JP2005166309A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimally control a dew point of a reaction gas supplied to a fuel cell.
A fuel cell system (10) according to the present invention includes a fuel cell (80) that receives power supply to generate power and a reaction gas supply device (60) that supplies the reaction gas to the fuel cell (80). ), A humidifier (63) for humidifying the reaction gas, a gas temperature control means (20) for controlling the temperature of the reaction gas, and a dew point measurement device (64) for measuring the dew point of the reaction gas. The gas temperature control means (20) controls the dew point of the reaction gas by heating or cooling the reaction gas based on the dew point of the reaction gas measured by the dew point measuring device (64).
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to an improved technique for optimally controlling the dew point of a reaction gas according to the operating state of the fuel cell.

A polymer electrolyte fuel cell is formed by laminating a plurality of single cells each having a solid polymer electrolyte membrane sandwiched between an anode and a cathode through a separator. In this type of fuel cell, it is necessary to maintain the solid polymer electrolyte membrane in an appropriate wet state, so it is necessary to humidify the reaction gas (fuel gas, oxidizing gas) supplied to the fuel cell. In Japanese Patent Laid-Open No. 2002-280029, the amount of moisture added to the reaction gas is adjusted by controlling the driving amount of the humidifying pure water pump according to the power generation state of the fuel cell, and according to the operating state of the fuel cell. A technique for obtaining the optimum dew point of the reactive gas has been proposed. Furthermore, Japanese Patent Application Laid-Open No. 2003-3242 proposes a technique for obtaining a reaction gas having a target dew point temperature by controlling the temperature of the reaction gas humidified by a humidifier using a heating means such as a heater.
JP 2002-280029 A Japanese Patent Laid-Open No. 2003-3142

  However, in the technique described in Patent Document 1, the amount of moisture added to the reaction gas is controlled in controlling the dew point of the reaction gas, but the configuration for controlling the reaction gas temperature is not provided. If the reaction gas temperature changes greatly due to a change or the like, the target dew point temperature of the reaction gas cannot be obtained. Further, in the technique described in Patent Document 2, the reaction gas dew point is controlled by controlling the reaction gas to be heated. However, since the reaction gas is not actively cooled, the humidified reaction gas is not provided. When the temperature is high, a reaction gas having a target dew point temperature cannot be obtained.

  On the other hand, in a system that generates a low dew point gas by humidifying the reaction gas with steam or the like to a saturated state or a state close thereto, cooling the reaction gas with a heat exchanger to remove excess moisture, In order to generate a low dew point gas of ℃ or less, it is necessary to supply conditioned water with a negative temperature to the heat exchanger by a cooling means such as a chiller. When cooled, surplus moisture in the reaction gas may freeze inside the heat exchanger, and the reaction gas may not easily flow through the gas flow path.

  Accordingly, an object of the present invention is to solve the above-described problems and to propose a fuel cell system for controlling the reaction gas to an appropriate dew point.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell that generates power by receiving supply of a reaction gas, a reaction gas supply device that supplies the reaction gas to the fuel cell, and humidifies the reaction gas. A humidifier, a gas temperature control means for controlling the temperature of the reaction gas, and a dew point measurement device for measuring the dew point of the reaction gas, the gas temperature control means being based on the reaction gas dew point measured by the dew point measurement device The dew point of the reaction gas is controlled by heating or cooling. By heating or cooling the reaction gas, the dew point of the reaction gas can be optimally controlled. The reaction gas to be controlled for the dew point may be either fuel gas or oxidizing gas, or both.

  A fuel cell system of the present invention includes a fuel cell that receives power supply of a reactive gas to generate electric power, a reactive gas supply device that supplies the reactive gas to the fuel cell, a humidifier that humidifies the reactive gas, and a reactive gas A plurality of gas temperature control means arranged in the reaction gas supply path for controlling the temperature, and a dew point measurement device for measuring the dew point of the reaction gas, each gas temperature control means measured by the dew point measurement device By controlling the temperature of the reaction gas based on the dew point of the reaction gas, the dew point of the reaction gas is controlled stepwise. By controlling the temperature of the reaction gas stepwise, it is possible to control the reaction gas to an optimum dew point while enabling a stable supply of the reaction gas.

