JP7827014B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system equipped with a fuel cell that generates electricity using hydrogen gas as fuel gas, and a water electrolysis device that produces hydrogen gas by electrolyzing water.

For example, Patent Document 1 proposes a fuel cell system having multiple fuel cells connected in parallel. In the fuel cell system, a cooling path is formed in each fuel cell through which a refrigerant flows. The cooling path includes a cooling device that cools the refrigerant, and a pump that pressure-feeds the refrigerant cooled by the cooling device to each fuel cell.

Japanese Patent Application Laid-Open No. 2022-118947

Now, fuel cells generate electricity using hydrogen gas as fuel gas. Let's imagine that one of the two fuel cells is replaced with a water electrolysis device that generates hydrogen gas by electrolyzing water. A refrigerant is supplied to the fuel cell and the water electrolysis device, but the heat of the refrigerant discharged from the fuel cell and the water electrolysis device is not used as waste heat, but is instead absorbed by a cooling device.

The present invention was made in consideration of these problems, and its purpose is to provide a fuel cell system that can efficiently utilize the heat of the refrigerant discharged from the fuel cell and water electrolysis device.

In consideration of the above-mentioned problems, the fuel cell system of the present invention is a fuel cell system including a fuel cell that generates electricity using hydrogen gas as fuel gas, and a water electrolysis device that produces the hydrogen gas by electrolyzing water. A cooling path through which a refrigerant flows is connected to the fuel cell and the water electrolysis device. The cooling path is provided with a cooling device that cools the refrigerant, a pump that pressure-feeds the refrigerant cooled by the cooling device to the fuel cell and the water electrolysis device, a supply valve that selectively supplies the refrigerant pressure-feed by the pump to the fuel cell or the water electrolysis device, a first valve that selectively flows the refrigerant discharged from the fuel cell to the water electrolysis device or the cooling device, and a second valve that selectively flows the refrigerant discharged from the water electrolysis device to the fuel cell or the cooling device. The fuel cell system is provided with a control device that controls at least the start and stop of the fuel cell and the water electrolysis device, the opening and closing of the supply valve, and the opening and closing of the first and second valves. The control device performs switching control to alternately start and stop the fuel cell and the water electrolysis device so that one of the fuel cell and the water electrolysis device is in an operating state and the other device is in a non-operating state, and performs refrigerant supply control by opening and closing the supply valve so that the refrigerant flows to the one of the devices that is started by the switching control. Before performing the switching control, the control device performs warm-up control of the one of the devices, the fuel cell or the water electrolysis device, by controlling the opening and closing of the first and second valves so that refrigerant discharged from the other device flows to the one of the devices that is started.

Preferably, the control device terminates warm-up control when the difference between the inlet temperature and outlet temperature of the refrigerant flowing into one of the fuel cell and the water electrolysis device becomes equal to or less than a preset value during warm-up control of the one of the devices being started. In conjunction with the termination of the warm-up control, the control device performs the switching control to stop the other device and start the one device, and the refrigerant supply control by opening and closing the supply valve so that the refrigerant flows from the other device to the one device.

Preferably, the water electrolysis device includes a device main body that electrolyzes water and a water tank that stores water to be supplied to the device main body. The cooling path includes a path through which refrigerant discharged from the fuel cell and the water electrolysis device flows to the cooling device via the water tank.

Preferably, the refrigerant is water, and the water electrolysis device is a device that produces the hydrogen gas by electrolyzing a portion of the water refrigerant. A heat exchanger that absorbs heat from the refrigerant discharged from the fuel cell is disposed in the cooling path between the first valve and the water electrolysis device. When the temperature of the refrigerant flowing into the water electrolysis device reaches or exceeds the heat resistance temperature of the water electrolysis device, the control device activates the heat exchanger to absorb heat from the refrigerant passing through the heat exchanger.

This invention makes it possible to efficiently utilize the heat of the refrigerant discharged from the fuel cell and water electrolysis device.

