JP5141893B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

The fuel cell system generates electric power and water by an electrochemical reaction between hydrogen supplied to the anode electrode and oxygen supplied to the cathode electrode. If the generated water remains in the fuel cell, it may cause water clogging and may freeze at low temperatures. Patent Documents 1 to 4 below disclose techniques for purging residual water in a fuel cell by supplying gas to the fuel cell when power generation is stopped.
Japanese Patent Laying-Open No. 2005-310567 JP 2007-123040 A JP 2007-193983 A JP 2006-185904 A

  By the way, when the fuel cell is stopped and then purged by supplying the oxidizing gas to the fuel cell, the electrolyte depends on the reaction temperature between hydrogen remaining in the anode electrode and oxygen contained in the oxidizing gas supplied for purge. There is a risk that the film and the like will deteriorate. In the above-mentioned Patent Document 1, purging is performed using an oxidation off gas with less oxygen. However, since the oxidation off gas also contains oxygen, the electrolyte membrane depends on the reaction temperature between the oxygen and the hydrogen remaining in the anode electrode. Etc. may deteriorate. In Patent Documents 2 and 3, the residual hydrogen in the anode electrode is reduced by generating power after the fuel cell is stopped. However, since a small amount of residual hydrogen exists in the anode electrode even after power generation, There is a possibility that the electrolyte membrane or the like may be deteriorated by the reaction temperature with oxygen contained in the oxidizing gas supplied for purging. Further, in Patent Document 4 described above, after generating power after the fuel cell is stopped, the residual hydrogen at the anode electrode and the residual oxygen at the cathode electrode are reduced and purged using the residual gas at the cathode electrode. In addition, since a small amount of residual hydrogen exists in the anode electrode and a small amount of oxygen also exists in the residual gas of the cathode electrode, there is a possibility that the electrolyte membrane or the like may deteriorate due to the reaction temperature between the residual hydrogen and the residual oxygen. .

  The present invention has been made to solve the above-described problems caused by the prior art, and an object thereof is to provide a fuel cell system capable of preventing deterioration of an electrolyte membrane and the like.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell that receives supply of an oxidizing gas and a fuel gas as reaction gases and generates electric power through an electrochemical reaction of the reaction gas, and an oxidizing gas. An oxidizing gas supply channel for supplying to the cathode of the fuel cell, a compressor for supplying the oxidizing gas to the fuel cell provided in the oxidizing gas supply channel, and an oxidation for discharging the oxidizing off-gas discharged from the fuel cell A first valve for adjusting the pressure of the oxidizing gas in the fuel cell, and a fuel gas supply channel for supplying the fuel gas to the anode of the fuel cell, provided in the off-gas discharging channel and the oxidizing off-gas discharging channel A second valve that is provided in the fuel gas supply channel and blocks or allows the supply of the fuel gas from the fuel supply source, and the fuel off-gas discharged from the fuel cell is supplied to the fuel gas supply channel. A fuel circulation passage for returning, a third valve for discharging the fuel off-gas and moisture to the outside, provided on the fuel circulation passage, and the fuel cell side from the first valve of the oxidation off-gas discharge passage. A communication channel that communicates with the fuel cell from the second valve of the fuel gas supply channel, and supply of the oxidizing off gas from the oxidizing off gas discharge channel to the fuel gas supply channel. A fourth valve that shuts off or allows the fuel cell, and when the fuel cell is stopped, the compressor is controlled to set the supply amount of the oxidizing gas to a predetermined supply amount, and the first valve is controlled to set the pressure of the oxidizing gas on the cathode side to a predetermined level. The first pressure was set, the second valve was closed, and the fuel cell was made to generate electricity, and the pressure of the fuel gas on the anode side was lowered to a predetermined second pressure that caused a predetermined pressure difference with the first pressure. Later, the fourth valve is opened, and then the third valve is opened. Characterized in that it comprises a control means.

