JPWO2012029714A1 - Nuclear exhaust gas recombination catalyst and recombiner - Google Patents

Abstract

An object of the present invention is to suppress the performance degradation of the recombination catalyst due to the low-molecular siloxane that flows in in the treatment of radioactive gas waste discharged from a nuclear reactor. And, the present invention is a nuclear exhaust gas recombination catalyst that recombines hydrogen and oxygen in water vapor contained in radioactive gas waste discharged from a nuclear reactor at a nuclear power plant, and the carrier is finely and closely mixed. It includes a composite phase of γ-Al 2 O 3 and α-Al 2 O 3.

Description

The present invention relates to a recombiner employing nuclear waste gas recombination catalyst and catalyst to convert and H ₂ contained in the radioactive gaseous waste discharged from the reactor in a nuclear power plant in H _{2 O.}

In a boiling water nuclear power plant, reactor water in a nuclear reactor is partially decomposed into hydrogen and oxygen by radiation decomposition. The hydrogen and oxygen are discharged from the reactor as radioactive gas waste together with the water vapor evaporated from the reactor water. The water vapor containing hydrogen and oxygen passes through the recombination catalyst filled in the recombiner at the rear stage of the reactor, and the hydrogen and oxygen recombine with H ₂ O on the catalyst. In order to efficiently perform the recombination reaction on the catalyst, air is added between the nuclear reactor and the recombination apparatus.

The recombination catalyst includes a support containing at least one substance selected from SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and C, Ru, Pd, Pt, Ir, W, Ag, Au Patent Document 1 discloses a catalyst comprising at least one substance selected from R, Rh, and Re. Patent Document 2 discloses a recombination catalyst in which Pd is supported on an α-Al ₂ O ₃ support. Patent Document 3 also includes α-Al ₂ O ₃ and θ-Al ₂ O ₃ in which active Al ₂ O ₃ of an Al ₂ O ₃ coat on a substrate can be identified by X-ray diffraction, and A material containing at least one selected from δ-Al ₂ O ₃ , γ-Al ₂ O ₃ , κ-Al ₂ O ₃ , χ-Al ₂ O ₃ , and ρ-Al ₂ O ₃ is described. However, the object is detoxification of hydrocarbons, carbon monoxide, and nitric oxide, especially automobile exhaust gas.

JP 2001-56391 A JP-A-5-38432 JP-A-62-241552

In recent years, in nuclear power plants, silicone-based elastic bodies have been used for radioactive gas waste discharged from nuclear reactors as a sealant material in piping systems of equipment inside the reactor and upstream from the reactor. As a hydrolysis component of this sealant material, it has been found that a low molecular siloxane compound in exhaust gas is included depending on operating conditions, and the recombination catalyst filled in the recombination apparatus is poisoned by this low molecular siloxane compound. . As a result, it was found that H ₂ remained at a high concentration in the exhaust gas discharged from the recombiner. In addition, when the alumina support is heated in the presence of water vapor, sintering occurs, and the specific surface area is reduced to lower the catalyst performance.

For this reason, in order to prevent an increase in the H ₂ concentration in the exhaust gas from the recombiner and to safely operate the nuclear power plant, the poisoning of siloxanes, particularly low molecular siloxanes contained in radioactive gas waste, is suppressed, In addition, suppression of sintering by water vapor and suppression of performance degradation of the recombination catalyst of the recombination apparatus are new issues.

The present invention has been made to solve the above-described problems, and can operate a nuclear power plant without causing an abnormal increase in the H ₂ concentration in the exhaust gas from the recombiner.

The present invention relates to a nuclear exhaust gas recombination catalyst for recombining hydrogen and oxygen in water vapor contained in a radioactive gas waste discharged from a nuclear reactor at a nuclear power plant, wherein the catalyst is supported on the carrier. Provided is a nuclear exhaust gas recombination catalyst comprising a catalyst component, wherein the carrier is composed of a composite phase in which γ-Al ₂ O ₃ and α-Al ₂ O ₃ are mixed, and α-Al ₂ O ₃ is a main component. Is. In addition to γ-Al ₂ O ₃ and α-Al ₂ O ₃ , the carrier can contain a small amount of other crystal structures of Al ₂ O ₃ .

The present invention also includes a support and a catalyst component supported on the support, and the support comprises a composite phase in which γ-Al ₂ O ₃ and α-Al ₂ O ₃ are finely intimately mixed. The present invention provides a nuclear exhaust gas recombiner containing a recombination catalyst using a carrier composed of γ-Al ₂ O ₃ dispersed in α _- Al ₂ O ₃ , the main component of which is Al ₂ O ₃ .

According to the present invention, poisoning of the recombination catalyst by the low-molecular siloxane compound in the radioactive gas waste discharged from the nuclear reactor and / or simple substance sintering by water vapor is suppressed, and H in the exhaust gas at the recombiner outlet is suppressed. _{2 The} nuclear power plant can be operated safely without increasing the concentration.

