KR100509818B1 - A Method and device for performing internal purge in fuel cell system - Google Patents

Abstract

The present invention relates to a method and apparatus for performing internal purging to control a fuel recycle pump and a purge valve using a stack voltage and intercell variation within a stack. The present invention can be recycled 100% without flowing out the reaction gas of hydrogen, oxygen (or air) and the generated water by using a pressure difference close to the vacuum at the rear end of the stack during the discharge of water generated in the electrode reaction. The purge method includes (a) detecting a cell voltage of a stack including a plurality of cells, (b) determining whether there is a flooding occurrence using the cell voltage, and (c) a fuzzy coupled to the rear end of the stack when flooding occurs. Controlling the valve and the recirculation pump to reduce the pressure between the purge valve and the recirculation pump, thereby creating a pressure difference between the stack and the purge valve and the recirculation pump, (d) by opening the purge valve, (E) separating the gas mixture into water and gas in a water separator provided between the rear end of the stack and the front of the purge valve; (f) stacking the moisture Resupplying to the stack via a water storage tank coupled to the gas, and gas may be resupplied to the stack via a recycle pump.

Description

A method and device for performing internal purge in fuel cell system

The present invention relates to a method and apparatus for performing an internal purge in a fuel cell system, and more particularly, to an internal purge controlling a fuel recycle pump and a purge valve using a stack voltage and an intercell variation within a stack. A method and apparatus for the same.

A fuel cell is a device that produces electricity electrochemically by using hydrogen gas and oxygen gas, and converts fuel (hydrogen) and air (oxygen) continuously supplied from the outside into electrical energy and heat by an electrochemical reaction. to be. Currently, fuel cells have been used for various purposes as alternative power sources. Hereinafter, polymer fuel cells of such fuel cells will be described below for convenience of description. The polymer fuel cell has a high power density and energy conversion efficiency and can be operated at a low temperature below 80 ° C., and can be miniaturized and encapsulated. It is used in a wide variety of fields.

In such polymer fuel cells, the output of electrical energy depends on the extent to which protons, hydrogen ions, are transported through a polymer membrane called Nafion ™, which must be hydrated with adequate moisture to conduct the hydrogen ions. The hydration of the polymer membrane humidifies the reaction gas input to the anode and the cathode of the fuel cell through a separate humidifier so that the relative humidity is 100% at the operating temperature of the fuel cell stack.

During operation of the fuel cell, water is generated as a reaction product of the cathode, and a condition may occur in which excessive water may exist. Due to the excessive amount of water produced in the cathode, since the back diffusion of the anode may occur through the polymer membrane, the moisture control of the cathode and the anode around the polymer membrane is an important factor in the fuel cell operation.

That is, when the electrode and the cathode including the cathode lacks humidification, the polymer film is dehydrated to increase the resistance value of the polymer film. Increasing the resistance value of the polymer membrane may inhibit the movement of protons, thereby reducing the electrical efficiency of the fuel cell. In addition, the presence of excessive water (flooding) can interfere with the movement of gas to the electrode and the diffusion of protons, can reduce the stability of the fuel cell and at the same time reduce the electrical conversion efficiency. In general, in a polymer fuel cell, a problem of excess (flooding) problem is more important than dehydrate.

In particular, in the operating environment in the high current region, the reactant is excessively generated in the cathode, and the excessive drop of water causes the supply of gas to the catalyst layer and the diffusion of protons into the polymer membrane to suppress the performance of the entire stack. More seriously, normal cell is difficult to operate due to deterioration of some cells due to inhomogeneous water distribution per unit cell existing in the stack. As such, flooding generated in the polymer fuel cell is an important factor that makes it difficult to stably operate the fuel cell as well as to decrease the reaction efficiency, and it is essential to discharge the excess water out of the stack.

Fuel cell water discharge method according to the conventional method can be divided into a structural method and a purge method. In the structural method, there is a method of designing the flow path of the separator plate in the form of a serpentine that facilitates the discharge of water, thereby facilitating the discharge of water according to the pressure drop and the flow rate. The purge method refers to a method of promoting water discharge by mixing water and gas by using a purge valve installed at the rear of the stack. The prior art associated with the purge method is as follows.

First, after opening and closing the solenoid valve periodically at the rear end of the stack to reduce the pressure of the gas, the water present in the stack is discharged out of the stack together with the gas by the differential pressure. However, this method has a disadvantage in that the time for opening the purge valve and the purge interval are fixed fixedly so that the water discharge effect is not high.

Since the amount of water produced in the stack depends on the operating current and the temperature of the stack, the purge condition and the water discharge are not proportional to each other, so that the uniform purge performed corresponding to the preset time is not efficient. For example, when operating in a high current region, water generation is high and a flooding situation may still occur despite a preset purge cycle, and if the purge cycle is shorter than the water generation or the purge interval is longer than the water generation, Emissions can result in loss of reactive gases. In the case of the anode in particular, there is a possibility of reducing the ion conductivity of the polymer membrane by causing the membrane to dry due to excessive water loss.

