Abstract:
A reactor has multiple reactor modules for endothermic reactions. Each reactor module comprises a reaction channel enclosed by a tubular boundary wall and having first and second ends. The reactor module has an inlet element for introducing reactants into the reaction channel. The inlet element is arranged at the first end of the reaction channel. The reactor module has an outlet element for discharging the reaction products from the reaction channel. The outlet element is arranged at the second end of the reaction channel. The reactor module has a heat supply device in the form of a porous burner arrangement that is arranged on the outside of the tubular boundary wall of the reaction channel. Because a porous burner arrangement is used instead of a heat source having catalytic combustion, high reactor performance is achieved at an economical price. The porous burner is substantially less expensive than a combustion catalyst.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is filed under 35 U.S.C. §111(a) and is based on and hereby claims priority under 35 U.S.C. §120 and §365(c) from International Application No. PCT/DE2010/001005, filed on Aug. 27, 2010, and published as WO 2011/023177 A1 on Mar. 3, 2011, which in turn claims priority from German Application No. 102009039276.9, filed on Aug. 28, 2009, in Germany. This application is a continuation-in-part of International Application No. PCT/DE2010/001005, which is a continuation of German Application No. 102009039276.9. International Application No. PCT/DE2010/001005 is pending as of the filing date of this application, and the United States is an elected state in International Application No. PCT/DE2010/001005. This application claims the benefit under 35 U.S.C. §119 from German Application No. 102009039276.9. The disclosure of each of the foregoing documents is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a reactor for generating a product gas through allothermal gasification of carbonaceous raw materials. 
       BACKGROUND 
       [0003]    The invention relates to a reactor module for endothermic reactions that produce one or more products, a reactor with a plurality of such reactor modules, and a method for operating a reactor module or a reactor. A cylindrical reactor module is known from U.S. Patent Pub. 2006/0122446 A1 that includes a reaction conduit with a first and a second end, as well as an outer side and an inner side. Two reaction feed materials are introduced into the reaction conduit via a first inlet element at the first end and via a second inlet element at the second end. Reaction products are drawn out of the reaction conduit via a first outlet element at the second end and via a second outlet element at the first end. The reaction heat necessary for an endothermic chemical reaction is coupled into the reaction conduit via a heat exchanger. The high thermal currents necessary for the allothermal gasification of water vapor cannot be achieved with this known reactor module. Allothermal means that the required heat for the reaction is produced outside of the reactor. In addition, a similar reactor module is described in U.S. Pat. No. 5,487,876 B1. 
         [0004]    A reactor module for the water vapor reformation of methanol is known from German Patent Application No. DE69835503 T2. The reactor module comprises an inlet element for the supplying of methanol and water vapor, an annular, tubular reaction conduit and an outlet element for carbon dioxide and hydrogen. A porous combustion catalyzer is arranged on the outer side of the reaction conduit and burns a portion of the generated hydrogen and, in this manner, generates heat into the endothermic reforming process in the annular, tubular reaction conduit. An exothermic methanization reaction takes place in the innermost tube that also gives off heat into the annular, tubular reaction conduit. 
         [0005]    Catalytic reformation reactors for generating hydrogen and methane are known from WO 2008/146052 A1, U.S. Patent Pub. US2008/0170975 A1, German Patent Pub. DE10213891 A1 and from German utility model 69320711.5. Catalytic reformation reactors have the disadvantage that they are not suitable for high-performance reactors on account of the expensive catalyzer materials. 
         [0006]    A so-called heat-pipe reformer is known from European Patent No. EP1187892 B1 that comprises a fluidized bed firing and a fluidized bed gasification chamber. Fuel gas is produced from carbon-containing feed material in the fluid bed gasification chamber by allothermal water vapor gasification. The heat necessary for this is generated in the fluidized bed flame by combustion and is transmitted into the fluidized bed gasification chamber via heat pipes and/or heat tubes. A reactor in accordance with European Patent No. EP1187892 B1 has the disadvantage that the reaction energy of the fluidized bed gasification chamber is supplied via heat conduction tubes. This results in complicated structures and in a plurality of parts in the interior of the fluidized bed gasification chamber that the fluidized bed flows around and consequently results in high wear. Therefore, such a reactor must be serviced at regular intervals. Moreover, the amount of heat conducted via the heat conduction tubes is limited. Therefore, the reaction energy for the allothermal water vapor gasification is also limited. 