The outlet concentration of H ₂ in the reaction tube at various reaction gas conditions in recombination catalyst according to the invention is a graph showing. In recombination catalyst according to the invention, it is a graph showing the outlet concentration of H ₂ time course of the reaction tube at each reaction gas conditions in the low molecular weight siloxane compound (D5) flows. In recombination catalyst according to the invention, it is a graph showing the outlet concentration of H ₂ time course of the reaction tube at each reaction gas conditions in the low molecular weight siloxane compound (D5) flows. In recombination catalyst according to the invention, it is a graph showing the outlet concentration of H ₂ time course of the reaction tube at each reaction gas conditions in the low molecular weight siloxane compound (D5) flows. The XRD analysis result of the crystal | crystallization of the comparative catalyst 1 and the catalyst by this invention is shown. 1 is a schematic view of an exhaust gas treatment system of a nuclear power plant to which the present invention is applied. 1 is a schematic view of a nuclear power plant to which the present invention is applied. The outlet concentration of H ₂ in the reaction tube at various reaction gas conditions in recombination catalyst according to the invention is a graph showing. The XRD analysis result of the crystal | crystallization of the catalyst by this invention is shown.

  Hereinafter, some preferred embodiments of the present invention will be described.

(1) In the nuclear exhaust gas recombination catalyst, the blending ratio of γ-Al ₂ O ₃ and α-Al ₂ O ₃ is such that α-Al ₂ O ₃ is 75 to 99% by weight and γ-Al ₂ O ₃ is A recombination catalyst that is 1 to 25% by weight and that Al ₂ O ₃ of other crystal structures is 5% by weight or less (including zero%). This carrier calcinates γ-Al ₂ O ₃ at a predetermined temperature and causes a phase change to generate θ-Al ₂ O ₃ (where all change to θ-Al ₂ O ₃ Is not changed to α-Al ₂ O ₃ , or α-Al ₂ O ₃ and γ-Al ₂ O ₃ are mixed with a binder, molded and fired.

When γ-Al ₂ O ₃ is heated at a temperature exceeding 1200 ° C. for a long time, the whole may be changed to α-Al ₂ O ₃ , but when heated at a temperature of about 1150 ° C. or less, a part of the γ-Al ₂ O ₃ is γ Al ₂ O ₃ is formed by mixing a small amount of θ-Al ₂ O _{3 in} α-Al ₂ O ₃ with the other being -Al ₂ O ₃ . Catalyst Engineering Course 10 Elemental Catalyst Manual (published by Jinshokan Co., Ltd.), page 30 shows that when γ-Al ₂ O ₃ is heated to 1100 ° C or higher, the whole becomes θ-Al ₂ O ₃ and 1200 ° C. Although the whole can be interpreted as a phase change to α-Al ₂ O ₃ as described above, actually, γ-Al ₂ O ₃ remains as described above even at a temperature exceeding 1000 ° C., or in some cases, θ-Al ₂ O ₃ It was discovered that it may remain. This is because the carrier of the present invention has useful properties of γ-Al ₂ O ₃ and α-Al ₂ O ₃ , and without using a binder that is a negative factor for catalyst performance, γ-Al ₂ O ₃ And α-Al ₂ O ₃ are mixed, and an integrated support can be formed.

In addition, since the carrier of the present invention changes the phase of the integral γ-Al ₂ O ₃ raw material in the form of spheres and pellets only by heat treatment, α-Al ₂ O ₃ and γ-Al ₂ O ₃ after heat treatment are Even if it is finely and closely mixed, even if water vapor is present, α-Al ₂ O ₃ suppresses sintering of γ-Al ₂ O ₃ and does not deteriorate the catalyst performance.

On the other hand, α-Al ₂ O ₃ and γ-Al ₂ O ₃ may be mixed, and a binder may be added to this to be molded, fired, and supported by a catalyst. Therefore, there is a concern that the surface of γ-Al ₂ O ₃ is covered and the catalyst performance is impaired. In the case of such physical mixing, since γ-Al ₂ O ₃ and α-Al ₂ O ₃ are bonded by a binder, it cannot be said to be integrated in the present invention, but γ-Al ₂ O _{When 3} and α-Al ₂ O ₃ are mixed as fine particles, characteristics similar to (α + γ) Al ₂ O ₃ produced by the phase change of γ-Al ₂ O ₃ by heating can be obtained.

  In addition, when it mixes physically without using a binder, intensity | strength becomes low. Further, the yield of the catalyst is lowered.

In the present invention, “γ-Al ₂ O ₃ and α-Al ₂ O ₃ are integrated” means that γ-Al ₂ O ₃ and α-Al ₂ O ₃ are sintered or fired without a binder or the like. Means a state of being directly coupled by. On the other hand, when γ-Al ₂ O ₃ powder and α-Al ₂ O ₃ are mixed using a binder with a sufficiently small particle size and uniformly mixed and fired, they are bonded via the binder and γ- An intimate mixed layer of Al ₂ O ₃ and α-Al ₂ O ₃ can be obtained.

In the carrier of the present invention, γ-Al ₂ O ₃ and α-Al ₂ O ₃ account for 95% by weight or more of Al ₂ O ₃ weight, and the balance is other crystal structures such as θ-Al ₂ O ₃ and inevitable impurities. Consists of. It is desirable that γ-Al ₂ O ₃ and α-Al ₂ O ₃ are finely and closely integrated, and the most preferred support according to the present invention is substantially free of binder components other than Al ₂ O ₃ , Therefore, adverse effects due to elution of the binder component can be prevented. However, γ-Al ₂ O ₃ and α-Al ₂ O ₃ may be mixed as a fine powder, molded into a columnar shape or a pellet shape, and fired. Further, the above mixture may be fired and pulverized to make this powder into a slurry, which may be applied to a honeycomb or plate-like substrate.

