Fuel cell system and method for draining water from fuel cell system

Abstract

To provide a fuel cell system capable of discharging residual water inside a fuel cell stack and an exhaust system.SOLUTION: A fuel cell system includes a fuel cell stack having a fuel electrode layer to which a fuel gas is supplied, an oxidizer electrode layer to which an oxygen-containing gas is supplied, and a cooling layer to which cooling water is supplied, a fuel gas flow passage for passing the fuel gas from the fuel electrode layer, an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer, a cooling water flow passage for passing the cooling water from the cooling layer, a first bypass pipe for guiding water in the fuel gas flow passage to the cooling water flow passage, a second bypass pipe for guiding water in the oxygen-containing gas flow passage to the cooling water flow passage, and a suction pump provided in the cooling water passage downside of a connection portion between the cooling water flow passage and the first bypass pipe and a connection portion between the cooling water flow passage and the second bypass pipe.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a fuel cell system and a method for draining water from a fuel cell. [Background technology]

[0002] In a fuel cell stack having a layered structure of a fuel electrode layer, an electrolyte layer, an oxidizer electrode layer, and a separator, power is generated by an electrochemical reaction between hydrogen contained in a fuel gas supplied to the fuel electrode layer and oxygen contained in an oxygen-containing gas supplied to the oxidizer electrode layer, and water is generated in the oxidizer electrode layer. The water generated in the oxidizer electrode layer reaches the fuel electrode layer through the electrolyte layer. A part of the water generated in the fuel cell stack is discharged to the outside through the piping of the exhaust system, but the remaining water may remain inside the fuel cell stack and inside the piping of the exhaust system. When the power generation of the fuel cell system is stopped in an environment where the outside air temperature is low, the water remaining inside the fuel cell stack and inside the piping of the exhaust system may freeze. If the water remaining inside the fuel cell stack and inside the piping of the exhaust system freezes, the fuel cell system may not operate normally even if it is restarted due to the influence of the freezing of each part. For this reason, when the outside air temperature is expected to be low after the power generation of the fuel cell system is stopped, it is desirable to discharge the water remaining inside the fuel cell stack and inside the piping of the exhaust system to the outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-39526 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, when it is expected that the outside air temperature will be low after power generation by a fuel cell system is stopped, a method has been adopted in which oxygen-containing gas is discharged from an air compressor that supplies oxygen-containing gas to the oxidizer electrode layer, thereby blowing away water remaining inside the fuel cell stack and inside the piping of the exhaust system to the outside.

[0005] However, this method of discharging water remaining inside the fuel cell stack and inside the piping of the exhaust system to the outside using the exhaust pressure of the air compressor requires increasing the output of the air compressor to increase the pressure inside the fuel cell stack, which causes problems such as consuming more power than necessary from the storage battery used as an auxiliary power source when the fuel cell is not generating electricity, etc. In addition, since it is necessary to flow a large amount of oxygen-containing gas into the fuel cell stack using the air compressor, there are problems such as oxidation of the electrolyte layer, accelerating deterioration of the electrolyte layer, and even if oxygen-containing gas is discharged by the air compressor, there is still a possibility that water will remain inside the fuel cell stack and inside the piping of the exhaust system, making it impossible to prevent the effects of freezing on the fuel cell system.

[0006] Therefore, the problem that the present invention aims to solve is to provide a fuel cell system and a method for draining water from a fuel cell system that can prevent water remaining inside the fuel cell stack and inside the piping of the exhaust system from freezing while suppressing power consumption of the storage battery and oxidation of the electrolyte layer in the fuel cell system. [Means for solving the problem]

[0007] In order to achieve the above object, a fuel cell system of an embodiment includes a fuel cell stack having a fuel electrode layer to which a fuel gas is supplied, an oxidizer electrode layer to which an oxygen-containing gas is supplied, and a cooling layer to which cooling water is supplied, a fuel gas flow passage for passing the fuel gas from the fuel electrode layer of the fuel cell stack, an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack, a cooling water flow passage for passing the cooling water from the cooling layer of the fuel cell stack, a first bypass pipe for guiding water in the fuel gas flow passage to the cooling water flow passage, a second bypass pipe for guiding water in the oxygen-containing gas flow passage to the cooling water flow passage, and a suction pump provided at a connection portion between the cooling water flow passage and the first bypass pipe, and in the cooling water flow passage downstream of a connection portion between the cooling water flow passage and the second bypass pipe.

[0008] In order to achieve the above object, a method for draining water from a fuel cell system according to an embodiment includes a fuel cell stack having a fuel electrode layer to which a fuel gas is supplied, an oxidizer electrode layer to which an oxygen-containing gas is supplied, and a cooling layer to which cooling water is supplied, a fuel gas flow passage for passing the fuel gas from the fuel electrode layer of the fuel cell stack, an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack, a cooling water flow passage for passing the cooling water from the cooling layer of the fuel cell stack, and guiding water in the fuel gas flow passage to the cooling water flow passage. a first bypass pipe, a second bypass pipe that guides water in the oxygen-containing gas flow passage to the cooling water flow passage, a suction pump that is provided at a connection between the cooling water flow passage and the first bypass pipe, and in the cooling water flow passage downstream of a connection between the cooling water flow passage and the second bypass pipe, and a shutoff valve that is provided on each of the pipes that constitute the fuel gas flow passage, the oxygen-containing gas flow passage, the cooling water flow passage, the first bypass pipe, and the second bypass pipe, and that opens and closes the flow passage of each of the pipes, a first pressurizing step of controlling the fuel gas flow passage and the predetermined shutoff valves on the first bypass pipe and pressurizing the fuel gas flow passage with the fuel gas; a first drainage step of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurizing step; and a first drainage step of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe and sucking water in the fuel gas flow passage through the first bypass pipe by the suction pump. a first suction step of pushing water out of the oxygen-containing gas flow passage by controlling the predetermined shutoff valves of the oxygen-containing gas flow passage and the cooling water flow passage; a second pressurizing step of pressurizing the oxygen-containing gas flow passage and the cooling water flow passage with the oxygen-containing gas while controlling the predetermined shutoff valves on the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe while pushing water out of the oxygen-containing gas flow passage by the pressure applied in the second pressurizing step;and a second suction step in which the suction pump sucks out water from within the oxygen-containing gas flow passage and the cooling water flow passage through the second bypass pipe.

[0009] In order to achieve the above object, a fuel cell system of an embodiment is characterized by comprising: a fuel cell stack including a fuel electrode layer to which a fuel gas is supplied and an oxidizer electrode layer to which an oxygen-containing gas is supplied; a fuel gas flow passage through which the fuel gas from the fuel electrode layer of the fuel cell stack passes; an oxygen-containing gas flow passage through which the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack passes; a bypass pipe that guides water in the fuel gas flow passage to the oxygen-containing gas flow passage; and a suction pump provided in the oxygen-containing gas flow passage downstream of a connection between the oxygen-containing gas flow passage and the bypass pipe.

