Abstract:
An apparatus for treating air containing hydrogen gas used in an area such as an interior of a nuclear reactor containment vessel where hydrogen gas is generated and apt to be accumulated so as to treat rapidly and safely the hydrogen. A treating apparatus ( 30 ) for treating air containing hydrogen gas in a nuclear reactor containment vessel, comprises a housing ( 31 ) provided with an air intake port ( 33 ) and an exhaust port ( 35 ) and defining a gas passage therein, a catalyst bed ( 37 ) disposed in said gas passage, and a heater ( 39 ) disposed in or close to said catalyst bed. The catalyst bed is composed of plate type catalysts, honeycomb type catalysts, or spherical catalysts and activated by being heated with an electric heater. Hydrogen and oxygen in the air containing hydrogen gas flowing in come into contact with the catalyst bed and recombine together such that the hydrogen gas is thus removed from the air.

Description:
[0001]    This patent is a continuation-in-part of application Ser. No. 09/155,962 filed Oct. 6, 1998. 
     
    
     
       FIELD OF THE TECHNOLOGY  
         [0002]    The present invention relates to an apparatus for treating air containing hydrogen gas, and in particular, an apparatus for safely treating the hydrogen gas contained in the air in a nuclear reactor containment vessel.  
         BACKGROUND TECHNOLOGY  
         [0003]    When hydrogen gas is contained in air, hydrogen and oxygen coexist, making it easy for the hydrogen to begin a combustion reaction. Further, since hydrogen reacts explosively with oxygen when the hydrogen concentration rises above a certain value, sufficient countermeasures must be provided in certain kinds of plants handling hydrogen gas or generating hydrogen gas. For example, in a nuclear power plant, if a nuclear core is heated excessively, zirconium in the zirconium base alloy used for fuel cladding tubes of the nuclear reactor fuel, etc., and water steam react with each other to produce a large quantity of hydrogen gas. Furthermore, radiolysis of water caused by radioactive material that flows into a sump in the nuclear reactor containment vessel during an accident slowly generates a large quantity of hydrogen gas, which over a long period accumulates in the reactor containment vessel. When the hydrogen concentration in the atmosphere within the containment vessel rises above four percent, particularly above six percent, there is a possibility that the hydrogen will burn and that, if the concentration goes above ten percent, the hydrogen will burn explosively. Accordingly, to insure safety, the hydrogen gas must be treated and removed when it is in lower concentrations, and the rise of concentration to higher levels must be prevented.  
           [0004]    In response to the needs described above, an electric hydrogen recombining unit, an ignition type hydrogen burner, a catalytic hydrogen recombining unit and the like have been proposed, are under development, or are being used. Describing them in outline, the electric hydrogen recombining unit shown in FIG. 4, mainly used where the generation of hydrogen gas is slow and the concentration of hydrogen is less than four percent, treats hydrogen by taking a gas mixture of hydrogen and air though a suction port  3  into a recombining unit and discharges an exhaust gas from an exhaust port  7  after the hydrogen and oxygen are recombined by the action of an electric heater  5 .  
           [0005]    The ignition type hydrogen burner  10  shown in FIGS. 5 and 6 is installed in a free space and a heater  13  is energized from an electric source  11  of about 120V to ignite a gas mixture containing hydrogen and to burn the hydrogen content by propagating a flame. In addition, the ignition type hydrogen burner  10  has a protective housing  15 , a conduit for electric supply, and a protective umbrella  19  in addition to the heater  13 .  
           [0006]    This protective umbrella  19  protects the heater  13  from liquid droplets sprayed from emergency cooling sprays in the containment vessel.  
           [0007]    Furthermore, the catalytic hydrogen recombining unit  20  shown in FIG. 7 is composed of a removable catalyzer bed  21  consisting of a stack of plate type catalyst carrying platinum or palladium as the catalytic substance deposited thereon, an intake opening  23 , an exhaust opening  25  and a protective housing  27 . Then, when hydrogen gas is generated in a containment vessel where the catalytic hydrogen recombining is installed, a gas mixture containing hydrogen and oxygen flows into the catalyzer bed  21  through the intake opening  23  under natural circulation. Hydrogen and oxygen recombine on the catalytic surface in the catalyzer bed  21 , the catalyzer bed  21  is heated by the heat of reaction, and the gas takes on a hot state as it passes through the catalyzer bed  21 . The catalyst is activated by being heated and the reaction is further activated. Thereafter, the heated hot discharge gas is exhausted through the exhaust opening  25  to complete the treatment of the hydrogen gas.  
