JP5142004B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system having a function of removing generated water and a control method thereof.

In recent years, a fuel cell system using a fuel cell that generates power by an electrochemical reaction between a fuel gas and an oxidizing gas as an energy source has attracted attention. In this type of fuel cell system, since water is generated by an electrochemical reaction, a technique for discharging water generated by sending an amount of purge gas corresponding to the internal state of the fuel cell is known (for example, patents). Reference 1).
JP 2004-71307 A

  With the above technique, moisture can be discharged during the operation of the system, but the moisture may remain without being completely removed after the operation is stopped. In particular, when the temperature is low, the saturated water vapor amount of the gas is small and the gas purge cannot sufficiently remove the moisture. For this reason, the remaining moisture freezes in a low temperature environment, and the gas flow in the gas flow path is reduced. The power generation efficiency may be reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel cell system capable of efficiently removing moisture even after the system is stopped and obtaining high power generation efficiency and a control method thereof. It is said.

  In order to achieve the above object, a fuel cell system of the present invention supplies a reactive gas to a gas flow path in a fuel cell stack in which a plurality of cells are stacked, and generates an electric power by electrochemically reacting the reactive gas. A pressure control mechanism capable of adjusting a tightening load in the cell stacking direction of the fuel cell stack, and the gas while adjusting the tightening load of the fuel cell stack by the pressure control mechanism when the operation is stopped. And a control unit that performs a gas supply process of supplying the gas to the flow path and scavenging.

  According to this fuel cell system, by adjusting the tightening load of the fuel cell stack when the operation is stopped, water is smoothly discharged by the gas supplied into the gas flow channel while smoothly guiding the generated water to the gas flow channel. Can be made. Specifically, by reducing the tightening load when the operation is stopped, the contact surface pressure between the cell components in the cell can be reduced, drainage can be improved, and the generated water can be smoothly discharged. it can.

  As a result, moisture can be removed efficiently even after the operation is stopped, the influence of freezing of residual water on the gas flow in the gas flow path in a low-temperature environment is suppressed, and high power generation efficiency during subsequent operation is achieved. Can be secured.

  Moreover, it is preferable that the cell includes, in its constituent elements, a diffusion layer and a separator arranged with a gas flow channel groove formed on one surface side facing the diffusion layer.

  By reducing the tightening load when the operation is stopped, the contact surface pressure between the diffusion layer (one cell component) and the separator (other cell component) in the cell is reduced, and the drainage of the diffusion layer is reduced. It is possible to improve the performance and facilitate the discharge of the generated water.

  And it is preferable that the said control part controls the said pressure control mechanism according to the state of the said fuel cell stack.

  Moreover, it is preferable that the said control part controls the said pressure control mechanism according to content of the water | moisture content in the said fuel cell stack.

  The controller preferably controls the pressure control mechanism according to the temperature of the fuel cell stack.

  Furthermore, it is preferable that the control unit obtains a processing time of the gas supply process according to the state of the fuel cell stack.

  A control method for a fuel cell system according to the present invention is a control method for a fuel cell system in which a reaction gas is supplied to a gas flow path in a fuel cell stack in which a plurality of cells are stacked and the reaction gas is electrochemically reacted to generate power. Then, a gas supply process for supplying the gas to the gas flow path and scavenging while adjusting the tightening load of the fuel cell stack is performed.

  According to the control method of the fuel cell system, by adjusting the tightening load of the fuel cell stack when the operation is stopped, water is supplied by the gas supplied into the gas flow path while smoothly guiding the generated water to the gas flow path. It can be discharged smoothly. Specifically, by reducing the tightening load when the operation is stopped, the contact pressure between the components of the cell in the cell is reduced, the drainage is improved, and the generated water is smoothly discharged. Can do.

  As a result, moisture can be removed efficiently even after the operation is stopped, the influence of freezing of residual water on the gas flow in the gas flow path in a low-temperature environment is suppressed, and high power generation efficiency during subsequent operation is achieved. Can be secured.

  In this case, it is preferable to adjust the tightening load of the fuel cell stack according to the state of the fuel cell stack.

