Abstract:
A wall structure ( 21 ) for a burner ( 19 ), with a first wall ( 40 ), which has elevations ( 41 ) and which defines a first supply chamber ( 22 ), and with a second wall ( 43 ), which has recesses ( 44 ) cooperating with end sections ( 42 ) of the elevations ( 41 ) and which defines a reaction chamber ( 20 ). The first wall ( 40 ) has first openings ( 34 ), which connect the first supply chamber ( 23 ) to the reaction chamber ( 20 ). The second wall ( 43 ) has second openings ( 37 ), which connect a second supply chamber ( 24 ) located between the walls ( 40, 43 ) to the reaction chamber ( 20 ). The first openings ( 34 ) are arranged in first rows ( 35 ) and the second openings ( 37 ) in second rows ( 38 ). The mixture formation or homogenization of the gases in the reaction chamber ( 20 ) can be improved if at least one second opening ( 37 ) is arranged within the first row ( 35 ) between two openings ( 34 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2008 019 854.4 filed Apr. 21, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a wall structure for defining a reaction chamber of a burner. The present invention pertains, besides, to a burner equipped with such a wall structure as well as to a system with such a burner. 
     BACKGROUND OF THE INVENTION 
     A gaseous oxidant is burned with a gaseous fuel by means of such a burner in a combustion reaction taking place in the reaction chamber. Such a burner may be used, e.g., in a fuel cell, to burn an anode waste gas containing hydrogen gas with a cathode waste gas containing oxygen gas in order to reduce undesired pollutant emissions of the fuel cell. Such a fuel is known, e.g., from DE 10 2004 033 545. 
     It is essential for such a burner that the oxidant gas and the fuel gas are fed separately into the reaction chamber in order for the highly reactive gases to react with one another in the reaction chamber only. A wall structure of the burner, which defines the reaction chamber at least on one side, has first openings for this for feeding one gas and second openings, which are separate therefrom, for feeding the second gas. Such a wall structure is known, e.g., from DE 10 2006 010 375. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an improved embodiment for a wall structure or for a burner or for a fuel cell system of the type mentioned above, which embodiment is characterized especially in that improved homogenization of the mixture being formed in the reaction chamber becomes established already when the gases are flowing into the reaction chamber. 
     The present invention is based on the general idea of equipping a first wall for defining a first supply chamber with elevations, which contain at least one first opening. At the same time, a second wall is provided, which contains recesses as well as second openings and defines, together with the first wall, a second supply chamber, on the one hand, and defines a reaction chamber, on the other hand. The walls are arranged at each other such that end sections of the elevations of the first wall cover or close the recesses of the second wall, so that the first openings in the area of the recesses connect the first supply chamber to the reaction chamber. The first openings are arranged in parallel to a longitudinal direction in rows, which are located at spaced locations from one another in relation to a transverse direction, which also applies to the recesses. At the same time, at least one row of second openings is arranged each between two adjacent rows of first openings. In addition, at least one second opening each is arranged within the respective longitudinal row of the first openings between two adjacent first openings. It is achieved as a result that the gas fed via the first openings is laterally bordered by the other gas in the two directions, which are at right angles to one another and extend at right angles to the direction of flow of the gases, as a result of which concentration of the first gas can be avoided and homogenization of the mixture being formed in the reaction chamber can be improved. 
     An embodiment in which the elevations of the first wall are of a pyramidal or conical or cuboid or cylindrical shape is especially advantageous. Such elevations can be prepared within the first wall, e.g., by deep-drawing or casting. 
     Other important features and advantages of the present invention appear from the subclaims, from the drawings and from the corresponding description of the figures based on the drawings. 
     It is apparent that the above-mentioned features, which will still be explained below, can be used not only in the particular combination indicated, but in other combinations or alone as well without going beyond the scope of the present invention. 
