Process and apparatus for catalytically reacting a reducing gas and water vapor
This is a continuation, of application Ser. No. 895,464, filed Apr. 11, 1978 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a process and apparatus for catalytically reacting a gas containing a reducing component or components with water vapor in a pressure reactor of the type including an external pressure resistant container as well as an inner container containing a volume of catalyst. 
     Processes and apparatuses of the above type are known and are frequently employed for CO-methanization reactions and for CO-conversion reactions, as well as for reactions employing water vapor and other gases containing reducing components. Temperatures involved in such reactions are normally in the range of from approximately 623° K. to 723° K. (i.e. from 350° C. to 450° C.). The pressures involved in such reactions normally amount to approximately between 10 and 100 bar. Under such reaction conditions, i.e. quite high temperatures and pressures, the reducing components of the gases involved, for example carbon monoxide and hydrogen, may readily attack and penetrate the wall of the pressure resistant container, if such container is made of simple steel material, thereby leading to brittleness of the material and substantial premature corrosion damage. 
     Previous attempts to avoid such corrosion damage have involved the use of special alloy steels, particularly of the so-called pressure and hydrogen resistant type steels. Such special alloys steels are capable of withstanding the above described stresses. However, such special alloy steels involve certain inherent disadvantages which have prevented them from achieving widespread use. Specifically, such special alloy steels are extremely difficult to work. Additionally, such special alloy steels are extremely expensive, and this is an important disadvantage when considering the substantial size of the reactors involved. 
     Accordingly, most prior art reactors of this type have not employed such special alloy steels, but rather have employed simple steels, thereby resulting in substantial installation and repair costs due to premature corrosion damage. 
     German DT-OS 24 27 530 discloses a methanization reactor wherein the wall of the pressure container is shielded against the high exothermic temperatures that occur during the methanization reaction by means of an inner container containing at least a portion of the volume of the catalyst. The inner container is arranged within the pressure container with an intermediate space therebetween. The gas mixture to be reacted, consisting predominantly of methane and additionally containing carbon monoxide, carbon dioxide, hydrogen and water vapor required for the methanization reaction, is led through an inlet into the intermediate space around the inner container, and thus comes directly into contact with the wall of the outer pressure container. The gas then flows radially inwardly through the catalyst. It will be apparent that this type of reactor is associated with the above discussed disadvantages, namely that the reducing components of the gas are allowed to react on the wall of the pressure container. Therefore, this prior art device is still subject to the above discussed high cost of manufacture or to the danger of premature corrosion damage. 
     Austrian Pat. No. 215436 discloses a reactor having in the interior thereof plural intermediate limited spaces. The gas is divided into a number of partial flows and supplied to these intermediate spaces. One such gas flow cools the wall of the pressure container from the inside thereof. However, such partial flow is of the reaction gas itself and therefore includes reducing components. Accordingly, the wall of the pressure container is still subjected to the action of such reducing components, and accordingly this prior art device is also subject to the above discussed disadvantages. 
     SUMMARY OF THE INVENTION 
     With the above discussion in mind, it is the primary object of the present invention to provide a process and apparatus for catalytically reacting a gas containing reducing components with water vapor, wherein the pressure container may be formed of simple steel, while avoiding premature corrosion damage to the pressure container, thereby ensuring a more economical manufacture and operation of the pressure reactor than has heretofore been possible. 
     This object is achieved in accordance with the present invention by providing an outer pressure container formed of simple steel material, and an inner container also formed of simple steel material and containing the catalyst volume. The inner container is inwardly spaced from the outer pressure container to provide an intermediate space therebetween. The inner container is enclosed and the interior thereof is isolated from the intermediate space. The water vapor and the gas containing the reducing component or components are introduced into the inner container in a specific manner. More particularly, the gas containing the reducing components is introduced only to the inner container and is never introduced into the intermediate space. However, at least a portion of the water vapor is initially introduced into the intermediate space and is maintained at a pressure substantially equal to the pressure within the interior of the inner container. Thus, the inner container, although formed of simple steel and subjected to the reducing components, is not subjected to a unilateral high pressure. Rather, the pressures on both sides of the inner container are substantially equal. Furthermore, the water vapor passing through the intermediate space operates to protect the wall of the pressure container from the high temperatures occurring during the catalytic reaction within the inner container. The water vapor passes from the intermediate space, and then at least a portion of such water vapor is added to the gas containing the reducing components before the introduction thereof into the inner container. 
     Accordingly, although the pressure container is unavoidably subjected to a high pressure, the pressure container is protected against extremely high temperatures, and further the pressure container is never subjected to the reducing components. Thus, it is not necessary to employ expensive special alloy steels for the pressure container. Further, although the inner container is unavoidably subjected to the reducing components, the pressures on opposite sides of the container are substantially equal. Therefore, the inner container is less subject to corrosion which would otherwise occur at unilateral high pressures, and it is also unnecessary to form the inner container of expensive special alloy steels. 
