CROSS REFERENCE TO RELATED APPLICATIONS

This application claims under 35 U.S.C. § 119(a) the benefit of priority to Korean Patent Application No. 10-2020-0149012 filed on Nov. 10, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates to a system and a method for purging the condensate water and hydrogen of a fuel cell stack, and more specifically, to a system and a method for purging the condensate water and hydrogen of a fuel cell stack, which may directly discharge parts of condensate water and hydrogen discharged from a fuel cell stack to the atmosphere according to the state and operation condition of the fuel cell stack, thereby improving operation stability and operation efficiency of the fuel cell stack.

(b) Background Art

A fuel cell system is configured to include a fuel cell stack configured to generate electrical energy, a hydrogen supply system configured to supply fuel (hydrogen) to a fuel cell stack, an air supply system configured to supply oxygen in the air, which is an oxidizer necessary for electrochemical reactions, to the fuel cell stack, a heat and water management system configured to control the operation temperature of the fuel cell stack, and the like.

Generally, the fuel cell stack (hereinafter, referred to as ‘stack’) is provided as a structure in which a plurality of unit cells including an electrolyte membrane, an anode which is an object to which hydrogen (H2) is supplied as a catalyst electrode layer located on one side of the electrolyte membrane, a cathode which is an object to which air is supplied as a catalyst electrode layer located on the other side of the electrolyte membrane, a gas diffusion layer disposed on the outsides of the anode and the cathode, and the like are laminated and assembled, in order to react hydrogen (H2) and oxygen (O2) to generate electrical energy.

Therefore, when the fuel cell system is operated, the hydrogen supplied to the anode of the stack is separated into proton and electron, and then the proton moves toward the cathode through the electrolyte membrane, and the electron moves to the cathode through an external circuit, such that the oxygen molecule, the hydrogen ion, and the electron react together on the cathode to generate electricity and heat and generate condensate water (H2O) as a reaction byproduct.

Referring toFIG. 1, the condensate water generated by the stack10is discharged through the cathode outlet of the stack10to be collected in a water trap20, and when an amount of the condensate water collected in the water trap20is sensed by a level sensor (not illustrated) as being a predetermined level or more, a drain valve22mounted on the outlet of the water trap20is opened for a predetermined time, such that a part of the condensate water collected in the water trap20is discharged to a shell side of a humidifier30.

For reference, the humidifier converts dry air supplied from the air supply system into humidified air to supply the humidified air to the cathode of the stack, and has a bundle type hollow fiber membrane through which the dry air passes disposed therein.

Therefore, the condensate water discharged to the shell side of the humidifier30from the water trap20serves to penetrate into the hollow fiber membrane arranged on the central portion of the shell of the humidifier30to convert the dry air into the humidified air.

Meanwhile, the hydrogen supplied to the stack from the hydrogen supply system reacts with the air to generate nitrogen, and when the nitrogen gradually builds up within the stack, the concentration of the hydrogen within the stack is reduced, and furthermore, when the concentration of the hydrogen is reduced to a predetermined level or more, the reaction hydrogen for generating electricity may be reduced, thereby resulting in the reduction in the performance of the stack while a voltage of the unit cell is reduced.

Therefore, to reduce the concentration of the nitrogen which builds up within the stack, as illustrated inFIG. 1, a hydrogen purge valve12mounted on a hydrogen purge line of the stack10is opened during a predetermined time such that the nitrogen and the non-reaction hydrogen are purged to the shell side of the humidifier30, thereby maintaining the concentration of the hydrogen within the stack to a predetermined level or more to prevent the reduction in the performance of the stack.

At this time, the nitrogen and oxygen purged to the shell side of the humidifier30are discharged to the atmosphere through an exhaust line32connected to the humidifier30.

However, upon cold operation of the fuel cell system, as the condensate water is frozen on the outlet of the cathode of the stack, when the nitrogen and the non-reaction hydrogen are purged to the shell side of the humidifier through the outlet of the cathode, the pressure of the cathode side is increased by the frozen condensate water, such that there is a problem in that an inverse voltage due to the backflow of the air supplied to the cathode of the stack toward the anode is generated.

Further, if the air is excessively supplied from the air supply system toward the humidifier in the state where the condensate water generated by the stack is collected in the water trap and then discharged to the shell side of the humidifier, there is a problem in that the condensate water discharged to the shell side of the humidifier is sucked to the inlet of the cathode of the stack together with the air, thereby causing a flooding phenomenon in the stack.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and accordingly it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present disclosure is devised to solve the above problems, and an object of the present disclosure is to provide a system and a method for purging the condensate water and hydrogen of a fuel cell stack, which may directly bypass the condensate water and hydrogen discharged from a stack to an exhaust line of a humidifier rather than a shell side of the humidifier to be purged to the atmosphere according to the operation state and operation condition of the stack, thereby eliminating a problem in that an inverse voltage is generated upon cold operation of a fuel cell system, a flooding phenomenon occurs in the stack, or the like to improve the operation stability of the stack and the operation efficiency of the fuel cell system.

An exemplary embodiment of the present disclosure for achieving the object provides a system for purging the condensate water and hydrogen of a fuel cell stack including an integrated purge valve to which a hydrogen purge line of a stack, and an outlet line of a water trap collecting condensate water generated by the stack are connected together, a three-way purge bypass valve mounted on the outlet of the integrated purge valve, a discharge line connected between a first outlet of the three-way purge bypass valve and a shell side of a humidifier, and a bypass line connected between a second outlet of the three-way purge bypass valve and an exhaust line of the humidifier.

