KR20070039362A - Level detecting device and fuel cell system - Google Patents

Abstract

The present invention relates to a fuel cell system for recycling water and unreacted fuel generated by the operation of a fuel cell, and to a fuel cell system capable of condensing only an appropriate amount according to the capacity of a concentration control tank in a cathode electrode exhaust gas. It is about.

A fuel cell system of the present invention includes a stack including an anode electrode supplied with an aqueous solution fuel and a cathode electrode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode electrode; And a concentration control tank for mixing the condensate condensed by the condenser and the high concentration fuel, wherein the condensation operation of the condenser is controlled according to the accumulation amount of the fuel aqueous solution in the concentration control tank.

By implementing a fuel cell system capable of dynamically adjusting the condensation amount of the condenser as described above, there is an effect that can ensure a stable operation even with a smaller mixing tank.

Fuel cell, condenser, recycle, level detect, mixing tank

Description

Level Detecting Device and Fuel Cell System

1 is a block diagram showing the overall structure of a fuel cell system according to an embodiment of the present invention;

2 is a structural diagram showing the structure of a linear water level detection means according to an embodiment of the present invention;

Figure 3 is a structural diagram showing the structure of the non-linear water level detecting means according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system for recycling water and unreacted fuel generated by operation of a fuel cell, and more particularly, to a fuel cell system capable of constantly adjusting the concentration of such recycled fuel.

In general, various technologies related to fuel cells have been proposed as a device for directly converting energy contained in fuel into electrical energy, and such fuel cells typically have anodes on both sides of an electrolyte membrane capable of transporting hydrogen ions. It has a basic form with a cathode attached. At the anode (electrode or anode), electrochemical oxidation of hydrogen as a fuel occurs, and at the cathode (reduction electrode or cathode), electrochemical reduction of oxygen as an oxidant occurs and electrical energy is generated by the movement of electrons generated at this time. .

The type of fuel finally supplied to the anode may be hydrogen or alcohol (methanol, ethanol, etc.). In the former case, a carbon atom is removed from a hydrocarbon-based fuel such as LNG, LPG, and gasoline to generate hydrogen gas. A reformer is needed.

In the latter case, a direct methanol fuel cell (DMFC) is a mixture of methanol and water in a proportion (approximately 10%: 90%) at the anode of the stack, STACK, without using a reformer. Since the reforming reaction occurs at the electrode by directly supplying the mixed liquid, there is an advantage that the reformer is unnecessary and the entire system can be simplified.

On the other hand, in a direct methanol fuel cell, there is a limit condition that the concentration of the methanol solution supplied directly to the stack must be constant at a low concentration (3 to 5%) level. On the other hand, water is generated as a by-product as a result of the reduction action at the cathode, and the aqueous methanol solution supplied to the anode is discharged through the separator after methanol is consumed by the oxidation action, and methanol, which is not oxidized even in the discharged liquid, Included.

However, when the water generated in the cathode and the unreacted methanol are discharged to the outside as they are, they not only waste fuel, but also waste of space for storing water for making the aqueous methanol solution for stack supply. This results in a waste of space due to the device for discharging large amounts of water.

In order to prevent the waste, the cathode electrode exhaust gas in which unreacted methanol and reactant water are mixed is condensed, and an appropriate amount of fuel methanol is added thereto to make an appropriate concentration of methanol aqueous solution and supplied as fuel to the anode electrode. The method is implemented. To this end, the fuel cell system has a concentration control tank for mixing the unreacted methanol, the reaction product and the high concentration methanol, and if the cathode electrode exhaust gas is condensed most of the time to increase the recyclability, If the capacity is exceeded, and the structure to discharge the excess condensed liquid is implemented again, the unnecessary condensation-draining process is repeated, resulting in a waste of the entire system space.

An object of the present invention devised to solve the above problems is to provide a fuel cell system capable of condensing only an appropriate amount according to the capacity of the concentration control tank in the cathode electrode exhaust gas.

It is further an object of the present invention to provide a fuel cell system capable of adjusting the amount of condensation of the cathode electrode exhaust gas according to the amount of the fuel aqueous solution stored in the concentration control tank.

