JP2005158662A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a reactant gas from passing through a separator and being mixed into deionized water. <P>SOLUTION: When a controller 2 detects a reactant gas mixing into deionized water for humidification in a fuel cell stack 1 during it generates electricity, the controller 2 reduces the temperature of the fuel cell stack 1. At this time, the controller 2 controls a pump 3 for supplying air and a pump 5 for supplying hydrogen so that the flow rate of the reactant gas supplied to the fuel cell stack 1 is reduced, narrows an opening of a valve 11 for controlling the flow rate of the deionized water, and regulates a pump 8 for circulating the cooling water so that the amount of cooling water is increased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system in which when a fuel cell is generated, a reaction gas is supplied to generate the fuel cell, and humidified pure water is circulated in the fuel cell to humidify the fuel cell.

Conventionally, a fuel cell system that generates electricity while humidifying an electrolyte membrane inside a fuel cell stack by supplying not only fuel gas and oxidant gas but also pure water for humidification to a fuel cell stack composed of a plurality of fuel cells. It has been known. Such a fuel cell system uses a fuel cell stack in which each fuel cell is divided by a porous separator (WPT) having a pure water channel (see, for example, Patent Document 1 below).
US6248462

  However, since the conventional fuel cell system described above seals the reaction gas of the fuel gas and the oxidant gas and the pure water for humidification with the pure water in the minute holes of the WRT, depending on the operating conditions of the fuel cell stack. There is a problem that the reaction gas passes through the pure water in the WRT and is mixed into the pure water.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and an object of the present invention is to provide a fuel cell system capable of suppressing reaction gas from passing through a separator and mixing into pure water. To do.

  A fuel cell system according to the present invention includes a plurality of fuel cells that generate power when a reaction gas comprising a fuel gas and an oxidant gas is supplied to a reaction gas flow path, and each fuel cell provided between the fuel cells. A fuel cell comprising a plurality of porous separators having a humidified pure water flow path for humidifying the cells, a reaction gas supply means for supplying a reaction gas to a reaction gas flow path of the fuel cell, and a pure water for humidifying the porous separator Pure water circulation means for circulating the humidified pure water in the water flow path and cooling medium circulation means for circulating the cooling medium in the fuel cell are provided.

  When the fuel cell is generating power in such a fuel cell system, the control means reduces the temperature of the fuel cell when it is determined that the reaction gas has passed through the porous separator and has been mixed into the pure water for humidification. This solves the above-mentioned problem.

  Further, in another fuel cell system according to the present invention, when the control means determines that the reaction gas has passed through the porous separator and has been mixed into the pure water for humidification, the reaction gas pressure in the reaction gas flow path and The above-mentioned problems are solved by reducing the differential pressure from the humidifying pure water pressure in the humidifying pure water flow path.

  According to the fuel cell system of the present invention, the temperature of the fuel cell is decreased when it is determined that the reaction gas has passed through the porous separator and mixed into the humidified pure water when the fuel cell is generating power. Therefore, the evaporation amount of pure water in the porous separator can be reduced. Therefore, according to this fuel cell system, it is possible to suppress an increase in pressure in the reaction gas channel due to evaporation of pure water, and to prevent the reaction gas from entering the pure water channel of the porous separator. .

  Further, according to another fuel cell system according to the present invention, when it is determined that the reaction gas passes through the porous separator and is mixed into the humidified pure water when the fuel cell is generating electric power, Since the pressure difference between the reaction gas pressure in the flow path and the humidification pure water pressure in the humidification pure water flow path is reduced, it is possible to prevent the reaction gas from passing through the humidification pure water flow path, The reaction gas can be prevented from entering the pure water flow path.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The present invention is applied to a fuel cell system configured as shown in FIG. 1, for example.