[0010] In order to achieve the above object, a water draining method for a fuel cell system according to an embodiment includes a fuel cell stack including a fuel electrode layer to which a fuel gas is supplied and an oxidizer electrode layer to which an oxygen-containing gas is supplied, a fuel gas flow passage through which the fuel gas from the fuel electrode layer of the fuel cell stack passes, an oxygen-containing gas flow passage through which the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack passes, a bypass pipe that guides water in the fuel gas flow passage to the oxygen-containing gas flow passage, a suction pump provided in the oxygen-containing gas flow passage downstream of a connection between the oxygen-containing gas flow passage and the bypass pipe, and shutoff valves provided on each of the pipes constituting the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe, for opening and closing the flow passages of each of the pipes, a first pressurization step of controlling the fuel gas flow passage with the fuel gas while controlling the predetermined shutoff valves on the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe, and pushing out the water in the fuel gas flow passage with the pressure applied in the first pressurization step, and in addition, the suction pump sucks out the water in the fuel gas flow passage via the bypass pipe; a second pressurization step of controlling the predetermined shutoff valves on the oxygen-containing gas flow passage and pressurizing the oxygen-containing gas flow passage with the oxygen-containing gas; and a second suction step of controlling the oxygen-containing gas flow passage and the predetermined shutoff valves on the bypass pipe, and pushing out the water in the oxygen-containing gas flow passage with the pressure applied in the second pressurization step, and in addition, the suction pump sucks out the water in the oxygen-containing gas flow passage. [Brief description of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram of an internal humidification stack type fuel cell system according to a first embodiment; [Diagram 2] 4 is a flowchart of a water draining method for the fuel cell system according to the first embodiment. [Diagram 3]4 is a table showing the opening and closing of each shutoff valve in each control step of the water draining method for the fuel cell system according to the first embodiment. [Figure 4] 5A to 5C are diagrams illustrating a water draining method for the fuel cell system according to the first embodiment, where (a) is a diagram illustrating a first pressurizing step, (b) is a diagram illustrating a first drainage step, and (c) is a diagram illustrating a first suction step. [Diagram 5] 5A to 5C are diagrams illustrating a water draining method for the fuel cell system according to the first embodiment, where (a) is a diagram illustrating a second pressurizing step, (b) is a diagram illustrating a second drainage step, and (c) is a diagram illustrating a second suction step. [Figure 6] FIG. 11 is a diagram showing the overall configuration of an external humidification stack type fuel cell system according to a second embodiment. [Figure 7] 10 is a flowchart of a water draining method for a fuel cell system according to a second embodiment. [Figure 8] 13 is a table showing the opening and closing of each shutoff valve in each control step of the water draining method for a fuel cell system according to a second embodiment. [Figure 9] 7A and 7B are explanatory diagrams of a water draining method for a fuel cell system according to a second embodiment, where (a) is an explanatory diagram of a first pressurizing step, and (b) is an explanatory diagram of a first suction step. [Figure 10] 7A and 7B are explanatory diagrams of a water draining method for a fuel cell system according to a second embodiment, where (a) is an explanatory diagram of a second pressurizing step, and (b) is an explanatory diagram of a second suction step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a fuel cell system and a method for draining water from a fuel cell system according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the following embodiment is merely an example of the present invention, and is not intended to limit the scope of the invention. In addition, in the drawings referred to in the following embodiment, the same parts or parts having similar functions are given the same or similar reference symbols, and their description may be omitted. Also, the dimensional ratios in the drawings may differ from the actual ratios, and some of the configurations may be omitted from the drawings.

[0013] (First embodiment) The overall configuration of an internal humidification stack type fuel cell system 1 will be described with reference to FIG. 1. The internal humidification stack type fuel cell system 1 of this embodiment includes a fuel gas supply unit 2, a fuel gas supply pipe 3, a fuel gas supply pipe shutoff valve 4, a first fuel gas exhaust pipe 5, a first fuel gas exhaust pipe shutoff valve 6, a first pressure sensor 7, a separator 8, a second fuel gas exhaust pipe 9, a second fuel gas exhaust pipe shutoff valve 10, a fuel gas recycle pipe 11, a fuel gas circulation pump 12, and a fuel gas recycle pipe shutoff valve 13. The fuel cell system 1 also includes an oxygen-containing gas supply unit 14, an oxygen-containing gas supply pipe 15, an oxygen-containing gas supply pipe shutoff valve 16, a first oxygen-containing gas exhaust pipe 17, a first oxygen-containing gas exhaust pipe shutoff valve 18, a second pressure sensor 19, a first heat exchanger 20, a second oxygen-containing gas exhaust pipe 21, and a second oxygen-containing gas exhaust pipe shutoff valve 22. The fuel cell system 1 also includes a humidification section 23, a cooling water supply pipe 24, a cooling water supply pipe shutoff valve 25, a first cooling water discharge pipe 26, a first cooling water discharge pipe shutoff valve 27, a third pressure sensor 28, a second heat exchanger 29, a second cooling water discharge pipe 30, a second cooling water discharge pipe shutoff valve 31, a first bypass pipe 32, a first bypass pipe shutoff valve 33, a second bypass pipe 34, a second bypass pipe shutoff valve 35, a suction pump 36, a humidification section exhaust pipe 37, a humidification section drain pipe 38, a humidification section drain pipe shutoff valve 39, a fuel cell stack 40, and a control section 44.

[0014] The fuel cell stack 40 has a fuel electrode layer 41, an oxidizer electrode layer 42, and a cooling layer 43. In the fuel cell stack 40, power is generated by an electrochemical reaction between hydrogen contained in the fuel gas supplied to the fuel electrode layer 41 and oxygen contained in the oxygen-containing gas supplied to the oxidizer electrode layer 42, and water is produced in the oxidizer electrode layer 42. The cooling water supplied to the cooling layer 43 is used to internally humidify the fuel electrode layer 41 and the oxidizer electrode layer 42, and is also used to recover heat generated during power generation in the fuel cell stack 40.

[0015] The fuel gas supply unit 2 is connected to one end of the fuel gas supply pipe 3, and supplies fuel gas to the fuel gas supply pipe 3. For example, the fuel gas supply unit 2 is a hydrogen tank, and the fuel gas is pure hydrogen. The other end of the fuel gas supply pipe 3 connected to the fuel gas supply unit 2 is connected to the fuel electrode layer 41 of the fuel cell stack 40, and allows the fuel gas to pass from the fuel gas supply unit 2 toward the fuel electrode layer 41. The fuel gas supply pipe shutoff valve 4 is provided on the fuel gas supply pipe 3, and opens and closes the flow passage of the fuel gas supply pipe 3.

[0016] The first fuel gas exhaust pipe 5, which is connected to the outlet of the fuel electrode layer 41, has the other end connected to a separator 8 described later, and allows the anode off-gas to pass from the fuel electrode layer 41 toward the separator 8. The anode off-gas referred to here is gas discharged from the fuel electrode layer 41 during power generation in the fuel cell stack 40, and includes unreacted fuel gas, water, water vapor, and the like. The first fuel gas exhaust pipe shutoff valve 6 is provided on the first fuel gas exhaust pipe 5, and opens and closes the flow passage of the first fuel gas exhaust pipe 5. In addition, the first pressure sensor 7 is provided on the first fuel gas exhaust pipe 5 upstream of the first fuel gas exhaust pipe shutoff valve 6, and detects the pressure inside the first fuel gas exhaust pipe 5.

[0017] The separator 8 is connected to one end of the first fuel gas exhaust pipe 5. The separator 8 separates water from the anode off-gas, which contains water and has permeated from the oxidizer electrode layer 42 to the fuel electrode layer 41. The separator 8 is provided with a drain trap (not shown), which opens when a certain amount of water separated from the anode off-gas accumulates, and allows the water to pass toward the humidifier unit 23.

[0018] The second fuel gas discharge pipe 9, which is connected to the outlet of the separator 8, has the other end connected to the humidifier unit 23 described below, and passes the anode off-gas from the separator 8 toward the humidifier unit 23. The second fuel gas discharge pipe shutoff valve 10 is provided on the second fuel gas discharge pipe 9, and opens and closes the flow passage of the second fuel gas discharge pipe 9. For example, the second fuel gas discharge pipe shutoff valve 10 opens when the hydrogen concentration in the fuel gas flow passage falls to a certain level or lower.

[0019] The fuel gas recycle pipe 11, which is connected to the second fuel gas discharge pipe 9 upstream of the second fuel gas discharge pipe shutoff valve 10, has the other end connected to the fuel gas supply pipe 3 downstream of the fuel gas supply pipe shutoff valve 4, and passes the anode off gas from the second fuel gas discharge pipe 9 toward the fuel gas supply pipe 3. In the fuel gas recycle pipe 11, at least a part of the anode off gas containing water vapor generated by the electrochemical reaction in the fuel cell stack 40 is recirculated in order to prevent carbon deposition due to a lack of water vapor. The fuel gas circulation pump 12 is provided on the second fuel gas discharge pipe 9 upstream of the connection part between the second fuel gas discharge pipe 9 and the fuel gas recycle pipe 11, and sends the anode off gas from the second fuel gas discharge pipe 9 to the fuel gas supply pipe 3 via the fuel gas recycle pipe 11. The fuel gas recycle pipe shutoff valve 13 is provided on the fuel gas recycle pipe 11, and opens and closes the flow passage of the fuel gas recycle pipe 11.

[0020] The oxygen-containing gas supply unit 14 is connected to one end of the oxygen-containing gas supply pipe 15, and supplies an oxygen-containing gas to the oxygen-containing gas supply pipe 15. For example, the oxygen-containing gas supply unit 14 is an air compressor, and the oxygen-containing gas is air. The oxygen-containing gas supply pipe 15 connected to the oxygen-containing gas supply unit 14 has the other end connected to the oxidizer electrode layer 42 of the fuel cell stack 40, and passes the oxygen-containing gas from the oxygen-containing gas supply unit 14 toward the oxidizer electrode layer 42. The oxygen-containing gas supply pipe shutoff valve 16 is provided on the oxygen-containing gas supply pipe 15, and opens and closes the flow passage of the oxygen-containing gas supply pipe 15.

