RU2616447C1 - Method for cleaning liquid containing radionuclides, and device for its implementation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of purifying a liquid contaminated with radionuclides, involves placing into a contaminated liquid at least one element of different porous materials - hydrophilic and hydrophobic, one end of which is partially immersed in the contaminated liquid, and on the other by passing an electric current creates evaporation zone, in which contaminated liquid is transported by capillary properties of the porous material, and wherein the liquid by heating to the boiling impurities carried compaction. The water is transported on an element of a hydrophilic material and an organic component - the element of a hydrophobic material. Compaction is carried out by successive heating to complete evaporation of water, then - until complete evaporation of the organic component or vice versa. The steam is condensed to obtain a purified liquid. The method is implemented by a device for cleaning liquid.

EFFECT: increased efficiency of processing liquid, which contain radionuclides.

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Description

The group of inventions relates to the nuclear and radiochemical industries, namely to the purification of radionuclide-contaminated liquids containing organic substances, in particular petroleum products, and can be used to purify liquid radioactive waste.

The proportion of organic substances in contaminated liquids can range from several units to 100%. For example, spent organic liquids (petroleum products: lighting kerosene, reactor fluids RZh-3 and RZh-8, JonoPlus IME-MH fluid) used in electrical discharge machining of products with radioactive elements, practically do not contain water. The concentration in the waste water of a nuclear power plant of organic compounds, for example, mineral oils and kerosene, cutting fluids, can reach ten percent. Organic compounds can also be included in decontamination solutions. The method of processing such waste depends on the ratio of organic and inorganic components in them. The most common method for purifying a liquid from oil products is by passing such a liquid through de-oiling charcoal filters, whose service life is short, and whose coals are burned with oil products and radionuclides accumulated in them.

The presence of petroleum products in water wastes used as mixing water during the preparation of the cement compound leads to delamination of the mixture prepared for curing and complicates the manufacture of monolithic blocks with the necessary strength properties for disposal. For example, the introduction without preliminary preparation of organic waste into the compositions for the production of cement mortar is limited to four to five percent by weight. The placement of contaminated oil products in solid matrices under such restrictions leads to a significant increase in the volume of material required for disposal. Examples of the treatment of organic liquid radioactive waste are given in the work of Varlakova A.P., Germanova A.V. "The immobilization of organic liquid radioactive waste by the method of impregnation of porous cement matrices." Journal of Atomic Energy, vol. 113, no. 2, 2012, pp. 83-87.

The use of incineration or pyrolysis for processing liquid radioactive waste with organic fractions can reduce the amount of material for disposal, however, it significantly complicates and increases the cost of processing due to the need to clean the gaseous products of combustion.

With both approaches to the disposal of liquid radioactive waste, useful organic materials that can be reused are irretrievably lost.

There is a method of processing liquid radioactive waste containing water and organic materials (petroleum products), which consists in introducing into the liquid radioactive waste a hydrophobic porous absorber having sorption properties with respect to radionuclides, after which the mixture is kept until the oil products are completely absorbed by the absorber (patent RU No. 2312415 “Method for the immobilization of liquid radioactive waste containing water and oil products”, IPC G21F 9/16 and G21F 9/20 (2006.01), published on December 10, 2007). Then, the obtained solid phase with absorbed oil products is mixed in the required proportions with cement, and the water purified from organic matter is used as mixing water. As a scavenger (oil scavenger), a natural carbon sorbent is used, for example, foamed, split graphite, crumb rubber, slags, and the like. A device for implementing the known method consists of a tank for liquid radioactive waste, a mixer, a pump for pumping liquid radioactive waste into the mixer, a hopper with a dispenser for supplying an absorber to the mixer, a hopper with a dispenser for supplying cement to the mixer, a container for molding and drying geo-cement stone.

The known method and device have the following disadvantages - there is an increased volume of solid waste for disposal associated with the introduction of a filler into the liquid, the inability to isolate useful products for reuse.