     Preferred exemplary embodiments of the present invention are shown in the drawings and will be explained in more detail below, using identical reference numbers for identical or similar or functionally similar components. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a simplified circuit diagram-like basic schematic view of a fuel cell system according to the invention; 
         FIG. 2  is a sectional view of a burner corresponding to section lines II in  FIG. 1 ; 
         FIG. 3  is a sectional view of the burner corresponding to section lines III in  FIG. 2 ; 
         FIG. 4  is a sectional view of a different embodiment of a burner with a view as in  FIG. 3 ; 
         FIG. 5  is a sectional view of a different embodiment of a burner with a view as in  FIG. 3 ; 
         FIG. 6  is a sectional view of a different embodiment of a burner with a view as in  FIG. 3 ; 
         FIG. 7  is a top view of a first wall of a wall structure; and 
         FIG. 8  is a top view of a part of a wall from  FIG. 7  in one of different states of manufacture; 
         FIG. 9  is a top view of a part of a wall from  FIG. 7  in another of different states of manufacture; and 
         FIG. 10  is a top view of a part of a wall from  FIG. 7  in another of different states of manufacture; 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular, corresponding to  FIG. 1 , a fuel cell system  1  comprises a fuel cell  2 , which is used in the usual manner to generate electrical current and reacts an anode waste gas containing hydrogen gas with a cathode gas containing oxygen gas in the process. The fuel cell  2  has an anode side  3  as well as a cathode side  4  for this, which are separated from one another via an electrolyte  5 . The fuel cell  2  usually consists of a stack of individual fuel cell elements, which have an anode side  3  each, which is separated from the cathode side  4  by the electrolyte  5 . 
     The fuel cell system  1  comprises a reformer  6 , which is designed such that it can generate a fuel gas containing hydrogen gas, which fuel gas can be fed as an anode gas, e.g., to the fuel cell  2 . An outlet side  7  of the reformer  6  is connected for this to the anode side  3  of the fuel cell  2  via an anode gas line  8 . As an alternative, a hydrogen tank, which makes available hydrogen in the liquid or gaseous form, may also be provided instead of the reformer  6 . The stored hydrogen can be fed as an anode gas to the fuel cell  2  on the anode side. 
     To supply the fuel cell  2  with cathode gas, which is preferably air, a first air supply means  9  is provided, which has a cathode gas line  10  connected to the cathode side  4 . A delivery means  11 , for example, a pump or a fan, is arranged in the cathode gas line  10  to drive the cathode gas. 
     Reformer  6  generates the anode gas from an oxidant, which is preferably air, and a fuel, which is a hydrocarbon, e.g., diesel fuel, gasoline, biodiesel or any other synthetic fuel. The fuel cell system  1  may be preferably located in a motor vehicle and form an additional current source or the only current source there. Reformer  6  is preferably supplied for this with the fuel, with which an internal combustion engine of the vehicle is also operated. To supply the reformer  6  with fuel, a fuel supply means  12  is provided, which is, e.g., a pump and has a fuel line  14  connected to the inlet side  13  of the reformer  6  as well as a delivery means  15  integrated within the fuel line  14 . A second air supply means  16 , which may be a fan and comprises an oxidant line  17  connected to the inlet side  13  of reformer  6  and a delivery means  18  arranged in the oxidant line  17 , is provided for supplying the reformer  6  with oxidant, i.e., preferably with air. 
     The fuel cell system  1  has, besides, a residual gas burner  19  here, which will hereinafter be called burner  19  for short. Burner  19  contains a reaction chamber  20  and is used to burn the anode waste gas with cathode waste gas of the fuel cell  2 . Depending on the current production of the fuel cell  2 , the anode waste gas contains more or less hydrogen gas, while the cathode waste gas has an oxygen content that depends on the current production of the fuel cell  2 . To avoid the emission of hydrogen gas as well as of carbon monoxide into the environment, anode waste gas is reacted with cathode waste gas in burner  19 . 
     Burner  19  has a wall structure  21 , which defines the reaction chamber  20  on one side. This wall structure  21  is integrated here structurally in an outlet side of the fuel cell  2 . For example, wall structure  21  forms an end plate of the stacked, plate-like fuel cell elements. A structural unit comprising the fuel cell  2  and the burner  19  is obtained as a result. The wall structure  21  contains a first supply chamber  22 , into which the anode waste gas enters and from which the anode waste gas reaches the reaction chamber  20 . This anode gas flow is symbolized by arrows  23  in  FIG. 1 . Furthermore, wall structure  21  contains a second supply chamber  24 , into which the cathode waste gas is introduced and from which the cathode waste gas reaches the reaction chamber  20 . A corresponding cathode waste gas flow is indicated by arrows  25  in  FIG. 1 . 
     Opposite the wall structure  21 , which forms the inlet side of burner  19 , burner  19  has a heat exchanger  26 , which forms as a result an outlet side of burner  19 . Heat exchanger  26  defines the reaction chamber  20  against the wall structure  21  and combustion waste gases or burner waste gases are correspondingly admitted to it. These burner waste gases are led away from the burner  19  via a corresponding waste gas line  27 . The heat exchanger  26  is integrated within the cathode gas line  10 . Waste heat of the burner waste gas can be utilized as a result to heat the cathode gas. 
