Patent Publication Number: US-2015079486-A1

Title: Fuel cell system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority to Korean Patent Application No. 10-2013-0110153 filed on Sep. 13, 2013, the entire contents of which is incorporated herein for all purposes by this reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a fuel cell system which can remove moisture and hydrogen which leak out of a fuel cell stack when producing electricity via a fuel cell, thereby preventing damage to internal parts of the fuel cell and improving operation stability of the fuel cell. 
     BACKGROUND 
     Generally, a fuel cell stack for a fuel cell system triggers an electrochemical reaction between hydrogen used as fuel and oxygen in the air to produce electrical energy to drive a vehicle. 
     As shown in  FIG. 1 , a fuel cell vehicle includes a fuel cell stack  2  which produces electricity, a humidifier  4  which humidifies fuel and air and supplies the humidified mixture to the fuel cell stack  2 , a fuel feeder which feeds hydrogen to the humidifier  4 , and an oxygen feeder which feeds oxygen to the humidifier  4 . 
     The air feeder includes a filter  6  which removes foreign substances contained in the external air and an air compressor  8  which compresses air to supply to the humidifier  4 . 
     The fuel cell system includes a fuel processing system (FPS)  10  to control the pressure of hydrogen, which is supplied from the fuel feeder, i.e. a hydrogen tank, to the fuel cell stack, and the like. 
     According to the above-mentioned configuration, electricity is produced through an electrochemical reaction between hydrogen supplied from the fuel feeder, and oxygen supplied from the air feeder, while water and heat are additionally generated. 
     Heat is cooled by cooling water, and the generated water is discharged to the outside via an air-vent line. Here, some of hydrogen or moisture leak out of the fuel cell stack and are collected in an enclosure  12  of the fuel cell system. That is, although the fuel cell stack is configured in a gas-hermetic seal structure such that gas cannot leak inside and outside of the fuel cell stack, there is a sealing problem due to the design structure, causing some of the moisture and hydrogen to leak to the outside. 
     Such leak of hydrogen and moisture may cause problems in operational stability of the fuel cell system and corrosion of internal parts of the fuel cell stack and the enclosure of the fuel cell system, respectively. 
     In order to solve these problems, conventional methods in which, as shown in  FIG. 1 , a fan  14  is installed to the enclosure  12  so as to discharge the leaked hydrogen or water vapor to the outside, or otherwise, air in the enclosure is sucked to the outside using negative pressure formed by a suction filter. However, such methods have a poor sealing performance because the inside and outside of the enclosure are connected by a passage through which irregular discharge of leaks occurs. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY 
     The present disclosure has been made keeping in mind the above problems occurring in the related art and proposes a fuel cell system to remove moisture and hydrogen which leak out of a fuel cell stack during the production of electricity via a fuel cell, thereby preventing damage to internal parts of the fuel cell and improving operational stability of the fuel cell. 
     According to an embodiment of the present disclosure, a fuel cell system includes an enclosure having a fuel cell stack producing electricity via an electrochemical reaction between high temperature and high pressure compressed air generated by an air compressor and hydrogen used as fuel. A portion of the compressed air generated from the air compressor is introduced into the enclosure through a first pipe, and the compressed air flows towards the air compressor from the enclosure through a second pipe. The compressed air, which is introduced into the enclosure via the first pipe, removes moisture and hydrogen leaking out of the fuel cell stack and returns to the air compressor via the second pipe. 
     The enclosure may have an inlet and an outlet on opposite sides thereof, to which the first pipe and the second pipe are connected, respectively, and the inlet and the outlet are hermetically sealed with respect to an inside of the enclosure. 
     The first and second pipes may be connected to the enclosure and disposed opposite each other on the fuel cell stack. 
     The first pipe may be connected between an outlet flow line of the air compressor and the enclosure, and the second pipe may be connected between the enclosure and an inlet flow line of the air compressor. 
     The air compressor may have a power motor for rotating an impeller, and an air flow passage such that the compressed air generated by the rotation of the impeller partially passes through an inside of the motor so as to cool the motor. 
     The first pipe may be connected between an air outlet of the motor and the enclosure, and the second pipe may be connected between the enclosure and an inlet of the air compressor. 
