KR100858510B1 - Process for supercritical water oxidation of cationic exchange resin used in nuclear power - Google Patents

Abstract

A process for supercritical water oxidation of a cationic exchange resin used in a nuclear power plant is provided to remove additional post-processing equipment by not volatilizing a Co metal to a radioactive metal gas. A process for supercritical water oxidation of a cationic exchange resin used in a nuclear power plant includes the steps of: separating cationic exchange resin waste from ion exchange resin waste mixed with cationic and anodic exchange resins by using a fluidized bed specific gravity difference separator; manufacturing a slurry by mixing the separated cationic exchange resin waste with water and grinding the mixture; mixing additive for neutralizing sulfonic acid component with the slurry; increasing a temperature and a pressure near to a critical point of the water by quantitatively injecting the mixed slurry; oxidizing and decomposing an organic matter of the slurry in a supercritical condition of water by mixing the heated slurry with an oxidizer; heat-exchanging the slurry with processing water, cooling the slurry, and reducing the pressure to a normal pressure; and separating a gas and the processing water.

Description

Process for supercritical water oxidation of cationic exchange resin used in nuclear power}

1 is a block diagram illustrating a method for treating waste cation exchange resin generated in a nuclear power plant according to the present invention with supercritical hydroxide technology.

2 is a conceptual diagram of a continuous reaction facility for carrying out the treatment process of waste cation exchange resin according to the present invention.

1 ---- oxidant reservoir 2 ---- waste water reservoir

3, 4 ---- pump 5, 6 ---- preheater

7 ---- reactor 8 ---- chiller

9 ---- BPR 10 ---- gas-liquid separator

The present invention relates to a method for treating waste cation exchange resin generated in a nuclear power plant with supercritical hydroxide technology.

Currently, Nuclear Power Plant # 20 is in operation in Korea, and ion exchange resin is used to remove metal ions and corrosive anions from the secondary system of nuclear power plants. End-of-life ion exchange resins are generated as wastes (waste resins), and they are difficult to process due to their high volume and high water content. They are also very inefficient for long-term storage. Nuclear power plants in Korea are already storing a large amount of waste water due to long-term operation, which is occurring every year with operation. However, since there is no suitable technology for treating these waste resins, the technology is currently urgently needed because it is currently stored in a waste storage facility within a nuclear power plant, but the storage space is insufficient to be urgently disposed.

Incineration is the most widely used technique for the treatment of organic wastes such as waste ion exchange resins. However, it is not easy to secure the site for incinerator installation when treating wastes by incineration, and since organic decomposition temperature is about 800 ~ 1,200 ℃, secondary pollutants such as SOx, radioactive gas and dioxins can be generated. In particular, when the organic content of the waste is 10% or less, there is a disadvantage in that a large amount of energy source (auxiliary fuel) is required to treat the incineration wastewater.

Most of the non-degradable organic wastes generated in power plants have not been easily treated with conventional technologies, and various researches have been carried out for reduction treatment, but until now, domestically applicable technologies have not been developed.

The conventional landfill and storage technology for the waste ion exchange resin is a simple treatment and disposal technology that is difficult to solve the target waste fundamentally (Korean Patent Publication No. 1990-0000344).

In Japan, the first supercritical hydroxylation facility was built in 1995 in Organo's central research facility.Toshiba Corp. recently launched a unique reactor called `` integrated two-stage reactor '' per minute. We have a facility that can handle 1kg, and the treatment of waste ion exchange resins using this is being actively carried out [Japanese Patent Laid-Open No. 10-279728, Japanese Patent Laid-Open No. 10-204206].

It is known that European supercritical hydroxide related technology has not been studied much compared to the United States, but in Germany, many studies related to corrosion of metals have been conducted to solve the corrosive problem, which is the biggest problem of supercritical hydroxide technology. One patents have been introduced [European Patent Publication No. 1 477 579, 0 656 321].

The supercritical hydroxide process is a very good technique for the treatment of most organic wastes by oxidative decomposition, but as it has strong oxidation power, it also has side effects of corrosive material. In particular, since it is operated at high temperature and high pressure, a high corrosion rate of the material may cause serious safety problems.

