KR20090022521A - Sensor-less method and apparatus for controlling fuel concentration of liquid fuel cell, liquid fuel cell apparatus using the same - Google Patents

Abstract

A method for controlling the fuel concentration of s liquid fuel cell is provided to save the electricity used on system operation by making a simple and compact fuel cell system by using a sensor. A method for controlling the fuel concentration of s liquid fuel cell comprises a step of measuring the fuel consumption or consumption velocity of a liquid type fuel battery while changing the operation condition, and determining the fuel consumption or consumption velocity of the fuel; and a step of controlling the fuel concentration of a liquid type fuel battery by controlling the fuel supply amount or the feed rate supplied to the fuel battery corresponding to the fuel consumption or consumption velocity of the fuel.

Description

Method and apparatus for controlling fuel concentration of a liquid fuel cell that does not use a concentration sensor, and a liquid fuel cell device using the same TECHNICAL FIELD

The present invention relates to a fuel concentration control method and apparatus for a liquid fuel cell that does not use a concentration sensor, and a liquid fuel cell apparatus using the same. In detail, the present invention relates to a method for controlling fuel concentration in a fuel circulation system for supplying fuel. Instead of using the concentration sensor to measure the concentration of the fuel cell, the fuel consumption is estimated using the fuel cell operating conditions, in particular, the fuel cell temperature, pressure and output current at the set fuel concentration, and based on the fuel consumption, A fuel concentration control method and apparatus for a liquid fuel cell that does not use a concentration sensor that maintains a constant concentration of fuel by adjusting a supply amount, and a liquid fuel cell apparatus using the same.

Liquid fuel cell is a device that converts chemical energy of reactant directly into electrical energy by using redox reaction of oxygen, ethanol, formic acid, isopropanol, propanol, ethylene glycol, dimethyl ether, butanol alone or two or more mixed fuels and oxygen As a result, the energy density of the fuel is high, and no charging time is required, so it is suitable as a future small mobile power source.

Reaction Schemes 1 to 3 below show an anode reaction scheme, a cathode reaction scheme, and an overall reaction scheme of a direct methanol fuel cell using methanol as a fuel in a liquid fuel cell, respectively.

_{CH 3 OH + H 2 O →} CO 2 + 6H + + 6e -, E 0 = 0.043V

^{_{3 / 2O 2 + 6H + +}} 6e - → 3H 2 O, E 0 = 1.229V

CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O, E ₀ = 1.186 V

As shown in the above scheme, in the case of the direct methanol fuel cell, methanol oxidation reaction and oxygen reduction reaction occur at both electrodes with the electrolyte in between, and the resulting hydrogen ions move from the anode to the cathode side through the electrolyte, and the electrons Move to an external electrical circuit. The electrons moving to the external electric circuit generate power to operate the electronic products.

The concentration of fuel supplied in a liquid fuel cell including such a direct methanol fuel cell affects fuel cell performance and fuel use efficiency.

On the other hand, the liquid fuel crosses the electrolyte membrane and moves from the anode to the cathode. Crossover of the fuel causes various problems such as deterioration of the fuel cell performance and reduction of fuel use efficiency.

This crossover phenomenon is proportional to the concentration of the fuel. For example, direct methanol fuel cells typically supply fuel at low concentrations of 2M or less to reduce fuel crossover.

However, when the fuel is stored and used inside the liquid fuel cell system in the form of a diluted solution, the energy density (per unit volume) of the entire fuel cell system is very low, thus losing the advantages as a portable high density energy device.

Therefore, fuel is recycled and used to increase energy density in the system while supplying low concentrations of fuel.

Recirculation of fuel is a method of replenishing fuel, adjusting its concentration, and then feeding it back to a fuel cell system without releasing unreacted fuel discharged from a fuel cell to the outside.

That is, when the reaction solution containing fuel is supplied to the fuel cell stack, the fuel is consumed by the reaction in the fuel cell stack, and the fuel concentration in the reaction solution is reduced. Therefore, in order to maintain the concentration of the fuel to the desired level, a high concentration of fuel must be injected into the circulation system to adjust the concentration.

To this end, in a fuel cell system, a high concentration of fuel is injected into a fuel mixing device and mixed with a circulating solution to adjust the concentration of the fuel in the reaction solution, and then the solution is injected into the fuel cell.

For reference, a representative fuel concentration control method that is conventionally used is a feedback control method.

