JP2016074554A - Recombination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst type recombination device of hydrogen and oxygen, suitable for installation of a facility having a narrow internal space region and requiring airtightness such as a radioactive waste storage tank.SOLUTION: A recombination device 1 attached to a container 50, for recombining hydrogen generated inside the container with oxygen by using a catalyst, includes such a first cylindrical body 2 that gas including hydrogen flowing in from the container 50 and oxygen is circulated through the inside, and a return part 3 connected to an outlet of the first cylindrical body 2, for returning the gas flowing in from the first cylindrical body 2 into the container 50. The first cylindrical body 2 has a catalyst part 9 for combining hydrogen with oxygen on the inlet side.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a recombination apparatus for combining hydrogen and oxygen using a catalyst.

  In a radioactive waste storage tank in which high-level radioactive waste is stored, it is considered that hydrogen is generated in the radioactive waste storage tank due to radioactive decomposition of water. If the internal hydrogen concentration increases with time and reaches the explosion limit, hydrogen explosion may occur in the storage tank. When a hydrogen explosion occurs in a radioactive waste storage tank, the confinement function of the radioactive material is lost, and the radioactive material may be released to the outside.

  In order to prevent such a hydrogen explosion, a means for reducing the hydrogen concentration is required so that the hydrogen concentration in the radioactive waste storage tank does not reach the explosion limit.

  Conventionally, as a countermeasure against severe accidents at nuclear power plants, a device is known that reduces the hydrogen concentration by recombining a large amount of hydrogen generated by the zirconium-water reaction with oxygen using a catalyst (patent). Reference 1).

JP 2011-174773 A

  However, the existing recombination device developed as a countermeasure against severe accidents is installed inside the reactor containment vessel or reactor building and does not support installation in a radioactive waste storage tank. In other words, the existing recombination apparatus cannot be installed in facilities such as radioactive waste storage tanks that have a narrow internal space area and require airtightness.

  In addition to radioactive waste storage tanks, in containers and tanks where hydrogen may be generated and the hydrogen concentration may increase over time, the hydrogen concentration is reduced before the explosion limit is reached. A means for making it necessary is necessary.

  However, such containers and tanks usually do not have a large internal space like a reactor containment vessel and are required to be airtight. For this reason, it is difficult or impossible to install an existing large recombination device developed as a countermeasure against severe accidents.

  The present invention has been made in view of the above-mentioned problems of the prior art, and is a catalyst suitable for installation in facilities where the internal space area is narrow and airtightness is required such as a radioactive waste storage tank. An object is to provide a recombination device of the formula.

  In order to solve the above-mentioned problem, the present invention according to the first aspect is a recombination apparatus for attaching hydrogen generated inside a container to oxygen using a catalyst, and flowing from the container The hydrogen and the oxygen-containing gas are connected to a first cylindrical body through which the gas flows and the outlet of the first cylindrical body, and the gas flowing from the first cylindrical body is And a return part that returns to the container, wherein the first cylindrical body has a catalyst part that combines the hydrogen and the oxygen on the inlet side.

  The present invention according to a second aspect is the present invention according to the first aspect, wherein the return portion is formed so as to surround an outer surface of the first cylindrical body, and A direction changing part connected to one cylindrical body and changing the direction of the gas flowing in from the first cylindrical body and flowing out to the second cylindrical body is provided.

  According to a third aspect of the present invention, in the present invention according to the first or second aspect, the first cylindrical body and the return portion are configured so as to be detachable as a unit from the container. It is characterized by.

  The present invention according to a fourth aspect is characterized in that the first cylindrical body and / or the return portion includes an opening sealing member that hermetically seals the opening formed in the container. And

  The present invention according to a fifth aspect is the present invention according to any one of the first to fourth aspects, wherein the catalyst portion has a large number of through-holes carrying the catalyst on the surface, and includes the hydrogen and the oxygen. It has a substantially plate-like or cylindrical member that introduces the gas to be treated and recombines the hydrogen and the oxygen.

  The present invention according to a sixth aspect is characterized in that, in the present invention according to any one of the first to fifth aspects, the catalyst portion is formed by partitioning through-holes adjacent to each other with a thin wall. And

  The present invention according to a seventh aspect is characterized in that, in the present invention according to the sixth aspect, a cross section of the catalyst portion is a polygon.

  The present invention according to an eighth aspect is the present invention according to the sixth or seventh aspect, wherein the plurality of penetrations are caused by gas buoyancy caused by heat generated by the recombination reaction of the hydrogen and oxygen in the catalyst section. The effective length of the first cylindrical body and the thickness of the catalyst part are set so that natural convection occurs in the first cylindrical body against the flow resistance in the holes. Features.