The present invention is to solve such a conventional problem, the waste cation exchange resin can be made into a slurry in which particles of less than 45㎛ uniformly dispersed and injected into the reactor with a high-pressure slurry pump, the waste cation exchange resin Although caustic soda (NaOH) is used as a neutralizer for degassing of sulfonic acid (SO ₃ H), which is a functional group of, there is no plugging due to precipitation of the neutralizer, and it can be treated in supercritical conditions as well as near critical conditions. Co-metals generated from waste cation exchange resins are various types of metal oxides, which are precipitated in the treated water and do not volatilize into radioactive metal gases. Its purpose is to provide a method for treating by counting oxidation technique.

The method for treating the waste cation exchange resin generated in the nuclear power plant of the present invention to achieve the above object by the supercritical hydroxide technology, the cation from the ion exchange resin waste mixed with cation and anion exchange resin using a fluidized bed specific gravity separator Separating the exchange resin waste; Mixing the separated waste cation exchange resin with water and then grinding to prepare a slurry; Mixing in the slurry an additive that neutralizes the sulfonic acid component; Raising the temperature and pressure above the critical point of water while metering the mixed slurry; Mixing the heated slurry with an oxidant to oxidatively decompose the organics of the slurry under supercritical conditions of water; Exchanging the treated water with the introduced slurry after oxidative decomposition and cooling and lowering the pressure to atmospheric pressure; It is characterized by consisting of the step of separating the gas and the treated water.

In the present invention, at least one selected from caustic soda and caustic is used as an additive for neutralizing the sulfonic acid component, and when the concentration is 0.4 to 0.7%, there is no clogging due to precipitation of the neutralizer.

The present invention is characterized in that the mixture is heated to 300 ° C to 430 ° C and then mixed with an oxidant and the pressure is raised to 22.1 MPa to 30.0 MPa.

In particular, the oxidizing agent is used by selecting at least one or more of hydrogen peroxide aqueous solution, oxygen, air, and when 20 to 50% of the chemical equivalence ratio is added, the absolute corrosion amount is reduced so that the corrosion of the facility does not occur. There is this. Hereinafter, the present invention will be described in more detail.

  The method for treating the waste cation exchange resin generated in the nuclear power plant of the present invention with supercritical hydroxide technology, as shown in FIG. 1, uses a mixed bed specific gravity separator using a fluidized bed specific gravity separator as shown in FIG. The waste cation resin of 1) was separated, and then wet milled with a ball mill to prepare a slurry in which particles of 45 μm or less were uniformly dispersed. The slurry thus obtained was diluted with water to form a slurry having a desired concentration, followed by a high pressure slurry pump. The sample is injected into the reactor through a preheater and oxidized and decomposed in the cationic resin by supercritical hydroxide reaction, but supercritical hydroxide, for example, at a temperature of 374 ° C. and a pressure of 22.1 MPa near the critical pressure. It is a method of oxidizing and decomposing waste cation exchange resin into water and carbon dioxide using an oxidizing agent such as hydrogen peroxide water, air or oxygen.

The method of treating the waste cation exchange resin generated in the nuclear power plant of the present invention with supercritical hydroxide technology has the following advantages.

First, the waste cation exchange resin can be made into a slurry in which particles of 45 μm or less are uniformly dispersed and injected into the reactor by a high pressure slurry pump for treatment.

Second, even if sodium hydroxide (NaOH) is used as a neutralizer for degassing of sulfonic acid (SO ₃ H), which is a functional group of waste cation exchange resin, there is no blockage due to precipitation of neutralizer.

Third, it is possible to process not only supercritical conditions but also near critical conditions.

Fourth, the typical Co metal generated in the waste cation exchange resin of the nuclear power plant is precipitated in the treated water as various types of metal oxides and is not volatilized into the radioactive metal gas.

In the present invention, the super critical water oxidization technology is characterized in that the organic matter contained in the water at a temperature and pressure near the critical point of water (critical temperature: 374 ° C., critical pressure: 22.1 MPa) is combined with aqueous hydrogen peroxide solution, oxygen or air. Oxidation and decomposition using the same oxidant. Supercritical hydroxide technology can solve the technical difficulties of conventional commercial processes by taking advantage of supercritical fluids such as high dissolving power, fast mass transfer and heat transfer, low viscosity, high diffusion coefficient and low surface tension. It is a new technology. In addition, since the supercritical hydroxylation process is a closed system, it is possible to perform an oxidative decomposition reaction in which all reactants are not exposed to the outside. There is an advantage in decomposing military chemicals, nuclear power waste, etc., which can cause big problems.