  According to the present invention, when the operation is stopped, the tightening load is reduced, the contact surface pressure between the cell components in the cell is reduced, and the drainage is improved. However, this generated water can be discharged smoothly, and high power generation efficiency during subsequent operation can be ensured.

  Hereinafter, embodiments of a fuel cell system and a control method thereof according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a system configuration diagram of a main part of a fuel cell system. The fuel cell 10 shown in the figure is used as an in-vehicle power generation system for a fuel cell vehicle, a power generation system for any moving body such as a ship, an aircraft, a train, or a walking robot, and also as a power generation facility for a building (house, building, etc.). It can be applied to a stationary power generation system and the like, but specifically, is for automobiles.

  As shown in the figure, the fuel cell system includes a hydrogen supply pipe 11 that supplies hydrogen gas, which is a fuel gas (reactive gas), to the fuel cell 10, a hydrogen circulation pipe 12 that guides the hydrogen off-gas discharged from the fuel cell 10, An air supply pipe 13 for supplying air as an oxidizing gas (reactive gas), an air discharge pipe 14 for discharging air off-gas discharged from the fuel cell 10 to the outside, and a cooling system pipe (not shown) for cooling the fuel cell 10 It is configured with.

  An air cleaner 21 is provided in the air supply pipe 13, and an air compressor 22 is provided at a position between the air cleaner 21 and the fuel cell 10. Thus, when the air compressor 22 is driven, the air supply pipe 13 sucks outside air and captures dust and the like with the air cleaner 21 and then introduces it into the fuel cell 10.

  Hydrogen gas as fuel gas is sent from a hydrogen supply source (not shown) to the hydrogen supply pipe 11 via the opening / closing control valve 23 and supplied to the fuel cell 10. Then, the hydrogen gas that has not been consumed in the fuel cell 10 is discharged as a hydrogen off-gas to the hydrogen circulation pipe 12 and returned to the hydrogen supply pipe 11 for reuse.

  The hydrogen circulation pipe 12 includes a gas-liquid separator 24 that recovers moisture from the hydrogen off-gas, a hydrogen pump 25 that pressurizes the hydrogen off-gas, and a reverse flow that prevents reverse flow of hydrogen gas from the hydrogen supply pipe 11 toward the hydrogen circulation pipe 12. A stop valve 26 is provided. In addition, a purge flow path 28 having a discharge control valve 27 is connected to the hydrogen circulation pipe 12, and the discharge control valve 27 is intermittently opened to suppress an increase in the impurity concentration of hydrogen gas. The hydrogen off gas inside is discharged outside.

  The fuel cell 10 has a plurality of fuel cell stacks 31 in which a required number of cells that generate power upon receiving the supply of fuel gas and oxidant gas are stacked, and these fuel cell stacks 31 have an end on one end side. A plate 32 is provided. In addition, a tightening load (a load in the thrust direction) is applied to the other end side of these fuel cell stacks 31 in the stacking direction of the cells constituting each fuel cell stack 31, and an actuator (pressure) for adjusting the load is applied. Control mechanism) 33 is provided.

  As shown in FIG. 2, the fuel cell stack 31 is a cell composed of a separator 41 made of an electrically conductive and gas-impermeable material and a MEA (Membrane Electrode Assembly) 42 sandwiched between the pair of separators 41. A stack structure in which a plurality of layers are stacked. Has a flow path for hydrogen gas, air, and cooling water

  The MEA 42 includes an electrolyte membrane 43 and a pair of electrodes 44 disposed on both surfaces thereof. The electrode 44 has a structure in which a catalyst layer 44a and a diffusion layer 44b are laminated from the electrolyte membrane 43 side.

  The catalyst layer 44a is disposed adjacent to the electrolyte membrane 43, and includes, for example, a solid electrolyte, carbon particles, and a catalyst supported on the carbon particles. As the catalyst, for example, platinum or a platinum alloy is preferably used. On the other hand, the diffusion layer 44b is a conductor having a function of passing a fluid (fuel gas, oxidizing gas, generated water) and a function of conducting the catalyst layer 44a and the separator 41.

