow rate and the inlet temperature is repeated as described above.
When it is checked that the vehicle is in an idling operation state (S5, YES), the control unit 40 performs control to increase the inlet temperature of the fuel cell.
That is, the control unit 40 is provided with an inlet temperature corresponding to the load indicated by the line 2 in FIG. 3 as a map, and the inlet temperature read from the map according to the detected load is the refrigerant temperature supplied to the fuel cell 1. As the target value of the inlet temperature, the operating temperature of the refrigerant temperature adjustment valve 19 is controlled.
In order to raise the temperature of the fuel cell 1 when the automobile is in idling operation, the inlet temperature indicated by the line 2 in FIG. 3 is set to be higher as the load is lower according to the load.
In setting the inlet temperature, it is assumed that the outlet temperature during idling (low load region a) is the same as the outlet temperature in the middle load region b during traveling, as indicated by line 5 in FIG. Is set to the inlet temperature indicated by line 2. Therefore, when the vehicle enters the idling operation state, the control unit 40 controls the operating temperature of the refrigerant temperature adjustment valve 19 so that the refrigerant inlet temperature increases as the load decreases according to the load. Thus, the outlet temperature of the refrigerant is raised, and the temperature of the fuel cell 1 is raised.

The control unit 40 checks whether or not the ignition switch signal is turned off (S8). If not (S8, NO), the control unit 40 returns to step S3 and repeats the control. When it is checked that the ignition switch signal is turned off (S8, YES), the control unit 40 closes the shutoff valve 6 to shut off the supply of hydrogen gas to the fuel cell 1 and stop power generation. Then, the refrigerant pump 15 is stopped. As a result, the supply of refrigerant to the fuel cell 1 is stopped when power generation is stopped (S9).
Thereafter, the control unit 40 fully opens the purge valve 9 and opens the shut-off valve 27 to perform scavenging (S10).

As for scavenging, an automatic freezing prediction mode for predicting that the fuel cell is frozen at the time of restarting is provided, and scavenging can be performed only when freezing is predicted.
The control unit 40 utilizes the fact that the pressure loss is reduced during scavenging as a result of the residual water in the fuel cell 1 being discharged by scavenging, so that the pressure sensor Pa provided on the fuel cell 1 side of the anode gas inflow path 2. It is determined whether or not scavenging is completed by inputting the detected value. When scavenging is completed, the compressor 13 is stopped, the shutoff valve 27 is closed, and the purge valve 9 is closed. As a result, the operation of the fuel cell system is stopped (S11).

The fuel cell system is configured as described above. When the automobile is in an idling operation state, the inlet temperature of the refrigerant supplied to the fuel cell 1 is increased and the fuel cell 1 is raised as the load is reduced according to the load of the fuel cell 1. Therefore, when the vehicle stops and the power generation of the fuel cell 1 stops, the temperature of the fuel cell 1 can be raised. Therefore, when scavenging, the scavenging gas is warmed inside the fuel cell 1, and residual water can be effectively removed by increasing the volume flow rate and the saturated water vapor amount. As a result, the amount of gas required for scavenging can be reduced, and the energy consumed for scavenging can be suppressed.
Regarding the temperature rise of the fuel cell 1, in addition to raising the refrigerant inlet temperature, for example, a heater may be provided to heat the fuel cell 1 from the outside to raise the temperature.

  In the present embodiment, the temperature of the fuel cell 1 is raised when the vehicle is in the idling operation state. However, for example, the load of the fuel cell 1 is directly detected, and the load is equal to or lower than a predetermined value (for example, the low value in FIG. 3). When the load region a) is reached, the temperature of the fuel cell 1 can be raised. However, in this case, for example, when traveling on a down road, the load may become lower than a predetermined value, so that the temperature of the fuel cell may be increased although it is not necessary. On the other hand, in this embodiment, since the temperature of the fuel cell 1 is raised during the idling operation state, the certainty of scavenging is high after the temperature rise.

It is a figure which shows the structure of a fuel cell system. It is a flowchart which shows the flow of fuel cell control. It is a figure which shows the relationship between a refrigerant | coolant temperature, a refrigerant | coolant flow volume, and load.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Anode gas inflow path 3 Ejector 4 Electric equipment 5 Regulator 6 Shut off valve 7 Hydrogen cylinder 8 Anode off-gas outflow path 9 Purge valve 10 Circulation path 12 Cathode gas inflow path 13 Compressor 14 Cathode off-gas outflow path 15 Refrigerant pump 16 Refrigerant inflow path 17 Refrigerant outflow path 19 Refrigerant temperature adjustment valve 20 Communication path 22 Radiator 26 Communication path 27 Shut-off valve 40 Control unit

Claims (4)

A fuel cell that generates electricity by a chemical reaction between a fuel gas supplied to the anode and an oxidant gas supplied to the cathode;
Low load detection means for detecting that the load of the fuel cell is low; and
When the load of the fuel cell is detected by the low load detection means as a low load, a temperature raising means for raising the temperature of the fuel cell;
A fuel cell system, comprising: scavenging means for supplying scavenging gas to the fuel cell and scavenging when power generation of the fuel cell is stopped.   2. The temperature raising means includes a cooling means for cooling the fuel cell, and raises the temperature of the fuel cell by raising a temperature of a refrigerant supplied from the cooling means to the fuel cell. The fuel cell system described in 1. Installed in automobiles as a power source,
3. The fuel cell system according to claim 1, wherein the low load detection unit detects that the load of the fuel cell is a low load when the automobile is in an idling operation state. 4. A scavenging method of a fuel cell system having a fuel cell that generates power by a chemical reaction between a fuel gas supplied to an anode and an oxidant gas supplied to a cathode,
Detecting that the load of the fuel cell is a low load, and heating the fuel cell when the load of the fuel cell is a low load,
A scavenging method for a fuel cell system, wherein scavenging is performed by supplying scavenging gas to the fuel cell when power generation of the fuel cell is stopped.

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