A fuel cell system of the present invention for achieving the above object is a stack comprising an anode electrode supplied with an aqueous solution fuel and a cathode electrode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode electrode; And a concentration control tank for mixing the condensate condensed by the condenser and the high concentration fuel, wherein the condensation operation of the condenser is controlled according to the accumulation amount of the fuel aqueous solution in the concentration control tank.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

For example, it is applicable to fuel cells such as pure hydrogen and hydrogen-containing organic compounds, and is applicable to fuel cell systems using all fuels that can be dissolved in water (mostly will be water-soluble organic compounds such as methanol and formic acid). It is possible. However, in the following embodiments of the present invention, a fuel cell system using a fuel supplied in an aqueous solution of a predetermined concentration for the sake of convenience of understanding and for avoiding duplication of description is embodied as being applied to the most widely used direct methanol fuel cell system. Let's do it. If the present invention is implemented in a fuel cell system using hydrocarbons, it will be obvious to further include a reformer for generating hydrogen gas from hydrocarbons.

( Example  One)

The fuel cell system of the present embodiment as shown in FIG. 1 includes a stack including an anode electrode supplied with an aqueous methanol solution fuel and a cathode electrode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode electrode; A mixing tank for mixing the condensate condensed by the condenser and high concentration methanol; A linear accumulation meter for linearly measuring the accumulation amount of the aqueous methanol solution in the concentration control tank; And a control device for maintaining a constant amount and concentration of the solution in the mixing tank.

The stack 120 may include a membrane-electrode assembly having a structure in which an anode electrode and a cathode electrode are bonded to both sides of the polymer electrolyte membrane. In addition, the fuel cell stack 120 may have a multi-cell structure in which a plurality of unit fuel cells display a separator or a bipola plate and have a stacked multi-cell structure, or physically include only one layer of membrane-electrode assembly. It may have a single cell structure, or a dual cell structure that physically comprises only one layer of membrane-electrode assembly.

In addition, the stack 120 generates electric energy using a mixed fuel supplied to the anode and an oxidant supplied to the cathode. Here, the mixed fuel is an aqueous methanol solution having a predetermined concentration which is a fuel containing hydrogen atoms, and the oxidant contains air, oxygen, or the like. The cathode-side effluent of the fuel cell stack 120 is introduced into the condenser through the first pipe 122, and the liquid component collected in the condenser is again reconstructed by a third method. The pipe is introduced into the mixing tank 130, and the anode side effluent of the fuel cell stack 120 is introduced into the mixing tank 130 through the second pipe 124.

The cathode side by-product supplied to the condenser through the first pipe is discharged as a mixture of liquid and gaseous state (mostly gaseous components) of water and cross-over unreacted methanol, and a considerable amount by the condenser Condensed in a liquid state and flows into the mixing tank through the third pipe, and gaseous components which have not yet condensed are discharged into the atmosphere.

The condenser may include a heat exchanger for absorbing the heat of the effluent gas in the first pipe and a heat radiator for discharging the heat absorbed by the heat exchanger to the outside of the fuel cell system. For example, the heat exchange part may be implemented by a condensing plate in contact with the effluent gas, and the heat dissipation part may include a heat sink connected to the condensation plate in a state capable of thermal conduction, and a cooling fan for blowing external air to cool the heat sink. have. Or an exposure pipe such as a radiator grille as a heat exchanger, and a cooling fan for blowing external air to cool the exposed pipe as a heat dissipation part.

The mixing tank is for supplying a constant concentration of aqueous methanol solution to the stack, by mixing the output of the anode side of the stack, the condensate of the condenser and the high concentration methanol supplied from the fuel tank, to prepare a suitable aqueous methanol solution Feed to the anode of the stack. In order to perform the operation, an aqueous solution supply pump may be provided to actively supply an aqueous methanol solution from the mixing tank to the stack, and a fuel supply pump may be provided to actively supply a high concentration of methanol from the fuel tank to the mixing tank. It can be provided. Although the first pipe to the third pipe may be provided with a control device such as a valve or a pump for adjusting the fluid flow amount, the advantage of the addition of the pump is not as great as the aqueous solution / fuel supply pump. In addition, the fuel cell may further include a water tank and a water supply pump for supplying water for making an aqueous methanol solution at the start of the fuel cell. The fluid flow rate adjusting means such as the various pumps are implemented to operate under the control of the control unit, it is preferable to implement the control unit to adjust the concentration and / or accumulation amount of the aqueous methanol solution in the mixing device.

