Patent Publication Number: US-6982060-B2

Title: Chemical decontamination liquid decomposing system having catalyst tower and catalyst tower therefor

Description:
This is a continuation application of U.S. Ser. No. 09/791,693, filed on Feb. 26, 2001 now U.S. Pat. No. 6,767,519. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a catalyst tower and a chemical decontamination liquid decomposing system having the catalyst tower. 
     2. Description of the Prior Art 
       FIG. 6  is a view showing the structure of an example of a conventional catalyst tower. In this catalyst tower, a chemical decontamination liquid flowing out of an inlet pipe  11  is turned upward and distributed in a lower chamber  12 , and after that, flows through an inlet mesh filter  13 , and flows upward in a catalyst  14 , and then flows through an outlet mesh filter  15  to be discharged through an outlet pipe  16 . When the catalyst is charged in a catalyst tower container  18 , the catalyst is charged by removing a catalyst tower upper lid  17  and the outlet mesh filter  15 . Further, in order to prevent the catalyst from occurring convection inside the catalyst tower container  18  due to a gas produced by decomposition reaction of the chemical decontamination liquid, the outlet mesh filter  15  is constructed so as to push down the catalyst using springs  21 . Therefore, the outlet mesh filter  15  needs to have a detachable and movable structure. 
     In order to made the structure of the outlet mesh filter  15  detachable and movable, it is necessary that gaps are provided both in a portion between the outer periphery of the outlet mesh filter  15  and the inner peripheral wall of the catalyst tower container  18 , and in a penetration portion of the inlet pipe  11  of the outlet mesh filter  15 . The gaps need to be made as small as possible from the viewpoint of preventing the catalyst from flowing out. Although the penetration portion of the inlet pipe  11  of the outlet mesh filter  15  can be eliminated by making the inlet pipe  11  so as to penetrate the side wall portion of the catalyst tower container  18 , it is uneconomical because the height of the catalyst tower container  18  is increased and accordingly a shielding container for containing the catalyst tower  5  becomes larger. Further, another method of narrowing the gaps considered is that O-rings are provided in the outer periphery of the outlet mesh filter  15  and in a penetration portion of the inlet pipe  11 , but in that case, the movability of the outer mesh filter  15  is decreased to deteriorate the function of pushing down the catalyst. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a chemical decontamination liquid decomposing system having a catalyst tower which has a mesh filter capable of certainly preventing catalyst from flowing out and a mechanism of pushing-down the catalyst capable of preventing convection of the catalyst caused by decomposition gas. 
     One of embodiment to attain the above object is a catalyst tower which comprises an outlet mesh filter arranged between a catalyst for decomposing the chemical decontamination liquid and an outlet pipe for making the chemical decontamination liquid flow out of the catalyst tower; and a catalyst charging port for charging said catalyst, and the outlet mesh filter is arranged so as to closely attached to an inner surface of the catalyst tower and to an inner surface of the catalyst charging port; and a catalyst pushing-down mechanism for suppressing convection of the catalyst is arranged inside the catalyst charging port. 
     As a concrete structure, the catalyst charging port  19  is arranged in a catalyst tower upper lid  17 , and the catalyst pushing-down mechanism  20  is arranged inside the catalyst charging port  19 , as shown in  FIG. 1 . Further, the outlet mesh filter  15  has a structure closely attached to the inner wall of the catalyst tower container  18  and to the catalyst charging port  19 . 
     According to this structure, the catalyst can be directly charged into the catalyst tower container  18  through the catalyst charging port  19 , and accordingly there is no need to remove the catalyst tower upper lid  17  and the outlet mesh filter  15 . Further, by arranging the catalyst pushing-down mechanism  20  inside the catalyst charging port  19 , there is no need to form the outlet mesh filter  15  movable. By employing such a structure, there is no need to construct the outlet mesh filter  15  detachable and movable. Therefore, the outlet mesh filter  15  can be formed in the structure of closely attaching to the inner wall of the catalyst tower container  18  and to the catalyst charging port  19 . 
     Consequently, it is possible to certainly prevent the catalyst from flowing out through the outlet mesh filter  15 . Further, since the catalyst  14  can be certainly pushed down by the catalyst pushing-down mechanism  20  arranged inside the catalyst charging port  19 , occurrence of convection of the catalyst caused by the decomposed gas can be prevented. 