(2) In the nuclear waste gas recombination catalyst, the mixing ratio of the _{γ-Al 2 O 3 α-} Al 2 O 3 is, _alpha-Al 2 _{O 3} is at 85 to 94 wt%, the _gamma-Al 2 _{O 3} A recombination catalyst comprising 6 to 15% by weight of Al ₂ O ₃ having a crystal structure other than α and γ of 5% by weight or less.

  (3) A recombination catalyst in which the catalyst component is Pd in the nuclear exhaust gas recombination catalyst.

(4) In the above nuclear exhaust gas recombination catalyst, the specific surface area of the catalyst is ^{5 m} 2 / g or more, recombination catalyst which is preferably 6~60m ² / g.

  (5) In the nuclear exhaust gas recombination catalyst, a recombination catalyst in which the CO adsorption amount of the catalyst is 2 μmol / g or more.

(6) Nuclear exhaust a recombiner, _gamma-Al mixing ratio of 2 _{O 3} and _alpha-Al 2 _{O 3} is in _alpha-Al 2 _{O 3} is 75 to 99 wt%, _gamma-Al 2 _{O 3} A recombiner using a catalyst in which a catalyst component is supported on a carrier composed of Al ₂ O _{3 having} another crystal structure of 1 to 25% by weight and the balance of 5% by weight or less (including zero%) and other inevitable impurities. In the above,% by weight is based on the weight of Al ₂ O ₃ .

(7) In the nuclear exhaust gas recombiner, the mixing ratio of the _γ-Al 2 _{O 3} and _α-Al 2 _{O 3} is, _α-Al 2 _{O 3} is at 85 to 94 wt%, _γ-Al 2 _{O 3} Is a recombiner in which Al ₂ O ₃ having a crystal structure other than α and γ is 5% by weight or less.

(8) In the nuclear exhaust gas recombiner, the nuclear exhaust gas recombiner is characterized in that a part of the γ-Al ₂ O ₃ and α-Al ₂ O ₃ are chemically bonded.

  (9) In the nuclear exhaust gas recombiner, the recombiner in which the catalyst component is Pd.

The carrier composed of α-Al ₂ O ₃ alone does not cause a phase change in a water vapor atmosphere and is advantageous in that it is relatively durable compared to other phases, but the surface area of the carrier is very low. Therefore, the surface area of the impregnated Pd is also low, and as described above, the performance is likely to deteriorate when the siloxane flows. On the other hand, a carrier made of γ-Al ₂ O ₃ alone can have a high Pd surface area because of the high specific surface area of the carrier, but it tends to cause a reduction in surface area or phase change due to sintering in a water vapor atmosphere.

In a particularly preferred embodiment of the present invention, rather than simply physically mixing α-Al ₂ O ₃ and γ-Al ₂ O ₃ , the α phase and the γ phase are closely mixed at the molecular level, The γ phase surrounded by the α phase becomes difficult to sinter, and by supporting Pd on such a carrier, the surface area can be kept high to some extent and the hydrothermal resistance can also be imparted. In the case of a carrier in which α-Al ₂ O ₃ and γ-Al ₂ O ₃ are simply physically mixed, the above effects cannot be expected.

In order to form a γ phase surrounded by an α phase, α-Al ₂ O ₃ is preferably the main component of the support. That is, with respect to the composition ratio of α-Al ₂ O ₃ and γ-Al ₂ O ₃ , the proportion of α-Al ₂ O ₃ is preferably 75 to 99% by weight, more preferably 85 to 96% by weight. In the case of 75% by weight or less, since the influence of sintering under a steam atmosphere is large, the surface area is likely to be reduced and the phase is likely to change. In the case of 99% by weight or more, the surface area of the supported Pd does not become sufficiently large.

As shown in FIGS. 6 and 7, the radioactive gaseous waste (exhaust gas) 1 from the reactor 8 mainly composed of water vapor passes through a turbine 9 and a preheater 7 to form a low molecular siloxane compound contained in the exhaust gas. If the recombination catalyst 2 flows into the recombination catalyst layer of the recombiner 3 and poisons the recombination catalyst 2, the catalyst performance deteriorates, and H ₂ remains at a high concentration in the exhaust gas discharged from the recombiner. This exhaust gas is discharged to the outside through the condenser 10 and the dehumidifying cooler 11, but it is necessary to prevent the H ₂ concentration in the exhaust gas from increasing in order to operate the nuclear power plant safely. For this reason, it is necessary to suppress the catalyst performance fall by a low molecular siloxane compound. In addition, it was confirmed that the carrier of the recombination catalyst causes sintering in the presence of water vapor and deteriorates the catalyst performance. Therefore, it is also important to prevent carrier sintering.

  Controlling the temperature of the recombination catalyst is important in order to suppress poisoning by low molecular weight siloxane. FIG. 6 is an example in which the temperature of the recombination catalyst is controlled by controlling the preheater temperature while measuring the temperature of the lower part of the recombiner. The same applies to the upflow structure from the top to the bottom. Further, as means for controlling the temperature of the recombination catalyst, in addition to the temperature at the lower part of the recombiner, the temperature at the upper part of the recombiner and the internal temperature of the recombination catalyst can be used. If the temperature management is unnecessary, the preheater temperature control is not particularly required.