         [0007]    So-called pore burners consist of a temperature-resistant, porous material that is connected to an inlet and to an outlet. A pre-mixed fuel-air mixture is introduced into the inlet that reacts exothermally in a flameless, volumetric combustion that is stabilized in many pores (small reactors). As a result of the resulting combustion heat, each pore body begins to glow. Such a pore burner is known, for example, from the article “Gaswärme International (54), August 2005.” Other pore burners for different applications and with different constructions are disclosed in DE102005056629 B4, DE10344979 A1, DE102004041815 A1, DE102006012168 A1, DE202005003843U1, WO 00/46548, DE10114902 A1, DE10114903 A1, DE102006013445 A1 and EP0995014 B1. 
         [0008]    Therefore, the invention has the objective, starting from U.S. Patent Pub. 2006/0122446 A1 or German Patent Pub. DE69835503 T2, of indicating a reactor module for endothermic reactions that has a simple construction and that is suitable in particular for generating fuel gas from carbon-containing feed materials by allothermal water vapor gasification. The invention has the further objective of providing a reactor that includes a plurality of such reactor modules as well as of providing a method for operating such a reactor or reactor module. 
       SUMMARY 
       [0009]    The novel reactor enables higher reactor performance to be achieved at an economically reasonable price by using a pore burner arrangement instead of a heat source with catalytic combustion. The porous material of the pore burner can be ceramic or sintered metal. The improved reactor performance is due to the fact that the pore burner arrangement is itself significantly more economical than a combustion catalyzer. Because the pore burner arrangement is arranged on the outer side of the reaction conduit, the heat necessary for the endothermic reaction passes from the sites of its production in the porous body directly by thermal conduction and thermal radiation through the outer casing of the reactor conduit into the reaction conduit. Because the pore burner arrangement is arranged around the reaction conduit, the heat can no longer escape from the reaction conduit. The dimensions of the reaction conduit and of the pore burner arrangement in the axial and radial directions is selected in such a manner that sufficient thermal energy is produced in the pore burner arrangement and transferred into the reaction conduit in order to carry out an endothermic chemical reaction in the interior of the reaction conduit. The cross-section and the diameter of the reaction conduit is dimensioned in such a manner that the most uniform temperature distribution possible is achieved over the cross-section. Therefore, a diameter range that makes this uniform temperature distribution possible over the cross-section of the reaction conduit results as a function of the thermal output of the pore burner arrangement. 
         [0010]    The cross section of the reaction conduit can be circular or also constructed as a regular polygon. In every possible embodiment, the pore burner arrangement stands in direct contact with the largest possible amount of the outer side of the reaction conduit so that the largest possible heat transfer surface is provided between the pore burner arrangement of the reaction conduit. The thermal screening and insulation of the reaction conduit is additionally improved by this advantageous construction. 
         [0011]    It is possible to introduce and/or remove at least one reaction feed material and at least one reaction product during the operation of the reactor module via an inlet lock or outlet lock into the reaction conduit or out of the reaction conduit. This permits a continuous chemical reaction to take place in the reactor module. 
         [0012]    In another embodiment, the reaction conduit is vertically arranged. This makes it possible to utilize the force of gravity or thermodynamic effects such as, e.g., warm gas expanding and rising upward, in order to transport at least one reaction feed material or at least one reaction product through the reaction conduit. This can simplify, for example, the separation of reaction products, e.g., gases and liquids and/or solids. 
         [0013]    According to another embodiment, a first reaction feed material is introduced via an inlet lock into the reaction conduit, and a first reaction product is removed from the reaction conduit via an outlet lock. A second reaction feed material is introduced via a second inlet element into the reaction conduit and a second reaction product is removed from the reaction conduit via a second outlet element. The second inlet element is arranged here between the inlet lock and the pore burner arrangement or between the outlet lock and the pore burner arrangement. Likewise, the second outlet element can be arranged between the inlet lock and the pore burner arrangement or between the outlet lock and the pore burner arrangement. In addition, these two inlet and outlet elements can also conduct out of the reaction conduit into the reaction conduit even in the area of the pore burner arrangement. The variability of such a reactor module makes it possible to carry out a plurality of endothermic chemical reactions. 
         [0014]    Furthermore, the design of the reactor also makes it possible to conduct different reaction feed materials in countercurrent through the reaction conduit. The introduced amounts of the reaction feed materials can be controlled here in such an advantageous manner that an optimal conversion of the reaction feed materials into reaction products is achieved. 
