Abstract:
The present invention provides a hydrogen discharge system for a fuel cell system, which can ensure safety of a fuel cell vehicle by optimizing the dilution of hydrogen discharged from a fuel cell during discharge and ensure silence of the vehicle by reducing noise generated during discharge. 
     For this purpose, the present invention provides a hydrogen discharge system for a fuel cell system including a purge valve for purging hydrogen discharged from a fuel electrode of a fuel cell stack, the hydrogen discharge system including: an ejector mounted to a hydrogen purge line extending from the purge valve to introduce air from the outside; and a post-treatment system connected to an exhaust line of the ejector to remove hydrogen discharged therethrough.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2008-0023609 filed Mar. 14, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (a) Technical Field 
     The present invention relates to a hydrogen discharge system for a fuel cell system. More particularly, the present invention relates to a hydrogen discharge system for a fuel cell system, which can ensure safety of a fuel cell vehicle by optimizing the dilution of hydrogen discharged from a fuel cell during discharge and ensure silence of the vehicle by reducing noise generated during discharge. 
     (b) Background Art 
     A fuel cell system can generally comprise a fuel cell stack for generating electricity, a fuel supply system for supplying fuel (hydrogen) to the fuel cell stack, an air supply system for supplying oxygen in the air as an oxidant required for an electrochemical reaction to the fuel cell stack, and a thermal management system for controlling the operation temperature of the fuel cell stack. 
     In exemplary fuel cell systems having the above configuration, a hydrogen recirculation blower is preferably connected to a hydrogen outlet of the fuel cell stack to recirculate hydrogen remaining after a reaction at a fuel electrode (anode) of the fuel cell stack to the fuel electrode to be reused. 
     Nitrogen or water accumulated in the fuel electrode is discharged from the fuel cell stack through a periodic purge. 
     Accordingly, in the operation of the fuel cell stack applied to a fuel cell vehicle, nitrogen or water accumulates in the fuel electrode (hydrogen electrode) and deteriorates the performance of the fuel cell stack, and thus it is necessary to ensure stable performance of the fuel cell stack through the periodic purge of the hydrogen electrode. 
     When the nitrogen or water is discharged from the fuel cell stack through the periodic purge, some residual hydrogen is discharged together with the nitrogen or water and, if the concentration of the discharged hydrogen is high, there may be a risk of explosion. 
     Accordingly, the concentration of the discharged hydrogen should be reduced or diluted within the range of explosion in order to avoid explosion. 
     For this purpose, conventionally, a diluter is provided in a hydrogen purge line to dilute the concentration of hydrogen in the air. 
     However, in the case where the diluter is used for example, hydrogen and air are merely mixed with each other, but the absolute amount of hydrogen is not reduced. Accordingly, the hydrogen may be accumulated in the inside of the vehicle and may cause safety accidents. A pipe channel for introducing air into the diluter or an air supply device may be provided, which increases the manufacturing cost and results in complexity of the piping. 
     As a post-treatment system for treating hydrogen discharged from the fuel cell stack, there has been conventionally proposed a catalyst combustion device or a flame combustion device, in which a large amount of air is introduced into a reactor to remove exhaust hydrogen discharged from the fuel cell stack. However, it results in complexity of the piping and increases the load of an air blower for supplying air to the catalyst combustion or flame combustion device. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore 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 OF THE DISCLOSURE 
     In one aspect, the present invention is directed to a hydrogen discharge system for a fuel cell system, in which an ejector for introducing air is preferably connected to a hydrogen purge line and a post-treatment system, such as a humidifier, a catalyst combustion reactor, and a burner, is provided at an outlet port of the ejector so as to remove a significant amount of hydrogen and, at the same time, to improve humidification of a fuel cell stack, thus improving the performance and durability of the fuel cell stack. 
     In one embodiment, the present invention provides a hydrogen discharge system for a fuel cell system including a purge valve for purging hydrogen discharged from a fuel electrode of a fuel cell stack, the hydrogen discharge system suitably comprising an ejector mounted to a hydrogen purge line extending from the purge valve to introduce air from the outside; and a post-treatment system preferably connected to an exhaust line of the ejector to remove hydrogen discharged therefrom. 
     In a preferred embodiment, the post-treatment system is a humidifier for supplying humidified air to an air electrode of the fuel cell stack, and the exhaust line of the ejector is preferably connected to the inside of the humidifier. 
     In another preferred embodiment, the post-treatment system is a catalyst combustion device suitably mounted to the exhaust line of the ejector, and an exhaust line of the catalyst combustion device extends to the outside or is connected to the inside of the humidifier. 
     In still another preferred embodiment, the post-treatment system is a burner mounted to the exhaust line of the ejector, and an exhaust line of the burner extends to the outside or is connected to the inside of the humidifier. 
     In yet another preferred embodiment, a branch line having an air supply valve is preferably connected between an air exhaust line extending from the air electrode of the fuel cell stack and the exhaust line of the ejector. 
     It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like. 
     The above features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description, which together serve to explain by way of example the principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinafter by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a first embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a second embodiment of the present invention. 
         FIG. 3  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a third embodiment of the present invention. 
         FIG. 4  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a fourth embodiment of the present invention. 
         FIG. 5  is a cross-sectional view illustrating an operation principle of an ejector applied to the hydrogen discharge system for a fuel cell system in accordance with the present invention. 
     
