JP5262125B2 - Fuel cell system and fuel cell operating method - Google Patents

Description

  The present invention relates to a fuel cell system and a fuel cell operating method.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. This fuel cell is environmentally superior and can realize high energy efficiency, and therefore has been widely developed as a future energy supply system. In particular, since the polymer electrolyte fuel cell operates at a relatively low temperature among various types of fuel cells, it has a good startability. For this reason, research has been actively conducted for practical application in various fields.

  A polymer electrolyte fuel cell has a membrane-electrode assembly (MEA) in which an anode and a cathode are provided on both sides of an electrolyte membrane made of a solid polymer electrolyte having proton conductivity, respectively, by means of a separator. It has a sandwiched structure.

  When this fuel cell is started below freezing point, the water generated at the cathode may freeze, reducing the effective power generation area. Therefore, a technique for gradually warming up the fuel cell by intermittently flowing a refrigerant at the time of starting below sub-freezing is disclosed (for example, see Patent Document 1).

JP 2005-276568 A

  However, in the technique of Patent Document 1, the power generation electrode of the fuel cell is frozen as a whole, the effective power generation area is reduced, and there is a possibility that the time until startup becomes longer.

  An object of the present invention is to provide a fuel cell system and a fuel cell operating method that can efficiently start a fuel cell at the time of starting below freezing.

A fuel cell system according to the present invention supplies a refrigerant from an inlet of a refrigerant channel provided in a fuel cell stack in which a plurality of polymer electrolyte fuel cells are stacked and collects the refrigerant from an outlet of the refrigerant channel. and circulation means for circulating the inlet, when the average temperature of a fuel cell stack is less than 0 ℃ by start power generation in the fuel cell stack coolant is circulated through the circulating means, the average temperature of a fuel cell stack in the power generation 0 And a control means for controlling the circulation means so that the amount of heat removed from the fuel cell by the refrigerant in a predetermined period from before exceeding 0 ° C. to exceeding 0 ° C. is provided.

  In the fuel cell system according to the present invention, the temperature of the cathode catalyst layer is efficiently reduced by reducing the amount of heat removed by the refrigerant during the period from the freezing point to the average temperature of the fuel cell during power generation exceeding 0 ° C. Can exceed 0 ° C. Thereby, frozen moisture can be thawed and an effective power generation area can be secured. As a result, the fuel cell can be started up efficiently and the output after startup can be recovered early.

  The control means may control the circulation means so that the flow rate of the refrigerant decreases during a predetermined period. Further, the control means may control the circulation means so that the circulation of the refrigerant stops in a predetermined period.

The fuel cell operating method according to the present invention includes a fuel cell stack in which power generation is disclosed when the average temperature of a fuel cell stack in which a plurality of polymer electrolyte fuel cells are stacked is less than 0 ° C. A circulation step of supplying the refrigerant from the inlet of the refrigerant channel provided in the refrigerant, collecting the refrigerant from the outlet of the refrigerant channel and circulating it to the inlet, and before the average temperature of the fuel cell stack during power generation exceeds 0 ° C. And a reduction step for reducing the amount of heat removed from the fuel cell by the refrigerant in a predetermined period until the temperature exceeds 0 ° C.

  In the method of operating a fuel cell according to the present invention, the temperature of the cathode catalyst layer is effectively reduced to 0 by reducing the amount of heat taken away by the refrigerant in the period from the average temperature of the fuel cell to below 0 ° C. and above 0 ° C. It is possible to exceed ℃. Thereby, frozen moisture can be thawed and an effective power generation area can be secured. As a result, the fuel cell can be started up efficiently.

  The reduction step may be a step of reducing the flow rate of the refrigerant in a predetermined period. Further, the reduction step may be a step of stopping the circulation of the refrigerant in a predetermined period.

  According to the present invention, the fuel cell can be efficiently started at the time of starting below freezing.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a diagram for explaining a fuel cell system 100 according to a first embodiment of the present invention. FIG. 1A is a schematic diagram showing the overall configuration of the fuel cell system 100. FIG. 1B is a schematic cross-sectional view of a fuel cell 11 to be described later. As shown in FIG. 1A, the fuel cell system 100 includes a fuel cell stack 10, a fuel gas supply means 20, an oxidant gas supply means 30, a refrigerant circulation means 40, a control means 50, and the like.

  The fuel cell stack 10 has a structure in which a plurality of fuel cells 11 are stacked. As shown in FIG. 1B, the fuel cell 11 has a structure in which the membrane-electrode assembly 110 is sandwiched between the separator 120 and the separator 130. In the membrane-electrode assembly 110, the anode catalyst layer 112 and the gas diffusion layer 113 are sequentially bonded to the separator 120 side of the electrolyte membrane 111, and the cathode catalyst layer 114 and the gas diffusion layer 115 are sequentially bonded to the separator 130 side of the electrolyte membrane 111. Has a structured. The electrolyte membrane 111 is made of a solid polymer electrolyte such as a perfluorosulfonic acid type polymer having proton conductivity.

