KR20120081740A - Treatment method of radwaste - Google Patents

Abstract

PURPOSE: A method for treating radioactive waste is provided to prevent soot and excessive non-combustible vapor hydrocarbon. CONSTITUTION: Volatile organic elements and acid gas are discharged by firstly heating radioactive waste. The discharged acid gas is absorbed by using calcium hydroxide. The remaining volatile organic element is oxidized. The remaining organic element is oxidized and gasified by a second heating process. The generated gas is absorbed by using kaolin particles.

Description

Treatment method of acid gas-generating radioactive waste {Treatment method of radwaste}

The present invention relates to a method for treating an acid gas generating radioactive waste.

In nuclear facilities, waste organic solvents containing phosphoric acid and other acidic substances such as tributyl phosphate (TBP), vinyl chloride sheets and rubber gloves are used. They are flammable and decaying because their main components are organic, which makes them unacceptable at radioactive waste disposal sites. Accordingly, the conventional organic waste decomposition treatment method such as pyrolysis or incineration has been conventionally used. However, when treated by the above methods, as shown in the following formulas (1), (2) and (3), tributyl phosphate is instantaneous. There is a problem that excess acid gas is generated by the organic decomposition reaction. Recently, an improved decomposition process of organic components, such as steam reforming, which is less likely to generate dioxin by supplementing the disadvantages of existing pyrolysis or incineration, has been developed and put into practical use, but steam reforming also generates excessive acid gas. And this has a number of problems such as corrosion of the process, generation of excess secondary waste.

≪ Formula 1 >

(C ₄ H ₉ O) ₃ PO → Products (g) + P ₂ O ₅ (g) + H ₂ O (g)

<Formula 2>

PVC → Products (g) + HCl (g)

<Formula 3>

Rubber → Products (g) + SO ₂ (g)

In the United States, Germany, and Japan, an improved pyrolysis treatment process is used to solve in-process condensation problems of corrosive H ₃ PO ₄ from P ₂ O ₅ (g) and H ₂ O from pyrolysis or incineration of organic components. Have been developed and used.

THOR treatment process developed in the United States is a process to decompose organic compounds including inorganic salts such as tributyl phosphate (TBP) by steam reforming method and overheat organic liquid waste at a temperature of 700 ~ 750 ℃. It is then decomposed by mixing with steam and sodium aluminum silicate powder. Inorganic components separated during thermal decomposition of waste react with sodium aluminum silicate to form stable compounds, and organic components are converted to hydrogen, carbon monoxide and methane by steam reforming reaction, and thermal oxidizer Is converted to carbon dioxide and water vapor.

The pyrolysis process of NUKEM of Germany converts tributyl phosphate (TBP) waste into calcium phosphate and pyrolysis hydrocarbon gas by pyrolysis with calcium hydroxide at a temperature of about 600 ℃, and pyrolysis hydrocarbon gas is about 1000 ℃ Combustion treatment at the temperature of

THOR steam reforming process and pyrolysis process of NUKEM of Germany treats inorganic aluminum such as radionuclides by mixing sodium aluminum silicate, potassium and calcium phosphate, which are additives for waste and inorganic stabilization, with waste It is stabilized at high temperature and remains in a pyrolysis or steam reforming reactor, so there are no problems such as corrosion or clogging of the process equipment. However, excessive stabilizing additives have to be used, and since they are generated as waste mixed with additives and radionuclides, there is a problem of low volume reduction effect. Also, recyclable elements such as uranium are chemically combined with stabilizing additives and separated. It is difficult to separate and recycle because it forms a complex that is difficult to do.

In order to improve this problem, JAEA of Japan has recently been researching the treatment process of tributyl phosphate (TBP) organic waste liquid which pyrolyzes tributyl phosphate (TBP) waste liquid without additives and oxidizes the pyrolyzed gas. The main focus is on reducing the amount of radioactive waste generated. The process is the same as the conventional waste pyrolysis-incineration process concept except that it injects some steam into the pyrolysis reactor to inhibit soot generation that may occur during the pyrolysis of tributylphosphate (TBP). Do. In addition, since it does not suppress the generation of acidic gas at high temperature, a two-stage wet scrubber is used to clean it. Therefore, the exhaust gas treatment process is relatively complicated and secondary liquid wastes are generated a lot, and various corrosive compounds such as phosphorus compounds are accumulated in various parts of the process.