    
    
     Reference numerals set forth in the Drawings includes reference to the following elements as further discussed below: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                  10: fuel cell stack 
                  12: fuel electrode 
               
               
                   
                  14: hydrogen recirculation line 
                  16: purge valve 
               
               
                   
                  18: hydrogen purge line 
                  20: air electrode 
               
               
                   
                  22: air supply line 
                  24: air exhaust line 
               
               
                   
                  26: humidifier 
                  28: exhaust line of ejector 
               
               
                   
                  30: blower 
                  32: catalyst combustion device 
               
               
                   
                  34: exhaust line of catalyst 
               
               
                   
                 combustion device 
               
               
                   
                  36: burner 
                  38: exhaust line of burner 
               
               
                   
                  40: branch line 
                  42: air supply valve 
               
               
                   
                 100: ejector 
                 102: housing 
               
               
                   
                 104: ejector main body 
                 106: main inlet 
               
               
                   
                 110a, 110b and 110c: nozzles 
                 112a, 112b and 112c: sub-inlets 
               
               
                   
                 114: cover body 
                 116: check valve 
               
               
                   
                   
               
             
          
         
       
     
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     DETAILED DESCRIPTION 
     As described herein, the present invention includes a hydrogen discharge system for a fuel cell system including a purge valve for purging hydrogen discharged from a fuel electrode of a fuel cell stack, the hydrogen discharge system comprising an ejector mounted to a hydrogen purge line and a post-treatment system. In certain preferred embodiments, the ejector mounted to the hydrogen purge line extends from the purge valve to introduce air from the outside and the post-treatment system is connected to an exhaust line of the ejector to remove hydrogen discharged therefrom. In other preferred embodiments, the post-treatment system is a humidifier for supplying humidified air to an air electrode of the fuel cell stack, and the exhaust line of the ejector is connected to the inside of the humidifier. In still other embodiments, the post-treatment system further comprises a catalyst combustion device mounted to the exhaust line of the ejector, and an exhaust line of the catalyst combustion device extends to the outside or is connected to the inside of the humidifier. In exemplary embodiments, the post-treatment system further comprises a burner mounted to the exhaust line of the ejector, and an exhaust line of the burner extends to the outside or is connected to the inside of the humidifier. In other further embodiments, a branch line having an air supply valve is connected between an air exhaust line extending from the air electrode of the fuel cell stack and the exhaust line of the ejector. 
     The invention can also include a motor vehicle comprising a hydrogen discharge system according to any of the embodiments as described herein. 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the drawings attached hereinafter, wherein like reference numerals refer to like elements throughout. The embodiments are described below so as to explain the present invention by referring to the figures. 
     The present invention is directed to removing hydrogen by connecting an ejector to a hydrogen purge line (a pipe for discharging hydrogen) of a fuel cell stack and, at the same time, enabling removal, in certain examples complete removal, of hydrogen by suitably introducing the hydrogen into an inlet port of an air electrode of the fuel cell stack, or repeatedly diluting a small amount of hydrogen by suitably introducing the hydrogen into an outlet port of an air electrode of the fuel cell stack. Preferably, water produced by catalyst combustion is suitably introduced into the air electrode to suitably improve the humidification of the fuel cell stack. 