  The anode catalyst layer 112 is made of a conductive material or the like that supports the catalyst. The catalyst in the anode catalyst layer 112 is a catalyst for promoting protonation of hydrogen. For example, the anode catalyst layer 112 is made of platinum-supported carbon. The gas diffusion layer 113 is made of a conductive material having gas permeability such as carbon paper or carbon cloth.

  The cathode catalyst layer 114 is made of a conductive material or the like that supports the catalyst. The cathode catalyst layer 114 is a catalyst for promoting the reaction between protons and oxygen. For example, the cathode catalyst layer 114 is made of platinum-supported carbon. The gas diffusion layer 115 is made of a conductive material having gas permeability such as carbon paper or carbon cloth.

  Separator 120,130 is comprised from electroconductive materials, such as stainless steel. On the surface of the separator 120 on the membrane-electrode assembly 110 side, a fuel gas flow path 121 for flowing the fuel gas is formed. In addition, a coolant channel 122 for allowing the coolant to flow is formed on the surface of the separator 120 opposite to the membrane-electrode assembly 110. On the surface of the separator 130 on the membrane-electrode assembly 110 side, an oxidant gas flow path 131 is formed for the oxidant gas to flow. In addition, a coolant channel 132 for allowing the coolant to flow is formed on the surface of the separator 130 opposite to the membrane-electrode assembly 110. For example, the fuel gas flow path 121, the oxidant gas flow path 131, and the refrigerant flow paths 122 and 132 are formed of recesses formed on the surface of the separator.

  The fuel gas supply means 20 is a device that supplies a fuel gas containing hydrogen to the fuel gas passage 121 via the fuel gas inlet of the fuel cell stack 10. The fuel gas supply unit 20 includes, for example, a hydrogen cylinder, a reformer, and the like. The oxidant gas supply means 30 is a device that supplies an oxidant gas containing oxygen to the oxidant gas flow path 131 via the oxidant gas inlet of the fuel cell stack 10. The oxidant gas supply means 30 includes an air pump or the like.

  The refrigerant circulation means 40 is an apparatus that supplies refrigerant to the refrigerant flow paths 122 and 132 via the refrigerant inlet of the fuel cell stack 10 and collects the refrigerant from the refrigerant outlet of the fuel cell stack 10 and circulates it to the refrigerant inlet. is there. The refrigerant circulating means 40 includes a refrigerant pump or the like. For example, ethylene glycol or the like can be used as the refrigerant. A temperature sensor 41 that detects the temperature of the refrigerant is provided near the refrigerant outlet of the fuel cell stack 10.

  The control means 50 is composed of a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and is a means for controlling each part of the fuel cell system 100.

(Normal power generation)
Next, the operation of the fuel cell system 100 during normal power generation will be described with reference to FIGS. 1 (a) and 1 (b). First, the control unit 50 controls the fuel gas supply unit 20 so that the fuel gas is supplied to the fuel gas channel 121. The fuel gas passes through the gas diffusion layer 113 and reaches the anode catalyst layer 112. Hydrogen contained in the fuel gas is dissociated into protons and electrons via the catalyst of the anode catalyst layer 112. The protons conduct through the electrolyte membrane 111 and reach the cathode catalyst layer 114.

  Further, the control means 50 controls the oxidant gas supply means 30 so that the oxidant gas flow path 131 is supplied with the oxidant gas. The oxidant gas passes through the gas diffusion layer 115 and reaches the cathode catalyst layer 114. In the cathode catalyst layer 114, protons and oxygen react via the catalyst. Thereby, electric power is generated and water is generated. The generated water is discharged through the oxidant gas channel 131.

  The control means 50 controls the refrigerant circulation means 40 so that the refrigerant is supplied to the refrigerant flow paths 122 and 132. By the circulation of the refrigerant, the temperature of the fuel cell stack 10 is adjusted to a predetermined temperature. The temperature of the refrigerant discharged from the refrigerant outlet of the fuel cell stack 10 is approximately equal to the average temperature of the fuel cell stack 10. Therefore, the temperature sensor 41 detects the average temperature of the fuel cell stack 10 while detecting the temperature of the refrigerant.

(Start below freezing point)
Next, the operation of the fuel cell system 100 when the fuel cell stack 10 is started below the freezing point will be described with reference to FIG. FIG. 2 is a diagram showing the relationship between the elapsed time after startup and the temperature of each part. In FIG. 2, the horizontal axis indicates the elapsed time after startup, the left vertical axis indicates the temperature, and the right vertical axis indicates the flow rate.