[0021] The first oxygen-containing gas discharge pipe 17 connected to the outlet of the oxidizer electrode layer 42 has the other end connected to the first heat exchanger 20 described later, and passes the cathode off-gas and water generated in the oxidizer electrode layer 42 during power generation of the fuel cell stack 40 from the oxidizer electrode layer 42 toward the first heat exchanger 20. The cathode off-gas referred to here is gas discharged from the oxidizer electrode layer 42 during power generation of the fuel cell stack 40, and includes water and water vapor. The first oxygen-containing gas discharge pipe shutoff valve 18 is provided on the first oxygen-containing gas discharge pipe 17 and opens and closes the flow passage of the first oxygen-containing gas discharge pipe 17. The second pressure sensor 19 is provided on the first oxygen-containing gas discharge pipe 17 upstream of the first oxygen-containing gas discharge pipe shutoff valve 18, and detects the pressure inside the first oxygen-containing gas discharge pipe 17.

[0022] The first heat exchanger 20 is connected to one end of the first oxygen-containing gas discharge pipe 17. In the first heat exchanger 20, heat generated during power generation in the fuel cell stack 40 is recovered from the cathode off-gas, and water vapor contained in the cathode off-gas is condensed.

[0023] The second oxygen-containing gas discharge pipe 21 connected to the outlet of the first heat exchanger 20 has the other end connected to the humidification section 23 and passes the cathode off-gas from the first heat exchanger 20 toward the humidification section 23. The second oxygen-containing gas discharge pipe shutoff valve 22 is provided on the second oxygen-containing gas discharge pipe 21 and opens and closes the flow passage of the second oxygen-containing gas discharge pipe 21.

[0024] The humidifier 23 is connected to the second fuel gas discharge pipe 9, the second oxygen-containing gas discharge pipe 21, a cooling water supply pipe 24 described below, a second cooling water discharge pipe 30 described below, and one end of a humidifier exhaust pipe 37, and stores water generated in the fuel cell stack 40, as well as cooling water to be supplied to the cooling layer 43 of the fuel cell stack 40. For example, the humidifier 23 is a water tank.

[0025] The cooling water supply pipe 24, which is connected to the outlet of the humidification unit 23, has the other end connected to the cooling layer 43 of the fuel cell stack 40, and passes the cooling water from the humidification unit 23 toward the cooling layer 43. The cooling water supply pipe shutoff valve 25 is provided on the cooling water supply pipe 24, and opens and closes the flow passage of the cooling water supply pipe 24.

[0026] The first cooling water discharge pipe 26 connected to the outlet of the cooling layer 43 has the other end connected to a second heat exchanger 29 described later, and passes the cooling water from the cooling layer 43 toward the second heat exchanger. The first cooling water discharge pipe shutoff valve 27 is provided on the first cooling water discharge pipe 26 and opens and closes the flow passage of the first cooling water discharge pipe 26. In addition, the third pressure sensor 28 is provided on the first cooling water discharge pipe 26 upstream of the first cooling water discharge pipe shutoff valve 27 and detects the pressure inside the first cooling water discharge pipe 26.

[0027] The second heat exchanger 29 is connected to one end of the first cooling water discharge pipe 26, and cools the hot water by recovering heat generated during power generation by the fuel cell stack 40. For example, the second heat exchanger 29 is a radiator, and cools the hot water by using the wind generated by running or a cooling fan.

[0028] The second cooling water discharge pipe 30 connected to the outlet of the second heat exchanger 29 has the other end connected to the humidifying section 23 and passes the cooling water from the second heat exchanger 29 toward the humidifying section 23. The second cooling water discharge pipe shutoff valve 31 is provided on the second cooling water discharge pipe 30 and opens and closes the flow passage of the second cooling water discharge pipe 30.

[0029] The first bypass pipe 32 has one end connected to the separator 8 and the other end connected to the first cooling water discharge pipe 26 downstream of the first cooling water discharge pipe shutoff valve 27, and guides water remaining in the fuel gas flow passage from the fuel gas flow passage to the cooling water flow passage when draining the fuel cell system 1. The fuel gas flow passage here particularly refers to the inside of a pipe or device through which fuel gas can pass, and in this embodiment, includes the fuel gas supply pipe 3, the first fuel gas discharge pipe 5, the separator 8, the second fuel gas discharge pipe 9, the fuel gas recycle pipe 11, the fuel electrode layer 41 of the fuel cell stack 40, and the like. The cooling water flow passage here particularly refers to the inside of a pipe or device through which water can be produced, and in this embodiment, includes the humidifier 23, the cooling water supply pipe 24, the first cooling water discharge pipe 26, the second heat exchanger 29, the second cooling water discharge pipe 30, the humidifier drain pipe 38, the cooling layer 43 of the fuel cell stack 40, and the like. In the present embodiment, a configuration in which one end of the first bypass pipe 32 is connected to the separator 8 is illustrated, but the first bypass pipe 32 is only required to be configured to guide at least the water remaining in the fuel gas flow passage from the fuel gas flow passage to the cooling water flow passage, and one end of the first bypass pipe 32 may be connected to another fuel gas flow passage within the scope of the invention. In addition, in the present embodiment, a configuration in which the other end of the first bypass pipe 32 is connected to the first cooling water discharge pipe 26 downstream of the first cooling water discharge pipe shutoff valve 27 is illustrated, but the first bypass pipe 32 is only required to be configured to guide at least the water remaining in the fuel gas flow passage from the fuel gas flow passage to the cooling water flow passage, and one end of the first bypass pipe 32 may be connected to another cooling water flow passage within the scope of the invention. The first bypass pipe shutoff valve 33 is provided on the first bypass pipe 32 and opens and closes the flow passage of the first bypass pipe 32.

[0030] The second bypass pipe 34 has one end connected to the first heat exchanger 20 and the other end connected to the first cooling water discharge pipe 26 downstream of the first cooling water discharge pipe shutoff valve 27, and guides water remaining in the oxygen-containing gas flow passage from the oxygen-containing gas flow passage to the cooling water flow passage when draining water from the fuel cell system 1. The oxygen-containing gas flow passage here particularly refers to the inside of piping, equipment, etc. through which an oxygen-containing gas can pass, and in this embodiment includes the oxygen-containing gas supply pipe 15, the first oxygen-containing gas discharge pipe 17, the first heat exchanger 20, the second oxygen-containing gas discharge pipe 21, the oxidizer electrode layer 42 of the fuel cell stack 40, etc. In the present embodiment, a configuration in which one end of the second bypass pipe 34 is connected to the first heat exchanger 20 is illustrated, but the second bypass pipe 34 may be configured to guide at least water remaining in the oxygen-containing gas flow passage from the oxygen-containing gas flow passage to the cooling water flow passage, and one end of the second bypass pipe 34 may be connected to another oxygen-containing gas flow passage within the scope of the invention. In addition, a configuration in which the other end of the second bypass pipe 34 is connected to the first cooling water discharge pipe 26 downstream of the first cooling water discharge pipe shutoff valve 27 is illustrated, but the second bypass pipe 34 may be configured to guide at least water remaining in the oxygen-containing gas flow passage from the oxygen-containing gas flow passage to the cooling water flow passage, and one end of the second bypass pipe 34 may be connected to another cooling water flow passage within the scope of the invention. The second bypass pipe shutoff valve 35 is provided on the second bypass pipe 34 and opens and closes the flow passage of the second bypass pipe 34.

[0031] The suction pump 36 is provided at the connection between the first cooling water discharge pipe 26 and the first bypass pipe 32, and at the first cooling water discharge pipe 26 downstream of the connection between the first cooling water discharge pipe 26 and the second bypass pipe 34, and during normal operation of the fuel cell system 1, circulates cooling water in the cooling water flow passage, and when draining the fuel cell system 1, sucks out water remaining in the fuel gas flow passage, the oxygen-containing gas flow passage, or the cooling water flow passage from each passage toward the humidification section 23 or the outside. In this embodiment, a configuration is exemplified in which the suction pump 36 is provided in the first cooling water discharge pipe 26 downstream of the connection part between the first cooling water discharge pipe 26 and the first bypass pipe 32, and the connection part between the first cooling water discharge pipe 26 and the second bypass pipe 34. However, it is sufficient that the suction pump 26 is located in a position where it can suck out water remaining in at least the fuel gas flow passage and the oxygen-containing gas flow passage via the first bypass pipe 32 and the second bypass pipe 34. Within the scope that does not deviate from the gist of the invention, the suction pump 36 may be provided in other cooling water flow passages downstream of the connection part between the cooling water flow passage and the first bypass pipe 32, and the connection part between the cooling water flow passage and the second bypass pipe 34.