The control device may be implemented to be a main CPU that controls the overall operation of each component of the fuel cell system, or may be separately implemented as a simple logic operation element (eg, logic gate chip) dedicated to the mixing tank control. When implemented with a main MCU, the concentration control method of the present embodiment to be described later may be implemented in the form of a program to be executed in the main CPU.

The linear accumulator is for measuring the accumulated capacity of the aqueous methanol solution stored in the mixing tank as a continuous value, for example, may be implemented by the apparatus as shown in FIG.

The linear accumulator shown includes a buoy 144 which floats on the surface of the liquid stored inside the tank 130; Displacement transfer means (146) for transmitting a change in position of the buoy (144) to a detection signal generator (148) below; It characterized in that it comprises a detection signal generator 148 for generating an electrical signal according to the degree of position change of the buoy 144. In addition, in order to more accurately detect the accumulation amount by the buoy 144, a buoy guide for preventing the surface movement of the buoy 144 may be further included.

The buoy 144 should be less dense than the aqueous methanol solution stored in the tank 130. The displacement transmission means 146 has a buoy connecting rod 146a, one end of which is connected to the buoy, the other end of which is connected to the buoy connecting rod, and the other end of which is connected to the detection signal generator. ) May be included. The displacement of the other end of the lever means 146b may be implemented to adjust the variable resistance in the detection signal generator 148, and the variable resistor may apply a variable resistor in a manner in which the resistance value is adjusted by the amount of rotation of the rotary knob. Can be.

The variable resistance value in the detection signal generator 148 may be easily converted into a voltage value or a current value using a means such as a voltage divider connected in series. The accumulated amount measured value changed into a voltage value or a current value may be input to the control device as it is an analog value, or may be converted into a digital value and input to the control device. The former case may be applied when the control device is a digital operation element having a DSP (Digital Signal Processing) function or an analog operation element (for example, Operationa Amplifier).

The linear accumulator can be implemented in various ways, for example, it is also possible to apply an ultrasonic sensor set (ultrasonic generator and sensor) installed at one or more points in the mixing tank. This is because the ultrasonic waves radiated in the air are reflected on the surface of the aqueous methanol solution, or the ultrasonic velocity difference between the aqueous methanol solution and the air is used. In the former case, one set of ultrasonic generator and sensor pairs is located at about the same point, and in the latter case, one set of ultrasonic generator and sensor pairs is preferably located at points facing each other in the tank. In any case, if only one pair of the ultrasonic sensors is provided, accurate operation is performed only when the arrangement direction of the mixing tank such as a vehicle is constant with respect to the gravity direction. Therefore, in order to further increase the direction-free degree of the mixing tank, it is preferable to install the ultrasonic sensor pairs in a uniform distribution at a plurality of points on the inner surface of the mixing tank.

Hereinafter, operations of the elements constituting the fuel cell system of the present embodiment will be described.

When the fuel cell system of the present embodiment is started for the first time, water input from a separate water tank (not shown) or injected by a user as a default is filled with the mixing tank. A high concentration of methanol is introduced into the mixing tank from the fuel supply device so that a predetermined amount of aqueous methanol solution is formed together with the water.

Thereafter, an aqueous methanol solution of the mixing tank is supplied to the anode of the stack, and power is generated by the stack while air, which is an oxidant, is supplied to the cathode of the stack. The DC power generated in the stack is supplied to an external load via a power converter or is stored in a battery in the fuel cell system.

