Fuel cell system

Abstract

To provide a fuel cell system capable of preventing damage caused by freezing expansion of humidification water.SOLUTION: A fuel cell system comprises a fuel cell stack, an oxidant gas supply drive section, an oxidant gas exhaust line, a first gas pressure regulation section, a sealed type humidification water tank, a humidification water supply line, and a humidification water drain line. The humidification water tank is connected to a portion in the oxidant gas exhaust line on an upstream side of the first gas pressure regulation section and stores humidification water to be supplied to the fuel cell stack. The humidification water supply line supplies humidification water from the humidification water tank to the fuel cell stack. The humidification water drain line drains humidification water from the fuel cell stack to the outside of the fuel cell system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present embodiment relates to a fuel cell system. [Background technology]

[0002] Fuel cell systems are known that include a fuel cell stack, which is made up of a fuel electrode, a solid polymer electrolyte membrane, an oxidizer electrode, and a separator. The fuel cell stack generates electricity by supplying fuel gas containing hydrogen and an oxidizer gas such as air. To maximize the performance of the fuel cell stack, it is effective to manage the moisture content inside the fuel cell stack. For this purpose, humidified water is supplied to the fuel cell stack.

[0003] The internal humidification method, known as one of the moisture management methods inside a fuel cell stack, humidifies the interior of the fuel cell stack through a separator. In this case, the humidifying water flow path and the oxidizing gas flow path are separated by a separator made of a conductive porous plate with microscopic holes. As a result, a portion of the humidifying water flowing through the separator's flow path passes through the separator and enters the oxidizing gas flow path to humidify the oxidizing gas. Meanwhile, excess water generated during power generation can also be moved from the oxidizing gas flow path through the separator to the humidifying water flow path. Furthermore, by separating the fuel gas flow path and the humidifying water flow path with a separator made of a conductive porous plate, the fuel gas flowing through the fuel gas flow path can be humidified and excess water can be removed.

[0004] Furthermore, the humidifying water recovers heat when the fuel cell stack generates electricity, and some of the humidifying water evaporates. This allows the fuel cell stack to be cooled by the latent heat of evaporation of the water. Furthermore, since the fuel cell stack can also be cooled by the sensible heat of the humidifying water, increasing the flow rate of the humidifying water in the system can sometimes enhance the cooling function of the fuel cell stack.

[0005] The humidifying water passes through a separator made of a conductive porous plate and comes into contact with the fuel electrode and the oxidizer electrode. Therefore, to prevent the performance of each electrode from deteriorating, pure water containing no impurities is used as the humidifying water.

[0006] However, if the ambient temperature drops below freezing while the fuel cell system is shut down, the humidifying water remaining inside the fuel cell stack and in the humidifying water system may freeze and expand, as it is pure water, potentially damaging the piping and various devices that make up the fuel cell stack and humidifying water system. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7102358 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the embodiment is to provide a fuel cell system that can prevent damage caused by expansion of humidifying water upon freezing. [Means for solving the problem]

[0009] A fuel cell system according to an embodiment includes a fuel cell stack that generates electricity by being supplied with fuel gas and oxidant gas, an oxidant gas supply drive unit that supplies oxidant gas to the fuel cell stack, an oxidant gas discharge line that discharges the oxidant gas from the fuel cell stack, a first gas pressure adjuster, a sealed humidifying water tank, a humidifying water supply line, and a humidifying water discharge line. The first gas pressure adjuster adjusts the pressure of the oxidant gas in the oxidant gas discharge line. The humidifying water tank is connected to a portion of the oxidant gas discharge line upstream of the first gas pressure adjuster and stores humidifying water to be supplied to the fuel cell stack. The humidifying water supply line supplies humidifying water from the humidifying water tank to the fuel cell stack. The humidifying water discharge line discharges humidifying water from the fuel cell stack to the outside of the fuel cell system. [Effects of the Invention]

[0010] According to the embodiment, damage caused by expansion of humidifying water upon freezing can be prevented. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a fuel cell system according to a first embodiment. [Figure 2] FIG. 2 is a partial cross-sectional view showing the fuel cell stack shown in FIG. [Figure 3] FIG. 3 is a diagram showing a modification of the fuel cell system shown in FIG. [Figure 4] FIG. 4 is a diagram showing another modified example of the fuel cell system shown in FIG. [Figure 5] FIG. 5 is a diagram showing another modified example of the fuel cell system shown in FIG. [Figure 6] FIG. 6 is a diagram showing another modified example of the fuel cell system shown in FIG. [Figure 7] FIG. 7 is a diagram showing a fuel cell system according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing a modification of the fuel cell system shown in FIG. [Figure 9]FIG. 9 is a diagram showing another modified example of the fuel cell system shown in FIG. [Figure 10] FIG. 10 is a diagram showing another modified example of the fuel cell system shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment will be described with reference to the drawings.