         [0015]    In yet another embodiment, fuel gases such as hydrogen and carbon monoxide are generated from carbon-containing feed materials and superheated water through the process of allothermal water vapor gasification in the reactor module. The carbon-containing feed materials that can be used in the reaction include, e.g., coals, tar, tar sand, plastic waste, remnants from the manufacture of paper and cellulose, remnants from the petrochemical industry, electronic scrap and light shredder fraction and in particular biomass feedstock such as, e.g., harvest waste, energy plants ( miscanthus ), chopped wood chips or a mixture of the above. The allothermal water vapor gasification process converts water vapor plus the carbon-containing feed materials into carbon monoxide and hydrogen. A cleaner reaction with a higher concentration of these end products can be obtained at the higher temperatures achievable using the heat from the porous material surrounding the reaction conduit. In a separate step, the carbon monoxide and hydrogen can be converted into methane and water. 
         [0016]    The construction of the reactor module makes it possible in an advantageous manner for the carbon-containing feed materials to be introduced from above through the inlet lock and the superheated water vapor to be introduced from below through the inlet into the reaction conduit in such a manner that the carbon-containing feed materials and the superheated water vapor flow in opposite directions through the reaction conduit. The reaction energy necessary for the production of fuel gases is supplied to the reaction conduit through the pore burner arrangement, whereby the carbon-containing feed materials and the superheated water vapor are converted into fuel gas and carbon-poor feed byproducts, called ash in the following description. The introduced amounts can be advantageously dosed in such a manner that an optimal conversion of the carbon-containing feed materials and of the superheated water vapor into fuel gas and ash is achieved in the reaction conduit. The optimal conversion with fewer byproducts is also made possible by the high temperatures achievable by encasing the reaction conduit in the pore burner elements. After the chemical reaction, the fuel gas collects in the upper part of the reaction conduit and can be removed via the outlet from the reaction conduit. A major component of the fuel gas is hydrogen. The ash byproduct collects in the lower part of the reaction conduit and can be removed via the outlet lock from the reaction conduit. 
         [0017]    In another embodiment, a condenser is connected after the second outlet element. Water vapor contained in the exiting fuel gas is condensed by this condenser and is thus removed from the fuel gas. 
         [0018]    The pore burner arrangement comprises a plurality of pore burner elements. A pore burner element includes a burner inlet for introducing oxygen and fuel, the pore burner and the fuel outlet for discharging the burnt oxygen-fuel mixture. The fuel can be introduced in liquid or gaseous form or in a mixture thereof into the pore body. An individual pore burner element is construed and dimensioned such that the volumetric combustion extends over a great part of the pore body. In the pore burner arrangement around the reaction conduit, each individual pore burner element annularly surrounds the reaction conduit in a first structural form. The pore burner arrangement can also be subdivided along the circumference into a plurality of pore burner elements, whereby all pore burner elements jointly surround the reaction conduit in an annular manner in a second structural form. Moreover, the pore burner element can also be constructed from a combination of these two structural forms. A subdivision of the pore burner element into a plurality of pore burner elements makes it possible, for example, to form a temperature gradient inside the reaction conduit. Moreover, maintenance and repair work is simplified because individual pore burner elements can be readily exchanged. 
         [0019]    In another embodiment, the pore burner elements are arranged at a distance from each other along the reaction conduit in a reactor module. The variability of a reactor module is advantageously increased by such an arrangement. Because intervals are present between two adjacent pore burner elements along the reaction conduit, at least one inlet element and/or outlet element can be arranged in these elements on the reaction conduit, as a result of which at least one reaction feed material and/or reaction product can be introduced into the reaction conduit or brought out of the reaction conduit. This allows the conversion of a multistage chemical reaction in the reactor module. Moreover, this creates space for making accessible supply lines available for the individual pore burner elements, which also simplifies maintenance and repair work. 
         [0020]    In another embodiment, the reaction conduit is constructed in an annular, tubular manner. Because at least one first pore burner element surrounds the outer outside of the annular, tubular reaction conduit and at least one second pore burner element is arranged on the inner side of the inner boundary wall on the outside of the annular, tubular reaction conduit, the reaction conduit is encompassed on two sides by a heat source, and therefore heat flows from two sides into the reaction conduit. As a consequence of this design, the cross-sectional area of the reaction conduit can be enlarged without having to increase the uniformity of the “thickness” of the reaction conduit influencing the temperature distribution. Also, this design allows greater heat flow densities on account of the greater heat transfer surface between the pore burner arrangement and the reaction conduit at the given dimensions. The uniformity of the heat input and the distribution of heat in the reaction conduit are improved. 
         [0021]    Another embodiment enables the production of fuel gas from solid feed materials. The solid feed materials are apportioned, e.g., in the form of pellets, at the top via the inlet lock and travel downward under the force of gravity in the reaction conduit. The carbon-poor, solid residual substances are taken out at intervals at the lower end via the outlet lock. The pellets can be made available, for example, by a pelletizing apparatus connected in front of the inlet lock or integrated into the inlet lock. 
         [0022]    In another embodiment, a plurality of reactor modules forms a reactor. The connecting in parallel of the individual reactor modules results in a system that enables the large-scale production of at least one reaction product. A portion of the produced fuel gas is used as a fuel for the pore burner arrangement. Therefore, additional fuel for the pore burner arrangement need only be supplied in the startup phase. 
         [0023]    Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
           [0025]      FIG. 1  is a longitudinal sectional view of a first embodiment of the invention. 
           [0026]      FIG. 2  is a cross sectional view of a first embodiment of the invention along the line A-A in  FIG. 1 . 
           [0027]      FIG. 3  is a longitudinal sectional view of a second embodiment of the invention. 
           [0028]      FIG. 4  is a longitudinal sectional view of a third embodiment of the invention. 
           [0029]      FIG. 5  is a cross sectional view to the reaction conduit through the pore burner arrangement of a fourth embodiment of the invention along the line B-B in  FIG. 6 . 
           [0030]      FIG. 6  is a longitudinal sectional view of a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0032]      FIGS. 1 and 2  show a first embodiment of the invention. A reactor module  1  comprises a reaction conduit  2  that is surrounded by a tubular boundary wall  2   a  and comprises a first end  3 , a second end  4  and a middle section  5  between the first end  3  and the second end  4 . At least one reaction feed material is introduced into the reaction conduit  2  at the first end  3 . At the second end  4  at least one reaction product is removed from the reaction conduit  2 . A pore burner arrangement  10  encloses the reaction conduit  2  annularly at the middle section  5 . As can be seen from the cross sectional view in  FIG. 2  along A-A in  FIG. 1 , the pore burner arrangement  10  includes a first pore burner element  11  and a second pore burner element  21 . The two pore burner elements  11 ,  21  each form half of a cylindrical hollow body divided along the longitudinal axis. Each pore burner element  11 ,  21  includes a pore body  12 ,  22  that comprises an inner surface area  13 ,  23 , an outer surface area  14 ,  24 , a first base surface  15 ,  25  and a second base surface  16 ,  26 , as well as a fuel inlet  17 ,  27  and a fuel outlet  18 ,  28 . In the first embodiment, the first base surface  15 ,  25  of each pore body is provided with the fuel inlet  17 ,  27  for the introduction of oxygen and liquid or gaseous fuel. The second base surface  16 ,  26  of each pore body  12 ,  22  is provided with the fuel outlet  18 ,  28  for removal of the burned fuel-oxygen mixture. However, the fuel inlets  17 ,  27  of one or both pore bodies  12 ,  22  can also be arranged in one or both pore burner elements  11 ,  21  on the second base surface  16 ,  26  of the pore body  12 ,  22 . And the fuel outlet  18 ,  28  can be arranged on the base body  15 ,  25  of the pore body  12 ,  22 . 
         [0033]    The inside diameter of each pore burner element  11 ,  21  is selected in such a manner that the inner surface area  13 ,  23  of each pore body  12 ,  22  firmly surrounds the boundary wall  2   a  of the reaction conduit  2 . Because each pore body  12 ,  22  rests directly on the boundary wall  2   a  of the reaction conduit  2 , the thermal energy produced in the pore bodies  12 ,  22  is given off directly to the reaction conduit  2 . Thus, a direct thermal transfer from the pore burner elements  11 ,  21  onto the reaction conduit  2  is achieved. The temperature achievable in the reaction conduit  2  can be further increased by insulating the pore burner elements  11 ,  21  outwardly. At least one reaction product is produced by the transferred thermal energy in the reaction conduit  2  in an endothermic chemical reaction. 