  According to the present invention, when the fuel cell is stopped, on the cathode side, the pressure of the oxidizing gas in the fuel cell can be set to the predetermined first pressure while supplying a predetermined supply amount of the oxidizing gas to the fuel cell. On the side, the supply of the fuel gas to the fuel cell is stopped, and the pressure of the fuel gas in the fuel cell can be lowered to a predetermined second pressure lower than the first pressure while generating power in the fuel cell. Accordingly, the fuel gas remaining in the fuel cell can be consumed by power generation, and the pressure on the anode side can be made lower than the pressure on the cathode side to generate a predetermined pressure difference. In addition, after the transition to such a state, by opening the fourth valve provided in the communication channel, the flow rate of the oxidizing off gas supplied to the anode using a predetermined pressure difference generated between the two electrodes Since the oxidation off gas can flow into the fuel cell vigorously, it is possible to shorten the time for discharging the fuel gas and moisture remaining in the fuel cell to the outside of the fuel cell. It becomes. Therefore, the fuel gas remaining in the fuel cell is used as the fuel offgas without giving time for the fuel gas remaining in the fuel cell to react with the oxidizing gas contained in the oxidizing offgas supplied in the fuel cell. It becomes possible to discharge to the fuel circulation channel. Thereby, the situation where the electrolyte membrane of a fuel cell etc. deteriorates with the reaction temperature of fuel gas and oxidizing gas can be avoided. Further, by opening the third valve provided in the fuel circulation channel, fuel off gas, moisture, and the like can be discharged out of the fuel cell system.

  In the fuel cell system, the control means may open the third valve after the fourth valve is opened and the pressure of the fuel gas on the anode side becomes higher than the atmospheric pressure. it can.

  As a result, it is possible to prevent a situation in which moisture, fuel off gas, or the like flows backward from the third valve to the fuel circulation passage.

  In the fuel cell system, the predetermined supply amount may be a supply amount capable of removing residual moisture in the fuel cell.

  Thereby, when the fuel cell is stopped, the residual moisture in the fuel cell can be removed by the oxidizing gas supplied by a predetermined supply amount.

  According to the present invention, it is possible to prevent deterioration of the electrolyte membrane and the like.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a fuel cell system according to the invention will be described with reference to the accompanying drawings. This embodiment demonstrates the case where the fuel cell system which concerns on this invention is used as a vehicle-mounted power generation system of a fuel cell vehicle (FCHV; Fuel Cell Hybrid Vehicle).

  First, the configuration of the fuel cell system in the present embodiment will be described with reference to FIG. FIG. 1 is a configuration diagram schematically showing a fuel cell system in the present embodiment.

  As shown in the figure, a fuel cell system 1 includes a fuel cell 2 that generates electric power by an electrochemical reaction upon receiving supply of an oxidizing gas and a fuel gas as reaction gases, and air as an oxidizing gas to the fuel cell 2. It has an oxidizing gas piping system 3 to be supplied, a hydrogen gas piping system 4 for supplying hydrogen as a fuel gas to the fuel cell 2, and a control unit 5 for overall control of the entire system.

  The fuel cell 2 is, for example, a polymer electrolyte fuel cell, and has a stack structure in which a large number of single cells are stacked. The unit cell has a structure having a cathode electrode on one surface of an electrolyte made of an ion exchange membrane, an anode electrode on the other surface, and a pair of separators so as to sandwich the cathode electrode and the anode electrode from both sides. It has become. In this case, hydrogen gas is supplied to the hydrogen gas flow path of one separator, oxidizing gas is supplied to the oxidizing gas flow path of the other separator, and electric power is generated by the chemical reaction of these reaction gases.