According to the exemplary embodiment of the present disclosure, when the pressure of a cathode of the stack is increased to a predetermined level or more in the cold start and cold operation state of a fuel cell system, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward the bypass line connected to the exhaust line of the humidifier.

On the other hand, when the pressure of the cathode of the stack is at a normal level which is less than the predetermined level, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward the discharge line connected to the shell side of the humidifier.

According to the exemplary embodiment of the present disclosure, when it is determined that the relative humidity within the stack exceeds a reference value, it is determined that the concentration of hydrogen at an anode side within the stack is a reference value or less, or it is determined that a cell flooding occurs, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward the bypass line connected to the exhaust line of the humidifier.

On the other hand, when it is determined that the relative humidity within the stack satisfies a reference value, the concentration of hydrogen at an anode side within the stack satisfies a reference value, and a cell flooding does not occur within the stack, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward the discharge line connected to the shell side of the humidifier.

Another exemplary embodiment of the present disclosure for achieving the object provides a method for purging the condensate water and hydrogen of a fuel cell stack including determining whether the cold start and cold operation of a fuel cell system are performed, determining whether the pressure of a cathode of the stack is increased, when the fuel cell system is in the cold start and cold operation state, discharging the condensate water and non-reaction residual hydrogen discharged from the cathode of the stack to the atmosphere through an exhaust line of a humidifier, when it is determined that the pressure of the cathode of the stack is increased to a predetermined level or more, and discharging the condensate water and non-reaction residual hydrogen discharged from the cathode of the stack to a shell side of the humidifier, when the pressure of the cathode of the stack is at a normal level which is less than the predetermined level.

In the discharging of the condensate water and the non-reaction residual hydrogen to the atmosphere through the exhaust line of the humidifier, an integrated purge valve to which a hydrogen purge line of the stack and an outlet line of a water trap are connected together is opened and, at the same time, a three-way purge bypass valve mounted on the outlet of the integrated purge valve is opened toward the exhaust line of the humidifier.

In the discharging of the condensate water and the non-reaction residual hydrogen to the shell side of the humidifier, an integrated purge valve to which a hydrogen purge line of the stack and an outlet line of a water trap are connected together is opened and, at the same time, a three-way purge bypass valve mounted on the outlet of the integrated purge valve is opened toward the shell side of the humidifier.

Another exemplary embodiment of the present disclosure further includes determining whether the relative humidity within the stack satisfies a reference value, whether the concentration of hydrogen within the stack satisfies a reference value, or whether a cell flooding occurs in a plurality of cells configuring the stack due to the condensate water is performed, when it is determined that the fuel cell system is in the normal start and normal operation state rather than the cold start and cold operation state.

Therefore, when it is determined that the relative humidity within the stack exceeds the reference value, it is determined that the concentration of the hydrogen at an anode side within the stack is a reference value or less, or it is determined that the cell flooding occurs within the stack, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward the exhaust line of the humidifier.

On the other hand, when it is determined that the relative humidity within the stack satisfies the reference value, the concentration of the hydrogen at the anode side within the stack satisfies the reference value, and the cell flooding does not occur within the stack, the integrated purge valve is opened and, at the same time, the three-way purge bypass valve is opened toward a discharge line connected to the shell side of the humidifier.

The present disclosure provides the following effects through the above configuration.

First, it is possible to prevent the inverse voltage phenomenon caused by the backflow of the air of the cathode side toward the anode when hydrogen is purged by increasing the pressure of the cathode as the condensate water condensed on the outlet of the cathode of the stack is frozen, upon cold start and cold operation of the fuel cell system.

Second, by allowing the nitrogen and the residual hydrogen building up within the stack to be directly purged to the atmosphere without passing through the humidifier, a large amount of nitrogen and residual hydrogen may be purged at once, thereby preventing the reduction in the durability and lifespan of related valve series and the like due to the conventional frequent purge of the hydrogen.

Third, it is possible to allow the condensate water from the stack to be directly purged to the atmosphere using the differential pressure with the atmosphere without being discharged to the shell side of the humidifier, thereby preventing the conventional flooding phenomenon caused by the suction of the condensate water discharged to the shell side of the humidifier to the inlet of the cathode of the stack together with the air to prevent the shell flooding phenomenon.

Fourth, when it is determined that the relative humidity (RH) within the stack exceeds the reference value, or it is determined that the concentration of the hydrogen at the anode side within the stack is the reference value or less, the purge of the residual hydrogen including the condensate water and the nitrogen to the atmosphere is performed by the three-way purge bypass valve and the bypass line, such that the relative humidity and the concentration of the hydrogen of the stack may be adjusted to the proper levels according to the operation condition and state of the stack, thereby achieving the improvement in the durability of the stack.

It is understood that the term “automotive” or “vehicular” or other similar term as used herein is inclusive of motor automotives in general such as passenger automobiles including sports utility automotives (operation SUV), buses, trucks, various commercial automotives, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid automotives, electric automotives, plug-in hybrid electric automotives, hydrogen-powered automotives and other alternative fuel automotives (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid automotive is an automotive that has two or more sources of power, for example both gasoline-powered and electric-powered automotives.