In the case of incinerator, the decomposition temperature of organic matter is about 800 ~ 1,200 ℃, whereas the reaction temperature of supercritical hydroxide is usually 400 ~ 600 ℃, so it rarely generates sulfate (SOx) and uses relatively little energy. In particular, when the organic content of the waste is 10% or less, a large amount of energy source (auxiliary fuel) is required to treat the wastewater by incineration, whereas the supercritical hydration process is operated at a relatively low temperature, and There is an advantage that can fully recover the thermal energy.

Method for producing a slurry of waste cation exchange resin applicable to the present invention is as follows.

That is, waste ion exchange resin is IRN-150 and similar products produced by Rohm & Haas, and its size is 300 ~ 1200㎛, shape is spherical particles, and the product is mixed with cation resin and anion resin. The cation exchange resin is prepared by adding sulfonic acid (SO ₃ H) to a copolymer of styrene and divinyl benzene. Each ion exchange resin contains about 50% water. Since the cation resin is 1.26 and the anion resin is 1.11, it is separated by a fluidized bed specific gravity separator to secure a cation exchange resin. Since the separated sample is in the form of several hundred microns of spherical grains, it must be pulverized and converted into a slurry in which particles of an appropriate particle size are uniformly dispersed in order to be injected at high pressure in a supercritical hydroxide apparatus. A ball mill made of 5L alumina is used to grind the separated cationic resin to a particle size of 45 μm or less. That is, the ball mill is filled with 2L of 20mm ceramic balls and 1L of waste resin to be crushed together with water, and then sealed, and then wet milled by rotating at a rotational speed of about 200 rpm for 24 hours to obtain a high concentration slurry. Dilution yields a slurry of the desired concentration.

The treatment process of the waste cation exchange resin generated in the nuclear power plant according to the present invention is as follows.

In order to treat the waste resin slurry obtained by wet grinding in a supercritical hydroxide process, the continuous reaction facility shown in FIG. 2 is used. This unit consists of two high pressure pumps (3, 4), preheater (5, 6), reactor (7) and cooler (8), and the reactor (7) is a tubular reactor made of 1/4 inch tube. The inner volume is 220 mL. In FIG. 2, reference numeral 1 denotes a hydrogen peroxide storage tank which is an oxidant, reference numeral 2 denotes a wastewater storage tank, 9 denotes a BPR (Back Pressure Regulator), and reference numeral 10 denotes a gas-liquid separator.

First, the chemical oxygen demand (hereinafter referred to as COD) of the slurry to be treated is determined in advance to determine the required oxygen amount, and then the injection flow rate of each raw material pump is determined to be suitable for the reactor residence time. The system pressure is fixed at 250 bar and 50% hydrogen peroxide (H ₂ O ₂ ), oxygen or air is used as the oxygen source. The pressure of the system is controlled by a BPR (Back Pressure Regulator) 9 installed at the rear end of the cooler 8. After injecting and mixing the slurry and the oxidant into the high pressure pumps 3 and 4, respectively, the mixture is heated to a proper temperature through the preheaters 5 and 6 of the electric heating method, and then introduced into the reactor 7 to maintain a constant residence time. During the supercritical hydroxide reaction at a temperature of 300 ~ 430 ℃ and a pressure of 22.1 ~ 30.0MPa. After the reaction, the treated water passes through the BPR (9) and the gas-liquid separator (10) after passing through the cooler (8) and is separated after the liquid and gas is discharged.

Since cationic resins have sulfonic acid functional groups, sulfuric acid is more likely to occur during preheating or oxidative decomposition, which can cause serious system corrosion.

4 (C ₁₆ H ₁₅ O ₃ S) n + 79nO _2- > 64nCO ₂ + 26nH ₂ O + 4nH ₂ SO ₄ (1)

Therefore, it is necessary to neutralize the generated sulfuric acid, and it is common to prescribe a small amount of alkali such as caustic soda and neutralize it through the reaction path as shown in Equation (2).