The feedback control method uses a concentration sensor to measure the concentration of the fuel in the circulation system, and calculates and supplies an injection amount of the fuel stock solution required to keep the concentration of the fuel constant while observing the concentration change, thereby providing a concentration of the fuel in the reaction solution. Say how to control it.

However, the existing concentration control method should be attached to a concentration sensor that can measure the concentration of the fuel supplied to the fuel cell as described above, for the separate sample transfer inside the fuel circulation system to measure the concentration of the fuel in the sensor Piping and pumps are needed.

This increases the complexity of the system, making it difficult to miniaturize, and increases the power consumption of the sensor and the pump, thereby reducing the energy efficiency of the fuel cell system.

Furthermore, currently developed concentration sensors have a higher price point than other physical quantity sensors, and when applied to fuel cell systems, manufacturing cost of fuel cell systems increases, making it difficult to maintain price competitiveness as portable power supplies. There is a problem that is difficult.

In order to solve this problem, studies have been conducted to develop a concentration sensor using an electrochemical reaction.

The concentration sensor using the electrochemical reaction has the advantage that it can be manufactured at a lower price than the conventional concentration sensor. However, over time, there is a problem that the reproducibility of the measurement becomes low as the catalyst inside the sensor loses activity.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is that the fuel cell system is simple and miniaturized because it does not use a concentration sensor, thereby saving power consumed in system operation and lowering the price of the system itself. As a sensorless concentration control of fuel cells, the dynamic performance of the electrode performance, the operating conditions, or the electrical load changes without being affected by the natural deterioration of the fuel cell due to the poisoning of the catalyst during concentration control. The present invention provides a method and apparatus for controlling fuel concentration of a liquid fuel cell without using a concentration sensor and a liquid fuel cell apparatus using the same, which can be used even in a state and can guarantee stable fuel cell operation because the error control range is not large. It is.

In order to achieve the above object, in the present invention, as a method of controlling the fuel concentration of a liquid fuel cell without a concentration sensor, the fuel consumption or consumption rate of the liquid fuel cell is measured while changing the operating conditions including the fuel concentration. And a first step of determining the consumption or consumption rate of the fuel at the set fuel concentration from the measured fuel consumption or consumption rate; And a second step of controlling a fuel concentration of the liquid fuel cell by adjusting a fuel supply amount or a supply speed supplied to the fuel cell in response to the determined consumption amount or the consumption speed of the fuel. It provides a method for controlling the concentration of a liquid fuel cell that does not use.

In an embodiment of the present invention, in the first step, the fuel consumption amount or the consumption rate may be determined by a fuel consumption amount or a consumption rate required when a current is generated in a fuel cell; And fuel consumption or rate of consumption due to crossover of fuel.

In an embodiment of the present invention, the first step includes measuring the fuel consumption or consumption rate of the liquid fuel cell while changing the output current, the temperature and pressure inside the fuel cell, and the fuel concentration, thereby outputting the output current and the fuel cell. 1-1 step of obtaining a database or correlation of fuel consumption or consumption rate with variables of internal temperature and pressure and fuel concentration; And measuring the output current, the temperature and pressure inside the fuel cell under the set fuel concentration, and correlating the set fuel concentration, measured current, temperature and pressure with the database or correlation of the fuel consumption or consumption rate obtained in step 1-1. And the first and second steps of determining fuel consumption or consumption rate at the set fuel concentration, measured current, temperature, and pressure in relation to the relationship.

In an embodiment of the present invention, the fuel consumption or consumption rate required for generating the current is determined using the current measurement value and the Faraday constant.

In an embodiment of the present invention, the fuel consumption or consumption rate due to the crossover of the fuel is determined by measuring the generation amount or the generation rate of carbon dioxide from the cathode of the fuel cell.

In an embodiment of the invention, the amount or rate of generation of carbon dioxide is determined by measuring the amount or rate of release of gas from the cathode and the concentration of carbon dioxide in the gas from the cathode.

In an embodiment of the present invention, the amount or rate of release of gas from the cathode subtracts the flow rate or flow rate of oxygen consumed due to the generation of current from the flow rate or flow rate of air supplied to the fuel cell, and crossovers of the fuel. It is determined by subtracting the flow rate or flow rate of the generated carbon dioxide, and then subtracting the flow rate or flow rate of oxygen consumed due to the crossover of the fuel.

In an embodiment of the present invention, in the second step, the flow rate or the same as the consumption amount or consumption rate of the determined fuel, with the volume or liquid level of the fuel mixer supplying the concentration-adjusted fuel to the fuel cell constant Fuel at a flow rate is supplied to the fuel cell mixer.

