JP2004335269A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain deterioration of a battery material caused by frequent start and stop, in a fuel cell power generation system. <P>SOLUTION: This fuel cell system is characterized in that a part of cooling water branched from a cooling water line for running the cooling water is connected to at least an anode line and a cathode line, in a fuel cell that is so structured that an off-gas exhausted from a power generation part is brought into contact with a supply gas through a humidification material, and a humidification part for adding steam to the supply gas is connected with the power generation part having a cooling function by the cooling water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power generation system using a fuel cell.
[0002]
[Prior art]
A fuel cell is an electrochemical device that directly converts fuel energy into electrical energy by an electrochemical reaction. Fuel cells are roughly classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte fuel cells (hereinafter abbreviated as PEFC), and alkaline fuel cells, depending on the charge carriers used. Is done.
[0003]
Among these various fuel cells, PEFC can be used for high current density power generation and operation at a relatively low temperature, and thus is expected to be applied to various uses including a mobile power source.
[0004]
For the electrolyte of the PEFC, an ion exchange membrane having a film thickness of several tens to one hundred and several tens μm is used. The ion exchange membrane generally has a structure in which a side chain having a sulfonic acid group is bonded to a fluorocarbon constituting a main chain. Ion exchange membranes have proton conductivity, for which the membrane material must contain moisture. This is because the sulfonic acid group has a cluster structure in the material, the clusters are connected by a channel, and protons (H ₃ O ⁺ ) are conducted in the channel. Therefore, the presence of water is essential for the present material to exhibit proton conductivity.
[0005]
For this reason, in a power generation system using a PEFC, when operating a battery, a method is generally used in which a supplied gas contains moisture for humidifying an electrolyte. At the time of PEFC power generation, water is generated by the chemical reaction, but it is not enough to wet the electrolyte, and it is currently difficult to construct a system that does not supply any external moisture.
[0006]
Means for humidifying the gas supplied to the battery include a bubbler method and a material permeation method. Of these, the bubbler method is difficult to adopt as a humidifier for a small high-efficiency power supply system due to problems of heat loss and installation space. Therefore, a gas humidification method using a water permeable material is widely used. This is a method in which a humidifying fluid and a humidifying fluid are caused to flow through a water-permeable material, and humidification is performed by utilizing a characteristic in which water molecules move to the humidifying fluid using a difference in water pressure as a driving force.
[0007]
When water is used as the humidifying fluid, the water that has moved through the permeable material evaporates on the contact surface with the humidifying fluid, and heat of evaporation is lost. Therefore, high humidification can be realized by using high-temperature water as the humidification fluid. From these facts, there has been reported a system that uses battery cooling water as a humidifying fluid and dry gas as a humidifying fluid via a water-permeable material as a humidifier for humidifying a gas supplied to the battery.
[0008]
However, in the case of so-called combined heat and power supply that supplies heat (hot water) in addition to electric power as a power supply system, this humidification method consumes a part of the generated heat due to the evaporation heat of the humidifier, so the overall efficiency is reduced. There was a problem to be reduced.
[0009]
Therefore, a method has been proposed in which a cathode exhaust gas (off-gas) is used as the humidifying fluid instead of the cooling water that exchanges the heat of the battery. Since water generated by power generation is theoretically generated on the cathode, this method uses the water for humidification. Japanese Patent Application Laid-Open No. 6-132038 is an example of a report of this method.
[0010]
[Patent Document 1]
JP-A-6-132038
[Problems to be solved by the invention]
However, in the humidification method using off-gas, when power is not being generated, that is, during warming-up when the battery is activated, or during cool-down when the battery is stopped, humidification of the supplied gas is insufficient or humidification cannot be performed at all. Or had problems. In particular, in the case of a sequence in which the power supply system is stopped by the supply state of electric power or hot water, the number of times of starting / stopping increases, and the insufficient humidification of the supplied gas causes deterioration of the electrolyte material and a main factor for shortening the life of the battery. Was one of SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell power generation system that is less deteriorated even when the system is frequently started and stopped.