1A and 1B are schematic diagrams of a fuel cell system according to a first embodiment. 2 is a timing chart of the control device of the fuel cell system shown in FIG. 1 . 5A and 5B are schematic diagrams of a fuel cell system according to a modification of the first embodiment. 10A and 10B are schematic diagrams of a fuel cell system according to a second embodiment. 10A and 10B are schematic diagrams of a fuel cell system according to a third embodiment.

Fuel cell systems according to several embodiments are described below. Figure 1 is a schematic diagram of a fuel cell system according to a first embodiment, where (a) is an explanatory diagram illustrating the state in which fuel cell warm-up control is performed while refrigerant is flowing through the water electrolysis device, and (b) is an explanatory diagram illustrating the state in which water electrolysis device warm-up control is performed while refrigerant is flowing through the fuel cell.

The fuel cell system 1 according to this embodiment includes a fuel cell 10 that generates electricity using hydrogen gas as fuel gas, and a water electrolysis device 20 that produces hydrogen gas by electrolyzing water.

The fuel cell 10 has a fuel cell stack in which solid polymer fuel cell unit cells are stacked. Although not shown, each unit cell has a membrane electrode assembly in which catalyst layers are formed on both sides of an electrolyte membrane. Diffusion layers are further stacked on both sides of the membrane electrode assembly, and a unit cell is formed by sandwiching a pair of separators on both sides of this stacked assembly (MEGA). Fuel gas or oxidant gas (air) is supplied to each separator. Cooling channels through which a refrigerant flows are formed between the stacked unit cells.

The fuel cell 10 generates electricity by supplying hydrogen gas and air (atmospheric air) to the fuel cell stack (each unit cell) by driving auxiliary equipment (not shown). When the fuel cell 10 generates electricity using hydrogen gas and air, water is produced and discharged. Note that the fuel cell 10 may be referred to as "FC" in the drawings of this application.

Each unit cell constituting the fuel cell 10 has a flow path (anode-side flow path) through which hydrogen gas flows as fuel gas on the anode side, and a flow path (cathode-side flow path) through which air flows as oxidant gas on the cathode side, with an electrolyte membrane interposed between them. In this specification, the operation of supplying hydrogen gas and air to the fuel cell 10 and starting power generation by the fuel cell 10 is referred to as "starting up the fuel cell." The state in which power generation by the fuel cell 10 continues is referred to as the "operating state of the fuel cell." Furthermore, the operation of ending power generation by the fuel cell 10 from the operating state is referred to as "shutting down the fuel cell." Note that the ancillary devices used to perform electrolysis by the fuel cell 10 are generally known devices, and therefore detailed description thereof will be omitted.

The water electrolysis device 20 basically has a water electrolysis stack with a structure similar to that of the fuel cell stack of the fuel cell 10. It introduces water into the oxygen electrode of the single cell, electrolyzes it to release oxygen gas, and generates hydrogen gas from the hydrogen electrode. In this embodiment, since the refrigerant described below is water, some of this water is supplied to the water electrolysis stack to generate hydrogen gas. The generated hydrogen gas is stored in a hydrogen gas storage tank (not shown) and is used as fuel gas for the fuel cell 10.

In this specification, the operation of supplying water to the water electrolysis device 20, activating the power supply (not shown) of the water electrolysis device 20, and starting electrolysis is referred to as "starting the water electrolysis device." The state in which electrolysis is continued by the water electrolysis device 20 is referred to as the "operating state of the water electrolysis device." Furthermore, the operation of ending electrolysis by the water electrolysis device 20 from the operating state is referred to as "stopping the water electrolysis device." Note that the ancillary devices used to perform electrolysis by the water electrolysis device 20 are generally known devices, and therefore detailed description thereof will be omitted.

In this embodiment, a cooling path 3 through which a refrigerant flows is connected to the fuel cell 10 and the water electrolysis device 20. Specifically, the cooling path 3 connects the fuel cell 10 and the water electrolysis device 20 in parallel. The cooling path 3 is provided with a cooling device 31 that cools the refrigerant, and a pump 32 that pressure-feeds the refrigerant cooled by the cooling device 31 to the fuel cell 10 and the water electrolysis device 20. The cooling device 31 is, for example, an air-cooled radiator that cools the refrigerant. An ion exchanger 33 may also be provided downstream of the pump 32.