  The present invention according to a ninth aspect is characterized in that, in the present invention according to the eighth aspect, the thickness of the catalyst portion is about 5 mm.

  According to the present invention, it is possible to provide a catalytic recombination apparatus that is suitable for installation in facilities where a space area such as a radioactive waste storage tank is narrow and airtightness is required.

The front view which showed the catalytic-type recombination apparatus by 1st embodiment of this invention with the radioactive waste storage tank mounted | worn. The top view of the recombination apparatus shown in FIG. The longitudinal cross-sectional view of the recombination apparatus shown in FIG. FIG. 4 is an arrow view along line IV-IV in FIG. 1. FIG. 6 is an arrow view along the line V-V in FIG. 5. The top view which showed the catalyst holder of the recombination apparatus shown in FIG. The longitudinal cross-sectional view of the catalyst holder shown in FIG. The bottom view of the catalyst holder shown in FIG. It is a figure for demonstrating the structure of the catalyst part of the recombination apparatus shown in FIG. 1, (a) is the top view which showed the catalyst part typically, (b) is AA sectional drawing of (a). . FIG. 9A is an enlarged plan view of the Xa portion of FIG. 9A, and FIG. 9B is an enlarged longitudinal sectional view of the Xb portion of FIG. 9B. The longitudinal cross-sectional view which expanded and showed the XI part of FIG. The graph which showed the relationship between the thickness of a catalyst part, and the amount of hydrogen treatment. The schematic diagram which showed the flow-path structural model of the recombination apparatus shown in FIG. The graph which showed the optimal range of the recombination apparatus shown in FIG.

  Hereinafter, a catalytic recombination apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  The recombination apparatus according to the present embodiment is an apparatus for combining hydrogen and oxygen using a catalyst, and is particularly suitable for installation in a radioactive waste storage tank. In particular, it is suitable for mounting on the nozzle portion provided in the radioactive waste storage tank.

  However, the recombination apparatus according to the present invention can be installed not only in the radioactive waste storage tank but also in a container or a tank in which hydrogen is generated inside and the hydrogen concentration may increase with time.

  As shown in FIGS. 1 and 3, a cylindrical nozzle 51 is provided on the upper part of the radioactive waste storage tank 50, and the recombination device 1 according to the present embodiment is detachably attached to the nozzle 51. It is installed.

  As shown in FIGS. 1 and 3, the recombination apparatus 1 according to the present embodiment has a first cylindrical body 2 through which a processing target gas containing hydrogen and oxygen flows. The 1st cylindrical body 2 is comprised with the cylindrical member. However, the member which comprises the 1st cylindrical body 2 is not restricted to a cylindrical member, For example, the cylindrical member of a square cross section can also be used.

  As shown in FIGS. 1 to 4, the flow direction of the gas flowing out from the first tubular body 2 is changed at the outlet of the first tubular body 2 and returned to the radioactive waste storage tank again. A return portion is provided. Specifically, the return portion includes a second cylindrical body 4 formed so as to surround the outer surface of the first cylindrical body 2, and an end plate (return plate) connected to the upper portion of the second cylindrical body. Part) 3 (shaped with the bowl turned down), and the gas flowing out from the upper part of the first cylindrical body spreads in the radial direction in the direction changing part of the end plate part, while vertically extending from vertically upward to vertically downward The flow direction is changed to flow downward in the flow path between the first cylindrical body and the second cylindrical body, and returned again to the radioactive waste storage tank. The 2nd cylindrical body 4 has the flange part 5 formed in the lower end.

  The flange portion 5 of the second cylindrical body 4 is fixed with bolts 6 to a flange portion 52 formed at the upper end of the nozzle 51 of the radioactive waste storage tank 50. An airtight seal is formed between the flange portions 5 and 52, thereby ensuring airtightness inside the radioactive waste storage tank 50.

  As shown in FIGS. 3 and 4, an elongated plate-like shape in which the inner peripheral surface of the second cylindrical body 4 and the outer peripheral surface of the first cylindrical body 2 are arranged at intervals of 90 degrees in the circumferential direction. They are connected by an internal connecting member 7.

  As shown in FIG. 1, the upper half of the first cylindrical body 2 is disposed inside the nozzle 51 of the radioactive waste storage tank 50, and the inner peripheral surfaces of the nozzle 51 and the second cylindrical body 4. And an annular flow path 8 of gas is formed between the outer peripheral surface of the first cylindrical body 2. The gas that has flowed upward from the upper end opening of the first cylindrical body 2 changes its flow downward in the flow direction changing section (return section) 3 and returns to the radioactive waste storage tank 50 through the annular flow path 8. To do.