In an embodiment of the present invention, the liquid fuel is one or more mixed fuels selected from the group consisting of methanol, ethanol, formic acid, isopropanol, propanol, ethylene glycol, dimethyl ether and butanol.

In order to achieve the above object, in the present invention, as a concentration control device for controlling the fuel concentration of a liquid fuel cell without a concentration sensor, changing the operating conditions including the fuel concentration or the fuel consumption or consumption rate of the liquid fuel cell; A processor that determines, from the fuel consumption or consumption rate obtained by measuring, the consumption or consumption rate of the fuel at the set fuel concentration; And a control unit which transmits a control signal relating to a fuel supply amount or a supply speed to a fuel supply unit of the liquid fuel cell in response to the determined consumption amount or the consumption speed of the fuel. Provided is a concentration control apparatus for a battery.

In an embodiment of the invention, the processor is connected to a measuring device for measuring the output current of the liquid fuel cell, the temperature and the pressure inside the fuel cell at a set fuel concentration, and the fuel consumption or consumption rate of the liquid fuel cell. Is determined by varying the output current, temperature and pressure inside the fuel cell, and fuel concentration, and a database or correlation of fuel consumption or rate of consumption with the output current, temperature and pressure inside the fuel cell, and fuel concentration as variables. A first processor to accumulate; And calling a database or correlation of fuel consumption or consumption rate from the first processing unit, and converting the set concentration, current, temperature and pressure input from the measuring device to the database or correlation of fuel consumption or consumption rate. And a second processor configured to determine fuel consumption at the set concentration.

In order to achieve the above object, in the present invention, the fuel supply unit; A liquid fuel cell connected to the fuel supply unit; And the concentration control device connected to the fuel supply unit and the liquid fuel cell, respectively.

In an embodiment of the present invention, the fuel supply unit comprises: a fuel stock solution cartridge for storing the fuel stock solution; A fuel mixer for supplying a fuel stock solution from the fuel stock cartridge and supplying a concentration-adjusted fuel to the liquid fuel cell; And a pump for supplying the fuel stock solution from the fuel stock cartridge to the fuel mixer, wherein the concentration control device is connected to the pump of the fuel supply section.

Since the sensorless concentration control method according to the present invention does not use the concentration sensor, the fuel cell system can be simplified and miniaturized, thereby saving power consumed in system operation and lowering the price of the system itself. In particular, in the concentration control, it is possible to use the battery in a dynamic state in which the performance of the electrode is deteriorated, the operating conditions are changed, or the electrical load is changed, without being affected by the natural deterioration of the fuel cell due to the poisoning of the catalyst. In addition, since the error range of the concentration control is not large, it is possible to implement the sensorless concentration control of the fuel cell which can ensure stable fuel cell operation.

Hereinafter, a fuel concentration control method and apparatus for a liquid fuel cell that does not use the concentration sensor according to the present invention, and a liquid fuel cell apparatus using the same will be described in detail.

In the present invention, the stock solution of the fuel is used in the sense to include not only 100% of the stock solution but also a high concentration of fuel that requires dilution.

Fuel consumption in a certain operating condition has a clear correlation with the corresponding operating conditions, but always constant regardless of the performance of the fuel cell electrode, it is possible to measure the fuel consumption and use it as a basis for the concentration control.

In the present invention, as a method of performing the concentration control of the liquid fuel cell without the concentration sensor on the basis of the above point, in particular, the fuel consumption is measured and the fuel concentration control is performed based on this.

1 is a flowchart illustrating a process of determining fuel supply amount and concentration control according to fuel consumption prediction according to an embodiment of the present invention.

Referring to FIG. 1, first, fuel consumption according to concentration is measured under various operating conditions, and based on this, a database or correlation (function) of fuel consumption, in particular concentration, current, temperature, and pressure, is obtained (S1). ).

Specifically, the fuel consumption may be classified into fuel consumption consumed in the fuel cell when current is generated and fuel consumption by the liquid fuel crossovering the electrolyte. This is expressed by the following equation.

N _{m , t}  = N _{m , e}  + N _{m , x}

[N _{m , t} : Fuel consumption per unit time, N _{m , e} : Fuel consumption per unit time when current is generated, N _{m , x} : Fuel consumption per unit time due to crossover]

The fuel consumption per unit time at the time of generation of current depends only on the magnitude of the current and is independent of other operating conditions. This is expressed by the following equation.

N _{m , e}  = f (I) = I / 6F

[N _{m , e} : Fuel consumption per unit time when current is generated, I: Current, F: Faraday constant]

The consumption of fuel by the crossover is various operating conditions, that is, the output current or voltage of the fuel cell, the temperature and pressure inside the fuel cell, the temperature and pressure around the fuel cell, the flow rate and temperature of the supplied fuel, and the supplied air. Depends on the flow rate and temperature of the fuel, the concentration and flow rate of the fuel, and the like. For reference, the temperature and pressure around the fuel cell, the temperature of the supply fuel, and the temperature of the supply air are eventually reflected by the temperature and pressure inside the fuel cell. In addition, the consumption of fuel by the crossover is characterized by the structural characteristics of the fuel cell, that is, the size and shape of the fuel cell, the type and size of the membrane-electrode assembly used, the type of catalyst used for the electrode, the type of electrode, and the type of electrolyte membrane used. It may also change depending on the back.

However, since the structural characteristics of the fuel cell, such as the size and shape of the fuel cell, are constant in the same fuel cell for which fuel concentration control is desired, the consumption of fuel due to crossover depends on the operating conditions, and in particular, can be expressed by the following equation.

N _{m , x}  = f (I, T, C, Fa , Fc , P)

[N _{m , x} : fuel consumption per unit time according to crossover, I: output current, T: temperature inside fuel cell, C: fuel concentration, Fa: amount of fuel supplied, Fc: amount of air supplied, P : Pressure inside the fuel cell]

In general, however, liquid fuel cells operate at fixed fuel and air supply, and atmospheric pressure conditions. Therefore, in the liquid fuel cell system which eventually wants to control the concentration, the operating conditions affecting the crossover of the fuel result in three variables: the output current, the temperature inside the fuel cell, and the fuel concentration. This is expressed by the following equation.

N _{m , x}  = f (I, T, C)

[N _{m , x} : fuel consumption per unit time according to crossover, I: output current, T: temperature inside fuel cell, C: fuel concentration]

On the other hand, when the fuel cell operates in the pressurized condition, four variables including pressure are applied as in the following equation.

N _{m , x}  = f (I, T, C, P)

[N _{m , x} : fuel consumption per unit time according to crossover, I: output current, T: temperature inside the fuel cell, C: fuel concentration, P: internal pressure of the fuel cell]

In summary, the consumption of fuel due to crossover under atmospheric pressure is determined by three variables: the output current, the temperature inside the fuel cell, and the concentration of the fuel. The amount of fuel consumed is also determined according to the output current, the temperature inside the fuel cell, and the fuel concentration. And, in the case of pressurized conditions, a pressure variable is added thereto.

Therefore, the fuel consumption can be measured in advance according to the output current, the temperature and pressure inside the fuel cell, and the fuel concentration to obtain a database or correlation (function) on the fuel consumption, which is then the basis of the fuel consumption prediction. Can be utilized as

Here, since the consumption of the fuel consumed at the time of generation of current can be determined only by the current (output current), the consumption of the fuel is determined by measuring the consumption of the fuel by the crossover, and the consumption of the fuel by the crossover is measured. Since the crossover fuel reacts with oxygen in the air at the cathode surface to become carbon dioxide, it can be determined by measuring the amount of carbon dioxide contained in the gas discharged from the cathode as in the following experimental example.

Referring back to FIG. 1, after determining the database or correlation (function) of the fuel consumption in step S1 as above, the target concentration is set next, and at the set concentration, the temperature of the output current measuring device and the temperature inside the fuel cell, Using a pressure measuring device to measure each current, temperature and pressure (S2).

Next, by calling the database or correlation (function) of the fuel consumption obtained as described above, and substituting the set concentration, the output current and the temperature and pressure inside the fuel cell into the called database or correlation (function). The fuel consumption at the set concentration can be predicted (S3).

Next, fuel concentration is controlled by supplying fuel corresponding to the predicted consumption amount (S4).

In detail, the concentration and volume of the fuel in the fuel cell system are determined by adding the accumulation of changes occurring per unit time to the concentration and volume in the initial state. This is expressed by the following equation.

[V: fuel volume, C: fuel concentration, Vi: initial fuel volume, Ci: initial fuel concentration. t: time]

By the way, if the volume level is kept constant by making the water level in the fuel mixer constant, that is, when V = Vi, only concentration changes over time. This is expressed by the following equation.

(V: fuel volume, C: fuel concentration, t: time)

The fuel concentration depends on the initial concentration and the accumulation of concentration changes occurring per unit time. This is expressed by the following equation.

[C: fuel concentration, Ci: initial fuel concentration, t: time]

The concentration change occurring per unit time is determined by the fuel consumed and the fuel supplied per unit time, which is expressed by the following equation.

∂C / ∂t = ( N _{m , f}  - N _{m , t} ) / V

[N _{m , f} : amount of fuel supplied per unit time, N _{m , t} : fuel consumption per unit time]

Here, if the supply amount of the fuel by the fuel supply pump and the consumption amount of the fuel at the target concentration are set to N _{m , f} = N _{m , t} in Equation 9 above _{, the} concentration change per unit time is no longer. Does not occur. This is expressed by the following equation.

∂C / ∂t = 0

Substituting Equation 10 into Equation 7 results in C = Ci when the fuel supply amount by the fuel supply pump coincides with the consumption of fuel at the set concentration predicted in the step S2. The set concentration (C) can be maintained at the initial concentration (Ci), and furthermore, even if the initial concentration (Ci) is high or low compared to the set concentration (C), the fuel cell system is controlled by adjusting the fuel supply amount. Since the fuel concentration of the fuel circulation supply system changes in the direction of convergence to the set concentration, the concentration control becomes possible.

On the other hand, the apparatus according to the present invention largely includes a fuel supply unit, a liquid fuel cell connected to the fuel supply unit, and a concentration control apparatus for performing concentration control as described above connected to the fuel supply unit and the liquid fuel cell, respectively. .

2 is a schematic view showing a fuel cell device according to an embodiment of the present invention together with a fuel circulation supply system.

As shown in FIG. 2, the fuel cell apparatus according to the embodiment of the present invention is supplied with fuel from the fuel mixer 20 to the fuel cell stack 40 through the fuel circulation pump 31. In addition, the fuel cell stack 40 is supplied with air from the air supply pump 32.

The fuel mixer 20 receives the fuel stock solution from the fuel stock cartridge 10 through the fuel stock pump 12. Here, the fuel stock solution cartridge 10 is coupled to the subsequent fuel circulation system by the coupling portion (11).

In addition, the fuel mixer 20 receives water from a water supply pump 34, which is connected to a water recovery device 33 from the fuel cell stack 40.

The fuel mixer 20 is equipped with a liquid level measuring device 22 for measuring the level of the mixed fuel in the apparatus for measuring the volume of the mixed fuel.

Gas (carbon dioxide, etc.) discharged from the fuel cell stack 40 is introduced into the fuel mixer 20 through a circulation system cooling device 30, and an emission gas discharge part 21 mounted on the fuel mixer 20 is provided. Out).

The fuel cell stack 40 is equipped with a temperature and pressure measuring device 41 and an output current measuring device 42, respectively, to measure temperature and output current under operating conditions.

The temperature and pressure measuring device 41 and the output current measuring device 42 are connected to the concentration control device P.

The concentration control device P is composed of a processor and a control unit for transmitting a control signal relating to the fuel supply amount or the supply speed to the fuel feed liquid supply pump 12.

The processor accumulates a database and correlations (functions) for fuel consumption, in particular the concentration, output current and temperature and pressure inside the fuel cell, which are obtained on the basis of fuel consumption measurements according to set concentrations under various operating conditions. A first processing unit and a database or correlation of fuel consumption or consumption rate from the first processing unit and calling the set concentration, the output current input from the measuring device, and the temperature and pressure inside the fuel cell. Or a second processor that determines the fuel consumption at the set concentration by substituting the database or correlation of the consumption speed.

Experimental Example

The experiment was carried out using a unit cell fueled by methanol. The unit cell was used that can be artificially temperature controlled. For reference, in the unit cell, the electrode area was 138 cm ² , and Nafion 115 manufactured by DuPont was used as the electrolyte membrane. Pt-Ru 6 mg / cm ² was used as the anode electrode catalyst and Pt 4 mg / cm ² was used as the cathode electrode catalyst. A parallel serpentine type flow path was used, the fuel supply flow rate was 9.23 ml / min, and the air supply flow rate was 1170 ml / min (dry air).

First, in order to predict fuel consumption according to current and temperature, fuel consumption was measured by driving a fuel cell under operating conditions in which current and temperature were maintained.