     First Embodiment 
       FIG. 1  is a schematic diagram showing a preferred hydrogen discharge system for a fuel cell system in accordance with a first exemplary embodiment of the present invention. 
     As shown in the figure, a hydrogen recirculation line  14  and a hydrogen purge line  18  including a purge valve  16  are suitably connected to a fuel electrode  12  of a fuel cell stack  10 . Preferably, an air supply line  22  and an air exhaust line  24  are suitably connected to an air electrode  20  of the fuel cell stack  10 , and a humidifier  26  for supplying humidified air to the air electrode  20  is suitably connected thereto. 
     In preferred embodiments, an ejector  100  for introducing air from the outside is connected to the hydrogen purge line  18  extending from the purge valve  16 , and an exhaust line  28  of the ejector  100  suitably extends to the outside as it is. 
     According to exemplary embodiments, the purge valve  16  is preferably an ON/OFF valve and serves to discharge nitrogen, or any other by-products that are contained in exhaust gas discharged from an outlet of the fuel cell stack  10 , to the outside in order to maintain optimal properties of recirculated gas. Accordingly, during purge, nitrogen, hydrogen, water vapor, water, and other by-products are discharged through the purge valve  16 , and the number of times of ON/OFF and the opening time are suitably controlled according to the load. 
     Any kind of ejector capable of sucking air may be used as the ejector  100 . According to certain embodiments, it is preferable to use a multi-stage in-line cartridge ejector suitably comprising a housing  102  and an ejector main body  104 . 
     An exemplary structure of the ejector  100  is described with reference to  FIG. 5  below. 
     In exemplary embodiments, the ejector main body  104  is suitably fixedly mounted in the housing  102  having a main inlet  106 , and preferably at least three nozzles  110   a ,  110   b , and  110   c  that are sequentially arranged with a predetermined gap in the ejector main body  104 . In certain embodiments, the respective nozzles  110   a ,  110   b , and  110   c  have diameters which suitably become progressively larger from the inlet port to the outlet port in the order of arrangement. 
     In exemplary embodiments, a cover body  114  suitably having at least three sub-inlets  112   a ,  112   b , and  112   c  is provided on the outer circumference of the respective nozzles  110   a ,  110   b , and  110   c  such that the respective nozzles  110   a ,  110   b , and  110   c  are suitably fixed. In further exemplary embodiments, the three sub-inlets  112   a ,  112   b , and  112   c  are preferably connected to gap spaces between the respective nozzles  110   a ,  110   b , and  110   c.    
     Preferably, a check valve  116  is mounted on the three sub-inlets  112   a ,  112   b , and  112   c  to suitably prevent the introduced air from leaking to the outside. 
     An example of the operation of the hydrogen discharge system in accordance with the first embodiment of the present invention is described below. 
     In an exemplary embodiment, when the hydrogen discharged through the hydrogen purge line  18  is introduced into the ejector  100 , the respective nozzles  110   a ,  110   b , and  110   c  of the ejector main body  104  suitably perform an amplification operation that continuously increases the flux of introduced hydrogen while in other preferred embodiments at the same time, outside air is suitably introduced into the ejector main body  104  and mixed with the exhaust hydrogen, thus suitably providing hydrogen dilution. 
     The operation principle of the ejector for providing the hydrogen dilution is described in more detail in the example below. 
     (1) Exhaust hydrogen discharged from the hydrogen purge line  18  of the fuel cell stack  10  can be injected through the first-stage nozzle  110   a.    
     (2) The injected hydrogen from the first-stage nozzle  110   a  preferably creates a vacuum pressure (low pressure) in the first-stage nozzle portion, and the check valve  116  is opened by the vacuum pressure to suitably introduce outside air through the first-stage sub-inlet  112   a.    
     (3) While the introduced outside air is mixed with hydrogen, the gas density is preferably increased, and thereby a higher vacuum pressure is created in the second-stage nozzle  110   b.    
