Patent Publication Number: US-2007104997-A1

Title: Fuel cell system

Description:
RELATED APPLICATION  
      The present disclosure relates to subject matter contained in priority Korean Application No. 10-2005-0115145, filed on Nov. 29, 2005, which is herein expressly incorporated by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a fuel cell system, and more particularly, to a fuel cell system that includes a residual gas storage unit storing residual hydrogen exhausted from a stack unit or a fuel supply unit and then supplying the stored residual hydrogen to the stack unit again or to another system requiring hydrogen.  
      2. Description of the Background Art  
       FIG. 1  is a schematic view illustrating a conventional PEMEF (proton exchange membrane fuel cell) type fuel cell system (hereinafter, referred to as a fuel cell system), in which a desulfurizing process, a reforming reaction and a hydrogen purifying process are performed on a hydrocarbon-based (CH-based) fuel such as LNG, LPG, CH 3 OH, gasoline, or the like to purify and use only hydrogen (H 2 ) as a fuel.  
      As illustrated in  FIG. 1 , the conventional fuel cell system includes a fuel supply unit  10  extracting only hydrogen (H 2 ) from LNG and supplying extracted hydrogen to a stack unit  30 , an air supply unit  20  supplying the air to the stack unit  30  and the fuel supply unit  10 , the stack unit  30  generating electricity using supplied hydrogen (H 2 ) and the air, and an electricity output unit  40  converting electricity generated by the stack unit  30  into an alternating current (AC) and supplying the AC to a load.  
      In the fuel supply unit  10 , hydrogen is generated by a reforming reaction between fuel and vapor. To generate vapor required for the reforming reaction, the fuel supply unit  10  includes a steam generator  10   b,  and a burner  10   a  supplying heat needed by the steam generator  10   b.    
      Hydrogen supplied to the stack unit  30  from the fuel supply unit  10  may not react with the air one hundred percent but remain according to the current amount required by a consumer. The residual hydrogen left in the fuel supply unit  10  or the stack unit  30  is being discarded in the conventional fuel cell system.  
      Consequently, even if hydrogen is required as much as the residual hydrogen having been discarded, there is no way to reuse the discarded hydrogen. For this reason, hydrogen should be newly generated as much as required, causing a waste of additional raw materials and an increase in cost.  
     BRIEF DESCRIPTION OF THE INVENTION  
      Therefore, an object of the present invention is to provide a fuel cell system capable of re-supplying residual hydrogen to a stack unit.  
      Another object of the present invention is to provide a fuel cell system capable of supplying residual hydrogen to another system requiring hydrogen.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a fuel cell system including: a stack unit including a fuel electrode and an air electrode and generating electricity by an electrochemical reaction between hydrogen and oxygen; a fuel supply unit supplying hydrogen to the fuel electrode of the stack unit; an air supply unit supplying the air to the air electrode of the stack unit; and a residual gas storage unit storing residual hydrogen exhausted from the stack unit or the fuel supply unit and then supplying the residual hydrogen to the stack unit again or to another system requiring hydrogen.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
      In the drawings:  
       FIG. 1  is a schematic view of a conventional fuel cell system;  
       FIG. 2  is a block diagram of a fuel cell system according to a first embodiment of the present invention;  
       FIG. 3  is a schematic view showing relations between a reformer, a stack unit and a residual gas storage unit of  FIG. 2 ;  
       FIG. 4  is a view showing a configuration of the residual gas storage unit of  FIG. 3 ;  
       FIG. 5  is a view showing that a hydrogen storage chamber and a carbon monoxide collecting chamber are disposed in different order from that illustrated in  FIG. 4 ;  
       FIG. 6  is a schematic view showing relations between a reformer, a stack unit, and a storage gas storage unit of a fuel cell system according to a second embodiment of the present invention; and  
       FIG. 7  is a view showing a configuration of the residual gas storage unit of  FIG. 6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
      A fuel cell system according to the first embodiment of the present invention will now be described in detail with reference to accompanying drawings.  
