Abstract:
An apparatus for the catalytic reaction of gaseous hydrocarbons into synthesis gas by means of oxygen is disclosed. In order to improve the apparatus it is provided for the catalyst chamber containing the gas and the catalyst particle to be separated from the oxygen chamber containing the oxygen by a gas-permeable wall.

Description:
[0001]    The invention relates to a catalytic method for producing synthesis gas from gaseous hydrocarbons, in particular natural gas, by means of oxygen-containing gases, wherein the chamber containing the catalyst is separated from the chamber containing the oxygen by a gas-permeable wall. Further, the invention relates to an apparatus for carrying out the method. 
       PRIOR ART 
       [0002]    Reformers for the catalytic reformation of natural gas as well as corresponding methods have been known for a long time. It is necessary in this respect to distinguish in particular between commercial-scale reformers and reformers for the decentralised provision of small amounts of synthesis gas, in particular for operating decentralised fuel cells. The latter do not constitute commercial-scale systems. Rather, these are small, compact systems which are in some cases mobile. Therefore, and because they are operated together with expensive devices such as fuel cells, which place high demands on the purity of the produced synthesis gas, partially rather complex designs are required for such reformers. 
         [0003]    In the case of commercial-scale reformers that produce for example more than 100 m 3  synthesis gas per hour, due to the size of such systems and the very high throughput, only simple systems are contemplated not least for cost reasons, which can therefore also be produced and operated at low costs. Therefore, the present invention relates in particular to commercial-scale reformers. 
         [0004]    Allothermal reformers for reforming gaseous hydrocarbons on a commercial scale typically have a fixed bed of catalyst pellets, through which hydrocarbons and steam flow. The steam and the hydrocarbons react with each other on the catalyst pellets under formation of synthesis gas. The allothermal reformation of gaseous hydrocarbons constitutes an endothermal process, to which heat has to be supplied. The heating of the tubular catalyst chambers takes place from the outside through air powered gas burners, wherein the heat exchange of the flue gases takes place via the walls of the tubes onto the resting catalyst particles in the tubes. The tubes of typically 100 mm diameter are designed for an internal pressure of 25 bars to 50 bars. The poor heat transfer on the outside and the inside results in large reaction chambers. This is a considerable disadvantage. In addition, due to the high temperatures on the burners, large amounts of air pollutants are formed. 
         [0005]    An autothermal reaction of gaseous hydrocarbons with pure oxygen usually takes place on catalyst-coated ceramic honeycomb bodies. The reaction takes place here very quickly, which results in temperatures that can hardly be controllable and that cannot be withstood by cheap nickel-based catalysts. 
       OBJECT OF THE INVENTION 
       [0006]    The invention is therefore based on the object of developing and implementing a method and an apparatus of the respectively mentioned type in such a way that the disadvantages described are avoided. 
         [0007]    The object is achieved by means of a burnerless apparatus, which can be operated in an allothermal and an autothermal manner, and a method according to the preambles of claims  1  and  12 . Claims  2  to  11  and  3  to  17  relate to further advantageous embodiments of the invention. 
       DESCRIPTION 
       [0008]    The steam reformation of natural gas into synthesis gas is an endothermal process. In the method according to the invention, the endothermal energy is carried out by a partial oxidation of the fuel gas with oxygen. Fuel gas is to be understood to mean natural gas, synthesis gas or intermediate stages which are formed during the process. The term oxygen also includes oxygen-containing gases such as air. 
         [0009]    The apparatus according to the invention consists of a reactor that is divided into an oxygen chamber and a catalyst chamber by gas-permeable walls. The gas-permeable walls are preferably formed as tubes. 
         [0010]    The pressure differential can now be adjusted in such a way that the fuel gas flows into the oxygen chamber and is combusted directly on the tubes. In this way, an allothermal process is achieved. 
