JPS6366860A - Methanol fuel cell - Google Patents

Abstract

PURPOSE:To make the supply of water from the outside of a cell unnecessary by installing a heat exchanger into which exhaust gas of oxygen containing gas supplied to a cathode is introduced and in which water vapor in the exhaust gas is cooled and condensed, and a circulator by which condensed water is circulated to an anolyte. CONSTITUTION:When liquid level is lower than a specified value, a control signal from a liquid level sensor 8 is sent to a passage valve 10 and a passage valve 9. The passage valve 9 is opened by a signal S1 from the sensor 8, and the air is supplied to a cell stack 1 by the operation of a blower 4 through a heat exchanger 6. The air passed through the cell stack 1 is exhausted as exhaust gas. The exhaust gas containing a large volume of water vapor passes through the heat exchanger 6 through the passage valve 9 since the passage valve 10 is closed, then the gas is exhausted to the outside of the cell. In the heat exchanger, heat exchange is performed between the exhaust gas and the air, and a large volume of water vapor in the exhaust gas is condensed as condensed water 30, and the condensed water is supplied to an anolyte tank 2 through a pipeline 7. When the liquid level in the tank 2 reaches a specified value, the recovery of the condensed water is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a methanol fuel cell, and is particularly applicable to a power generation system that uses methanol as fuel and uses an acidic electrolyte such as an aqueous sulfuric acid solution.

[Conventional technology]

A fuel cell directly extracts the reaction energy of a fuel and an oxidant as electrical energy.

It is expected to be a new power generation method because it has high power generation efficiency, low noise and vibration, and clean exhaust gas.

In particular, acidic electrolyte methanol fuel cells (hereinafter referred to as "methanol fuel cells") that use liquid methanol as fuel operate at normal pressure and relatively low temperatures (approximately 60°C), and are easy to miniaturize. It is suitable as a portable power source. However, in order to put a single battery into practical use, it is necessary to take advantage of these fundamental features to construct a power generation system that is easy to operate and maintain.

Conventionally, there is a conventional example of a fuel supply system to solve this problem, as seen in Japanese Patent Laid-Open No. 56-93268.

Next, the structure and operation of the methanol fuel cell will be explained.

In a methanol fuel cell, the anode (fuel electrode).

The electrolyte (GH ion exchange membrane and A acid) and the cathode (A and other agents) form a unit battery, and a large number of unit batteries are stacked with separators in between (configuring a series circuit of unit batteries). , a fuel cell stack is constructed. A predetermined output voltage can be obtained with this battery stack.

The separator is a connector that electrically connects the unit batteries, and is therefore made of a conductive material.

Furthermore, grooves are provided on both sides of the separator, and methanol as a fuel is supplied to the anode, and air as an oxidizer is supplied to the cathode through the flow path formed between the grooves and the electrodes. .

Methanol is supplied to the anode by circulating anolite (a mixture of methanol, sulfuric acid, and water) from the anode tank to the anode. In the above separator, methanol and air are mixed between adjacent unit cells. It is designed to prevent mixing.

At the methanol pole (anode), CHsOH+HzO-4COz+6H+6e-...(
1) The following reaction has occurred, resulting in an excess of electrons.

Conversely, at the air electrode (cathode), a reaction of 6H++3/20"+6e""→3HzO-(2) occurs, and there is a shortage of electrons. When the anode and cathode are connected with an external circuit, a flow of electrons occurs. You can extract electricity.

In the end, the total reaction is CH30H+H20+3/20z4COz+3)+12
0...(3) The following reaction occurs.

[Problem that the invention seeks to solve]

However, in reality, there is water that does not participate in the reaction and is discharged from the system, and water is produced by combustion of methanol and air, so the actual mass balance is complicated.

Although it depends on the operating conditions of the methanol fuel cell, the cell structure, and the cell scale, the inventor of the present invention has investigated and found that the actual material balance is as follows.