  The oxidizing gas piping system 3 includes a compressor 31 that takes in and compresses atmospheric oxidizing gas through a filter 30, and an air supply passage 32 (oxidizing gas supply) for supplying the oxidizing gas to the fuel cell 2. And an air discharge passage 33 (oxidation off-gas discharge passage) for discharging the oxidation off-gas discharged from the fuel cell 2. The air discharge passage 33 is provided with a back pressure adjusting valve 34 (first valve) for adjusting the pressure of the oxidizing gas in the fuel cell 2. A pressure sensor P <b> 1 for detecting the pressure of the oxidizing gas on the cathode electrode side is provided on the outlet side of the fuel cell 2 in the air discharge channel 33. The air supply channel 32 and the air discharge channel 33 are provided with a humidifier 35 that humidifies the oxidizing gas pumped from the compressor 31 using the oxidizing off-gas discharged from the fuel cell 2. The oxidizing off gas that has undergone moisture exchange or the like in the humidifier 35 is finally exhausted into the atmosphere outside the system as exhaust gas.

  The hydrogen gas piping system 4 includes a hydrogen tank 40 as a fuel supply source storing high-pressure hydrogen gas, and a hydrogen supply channel 41 (fuel gas supply channel) for supplying the hydrogen gas in the hydrogen tank 40 to the fuel cell 2. ) And a hydrogen circulation channel 42 (fuel circulation channel) for returning the hydrogen off-gas discharged from the fuel cell 2 to the hydrogen supply channel 41. The hydrogen supply channel 41 includes a main stop valve 43 (second valve) that shuts off or allows the supply of hydrogen gas from the hydrogen tank 40, and a regulator 44 that adjusts the pressure of the hydrogen gas to a preset secondary pressure. Is provided. A pressure sensor P <b> 2 for detecting the pressure of hydrogen gas on the anode electrode side is provided on the inlet side of the fuel cell 2 in the hydrogen supply channel 41.

  The hydrogen circulation channel 42 is provided with a hydrogen pump 45 that pressurizes the hydrogen off-gas in the hydrogen circulation channel 42 and sends it to the hydrogen supply channel 41 side. In addition, a discharge flow path 48 is connected to the hydrogen circulation flow path 42 via a gas-liquid separator 46 and an exhaust / drain valve 47 (third valve). The gas-liquid separator 46 recovers moisture from the hydrogen off gas. When the exhaust / drain valve 47 shifts from the closed state to the open state in accordance with a command from the control unit 5, the water and the hydrogen off-gas containing impurities in the hydrogen circulation passage 42 are collected by the gas-liquid separator 46. (Purge). The hydrogen off-gas discharged from the exhaust / drain valve 47 is diluted by the diluter 49 and merges with the oxidizing off-gas in the air discharge passage 33.

  The oxidizing gas piping system 3 and the hydrogen gas piping system 4 are connected to the fuel cell 2 side of the back pressure regulating valve 34 in the air discharge channel 33 and the hydrogen circulation channel 42 in the hydrogen supply channel 41. A communication channel 60 is provided to communicate with the fuel cell 2 side from the junction. The communication flow path 60 is provided with an off gas supply valve 61 (fourth valve) that blocks or allows the supply of the oxidizing off gas from the air discharge flow path 33 to the hydrogen supply flow path 41.

  The control unit 5 detects an operation amount of an acceleration operation member (for example, an accelerator) provided in the fuel cell vehicle, and controls information such as an acceleration request value (for example, a required power generation amount from a power consumption device such as a traction motor). In response, the operation of various devices in the system is controlled. In addition to the traction motor, the power consuming device includes, for example, an auxiliary device (for example, a motor for the compressor 31 and the hydrogen pump 45) necessary for operating the fuel cell 2, and various devices involved in traveling of the vehicle. These include actuators used in (transmissions, wheel control devices, steering devices, suspension devices, etc.), air conditioning devices (air conditioners) for passenger spaces, lighting, audio, and the like.

  The control unit 5 (control means) executes a stop control process when the fuel cell 2 is stopped. The processing contents included in this stop control processing will be specifically described below. The stop of the fuel cell 2 includes the time of stopping the fuel cell and the time of stopping the fuel cell.