     According to the present invention, it is possible to provide a catalyst tower which can prevent the catalyst from flowing out to the system, and can prevent convection of the catalyst caused by the decomposed gas generated in the catalyst tower from occurring, and to provide a chemical decontamination liquid decomposing system having the catalyst tower. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing the structure of an embodiment of a catalyst tower in accordance with the present invention. 
         FIG. 2  is a diagram showing the overall structure of a chemical decontamination liquid decomposing system under decomposing a chemical decontamination liquid. 
         FIG. 3  is a view showing the structure of an embodiment of a catalyst tower in accordance with the present invention. 
         FIG. 4  is a view showing the structure of an embodiment of a catalyst tower in accordance with the present invention. 
         FIG. 5  is a view showing the structure of an embodiment of a catalyst tower in accordance with the present invention. 
         FIG. 6  is a view showing the structure of an example of a conventional catalyst tower. 
         FIG. 7  is a view showing the detailed structure of another embodiment of a catalyst tower in accordance with the present invention. 
         FIG. 8  is a system diagram of Embodiment 5. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments will be described below, referring to  FIG. 1  to  FIG. 8 . Arrow marks shown in each of the figures indicate flow of the chemical decontamination liquid. 
     (Embodiment 1) 
       FIG. 2  is a diagram showing the overall structure of a chemical decontamination liquid decomposing system under decomposing a chemical decontamination liquid. A chemical decontamination liquid flowing out from an object  1  to be decontaminated is pressurized (pumped up) by a pump  2  and flows into an ion-exchange resin column  3  to remove metallic ions in the liquid. The chemical decontamination liquid flowing out of the ion-exchange resin column  3  is heated up by a heater  4 , and added with hydrogen peroxide in order to accelerate decomposition, and then flows into a catalyst tower  5 . The chemical decontamination liquid is decomposed in the catalyst tower  5 , and decomposed gas is discharged and the chemical decontamination liquid is returned to the object  1  to be decontaminated to form a closed loop. 
       FIG. 1  is a view showing the structure of an embodiment of a catalyst tower in accordance with the present invention. The chemical decontamination liquid flows though the inlet pipe  11  of the catalyst tower  5 , and then the flow direction of the chemical decontamination liquid is inversely turned in the lower chamber  12 . At the same time, the flow of the chemical decontamination liquid is distributed inside the lower chamber  12  to pass through the inlet mesh filter  13 . The chemical decontamination liquid passed through the inlet mesh filter  13  is decomposed by chemical reaction while passing between the catalyst  14 . Gas generated by the decomposition passes through the outlet mesh filter  15  together with the chemical decontamination liquid to flow out of the outlet pipe  16 . When the catalyst is charged into the catalyst tower  5 , the catalyst can be directly charged only by removing the catalyst charging port  19  and the catalyst pushing-down mechanism  20 . 
     The outlet mesh filter  15  of the catalyst tower  5  is welded to the inner side wall of the catalyst tower container  18  and to the lower portion of the catalyst charging port  19 . Further, the outlet mesh filter  15  is also welded to the outer side wall of the inlet pipe  11  in the penetration portion of the inlet pipe  11 . Therefore, the outlet mesh filter  15  has such a structure that there is no gap to make the catalyst  14  flow out. Thereby, it is possible to prevent the catalyst  14  from flowing out. 
     Furthermore, the catalyst pushing-down mechanism  20  is arranged inside the catalyst charging port  19  of the catalyst tower  5 . The catalyst pushing-down mechanism  20  is formed by a weight, and the function of pushing-downward the catalyst  14  is performed by pushing the catalyst using the gravitational force of the weight. By doing so, occurrence of convection of the catalyst  14  caused by the decomposed gas can be prevented. As an example of the catalyst pushing-down mechanism  20 , when the catalyst pushing-down mechanism  20  is made of lead and has a thickness of 180 mm, it can push down the catalyst  14  with a pressure approximately 0.02 MPa. 
