JPS60122400A - Method of heating and decomposing used ion exchange resin - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the treatment of used ion exchange resins (hereinafter also referred to as waste resins), particularly radioactive used ion exchange resins generated from atomic couplants such as nuclear power plants. The present invention relates to a method for preventing the generation of harmful gases such as sulfur oxides (SOx) and ammonia (NH3) during thermal decomposition treatment.

[Background of the invention]

BACKGROUND OF THE INVENTION During the operation of nuclear power plants and the like, waste fluids containing various radioactive substances are generated, and these waste fluids are often treated using ion exchange resins. Disposal of radioactive used ion exchange resin (waste resin) generated in conjunction with this is considered to be one of the critical aspects of nuclear power plant operation. For example, in boiling water nuclear power plants, a significant portion of the radioactive waste generated is spent ion exchange resin.

Conventionally, this used ion exchange resin is mixed with an assimilating agent such as cement or asphalt, solidified in drums, and stored in a facility.

However, the amount of radioactive waste tends to increase year by year, and securing storage space and ensuring safety during storage have become important issues.

Furthermore, since used resin is an organic substance, there is a possibility that it will decompose and rot if stored for a long period of time. Therefore, when solidifying used resin, great attention has been paid to reducing the volume as much as possible (volume reduction) and converting it into a stable inorganic substance (mineralization). for example,
A method using acid decomposition has been proposed as a volume reduction and mineralization treatment method for used resin. HED is one of the acid decomposition methods.
L method (Hanford Engineering De
There is a method called vslopment laboratory method). This is a method of acid decomposing the waste resin using concentrated sulfuric acid (approximately 97% by weight) and nitric acid (approximately 60% by weight) at a temperature of 150 to 3000°C. Another example of the acid decomposition method is disclosed in JP-A-53-88500. This is a method of acid decomposing resin using concentrated sulfuric acid and hydrogen peroxide (approximately 30%). However, in these acid decomposition methods, the resin is dissolved and decomposed, and the decomposed liquid is evaporated and concentrated, so a large volume reduction ratio can be achieved, but the handling of the strongly acidic liquid and the operation of the equipment using the concentrated strong acidic liquid are difficult. There are many difficult problems such as corrosion and unestablished assimilation technology for the recovered concentrated liquid.

Therefore, as shown in JP-A-57-1446, a method has been proposed in which waste resin is decomposed using hydrogen peroxide in the presence of an iron catalyst, avoiding the use of strong acidic liquids. However, this method requires large amounts of hydrogen peroxide,
Considering that hydrogen peroxide is a silica, there are problems in that the cost is high and that the waste resin is not sufficiently decomposed and remains as an organic substance.

In order to avoid the above problems of the acid decomposition method, a volume reduction mineralization treatment method using a dry method has been developed. For example, as shown in Japanese Unexamined Patent Publication No. 57-12400, a method of burning waste resin using a fluidized bed has been proposed. Also,
JP-A-58-55608 discloses an incineration method using a multistage incinerator, JP-A-53-107,600 describes a decomposition method using steam, and JP-A-57-91500 describes a decomposition method using microwave heating. The law is published in Japanese Unexamined Patent Publication No. 52-13350.
Publication No. 0' proposes a decomposition method using molten salt.

Additionally, thermal decomposition methods using catalysts are currently being developed.

A common problem in these dry methods is that harmful sulfur oxide gas (SOX) and ammonia gas (NH) are generated when waste resin is thermally decomposed.

Therefore, as a countermeasure, exhaust gas treatment using an alkaline scrubber is being carried out. That is, the exhaust gas containing these harmful gases is passed through an aqueous sodium hydroxide solution, and the SOx and NH5 gases in the exhaust gas are reacted with sodium hydroxide to be treated as sodium sulfate and ammonium hydroxide.

However, this method only requires large-scale exhaust gas treatment equipment, and the decomposition residues and radionuclides scattered in the exhaust gas are also hydroxylated at the same time. some sodium sulfate,
Ammonium hydroxide must also be treated as radioactive waste.