  The control unit 5 controls the compressor 31 to set the flow rate (supply amount) of the oxidizing gas to a predetermined flow rate. The predetermined flow rate corresponds to, for example, a flow rate that can remove moisture remaining in the fuel cell 2. By supplying an oxidizing gas at a predetermined flow rate when the fuel cell is stopped, moisture or the like remaining in the fuel cell 2 can be discharged to the air discharge channel 33.

  The controller 5 sets the pressure of the oxidizing gas on the cathode electrode side to a predetermined pressure Pa (first pressure) and sets the pressure of the hydrogen gas on the anode electrode side to a predetermined pressure Pb (second pressure). The pressure Pa is higher than the pressure Pb. By controlling the pressure difference between the pressure Pa and the pressure Pb, it is possible to adjust the flow rate of the oxidizing off gas flowing through the communication channel 60 when the off gas supply valve 61 is opened.

  Here, the pressure Pa and the pressure Pb are set so that a pressure difference that can secure the flow rate of the oxidizing off gas that can remove the hydrogen gas, moisture, and the like remaining in the fuel cell 2 is generated. By opening the off-gas supply valve 61 after such a pressure difference is generated, an oxidizing off-gas with less oxygen can be supplied into the fuel cell 2 at a stretch, and the oxidizing off-gas remains in the fuel cell 2 with this oxidizing off-gas. The hydrogen gas, moisture and the like that are present can be discharged to the hydrogen circulation passage 42. As the pressure difference is larger, the flow rate of the oxidation off gas can be increased, and the oxidation off gas can flow into the fuel cell 2 vigorously, and the time for discharging the remaining hydrogen gas, moisture, etc. can be increased. It can be shortened.

  Therefore, depending on the pressure difference, it is possible to discharge the residual hydrogen gas to the hydrogen circulation passage 42 before the hydrogen contained in the residual hydrogen gas and the oxygen contained in the oxidation off gas come into contact with each other and react. As a result, it is possible to avoid a situation in which the electrolyte membrane of the fuel cell 2 deteriorates due to the reaction temperature between hydrogen and oxygen.

  The control unit 5 controls the back pressure adjusting valve 34 to set the pressure of the oxidizing gas on the cathode electrode side to the pressure Pa. The control unit 5 closes the main stop valve 43 to stop the supply of hydrogen gas and cause the fuel cell 2 to generate power, thereby reducing the pressure of the hydrogen gas on the anode electrode side to the pressure Pb. Specifically, for example, by operating a power consuming device such as the compressor 31 to consume hydrogen contained in the hydrogen gas remaining in the fuel cell 2, the pressure of the hydrogen gas on the anode electrode side is reduced to the pressure Pb. Let Thereby, the amount of hydrogen contained in the hydrogen gas remaining in the fuel cell 2 can be reduced.

  The control unit 5 opens the off-gas supply valve 61 in a state where the pressure of the oxidizing gas on the cathode side becomes the pressure Pa and the pressure of the hydrogen gas on the anode side becomes the pressure Pb. Thereby, the oxidizing off gas with less oxygen can be vigorously supplied into the fuel cell, and the hydrogen gas, moisture, etc. remaining in the fuel cell 2 can be discharged to the hydrogen circulation passage 42 in a short time. .

  The controller 5 opens the exhaust / drain valve 47 after opening the off-gas supply valve 61 and when the pressure of the hydrogen gas on the anode electrode side becomes higher than the atmospheric pressure. As a result, it is possible to prevent the hydrogen offgas and moisture from flowing backward from the exhaust / drain valve 47.

  Here, the control unit 5 physically includes, for example, a CPU, a ROM that stores a control program and control data processed by the CPU, a RAM that is mainly used as various work areas for control processing, And an input / output interface. These elements are connected to each other via a bus. Various sensors such as pressure sensors P1 and P2 are connected to the input / output interface, and the compressor 31, the back pressure adjustment valve 34, the main stop valve 43, the hydrogen pump 45, the exhaust drain valve 47, the off gas supply valve 61, and the like. Various drivers for driving are connected.