Secondly, a purge method for solving this problem is disclosed in US Pat. No. 6,242,120. That is, by measuring the performance items of the stack proportional to the amount of water generated, it is a method of determining when the purge valve is opened. In other words, when the measured value of the stack reaches a predetermined value, the purge valve is opened. Here, as the measurement items expressing the stack performance, items such as hydrogen consumption rate, current, and power that can indicate the degree of water generation were presented. As a method of performance measurement, a method based on real-time measurements and cumulative values of these values for a predetermined time is presented. This method has the advantage of receiving a performance signal from the stack instead of a predetermined average purge interval and purging when the water reaches an excessive condition.However, it is a problem in actual flooding by taking the average value of the entire stack as a control signal. There is a problem that can not respond to the non-uniformity between cells.

In more detail, flooding in a stack involves unevenness of inter-cell currents and voltages before degrading the stack as a whole, and controlling the purge to the average value of the stack is not efficient. In addition, since the gas and water discharged at the time of purge is discharged to the outside, a loss occurs to lower the fuel utilization rate, which in turn lowers stack efficiency and system efficiency. In particular, in the case of a regenerative fuel cell system or a mobile fuel cell system in which the external water supply line is disconnected, it means the loss of water required for humidification.

As described above, the purge according to the prior art causes waste of the fuel by discharging the fuel to the outside, and at the same time, the discharged hydrogen or oxygen can affect the outside air. In addition, there is a problem that can not be collected as the water is discharged to the outside during purge. Such waste of fuel and water causes problems such as lower gas utilization, lower fuel cell efficiency, and lower performance. In particular, there is a problem that the use is limited in the operating environment (ventilation Nexa is very important for indoor use according to the external discharge of the fuel), the ventilation is important when using indoors.

Accordingly, the present invention has been made to solve the above problems, and provides a purge method and apparatus having a fuel utilization of 100%. That is, the present invention provides a purge method and apparatus which can fully utilize fuel having 100% fuel utilization while improving the effect of purging through an internal purge method and apparatus for facilitating discharge of water from the stack.

In addition, another object of the present invention is to determine the measurement signal of the stack required for the purge operation using not only the average voltage of the stack, but also the voltage difference between cells in the stack, thereby purging the operation stability and stack efficiency of the fuel cell. And providing an apparatus.

Still another object of the present invention is to construct a blocking system capable of utilizing 100% of fuel and water, and to recycle 100% of the discharged water. That is, the present invention can be used in a highly efficient renewable fuel cell, a mobile fuel cell, etc., because the fuel cell system humidifies using internal water by itself even in an operating environment in which the fuel cell system is not connected to an infrastructure capable of continuously supplying water.

According to one aspect of the present invention to achieve the above objects, there can be provided a purge method for removing the flooding of the fuel cell system.

The purge method includes the steps of (a) detecting a cell voltage of a stack including a plurality of cells, (b) determining whether flooding is generated using the cell voltage, and (c) when flooding occurs, coupled to a rear end of the stack. Controlling the purge valve and the recirculation pump to reduce the pressure between the purge valve and the recirculation pump, thereby forming a pressure difference between the inside of the stack and the purge valve and the recirculation pump, (d) by opening the purge valve. Using the pressure difference to discharge a gas mixture containing moisture in the stack to the outside of the stack, (e) water and the gas mixture in a water separator provided between the rear end of the stack and the front end of the purge valve. Separating into gas, (f) refeeding the moisture to the stack through a water storage tank coupled to the stack, the gas being recirculated It may comprise the step of re-supplied to the stack through the pump.

Here, step (b) may be performed by determining whether at least one of the plurality of cell voltages is out of a preset deviation range based on the average voltage of the cell voltages. The step (b) may further include determining at least one of whether at least one of the plurality of cell voltages is less than or equal to a preset cell lower limit and whether the voltage of the stack is less than or equal to a preset stack lower limit. have.

In addition, in the step (c), when the purge valve is open and the recirculation pump is in operation, the step of closing the purge valve for a predetermined time is performed, the purge valve is closed, and the recirculation pump is not operated. If not, it may be configured to perform a process of operating the recirculation pump for a predetermined time.

And step (c) may be configured to be made in the buffer unit provided between the purge valve and the recirculation pump, not the discharge line.

According to another aspect of the present invention to achieve the above objects, a purge device for removing flooding of a fuel cell system can be provided.