  That is, the cell constituting the fuel cell stack 31 includes the electrolyte membrane 43, the catalyst layer 44a, and the diffusion layer 44b constituting the MEA 42, and the gas passage groove (fuel gas passage, oxidizing gas passage) formed on one surface side. The separator 41 is disposed as a constituent element with the MEA 42 facing the diffusion layer 44b side.

  In the fuel cell stack 31, gas flow paths 45 defined by a diffusion layer 44b and a separator 41 are formed on both sides of the MEA 42, and hydrogen gas as a fuel gas and Air is flowed as an oxidizing gas, and electricity is generated by an electrochemical reaction between hydrogen gas and oxygen in the air via the MEA 42.

  The fuel cell system having the above structure includes a control unit 51. The control unit 51 is connected to the air compressor 22, the opening / closing control valve 23, the discharge control valve 27, the hydrogen pump 25, and the actuator 33, and controls these drives. Further, the fuel cell 10 is provided with a temperature sensor 52 that detects the temperature of the cooling water in the fuel cell stack 31, and this temperature sensor 52 is connected to the control unit 51, and a detection signal is sent to the control unit 51. Send.

  In this fuel cell system, the water remaining in the fuel cell stack 31 is discharged based on the detection signal from the temperature sensor 52.

  Next, the water discharging operation by the control unit 51 will be described along the flowchart of FIG.

  When the ignition switch is turned off by the driver and the fuel cell system is commanded to stop operation (step S01), the control unit 51 determines the stack temperature t of the fuel cell stack 31 based on the detection signal from the temperature sensor 52. Ask for.

  Then, when the obtained stack temperature t of the fuel cell stack 31 is equal to or lower than a predetermined threshold (step S02: YES), the control unit 51 determines the stacking pressure P that is the tightening load of the fuel cell stack 31. Is performed (step S03).

  In the determination process of the stacking pressure P, for example, as shown in FIG. 4, the control unit 51 corresponds to the obtained stack temperature t from the map data relating the stack temperature t and the stacking pressure P obtained in advance. Determine the stacking pressure P.

  Further, as shown in FIG. 5, for example, the control unit 51 determines the stack obtained from the map data in which the stack temperature t and the flow rate Q of the purge gas respectively obtained in advance on both the hydrogen side and the oxygen side are related. A gas flow rate Q corresponding to the temperature t is determined.

  Further, as shown in FIG. 6, for example, the control unit 51 determines the scavenging time T based on the determined purge gas flow rate Q from the map data in which the stack temperature t and the scavenging time T obtained in advance are related. To decide.

  Next, the control unit 51 outputs a control signal to the actuator 33, and changes the stacking pressure in the fuel cell stack 31 to the stacking pressure P obtained from the map data based on the stack temperature t (step S04).

  As described above, when the tightening load of the fuel cell stack 31 is set to the stacking pressure P lower than usual, the contact surface pressure between the components in the cell is reduced and compressed by the separator 41 as shown in FIG. As shown in FIG. 8, the compressed state of the diffusion layer 44b was weakened.

  As a result, the diffusion layer 44b whose moisture diffusibility has been reduced by the compression from the separator 41 is improved in drainage due to weakening of the compression from the separator 41, so that the generated water flows more smoothly into the gas channel 45. Sent out.

  Further, the control unit 51 controls the air compressor 22, the hydrogen pump 25, the open / close control valve 23, and the discharge control valve 27, and in the fuel cell stack 31 at the purge gas flow rate Q obtained from the map data based on the stack temperature t. A stop process including a gas supply process for scavenging by flowing air and hydrogen gas is started (step S04).

  In this way, the generated water that has flowed into the gas flow path 45 of the fuel cell stack 31 is discharged from the fuel cell stack 31 by air and hydrogen gas.

  Then, the control unit 51 starts the stop process, and after the elapse of a predetermined scavenging time T obtained from the map data based on the stack temperature t (step S05: YES), the air compressor 22, the hydrogen pump 25, the open / close state The control valve 23 and the discharge control valve 27 are controlled to terminate the stop process of discharging generated water by air and hydrogen gas, and the actuator 33 is controlled to set the stacking pressure P in the fuel cell stack 31 to a predetermined value during operation. (Step S06).