Methanol constituting the aqueous methanol solution supplied to the anode is converted to carbon dioxide generated on the anode side and water vapor generated on the cathode side in the substantial portion is oxidized at the anode. However, due to the incomplete nature of the electrolyte membrane partitioning the anode electrode and the cathode electrode, a significant amount of methanol molecules are cross-over and transferred to the cathode electrode, some of which are oxidized at the cathode electrode and converted into water vapor and carbon dioxide The other part remains unreacted methanol, and a large part becomes gaseous due to the high temperature of the cathode electrode. Since the water contained in the original aqueous methanol solution is not involved in the chemical reaction of the fuel cell, it is logical to recover the entire amount through the second pipe to the mixing tank, but in reality, a considerable amount is passed to the cathode together with the methanol molecules and the proton ions. The water in the aqueous methanol solution that has passed to the cathode also becomes gaseous due to the high temperature of the cathode electrode.

As above, the effluent of the cathode, which is a mixture of liquid and gaseous substances comprising water molecules, methanol molecules and carbon dioxide molecules, is fed to the condenser along the first piping. The cathode effluent in the first conduit, which is in contact with the exposed conduit (or condensation plate) of the condenser having a relatively low temperature, condenses in a liquid state, and the amount of condensation is the cathode effluent in the first conduit and the exposed conduit (or condensation). It is proportional to the temperature difference of the plate). The temperature difference between the cathode effluent in the first pipe and the exposed pipe (or condensation plate) is controlled by the cooling fan. That is, the amount of cooling of the exposed pipe (or condensation plate) is controlled according to the amount and / or flow rate of external air blown into the exposed pipe (or condensation plate) by the cooling fan, which is the first pipe By controlling the temperature difference between the cathode effluent and the exposed piping (or condensate plate), it is possible to ultimately control the amount of solidification of the cathode effluent.

The cathode effluent changed into the liquid state by the condenser is brought into the mixing tank through the third pipe, and the cathode effluent, which has not yet condensed and remains in the gaseous state, is moved out of the condenser, the third pipe and the mixing tank. It is discharged to the atmosphere where the discharge path is formed.

Since the effluent flowing into the mixing tank is an aqueous methanol solution at a concentration lower than the proper concentration supplied to the anode, it is necessary to supply an appropriate amount of high concentration methanol from the fuel supply device. This is to maintain a constant concentration of the aqueous methanol solution in the mixing tank.

In order to maintain a constant concentration of the aqueous methanol solution in the mixing tank, it is preferable to periodically measure the concentration of the aqueous methanol solution in the mixing tank. To this end, it can be implemented to install a concentration sensor on the bottom surface of the mixing tank, it can be implemented to estimate the concentration of the aqueous methanol solution in the mixing tank from other factors according to a predetermined formula. Additional components required in the latter case will be described later. As the concentration sensor, an ion conductive polymer resin or a composite resin whose volume changes depending on the concentration of fuel such as methanol may be used.

The linear accumulation meter measures the accumulation amount (water level) of the methanol aqueous solution in the mixing tank as a continuous value and periodically provides it to the control device. The control device controls the speed of the cooling fan, and the greater the amount of accumulation, the slower the speed of the cooling fan, and the smaller the amount of accumulation, the faster the speed of the cooling fan. When the control device is an analog processing means such as an operational amplifier, the control signal for the cooler also has linear values, and when the control device is a general CUP or DSP chip, The control signal will have discrete multistep values.

Hereinafter, various additional components, which can be added to quantitatively improve the performance of the fuel cell system of the present embodiment, will be described.

The controller 150 may include a memory in which a predetermined program is stored and a central processing unit coupled to the memory to control the fuel cell system by the program. In addition, the controller 150 may maintain a reference concentration value of the mixed fuel determined in accordance with the structure and characteristics of the fuel cell stack 120 in the memory. In addition, the controller 150 may retain data about an output voltage value and an output current value that change according to a change in the concentration value of the mixed fuel within a predetermined range. For example, the controller 150 may include a lookup table in which concentration values of the mixed fuel, corresponding output voltage values, and output current values are stored.