A known method of wastewater treatment, which includes water, mineral oil (dissolved and / or in the form of an emulsion), dissolved and solid particles of radioactive components of uranium and its decay products, which consists in concentrating radioactive components and mineral oil (patent RU No. 2305335 " The method of wastewater treatment from radioactive components and oil ", IPC G21F 9/00 and G21F 9/20 (2006.01), published on 08.27.2007). At a high oil content, contaminated waters cannot be cleaned by evaporation; therefore, before treatment, the wastewater is acidified to pH 2.5 ÷ 3.0; then a coagulant based on iron salts is introduced, then a cationic flocculant based on a modified polyacrylamide, after which the composition is neutralized with alkali to a pH of more than 7 and centrifuged to obtain purified water and a concentrate containing radioactive components and mineral oil after centrifugation.

The known method has the following disadvantages - there is an increased volume of waste for disposal due to the addition of coagulant and flocculant, the need for chemical treatment of contaminated water before separation of the organic liquid, the inability to purify the organic liquid on the same device after it is separated from the water.

As a prototype, the method of purification of liquids containing radionuclides and the device for its implementation (patent RU No. 2550367 "Method for purification of liquids containing radionuclides, and a device for its implementation), which is closest to the claimed method and device for the problem to be solved and achieved using the technical result, were selected. ”, IPC G21F 9/16 (2006.01), published on 05/10/2015). The method consists in cleaning the contaminated liquid by placing an element of a porous material in it, one end of which is partially immersed in the contaminated liquid, and on the other by passing an electric current through the liquid, an evaporation zone is created into which the contaminated liquid is transported due to the capillary properties of the porous material, and where by heating the liquid to a boil, compacting the contaminants is carried out, and the resulting vapor is condensed to obtain a purified liquid. A device for cleaning contaminated liquid is a working container for such a liquid with an element of porous material placed in it, which is equipped with electrodes. An element of a porous material is essentially a wick, the lower part of which is immersed in a liquid, and the upper part is placed between the electrodes to ensure contact.

The known method and device have the following disadvantages - the inability to clean non-conductive (dielectric) fluids, which include organic fluids used in technological operations with radioactive materials (kerosene, RZh-3 and the like), as well as the inability to separate and extract organic and inorganic components for example, water and oil, distributed in water in the form of an emulsion.

The task and the technical result achieved by using the group of inventions is to increase the efficiency of processing a liquid containing radionuclides with a high concentration of organic substances, separation and extraction of their components for reuse, and reduction of waste volume for disposal.

The technical result is achieved in that in a method for purifying a liquid contaminated with radionuclides and consisting of components such as water and an organic component, comprising placing an element of a porous material in the contaminated liquid, one end of which is partially immersed in the contaminated liquid, and on the other by passing ( through a liquid) of an electric current, an evaporation zone is created, into which the contaminated liquid is transported due to the capillary properties of the porous material, and where by heating the liquid to bales Nia compaction carried contaminants and the resulting vapor is condensed to obtain a purified liquid. According to the invention, it is proposed to place at least one element from different porous materials — hydrophilic and hydrophobic — in the contaminated liquid, it is proposed to transport water through the element from the hydrophilic material, and the organic component through the element from the hydrophobic material. Compaction is proposed to be carried out by sequential heating until the water is completely evaporated, then - until the organic component is completely evaporated or vice versa.

It is proposed that the sequence of heating to complete evaporation of the components (water and the organic component) be established in the order of increase in their boiling point.

It is proposed to use porous alumina ceramics as a hydrophilic material, and graphite felt as a hydrophobic material with sorbing properties with respect to radionuclides.

It is proposed to pre-filter the contaminated liquid according to the invention in order to separate its coarse particles.

The claimed method of purification of a liquid contaminated with radionuclides and consisting of components such as water and an organic component is implemented using a device comprising an external and a working tank connected to each other through a channel (in the lower part), an element made of a porous material placed in the working tank equipped with electrodes. An element of a porous material is essentially a wick, the lower part of which is immersed in a liquid, and the upper part is placed between the electrodes to ensure contact. According to the invention, it is proposed that at least one wick of different porous materials — hydrophilic and hydrophobic — be placed in a working vessel. It is also proposed that the device is additionally equipped with a cooled chamber in which to place the working container, and the cooled chamber should be equipped with a pipe in the lower part for draining the purified liquid into the collection container. It is proposed to connect the cooled chamber and the external container with a pipeline.

It is proposed to provide an external container with a removable filter through which liquid contaminated with radionuclides is passed, and it is also proposed to provide it with a level indicator.