The purge device includes (a) a stack including a plurality of cells, (b) a sensing unit connected to each of the plurality of cells to sense a voltage of a cell included in the stack, and (c) a rear end of the stack. And a water separator for separating a gas mixture including water discharged from the stack into water and gas, (d) coupled to a rear end of the water separator, and configured to perform opening and blocking operations in response to a control signal of the sensing unit. A purge valve, (e) coupled to a rear end of the purge valve and operated in conjunction with the purge valve in response to the control signal, thereby reducing the pressure between the purge valve and the recirculation pump to a pressure lower than the pressure formed within the stack. And a recirculation pump for resupplying the gas to the stack, (f) a water storage tank coupled to the stack, for resupplying the moisture to the stack, and (g) on Detects whether flooding is generated using the cell voltage received from the sensing unit, and controls the purge valve and the recirculation pump in response to the flooding to form a pressure difference between the stack and the purge valve and the recirculation pump, And a system controller for opening a purge valve to discharge a gas mixture including moisture in the stack to the outside of the stack.

Here, in order to reduce the pressure between the purge valve and the recirculation pump to a pressure lower than the pressure formed in the stack, a buffer unit provided between the purge valve and the recirculation pump may be further included.

The system controller may determine whether at least one of the plurality of cell voltages is out of a preset deviation range based on the average voltage of the cell voltages, or at least one of the plurality of cell voltages is previously determined. The electronic device may be configured to further determine at least one of whether the value is less than or equal to a set cell lower limit value and whether the voltage of the stack is less than or equal to a preset stack lower limit value.

And when the purge valve is open and the recirculation pump is in operation, closing the purge valve for a predetermined time to form the pressure difference, the purge valve is closed, and the recirculation pump is not operated. If not, the recirculation pump may be operated for a predetermined time to form the pressure difference.

DETAILED DESCRIPTION In order to achieve the above objects, a preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings, and in the following description with reference to the accompanying drawings, the same or corresponding components regardless of reference numerals are the same reference numerals. The numbering and duplicate description thereof will be omitted.

Overall System Diagram and Operation Procedure

1A is a diagram illustrating a configuration of a fuel cell system for performing an internal purge method according to a preferred embodiment of the present invention.

Since the internal purge method according to the present invention performs purging in the fuel cell system, water and fuel are not wasted at all, and a fuel cell system having a recycling rate of 100% can be provided. Hereinafter, the purge method according to the present invention will be referred to as 'internal purge' to distinguish the purge according to the existing method.

That is, according to the internal purge according to the present invention, since the water is not wasted, and the whole amount is collected, it can be used especially in an environment in which water is not supplied from the outside in a renewable fuel cell or a mobile fuel cell. In addition, since purging is performed internally, hydrogen and oxygen do not flow to the outside, so there is no fuel waste, thereby increasing fuel cell efficiency, and it can be used indoors without restriction such as an enclosed space and a place where ventilation is important. .

Hereinafter, referring to FIG. 1A, in which the fuel cell system is illustrated, the fuel cell system 100 to which the internal purge is applied according to the present invention includes a fuel injection unit 122 for supplying fuel to the fuel cell stack 130. Sensing a humidifier 123 for humidifying the injected fuel, a fuel cell stack 130 connected to the humidifier 123, a stack voltage of the fuel cell stack 130, or a voltage of a unit cell constituting the stack, respectively. Sensing unit 132 for, the rear end of the stack and the water separator 125 for separating water from hydrated hydrogen and oxygen (air), the purge valve 126 and the recirculation pump 127 for performing an internal purge The system control unit 140 is connected to the purge valve 126 and the recirculation pump 127 through the communication line 148 and the control line 149. The components are coupled to each other by a gas supply line 141, a gas discharge line 142, a gas recycle line 143, a water recycle line 144, a water supply line 145, and a water discharge line 146. It is. Here, the purge valve 126 may be implemented as a solenoid valve.

According to an embodiment of the present invention, the components of the fuel cell system described above are respectively configured to correspond to the gas to be injected, that is, oxygen and hydrogen, and in more detail, the fuel injection unit 122 is a hydrogen fuel injection unit The hydrogen humidifier 123a and the oxygen humidifier 123b and the water separator are the hydrogen water separator 125a and the oxygen water separator 125b and the purge valve 126. ) May be composed of a hydrogen purge valve 126a and an oxygen purge valve 126b, and a recycle pump 127 may include a hydrogen recycle pump 127a and an oxygen recycle pump 127b.

Similarly, the above-described lines are also configured to correspond to oxygen and hydrogen, respectively, the gas supply line 141 is a hydrogen supply line 141a and an oxygen supply line 141b, and the gas discharge line 142 is a hydrogen discharge line 142a. And an oxygen discharge line 142b, a gas recycle line 143, a hydrogen recycle line 143a, an oxygen recycle line 143b, and a water recycle line 144 are connected to a hydrogen water separator 125a. And a water recycle line 144b connected to the oxygen water separator.

Hereinafter, the overall operating procedure of the fuel cell system according to the present invention will be described with reference to FIG. 1B.