     An outlet of the air compressor may have a bypass through which a portion of the compressed air is bypassed, the first pipe may be connected between the outlet of the air compressor and the enclosure so that the compressed air bypassed from the air compressor is introduced into the enclosure, and the second pipe may be connected between the enclosure and an inlet of the air compressor so that the air passing through the enclosure flows back to the air compressor. 
     According to the present disclosure, the fuel cell system having the above-mentioned configuration removes the moisture and hydrogen which leak out of the fuel cell stack when producing electricity, thereby preventing damage to internal parts of the fuel cell stack and improving operational stability of the fuel cell. 
     Warm air, which is heated during cooling the motor of the air compressor, is supplied to the inside of the enclosure, thereby improving a moisture-removal efficiency in the enclosure. 
     Furthermore, the compressed air generated by the air compressor is bypassed and supplied to the inside of the enclosure, thereby improving cooling efficiency of the fuel cell stack, and securing a surge margin to improve the operational performance of the air compressor at the same time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings. 
         FIG. 1  is a view showing a conventional fuel cell system. 
         FIG. 2  is a view showing a configuration of a fuel cell system according to a first embodiment of the present disclosure. 
         FIG. 3  is a view showing a configuration of a fuel cell system according to a second embodiment of the present disclosure. 
         FIG. 4  is a view showing a configuration of a fuel cell system according to a third embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinbelow, a description is made in detail for a fuel cell system according to embodiments of the present disclosure with reference to the accompanying drawings. 
     Referring to  FIG. 2 , a fuel cell system, which is adapted to fuel cell vehicles, includes a fuel cell stack  100  which produces electricity, and a humidifier  200  which humidifies a fuel and air mixture and supplies the humidified mixture to the fuel cell stack  100 . A fuel feeder feeds hydrogen to the humidifier  200 , and an air feeder feeds air containing oxygen to the humidifier. The air feeder includes a filter  300  which removes foreign substances contained in the external air, and an air compressor  400  which supplies compressed air to the humidifier. 
     Such fuel cell systems have been already known in the art, so that a detailed description of respective elements thereof will be omitted. However, the present disclosure is not limited to the technical features of the constitutional elements of the fuel cell system. 
     The present disclosure provides a fuel cell system to efficiently remove hydrogen and water steam collected in an enclosure  500  in which a fuel cell stack  100  is provided and to secure a surge margin at the same time, while cooling a motor  440  of an air compressor  400 . 
     The fuel cell system includes an enclosure  500  having a fuel cell stack  100  which produces electricity via an electrochemical reaction between high temperature and high pressure compressed air generated by an air compressor  400  and hydrogen used as fuel. A portion of the compressed air generated from the air compressor  400  is introduced into the enclosure  500  through a first pipe  600 , and the compressed air flows back to the air compressor  400  from the enclosure  500  through a second pipe  700 . The compressed air introduced into the enclosure  500  via the first pipe  600  removes moisture and hydrogen leaking out of the fuel cell stack  100  and returns to the air compressor  400  via the second pipe  700 . 
     That is, the moisture collected in the enclosure  500  evaporates due to the compressed air and is discharged from an inside of the enclosure  500  along with the compressed air flowing from the first pipe  600  to the second pipe  700 . In this way, the air removes the moisture and hydrogen in the enclosure  500  and flows back to the air compressor  400  to repeat the circulation. 
     The enclosure  500  pressure-seals the fuel cell stack  100  in order to stably mount the fuel cell stack  100  and protect the same from external shock. Known technologies can be widely adapted to the enclosure, and the present disclosure is not limited thereto. 
     The enclosure  500  connects the first and second pipes  600  and  700 . The first and second pipes  600  and  700  allow the compressed air, which is generated by the air compressor  400 , to pass through the enclosure  500  and flow back to the air compressor  400 . That is, the compressed air removes moisture and hydrogen in the enclosure  500  and returns to the air compressor  400  so as to supplement air flow in the air compressor. The connection to the first and second pipes  600  and  700  will be described hereinafter. 
     The enclosure  500  may have an inlet  520  and an outlet  540  on opposite sides thereof, to which the first pipe  600  and the second pipe  700  are connected, respectively, wherein the inlet  520  and the outlet  540  are hermetically sealed with respect to the inside of the enclosure  500 . 