  The CPU receives the detection results of various sensors via the input / output interface according to the control program stored in the ROM, and processes them using various data in the RAM, etc. To control. Further, the CPU controls the entire fuel cell system 1 by outputting control signals to various drivers via the input / output interface.

  Next, the stop control process of the fuel cell system in the present embodiment will be described using the flowchart shown in FIG.

  First, when the fuel cell 2 is stopped, as a process on the cathode electrode side, the control unit 5 controls the compressor 31 to set the flow rate of the oxidizing gas to a predetermined flow rate, and controls the back pressure adjustment valve 34 to control the cathode electrode side. The pressure of the oxidizing gas is set to pressure Pa (step S101).

  On the other hand, as a process on the anode electrode side, the control unit 5 controls the main stop valve 43 to stop the supply of hydrogen gas, causes the fuel cell 2 to generate power, and reduces the pressure of the hydrogen gas on the anode electrode side to the pressure Pb. (Step S102).

  Subsequently, the controller 5 opens the off-gas supply valve 61 in the closed state (step S103), and determines whether or not the pressure of the hydrogen gas on the anode electrode side is higher than the atmospheric pressure (step S104). When this determination is YES (step S104; YES), the control unit 5 opens the exhaust / drain valve 47 in the closed state (step S105). As a result, hydrogen off gas and moisture are purged into the atmosphere outside the system (step S106).

  Subsequently, the control unit 5 stops the supply of the oxidizing gas and closes the off-gas supply valve 61 and the exhaust / drain valve 47 (step S107).

  As described above, according to the fuel cell system 1 in the embodiment, when the fuel cell 2 is stopped, the pressure of the oxidizing gas on the cathode electrode side while supplying the oxidizing gas at a predetermined flow rate to the fuel cell 2 on the cathode electrode side. The pressure of hydrogen gas on the anode electrode side is lower than the pressure Pa while stopping the supply of hydrogen gas to the fuel cell 2 and generating power on the fuel cell 2 on the anode electrode side. The pressure can be lowered to a predetermined pressure Pb. Thereby, the hydrogen gas remaining in the fuel cell 2 can be consumed by power generation, and the pressure on the anode electrode side can be made lower than the pressure on the cathode electrode side to generate a predetermined pressure difference.

  Further, after the transition to such a state, the off-gas supply valve 61 provided in the communication flow path 60 is opened so that the oxidation supplied to the anode electrode by utilizing a predetermined pressure difference generated between both electrodes. Since the off-gas flow rate can be increased and the oxidizing off-gas can flow into the fuel cell 2 vigorously, the time for discharging the hydrogen gas, moisture, etc. remaining in the fuel cell 2 to the outside of the fuel cell 2 Can be shortened. Therefore, the hydrogen gas remaining in the fuel cell is not allowed to react with the hydrogen contained in the hydrogen gas remaining in the fuel cell and the oxygen contained in the oxidation off-gas supplied into the fuel cell. It becomes possible to discharge the hydrogen circulation channel 42 as hydrogen off gas.

  Thereby, it is possible to avoid a situation in which the electrolyte membrane of the fuel cell is deteriorated due to the reaction temperature between hydrogen contained in the hydrogen gas and oxygen contained in the oxidizing gas. Further, by opening the exhaust / drain valve 47 provided in the hydrogen circulation passage 42, hydrogen off-gas, moisture and the like can be discharged out of the fuel cell system 1.

  In the above-described embodiment, the fuel cell system in which the hydrogen circulation channel 42 is provided with the hydrogen pump 45 is described. However, the fuel cell system in which the ejector is provided instead of the hydrogen pump, or the hydrogen pump and the ejector. The present invention can be applied to a fuel cell system provided with both of the above as in the fuel cell system provided with the hydrogen pump 45 described above.