[Configuration of fuel cell system]
As shown in FIG. 1, the fuel cell system includes a fuel cell stack 1 that generates electric power when supplied with a fuel gas and an oxidant gas. This fuel cell stack 1 is configured by sandwiching a fuel cell structure having an air electrode and a hydrogen electrode facing each other with a solid polymer electrolyte membrane interposed between separators, and laminating a plurality of cell structures. Such a fuel cell stack 1 includes a hydrogen gas flow path at the hydrogen electrode and an air flow path at the air electrode. In the following description, the hydrogen gas channel and the air channel are collectively referred to as a reaction gas channel. In this example, a fuel cell system that supplies hydrogen gas to the hydrogen electrode as a fuel gas for causing the fuel cell stack 1 to generate a power generation reaction and supplies air containing oxygen as an oxidant gas to the air electrode will be described. .

  In the fuel cell stack 1, although not shown in the drawing, each fuel cell is divided by a porous separator (porous separator: WTP) in which humidifying pure water for humidifying the solid polymer electrolyte membrane is circulated. This porous separator has one surface in contact with the adjacent fuel cell, and the other surface is provided with a humidified pure water circulation channel. The porous surface of the humidified pure water circulation channel and the fuel cell stack It is made to contact with the reaction gas flow path in 1. As a result, the fuel cell stack 1 is supplied with humidified pure water, so that the porous surface of the porous separator is filled with the humidified pure water, and is supplied to the fuel cell stack 1 with the humidified pure water. The reaction gas (air, hydrogen) is humidified to humidify the solid polymer electrolyte membrane.

  When the fuel cell stack 1 generates power, the fuel cell system supplies humidified hydrogen gas to the hydrogen electrode, supplies humidified air to the air electrode, and further cools the fuel cell stack 1 to a predetermined temperature. While circulating the cooling water held in the range, pure water for humidification for humidifying the solid polymer electrolyte membrane in the fuel cell stack 1 is circulated. At this time, the fuel cell system controls each part to be described later by the controller 2.

  The air is pressurized by the air supply pump 3 and is humidified by, for example, an air humidifier, and then supplied to the air electrode of the fuel cell stack 1 via the air supply pipe L1. At this time, the controller 2 controls the rotation speed of a motor connected to the air supply pump 3 and also controls the opening degree of an air pressure regulating valve (not shown) provided on the air discharge side of the air electrode. To adjust the air flow rate and air pressure supplied to the air electrode.

  Hydrogen is taken into the hydrogen supply pump 5 from the state stored in the hydrogen tank 4 and supplied to the hydrogen electrode of the fuel cell stack 1 via the hydrogen supply pipe L2. Further, unused hydrogen discharged from the hydrogen electrode is normally circulated again to the hydrogen electrode. At this time, the controller 2 adjusts the hydrogen pressure supplied to the hydrogen electrode, for example, by controlling the opening of the hydrogen pressure regulating valve.

  The cooling water is cooled by the radiator 6 and the blower fan 7, is taken in by the cooling water circulation pump 8, and is supplied to the fuel cell stack 1 through the cooling water circulation passage L3. The cooling water absorbs heat generated by the power generation by the fuel cell stack 1 and is discharged from the fuel cell stack 1 toward the radiator 6. At this time, the controller 2 adjusts the cooling capacity of the radiator 6 by controlling the rotational speed of the blower fan 7 and controls the circulation amount of the cooling water by controlling the discharge amount of the cooling water circulation pump 8. Thereby, the fuel cell system adjusts the temperature of the fuel cell stack 1.

  The humidified pure water is taken into the pure water circulation pump 10 from the state stored in the pure water tank 9 and supplied to the fuel cell stack 1 through the pure water circulation flow path L4. The pure water for humidification supplied to the fuel cell stack 1 fills the porous surface of the porous separator with moisture and humidifies the reaction gas, so that the pure water circulation channel L4 and the pure water flow rate from the fuel cell stack 1 are supplied. The water is returned to the pure water tank 9 through the control valve 11. At this time, the controller 2 controls the amount of pure water for humidification supplied to the fuel cell stack 1 by controlling the amount of pure water discharged from the pure water circulation pump 10, and an actuator connected to the pure water flow rate control valve 11. 12 is adjusted to adjust the opening degree of the pure water flow rate control valve 11 to adjust the pure water pressure for humidification in the fuel cell stack 1.