     Conventionally, hydrogen and water steam in the enclosure  500  are removed using a cooling fan or negative pressure. However, according to such conventional method, gas is permeable through the enclosure, degrading the hermetic-sealing capability. 
     On the contrary, according to the present disclosure, hydrogen and moisture in the enclosure  500  are removed using high temperature and high pressure compressed air, which is generated by the air compressor  400 . To this end, the enclosure  500  has the inlet  520  and the outlet  540  to which the first and second pipes  600  and  700  are connected, respectively, so that the compressed air from the air compressor  400  flows in and out of the enclosure  500  through the respective pipes. 
     The inlet  520  and the outlet  540  of the enclosure  500  are hermetically sealed so as to improve the sealing capability. The internal space of the enclosure  500  is completely sealed, so that the compressed air introduced through the inlet  520  is completely discharged from the enclosure  500  through the outlet  540 . Thus, smooth circulation of the compressed air is ensured, and loss of the compressed air is prevented. 
     The first and second pipes  600  and  700  may be connected to the enclosure  500  in such a way as to be opposite each other on the fuel cell stack  100 . 
     As described before, the enclosure  500  is connected between the first and second pipes  600  and  700  such that the compressed air introduced through the first pipe  600  is sufficiently circulated in the enclosure  500  and then discharged from the enclosure  500  through the second pipe  700 , while removing the hydrogen and moisture in the enclosure. 
     If the first and second pipes  600  and  700  are too close to each other, in other words adjacent each other, when connected to the enclosure  500 , the compressed air introduced through the first pipe  600  cannot be sufficiently circulated in the enclosure  500  and is discharged from the enclosure  500  through the second pipe  700 , so the hydrogen and moisture in the enclosure may not be sufficiently removed. Thus, the first and second pipes  600  and  700  may be installed farther away from each other. 
     That is, the first and second pipes  600  and  700  are connected to the enclosure  500  opposite each other on the fuel cell stack  100 , so that the compressed air introduced through the first pipe  600  can be sufficiently circulated in the enclosure  500  and discharged therefrom through the second pipe  700 . 
     Other embodiments of the present disclosure will now be described. 
     As shown in  FIG. 2 , the first pipe  600  may be connected between an outlet flow line a of the air compressor  400  and the enclosure  500 , and the second pipe  700  may be connected between the enclosure  500  and an inlet flow line b of the air compressor  400 . 
     Here, the flow line means a passage through which oxygen flows to the fuel cell stack  100  through the filter  300 , the air compressor  400 , and the humidifier  200  as shown in  FIG. 2 . 
     The first embodiment of the present disclosure described above provides a basic conceptual structure of the fuel cell system in which the first pipe  600  is connected between the outlet flow line a of the air compressor  400  and the enclosure  500  so that the compressed air generated by the air compressor  400  partially flows to the first pipe  600  when flowing towards the humidifier  200 . According to an embodiment of the present disclosure, the first pipe  600  is connected to the flow line a through which the compressed air flows, and a portion of the compressed air can be introduced into the enclosure  500  so as to remove the moisture leaking out of the fuel cell stack  100 . 
     When the second pipe  700  is connected between the enclosure  500  and the inlet flow line b of the air compressor according to an embodiment of the present disclosure, the compressed air can be discharged from the enclosure  500  through the second pipe  700  after removing the moisture. Here, the compressed air discharged through the second pipe  700  can be discharged together with hydrogen contained in the enclosure  500 . That is, the moisture and hydrogen in the enclosure  500  can be removed at the same time. 
     With the configuration in which the compressed air discharged through the second pipe  700  flows through the inlet flow line b of the air compressor  400  so that the air passing through the inside of the enclosure  500  flows back to the air compressor  400 , the compressed air can be preserved. 
     Further, the air compressor  400  may have a power motor  440  to rotate an impeller  420  and an air flow passage  460  to partially pass the compressed air generated with the rotation of the impeller  420  through the inside of the motor  440  so as to cool the motor  440 . 
     Generally, an air compressor  400  used in a fuel cell vehicle rotates an impeller  420  with activation of a motor  440  so as to generate compressed air. The air compressor  400  of the present disclosure has the air flow passage  460  for the compressed air generated with the rotation of the impeller  420  such that the compressed air passes through the inside of the motor  440  to cool the motor  440 . 