     (Embodiment 2) 
       FIG. 3  is a view showing the structure of another embodiment of a catalyst tower in accordance with the present invention. In this embodiment, the inlet pipe  11  is arranged in the lower portion of the side surface of the catalyst tower container  18  and directly connected to the lower chamber  12 . In this case, the same effect as that in Embodiment 1 can be obtained. Further, in the embodiment, since the penetration portion of the inlet pipe  11  can be eliminated in the outlet mesh filter  15 , manufacturing ability of the outlet mesh filter  15  can be also improved. 
     (Embodiment 3) 
       FIG. 4  is a view showing the structure of another embodiment of a catalyst tower in accordance with the present invention. In this embodiment, the structure of the outlet mesh filter  15  is formed in a disk shape. In this case, the same effect as that in Embodiment 1 can be obtained. Further, in this embodiment, since the structure of the outlet mesh filter  15  can be simplified, manufacturing ability of the outlet mesh filter  15  can be also improved. 
     (Embodiment 4) 
       FIG. 5  is a view showing the structure of another embodiment of a catalyst tower in accordance with the present invention. In this embodiment, the catalyst pushing-down mechanism  20  placed inside the catalyst charging port  19  is composed of springs  21  and a catalyst pushing-down plate  22 . In this case, the same effect as that in Embodiment 1 can be obtained. Further, in this embodiment, since there is no need to remove a heavy body of the weight by the structure of pushing down the catalyst using the springs  12 , workability of charging the catalyst can be also improved. 
     Although Embodiment 2, Embodiment 3 and Embodiment 4 show modifications of Embodiment 1 in the inlet pipe  11 , the outlet mesh filter  15  and the catalyst pushing-down mechanism  20 , respectively, it is possible to combine these. The key point is that the outlet mesh filter  15  is closely contact to the inner wall of the catalyst tower container  18  and to the catalyst charging port  19 . In addition, the catalyst pushing-down mechanism  20  may be constructed any structure as far as capable of applying a pressing force to the catalyst, and accordingly the catalyst may be pushed down by air pressure or oil hydraulic pressure. 
     (Embodiment 5) 
       FIG. 7  is a view showing the structure of another embodiment of a catalyst tower in accordance with the present invention.  FIG. 8  is a diagram showing the overall structure of an embodiment of a chemical decontamination liquid decomposing system in accordance with the present invention. The embodiment of a chemical decontamination liquid decomposing system has five operation modes of oxidation, oxidizing agent decomposition, reduction, reducing agent decomposition and cleaning. Each of the modes will be described below. 
     Initially the oxidation mode will be described. In this embodiment, potassium permanganate is used as the oxidizing agent. Valves  36 ,  37 ,  38 ,  39 ,  32  and  33  are closed, and valves  53 ,  52 ,  35  and  34  are opened. A chemical decontamination liquid flowing out of an object to be decontaminated  1  is pressurized (pumped up) by a pump  2 , and added with the oxidizing agent from an oxidizing agent injection system  54  to be oxidized. After that, the chemical decontamination liquid is heated up by a heater  4 , and returned to the object to be decontaminated  1 . In this mode, the temperature of the chemical decontamination liquid is gradually increased during recirculating because the liquid is heated by the heater  4 . 
     Next, the oxidizing agent decomposition mode will be described. In this embodiment, oxalic acid is used to decomposing the oxidizing agent. The valves  36 ,  37 ,  38 ,  39 ,  32  and  33  are closed, and the valves  53 ,  52 ,  35  and  34  are opened. The chemical decontamination liquid flowing out of the object to be decontaminated  1  is pressurized (pumped up) by the pump  2 , and added with the reducing agent (oxalic acid) from a reducing agent injection system  55  to reduce the oxidizing agent. After that, the chemical decontamination liquid is heated up by a heater  4 , and returned to the object to be decontaminated  1 . In this mode, the temperature of the chemical decontamination liquid is gradually increased during recirculating because the liquid is heated by the heater  4 . 
     Next, the reduction mode will be described. In this mode, the valves  36 ,  39 ,  32 ,  33 ,  53  and  52  are closed, and the valves  37 ,  38 ,  35  and  34  are opened. The chemical decontamination liquid flowing out of the object to be decontaminated  1  is pressurized (pumped up) by the pump  2 , and added with the reducing agent (oxalic acid) from a reducing agent injection system  55  to be reduced. Then the chemical decontamination liquid flows through a cation exchanging resin column  3   a  to remove impurities. After that, the chemical decontamination liquid is heated up by a heater  4 , and returned to the object to be decontaminated  1 . In this mode, the temperature of the chemical decontamination liquid is gradually increased during recirculating because the liquid is heated by the heater  4 . 