[0032] The other end of the humidifier exhaust pipe 37 connected to the humidifier 23 is open to the outside, and passes exhaust gas from inside the humidifier 23 to the outside from the humidifier 23. The exhaust gas here includes the anode off-gas sent from the second fuel gas exhaust pipe 9, the cathode off-gas sent from the second oxygen-containing gas exhaust pipe 21, and the like.

[0033] The other end of the humidification section drain pipe 38 connected to the cooling water supply pipe 24 is open to the outside, and allows drainage water from inside the humidification section 23 to pass from the humidification section 23 to the outside. The drainage water referred to here includes water sent from the fuel gas flow passage through the first bypass pipe 32, water sent from the oxygen-containing gas flow passage through the second bypass pipe 34, and cooling water stored in the humidification section 23 and circulating through the cooling water flow passage. In this embodiment, a configuration in which one end of the humidification section drain pipe 38 is connected to the cooling water supply pipe 24 is exemplified, but the humidification section drain pipe 38 only needs to have at least a drainage function, and one end of the humidification section drain pipe 38 may be connected to the humidification section 23 or another cooling water flow passage within the scope of the invention. The humidification section drain pipe shutoff valve 39 is provided on the humidification section drain pipe 38 and opens and closes the flow passage of the humidification section drain pipe 38. For example, the humidifier drain pipe shutoff valve 39 opens when the humidifier 23 is full of water.

[0034] The control unit 44 is for controlling various operations of the fuel cell system 1, and controls the operating state of the fuel cell stack 40, the open / close state of the shutoff valve, the operation of the suction pump 36, and the draining of water from the fuel cell system 1. In the figure, the connections with each device of the fuel cell system 1 are omitted to avoid complicating the drawing. Naturally, the control unit 44 not only outputs control instructions, but also includes input functions such as reading data, including a function for referencing the results of measurements from a pressure gauge, etc.

[0035] According to the fuel cell system 1 of FIG. 1, a part of the fuel gas introduced from the fuel gas supply unit 2 through the fuel gas supply pipe 3 to the fuel electrode layer 41 of the fuel cell stack 40 is used for power generation in the fuel cell stack 40, and an electrochemical reaction occurs, generating protons and electrons in the fuel electrode layer 41. Thereafter, the surplus fuel gas not used for power generation is introduced as anode off-gas from the fuel electrode layer 41 through the first fuel gas discharge pipe 5 to the separator 8. In the separator 8, water that has permeated from the oxidizer electrode layer 42 to the fuel electrode layer 41 is separated from the anode off-gas. When the second fuel gas discharge pipe shutoff valve 10 is closed and the fuel gas recycle pipe shutoff valve 13 is open, the anode off-gas that leaves the separator 8 and passes through the second fuel gas discharge pipe 9 is sent to the fuel gas supply pipe 3 through the fuel gas recycle pipe 11 by the operation of the fuel gas circulation pump 12, and is introduced again to the fuel electrode layer 41, where it is reused for power generation. On the other hand, when the hydrogen concentration in the fuel gas flow passage falls below a certain level, the second fuel gas discharge pipe shutoff valve 10 opens, and the anode off-gas leaving the separator 8 and passing through the second fuel gas discharge pipe 9 is guided to the humidifier 23 and then passes through the humidifier exhaust pipe 37 to be exhausted to the outside. When a certain amount of water accumulates in a drain trap (not shown) above the separator 8, the water separated by the separator 8 is guided from the drain trap to the humidifier 23.

[0036] In addition, a part of the oxygen-containing gas introduced from the oxygen-containing gas supply unit 14 through the oxygen-containing gas supply pipe 15 to the oxidizer electrode layer 42 of the fuel cell stack 40 is used for power generation in the fuel cell stack 40, and an electrochemical reaction occurs, thereby generating water in the oxidizer electrode layer 42. The cathode off-gas and water discharged from the oxidizer electrode layer 42 pass through the first oxygen-containing gas exhaust pipe 17 and are introduced to the first heat exchanger 20. In the first heat exchanger 20, the cathode off-gas heated to a high temperature by power generation is condensed. When the cathode off-gas containing water discharged from the first heat exchanger 20 passes through the second oxygen-containing gas exhaust pipe 21 and is introduced to the humidifier 23, the water is stored in the humidifier 23, and the cathode off-gas passes through the humidifier exhaust pipe 37 from the humidifier 23 and is exhausted to the outside.

[0037] Furthermore, when the cooling water supply pipe shutoff valve 25 is in an open state and the humidification section drain pipe shutoff valve 39 is in a closed state, a part of the cooling water that passes through the cooling water supply pipe 24 from the humidification section 23 and is guided to the cooling layer 43 of the fuel cell stack 40 is used to internally humidify the fuel electrode layer 41 and the oxidizer electrode layer 42, and is also used to recover heat generated during power generation by the fuel cell stack 40. The cooling water that leaves the cooling layer 43 passes through the first cooling water discharge pipe 26 and is guided to the second heat exchanger 29. In the second heat exchanger 29, the high-temperature cooling water is cooled by recovering heat generated by power generation. The cooling water that leaves the second heat exchanger 29 passes through the second cooling water discharge pipe 30 and is guided to the humidification section 23. On the other hand, when the humidification section 23 is full of water, the humidification section drain pipe shutoff valve 39 opens, and the water inside the humidification section 23 is drained to the outside through the humidification section drain pipe 38 to lower the water level of the humidification section 23.

[0038] Next, the flow of water in the water draining method 100 of the internal humidification stack type fuel cell system 1 that operates when there is a risk of the fuel cell stack 40 freezing will be described with reference to Figs. 2 to 5. The case where there is a risk of the fuel cell stack 40 freezing may include a case where the control unit 44 detects that the outside air temperature is or will become 0°C or lower when the fuel cell stack 40 stops generating electricity, as well as a case where the fuel cell stack 40 stops abnormally or simply stops generating electricity. At this time, in each control step of the water draining method 100 of the fuel cell system 1, the control unit 44 controls the opening and closing of a predetermined shutoff valve as shown in Fig. 3. Note that Fig. 3 shows at least the shutoff valves that are controlled to open and close in each control step, but it is preferable that other shutoff valves not shown in each control step are in a closed state.

[0039] First, a first pressurizing step 101 is performed to pressurize the fuel gas flow passage (see FIG. 2). At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves on the fuel gas flow passage and the first bypass pipe 32. Specifically, it instructs the fuel gas supply pipe shutoff valve 4, the first fuel gas exhaust pipe shutoff valve 6, and the fuel gas recycle pipe shutoff valve 13 to be in an open state, and the second fuel gas exhaust pipe shutoff valve 10 and the first bypass pipe shutoff valve 33 to be in a closed state (see FIG. 3). As a result, a flow path is formed as shown by the thick line in FIG. 4(a). Here, the fuel gas is supplied from the fuel gas supply unit 3 to the fuel gas flow passage, thereby pressurizing the fuel gas flow passage.

[0040] Next, when the control unit 44 acquires the measurement value of the first pressure sensor 7 and detects that the pressure inside the fuel gas flow passage exceeds a predetermined pressure, a first drainage step 102 is performed to drain the water inside the fuel gas flow passage (see FIG. 2). The predetermined pressure here is a pressure value that is lower than the maximum operating pressure in the fuel cell system 1 and is a pressure value that can blow the water inside the fuel gas flow passage to the outside. At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32. Specifically, it instructs that the fuel gas exhaust pipe shutoff valve 6, the second fuel gas exhaust pipe shutoff valve 10, the fuel gas recycle pipe shutoff valve 13, and the humidification section drain pipe shutoff valve 39 are opened, and that the fuel gas supply pipe shutoff valve 4, the second oxygen-containing gas exhaust pipe shutoff valve 22, the cooling water supply pipe shutoff valve 25, the second cooling water exhaust pipe shutoff valve 31, and the first bypass pipe shutoff valve 33 are closed (see FIG. 3). As a result, a flow path is formed as shown by the thick line in Fig. 4(b). Here, the water in the fuel gas flow path is pushed out by the pressure applied in the first pressurizing step 101, thereby discharging the water in the fuel gas flow path to the outside.