[0013] (First embodiment) A fuel cell system 1 according to a first embodiment will be described with reference to Figures 1 and 2. The fuel cell system 1 according to this embodiment may be installed in a building or mounted on a mobile object, for example. Examples of buildings include apartment buildings, office buildings, factories, and commercial facilities. In this case, the power generated by the fuel cell system 1 may be used to drive elevators, and for lighting and air conditioning within the building. Examples of mobile objects include ships, automobiles, and railroad cars. In this case, the power generated by the fuel cell system 1 may be used to drive the mobile object, and for lighting and air conditioning within the mobile object.

[0014] As shown in FIG. 1, the fuel cell system 1 includes a fuel cell stack 2, a fuel gas supply line 3, a fuel gas circulation line 4, a circulation blower 5, a degassing line 6, an oxidant gas supply line 7, an oxidant gas blower 8, an oxidant gas discharge line 9, a first gas pressure regulating valve 10, a humidification water tank 11, a humidification water supply line 12, a pressure loss section 13, a humidification water discharge line 14, and a control section 15.

[0015] The fuel cell stack 2 is configured to generate power using a fuel gas and an oxidant gas. Examples of the fuel gas include hydrogen gas and mixed gases containing hydrogen gas. Examples of the oxidant gas include air.

[0016] As shown in Fig. 2, the fuel cell stack 2 has a stacked structure in which a plurality of cells 30 are stacked. Each cell 30 includes a fuel electrode 31 (anode), an oxidizer electrode 32 (cathode), and an electrolyte membrane 33 interposed between the fuel electrode 31 and the oxidizer electrode 32. The cell 30 is also called a membrane electrode assembly (MEA). A fuel gas supplied to the fuel electrode 31 and an oxidizer gas supplied to the oxidizer electrode 32 electrochemically react with each other via the electrolyte membrane 33. In this way, chemical energy is converted into electrical energy, enabling the fuel cell stack 2 to generate electricity.

[0017] The cells 30 are stacked with a first separator 34 and a second separator 35 interposed therebetween. That is, the cells 30, the first separator 34, and the second separator 35 are stacked in this order. The first separator 34 and the second separator 35 are formed of conductive porous plates having minute pores. A fuel gas flow channel 36 through which fuel gas flows is formed on one surface of the first separator 34. The fuel gas flow channel 36 is in contact with the fuel electrode 31. An oxidizer gas flow channel 37 through which oxidizer gas flows is formed on one surface of the second separator 35, and the oxidizer gas flow channel 37 is in contact with the oxidizer electrode 32. A humidification water flow channel 38 through which humidification water flows is formed on the other surface of the second separator 35, and is in contact with the first separator 34.

[0018] As shown in Fig. 1, the fuel gas supply line 3 supplies fuel gas stored in a fuel tank (not shown) to a fuel gas flow path 36 (see Fig. 2) of the fuel cell stack 2. High-pressure fuel gas is stored in the fuel tank. The fuel gas supply line 3 is connected to the fuel gas flow path 36 via a fuel inlet manifold (not shown).

[0019] The fuel gas circulation line 4 is configured to return the fuel gas discharged from the fuel gas flow path 36 of the fuel cell stack 2 to the fuel gas flow path 36. The upstream end of the fuel gas circulation line 4 is connected to the fuel gas flow path 36 via a fuel outlet manifold (not shown), and the downstream end of the fuel gas circulation line 4 is connected to the above-mentioned fuel gas supply line 3. In this case, the fuel gas discharged from the fuel gas flow path 36 can be supplied to the fuel gas supply line 3, allowing the fuel gas to be recycled. A circulation blower 5 may be provided in the fuel gas circulation line 4. The circulation blower 5 is configured to draw fuel gas from the fuel gas flow path 36 and send the fuel gas to the fuel gas supply line 3.

[0020] The degassing line 6 is configured to discharge the fuel gas from the fuel gas circulation line 4 to the outside of the fuel cell system 1. Although not shown, the degassing line 6 is provided with a degassing valve, and the fuel gas is discharged to the outside of the fuel cell system 1 by opening the degassing valve under predetermined conditions.

[0021] The oxidizing gas supply line 7 supplies an oxidizing gas such as air to an oxidizing gas flow path 37 (see FIG. 2) of the fuel cell stack 2. The oxidizing gas supply line 7 is connected to the oxidizing gas flow path 37 via an oxidizing gas inlet manifold (not shown).

[0022] The oxidant gas blower 8 is an example of an oxidant gas supply drive unit. The oxidant gas blower 8 is provided in the oxidant gas supply line 7. The oxidant gas blower 8 is configured to supply the oxidant gas to the oxidant gas flow path 37 and discharge the oxidant gas from the oxidant gas flow path 37 to the oxidant gas discharge line 9. The oxidant gas blower 8 may be, for example, a centrifugal blower, a roots blower, or a compressor.

[0023] The oxidant gas discharge line 9 discharges the oxidant gas from the oxidant gas flow path 37 of the fuel cell stack 2. The oxidant gas discharge line 9 is connected to the oxidant gas flow path 37 via an oxidant outlet manifold (not shown). The oxidant gas is discharged to the outside of the fuel cell system 1.