(5) Therefore, in order to simplify the exhaust gas treatment equipment, we added a harmful waste scavenger (calcium carbonate, etc.) used in coal gasification systems into the reaction vessel during thermal decomposition of waste resin. Methods to capture the gas are being considered. However, in this method, 5 to 6 equivalents of the harmful gas generated
It is necessary to add twice the amount of scavenger, which causes a significant deterioration in the volume reduction ratio.

[Purpose of the invention]

The purpose of the present invention is to eliminate harmful sulfur oxide gas (SOx) and a...
The purpose of the present invention is to provide a method for preventing the occurrence of C.7nia.

[Summary of the invention]

The present invention provides a method for thermally decomposing a used ion exchange resin generated in an atomic couplant such as a nuclear power plant, in which the ion exchange resin is a cation exchange resin having a sulfosic acid group as an ion exchange group. An alkali metal or alkaline earth metal (6) that reacts with the sulfosic acid group to produce a solid sulfate is attached to the used ion exchange resin by an ion exchange reaction prior to thermal decomposition, and the ion exchange resin is an anion exchange resin having two and six quaternary A,7 groups as ion exchange groups, the A'J'f:
Prior to thermal decomposition, a sulfur oxide group, which reacts with a solid ammonium group to form a solid ammonium group, is attached to the used ion exchange resin by an ion exchange reaction, and during thermal decomposition, a sulfur oxide bath is added to the spent ion exchange resin. Another gist is a method for thermally decomposing a user's ion exchange resin, which is characterized by preventing the generation of ammonia gas.

The basic principle of the present invention will be explained below. Ion exchange resins generally have a combination of styryl and didinylbechase (D, V, B,) as a base, and a cation exchange resin is added to this as an ion exchange group. In case of sulfonic acid group (-8O3H), in case of anion exchange resin, quaternary anion ℃ 2 6 groups (-NR30H2, where R is CH3
It is an aromatic organic polymer compound having a structure in which the

Strongly acidic cation exchange resins having sulfonic acid groups and weakly basic anion exchange resins having quaternary ammonium groups pose a problem in terms of harmful gas generation when ion exchange resins are thermally decomposed. That is, when the above cation exchange resin is thermally decomposed, the sulfonic acid group, which is an ion exchange group, is decomposed and harmful sulfur oxide gas (SO gas) is generated.On the other hand, when the above anion exchange resin is thermally decomposed, ion exchange The quaternary ammonium group decomposes and generates harmful ammonia gas (NH5).In order to treat these exhaust gases, there are many problems as mentioned above. In order to solve this problem, we focused on utilizing the ion exchange ability, which is a characteristic of ion exchange resins, and added alkaline earth metal ions such as Ca2+r Na+ or alkali to the cation exchange resin to be thermally decomposed prior to thermal decomposition. After ion exchange of metal ions,
It performs thermal decomposition. Further, when thermally decomposing an anion exchange resin, prior to thermal decomposition, halodane ions are ion-exchanged and then thermally decomposed.

The ion exchange resin used in atomic couplants is disposed of as waste resin depending on its deterioration, but even when it becomes waste resin, it has the ability to perform ion exchange reactions with the above-mentioned alkaline earth metal ions, alkali metal ions, or halodane ions. has.

Therefore, by ion-exchanging the above ions in advance, when the cation-exchange resin is thermally decomposed, the ion-exchange group (-so5- group) and Ca ion react to form calcium sulfate, generating SOx. This is to prevent In this way, the ion exchange groups and (a ions) react on a one-to-one basis, so compared to the conventional method of adding SOx scavengers such as calcium carbonate, the amount of C& added can be reduced to IA to IA. The volume reduction ratio can be set to 1/4 to 115.

