Wall structure and burner as well as system

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).

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in particular, corresponding toFIG. 1, a fuel cell system1comprises a fuel cell2, 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 cell2has an anode side3as well as a cathode side4for this, which are separated from one another via an electrolyte5. The fuel cell2usually consists of a stack of individual fuel cell elements, which have an anode side3each, which is separated from the cathode side4by the electrolyte5.

The fuel cell system1comprises a reformer6, 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 cell2. An outlet side7of the reformer6is connected for this to the anode side3of the fuel cell2via an anode gas line8. As an alternative, a hydrogen tank, which makes available hydrogen in the liquid or gaseous form, may also be provided instead of the reformer6. The stored hydrogen can be fed as an anode gas to the fuel cell2on the anode side.

To supply the fuel cell2with cathode gas, which is preferably air, a first air supply means9is provided, which has a cathode gas line10connected to the cathode side4. A delivery means11, for example, a pump or a fan, is arranged in the cathode gas line10to drive the cathode gas.

Reformer6generates 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 system1may be preferably located in a motor vehicle and form an additional current source or the only current source there. Reformer6is preferably supplied for this with the fuel, with which an internal combustion engine of the vehicle is also operated. To supply the reformer6with fuel, a fuel supply means12is provided, which is, e.g., a pump and has a fuel line14connected to the inlet side13of the reformer6as well as a delivery means15integrated within the fuel line14. A second air supply means16, which may be a fan and comprises an oxidant line17connected to the inlet side13of reformer6and a delivery means18arranged in the oxidant line17, is provided for supplying the reformer6with oxidant, i.e., preferably with air.

The fuel cell system1has, besides, a residual gas burner19here, which will hereinafter be called burner19for short. Burner19contains a reaction chamber20and is used to burn the anode waste gas with cathode waste gas of the fuel cell2. Depending on the current production of the fuel cell2, 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 cell2. 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 burner19.

Burner19has a wall structure21, which defines the reaction chamber20on one side. This wall structure21is integrated here structurally in an outlet side of the fuel cell2. For example, wall structure21forms an end plate of the stacked, plate-like fuel cell elements. A structural unit comprising the fuel cell2and the burner19is obtained as a result. The wall structure21contains a first supply chamber22, into which the anode waste gas enters and from which the anode waste gas reaches the reaction chamber20. This anode gas flow is symbolized by arrows23inFIG. 1. Furthermore, wall structure21contains a second supply chamber24, into which the cathode waste gas is introduced and from which the cathode waste gas reaches the reaction chamber20. A corresponding cathode waste gas flow is indicated by arrows25inFIG. 1.

Opposite the wall structure21, which forms the inlet side of burner19, burner19has a heat exchanger26, which forms as a result an outlet side of burner19. Heat exchanger26defines the reaction chamber20against the wall structure21and combustion waste gases or burner waste gases are correspondingly admitted to it. These burner waste gases are led away from the burner19via a corresponding waste gas line27. The heat exchanger26is integrated within the cathode gas line10. Waste heat of the burner waste gas can be utilized as a result to heat the cathode gas.

Burner19may be optionally equipped with an igniting means48, e.g., with a spark plug or glow plug. A temperature sensor49may be optionally provided in order to monitor the overheating of burner19or the combustion process; for example, temperature sensor49is used as a flame failure safeguard.

Heat exchanger26may 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 means9has here, as an example, a valve means28, by means of which a cooling gas flow can be branched off via a cooling gas line29from the cathode gas line10and can be fed into the second supply chamber24.

Furthermore, the fuel cell system1is equipped here with a recycling means30, by means of which anode waste gas can be recycled to the reformer6. The recycling means30has a return line31for this, which is connected on the inlet side, for example, to the first supply chamber20, and which is connected on the outlet side to the inlet side13of reformer6. The return line31contains a delivery means32, e.g., a pump, a compressor or a fan. Furthermore, another heat exchanger33is provided, which is integrated, on the one hand, in the return line31and, on the other hand, in the oxidant line17. The returned anode waste gas can be cooled by means of this heat exchanger33upstream of the delivery means32to the extent that a risk of damage to the delivery means32can be ruled out. However, the heat of the returned anode waste gas can be fed at the same time to reformer6via the oxidant gas.

Burner19may also be used in another system without a fuel cell2, e.g., with the reformer6or 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 toFIG. 2, the wall structure21has a plurality of first openings34, through which the anode waste gas reaches the reaction chamber20from the first supply chamber22. These first openings34are arranged in a plurality of straight first rows35, which are indicated by broken lines here. These first rows35extend in parallel to a longitudinal direction36.

Furthermore, the wall structure21has a plurality of second openings37, through which the cathode waste gas reaches the reaction chamber20from the second supply chamber24. The second openings37are arranged in a plurality of straight second rows38, which are again indicated by broken lines inFIG. 2. The second rows38also extend in parallel to the longitudinal direction36, and they are also arranged between two adjacent first rows35each in relation to a transverse direction39extending at right angles to the longitudinal direction36. It is remarkable now that additional second openings37, which are arranged between two first openings34located adjacent each in the longitudinal direction, are present within the first rows35. As a result, every individual first opening34for anode waste gas is adjacent to a second opening37for cathode waste gas in both the longitudinal direction36and in the transverse direction39. Each first opening34is correspondingly bordered laterally by two openings37in a plane defined by the longitudinal direction36and the transverse direction39.