  The control unit 50 controls the fuel gas supply unit 20 so that the fuel gas is supplied to the fuel gas channel 121, and the oxidant gas supply unit 30 so that the oxidant gas is supplied to the oxidant gas channel 131. And the refrigerant circulation means 40 is controlled so that the refrigerant is supplied to the refrigerant flow paths 122 and 132. Thereby, power generation is performed in each fuel cell 11. As a result, the average temperature of each fuel cell 11 rises due to the heat generated with power generation.

  When the average temperature of the fuel cell 11 reaches a predetermined temperature (for example, −10 ° C.), the control unit 50 controls the circulation unit 40 so that the circulation of the refrigerant stops. In this case, the amount of heat removed from the fuel cell 11 decreases. As a result, the rate of temperature increase of the cathode catalyst layer 114 where the power generation reaction is continued increases, and the temperature of the cathode catalyst layer 114 tends to exceed 0 ° C. As a result, re-freezing of generated water accompanying power generation is suppressed and frozen water is melted to secure an effective power generation area.

  After the temperature of the cathode catalyst layer 114 exceeds 0 ° C., the control means 50 controls the circulation means 40 so that the circulation of the refrigerant is resumed. In this case, the average temperature of the fuel cell 11 temporarily decreases due to the circulation of the refrigerant, but immediately increases. This is because an effective power generation area is secured.

  As in this embodiment, the temperature of the cathode catalyst layer is efficiently exceeded above 0 ° C. by reducing the amount of heat taken away by the refrigerant in a predetermined period from the average temperature of the fuel cell to below 0 ° C. and exceeding 0 ° C. be able to. Thereby, frozen moisture can be thawed and an effective power generation area can be secured. As a result, the fuel cell can be started up efficiently.

  The method for estimating that the temperature of the cathode catalyst layer 114 exceeds 0 ° C. is not particularly limited, but the following method can be used. For example, it can be estimated that the temperature of the cathode catalyst layer 114 is higher than 0 ° C. when a predetermined time exceeds a predetermined time after the circulation of the refrigerant is stopped. Further, when the temperature of at least one of the fuel off-gas and the oxidant off-gas exceeds 0 ° C., it can be estimated that the temperature of the cathode catalyst layer 114 exceeds 0 ° C. In consideration of the time difference, it may be estimated that the temperature of the cathode catalyst layer 114 has exceeded 0 ° C. after a predetermined time has elapsed since the temperature of at least one of the fuel off-gas and the oxidant off-gas has exceeded 0 ° C.

  When the heating rate obtained by dividing the calorific value calculated from the generated current, generated voltage and generated duration by the heat capacity of the fuel cell 11 reaches a specified temperature, it is estimated that the temperature of the cathode catalyst layer 114 exceeds 0 ° C. Also good. This is because the current value is the same as the reaction amount, the amount of heat generated is determined if the control voltage is determined, and the amount of heat accumulated in the system is determined if the amount of heat taken away from the system by the cooling water is determined. Since the heat capacity of the structure is obtained in advance, the temperature increase allowance can be estimated. In addition, when the fuel cell 11 generates power at a constant voltage, it may be estimated that the temperature of the cathode catalyst layer 114 exceeds 0 ° C. when the generated current value exceeds a predetermined value. This is because the current value is a function of temperature. In power generation below freezing, the power generation performance of the fuel cell deteriorates as the temperature decreases. Even at the same temperature, the performance deteriorates when the effective power generation area decreases because the gas does not reach the catalyst due to ice. For this reason, it is not a big mistake to look at the power generation state of the fuel cell and determine whether the freezing point has been locally exceeded or the effective power generation area has been restored.

  In order to increase the temperature of the cathode catalyst layer 114 efficiently, it is conceivable to stop the circulation of the refrigerant from the start of the fuel cell 11. However, in this case, since it becomes difficult to detect the average temperature of the fuel cell 11, it may be difficult to control the fuel cell 11. Further, when the circulation of the refrigerant is stopped, the temperature locally increases in the cathode catalyst layer 114. In this case, each part of the fuel cell 11 may be damaged. Therefore, the refrigerant is preferably circulated as much as possible. In the present embodiment, since the circulation stop of the refrigerant is limited to a predetermined period, the fuel cell 11 can be efficiently started up while suppressing damage to each part of the fuel cell 11 and the like.

