JP2008004310A - Temperature control method and temperature control device of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately conduct the temperature control of a fuel cell cooled by evaporation latent heat of water. <P>SOLUTION: Air is supplied to a cathode 5 of a fuel cell 1, water 35 is supplied with a water pump 41, cooling is conducted by the evaporation latent heat of water, and air is humidified by steam. Control is conducted so that steam partial pressure in the vicinity of a reaction gas outlet part in the cathode 5 of the fuel cell 1 becomes saturated vapor pressure at target temperature in the temperature control of the fuel cell 1. Since the steam partial pressure in the reaction gas outlet of the fuel cell 1 is decided by the amount of steam in the reaction gas outlet, the amount of non-condensing gas, and gas pressure, by controlling the amount of the non-condensing gas (reaction gas) in the reaction gas outlet of the fuel cell1, the temperature of the fuel cell 1 can be controlled to the target temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a temperature control method and a temperature control apparatus for a fuel cell in which water is supplied together with a reaction gas to an electrode of a fuel cell, cooling is performed by water vaporization latent heat, and the reaction gas is humidified by water vapor.

  In a fuel cell using a polymer solid electrolyte membrane, humidification is generally required to maintain the ionic conductivity of the polymer solid electrolyte membrane. Moreover, in order to suppress the temperature rise accompanying the power generation of the fuel cell, cooling water is generally introduced into the fuel cell, heat is transferred to the cooling water, and the cooling water after receiving heat is discharged to the outside.

  For this reason, a humidifier is required outside the fuel cell, and a space for flowing cooling water is required inside the fuel cell, and space for humidification and cooling is required inside and outside the fuel cell body. There is a problem that the entire fuel cell device is increased in size.

In order to solve such a problem, for example, as described in Patent Document 1 below, the reaction gas and water are simultaneously supplied into the fuel cell, and the water is cooled by the latent heat of vaporization and vaporized. A fuel cell that humidifies a reaction gas with water vapor is known.
JP-A-8-306375

  However, in a fuel cell in which a reaction gas and water are supplied into the fuel cell at the same time and cooling is performed by latent heat of vaporization of the fuel, the fuel that is cooled by flowing cooling water through a cooling water passage provided in the fuel cell. Compared with a battery, the degree of freedom of temperature control is low, and the temperature of the fuel cell cannot be ensured properly, so that a stable operation cannot be ensured.

  Therefore, an object of the present invention is to appropriately control the temperature of a fuel cell that is cooled by the latent heat of vaporization of water.

  The present invention provides a fuel cell temperature control method in which water is supplied together with a reaction gas to an electrode of a fuel cell, the water is cooled by latent heat of vaporization of the water, and the reaction gas is humidified by the water vapor. The most important feature is that the temperature of the fuel cell is controlled by the water vapor partial pressure in the vicinity of the reaction gas outlet where the cell reaction gas flows out.

  According to the present invention, since the temperature of the fuel cell is controlled by the water vapor partial pressure in the vicinity of the reaction gas outlet from which the reaction gas of the fuel cell is discharged, the target when the water vapor partial pressure controls the temperature of the fuel cell. By controlling so as to reach the saturated water vapor pressure at the temperature, the temperature of the fuel cell can be appropriately controlled so as to become the target temperature.

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

  FIG. 1 is a configuration diagram of an entire fuel cell system including a temperature control device for a fuel cell according to a first embodiment of the present invention. The fuel cell 1 includes a membrane electrode assembly (MEA) in which a cathode electrode 5 and an anode electrode 7 are provided on both sides of a polymer solid electrolyte membrane 3. Actually, as shown in a cross-sectional view in FIG. 2, one battery cell 9 is placed outside the cathode electrode 5 and the anode electrode 7 positioned on both sides of the polymer solid electrolyte membrane 3 so as to sandwich the polymer cell 3. Bipolar plates 11 and 13 that form a partition wall between the nine are provided, and a fuel cell stack is usually configured by laminating a plurality of battery cells 9.

  The polymer solid electrolyte membrane 3 is formed as a proton conductive membrane from a solid polymer material such as a fluorine-based resin. The cathode electrode 5 and the anode electrode 7 on both surfaces of the solid polymer electrolyte membrane 3 are made of platinum, carbon cloth coated with carbon fine particles carrying a catalyst made of platinum and other metals, or carbon paper. The existing coated surface is in contact with the polymer solid electrolyte membrane 3.

