Fuel Cell Systems

Abstract

To provide a technique for completing a fuel gas replacement processing in a short time.SOLUTION: A fuel battery system comprises: a fuel battery stack; a fuel gas supply path that is connected to a supply port of the fuel battery stack, and provided with a supply control valve; an exhaust drain path that is connected to an exhaust port of the fuel battery stack, and provided with an exhaust drain valve; a circulation path that is extended to the fuel gas supply path from the exhaust drain path, and circulates an off gas exhausted from the fuel battery stack to the fuel gas supply path; a pump that is provided in the circulation path, and sends the off gas to the fuel gas supply path by a forward rotation; and a control device that can execute fuel gas replacement processing at a time of start of the fuel battery stack by controlling an operation of the supply control valve, the pump, and the exhaust drain valve. In the fuel gas replacement processing, the control device opens the supply control valve, and reversely rotates the pump in a state where the exhaust drain valve is opened.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a fuel cell system. [Background technology]

[0002] Patent Document 1 describes a fuel cell system. This fuel cell system includes a circulation path that re-supplies off-gas discharged from a fuel cell stack to a fuel gas supply path. The circulation path is provided with a pump that sends the off-gas toward the fuel gas supply path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-220425 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a fuel cell system, when operating at low temperatures, for example, below freezing, if the fuel gas concentration (e.g., hydrogen gas concentration) in the residual gas present in the fuel cell stack is reduced, this may lead to deterioration of the fuel cell stack. Therefore, particularly in environments below freezing, when starting up the fuel cell system, it is preferable to perform a process of replacing the residual gas in the fuel cell stack with fuel gas (hereinafter referred to as a fuel gas replacement process) to increase the fuel gas concentration in the fuel cell stack.

[0005] In the fuel gas replacement process, the fuel gas is supplied to the fuel cell stack from the fuel gas supply path, while the residual gas in the fuel cell stack is discharged from the exhaust drainage path. At this time, the pump in the circulation path is stopped, and the circulation of the discharged residual gas is prohibited. However, even if the pump in the circulation path is stopped, there is a gap in the pump, so that the residual gas flowing out from the fuel cell stack may flow into the fuel gas supply path through the circulation path. In this case, some of the residual gas circulates without being discharged to the outside, so the time required for the fuel gas replacement process becomes longer. In order to avoid this, it is possible to provide a shutoff valve in the circulation path, but this has problems such as large pressure loss in the shutoff valve and a complicated configuration of the fuel cell system.

[0006] In view of the above circumstances, this specification provides a technique for completing the fuel gas replacement process in a short time without complicating the configuration of the fuel cell system. [Means for solving the problem]

[0007] The technology disclosed in this specification is embodied in a fuel cell system. In a first aspect, the fuel cell system includes a fuel cell stack, a fuel gas supply path connected to a supply port of the fuel cell stack and provided with a supply control valve, an exhaust drainage path connected to an exhaust port of the fuel cell stack and provided with an exhaust drainage valve, a circulation path extending from the exhaust drainage path to the fuel gas supply path and circulating off-gas discharged from the fuel cell stack to the fuel gas supply path, a pump provided in the circulation path and rotating forward to send the off-gas to the fuel gas supply path, and a control device capable of executing a fuel gas replacement process at the start of the fuel cell stack by controlling the operation of the supply control valve, the pump, and the exhaust drainage valve. In the fuel gas replacement process, the control device opens the supply control valve and rotates the pump in reverse while the exhaust drainage valve is open.

[0008] In the above-mentioned fuel gas replacement process, fuel gas is supplied to the fuel cell stack from the fuel gas supply path while the residual gas in the fuel cell stack is discharged from the exhaust drainage path. At this time, by rotating the pump provided in the circulation path in reverse, the residual gas flowing out from the fuel cell stack can be prevented from flowing into the fuel cell stack through the circulation path. As a result, during the fuel gas replacement process, only the fuel gas supplied by the fuel gas supply mechanism is supplied to the fuel cell stack, and the fuel gas replacement process can be completed in a short time.