[0041] Thereafter, a first suction step 103 is performed to drain the residual water in the fuel gas flow passage (see FIG. 2). At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves in the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32. Specifically, the control unit 44 instructs the fuel gas discharge pipe shutoff valve 6, the fuel gas recycle pipe shutoff valve 13, the second cooling water discharge pipe shutoff valve 31, the first bypass pipe shutoff valve 33, and the humidification unit drain pipe shutoff valve 39 to be in an open state, and the fuel gas supply pipe shutoff valve 4, the second fuel gas discharge pipe shutoff valve 10, the second oxygen-containing gas discharge pipe shutoff valve 22, the cooling water supply pipe shutoff valve 25, the first cooling water discharge pipe shutoff valve 27, and the second bypass pipe shutoff valve 35 to be in a closed state (see FIG. 3). As a result, a flow path is formed as shown by the thick line in FIG. 4(c). Here, under the control of the control unit 44, the suction pump 36 sucks out the water remaining in the fuel gas flow passage through the first bypass pipe 32, thereby discharging the remaining water in the fuel gas flow passage to the outside.

[0042] Note that steps 101 to 103 may be repeated multiple times to sufficiently drain the water from within the fuel gas flow passage.

[0043] Next, a second pressurizing step 104 is performed to pressurize the oxidizer electrode layer 42 and the cooling layer 43 (see FIG. 2). At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves on the oxygen-containing gas flow passage and the cooling water flow passage. Specifically, it instructs the oxygen-containing gas supply pipe shutoff valve 16 to be in an open state, and the first oxygen-containing gas discharge pipe shutoff valve 18, the cooling water supply pipe shutoff valve 25, and the first cooling water discharge pipe shutoff valve 27 to be in a closed state (see FIG. 3). As a result, a flow path is formed as shown by the thick line in FIG. 5(a). Here, the oxygen-containing gas is supplied from the oxygen-containing gas supply unit 14 to the oxidizer electrode layer 42 and the cooling layer 43, thereby pressurizing the oxidizer electrode layer 42 and the cooling layer 43. The reason why the fuel gas flow passage is pressurized in the first pressurizing step, whereas the oxidizer electrode layer 42 and the cooling layer 43 are pressurized in the second pressurizing step, is that water is generated in the oxidizer electrode layer 42 during power generation, and there is more water in the oxidizer electrode layer 42 than in the fuel electrode layer 41, and therefore it is necessary to drain the water in a focused manner. In addition, although the present embodiment illustrates an example in which an oxygen-containing gas is supplied from the oxygen-containing gas supply unit 14, for example, a nitrogen cylinder may be provided to supply nitrogen.

[0044] Subsequently, when the control unit 44 acquires the measured values ​​of the second pressure sensor 19 and the third pressure sensor 28 and detects that the pressures of the oxidizer electrode layer 42 and the cooling layer 43 exceed a predetermined pressure, a second drainage step 105 is performed to drain the water in the oxygen-containing gas flow passage (see FIG. 2). The predetermined pressure here is a pressure value that is lower than the maximum operating pressure in the fuel cell system 1 and is a pressure value that can blow the water in the oxygen-containing gas flow passage to the outside. At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves in the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe 34. Specifically, the first oxygen-containing gas discharge pipe shutoff valve 18, the second oxygen-containing gas discharge pipe shutoff valve 22, and the humidification section drain pipe shutoff valve 39 are in an open state, and the second fuel gas discharge pipe shutoff valve 10, the oxygen-containing gas supply pipe shutoff valve 16, the cooling water supply pipe shutoff valve 25, the first cooling water discharge pipe shutoff valve 27, the second cooling water discharge pipe shutoff valve 31, and the second bypass pipe shutoff valve 35 are in a closed state (see FIG. 3). As a result, a flow path is formed as shown by the thick line in FIG. 5(b). Here, the water in the oxygen-containing gas flow passage is pushed out by the pressure applied in the second pressurization step 104, thereby discharging the water in the oxygen-containing gas flow passage to the outside.

[0045] Thereafter, a second suction step 106 is performed to drain the remaining water in the oxygen-containing gas flow passage and the cooling water flow passage (see FIG. 2). At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves in the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe 34. Specifically, the control unit 44 instructs the first oxygen-containing gas discharge pipe shutoff valve 18, the first cooling water discharge pipe shutoff valve 27, the second cooling water discharge pipe shutoff valve 31, the second bypass pipe shutoff valve 35, and the humidification unit drain pipe shutoff valve 39 to be in an open state, and the second fuel gas discharge pipe shutoff valve 10, the oxygen-containing gas supply pipe shutoff valve 16, the second oxygen-containing gas discharge pipe shutoff valve 22, the cooling water supply pipe shutoff valve 25, and the first bypass pipe shutoff valve 33 to be in a closed state (see FIG. 3). As a result, a flow path is formed as shown by the thick line in FIG. 5(c). Here, under the control of the control unit 44, the suction pump 36 sucks out the water remaining in the oxygen-containing gas flow passage and the cooling water flow passage through the second bypass pipe 34, thereby discharging the remaining water in the oxygen-containing gas flow passage and the cooling water flow passage to the outside.

[0046] Note that steps 104 to 106 may be repeated multiple times to sufficiently drain the water remaining in the oxygen-containing gas flow passage and the cooling water flow passage.

[0047] As described above, according to the internal humidification stack type fuel cell system 1 and the water draining method 100 of the fuel cell system 1 of this embodiment, by newly providing the first bypass pipe 32 connecting the fuel gas flow passage and the cooling water flow passage, and the second bypass pipe 34 connecting the oxygen-containing gas flow passage and the cooling water flow passage, when there is a risk of the fuel cell system 1 freezing, a first pressurization step 101 of controlling predetermined shutoff valves on the fuel gas flow passage and the first bypass pipe 32 and pressurizing the fuel gas flow passage with fuel gas, a first drainage step 102 of controlling predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurization step 101, and a first drainage step 103 of controlling predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurization step 101, and a second drainage step 104 of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurization step 101, and a second drainage step 105 of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurization step 101, and a second drainage step 106 of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurization step 101, and a second drainage step 107 of controlling the predetermined shutoff valves on the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe 32 and pushing out water in 2 to suck out water from the fuel gas flow passage; a second pressurizing step 104 to control predetermined shutoff valves in the oxygen-containing gas flow passage and the cooling water flow passage and to pressurize the oxidizer electrode layer 42 and the cooling layer 43 with an oxygen-containing gas; a second drainage step 105 to control predetermined shutoff valves in the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe 34 and to push out the water from the oxygen-containing gas flow passage with the pressure applied in the second pressurizing step 104; and a second suction step 106 to control predetermined shutoff valves in the fuel gas flow passage, the cooling water flow passage, and the second bypass pipe 34 and to have the suction pump 36 suck out water from the oxygen-containing gas flow passage and the cooling water flow passage via the second bypass pipe 34. As a result, in the past, even if oxygen-containing gas was discharged by an air compressor, there was a possibility that water would remain inside the fuel cell stack and inside the piping of the exhaust system, and there was a problem that the effects of freezing on the fuel cell system could not be prevented. However, in this embodiment, the water remaining inside the fuel cell stack and inside the piping of the exhaust system can be drained to a level that prevents the effects of freezing.Furthermore, instead of continuously discharging the air compressor as in the conventional method, the present embodiment uses an air compressor in combination with a suction pump, thereby reducing the total power consumption required to discharge water remaining inside the fuel cell stack and inside the piping of the exhaust system to the outside. It is also possible to reduce the amount of oxygen-containing gas flowing into the fuel cell stack by the air compressor, thereby suppressing oxidation of the electrolyte layer.