  The bipolar plates 11 and 13 are made of a dense carbon material that is impermeable to gas. One bipolar plate 11 has an air flow path 11 a through which air containing oxygen as a reaction gas flows on the surface facing the cathode electrode 5. The other bipolar plate 13 forms a hydrogen flow path 13a through which hydrogen flows as fuel gas on the surface facing the anode electrode 7.

  In the fuel cell 1 as described above, air is pumped to the cathode electrode 5 through the air supply passage 17 by the air blower 15 as a reaction gas supply means, and the hydrogen supply passage from the hydrogen tank 19 to the anode electrode 7. Hydrogen is introduced through a hydrogen pressure regulating valve 23 and an ejector 25 provided at 21.

  The fuel cell 1 that generates electric power by receiving supply of air and hydrogen uses air pressure sensor 28 provided in the air discharge passage 27, air temperature sensor 29 as temperature detecting means, and pressure adjusting means for discharging air discharged from the cathode electrode 5. The excess hydrogen discharged from the air pressure adjusting valve 31 and discharged from the anode electrode 7 flows out to the hydrogen circulation passage 33 and is sucked by the ejector 25 and supplied to the anode electrode 7 again.

  Water 35 for cooling the fuel cell 1 with latent heat of vaporization and humidifying the reaction gas (air in this case) with steam is pumped from a water tank 37 by a water pump 41 provided in a water pipe 39, and a water pressure adjusting valve. 43 is supplied to the cathode 5 together with the air described above.

  The controller 45 as control means takes in the detection signals of the air pressure sensor 28 and the air temperature sensor 29 described above, and the air blower 15, air pressure adjustment valve 31, hydrogen pressure adjustment valve 23, water pump 41, water pressure adjustment. The drive control for the valve 43 is performed to control the temperature of the fuel cell 1.

  In the fuel cell 1 having the above-described configuration, air is supplied to the cathode electrode 5 and hydrogen is supplied to the anode electrode 7 to generate electric power, and heat is generated together with power generation. At this time, by supplying water 35 to the cathode electrode 5, the fuel cell 1 is cooled by the latent heat of vaporization of the water, and at the same time, air as the reaction gas is humidified by the evaporated water vapor.

  While cooling the fuel cell 1 suppresses the increase in temperature, the ionic conductivity of the polymer solid electrolyte membrane 3 is maintained by humidifying the air, whereby the fuel cell 1 can be stably operated.

  Next, temperature control of the fuel cell using the water vapor partial pressure in the present invention will be described.

The following equation (1) is an equation for determining the amount of water vapor N _{H2O, evp} evaporated in the fuel cell 1 of the water 35 supplied to the cathode electrode 5.

N _{H2O, evp} = Heat / L (1)
By dividing the heat value Heat of the fuel cell 1 by the latent heat L of water evaporation, the amount of water vapor N _{H2O, evp} evaporated in the fuel cell 1 is obtained. Strictly speaking, a part of the heat generation amount Heat is also transferred to a non-condensable gas (such as nitrogen contained in the air), but can be roughly predicted by the above equation (1).

  The calculation of the heat generation amount Heat is performed as follows. Since the numerical value obtained by dividing the generated voltage of one battery cell 9 in the fuel cell 1 by the rated voltage (1.25 V: equivalent to the calorific value converted to voltage) specific to the battery cell 9 is the power generation efficiency η of the fuel cell 1 From the efficiency η and the power generation amount P, the following is obtained.

Heat = P (1 / η−1)
That is, the difference between the energy of hydrogen and the power generation amount is the heat generation amount Heat.

  Note that the calculation of the heat generation amount Heat in the above formula is a simple method, and it is actually necessary to consider the influence of the sensible heat of the cathode gas (air).

Further, the following equation (2) is an equation for _obtaining the water vapor amount N _H2O at the air outlet to the air discharge passage 27 of the cathode electrode 5.

N _H2O = N _{H2O, evp} + N _{H2O, gen} (2)
This water vapor amount N _H2O is obtained by adding the generated water (steam) amount N _{H2O, gen} generated by power generation of the fuel cell 1 to the water vapor amount N _{H2O, evp} in the fuel cell 1 described above. Strictly speaking, a part of the amount of water vapor N _{H2O, evp} that evaporates in the fuel cell 1 passes through the polymer solid electrolyte membrane 3 and flows to the anode electrode 7, but is roughly predicted by the above equation (2). it can.

Note that the generated water amount N _{H2O, gen} is the same as the amount of hydrogen consumed in the fuel cell 1, and therefore can be obtained from this consumed hydrogen amount. Alternatively, it can be obtained from the number n of battery cells 9, the current value I, and the Faraday constant F by the following formula.