1B is a flowchart illustrating an operating procedure of a fuel cell system according to a preferred embodiment of the present invention.

Referring to FIG. 1B, in step S150, hydrogen and oxygen (or air), which are reaction gases, are supplied to the fuel cell stack 130. That is, hydrogen (or fuel) is supplied to the anode of the fuel cell stack 130 via the hydrogen supply line 141a and the hydrogen humidifier 123a, and oxygen (or air) is supplied to the oxygen supply line 141b and the oxygen humidifier ( It is supplied to the cathode of the fuel cell stack 130 via 123b.

 The gas supplied in step S160 is supplied to each cell included in the fuel cell stack 130 through a manifold and a flow path configured inside the stack, and in the membrane electrode assembly of each cell, hydrogen and oxygen are electrochemically bounded by the polymer membrane. Accompanying the reaction produces electricity, water and heat. Here, in order to reduce heat generated during the reaction, the fuel cell stack 130 is supplied with water from the water storage tank 134 to the fuel cell stack 130 through the water supply line 145 and used for cooling. The collected water is returned to the water storage tank 134 through the water discharge line 146.

Since flooding occurs due to the water generated in the electrochemical reaction of step S160, in step S170, the present invention determines whether flooding occurs using the stack or cell voltage sensed by the sensing unit 132. Since the present invention detects flooding using the cell voltage, the flooding can be detected earlier than the flooding detection method according to the conventional method.

If it is determined in step S170 that flooding has occurred, the system controller 140 may remove the flooding by the internal purge according to the present invention in step S180 (see FIGS. 4 and 5).

And the gas containing the water discharged in step S190 is separated from the water in the water separator 125, the gas is recycled and used again as a reaction gas.

That is, when hydrogen, which is not used for the reaction, is discharged in the fuel cell stack 130 while containing water, water is first separated through the hydrogen water separator 125a. The moisture-depleted hydrogen is supplied to the hydrogen humidifier 123a through the hydrogen recycle line 143a by the hydrogen purge valve 126a and the hydrogen recycle pump 127a, and the humidified hydrogen is again supplied to the fuel cell stack 130. Supplied to the anode.

Similarly, when the oxygen not used for reaction in the fuel cell stack 130 is discharged while containing water, the water is first separated through the oxygen water separator 125b. The moisture-depleted oxygen is supplied to the oxygen humidifier 123b through the oxygen recycle line 143b by the oxygen purge valve 126b and the oxygen recycle pump 127b, and the humidified oxygen is again supplied to the fuel cell stack 130. Supplied to the cathode.

The water separated in the hydrogen water separator 125a and the oxygen water separator 125b is supplied to the water storage tank 134 through the water recycling lines 144a and 144b.

Flooding detection

In the conventional method, the average value of the entire stack is used as a control signal. However, the problem in actual flooding is the intercell nonuniformity and the voltage drop occurring in each cell. In other words, flooding in a stack is accompanied by nonuniformity of current distribution and voltage in the cell before the performance degradation of the entire stack occurs. The present invention can detect the voltage unevenness of each cell to quickly and efficiently detect the occurrence of flooding, and eliminate it.

2 is a view showing a method for determining whether flooding according to an embodiment of the present invention.

Hereinafter, referring to FIG. 2, the stack voltage measured in real time by the sensing unit 132 of the fuel cell stack 130 or the voltage measurement of each cell is measured through a communication line connected to the system controller 140. It is transmitted to the control unit 140. In order to determine whether flooding has occurred, the controller 140 may determine whether flooding has occurred by comparing a preset threshold or lower limit with a measured value input in real time.

The internal purge method according to the present invention detects the voltages of the plurality of cells 200-1, 200-2, 200-3,. The purge timing can be efficiently set.

That is, even if the total stack potential maintains a predetermined voltage, it may be detected that flooding has occurred when the variation between cells is large or the output voltage of the unit cell decreases. According to an exemplary embodiment of the present invention, not only the voltage of the unit cell can be sensed through a sensing line connected to each unit cell, but the sensed cell voltage can be displayed through a preset interface screen.

According to an embodiment, the determination criterion may determine whether flooding occurs by using at least one of the plurality of cell voltages being out of a predetermined reference value and a reference deviation based on the average voltage. According to the present invention, the reference deviation is preferably set in the range of 0.01 volt to 0.2 volt, and more preferably in the range of 0.05 to 0.1 volt.

In order to increase the efficiency of flooding detection, it is determined whether at least one of the plurality of cell voltages is equal to or less than a preset lower limit (cell lower limit) or whether the stack voltage is equal to or less than a preset lower limit (stack lower limit). It can be configured to determine. In this case, the reference value and the lower limit value may be set according to the performance of the cell.

3 is a view showing an interface screen according to a preferred embodiment of the present invention.