[0048] Second embodiment The overall configuration of an external humidification stack type fuel cell system 50 will be described with reference to Fig. 6. Note that only the parts different from the first embodiment will be described below, and the other parts will be given the same reference numerals as those in the first embodiment and the description thereof may be omitted. The external humidification stack type fuel cell system 50 of this embodiment includes a fuel gas supply unit 2, a fuel gas supply pipe 3, a fuel gas supply pipe shutoff valve 4, a first fuel gas exhaust pipe 5, a first fuel gas exhaust pipe shutoff valve 6, a first pressure sensor 7, a separator 8, a fuel gas recycle pipe 51, and a fuel gas circulation pump 52. The fuel cell system 50 also includes an oxygen-containing gas supply unit 14, an oxygen-containing gas supply pipe 15, an oxygen-containing gas supply pipe shutoff valve 16, a first oxygen-containing gas exhaust pipe 53, a first oxygen-containing gas exhaust pipe shutoff valve 18, a second pressure sensor 19, a first oxygen-containing gas exhaust pipe shutoff valve 54, a suction pipe 55, a suction pump 56, a bypass pipe 57, and a bypass pipe shutoff valve 58. The fuel cell system 50 also includes a first cooling water exhaust pipe 26, a second heat exchanger 29, a cooling water supply pipe 59, a circulation pump 60, the fuel cell stack 40, and a control unit 44.

[0049] The fuel cell stack 40 of this embodiment differs from the first embodiment in that the fuel electrode layer 41 and the oxidizer electrode layer 42 are not humidified by cooling water supplied to the cooling layer 43, i.e., internal humidification, but rather fuel gas and oxygen-containing gas humidified by a humidifier (not shown) are supplied to the fuel electrode layer 41 and the oxidizer electrode layer 42, i.e., external humidification.

[0050] The fuel gas recycle pipe 51 has one end connected to the outlet of the separator 8 and the other end connected to the fuel gas supply pipe 3 downstream of the fuel gas supply pipe shutoff valve 4, and passes the anode off-gas from the separator 8 toward the fuel gas supply pipe 3. The fuel gas circulation pump 52 is provided on the fuel gas recycle pipe 51, and sends the anode off-gas from the separator 8 to the fuel gas supply pipe 3.

[0051] The first oxygen-containing gas exhaust pipe 53 has one end connected to the outlet of the oxidizer electrode layer 42 and the other end open to the outside, and allows the cathode off-gas to pass from the oxidizer electrode layer 42 to the outside. The first oxygen-containing gas exhaust pipe shutoff valve 54 is provided on the first oxygen-containing gas exhaust pipe 53 downstream of the first oxygen-containing gas exhaust pipe shutoff valve 18, and opens and closes the flow passage of the first oxygen-containing gas exhaust pipe 53.

[0052] The suction pipe 55 has one end connected to the first oxygen-containing gas discharge pipe 53 downstream of the first oxygen-containing gas discharge pipe shutoff valve 18 and upstream of the first oxygen-containing gas discharge pipe shutoff valve 54, and the other end connected to the first oxygen-containing gas discharge pipe 53 downstream of the first oxygen-containing gas discharge pipe shutoff valve 54, and passes water sucked in by the suction pump 56 when draining water from the fuel cell system 50. The suction pump 56 is provided on the suction pipe 55, and sucks water from the fuel gas flow passage or the oxygen-containing gas flow passage to the outside when draining water from the fuel cell system 50.

[0053] The bypass pipe 57 has one end connected to the separator 8 and the other end connected to the first oxygen-containing gas discharge pipe 53 downstream of the first oxygen-containing gas discharge pipe shutoff valve 18 and upstream of the suction pipe 55, and serves to guide water in the fuel gas flow passage from the fuel gas flow passage to the oxygen-containing gas flow passage when draining water from the fuel cell system 50. In this embodiment, the fuel gas flow passage includes the fuel gas supply pipe 3, the first fuel gas discharge pipe 5, the separator 8, the fuel electrode layer 41 of the fuel cell stack 40, the fuel gas recycle pipe 51, and the like. In this embodiment, the oxygen-containing gas flow passage includes the oxygen-containing gas supply pipe 15, the oxidizer electrode layer 42 of the fuel cell stack 40, the first oxygen-containing gas discharge pipe 53, the suction pipe 55, and the like. In this embodiment, one end of the bypass pipe 57 is connected to the separator 8, but the bypass pipe 57 may be configured to guide at least the water in the fuel gas flow passage from the fuel gas flow passage to the oxygen-containing gas flow passage, and one end of the bypass pipe 57 may be connected to another fuel gas flow passage without departing from the gist of the invention. The bypass pipe shutoff valve 58 is provided on the bypass pipe 57 and opens and closes the flow passage of the bypass pipe 57.

[0054] The cooling water supply pipe 59 has one end connected to the outlet of the second heat exchanger 29 and the other end connected to the cooling layer 43 of the fuel cell stack 40, and passes the cooling water from the second heat exchanger 29 toward the cooling layer 43. The cooling water here is not limited to water, and antifreeze may also be used. The circulation pump 60 is provided on the cooling water supply pipe 59, and circulates the cooling water in the cooling water flow passage.

[0055] According to the fuel cell system 50 of FIG. 6, a part of the fuel gas introduced from the fuel gas supply unit 2 through the fuel gas supply pipe 3 to the fuel electrode layer 41 of the fuel cell stack 40 is used for power generation in the fuel cell stack 40, and an electrochemical reaction occurs, generating protons and electrons in the fuel electrode layer 41. Thereafter, the surplus fuel gas not used for power generation is introduced as anode off-gas from the fuel electrode layer 41 through the first fuel gas discharge pipe 5 to the separator 8. In the separator 8, water that has permeated from the oxidizer electrode layer 42 to the fuel electrode layer 41 is separated from the anode off-gas. The anode off-gas discharged from the separator 8 is sent to the fuel gas supply pipe 3 through the fuel gas recycle pipe 51 by the operation of the fuel gas circulation pump 52, and is introduced again to the fuel electrode layer 41, where it is reused for power generation. When a certain amount of water accumulates in a drain trap (not shown) on the separator 8, the water separated by the separator 8 is discharged from the drain trap to the outside.

[0056] A part of the oxygen-containing gas introduced from the oxygen-containing gas supply unit 14 through the oxygen-containing gas supply pipe 15 to the oxidizer electrode layer 42 of the fuel cell stack 40 is used for power generation in the fuel cell stack 40, and an electrochemical reaction occurs to generate water in the oxidizer electrode layer 42. The cathode off-gas and water discharged from the oxidizer electrode layer 42 pass through the first oxygen-containing gas discharge pipe 17 and are discharged to the outside.

[0057] Furthermore, the cooling water guided from the cooling water supply pipe 59 to the cooling layer 43 of the fuel cell stack 40 is used to recover heat generated during power generation by the fuel cell stack 40. The cooling water leaving the cooling layer 43 passes through the first cooling water discharge pipe 26 and is guided to the second heat exchanger 29. In the second heat exchanger 29, the high-temperature cooling water is cooled by recovering the heat generated by power generation. The cooling water leaving the second heat exchanger 29 passes through the cooling water supply pipe 59 again and is sent to the cooling layer 43 by the operation of the circulation pump 60.

[0058] Next, the flow of water according to a water draining method 200 of an external humidification stack type fuel cell system 50 that operates when there is a risk of the fuel cell stack 40 freezing will be described with reference to Figures 7 to 10. At this time, in each control step of the water draining method 200 of the fuel cell system 50, the control unit 44 controls the opening and closing of predetermined shutoff valves as shown in Figure 8. Note that while Figure 8 shows at least the shutoff valves whose opening and closing are controlled in each control step, it is preferable that other shutoff valves not shown in each control step are in a closed state.

[0059] First, a first pressurizing step 201 is performed to pressurize the fuel gas flow passage (see FIG. 7). At this time, the control unit 44 issues instructions to open and close predetermined shutoff valves on the fuel gas flow passage and the bypass pipe 57. Specifically, it issues instructions to open the fuel gas supply pipe shutoff valve 4 and the first fuel gas exhaust pipe shutoff valve 6, and to close the bypass pipe shutoff valve 58 (see FIG. 8). As a result, a flow path is formed as shown by the thick line in FIG. 9(a). Here, the fuel gas is supplied from the fuel gas supply unit 3 to the fuel gas flow passage, thereby pressurizing the fuel gas flow passage.