       FIG. 1  is a schematic view of a conventional fuel cell system,  FIG. 2  is a block diagram of a fuel cell system according to the first embodiment of the present invention, and  FIG. 3  is a schematic view showing relations between a reformer, a stack unit and a residual gas storage unit of  FIG. 2 .  FIG. 4  is a view showing a configuration of the residual gas storage unit of  FIG. 3 , and  FIG. 5  is a view showing that a hydrogen storage chamber and a carbon monoxide collecting chamber are disposed in different order from that of  FIG. 4 . In reference, a solid line represents a pipe, and a dotted line represents a line.  
      Referring to  FIG. 2 , the fuel cell system according to the first embodiment of the present invention includes a fuel supply unit  110 , an air supply unit  120 , a stack unit  130 , an electricity output unit  140 , a water supply unit  150 , a hot water supply unit  170 , and a residual gas storage unit  200 .  
      The fuel supply unit  110  includes a reformer  111  purifying hydrogen (H 2 ) from LNG and supplying the hydrogen to a fuel electrode  131  of the stack unit  130 , and a pipe  112  supplying LNG to the reformer  111 . The reformer  111  includes a desulfurization reactor  111   a  removing sulfur from a fuel, a reforming reactor  111   b  generating hydrogen by a reforming reaction between fuel and vapor, a high temperature water reactor  111   c  and a low temperature reactor  111   d  additionally generating hydrogen by making carbon monoxide, which is generated via the reforming reactor  111   b,  react again, a partial oxidation reactor  111   e  purifying hydrogen by removing carbon monoxide contained in a fuel using the air as a catalyzer, a steam generator  111   f  supplying vapor to the reforming reactor  111   b , and a burner  111   g  supplying heat required by the steam generator  111   f.    
      The air supply unit  120  includes first and second supply lines  121  and  123 , and an air supply fan  122 . The first air supply line  121  is installed between the air supply fan  122  and a second preheater  162  in order to supply the air to an air electrode  132 . The second air supply line  123  is installed between the air supply fan  122  and the burner  111   g  to supply the air to the burner  111   g.    
      The stack unit  130  includes the fuel electrode  131  and the air electrode  132  to simultaneously generate electrical energy and thermal energy by an electrochemical reaction between hydrogen and oxygen that are supplied, respectively, from the fuel supply unit  110  and the air supply unit  120 .  
      The electricity output unit  140  converts electrical energy generated in the stack unit  130  into an alternating current (AC) and supplies the AC to a load.  
      The water supply unit  150  supplies water to the stack unit  130  of the fuel supply unit  110  to cool the stack unit  130 . The water supply unit  150  includes a water supply container  151  filled with a predetermined amount of water, a water circulation line  152  circulatively connecting the stack unit  130  with the water supply container  151 , a water circulation pump  153  installed in the middle of the water circulation line  152  and pumping water within the water supply container  151 , and a heat exchanger  154  and a cooling fan  155  provided in the middle of the water circulation line  152  and cooling water being circulatively supplied.  
      The hot water supply unit  170  supplies stored hot water to the steam generator  111   f  through a pipe  156 .  
      Referring to  FIGS. 2 and 3 , the residual gas storage unit  200  is installed on a residual gas exhaust line of the stack unit  130 , that is, on a first line (L 1 ), stores residual hydrogen that is discarded from the stack unit  130  for not reacting with the air therein, and supplies such hydrogen to the stack unit  130  again or to another system requiring hydrogen. Here, another system refers to a boiler for home use and a hydrogen car that require hydrogen as a fuel. Because such residual hydrogen can be supplied to another system, the application field of the fuel cell system may expand.  