  As described above, according to the fuel cell system and the control method thereof according to the above embodiment, the generated water is smoothly led to the gas flow path 45 by adjusting the tightening load of the fuel cell stack 31 when the operation is stopped. Water can be smoothly discharged by the gas supplied into the gas flow path 45.

  Specifically, by reducing the tightening load when the operation is stopped, the contact surface pressure between the diffusion layer 44b, which is a component of the cell, and the separator 41 in the cell is reduced, thereby improving the drainage of the diffusion layer 44b. And smooth discharge of generated water.

  As a result, water can be efficiently removed even after the operation is stopped, and the influence of the freezing of the residual water in the low temperature environment on the gas flow in the gas flow path 45 is suppressed, and the high power generation efficiency during the subsequent operation Can be secured.

  In the above embodiment, the control unit 51 obtains the temperature of the fuel cell stack 31 based on the detection signal from the temperature sensor 52 provided in the fuel cell stack 31, and controls the actuator 33. The state of the fuel cell stack 31 as a parameter is not limited to the temperature of the fuel cell stack 31.

  For example, a dew point meter may be provided in the fuel cell stack 31, and the moisture content in the gas flow path 45 may be detected by the dew point meter, and the actuator 33 may be controlled using the moisture content as a parameter.

  Of course, the water discharging operation in the above embodiment can be performed not only when the operation is stopped by turning off the ignition switch, but also when the fuel cell system is intermittently stopped during normal operation. Here, the intermittent operation refers to, for example, temporarily stopping power generation of the fuel cell during low load operation such as idling, low-speed traveling, or regenerative braking, and the load (vehicle motor and auxiliary machine) from power storage means such as a battery or a capacitor. An operation mode for supplying power to

1 is a system configuration diagram showing a fuel cell system according to an embodiment. It is a schematic sectional drawing explaining the structure of a fuel cell stack. It is a flowchart explaining the discharge operation | movement of water. It is a graph which shows the map data used in the discharge operation | movement of water. It is a graph which shows the map data used in the discharge operation | movement of water. It is a graph which shows the map data used in the discharge operation | movement of water. It is sectional drawing which shows the state of the cell in a fuel cell stack. It is sectional drawing which shows the state of the cell in a fuel cell stack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 31 ... Fuel cell stack, 33 ... Actuator (pressure control mechanism), 41 ... Separator (cell component), 42 ... MEA (cell component), 43 ... Electrolyte membrane (cell component), 44 ... Electrode (cell component) ), 44a... Catalyst layer (cell constituent element), 44b... Diffusion layer (cell constituent element), 45... Gas flow path, 51.

Claims (3)

A fuel cell system for supplying a reaction gas to a gas flow path in a fuel cell stack in which a plurality of cells are stacked and generating an electric power by electrochemical reaction of the reaction gas,
A pressure control mechanism capable of adjusting a tightening load in a cell stacking direction of the fuel cell stack;
When the operation is stopped, the pressure control mechanism reduces the tightening load of the fuel cell stack from the tightening load during normal operation to reduce the contact surface pressure between the components in the cell and to the gas flow path. A gas supply process for supplying and scavenging the gas, and
Wherein the control unit obtains the processing time of the gas supply process according to the state of the fuel cell stack at the time of the shutdown, the pressure control in accordance with the content of water in the fuel cell stack at the time of the shutdown A fuel cell system that controls the mechanism .   2. The fuel cell system according to claim 1, wherein the cell includes, in the component, a diffusion layer, and a separator disposed with a gas flow channel groove formed on one surface side facing the diffusion layer. A control method of a fuel cell system for generating a power by supplying a reaction gas to a gas flow path in a fuel cell stack in which a plurality of cells are stacked and electrochemically reacting the reaction gas,
When the operation is stopped, the gas is supplied to the gas flow path while reducing the contact load between the components in the cell by reducing the tightening load of the fuel cell stack from the tightening load during normal operation. performs gas supply process for scavenging Te, the gas supply process is carried out over the processing time of the gas supply process determined in accordance with the state of the fuel cell stack at the time of the shutdown, the fuel cell stack at the time of the shutdown A control method of a fuel cell system , wherein a tightening load of the fuel cell stack is adjusted according to a moisture content in the fuel cell stack .

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