In addition, during thermal decomposition of the anion exchange resin, a quaternary ammonium group (-N(CH5)5), which is an ion exchange group, is
decomposes and generates harmful ammonia gas.However, using the same concept as cation exchange resins, if you ion-exchange halodane (9) ions such as iodine ions with anion exchange resin in advance and then heat decompose them, halodane can be produced. ammonium chloride is formed, and the generation of ammonia gas can be prevented.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to the drawings.

First, the case of a cation exchange resin will be explained.

It has a crosslinked structure in which a polymer is used as a polymer base and a sulfonic acid group (SO5H), which is an ion exchange group, is bonded thereto, and has a three-dimensional structure, and has the following structural formula. Moreover, the molecular formula is (C16H1503S)n.

(10) When such a cation exchange resin undergoes thermal decomposition, its ion exchange group, the sulfonic acid group (-8O5H), becomes
Sulfur oxides such as so2 and so3 become sulfur (SOX). On the other hand, when the resin body decomposes, CO2 and H2O are released.

It becomes a gas such as H2. For example, cation exchange resin 1
When kg is thermally decomposed, 781 SOx is generated, while CO2 is 125OA! Occur. Among these gases, gases such as CO2 are allowed to be released into the atmosphere, but SOx is harmful, so its release into the atmosphere is regulated.

Therefore, in the embodiment of the present invention, in order to prevent the generation of SOx during thermal decomposition, thermal decomposition is performed after calcium ions are ion-exchanged with a cation exchange resin in advance, as shown in equation (1) below.

The reaction equation during this thermal decomposition is shown in equation (2),
Instead of harmful SOx being generated, harmless CaSO4 is generated.

At this time, the so3 group and calcium react on a one-to-one basis.

Therefore, the amount of calcium ions required to decompose 1 kg of cation exchange resin is 0.14 klj.

On the other hand, in SOx recovery by adding calcium carbonate as in the prior art, since gaseous SOX and calcium carbonate react, only a portion of the added calcium carbonate reacts with SOX. Therefore, 5 to 6 of the equivalent of SoX
Double the amount of calcium carbonate must be added. In other words, in order to recover 90 parts of SOx generated when decomposing a 1 to 9 cation exchange resin, 1 part of calcium carbonate is
．． 75-2.1 kg must be added. The reaction formula at this time is shown in formula (3).

Figure 1 shows calcium (C
&) addition amount and SOx capture rate (1-SOX generation F theory S
(Ox generation amount). In the embodiment of the present invention in which Ca is ion-exchanged, S is added by adding Ca in an amount equivalent to S.
While the OX collection rate can be set to 100 cm, the conventional CaCO3 addition method can achieve a collection rate of 5 to 100 cm of S equivalent.
Even if 6 times as much Ca is added, a collection rate of only 90 to 95% can be obtained.

In the present invention, there are the following two conditions regarding elements (ions) that can be used as having an SOX trapping effect.

(1) It reacts with an ion exchange group (-so5 group) during thermal decomposition to form a sulfuric acid compound.

(2) The sulfuric acid compound formed during thermal decomposition is stable.

(13) Elements that satisfy the condition (1) are alkali metals such as sodium and alkaline earth metals such as calcium. Table 1 shows the decomposition temperatures of sulfuric compounds of these elements.

Table 1 The element (ion) added as a SOx scavenger must have a decomposition temperature higher than that of the sulfuric compound (14) than the temperature at which the resin is decomposed. for example,
In the thermal decomposition method using a catalyst, the decomposition temperature is 350°C, so all the elements in Table 1 can be used, but on the other hand,
Since the decomposition temperature is 700 to 900°C in a fluidized bed, it is desirable to use elements other than Ll, N & %B11 in Table 1.

Next, the case of an anion exchange resin will be explained.

Anion exchange resins have quaternary ammonium groups (Na30
H), and has the following structural formula. Moreover, the molecular formula is (C2oH26ON)n.