As described above, the fuel consumption at the time of generating the current was understood through the amount of current, and the fuel consumption by the crossover could be measured by the amount of carbon dioxide contained in the gas emitted from the cathode.

The amount of carbon dioxide was calculated by measuring the flow rate of the gas discharged and the concentration of carbon dioxide. That is, the flow rate of the discharged gas measures the flow rate of the gas (oxygen + nitrogen) to be supplied, and then subtracts the oxygen consumption at the time of current generation from this measured value, subtracts the oxygen consumption due to crossover, and crossovers Calculated by adding the amount of carbon dioxide generated by. Here, the amount of nitrogen and oxygen that migrates from the cathode pole through the electrolyte membrane to the anode pole by diffusion is negligible.

In the case of a fuel cell using methanol as a fuel, the amount of carbon dioxide generated by crossover is calculated as follows. First, when methanol is used as a fuel, the crossover reaction is shown in the following reaction formula.

CH ₃ OH + 3/2 O _2- > CO ₂ + 2H ₂ O

As can be seen from the reaction scheme, when one carbon dioxide is generated, 1.5 oxygen are consumed. Assuming all gases are ideal gases, the amount of oxygen consumed due to methanol crossover becomes the amount of carbon dioxide generated by 1.5 × methanol crossover (Nm-co ₂ ), and the amount of carbon dioxide generated due to methanol crossover ( Nm-co ₂ ) is the consumption by the crossover of methanol as a fuel.

The total amount of gas released (Ntotal) is the amount of oxygen supplied (Fo ₂ ) plus the amount of nitrogen supplied (Fn ₂ ), and then the amount of oxygen consumed due to power generation (l / 4F; I is the current and F is the Faraday constant ) After deducting), the amount of carbon dioxide generated due to 0.5 × methanol crossover (Nm-co ₂ ) [the amount of oxygen consumed by methanol crossover (= 1.5 amount generated by methanol crossover) —the amount of carbon dioxide generated by methanol crossover] Obtain by subtracting

Therefore, the ratio (Xco ₂ ) of the generation amount of carbon dioxide (Nm-co ₂ ) by methanol crossover to the total amount of gas (Ntotal) emitted is expressed by the following equation.

[Nm-co ₂ : Flow rate of carbon dioxide emitted from fuel cell (unit: mol / min), Xco ₂ : volume fraction of carbon dioxide in gas emitted from fuel cell, Fo ₂ : Flow rate of supplied oxygen (unit: mol / min), Fn ₂ : Flow rate of supplied nitrogen (unit: mol / min), I: current (unit: C / sec; here, applied current value to determine the effect on methanol crossover), F: Faraday constant (unit: C / mol)]

When the above expression is expressed with respect to the amount of carbon dioxide generated by methanol crossover (Nm-co ₂ ), the following equation is obtained.

As described above, the sum of the fuel consumption (I / 6F) at the time of generation of current and the fuel consumption by the crossover obtained by the carbon dioxide measurement is the total fuel consumption.

Through the measurement of the total fuel consumption at each current and temperature, data of fuel consumption according to the change of operating conditions were obtained and correlated.

FIG. 3 is data of measuring fuel consumption according to an output current, a temperature inside a fuel cell, and a fuel concentration in an atmospheric pressure condition. For reference, in FIG. 3, the temperature was 40 ° C., 60 ° C., 80 ° C., and the concentrations were 0.4 mole, 0.8 mole, and 1.2 mole. The output current started at 0 A, increased by 4 A, and stopped when the voltage reached 0.4 V or less. .

Referring to FIG. 3, in most cases, the consumption of methanol as fuel increases linearly with the increase of the output current. That is, based on this result, it is possible to determine the consumption of methanol as fuel at the set concentration and at a given current and temperature.

Meanwhile, according to the present invention, when the initial concentration and the target concentration are the same, not only the concentration is maintained but also the convergence to the target concentration when an error occurs in the initial concentration is possible.

That is, in the concentration control according to the present invention, it is assumed that the actual concentration is the target concentration, and the methanol consumption under the conditions is calculated. Therefore, when the initial concentration is lower than the target concentration, a larger amount of methanol is supplied than necessary to maintain the concentration. Conversely, when the initial concentration is higher than the target concentration, less methanol is supplied than is necessary to maintain the concentration. As a result, even if the initial concentration is out of the target concentration, the actual concentration gradually converges to the target value.