         [0034]      FIG. 3  shows a second embodiment of the invention. Carbon-containing feed materials and superheated water vapor react in a reactor module  30  in an endothermic chemical reaction to form fuel gas by allothermal water vapor gasification. The reactor module  30  comprises a reaction conduit  31  that is surrounded by a tubular boundary wall  31   a  and is vertically arranged. The reaction conduit  31  has an upper end  32 , a lower end  33  and a middle section  34  between the upper end  32  and the lower end  33 . An inlet lock  35  is arranged on the upper end  32  of which only a lock valve  36  is shown in  FIG. 3 . A pipeline  37  for bringing out the fuel gas is arranged between the inlet lock  35  and the middle section  34 . The pipeline branches off from the reaction conduit  31 . An outlet lock  38  is arranged on the lower end  33 , of which only a lock valve  39  is shown in  FIG. 3 . A pipeline  40  for bringing in the superheated water vapor necessary for the allothermal water vapor gasification is arranged between the middle section  34  and the outlet lock  38 . The pipeline  40  is constructed in such a manner that its end piece  41  projects in a radial manner into the middle of the reaction conduit  31  and is bent such that the cross-sectional area of the outlet  42  is aligned vertically to the axial line of the reaction conduit  41  and such that the outlet  42  opens upward. 
         [0035]    A pore burner arrangement  50  surrounds the reaction conduit  31  annularly on the middle section  34  and includes four pore burner elements  51 . Each individual pore burner element  51  includes a pore body  52  constructed in the form of a cylindrical hollow body with an inner surface area  53 , an outer surface area  54 , a first base surface  55  and a second base surface  56  and including a fuel inlet  57  and a fuel outlet  58 . In the present embodiment, the fuel inlet  57  is arranged in each pore burner element  51  on the first base surface  55  of the pore body  52  and the fuel outlet  58  is arranged on the second base surface  56  of the pore body  52 . The fuel flows from below upward in each pore burner element  51 , as indicated by the arrows. However, the fuel inlet  57  can also be arranged in a pore burner element  51  on the second base surface  56  of the pore body  52 , and the fuel outlet  58  can be arranged on the first base surface  55  of the pore body  52  such that the fuel flows from the top downward (not shown) in the pore burner element  51 . In addition, pore burner elements  51  in which the fuel flows in different directions can also be arranged in a pore burner arrangement  50 . 
         [0036]    The inside diameter of each pore burner element  51  is designed such that the inner surface area  53  of the pore body  52  firmly surrounds the tubular boundary wall  31   a  of the reaction conduit  31 . Because each pore body  52  rests directly on the reaction conduit  31 , the thermal energy produced in each pore body  52  is transferred directly to the reaction conduit  31 . Thus, a direct heat transfer from each pore burner element  51  to the reaction conduit  31  is achieved. 
         [0037]    In the present embodiment, all pore burner elements  51  have the same height and the same diameter, as shown in  FIG. 3 . However, the pore burner elements  51  can also differ from each other in height and diameter, whereby the diameter of the reaction conduit  31  is adapted to the diameter of the particular pore burner element  51 . 
         [0038]    In order to produce the fuel gas, the carbon-containing feed materials are introduced via the inlet lock  35  into the reaction conduit  31 , and the superheated water vapor is introduced through the pipeline  40  into the reaction conduit  31 . The reaction conduit  31  can be filled up to the level of the second base surface  56  of the uppermost pore burner element  51 . The thermal energy produced by all pore burner elements  51  is supplied to the reaction conduit  31 . Likewise, the reaction conduit  31  can be filled with the carbon-containing feed materials only up to the second base surface  56  of any pore burner element  51 , whereby only those pore burner elements  51  are used to supply thermal energy to the reaction conduit  31  until the reaction conduit  31  has been filled with the carbon-containing feed materials to their second base surface  56 . 
         [0039]    In order to produce the fuel gas, the carbon-containing feed materials can be introduced through the inlet lock  35 , and the superheated water vapor through the pipeline  40  into the reaction conduit  31  in such a manner that the carbon-containing feed materials and the superheated water vapor flow in countercurrent through the reaction conduit  31 . The introduced amounts can be controlled such that an optimal conversion of the carbon-containing feed materials and of the superheated water vapor into fuel gas and ash is achieved in the reaction conduit  31 . The ash present at the lower end  33  of the reaction conduit  31  can be discharged after the chemical reaction via the outlet lock  38 . 