     Burner  19  may be optionally equipped with an igniting means  48 , e.g., with a spark plug or glow plug. A temperature sensor  49  may be optionally provided in order to monitor the overheating of burner  19  or the combustion process; for example, temperature sensor  49  is used as a flame failure safeguard. 
     Heat exchanger  26  may be provided with a catalytically active coating in the waste gas path in an especially advantageous embodiment, as a result of which it additionally acts as an oxidation catalyst. 
     The first air supply means  9  has here, as an example, a valve means  28 , by means of which a cooling gas flow can be branched off via a cooling gas line  29  from the cathode gas line  10  and can be fed into the second supply chamber  24 . 
     Furthermore, the fuel cell system  1  is equipped here with a recycling means  30 , by means of which anode waste gas can be recycled to the reformer  6 . The recycling means  30  has a return line  31  for this, which is connected on the inlet side, for example, to the first supply chamber  20 , and which is connected on the outlet side to the inlet side  13  of reformer  6 . The return line  31  contains a delivery means  32 , e.g., a pump, a compressor or a fan. Furthermore, another heat exchanger  33  is provided, which is integrated, on the one hand, in the return line  31  and, on the other hand, in the oxidant line  17 . The returned anode waste gas can be cooled by means of this heat exchanger  33  upstream of the delivery means  32  to the extent that a risk of damage to the delivery means  32  can be ruled out. However, the heat of the returned anode waste gas can be fed at the same time to reformer  6  via the oxidant gas. 
     Burner  19  may also be used in another system without a fuel cell  2 , e.g., with the reformer  6  or with a hydrogen tank, the latter being located, e.g., in a hydrogen-powered vehicle, whose internal combustion engine is operated with hydrogen gas. 
     Corresponding to  FIG. 2 , the wall structure  21  has a plurality of first openings  34 , through which the anode waste gas reaches the reaction chamber  20  from the first supply chamber  22 . These first openings  34  are arranged in a plurality of straight first rows  35 , which are indicated by broken lines here. These first rows  35  extend in parallel to a longitudinal direction  36 . 
     Furthermore, the wall structure  21  has a plurality of second openings  37 , through which the cathode waste gas reaches the reaction chamber  20  from the second supply chamber  24 . The second openings  37  are arranged in a plurality of straight second rows  38 , which are again indicated by broken lines in  FIG. 2 . The second rows  38  also extend in parallel to the longitudinal direction  36 , and they are also arranged between two adjacent first rows  35  each in relation to a transverse direction  39  extending at right angles to the longitudinal direction  36 . It is remarkable now that additional second openings  37 , which are arranged between two first openings  34  located adjacent each in the longitudinal direction, are present within the first rows  35 . As a result, every individual first opening  34  for anode waste gas is adjacent to a second opening  37  for cathode waste gas in both the longitudinal direction  36  and in the transverse direction  39 . Each first opening  34  is correspondingly bordered laterally by two openings  37  in a plane defined by the longitudinal direction  36  and the transverse direction  39 . 
     Corresponding to  FIGS. 2 and 3 , the wall structure  21  comprises a first wall  40 , which defines the first supply chamber  22  in the installed state on a rear side of the wall structure  21  facing away from the reaction chamber  20 . The first wall  40  has a plurality of elevations  41 . These elevations  41  may have a conical shape. The elevations  41  may likewise be pyramidal with a triangular or tetragonal cross section or a cross section formed by a polygon having any desired number of corners. Furthermore, the elevations  41  may also be cylindrical or cuboid. The first wall  40  contains the first openings  34 , doing so in the area of end sections  42  of the elevations  41 . 
     Furthermore, the wall structure  21  has a second wall  43 , which contains the second openings  37 . Furthermore, the second wall  43  contains a plurality of recesses  44 , which are respective perforations and which are closed by the respective end sections  42  of the elevations  41 . Together with the end sections  42  on a front side of the wall structure  21  facing the reaction chamber  20 , the second wall  43  forms a limitation of the reaction chamber  20 . The second reaction chamber  24  is formed between the first wall  40  and the second wall  43 . 
     Corresponding to  FIG. 2 , recesses  44  form a round cross section in this example. It is clear that rectangular or any other desired cross sections are also conceivable in other embodiments. 