  As shown in FIGS. 1 and 3, a dome in which the end plate portion 4 </ b> A of the second cylindrical body 4, that is, the portion facing the outlet of the first cylindrical body 2 is inclined downward from the center toward the outside. It is formed in a shape.

  As shown in FIGS. 1 and 3, the catalyst structure 9 is provided on the inlet side (lower end side) of the first cylindrical body 2. The catalyst structure 9 includes the catalyst holder 10 shown in FIGS. 6 to 8 and the substantially disk-like or substantially cylindrical catalyst portion 11 shown in FIG.

The catalyst unit 11 is filled with a small diameter pebble carrying a catalyst on its surface in a flow path through which a gas passes, or a plurality of honeycombs carrying a catalyst on the surface are arranged on the surface. The wall surfaces are arranged.
The catalyst holder 10 is composed of a substantially annular frame-shaped holding member that holds the peripheral edge of the catalyst part 11, and the substantially disk-like or substantially cylindrical catalyst part 11 is fitted into the recess of the catalyst holder 10. The catalyst holder can be formed of, for example, a stainless material.

  Below, it demonstrates regarding the catalyst part which has a honeycomb structure with high possibility that small size and high performance can be implement | achieved, and the structure relevant to it.

  A large number of through holes (flow channels) provided in the catalyst unit 11 have a polygonal cross section such as a triangle, a quadrangle, a pentagon, or a hexagon, and the channels adjacent to each other are partitioned by thin walls. (Honeycomb structure). The catalyst portion uses porous ceramics or stainless steel as a support. That is, the catalyst part 11 has a large number of through holes 12 as shown in FIG. The through-hole 12 extends along the direction in which the gas to be processed is introduced into the first cylindrical body 2 (in this example, the axial direction of the first cylindrical body 2), and the inside thereof is processed. Target gas (including hydrogen and oxygen) circulates.

  A catalyst is applied to the catalyst portion at least on the inner peripheral surface of each through hole 12. By adopting the honeycomb structure, the specific surface area (surface area per unit volume) of the catalyst part 11 can be increased, so that the contact efficiency between the gas to be treated and the catalyst can be greatly increased.

  FIG. 11 shows a structure for attaching the catalyst structure 9 to the first cylindrical body 2. An annular projection 13 is formed on the inner peripheral surface of the first cylindrical body 2. Below the annular protrusion 13, a short cylindrical support member 15 having an annular support portion 14 formed at the upper end is disposed. The peripheral edge of the catalyst structure 9 is disposed between the annular protrusion 13 and the annular support 14. A short cylindrical support member 15 is fixed to the first cylindrical body 2 with a bolt 16, and the catalyst structure 9 is fixed to the cylindrical portion 2.

  Next, the recombination action of hydrogen and oxygen in the recombination apparatus 1 according to the present embodiment will be described.

  The recombination device 1 according to the present embodiment does not require a power source when used, and uses natural convection in the first cylindrical body 2 as a driving force. That is, in the first cylindrical body 2 against the flow resistance in the plurality of through holes 12 of the catalyst portion 11 due to the buoyancy of the gas due to the heat generated by the recombination reaction of hydrogen and oxygen in the catalyst structure 9 The effective length of the first cylindrical body 2 (the length of the portion that contributes to the occurrence of natural convection) and the thickness of the catalyst portion 11 are set so that natural convection occurs.

  That is, when the processing target gas containing high-concentration hydrogen generated in the radioactive waste storage tank 50 and accumulated in the upper part of the storage tank flows in from the lower end inlet of the first cylindrical body 2 and passes through the catalyst structure 9. In addition, water vapor is generated by the recombination reaction of hydrogen and oxygen. In the presence of a catalyst, the recombination reaction occurs even at room temperature. The gas is heated by the heat generated by the recombination reaction to generate buoyancy due to the density difference, and natural convection is generated using this as a driving force (chimney effect).

  The treated gas containing water vapor generated by the recombination reaction is released upward from the upper end opening of the first cylindrical body 2. The released gas changes its flow downward and returns to the radioactive waste storage tank 50 through the annular flow path 8.

  FIG. 12 shows the relationship between the catalyst height (the height of the catalyst unit 11) and the hydrogen treatment amount in the case of a hydrogen concentration of 4 vol%, a reaction rate of 100%, and natural convection. The hydrogen processing amount indicates the processing amount (kg / h) per unit inflow area of the gas to be processed into the recombination apparatus 1.