CHs○H+4.1HzO+1.502→COz+ 6
, I H2O...(4) That is, the theoretically equivalent mole of water required for methanol is 4.1 times the theoretical value. Therefore, a large amount of distilled water must be constantly replenished to ensure that the cell reaction proceeds smoothly.

In order to solve such problems, the present invention provides i2! The purpose of the present invention is to provide a methanol fuel cell that does not require water supply from outside the pond.

[Means for solving problems]

The present invention provides a fuel cell stack in which a plurality of unit cells each consisting of a cathode and an anode facing each other while sandwiching an electrolyte are stacked together with a separator interposed therebetween; A methanol fuel cell comprising: a gas supply device for supplying a gas containing oxygen; This methanol fuel cell is characterized by comprising a reflux device for refluxing water to the 7-nolite.

[Effect]

According to the configuration of the present invention described above, exhaust gas from the air electrode containing a large amount of water vapor can be guided to the heat exchanger, cooled, and water can be recovered. By circulating this collected water to the anolyte tank, there is no need to replenish water from outside the yarn.

〔Example〕

Next, examples of the methanol fuel cell according to the present invention will be described.

FIG. 1 shows a block diagram of an embodiment. In FIG. 1, a battery stack 1 having a cathode and an anode is provided. The anode is equipped with a pipe 23 through which the anolite in the anolite tank 2 is supplied via a pump 3. This pipe 23 has a loop shape, and an anolite circulates inside.

Anolyte is a mixture of methanol, sulfuric acid and water. A liquid level sensor 8 is provided near the anolite liquid level in the anolite tank 2.

From the methanol tank 24 to the anorite tank 2,
Methanol is now supplied.

Further, a pipe 25 is provided in the battery stack 1, and air is supplied to the cathode by a blower 4, and after the reaction, air is discharged as exhaust gas.

The pipe 25 leading to the cathode passes through the heat exchanger 6, and the pipe exiting the cathode also passes through the heat exchanger 6.

A flow path valve 9 is provided on the downstream side of the battery stack of the piping 25 and on the upstream side of the heat exchanger 6. Further, a similar flow valve 11 is provided upstream of the battery stack and downstream of the heat exchanger 6.

A pipe 26 that bypasses the heat exchanger 6 is connected to the pipe 25 . A flow path valve 12 is provided on the upstream side of the pipe 25 of the pipe 26 .

A pipe 27 having a flow path valve 10 is provided upstream of the pipe 25 in which the flow path valve 9 is provided.

In the methanol fuel cell according to this embodiment configured as described above, coagulated water is recovered from the water vapor discharged from the air electrode (cathode) and supplied to the fuel electrode (anode), thereby eliminating the need for water replenishment. It can be achieved.

This specific operation will be explained.

Condensed water is collected by a liquid level sensor 8 provided in the anorite tank 2. That is, the liquid level sensor 8 detects that the amount of liquid in the anorite tank is at a predetermined value. If the water amount is at a predetermined value, water will not be collected;
If the amount of water is less than a predetermined value, water is recovered.

First, a case where the liquid level is lower than a predetermined value will be explained.

A control signal from the liquid level sensor 8 is sent to the flow path valve 1o and the flow path valve 9. A signal S1 sent to the flow path valve 9 opens the flow path valve 9°. - channel valve 10 by force signal S2;
is closed. Further, when water is to be recovered, the flow path valve 12 is closed and the flow path valve 11 is opened. first,
The movement of the blower 4 supplies air into the battery stack 1 through the heat exchanger. The air that has passed through the battery stack becomes exhaust gas, which contains a large amount of water vapor.