  As a result of detailed examination, it was found that the influence of the low-molecular siloxane compound and / or water vapor flowing into the recombination catalyst layer can be suppressed by improving the support of the recombination catalyst.

As a low molecular siloxane compound contained in the radioactive gas waste, there is a silicon compound, and an example is siloxane. The low molecular siloxane has a standard structure of —OSi (CH ₃ ) ₂ — continuously bonded. In particular, a compound having a cyclic shape is described as D5 when the aforementioned reference structure is five. Usually, a compound of about D3 to D8 is targeted, but in the present invention, a compound having two or less reference structures can also be used as a low molecular siloxane. In a compound having two or less reference structures, a cyclic structure cannot be formed, and thus a linear structure is assumed, and a terminal is assumed to be —OH. Therefore, the low molecular siloxane compounds targeted in the present invention are D1 to D8.

  The low molecular weight siloxane compound that has flowed into the recombination catalyst is present on the surface of the catalyst so as to cover the catalytically active component. For this reason, it becomes difficult for the original reactant to be adsorbed on the catalytically active component, and the performance of the catalyst is lowered. However, by controlling the specific surface area of the catalyst appropriately, the normal catalyst performance can be maintained at a high level, and the performance degradation during the inflow of the low molecular weight siloxane compound can be suppressed.

The specific surface area of the catalyst is desirably 5 m ² / g or more. When the molecular weight is 5 m ² / g or less, when low-molecular siloxane accumulates on the surface, the catalytically active component is easily covered, and the performance is deteriorated quickly. Although the specific surface area should just be large, 6-60 m < ² > / g is preferable and since there also exists a problem of the fall of the mechanical strength in use, 35 m < ² > / g or less is especially preferable.

Pd, Pt, etc. can be used as the catalytically active component. In particular, Pd is preferable because it exhibits high recombination performance even under conditions where the O ₂ / H ₂ ratio is large. The catalytically active component is preferably supported at 0.1 to 1.0% by weight, and preferably 0.3 to 0.8% by weight.

  The amount of the catalyst active component exposed on the support surface is also important. There is a CO adsorption amount as an index for evaluating the surface exposure amount of Pd or the like. A large amount of CO adsorption indicates that a large amount of Pd is present on the surface of the carrier. On the other hand, when the amount of CO adsorption is small, it indicates that Pd is small on the surface of the carrier. If the resorption catalyst also has a small amount of CO adsorption, the influence of the inflowing low molecular weight siloxane is likely to occur. Therefore, the CO adsorption amount is desirably 2 μmol / g or more.

  The surface exposure amount of the catalytic active component depends on the size of the specific surface area when the catalytic active component loading amount is equal. When the specific surface area is small, the catalytically active component is buried in the support or exists on the surface as coarse agglomerated particles, so that the performance is likely to deteriorate when the low molecular siloxane compound flows in. As described above, the present invention is particularly suitable for the treatment of exhaust gas containing a low-molecular-weight siloxane compound in the reactor exhaust gas, but it is difficult to cause sintering even when exposed to high temperature of the exhaust gas. Since the surface area can be maintained, it can also be used as a recombination catalyst for reactor exhaust gas that does not contain a low-molecular siloxane compound.

In the following description, the composite phase of γ-Al ₂ O ₃ and α-Al ₂ O _{3 according} to the present invention may be expressed as (γ + α) Al ₂ O ₃ . The carrier made of (γ + α) Al ₂ O ₃ can maintain the performance for a long time without lowering the catalyst performance due to the strength deterioration. γ-Al ₂ O ₃ is not simply a physical mixture of γ-Al ₂ O ₃ and α-Al ₂ O _3, but very finely and closely mixed or partially chemically at the molecular level. It is what is combined. In such (γ + α) Al ₂ O ₃ , for example, by heating γ-Al ₂ O ₃ at 1000 to 1150 ° C. for 30 minutes to 3 hours, a part of γ-Al ₂ O ₃ undergoes a phase change. Α-Al ₂ O ₃ , and α-Al ₂ O ₃ and γ-Al ₂ O ₃ are considered to be very finely and closely mixed or partially chemically bonded at the molecular level. When the crystal structure of the heat-treated γ-Al ₂ O ₃ was examined by XRD, it was confirmed that α-Al ₂ O ₃ and γ-Al ₂ O ₃ were mixed. When α-Al ₂ O ₃ and γ-Al ₂ O ₃ are finely and closely mixed at the molecular level, the low molecular siloxane compound is a surface of α-Al ₂ O ₃ and γ-Al ₂ O ₃ . As a result, it is difficult to adhere to and coat the catalyst and suppress sintering, so that the catalyst performance is not deteriorated. In the case of catalyst 1 to catalyst 3, α-Al ₂ O ₃ and γ-Al ₂ O ₃ are mixed, but only a peak of α-Al ₂ O ₃ was observed in comparative catalyst 1.

