JP2024012923A - Fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2024,JPO&INPIT

Description

The technology disclosed herein relates to a fuel cell system.

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

Japanese Patent Application Publication No. 2007-220425

In a fuel cell system, for example, when operating at a low temperature below freezing, if the fuel gas concentration (e.g. hydrogen gas concentration) in the residual gas present in the fuel cell stack decreases, the fuel cell stack will deteriorate. There is a risk. Therefore, especially in environments below freezing, when starting the fuel cell system, a process is performed to replace the residual gas in the fuel cell stack with fuel gas (hereinafter referred to as fuel gas replacement process), and the fuel cell It is preferable to increase the fuel gas concentration within the stack.

In the fuel gas replacement process, while supplying fuel gas to the fuel cell stack from the fuel gas supply path, 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 circulation of the discharged residual gas is prohibited. However, even if the pump in the circulation path is stopped, there is a gap inside the pump, so there is a risk that residual gas flowing out from the fuel cell stack may flow into the fuel gas supply path through the circulation path. In this case, a portion of the residual gas is circulated without being discharged to the outside, which increases the time required for the fuel gas replacement process. In order to avoid this, it is possible to provide a cutoff valve in the circulation path, but there are problems in that the pressure loss in the cutoff valve becomes large and that the configuration of the fuel cell system becomes complicated.

In view of the above circumstances, the present specification provides a technique for completing fuel gas replacement processing in a short time without complicating the configuration of the fuel cell system.

The technology disclosed in this specification is embodied in a fuel cell system. In the 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, and an exhaust gas supply path of the fuel cell stack. an exhaust drainage path connected to the outlet and provided with an exhaust drainage valve; and an exhaust drainage path extending from the exhaust drainage path to the fuel gas supply path, the off-gas discharged from the fuel cell stack being transferred 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 rotating in the forward direction, the supply control valve, the pump, and the exhaust drainage valve. and a control device capable of executing fuel gas replacement processing at the time of startup of the fuel cell stack by controlling the operation of the fuel cell stack. In the fuel gas replacement process, the control device opens the supply control valve and reversely rotates the pump with the exhaust and drain valve open.

In the above-described fuel gas replacement process, while supplying fuel gas to the fuel cell stack from the fuel gas supply path, 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 the reverse direction, it is possible to prevent the residual gas that has flowed out of the fuel cell stack from flowing into the fuel cell stack through the circulation path. Thereby, 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.

In a second aspect, in the first aspect, the control device controls 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. You may decide. If the rotation speed when rotating the pump in reverse is too low, the circulation of residual gas through the circulation path cannot be sufficiently suppressed. On the other hand, if the rotation speed when rotating the pump in reverse is too high, the fuel gas in the fuel gas supply path will flow back through the circulation path to the exhaust drainage path, blocking the flow of residual gas discharged from the fuel cell stack. Put it away. In this regard, the appropriate rotational speed for reverse rotation of the pump 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 to just the right amount by determining the rotational speed of the pump depending on the fuel gas supply flow rate.

In a third aspect, in the first or second aspect, the control device may determine the rotation speed at which the pump is reversely rotated to be equal to or lower than a predetermined upper limit value, regardless of the fuel gas supply flow rate. According to such a configuration, it is possible to prevent the fuel gas in the fuel gas supply path from flowing back from the circulation path to the fuel cell stack through the exhaust drainage path.

1 is a diagram schematically showing the configuration of a fuel cell system 10 according to an example. FIG. 6 is a flow diagram showing an example of a hydrogen gas replacement process executed by the control device 60. FIG. 5 is a diagram showing an example of the relationship between the supply flow rate of fuel gas and the reverse rotation speed of the pump 54. FIG. Note that NL (normal liter)/min, which is the unit of fuel gas supply flow rate, is one minute measured at atmospheric pressure (i.e., pressure 0.1013 MPa), temperature 0 degrees, and relative humidity 0 percent. means the gas flow rate per. Further, regarding the reverse rotation speed of the pump 54, when the reverse rotation speed is a positive value, it means that the pump 54 rotates in the reverse direction.

A fuel cell system 10 according to an embodiment will be described with reference to the drawings. The fuel cell system 10 of this embodiment is installed in a fuel cell vehicle (for example, a car, a bus, a truck, a train), a stationary fuel cell device, or the like. Note that the fuel cell system 10 may be mounted on various types of moving bodies (for example, ships and airplanes) other than vehicles.

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 cells 22 are stacked. The fuel cell stack 20 generates electricity by chemically reacting oxidizing gas and fuel gas within a plurality of fuel cells 22 . In the fuel cell system 10 of this embodiment, air is used as the oxidizing gas, and gas containing hydrogen gas at a high concentration is used as the fuel gas.

Note that the specific configuration of the fuel cell 22 is not particularly limited. Although not shown, each fuel cell 22 includes, for example, a membrane electrode and gas diffusion layer assembly (MEGA), an anode separator, a cathode separator, and a support frame. The membrane electrode gas diffusion layer assembly is constructed by laminating an anode gas diffusion layer, an anode electrode, an electrolyte membrane, a cathode electrode, and a cathode gas diffusion layer in this order.

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 exhaust path 36 , and a branch path 38 . The compressor 32 is connected to the fuel cell stack 20 via an oxidizing gas supply path 34. The fuel cell stack 20 is connected to an oxidizing gas exhaust path 36. The oxidizing gas supply path 34 is connected to the oxidizing gas exhaust path 36 via a branch path 38. The diversion path 38 is provided with a diversion valve (not shown).

In the above configuration, air taken into the compressor 32 from the outside 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 the diversion valve provided in the diversion path 38 is opened, part of the air in the oxidant gas supply path 34 flows into the fuel cell stack 20, and the air in the oxidation gas supply path 34 flows into the fuel cell stack 20. The remainder flows into the oxidizing gas discharge path 36 via the branch 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 branch path 38 . Note that, although not particularly limited, the oxidizing gas supply unit 30 includes a pressure regulating valve for regulating the pressure of air supplied to the fuel cell stack 20, and a pressure of air discharged from the fuel cell stack 20 (i.e., back pressure). It may further include a back pressure valve or the like for adjusting the pressure.

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 drainage path 48, a gas-liquid separator 50, a circulation path 52, a pump 54, and an exhaust drainage valve. 56. The fuel gas tank 42 stores fuel gas (mainly hydrogen gas). The fuel gas tank 42 is connected to the supply port 20a of the fuel cell stack 20 via a fuel gas supply path 44. The supply port 20a of the fuel cell stack 20 is connected to each of the plurality of fuel cells 22 within the fuel cell stack 20. A supply control valve 46 is provided in the fuel gas supply path 44 . Although not particularly limited, 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 drainage path 48. The exhaust port 20b of the fuel cell stack 20 is connected to each of the plurality of fuel cells 22 within the fuel cell stack 20. The exhaust drainage path 48 is provided with an exhaust drainage valve 56 .

The circulation path 52 branches from the exhaust drainage path 48 and extends to the fuel gas supply path 44 . A gas-liquid separator 50 is provided at a position where the circulation path 52 branches from the exhaust drainage path 48 . A pump 54 is provided in the circulation path 52 . By rotating forward, the pump 54 forms a flow from the exhaust drainage path 48 to the fuel gas supply path 44 . Thereby, 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.

Although this is just one example, the pump 54 is a pump that uses a three-phase alternating current motor and includes an emperor that can rotate in reverse, and a Wesco type, Roots type, scroll type pump, etc. can be adopted. Therefore, the control device 60 can control the alternating current of the motor to rotate the propeller of the pump 54 in forward and reverse directions, and can also control the rotation speed of the forward and reverse rotations. Note that, in this specification, rotating the pump 54 in forward and reverse directions includes rotating the emperor of the pump 54 in forward and reverse directions.

In the above configuration, when the supply control valve 46 opens, the fuel gas supplied from the fuel gas tank 42 passes through the fuel gas supply path 44 and is sent 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. Thereby, the fuel gas supplied from the fuel gas tank 42 is supplied to the fuel cell stack 20 together with the off-gas that merges from the circulation path 52.

After the fuel gas supplied to the fuel cell stack 20 undergoes a reaction within the fuel cell stack 20, it is discharged from the exhaust port 20b as an off-gas. The discharged off-gas flows into the gas-liquid separator 50 via the exhaust drainage path 48. In the gas-liquid separator 50, water and some off-gas generated by the chemical reaction in the fuel cell stack 20 are removed. The water and a portion 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 water has been removed is supplied to the circulation path 52. By rotating the pump 54 provided in the circulation path 52 in the forward direction, the remaining off-gas is delivered to the fuel gas supply path 44 . Therefore, as described above, the remaining off-gas is circulated through the circulation path 52 to the fuel gas supply path 44 . In this manner, in the fuel cell system 10, off-gas is reused in the fuel cell stack 20.

As shown in FIG. 1, the control device 60 is a computer device including a processor, 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 controls their operations. and can be monitored. The control device 60 calculates the required power to the fuel cell stack 20 based on the externally requested power. Based on the calculated required power, the control device 60 controls each of the compressor 32, supply control valve 46, and pump 54. Thereby, 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 required power. Further, the control device 60 can also control opening and closing of the exhaust and drain valve 56. As will be described in detail later, the control device 60 is configured to be able to perform a process of replacing residual gas in the fuel cell stack 20 with fuel gas, that is, a fuel gas replacement process when the fuel cell stack 20 is started. Note that the control device 60 may be configured with a single computer device or a combination of multiple computer devices.