[0060] Next, when the control unit 44 acquires the measurement value of the first pressure sensor 7 and detects that the pressure inside the fuel gas flow passage exceeds a predetermined pressure, a first suction step 202 is performed to drain the water inside the fuel gas flow passage (see FIG. 7). The predetermined pressure here is a pressure value that is lower than the maximum operating pressure in the fuel cell system 1 and is a pressure value that can blow the water inside the fuel gas flow passage to the outside. At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves on the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe 57. Specifically, it instructs the fuel gas discharge pipe shutoff valve 6 and the bypass pipe shutoff valve 58 to be in an open state, and the fuel gas supply pipe shutoff valve 4, the first oxygen-containing gas discharge pipe shutoff valve 18, and the first oxygen-containing gas discharge pipe shutoff valve 54 to be in a closed state (see FIG. 8). As a result, a flow path is formed as shown by a thick line in FIG. 9(b). Here, in addition to pushing out the water from within the fuel gas flow passage with the pressure applied in the first pressurization step 201, the suction pump 36 sucks out the water from within the fuel gas flow passage under the control of the control unit 44, thereby draining the water from within the fuel gas flow passage to the outside.

[0061] Note that steps 201 and 202 may be repeated multiple times to sufficiently drain the water from within the fuel gas flow passage.

[0062] Next, a second pressurizing step 203 is performed to pressurize the oxidizer electrode layer 42 (see FIG. 7). At this time, the control unit 44 instructs the opening and closing of a predetermined shutoff valve on the oxygen-containing gas flow passage. Specifically, the control unit 44 instructs the oxygen-containing gas supply pipe shutoff valve 16 to be in an open state and the first oxygen-containing gas discharge pipe shutoff valve 18 to be in a closed state (see FIG. 8). As a result, a flow passage is formed as shown by a thick line in FIG. 10(a). Here, the oxygen-containing gas is supplied from the oxygen-containing gas supply unit 14 to the oxidizer electrode layer 42, thereby pressurizing the oxidizer electrode layer 42. Note that while the fuel gas flow passage is pressurized in the first pressurizing step, the oxidizer electrode layer 42 is pressurized in the second pressurizing step because water is generated in the oxidizer electrode layer 42 during power generation and there is more water in the oxidizer electrode layer 42 than in the fuel electrode layer 41, and therefore it is necessary to drain the water in a focused manner. In addition, in this embodiment, an example is shown in which the oxygen-containing gas is supplied from the oxygen-containing gas supply unit 14, but for example, a nitrogen cylinder may be provided to supply nitrogen.

[0063] Subsequently, when the control unit 44 acquires the measurement value of the second pressure sensor 19 and detects that the pressure of the oxidizer electrode layer 42 exceeds a predetermined pressure, a second suction step 204 is performed to drain the water in the oxygen-containing gas flow passage (see FIG. 7). The predetermined pressure here is a pressure value that is lower than the maximum operating pressure in the fuel cell system 1 and is a pressure value that can blow the water in the oxygen-containing gas flow passage to the outside. At this time, the control unit 44 instructs the opening and closing of predetermined shutoff valves on the oxygen-containing gas flow passage and the bypass pipe 57. Specifically, the control unit 44 instructs the first oxygen-containing gas discharge pipe shutoff valve 18 to be in an open state, and the oxygen-containing gas supply pipe shutoff valve 16, the first oxygen-containing gas discharge pipe shutoff valve 54, and the bypass pipe shutoff valve 58 to be in a closed state (see FIG. 8). As a result, a flow passage is formed as shown by the thick line in FIG. 10(b). Here, in addition to pushing out the water from within the oxygen-containing gas flow passage with the pressure applied in the second pressurization step 203, the suction pump 36 sucks out the water from within the oxygen-containing gas flow passage under the control of the control unit 44, thereby discharging the water from within the oxygen-containing gas flow passage to the outside.

[0064] Incidentally, steps 203 and 204 may be repeated a number of times to sufficiently drain the water from within the oxygen-containing gas flow passage.

[0065] As described above, according to the external humidification stack type fuel cell system 50 and the water draining method 200 for the fuel cell system 50 of this embodiment, by newly providing the suction pipe 55 and the suction pump 56, when there is a risk of the fuel cell system 50 freezing, a first pressurizing step 201 is performed in which predetermined shutoff valves on the fuel gas flow passage and the bypass pipe 57 are controlled and the fuel gas flow passage is pressurized with fuel gas, and a predetermined shutoff valves on the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe 57 are controlled and the fuel gas flow passage is pressurized with the pressure applied in the first pressurizing step 201 is pressurized with the pressure applied in the first pressurizing step 201. The first suction step 202 in which the suction pump 36 sucks out water in the fuel gas flow passage via the bypass pipe 57 while pushing out the water in the fuel gas flow passage, the second pressurizing step 203 in which a predetermined shutoff valve in the oxygen-containing gas flow passage is controlled and the oxidizer electrode layer 42 is pressurized with the oxygen-containing gas, and the second suction step 204 in which the suction pump 36 sucks out water in the oxygen-containing gas flow passage while controlling a predetermined shutoff valve in the oxygen-containing gas flow passage and the bypass pipe 57 and pushing out the water in the oxygen-containing gas flow passage with the pressure applied in the second pressurizing step 203 are sequentially performed. As a result, even if the oxygen-containing gas is discharged by the air compressor in the past, there is a possibility that water remains in the fuel cell stack and in the piping of the exhaust system, and there was a problem that the influence of freezing on the fuel cell system could not be prevented. However, in this embodiment, the water remaining in the fuel cell stack and in the piping of the exhaust system can be drained to an extent that the influence of freezing can be prevented. Furthermore, instead of continuously discharging the air compressor as in the conventional method, the present embodiment uses an air compressor in combination with a suction pump, thereby reducing the total power consumption required to discharge water remaining inside the fuel cell stack and inside the piping of the exhaust system to the outside. It is also possible to reduce the amount of oxygen-containing gas flowing into the fuel cell stack by the air compressor, thereby suppressing oxidation of the electrolyte layer.

[0066] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the invention and its equivalents described in the claims. [Explanation of symbols]

[0067] 1... fuel cell system, 2... fuel gas supply section, 3... fuel gas supply pipe, 4... fuel gas supply pipe shutoff valve, 5... first fuel gas exhaust pipe, 6... first fuel gas exhaust pipe shutoff valve, 7... first pressure sensor, 8... separator, 9... second fuel gas exhaust pipe, 10... second fuel gas exhaust pipe shutoff valve, 11... fuel gas recycle pipe, 12... fuel gas circulation pump, 13... fuel gas recycle pipe shutoff valve, 14... oxygen-containing gas supply section, 15... oxygen-containing gas supply pipe, 16... oxygen-containing gas supply pipe shutoff valve, 17... First oxygen-containing gas exhaust pipe, 18...first oxygen-containing gas exhaust pipe shutoff valve, 19...second pressure sensor, 20...first heat exchanger, 21...second oxygen-containing gas exhaust pipe, 22...second oxygen-containing gas exhaust pipe shutoff valve, 23...humidification section, 24...cooling water supply pipe, 25...cooling water supply pipe shutoff valve, 26...first cooling water exhaust pipe, 27...first cooling water exhaust pipe shutoff valve, 28...third pressure sensor, 29...second heat exchanger, 30...second cooling water exhaust pipe, 31...second cooling water exhaust pipe shutoff valve, 32...first bypass pipe, 33...first bypass 3. A bypass pipe shutoff valve, 34...second bypass pipe, 35...second bypass pipe shutoff valve, 36...suction pump, 37...humidification section exhaust pipe, 38...humidification section drain pipe, 39...humidification section drain pipe shutoff valve, 40...fuel cell stack, 41...fuel electrode layer, 42...oxidizer electrode layer, 43...cooling layer, 44...control unit, 50...fuel cell system, 51...fuel gas recycle pipe, 52...fuel gas circulation pump, 53...first oxygen-containing gas exhaust pipe, 54...first oxygen-containing gas exhaust pipe shutoff valve, 55...suction pipe, 56...suction pump, 5 7...bypass pipe, 58...bypass pipe shut-off valve, 59...cooling water supply pipe, 60...circulation pump, 100...method of draining water from fuel cell system, 101...first pressurization step, 102...first drainage step, 103...first suction step, 104...second pressurization step, 105...second drainage step, 106...second suction step, 200...method of draining water from fuel cell system, 201...first pressurization step, 202...first suction step, 203...second pressurization step, 204...second suction step.

