RU2275233C2 - Method and the device for the deep purification of xenon isotopes from the gaseous impurities - Google Patents

Abstract

FIELD: chemical industry; metallurgy industry; medical equipment; lighting engineering and nuclear physics; methods and the devices for the deep purification of xenon isotopes from the gaseous impurities.

SUBSTANCE: the invention is pertaining to the method and the device for the deep purification of xenon isotopes from the gaseous impurities. The invention may be used in chemical industry, metallurgy, in production of medical equipment, in lighting engineering and nuclear physics for determination of mass of a neutrino. The initial mixture of xenon isotopes with impurities is fed into one of the freezing devices 2 or 3 of the stage of the gaseous centrifuges 1 through one of the branch-pipes 19 or 20 at the open gate units 7, 8 or 9, 10. Isotopes of xenon and the part of the gaseous impurities are settling on the walls of the one of the freezing devices 2 or 3. The non-settled gaseous impurities having the pressure of the saturated steam exceeding the pressure of the isotopes of are removed by the vacuum system 6. Then terminate feeding of the initial mixture by closing gates 7, 8 on the branch-pipe 19 or gates 9, 10 on the branch-pipe 20. For keeping the process continuity the device contains of no less than two freezing devices 2 or 3, each of which is connected in parallel to the stage of the centrifuges 1 and in series - to the accumulating balloon 4 or 5, which is in advance frozen refrigerated in the Dewar flask 16. At first the freezing device 2 or 3 works in the mode of freezing, and then - in the mode of warming-up and taking the isotopes off. The modes switching is exercised by opening gates 8, 26 and 13 of the pipeline 24 or gates 10, 27 and 14 of the pipeline 25. The heating-up of the freezing device 2 or 3 up to the temperature of (-70°C)-(-80°C) is exercised by removing the Dewar flask 15 or 23. The withdrawal of the purified xenon isotopes is conducted at the residual pressure of(3-10)·10^-3 mmHg. Operation of the freezing device 2 or 3 with the accumulating balloon 4 or 5 in pairs is interleaved in the indicated modes of operation. The invention ensures a continuity of the process of deep purification of xenon isotopes from the various gaseous impurities, does not require the complex installations, allows to reduce expenditures. The contents of the gaseous impurities in the final product does not exceed 4.4 ppm.

EFFECT: the invention ensures a continuity of the process of deep purification of xenon isotopes from the various gaseous impurities, absence of the need in the complex installations, reduced expenditures.

5 cl, 5 dwg, 1 tbl

Description

The invention relates to a technology for the separation of stable isotopes, in particular to the purification of xenon isotopes obtained on a cascade of centrifuges with a given isotopic composition and used in nuclear physics to determine the neutrino mass. In addition, the invention can be applied in the chemical, metallurgical industries, in medicine, lighting, etc.

A known method of cleaning isotopes of chemical elements from air impurities penetrating the cascade through vacuum leaks in compounds from the atmosphere of the room, which is carried out by condensation of the gas mixture in the freezer (capacity) [1] of the condensation-evaporation unit by removing impurities from it by vacuum at a given temperature cooling (see J. Katz and E. Rabinovich. Uranium Chemistry. Moscow: Foreign Literature, 1954, p. 327; V. Yu. Baranov. Isotopes. Moscow: Atomic Science and Technology, 2000, p. 145).

The disadvantages of the known method of purification of gases from impurities in a condensation-evaporation plant include the impossibility of removing impurities that have higher boiling points of saturated vapors than shared isotopes.

So, in the process of separation of isotopes due to the burning of structural materials of rotors of gas centrifuges in the internal cavities of the cascade, organic gas impurities are formed, in addition to air, consisting of acetone, xylene, toluene, butyl acetate, propanol, ethanol, butyl alcohol, water vapor, etc. . which condense in the freezer together with the shared isotopes. As a result, they significantly pollute commercial products, and therefore requires the development of a new method for cleaning isotopes of these impurities in the separation process.

A method for purifying xenon obtained in air separation plants from a gas mixture containing krypton, oxygen, nitrogen, methane, acetylene, carbon dioxide, water vapor, etc., by burning hydrocarbons (acetylene, methane) in heating furnaces at a temperature plus 700 ° С and absorption of other impurities by solid adsorbents - activated carbon, zeolites, sponge titanium, etc., with the selection of purified xenon in a freezer cooled with liquid nitrogen (see V.G. Fastovsky et al. Inert gases. Moscow: Atomizdat , 1972, pp. 150-161).

The disadvantage of this method is its high complexity, complexity and high cost of the cleaning process, because To implement this cleaning method, it is necessary to use a special installation, including heating furnaces, adsorbers, compressors, heat exchangers, etc.

Closest to the depth of purification from impurities is the "Method for the separation of xenon and installation for its implementation" according to the patent of Russia, No. 2134387, IPC ⁶ F 25 J 3/08, publ. 08/10/1999

In this method, the purification of xenon, obtained not at the cascade, but at the air separation unit, is carried out by condensation of the gas mixture (containing oxygen and methane) in the freezer [Fig. 2] with interruption of the mixture supply and the working volume evacuation at a temperature of minus 196 ° С to residual pressure (3 ... 4) × 10 ^-3 mm Hg (oxygen and methane are removed), by selection of xenon after the cessation of evacuation by smooth heating of the freezer to positive temperatures plus 27 ... 27 ° С with the removal of xenon vapor into a thermocompressor or into an accumulation cylinder, previously cooled to a temperature of minus 196 ° С.