     (4) The mixed gas is preferably reinjected through the second-stage nozzle  110   b  to create a low pressure in the second stage, and thereby the corresponding check valve  116  is opened to introduce outside air through the second-stage sub-inlet  112   b.    
     (5) By the above principle, a suitably higher vacuum pressure is created in the third stage by the third-stage nozzle  110   c , and accordingly outside air is introduced into the third-stage sub-inlet  112   c.    
     (6) According to certain embodiments of the invention, the above processes (1) to (5) are repeated in the respective steps, and the more the stages, the more the amount of introduced air is preferably increased. 
     As set forth in the examples above, since at least one ejector  100  is preferably connected to the hydrogen purge line  18  of the fuel cell stack  10 , the exhaust hydrogen is suitably mixed with outside air, and thus the dilution of the exhaust hydrogen is facilitated. The diluted hydrogen is discharged to the outside through the exhaust line  28  of the ejector  100 . 
     In certain embodiments, since the dilution operation of the exhaust hydrogen is preferably spontaneously performed by the spontaneous introduction of air through the ejector, the present invention provides advantages in that it is easy to control the amount of air supply based on the selection of ejectors, and in certain embodiments of the invention, separate control logic is not required, and it is easy to prevent excessive rise of temperature by controlling the amount of outside air. 
     Second Embodiment 
       FIG. 2  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a second embodiment of the present invention. 
     As shown in the figure, a second embodiment of the present invention features an exhaust line  28  of the ejector  100  that does not extend to the outside, but is preferably connected to the humidifier  26  for supplying humidified air to the air electrode  20 . 
     In preferred embodiments, the diluted gas, i.e., the air and exhaust hydrogen, discharged through the exhaust line  28  of the ejector  100  is not exhausted to the outside but is suitably introduced into the humidifier  26 . 
     For example, when the diluted gas is not discharged to the outside but is introduced into the humidifier  26 , the humidifier  26  can preferably serve as a buffer tank, i.e., a silencer, and at the same time may preferably serve as a diluter for diluting a large amount of air and hydrogen. 
     According to preferred embodiments, since water is contained in the exhaust hydrogen, the exhaust hydrogen suitably introduced into the humidifier  26  becomes a humidification source for the air supplied to the fuel cell, and surplus air preferably becomes an additional supply source of oxygen, a reactant of the fuel cell. 
     Thus, in preferred embodiments, the water contained in the exhaust hydrogen may serve to suitably humidify outside air introduced by a blower  30 , and the surplus air is mixed with the outside air introduced by the blower  30  to become an additional supply source of oxygen supplied to the air electrode  20 . 
     Third Embodiment 
       FIG. 3  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a third embodiment of the present invention. 
     As shown in the figure, the third the second embodiments of the present invention exemplify features of the invention comprising a catalyst combustion device  32  as a post-treatment system that is connected to the exhaust line  28  of the ejector  100 . 
     In exemplary embodiments, an exhaust line  34  of the catalyst combustion device  32  extends to the outside or is connected to the inside of the humidifier  26 . 
     According to certain embodiments, when the hydrogen discharged from the fuel cell stack  10  passes through the ejector  100  to be mixed with air and is introduced into the catalyst combustion device  32 , the hydrogen can preferably be easily removed by a catalyst combustion reaction. 
     In exemplary embodiments, a catalyst combustion reactor in the catalyst combustion device  32  acts as a buffer preferably to remove noise generated during introduction of exhaust hydrogen. 
     In preferred embodiments, the air exhaust line  24  extending from the air electrode  20  of the fuel cell stack  10  and the exhaust line  28  of the ejector  100  are suitably connected to a branch line  40  having an air supply valve  42 . 