           [0008]    In the electric hydrogen recombining unit described before, there are problems in that the treatment is slow because it is performed under recombining reaction without burning propagation and in that the apparatus can not be actually used for gas mixtures with a hydrogen concentration above four percent in order to protect the apparatus from the strong combustion that would occur.  
           [0009]    Further, although the ignition type hydrogen burner can treat a large quantity of hydrogen within a free space in a short period of time because the gas mixture containing hydrogen is directly ignited and a pilot (flame) is propagated therein, there is another problem in that hydrogen cannot be treated when the hydrogen concentration is below about six percent above which the flame can propagate with burning. In spite of the advantages of the burner, it can be said that the use thereof should be confined to emergency situations where a large quantity of hydrogen gas is produced, because the treatment uses flames and there is a fear that other equipment such as safety system components, electricity supply cables and nuclear instrumentation systems may be adversely influenced.  
           [0010]    Furthermore, though the catalytic hydrogen recombining unit can treat gas mixtures to remove hydrogen in a wide range of lower to higher concentrations, the treatment speed is so slow that generated hydrogen gas can not be wholly treated when a large quantity of the gas is generated in a short period, thereby allowing the generation of higher hydrogen concentrations. An ignition in those states of higher hydrogen concentration raises another problem by causing deflagration or detonation. Besides, in an emergency situation such as a case when a large amount of hydrogen gas is generated, there is a problem that various kinds of substances are included into the atmosphere in the containment vessel and the catalyst can be poisoned by poisoning substances among the included ones so as to lower the activity of the catalyst, preventing the treatment of the hydrogen gas.  
           [0011]    Accordingly, an object of the present invention is to provide a treatment apparatus for an air containing hydrogen gas which can reliably and safely treat hydrogen in a gaseous mixture containing hydrogen for any concentration of hydrogen or with various kinds of poisoning substances contained in the gaseous mixture.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0012]    In order to solve the problems described above, according to the present invention, an apparatus for treating air containing hydrogen gas comprises a housing defining a gas passage therein with an intake port and an exhaust port, a catalyst bed disposed in the gas passage and a heater disposed in or adjacent to the catalyst bed. In an embodiment where the catalyst bed is composed of a plate type catalyzer, an electric heater maybe disposed by extending it through and laying it in contact with the catalyst bed. In another embodiment where the catalyst is composed of a honey comb type catalyzer, it is preferred that an electric heater be disposed in the gas passage at an upstream side of and close to the honey comb type catalyzer. In a still further embodiment, the catalyst bed uses spherical catalyzers in a bed as an alternative to plate type catalyzers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic view showing a general construction of the embodiment according to the present invention.  
         [0014]    [0014]FIG. 2 is a sectional elevational view showing another embodiment according to the present invention.  
         [0015]    [0015]FIG. 3 is a horizontal sectional view taken off along line III-III in FIG. 2.  
         [0016]    [0016]FIG. 4 is a general perspective view showing an example of prior art apparatus.  
         [0017]    [0017]FIG. 5 is a general perspective view of another prior art apparatus.  
         [0018]    [0018]FIG. 6 is an enlarged view showing a portion in FIG. 5.  
         [0019]    [0019]FIG. 7 is an exploded view of another prior art apparatus.  
         [0020]    [0020]FIG. 8 is a horizontal section view of a hydrogen recombining unit of the present invention.  
         [0021]    [0021]FIG. 9 is a partial vertical sectional view of a recombining unit of the present invention.  
         [0022]    [0022]FIG. 10 is an overall view of an electric heater of the present invention.  
         [0023]    [0023]FIG. 11 depicts a catalyst bed using spherical catalysts of the present invention.  
         [0024]    [0024]FIG. 11 a  depicts a horizontal section al view of a recombining unit having an arrangement of spherical catalyst beds.  
         [0025]    [0025]FIG. 11 b  depicts a vertical sectional view of a recombining unit having an arrangement of spherical catalyst beds.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    In reference to the drawings attached, an embodiment of the present invention is hereinbelow described. Referring to FIG. 1 first, a protective housing or cover  31  of a hydrogen recombining unit  30  for treating atmosphere containing hydrogen gas in a nuclear reactor containment vessel is provided with an intake port  33  at its lower portion and an exhaust port  35  at its upper side portion, respectively, and an air passage communicating thereto is defined therein. Further, a catalyst bed  37  comprising a plurality of plate type catalyzers  37   a  is disposed in the air passage close to the intake port  33 . Air flow paths are defined between the plate type catalyzers  37   a  thereby allowing the air to flow therethrough. Further, an electric heater  39  is disposed extending through the plate type catalyzers  37   a  and its heating section is adjacent to the plate type catalyzers.  