The composition ratio of (α + γ) Al ₂ O ₃ was estimated as follows.
α-Al ₂ O ₃ surface area = 5 m ² / g
γ-Al ₂ O ₃ surface area = 230 m ² / g
When the ratio of α phase and γ phase at a predetermined surface area is calculated,
In Al ₂ O ₃ having a surface area of 15 m ² / g, α: γ = 0.96: 0.04
In Al ₂ O ₃ having a surface area of 30 m ² / g, α: γ = 0.87: 0.13
It becomes. Therefore, when evaluated in the above _α-Al 2 _{O 3} and _γ-Al 2 _{O 3,} the amount of the _{α-Al 2 O 3 γ-} Al 2 O 3 is 87-96 wt%, gamma-Al The amount of ₂ O ₃ is 4 to 13% by weight.

The shape of the catalyst to which the present invention is applied includes a spherical shape, a pellet shape, and a column shape, and further includes a honeycomb and a plate-shaped catalyst. In preparing the carrier according to the present invention, γ-Al ₂ O ₃ formed into a spherical shape, a pellet shape, a column shape or the like is heat-treated at a predetermined temperature to obtain (α + γ) Al ₂ O ₃ , and the catalyst component is contained on the surface thereof. You may carry | support by methods, such as erosion and adhesion. Further, the catalyst component and the (α + γ) Al ₂ O ₃ carrier are prepared as a slurry or solution to prepare a wash coat, applied to a honeycomb substrate or a plate-like substrate, and then the (α + γ) Al ₂ O ₃ carrier is baked before the catalyst component. May be supported.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

In this example, the process gas at the time of reactor startup was adjusted and a startup simulation test was performed. As the catalyst, Pd / (γ + α) -Al ₂ O ₃ supporting Pd was used. For comparison, Pd / α-Al ₂ O ₃ was also evaluated as the comparative catalyst 1 under the same conditions.

(Manufacture of catalyst 1)
By firing γ-Al ₂ O ₃ balls having a surface area of 230 m ² / g and a diameter of 5 to 7 mm at 1,150 ° C., both (α + γ) -Al ₂ O ₃ of 15 m ² / g are mixed. An Al ₂ O ₃ support was prepared. The Al ₂ O ₃ carrier (950 g) was impregnated with 410 mL of dinitrodiamine palladium aqueous solution containing 4.8 g of Pd metal by a pore filling method, dried at 100 ° C. for 2 hours, and then calcined at 400 ° C. for 5 hours. Thereafter, the calcined product was put into 3 L of 5% sodium formate aqueous solution, liquid phase reduction was performed, and then drying at 100 ° C. was performed for 6 hours to obtain Catalyst 1. The amount of Pd supported was 0.5%. As a result of XRD measurement, as shown in FIG. 5, it was confirmed that the carrier coexisted with α phase and γ phase.

This catalyst has a specific surface area of 14 m ² / g measured by BET method by N ₂ adsorption with BELSORP-miniII manufactured by Nippon Bell, and a CO adsorption amount measured by BELCAT-A manufactured by Nippon Bell is 3.9 μmol / g. . The CO adsorption amount is an index indicating the dispersibility of the supported Pd.

(Production of comparative catalyst 1)
Surface area 230 m ² / g, diameter by a _γ-Al 2 _{O 3} balls 7mm firing 1,300 ° C. from 5 to prepare the _α-Al 2 _{O 3} carrier is ^{5 m} 2 / g. The Al ₂ O ₃ carrier (950 g) was impregnated with 410 mL of dinitrodiamine palladium aqueous solution containing 4.8 g of Pd metal by a pore filling method, dried at 100 ° C. for 2 hours, and then calcined at 400 ° C. for 5 hours. Thereafter, the calcined product was put into 3 L of 5% sodium formate aqueous solution, liquid phase reduction was performed, and then drying at 100 ° C. was performed for 6 hours to obtain Comparative Catalyst 1. The amount of Pd supported was 0.5%, and XRD measurement confirmed that the carrier was an α phase as shown in FIG.

This catalyst has a specific surface area of 4.8 m ² / g and a CO adsorption amount of 1.7 μmol / g as measured in the same manner as in Example 1.

Example 1
In the following experiment, it was compared with the comparative catalyst 1 how the catalyst performance using the carrier according to the present invention changes in the exhaust gas in the steam-containing exhaust gas (model gas). In cases 1 to 4 in which the reaction gas flow rate was changed, the steam-containing reaction gas was treated using the catalyst 1 and the comparative catalyst 1. The results are shown in FIG.

As the reaction gas, a gas obtained by evaporating a predetermined amount of pure water into water vapor with a water vapor generator and adding H ₂ , O ₂ , and air was used. This reaction gas was caused to flow into the recombination catalyst layer at 140 ° C. As the relationship between the catalyst amount and the reaction gas amount, the space velocity represented by (Expression 1) and the linear velocity represented by (Expression 2) were calculated.

Space velocity (h ⁻¹ ) = reaction gas amount (mL / h) / catalyst amount (mL) (Formula 1)
Linear velocity (m / s) = reaction gas flow rate (m ³ / s) / catalyst cross-sectional area (m ² ) (Formula 2)
The reaction tube was filled with a recombination catalyst at the center in the length direction to form a recombination catalyst layer. The reaction gas introduced into the reaction tube passes through the recombination catalyst layer and reaches the outlet. The reaction gas conditions were Cases 1 to 4 in which each gas flow rate was changed. In the above (Formula 2), the catalyst cross-sectional area is the cross-sectional area of the reaction tube calculated using the inner diameter of the reaction vessel.