     The passage of the water vapor through the intermediate space protects the wall of the pressure container against high temperature peaks which may occur in the catalyst within the inner container. Such high temperature peaks are prevented from affecting the pressure container by the continuous removal of heat from the intermediate space by the passage therethrough of water vapor. This avoids irregular thermal absorption by the pressure container and consequent irregular thermal expansion and differential stressing of the wall of the pressure container. 
     Additionally, during start-up of the reactor of the invention, the wall of the pressure container can be warmed up with pure water vapor passing through the intermediate space, prior to the introduction of the mixture of water vapor and gas containing reducing components into the reaction chamber of the inner container. Thus, any condensates which are formed in the intermediate space during the start-up operation do not contain harmful gas components, for example carbon monoxide, which would lead to corrosion. Further, any such condensates can be readily removed from the intermediate space before the commencing of normal operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other objects, features and advantages of the present invention will be apparent from the following detailed description thereof with reference to the accompanying drawing, wherein: 
     The single FIGURE is a schematic view of one embodiment of a pressure reactor in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description will generally be made with reference to a CO-conversion reaction, wherein an input gas contains carbon monoxide as a reducing component to be reacted with water vapor on a catalyst into hydrogen and carbon dioxide. It is specifically to be understood however that the scope of the present invention is not intended to be limited to such specific conversion reaction. Rather, the scope of the present invention is intended to encompass CO-methanization reactions, as well as any other conventional and known catalytic reactions involving the use of water vapor and a gas containing a reducing component. 
     It is further to be understood that the present invention is not directed to the specific catalysts employed, the specific gases employed, or to the specific temperatures and pressures involved. Rather, the present invention is directed to the novel process and apparatus described hereinbelow and intended to be employed in any otherwise conventional catalytic reaction employing known catalysts, known gases containing reducing components, and at temperatures and pressures which are conventional and known for such reactions. 
     In the drawing there is shown a pressure resistant pressure container 1 having positioned therein a closed inner container 2 containing therein a catalyst volume. Inner container 2 is inwardly spaced from pressure container 1 to define therebetween an intermediate space 5. In the illustrated embodiment there are shown three vertically separated catalyst layers 4, each supported on a catalyst support 3. It is specifically to be understood however that the present invention is not intended to be limited by the specific manner of location and placement of the catalyst. More particularly, the present invention may employ a greater lesser number of catalyst layers. Further, as stated above, the present invention is not intended to be limited to any specific catalyst. Catalysts employed in catalytic reactions of this type may be any known such catalysts, generally containing contact materials of iron mixtures. 
     Intermediate space 5 is isolated from the interior of inner container 2. A water vapor feed or inlet 6 opens into the intermediate space 5, preferably near the bottom portion thereof. A water vapor outlet 7 extends from intermediate space 5, preferably at the upper head portion thereof. An inlet 8 for supplying water vapor and a gas containing a reducing component or components extends through pressure container 1 and intermediate space 5 and opens into the interior of inner container 2. Inlet 8 does not open into intermediate space 5. A reaction product gas outlet 9 extends from the interior of inner container 2 through intermediate space 5 and pressure container 1. Outlet 9 does not communicate with intermediate space 5. An outlet 10 extends from the bottom of intermediate space 5 to remove therefrom condensates which may be formed during the start-up of the reactor. It will be understood that during normal operation of the reactor, condensate outlet 10 is closed. 
     One or a plurality of cooling devices 11 may extend through pressure container 1 and open into intermediate space 5. Such cooling devices are connected to a source of cooling fluid, for example water (not shown) and may include injection nozzles for injecting a cooling fluid into intermediate space 5 to cool the water vapor passing therethrough. In the illustrated embodiment, two such cooling devices 11 are shown, one each located in the general vicinity of the lower portion of the two upper catalyst beds, i.e. areas likely to be subjected to high temperature peaks. It is to be understood however that fewer or more cooling devices 11 could be provided. 
     Additionally, to control the heat within the reaction chamber of the inner container 2, i.e. the heat of reaction, indirect heat exchanger cooling devices 12 may be provided between adjacent layers of catalyst 4. Such cooling devices 12 may be connected through cooling inlet and cooling outlet pipes 13 and 14, respectively, to a conventional cooling system (not shown). 
     In order to obtain the smallest possible temperature variation of the wall of the pressure container during normal operation, and to thereby avoid to the greatest extent possible the condensation of the water vapor in intermediate space 5, the exterior of pressure container 1 may be covered by a relatively thick layer of conventional insulating material 15. 