[0009] In a second aspect, in the first aspect, the control device may determine the rotation speed at which the pump is rotated in reverse according to the fuel gas supply flow rate supplied to the fuel cell stack by controlling the operation of the supply control valve. If the rotation speed at which the pump is rotated in reverse is too low, the circulation of the residual gas through the circulation path cannot be sufficiently suppressed. On the other hand, if the rotation speed at which the pump is rotated in reverse is too high, the fuel gas in the fuel gas supply path flows back through the circulation path to the exhaust drainage path, obstructing the flow of the residual gas discharged from the fuel cell stack. In this regard, the appropriate rotation speed at which the pump is rotated in reverse depends on the fuel gas supply flow rate supplied from the fuel gas supply path to the fuel cell stack. Therefore, when the pump is rotated in reverse, the flow of gas in the circulation path can be suppressed without excess or deficiency by determining the rotation speed of the pump according to the fuel gas supply flow rate.

[0010] In a third aspect, in the first or second aspect, the control device may determine the number of revolutions of the pump to be equal to or less than a predetermined upper limit regardless of the fuel gas supply flow rate. With this configuration, it is possible to prevent the fuel gas in the fuel gas supply path from flowing back from the circulation path through the exhaust drainage path to the fuel cell stack. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic configuration of a fuel cell system 10 according to an embodiment. [Diagram 2]FIG. 4 is a flow diagram showing an example of a hydrogen gas replacement process executed by the control device 60. [Diagram 3] 1 is a diagram showing an example of the relationship between the supply flow rate of fuel gas and the reverse rotation speed of pump 54. Note that NL (normal liter) / min, which is the unit of the supply flow rate of fuel gas, means the gas flow rate per minute measured under conditions of atmospheric pressure (i.e., pressure 0.1013 MPa), temperature 0 degrees, and relative humidity 0 percent. Also, regarding the reverse rotation speed of pump 54, when the reverse rotation speed is a positive value, it means that pump 54 rotates in reverse. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A fuel cell system 10 according to an embodiment will be described with reference to the drawings. The fuel cell system 10 according to the embodiment is mounted on a fuel cell vehicle (e.g., an automobile, a bus, a truck, a train) or a stationary fuel cell device. The fuel cell system 10 may also be mounted on various moving bodies other than a vehicle (e.g., a ship or an airplane).

[0013] As shown in Fig. 1, the fuel cell system 10 includes a fuel cell stack 20, an oxidizing gas supply unit 30, a fuel gas supply unit 40, and a control device 60. The fuel cell stack 20 has a structure in which a plurality of fuel cell cells 22 are stacked. The fuel cell stack 20 generates power by causing a chemical reaction between an oxidizing gas and a fuel gas in the plurality of fuel cell cells 22. In the fuel cell system 10 of this embodiment, air is used as the oxidizing gas, and a gas containing a high concentration of hydrogen gas is used as the fuel gas.

[0014] The specific configuration of the fuel cell 22 is not particularly limited. Although not shown, for example, each fuel cell 22 includes a membrane electrode and gas diffusion layer assembly (MEGA), an anode side separator, a cathode side separator, and a support frame. The membrane electrode and gas diffusion layer assembly is configured by stacking an anode side gas diffusion layer, an anode electrode, an electrolyte membrane, a cathode electrode, and a cathode side gas diffusion layer in order.

[0015] As shown in Fig. 1, the oxidizing gas supply unit 30 is a unit for supplying oxidizing gas (air) to the fuel cell stack 20. The oxidizing gas supply unit 30 includes a compressor 32, an oxidizing gas supply path 34, an oxidizing gas discharge path 36, and a diversion path 38. The compressor 32 is connected to the fuel cell stack 20 via the oxidizing gas supply path 34. The fuel cell stack 20 is connected to the oxidizing gas discharge path 36. The oxidizing gas supply path 34 is connected to the oxidizing gas discharge path 36 via the diversion path 38. A diversion valve (not shown) is provided in the diversion path 38.

[0016] In the above configuration, air taken in from the outside by the compressor 32 is compressed by the compressor 32 and then flows into the fuel cell stack 20 via the oxidizing gas supply path 34. At this time, if a shunt valve provided in the shunt path 38 is opened, part of the air in the oxidizing gas supply path 34 flows into the fuel cell stack 20, and the remaining part of the air in the oxidizing gas supply path 34 flows into the oxidizing gas exhaust path 36 via the shunt path 38. The air that has flowed into the fuel cell stack 20 is discharged to the outside from the oxidizing gas exhaust path 36 together with the air that has joined from the shunt path 38. Although not particularly limited, the oxidizing gas supply unit 30 may further include a pressure regulating valve for adjusting the pressure of the air supplied to the fuel cell stack 20, a back pressure valve for adjusting the pressure of the air discharged from the fuel cell stack 20 (i.e., the back pressure), and the like.