[0012]
[Means for Solving the Problems]
Therefore, in the present invention, in the fuel cell in which the off gas discharged from the power generation unit and the supply gas are brought into contact via a humidifying material, and the humidification unit for adding water vapor to the supply gas and the power generation unit having a cooling function of cooling water are connected. There is proposed a structure in which a part of cooling water branched from a cooling water line through which the cooling water flows is connected to at least an anode line and a cathode line.
[0013]
In this structure, water from the cooling water line is added to the off-gas which is a humidifying fluid at the time of starting / stopping the battery where the supply gas is insufficiently humidified, so that the water pressure of the humidifying fluid is improved, and the battery which is the humidifying fluid is added. The humidification of the supply gas can be made sufficient.
[0014]
Further, a connecting portion where the part of the cooling water branched from the cooling water line and the anode or the cathode gas line are connected to each other constitutes the power generation unit from the collecting portion where the anode or the cathode off gas of each cell is assembled. A structure located between the entrances is proposed.
[0015]
In this structure, the cooling water branched from the cooling water line is not directly supplied to the battery, but can be humidified as steam by the humidifier to the supply gas. In the case of PEFC, if liquid water is present in the vicinity of the electrode reaction section inside the battery, diffusion of oxygen (air) or hydrogen, which is a reactive species, is hindered and battery performance may be rapidly deteriorated. For this reason, as in this structure, it is effective to stabilize the performance of the battery if a humidified form in which water is added to the supply gas can be taken. The connecting portion where the cooling water and the gas line are connected in claim 2 may be set on the downstream side from the collecting portion where the exhaust gas of each cell is collected. For example, even if the power generating portion and the humidifying portion are integrated, It is obvious that the same effect can be obtained by directly attaching a water injector from the outside to the exhaust gas manifold structure portion flowing through the portion.
[0016]
In addition, a structure is proposed in which an adjustment mechanism is provided for controlling the temperature of a part of the cooling water connected to the anode or cathode gas line.
[0017]
According to this structure, since the temperature of the humidifying fluid can be arbitrarily controlled and the water pressure in the humidifying fluid can be increased, the humidification amount in the humidified fluid in the humidifier can also be effectively increased, and the humidification of the electrolyte material can be performed. Deterioration due to shortage can be greatly suppressed. As a method of controlling the temperature, a heater, a sensor, and a temperature controller that directly heats the cooling water may be used, or the heat of the battery may be recovered, and the high-temperature cooling water may be reserved in a buffer tank or the like. It may be used by mixing with low-temperature cooling water and adjusting the temperature accordingly.
[0018]
Further, a flow control valve is provided at a connection portion where a part of the cooling water branched from the cooling water line and the anode or the cathode gas line are connected, and at least a power generation unit voltage, a power generation unit load current, a power generation unit temperature, a supply gas type, A structure having a mechanism for determining whether the valve is opened or closed from one signal of the gas flow rate has been proposed.
[0019]
According to this structure, the control unit determines whether the humidification is insufficient by various sensors based on the status of the battery and the humidification unit accompanying the start / stop, and connects a part of the cooling water branched from the cooling water line to the gas line. Since the amount of water can be optimally controlled in a timely manner by the valve of the section, the situation of insufficient humidification of the electrolyte hardly occurs, and as a result, the deterioration of the battery can be extremely reduced.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
(Example 1)
FIG. 1 shows a configuration of a fuel cell system according to Embodiment 1 of the present invention. The fuel cell power generation unit 1 in FIG. 1 is connected to an anode gas line for supplying a hydrogen-rich gas, and the anode gas is limited to a predetermined amount by an anode gas flow controller 3. Further, a cathode gas line for supplying a gas containing oxygen is also connected, and the supply amount is controlled by a cathode gas flow controller 4. Water vapor is added to the cathode gas whose flow rate is controlled from the surface of a water-permeable material disposed inside the humidifying unit 2, and is introduced into the cathode of the power generation unit 1. Oxygen in the cathode gas is consumed in the electrode reaction in the power generation unit 1, but gas that does not participate in the reaction is discharged from the power generation unit as off-gas. At this time, since the reaction off-gas is added to the cathode off-gas, the cathode off-gas contains a large amount of water vapor. The cathode off-gas is supplied to the humidifier 2, comes into contact with the water-permeable material disposed in the humidifier, transfers the contained moisture to the water-permeable material, and is discharged from the humidifier outlet.
