JPH05258760A - Operation control method and apparatus for liquid fuel battery - Google Patents

Abstract

PURPOSE:To enable automatic long-term operation of a small-capacity liquid fuel cell with the use of no manpower. CONSTITUTION:A fuel tank 12 is additionally provided to a fuel battery body 11 of a liquid fuel battery 10 in which unit cells are plurally laminated with separators interposed therebetween and liquid fuel is used as direct fuel. The fuel temperature inside the fuel tank 12 is metered by a temperature gauge 16 in each specified unit of time. When the liquid temperature exceeds a value set beforehand, purified water in a water tank 40 is supplied to the fuel tank 12. When the liquid temperature falls below a lower limit, liquid fuel in a preliminary fuel tank 30 is supplied to the fuel tank 12. By causing control to be made through use of the liquid temperature only, the apparatus is simplified and the operation control under no manpower becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid fuel cell operation control method and device, and more particularly, to a liquid fuel cell operation control method capable of continuous operation in an unmanned state for a long time even though the capacity is small. And equipment.

[0002]

2. Description of the Related Art A liquid fuel cell that uses a liquid fuel such as methanol or hydracin as a negative electrode active material, air as a positive electrode active material, and potassium hydroxide or sulfuric acid as an electrolyte has a simple structure. For these reasons, it is expected to be used as a remote power source or a communication power source. However, there is a particular problem in controlling the operation of a small capacity liquid fuel cell continuously for a long time.

That is, FIG. 5 is an explanatory view showing a cell system in a conventional liquid fuel cell of 100 watt class. As shown in the figure, the cell body and the fuel tank are manufactured as separate bodies, and cold start is performed. In order to maintain constant operating conditions from time to steady operation, many devices are used, such as heaters for heating liquid fuel, radiators for liquid cooling, and temperature detectors, concentration detectors, tank liquids as control devices. It requires auxiliary devices such as level detectors, solenoid valves, and controllers, or fuel transfer pumps, and at the same time requires external power.

As a basic control method, the fuel concentration is measured by a densitometer and the temperature is separately detected by a thermometer, and the fuel or water is selectively replenished based on the values of both, to determine the fuel concentration. It is designed to control. However, densitometers are generally complicated and expensive, but lack reliability, and satisfactory results have not always been obtained.

The present inventors actually operated the above-mentioned device for a certain period of time with an effective output of 100 watts, and measured the power required to operate the auxiliary device at that time, and it was about 25 watts (Table) See the section on conventional equipment in 1). Further, by further conducting experiments, in the above-mentioned conventional operation method using the auxiliary device, the effective output of the battery main body and the auxiliary power required for the operation of the auxiliary device are not proportional to each other. We also perceived that a certain amount of auxiliary power is required even for a large-scale driving system. Therefore, when a liquid fuel cell is used as a small-capacity power source, the ratio of reactive power (power consumed in the system to operate the battery system) to active power increases sharply and is not economically viable system. It turns out that

Further, since it is a control system in which many means are combined, it is practically impossible to operate in an unmanned state for a long period of time, and when a heater is used, an external power source is inevitably required. Therefore, it was difficult to use it as a completely independent power source. Furthermore, as an example of fuel concentration control of a conventional methanol-air fuel cell, J. Electrochem. Soc., Vol.
o. 9, P1523 (1971), "Fu by KJ Cathro.
el Cintrol in Methanol-Air and Formaldehyde-Air Fu
El Cell System ". In this document, two methods are used: (1) direct concentration sensing method using cyclic voltammetry, (2) load current, Faraday method for calculating fuel consumption. Two methods are described.
In either method, it is necessary to externally apply some kind of reaction electrochemically, the apparatus becomes complicated, and the point that the temperature largely depends is a problem to be overcome.

For the above reasons, the liquid fuel cell is
Although expected as a small output power source in remote areas, the reality is that it has not yet reached the level of practical use. The purpose of the present invention is to
An object of the present invention is to solve the above-mentioned disadvantages of the conventional liquid fuel cell and to provide a continuous operation small capacity, self-sustaining fuel cell capable of long-time completely unattended operation-no preparation, no maintenance. ..

[0008]

In order to solve the above problems and achieve the object, the inventors of the present invention have simplified the auxiliary device for controlling the operation of the liquid fuel cell (abolition of parts or reduction in capacity). ) Was conducted, and a diligent research was conducted on a system that enables unmanned operation without being affected by changes in the outside temperature due to the four seasons.