  As is apparent from FIG. 1, it can be seen that the catalyst according to the present invention maintains higher catalyst performance than Comparative Catalyst 1 in any of Cases 1 to 4.

(Case 1)
Pure water 17.1 mL / min is vaporized into water vapor by a water vapor generator, H ₂ 175.4 mL / min and O ₂ 87.9 mL / min are mixed, and air is added at 32.0 mL / min. It was. The space velocity was 41,129 h ⁻¹ and the linear velocity was 0.63 m / s.

(Case 2)
Pure water 17.2mL / min is vaporized into water vapor with a water vapor generator, H ₂ 351.6mL / min and O ₂ 125.7mL / min are mixed, and air is added at 64.0mL / min. It was. The space velocity was 41,835 h ⁻¹ and the linear velocity was 0.64 m / s.

(Case 3)
Pure water 17.2 mL / min is vaporized with a water vapor generator, and H ₂ 528.5 mL / min and O ₂ 264.3 mL / min are mixed and air is added 96.1 mL / min. It was. The space velocity was 42,498 h ⁻¹ and the linear velocity was 0.65 m / s.

(Case 4)
17.3 mL / min of pure water is vaporized into water vapor with a steam generator, H ₂ 706.2 mL / min and O ₂ 353.1 mL / min are mixed, and air is added to 128.4 mL / min. It was. The space velocity was 43,305 h ⁻¹ and the linear velocity was 0.66 m / s.

The H ₂ concentration in the reaction gas that has passed through the recombination catalyst layer is determined by using a PDD (Pulsed Discharge Detector) gas chromatograph analyzer (GC Science Co., Ltd. GC) after condensing water vapor into water in an ice-cooled cooling bath. -4000) and measured. As the mode of the PDD detector, HID (Helium Ionization Detector) was used. 100 μL of sample gas (reactive gas that passed through the recombination catalyst layer) was sucked with a pump. The gas inlet temperature of the gas chromatograph was room temperature, the detector temperature was 150 ° C., and the oven temperature was 50 ° C. The column had an outer diameter of 1/8 inch φ × length of 2 m, and Molecular Sieve 13X-S (60-80 mesh) was used as a packing material. As the carrier gas, He was allowed to flow at 20 mL / min. Moreover, He was flowed at 30 mL / min as discharge gas.

FIG. 1 shows the outlet H ₂ concentration after 60 minutes after adjusting to each reaction gas condition. The catalyst of Example 1 was found to have a lower outlet H ₂ concentration than the catalyst of Reference 1 under the conditions of Cases 1 to 4, and the recombination performance of the catalyst itself was high.

(Example 2)
Changes in recombination performance with time when a low molecular siloxane compound was added to the reaction gas were examined. Specifically, the reaction gas to which the low molecular siloxane compound was added was introduced into the reaction tube filled with the recombination catalyst layer, and the H ₂ concentration at the outlet of the reaction tube was measured.

The reaction gas was introduced into the reaction tube filled with the recombination catalyst, and D5, which is a kind of siloxane, was introduced from the top of the reaction tube to 6.47 × while the H ₂ concentration at the outlet of the reaction tube (outlet H ₂ concentration) was stable. The ^{solution was} added dropwise at 10 ⁻⁸ mol / min. The reaction gas conditions were set to Case 1 described in Example 1 where the influence of the low molecular weight siloxane compound is most likely to occur. In FIG. 2, the change with time of the outlet H ₂ concentration of the reaction tube is shown. The reaction time and the outlet concentration of H ₂ in the figure relative to the reaction time and the outlet concentration of H ₂ at D5 is turned on. Catalyst 1 had an outlet H ₂ concentration of 210 vol% after 210 minutes from the start of the test, whereas Comparative Catalyst 1 had increased to 3.7 vol%, and Catalyst 1 had an increased outlet H ₂ concentration. It can be suppressed to about ½ of the comparative catalyst 1, and it was found that the low-molecular siloxane compound exhibits high durability.

(Example 3)
In this example, the change over time in the recombination performance when a low molecular siloxane compound was added to the reaction gas using the catalyst 2 was examined.

(Adjustment of catalyst 2)
By firing γ-Al ₂ O ₃ balls having a surface area of 230 m ² / g and a diameter of 6 to 8 mm at 1,100 ° C., α-Al ₂ O ₃ and γ-Al ₂ O ₃ that are 30 m ² / g are obtained. (Α + γ) -Al ₂ O ₃ support in which both of the above were mixed was prepared. The Al ₂ O ₃ carrier (950 g) was impregnated with 410 mL of dinitrodiamine palladium aqueous solution containing 4.8 g of Pd metal by a pore filling method, dried at 100 ° C. for 2 hours, and then calcined at 400 ° C. for 5 hours. Thereafter, the calcined product was put into 3 L of 5% sodium formate aqueous solution, liquid phase reduction was performed, and then drying at 100 ° C. was performed for 6 hours to obtain Catalyst 2. The amount of Pd supported was 0.5%, and XRD measurement confirmed that the α phase and the γ phase coexisted as shown in FIG.