[0022]
Since the electrode reaction occurring in the battery is an exothermic reaction, the temperature of the battery becomes high. Since the electrolyte membrane, which is one of the constituent materials of the battery, deteriorates at a high temperature, a cooling means is required. This system adopts a water cooling system that circulates cooling water and cools. The amount of the cooling water from which the contained ions have been removed by the pretreatment is controlled by the water amount controller 1 of 5 and supplied to the power generation unit. After performing heat exchange in the power generation unit, a part of the cooling water is branched, and after its flow rate is controlled by the water amount controller 2 of 6, the cooling water is added to the cathode gas supplied to the power generation unit.
[0023]
(Example 2)
FIG. 2 shows the configuration of the fuel cell system according to Embodiment 2 of the present invention. In the present system, the amount of the cooling water from which the contained ions have been removed by the pretreatment is controlled by the water amount controller 1 of 5, and supplied to the power generation unit. Here, the cooling water is located on the downstream side in the gas flow from the collection portion of the cathode gas in the power generation unit, and is connected to the upstream side from the humidification unit off gas inlet. Other configurations in the present system are in accordance with the first embodiment.
[0024]
(Example 3)
Third Embodiment FIG. 3 shows the configuration of a fuel cell system according to a third embodiment of the present invention. In this system, the amount of water is controlled by a water amount controller 6 of 6, and a cooling water branch line supplied to the humidifier 2 is equipped with a temperature control heater. Other configurations in this system are in accordance with the second embodiment.
[0025]
(Example 4)
Fourth Embodiment FIG. 4 shows the configuration of a fuel cell system according to a fourth embodiment of the present invention. In this system, a water flow controller 1 that controls the water flow and automatically controls the water flow is connected to six water flow controllers 2 installed in a cooling water branch line that supplies the humidifying section 2. The water volume controller 2 uses the power generation unit temperature signal line 14 to indicate the power generation unit temperature, the power generation unit voltage signal line 15 to indicate the voltage of the power generation unit, the load signal line 13 to indicate the load value of the load detector 11, and the humidification unit temperature signal line 17. Monitoring the temperature of the humidifying unit 2 and the flow rate of the supplied gas with the flow signal line 16 respectively, and based on at least one signal, obtain the amount of water required to suppress the deterioration of the battery electrolyte material and secure the flow rate. The water regulator 2 is controlled in order to achieve this. Other configurations in this system are in accordance with the third embodiment.
[0026]
(Comparative example)
FIG. 5 shows a fuel cell system configuration of a comparative example. An anode gas line for supplying a hydrogen-rich gas is connected to the fuel cell power generation unit 1 in FIG. 5, and the anode gas is limited to a predetermined amount by an anode gas flow controller 3. Further, a cathode gas line for supplying a gas containing oxygen is also connected, and the supply amount is controlled by a cathode gas flow controller 4. In the humidifying section 2, steam is added to the cathode gas whose flow rate is controlled from the surface of a humidifying film disposed inside the humidifying section 2, and is introduced into the cathode of the power generation section 1. Oxygen in the cathode gas is consumed in the electrode reaction in the power generation unit 1, but gas that does not participate in the reaction is discharged from the power generation unit as off-gas. At this time, since the reaction off-gas is added to the cathode off-gas, the cathode off-gas contains a large amount of water vapor. The cathode off-gas is supplied to the humidifier 2, comes into contact with the water-permeable material disposed in the humidifier, transfers the contained moisture to the water-permeable material, and is discharged from the humidifier outlet.