The cooling path 3 is provided with supply valves 341 and 342 that selectively supply the refrigerant pressurized by the pump 32 to either the fuel cell 10 or the water electrolysis device 20. In this embodiment, when supply valve 341 is opened and supply valve 342 is closed, the refrigerant is supplied to the fuel cell 10, and when supply valve 341 is closed and supply valve 342 is opened, the refrigerant is supplied to the water electrolysis device 20. In this embodiment, instead of the two supply valves 341 and 342, a three-way valve may be provided as a supply valve at a position where the refrigerant is divided between the fuel cell 10 and the water electrolysis device 20.

The cooling path 3 further includes a first valve 351 that selectively directs the refrigerant discharged from the fuel cell 10 to either the water electrolysis device 20 or the cooling device 31, and a second valve 352 that selectively directs the refrigerant discharged from the water electrolysis device 20 to either the fuel cell 10 or the cooling device 31.

The first valve 351 is a three-way valve, and by controlling the opening and closing of the three-way valve, the refrigerant discharged from the fuel cell 10 can be selectively routed to either the water electrolysis device 20 or the cooling device 31. A check valve 361 is provided between the first valve 351 and the water electrolysis device 20, allowing the refrigerant to flow in only one direction, from the first valve 351 to the water electrolysis device 20.

The second valve 352 is also a three-way valve, and by controlling the opening and closing of the three-way valve, the refrigerant discharged from the water electrolysis device 20 can be selectively flowed to either the fuel cell 10 or the cooling device 31. A check valve 362 is provided between the second valve 352 and the fuel cell 10, allowing the refrigerant to flow in only one direction, from the second valve 352 to the fuel cell 10.

The fuel cell system 1 is further provided with a control device 50. The control device 50 is electrically connected to the fuel cell 10, the water electrolysis device 20, the supply valves 341, 342, and the first and second valves 351, 352. Furthermore, the cooling path 3 is provided with temperature sensors 61A, 61B that detect the inlet and outlet temperatures of the refrigerant flowing into the fuel cell 10. The cooling path 3 is also provided with temperature sensors 62A, 62B that detect the inlet and outlet temperatures of the refrigerant flowing into the water electrolysis device 20. The detection signals of these inlet and outlet temperatures are input to the control device 50.

The control device 50 controls at least the start and stop of the fuel cell 10 and the water electrolysis device 20, the opening and closing of the supply valves 341 and 342, and the opening and closing of the first and second valves 351 and 352.

The control device 50 executes switching control to alternately start and stop the fuel cell 10 and the water electrolysis device 20 so that either the fuel cell 10 or the water electrolysis device 20 is in an operating state and the other is in an inoperable state. In other words, the control device 50 operates (drives) the fuel cell 10 and the water electrolysis device 20 independently; when one is operating, the other is in an inoperable state. Therefore, the fuel cell 10 and the water electrolysis device 20 are never operating simultaneously.

Furthermore, while the control device 50 executes switching control, the control device 50 also executes refrigerant supply control by opening and closing supply valves 341 and 342 so that refrigerant flows to one of the devices activated by the switching control.

Before switching control, the control device 50 performs warm-up control of one of the fuel cell 10 and water electrolysis device 20, by controlling the opening and closing of the first and second valves 351, 352 so that the refrigerant discharged from the other device flows into the other device.

When the control device 50 is executing warm-up control for one of the fuel cell 10 and water electrolysis device 20 that is being started, and the difference between the inlet temperature and outlet temperature of the refrigerant flowing into that device falls below a preset value, the control device 50 terminates the warm-up control. Upon termination of the warm-up control, the control device stops the other device and executes switching control to start up the one device, and executes refrigerant supply control by opening and closing supply valves 341 and 342 so that refrigerant flows from the other device to the one device.

The control by the control device 50 of the fuel cell system 1 will be explained below with reference to the timing chart of the control device 50 shown in Figure 2. First, at time TA in Figure 2, the control device 50 places the water electrolysis device 20 in an operating state and the fuel cell 10 in a non-operating state. In this state, the supply valve 341 is open and the supply valve 342 is closed. Furthermore, the second valve 352 is open to the cooling device 31 side. As a result, as shown by the white arrow in Figure 1(a), the refrigerant flows only through the operating water electrolysis device 20, and does not flow through the non-operating fuel cell 10.