[0024] The oxidant gas discharge line 9 according to this embodiment includes a discharge main line 9a and a branch line 9b. The discharge main line 9a discharges the oxidant gas from the oxidant gas flow path 37 of the fuel cell stack 2 to the outside of the fuel cell system 1. The discharge main line 9a may include an outlet (not shown) that discharges the oxidant gas to the outside of the fuel cell system 1. The branch line 9b branches off from the discharge main line 9a and is connected to the humidification water tank 11. The branch line 9b connects the discharge main line 9a and the humidification water tank 11. The humidification water tank 11 is pressurized by the pressure of the oxidant gas in the branch line 9b. The pressure of the oxidant gas in the branch line 9b is equal to the pressure of the oxidant gas in a portion of the discharge main line 9a upstream of a first gas pressure regulating valve 10 (described later), and is regulated by the first gas pressure regulating valve 10.

[0025] The first gas pressure regulating valve 10 is an example of a first gas pressure regulating unit. The first gas pressure regulating valve 10 regulates the pressure of the oxidant gas in the oxidant gas discharge line 9. In this embodiment, the first gas pressure regulating valve 10 is located in the discharge main line 9a downstream of the branch point B1 with the branch line 9b. The first gas pressure regulating valve 10 regulates the pressure of the oxidant gas in the portion of the discharge main line 9a upstream of the first gas pressure regulating valve 10, and the pressure of the oxidant gas in the branch line 9b. Other examples of the first gas pressure regulating unit include, for example, an orifice or a turbine for recovering power from the oxidant gas.

[0026] The humidifying water tank 11 stores humidifying water to be supplied to the fuel cell stack 2. The humidifying water tank 11 is a sealed tank. The humidifying water tank 11 is connected to a portion of the oxidizing gas discharge line 9 that is upstream of the first gas pressure regulating valve 10. The humidifying water tank 11 according to this embodiment is connected to a branch line 9b of the oxidizing gas discharge line 9, and a gas phase composed of oxidizing gas exists within the humidifying water tank 11. As a result, the humidifying water stored in the humidifying water tank 11 is pressurized by the pressure of the oxidizing gas in the branch line 9b. The humidifying water tank 11 may be replenished with humidifying water by being supplied with humidifying water from a humidifying water supply unit (not shown). Examples of the humidifying water supply unit include the oxidizing gas cooling device 20 (described later) and a tank (not shown) that stores pure water. Another example of the humidifying water supply unit is a device that can supply tap water from which impurities have been removed using a filter, ion exchange resin, or the like. The humidifying water is sometimes used mainly as water for humidifying the inside of the fuel cell stack 2, and is also called water management water.

[0027] The humidifying water supply line 12 supplies humidifying water from the humidifying water tank 11 to a humidifying water flow path 38 (see FIG. 2) of the fuel cell stack 2. The humidifying water supply line 12 is connected to the humidifying water flow path 38 via a humidifying water inlet manifold (not shown). The humidifying water is pressurized to a pressure higher than atmospheric pressure by the pressure of the oxidant gas in branch line 9b, and is supplied to the fuel cell stack 2 under this pressure. The humidifying water supply line 12 does not necessarily have to be provided with a pump or the like for supplying humidifying water to the humidifying water flow path 38.

[0028] Pressure loss unit 13 is provided in humidification water supply line 12. Pressure loss unit 13 reduces the pressure of humidification water supplied from humidification water tank 11 to fuel cell stack 2. Pressure loss unit 13 reduces the pressure of the humidification water by causing a loss in the pressure of the humidification water. Pressure loss unit 13 may include, for example, an orifice, and the pressure of the humidification water may be reduced by the orifice. Alternatively, pressure loss unit 13 may include a pressure adjustment valve such as a needle valve, and the pressure of the humidification water may be reduced by the pressure adjustment valve.

[0029] The humidifying water discharge line 14 discharges the humidifying water from the humidifying water flow path 38 of the fuel cell stack 2 to the outside of the fuel cell system 1. The humidifying water discharge line 14 is connected to the humidifying water flow path 38 via a humidifying water outlet manifold (not shown). The humidifying water discharge line 14 may include an outlet (not shown) for discharging the humidifying water to the outside of the fuel cell system 1. The humidifying water discharge line 14 may also be fitted with a check valve (not shown) to prevent backflow of the humidifying water.

[0030] The control unit 15 controls the circulation blower 5, the oxidant gas blower 8, and the first gas pressure regulating valve 10. The control unit 15 may control the circulation blower 5, the oxidant gas blower 8, and the first gas pressure regulating valve 10 depending on the operating conditions of the fuel cell system 1.

[0031] Next, the operation of the fuel cell system 1 according to this embodiment configured as described above will be described.

