Fuel cell system

Abstract

To provide a fuel cell system which can prevent deterioration of a catalyst in a fuel cell and freezing of a component.SOLUTION: A fuel cell system comprises a fuel cell, a fuel gas system, and a control part. The fuel gas system at least comprises an ejector, a circulation passage, a first supply line, and a second supply line. The circulation passage circulates fuel gas, which is to be supplied from the ejector to the fuel cell, to the ejector via the fuel cell. The first supply line supplies the fuel gas to the ejector. The second supply line supplies the fuel gas to the ejector, and it has a higher circulation gas flow than that of the first supply line.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system.

Background Art

[0002] Regarding fuel cells (FCs) as disclosed in Patent Document 1, various techniques have been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, an ejector and a circulation pump are adopted for hydrogen supply, and a fuel cell system that controls the circulation pump when the temperature is equal to or lower than the equivalent temperature of starting at sub - zero is disclosed. In the prior art, as control at sub - zero start, only suppression of deterioration of the catalyst of the fuel cell is considered, so there is a possibility that components (ejector) will freeze.

[0005] The present disclosure has been made in view of the above circumstances, and the main object is to provide a fuel cell system capable of suppressing deterioration of the catalyst of the fuel cell and freezing of components.

Means for Solving the Problems

[0006] That is, the present disclosure includes the following aspects. <1> A fuel cell system, wherein the fuel cell system includes a fuel cell, a fuel gas system, and a control unit, the fuel gas system includes at least an ejector, a circulation flow path, a first supply line, and a second supply line, The circulation flow path circulates the fuel gas supplied from the ejector to the fuel cell through the fuel cell and back to the ejector. The first supply line supplies the fuel gas to the ejector. The second supply line supplies the fuel gas to the ejector and has a larger circulating gas flow rate than the first supply line. When starting the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is equal to or lower than a predetermined temperature, the control unit supplies the fuel gas to the ejector from the first supply line with a relatively small circulating gas flow rate. When starting the fuel cell system below freezing point, if the temperature of the cooling water is higher than the predetermined temperature, the control unit supplies the fuel gas to the ejector from the second supply line with a relatively large circulating gas flow rate. A fuel cell system.

[0007] <2>A first valve is provided in the first supply line. A second valve is provided in the second supply line. When starting the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is equal to or lower than the predetermined temperature, the control unit opens the first valve. When starting the fuel cell system below freezing point, if the temperature of the cooling water is higher than the predetermined temperature, the control unit opens the second valve. The opening degree when the second valve is opened is smaller than the opening degree when the first valve is opened. The fuel cell system according to <1>.

Advantages of the Invention

[0008] The fuel cell system of the present disclosure can suppress the deterioration of the catalyst of the fuel cell and the freezing of components.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments according to the present disclosure will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present disclosure (for example, general configurations and manufacturing processes of fuel cell systems that do not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field. Also, the dimensional relationships (length, width, thickness, etc.) in the figures do not reflect actual dimensional relationships. In the present disclosure, the gas supplied to the anode of the fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas mainly containing hydrogen and may be hydrogen. The oxidant gas is a gas containing oxygen and may be oxygen, air, etc.

[0011] In the present disclosure, there is provided a fuel cell system, the fuel cell system includes a fuel cell, a fuel gas system, and a control unit, the fuel gas system includes at least an ejector, a circulation flow path, a first supply line, and a second supply line, the circulation flow path circulates the fuel gas supplied from the ejector to the fuel cell through the fuel cell and back to the ejector, the first supply line supplies the fuel gas to the ejector, the second supply line supplies the fuel gas to the ejector and has a larger circulation gas flow rate than the first supply line, When the control unit starts the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is equal to or lower than a predetermined temperature, the fuel gas is supplied from the first supply line with a relatively small circulating gas flow rate to the ejector. When the control unit starts the fuel cell system below freezing point, if the temperature of the cooling water is higher than a predetermined temperature, the fuel gas is supplied from the second supply line with a relatively large circulating gas flow rate to the ejector, providing a fuel cell system.