The present inventors minimize the amount of waste generated during the treatment of radioactive organic waste, and while studying a process for solving environmental pollution problems by treating harmful gases, the hazardous gases and solid wastes are treated through a two-step heat treatment. And developed a waste treatment method for adsorbing and oxidizing residual gas and completed the present invention.

An object of the present invention is to provide a method for treating an acid gas-generating radioactive waste.

In order to achieve the above object, the present invention is the first heating the radioactive waste to discharge the volatile organic components and acid gas, the discharged acid gas is adsorbed using calcium hydroxide, the remaining volatile organic components are oxidized (step 1) ; And oxidizing and gasifying the organic components remaining after the first heating in step 1 by secondary heating, and adsorbing the generated gas by using kaolin particles to oxidize the residual gas (step 2). It provides a decomposition treatment method of.

The acid gas generating radioactive waste treatment method according to the present invention does not generate acidic waste water during the treatment of radioactive organic waste, and can be recovered and treated with inorganic salts such as calcium chloride (CaCl ₂ ) which can be recycled. In addition, when directly pyrolyzing radioactive organic waste at a high temperature of about 700 ° C. or more, the problem of generation of excessive unburned gaseous hydrocarbons and soot caused by explosive gasification of volatile organic components may be solved.

1 is a graph of the change in free energy for the reaction adsorption of acid gas and calcium hydroxide;
2 is a schematic view of a decomposition apparatus used in the decomposition treatment method according to the present invention.

The present invention comprises the step of first heating the radioactive waste to discharge volatile organic components and acidic gas, the discharged acidic gas is adsorbed using calcium hydroxide, the remaining volatile organic components are oxidized (step 1); And

The organic component remaining after the first heating in step 1 is oxidized and gasified by secondary heating, and the resulting gas is adsorbed using kaolin particles and then the residual gas is oxidized (step 2). Provide a decomposition treatment method.

Hereinafter, the decomposition treatment method of the radioactive waste according to the present invention will be described in detail.

In the decomposition treatment method of radioactive waste according to the present invention, excessive secondary waste generation and corrosiveness are obtained by pyrolysis or incineration of organic radioactive waste such as tributyl phosphate (TBP), polyvinyl chloride (PVC), and rubber, which are highly acidic. It is possible to solve the problem of the deposition of the components in the process, such as high-temperature dry decomposition of the radioactive waste, and in the decomposition treatment method of the radioactive waste according to the present invention, step 1 is the primary heating of the radioactive waste by volatile organic The powder and acid gas are discharged, the discharged acid gas is adsorbed using calcium hydroxide, and residual volatile organic components are oxidized. The radioactive waste contains volatile hydrocarbon components and acid gas generating elements such as P ₂ O ₅ , HCl, SO ₂ , and the like, in the case of the conventional simple incineration method. The first heating of the step 1 is a step of gasifying the volatile hydrocarbon component and acid gas generating elements such as P ₂ O ₅ , HCl, SO ₂ , the volatile hydrocarbon gas and acid gas contained in the radioactive waste is generated first do. In this case, the radioactive waste may be a container or rubber gloves of a solvent used in a nuclear power plant as an organic radioactive waste.

The primary heating of step 1 is preferably performed at a temperature of 200 to 500 ℃. The primary heating is carried out at a temperature in the above range, so that only volatile organic components and acidic gas generating elements are separated from the radioactive wastes and gasified, and fixed organic components and semivolatile volatile species cesium (Cs), which are decomposed at higher temperatures, and quasi-volatile hazards. Heavy metals such as cadmium (Cd) and lead (Pb) remain. If the primary heating is performed at a temperature below 200 ° C., there is a problem in that volatile hydrocarbon gas and acid gas are not sufficiently generated, so that the volatile hydrocarbon component and the acid gas generating element cannot be decomposed smoothly. When performed at a temperature exceeding 500 ° C, heavy metals, radionuclides, etc., as well as volatile hydrocarbon gases and acid gases are simultaneously volatilized, thus making it difficult to treat them.