2NaOH + H ₂ SO _4- > Na ₂ SO ₄ + 2H ₂ O (2)

The present invention will be described in more detail based on the following examples.

Example 1

The slurry was prepared by the aforementioned method and then the COD concentration was measured in advance. Decomposition reactions were carried out under various experimental conditions using the supercritical oxidation apparatus of FIG. 2, and the experimental results for waste cation exchange resins are shown in Table 1.

As shown in Table 1, the concentration of Na was very low in the treated water after the decomposition reaction under supercritical (430 ° C) conditions. This means that most of the caustic soda precipitated and deposited in the system. In addition, in the previous experiment, black solid particles were generated, which may cause damage to BPR, and the experiment was performed after filtering the solid particles contained in the treated water using a filter.

Table 1. Test results of waste cation exchange resin

Example 2

In the process of decomposing cationic resins discharged from nuclear power plants, there is an important consideration that must not release radioactive metals as much as organic decomposition rate. Metal components that can be substituted for waste cation resins in nuclear power plants are mainly known as Co and Cs. Therefore, experiments were carried out to prepare and treat simulated wastewater in which non-radioactive Co was substituted, and to determine Co behavior in the process. The COD of the simulated wastewater prepared before the decomposition reaction was measured to be 25,000 ppm and Co concentration of 890 ppm.

Table 2 shows the results of experiments on the simulated wastewater prepared by varying the reaction temperature, residence time, and oxygen input amount, and only varying the amount of neutralizing agent.

[Table 2] Simulated Wastewater Treatment Results with Co Substitution

As can be seen from this result, it was confirmed that the decomposition rate of organic matter satisfying the discharge standard under 0.5 wt% of neutralizing agent, and only less than 1 ppm of Co was present in the treated water filtered with a 0.2 μm filter, and the Co recovery was 99.9%. It secured as above.

In the method for treating the waste cation exchange resin according to the present invention by supercritical hydroxide technology, the waste cation exchange resin can be prepared into a slurry in which particles having a particle size of 45 μm or less is uniformly dispersed and injected into the reactor by a high pressure slurry pump. Although caustic soda (NaOH) is used as a neutralizer for the degassing of sulfonic acid (SO ₃ H), a functional group of waste cation exchange resin, there is no plugging due to precipitation of neutralizer, and it can be processed in supercritical conditions as well as near critical conditions. In addition, the typical Co metal generated in the waste cation exchange resin of the nuclear power plant is precipitated in the treated water as various types of metal oxides, and thus does not volatilize into the radioactive metal gas.

Claims (5)

Separating the cation exchange resin waste from the ion exchange resin waste in which the cation and anion exchange resin are mixed using a fluidized bed specific gravity separator; Mixing the separated cation exchange resin waste with water and then grinding to prepare a slurry; Mixing in the slurry an additive that neutralizes the sulfonic acid component; Raising the temperature and pressure near the critical point of water while metering the mixed slurry; Mixing the heated slurry with an oxidant to oxidatively decompose the organics of the slurry under supercritical conditions of water; Exchanging the treated water with the introduced slurry after oxidative decomposition and cooling and lowering the pressure to atmospheric pressure; A method for treating waste cation exchange resins generated in a nuclear power plant by supercritical hydroxide technology, comprising separating gas and treated water. The waste cation exchange resin of claim 1, wherein the additive for neutralizing the sulfonic acid component is selected from at least one of caustic soda and caustic, and the concentration thereof is 0.4 to 0.7%. Process by supercritical hydroxide technology. The method of claim 1, wherein the step of raising the temperature near the critical point of the water is heated by heating at a temperature of 300 ℃ to 430 ℃ to treat the waste cation exchange resin generated in a nuclear power plant by supercritical hydroxide technology. How to. The method of claim 1, wherein the step of raising the pressure near the critical point of the water comprises raising the pressure to 22.1 MPa to 30.0 MPa pressure by using supercritical hydroxide technology. The supercritical water according to claim 1, wherein the oxidant is selected from at least one of an aqueous hydrogen peroxide solution, oxygen, and air, and 20 to 50% of a chemical equivalent ratio is added. Process by oxidation technique.

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