This catalyst has a specific surface area of 24.0 m ² / g and a CO adsorption amount of 8.4 μmol / g as measured in the same manner as in Example 1. The reaction gas conditions were Case 5, and D5 was dropped from the upper part of the reaction tube at 2.95 × 10 ⁻⁷ mol / min.

(Case 5)
Pure water 88.4 L / min is vaporized into water vapor by a water vapor generator, H ₂ 2.0 L / min and O ₂ 1.01 L / min are mixed, and nitrogen is added at 0.21 L / min. Using. The space velocity was 5344 h ⁻¹ and the linear velocity was 0.65 Nm / s.

FIG. 3 shows the change with time of the outlet H ₂ concentration of the reaction tube. The reaction time and the outlet concentration of H ₂ in the figure relative to the reaction time and the outlet concentration of H ₂ at D5 is turned on. It was found that the catalyst 2 had an outlet H ₂ concentration of 0.05 vol% or less during the test time of 120 hours and exhibited high durability against the low molecular siloxane compound.

Example 4
In this example, the change over time in the recombination performance when a low molecular weight siloxane compound was added to the reaction gas using the catalyst 3 was examined in the same manner as in Example 2. The reaction gas conditions were Case 1.

(Manufacture of catalyst 3)
By firing γ-Al ₂ O ₃ balls having a surface area of 230 m ² / g and a diameter of 3 to 5 mm at 1,100 ° C., α-Al ₂ O ₃ and γ-Al ₂ O ₃ of 33 m ² / g were obtained. An Al ₂ O ₃ support in which both were mixed was prepared. The Al ₂ O ₃ carrier 1100 g was impregnated with 560 mL of dinitrodiamine palladium aqueous solution containing 3.3 g of Pd metal by a pore filling method, dried at 100 ° C. for 2 hours, and then calcined at 400 ° C. for 5 hours. Thereafter, the fired product was put into 3 L of 5% sodium formate aqueous solution, liquid phase reduction was performed, and then drying at 100 ° C. was performed for 6 hours to obtain Catalyst 3. The amount of Pd supported was 0.3%, and XRD measurement confirmed that an α phase and a γ phase coexisted as shown in FIG.

This catalyst has a specific surface area of 33.2 m ² / g and a CO adsorption amount of 7.0 μmol / g as measured in the same manner as in Example 1.

FIG. 4 shows the change over time in the outlet H ₂ concentration of the reaction tube. The reaction time and the outlet concentration of H ₂ in the figure relative to the reaction time and the outlet concentration of H ₂ at D5 is turned on. It was found that the catalyst 3 had a high outlet port H ₂ concentration of 0.05 vol% or less during the test time of 210 minutes, and showed high durability against the low molecular siloxane compound.

(Example 5)
In this example, the process gas at the time of reactor startup was adjusted and a startup simulation test was performed. As the catalyst, Pd / (γ + α) -Al ₂ O ₃ supporting Pd was used. As (γ + α) -Al ₂ O _3, a catalyst 4 in which γ-Al ₂ O ₃ and α-Al ₂ O ₃ were chemically mixed and a catalyst 5 in which physical mixing was performed were used.

(Manufacture of catalyst 4)
Boehmite powder was formed into a cylindrical catalyst having a diameter of 1.6 mm by an extruder and baked at 1100 ° C. The specific surface area of the obtained molded body was 32 m ² / g. Further, when the crystal structure was examined by XRD, it was confirmed that α-Al ₂ O ₃ and γ-Al ₂ O ₃ were mixed. 100 g of this molded body was impregnated with 6.92 mL of a dinitrodiamine palladium aqueous solution containing 0.50 g of Pd metal by a pore filling method, dried at 100 ° C. for 2 hours, and then fired at 400 ° C. for 4 hours. Thereafter, the calcined product was put into 3 L of 5% sodium formate aqueous solution, liquid phase reduction was performed, and then drying at 100 ° C. was performed for 6 hours to obtain Catalyst 4.

(Manufacture of catalyst 5)
Boehmite powder was fired at 600 ° C and 1200 ° C. The specific surface areas of the respective fired powders were 189 m ² / g and 4 m ² / g. Moreover, when the crystal structure was investigated by XRD, it was confirmed that each baked powder was a single phase of γ-Al ₂ O ₃ and α-Al ₂ O ₃ . These γ-Al ₂ O ₃ and α-Al ₂ O ₃ are physically mixed with 10% by weight of γ-Al ₂ O ₃ and 85% by weight of α-Al ₂ O ₃ as a binder and 5% by weight of boehmite. Then, it was fired at 600 ° C. after being formed into a cylindrical shape having a diameter of 1.6 mm by an extruder. The specific surface area of this molded body was 34 m ² / g. The same operation as that of the catalyst 4 was performed on this molded body, and a Pd loading operation was performed, whereby a catalyst 5 was obtained.

In both catalysts 4 and 5, the amount of Pd supported was 0.5%. The result of analyzing the crystal form by XRD is shown in FIG. X'Pert Pro manufactured by PANalytical was used as the XRD measuring device. With catalyst 4, it was confirmed that the α phase and γ phase coexisted in the carrier. On the other hand, in the catalyst 5, the α phase was detected, and the γ phase was not clearly recognized. This is because the final specific surface area was mixed so as to be 30 m ² / g, so the mixing ratio of γ-Al ₂ O ₃ was small, but from the specific surface area measurement result described later, γ-Al ₂ O ₃ was included. It is clear that As a specific surface area measuring device, HM Model-1210 manufactured by Nippon Bell was used.