[0032] During operation of the fuel cell system 1, fuel gas is supplied from the fuel gas supply line 3 to the fuel gas flow path 36 of the fuel cell stack 2, and oxidant gas is supplied from the oxidant gas supply line 7 to the oxidant gas flow path 37 of the fuel cell stack 2. The fuel gas flows in the fuel gas flow path 36 while contacting the fuel electrode 31. The oxidant gas flows in the oxidant gas flow path 37 while contacting the oxidant electrode 32. This causes the fuel gas and oxidant gas to electrochemically react, and the fuel cell stack 2 generates electricity.

[0033] The fuel gas that has passed through the fuel gas flow path 36 is discharged to the fuel gas circulation line 4. From the fuel gas circulation line 4, the fuel gas passes through the fuel gas supply line 3 and is supplied to the fuel gas flow path 36 of the fuel cell stack 2 again.

[0034] The oxidant gas that has passed through the oxidant gas flow path 37 is discharged into the oxidant gas discharge line 9, passes through the discharge main line 9a, and is discharged to the outside of the fuel cell system 1. A portion of the oxidant gas discharged into the oxidant gas discharge line 9 is supplied to the branch line 9b. The pressure of the oxidant gas in the branch line 9b is adjusted by the first gas pressure regulating valve 10. As a result, the gas phase in the humidification water tank 11, which is composed of the oxidant gas, is pressurized to a desired pressure. The gas phase in the humidification water tank 11 is pressurized to a pressure P1 higher than atmospheric pressure. In this case, the pressure of the oxidant gas in the portion of the discharge main line 9a upstream of the first gas pressure regulating valve 10 and the pressure of the oxidant gas in the branch line 9b are both substantially P1. The pressure of the oxidant gas in the oxidant gas flow path 37 of the fuel cell stack 2 is also substantially P1.

[0035] During operation of the fuel cell system 1, humidification water is supplied from the humidification water tank 11 to the humidification water flow path 38 of the fuel cell stack 2. The humidification water in the humidification water tank 11 is subjected to the above-mentioned pressure P1 and is supplied from the humidification water tank 11 to the humidification water supply line 12. The pressure of the humidification water in the humidification water supply line 12 is reduced by passing through the pressure loss section 13. If the reduced pressure of the humidification water is P2, then the pressure P2 is lower than the above-mentioned pressure P1. The humidification water is supplied to the humidification water flow path 38 at this pressure P2.

[0036] In this way, the pressure P2 of the humidifying water flowing through the humidifying water flow path 38 is lower than the pressure P1 of the oxidizing gas in the oxidizing gas flow path 37. This makes it possible to prevent the humidifying water from passing through the second separator 35 and moving to the oxidizing gas flow path 37. In this case, it is possible to prevent the oxidizing gas flow path 37 from being blocked by the humidifying water and to prevent the electrochemical reaction in the oxidizer electrode 32 from being inhibited.

[0037] The humidifying water manages the moisture content inside the fuel cell stack 2 while flowing through the humidifying water flow path 38. For example, when the humidity of the fuel gas flowing through the fuel gas flow path 36 is low, moisture moves from the humidifying water to the fuel gas flow path 36 through the first separator 34, thereby humidifying the fuel gas. Similarly, when the humidity of the oxidizing gas flowing through the oxidizing gas flow path 37 is low, moisture moves from the humidifying water to the oxidizing gas flow path 37 through the second separator 35, thereby humidifying the oxidizing gas. Furthermore, water produced by power generation moves from the oxidizing gas flow path 37 to the humidifying water flow path 38, and excess water is removed.

[0038] The humidifying water that has passed through the humidifying water flow path 38 is discharged to the humidifying water discharge line 14. The humidifying water in the humidifying water discharge line 14 is discharged to the outside of the fuel cell system 1 from an outlet (not shown).

[0039] A case where the operation of the fuel cell system 1 is stopped will be described.

[0040] Even when the operation of the fuel cell system 1 is stopped, the oxidant gas blower 8 may continue to supply oxidant gas under the control of the control unit 15. This maintains the gas phase pressure in the humidifying water tank 11, and humidifying water is supplied from the humidifying water tank 11 to the humidifying water supply line 12. When the supply of humidifying water from a humidifying water supply unit (not shown) to the humidifying water tank 11 is stopped, the amount of humidifying water stored in the humidifying water tank 11 eventually decreases, and the supply of humidifying water from the humidifying water tank 11 to the humidifying water supply line 12 ceases. Thereafter, the oxidant gas is supplied from the humidifying water tank 11 to the humidifying water supply line 12 under the gas phase pressure in the humidifying water tank 11. As a result, humidifying water is discharged from the humidifying water supply line 12, the humidifying water flow path 38 of the fuel cell stack 2, and the humidifying water discharge line 14.

[0041] Alternatively, before stopping the operation of the fuel cell system 1, the supply of humidifying water from a humidifying water supply unit (not shown) to the humidifying water tank 11 may be stopped or the amount of humidifying water supplied may be reduced. In this case, the amount of humidifying water stored in the humidifying water tank 11 decreases. When the operation of the fuel cell system 1 is then stopped, the gas phase pressure in the humidifying water tank 11 causes oxidant gas to be supplied from the humidifying water tank 11 to the humidifying water supply line 12. As a result, humidifying water is discharged from the humidifying water supply line 12, the humidifying water flow path 38 of the fuel cell stack 2, and the humidifying water discharge line 14.