Since the flow path valve 10 is closed, this exhaust gas containing a large amount of water vapor passes through the heat exchanger 6 via the flow path valve 9 and is discharged to the outside of the system as exhaust gas. In the heat exchanger 6, heat exchange is performed between the exhaust gas and air, and a large amount of water vapor in the exhaust gas becomes condensed water 30, which is generated in the heat exchanger 6 and then transferred to the anolyte tank 2 via piping 7. supplied inside. In this way, when the liquid level in the anolyte tank 2 reaches a predetermined level, collection of condensed water is stopped.

Next, the operation when stopping recovery of condensed water will be explained. When the amount of anolite in the anolite tank 2 reaches a predetermined height according to the liquid level sensor 8, the flow path valve 10 is opened by the control signal S2, and the flow path is opened by the control signal S1 from the liquid level sensor 8. Valve 9 is closed.

When the flow path valves are controlled in this manner, the exhaust gas that has passed through the battery stack is not supplied to the heat exchanger 6, but instead flows through the flow path valve 1.
Exhaust gas is discharged to the outside of the system via o. At this time, there is no heat exchange between the air and the exhaust gas.

No condensed water forms in the heat exchanger 6 and therefore no water is supplied into the anolyte tank.

By controlling the flow path valves as described above, condensed water can be recovered. This condensed water can be collected not only by opening and closing the flow path valve but also by adjusting the opening degree of the flow path valve. That is, by adjusting the opening degrees of the flow path valves 10 and 9, the amount of exhaust gas introduced into the heat exchanger 6 can be adjusted to a predetermined amount.

As a result, since the amount of condensed water can also be adjusted, the amount of anolyte in the anolyte tank can be adjusted to a predetermined value. Such adjustment of the valve opening degree is effective in the following cases.

Exhaust gas temperature (varies depending on operating conditions) and heat exchanger 6
Even if the operating temperature (cooling temperature) fluctuates and the production rate of condensed water changes, the necessary water can be reliably recovered regardless of this. Moreover, the control method is simple, and in particular, by opening/closing the valve and adjusting the valve opening degree, water can be recovered reliably without the need for equipment with complicated functions.

As can be seen from the above mass balance equation, the cell reaction of a methanol fuel cell requires about 4 times as much water (in molar ratio) as methanol, but about 6 times as much water (in molar ratio) as water vapor is required. Since it is contained in the exhaust gas discharged from the air electrode, the entire required amount of water can be recovered from the exhaust gas. As a result, only methanol can be used as a replenisher to the anolyte tank 2 during operation, and there is no need to replenish water. The quality of the recovered water is such that, other than water, the only substances contained are a trace amount of unreacted methanol and a substance produced by its partial oxidation, and there are no other impurities, so there is no problem in the battery reaction.

If condensed water is not recovered, it is necessary to supply distilled water to the anolyte tank 2 from outside the system, but it is normal for a considerable amount of impurities to be present in the distilled water as well.

As a result, impurities may accumulate in the anorite tank over a long period of time, but if pure condensed water can be obtained as in this example, it is suitable for stable battery operation. It can be said that

The anolite in the anolyte tank 2 flows through the battery stack 1 by the action of the pump 3 and enters the anolyte tank 2! # It is designed to be linked.

The water in the anolyte will be consumed at the anode of the battery stack, causing the liquid level in the anolyte tank 2 to drop. As described above, in this embodiment, the drop in the liquid level can be detected by the liquid level sensor 8 and the condensed water can be recovered. Furthermore, if a large amount of water needs to be recovered, a large amount of exhaust gas may be guided to the heat exchanger 6, and conversely, if only a small amount of water is required, a small amount of exhaust gas may be guided to the heat exchanger 6.

In this embodiment, the air absorbs heat from the exhaust gas, causing the air temperature to rise. Therefore, preheated air is sent into the battery stack 1, making it possible to keep the batteries warm and control the temperature.

Furthermore, since the air supplied to the battery stack is heated at the start of battery operation, the predetermined operating temperature can be quickly maintained to about 60°C. Therefore, a quick start is possible.