[0017] As shown in FIG. 1, the fuel gas supply unit 40 is a unit for supplying fuel gas (mainly hydrogen gas) to the fuel cell stack 20. The fuel gas supply unit 40 includes a fuel gas tank 42, a fuel gas supply path 44, a supply control valve 46, an exhaust / drain path 48, a gas / liquid separator 50, a circulation path 52, a pump 54, and an exhaust / drain valve 56. The fuel gas tank 42 stores fuel gas (mainly hydrogen gas). The fuel gas tank 42 is connected to a supply port 20a of the fuel cell stack 20 via the fuel gas supply path 44. The supply port 20a of the fuel cell stack 20 is connected to each of the multiple fuel cell cells 22 in the fuel cell stack 20. The fuel gas supply path 44 is provided with a supply control valve 46. Although not limited to this, the supply control valve 46 is an injector valve or a solenoid valve. The exhaust port 20b of the fuel cell stack 20 is connected to the exhaust / drain path 48. The exhaust port 20b of the fuel cell stack 20 is connected to each of the plurality of fuel cell units 22 within the fuel cell stack 20. An exhaust drainage valve 56 is provided in the exhaust drainage path .

[0018] The circulation path 52 branches off from the exhaust drainage path 48 and extends to the fuel gas supply path 44. A gas-liquid separator 50 is provided at the position where the circulation path 52 branches off from the exhaust drainage path 48. A pump 54 is provided in the circulation path 52. The pump 54 rotates forward to form a flow from the exhaust drainage path 48 to the fuel gas supply path 44. As a result, the off-gas discharged from the exhaust port 20b of the fuel cell stack 20 passes through the gas-liquid separator 50, and then circulates through the circulation path 52 to the fuel gas supply path 44.

[0019] As one example, the pump 54 is a pump equipped with an impeller that can be rotated in reverse using a three-phase AC motor, and a Westco type, Roots type, scroll type pump, or the like can be adopted. Therefore, the control device 60 can control the AC current of the motor to rotate the impeller of the pump 54 forward and reverse, and can also control the rotation speed of the forward and reverse rotations. In this specification, rotating the pump 54 forward and reverse includes rotating the impeller of the pump 54 forward and reverse.

[0020] In the above configuration, when the supply control valve 46 is opened, the fuel gas supplied from the fuel gas tank 42 passes through the fuel gas supply path 44 and is delivered to the supply port 20a of the fuel cell stack 20. In addition, off-gas discharged from the exhaust port 20b of the fuel cell stack 20 joins the fuel gas supply path 44 from the circulation path 52. As a result, the fuel gas supplied from the fuel gas tank 42 is supplied to the fuel cell stack 20 together with the off-gas joined from the circulation path 52.

[0021] The fuel gas supplied to the fuel cell stack 20 is discharged as off-gas from the exhaust port 20b after the reaction in the fuel cell stack 20. The discharged off-gas flows into the gas-liquid separator 50 through the exhaust drainage path 48. In the gas-liquid separator 50, water and a part of the off-gas generated by the chemical reaction in the fuel cell stack 20 are removed. The water and a part of the off-gas are discharged to the outside from the exhaust drainage path 48 by opening the exhaust drainage valve 56. On the other hand, the remaining off-gas from which the water has been removed is supplied to the circulation path 52. By forwardly rotating the pump 54 provided in the circulation path 52, the remaining off-gas is sent to the fuel gas supply path 44. Therefore, as described above, the remaining off-gas is circulated to the fuel gas supply path 44 through the circulation path 52. In this way, in the fuel cell system 10, the off-gas is reused in the fuel cell stack 20.

[0022] As shown in FIG. 1, the control device 60 is a computer device having a processor, a memory, and the like. The control device 60 is communicably connected to each of the fuel cell stack 20, the compressor 32 of the oxidizing gas supply unit 30, the supply control valve 46 of the fuel gas supply unit 40, and the pump 54, and can control and monitor their operations. The control device 60 calculates the power required for the fuel cell stack 20 based on the power required from the outside. Based on the calculated power required, the control device 60 controls each of the compressor 32, the supply control valve 46, and the pump 54. As a result, the pressure of the air and the pressure of the fuel gas supplied to the fuel cell stack 20 are controlled, and the output power from the fuel cell stack 20 is adjusted to the above-mentioned power required. The control device 60 can also control the opening and closing of the exhaust drain valve 56. Although the details will be described later, the control device 60 is configured to be able to execute a process of replacing the residual gas in the fuel cell stack 20 with fuel gas, i.e., a fuel gas replacement process, when the fuel cell stack 20 is started. The control device 60 may be configured as a single computer device, or may be configured as a combination of multiple computer devices.