N _{H2O, gen} = nI / 2F
The following equation (3) is an equation for _obtaining the water vapor partial pressure P _H2O at the air outlet portion from the cathode electrode 5 to the air discharge passage 27.

P _H2O = {(N _H2O / (N _H2O + N _dry )) × P = P _sat (Tset) (3)
The water vapor partial pressure P _H2O is obtained by multiplying the water vapor fraction (N _H2O / (N _H2O + N _dry ) in the air discharged into the air discharge passage 27 by the gas pressure P detected by the air pressure sensor 28. N _dry is the amount of non-condensable gas in the exhaust air.

FIG. 3 is a diagram showing the relationship between the saturated water vapor pressure P _sat (Tset) [Pa] at the target temperature Tset of the fuel cell 1 and the temperature [K] of the fuel cell 1. The water vapor partial pressure P _H2O is adjusted so that the saturated water vapor pressure P _sat (Tset) is stored.

Next, the operation will be described. The controller 45 calculates a saturated water vapor pressure P _sat (Tset) corresponding to the target temperature Tset of the fuel cell 1 from the map of FIG. On the other hand, the controller 45 calculates the outlet water vapor amount N _H2O of the fuel cell 1 from the above formulas (1) and (2).

Subsequently, the controller 45 sets the air blower 15 and the air blower 15 so that the relationship of the above-described equation (3) is established, that is, the relationship between the non-condensable gas amount N _dry and the outlet gas pressure P in the equation (3) is established. The air pressure adjustment valve 31 is driven and controlled.

  Then, the controller 45 adjusts the water pressure by the water pressure adjusting valve 43 and the pressure of the anode 7 by the hydrogen pressure adjusting valve 23 so as to follow the outlet gas pressure P of the cathode electrode 5 determined in this way. Control.

In FIG. 4, the controller 45 that calculates the water vapor partial pressure P _H2O corresponding to the target temperature Tset as described above performs feedback control with reference to the detection value of the air temperature sensor 29 that is the temperature of the fuel cell 1 to be controlled. It is a flowchart at the time.

  First, it is determined whether or not the difference between the target temperature Tset and the detected temperature Tsen of the air temperature sensor 29 is less than or equal to the threshold ε (step 101). If the difference exceeds the threshold ε (NO in step 101), the detected temperature Tsen is determined. Is determined to be lower than the target temperature Tset (step 103).

  Here, when the detected temperature Tsen is lower than the target temperature Tset (YES in step 103), the air blower 15 is driven and controlled to reduce the flow rate of the non-condensable gas (reaction gas, air) (step 105). . By reducing the flow rate of the non-condensable gas, the cooling action on the fuel cell 1 due to the latent heat of vaporization of water is suppressed. Conversely, when the detected temperature Tsen is equal to or higher than the target temperature Tset (NO in step 103), the air blower 15 is driven and controlled to increase the flow rate of the non-condensable gas (reactive gas). By increasing the flow rate of the non-condensable gas, the cooling action on the fuel cell 1 due to the latent heat of vaporization of water is increased.

  That is, since the amount of heat generated is fixed during steady operation of the fuel cell 1, the amount of evaporation hardly changes. For this reason, if the amount of non-condensable gas is increased, the partial pressure of water vapor decreases. In particular, in a transient operation state, increasing the amount of noncondensable gas increases the amount of evaporation compared to before increasing the amount of noncondensable gas so as to maintain the saturated water vapor pressure at that temperature. An increase in the amount of evaporation means that the state in which the amount of heat generation and the amount of evaporation (cooling amount) have been balanced so far becomes a state in which the amount of cooling exceeds the amount of heat generation, thereby cooling proceeds and the temperature decreases. That is, the evaporation amount falls within a temperature that balances the heat generation amount.

  If the difference between the target temperature Tset and the detected temperature Tsen is not more than the threshold value ε in step 101 (YES in step 101), the increase / decrease control of the flow rate of the non-condensable gas is not performed.

  As a result, the difference between the detected temperature Tsen of the air temperature sensor 29 and the target temperature Tset can be controlled to be equal to or less than the threshold ε.

As described above, according to the present embodiment, the temperature of the fuel cell 1 is controlled by the water vapor partial pressure in the vicinity of the outlet portion of the reaction gas (air) from which the air that is the reaction gas of the fuel cell 1 flows out. By controlling the partial pressure to be the saturated water vapor pressure P _sat (Tset) at the target temperature Tset when the temperature of the fuel cell 1 is controlled, the temperature of the fuel cell 1 is appropriately controlled to become the target temperature Tset. And stable operation can be ensured.