[0027]
Since the electrode reaction occurring in the battery is an exothermic reaction, the temperature of the battery becomes high. Since the electrolyte membrane, which is one of the constituent materials of the battery, deteriorates at a high temperature, a cooling means is required. This system adopts a water cooling system that circulates cooling water and cools. The amount of the cooling water from which the contained ions have been removed by the pretreatment is controlled by the water amount controller 1 of 5 and supplied to the power generation unit.
[0028]
A fuel cell power generation system having a stacking number of 60 cells and an output of 0.8 kW having the basic structure of the system shown in the above-described Examples and Comparative Examples was manufactured, and a power generation test was performed. For the power generation, an operation mode in which the system was stopped every day at 24:00 and the system was started at 6:00 was adopted with reference to a typical general household power usage pattern. The power generation pattern was 100% load from 6:00 to 9:00, 11:00 to 15:00, 18:00 to 21:00, and the other 50% load. After performing this pattern for 2 months, the open circuit voltage (OCV) of the battery, the battery voltage when the current value per electrode area is 0.33 A / cm ² , and the voltage variation of each unit battery constituting the power generation unit are compared. did. FIG. 6 shows the result.
[0029]
In the comparative example, the average OCV per cell from the initial stage was 990 mV, and after the test, the average OCV was 940 mV, a decrease of 50 mV. The average battery voltage at 0.33 A / cm ² dropped 70 mV from the initial 720 mV to 650 mV. The variation of each unit voltage at this time was ± 15 mV. In this comparative example, the battery performance after the test was deteriorated because the amount of absolute water supplied to the power generation unit at the time of starting and stopping the system was insufficient, and the deterioration of the electrolyte material proceeded. It is considered that the gas separation property was reduced.
[0030]
In Example 1, the OCV drop after the test was −30 mV, and the average battery voltage at 0.33 A / cm ² dropped from the initial 720 mV to 670 mV by 50 mV. The variation of each unit battery was ± 25 mV. In Example 1, the suppression of deterioration was confirmed at the OCV and the average battery voltage value at 0.33 A / cm ² compared to the comparative example. This is considered to be because the shortage of the absolute water amount supplied to the power generation unit at the time of starting and stopping the system is reduced. The large voltage variation means that the cooling water branch line is connected upstream of the power generation unit with a gas flow, so that liquid water is supplied to the power generation unit and the gas that contributes to the electrode reaction to block the gas channel in the battery. This is thought to be due to the phenomenon that the diffusion of the chromium is prevented (flooding) and the voltage temporarily drops.
[0031]
In Example 2, the drop after the OCV test was −20 mV, and the average battery voltage at 0.33 A / cm ² dropped from the initial 720 mV to 700 mV by 20 mV. The variation of each unit battery was ± 16 mV. In Example 2, as compared with Example 1, suppression of deterioration was confirmed at the OCV and the average battery voltage value at 0.33 A / cm ² . Further, the voltage variation is improved. This is because, in the structure shown in the second embodiment, the cooling water branched from the cooling water line is not directly supplied to the battery, but can be humidified to the supply gas as water vapor through the humidifier by the humidifier, and flooding is performed. It is considered that it can be suppressed.
[0032]
Decrease after the test of the OCV in Example 3 is -2 mV, the average battery voltage at 0.33 A / cm ² was 10mV decreased from an initial 720mV to 710mV. The variation of each unit battery was ± 5 mV. Example 3 was able to further improve OCV and average battery voltage value at 0.33 A / cm ² and voltage variation as compared with Example 2. This is because the temperature of the cooling water supplied to the humidifying unit can be arbitrarily controlled by the heater, and the energy of the humidifying fluid in the humidifier can be increased. The humidification amount can also be effectively increased. It is considered that as a result, deterioration due to insufficient humidification of the electrolyte material can be significantly suppressed.