      Referring to  FIG. 4 , the residual gas storage unit  200  includes a hydrogen storage chamber  210  storing residual hydrogen exhausted from the stack unit  130 , a carbon monoxide collecting chamber  220  collecting carbon monoxide (CO) contained in hydrogen exhausted from the hydrogen storage chamber  210 , a plurality of valves (V 1 , V 2 , V 3 , V 4  and V 5 ) installed on inlet/outlet lines (L 1 , L 2 , L 3 , L 4  and L 5 ) of the hydrogen storage chamber  210  and the carbon monoxide collecting chamber  220  and opened and closed to control inflow/outflow of hydrogen and carbon dioxide (CO 2 ), and a controller  230  controlling opening and closing of the valves (V 1 , V 2 , V 3 , V 4  and V 5 ).  
      A temperature sensor (T 1 ) and a pressure sensor (P 1 ) are installed at the hydrogen storage chamber  210  in order to measure a temperature and pressure of hydrogen stored in the hydrogen storage chamber  210 .  
      A carbon monoxide collecting filter is included in the carbon monoxide collecting chamber  220  and collects carbon monoxide contained in hydrogen.  
      The valves (V 1 , V 2 , V 3 , V 4  and V 5 ) include a first valve (V 1 ) installed on a first line (L 1 ) connecting the stack unit  130  with the hydrogen storage chamber  210 , a second valve(V 2 ) installed on a second line (L 2 ) connecting the hydrogen storage chamber  210  with the carbon monoxide collecting chamber  220 , a third valve (V 3 ) installed on the third line (L 3 ) through which a fine gas from which carbon monoxide has been removed is exhausted to the outside, a fourth valve (V 4 ) installed on a fourth line (L 4 ) through which hydrogen stored in the hydrogen storage chamber  210  is supplied to another system, and a fifth valve (V 5 ) installed on a fifth line (L 5 ) through which hydrogen stored in the hydrogen storage chamber  210  is supplied to the stack unit  130 .  
      The controller  230  receives a temperature or pressure of hydrogen stored in the hydrogen storage chamber  210  in the form of signal from the temperature sensor (T 1 ) or the pressure sensor (P 1 ). When the temperature of hydrogen stored in the hydrogen storage chamber  210  is the same as or higher than a reference temperature or when the pressure of hydrogen is the same as or greater than reference pressure, the controller  230  opens the fifth valve (V 5 ) to supply hydrogen to the stack unit  130  through the fifth line (L 5 ). Also, the third valve (V 3 ) is opened so as to allow a fine gas (CO 2 , or the like) from which carbon monoxide has been removed to be exhausted to the outside through the third line (L 3 ). The controller  230  properly controls the first, second, third and fourth valves (V 1 , V 2 , V 3  and V 4 ) according to the temperature or pressure of the hydrogen stored in the hydrogen storage chamber  210 .  
      Of course, programming may be performed by software instead of using the temperature sensor (T 1 ) and the pressure sensor (P 1 ) such that when a predetermined time elapses, the controller  230  may open the fifth valve (V 5 ) to supply hydrogen to the stack unit  130  through the fifth line (L 5 ). Also, the residual gas storage unit  200  does not have to include the aforementioned controller  230 , and a central controller (not shown) of the fuel cell system, not the separate controller  230 , may directly control the residual gas storage unit  200 .  
      Of course, as illustrated in  FIG. 5 , the residual gas storage unit  200  may be constructed with the disposition order of the hydrogen storage chamber  210  and the carbon monoxide collecting chamber  220  switched. In this case, the residual gas exhausted from the stack unit  130  passes first through the carbon monoxide collecting chamber  220 , and then flows into the hydrogen storage chamber  210 . In this case, the first line (L 1 ) connects the stack unit  130  with the carbon monoxide collecting chamber  220 . Remaining other structures are the same as those described above, the description thereon will be omitted.  
      Referring to FIGS.  2  to  4 , operations and effects of the fuel cell system according to the first embodiment of the present invention will now be described.  