  As can be seen from FIG. 12, the hydrogen treatment amount decreases as the catalyst height (the height of the catalyst unit 11) increases. Since the reaction between hydrogen and oxygen is very fast, the reaction is substantially completed immediately after the gas to be treated is introduced into the catalyst unit 11. For this reason, even if the catalyst height is increased, there is almost no contribution to reaction promotion. Rather, since the flow resistance in the catalyst unit 11 increases, the flow rate of the gas to be processed decreases, and as a result, the hydrogen processing amount decreases.

  Therefore, even if the height of the catalyst part is larger than 5 mm, the hydrogen treatment capacity is lowered, while the recombination apparatus is enlarged, whereas when the height of the catalyst part is smaller than 5 mm, the hydrogen treatment capacity is reduced. It can be seen that this is improved and the recombination apparatus is miniaturized.

  Next, the range (principal part dimensions) desirable for the recombination apparatus in this embodiment will be examined.

  FIG. 13 shows a flow path configuration model of the recombination device 1 according to the present embodiment.

  The buoyancy accompanying heat generated by the catalytic reaction of hydrogen and oxygen is expressed by the following formula (1) when the flow is in a laminar flow region.

P _A = Δρ × g × h ₂ (1)
here,
P _A : Buoyancy due to heat generation by catalytic reaction [N / m ² ]
Δρ: density difference ρ _IN −ρ _OUT [kg / m ³ ]
ρ _IN : Inlet side gas density [kg / m ³ ]
ρ _OUT : outlet side gas density [kg / m ³ ]
g: Gravity acceleration [m / s ² ]
h ₂ : Chimney height [m]
The chimney height is an effective height corresponding to a portion where the chimney effect occurs in the cylindrical portion 2.

  The flow resistance in the catalyst part 11 is represented by the following formula (2).

P _B = 32 × μ × h ₁ × V _IN / d ₁ ² (2)
here,
P _B : Flow resistance [N / m ² ]
μ: Viscosity coefficient [Pa · s]
h ₁ : catalyst height [m]
V _IN : Inlet flow velocity [m / s]
d ₁ : catalyst channel equivalent diameter [m]
Assuming the flow resistance _{P B} in buoyancy _{P A} and the catalyst portion 11 due to the heat generated by the catalyst are balanced with _(P A = _{P B),} and formula (1) from equation (2) becomes less.

h ₂ / h ₁ = 32 × μ × V _IN / d ₁ ² / (Δρ × g) (3)
When H = h ₁ + h ₂ , the following is obtained.

H / h ₁ = 32 × μ × V _IN / d ₁ ² / (Δρ × g) +1 (4)
FIG. 14 shows a desirable range (blacked portion in the graph) as the recombination device 1 according to the present embodiment based on the formula (4).

In FIG. 14, the upper limit of H is set to 300 mm for downsizing of the recombination apparatus, and the lower limit of h ₁ is set to 3 mm from the manufacturing limit. Therefore, in FIG. 14, H / h ₁ is set to 100 for the upper limit and about the lower limit. , H = h ₁ (h ₂ = 0 mm). The lower limit of _VIN is set to 0.3 m / s in consideration of the hydrogen treatment amount of the existing recombination apparatus. The upper limit of d ₁ is 1.79 mm based on the catalyst part that can be manufactured.

  As described above, according to the catalytic recombination device 1 according to the present embodiment, the return portion 3 is provided at the outlet portion of the first cylindrical body 2 provided with the catalyst structure 9, and the return portion 3 is radioactive. Since the opening of the nozzle 51 of the waste storage tank 50 is hermetically sealed, the recombination apparatus 1 can be mounted without any trouble even in the radioactive waste storage tank 50 in which the internal space region is narrow and airtightness is required. .

  By attaching the recombination device 1 to the radioactive waste storage tank 50 in this way, the concentration of hydrogen generated inside the radioactive waste storage tank 50 is controlled to prevent reaching the explosion limit, and the occurrence of a hydrogen explosion. The possibility can be excluded. In the recombination device 1 according to the present embodiment, the gas temperature between the first cylindrical body 2 and the second cylindrical body 4 is maintained at a low temperature in order to ensure a reliable natural circulation force. Since it is necessary, the second cylindrical body 4 is forcibly cooled as necessary by providing a cooling fan (not shown in the figure, which is independent of the recombination device) around it. However, even if such a cooling mechanism is provided, the radioactive waste storage tank including the recombination device can have an airtight structure, and since the cooling mechanism is simple, it is much simpler than the conventional one. Hydrogen explosion can be prevented by a simple recombination device.