As described above, during the operation in the high current region, the reactant is excessively generated at the cathode, and the gas supply to the catalyst layer is suppressed due to the excess water droplets, resulting in deterioration of the overall stack performance. Moreover, there is a problem that normal operation becomes difficult due to deterioration of some cells due to inhomogeneous water distribution for each unit cell present in the stack. The present invention can detect inter-cell nonuniformity and prevent or eliminate occurrence of flooding at the beginning of flooding.

Hereinafter, the interface screen will be described based on a stack composed of 15 unit cells with reference to FIG. 3. The interface screen according to the present invention may provide a stack output 310 indicating a stack voltage 310, a stack current 320 flowing out of the stack, and an output applied to an external load.

In addition, the interface screen may provide each cell potential by displaying a bar graph 350, and may also provide a cell average voltage 340.

According to the exemplary embodiment of the present invention, when the potential deviation is out of a preset reference value, an internal purge is performed to reduce the deviation between cells. Therefore, it is possible to detect this at the beginning of flooding occurrence and prevent flooding occurrence. That is, when it is determined that flooding has occurred through the above-described determination method, as shown in FIG. 1A, the system controller 140 transmits a control signal through the control line 149 to purge the valve 126 and the recirculation pump 127. Can be controlled to eliminate flooding.

Internal purge procedure

When the occurrence of flooding is detected, the present invention controls the purge valve 126 and the recirculation pump 127 by a preset method, and can effectively prevent or eliminate flooding.

The biggest disadvantage of the conventional purging method, which is only for water discharge, is that the hydrogen or oxygen (or air) discharged during the purge as well as the generated water are discharged to the outside. This reduces the fuel utilization of the stack, resulting in a reduction in stack efficiency. The present invention includes a water separator 125 at the front of the purge valve 126 to allow 100% recovery of water and 100% use of fuel through a recirculation scheme.

In addition, the recirculation pump 127 may be positioned at the rear end of the purge valve 126 to effectively remove flooding by utilizing the pressure drop of the gas discharge line 142 between the purge valve 126 and the recirculation pump 127. . Here, it is natural that the buffer unit having a separate space between the purge valve 126 and the recirculation pump 127 may further increase the purge efficiency.

Hereinafter, an internal purge procedure will be described in detail with reference to FIG. 4 illustrating an internal purge method and a method of applying an internal purge to a conventional dead end method. Here, only one cycle of the purge flow according to the present invention will be extracted and described, and the cycle may be repeated during fuel cell operation.

4 shows a control flow diagram of recycling and purging according to the first preferred embodiment of the present invention.

In the conventional purge, purging is performed using data related to the performance of the entire stack as a signal of purge operation, for example, stack current, stack output, and hydrogen consumption. However, when flooding occurs due to excessive water, there is a difference in flooding between cells, and it is common for some specific unit cells to exhibit relatively severe flooding first. Therefore, it is not desirable to purge the signal with the average performance value of the stack. In addition, the conventional external purge method has a problem that the utilization rate of water and fuel is inefficient by discharging the discharged gas and water to the outside of the fuel cell system.

In the present invention, when the total voltage of the stack or the voltage of each cell is below a predetermined lower limit or at least one cell voltage is out of a predetermined level compared to the average value, the purge may be operated to ensure stable operation of the fuel cell. Of course, you can protect the stack.

In addition, the present invention forms the pressure at the rear end of the purge valve in a state close to the vacuum state, increases the differential pressure required for purging, and then performs the internal purge according to the present invention, thereby improving the effect of the purge. In addition, the gas and water discharged from the purge are recycled again, enabling 100% fuel utilization.

Hereinafter, referring to FIG. 4, in step S400, the fuel cell system 100 is in operation. That is, when the supply valve (not shown in the figure) is opened to supply the reaction gas, the fuel cell stack 130 performs an electrochemical reaction to generate electricity, and in this operating state, the purge valve 126 is in an open state. . The recirculation pump 127 is in operation to recycle 100% of the gas and water normally discharged.

In step S410, the present invention monitors the fuel cell stack and cells in real time to determine whether flooding has occurred. According to a preferred embodiment, when the deviation between the cells deviates from the preset deviation, the flooding further comprises a case where the stack voltage is less than the lower limit of the preset stack voltage, or if at least one cell voltage is less than the lower limit of the preset cell voltage The occurrence can be determined.

As a result of the determination in step S410, if it corresponds to a predetermined flooding generation criterion, the system controller 140 transmits a shutoff command of the purge valve to the purge valve 126 through the control line 149 in step S420, and the purge valve 126. ) Is blocked. The purge valve immediately closes the purge valve only for a predetermined time. Here, the time may be configured to be included in the range of 0.5 seconds to 5 seconds.

Since the recirculation pump 127 continues to operate in the state in which the purge valve 126 is blocked in step S430, the pressure decreases rapidly between the recirculation pump 127 and the purge valve 126 so that the recirculation pump 127 and the purge valve ( The pressure between 126 is lower than the pressure inside the stack. According to a preferred embodiment, the pressure between the recirculation pump 127 and the purge valve 126 may be configured to be close to vacuum.