[0012] The supply of fuel gas to the fuel cell usually includes the supply of fuel gas from a fuel gas tank and the supply of fuel off-gas discharged from the fuel cell as circulating gas. By considering the fuel gas distribution variation with the flow rate of the circulating gas, the necessary amount of fuel gas can be supplied so that the fuel gas can reach each cell in the fuel cell. If the control is such that no circulating gas is generated, fuel gas will be lacking in part of the fuel cell. When generating electricity in a fuel gas lacking state, it will cause performance deterioration of the fuel cell. On the other hand, when starting the fuel cell system below freezing point, the fuel gas in the fuel gas tank becomes below freezing point. When the fuel gas merges with the circulating gas containing cold water vapor in the ejector, the water vapor in the circulating gas may freeze and the ejector may freeze. Also, when starting below freezing point, if no circulating gas is generated, there is a concern about deterioration of the fuel cell due to insufficient fuel gas. In the present disclosure, by switching the fuel gas supply method (the magnitude of the circulating flow rate) according to the state of the fuel cell when starting below freezing point, it is possible to suppress the deterioration of the catalyst and the freezing of components of the fuel cell when starting below freezing point.

[0013] FIG. 1 is a system configuration diagram showing an example of the fuel cell system of the present disclosure. The fuel cell system shown in Fig. 1 includes a fuel cell 10, a fuel gas system 20, and a control unit 50. The fuel gas system 20 includes an ejector 21, a gas-liquid separator 22, an exhaust and drainage valve 23, a first supply line 24, a second supply line 25, and the like. A linear solenoid valve is provided as a first valve 30 with a relatively small circulating gas flow rate in the first supply line 24, and an injector is provided as a second valve 31 with a relatively large circulating gas flow rate in the second supply line 25. In Fig. 1, the oxidant gas system and the cooling system are omitted from the description for the sake of convenience. By setting the opening degree when the second valve 31 is opened to be smaller than the opening degree when the first valve 30 is opened, when supplying fuel gas from the second supply line 25 to the ejector 21, the supply amount of fuel gas to the ejector 21 is less than when supplying fuel gas from the first supply line 24 to the ejector 21. Thereby, in the second supply line 25, the flow rate of the circulating gas circulating through the fuel cell 10 may be made larger than the flow rate of the fuel gas supplied from a fuel gas tank (not shown) to the ejector 21.

[0014] The fuel cell system of the present disclosure may be mounted on a moving body such as a vehicle and used. Further, the fuel cell system of the present disclosure may be mounted on a stationary power generation system such as a generator that supplies power to the outside of the fuel cell system and used. The vehicle may be a fuel cell vehicle or the like. Examples of moving bodies other than vehicles include railways, ships, and airplanes. Further, the fuel cell system of the present disclosure may be mounted on a moving body such as a vehicle that can also run on the power of a secondary battery and used. The moving body and the stationary power generation system may include the fuel cell system of the present disclosure. The moving body may have a drive unit such as a motor, an inverter, and a hybrid control system. The hybrid control system may be capable of running the moving body by using the output of the fuel cell and the power of the secondary battery in combination.

[0015] A fuel cell system includes a fuel cell in which hydrogen and oxygen react to generate electricity, a fuel gas system that supplies a fuel gas containing hydrogen necessary for power generation of the fuel cell to the fuel cell, and a control unit. The fuel cell system usually further includes an oxidant gas system that supplies an oxidant gas containing oxygen to the fuel cell, a cooling system that supplies cooling water for cooling the heat generated by power generation to the fuel cell, and the like.

[0016] The fuel cell may have only one single cell of the fuel cell, or may be a fuel cell stack (stack) that is a laminate of a plurality of single cells. In the present disclosure, both the single cell and the fuel cell stack may be referred to as a fuel cell in some cases. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, 2 to several hundred. The fuel cell stack may have a current collector plate, a pressure plate, etc. at the ends in the stacking direction.