As a result, regarding the simplification of the auxiliary device and the minimization of the electric power consumed by the cell itself during the operation of the fuel cell,
The fuel concentration control, which is the main element of cell operation, was achieved by changing to the operation control method based only on the fuel temperature. Specifically, the fuel cell body and the fuel tank are integrated to measure the liquid temperature close to the chemical reaction state at the time of power generation at fixed time intervals, and the measured value is compared with a preset operating temperature range, and measured. When the temperature is lower than the set lower limit value, the fuel is supplied from a separately installed spare fuel tank to raise the fuel concentration in the battery attached tank and raise the temperature, and the measured temperature becomes higher than the upper limit value of the set temperature. In this case, a series of controls, for example, to supply pure water from another separate diluent tank to lower the fuel concentration in the tank attached to the battery to lower the temperature,
Concentration control and fuel temperature control were performed simultaneously. With the sled, the start-up heater, radiator, fuel cooling fan, water circulation pump, temperature sensor, and various control devices, which were required in the conventional method, can be omitted. As a result of being integrated with the main body, the fuel supply pump between the fuel tank and the cell main body or in the fuel tank can be omitted, and a small battery system with simple and stable operation performance compared to the conventional concentration control method is constructed. I was able to do it.

[0010]

The present invention will be described in more detail based on the following examples. FIG. 1 shows the configuration of an embodiment of a liquid fuel cell for carrying out the present invention. Reference numeral 10 is a small-capacity acidic electrolysis type methanol-air fuel cell of 1 to 2 watts, which is a fuel and a fuel cell main body 11 in which a plurality of unit cells composed of an oxidizer electrode, a fuel electrode, and an electrolyte are stacked with a separator interposed therebetween. A fuel tank 12 containing methanol is integrally formed. Air is supplied to the oxidizer electrode of the cell body 11 by an air supply fan 13 installed above the cell case, and the fuel electrode is provided in the fuel tank 12. Methanol is supplied by natural circulation through the groove 14 of each cell.

A float sensor 15 and a thermometer 16 which are liquid level gauges are attached to the fuel tank 12, and the measurement information of the float sensor 15 and the thermometer 16 is sent to a controller 20. A spare fuel tank 30 and a water tank 40 are provided separately from the fuel cell 10. The spare fuel tank 30 stores methanol as a fuel and the water tank 40 stores pure water as a diluent. Spare fuel tank 3
0 and the water tank 40 are connected to the fuel tank 12 via a pipe 50.
And solenoid valves 31 and 41 are provided in the middle of the pipeline. The solenoid valves 31 and 41 are opened / closed by a signal from a controller to supply fuel or pure fuel to the fuel tank 12.

Further, in this embodiment, the voltage is boosted to a certain value or more by the DC / DC converter 50 in order to both boost and stabilize the voltage, and the storage battery 60 is charged before power is supplied to the load side 70. I am trying. Controller 2
0 measures the signal from the thermometer 16 at every predetermined time interval, and when it exceeds the upper limit value of the predetermined temperature range, issues a signal to open the solenoid valve 41, and from the lower limit value. If is also low, a signal to open the solenoid valve 31 is issued. Further, it receives a signal from the float sensor 15 and outputs a signal to close the solenoid valve 31 or 41 when the liquid level of the fuel tank 12 reaches a predetermined upper limit level.

A method for controlling the operation of the fuel cell according to the present invention using the above apparatus will be described. In this type of fuel cell, when power generation starts and time elapses, the concentration of methanol in the fuel tank 12 gradually decreases, the chemical reaction in the cell decreases, and the liquid temperature in the fuel tank decreases. When the liquid temperature becomes lower than a predetermined lower limit value, methanol is replenished from the auxiliary fuel tank 30. As a result, the concentration of methanol in the fuel tank rises and the liquid temperature also rises.
When the liquid temperature exceeds a preset upper limit value, water is replenished from the water tank 40. This water causes the liquid temperature to suddenly drop sharply and lowers the concentration of methanol in the tank 12 to suppress an excessive chemical reaction. Therefore, according to the operation control method of the present invention, it is possible to simultaneously maintain the fuel concentration and temperature within a predetermined numerical range.

Next, an example in which the operation control method of the present invention is executed by using the actual machine shown in FIG. 1 will be described. The fuel cell 10 used was a platinum catalyst electrode with an effective output of 1 watt, the electrolyte was a cation exchange membrane (Nafion, Du Pont),
An experiment was conducted by using styrene sulfonic acid, the number of stacked batteries was 8, and the battery output voltage of 1.6 to 3.2 V was boosted to 14 V through the DC / DC converter 50.