It is proposed to equip the working capacity with a fire protection insert.

In special cases of execution, the cooled chamber is proposed to be sealed, which will make the process of cleaning the liquid less energy-intensive (will allow you to work in energy saving mode).

It is proposed to connect the pipeline connecting the cooled chamber and the external container to a high-pressure cylinder.

A wick made of hydrophobic material is proposed to be equipped with a device for measuring temperature from the point of view of the information content of the ongoing process.

The proposed design of the device allows you to implement the inventive method without using an additional circuit for the organic component, separating the components of the liquid containing radionuclides in time, that is, making the cleaning process discontinuous in time.

The invention is illustrated by drawings, where in FIG. 1 shows a general view of a device for purifying a liquid contaminated with radionuclides, and FIG. 2 - working tank with a node for the thermal treatment of contaminated liquids.

A device for cleaning a liquid contaminated with radionuclides consists of a sealed collapsible cooled chamber 1, inside of which there is a working container 2 with electrodes 3 installed in it and at least one wick 4 of a capillary-porous hydrophobic material and one wick 5 of a capillary-porous hydrophilic material permeable flame retardant insert 6 of a porous ceramic material. In the material of the wick 4 there is a device for measuring temperature, which is a thermocouple 7. The cooled chamber 1 is cooled by means of a cooled liquid (water). The working tank 2 is connected by a channel 8 with an external tank 9, designed to fill the contaminated liquid. A removable filter 10 is placed in the upper part of the external container 9, a level gauge 11 in the form of a gauge glass is installed outside the external container 9, and the external container 9 is closed by a lid 12, in which there is a nozzle for the inlet 13 of liquid contaminated with radionuclides.

The cooled chamber 1 and the external tank 9 are equipped with a pipe 14 with taps 15, 16 and 17 for balancing the pressure in the cooled chamber 1 and the external tank 9. The pipe 14 is also connected to a high-pressure cylinder 18. At the bottom of the cooled chamber 1 there is a pipe 19 with a crane 20 for draining the purified liquid into a collection tank 21.

The device operates as follows: the liquid to be cleaned, contaminated with fine solid particles and water with salts, is poured into the external container 9 through the nozzle for the bay 13 in the lid 12 and passed through a removable filter 10, controlling the level according to the level indicator 11. Large particles (more than 0, 2 mm) are held by a removable filter 10. The position of the taps 15, 16 and 20 is “open”, and the valve 17 is “closed”. Next, the cleaned fluid through channel 8 enters the working tank 2.

According to wick 4, from the hydrophobic carbon material, due to capillary forces, the organic component of the contaminated liquid enters the evaporation zone located between the electrodes 3. The liquid is heated to boiling and evaporated by passing current between the electrodes 3 first, using the material of the wick 4. The temperature in the evaporation zone is determined from using a thermocouple 7, placed in the material of the wick 4. Gaseous products of evaporation through the fire barrier insert 6 enter the cavity of the cooled chamber 1, condenses and its cooled walls run down to the bottom, and then through the nozzle 19, the purified liquid is discharged into a collection vessel 21. Solid fine particles containing radionuclides are collected at the bottom of the working vessel 2, and ultrafine particles (less than 10 nm) fall into the liquid wick material 4 and remain there after evaporation. When processing petroleum products in the material of the wick 4 can also accumulate resin.

After the organic component of the liquid radioactive waste is completely processed, the electric current is switched to a pair of electrodes 3, between which a wick 5 of hydrophilic material is placed. Water with salts dissolved in it through the wick 5 enters the evaporation zone, steam passes through the fire barrier insert 6, enters the cavity of the cooled chamber 1, condenses on its cooled walls and flows to the bottom, and then flows through the pipe 19 into a collection tank 21. Salts containing radionuclides remain in the wick material 5.

Depending on the type, value and economic feasibility, the materials accumulated on the removable filter 10 in wicks 4 and 5, together with the wicks 4, 5 themselves, are transferred for burial or for further processing to extract radioactive metals from them.

Examples of specific implementation of the method.