[0017] The single cell may have a power generation part. The shape of the power generation part may be rectangular in plan view. The power generation part may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing moisture, and hydrocarbon-based electrolyte membranes. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont). One of the two electrodes is an anode (fuel electrode), and the other is a cathode (oxidant electrode). The electrode includes a catalyst layer, and may include a gas diffusion layer as necessary, and the power generation part may be a membrane electrode gas diffusion layer assembly (MEGA). The catalyst layer includes a catalyst, and the catalyst may include a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, a carrier having electron conductivity, and the like. As the catalyst metal, for example, platinum (Pt), an alloy composed of Pt and other metals (for example, a Pt alloy mixed with cobalt, nickel, etc.) can be used. The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different. As the electrolyte, a fluororesin or the like may be used. As the fluororesin, for example, Nafion solution or the like may be used. The above catalyst metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supported carrier) and the electrolyte may be mixed. Examples of the carrier for supporting the catalyst metal include carbon materials such as generally commercially available carbon. The gas diffusion layer may be a conductive member having pores or the like. Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous members such as metal mesh and foamed metal. The single cell of the fuel cell may include a separator. The separator collects the current generated by power generation and functions as a partition. In the single cell of the fuel cell, usually, a pair of separators are arranged on both sides in the stacking direction of the power generation part so as to sandwich the power generation part. One of the pair of separators is an anode separator, and the other is a cathode separator. The anode separator may have a groove serving as a fuel gas flow path on the surface on the power generation part side. The cathode separator may have a groove serving as an oxidant gas flow path on the surface on the power generation part side. The separator may have holes constituting a manifold such as supply holes and discharge holes for allowing a fluid to flow in the stacking direction of the cell. Examples of the separator include dense carbon obtained by compressing carbon to make it gas-impermeable, and press-molded metals (for example, iron, titanium, stainless steel, etc.). The single cell may include an insulating resin frame disposed on the outer side (outer periphery) in the plane direction of the membrane electrode assembly between the anode separator and the cathode separator. The resin frame is formed into a plate-like and frame-like shape using a thermoplastic resin, and seals the space between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. As the resin frame, for example, resins such as PE, PP, PET, and PEN can be used. The resin frame may be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0018] The fuel gas system supplies fuel gas to the fuel cell and adjusts the flow rate of the fuel gas. The fuel gas system includes at least an ejector, a circulation flow path, a first supply line, and a second supply line, and may optionally include a fuel gas tank, a gas-liquid separator, an exhaust and drainage valve, a fuel gas pump for fuel gas circulation, etc. The ejector may be disposed at the confluence of the first supply line and the second supply line on the circulation flow path. The ejector may have two nozzles with different flow rates of the circulation gas, such as different diameters of the injection ports. The circulation flow path circulates the fuel gas supplied from the ejector to the fuel cell back to the ejector via the fuel cell. That is, the fuel off-gas discharged from the fuel cell is circulated to the ejector as the circulation gas. The first supply line supplies the fuel gas to the ejector. The second supply line supplies the fuel gas to the ejector and has a larger circulation gas flow rate than the first supply line. The supply amount of the fuel gas in the second supply line may be the same as or less than the supply amount of the fuel gas in the first supply line. A first valve may be provided in the first supply line. A second valve may be provided in the second supply line. The opening degree when the second valve is opened may be smaller than the opening degree when the first valve is opened. The first valve may be a fuel gas supply valve to the nozzle with a relatively small flow rate of the circulating gas among the two nozzles with different flow rates of the circulating gas of the ejector. The second valve may be a fuel gas supply valve to the nozzle with a relatively large flow rate of the circulating gas among the two nozzles with different flow rates of the circulating gas of the ejector. The first valve and the second valve may be those capable of individually controlling the opening / closing and opening degree of the valve, such as an injector and a linear solenoid valve. By controlling the valve opening of the first valve and the second valve, a first supply line with a relatively large supply amount of fuel gas and a second supply line with a relatively small supply amount of fuel gas may be provided.

[0019] The oxidant gas system supplies the fuel cell with the oxidant gas and adjusts the flow rate of the oxidant gas. The oxidant gas system may include an oxidant gas supply means, a flow path for the oxidant gas, an inlet side sealing valve at the oxidant gas inlet of the fuel cell, and an outlet side sealing valve at the oxidant gas outlet of the fuel cell. The oxidant gas supply means may be an air compressor or the like.

[0020] The cooling system supplies cooling water as a cooling medium to the fuel cell. The cooling water may include water, ethylene glycol, etc., and may be a mixture thereof. The cooling system may include a cooling water pump, a cooling flow path, a radiator, a bypass flow path, a rotary valve, a reserve tank, an ion exchanger, an intercooler, and a cooling water temperature sensor. The cooling water pump circulates the cooling water for cooling the fuel cell and adjusts the flow rate of the cooling water supplied to the fuel cell. The reserve tank is a tank that temporarily stores the cooling water overflowing from the cooling flow path whose internal pressure has increased due to the temperature rise of the cooling water. The cooling flow path is a flow path that circulates the cooling water for cooling the fuel cell inside and outside the fuel cell. The radiator is arranged on the cooling flow path and cools the cooling water. The bypass passage branches off from the cooling passage upstream of the radiator of the cooling passage, bypasses the radiator, and merges with the cooling passage downstream of the radiator of the cooling passage. The rotary valve is disposed at the branch point between the bypass passage of the cooling passage, and performs a flow path switching to switch whether to flow the cooling water discharged from the fuel cell to the radiator or to the bypass passage. The rotary valve may include an electric motor such as an electric actuator for performing the flow path switching. The cooling water temperature sensor measures the temperature of the cooling water. The temperature of the cooling water may be the temperature of the cooling water discharged from the cooling water outlet of the fuel cell (cooling water outlet temperature).