At time TB in FIG. 2 , warm-up control of the fuel cell 10 is initiated. The warm-up starts when certain conditions are met, such as when the pressure of the hydrogen gas stored in the tank (not shown) reaches or exceeds a predetermined pressure, when a power supply is requested from the outside, or when a certain amount of time has elapsed since the water electrolysis device 20 was started. Here, at time TC (described below), before switching control is performed to stop the water electrolysis device 20 and start the fuel cell 10, warm-up control of the fuel cell 10 is executed by controlling the opening and closing of the second valve 352 so that the refrigerant discharged from the water electrolysis device 20 flows to the fuel cell 10. Specifically, the control device 50 controls the second valve 352 to open toward the fuel cell 10.

As a result, as shown by the black arrows in Figure 1(a), the refrigerant discharged from the water electrolysis device 20 and passing through the second valve 352 passes through the check valve 362 and is introduced into the fuel cell 10. The refrigerant discharged from the fuel cell 10 flows into the cooling device 31. In this way, the heat of the refrigerant discharged from the water electrolysis device 20 can be efficiently used to warm up the fuel cell 10.

The control device 50 may terminate the warm-up control after a preset time has elapsed since receiving the request signal. However, in this embodiment, the control device 50 terminates the warm-up control when the difference between the inlet and outlet temperatures of the refrigerant flowing into the fuel cell 10, detected by the temperature sensors 61A and 61B, falls below a preset value during the warm-up control of the fuel cell 10. This allows for efficient warm-up control of the fuel cell 10 using the refrigerant. After the warm-up control ends at time TC, the control device 50 shuts down the water electrolysis device 20 and performs switching control to start the fuel cell 10. In conjunction with this switching control, the control device 50 performs refrigerant supply control by opening the supply valve 341 and closing the supply valve 342 so that the refrigerant flows from the water electrolysis device 20 to the fuel cell 10. Furthermore, the control device 50 opens the second valve 352 to the cooling device 31 side.

After the switching control at time TC in Figure 2, the control device 50 places the fuel cell 10 in an operating state and the water electrolysis device 20 in a non-operating state. In this state, the supply valve 341 is open and the supply valve 342 is closed. Furthermore, the first valve 351 is open to the cooling device 31 side. As a result, as shown by the white arrow in Figure 1(b), the refrigerant flows only through the fuel cell 10 in an operating state, and does not flow through the water electrolysis device 20 in a non-operating state.

At time TD in FIG. 2 , warm-up control of the water electrolysis device 20 is initiated. The warm-up starts when certain conditions are met, such as when the hydrogen gas stored in the tank drops below a certain pressure, when external power supply is no longer required, or when a certain amount of time has passed since the fuel cell 10 was started. Here, at time TE (described below), before switching control is performed to stop the fuel cell 10 and start the water electrolysis device 20, warm-up control of the water electrolysis device 20 is executed by controlling the opening and closing of the first valve 351 so that the refrigerant discharged from the fuel cell 10 flows to the water electrolysis device 20. Specifically, the control device 50 controls the first valve 351 to open toward the water electrolysis device 20.

As a result, as shown by the black arrow in Figure 1(b), the refrigerant discharged from the fuel cell 10 and passing through the first valve 351 passes through the check valve 361 and is introduced into the water electrolysis device 20. The refrigerant discharged from the fuel cell 10 flows into the cooling device 31. In this way, the heat of the refrigerant discharged from the fuel cell 10 can be efficiently used to warm up the water electrolysis device 20.

The control device 50 may terminate the warm-up control after a preset time has elapsed since receiving the request signal. However, in this embodiment, the control device 50 terminates the warm-up control when the difference between the inlet and outlet temperatures of the refrigerant flowing into the fuel cell 10, detected by the temperature sensors 62A and 62B, falls below a preset value during warm-up control of the water electrolysis device 20. This allows for efficient warm-up control of the water electrolysis device 20 using the refrigerant. After warm-up control ends at time TE, the control device 50 performs switching control to shut down the fuel cell 10 and start up the water electrolysis device 20. In conjunction with this switching control, the control device 50 performs refrigerant supply control by closing the supply valve 341 and opening the supply valve 342 so that the refrigerant flows from the fuel cell 10 to the water electrolysis device 20. Furthermore, the control device 50 opens the first valve 351 to the cooling device 31 side.