Example 1. Electroerosive dimensional cutting of fuel elements of reactors is carried out in an organic liquid RZh-3 - a fraction extracted from sulfur dioxide. During cutting, particles of uranium, zirconium and their carbides accumulate in the liquid. Particle sizes range from hundreds of microns to units of nanometers, and the predominant amount (up to 80%) of particles is in the range of 0.01 ÷ 10 microns. Small particles can be combined into conglomerates and, together with large ones, can be collected in the sediment, while particles smaller than 100 nm in size form colloidal systems in liquids that do not precipitate. In addition to particles in the liquid, spark decomposition products accumulate the decomposition products of hydrocarbons in the form of resins and water.

The spent liquid with sediment is poured into the external container 9 through the nozzle for the bay 13 in the cover 12, then the liquid passes through a removable filter 10, on which part of the sediment is collected during the filling of the liquid (pre-filtering). Preliminarily purified from large particles, the liquid through the channel 8, connecting the external container 9 and the working capacity 2, by gravity enters the working capacity 2, which is a cylinder with a diameter of 200 mm and a depth of 200 mm. Three electrodes 3 in the form of stainless steel plates 2 × 100 × 100 mm are installed vertically in the working container 2, and wicks 4, 5 with dimensions 40 × 120 × 120 mm are placed between them - one of the hydrophobic material (graphite felt) (wick 4 ), the other from hydrophilic (alumina) (wick 5). The electrodes 3 are pressed to the top of the wicks 4, 5 with electrical contact. The extreme of the three electrodes 3 are connected to one pole of the power source, and the middle to the other pole (not shown). The lower part of the wicks 4, 5 is placed in the liquid to be cleaned so that it reaches the bottom of the working vessel 2. The thickness of the wicks 4, 5 corresponds to the distance between the electrodes 3, which is 40 mm. The heating of the liquid RZH-3 to a temperature of 380 ÷ 400 ° C is carried out by passing an alternating current of 40 ÷ 60 A and a voltage of up to 20 V through the wick 4 of graphite felt, placed between the leftmost and the middle of the three electrodes 3 (Fig. 1). Temperature control is performed by changing the current in automatic mode by a signal from a thermocouple 19. Boiling of the liquid begins at a temperature of 265 ° C, and at a temperature of 400 ° C, the liquid boils off completely. Vapors of liquid through a flameproof insert 6 made of porous ceramics, for example, of foam corundum, pass into the cavity of the cooled chamber 1, condense on its walls and through the hole in the bottom of the cooled chamber 1 through the pipe 19 flow into a container for collecting 21 purified liquid for the purpose of further reuse of the obtained liquids. The cooled chamber 1 is cooled by means of a liquid (water). The volume of purified liquid after processing is at least 0.9 of the original volume.

After complete evaporation of the organic component, the electric current is switched to the second pair of electrodes 3 (to the middle and rightmost of the three electrodes 3) (Fig. 1), between which a wick 5 of hydrophilic material (porous ceramic) is placed. The water accumulated after evaporation of one or more fillings of the spent liquid through wick 5 enters the evaporation zone and evaporates at a temperature of 100 ÷ 110 ° C. The water in the wick 5 is heated by passing a current of 1 ÷ 5 A through it at a voltage of 100 ÷ 150 V. Liquid vapor passes through the flameproof insert 6 into the cavity of the cooled chamber 1, condenses on its walls and flows through the pipe 19 through the hole in the bottom of the cooled chamber 1 in a new container for collecting 21 purified liquid in order to further reuse the resulting liquid.

The graphite felt used as a material for wick 4 has an open porosity of 0.80 ÷ 0.90 and, with the dimensions of wick 4 given in the specific use example, it is able to collect up to 0.5 dm of solid particles, including particles from colloidal suspensions remaining in the material of the wick 4 after evaporation.

The spent wick 4 from graphite felt with the resins accumulated in it is burned, and the ash residue is transferred either to burial or to extract radionuclides. Wick 5 made of porous ceramics is transferred for burial.

Example 2. Water obtained after machining a material containing radionuclides, in addition to contaminants from suspended solids of fine particles also contains an organic liquid, for example, mineral oil, which is distributed in water in the form of an emulsion. It is almost impossible to separate the oil by settling in such a liquid. However, the processing of such a liquid according to the proposed method and a device for implementing such a method make it possible to separate water and oil and clean them of radionuclides.