     Water vapor outlet 7 which extends from the head portion of intermediate space 5 is connected via a valve 16 to gas inlet 8, at a position thereof exterior of the pressure container. Thus, valve 16 may be employed to regulate the amount of water vapor fed from intermediate space 5 to be mixed with the gas flow, dependent upon the requirements of the particular reaction involved. To remove any excess quantity of water vapor not necessary for the particular reaction involved, a return pipe 17 is connected to outlet 7 at a position upstream of valve 16. Return pipe 17 may lead back to inlet 6 or to a conventional steam generator. Return pipe 17 includes a valve 18 which may be employed to shut off entirely or to regulate the amount of flow through return pipe 17. 
     In the event that the quantity of steam passing through intermediate space 5 and joining gas inlet 8 via outlet 7 is insufficient for the requirements of the particular reaction involved, additional water vapor may be supplied to the gas inlet 8 via a water vapor bypass pipe 19. Bypass pipe 19 branches from inlet 6 and extends outwardly of pressure container 1 to join gas inlet 8 in the area of the head of the reactor. Bypass pipe 19 may be provided with a valve 20 to regulate the amount of additional water vapor required for the particular reaction involved. 
     The water vapor is preferably supplied superheated from an external steam generator through inlet 6 at a pressure of from approximately 16 to 101 bar and at a temperature of approximately from 500° to 700° K., during normal operation of the reactor. The pressure of the gas flow in gas inlet 8 is approximately the same as that of the water vapor within intermediate space 5, but preferably may be slightly lower, for example one bar lower, i.e. from between approximately 15 and 100 bar. However, the temperature of the gas flow through gas inlet 8 into inner container 2 is advantageously approximately 30° K. higher than the temperature of the water vapor, in order to attain the required ignition temperature when flowing through the catalyst. The exothermal heat generated by the mixture of gas and steam on the catalyst layers is controlled and throttled by means of cooling devices 12, so that a maximum temperature, for example 750° K. is not exceeded in the catalyst beds. 
     Although it is believed that the process of the present invention will be readily apparent from the above description, such process will become even further apparent from the following example. 
     EXAMPLE 
     During the start-up of the reactor, pure water vapor at a temperature of 623° K. and a low pressure of two bar is first fed through inlet 6 into intermediate space 5, for the purpose of warming up the wall of the pressure container 1. Steam condensate formed during such warm-up operation is removed through condensate outlet 10. Only after the pressure container 1 is satisfactorily warmed up, is the water vapor from outlet 7 passed into gas inlet 8 and is the gas containing reducing components supplied through gas inlet 8 into the interior of inner container 2. The gas fed through inlet 8 has a composition of approximately 29% by volume CO, 40% by volume H 2 , 4% by volume CO 2 , and 27% by volume CH 4 . Such gas is supplied at a temperature of 653° K., and its pressure is intially temporarily just as low as that of the water vapor, i.e. approximately two bar. The gas, together with the admixed water vapor from outlet 7, directly enters inner container 2 and is therein serially reacted in the three catalyst layers 4. The pressure of the water vapor within intermediate space 5 and the mixture of water vapor and gas within the interior of inner container 2 are then slowly raised to the desired higher normal operational pressure level, for example to at least fifteen bar. 
     The heat generated during the catalytic reaction is removed and controlled by cooling devices 12 such that the temperature on the first or upper catalyst layer is maintained at approximately 723° K., at the second or central catalyst layer at approximately 703° K., and the third or lower catalyst layer at approximately 693° K. The water vapor flowing through the intermediate space 5 also operates to protect the wall of pressure container 1 from the high temperature generated within inner container 2. Additionally, injection of a cooling fluid such as water through cooling devices 11 into intermediate space 5 may additionally cool the water vapor, for example when substantial temperature peaks are generated in the catalyst beds which would otherwise superheat the steam to an undesirable extent. 
     The gaseous reaction products are removed from the reactor at an outlet temperature of 693° K. through outlet 9. 
     It is to be understood, as discussed above, that the present invention is suitable not only for CO-conversion reactions, but also for CO-methanization reactions, as well as for other reactions involving water vapor and a gas containing reducing components. The specific amount of water vapor required for each particular reaction, as well as the specific amounts of water vapor passed through intermediate space 5 in a given reactor may be readily regulated by suitable adjustment of valves 16, 18 and 20. To the gas flow in gas inlet 8, it is possible to admix as required the entire amount of water vapor flowing through intermediate space 5, or a portion thereof, with valve 20 closed, or when valve 20 is opened, it is possible to additionally admix an additional amount of water vapor required for the particular reaction involved. 
     Since the inner wall of the pressure container is subjected throughout the entire operation only to water vapor at a determinable pressure and at a constantly equalized temperature, the wall of the pressure container may be maintained free of chemical or physical corrosions which are inherent in prior art devices. Further, since the pressures on opposite sides of inner container 2 are equalized, it is also possible to reduce the danger of corrosion of the inner container. Accordingly, both the inner container and the pressure container may be formed of relatively inexpensive materials, and additionally the expense of maintaining the reactor will be substantially reduced. 
     It will be apparent that various modifications may be made to the specifically described and illustrated structural arrangements and process steps without departing from the scope of the present invention.