When such anion exchange resin undergoes thermal decomposition, the quaternary ammonium group, which is an ion exchange group, is decomposed to produce p1 ammonia (NHs), trimethylamine (N(CH3)3), dimethylamine (NH( C
Gases such as H3)2) and methylamine (NH2(CH3)) are generated. Among these, ammonia gas is harmful, and its release into the atmosphere is regulated.

On the other hand, when the resin body decomposes, gases such as CO2 are generated, similar to cation exchange resins. For example, assuming that 1 kg of anion exchange resin decomposes and all of the ion exchange groups become ammonia gas, ammonia gas is '16
1 occurs.

Therefore, in the embodiment of the present invention, in order to prevent the generation of ammonia gas during thermal decomposition, after ion-exchanging iodine ions with an anion exchange resin, as shown in the following formula (4), the thermal decomposition This is what we do.

As a result, ammonia becomes ammonium iodide (NH4I) and remains in the residue based on the same principle as that of a cation exchange resin. This can prevent the generation of ammonia gas.

In the present invention, the following two conditions apply to the element that can be used as having an ammonia-trapping effect.

(1) It must be an element that reacts with ammonia to form ammonium salt during thermal decomposition.

(2) The ammonium salt formed is stable.

Elements that satisfy the condition (1) are halogen group, and Table 2 shows the decomposition temperatures of ammonium halides. ☆ Table 2 (17) Elements (ions) added as an ammonia scavenger are anion exchange resins. The decomposition temperature of the ammonium salt must be higher than that of the ammonium salt.

For example, in the thermal decomposition method using a catalyst described below, the decomposition temperature is 350° C., so ■ or Br is preferable. on the other hand,
A fluidized bed cannot be used because the decomposition temperature is 700 to 900°C. Next, an embodiment of the method of the present invention will be described together with an apparatus for implementing the method. FIG. 2 is a diagram schematically showing the process, in which waste resin is supplied from a waste resin tank 1 to an ion exchange tank 2. Further, a calcium ion solution is supplied from the calcium ion solution tank 3 to the ion exchange tank 2. In the ion exchange tank 2, calcium is attached to the waste resin by an ion exchange reaction. The ion exchange reaction at this time is an equilibrium reaction, so in order to completely cause the ion exchange reaction of calcium ions to the waste resin, the amount of calcium ions in the ion exchange tank 2 must be set to at least 10 times the ion exchange capacity of the waste resin. There is a need to. Ion exchange (18) The waste resin that has completed the exchange is sent to the separation tank 5, where the waste resin and calcium ion solution are separated, the waste resin is thermally decomposed in the reaction vessel 6, and the calcium ion solution is sent to the ion exchange tank 2. returned to and reused. Although the above is for a cation exchange resin, the same apparatus can be used for an anion exchange resin as well.

Example 1 This example is an example in which a thermal decomposition method using a catalyst developed by the present inventors was applied, and will be explained with reference to FIG.

FIG. 3 shows a process flow for reducing the volume of spent cation exchange resin (waste resin) generated from a condensate purifier of a boiling water reactor and making it inorganic. The waste resin is in the form of a slurry because it is disposed of by backwashing from the condensate demineralizer. This waste resin slurry is sent from the slurry tank 7 to the calcium ion exchange tank 8. Calcium ions are transferred from calcium ion solution tank 9 to calcium ion exchange tank 8
Calcium ions are ion-exchanged with the waste resin. After ion-exchanging the calcium ions, the Kuusei resin is sent to the iron ion (catalyst) exchange tank 10, where the optimal amount of iron ions (based on the ion exchange capacity of the waste resin) to serve as a catalyst is supplied from the iron ion solution tank 11. 2-10ch)
exchange ions with. The waste resin that has been ion-exchanged with calcium ions and iron ions that serve as a catalyst is transferred to a thermal decomposition reactor 13.
Here, the waste resin is heated to 350° C. by a heating heater 19 to decompose the waste resin in an air atmosphere. At this time, water vapor generated from the waste resin is condensed by a condenser 15 and becomes reused water 16.