In some embodiments, an aqueous solution of methanol in the mixing tank may be provided by applying a predetermined equation from the output voltage value and the output current value of the stack or power converter according to the look up table, without having a separate concentration sensor in the mixing tank. It may be configured to estimate the concentration of. In this case, the temperature of the stack may be measured and applied to the calculation formula in order to increase the accuracy of the estimation calculation.

In some embodiments, the controller 150 may receive an electric signal of a predetermined level for the output voltage and the output current of the fuel cell stack 120 from the power converter 160. Then, the heat exchanger 170 is controlled according to the fuel concentration value corresponding to the input electric signal. In this case, the amount of power generated is controlled by adjusting the concentration of the aqueous methanol solution supplied to the anode of the stack according to the power requirement of the external load connected to the power converter.

In order to remove impurities, particularly carbon dioxide, of the aqueous solution flowing into the mixing tank through the first pipe and the third pipe, a circulation treatment device may be installed between the first pipe and the third pipe and the mixing tank. In this case, the cathode-side output liquid and the anode-side condensation liquid are introduced into the mixing tank after passing through the circulation processing device once.

The circulation processing device 180 stores the unreacted fuel from the anode side outlet of the fuel cell stack 110 and properly discharges the reaction product such as carbon dioxide. The water exiting from the cathode side outlet of the fuel cell stack 110 is stored, and reaction products such as nitrogen and oxygen are properly discharged. In addition, the circulation processing device 180 supplies a low concentration fuel in which unreacted fuel and water are mixed to the fuel mixing device 132 through the pump 142. Such a circulation processing device 180 is installed between the lower half and the upper half so that, for example, the lower half into which the anode side effluent flows and the upper half into which the cathode side effluent flows, and the gaseous phase permeate into the upper half, and the liquid phase permeate into the lower half. It may comprise a selective permeable membrane.

The mixing tank 130 may have a structure in which a high concentration of methanol input from the fuel supply device 110 and a low concentration of methanol aqueous solution input from the condenser 160 may be smoothly mixed. For example, the inflow of low concentration methanol and high concentration methanol may be implemented to pass through the porous member.

The control device 150, which is a kind of electrical computing device, needs to be supplied with driving power. The driving power for the control device is input from the power converter 180 or from a battery for stabilizing the output of a fuel cell system. It may be implemented to receive from, or from a separate battery for the control device 150.

( Example  2)

The fuel cell system of the present embodiment includes a stack including an anode electrode supplied with an aqueous solution fuel and a cathode electrode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode electrode; And a concentration control tank for mixing the condensate condensed by the condenser and the high concentration methanol; A nonlinear multi-stage accumulator for measuring the accumulation amount of the aqueous methanol solution in the concentration control tank step by step; And a control device for maintaining a constant accumulation amount and concentration of the solution in the mixing tank, wherein the entire connection structure includes the first embodiment as shown in FIG. 1 except that the linear accumulation meter is replaced with a nonlinear multistage accumulation meter. It is the same as the block diagram of an example.

Since the stack, the power converter, the condenser and the fuel supply device are almost the same as in the case of the first embodiment, the detailed structure and operation description thereof will be omitted. In addition, various additional components that may be added to quantitatively improve the performance of the fuel cell system of the present embodiment are also the same as the first embodiment, and thus description thereof is omitted. Hereinafter, the operation of the multi-stage accumulation meter and the control device according to the present embodiment will be described.

The control device may be implemented to be a main MCU that controls the overall operation of each component of the fuel cell system, or may be separately implemented as a simple logic operation element (eg, a logic gate chip) dedicated to the mixing tank control. When implemented in the main MCU The concentration control method of the present embodiment to be described later, may be implemented in the form of a program to be executed in the main MCU.

Although the control device may be implemented by an analog processing means such as an operational amplifier, an input accumulation amount value is a discrete value and thus an efficient configuration may not be achieved. If the control device is a general MCP, the control signal for the cooler will also have discrete multistep values.

The nonlinear multi-stage accumulator as shown in FIG. 3 is for measuring the accumulated volume of the methanol aqueous solution stored in the mixing tank 230 at a continuous value, and at least three measuring points are distinguished from the conventional single accumulator. The more measurement points, the finer the control of condensation by the controller. The minimum three measurement points are the high water level causing minimization (e.g. stopping) of the condensation action, the low water level leading to the maximization of the condensation action, and the intermediate water level being a reference point for selecting one of the mass condensation action and the small amount condensation action. .