         [0011]    If the pressure differential is adjusted in such a way that the oxygen flows into the catalyst chamber, the fuel gas will be at least partially oxidised directly on the tubes. In this way, an autothermal process with an enhanced CO2 content in the synthesis gas is achieved. 
         [0012]    All kinds of gas-permeable tubes can be used which are able to withstand the usual temperatures of 500° C. to 1100° C., i.e. metal tubes with small holes, tubes formed from metal sheet plates having internal supports, sintered tubes made from metal or ceramics and fibre material tubes. Ceramic tubes should, due to the risk of breaking, preferably be made from short cylinder sections which are centred from the inside and pre-tensioned using a metal structure. The openings and pores should be smaller than the catalyst particles. What is of advantage is a structure having a large pore space on the tube wall where oxygen and fuel gas meet, and a less gas-permeable structure on the other side of the tube wall. Such a structure may also be provided by means of concentric tubes. The less gas-permeable structure is primarily used for metering gas through a pressure differential, a coarser structure with a higher proportion of pores is used for achieving better oxidation and better heat transfer onto the tube. 
         [0013]    Ceramic tubes have a high compressive strength. Therefore, a higher pressure should preferably be applied to these tubes on the outside, but not on the inside. What is of advantage in this sense is if the tubes have a small diameter. 
         [0014]    Oxidation takes place directly on or in the tube wall. Due to the short distance between the oxidation zone and the tube wall, the heat is directly transferred by heat conduction. Therefore, the heat input is by several orders of magnitude higher than the heat transfer of hot flue gases onto a tube wall. This means that the method according to the invention acts as though the tubes were directly electrically heated. Thus, the good heat transfer from a fluidised bed to a tube can be fully utilised, as a result of which a very high power density is achieved in the reactor. 
         [0015]    The catalyst chamber may be located both in the tubes and around the tubes. The gas velocity and the size of the catalyst particles can be selected in such a way that the catalyst particles form a fixed bed or a stationary fluidised bed or are partially kept mainly in suspension. In this case it is particularly advantageous if the catalyst particles are separated at the top end of the catalyst chamber by means of a separation device and flow back into the catalyst chamber. 
         [0016]    As a result of the use of the separation device, the space between the top side of the fluidised bed and the outlet can be designed to be smaller, because any catalyst particles that overspill are separated by the separation device and are returned. 
         [0017]    The separation device may be formed from devices which utilise gravity, utilise centrifugal force or act as filters. Separation devices operating on the basis of gravity are for example lamella separators which are made from metal sheet and have oblique passageways which are inclined towards the vertical. The metal sheets preferably have a corrugated or honeycomb structure, so that the catalyst particles in the grooves can flow back more easily into the catalyst chamber. The lamella separators may also be formed from ceramics, as is customary in the case of exhaust gas or flue gas catalysts. Lamella separators are particularly suitable on account of their low design profile and their gentle separation. Lamella separators also allow a gentle classification. Thus, carbon particles and soot that may form during the process can pass through the lamella separator, whereas the larger and heavier catalyst particles are returned back into the catalyst chamber. Therefore, gravity-based lamella separators are particularly preferred. 
         [0018]    Lamellae are also known as cyclone type separators. These have a curved shape and the flow through them is preferably horizontal. As a result of the curved shape, the catalyst particles collect on the walls and are thus separated. 
         [0019]    One popular type of centrifugal separators are cyclones. They may be installed both inside and outside of the reactor. 
         [0020]    Another very effective type of separator device are filter elements such as for example cartridge filters. By shaking or as a result of short pressure pulses from the pure gas side, the catalyst particles can be returned back into the catalyst chamber. 
         [0021]    The apparatus according to the invention is not only suitable for reformers that are operated at a typical temperature of 850° C., but also for pre-reformers which are operated at significantly lower temperatures. 
     
    
     
       EXAMPLES 
         [0022]    The invention will be described below by way of example with reference to  FIGS. 1 to 14 . 