         [0027]    The general view of the electric heaters  39 ,  49  is shown in FIG. 10. The heaters are conventional and essentially of same structure. The heater is a sheathed heater with electric cables, which includes a connection sleeve  101 , cables  103 , a lead sleeve  105 , lead wires  107  and crimp terminals  109 . The sheathed heater  111  comprises a cylindrical protective sheath and a heating wire disposed therein together with insulating material. From the viewpoint of heat generation, the sheathed heater includes a heating section and a non-heating section adjacent to the connection sleeve, which is a heat insulating section for preventing heat transmission from the heating section to the connection sleeve. The heater can rise up to 800° C. and over in temperature for the effective activation of the catalyst and an ignition to the hydrogen contained gas.  
         [0028]    [0028]FIG. 8 is a horizontal sectional view of the hydrogen recombining unit  30  containing an electric heater  39  as shown generally in FIG. 1. Though the heater  39  is shown as a single line in FIG. 1 because it is very small relative to the overall dimension of the recombining unit  30 , the heater  39  of the sheathed heater type is preferably employed therein. Referring to FIG. 8, plate type catalyzers  37   a  are supported on lateral support frames  51  positioned at the lower portion of the cover  31 . As shown, the catalyzers  37   a  are spaced apart from each other by a spacer  53  disposed therebetween so as to define an air flow paths  55  communicating to the intake port  33 .  
         [0029]    The electric heater  39  of sheathed heater type extends laterally through a wall of the cover  31  and holes of the catalyzers  37   a . The connection sleeve  39   a  of the heater  39  is positioned in a mounting sleeve  57  that is in turn secured to the cover  31  by a fastener  59 . Thus the heater  39  is firmly mounted in the cover  31 . The protective sheath  39   b  of the heater  30  extends through the catalyzers  37   a  at through holes formed therein and the heating section is positioned in the holes. In other words, the heating section in the sheath  39   b  of the heater  39  is positioned adjacent to the plate type catalyzers  37   a.    
         [0030]    In the hydrogen recombining unit  30  with the construction described above, when hydrogen gas is generated resulting from an accident in the nuclear reactor containment vessel, a gaseous mixture containing hydrogen and oxygen, that is, air containing hydrogen gas, flows through the intake port  33  into the gas passage in the cover  31 . On the catalytic surfaces of the plate type catalyzers  37   a  the hydrogen and oxygen combine causing the generation of heat. During an accident in which there is the generation of hydrogen gas, the electric heater  39  is designed to be energized to generate electric resistance-heat thereby heating adjacent catalysts, activating them and promoting a recombination reaction. The catalysts adjacent to the area where recombination reactions are generated are heated by heat conduction of the generated heat and the recombination reaction is promoted there to thus activate the entire area of the plate type catalyzers  37   a . This activation promoting phenomenon on the plate type catalyzers  37   a  is generated over the entire catalyst bed  37  and the recombination of hydrogen and oxygen is promoted, thereby resulting in rapid treatment of the hydrogen. Air that has risen in temperature through heat generated in the recombination reaction flows farther on through the gas passage and is discharged from the exhaust port  35 .  
         [0031]    During abnormal conditions when hydrogen gas is generated, although the mixture containing water steam and poison material produced with the leaking out of the coolant at high pressure and high temperature flows in though the intake opening  33  and comes into contact with the catalyzer bed  37 , the hydrogen gas treatment is rapidly performed with the aid of catalyst activation caused by the heating of the electric heater  39 .  
         [0032]    In addition, when the hydrogen concentration rises above four percent from the generation of large quantities of hydrogen gas, the electric heater  39  becomes a source of ignition and treats a large quantity of hydrogen gas by propagated combustion out of the device through the intake opening  33  or discharge opening  35 .  
         [0033]    Next, a hydrogen recombining unit using a honey comb type catalyst will be described. Referring to FIGS. 2 and 3, a housing or container  41  of a hydrogen recombining unit  40  for treating an air containing hydrogen gas in a nuclear reactor containment vessel is provided with an intake port  43  at its lower portion and a discharge port  44  at its upper portion and an air passage  42  communicating therewith is defined therein. The discharge port  44  of the container  41  is covered with a protective cover  46  apart therefrom, and an annular exhaust opening  4 . 5  is defined at the side thereof. Then, a catalyst bed  47  composed of honeycomb type catalysts is disposed in the air passage  42  inside of the container, and an electric heater  49  is disposed in the air passage  42  below the catalyst bed  47 . A heating section of the electric heater  49  is close, but not adjacent to the catalyst bed  47 .  