      Referring to  FIG. 2 , the fuel supply unit  110  reforms LNG and vapor in the reformer  111  to thus generate hydrogen, and then supplies the hydrogen to the fuel electrode  131  of the stack unit  130 . The air supply unit  120  supplies the air to the air electrode  132  of the stack unit  130 . The stack unit  130  generates electricity by an electrochemical reaction between the supplied hydrogen and the air. The generated electricity is converted into an alternating current (AC) in the electricity output unit  150 , and the AC is supplied to electrical appliances (illustrated as ‘Load’ on the drawing).  
      Referring to  FIGS. 3 and 4 , residual hydrogen, which is exhausted because hydrogen does not react with the air one hundred percent, is stored in the hydrogen storage chamber  210  of the residual gas storage unit  200  via the first line (L 1 ) when the first valve (V 1 ) is opened. The controller  230  of the residual gas storage unit  200  receives a temperature or pressure of the hydrogen stored in the hydrogen storage chamber  210  in the form of a signal from the temperature sensor (T 1 ) or the pressure sensor (P 1 ). When the received temperature or pressure is the same as or greater than a predetermined temperature or pressure, the controller  230  opens the fifth valve (V 5 ) to supply hydrogen to the stack unit  130  through the fifth line (L 5 ).  
      Accordingly, the residual hydrogen can be re-supplied to the stack unit  130  if necessary, so that a waste of raw materials for generating hydrogen can be reduced and thus a cost can be reduced. Also, hydrogen may be supplied to another system requiring hydrogen through the fourth line (L 4 ) by opening the fourth valve (V 4 ) if necessary, so that the application field of the fuel cell system can expand.  
      Hereinafter, a fuel cell system according to the second embodiment of the present invention will now be described in detail with reference to accompanying drawings. The same reference numerals are designated to the same constructions as those of the first embodiment, and the detailed description thereon will be omitted.  
       FIG. 6  is a schematic view showing relations between a reformer, a stack unit and a residual gas storage unit of the fuel cell system according to the second embodiment of the present invention, and  FIG. 7  is a view illustrating a construction of the residual gas storage unit of  FIG. 6 .  
      A residual gas storage unit  300  according to the second embodiment is installed on a residual hydrogen exhaust line within a reformer  111  of a fuel supply unit  110 , that is, on a first line (L 1 ′). Thus, residual gas hydrogen of the second embodiment contains less carbon monoxide (CO) than the residual gas of the first embodiment, which remains after the reaction with the air in the stack unit  130 . For this reason, there is no need to install the carbon monoxide collecting chamber  220  of  FIG. 4  of the first embodiment. Also, because only very small amount of hydrogen remains after reaction in the stack unit  130 , the residual hydrogen does not recovered but is exhausted to the outside together with the air.  
      Referring to  FIGS. 6 and 7 , the residual gas storage unit  300  includes a hydrogen storage chamber  310  storing residual hydrogen exhausted from the stack unit  130 , a plurality of valves (V 1 ′, V 2 ′ and V 3 ′) installed on inlet/outlet lines (L 1 ′, L 2 ′ and L 3 ′) of the hydrogen storage chamber  310  and opened and closed to control the inflow/outflow of hydrogen, and a controller  330  controlling opening and closing of the valves (V 1 ′, V 2 ′ and V 3 ′).  
      A temperature sensor (T 1 ′) and a pressure sensor (P 1 ′) are installed at the hydrogen storage chamber  310  to measure a temperature and pressure of residual hydrogen stored in the hydrogen storage chamber  310 .  
      The valves (V 1 ′, V 2 ′ and V 3 ′) include a first valve (V 1 ′) installed on a first line (L 1 ′) connecting the stack unit  130  with the hydrogen storage chamber  310 , a second valve (V 2 ′) installed on a second line (L 2 ′) through which hydrogen stored in the hydrogen storage chamber  310  is supplied to another system, and a third valve (V 3 ′) installed on a third line (L 3 ′) through which hydrogen stored in the hydrogen storage chamber  310  is supplied to the stack unit  130 .  