At the start of the battery operation, the battery temperature (liquid temperature temperature of the fuel tank 12) was set to 42 ° C. Thereafter, the temperature is measured every 60 minutes, and when the liquid temperature T is T> 60 ° C, water is supplied from the water tank (normal temperature), and when T <= 60 ° C, the reserve tank 3 is used.
Controller 20 gives a command to inject methanol from 0 (normal temperature)
Emitted from. After water supply or methanol injection, the liquid level of the fuel tank 12 was detected, and when it reached a predetermined level, a signal was issued to close the solenoid valve 41 or 31. The result shows that T <= 6 at the first, second, and third measurement points after activation.
Since it was 0 ° C, methanol was injected. At the time of the fourth measurement, T> 60 ° C., so water was injected.
After that, the cycle of methanol twice and water once was repeated. As a result, the average liquid temperature was kept at T = 54 + -6 ° C. The converter output voltage was constant at about 14 volts.

The above-mentioned reactive power at that time is shown in the section "this device" in Table 1. In Table 1, it is difficult to compare the conventional device and this device as they are, because the effective outputs of both are significantly different, but items (5) to (9) in the table are relatively linked to the battery capacity. Yes, since (1) to (4) are almost constant regardless of the capacity of the battery, if a 1-watt class battery is constructed by the conventional method, the reactive power is 10 times or more the active power and it is difficult to practically implement. However, in the case of the present invention, it can be easily inferred that it can be sufficiently executed (note that the power for the starting heater in (10) is excluded from the calculation).

[0017]

[Table 1]

Next, similar operation control was performed using the same actual machine under different outside air conditions. One is under the condition of outside temperature -2 ° C, and the other is under the condition of outside temperature 40 ° C.
It continued to run unattended for 0 hours. The change in liquid temperature and the change in converter output at that time are shown in FIG. 2 (outside temperature-2 ° C.) and FIG. 3 (outside temperature 40 ° C.). Shows the change in the liquid temperature and the converter output voltage. As shown in the figure, in all cases, the output voltage was almost constant over the entire period.

Further, the same apparatus was installed under a natural environment and unattended, and a continuous experiment was conducted for 4400 hours.
The result is shown in FIG. As shown in the figure, the desired performance was obtained for both the battery temperature (liquid temperature) and the output voltage.

[0020]

As is clear from the above experimental results,
In the present invention, instead of the complicated and expensive concentration control which is lacking in reliability which was performed as the operation control element of the conventional fuel cell, the control is performed only by the liquid temperature, so that the apparatus is simplified. It is possible to achieve unmanned operation control.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an operation control device of a liquid fuel cell according to the present invention.

FIG. 2 is a diagram showing changes with time in battery temperature and output voltage in the case of the operation control method according to the present invention.

FIG. 3 is a diagram showing changes over time in battery temperature and output voltage under other conditions.

FIG. 4 is a diagram showing changes over time in battery temperature and output voltage under other conditions.

FIG. 5 is an explanatory diagram showing an operation control device for a liquid fuel cell according to a conventional method.

[Explanation of symbols]

10 ... Liquid fuel cell, 11 ... Fuel cell other body, 12 ... Attached fuel tank, 13 ... Air supply fan, 15 ... Liquid level detection float sensor 15, 16 ... Thermometer, 20 ... Controller 2
0, 30 ... Spare fuel tank, 40 ... Diluent tank.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seitaka Asahi 330 Funakura-cho, Yokosuka City, Kanagawa Prefecture Hitachi Machine Engineering Co., Ltd. Kurihama Branch Factory

Claims (3)

[Claims] 1. A method for controlling the operation of a liquid fuel cell in which a plurality of unit cells composed of an oxidizer electrode, a fuel electrode, and an electrolyte are stacked with a separator interposed therebetween, and the liquid fuel is directly used as a fuel. Measure the fuel temperature in the fuel tank,
When the measured value exceeds the upper limit of the preset operating temperature range, the diluent is supplied to the fuel tank,
An operation control method for a liquid fuel cell, characterized in that, when the measured value is equal to or lower than a lower limit value, the liquid fuel is supplied to a fuel tank to maintain the fuel concentration substantially constant for operation. 2. The liquid fuel according to claim 1, wherein the liquid fuel is at least one liquid substance selected from methanol, formalin, formic acid, and hydrazine, and the diluent is “pure water”. Liquid fuel cell operation control method. 3. An operation control device for a liquid fuel cell in which a plurality of unit cells each composed of an oxidizer electrode, a fuel electrode and an electrolyte are stacked with a separator interposed therebetween and a liquid fuel is used directly as a fuel, which is attached to a fuel cell body. It has at least a temperature measuring means for measuring the fuel temperature in the fuel tank, a spare liquid fuel tank, and a diluent tank, and the measured value of the temperature measuring means has an upper limit value with respect to a preset operating temperature range. When it exceeds the limit, it further has a means for supplying the diluent in the diluent tank to the fuel tank, and a means for supplying the liquid fuel in the auxiliary fuel tank to the fuel tank when the measured value becomes less than or equal to the lower limit value. An operation control device for a liquid fuel cell, which is characterized in that: