Abstract:
A reformer for a fuel cell system, and a method of controlling the reformer. The reformer includes a cylindrical reforming catalyst; a burner disposed inside of the reforming catalyst and comprising a plurality of nozzles to direct flames at the reforming catalyst; a nozzle covering element to selectively cover a portion of each of the nozzles; a combustion fuel supply valve to change the amount of a combustion fuel that is supplied to the burner; and a controller that controls the nozzle covering units and the combustion supply valve. The method of controlling the reformer includes: moving the nozzle covering element to cover a decreasing portion of each of the nozzles in response to an increasing amount of the combustion fuel being supplied to the burner; and moving the nozzle covering element to cover a increasing portion of each of the nozzles in response to a decreasing amount of the combustion fuel supplied to the burner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Application No. 2006-103613, filed on Oct. 24, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Aspects of the present invention relate to a fuel processor of a fuel cell system, and more particularly, to a reformer included in a fuel processor, and a method of controlling the same. 
         [0004]    2. Description of the Related Art 
         [0005]    A fuel cell is a generator of electricity that changes the chemical energy of a fuel into electrical energy, through a chemical reaction. A fuel cell can continuously generate electricity as long as the fuel is supplied. Fuel cell systems can be broadly divided into fuel cell systems that use liquid hydrogen, and fuel cell systems that use hydrogen gas. The fuel cell systems that use hydrogen gas include fuel cell stacks and fuel processors. The fuel cell stacks have a structure in which a few to a few tens of unit cells, each including a membrane electrode assembly (MEA), and a separator, are stacked. 
         [0006]      FIG. 1  is a schematic diagram showing a configuration of a conventional fuel cell system. 
         [0007]    Referring to  FIG. 1 , a fuel, that includes hydrogen atoms, is reformed into hydrogen gas in a fuel processor, and the hydrogen gas is supplied to a fuel cell stack. In the fuel cell stack, the hydrogen gas is electrochemically reacted with oxygen to generate electrical energy. 
         [0008]    The fuel processor includes a desulfurizer and a hydrogen generation apparatus. The hydrogen generation apparatus includes a reformer and a shift reactor. The desulfurizer removes sulfur from the fuel so that catalysts, in the reformer and the shift reactor, are not poisoned by sulfur compounds. 
         [0009]    Hydrogen gas is generated from the hydrocarbons in the reformer, but in addition to the hydrogen gas, carbon dioxide (CO 2 ) and carbon monoxide (CO), are also produced. However, CO acts as a poison to the catalysts used on electrodes of the fuel cell stack. Therefore, the hydrogen gas generated in the reformer is not directly supplied to the fuel cell stack, but rather is supplied after the CO is removed by the shift reactor. Conventionally, the hydrogen gas that has passed through the shift reactor has a CO content of 10 ppm or less. 
         [0010]      FIG. 2  is a cross-sectional view illustrating a conventional reformer.  FIG. 3  is a graph showing the temperature distribution in the reformer of  FIG. 2 , at different locations of a reforming catalyst. In  FIG. 3 , the temperature distributions in the reformer are compared at different positions, in a combustion chamber thereof, when loads of 100% and 25% are applied to a burner. 
         [0011]    Referring to  FIG. 2 , a conventional reformer  10  includes a burner  15  that can eject one large flame  25  into a combustion chamber  11 , which is disposed inside a pipe-shaped reforming catalyst  20 . When a combustion fuel, composed of methane CH 4  and air, is ignited by ejecting the combustion fuel into the combustion chamber  11 , via the burner  15 , the combustion fuel is combusted, and a flame  25  is generated, heating the reforming catalyst  20 . Thus, a hydrogen generation reaction occurs in the reforming catalyst  20 . 
         [0012]    A fuel cell system may operate at 100% of a designed power production capacity (load), or may operate at less than 100% of the designed capacity, according to power consumption of electrical equipment electrically connected to the fuel cell system. When the fuel cell system is operated with a load that is less than 100% of the designed capacity, the burner  15  of the reformer  10  is also operated at a reduced load. More specifically, the loads to the burner  15 , and the reformer  10 , are proportional to the load to the fuel cell system  100  as a whole. 
         [0013]    Referring to  FIG. 3 , different portions H, of the reforming catalyst  20 , in the reformer  10  of  FIG. 2 , have different temperatures. More specifically, a central portion B, of the reforming catalyst  20 , which is closer to the flame  25 , has a relatively high temperature, and a lower and upper portions A and C of the reforming catalyst  20 , which are relatively farther from the flame  25 , have relatively lower temperatures. Also, the size of the flame  25  is larger when a load to the burner  15  is 100%, than when the load to the burner  15  is 25%. Thus, the overall temperature of the reforming catalyst  20 , when a load to the burner  15  is 100%, is higher than when the load to the burner  15  is 25%. 
         [0014]    The hydrogen generation reaction, on the reforming catalyst  20 , is an endothermic reaction, and the hydrogen generation reaction is conducted at a temperature of approximately 700° C., or more. In the reformer  10 , there are large temperature differences, according to the height of the reforming catalyst  20 . The temperature of the central portion B can be maintained at 700° C., or more, regardless of the load to the burner  15 , but it is difficult to maintain the temperatures of the lower and upper portions A and C at 700° C., or more. In particular, it is particularly difficult to maintain the temperature of 700° C. at the lower and upper portions A and C, when the load to the burner  15  is small. Accordingly, there is a problem that, although the reforming catalysts at the lower and upper portions A and C, of the reforming catalyst  20 , are not completely consumed, all of the reforming catalyst  20  must be replaced, due to the exhaustion of the reforming catalysts in the central portion B. 
       SUMMARY OF THE INVENTION 
       [0015]    Aspects of the present invention provide a reformer in which all portions of a reforming catalyst can be heated to a uniform temperature. 
         [0016]    Aspects of the present invention also provide a reformer in which a flame can be ejected to all portions of a reforming catalyst, regardless of the load on a corresponding burner. 
         [0017]    According to an aspect of the present invention, there is provided a reformer comprising: a reforming catalyst having a cylindrical shape; a burner comprising nozzles, which is disposed in the reformer inside of the reforming catalyst; a nozzle covering element to control the flow of a combustion fuel through the nozzles; a combustion fuel supply element that changes the amount of combustion fuel supplied to the burner; and a controller that controls the nozzle covering element, to change the degree of opening of the nozzles in connection with the amount of the combustion fuel supplied to the burner. The nozzles are disposed on an outer surface of the burner and face the reforming catalyst, and are to make flames by directing the ejection of the ignited combustion fuel towards the reforming catalyst. 
         [0018]    The nozzle covering element may comprise a cam comprising: a central part that extends in a lengthwise direction along the length of burner, and can be rotated inside of the burner; and a plurality of covering units, attached to the central part, that each correspond to a single nozzle, and change the size of the respective openings to the nozzles, according to a rotation angle of the central part. The nozzles may have oval-shaped openings. 
         [0019]    An inner surface of the reforming catalyst may face the plurality of nozzles. The controller may control the position of the covering units, so that flames, formed by ejecting the combustion fuel from the nozzles, reach the reforming catalyst, regardless of variations in the supply of the combustion fuel to the burner, so long as a minimum amount of combustion fuel is supplied to the burner. 
         [0020]    The controller may control the position of the covering units so that the hottest portions of the flames, formed by ejecting the combustion fuel from the nozzles, reach the reforming catalyst. 
         [0021]    The controller may control the position of the covering units so that the portion of each nozzle that is covered is decreased, when the amount of the combustion fuel supplied to the burner is increased, and the portion of each nozzle that is covered is increased, when the amount of the combustion fuel supplied to the burner is decreased. 
         [0022]    According to an aspect of the present invention, there is provided a method of controlling a reformer that comprises a reforming catalyst having a cylindrical shape, and a burner which is disposed on the inside of the reforming catalyst, and comprises a plurality of nozzles on an outer surface thereof, facing the reforming catalyst. The method comprising: covering a smaller portion of each of the nozzles, when the amount of the combustion fuel supplied to the burner is increased; and covering a larger portion of each of the nozzles, when the amount of the combustion fuel supplied to the burner is reduced. 
         [0023]    The portion of each of the nozzles that is covered may be controlled so that flames, formed by ejecting the combustion fuel from the nozzles, reach the reforming catalyst, regardless of the amount of the combustion fuel supplied to the burner, so long that a minimum amount of combustion fuel is supplied to the burner. 
         [0024]    The degree of covering of the nozzles may be controlled so that the hottest portions of the flames, formed by ejecting the combustion fuel from the nozzles, reach the reforming catalyst. 
         [0025]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0027]      FIG. 1  is a schematic diagram showing a configuration of a conventional fuel cell system; 
           [0028]      FIG. 2  is a cross-sectional view illustrating a conventional reformer; 
           [0029]      FIG. 3  is a graph showing the comparison of temperature distribution in the reformer of  FIG. 2 , according to height of a reforming catalyst, when loads of 100% and 25% are applied to a burner; 
           [0030]      FIG. 4  is a partial cutaway perspective view of a reformer, according to an embodiment of the present invention; 
           [0031]      FIG. 5  is a vertical cross-sectional view of the reformer of  FIG. 4 ; 
           [0032]      FIGS. 6 and 7  respectively are horizontal cross-sectional views of the reformer of  FIG. 4 , when loads of 100% and 50% are applied to the reformer; and 
           [0033]      FIGS. 8 and 9  are views of outer surfaces of the burner showing the openings of nozzles, and the relative position of covering units depicted by virtual (dashed) lines,  FIG. 8  showing when a load of 100% is applied to the reformer, and  FIG. 9  showing when a load of 50% is applied to the reformer. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0034]    Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0035]      FIG. 4  is a partial cutaway perspective view of a reformer  100  according to an embodiment of the present invention.  FIG. 5  is a vertical cross-sectional view of the reformer  100  of  FIG. 4 . 
         [0036]    Referring to  FIGS. 4 and 5 , the reformer  100  includes a cylindrically shaped reforming catalyst  101  and a cylindrically shaped burner  105 . The reforming catalyst  101  is disposed inside the reformer  100 , and the burner  105  is disposed inside of the reforming catalyst  101 . The reformer has a first end shown at the top of  FIG. 5 , and a second end shown at the bottom of  FIG. 5 . 
         [0037]    A plurality of nozzles  107  are disposed on the outer surface of the burner  105 . The nozzles  107  are to make flames  150  by directing a combustion fuel towards the reforming catalyst  101 . The nozzles  107  are uniformly distributed on the outer surface of the burner  105 , so that the entire inner surface of the reforming catalyst  101  can face the plurality of nozzles  107 . Accordingly, the flames  150  can be uniformly formed to point towards the entire inner surface of the reforming catalyst  101 . As depicted in  FIGS. 8 and 9 , each nozzle  107  has an oval shaped opening. 
         [0038]    The reformer  100  includes a cam  110 , and a motor  125  to drive the cam  110 . The cam  110  is a nozzle covering element that can control the degree of opening of the nozzles  107 . The cam  110  is installed inside of the burner  105 , and includes: a central part  111 , extending in a lengthwise direction, with respect to the length of the burner  105 ; a plurality of covering units  113  which extend in a radial direction towards the inner surface of the burner  105 , with each covering unit  113  corresponding to a single nozzle  107 ; and a shaft  115  that is connected to a second end of the central part  111 , and extends out of the burner  105 . The shaft  115  transmits a rotational force from the motor  125 , to the central part  111 , to rotate the cam  110 . 
         [0039]    The central part  111  can rotate around a central axis CL, of the central part  111 , which extends along the length of the burner  105 . The rotation can be driven by the motor  125 . The covering units  113  can control the degree of covering of the nozzles  107 , according to the amount of rotation of the central part  111 . That is, the covering units  113  can be positioned to not cover any part of the openings of the nozzles  107 , to leave the nozzles  107  entirely open as depicted in  FIGS. 6 and 8 , or can be positioned to cover a portion of the openings of the nozzles  107 , as depicted in  FIGS. 7 and 9 . In  FIG. 9 , shaded regions indicate the regions of the openings of the nozzles  107  that are covered by the covering units  113 . The covering unit  113  is formed so that an end of the covering unit  113 , that contacts the inner surface of the burner  105 , has a concave portion  113   a . The concave portion  113   a  has a shape corresponding to a side of the oval opening of the nozzle  107 . Accordingly, as depicted in  FIG. 9 , when the openings of the nozzles  107  are partly covered, the uncovered portion of the openings forms a circle, or an oval with a smooth surface, thereby smoothly directing the fuel to make flames  150 . The phrases “covering the nozzles”, and “covering the openings of the nozzles”, and variations thereof, are used interchangeably herein, and refer to the same activity. 