When a predetermined time elapses in step S440, the system controller 140 transmits a command to open the purge valve to the purge valve 126 through the control line 149. Here, the predetermined time may be set corresponding to the performance of the recirculation pump and the recirculation pump 127 and the purge valve 126. Here, the time can be configured to be included in the range of 0.01 seconds to 5 seconds, the time can be adjusted according to the capacity of the recycle pump and the volume of the gas line.

Flooding generated in the stack may be removed due to the opening of the purge valve in step S450. That is, when the purge valve 126 is opened, excessive moisture, which is a cause of flooding in the stack due to the pressure difference, that is, the differential pressure, is rapidly discharged together with the gas.

Here, in order to increase the pressure difference, the gas pressure inside the stack may be pressurized to a predetermined pressure, for example, 1 atm, and in this case, the performance of the fuel cell stack may be improved and water discharge may be promoted.

Through the above configuration, it is possible to use 100% of the total amount of the water generated by the fuel cell and the reaction gas. On the other hand, the purge valve and the recirculation pump at the rear of the fuel cell are used to form the line 142 at the rear of the fuel cell at a lower pressure than the pressure in the fuel cell stack, or to form a situation close to vacuum by the recirculation pump to quickly and effectively remove excess moisture Can be discharged.

5 is a flowchart illustrating a control of recycling and purging according to a second preferred embodiment of the present invention.

 In the dead end method which prevents the rear end of the stack and supplies only as much gas as necessary at the front end of the stack, a signal generated from the controller 140 is first transmitted to the recirculation pump 127 when the flooding occurs to operate the pump. The pressure in the space between the closed purge valve 126 and the recirculation pump 127 is lowered. Then, the purge valve 126 is opened after a predetermined time passes to remove a mixture of excess moisture and gas present in the stack 130.

Hereinafter, referring to FIG. 5, in operation S500, the fuel cell system 100 is operating in a dead end manner. That is, the reactant gas is supplied to the fuel exhibit stack 140 to generate electricity, and the purge valve 126 is in a blocked state. And the recirculation pump 127 is off.

In operation S510, it is detected whether flooding occurs due to excessive water in the stack during operation of the fuel cell. As a result of the determination in step S510, if it corresponds to a preset flooding criterion, the system controller 140 transmits an operation command of the recirculation pump 127 to the recirculation pump 127 through the control line 149 in step S520.

When the recirculation pump 127 starts to operate in the state in which the purge valve 126 is shut off in step S530, the pressure between the recirculation pump 127 and the purge valve 126 decreases rapidly.

In operation S520, when the recirculation pump is operated for a predetermined time and the pressure drops, the system controller 140 transmits a command to the purge valve 126 through the control line 149 to open the purge valve 126. The predetermined time is adjustable according to the capacity of the recirculation pump and the volume of the discharge line, and generally a time in the range of 0.1 seconds to 5 seconds is sufficient.

Flooding generated inside the stack may be removed due to the opening of the purge valve in step S550. Since other operations are the same as or similar to those described above with reference to FIG. 4, descriptions thereof will be omitted.

Performance Comparison

Hereinafter, the performance of the embodiment of the fuel cell system to which the internal purge according to the present invention is applied and the comparative example of the conventional fuel cell system will be described in detail with reference to FIGS. 6A to 6C. Here, the operating environment of the fuel cell system is performed under common conditions, and only the purge method will be differently compared.

The common conditions of the examples and the comparative examples are the active area 300 cm 2, the catalyst is a state of 0.4 mgPt / cm 2 supported on the anode and the cathode, as a polymer film using a stack consisting of 15 cells using Dupont's N112 membrane (thickness 50 ㎛) By comparison. The fuel cell system is the result of the experiment under the fuel cell system shown in FIG. 1A. 6A and 6C are graphs showing the inter-cell voltages according to the operating time, and the graphs showing the inter-cell voltages according to the operating time according to the comparative example of the present invention.

Example-Internal purge according to the present invention

Referring to FIG. 6A, there is shown a graph showing intercell voltages according to operation time.

Here, the operating conditions are the stack temperature 60 ℃, humidification temperature anode 50 ℃, cathode 50 ℃, fuel flow rate is 15 lpm hydrogen, 7.5 lpm oxygen, gas pressure is 0.2 bar during operation. In the purge signal, if at least one cell is 0.05 volt deviation or more than the average cell voltage of the stack, the purge valve is removed by opening the purge valve after removing the purge valve for 0.1 to 5 seconds according to the operation sequence shown in FIG. 4. 6A is a graph of experiments after performing a stack operation for 10 hours to fully activate. Table 1 below summarizes the measurement results according to the embodiment of the present invention.