  In such a fuel cell system, the controller 2 performs a control process for suppressing the reaction gas from passing through the porous separator and mixing into the humidifying pure water when the fuel cell stack 1 is generating power.

  In addition, this fuel cell system includes various sensors so that the controller 2 recognizes the state of each part. Specifically, the fuel cell system includes a reaction gas pressure sensor that detects air pressure and hydrogen gas pressure in the fuel cell stack 1, a pure water pressure sensor that detects pure water pressure in the fuel cell stack 1, and a fuel cell stack. 1 is provided with a cooling water pressure sensor for detecting the cooling water pressure in 1, a hydrogen concentration sensor for detecting the hydrogen concentration in the pure water for humidification, a cell voltage sensor for detecting the output voltage of the fuel cell, and the like. The detection values of these various sensors are read by the controller 2.

[Operation of fuel cell system]
Next, the operation of the fuel cell system configured as described above will be described with reference to the flowchart of FIG. The operation shown in FIG. 2 is performed at predetermined intervals by the controller 2 when the reaction gas, the pure water for humidification, and the cooling water are supplied into the fuel cell stack 1 to generate power. Done.

  First, in step S1, the controller 2 determines whether or not the reaction gas passes through the porous separator in the fuel cell stack 1 and is mixed with the pure water for humidification. At this time, the controller 2 reads, for example, a sensor signal from a hydrogen concentration sensor provided in the pure water circulation passage L4 at the pure water outlet of the fuel cell stack 1 or a hydrogen concentration sensor in the pure water tank 9, When it is determined that the concentration is equal to or higher than the predetermined concentration, it may be determined that the reaction gas is mixed in the humidifying pure water. Further, the controller 2 may read the sensor signal from the cell voltage sensor and determine that the reaction gas is mixed in the humidified pure water when it is determined that the cell voltage is equal to or lower than the predetermined voltage.

  When the controller 2 determines that the reaction gas is mixed in the humidified pure water, the controller 2 proceeds to step S2, and when it is determined that the reaction gas is not mixed in the humidified pure water. Advances the process to step S7 and terminates the process on the assumption that the normal operation that does not suppress the reaction gas from being mixed into the humidified pure water is continued.

  In step S2, the controller 2 compares the pressure of the humidified pure water in the fuel cell stack 1 with a predetermined value set in advance, and determines whether or not the humidified pure water pressure is higher than the predetermined value. Determine. As a result, the reaction gas pressure is higher than the humidifying pure water pressure in the fuel cell stack 1, and the reaction gas easily enters the humidifying pure water passage of the porous separator from the reaction gas passage. It is determined whether or not there is.

  Here, the predetermined value in step S2 is the pure water for humidification that does not cause deterioration of the fuel cell stack 1 due to an increase in the differential pressure between the pure water pressure for humidification, the reaction gas pressure, and the cooling water pressure. Is set to a value obtained by subtracting a marginal pressure value set separately to ensure that the humidifying pure water pressure does not reach the upper limit pressure.

  When the controller 2 determines that the humidifying pure water pressure is higher than the predetermined value, the controller 2 proceeds to step S3. When the controller 2 determines that the humidifying pure water pressure is not higher than the predetermined value, step S4 is performed. Proceed with the process.

  In step S3, the controller 2 determines that the humidifying pure water pressure is higher than the predetermined value in step S2, and therefore the humidifying pure water pressure cannot be increased, and is supplied to the fuel cell stack 1. Reduce the flow rate of the reaction gas. At this time, the controller 2 performs control to reduce the drive amounts of the air supply pump 3 and the hydrogen supply pump 5.

  When the flow rate of the reaction gas supplied to the fuel cell stack 1 is reduced in this way, the amount of power generated by the fuel cell stack 1 is reduced, so that the heat generation amount is reduced and the temperature of the fuel cell stack 1 is reduced. Thereby, the evaporation amount of the pure water for humidification in the reaction gas flow path in the fuel cell stack 1 is decreased, the partial pressure of water vapor contained in the reaction gas is decreased, and the reaction gas pressure is decreased. When the reaction gas pressure is reduced in this way, the reaction with the humidified pure water pressure and the reaction from the situation where the reaction gas pressure is higher than the humidifying pure water pressure such that the reaction gas is mixed into the humidifying pure water in step S1. It becomes the situation where the differential pressure of the gas pressure is lowered.