4 is a graph showing that, in an embodiment of the present invention, the concentration of fuel reaches a target concentration in an open circuit under atmospheric pressure. For reference, in FIG. 4, the temperature was 60 ° C., the set concentration was 0.8 mol, and the initial concentration was 0.6 mol.

Referring to FIG. 4, it was confirmed that the concentration of the fuel converged to the set concentration of 0.8 M while the starting concentration was 0.6 M. FIG.

5 is an embodiment of the present invention, the fuel concentration is maintained under the condition that the magnitude of the output current changes from 0 mA / cm ² to 110 mA / cm ² when the set concentration of the fuel 0.4M under atmospheric pressure conditions This graph shows what happens. For reference, in FIG. 5, the temperature was 60 ° C. and the set concentration was 0.4 mol.

Referring to FIG. 5, the concentration fluctuated near the set value while the fuel stock solution and the water were supplied by the concentration control at the set concentration 0.4M. As the output current increased, the actual concentration was higher than the set concentration, and the output current density increased to 0.52M at 100 mA / cm ² . In the enlarged graph of the graph of Figure 5 it can be seen that the sharp decrease in fuel concentration is due to the water supply for maintaining the water level of the fuel mixing vessel. The lowered concentration gradually increased after the water supply was stopped.

FIG. 6 shows that the fuel concentration is maintained under the condition that the magnitude of the output current varies from 0 mA / cm ² to 110 mA / cm ² when the set concentration of the fuel is 0.8 M under atmospheric pressure. This graph shows what happens. For reference, in FIG. 6, the temperature was 60 ° C. and the set concentration was 0.8 mol.

Referring to FIG. 6, the trend of change even at the set concentration of 0.8 M was almost similar to that of the 0.4 M experiment of FIG. 5, and only the magnitude of the fluctuation was larger. In this case, as the current increased, the concentration was maintained higher than the set concentration, and the concentration increased to 1.0 M at the current density of 110 mA / cm ² .

From the above results, it was confirmed by the sensorless concentration control of the present invention that the fuel concentration was maintained at a satisfactory level according to the fuel cell operation. In particular, as the output current increased, the error between the set concentration and the actual concentration increased. The size of was confirmed that the concentration is maintained without exceeding 20%.

1 is a flowchart illustrating a process of determining fuel supply amount and concentration control according to fuel consumption prediction according to an embodiment of the present invention.

2 is a schematic view showing a fuel cell device according to an embodiment of the present invention together with its fuel circulation system.

FIG. 3 is a measurement data of fuel consumption according to an output current, a temperature inside a fuel cell, and a fuel concentration in an atmospheric pressure condition in an embodiment of the present invention.

4 is a graph showing that the concentration of the fuel reaches the target concentration in the open loop state under the atmospheric pressure condition in the embodiment of the present invention.

5 is an embodiment of the present invention, the fuel concentration in the condition that the output current is changed from 0 mA / cm ² to 110 mA / cm ² when the set concentration of the fuel is 0.4M, under atmospheric pressure conditions A graph showing what is kept.

6 is an embodiment of the present invention, when the set concentration of the fuel is 0.8M under atmospheric pressure conditions, the concentration of the fuel under the condition that the magnitude of the output current varies from 0 mA / cm ² to 110 mA / cm ² A graph showing what is kept.

* Description of Major Reference Marks *

10: fuel stock cartridge 11: cartridge and fuel circulation system coupling portion

12: fuel feed pump 20: fuel mixer

21: carbon dioxide emitter 22: liquid level measuring device

30: circulation system cooling device 31: fuel circulation pump

32: air supply pump 33: water recovery device

34: water supply pump 40: fuel cell stack

41: temperature and pressure measuring device 42: output current measuring device

P: concentration control device

Claims (13)