     As shown in  FIG. 3 , air moves through the air flow passage  460 , which is introduced into the casing of the impeller  420  via an inlet through-hole  480 a at a rear side of the impeller  420  towards the motor  440 , thereby cooling the motor  440 . After cooling the motor  440 , the air is discharged through an outlet through-hole  480 b. 
     According to a second embodiment of the present disclosure, the first pipe  600  may be connected between an air outlet (or the outlet through-hole  480 b) of the motor  440  and the enclosure  500 , and the second pipe  700  may be connected between the enclosure  500  and an inlet of the air compressor  400 . 
     Here, the compressed air, which is generated with the rotation of the impeller  420 , partially passes through the motor  440  and cools the motor  440 , and the compressed air is heated during this process. The heated compressed air is supplied to the enclosure  500  through the first pipe  600 , thereby removing moisture collected in the enclosure  500 . 
     Therefore, the air that has cooled the motor  440  of the air compressor  400  completely removes the moisture in the enclosure  500  after passing through the first pipe  600 , and then is discharged out of the enclosure  500  through the second pipe  700  together with water steam and hydrogen. 
     Here, the second pipe  700  is connected to the inlet of the air compressor  400  at the enclosure  500 , so that the air discharged through the second pipe  700  flows back to the air compressor  400  for reuse in the fuel cell stack  100 , or otherwise former processes are repeated. 
     According to a third embodiment of the present disclosure, as shown in  FIG. 4 , an outlet  430  of the air compressor  400  may have a bypass through which a portion of the compressed air is bypassed. The first pipe  600  may be connected between the outlet  430  of the air compressor  400  and the enclosure  500  so that the compressed air bypassed from the air compressor  400  is introduced into the enclosure  500 . The second pipe  700  may be connected between the enclosure  500  and an inlet  470  of the air compressor  400  so that the air passing through the enclosure  500  flows back to the air compressor  400 . Here, the outlet  430  of the air compressor  400  is a flow passage through which the compressed air flows towards the fuel cell stack  100 , and the inlet  470  is a passage through which the air is introduced towards the impeller  420  for compression. 
     The compressed air, which is generated by the air compressor  400 , is not entirely supplied to the fuel cell stack  100  according to another embodiment of the present disclosure, a portion of the compressed air is bypassed at the outlet  430  of the air compressor  400 , and the compressed air bypassed through the first pipe  600  is supplied into the enclosure  500 , thus improving cooling performance of the fuel cell stack  100  and securing surge margin of the air compressor. 
     That is, according to the conventional technology, the compressed air is discharged to the outside because the conventional air compressor experiences a surge phenomenon at a low flow rate. However, according to the present disclosure, the compressed air is supplied from the air compressor  400  to the enclosure  500  through the first pipe  600 , so that loss of flow rate is reduced. The surge margin is secured, and simultaneously, the fuel cell stack, which needs to maintain a temperature, is cooled, thus improving cooling efficiency thereof. 
     In this way, the air introduced into the enclosure  500  through the first pipe  600  flows back to the inlet  470  of the air compressor  400  through the second pipe  700 , so that air flow rate can be maintained, the hydrogen and moisture in the enclosure  500  can be removed, the surge margin can also be secured, and the cooling efficiency of the stack can be improved. 
     The above-mentioned first to third embodiments can be selectively applied or as combination depending upon the design and specification of a vehicle. 
     The fuel cell system according to the present disclosure removes moisture and hydrogen which leak out of the fuel cell stack when producing electricity from the fuel cell stack  100 , thereby preventing damage to internal parts of the fuel cell stack and improving operational stability of the fuel cell. Further, warm air, which is heated during cooling the motor  440  of the air compressor  400 , is supplied to the inside of the enclosure  500 , thereby improving moisture-removal efficiency in the enclosure  500 . 
     In addition, the compressed air generated by the air compressor  400  is bypassed and supplied to the inside of the enclosure  500 , thereby improving the cooling efficiency of the fuel cell stack  100 , and at the same time, securing the surge margin to improve the operational performance of the air compressor  400 . 
     Although an embodiment of the present disclosure has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.