  Each gas temperature control means desirably controls the dew point of the reaction gas stepwise by cooling the reaction gas. By cooling the reaction gas in stages, a reaction gas having a low dew point temperature can be generated without freezing the gas flow path.

  According to the present invention, the reaction gas dew point can be optimally controlled by heating or cooling the reaction gas. In addition, by controlling the temperature of the reaction gas stepwise, it is possible to control the reaction gas to an optimum dew point while enabling stable supply of the reaction gas. In particular, in order to generate a reaction gas having a low dew point temperature, the reaction gas having a target dew point can be generated without freezing the gas flow path by cooling the reaction gas in stages.

Embodiment 1 of the Invention
FIG. 1 is a schematic configuration diagram of a fuel cell system according to a preferred first embodiment of the present invention.
The fuel cell system 10 is configured as a power generation device that is mounted on a fuel cell electric vehicle and generates power, and includes a fuel cell 80 that generates power by receiving supply of reaction gas (fuel gas, oxidizing gas). . The fuel cell 80 is a membrane / electrode assembly in which a cathode electrode 82 and an anode electrode 83 are formed by screen printing or the like on both surfaces of a solid polymer electrolyte membrane 81 made of a proton conductive ion exchange membrane or the like made of a fluorine resin or the like. 84. Both surfaces of the membrane / electrode assembly 84 are sandwiched by a ribbed separator (not shown), and a grooved cathode gas channel 85 and anode gas channel 86 are formed between the separator and the cathode electrode 82 and anode electrode 83, respectively. .

The reactive gas supply device 60 includes an oxidizing gas supply device 61 and a fuel gas supply device 62, and supplies the reactive gas to the fuel cell 80. The oxidizing gas supply device 61 supplies the oxidizing gas to the cathode gas channel 85 via the oxidizing gas channel 91. The fuel gas supply device 62 supplies the fuel gas to the anode gas channel 86 through the fuel gas channel 92. An oxidation reaction of the formula (1) occurs at the anode 83, and a reduction reaction of the formula (2) occurs at the cathode 82. In the fuel cell 80 as a whole, an electromotive reaction of the formula (3) occurs.
H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)
For convenience of explanation, the figure schematically shows the structure of a single cell consisting of a membrane / electrode assembly 84, a cathode gas channel 85, and an anode gas channel 86. A stack structure in which a plurality of single cells are connected in series via

  In order to maintain the proton conductivity of the solid polymer electrolyte membrane 81 in a good state, the solid polymer electrolyte membrane 81 needs to be appropriately wetted. Water replenishment to the solid polymer electrolyte membrane 81 is covered by water added to the reaction gas. Here, when the humidification amount of the reaction gas is too small, the solid polymer electrolyte membrane 81 is dried and the proton conductivity is lowered, so that sufficient generated power cannot be obtained. On the other hand, if the amount of humidification of the reaction gas is too large, the amount of condensed water in the gas channels 85 and 86 may increase and clogging may occur. If the gas channels 85 and 86 are clogged with water, the effective electrode area of the cell is reduced, and the reaction gas may not be supplied uniformly to each cell. In such a situation, voltage distribution occurs between the cells, and the cell having the lowest voltage may be stepped down to 0 V or less and overdischarged. For this reason, the reaction gas supplied to the fuel cell 80 is required to be maintained at an appropriate dew point (humidified state).

  Here, a case where the solid polymer electrolyte membrane 81 is maintained in an appropriate wet state by controlling the fuel gas to an appropriate dew point will be exemplified. A humidifier 63 that humidifies the fuel gas, a gas temperature control means 20 that controls the temperature of the fuel gas, and a dew point measuring device 64 that measures the dew point of the humidified fuel gas are disposed in the fuel gas flow path 92. ing. Since the dew point of the fuel gas can be controlled by the gas temperature and the water content, the fuel gas dew point can be adjusted by adjusting the humidification of the fuel gas by the humidifier 63 and adjusting the temperature of the fuel gas by the gas temperature control means 20. It can be adjusted optimally. The humidifier 63 supplies an appropriate amount of water to the fuel gas, saturates the water vapor in the gas, or adjusts it to a state close to this. As a method of supplying moisture to the fuel gas by the humidifier 63, a method that can stably supply moisture regardless of the operating state of the fuel cell 80 is desirable. For example, by installing a heat exchanger (not shown) in the oxygen off-gas exhaust system, the amount of water recovered from the oxygen off-gas is controlled, and the recovered water is pumped and supplied to the humidifier 63. Is preferred.