Stack voltage  11.5 V at 150 A (0.75V at 500mA / cm2 as a unit cell) Cell-to-cell variation   ≤ ± | 0.05 ｜ V (operating time 10 hours) Cell voltage changes  stable Stack efficiency  60% (based on LHV) Fuel utilization  100% (Hydrogen & Oxygen) Water recovery  100%

Referring to FIG. 6A, the stack voltage was 11.5 V at 150 A and the cell average value was 0.75 V at 500 mA / cm 2. During 10 hours of operation test time, the variation between cells is kept within 0.05V, and as shown in FIG. 6A, it can be seen that the cell voltage is uniform throughout the stack. The stack efficiency is calculated based on the LHV criterion, that is, the fuel utilization rate x (cell voltage / 1.25).

<Comparative Example 1-Existing Fuzzy Method>

Referring to FIG. 6B, an intercell operating voltage graph according to a conventional purge method is illustrated. The comparative example used the same stack as the stack configured in the embodiment, and is set to operate in the existing dead-end method. It is configured to open the purge valve for 1 second at 20 second intervals without using a control method using a signal spreading during operation, and the purged fuel and water are discharged to the outside. Table 2 below summarizes the measurement results according to the first comparative example.

Stack voltage  11.5 V at 150 A (0.75V at 500mA / cm2 as a unit cell) Cell-to-cell variation  ≤ ± | 0.05 | V (deviation from average cell voltage) (2 hours maintenance) ≤ ± | 0.05 | V (deviation from average cell voltage) (8 hours maintenance) Cell voltage changes  Deviation increases with time Stack efficiency  59.4% (based on LHV) Fuel utilization  99% (hydrogen and oxygen) Water recovery  95%

Referring to FIG. 6B, the stack voltage of the first comparative example was 11.5 V at 150 A as in the example, and the cell average value was 0.75 V at 500 mA / cm 2. However, it can be seen that the deviation between cells during the 10 hour operation test time is larger than that of the embodiment, and the deviation between cells increases as the time maintained within 0.05 V is 2 hours and over time. And when 8 hours of operation time passes, it turns out that the deviation between cells deviates from 0.05V.

That is, according to the conventional purge method, the change of the cell voltage with time increases, and the degree of non-cell nonuniformity is large. The stack efficiency according to the first comparative example is 59.4% based on the LHV standard.

<Comparative Example 2-Without Fuzzy>

Hereinafter, a second comparative example without purging will be described with reference to FIG. 6C. In Comparative Example 2, the same stack as that used in the example was used, and normal pressure operation was performed without using a recirculation pump. There was no purge during operation, and the fuel utilization rate was operated at 70% for hydrogen and 50% for oxygen, and the remaining gas and water used for the reaction were set to discharge to the outside. Table 3 below summarizes the measurement results according to the second comparative example.

Stack voltage  10.5 V at 150 A (0.70V at 500mA / cm2 as a unit cell) Cell-to-cell variation  ≤ ± | 0.05 | V (deviation from average cell voltage) (2 hours maintenance) ≥ ± | 0.05 | V (deviation from average cell voltage) (8 hours maintenance) Cell voltage changes  Instability Stack efficiency  ≤40% (based on LHV) (considering 70% utilization) Fuel utilization  70% (hydrogen and oxygen) Water recovery  70%

Referring to FIG. 6C, it can be seen that the stack voltage was 10.5 V at 150 A and the cell average value was 0.70 V at 500 mA / cm 2 as in the embodiment. In this case, the variation between cells is lower than that of the embodiment or the first comparative example and the variation between cells is maintained within 0.05 V during the operation test time of 15 hours. However, when flooding occurs, the variation between cells increases rapidly, and the stack voltage drops and becomes unstable. It can work. Further, according to the second comparative example, the gas utilization rate of the fuel cell system is low and a considerable amount of water is discharged to the outside, which is inefficient. The stack efficiency of the second comparative example is 39.2% based on the LHV standard in consideration of the gas utilization rate.

As described above, it can be seen that the embodiment of the internal purge according to the present invention provides remarkable stack performance and stable driving performance in comparison with the conventional purging method and the non-purging operation conditions.

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. It belongs to the scope of the invention.

As described above, the present invention provides a method and apparatus for performing internal purging to control a fuel recycle pump and a purge valve using a stack voltage and an intercell variation within a stack. That is, the present invention may provide an environment capable of stably operating the stack through efficient water discharge while providing 100% utilization of fuel and water.

In addition, the present invention is a determination method for performing an internal purge, after detecting the voltage of each of the unit cells, it is determined by using the deviation of each cell it is possible to quickly and efficiently calculate the purge timing and perform the purge It also works.