Further, according to the present embodiment, the water vapor partial pressure is changed by changing the flow rate of the reaction gas (air) of the fuel cell 1. Here, the water vapor partial pressure P _H2O of the gas at the reaction gas outlet of the fuel cell 1 is equal to the amount of water vapor N _{H2O at} the reaction gas outlet of the fuel cell 1, as shown in the above equation (3). Since the amount N _dry is determined by the gas pressure P, the temperature N of the fuel cell 1 is controlled to the target temperature Tset by controlling the amount N _dry of the non-condensable gas (reaction gas) at the reaction gas outlet of the fuel cell 1. it can.

  Further, in the present embodiment, the temperature of the fuel cell 1 to be controlled is set near the reaction gas outlet. When taking a reference temperature in the case of feedback system control, it is desirable to use the solid polymer electrolyte membrane 3 which is a portion in the fuel cell 9 that is predicted to be the maximum temperature. Is extremely close to the polymer solid electrolyte membrane 3, and therefore has the advantage that the maximum temperature of the fuel cell 1 can be controlled more accurately.

  At this time, in the present embodiment, the temperature of the fuel cell 1 to be controlled is set as the outlet temperature of air that is the reaction gas having the larger gas flow rate flowing out of the fuel cell 1. When taking the reference temperature when the feedback system control is set, the gas outlet temperature with the larger reaction gas flow rate becomes the maximum gas temperature of the fuel cell 1, so that the maximum temperature of the fuel cell 1 can be controlled more accurately. This is because the amount of heat is larger on the air side where the reaction gas flow rate is larger than on the hydrogen side where the reaction gas flow rate is smaller, and the temperature change becomes clearer.

  As a second embodiment of the present invention, instead of controlling the amount of non-condensable gas (reactive gas) in the first embodiment, the reaction gas pressure of the fuel cell 1 is expressed by the above equation (3). The outlet gas pressure P is controlled. Thereby, the temperature of the fuel cell 1 can be controlled to the target temperature Tset as in the first embodiment.

In the third embodiment, the water vapor partial pressure described above controls the amount N _dry of the non-condensable gas (reactive gas) in the first embodiment, and the outlet which is the reactive gas pressure of the fuel cell 1. It may be changed by controlling the gas pressure P. When the reaction gas flow rate and reaction gas pressure are changed, the pressure loss of the reaction gas also changes. Therefore, just controlling one of the reaction gas outlet flow rate and pressure changes the inlet pressure. Are controlled simultaneously, the pressure change at the inlet can be suppressed when the temperature of the fuel cell 1 is controlled to the target temperature Tset. By suppressing the pressure change at the inlet, the power generation efficiency of the fuel cell 1 can be increased as a result, for example, by stabilizing the power consumption of the air blower 15.

  As a fourth embodiment of the present invention, the outlet of the water supplied to the cathode 5 is set near the outlet of the air as the reaction gas in FIG. 1, and the temperature of the fuel cell 1 to be controlled is set as the outlet of the water. Let it be temperature.

  FIG. 5 shows a plan view of the bipolar plate 11 provided with the air flow path 11a on the surface thereof, in the direction perpendicular to the paper surface at the left end in FIG. 5, that is, in the stacking direction of each component of the fuel cell 1. Along with this, an air inlet manifold 47 serving as a reaction gas inlet penetrating the fuel cell 1 is provided, and an air outlet manifold serving as a reaction gas outlet penetrating the fuel cell 1 along the direction perpendicular to the paper surface at the right end portion. 49, and the air inlet / outlet manifolds 47 and 49 communicate with each other through the air flow path 11a.

  That is, the air flowing through the air inlet manifold 47 is distributed and supplied to the air flow paths 11a of the battery cells 9 shown in FIG.

  Similarly, hydrogen inlet and outlet manifolds 51 and 53 are provided adjacent to the air inlet and outlet manifolds 47 and 49, respectively, penetrating in the direction perpendicular to the paper surface in FIG. And this hydrogen is also distributed and supplied to the hydrogen flow path 13a of each battery cell 9 like the above-mentioned air.

  In the present embodiment, the vertically downward position of the air outlet manifold 49 is a water discharge manifold 55 that serves as a water discharge port penetrating in a direction perpendicular to the paper surface in FIG. The water discharge passage 57 is connected. The water discharge passage 57 is provided with an opening / closing valve 59, and the discharged water is returned to the water tank 37 shown in FIG.