  Moreover, since the recombination device 1 according to the present embodiment can be attached to the existing nozzle 51 provided on the upper part of the radioactive waste storage tank 50, a special structure for installing the recombination device 1 is required. Therefore, the labor and cost of installation work can be reduced.

  Further, the recombination device 1 according to the present embodiment uses, as the catalyst unit 11, a catalyst unit in which a large number of through holes 12 are formed along the introduction direction of the gas to be processed into the first cylindrical body 2. Therefore, the amount of hydrogen treated per unit volume of the catalyst can be greatly increased as compared with the conventional recombination apparatus while ensuring natural convection due to the chimney effect.

  As a result, the size of the catalyst structure 9 including the catalyst portion 11 can be significantly reduced as compared with the conventional catalytic recombination apparatus. Thereby, size reduction and weight reduction of the whole apparatus can be achieved. Even if a cooling fan is required due to the size and weight of the recombination device 1, it is easy to install and remove the device independently, and the amount of worker exposure due to shortening of the work time Can also be reduced.

  Further, according to the recombination device 1 according to the present embodiment, since the catalyst structure 9 is detachably attached to the inside of the first cylindrical body 2, the catalyst structure 9 is removed from the first cylindrical body 2. By removing the, the catalyst can be easily replaced.

  Further, according to the recombination device 1 according to the present embodiment, the end plate portion 4A of the second cylindrical body 4, that is, the portion facing the outlet of the first cylindrical body 2 is downward from the center toward the outside. Since it is formed in an inclined dome shape, when water vapor is cooled by the end plate portion 4A of the second cylindrical body 4 and condensed water adheres to the surface thereof, the condensed water is radially directed on the surface of the end plate portion 4A. Flows outward. Therefore, it is possible to prevent the condensed water from dripping into the upper end opening of the first cylindrical body 2, and it is possible to prevent water from adhering to the catalyst and inhibiting the basic reaction.

DESCRIPTION OF SYMBOLS 1 Catalytic recombination device 2 Cylindrical part 3 Return part (opening sealing member, end plate, flow direction conversion part)
DESCRIPTION OF SYMBOLS 4 2nd cylindrical body 4A End plate part of 2nd cylindrical body 5 Flange part 6 Bolt 7 Internal connection member 8 Annular flow path 9 Catalyst structure 10 Catalyst holder 11 Catalyst part 12 Through-hole 13 of catalyst part 13 Annular projection Part 14 Annular support part 15 Short cylindrical support member 16 Bolt 50 Radioactive waste storage tank 51 Nozzle 52 Flange part

Claims (9)

A recombination device for attaching hydrogen generated inside the container to oxygen using a catalyst, attached to the container,
A first tubular body through which the hydrogen and oxygen-containing gas flowing from the container flows;
A return part connected to the outlet of the first cylindrical body and returning the gas flowing in from the first cylindrical body to the container;
The recombination apparatus, wherein the first cylindrical body has a catalyst unit that combines the hydrogen and the oxygen on the inlet side.   The return portion is connected to the first cylindrical body and flows into the second cylindrical body formed so as to surround the outer surface of the first cylindrical body. The recombination apparatus according to claim 1, further comprising: a direction changing unit that changes the direction of the gas and flows the gas into the second cylindrical body.   The recombination apparatus according to claim 1 or 2, wherein the first cylindrical body and the return portion are configured so as to be detachable from the container as a unit.   The said 1st cylindrical body and / or the said return part are provided with the opening sealing member which airtightly seals the opening part formed in the said container, The re-according to any one of Claims 1 thru | or 3 Coupling device.   The catalyst part has a large number of through-holes carrying the catalyst on the surface, and has a substantially plate-like or cylindrical member that introduces the gas containing the hydrogen and oxygen and recombines the hydrogen and oxygen. The recombination device according to any one of claims 1 to 4.   The recombination device according to any one of claims 1 to 5, wherein the catalyst part is formed by partitioning through holes adjacent to each other with a thin wall.   The recombination apparatus according to claim 6, wherein a cross section of the catalyst portion is a polygon.   Natural convection is generated in the first cylindrical body against the flow resistance in the plurality of through holes due to the buoyancy of the gas caused by the heat generated by the recombination reaction of the hydrogen and oxygen in the catalyst portion. The recombination apparatus according to claim 6 or 7, wherein the effective length of the first cylindrical body and the thickness of the catalyst portion are set. The recombination apparatus according to claim 8, wherein the catalyst portion has a thickness of about 5 mm or less.

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