In particular, in the present invention, when a separate water supply or fuel supply through an external infrastructure is not possible, water may be used through a cutoff circuit by itself, so that external water supply is impossible such as a renewable fuel cell or a mobile fuel cell. Can be used without restrictions. Moreover, the present invention can utilize 100% of fuel as well as water, and can provide excellent performance in a renewable energy system incorporating solar and electrolytic devices.

In addition, the internal purge method according to the present invention can prevent the waste of water and fuel through the entire amount of water and fuel recycling, in particular, since it can be used in a closed space, can be used indoors, even in a completely closed space Can be used without limitation.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and variations can be made.

1A illustrates a fuel cell system in accordance with a preferred embodiment of the present invention.

1B is a flow chart illustrating an operation procedure of a fuel cell system according to a preferred embodiment of the present invention.

2 is a view showing a method for determining whether flooding according to an embodiment of the present invention.

3 is a view showing an interface screen according to a preferred embodiment of the present invention.

4 is a flow chart showing an internal purge procedure according to the first preferred embodiment of the present invention.

5 is a flow chart showing an internal purge procedure according to a second preferred embodiment of the present invention.

Figure 6a is a graph showing the inter-cell voltage according to the operating time according to an embodiment of the present invention.

6B and 6C are graphs showing intercell voltages according to operating times according to a comparative example of the present invention.

<Description of the symbols for the main parts of the drawings>

100: fuel cell system 122: fuel injection unit

123: humidifier 125: water separator

126: purge valve 127: recirculation pump

130: fuel cell stack 132: sensing unit

140: system control unit

Claims (12)

A purge method for removing flooding of a fuel cell system, (a) sensing a cell voltage of a stack comprising a plurality of cells; (b) determining whether flooding has occurred using the cell voltage; (c) when the flooding occurs, controlling the purge valve and the recirculation pump coupled to the rear end of the stack to reduce the pressure between the purge valve and the recirculation pump, thereby forming a pressure difference between the stack and the purge valve and the recirculation pump. step; (d) opening the purge valve to use the pressure differential to discharge a gas mixture containing moisture within the stack out of the stack; (e) separating the gas mixture into water and gas in a water separator provided between the rear end of the stack and the front of the purge valve; And (f) purging the moisture to the stack through a water storage tank coupled to the stack, wherein the gas is supplied to the stack through the recirculation pump. The method of claim 1, In step (b), And determining whether at least one of the plurality of cell voltages is out of a preset deviation range based on the average voltage of the cell voltages. The method of claim 2, In step (b), And at least one of whether the at least one voltage of the plurality of cell voltages is equal to or less than a preset cell lower limit value and whether the voltage of the stack is equal to or less than a preset stack lower limit value. The method of claim 1, Step (c) is, And the purge valve is closed for a preset time when the purge valve is open and the recirculation pump is in operation. The method of claim 1, In step (c), And if the purge valve is closed and the recirculation pump does not operate, operating the recirculation pump for a preset time. The method of claim 1, In step (c), The purge method characterized in that the buffer portion provided between the purge valve and the recirculation pump. A purge apparatus for removing flooding of a fuel cell system, (a) a stack comprising a plurality of cells; (b) a sensing unit connected to each of the plurality of cells to sense a voltage of a cell included in the stack; (c) a water separator coupled to the rear end of the stack and separating a gas mixture including water discharged from the stack into water and gas; (d) a purge valve coupled to a rear end of the water separator and configured to perform an opening and closing operation according to a control signal of the sensing unit; (e) coupled to a rear end of the purge valve and operated in conjunction with the purge valve in response to the control signal to form a pressure between the purge valve and the recirculation pump to a pressure lower than the pressure formed in the stack. A recirculation pump for resupplying said gas to said stack; (f) a water storage tank coupled to the stack for resupplying the water separated from the water separator to the stack; And (g) detecting whether flooding is generated by using the cell voltage received from the sensing unit, and controlling the purge valve and the recirculation pump in response to the flooding to control the pressure between the stack and the purge valve and the recirculation pump. And a system control to form a difference and to open the purge valve to release a gas mixture containing moisture within the stack out of the stack. The method of claim 7, wherein And a buffer provided between the purge valve and the recirculation pump to reduce the pressure between the purge valve and the recirculation pump to a pressure lower than the pressure formed in the stack. The method of claim 7, wherein The system control unit, And a method for determining whether at least one of the plurality of cell voltages is out of a predetermined deviation range based on the average voltage of the cell voltages. The method of claim 9, The system control unit. And at least one of whether the voltage of at least one of the plurality of cell voltages is equal to or less than a predetermined cell lower limit value and whether the voltage of the stack is equal to or less than a preset stack lower limit value. The method of claim 7, wherein The system control unit, And the purge valve is open and the recirculation pump is in operation to close the purge valve for a preset time to form the pressure difference. The method of claim 7, wherein The system control unit, And if the purge valve is closed and the recirculation pump does not operate, operating the recirculation pump for a preset time to form the pressure difference.