The contaminated liquid is poured into the external container 9 through the nozzle for the bay 13 in the cover 12. Next, the liquid passes through a removable filter 10, on which part of the sediment collects during the liquid filling and mechanical impurities are retained (particles or conglomerates of particles larger than 0.2 mm). Next, the fluid through the channel 8 by gravity enters the working tank 2, in which four electrodes 3 2 × 100 × 100 mm are installed. Between the electrodes 3 are placed two wicks 4 of hydrophobic and one wick 5 of hydrophilic capillary-porous material (Fig. 2). Dimensions of wicks 4, 5 - 40 × 120 × 120 mm. Processing of fluid components is carried out sequentially. First, a current is supplied to the electrodes 3, between which a wick 5 of hydrophilic material (porous ceramic) is placed, and by adjusting the current, the temperature necessary for the evaporation of water is set in the evaporation zone (100 ÷ 110 ° C). Water contaminated with salts and finely dispersed solid particles with radionuclides is supplied to the heating zone only via a hydrophilic wick 5, while it does not enter the hydrophobic wicks 4. The process is conducted until the water is completely evaporated in the working vessel 2. Then, the current is switched to electrodes 3, between which are placed wicks 4 from a hydrophobic material, and heat the material in the evaporation zone to a temperature of about 125 ° C, which corresponds to the beginning of light fraction separation, then gradually increase the temperature until oil decomposition begins (400 ÷ 500 ° C). Vapors of the liquid through the fire barrier insert 6 pass into the cavity of the cooled chamber 1, condense on its walls and through the hole in the bottom of the cooled chamber 1 through the pipe 19 flow into the tank for collecting 21 purified liquid for the purpose of further reuse of the obtained liquid.

The spent wicks 4 from graphite felt with the resins accumulated in them are burnt, and the ash residue is transferred either to burial or to extract radionuclides. Wick 5 made of porous ceramics is transferred for burial.

The proposed method and device allows you to separate the organic and inorganic components of the liquid containing radionuclides, and return these components for reuse, while reducing the amount of waste for disposal.

Claims (11)

1. The method of purification of a liquid containing radionuclides and consisting of components such as water and an organic component, comprising placing an element of a porous material in a contaminated liquid, one end of which is partially immersed in a contaminated liquid, and on the other by creating an electric current through the liquid, create a zone evaporation, into which the contaminated liquid is transported due to the capillary properties of the porous material, and where, by heating the liquid to a boil, pollution is compacted, and the vaporized condensate is condensed to obtain a purified liquid, characterized in that at least one element from different porous materials — hydrophilic and hydrophobic — is placed in the contaminated liquid, and water is transported through the element from the hydrophilic material, and the organic component is transported through the element from the hydrophobic material, compacting carry out sequential heating until the water is completely evaporated, then - until the organic component is completely evaporated, or vice versa. 2. The method according to p. 1, characterized in that the heating sequence until complete evaporation of the components is set in order of increasing their boiling point. 3. The method according to p. 1, characterized in that as a hydrophilic material use porous ceramic from alumina, and as hydrophobic - graphite felt. 4. The method according to p. 1, characterized in that the contaminated liquid is pre-filtered. 5. A device for cleaning a liquid containing radionuclides, including external and working containers, connected to each other through a channel, an element of porous material placed in the working container equipped with electrodes, the element of porous material is essentially a wick, the lower part of which is immersed in liquid, and the upper part is placed between the electrodes to ensure contact, characterized in that at least one wick of different porous materials is placed in the working container - hydrophilic and hydrophilic This is a device that is optionally equipped with a cooled chamber in which the working container is placed, while the cooled chamber is connected by a pipe to an external container and is equipped at the bottom with a pipe for draining the purified liquid. 6. The device according to p. 5, characterized in that the external container is equipped with a removable filter. 7. The device according to p. 5, characterized in that the external container is equipped with a level indicator. 8. The device according to p. 5, characterized in that the working capacity is equipped with a flame-retardant insert. 9. The device according to p. 5, characterized in that the pipeline connecting the cooled chamber and the external container is connected to a high-pressure cylinder. 10. The device according to p. 5, characterized in that the cooled chamber is sealed. 11. The device according to p. 5, characterized in that the wick of a hydrophobic material is equipped with a device for measuring temperature.

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