[0042] Note that even when the supply of humidifying water from humidifying water tank 11 to humidifying water supply line 12 has ceased, a certain amount of humidifying water that is not supplied to humidifying water supply line 12 may remain stored in humidifying water tank 11. For example, if the outlet of humidifying water tank 11 to humidifying water supply line 12 is located higher than the tank bottom, a certain amount of humidifying water will be stored. For example, control unit 15 may stop oxidant gas blower 8 a predetermined time after the supply of humidifying water from humidifying water tank 11 to humidifying water supply line 12 has ceased. In this case, purging with oxidant gas allows humidifying water to be effectively discharged to the outside from humidifying water supply line 12, humidifying water flow path 38, and humidifying water discharge line 14.

[0043] As described above, according to the present embodiment, the humidifying water tank 11 is connected to the oxidizing gas discharge line 9 at a portion upstream of the first gas pressure regulating valve 10, and the first gas pressure regulating valve 10 regulates the pressure of the oxidizing gas in the oxidizing gas discharge line 9. This allows the oxidizing gas to pass through the humidifying water tank 11 and be supplied to the humidifying water supply line 12 at a pressure higher than atmospheric pressure. Therefore, the pressure of the oxidizing gas can be used to discharge humidifying water from the humidifying water supply line 12, the humidifying water flow path 38, and the humidifying water discharge line 14 to the outside of the fuel cell system 1. As a result, the humidifying water can be discharged from the fuel cell stack 2, preventing damage caused by expansion of the humidifying water due to freezing.

[0044] Furthermore, according to this embodiment, the pressure of the humidifying water supplied from the humidifying water tank 11 to the humidifying water flow path 38 of the fuel cell stack 2 is reduced by the pressure loss unit 13. This makes it possible to make the pressure of the humidifying water flowing through the humidifying water flow path 38 lower than the pressure of the oxidizing gas in the oxidizing gas flow path 37. This makes it possible to prevent the humidifying water from moving to the oxidizing gas flow path 37. In this case, it is possible to prevent the oxidizing gas flow path 37 from being blocked by the humidifying water and to prevent the electrochemical reaction at the oxidizer electrode 32 from being inhibited.

[0045] Furthermore, according to this embodiment, the oxidant gas discharge line 9 includes a main discharge line 9a that discharges the oxidant gas from the fuel cell stack 2 to the outside of the fuel cell system 1, and a branch line 9b that branches off from the main discharge line 9a and is connected to the humidification water tank 11. The first gas pressure regulating valve 10 is located on the main discharge line 9a downstream of a branch point B1 where the main discharge line 9a branches off from the branch line 9b. This simplifies the discharge path of the oxidant gas and reduces pressure loss. This improves the discharge efficiency of the oxidant gas and improves the power generation efficiency of the fuel cell stack 2.

[0046] In the above-described embodiment, an example has been described in which humidifying water is supplied to the humidifying water tank 11 from a humidifying water supply unit (not shown). However, the embodiment is not limited to this. For example, as shown in FIG. 3 , the humidifying water supply unit may include an oxidizing gas cooler 20 provided in the oxidizing gas discharge line 9. The oxidizing gas cooler 20 may be controlled by the control unit 15.

[0047] As shown in FIG. 3, the fuel cell system 1 further includes an oxidant gas cooling device 20 that cools the oxidant gas flowing through the discharge main line 9a of the oxidant gas discharge line 9 to generate condensed water. The oxidant gas cooling device 20 may be located upstream of the branch point B1 in the discharge main line 9a of the oxidant gas discharge line 9. The oxidant gas cooling device 20 includes a heat exchanger 20a and a medium cooling device 20b located in the discharge main line 9a. A pump (not shown) circulates a cooling medium between the heat exchanger 20a and the medium cooling device 20b, thereby cooling the oxidant gas flowing through the discharge main line 9a. Because the oxidant gas contains moisture, condensed water is generated by cooling the oxidant gas. Examples of the medium cooling device 20b include a cooling tower, a chiller, and a radiator.

[0048] The condensed water generated in the oxidant gas cooler 20 is supplied to the humidification water tank 11. For example, the main discharge line 9a, the branch line 9b, and the humidification water tank 11 may be configured so that the condensed water flows under the influence of gravity. This allows the condensed water to be supplied to the humidification water tank 11, and by storing the condensed water as humidification water, it is possible to prevent the humidification water from running out.