         [0034]    [0034]FIG. 9 is a partial vertical sectional view of the recombining unit  40  in FIG. 2, in which the electric heater  49  of sheathed heater type is clearly shown. In FIG. 9, the catalyst bed  47  of honeycomb type is held in the air passage  42  by support frames  61 , which are fixed on an inner surface of the container  41 . A plurality of air paths  47   a  each having an hexagonal cross section are formed in the catalyst bed  47 . Thus, gas having flowed into the air passage  42  through the intake port  43  farther flows through the air paths  47   a.    
         [0035]    The electric heater  49  extends through a mounting sleeve  63  and the connecting sleeve  49   a  thereof is mounted on the sleeve  63 , which is in turn secured to the container  41  by a threaded fastener  65 . The protective sheath  49   b  including a heating section extends out into the air passage  42  and is located at a position apart from the catalyst bed  47  by a small distance as shown in the drawing.  
         [0036]    In the hydrogen recombining unit  40  as described above, when hydrogen gas is generated resulting from an accident in the nuclear reactor containment vessel, a gas mixture containing hydrogen and oxygen, or hydrogen-gas-contained air flows into the air passage  42  in the container  41  through the intake port  43  and comes into contact with the catalyst bed  47 . Thereafter, hydrogen and oxygen combine on surfaces of the catalysts thereby generating heat. During the accident when the hydrogen gas is generated, the electric heater  49  is supplied with electricity and produces electric resistance heat thereby heating and activating a lower portion of the catalyst close thereto. As a result, the recombination reaction is promoted. The catalyst adjacent to an area where the combination reaction is caused is heated through conduction of heat by exothermic reaction and the recombination reaction there is promoted. Thus, the catalyst of the catalyst layer  47  is heated successively and the phenomenon of promoting the activation is created over the entire catalyst layer  47  thereby promoting combination of hydrogen and oxygen. The air that has risen in temperature from the heat of the recombination reaction flows through the air passage  42  and is discharged out through the exhaust opening  45 .  
         [0037]    During abnormal conditions when hydrogen gas is generated, although the mixture containing water steam and poison material produced with the leaking g out of the coolant at high pressure and high temperature flows in though the intake port  43  and comes into contact with the catalyzer layer  47 , the hydrogen gas treatment is rapidly performed with the aid of catalyst activation caused by the heating of the electric heater  49 .  
         [0038]    In addition, when the hydrogen concentration rises above four percent from the generation of a large quantities of hydrogen gas, the electric heater  49  functions as an ignition source and treats a large quantities of hydrogen gas by the propagation of combustion wave.  
         [0039]    In a further embodiment of the invention another catalyst bed is used having spherical catalysts as an alternative to the plate type catalyzers  37   a , as generally depicted in FIG. 11. The alternative bed is comprised of a wire mesh box  113  with a lid or cover  115  and a plurality of aluminum oxide carriers  117  packed in the box. The carriers have diameters ranging from 1 mm to 4 mm and the carriers having a generally spherical shape (herein spherical catalyst) which need not be perfectly spherical is covered with a coating of platinum or vanadium. The wire mesh box is made of SUS wires woven and has a partition sleeve  119  of wire mesh for the electric heater. The spherical catalyst beds  70  are arranged as shown in FIGS. 11 a  and  11   b , which are a horizontal sectional view and a vertical sectional view, respectively. In FIGS. 11 a  and  11   b , the spherical catalyst beds  70  are depicted in a conceptual manner. In a real situation, spherical catalysts  71  are not disposed in a described regular arrangement in a wire mesh box  73 , which is closed with a lid  77  (FIG. 11 b ) after the loading of the catalysts  73  therein. A partition sleeve  75  prevents the catalysts  71  from flowing out when the heater  39  is removed. The other members are the same as ones shown in FIGS. 1 and 8.  
       Applicability in Industry  
       [0040]    As described above, according to the invention, when hydrogen concentration in the air is low the hydrogen gas is treated by quick accomplishment of hydrogen recombination reaction with assistance of the catalyst activation which is promoted with the heater, while when the hydrogen concentration largely rises upon generation of a large quantity of the hydrogen gas, the heater serves as an ignition source and starts combustion reactions thereby rapidly treating the hydrogen.  
         [0041]    Although the invention has been described in terms of specific embodiments, it will be clear to persons of skill in the relevant art that the invention may be implemented by other embodiments that do not differ substantially therefrom and are within the scope of the following claims.