[0021] The fuel cell system may include a secondary battery. The secondary battery may be any rechargeable battery, and examples include conventionally known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. Further, the secondary battery may include a power storage element such as an electric double layer capacitor. The secondary battery may be configured with a plurality of them connected in series. The secondary battery supplies power to an air compressor or the like. The secondary battery may be rechargeable from an external power source of the fuel cell system such as a household power supply, for example. The secondary battery may be charged by the output of the fuel cell. The charging and discharging of the secondary battery may be controlled by the control unit.

[0022] The fuel cell system includes a control unit. The control unit may control the fuel gas system, the oxidant gas system, the cooling system, etc., and control the entire fuel cell system. Physically, the control unit is, for example, an arithmetic processing device such as a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a control program and control data processed by the CPU, and a RAM (Random Access Memory) mainly used as various work areas for control processing. And a storage device such as, and an input / output interface, and may be an ECU (Electronic Control Unit) or the like.

[0023] When starting the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is equal to or lower than a predetermined temperature, the control unit supplies fuel gas to the ejector from the first supply line with a relatively small circulating gas flow rate. When starting the fuel cell system below freezing point, if the temperature of the cooling water is higher than a predetermined temperature, the control unit supplies fuel gas to the ejector from the second supply line with a relatively large circulating gas flow rate. When starting the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is equal to or lower than a predetermined temperature, the control unit may open the first valve with a relatively small circulating gas flow rate. When starting the fuel cell system below freezing point, if the temperature of the cooling water of the fuel cell is higher than a predetermined temperature, the control unit may open the second valve with a relatively large circulating gas flow rate. The control unit may make the opening degree when the second valve is opened smaller than the opening degree when the first valve is opened.

[0024] The fuel cell system may be provided with an outside air temperature sensor. The outside air temperature sensor measures the outside air temperature when starting the fuel cell system. When the outside air temperature is below freezing point, the control unit may determine that it is the time to start the fuel cell system below freezing point. When the temperature of the cooling water of the fuel cell is below freezing point, the control unit may determine that it is the time to start the fuel cell system below freezing point.

[0025] FIG. 2 is a time chart showing an example of the control of the fuel cell system of the present disclosure. Until the temperature of the cooling water of the fuel cell reaches a predetermined value (for example, 50 ° C), fuel gas is supplied by the first valve with a relatively small circulating gas flow rate in the first supply line, and the inflow of water vapor is suppressed by reducing the circulation of the circulating gas, thereby suppressing the formation of ice in the flow path. After the temperature of the cooling water of the fuel cell reaches or exceeds the predetermined value, fuel gas is supplied by the second valve with a relatively large circulating gas flow rate in the second supply line, and freezing in the flow path is avoided by supplying circulating gas at a sufficient temperature. After the warm-up is completed, the supply of the circulating gas to the fuel cell is continued to avoid a shortage of fuel gas in the fuel cell and to avoid deterioration of the fuel cell.

[0026] Since there is an appropriate range for the timing of switching from the first supply line to the second supply line, it is defined within that range. In order to suppress the freezing of the ejector and the deterioration of the fuel cell, it is defined within a range where the following three items can be achieved simultaneously. [Amount of ice adhering to the ejector] When the temperature is too low, the circulating gas containing cold water vapor before the fuel cell warms up flows into the ejector, and the inside of the ejector freezes (ice adheres to the confluence part). If the amount of ice is large, the ejector becomes dysfunctional (unable to circulate). Switch at a timing when the amount of ice is below the level at which dysfunction occurs. [Circulating gas flow rate (circulating gas stoichiometric ratio)] As described above, when the amount of ice adhering to the ejector increases, the circulating gas flow rate decreases. Since there is a concern about the deterioration of the fuel cell due to fuel shortage, the circulating gas flow rate is controlled so that it is equal to or higher than the required circulating gas flow rate (circulating gas stoichiometric ratio). [Dry state of the fuel cell] The circulation of the fuel gas also serves to humidify the inside of the fuel cell. By circulating the moisture generated inside the fuel cell, the water balance of the fuel cell is adjusted. If the fuel cell is operated without circulating the fuel gas, the fuel cell becomes too dry, leading to the deterioration of the fuel cell. The dry state (water content) of the fuel cell is correlated with the impedance, and the circulating gas flow rate is controlled so that it is within the impedance range that does not lead to the deterioration of the fuel cell.