     Next, the reducing agent decomposition mode will be described. In this mode, the valves  36 ,  39 ,  35 ,  34 ,  52  and  53  are closed, and the valves  37 ,  38 ,  32  and  33  are opened. The chemical decontamination liquid flowing out of the object to be decontaminated  1  is pressurized (pumped up) by the pump  2 , and flows through a cation exchanging resin column  3   a  to to be reduced. Then after heated by the heater  4 , the chemical decontamination liquid is added with hydrogen peroxide by a hydrogen peroxide injection system  30 . The chemical decontamination liquid is decomposed by the hydrogen peroxide and the catalyst in the catalyst tower  51 , and decomposed gas is exhausted through a ventilation system  40 . Then, the chemical decontamination liquid is returned to the object to be decontaminated  1 . By performing the recirculation operation, the chemical decontamination liquid is decomposed. In this mode, the temperature of the chemical decontamination liquid is also gradually increased during recirculating because the liquid is heated by the heater  4 . 
     Next, the cleaning mode will be described. In this mode, the valves  37 ,  38 ,  32 ,  33 ,  52  and  53  are closed, and the valves  36 ,  39 ,  35  and  34  are opened. The chemical decontamination liquid flowing out of the object to be decontaminated  1  is pressurized (pumped up) by the pump  2 , and cooled by a cooler  31 . Then, the chemical decontamination liquid passes through a mixed bed ion-exchanging resin column  3   b  to remove impurities which can not have been completely removed by the cation ion-exchanging resin in the decomposition mode, and then is again heated up by the heater  4 . 
     By repeating the each of the modes described above in order of the oxidation mode, the oxidizing agent decomposing mode, the reduction mode, the reducing agent decomposition mode and the cleaning mode, the chemical decontamination liquid is decomposed. Therein, there are some cases where the each of the modes takes ten and several hours or longer. 
     Although opening and closing of each of the valves in this embodiment is manually performed by workers, electrically operated opening and closing devices may be used. Using the electrically operated devices is preferable because man-power of the workers can be saved. 
     The catalyst tower  51  used in this embodiment will be described below in detail. The catalyst tower  51  is shown in  FIG. 7 . 
     The chemical decontamination liquid flows through the inlet pipe  11  (in  FIG. 8 , the pipe in the valve  32  side) of the catalyst tower  51  and is conducted to the lower chamber  12 . The flow of the chemical decontamination liquid is distributed inside the lower chamber  12 , and passes through the inlet mesh filter  13 . The chemical decontamination liquid passed through the inlet mesh filter  13  is decomposed by chemical reaction while being passing between the catalyst  14 . The gas generated by the decomposition is passes through the outlet mesh filter  15  together with the chemical decontamination liquid, and flows out of the outlet pipe  16  (in  FIG. 8 , the pipe in the valve  33  side). When the catalyst is charged in the catalyst tower  51 , the catalyst is directly charged by removing the lid of the catalyst charging port  19  and the catalyst pushing-down mechanism  20 . The outlet mesh filter  15  of the catalyst tower  15  is welded to the inner side wall of the catalyst tower container  18  and to the lower end portion of the catalyst charging port  19 . Further, the outlet mesh filter  15  is also welded to the penetrating portion of the inlet pipe  11 . Therefore, the outlet mesh filter  15  has such a structure that there is no gap to make the catalyst  14  flow out to the outlet pipe  16  side. Thereby, it is possible to prevent the catalyst  14  from flowing out. 
     Furthermore, the catalyst pushing-down mechanism  20  is arranged inside the catalyst charging port  19  of the catalyst tower  5 . The catalyst pushing-down mechanism  20  is formed by a weight, and the function of pushing-downward the catalyst  14  is performed by pushing the catalyst using the gravitational force of the weight. By doing so, occurrence of convection of the catalyst  14  caused by the decomposed gas can be prevented. As an example of the catalyst pushing-down mechanism  20 , when the catalyst pushing-down mechanism  20  is made of lead and has a thickness of 180 mm, it can push down the catalyst  14  with a pressure approximately 0.02 MPa. 