After the switching control at time TE in Figure 2, the control device 50 places the water electrolysis device 20 in an operating state and the fuel cell 10 in a non-operating state. In this state, the supply valve 341 is closed and the supply valve 342 is open. Furthermore, the first valve 351 is open to the cooling device 31 side. As a result, as shown by the white arrow in Figure 1(b), refrigerant flows only through the operating fuel cell 10, and no refrigerant flows through the non-operating water electrolysis device 20. At times TF and TG, the control device 50 performs the same control as at times TB and TC. In other words, the control device 50 repeats the control from time TB to time TE.

Figures 3(a) and (b) are schematic diagrams of a fuel cell system according to a modified example of the first embodiment. Figure 3(a) is an explanatory diagram illustrating the state in which fuel cell warm-up control is performed while refrigerant is flowing through the water electrolysis device, and Figure 3(b) is an explanatory diagram illustrating the state in which water electrolysis device warm-up control is performed while refrigerant is flowing through the fuel cell.

This modified example differs from Figures 1(a) and 1(b) in that a coolant containing an additive such as an anticorrosive or antifreeze agent is used as the refrigerant, and in the device configuration of the water electrolysis device 20. The other device configurations and controls are the same as those in Figures 1(a) and 1(b), so the same symbols and arrows as in Figure 1 are used and detailed descriptions are omitted.

In this modified fuel cell system 1, water stored in a water tank 22 is electrolyzed rather than a portion of the refrigerant being electrolyzed. The water electrolysis device 20 includes a device main body 21 that electrolyzes water, a water tank 22 that stores water for electrolysis and is supplied to the device main body 21, and a water pump 23 that supplies water for electrolysis from the water tank 22 to the device main body 21. The device main body 21 corresponds to the water electrolysis device 20 in Figure 1. Note that the water pump 23 may be driven and stopped in response to the start and stop of the water electrolysis device 20, as shown in Figures 2(a) and 2(b).

Figures 4(a) and (b) are schematic diagrams of a fuel cell system according to a modification of the first embodiment. This modification differs from Figures 1(a) and (b) in that a coolant containing an additive such as an anticorrosive or antifreeze agent is used as the refrigerant, and in the device configuration of the water electrolysis device 20. The other device configurations and controls are the same as those in Figures 1(a) and (b), so the same symbols and arrows as in Figure 1 are used and detailed descriptions are omitted.

As with the modified first embodiment, the water electrolysis device 20 of the fuel cell system 1 includes a device main body 21 that electrolyzes water and a water tank 22 that stores water to be supplied to the device main body 21. In this embodiment, as shown in Figures 4(a) and 4(b), the cooling path 3 has a path 39 through which the refrigerant discharged from the fuel cell 10 and the water electrolysis device 20 flows to the cooling device 31 via the water tank 22. According to the second embodiment, the waste heat from the fuel cell 10 and the water electrolysis device 20 can be used to heat the water in the water tank 22, thereby preventing the water supplied to the water electrolysis device 20 from freezing.

Figures 5(a) and (b) are schematic diagrams of a fuel cell system according to a modification of the first embodiment. This modification differs from Figures 1(a) and (b) in that a coolant containing an additive such as an anticorrosive or antifreeze agent is used as the refrigerant, and in the device configuration of the water electrolysis device 20. The other device configurations and controls are the same as those in Figures 5(a) and (b), so the same symbols and arrows as in Figure 1 are used and detailed descriptions are omitted.