A method of controlling the fuel concentration of a liquid fuel cell without a concentration sensor, A first step of measuring the fuel consumption or consumption rate of the liquid fuel cell while changing operating conditions including fuel concentration, and determining the consumption or consumption rate of fuel at the set fuel concentration from the measured fuel consumption or consumption rate ; And And controlling a fuel concentration of the liquid fuel cell by adjusting a fuel supply amount or a supply speed supplied to the fuel cell in response to the determined consumption amount or consumption rate of the fuel. Concentration control method for an unused liquid fuel cell. The method of claim 1, In the first step, the fuel consumption or consumption rate may be determined by the fuel consumption or consumption rate required for generating current in the fuel cell; And a fuel consumption amount or a consumption rate due to the crossover of the fuel; and the concentration control method of the liquid fuel cell without using the concentration sensor. The method of claim 2, wherein the first step, By measuring the fuel consumption or consumption rate of the liquid fuel cell while changing the output current, the temperature and pressure inside the fuel cell, and the fuel concentration, the fuel consumption using the output current, the temperature and pressure inside the fuel cell, and the fuel concentration as variables Or step 1-1 of obtaining a database or correlation of rate of consumption; And Measure the output current, temperature and pressure inside the fuel cell under the set fuel concentration, and use the set fuel concentration, measured current, temperature and pressure as a database or correlation of the fuel consumption or consumption rate obtained in step 1-1. Controlling the concentration of the liquid fuel cell without using a concentration sensor, characterized in that consisting of; the first to second steps to determine the fuel consumption or consumption rate at the set fuel concentration, measured current, temperature and pressure Way. The method of claim 2, The method of controlling the concentration of a liquid fuel cell without using a concentration sensor, characterized in that for determining the fuel consumption or consumption rate required for the current generation using the current measurement value and the Faraday constant. The method of claim 2, The fuel consumption amount or the consumption rate due to the crossover of the fuel is determined by measuring the generation amount or the generation rate of carbon dioxide from the cathode of the fuel cell, the concentration control method of a liquid fuel cell without using a concentration sensor. The method of claim 5, wherein Wherein the amount or rate of generation of carbon dioxide is determined by measuring the amount or rate of release of gas from the cathode and the concentration of carbon dioxide in the gas from the cathode. The method of claim 6, The discharge amount or discharge rate of the gas from the cathode subtracts the flow rate or flow rate of oxygen consumed due to the generation of current from the flow rate or flow rate of the air supplied to the fuel cell, and the flow rate or flow rate of carbon dioxide generated due to the crossover of the fuel And adding, followed by determining by subtracting the flow rate or flow rate of the oxygen consumed due to the crossover of the fuel. The method of claim 1, In the second step, the fuel cell mixer is a fuel having a flow rate or flow rate equal to the consumption or consumption rate of the determined fuel, while the volume or liquid level of the fuel mixer for supplying the fuel with the concentration appropriate to the fuel cell is constant. A concentration control method for a liquid fuel cell that does not use a concentration sensor, characterized in that the supply to the. The method according to any one of claims 1 to 8, The liquid fuel is a concentration control method of a liquid fuel cell without using a concentration sensor, characterized in that one or two or more mixed fuels selected from the group consisting of methanol, ethanol, formic acid, isopropanol, propanol, ethylene glycol, dimethyl ether and butanol. . A concentration control device for controlling the fuel concentration of a liquid fuel cell without a concentration sensor, A processor for determining the consumption or consumption rate of the fuel at the set fuel concentration from the fuel consumption or consumption rate obtained by measuring the fuel consumption or consumption rate of the liquid fuel cell while changing the operating condition including the fuel concentration; And And a control unit for transmitting a control signal relating to the fuel supply amount or the supply speed to the fuel supply unit of the liquid fuel cell in response to the determined consumption amount or the consumption speed of the fuel. Concentration control device. The method of claim 10, The processor is connected to a measuring device for measuring the output current of the liquid fuel cell, the temperature and the pressure inside the fuel cell at a set fuel concentration, Fuel consumption using the output current, temperature and pressure inside the fuel cell, and fuel concentration as variables by measuring the fuel consumption or consumption rate of the liquid fuel cell while changing the output current, temperature and pressure inside the fuel cell, and fuel concentration. Or a first processing unit that accumulates a database or correlation of consumption rate; And Invoke a database or correlation of fuel consumption or consumption rate from the first processing unit, and substitute the set concentration, current, temperature and pressure input from the measuring device into the database or correlation of fuel consumption or consumption rate. And a second processor configured to determine the fuel consumption at the set concentration. Fuel supply section; A liquid fuel cell connected to the fuel supply unit; And And a concentration control device according to claim 10 or 11 respectively connected to the fuel supply unit and the liquid fuel cell. The method of claim 12, wherein the fuel supply unit, A fuel stock cartridge for storing the fuel stock solution; A fuel mixer for supplying a fuel stock solution from the fuel stock cartridge and supplying a concentration-adjusted fuel to the liquid fuel cell; And A pump for supplying the fuel stock solution from the fuel stock cartridge to the fuel mixer; And the concentration control device is connected to a pump of the fuel supply unit.

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