  According to the present embodiment, when taking the reference temperature when the feedback system control is set, the water discharge passage 57 is brought close to the reaction gas outlet having the larger flow rate of the reaction gas, so that the temperature of the water is substantially equal to the gas temperature. The maximum temperature of the fuel cell 1 can be controlled by referring to the water temperature. At this time, since water has a larger heat capacity than gas, there is an advantage that temperature measurement is easier when water is used than when gas is used.

  In the above-described embodiment of the present invention, the formulas (1) to (3) and the map of FIG. 5 are used as a means for calculating the temperature. Of course, in addition to the above formula and map, sensible heat is used. You may use the calculation means including.

  In the above-described embodiment, the water pump 41 is used as the water supply means. However, as a matter of course, the use of other pressure sources is not excluded.

  In the embodiment described above, water is supplied to the dense bipolar plate as a gas-liquid two-phase flow, but this does not exclude the method of supplying water from the porous bipolar plate.

  Furthermore, in the above-described embodiment, an example is shown in which water is supplied to the cathode electrode 5 together with air. This is because the flow rate of the non-condensable gas is generally larger at the cathode, and of course the non-condensable gas. Is large on the anode side, water is supplied to the anode electrode 7 together with hydrogen.

1 is a configuration diagram of an entire fuel cell system including a temperature control device for a fuel cell according to a first embodiment of the present invention. It is sectional drawing for one battery cell in a fuel cell. It is a correlation diagram of the saturated water vapor pressure in the target temperature of a fuel cell, and the temperature of a fuel cell. It is a flowchart at the time of performing feedback control with reference to the detection value of the air temperature sensor used as the temperature of a fuel cell. It is a top view of the bipolar plate which equips the surface with an air flow path.

Explanation of symbols

1 Fuel cell 5 Cathode electrode (fuel cell electrode)
7 Anode electrode (fuel cell electrode)
15 Air blower (reaction gas supply means)
29 Air temperature sensor (temperature detection means)
31 Air pressure adjusting valve (pressure adjusting means)
35 Water 55 Water discharge manifold (water discharge port)

Claims (10)

  In the fuel cell temperature control method, water is supplied to the electrode of the fuel cell together with the reaction gas, the water is cooled by latent heat of vaporization of the water, and the reaction gas is humidified by the water vapor. A temperature control method for a fuel cell, wherein the temperature of the fuel cell is controlled by a water vapor partial pressure in the vicinity of a reaction gas outlet where gas flows out.   2. The temperature control method for a fuel cell according to claim 1, wherein the water vapor partial pressure is changed by changing a flow rate of the reaction gas. 3.   3. The temperature control method for a fuel cell according to claim 1, wherein the water vapor partial pressure is changed by changing a pressure of the reaction gas.   The temperature control method of a fuel cell according to any one of claims 1 to 3, wherein the temperature of the fuel cell to be controlled is an outlet temperature of the reaction gas.   The temperature control method for a fuel cell according to claim 4, wherein the temperature of the fuel cell to be controlled is an outlet temperature of a reaction gas having a larger flow rate of gas flowing out of the fuel cell.   2. A water discharge port is provided in the vicinity of a reaction gas outlet from an electrode supplied with water together with the reaction gas, and the temperature of the fuel cell to be controlled is set to the water discharge port temperature. 4. The temperature control method for a fuel cell according to any one of 3 above.   In the fuel cell temperature control apparatus, water is supplied to the electrode of the fuel cell together with the reaction gas, cooling is performed by the latent heat of vaporization of the water, and the reaction gas is humidified by the vapor of the water. A temperature control device for a fuel cell, comprising a control means for controlling the temperature of the fuel cell by changing a partial pressure of water vapor in the vicinity of a reaction gas outlet where gas flows out.   The control means controls the driving of the reaction gas supply means for supplying the reaction gas to the electrode of the fuel cell, thereby changing the flow rate of the reaction gas and changing the water vapor partial pressure near the reaction gas outlet. The temperature control device for a fuel cell according to claim 7, wherein   The said control means changes the water vapor partial pressure of the said reaction gas exit part vicinity by drive-controlling the pressure adjustment means which changes the exit pressure of the said reaction gas, The Claim 7 or 8 characterized by the above-mentioned. Fuel cell temperature control device.   Temperature detection means for detecting the temperature of the reaction gas is provided in the vicinity of the reaction gas outlet, and the control means compares the detected temperature of the temperature detection means with the target fuel cell temperature, The temperature control device for a fuel cell according to any one of claims 7 to 9, wherein the temperature is controlled.

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