[0049] Alternatively, the humidification water tank 11 may be connected to a portion of the oxidant gas discharge line 9 upstream of the first gas pressure regulating valve 10. That is, the humidification water tank 11 may be connected directly to the main discharge line 9a at a midpoint of the main discharge line 9a without using the branch line 9b. In this case, the humidification water tank 11 may have a large inlet for the oxidant gas supplied from the main discharge line 9a. This allows condensed water to be separated from the oxidant gas while the oxidant gas passes through the gas phase in the humidification water tank 11. That is, the humidification water tank 11 can have a gas-liquid separation function. The separated condensed water can be stored in the humidification water tank 11 as humidification water. The oxidant gas from which the condensed water has been separated passes from the humidification water tank 11 through the first gas pressure regulating valve 10 and is discharged to the outside of the fuel cell system 1. Alternatively, when the humidification water tank 11 is directly connected to the main discharge line 9a, the humidification water tank 11 may be equipped with a gas-liquid separator capable of separating condensed water by centrifugal separation. In this case, too, the condensed water can be separated from the oxidizing gas while the oxidizing gas passes through the gas phase in the humidifying water tank 11 .

[0050] The oxidant gas cooler 20 may be stopped when the operation of the fuel cell system 1 is stopped. This stops the supply of condensed water to the humidifying water tank 11. Therefore, by continuing to drive the oxidant gas blower 8 described above, oxidant gas can be supplied from the humidifying water tank 11 to the humidifying water supply line 12, and humidifying water can be discharged from the humidifying water supply line 12, the humidifying water flow path 38 of the fuel cell stack 2, and the humidifying water discharge line 14.

[0051] Furthermore, in the above-described embodiment, a humidifying water flow rate adjustment valve 21 may be provided in the humidifying water discharge line 14, as shown in Fig. 4. The humidifying water flow rate adjustment valve 21 adjusts the flow rate of humidifying water in the humidifying water discharge line 14. This makes it possible to adjust the flow rate of humidifying water discharged from the humidifying water discharge line 14 to the outside of the fuel cell system 1. Therefore, according to the example shown in Fig. 4, the amount of humidifying water supplied to the humidifying water flow path 38 of the fuel cell stack 2 can be reduced, and the humidifying water in the humidifying water tank 11 can be prevented from running out. The humidifying water flow rate adjustment valve 21 may be controlled by the control unit 15.

[0052] The humidifying water flow rate adjusting valve 21 shown in FIG. 4 may be applied to the modified example shown in FIG.

[0053] Furthermore, in the above-described embodiment, an ejector 22 may be provided in the oxidant gas discharge line 9, as shown in FIG. 5. The ejector 22 is located downstream of the first gas pressure adjustment valve 10 in the main discharge line 9a of the oxidant gas discharge line 9. The humidification water discharge line 14 is connected to the ejector 22. The ejector 22 sucks humidification water from the humidification water discharge line 14 by the flow of oxidant gas. Inside the ejector 22, the humidification water merges with the flow of oxidant gas and is discharged outside the fuel cell system 1. Therefore, according to the example shown in FIG. 5, the flow of oxidant gas allows humidification water to be smoothly discharged from the humidification water flow path 38 of the fuel cell stack 2 to the outside of the fuel cell system 1.

[0054] The ejector 22 shown in FIG. 5 may be applied to the modified examples shown in FIGS.

[0055] In the above-described embodiment, a second gas pressure adjustment valve 23 may be provided in the oxidant gas discharge line 9 upstream of the first gas pressure adjustment valve 10, as shown in Fig. 6. The second gas pressure adjustment valve 23 is an example of a second gas pressure adjustment unit. The second gas pressure adjustment valve 23 is located in the main discharge line 9a of the oxidant gas discharge line 9 upstream of a branch point B1 with the branch line 9b. The second gas pressure adjustment valve 23 can adjust the pressure of the oxidant gas in the oxidant gas flow path 37 of the fuel cell stack 2. Other examples of the second gas pressure adjustment unit include an orifice or a compressor for recovering power from the oxidant gas.

[0056] 6, the pressure of the oxidant gas in the branch line 9b can be adjusted by the first gas pressure adjustment valve 10. This makes it possible to separately adjust the pressure of the oxidant gas in the oxidant gas flow path 37 and the pressure of the oxidant gas in the branch line 9b. For example, the pressure of the oxidant gas in the branch line 9b can be made lower than the pressure of the oxidant gas in the oxidant gas flow path 37. In this case, the gas phase pressure in the humidification water tank 11 can be lowered, and the amount of humidification water supplied to the humidification water flow path 38 of the fuel cell stack 2 can be reduced. This makes it possible to prevent the humidification water in the humidification water tank 11 from running out. The second gas pressure adjustment valve 23 may be controlled by the control unit 15.

[0057] The second gas pressure regulating valve 23 shown in FIG. 6 may be applied to the modified examples shown in FIGS.

[0058] (Second embodiment) Next, a fuel cell system according to a second embodiment will be described with reference to FIG.

[0059] The second embodiment shown in Figure 7 differs mainly in that a humidifying water return line branches off from the humidifying water discharge line, and other configurations are substantially the same as those of the first embodiment shown in Figures 1 and 2. In Figure 7, the same parts as those of the first embodiment shown in Figures 1 and 2 are designated by the same reference numerals and detailed description thereof will be omitted.