Next, the fuel gas replacement process executed by the control device 60 will be described with reference to FIGS. 2 and 3. The control device 60 executes the fuel gas replacement process shown in FIG. 2 when receiving a command to start the fuel cell stack 20 from the outside. In this fuel gas replacement process, when starting the fuel cell system 10 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, thereby eliminating exhaust drainage. Residual gas within the fuel cell stack 20 is exhausted from the path 48 . By operating the fuel cell system 10 after the hydrogen gas concentration within the fuel cell stack 20 reaches a predetermined value or more, deterioration of the fuel cell stack 20 can be avoided or suppressed.

As shown in FIG. 2, the control device 60 first determines whether the temperature of the fuel cell stack 20 is 0 degrees or less (step S10). Although this is an example, the temperature of the fuel cell stack 20 means the temperature of water discharged from the discharge port 20b of the fuel cell stack 20. If NO in step S10, the control device 60 ends the fuel gas replacement process. Note that in other embodiments, the temperature of the fuel cell stack 20 may be the temperature of each fuel cell 22 in the fuel cell stack 20 instead of the temperature of water discharged from the outlet 20b of the fuel cell stack 20. May be adopted.

If YES in step S10, the control device 60 opens the supply control valve 46 (step S12) and opens the exhaust drainage 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 reversely rotate the pump 54 provided in the circulation path 52 at an arbitrary rotation speed.

By opening the supply control valve 46, 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 discharge port 20b to the exhaust drainage path 48. be done. The residual gas in the exhaust drainage path 48 passes through the gas-liquid separator 50 and is discharged to the outside from the exhaust drainage valve 56. At this time, since the pump 54 is rotating in the reverse direction in the circulation path 52, the residual gas in the exhaust drainage path 48 is prohibited or suppressed from flowing into the circulation path 52 from the gas-liquid separator 50. Thereby, 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.

The number of reverse rotations when the pump 54 is reversely rotated may be a fixed value, or may be a value that is appropriately determined in consideration of various factors. Although this is just one example, the control device 60 of this embodiment is configured to determine the reverse rotation speed of the pump 54 in accordance with the supply flow rate of fuel gas supplied to the fuel cell stack 20. Specifically, in step S12 in FIG. 2, the control device 60 controls the operation of the supply control valve 46 according to the pressure of the fuel gas within the fuel cell stack 20. As a result, the flow rate of fuel gas supplied by the supply control valve 46 is adjusted so that the pressure of the fuel gas within the fuel cell stack 20 reaches a predetermined target pressure. Then, in step S16 in FIG. 2, the control device 60 determines the target reverse rotation speed of the pump 54 according to the flow rate of fuel gas supplied by the supply control valve 46.

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

Next, the control device 60 determines 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%. The fuel gas concentration within 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 generation in the fuel cell stack 20, etc. It 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 degrees 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. good.

If YES in step S20, the control device 60 closes the supply control valve 46 and the exhaust drainage valve 56, stops the pump 54 (step S22), and ends the fuel gas replacement process.

In the above configuration, in the fuel gas replacement process shown in FIG. 2, 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. , residual gas within the fuel cell stack 20 is discharged to the outside. At this time, the pump 54 provided in the circulation path 52 rotates in the opposite direction, thereby preventing the residual gas from circulating to the fuel cell stack 20. That is, 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. Thereby, the fuel gas replacement process can be completed in a short time.

In step S16 of FIG. 2 described above, the control device 60 may determine the rotation speed at which the pump 54 is rotated in reverse to a predetermined upper limit value or less, regardless of the supply flow rate of the fuel gas. Although this is an example, the rotation speed of the pump 54 that causes the maximum discharge flow rate of the exhaust and drain valve 56 can be adopted as the predetermined upper limit value. According to such a 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 to the fuel cell stack 20 through the exhaust drainage path 48. In other words, the technology according to this specification does not necessarily exclude that the fuel gas in the fuel gas supply path 44 flows into the circulation path 52 when the pump 54 is rotated in the reverse direction.

Although several specific examples have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility alone or in combination.

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

Claims (3)

fuel cell stack,
a fuel gas supply path connected to the supply port of the fuel cell stack and provided with a supply control valve;
an exhaust drainage path connected to the exhaust port of the fuel cell stack and provided with an exhaust drainage valve;
a circulation path that extends from the exhaust drainage path to the fuel gas supply path and circulates off-gas discharged from the fuel cell 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 rotating in the forward direction;
a control device capable of executing fuel gas replacement processing at the time of startup of the fuel cell stack by controlling operations of the supply control valve, the pump, and the exhaust and drain valve;
Equipped with
In the fuel gas replacement process, the control device opens the supply control valve and rotates the pump in the opposite direction with the exhaust and drainage valve open.
fuel cell system. In the fuel gas replacement process, the control device determines 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. , The fuel cell system according to claim 1. 3. The fuel cell system according to claim 2, wherein the control device determines the rotation speed at which the pump is reversely rotated to be equal to or less than a predetermined upper limit value, regardless of the fuel gas supply flow rate.

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