In the above embodiment, heat exchange is performed between air and exhaust gas. Therefore, only one cooling blower (4 blowers) is required, and the apparatus can be made more compact. Therefore, the range of application of methanol fuel cells, which are characterized by their portability, will be expanded. Note that since the temperature of the air with which the heat of the exhaust gas has been exchanged increases, the temperature of the battery stack may rise to a predetermined value or higher. In such a case, the following control can also be performed. That is,
A temperature sensor is placed inside the battery stack, and when the temperature signal from the temperature sensor exceeds a certain value, the valve 11 is closed and the flow path valve 12 is opened.

As a result, the air is supplied into the cathode 21 through the blower 4 at its normal air temperature without passing through the valve 11 and the heat exchanger 6. As a result, the internal temperature of the cathode can be cooled, and dangers in battery operation due to temperature rise can be prevented.

In this embodiment, as shown in FIG. 1, a heat exchanger 6 is provided above the anorite tank 2, and the condensed water 30 is supplied to the anorite tank 2 with a difference in water head without providing a liquid feeding means such as a pump. Can be done. Therefore, the device can be made more compact and its security can be made easier.

As described above, in this embodiment, the water vapor in the exhaust gas is condensed by detecting the liquid level in the anorite tank 2, and the condensed water is supplied into the anorite tank 2. Another possible control is to detect the sulfuric acid concentration in the anorite tank and control whether or not heat exchange is necessary and the degree of heat exchange between exhaust gas and air.

That is, the more water in the anorite tank, the lower the sulfuric acid concentration, and conversely, the less water, the higher the sulfuric acid concentration. By detecting the sulfuric acid concentration, heat exchange between exhaust gas and air can be controlled.

Next, specific examples will be described. For fuel cells,
A battery having an output of 100 watts and consisting of 48 stacked unit cells with an electrode area of 108 cXl was used. An anolyte tank was installed at the bottom of the battery, and a 40Ω anolyte (composition: methanol 17 mol/Q, sulfuric acid 1.5 mol/12, remaining water) was pumped to the air electrode inside the battery.

It circulated. Air is supplied to the battery air electrode using a blower 26Q/wi.
A flow rate of n was applied. A plate-type heat exchanger was used as the heat exchanger, and it was placed at the same height as the fuel cell, and a line leading condensed water to the anorite tank was provided in one direction in the downward direction to prevent water from accumulating along the way. By switching the valve, the battery exhaust gas can be either introduced into the heat exchanger or discharged directly outside the system without heat exchange. An electromagnetic valve was used for the valve, and a liquid level sensor was installed in the anorite tank.

The exhaust gas is directly discharged when the liquid level is at a predetermined level, and the exhaust gas is supplied to the heat exchanger when the liquid level is lower than the predetermined level.

Regarding the intake of supply air to the air electrode, it is now possible to select between direct external air intake and air intake after heat exchange by operating a valve. The following specific operations were performed using the methanol fuel cell configured as described above.

(Example 1) Power generation was performed while maintaining the battery operating temperature at 60°C±2°C. In this way, condensed water could be easily obtained from the exhaust gas, and the condensed water smoothly flowed into the anolyte tank 2 due to the head difference.

When obtaining an output of 100 watts, the cooling temperature of the exhaust gas required to recover the amount of water (174 g/h) required for replenishing the anorite was approximately 40°C6, that is, the exhaust gas was reduced from 60°C to 40°C. The required amount of water could be recovered by cooling to 20°C. Since this temperature difference can be achieved relatively easily using conventional technology, it is possible to reliably supply condensed water to the anolyte tank.

(Example 2) Under the operating conditions of Example 1 above, power generation was carried out while controlling the amount of water recovery, that is, the supply of exhaust gas to the heat exchanger, at the anolyte liquid level. When the liquid level is low, the exhaust gas is introduced into the heat exchanger, and when the liquid level is high, it is discharged from the system.