     Accordingly, in certain exemplary embodiments, when a controller (not shown) opens the air supply valve  42  at the very time when the purge valve  16  is opened, the air discharged from the air electrode  20  of the fuel cell stack  10  may be additionally supplied to the catalyst combustion reactor in the catalyst combustion device  32  through the branch line  40  in order to ensure a sufficient amount of air suitably required to remove the hydrogen by the catalyst combustion reaction. 
     In certain examples, after the hydrogen is removed by the catalyst combustion device  32 , a small amount of hydrogen and water may remain and is supplied to the humidifier  26 . 
     Accordingly, the water produced during the catalyst combustion reaction is introduced into the humidifier  26  to act as an additional humidification source for the air supplied to the fuel cell stack  10  by the air blower  30 , and the small amount of residual hydrogen is substantially or completely diluted with the air in the humidifier  26  and suitably discharged to the outside through an exhaust line of the humidifier  26 . 
     Fourth Embodiment 
       FIG. 4  is a schematic diagram showing an exemplary hydrogen discharge system for a fuel cell system in accordance with a fourth embodiment of the present invention. 
     As shown in the figure, the fourth the second embodiment of the present invention have certain preferred features in that a burner  36  as a post-treatment system is preferably connected to the exhaust line  28  of the ejector  100 . 
     In certain embodiments, an exhaust line  38  of the burner  36  extends to the outside or is connected to the inside of the humidifier  26 . 
     Accordingly, when the hydrogen discharged from the fuel cell stack  10  passes through the ejector  100  to be mixed with air and is suitably introduced into the burner  36 , the hydrogen can be easily removed by combustion in the burner  36 . 
     In the same manner, the air exhaust line  24  extending from the air electrode  20  of the fuel cell stack  10  and the exhaust line  28  of the ejector  100  are suitably connected to a branch line  40  having an air supply valve  42 . 
     Accordingly, in exemplary embodiments, when a controller (not shown) opens the air supply valve  42  at the very time when the purge valve  16  is opened, the air discharged from the air electrode  20  of the fuel cell stack  10  may preferably be additionally supplied to a combustion chamber in the burner  36  through the branch line  40  in order to suitably ensure a more sufficient amount of air required to remove the hydrogen by a combustion reaction. 
     In certain embodiments, even after the hydrogen is removed by the burner  36 , a small amount of hydrogen and water remains and is supplied to the humidifier  26 . 
     As a result, in certain cases, the water produced during the combustion reaction of the burner  36  is preferably introduced into the humidifier  26  to act as an additional humidification source for the air supplied to the fuel cell stack  10  by the air blower  30 , and the small amount of residual hydrogen is substantially or completely diluted with the air in the humidifier  26  and discharged to the outside through an exhaust line of the humidifier  26 . 
     As described above, the present invention provides the following effects. 
     In certain embodiments, the ejector is preferably connected to the hydrogen purge line of the fuel cell stack and the post-treatment system, such as the catalyst combustion device, burner, and humidifier, is preferably provided at the outlet port of the ejector, it is possible to dilute the hydrogen discharged from the fuel cell stack and, at the same time, readily to remove the exhaust hydrogen. 
     In other certain embodiments, the final hydrogen exhaust line is preferably connected to the inside of the humidifier such that the water contained in the exhaust hydrogen is introduced into the humidifier, it is possible to efficiently humidify the air supplied to air electrode. 
     According to preferred embodiments, since the final hydrogen exhaust line is suitably connected to the inside of the humidifier, the humidifier may act as a buffer, i.e., a silencer. 
     In other preferred embodiments, since the ejector is connected to the hydrogen purge line (pipe for discharging hydrogen) of the fuel cell stack, outside air is spontaneously introduced thereinto, and thus a pipe channel for supplying air for dilution and an air supply device are not required. 
     The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.