  FIG. 3 is a diagram illustrating an example of a flowchart at the time of starting below freezing. As shown in FIG. 3, the control means 50 acquires the detection result of the temperature sensor 41 (step S1). Next, the control means 50 determines whether or not the temperature detected by the temperature sensor 41 is less than 0 ° C. (step S2). If it is not determined in step S2 that the temperature detected by the temperature sensor 41 is less than 0 ° C., the control unit 50 ends the execution of the flowchart.

  When it is determined in step S <b> 2 that the temperature detected by the temperature sensor 41 is less than 0 ° C., the control unit 50 controls the fuel gas supply unit 20 so that the fuel gas is supplied to the fuel gas channel 121, and the oxidation is performed. The oxidant gas supply means 30 is controlled so that the oxidant gas is supplied to the agent gas flow path 131, and the refrigerant circulation means 40 is controlled so that the refrigerant is supplied to the refrigerant flow paths 122 and 132 (step S3). .

  Next, the control means 50 acquires the detection result of the temperature sensor 41 (step S4). Next, the control means 50 determines whether or not the temperature detected by the temperature sensor 41 is −10 ° C. or higher (step S5). When it is not determined in step S5 that the temperature detected by the temperature sensor 41 is equal to or higher than −10 ° C., the control unit 50 stands by. When it is determined in step S5 that the temperature detected by the temperature sensor 41 is −10 ° C. or higher, the control means 50 controls the refrigerant circulation means 40 so that the refrigerant circulation is stopped (step S6).

  Next, the control means 50 waits until the specified time has elapsed (step S7). Next, the control means 50 controls the refrigerant circulation means 40 so that the refrigerant circulation is resumed (step S8). Thereafter, the control unit 50 ends the execution of the flowchart.

  According to this flowchart, the amount of heat removed from the fuel cell 11 after the average temperature of the fuel cell 11 exceeds −10 ° C. decreases. Thereby, an effective power generation area is secured. As a result, it can start up efficiently. In step S7, it may be estimated that the temperature of the cathode catalyst layer 114 is higher than 0 ° C. using another method.

  In addition, although the temperature threshold value for determining a refrigerant | coolant circulation stop is -10 degreeC, if it is below freezing point, it will not specifically limit. Further, although the temperature of the cathode catalyst layer 114 is efficiently increased by stopping the refrigerant circulation, it is not always necessary to stop the temperature. For example, the temperature of the cathode catalyst layer 114 may be increased by reducing the refrigerant circulation rate.

It is a figure for demonstrating the fuel cell system which concerns on 1st Example of this invention. It is a figure which shows the relationship between the elapsed time after starting, and the temperature of each part of a fuel cell. It is a figure which shows an example of the flowchart at the time of a sub freezing start.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell stack 11 Fuel cell 20 Fuel gas supply means 30 Oxidant gas supply means 40 Refrigerant circulation means 41 Temperature sensor 50 Control means 100 Fuel cell system 110 Membrane-electrode assembly 111 Electrolyte membrane 114 Cathode catalyst layer 122,132 Refrigerant flow Road

Claims (6)

Circulating means for supplying a refrigerant from an inlet of a refrigerant channel provided in a fuel cell stack in which a plurality of polymer electrolyte fuel cells are stacked, and collecting the refrigerant from the outlet of the refrigerant channel and circulating it to the inlet When,
When the average temperature of the fuel cell stack is less than 0 ° C., the fuel cell stack starts power generation and the circulation means circulates the refrigerant, and the average temperature of the fuel cell stack during power generation exceeds 0 ° C. A fuel cell system comprising: control means for controlling the circulation means so that the amount of heat carried away from the fuel cell by the refrigerant decreases for a predetermined period from before to over 0 ° C.   2. The fuel cell system according to claim 1, wherein the control unit controls the circulation unit so that the flow rate of the refrigerant decreases during the predetermined period.   The fuel cell system according to claim 1, wherein the control unit controls the circulation unit so that the circulation of the refrigerant stops in the predetermined period. When an average temperature of a fuel cell stack in which a plurality of polymer electrolyte fuel cells are stacked is less than 0 ° C., the fuel cell stack starts power generation, and an inlet of a refrigerant flow path provided in the fuel cell stack A circulation step of supplying the refrigerant from the refrigerant flow path and collecting the refrigerant from the outlet of the refrigerant flow path and circulating it to the inlet;
A reduction step of reducing the amount of heat removed from the fuel cell by the refrigerant in a predetermined period from before the average temperature of the fuel cell stack during power generation exceeds 0 ° C. until it exceeds 0 ° C. A fuel cell operating method.   The method of operating a fuel cell according to claim 4, wherein the decreasing step is a step of reducing the flow rate of the refrigerant in the predetermined period.   The method of operating a fuel cell according to claim 4, wherein the lowering step is a step of stopping circulation of the refrigerant in the predetermined period.

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