The primary heating of step 1 is carried out in the absence of oxygen. When oxygen is present during the primary heating, the fixed carbon reacts with the oxygen to generate excess hydrocarbon gas, which makes it difficult to process the mixed gas due to the primary heating. Therefore, in the decomposition treatment method according to the present invention, heating is performed by injecting nitrogen, which is an inert gas, in the absence of oxygen during the first heating, thereby remaining fixed carbon and generating volatile hydrocarbon gas and acid gas.

In step 1, the acid gas is adsorbed using calcium hydroxide to collect the generated acid gas, and the residual volatile organic components are oxidized to convert carbon dioxide and water vapor. The acid gas is preferably passed through an adsorption tower including a calcium hydroxide layer to chemically adsorb the acid gas, but is not limited thereto.

The acid gas adsorption of step 1 is preferably performed at a temperature of 700 to 900 ℃. Figure 1 shows the change in free energy for the reaction adsorption of acid gas and calcium hydroxide, the removal reaction of P ₂ O ₅ and Cl ₂ gas increases the efficiency of the removal reaction with increasing temperature. However, the removal reaction of SO ₂ and HCl decreases with increasing temperature. Therefore, the adsorption reaction is performed at a temperature below 900 ℃, the reaction efficiency is lowered at a temperature exceeding 900 ℃, there is a problem that desorption reaction that HCl is separated occurs the acid gas adsorption is carried out at a temperature of 700 to 900 ℃ It is preferable to be.

In addition, oxidation of the volatile organic components remaining after the adsorption of step 1 may be performed using a metal oxide catalyst layer of platinum, palladium or rhodium, which is a catalytic oxidation apparatus of volatile organic compounds (VOC), which is widely used in industry. Can be. Passing through the metal oxide catalyst layer, residual volatile organic constituents are converted to exhaustable gases such as carbon dioxide and water vapor.

In the decomposition treatment method of radioactive organic waste according to the present invention, step 2 is a step of oxidizing and gasifying the organic components remaining after the first heating in step 1 by secondary heating. At the temperature at which the first heating of step 1 is performed, fixed carbon components, harmful heavy metals, radionuclides, etc., which are no longer decomposed, remain together with harmless ash. Step 2 is a step of oxidizing and gasifying the organic component remaining in the step 1 by secondary heating, the secondary heating is preferably carried out at a temperature of 800 to 1000 ℃. When the secondary heating is performed at a temperature of less than 800 ℃, there is a problem that the oxidation of the fixed carbon component is not sufficiently made, when the secondary heating is performed at a temperature exceeding 1000 ℃, the device in a high temperature oxidizing atmosphere In terms of corrosion and energy efficiency, excessive energy is consumed.

At this time, the secondary heating of the step 2 is carried out under the condition that oxygen, water vapor or air is supplied. By supplying oxygen, water vapor or air, the fixed carbon component reacts with oxygen and oxidizes.

In the decomposition treatment method of radioactive organic waste according to the present invention, the radionuclide and the harmful heavy metal gas contained in the gas generated through the secondary heating in step 2 are adsorbed using kaolin particles, and the residual gas is oxidized. By performing the secondary heating of step 2, radionuclides such as hydrocarbon gas and highly volatile cesium (Cs) and heavy metal gases such as lead (Pb) and cadmium (Cd) are generated. The generated radionuclides such as cesium (Cs) and heavy metals such as lead (Pb) and cadmium (Cd) are removed by passing through a high-temperature kaolin particle layer. The kaolin particles may exhibit excellent adsorption efficiency by including a large amount of kaolin (Al ₂ O ₃ ? 2 SiO ₂ ? X H ₂ O) components having a high temperature adsorption reactivity with the radionuclide and heavy metals. The radionuclides and heavy metals react with metascaolinite (Al ₂ O ₃ ? 2 SiO ₂ ) particles, which are unstable components produced by dehydration of kaolin at high temperatures, to produce Cs ₂ O? Al ₂ O ₃ ? 2SiO ₂ , PbO? Al ₂ O _3? 2SiO ₂ and CdO? Al ₂ O _3? are removed in the form of a stable reaction product of 2SiO _2. At this time, the adsorption removal using the kaolin particles is preferably carried out at a temperature of 700 to 900 ℃. This is because the adsorption of the radionuclide and heavy metal is a high temperature adsorption reaction that occurs more preferably at higher temperatures, so that the adsorption is carried out in the above temperature range, so that the high temperature reaction adsorption of the radionuclide and heavy metal is performed smoothly.