         [0040]      FIG. 4  shows a third embodiment of the invention. The same components as in the second embodiment are labeled with the same reference numerals. A new description of these parts is omitted with a reference to the second embodiment. 
         [0041]      FIG. 4  shows that the reactor module  30  includes a reaction conduit  31  whose middle section  34  is annularly surrounded by a pore burner arrangement  60 . In the fourth embodiment, the pore burner arrangement  60  includes a plurality of pore burner elements  61 . The pore burner elements  61  are, as described in the second embodiment, arranged around the tubular boundary wall  31   a  of the reaction conduit  31 . 
         [0042]    Each individual pore burner element  61  includes a pore body  62  constructed in the form of a cylindrical hollow body with an inner surface area  63 , an outer surface area  64 , a first base surface  65 , a second base surface  66 , and a cylindrical middle section  67 , as well as a fuel inlet  68  and a fuel outlet  69 . In the present embodiment, the fuel inlet  68  in each pore burner element  61  is arranged on the cylindrical middle section  67  of the pore body  62 , and the fuel outlet  69  is arranged on the first base surface  65  as well as on the second base surface  66  of the pore body  62  such that the fuel flows through each pore burner element  61 , as indicated by the arrows. However, the fuel inlet  68  can also be connected in each pore burner element  61  to the first base surface  65  and to the second base surface  66  of the pore body  62 . The fuel outlet  69  can be connected to the cylindrical middle section  67  of the pore body  62 . In addition, pore burner elements  61  in which the fuel flows in different directions can also be arranged in a pore burner arrangement  60 . 
         [0043]      FIGS. 5 and 6  show a fourth embodiment of the present invention.  FIG. 6  shows a longitudinal sectional view of a reactor module  70 , and  FIG. 5  shows a cross section along B-B in  FIG. 6 . 
         [0044]    The reactor module  70  includes a reaction conduit  71  that comprises an upper end  72 , a lower end  73  and a middle section  74  between the upper end  72  and the lower end  73 . The reaction conduit  71  is constructed at the upper end  72  and at the lower end  73  in the form of a circular, cylindrical tube and in the middle section  74  in an annular, tubular form. In the middle section  74 , the annular, tubular reaction conduit  71  is limited by an inner tubular boundary wall  76  and an outer tubular boundary wall  75  with circular cross sections. The two tubular boundary walls  75 - 76  with circular cross sections are concentrically arranged relative to one another. In the transition areas  77 - 78  between the upper end  72  and the middle section  74  and between the lower end  73  and the middle section  74  the reaction conduit  71  is constructed in a conical manner. 
         [0045]    In the middle section, a pore burner arrangement  80  is arranged in direct contact with the inner and the outer boundary walls  75 - 76  such that a first and a second outer pore burner element  82 ,  83  comprise a first and a second inner pore burner element  84 - 85 . The first outer and the first inner pore burner element  82 ,  84  and the second outer and the second inner pore burner element  83 ,  85  are associated with each other and enclose the annular, tubular middle section  74  of the reaction conduit  71  in a sandwich-like manner. The two outer pore burner elements  82 - 83  have the form of a hollow cylinder that is open on the top and on the bottom, with a specific wall thickness and circular cross section. The two inner pore burner elements  84 - 85  are constructed as a solid cylinder with circular cross section. Alternatively, even the two inner pore burner elements  84 - 85  can be constructed as cylindrical hollow bodies (not shown). The two inner and outer pore burner elements  84 - 85  and  82 - 83  are arranged at a distance from each other on the middle section  74  of the reaction conduit  71 . 
         [0046]    The two outer pore burner elements  82 - 83  are connected as described in the second or the third embodiment to a fuel inlet and to a fuel outlet (not shown). As  FIG. 6  shows, the first and the second inner pore burner elements  84 - 85  are connected to a fuel inlet  90  that extends through the middle section  74  of the reaction conduit  71  in the area between the first and the second pore burner elements. A fuel outlet  92  also runs to the outside from this area. 
         [0047]    In the fourth embodiment, a uniform distribution of temperature and thermal energy is achieved in the interior of the reaction conduit  71  using the inner and the outer pore burner element with the annular, tubular reaction conduit between them. At the same time, more thermal energy can be transferred from the four pore burner elements  82 ,  83 ,  84 ,  85  to the reaction conduit  71  on account of the greater contact area between the four burner elements  82 ,  83 ,  84 ,  85  and the middle section  74  of the reaction conduit  71 . 
         [0048]    Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.