In the fuel cell system 1 according to this embodiment, the refrigerant is water, and the water electrolysis device 20 is a device that generates hydrogen gas by electrolyzing a portion of the water refrigerant. In the fuel cell system 1 according to this embodiment, a heat exchanger 37 that absorbs heat from the refrigerant discharged from the fuel cell 10 is disposed in the cooling path 3 between the first valve 351 and the water electrolysis device 20. In this embodiment, when the temperature of the refrigerant flowing into the water electrolysis device 20 reaches or exceeds the heat resistance temperature of the water electrolysis device 20, the control device 50 activates the heat exchanger 37 to absorb heat from the refrigerant passing through the heat exchanger 37. Here, the heat exchanger 37 is, for example, an air-cooled radiator, and when the above-mentioned conditions are met, the control device 50 activates the fan of the heat exchanger 37.

If a portion of the refrigerant (water) released from the fuel cell 10 were introduced directly into the unit cell of the water electrolysis device 20 to perform electrolysis, there is a risk of thermal degradation of the unit cell (specifically, the electrolyte membrane, catalyst layer, etc.). Therefore, in this embodiment, the heat exchanger 37 absorbs the heat of the refrigerant (water) released from the fuel cell 10, thereby supplying the refrigerant to the water electrolysis device 20 so that the temperature does not exceed its heat resistance temperature, thereby warming up the water electrolysis device 20.

1: fuel cell system, 3: cooling path, 10: fuel cell, 20: water electrolysis device, 21: device body, 22: water tank, 31: cooling device, 32: pump, 37: heat exchanger, 341, 342: supply valves, 351: first valve, 352: second valve

Claims (4)

A fuel cell system including a fuel cell that generates electricity using hydrogen gas as fuel gas, and a water electrolysis device that generates the hydrogen gas by electrolyzing water,
a cooling path through which a refrigerant flows is connected to the fuel cell and the water electrolysis device;
The cooling path includes:
a cooling device that cools the refrigerant;
a pump that pressure-feeds the refrigerant cooled by the cooling device to the fuel cell and the water electrolysis device;
a supply valve that selectively supplies the refrigerant pressure-fed by the pump to the fuel cell or the water electrolysis device;
a first valve for selectively allowing the refrigerant discharged from the fuel cell to flow to the water electrolysis device or the cooling device;
a second valve that selectively allows the refrigerant discharged from the water electrolysis device to flow to the fuel cell or the cooling device,
the fuel cell system includes a control device that controls at least start-up and stop of the fuel cell and the water electrolysis device, opening and closing of the supply valve, and opening and closing of the first and second valves;
the control device performs switching control to alternately start and stop the fuel cell and the water electrolysis device so that one of the fuel cell and the water electrolysis device is in an operating state and the other device is in a non-operating state, and performs refrigerant supply control by opening and closing the supply valve so that the refrigerant flows to the one device that is started by the switching control,
the control device, before performing the switching control, performs warm-up control of one of the fuel cell and the water electrolysis device to be started by controlling opening and closing of the first and second valves so that refrigerant discharged from the other device flows into the one of the fuel cell and the water electrolysis device to be started. the control device terminates the warm-up control when a difference between an inflow temperature and an outflow temperature of a refrigerant flowing into the one of the fuel cell and the water electrolysis device that is started becomes equal to or less than a preset value during the warm-up control of the one of the fuel cell and the water electrolysis device that is started;
2. The fuel cell system according to claim 1, wherein the switching control is executed to stop the other device and start the one device in accordance with the end of the warm-up control, and the refrigerant supply control is executed by opening and closing the supply valve so that the refrigerant flows from the other device to the one device. the water electrolysis device includes a device main body that electrolyzes water and a water tank that stores water to be supplied to the device main body;
3. The fuel cell system according to claim 1, wherein the cooling path includes a path through which the refrigerant discharged from the fuel cell and the water electrolysis device flows to the cooling device via the water tank. the refrigerant is water,
the water electrolysis device is a device that generates the hydrogen gas by electrolyzing a part of water in the refrigerant,
a heat exchanger that absorbs heat of the refrigerant discharged from the fuel cell is disposed in the cooling path between the first valve and the water electrolysis device;
3. The fuel cell system according to claim 1, wherein the control device activates the heat exchanger to absorb heat from the refrigerant passing through the heat exchanger when the temperature of the refrigerant flowing into the water electrolysis device becomes equal to or higher than a heat resistance temperature of the water electrolysis device.