Carbon dioxide (CO2), -carbon oxide (CO), hydrogen (H2), hydrocarbons (CH4, etc.) generated by thermal decomposition
After the exhaust gas passes through the filter 17, it is burned in the flare stack 18 and discharged as gas such as CO2 or water vapor. The residue after decomposition consists of calcium sulfate (CaSO4), silica (8102), and ferric oxide (F
e20s) or crud (mainly iron oxide) in the reactor cooling water that had adhered to the ion exchange resin, and is stored in the tank 14. This is filled into a drum or the like, and finally solidified with a solidifying agent such as cement or silastic.

Calcium ion is 9% relative to the ion exchange capacity of waste resin.
When thermal decomposition was carried out with the addition of two iron ions as a catalyst, the amount of SOX generated by decomposition at 350C was reduced to 1150 compared to when no calcium ions were added.

In this example, iron ions are ion-exchanged into the waste resin as a catalyst in advance, but generation of SOx can be prevented even if only calcium ions are ion-exchanged without ion-exchanging iron ions. However, the thermal decomposition temperature at this time is 600
℃.

Example 2 The apparatus of Example 1 was used to thermally decompose a used anion exchange resin. 95 to iodine ion as an ammonia scavenger
% and 5% of ferrocyanine ions as a catalyst were ion-exchanged with an anion exchange resin, and thermal decomposition was performed at 350°C. As a result, the amount of ammonia gas generated could be reduced to 1/20 compared to the case where iodine ions were not ion-exchanged (21).

Example 3 The same procedure as in Example 1 was carried out except that the pyrolysis reaction vessel in Example 1 was changed to a fluidized bed type reactor. As a result, the amount of SO produced could be reduced to 1150 as in Example 1. did it. However, in this example, when no catalyst is added, the thermal decomposition temperature is 700 to 900°C, so among the elements shown in Table 1, the elements whose decomposition temperature of the sulfuric acid compound is 900°C or less (Ll 1Na s Be ) cannot be used. Further, when decomposing an anion exchange resin in a fluidized bed as in this example, since the decomposition temperature of ammonium salt is 550° C. or lower as shown in Table 2, a catalyst must be added.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the generation of harmful SOx and ammonia when thermally decomposing used ion exchange resin, and moreover, the amount of the SOX and ammonia scavenger used is the same as the equivalent amount thereof. 5 to 6 of the conventional technology is sufficient.
(22) The volume reduction ratio can be improved accordingly. Furthermore, relatively simple processing equipment is required, and the amount of by-product radioactive waste is also reduced.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the amount of calcium added and the SOX capture rate, Fig. 2 is a diagram showing the flow of implementing the present invention and the concept of the device, and Fig. 3 is an example of an implementation of the present invention. FIG. 3 is a diagram illustrating an example. 1... Waste resin slurry tank, 2... Ion exchange tank, 4... Stirring motor, 5... Separation tank, 6...
...Pyrolysis reactor, 7...Waste resin slurry tank, s
,i. ... Ion exchange tank, 12 ... Stirring motor, 13
...Pyrolysis reactor, 14...Residue tank, 15...
・Capacitor, 17...Filter, 18...Flare stack, 19...Heater (23) Figure 1 CCL addition (equivalence ratio with S) Figure 2

Claims (1)

[Claims] In a method for thermally decomposing a used ion exchange resin, when the ion exchange resin is a cation exchange resin having a sulfonic acid group as an ion exchange group, it reacts with the sulfonic acid group to produce a solid sulfate. An alkali metal or alkaline earth metal is attached to the used ion exchange resin by an ion exchange reaction prior to thermal decomposition, and the ion exchange resin has an anion having a quaternary acinanium salt as an ion exchange group. In the case of an exchange resin, a bald element that reacts with the acetate group to form a solid acetate group is attached to the used ion exchange resin by an ion exchange reaction prior to thermal decomposition. A method for thermally decomposing a used ion exchange resin, which is characterized by preventing the generation of sulfur oxide gas or anhydrous gas during thermal decomposition.