Claims

1. a fuel cell stack having a fuel electrode layer to which a fuel gas is supplied, an oxidizer electrode layer to which an oxygen-containing gas is supplied, and a cooling layer to which cooling water is supplied; a fuel gas flow passage for passing the fuel gas from the anode layer of the fuel cell stack; an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack; a cooling water flow passage for passing the cooling water from the cooling layer of the fuel cell stack; a first bypass pipe that guides water in the fuel gas flow passage to the cooling water flow passage; a second bypass pipe for guiding water in the oxygen-containing gas flow passage to the cooling water flow passage; a suction pump provided in the cooling water flow passage downstream of a connection portion between the cooling water flow passage and the first bypass pipe and a connection portion between the cooling water flow passage and the second bypass pipe; A fuel cell system comprising:

2. 2. The fuel cell system according to claim 1, further comprising a shutoff valve provided on each of the piping constituting the fuel gas flow passage, the oxygen-containing gas flow passage, the cooling water flow passage, the first bypass pipe, and the second bypass pipe, for opening and closing the flow passage of each of the piping.

3. a control unit for controlling operations of the fuel cell stack, the suction pump, and the shutoff valve, The control unit is instructing the opening and closing of predetermined shutoff valves in the fuel gas flow passage and the first bypass pipe, and instructing the fuel gas flow passage to be pressurized with the fuel gas; instructing the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe to open or close predetermined shutoff valves, and instructing the pressurization to push out water in the fuel gas flow passage by the pressurization; instructing the shutoff valves in the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe to open or close, and instructing the suction pump to suck out water in the fuel gas flow passage through the first bypass pipe; instructing the opening and closing of predetermined shutoff valves in the oxygen-containing gas flow passage and the cooling water flow passage, and instructing the oxygen-containing gas flow passage and the cooling water flow passage to be pressurized with the oxygen-containing gas; instructing the opening and closing of predetermined shutoff valves in the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe, and instructing the pressurization to push out water in the oxygen-containing gas flow passage by the pressure generated by the pressurization; 3. The fuel cell system according to claim 2, further comprising an instruction to open and close predetermined shutoff valves in the fuel gas flow passage, the cooling water flow passage, and the second bypass pipe, and an instruction to cause the suction pump to suck out water from within the oxygen-containing gas flow passage and the cooling water flow passage via the second bypass pipe.

4. a fuel cell stack having a fuel electrode layer to which a fuel gas is supplied, an oxidizer electrode layer to which an oxygen-containing gas is supplied, and a cooling layer to which cooling water is supplied; a fuel gas flow passage for passing the fuel gas from the anode layer of the fuel cell stack; an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack; a cooling water flow passage for passing the cooling water from the cooling layer of the fuel cell stack; a first bypass pipe that guides water in the fuel gas flow passage to the cooling water flow passage; a second bypass pipe for guiding water in the oxygen-containing gas flow passage to the cooling water flow passage; a suction pump provided in the cooling water flow passage downstream of a connection portion between the cooling water flow passage and the first bypass pipe and a connection portion between the cooling water flow passage and the second bypass pipe; a shutoff valve provided on each of the piping constituting the fuel gas flow passage, the oxygen-containing gas flow passage, the cooling water flow passage, the first bypass pipe, and the second bypass pipe, for opening and closing the flow passage of each of the piping; A method for controlling a fuel cell system, comprising: a first pressurizing step of controlling the predetermined shutoff valves in the fuel gas flow passage and the first bypass pipe and pressurizing the fuel gas flow passage with the fuel gas; a first drainage step of controlling predetermined shutoff valves in the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe, and pushing out water in the fuel gas flow passage with the pressure applied in the first pressurizing step; a first suction step of controlling the predetermined shutoff valves of the fuel gas flow passage, the cooling water flow passage, and the first bypass pipe, and causing the suction pump to suck out water in the fuel gas flow passage through the first bypass pipe; a second pressurizing step of controlling the predetermined shutoff valves of the oxygen-containing gas flow passage and the cooling water flow passage and pressurizing the oxygen-containing gas flow passage and the cooling water flow passage with the oxygen-containing gas; a second drainage step of controlling the predetermined shutoff valves on the oxygen-containing gas flow passage, the cooling water flow passage, and the second bypass pipe, and pushing out water in the oxygen-containing gas flow passage with the pressure applied in the second pressurizing step; a second suction step of controlling the predetermined shutoff valves of the fuel gas flow passage, the cooling water flow passage, and the second bypass pipe, and causing the suction pump to suck out water from within the oxygen-containing gas flow passage and the cooling water flow passage via the second bypass pipe; 1. A method for draining water from a fuel cell system, comprising:

5. In the first drainage step, when it is detected that the pressure in the fuel gas flow passage exceeds a predetermined pressure, opening and closing of a predetermined shutoff valve is controlled, 5. The method for draining water from a fuel cell system according to claim 4, wherein in the second drainage step, when it is detected that the pressure in the oxygen-containing gas flow passage and the cooling water flow passage exceeds a predetermined pressure, the opening and closing of a predetermined shut-off valve is controlled.

6. a fuel cell stack including an anode layer to which a fuel gas is supplied and an oxidizer electrode layer to which an oxygen-containing gas is supplied; a fuel gas flow passage for passing the fuel gas from the anode layer of the fuel cell stack; an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack; a bypass pipe for guiding water in the fuel gas flow passage to the oxygen-containing gas flow passage; a suction pump provided in the oxygen-containing gas flow passage downstream of a connection portion between the oxygen-containing gas flow passage and the bypass pipe; A fuel cell system comprising:

7. 7. The fuel cell system according to claim 6, further comprising shutoff valves provided on the respective pipes constituting the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe for opening and closing the flow passages of the respective pipes.

8. a control unit for controlling operations of the fuel cell stack, the suction pump, and the shutoff valve, The control unit is instructing the opening and closing of predetermined shutoff valves in the fuel gas flow passage and the bypass pipe, and instructing the fuel gas flow passage to be pressurized with the fuel gas; instructing the opening and closing of predetermined shutoff valves in the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe, and instructing the suction pump to suck out water in the fuel gas flow passage through the bypass pipe while pushing out water in the fuel gas flow passage with the pressure generated by the pressurization; instructing the shutoff valve in the oxygen-containing gas flow passage to open or close, and instructing the oxygen-containing gas flow passage to be pressurized with the oxygen-containing gas; 8. The fuel cell system according to claim 7, characterized in that the opening and closing of predetermined shutoff valves on the oxygen-containing gas flow passage and the bypass pipe is instructed, and the suction pump is instructed to suck out water from the oxygen-containing gas flow passage while pushing out water from the oxygen-containing gas flow passage with the pressure generated by the pressurization.

9. a fuel cell stack including an anode layer to which a fuel gas is supplied and an oxidizer electrode layer to which an oxygen-containing gas is supplied; a fuel gas flow passage for passing the fuel gas from the anode layer of the fuel cell stack; an oxygen-containing gas flow passage for passing the oxygen-containing gas from the oxidizer electrode layer of the fuel cell stack; a bypass pipe for guiding water in the fuel gas flow passage to the oxygen-containing gas flow passage; a suction pump provided in the oxygen-containing gas flow passage downstream of a connection portion between the oxygen-containing gas flow passage and the bypass pipe; a shutoff valve provided on each of the piping constituting the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe, for opening and closing the flow passage of each of the piping; A method for controlling a fuel cell system, comprising: a first pressurizing step of controlling the predetermined shutoff valves in the fuel gas flow passage and the bypass pipe and pressurizing the fuel gas flow passage with the fuel gas; a first suction step in which predetermined shutoff valves on the fuel gas flow passage, the oxygen-containing gas flow passage, and the bypass pipe are controlled, and water in the fuel gas flow passage is pushed out by the pressure applied in the first pressurizing step, and the suction pump sucks out water in the fuel gas flow passage through the bypass pipe; a second pressurizing step of controlling the predetermined shutoff valve in the oxygen-containing gas flow passage and pressurizing the oxygen-containing gas flow passage with the oxygen-containing gas; a second suction step in which the suction pump sucks out water from the oxygen-containing gas flow passage while controlling the predetermined shutoff valves on the oxygen-containing gas flow passage and the bypass pipe and pushing out water from the oxygen-containing gas flow passage with the pressure applied in the second pressurizing step; 1. A method for draining water from a fuel cell system, comprising:

10. In the first suction step, when it is detected that the pressure in the fuel gas flow passage exceeds a predetermined pressure, opening and closing of a predetermined shutoff valve is controlled, 10. The water draining method for a fuel cell system according to claim 9, wherein in the second suction step, when it is detected that the pressure in the oxygen-containing gas flow passage exceeds a predetermined pressure, the opening and closing of a predetermined shut-off valve is controlled.

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