      The controller  330  receives a temperature or pressure of hydrogen stored in the hydrogen storage chamber  310  in the form of a signal from the temperature sensor (T 1 ′) and the pressure sensor (P 1 ′). When the temperature of the hydrogen stored in the hydrogen storage chamber  310  is the same as or higher than a reference temperature or the pressure of the hydrogen is the same as or greater than reference pressure, the controller  330  opens the third valve (V 3 ′) to supply hydrogen to the stack unit  130  through the third line (L 3 ′). The controller  330  properly controls the first and second valves (V 1 ′ and V 2 ′) according to the temperature or the pressure of the hydrogen stored in the hydrogen storage chamber  310 .  
      Of course, programming may be performed by software instead of using the temperature sensor (T 1 ′) and the pressure sensor (P 1 ′) such that when a predetermined time elapses, the controller  330  may open the third valve (V 3 ′) to supply hydrogen to the stack unit  130  through the third line (L 3 ′). Also, the residual gas storage unit  300  does not have to include the aforementioned controller  330 , and a central controller (not shown) of the fuel cell system, not the separate controller  330 , may directly control the residual gas storage unit  300 .  
      Referring to  FIGS. 6 and 7 , operations and effects of the residual gas storage unit according to the second embodiment of the present invention will now be described.  
      Referring to  FIGS. 6 and 7 , residual hydrogen exceeding the required amount is introduced into the residual gas storage unit  300  via a three way valve  111   a  and the first line (L 1 ′). The residual hydrogen introduced into the residual gas storage unit  300  is stored in the hydrogen storage chamber  310  when the first valve (V 1 ′) is opened.  
      The controller  330  of the residual gas storage unit  300  receives a temperature or pressure of the hydrogen stored in the hydrogen storage chamber  310  in the form of a signal from the temperature sensor (T 1 ′) or the pressure sensor (P 1 ′). When the received temperature or pressure is same as or greater than a predetermined temperature or pressure, the controller  330  opens the third valve (V 3 ′) to supply hydrogen to the stack unit  130  through the third line (L 3 ′).  
      Accordingly, the residual hydrogen can be re-supplied to the stack unit  130  if necessary, so that a waste of raw materials for generating hydrogen can be reduced, and thus a cost can be reduced. Also, hydrogen may be supplied to another system requiring hydrogen through the second line (L 2 ′) by opening the second valve (V 2 ′) if necessary, so that the application field of the fuel cell system can expand. Besides, because the residual gas storage unit  30  is installed in the reformer having the inside at a high temperature, residual hydrogen whose temperature has been raised is introduced to the stack unit  130 , thereby desirably eliminating needs for a separate temperature raising process.  
      Also, because such residual hydrogen contains less carbon monoxide (CO) than residual hydrogen remaining after a reaction with the air in the stack unit  130 , there is no need to install the carbon monoxide collecting chamber  220 , thereby reducing a coast.  
      As described so far, a fuel cell system having a residual gas storage unit according to the present invention has the following advantages.  
      First, residual hydrogen discarded from a stack unit can be stored and re-supplied to the stack unit if necessary, so that a waste raw materials for generating hydrogen is reduced, and thus a cost is reduced.  
      Secondly, residual hydrogen stored in a residual gas storage unit may be supplied to another system requiring hydrogen, which expands the application range of the fuel cell system.  
      Thirdly, when the residual gas storage unit is stored within a reformer that is at a high temperature, residual hydrogen whose temperature has already been raised can be introduced to the stack unit, thereby eliminating a need to perform a temperature raising process.  
      Fourthly, when the residual gas storage unit is installed in the reformer, residual hydrogen contains less carbon monoxide than residual hydrogen remaining after a reaction with the air in the stack unit. Accordingly, a carbon monoxide collecting chamber is not needed, and thus a cost can be saved.  
      As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.