  The gas temperature control means 20 mainly circulates the temperature-controlled water, a heat exchanger 21 for exchanging heat between the fuel gas and the temperature-controlled water, a radiator 22 for raising the temperature-controlled water. It is provided with a circulation pump 23 for the purpose. The temperature adjustment of the temperature-controlled water is performed by adjusting the amount of water that bypasses the radiator 22 by controlling the opening and closing of the plurality of valves 24 to 26 arranged in the water channel. For example, when the valves 24 and 25 are opened and the valve 26 is closed, the temperature-controlled water is guided to the radiator 22 to increase the temperature. On the other hand, when the valves 24 and 25 are closed and the valve 26 is opened, the temperature adjusting water flows bypassing the radiator 22 and gradually cools down while exchanging heat with the outside air. The control unit 65 refers to the fuel gas dew point measured by the dew point measuring device 64, controls the gas temperature control means 20 so that the fuel gas dew point substantially matches the target dew point, and performs fuel gas dew point control.

Fuel gas dew point control is performed based on the following procedure.
(1) The humidifier 63 supplies an appropriate amount of moisture to the fuel gas and humidifies it in a saturated state or a state close thereto.
(2) The humidified fuel gas is supplied to the fuel cell 80 via the heat exchanger 21.
(3) The dew point measuring device 64 measures the dew point of the humidified fuel gas.
(4) The control unit 65 checks whether or not the fuel gas dew point substantially matches the target dew point. Here, when the measured dew point does not coincide with the target dew point, the following processing is performed.
(5) When the measured dew point is lower than the target dew point, the fuel gas is dry, so the fuel gas is cooled to condense the water droplets. As a result, the fuel gas in a dry state is in an appropriate humidified state, and the solid polymer electrolyte membrane 81 can be appropriately wetted.
In order to cool the fuel gas, the valves 24 and 25 are closed, the valve 26 is opened, and the temperature-controlled water is allowed to flow while the radiator 22 is bypassed. The temperature-adjusted water is gradually cooled while exchanging heat with the outside air without being supplied with heat from the radiator 22. The temperature-controlled water that has fallen to a low temperature exchanges heat with the fuel gas to cool the fuel gas. Open / close control signals for the valves 24 to 26 are output from the control unit 65 to the gas temperature control means 20.
(6) When the measured dew point is higher than the target dew point, since the fuel gas is excessively wet, the fuel gas is heated to evaporate excess water. As a result, the excessively wet fuel gas is in an appropriate humidified state, and the solid polymer electrolyte membrane 81 can be appropriately wetted.
In order to heat the fuel gas, the valves 24 and 25 are opened, the valve 26 is closed, and the temperature-controlled water is allowed to flow to the radiator 22. The temperature-controlled water gradually increases in temperature by receiving heat from the radiator 22. The temperature-controlled water heated to a high temperature exchanges heat with the fuel gas to heat the fuel gas. Open / close control signals for the valves 24 to 26 are output from the control unit 65 to the gas temperature control means 20.
(7) When battery operation is performed in an environment where the outside air temperature is low, or when the system is started up or warmed up, the temperature of the fuel gas is low and the dew point tends to be relatively high. It is desirable that the fuel gas is warmed by 21 to evaporate excess water.

  According to the present embodiment, by controlling the temperature of the fuel gas, it is possible to generate the fuel gas having the target dew point temperature. Therefore, it is possible to obtain an optimal fuel gas dew point (humidified state) suitable for battery operation.