         [0040]    The reformer  100  includes a combustion fuel supply tube  130  connected to the second end of the burner  105 , and a combustion fuel supply valve  132  located in the combustion fuel supply tube  130 , to control the supply of a combustion fuel composed of methane CH 4  and air, to the burner  105 . The combustion fuel supply valve  132  controls the amount of fuel supplied to the inside of the burner  105 , by controlling the amount to which the combustion fuel supply tube  130  is opened. 
         [0041]    The reformer  100  further includes a controller  140  that controls the motor  125  so that the covered portion of the nozzles  107  can be changed in connection with the amount of the combustion fuel supplied to the inside of the burner  105 . The controller  140  is connected to the combustion fuel supply valve  132 , and the motor  125 . The controller  140  is to control the rotation of the cam  110 , to change the amount of covering of the nozzles  107 , by controlling the rotation of the motor  125 , through a motor driving signal. Also, the controller  140  controls the fuel supply valve  132 , to control the amount of combustion fuel that is supplied to the burner  105 , by sending a valve driving signal to the combustion fuel supply valve  132 . 
         [0042]    A hydrogen guide  120  to convey hydrogen H 2 , obtained from a power generation fuel, out of the first end of the reformer  100 , is formed outside of the reforming catalyst  101 . An exhaust gas path  122  provides a fluid communication between the burner  105  and the reforming catalyst  101 . 
         [0043]    When the nozzles  107  are completely uncovered, a combustion fuel is supplied to the inside of the burner  105 , via the combustion fuel supply valve  132 . The combustion fuel is directed towards the reforming catalyst  101  by the nozzles  107 . At this point, the combustion fuel is ignited, and the flames  150  heat the reforming catalyst  101 . When the entire reforming catalyst  101  is heated to a temperature of 700° C., or more, a power generation fuel, that contains methane gas CH 4  and steam H 2 O, is supplied to the reforming catalyst  101 . Hydrogen H 2 , a small amount of carbon monoxide CO, and other gases are produced by a reforming reaction in the reforming catalyst  101 . The produced gas, that contains hydrogen H 2 , is discharged out of the first end of the reformer  100 , and can be supplied to a shift reactor (refer to  FIG. 1 ) via the hydrogen guide  120 . Exhaust gas produced from the combustion is discharged from the reformer  100  via the exhaust gas path  122 . 
         [0044]    A method of controlling the reformer  100  will now be described with reference to  FIGS. 5 through 9 . 
         [0045]      FIGS. 6 and 7  are horizontal cross-sectional views of the reformer  100  of  FIG. 4 .  FIG. 6  shows when a load of 100% is applied to the reformer  100 , and  FIG. 7  shows when a load of 50% is applied to the reformer  100 .  FIGS. 8 and 9  are views of the outer surfaces of a portion of the burner  105 , and show the openings of the nozzles, and the relative position of the covering units  113  depicted by virtual (dashed) lines.  FIG. 8  shows when a load of 100% is applied to the reformer  100 , and  FIG. 9  shows when a load of 50% is applied to the reformer  100 . 
         [0046]    Referring to  FIGS. 5 ,  6 , and  8 , in order to operate the burner  105  at a 100% load, the controller  140  applies an appropriate valve driving signal to the combustion fuel supply valve  132 , so that the combustion fuel supply valve  132  opens completely. Also, the controller  140  applies an appropriate motor driving signal to the motor  125 , so that the openings of the nozzles  107  are completely uncovered. As depicted in  FIGS. 6 and 8 , a large amount of combustion fuel is rapidly ejected through the completely uncovered nozzles  107 . When the combustion fuel ejected from the nozzles  107  is ignited, large flames  150   a  reach the reforming catalyst  101 . The flames  150   a  heat the reforming catalyst  101  while touching the reforming catalyst  101 , thereby increasing heating efficiency. Also, as described above, the plurality of nozzles  107  can be used to evenly heat the entire reforming catalyst  101 . The entire reforming catalyst  101  can be uniformly utilized, preventing the waste inherent with the localized utilization of the reforming catalyst  101 . 