[0023] Next, the fuel gas replacement process executed by the control device 60 will be described with reference to Figures 2 and 3. When the control device 60 receives a start command for the fuel cell stack 20 from the outside, it executes the fuel gas replacement process shown in Figure 2. In this fuel gas replacement process, when the fuel cell system 10 is started in an environment of 0 degrees or less, fuel gas is supplied from the fuel gas supply path 44 to the supply port 20a of the fuel cell stack 20, and residual gas in the fuel cell stack 20 is discharged from the exhaust drainage path 48. Then, by operating the fuel cell system 10 after the hydrogen gas concentration in the fuel cell stack 20 reaches or exceeds a predetermined value, deterioration of the fuel cell stack 20 can be avoided or suppressed.

[0024] 2, the control device 60 first determines whether the temperature of the fuel cell stack 20 is below 0 degrees (step S10). As one example, the temperature of the fuel cell stack 20 refers to the temperature of the water discharged from the exhaust port 20b of the fuel cell stack 20. If the answer is NO in step S10, the control device 60 ends the fuel gas replacement process. Note that in other embodiments, instead of the temperature of the water discharged from the exhaust port 20b of the fuel cell stack 20, the temperature of each fuel cell unit 22 in the fuel cell stack 20 may be used as the temperature of the fuel cell stack 20.

[0025] If the answer is YES in step S10, the control device 60 opens the supply control valve 46 (step S12) and opens the exhaust drain valve 56 (step S14). Furthermore, the control device 60 determines the reverse rotation speed for rotating the pump 54 in the reverse direction (step S16), and operates the pump 54 at the determined reverse rotation speed. As described above, the control device 60 can rotate the pump 54 provided in the circulation path 52 in the reverse direction at any rotation speed.

[0026] When the supply control valve 46 is opened, fuel gas is supplied from the fuel gas tank 42 to the supply port 20a of the fuel cell stack 20, and residual gas in the fuel cell stack 20 is discharged from the exhaust port 20b to the exhaust drainage path 48. The residual gas in the exhaust drainage path 48 passes through the gas-liquid separator 50 and is discharged to the outside through the exhaust drainage valve 56. At this time, since the pump 54 is rotating in reverse in the circulation path 52, the residual gas in the exhaust drainage path 48 is prohibited or suppressed from flowing from the gas-liquid separator 50 into the circulation path 52. As a result, the residual gas discharged from the fuel cell stack 20 is prohibited or suppressed from flowing into the fuel cell stack 20 through the circulation path 52.

[0027] The reverse rotation speed of the pump 54 when rotating in reverse may be a fixed value or may be a value that is appropriately determined taking into account various factors. As an example, the control device 60 of this embodiment is configured to determine the reverse rotation speed of the pump 54 according to the supply flow rate of the fuel gas supplied to the fuel cell stack 20. In detail, in step S12 of FIG. 2, the control device 60 controls the operation of the supply control valve 46 according to the pressure of the fuel gas in the fuel cell stack 20. As a result, the supply flow rate of the fuel gas by the supply control valve 46 is adjusted so that the pressure of the fuel gas in the fuel cell stack 20 becomes a predetermined target pressure. Then, in step S16 of FIG. 2, the control device 60 determines the target reverse rotation speed of the pump 54 according to the supply flow rate of the fuel gas by the supply control valve 46.

[0028] As shown in FIG. 3, the greater the supply flow rate of the fuel gas supplied to the fuel cell stack 20 by the supply control valve 46, the greater the reverse rotation speed of the pump 54 is set to. A rotation speed sufficient to prevent the residual gas discharged from the fuel cell stack 20 to the exhaust drainage path 48 from flowing into the circulation path 52 is adopted as the reverse rotation speed of the pump 54. The reverse rotation speed of the pump 54 is preferably a rotation speed that does not prevent the residual gas discharged from the fuel cell stack 20 to the exhaust drainage path 48 from being discharged to the outside through the exhaust drainage valve 56. The relationship between the supply flow rate of the fuel gas supplied to the fuel cell stack 20 and the reverse rotation speed of the pump 54 may be determined based on a map obtained experimentally, or may be determined by a calculation formula determined by simulation or the like. The supply flow rate of the fuel gas supplied to the fuel cell stack 20 may be an actual measurement value obtained by measuring the flow rate of the fuel gas supplied to the fuel cell stack 20, or may be an estimated value obtained by estimating the flow rate of the fuel gas based on the control of the supply control valve 46 by the control device 60.