Embodiment 2 of the Invention
FIG. 2 is a schematic configuration diagram of a fuel cell system according to a second preferred embodiment of the present invention.
About the apparatus etc. which attached | subjected the same code | symbol as FIG. 1, the same apparatus etc. shall be shown, and detailed description is abbreviate | omitted.
In the fuel gas flow path 92 of the fuel cell system 11, a humidifier 63 that humidifies the fuel gas and a plurality of gas temperature control means 30 and 40 installed in multiple stages in series to control the temperature of the fuel gas stepwise. A dew point measuring device 64 for measuring the dew point of the fuel gas is disposed. The gas temperature control means 30 mainly heats the temperature-controlled water, a heat exchanger 31 for exchanging heat between the fuel gas and the temperature-controlled water, a chiller 32 for cooling the temperature-controlled water. It comprises a heater 33 for circulation, a circulation pump 34 for circulating temperature-controlled water, and a trapper 35 for trapping condensed water. The gas temperature control means 40 has the same configuration. The control unit 65 refers to the fuel gas dew point measured by the dew point measuring device 64, controls the gas temperature control means 30 and 40 so that the fuel gas dew point substantially matches the target dew point, and controls the fuel gas dew point. Do.

Fuel gas dew point control is performed based on the following procedure.
(1) The humidifier 63 supplies an appropriate amount of moisture to the fuel gas and humidifies it in a saturated state or a state close thereto.
(2) The humidified fuel gas is supplied to the fuel cell 80 via the heat exchangers 31 and 32.
(3) The dew point measuring device 64 measures the dew point of the humidified fuel gas.
(4) The control unit 65 checks whether or not the fuel gas dew point substantially matches the target dew point. Here, when the measured dew point does not coincide with the target dew point, the following processing is performed.
(5) When the measured dew point is lower than the target dew point, the fuel gas is dry, so the fuel gas is cooled to condense moisture.
How much the temperature of the fuel gas is cooled depends on the target dew point. For example, assuming a case where dew point control is performed at a minus temperature (for example, −40 ° C.), the temperature at which excess moisture of the fuel gas is not frozen by the gas temperature control means 30 installed in the previous stage (for example, 1 to 3 ° C.). It is desirable to cool to a target dew point temperature (for example, −40 ° C.) by the gas temperature control means 40 in the subsequent stage after the water content is removed to a high level. Thus, freezing of excess water due to rapid cooling can be suppressed by lowering the gas temperature stepwise.
More specifically, the control unit 65 sets the temperature of the temperature-controlled water flowing through the heat exchangers 31 and 41 based on the target dew point temperature, and controls the gas temperature control means 30 and 40. Temperature-controlled water whose temperature is controlled by the chiller 32 and the heater 33 flows through the heat exchanger 31, and the fuel gas is cooled to a temperature at which the excess water does not freeze. Most of the water contained in the fuel gas aggregates and is trapped by the trapper 35.
The fuel gas from which most of the excess water has been removed is controlled by the heat exchanger 41 to a negative dew point temperature. Temperature-adjusted water having substantially the same water temperature as the target dew point temperature flows through the heat exchanger 41, and the temperature of the fuel gas is lowered to the target dew point temperature. Since most of the excess water is removed by the heat exchanger 31 in the front stage, only a small amount of water is condensed in the heat exchanger 41 in the rear stage, and the blockage of the gas flow due to water freezing can be suppressed.
(6) When the measured dew point is higher than the target dew point, since the fuel gas is excessively wet, the fuel gas is heated to evaporate excess water. When heating the fuel gas, it is not always necessary to control the temperature step by step with the temperature control means 30 and 40.
(7) When battery operation is performed in an environment where the outside air temperature is low, or when the system is started or warmed up, the temperature of the fuel gas is low and the dew point tends to be relatively high. It is desirable that the fuel gas is warmed by 31 and 41 to evaporate excess water.

  According to this embodiment, the reaction gas is cooled stepwise by the plurality of gas temperature control means 30 and 40 arranged in series along the reaction gas supply path, thereby blocking the gas flow path due to moisture freezing. Can be suppressed. Conventionally, when generating a low dew point gas, a method is known in which a humidified gas humidified with a bubbler or the like and a dry gas filled in a cylinder are mixed with high precision flow rate control. When the gas flow rate is small, the humidified gas flow rate becomes extremely small, and the dew point temperature accuracy is poor. On the other hand, according to the method of the present embodiment, dew point control can be performed with high accuracy.