[0033]
In Example 4, the decrease in OCV after the test was −0.5 mV, and the average battery voltage at 0.33 A / cm ² was equivalent to the initial value. The variation of each unit battery can be suppressed to ± 3 mV. In this structure, the control unit determines whether the humidification is insufficient by various sensors based on the status of the power generation unit and the humidification unit accompanying the start / stop of the system. Because it is possible to control the amount of water optimally and automatically and finely in a timely manner by the adjuster in the connecting part, it does not cause insufficient humidification of the electrolyte, and as a result, the deterioration of the battery can be extremely reduced. Conceivable.
[0034]
In the present embodiment, a test mainly using the exhaust gas on the cathode side was performed. However, the supplied anode gas is preliminarily added with water to prevent drying of the electrolyte, and a part of the water generated during power generation is added to the anode gas through the electrolyte membrane. The off-gas also contains sufficient moisture. Further, since the proposed structure can be applied equally to the anode and the cathode, it goes without saying that the structure can be used not only for the cathode but also for the structure on the anode side.
[0035]
When a so-called combined heat and power supply that supplies heat (hot water) in addition to electric power as a power supply system using a fuel cell is performed, a method of using battery exhaust gas (off gas) as a humidifying fluid has been proposed to improve overall efficiency. ing. This method has a problem that when power is not being generated, that is, during the warm-up when the battery is activated, or during the cool-down when the battery is stopped, the gas supplied is insufficiently humidified, or the humidification cannot be performed at all. As a result, the humidification of the supplied gas is insufficient, which causes deterioration of the electrolyte material, and shortens the life of the battery. According to the present invention, the fuel cell power generation system can be effectively wetted with the use of the battery cooling water during the warm-up of the system or during the cool-down, so that the deterioration of the fuel cell power generation system is extremely small even when the system is frequently started and stopped. Can be provided.
[0036]
【The invention's effect】
According to the present invention, it is possible to provide a fuel cell power generation system with less deterioration even when the system is frequently started and stopped.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a part of a power generation system configuration according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a part of a power generation system configuration according to a second embodiment of the present invention.
FIG. 3 is a diagram illustrating a part of a power generation system configuration according to a third embodiment of the present invention.
FIG. 4 is a diagram illustrating a part of a power generation system configuration according to a fourth embodiment of the present invention.
FIG. 5 is a diagram showing a part of a power generation system configuration in a comparative example.
FIG. 6 is a diagram showing the performance of an example and a comparative example before and after a test.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Power generation part, 2 ... Humidification part, 3 ... Anode gas flow rate regulator, 4 ... Cathode gas flow rate regulator, 5 ... Water volume regulator 1, 6 ... Water volume regulator 2, 7 ... Heater, 11 ... Load detector, 12: controller, 13: load signal line, 14: power generation unit temperature signal line, 15: power generation unit voltage signal line, 16: flow rate signal line, 17: humidification unit temperature signal line.

Claims (4)

A power generation unit in which a plurality of fuel cell single cells having a basic configuration including an anode, a cathode, an electrolyte, and a separator are stacked and a power generation unit having a cooling function is brought into contact with an off-gas and a supply gas discharged from the power generation unit via a humidifying material. A fuel cell system, wherein a part of cooling water branched from a cooling water line through which cooling water flows in a fuel cell in which a humidifying part for adding steam to water is connected to an anode or a cathode gas line. The connection part where the part of the cooling water branched from the cooling water line and the anode or the cathode gas line are connected is connected from the collecting part where the anode or the cathode off gas of each cell constituting the power generating part is gathered to the power generation part off gas inlet part of the humidifying part. The fuel cell according to claim 1, wherein the fuel cell is located between the fuel cells. 3. The fuel cell system according to claim 1, further comprising an adjusting mechanism for controlling the temperature of a part of the cooling water connected to the anode or cathode gas line. A flow control valve is provided at the connection between the part of the cooling water branched from the cooling water line and the anode or cathode gas line. 4. The fuel cell according to claim 1, further comprising a mechanism for determining whether the valve is opened or closed based on one of the signals.

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