While obtaining an output of 100 watts, we continued to replenish the anolyte tank with a constant amount of methanol (77g/h), and the composition of the anolite did not deviate significantly from the initially adjusted predetermined value, and the battery output remained stable. obtained. Furthermore, even when an output of 75 watts was obtained and the amount of methanol supplied was 60 g/h, the anolyte composition could be kept constant and a stable battery output could be obtained.

(Example 3) Power generation by the battery was started by operating a valve so that air supplied to the air electrode was introduced into the air electrode via a heat exchanger. That is, power generation was started by introducing air that had been preheated through heat exchange with exhaust gas into the electric electrode. At this time, the time required to raise the temperature from room temperature (28°C) to the operating rated temperature of 60°C was 18 minutes.

On the other hand, when we started up the operation in the same way by sending outside air directly to the air electrode, it took 45 minutes for the temperature to rise from room temperature to 60°C. It can be seen that a quick start of battery operation is possible in this way.

Next, another embodiment different from the embodiment shown in FIG. 1 will be described. FIG. 2 is a system diagram showing the configuration of this embodiment. In this embodiment, unlike the embodiment shown in FIG. 1, a gas separation membrane device 5 is provided in the exhaust gas passage discharged from the battery stack 1. Moreover, it is provided upstream of the exhaust gas heat exchanger 6.

Exhaust gas from the six fuel cell stack 1, the operation of which will be described next, is led to the gas separation membrane device 5.

In this gas separation membrane device 5, nitrogen and oxygen in the exhaust gas are selectively separated from water vapor, and the former two are discharged outside the device, and the vapor-rich gas is led to a heat exchanger 6 for recovery. Since the heat exchanger 6 cools a gas having a high water vapor partial pressure and a small amount of non-condensable gas components, the required condensed water can be obtained with a small temperature difference and heat transfer area.

In the embodiments shown in FIGS. 1 and 2 above, in the case of exhaust gas without water recovery, water is discharged outside the system as steam, so there is no need to treat it.

〔Effect of the invention〕

As explained above, according to the methanol fuel cell according to the present invention, the water vapor contained in the exhaust gas from the cathode can be cooled to form condensed water, and this condensed water can be supplied into the anolite tank. There is no need to supply water from outside, and as a result, battery operation can be performed efficiently, and the battery can be made more compact.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing the configuration of one embodiment of the methanol fuel cell according to the present invention, and Fig. 2 is a system diagram of another embodiment in which a gas separation membrane device is added to the tethanol fuel cell shown in Fig. 1. It is a figure. 1... Methanol fuel cell stack, 2... Anolite tank, 6... Heat exchanger, 7... Condensed water transfer piping. 21... Cathode, 22... Anode.

Claims (1)

[Scope of Claims] 1. A fuel cell stack comprising a plurality of unit cells stacked with a separator in between, each consisting of a cursor and an anode facing each other while holding an electrolyte between them; , a gas supply device for supplying oxygen-containing gas to the cathode, and a heat exchanger in which exhaust gas of the oxygen-containing gas supplied to the cathode is introduced and water vapor in the exhaust gas is cooled and condensed. 1. A methanol fuel cell, comprising: a reflux device for refluxing the coagulated water to the anolite. 2. In claim 1, the water vapor from the exhaust gas from the cathode is cooled by heat exchange between the exhaust gas and the oxygen-containing gas supplied to the cathode. A methanol fuel cell characterized by: 3. In claim 1, a liquid level sensor is provided in the anorite tank, and when the liquid level reaches a predetermined level, the exhaust gas from the cathode is discharged on the upstream side where it is introduced into the fuel exchanger. A methanol fuel cell characterized in that exhaust gas from the cathode is introduced into a heat exchanger when the liquid level drops below the liquid level. 4. The methanol fuel cell according to claim 1, characterized in that the heat exchanger is placed at a higher position than the anolite tank, and the condensed water is replenished to the anolite tank by a head difference.