Embodiment 3 of the Invention
FIG. 3 is a schematic configuration diagram of a fuel cell system according to a preferred third embodiment of the present invention.
About the apparatus etc. which attached | subjected the same code | symbol as FIG. 1, the same apparatus etc. shall be shown, and detailed description is abbreviate | omitted.
The fuel gas supply system of the fuel cell system 12 includes a fuel gas channel 92a piped upstream and fuel gas channels 92b and 92c piped in parallel downstream. A switching valve 70 is disposed at the bifurcated branch point of the fuel gas passages 92b and 92c so that the fuel gas supply passage (92a → 92b or 92a → 92c) can be switched. Gas temperature control means 30, 40, and 50 are disposed in the fuel gas flow paths 92a, 92b, and 92c, respectively, and the moisture condensed by these gas temperature control means 30, 40, and 50 is trapper 35, 45. , 55. The chiller 42 performs cooling control of temperature-controlled water flowing through the heat exchanger 41 and also serves as cooling control of temperature-controlled water flowing through the heat exchanger 51.

  In this way, by arranging the gas temperature control means 40 and 50 in the subsequent stage in parallel, the fuel gas flowing through one of the gas temperature control means 40 (or 50) is frozen or due to accumulation of ice blocks. By controlling the switching valve 70 so that the fuel gas flows to the other gas temperature control means 50 (or 40) when the stagnation of the gas flow occurs, a stable gas supply to the fuel cell 80 can be ensured. The switching operation of the switching valve 70 is controlled by the control unit 65. Freezing of the gas flow path can be detected, for example, when the differential pressure between the gas inlet pressure of the heat exchanger 41 or 51 and the gas outlet pressure exceeds a predetermined value. When the gas flow path is frozen, the heater 43 or 53 is operated to raise the temperature of the temperature-controlled water, thereby warming up the heat exchanger 41 or 51, thereby melting the ice and closing the gas flow. The road can be opened.

  According to the present embodiment, the reactive gas supply path that can switch the flow path is disposed, and when any one of the reactive gas supply paths is frozen when the low dew point gas is generated, the other reactive gas supply path is provided. In addition, by switching the gas flow path, a stable reaction gas supply to the fuel cell can be realized. Of course, it is not always necessary to be able to switch the flow path. For example, when a plurality of reaction gas supply paths are arranged in advance and one of the reaction gas supply paths is frozen, other reaction gas You may comprise so that reaction gas may be supplied from the reaction gas supply apparatus 60 toward a supply path.

  In each of the above-described embodiments, the case where the dew point of the fuel gas is controlled is exemplified. However, the present invention is not limited to this. For example, by controlling the temperature of the oxidizing gas, the dew point of the oxidizing gas is controlled. The dew point may be controlled by controlling the temperature of both the fuel gas and the oxidizing gas.

It is a principal lineblock diagram of the fuel cell system of a 1st embodiment. It is a principal block diagram of the fuel cell system of 2nd Embodiment. It is a principal block diagram of the fuel cell system of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 11, 12 ... Fuel cell system 20, 30, 40, 50 ... Gas temperature control means 63 ... Humidifier 64 ... Dew point measuring device 80 ... Fuel cell

Claims (3)

A fuel cell that generates power by receiving a supply of reaction gas; and
A reaction gas supply device for supplying the reaction gas to the fuel cell;
A humidifier for humidifying the reaction gas;
Gas temperature control means for controlling the temperature of the reaction gas;
A dew point measuring device for measuring the dew point of the reaction gas,
The fuel temperature system, wherein the gas temperature control means controls the dew point of the reaction gas by heating or cooling the reaction gas based on the dew point of the reaction gas measured by the dew point measuring device. A fuel cell that generates power by receiving a supply of reaction gas; and
A reaction gas supply device for supplying the reaction gas to the fuel cell;
A humidifier for humidifying the reaction gas;
A plurality of gas temperature control means disposed in a reaction gas supply path to control the temperature of the reaction gas;
A dew point measuring device for measuring the dew point of the reaction gas,
Each gas temperature control means controls the dew point of the reaction gas stepwise by controlling the temperature of the reaction gas based on the dew point of the reaction gas measured by the dew point measuring device. The fuel cell system according to claim 2, wherein
Each of the gas temperature control means controls the dew point of the reaction gas stepwise by cooling the reaction gas.

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