After the adsorption by kaolin particles is carried out, unburned hydrocarbon gas remains, and the unburned hydrocarbon gas is oxidized by a metal oxide catalyst of platinum, palladium or rhodium to be converted into an exhaustable gas such as carbon dioxide and water vapor.

In the decomposition treatment method of radioactive organic waste according to the present invention, the gas treated in step 1 or step 2 may be discharged into the atmosphere after being filtered by an air filter. By filtering the fine particles that may be present in the residual gas by the air filter can be discharged harmless gas to the atmosphere.

The decomposition treatment method of radioactive organic waste according to the present invention can be performed by the decomposition treatment apparatus shown in Figure 2, the decomposition treatment apparatus as shown in Figure 2 pyrolysis / oxidation reactor (1), calcium hydroxide particles (Ca (OH) ₂₎ comprises a suction layer _{(7), Al 2 O 3} ? 2SiO 2? xH 2 O the main component of radionuclides and heavy metals adsorption column 8 and the main oxidation catalyst device 10, the process reactor. In the decomposition treatment method using the decomposition treatment apparatus, the waste is first heated in a medium temperature and inert atmosphere of 300 to 500 ° C. to generate volatile components and acid gases, but retain the fixed carbon component. It is a step-by-step process in which two processes of different heating, oxidation and gasification are performed sequentially.

More specifically, radioactive wastes that generate excessive amounts of acid gases during pyrolysis or incineration, such as tributyl phosphate (TBP), vinyl chloride sheet, rubber, and the like, are oxygen at a temperature of about 200 to 500 ° C. When pyrolysis is carried out while inert gas such as nitrogen is injected under reducing conditions, volatile hydrocarbon gas components and acid gas generating elements such as P ₂ O ₅ , HCl and SO ₂ are gasified, and fixed carbon and volatile harmful heavy metals and lead, Ash components containing harmful heavy metals such as cadmium and radionuclides such as cobalt and cesium remain in the pyrolysis / oxidation reactor. The mixed gas of hydrocarbon gas and acid gas generated in this process passes through the calcium hydroxide (Ca (OH) ₂ ) adsorption layer 7 at about 700 to 900 ° C., and the acid gas is collected. It is oxidized in 10) and converted to carbon dioxide and water vapor. At this time, if the pyrolysis treatment is continued, alkali metal or earth metal in the alkali inorganic adsorption layer and phosphorus, sulfur, chlorine, etc., which are pyrolysis acid gas components, react to form inorganic salt components such as Ca (PO ₃ ) ₂ , CaCl ₂ , and CaSO ₄ . Accumulate, and the acid gas removal efficiency of the calcium hydroxide (Ca (OH) ₂ ) adsorption layer is gradually reduced. Therefore, it is necessary to replace the adsorbent at an appropriate operation time, and when the adsorbent is replaced, the fixed carbon is oxidized in a high temperature oxidizing atmosphere of 800 to 1000 ° C. to stop pyrolysis due to the injection of waste and supply oxygen, steam, or air. At this time, the generated gas is passed through the high temperature kaolin particle layer 9 of 700 to 900 ℃ and is processed through the catalytic oxidation device (10). Among the radionuclides and harmful heavy metals present in the radioactive waste, cesium, which is a highly volatile nuclide at high temperature, and lead and cadmium, which are volatile, are volatilized and discharged as a gas. Reaction adsorption is carried out in the form of Cs ₂ O? Al ₂ O ₃ ? 2 SiO ₂ , PbO? Al ₂ O ₃ ? 2SiO _2, and CdO? Al ₂ O ₃ ? 2SiO ₂ . The unburned hydrocarbon gas remaining after the reaction adsorption is completely oxidized through the catalytic oxidation device 10, and other air fine particles are removed through the air filter 12 and then discharged to the atmosphere.