  Therefore, in this step S3, by reducing the reaction gas flow rate, the pressure applied to the humidification pure water flow path by the reaction gas is reduced, and the porous surface of the porous separator is filled with pure water. Increase the water sealing ability. In step S3, the controller 2 compensates by supplying electric power corresponding to the output reduction of the fuel cell stack 1 by reducing the reaction gas flow rate from a secondary battery (not shown) to each part. To do.

  On the other hand, in step S4 after it is determined in step S2 that the pure water pressure for humidification is not higher than a predetermined value, the cooling water pressure circulating through the cooling water circulation passage L3 and a predetermined value set in advance. To determine whether or not the cooling water pressure is higher than a predetermined value. Here, the predetermined value in step S4 is the upper limit of the cooling water that does not cause deterioration of the fuel cell stack 1 due to an increase in the differential pressure between the cooling water pressure, the reaction gas pressure, and the humidifying pure water pressure. The pressure is set to a value obtained by subtracting a pressure value of a margin that is separately set to ensure that the cooling water pressure does not reach the upper limit pressure.

  When the controller 2 determines that the cooling water pressure is higher than the predetermined value, the controller 2 cannot proceed to step S5 because the cooling water flow rate cannot be increased any more. In step S5, the pure water flow rate control is performed. The opening degree of the valve 11 is reduced. At this time, the controller 2 opens the opening of the pure water flow control valve 11 so that the differential pressure between the humidifying pure water pressure and the reaction gas pressure becomes a value that can fill the porous surface of the porous separator with pure water. Set. This increases the pure water pressure for humidification in the pure water flow path of the porous separator, fills the porous surface of the porous separator with pure water, and regenerates the water sealing ability of the porous separator.

  On the other hand, in step S6 after determining that the cooling water pressure is not higher than the predetermined value in step S4, the controller 2 reduces the opening of the pure water flow rate control valve 11 and rotates the cooling water circulation pump 8. The cooling water pressure is increased by increasing the cooling water flow rate by increasing the number. As a result, the porous surface of the porous separator is filled with pure water, and the temperature of the fuel cell stack is lowered to reduce the evaporation amount of the pure water for humidification, thereby regenerating the water sealing ability of the porous separator.

[Effect of the embodiment]
As described above in detail, according to the fuel cell system according to the first embodiment to which the present invention is applied, during the operation of the fuel cell stack 1, the reaction gas passes through the porous surface of the porous separator for humidification. When it is determined that it has been mixed in pure water, the temperature of the fuel cell stack 1 is lowered, so that the amount of pure water evaporated in the porous separator can be reduced. Therefore, according to this fuel cell system, it is possible to suppress an increase in pressure in the reaction gas flow path due to evaporation of pure water, and to prevent the reaction gas from entering the pure water flow path of the porous separator. The water sealing performance of the porous separator can be increased.

  Further, according to this fuel cell system, when it is determined that the reaction gas has passed through the porous surface of the porous separator during operation of the fuel cell stack 1 and mixed into the pure water for humidification, the fuel cell stack 1 Therefore, the temperature of the fuel cell stack 1 can be lowered regardless of the coolant flow rate or the coolant temperature, and the reaction gas is reliably humidified. It is possible to suppress entry into the pure water.

  Further, according to this fuel cell system, when it is determined that the reaction gas has passed through the porous surface of the porous separator during operation of the fuel cell stack 1 and mixed into the humidified pure water, the cooling water flow rate is reduced. Since it is increased, the temperature of the fuel cell stack 1 can be lowered in a short time, and the rapid entry of the reaction gas into the humidified pure water can be suppressed.