[0027] As a method for setting the predetermined temperature, a data group showing the relationship between the temperature of the cooling water of the fuel cell at the switching timing, the amount of ice adhering to the ejector, the circulating gas stoichiometric ratio, and the water content of the fuel cell is prepared in advance. From the data group, the temperature of the cooling water of the fuel cell within the criteria for all items may be set as the predetermined temperature. The predetermined temperature may be within the range of 40°C to 60°C.

[0028] As parameters that can be used to determine the timing of switching from the first supply line to the second supply line other than the temperature of the cooling water of the fuel cell, the elapsed time since starting from sub-zero start, the integrated value of the heat generation amount of the fuel cell, the temperature increase rate of the fuel cell, etc. can be used. When the heat generation amount of the fuel cell is low, the switching timing may be delayed, and when the temperature increase rate of the fuel cell is high, the switching timing may be advanced.

[0029] Figure 3 is a flowchart showing an example of the control of the fuel cell system of the present disclosure. The control unit determines whether or not the temperature measured by the cooling water temperature sensor is below zero at the start of operation of the fuel cell system. If the temperature measured by the cooling water temperature sensor is not below zero, the control unit starts the normal operation of the fuel cell. On the other hand, if the temperature measured by the cooling water temperature sensor is below zero, the control unit determines that it is at the time of starting the fuel cell system below zero. At the time of starting the fuel cell system below zero, the control unit determines whether or not the temperature of the cooling water of the fuel cell is below a predetermined temperature. When the temperature of the cooling water of the fuel cell is higher than the predetermined temperature, the control unit supplies fuel gas from the second supply line with a relatively large circulation gas flow rate to the ejector, increases the flow rate of the circulation gas, and ends the control. On the other hand, when the temperature of the cooling water of the fuel cell is below the predetermined temperature, the control unit supplies fuel gas from the first supply line with a relatively small circulation gas flow rate to the ejector, decreases the flow rate of the circulation gas, and ends the control.

[0030] After the control unit ends the control by decreasing the flow rate of the circulation gas, it may determine again whether or not the temperature of the cooling water of the fuel cell is below the predetermined temperature after a predetermined period has elapsed or continuously. Instead of re-determining the temperature of the cooling water of the fuel cell, the control unit may perform at least one of a determination as to whether or not a predetermined time has elapsed since starting from sub-zero start, a determination as to whether or not the integrated value of the heat generation amount of the fuel cell is equal to or greater than a predetermined integrated value of the heat generation amount, and a determination as to whether or not the temperature increase rate of the fuel cell is equal to or greater than a predetermined temperature increase rate. When at least one of the following conditions is satisfied: when the temperature of the cooling water of the fuel cell is higher than a predetermined temperature, when the elapsed time since the sub-zero start has passed a predetermined time, when the integrated heat generation value of the fuel cell is equal to or greater than a predetermined integrated heat generation value, and when the temperature increase rate of the fuel cell is equal to or greater than a predetermined temperature increase rate, the control unit switches the supply of fuel gas to the ejector from the first supply line to the second supply line.

Description of Signs

[0031] 10. Fuel cell 20. Fuel gas system 21. Ejector 22. Gas-liquid separator 23. Exhaust and drain valve 24. First supply line 25. Second supply line 30. First valve 31. Second valve 50. Control unit

Claims

1. A fuel cell system, wherein the fuel cell system includes a fuel cell, a fuel gas system, and a control unit, the fuel gas system includes at least an ejector, a circulation flow path, a first supply line, and a second supply line, the circulation flow path circulates the fuel gas supplied from the ejector to the fuel cell back to the ejector via the fuel cell, the first supply line supplies the fuel gas to the ejector, the second supply line supplies the fuel gas to the ejector and has a larger circulating gas flow rate than the first supply line, when starting below freezing point of the fuel cell system, when the temperature of the cooling water of the fuel cell is equal to or lower than a predetermined temperature, the control unit supplies the fuel gas to the ejector from the first supply line with a relatively small circulating gas flow rate, when starting below freezing point of the fuel cell system, when the temperature of the cooling water is higher than the predetermined temperature, the control unit supplies the fuel gas to the ejector from the second supply line with a relatively large circulating gas flow rate. A fuel cell system.

2. A first valve is provided in the first supply line, a second valve is provided in the second supply line, when starting below freezing point of the fuel cell system, when the temperature of the cooling water of the fuel cell is equal to or lower than the predetermined temperature, the control unit opens the first valve, when starting below freezing point of the fuel cell system, when the temperature of the cooling water is higher than the predetermined temperature, the control unit opens the second valve, The opening degree when the second valve is opened is smaller than the opening degree when the first valve is opened. The fuel cell system according to claim 1.

Images