The specific surface area of this catalyst as measured in the same manner as in Example 1 is 34 m ² / g for catalyst 4 and 32 m ² / g for catalyst 5. Moreover, the CO adsorption amount measured in the same manner as in Example 1 is 13.2 μmol / g for catalyst 4 and 6.3 μmol / g for catalyst 5. Further, the strength at which 50 arbitrarily collected catalysts were crushed was measured using a Chatillon hardness tester TCD500. The average value of the breaking strength was 286 N for catalyst 4 and 10 N or less for catalyst 5.

  In the following experiment, in the same manner as in Example 1, it was examined how the catalyst performance of the catalysts 4 and 5 using the carrier according to the present invention changed in the steam-containing exhaust gas (model gas).

As for the reaction gas, pure water 17.1 mL / min is vaporized into water vapor by a water vapor generator, H ₂ 175.4 mL / min and O ₂ 87.7 mL / min are mixed, and air is added 31.9 mL / min. What was done was used. The space velocity was 41,236 h ⁻¹ and the linear velocity was 0.63 m / s.

The H ₂ concentration in the reaction gas that passed through the recombination catalyst layer was measured in the same manner as in Example 1.

FIG. 8 shows the change in outlet H ₂ concentration for 60 min after the start of the test. It was found that the catalyst 4 showed higher catalyst performance than the catalyst 5 for 60 minutes after starting the reaction.

  INDUSTRIAL APPLICABILITY The present invention can be used for the treatment of radioactive gas waste at a nuclear power plant, particularly for recombination removal of hydrogen gas.

1: radioactive gas waste, 2: recombiner catalyst, 3: recombiner, 4: heating equipment, 5: temperature measuring device, 6: controller, 7: preheater, 8: nuclear reactor, 9: turbine, 10: condenser, 11: dehumidifying cooler

Claims (12)

In a nuclear exhaust gas recombination catalyst for recombining hydrogen and oxygen in water vapor contained in radioactive gas waste discharged from a nuclear reactor at a nuclear power plant, the catalyst includes a support and a catalyst component supported on the support. The nuclear exhaust gas recombination catalyst, wherein the carrier is composed of a composite phase in which γ-Al ₂ O ₃ and α-Al ₂ O ₃ are mixed, and α-Al ₂ O ₃ is a main component. In claim 1 Nuclear exhaust gas recombination catalyst according, based on the weight of _Al 2 _{O 3,} the mixing ratio of the _γ-Al 2 _{O 3} and _α-Al 2 _{O 3} is, _α-Al 2 _{O 3} is 75 to 99 weight %, Γ-Al ₂ O ₃ is 1 to 25% by weight, other crystal structure is 5% by weight or less (including zero%), and unavoidable impurities. In nuclear exhaust gas recombination catalyst according to claim 1 or 2, wherein, based on the weight of _Al 2 _{O 3,} the mixing ratio of the _gamma-Al 2 _{O 3} and _α-Al 2 _{O 3} is, the _α-Al 2 _{O 3} 85~ A nuclear exhaust gas recombination catalyst comprising 94% by weight and 6-15% by weight of γ-Al ₂ O ₃ . The nuclear exhaust gas recombination catalyst according to any one of claims 1 to 3, wherein γ-Al ₂ O ₃ and a part of α-Al ₂ O ₃ are chemically bonded. Binding catalyst.   The nuclear exhaust gas recombination catalyst according to any one of claims 1 to 4, wherein the catalyst component is Pd. The nuclear exhaust gas recombination catalyst according to claim 1, wherein the catalyst has a specific surface area of 5 m ² / g or more.   The nuclear exhaust gas recombination catalyst according to any one of claims 1 to 6, wherein the CO adsorption amount of the catalyst is 2 µmol / g or more. And a catalyst component supported on the carrier, the carrier comprising a composite phase in which γ-Al ₂ O ₃ and α-Al ₂ O ₃ are mixed, and α-Al ₂ O ₃ being a main component. A nuclear exhaust gas recombiner characterized by containing a recombination catalyst. In nuclear exhaust gas recombiner according to claim 8, based on the weight of _Al 2 _{O 3,} the mixing ratio of the _γ-Al 2 _{O 3} and _α-Al 2 _{O 3} is, _α-Al 2 _{O 3} is 75 to 99 A nuclear exhaust gas recombiner characterized in that γ-Al ₂ O ₃ is 1 to 25% by weight, other crystal structure is 5% by weight or less (including zero%), and inevitable impurities. In nuclear exhaust gas recombiner according to claim 8 or 9, based on the weight of _Al 2 _{O 3,} the mixing ratio of the _γ-Al 2 _{O 3} and _α-Al 2 _{O 3} is, the _α-Al 2 _{O 3} A nuclear exhaust gas recombiner comprising 85 to 94% by weight and 6 to 15% by weight of γ-Al ₂ O ₃ . The nuclear exhaust gas recombiner according to any one of claims 8 to 10, wherein said γ-Al ₂ O ₃ and a part of α-Al ₂ O ₃ are chemically bonded. Recombiner.   The nuclear exhaust gas recombiner according to any one of claims 8 to 11, wherein the catalyst component is Pd.

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