  Furthermore, according to this fuel cell system, when it is determined that the reactive gas has passed through the porous surface of the porous separator and has been mixed into the humidified pure water, the humidified pure water pressure and the reactive gas pressure are reduced. The differential pressure can be reduced, and the porous surface of the porous separator can be filled with pure water to improve the water sealing performance of the porous separator.

  Furthermore, according to this fuel cell system, when it is determined that the reaction gas has passed through the porous surface of the porous separator and has been mixed into the pure water for humidification, the flow rate of the reaction gas is decreased and the fuel cell stack 1 The pressure of the reaction gas inside can be reduced, so that the differential pressure between the pure water pressure for humidification and the reaction gas pressure can be reduced, and the porous surface of the porous separator is filled with pure water to ensure that it is porous. The water seal performance of the quality separator can be increased.

  Furthermore, according to this fuel cell system, when it is determined that the reaction gas has passed through the porous surface of the porous separator and mixed into the humidified pure water, the opening degree of the pure water flow control valve 11 is reduced. The pressure of the pure water for humidification is increased to reduce the differential pressure between the pure water pressure for humidification and the reaction gas pressure, and the porous surface of the porous separator is filled with pure water. Water seal performance can be increased.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the design and the like as long as the technical idea according to the present invention is not deviated from this embodiment. Of course, it is possible to change.

It is a block diagram which shows the structure of the fuel cell system to which this invention is applied. It is a flowchart explaining operation | movement of the fuel cell system to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Controller 3 Air supply pump 4 Hydrogen tank 5 Hydrogen supply pump 6 Radiator 7 Blower fan 8 Cooling water circulation pump 9 Pure water tank 10 Pure water circulation pump 11 Pure water flow control valve L1 Air supply piping L2 Hydrogen supply piping L3 Cooling water circulation channel L4 Pure water circulation channel

Claims (6)

A plurality of fuel cells that generate power by supplying a reaction gas comprising a fuel gas and an oxidant gas to the reaction gas channel, and a pure water channel for humidification provided between the fuel cells to humidify each fuel cell A fuel cell comprising a plurality of porous separators comprising:
Reactive gas supply means for supplying a reactive gas to the reactive gas flow path of the fuel cell;
Pure water circulation means for circulating the pure water for humidification through the pure water flow path for humidification of the porous separator;
A cooling medium circulating means for circulating a cooling medium in the fuel cell;
And a control means for lowering the temperature of the fuel cell when it is determined that the reaction gas has passed through the porous separator and mixed into the humidified pure water.   The said control means reduces the output of the said fuel cell, when it is judged that the said reaction gas passed through the said porous separator and mixed in the said pure water for humidification. Fuel cell system.   When the control means determines that the reaction gas has passed through the porous separator and has been mixed into the humidified pure water, the control unit increases the flow rate of the cooling medium circulated in the fuel cell. The fuel cell system according to claim 1, wherein the circulation means is controlled. A plurality of fuel cells that generate power by supplying a reaction gas comprising a fuel gas and an oxidant gas to the reaction gas channel, and a pure water channel for humidification provided between the fuel cells to humidify each fuel cell A fuel cell comprising a plurality of porous separators comprising:
Reactive gas supply means for supplying a reactive gas to the reactive gas flow path of the fuel cell;
Pure water circulation means for circulating the pure water for humidification through the pure water flow path for humidification of the porous separator;
A cooling medium circulating means for circulating a cooling medium in the fuel cell;
When it is determined that the reaction gas has passed through the porous separator and mixed into the humidified pure water, the reaction gas pressure in the reaction gas channel and the humidified pure water in the humidification pure water channel The fuel cell system according to claim 1, further comprising: a control unit that reduces a differential pressure from the pressure.   The fuel cell system according to claim 4, wherein the control unit controls the reaction gas supply unit so as to reduce the reaction gas pressure. The humidifying pure water circulation means includes a valve provided in a pure water pipe on the pure water outlet side of the humidifying pure water flow path of the porous separator,
5. The fuel cell system according to claim 4, wherein the control unit decreases the opening degree of the valve to increase the humidifying pure water pressure in the humidifying pure water flow path.

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