  Further, in the above-described embodiment, the outlet of the communication channel 60 is connected to the fuel cell 2 side from the junction with the hydrogen circulation channel 42 in the hydrogen supply channel 41. The connection destination of the exit is not limited to this. For example, it is good also as connecting to the main stop valve 43 side rather than the said confluence | merging point.

  In the above-described embodiment, when the supply of hydrogen gas is stopped, the main stop valve 43 is closed, but the target of valve closing is not limited to the main stop valve. For example, the supply of hydrogen gas may be stopped by closing a pressure regulating valve such as an injector.

  In the above-described embodiment, the case where the fuel cell system according to the present invention is mounted on a fuel cell vehicle has been described. However, the present invention is also applied to various mobile bodies (robots, ships, aircrafts, etc.) other than the fuel cell vehicle. The fuel cell system according to the above can be applied. Moreover, the fuel cell system according to the present invention can also be applied to a stationary power generation system used as a power generation facility for buildings (houses, buildings, etc.).

It is a lineblock diagram showing typically the fuel cell system in an embodiment. It is a flowchart for demonstrating the stop control process of a fuel cell system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 3 ... Oxidation gas piping system, 4 ... Hydrogen gas piping system, 5 ... Control part, 31 ... Compressor, 32 ... Air supply flow path, 33 ... Air discharge flow path, 34 ... Back pressure regulating valve, 40 ... hydrogen tank, 41 ... hydrogen supply flow path, 42 ... hydrogen circulation flow path, 43 ... main stop valve, 45 ... hydrogen pump, 47 ... exhaust drain valve, 60 ... communication flow path, 61 ... off gas Supply valve.

Claims (3)

A fuel cell that receives supply of an oxidizing gas and a fuel gas, and generates electric power by an electrochemical reaction of the reactive gas;
An oxidizing gas supply channel for supplying the oxidizing gas to the cathode of the fuel cell;
A compressor that is provided in the oxidizing gas supply flow path and supplies the oxidizing gas to the fuel cell;
An oxidation off-gas discharge flow path for discharging the oxidation off-gas discharged from the fuel cell;
A first valve for adjusting the pressure of the oxidizing gas in the fuel cell, provided in the oxidizing off-gas discharge flow path;
A fuel gas supply channel for supplying the fuel gas to the anode of the fuel cell;
A second valve provided in the fuel gas supply flow path, for blocking or allowing the supply of the fuel gas from a fuel supply source;
A fuel circulation passage for returning the fuel off-gas discharged from the fuel cell to the fuel gas supply passage;
A third valve provided in the fuel circulation passage for discharging the fuel off gas and moisture to the outside;
A communication channel that communicates the fuel cell side with respect to the first valve in the oxidation off-gas discharge channel, and the fuel cell side with respect to the second valve in the fuel gas supply channel;
A fourth valve provided in the communication channel, for blocking or allowing the supply of the oxidation off gas from the oxidation off gas discharge channel to the fuel gas supply channel;
When the fuel cell is stopped, the compressor is controlled to set the supply amount of the oxidizing gas to a predetermined supply amount, and the first valve is controlled to set the pressure of the oxidizing gas on the cathode side to a predetermined first pressure. The second valve is closed, and the fuel cell is caused to generate electric power to reduce the pressure of the fuel gas on the anode side to a predetermined second pressure that causes a predetermined pressure difference with the first pressure. A control means for opening the fourth valve and then opening the third valve;
A fuel cell system comprising:   The control means opens the third valve after the fourth valve is opened and when the pressure of the fuel gas on the anode side becomes higher than the atmospheric pressure. The fuel cell system according to claim 1.   3. The fuel cell system according to claim 1, wherein the predetermined supply amount is a supply amount capable of removing residual moisture in the fuel cell.

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