     In the embodiment shown in  FIG. 3 , the end sections  42  of the elevations  41  are made complementary in respect to their circumferential contour to the cross sections of recesses  44 . It is possible as a result to plug the end sections  42  into the recesses  44  such that they fill these out and seal them as a result. In other words, the end sections  42  mesh with the recesses  44 . This meshing preferably takes place such that the end sections  42  are flush with the second wall  43  on the front side of wall structure  21  facing the reaction chamber  20 . 
       FIG. 4  shows an example in which the elevations  41  are cylindrical or cuboid. Furthermore, a step  45  is provided here, by which the particular end section  42  is offset from the rest of the elevation  41 . The second plate  43  can come into contact with this step  45 . At the same time, step  45  facilitates the establishment of a tight connection between the elevations  41  and the second plate  43 . The end sections  42  mesh with the respective recess  44  flush in this case as well. 
     While the elevations  41  are formed individually in the embodiments according to  FIGS. 3 and 4 ,  FIG. 5  shows an embodiment in which the elevations  41  are designed as a group  46 . Section plane III-III in  FIGS. 3 through 6  extends through one of the first rows  35  or coincides with same. Such a group of elevations  46  can be embodied, e.g., by the first wall  40  having a wave-shaped profile or a peak-and-valley profile in a section plane that extends in parallel to the transverse direction, the peak sections forming such a group of elevations  46  each. A depression  47  is formed between two end sections  42  located adjacent in the longitudinal direction  36  within the respective group of elevations  46 , which thus extends in the longitudinal direction  36  and forms a first row  35  each as a result. These depressions  47  are dimensioned such that the first wall  40  is located at a spaced location from the second wall  43  in the area of the respective depression  47 . Furthermore, the particular depression  47  is designed as a continuous depression in the transverse direction  39 . As a result, the two valley sections of the peak-and-valley profile communicate with one another via the respective depression  47 , which are separated from one another by the peak section, which forms the group of elevations  46 . The second openings  37  arranged in the second wall  43  in the area of the depressions  47  correspondingly communicate with the second supply chamber  34 . 
       FIG. 5  shows as an example a partition  50 , which separates the reaction chamber  20  from a cooling chamber  51 , through which only the cathode waste gas  25  or a cooling gas-cathode waste gas mixture flows and which defines the reaction chamber  20  on one side or on a plurality of sides and especially surrounds same laterally. 
     While the end sections  42  of the elevations  41  cooperate in the embodiments according to  FIGS. 2 through 5  with the recesses  44  such that they mesh with the corresponding recesses  44 ,  FIG. 6  shows an embodiment in which the end sections  42  have a surface that faces the second wall  43  and is larger than the cross-sectional area of the respective recess  44 . As a consequence, the end sections  42  cooperate here with the recesses  44  such that the end sections  42  are in contact in this embodiment by their respective surface with an underside of the second wall  43 , which said underside faces the first wall  40 . The recesses  44  are covered by the end sections  42  as a result. The first openings  34  of the first wall  40  are now aligned with the recesses  44  of the second wall  43 . In particular, the first openings  34  and the recesses  44  may have equal cross sections.  FIG. 6  shows, in addition, examples of different geometries for the elevations  41 . 
       FIG. 7  shows a top view of the first wall  40  when viewed from the second wall  43  or when viewed from the reaction chamber  20  with the second wall  43  removed. The first wall  40  shows in the detail shown two groups of elevations  46 , which extend each in the longitudinal direction  36  and form a first row  35  each. As can be recognized, a depression  47  each is formed in the longitudinal direction  36  between two end sections  42  each. While the end sections  42  contain a first opening  34  each, depressions  47  are made without openings. 
     Corresponding to an advantageous embodiment, the first wall  40  may be prepared, for example, as follows: 
     Corresponding to  FIG. 8 , continuous elevations  41 ′, which extend in parallel to the longitudinal direction  36  over the entire length of the respective first row  35 , are prepared in a first process step. However, only one such first row  35  is shown in  FIGS. 8 through 9 . This continuous elevation  41 ′ correspondingly also has an end section  42 ′ that passes through. 
     Corresponding to  FIG. 9 , a deformation, which forms the depressions  47 , is performed in a second process step. The passing-through end section  42 ′, which is still present in the state according to  FIG. 8 , is divided as a result into a plurality of end sections  42  in the longitudinal direction  36 . The individual elevations  41  are correspondingly also separated as a result from one another. 
     Corresponding to  FIG. 10 , the first openings  34  can be prepared in the area of the end sections  42  in a third process step. It is clear that the first openings  34  can also be prepared with the depressions  47  during the second process step. Furthermore, it is also possible to provide the first openings  34  already in the first step. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.