[0060] As shown in FIG. 7, the fuel cell system 1 according to this embodiment further includes a humidification water return line 40, a humidification water discharge valve 41, and a humidification water pump .

[0061] Humidification water return line 40 branches off from humidification water discharge line 14 and is connected to humidification water tank 11. Humidification water return line 40 connects humidification water discharge line 14 with the gas phase portion of humidification water tank 11, allowing humidification water in humidification water discharge line 14 to be discharged into humidification water tank 11.

[0062] The humidification water discharge valve 41 is located on the humidification water discharge line 14 downstream of the branch point B2 with the humidification water return line 40. The humidification water discharge valve 41 may be an on-off valve. The humidification water discharge valve 41 opens when humidification water is being discharged, and closes when humidification water is not being discharged. The opening and closing of the humidification water discharge valve 41 is controlled by the control unit 15.

[0063] The humidification water pump 42 supplies humidification water discharged from the fuel cell stack 2 to the humidification water tank 11. The humidification water pump 42 increases the pressure of the humidification water above the gas phase pressure in the humidification water tank 11 and supplies the humidification water to the humidification water tank 11. The humidification water pump 42 may be located on the humidification water discharge line 14 upstream of branch point B2 with the humidification water return line 40. However, the humidification water pump 42 may also be located on the humidification water return line 40.

[0064] During operation of the fuel cell system 1, the humidifying water discharge valve 41 is closed. As a result, the humidifying water discharged from the humidifying water flow path 38 of the fuel cell stack 2 passes through the humidifying water return line 40 and is supplied to the humidifying water tank 11. This allows the humidifying water to circulate, preventing it from running out.

[0065] When the operation of the fuel cell system 1 is stopped, the humidifying water pump 42 is stopped and the humidifying water discharge valve 41 is opened. Under control of the control unit 15, the oxidizing gas blower 8 may continue to supply oxidizing gas. This maintains the gas-phase pressure in the humidifying water tank 11, and humidifying water is supplied from the humidifying water tank 11 to the humidifying water supply line 12. Because the humidifying water pump 42 is stopped and the humidifying water discharge valve 41 is open, the amount of humidifying water stored in the humidifying water tank 11 eventually decreases, and humidifying water no longer is supplied from the humidifying water tank 11 to the humidifying water supply line 12. Thereafter, the gas-phase pressure of the humidifying water tank 11 causes oxidizing gas to be supplied from the humidifying water tank 11 to the humidifying water supply line 12. As a result, humidifying water is discharged from the humidifying water supply line 12, the humidifying water flow path 38 of the fuel cell stack 2, and the humidifying water discharge line 14. Humidifying water is also discharged from the humidifying water pump 42. The humidifying water return line 40 is connected to the gas phase portion of the humidifying water tank 11, and therefore, under the pressure of this gas phase, the humidifying water in the humidifying water return line 40 is discharged from the humidifying water discharge line 14.

[0066] As described above, according to the present embodiment, humidification water return line 40, which branches off from humidification water discharge line 14, is connected to humidification water tank 11, and humidification water discharge valve 41 is located on humidification water discharge line 14 downstream of branch point B2 with humidification water return line 40. Humidification water discharged from fuel cell stack 2 can be supplied to humidification water tank 11 by humidification water pump 42. This makes it possible to recycle humidification water, preventing the humidification water in humidification water tank 11 from running out.

[0067] In the above-described embodiment, an example has been described in which the humidifying water discharge valve 41 is an on-off valve. However, the embodiment is not limited to this. For example, the humidifying water discharge valve 41 may be a flow rate adjustment valve that can adjust the discharge flow rate of humidifying water. In this case, the humidifying water discharge valve 41 can adjust the flow rate of humidifying water discharged from the humidifying water discharge line 14 to the outside of the fuel cell system 1, similar to the humidifying water flow rate adjustment valve 21 shown in FIG. 4. In this case, the humidifying water discharge valve 41 may also be controlled by the control unit 15.

[0068] In the present embodiment described above, an ejector 22 may be provided in the oxidizing gas discharge line 9 as shown in Fig. 8. The ejector 22 may be configured similarly to the ejector 22 shown in Fig. 5 and may function similarly.

[0069] In the present embodiment described above, a second gas pressure regulating valve 23 may be provided in the oxidizing gas discharge line 9, as shown in Fig. 9. The second gas pressure regulating valve 23 may be configured similarly to the second gas pressure regulating valve 23 shown in Fig. 6 and may function similarly.

[0070] The second gas pressure regulating valve 23 shown in FIG. 9 may be applied to the modified example shown in FIG.

[0071] 10, the humidifying water may be cooled by a humidifying water cooling device 43. The humidifying water cooling device 43 may be controlled by the control unit 15.