         [0047]    The flame  150   a  can be divided into an external (oxidizing) flame  152   a , and an inner (reducing) flame  151   a . The tip of the inner flame  151   a  maintains higher temperature than the external flame  152   a . In the present embodiment, a combustion fuel supply pressure and a distance between the nozzle  107 , and the reforming catalyst  101 , are determined so that the tip of the inner flame  151   a  can reach the reforming catalyst  101 . Therefore, the heating efficiency of the reforming catalyst  101  is higher than when only the external flame  152   a  reaches the reforming catalyst  101 . 
         [0048]    Referring to  FIGS. 5 ,  7 , and  9 , in order to operate the burner  105  with a 50% load, the controller  140  partly closes the combustion fuel supply tube  130 , using the combustion fuel supply valve  132 . As a result, the supply of the combustion fuel to the inside of the burner  105  is reduced, as compared to the 100% load. Also, the controller  140  triggers the rotation the cam  110 , so that the openings of the nozzles  107  are partly covered by the covering units  113 . At this point, the amount of the combustion fuel supplied to the inner space of the burner  105  is reduced, as compared to the 100% load. However, the flow speed of the combustion fuel ejected from the nozzles  107  is not reduced, since the openings of the nozzles  107  are partially covered. When the combustion fuel ejected in this way is ignited, small flames  150   b , that are smaller than the large flames  150   a  (see  FIG. 6 ), made when 100% load is applied to the burner, reach the reforming catalyst  101 . The small flames  150   b  have an inner flame  151   b  and an outer flame  152   b . The controller  140  may control the flow rate of the combustion fuel to the burner  105 , and the degree of covering of the nozzles  107 , so that the tips of the inner flames  151   b  can reach the reforming catalyst  101 , in addition to the outer flames  152   b.    
         [0049]    The method of controlling the reformer  100  has been described by comparing cases when the loads to the burner  105  are 100% and 50%. When a load to the burner  105  is 75% and 25%, the reformer  100  can also be operated so that the flames  150  can reach the reforming catalyst  101 , and thereby directly heat the reforming catalyst  101 . The controller  140  can appropriately control the flow rate of the combustion fuel to the burner  105 , and the degree of covering of the nozzles  107 . For example, in order to switch the burner  105  from operating at the 50% load from the 100% load, the supply of the combustion fuel to the burner  105  is reduced, and the openings of the nozzles  107  are partly covered, as depicted in  FIG. 9 . Also, in order to switch the burner  105  to operating at a 75%, load from operating at the 50% load, the supply of the combustion fuel to the burner  105  is increased, and the openings of the nozzles are partially uncovered. The supply of fuel for operating at a 75% load is larger than the supply for operating at the 50% load, and the openings of the nozzles  107  are less covered. For example, the openings at the 75% load are less covered that the openings as depicted in  FIG. 9  and move covered than the openings depicted in  FIG. 8 . 
         [0050]    In a reformer according to aspects of the present invention, flames formed by ejecting a combustion fuel from nozzles directly heat a reforming catalyst. The size of the openings to the nozzles can be adjusted, to compensate for variations in the amount of fuel supplied to the nozzles, such that the flames always reach the reforming catalyst. The openings to the nozzles are adjusted by covering a portion of the nozzles. When the fuel supply to the nozzles is decreased, a larger portion of each of the nozzles is covered. When the supply of fuel to the nozzles in increased, a smaller portion of each of the nozzles is covered. Accordingly, the heating efficiency of the reforming catalyst can be increased, and an early replacement of the reforming catalyst, due to a localized consumption of the reforming catalyst, can thereby be prevented. This results in a more effective use of all of the reforming catalyst. 
         [0051]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.