Corresponding toFIGS. 2 and 3, the wall structure21comprises a first wall40, which defines the first supply chamber22in the installed state on a rear side of the wall structure21facing away from the reaction chamber20. The first wall40has a plurality of elevations41. These elevations41may have a conical shape. The elevations41may 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 elevations41may also be cylindrical or cuboid. The first wall40contains the first openings34, doing so in the area of end sections42of the elevations41.

Furthermore, the wall structure21has a second wall43, which contains the second openings37. Furthermore, the second wall43contains a plurality of recesses44, which are respective perforations and which are closed by the respective end sections42of the elevations41. Together with the end sections42on a front side of the wall structure21facing the reaction chamber20, the second wall43forms a limitation of the reaction chamber20. The second reaction chamber24is formed between the first wall40and the second wall43.

Corresponding toFIG. 2, recesses44form 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 inFIG. 3, the end sections42of the elevations41are made complementary in respect to their circumferential contour to the cross sections of recesses44. It is possible as a result to plug the end sections42into the recesses44such that they fill these out and seal them as a result. In other words, the end sections42mesh with the recesses44. This meshing preferably takes place such that the end sections42are flush with the second wall43on the front side of wall structure21facing the reaction chamber20.

FIG. 4shows an example in which the elevations41are cylindrical or cuboid. Furthermore, a step45is provided here, by which the particular end section42is offset from the rest of the elevation41. The second plate43can come into contact with this step45. At the same time, step45facilitates the establishment of a tight connection between the elevations41and the second plate43. The end sections42mesh with the respective recess44flush in this case as well.

While the elevations41are formed individually in the embodiments according toFIGS. 3 and 4,FIG. 5shows an embodiment in which the elevations41are designed as a group46. Section plane III-III inFIGS. 3 through 6extends through one of the first rows35or coincides with same. Such a group of elevations46can be embodied, e.g., by the first wall40having 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 elevations46each. A depression47is formed between two end sections42located adjacent in the longitudinal direction36within the respective group of elevations46, which thus extends in the longitudinal direction36and forms a first row35each as a result. These depressions47are dimensioned such that the first wall40is located at a spaced location from the second wall43in the area of the respective depression47. Furthermore, the particular depression47is designed as a continuous depression in the transverse direction39. As a result, the two valley sections of the peak-and-valley profile communicate with one another via the respective depression47, which are separated from one another by the peak section, which forms the group of elevations46. The second openings37arranged in the second wall43in the area of the depressions47correspondingly communicate with the second supply chamber34.

FIG. 5shows as an example a partition50, which separates the reaction chamber20from a cooling chamber51, through which only the cathode waste gas25or a cooling gas-cathode waste gas mixture flows and which defines the reaction chamber20on one side or on a plurality of sides and especially surrounds same laterally.

While the end sections42of the elevations41cooperate in the embodiments according toFIGS. 2 through 5with the recesses44such that they mesh with the corresponding recesses44,FIG. 6shows an embodiment in which the end sections42have a surface that faces the second wall43and is larger than the cross-sectional area of the respective recess44. As a consequence, the end sections42cooperate here with the recesses44such that the end sections42are in contact in this embodiment by their respective surface with an underside of the second wall43, which said underside faces the first wall40. The recesses44are covered by the end sections42as a result. The first openings34of the first wall40are now aligned with the recesses44of the second wall43. In particular, the first openings34and the recesses44may have equal cross sections.FIG. 6shows, in addition, examples of different geometries for the elevations41.

FIG. 7shows a top view of the first wall40when viewed from the second wall43or when viewed from the reaction chamber20with the second wall43removed. The first wall40shows in the detail shown two groups of elevations46, which extend each in the longitudinal direction36and form a first row35each. As can be recognized, a depression47each is formed in the longitudinal direction36between two end sections42each. While the end sections42contain a first opening34each, depressions47are made without openings.

Corresponding to an advantageous embodiment, the first wall40may be prepared, for example, as follows:

Corresponding toFIG. 8, continuous elevations41′, which extend in parallel to the longitudinal direction36over the entire length of the respective first row35, are prepared in a first process step. However, only one such first row35is shown inFIGS. 8 through 9. This continuous elevation41′ correspondingly also has an end section42′ that passes through.

Corresponding toFIG. 9, a deformation, which forms the depressions47, is performed in a second process step. The passing-through end section42′, which is still present in the state according toFIG. 8, is divided as a result into a plurality of end sections42in the longitudinal direction36. The individual elevations41are correspondingly also separated as a result from one another.

Corresponding toFIG. 10, the first openings34can be prepared in the area of the end sections42in a third process step. It is clear that the first openings34can also be prepared with the depressions47during the second process step. Furthermore, it is also possible to provide the first openings34already in the first step.