[0072] As shown in FIG. 10 , the fuel cell system 1 further includes a humidifying water cooling device 43 that cools the humidifying water supplied from the humidifying water tank 11 to the humidifying water flow path 38 of the fuel cell stack 2. The humidifying water cooling device 43 may be provided in the humidifying water supply line 12. More specifically, the humidifying water cooling device 43 may be located in a portion of the humidifying water supply line 12 between the humidifying water tank 11 and the pressure loss section 13. The humidifying water cooling device 43 includes a heat exchanger 43a and a medium cooling section 43b located in the humidifying water supply line 12. A pump (not shown) circulates a cooling medium between the heat exchanger 43a and the medium cooling section 43b, thereby cooling the humidifying water flowing through the humidifying water supply line 12. This allows the humidifying water to be cooled even if its temperature rises due to the circulation of the humidifying water, thereby effectively cooling the fuel cell stack 2. The humidifying water cooling device 43 may be configured similarly to the oxidizing gas cooling device 20 shown in FIG. 3.

[0073] The humidifying water cooling device 43 shown in FIG. 10 may be applied to the modified examples shown in FIGS.

[0074] According to the embodiment described above, damage caused by expansion of humidifying water due to freezing can be prevented.

[0075] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, it is of course possible to combine parts of these embodiments as appropriate within the spirit of the invention. [Explanation of symbols]

[0076] 1: fuel cell system, 2: fuel cell stack, 8: oxidant gas blower, 9: oxidant gas exhaust line, 9a: main exhaust line, 9b: branch line, 10: first gas pressure regulating valve, 11: humidification water tank, 12: humidification water supply line, 13: pressure loss section, 14: humidification water exhaust line, 20: oxidant gas cooler, 21: humidification water flow rate regulating valve, 22: ejector, 23: second gas pressure regulating valve, 40: humidification water return line, 41: humidification water exhaust valve, 42: humidification water pump, 43: humidification water cooler, B1, B2: branch point

Claims

1. 1. A fuel cell system, comprising: a fuel cell stack that generates electricity when supplied with fuel gas and oxidant gas; an oxidant gas supply drive unit that supplies the oxidant gas to the fuel cell stack; an oxidant gas discharge line for discharging the oxidant gas from the fuel cell stack; a first gas pressure adjusting unit that adjusts the pressure of the oxidant gas in the oxidant gas discharge line; a sealed humidification water tank connected to a portion of the oxidant gas discharge line upstream of the first gas pressure adjusting unit, the tank storing humidification water to be supplied to the fuel cell stack; a humidification water supply line for supplying the humidification water from the humidification water tank to the fuel cell stack; a humidification water discharge line that discharges the humidification water from the fuel cell stack to the outside of the fuel cell system; A fuel cell system comprising:

2. The humidification water supply system further includes a pressure loss section provided in the humidification water supply line to reduce the pressure of the humidification water. The fuel cell system according to claim 1 .

3. the oxidant gas discharge line includes a discharge main line that discharges the oxidant gas from the fuel cell stack to the outside of the fuel cell system, and a branch line that branches off from the discharge main line and is connected to the humidification water tank, The first gas pressure adjusting unit is located downstream of a branch point of the main exhaust line with the branch line.

3. The fuel cell system according to claim 1 or 2.

4. an oxidant gas cooling device provided in the oxidant gas discharge line that cools the oxidant gas to generate condensed water, the condensed water generated in the oxidant gas cooling device is supplied to the humidification water tank.

3. The fuel cell system according to claim 1 or 2.

5. The humidification water discharge system further includes a humidification water flow rate adjusting valve provided in the humidification water discharge line to adjust the flow rate of the humidification water.

3. The fuel cell system according to claim 1 or 2.

6. the humidification water discharge line is connected to an ejector located downstream of the first gas pressure adjusting unit in the oxidizing gas discharge line, the ejector sucks the humidification water from the humidification water discharge line by the flow of the oxidant gas.

3. The fuel cell system according to claim 1 or 2.

7. a second gas pressure adjusting unit located in the oxidant gas discharge line upstream of the first gas pressure adjusting unit, the second gas pressure adjusting unit adjusting the pressure of the oxidant gas in the fuel cell stack; 3. The fuel cell system according to claim 1 or 2.

8. a humidification water return line branching from the humidification water discharge line and connected to the humidification water tank; a humidification water discharge valve located in the humidification water discharge line downstream of a branch point with the humidification water return line; a humidification water pump that supplies the humidification water discharged from the fuel cell stack to the humidification water tank, 3. The fuel cell system according to claim 1 or 2.

9. the humidification water discharge valve is capable of adjusting the discharge flow rate of the humidification water. The fuel cell system according to claim 8 .

10. the humidification water discharge line is connected to an ejector located downstream of the first gas pressure adjusting unit in the oxidizing gas discharge line, the ejector sucks the humidification water from the humidification water discharge line by the flow of the oxidant gas. The fuel cell system according to claim 8 .

11. a second gas pressure adjusting unit located in the oxidant gas discharge line upstream of the first gas pressure adjusting unit, the second gas pressure adjusting unit adjusting the pressure of the oxidant gas in the fuel cell stack; The fuel cell system according to claim 8 .

12. a humidification water cooling device that cools the humidification water supplied from the humidification water tank to the fuel cell stack; The fuel cell system according to claim 8 .

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