           [0023]      FIG. 1  shows an allothermal reactor with a stationary fluidised bed. 
           [0024]      FIG. 2  shows an allothermal reactor with a stationary fluidised bed and a separation device. 
           [0025]      FIG. 3  shows an allothermal reactor with a circulating fluidised bed and a separation device. 
           [0026]      FIG. 4  shows a lateral view of a lamella separator. 
           [0027]      FIG. 5  and  FIG. 6  show a cross-sectional view of a lamella separator. 
           [0028]      FIG. 7  shows an autothermal reactor with a stationary fluidised bed. 
           [0029]      FIG. 8  shows an autothermal reactor with a stationary fluidised bed and a separation device. 
           [0030]      FIG. 9  shows an autothermal reactor with a highly fluidised bed and a separation device. 
           [0031]      FIG. 10  shows an allothermal reactor with a fixed bed. 
           [0032]      FIG. 11  shows a section of a fixed bed in the tube in an allothermal operating mode. 
           [0033]      FIG. 12  shows a multi-layered porous tube with fine pores on the inside and coarse pores on the outside. 
           [0034]      FIG. 13  shows a detail of  FIG. 12 . 
           [0035]      FIG. 14  shows an arrangement of porous tubes with an external oxygen chamber. 
           [0036]      FIG. 15  shows a tube cross section wherein the surface area of the tube wall is enlarged by a rib structure in the oxygen chamber. 
           [0037]      FIG. 16  shows a tube cross section, wherein the surface area of the tube wall to the oxygen chamber is enlarged by an increased porosity. 
           [0038]      FIG. 17  shows an arrangement of porous tubes with an internal oxygen chamber. 
       
    
    
       [0039]      FIG. 1  shows an allothermal reactor  1 , wherein the catalyst chamber  6  is formed as a stationary fluidised bed  6   a.  The reactor  1  further includes a gas chamber  7  above the fluidised bed. In the catalyst chamber  6 , a plurality of porous tubes  11  is provided, which form the oxygen chamber  4   a.  Oxygen  4  flows through the tube bottom  9  into the porous tubes  11  and exits the reactor  1  through the tube bottom  10  as flue gas  5  which substantially consists of CO2, O2, H2O and, if necessary, N2. The tube feed lines  12  and  13  outside of the fluidised bed  6   a  are not porous. The connection to the porous tubes  11  may be implemented as a plug-in connection with a labyrinth seal, because absolute density is not critical. The raw gas  2  to be reformed is introduced between the tube bottom  9  and the nozzle bottom  8  and exits the reactor  1  as synthesis gas  3 . The pressure difference between the catalyst chamber  6  and the oxygen chamber  4   a  will now be adjusted in such a way that part of the fuel gas  21  flows into the oxygen chamber  4   a,  namely just enough so that the energy needed for this endothermal process is provided. In a fluidised bed, the fuel gas  21  largely corresponds to the synthesis gas  3  at the outlet of the reactor  1 . Further details with regard to the porous tubes  11  will be described further below with reference to  FIGS. 15 to 17 .  FIG. 2  largely corresponds to  FIG. 1 . Instead of a tube bottom, however, the porous tubes  1  are here combined using manifolds  14 . The flue gas  5  is discharged via the conduit  13 . As a new element, a separation device  15  in the form of lamellae is provided above the stationary fluidised bed  6   a.  Any discharged catalyst particles are returned back into the free chamber  7  by the separation device  15 . This is symbolically indicated by falling catalyst particles  18 . 
         [0040]      FIG. 3  largely corresponds to  FIG. 2 . The difference consists here in the fact that the catalyst particles  18  are so small and the rate of fluidisation is so high that no detectable upper limit of the fluidised bed is formed. In this process, the catalyst particles  18  are partially kept suspended and any overshooting catalyst particles  18  are separated by the separation device  15  and are returned into the reactor  1 . Due to their small impulse, the small catalyst particles  18  experience only very minor mechanical stress. Therefore, the usual ceramic protective shell around the catalyst particles  18  may be dispensed with. Because of this and because of the small dimensions, the diffusion distances to the active centres of the catalysts are very short. This considerably reduces the required amount of catalyst. 
         [0041]      FIGS. 4 to 6  show details of a separation device  15 . The separation device  15  is here formed as a lamella separator, wherein the catalyst particles  18  are separated by way of gravity. 
         [0042]      FIG. 4  shows a vertical section through such a lamella separator. It consists of a plurality of sheets  16  that are positioned at an angle. As indicated by arrows  17 , the synthesis gas  3  flows through these narrow passageways. In the process, any entrained catalyst particles  18  will descend down to the bottom and will slide back into the reactor  1 .  FIG. 5  and  FIG. 6  show a view in the direction of the axis of the passageway of a lamella separator. It is particularly advantageous to form the sheets  16  in such a way that the catalyst particles  18  can collect in grooves  18 , where the flow velocity of the gas is lower than at the centre and therefore the return transfer of the catalyst particles  18  is facilitated. 
         [0043]      FIG. 7  shows an autothermal reactor  1  which is of a design similar to that of the reactor in  FIG. 1 . The difference is that the pressure difference between the oxygen chamber  4   a  and the catalyst chamber  6  is selected such that the oxygen  4  flows into the catalyst chamber  6 . The catalyst chamber  6  is here formed as a stationary fluidised bed  6   a.  The oxidation of the fuel gases  21  is carried out directly on the outer wall of the porous tubes  11 . In a fluidised bed, the fuel gas  21  largely corresponds to the synthesis gas  3 . As a result of the large surface area of the porous tubes  11  and the high turbulences in fluidised bed reactors it is ensured that the catalyst particles  18  will not overheat. 
         [0044]      FIGS. 8 and 9  respectively show an autothermal reactor  1  with a stationary fluidised bed  6   a  and a highly fluidised bed  6   b,  wherein the catalyst particles are at least partially kept in suspension. As in  FIG. 7 , here too the oxygen  4  flows from the oxygen chamber  4   a  into the catalyst chamber  6 . As in  FIGS. 2 and 3 , separation devices  15  are provided in the top part of the reactor  1  in  FIGS. 8 and 9 . 
         [0045]      FIG. 10  shows an allothermal reactor  1 , wherein the catalyst chamber  6  is formed as a fixed bed  6   c.  The catalyst particles  18  are here located in the catalyst chamber  6  in the porous tubes  11 . The oxygen chamber  4   a  is arranged around the tubes. The pressure difference is here adjusted such that the fuel gas  21  flows from the catalyst chamber  6  into the oxygen chamber  4   a.  The porous tubes  11  are prevented from falling out by a screen at the tube bottom  19 . At the top end, the porous tubes are surrounded by a gas-impermeable head tube  13  that is fastened in the head plate  20 . The raw gas  2  flows from the bottom into the reactor  1  and exits the reactor  1  as synthesis gas  3 . Oxygen  4  is introduced into the oxygen chamber  4   a  and exits the reactor  1  as flue gas  5 . The strength of the energy input along the longitudinal axis may be adjusted by means of a different gas resistance of the porous tubes  11  along the axis thereof. This advantage is absent when solid tubes are heated with flue gases. 
         [0046]      FIG. 11  shows the cross section of the porous tube  11  from  FIG. 10 . Flue gas  21  flows from the catalyst chamber  6  outwards into the oxygen chamber  4   a.  On the outer wall of the porous tube  11 , the flue gas  21  will now be oxidised by the oxygen  4 . The flue gas  5  mixes here with the oxygen. As is the case with all combustion processes, it is advantageous to work with a small amount of excess oxygen. For the sake of heat transfer it is advantageous if the porous tube  11  has a higher porosity in the oxidation zone. 
         [0047]    This principle is schematically shown in  FIGS. 12 and 13 . The different porosity is here achieved by fitting a fine-pored tube  11   a  and a coarse-pored tube  11   b  into each other.  FIG. 13  shows an enlarged section from  FIG. 12 . The flue gas  21  flowing out meets with the oxygen  4  as early as in the pore chamber  11   b  and oxidises the fuel gas into flue gas  5 . In this way, relationships similar to the ones in a pore burner are established. In this way, the heat is well transferred onto the tube and is transported to the inner wall by heat conduction. In this way, the hot tube  11   a  heats the catalyst chamber  6 . 
         [0048]      FIG. 14  shows a cross-sectional view of the arrangement of  FIG. 10 . Of course, the reactor can also be operated in such a way that the catalyst chamber  6  is arranged around the tubes  11  and the oxygen chamber  4   a  is disposed in the tubes  11 . In this case, the oxidation zone would be on the inner wall of the tubes  11 . The porosities of the tubes  11   a  and  11   b  would then have to be correspondingly swapped around. 
         [0049]      FIGS. 15 to 17  show such a case. In  FIG. 16 , the oxygen chamber  4   a  and therefore the oxidation zone are located in the porous tubes  11 . The coarser structure  11   b  is located on the inside and the finer metering structure  11   a  is located on the outside. The fuel gas  21  flows from the catalyst chamber  6 , which is arranged around the tubes, into the inside of the tube and is there oxidised directly on the inner wall or in the inner wall. Instead of a coarser structure  11   b  in  FIG. 16 , the coarser structure can also be supported by way of shaping. Such a case is illustrated by the rib structure in  FIG. 15 . A larger oxidation surface has here been provided by a rib structure on the tube  11   b.  In order to enhance turbulence, the grooves may also be arranged to be helical. In order to improve heat transfer to the catalyst particles  18 , a rib structure may be provided inside and outside on the tube wall  11 . 
         [0050]      FIG. 17  shows a reactor cross section wherein the catalyst chamber  6  is provided around the porous tubes  11 . The catalyst chamber may be designed as a stationary fluidised bed  6   a,  as a circulating fluidised bed  6   b  or as a fixed bed  6   c.    
       ADVANTAGES 
       [0051]    Oxidation in the pore chamber of the tube wall allows a heat transfer that is improved by orders of magnitude compared to the heat transfer from flue gases to a tube wall. This allows a small reactor volume with high performance also in the case of an allothermal operating mode. Moreover, the catalyst chamber may be formed as a fluidised bed, which improves heat transfer onto the catalyst particles and ensures an even temperature distribution in the catalyst bed. In the case of an autothermal operating mode with pure oxygen, the operating conditions with regard to temperature, dwell time, catalyst size, catalyst type and arrangement may be adjusted in a specific manner, because the oxygen no longer impacts directly on the catalyst particles. The oxidation in the porous structure of the tubes is similar to that of a pore burner, wherein the temperatures are also significantly lower than in a free flame. Moreover, the temperature difference between the combustion chamber in the pores and the catalyst particles is much smaller. As a result, fewer pollutants will be formed. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  Reactor 
           2  Raw gas 
           3  Synthesis gas 
           4  Oxygen 
           4   a  Oxygen chamber 
           5  Flue gas 
           6  Catalyst chamber 
           6   a  Stationary fluidised bed 
           6   b  Circulating fluidised bed 
           6   c  Fixed bed 
           7  Free chamber 
           8  Nozzle bottom 
           9  Tube bottom upper end 
           10  Tube bottom lower end 
           11  Gas-permeable wall in the form of a porous tube wall 
           11   a  Metering tube, fine-pored wall 
           11   b  Pore combustion chamber, coarse-pored wall 
           12  Bottom tube 
           13  Head tube 
           14  Manifolds 
           15  Separation device 
           16  Lamellae 
           17  Gas flow 
           18  Catalyst particles 
           19  Bottom plate 
           20  Head plate 
           21  Fuel gas