Hereinafter, the present invention will be described more specifically by way of examples. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited by the following examples.

Example 1 Decomposition of Tributyl Phosphate (TBP) Waste 1

Step 1: The TBP organic waste solution containing uranium was gasified by primary heating with nitrogen injection at a temperature of 350 ° C. and anoxic conditions.

Step 2: The generated gas produced by the gasification of the step 1 is injected into the adsorption tower (800 ℃) containing calcium hydroxide to adsorb the acid gas contained in the product gas, and after the adsorption of the acid gas, the residual hydrocarbon gas is platinum Oxidation was carried out through a catalytic oxidation device comprising a carbon dioxide and water vapor.

Step 3: The residue such as fixed carbon remaining after the first heating in Step 1 was oxidized and gasified by secondary heating while injecting air at a temperature of 900 ° C.

Step 4: Injecting the oxidized and gasified product gas in the step 3 into the adsorption tower (800 ℃) containing the kaolin particles, the radionuclide and harmful heavy metals contained in the product gas at high temperature adsorption, remaining after the high temperature reaction adsorption The unburned hydrocarbon gas was oxidized through a catalytic oxidation device containing platinum and converted to carbon dioxide and water vapor. At this time, volatile organic components corresponding to 70% of the tributyl phosphate (TBP) waste were volatilized and oxidized through the catalytic oxidation apparatus, and the generated phosphate gas was collected by adsorption at high temperature over 99%.

Example 2 Decomposition of Tributyl Phosphate (TBP) Waste 2

Tributyl phosphate (TBP) was carried out in the same manner as in Example 1 except that the gas subjected to oxidation through the catalytic oxidation apparatus of steps 2 and 4 was further filtered through an air filter and discharged into the atmosphere. Waste was decomposed.

1: pyrolysis / oxidation reactor
2: Waste organic solvent injector
3: solid waste supply hopper
4: nitrogen gas injection unit
5: oxygen injection unit
6. Acid gas adsorption tower
7. Ca (OH) ₂ adsorption layer
8. Radionuclide and heavy metal adsorption tower
9. Kaolin Grain Layer
10. Catalytic Oxidizer
11. Catalyst particle layer
12. Air filter

Claims (8)

First heating the radioactive waste to discharge volatile organic components and acidic gas, wherein the discharged acidic gas is adsorbed using calcium hydroxide and oxidizing residual volatile organic components (step 1); And
The organic component remaining after the first heating in step 1 is oxidized and gasified by secondary heating, and the resulting gas is adsorbed using kaolin particles and then the residual gas is oxidized (step 2). Decomposition Method.
The method of claim 1, wherein the radioactive waste of step 1 is an organic radioactive waste from which acidic gas is generated.
The method of claim 1, wherein the primary heating of step 1 is carried out in the decomposition of the radioactive waste, characterized in that carried out in the temperature range of 200 to 500 ℃ and the absence of oxygen.
The method of claim 1, wherein the adsorption using calcium hydroxide of step 1 is carried out at a temperature range of 700 to 900 ℃.
The method of claim 1, wherein the secondary heating of the step 2 is a decomposition treatment method of radioactive waste, characterized in that carried out under the conditions of supplying oxygen, water vapor or air in the temperature range of 800 to 1000 ℃.
The method of claim 1, wherein the adsorption using kaolin particles of step 2 is carried out at a temperature range of 700 to 900 ℃.
The method of claim 1, wherein the oxidation of steps 1 and 2 is carried out by a metal oxide catalyst of platinum, palladium or rhodium.
The method of claim 1, further comprising the step of filtering the fine particles by an air filter after the oxidation of step 1 or step 2 is carried out.

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