The nonlinear multi-stage accumulator 240 may be implemented by applying various sensor elements, as shown in FIG. 3, a set of a plurality of simple level on / off level sensing elements installed at each measurement level, 242, and It is easy to implement with the detection signal generator 244 for converting the logical combination of the output of the water level sensing element set 242 into a stepwise electrical signal.

The nonlinear multistage accumulator measures the amount of accumulated aqueous solution of methanol in the mixing tank (water level) as a discrete multistage value and provides it to the control device. The provision of the measured value may be performed at regular intervals or when a change occurs in a previously provided step.

The control device controls the speed of the cooling fan according to each step of the measured value received from the nonlinear multi-stage accumulator. When the water level is full, the speed of the cooling fan is minimized (stopped). To maximize the speed, the closer to the full water level, the faster the cooling fan. The closer to the lowest water level, the slower the cooling fan.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

By implementing the water level sensing means as described above, there is an effect of linearly measuring the accumulation amount of the liquid stored in the tank.

By implementing a fuel cell system capable of dynamically adjusting the condensation amount of the condenser as described above, there is an effect that can ensure a stable operation even with a smaller mixing tank.

Claims (13)

Buoy floating on the surface of the liquid stored inside the tank; Displacement transfer means for transferring a change in position of the buoy to a detection signal generator; Detection signal generator for generating an electrical signal according to the degree of change in the position of the buoy Level detection means comprising a. The method of claim 1, Buoy guides to prevent buoyancy movement Water level detection means further comprising. The method of claim 1, The detection signal generator, And a variable resistor having a resistance value adjusted according to an externally applied mechanical operation. A stack comprising an anode supplied with an aqueous solution fuel and a cathode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode; A mixing tank for mixing the condensate condensed by the condenser and the high concentration fuel; A linear accumulation meter for linearly measuring the accumulation amount of the fuel aqueous solution in the mixing tank; And Control device for maintaining a constant accumulation amount of the solution in the mixing tank Fuel cell system comprising a. The method of claim 4, wherein the condenser, A heat exchanger for absorbing heat of the cathode discharge gas; And Heat dissipation unit for discharging the heat absorbed by the heat exchanger to the outside Fuel cell system comprising a. The method of claim 5, wherein the heat dissipation unit, Cooling fan for blowing outside air to cool the heat exchange unit, And the control device adjusts the speed of the cooling fan in accordance with the detection value of the linear measurement meter. The method of claim 6, The detection value of the linear metrology meter input to the control device is a continuous value, And a speed control signal of the cooling fan output from the control device is a continuous value. The method of claim 6, The detection value of the linear metrology meter input to the control device is a continuous value, And a speed control signal of the cooling fan output from the control device is a step value. The method according to any one of claims 4 to 8, The linear accumulator is a fuel cell system, characterized in that the water level sensing means of claim 1. The method according to any one of claims 4 to 8, The fuel cell system, characterized in that the fuel is a water-soluble organic compound. A stack comprising an anode electrode supplied with an aqueous solution fuel and a cathode electrode supplied with an oxidant; A condenser for condensing the gas discharged from the cathode electrode; And a concentration control tank for mixing the condensate condensed by the condenser and the high concentration methanol; A nonlinear multi-stage accumulator for measuring the accumulation amount of the aqueous methanol solution in the concentration control tank step by step; Control device for maintaining a constant accumulation amount of the solution in the mixing tank Fuel cell system comprising a. The method of claim 11, wherein the condenser, A heat exchanger for absorbing heat of the cathode discharge gas; And Heat dissipation unit for discharging the heat absorbed by the heat exchanger to the outside Fuel cell system comprising a. The method of claim 12, wherein the heat dissipation unit, Cooling fan for blowing outside air to cool the heat exchange unit, And the control device adjusts the speed of the cooling fan in accordance with the detection value of the linear measurement meter.

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