[0029] Next, the control device 60 judges whether the fuel gas concentration (here, hydrogen gas concentration) in the fuel cell stack 20 is equal to or higher than a predetermined value (step S20). The predetermined value here is, for example, 95 percent. The fuel gas concentration in the fuel cell stack 20 may be an estimated value estimated based on the control of the supply control valve 46 and the exhaust / drain valve 56 by the control device 60, the amount of power generated in the fuel cell stack 20, etc., or may be an actual value measured by a sensor or the like. If NO in step S20, the control device 60 returns to the process of step S12. Although not particularly limited, the control device 60 may change the opening degree of the supply control valve 46 and the exhaust / drain valve 56, the reverse rotation speed of the pump 54, etc., when executing the processes from step S12 to step S18 again.

[0030] If the answer is YES in step S20, the controller 60 closes the supply control valve 46 and the exhaust drain valve 56, and stops the pump 54 (step S22), thereby completing the fuel gas replacement process.

[0031] 2, in the fuel gas replacement process, the supply control valve 46 is operated to supply fuel gas to the fuel cell stack 20, and the exhaust drain valve 56 is opened to discharge residual gas in the fuel cell stack 20 to the outside. At this time, the pump 54 provided in the circulation path 52 rotates in reverse, preventing the residual gas from circulating to the fuel cell stack 20. In other words, during the fuel gas replacement process, only the fuel gas supplied by opening the supply control valve 46 can be supplied to the fuel cell stack 20. This allows the fuel gas replacement process to be completed in a short time.

[0032] In step S16 in FIG. 2 described above, the control device 60 may determine the rotation speed at which the pump 54 is rotated in reverse to be equal to or lower than a predetermined upper limit value, regardless of the supply flow rate of the fuel gas. As an example, the rotation speed of the pump 54 that generates the maximum discharge flow rate of the exhaust drain valve 56 can be adopted as the predetermined upper limit value. With this configuration, it is possible to prevent the fuel gas supplied from the fuel gas supply path 44 from flowing back from the circulation path 52 through the exhaust drain path 48 to the fuel cell stack 20. In other words, the technology according to this specification does not necessarily prevent the fuel gas in the fuel gas supply path 44 from flowing into the circulation path 52 when the pump 54 is rotated in reverse.

[0033] Although several specific examples have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical usefulness alone or in combination. [Explanation of symbols]

[0034] 10: Fuel cell system 20: Fuel cell stack 20a: Supply port 20b: Outlet 22: Fuel cell 30: Oxidizing gas supply unit 32: Compressor 34: Oxidizing gas supply path 36: Oxidizing gas exhaust route 38: Diversion route 40: Fuel gas supply unit 42: Fuel gas tank 44: Fuel gas supply route 46: Supply control valve 48: Exhaust drainage route 50: Gas-liquid separator 52:Circulation route 54: Pump 56: Exhaust drain valve 60: Control device

Claims

1. A fuel cell stack; a fuel gas supply path connected to a supply port of the fuel cell stack and having a supply control valve; an exhaust drainage path connected to an exhaust port of the fuel cell stack and having an exhaust drainage valve; a circulation path extending from the exhaust drainage path to the fuel gas supply path, for circulating the off-gas discharged from the fuel cell stack to the fuel gas supply path; a pump that is provided in the circulation path and rotates in a forward direction to send the off-gas to the fuel gas supply path; a control device capable of executing a fuel gas replacement process at the start of the fuel cell stack by controlling the operation of the supply control valve, the pump, and the exhaust / drain valve; Equipped with the fuel gas replacement process is a process of opening the supply control valve and rotating the pump in a reverse direction while opening the exhaust drain valve, During the fuel gas replacement process, the control device adjusting the flow rate of the fuel gas supplied to the fuel cell stack by controlling the operation of the supply control valve so that the pressure of the fuel gas in the fuel cell stack becomes a predetermined target pressure; determining a rotation speed at which the pump is rotated in reverse in accordance with the adjusted fuel gas supply flow rate supplied to the fuel cell stack; and Fuel cell system.

2. 2. The fuel cell system according to claim 1, wherein the control device determines the rotation speed at which the pump is rotated in reverse to be equal to or lower than a predetermined upper limit value, regardless of the fuel gas supply flow rate.

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