     Further, in the catalyst tower, a lower reinforcing plate  25  is placed in the lower side of the inlet mesh filter  13 , and an upper reinforcing plate  24  is placed in the upper side of the outlet mesh filter  15 . Thereby, the strength of the mesh filters can be increased so as to withstanding the loads produced by the catalyst  14 , the catalyst pushing-down mechanism  20  and the fluid flow of the chemical decontamination fluid. By the reinforcement, the deforming amount of the mesh caused by the fluid flow of the chemical decontamination liquid can be decreased compared to that in the case without the lower reinforcing plate  25  and the upper reinforcing plate  24 . Both of the lower reinforcing plate  25  and the upper reinforcing plate  24  have through holes so as to make the chemical decontamination liquid easily flow through. 
     The mesh size of the inlet mesh filter  13  and the outlet mesh filter  15  is formed smaller than the size of the catalyst used. It is appropriate that the size of the mesh filters is about 20 mesh when the size of the catalyst  14  is 4 to 8 mesh, and that the size of the mesh filters is about 40 mesh when the size of the catalyst  14  is 10 to 20 mesh. When the mesh size is further fined, the wire diameter of the mesh is also fined to decrease the strength. Therefore, by laying a 70-mesh mesh filter on a 20-mesh mesh filter, it is possible to fine the mesh size and at the same time to secure the strength of the mesh filter. 
     The liquid remaining inside the catalyst tower  51  after using the catalyst tower  51  is discharged to the inlet pipe  11  by applying gas pressure to the inside of the catalyst tower  51  from the outlet pipe  16 . A groove  26  is formed in the catalyst tower lower plate  23 , and the end portion of the inlet pipe  11  is placed on the lower surface of the groove. Holes  27  are formed in the end portion of the inlet pipe  11 . By doing so, the holes can be positioned in a level lower than the upper surface  23 U of the catalyst tower lower plate. When the catalyst tower  51  is filled with the liquid, the liquid can be pushed out through the inlet pipe  11  by applying gas pressure from the outlet pipe  16 . At that time, at least the liquid in the vertically upper side of the upper surface  23 U of the catalyst tower lower plate can be discharged by placing the end portion of the inlet pipe  11  in the groove  26 . Thereby, since an amount of the decontamination liquid remaining in the catalyst tower  51  after using the catalyst tower can be made small, a radiation dose after using the catalyst tower  51  can be reduced. Furthermore, it is possible to reduce exposure of radiation dose of workers accessing to the catalyst tower  51  after using the catalyst tower  51 . The amount of liquid remaining in the catalyst tower  51  can be further reduced by making the diameter of the holes  27  smaller than the depth of the groove  26 . 
     When the diameter of the inlet pipe  11  is large, there are some cases where the remaining liquid can not be sufficiently drained. In such a case, an additional small diameter pipe for draining is provided separately from the inlet pipe  11 , and the connecting point of the small diameter pipe is formed in the similar structure to that of the inlet pipe  11 . By doing so, the amount of liquid incapable of being drained can be reduced. 
     Furthermore, the upper surface of the catalyst tower lower plate may be formed in a cone shape having the center at the position where the inlet pipe  11  connects to the catalyst tower lower plate  23 . By doing so, when the liquid in the catalyst tower  51  is drained, the liquid flows toward the position where the inlet pipe  11  connects to the catalyst tower lower plate  23 . Therefore, the drainage can be made easy. 
     According to the embodiments described above, the catalyst can be directly charged from the catalyst charging port into the catalyst tower container. Further, since the outlet mesh filter needs not to be formed in a detachable structure nor a movable structure by placing the catalyst pushing-down mechanism inside the catalyst charging port, the outlet mesh filter can be formed in the structure of closely attached to the inner wall of the catalyst tower container and to the catalyst charging port. Therefore, it is possible to certainly prevent the catalyst from flowing out of the outlet mesh filter. Furthermore, since the catalyst can be certainly pushed down by the catalyst pushing-down mechanism placed inside the catalyst charging port, it is possible to prevent occurrence of convection of the catalyst due to the decomposed gas.