The disadvantage of this method is its narrow focus, because only oxygen and methane are removed, while the cleaning process is carried out at a pressure above atmospheric in order to exclude xenon pollution by air impurities and water vapor penetrating the communications from the room atmosphere.

This method cannot be used in the case of a centrifugal separation method when obtaining highly pure xenon isotopes, because Along with xenon isotopes, gas centrifuges from the cascade of gas centrifuges under atmospheric pressure enter the freezer of the condensation-evaporation plant, as well, the products of the internal cavity cavities, in which the saturated vapor pressure is lower than the pressure of the saturated xenon vapor, which causes their combined condensation in the freezer and, as a result, contamination of the finished product.

Therefore, for the final cleaning of xenon isotopes from impurities, an additional cleaning operation is necessary, for which: to dismantle the storage cylinder from the condensation-evaporation unit of the cascade, install the storage cylinder in a special installation in which to carry out the final cleaning of xenon isotopes from organic impurities in a known manner (see V.G. Fastovsky et al. Inert Gases, Moscow: Atomizdat, 1972, pp. 150-161).

The present invention is the creation of such a cleaning method and device for its implementation, which would significantly increase the cleaning depth of xenon isotopes while simplifying the cleaning process and reduce the cost of obtaining the finished product by combining isotope separation and purification processes into a single continuous process.

The technical result is achieved by the fact that in the known method of purification of xenon isotopes by condensing the supplied gas mixture in the freezer, then evacuating the working volume of the freezer at a temperature of minus 196 ° C to a residual pressure of (3 ... 4) × 10 ^-3 mm Hg and selection of purified xenon isotopes, the supply of a gas mixture containing xenon, nitrogen, oxygen, krypton, methane, acetone, xylene, toluene, water vapor, etc. to the freezer is carried out directly from the centrifuge cascade, and the selection of purified xenon isotopes is carried out after the vacuum has been stopped by gradual heating of the freezer to a negative temperature of minus 70 ... 78 ° C with the simultaneous removal of vapors of purified xenon isotopes into a storage cylinder, previously frozen with liquid nitrogen to a temperature of minus 196 ° C.

A known installation for cleaning isotopes of various chemical elements from air impurities, including a freezer (capacity) and a vacuum system (see V.Yu. Baranov. Isotopes. Moscow: Atomic Science and Technology, 2000, p. 145).

In this installation, after completion of evacuation and freezing, the selection of purified isotopes is not carried out. The freezer (Fig. 1) is itself a store of marketable products. Under such conditions, the organic impurities coming from the cascade remain in the commercial product, i.e. in the freezer. Therefore, in an installation with such a freezer, the claimed technical result cannot be achieved.

Also known installation (figure 2) for the separation of xenon from a gas mixture (oxygen-methane), containing a freezer 1, having a housing 4 connected to an autonomous source of the gas mixture 2, two vacuum systems 3, 13, a thermal compressor or gas tank, an accumulation cylinder, equipped with tubes with common dish-shaped ribs 7, 8 for introducing the mixture, strainers 9, a heat exchanger 14, a channel 22 for supplying liquid nitrogen to the cooling bath 6, a channel for outputting purified xenon, sensors for two-phase current indicators 12, thermal insulation 18 (see Pat m Russia, №2134387, MPK ⁶ F 25 J 3/08, publ. 10.08.1999 g).

This setting by the number of essential features is the closest analogue.

However, in the known installation-analogue means are not provided for changing the temperature conditions of the freezer from a temperature of minus 196 ° C to a temperature of minus 70 ... 78 ° C and vice versa, which leads to the inefficiency of the cleaning process and the continuity of operation of the freezer as to remove air and organic impurities, as well as for packaging cylinders with commercial products. For this reason, and claimed in the method, the technical result claimed in the method cannot be achieved.

The objective of the invention is to develop such a device that would provide the possibility of combining the separation of xenon isotopes with its purification from multicomponent gas impurities and with the selection of commercial products into cylinders into a single continuous process.

The technical result is achieved in that in a known installation containing a freezer, the casing of which is connected to a gas mixture source, a vacuum system and an accumulation cylinder, the freezer is made in the form of a hollow vertical cylindrical vessel, in the openings of the upper end part of which there are two nozzles, the first of which is equipped with two valves for introducing the gas mixture from the cascade of centrifuges, one of these valves being also used to select purified isotopes in the storage cylinder by means of additional tional nozzle, disposed on the first pipe between the two valves, and the second branch pipe disposed at an end portion of said vessel, a valve is provided for connection to a vacuum system vymorazhivatelya, wherein vymorazhivatel placed in the Dewar vessel with a removable coolant (3). The pipe for introducing the gas mixture into the freezer during operation has a dual purpose - in the condensation mode it serves to enter the freezer, and in the evaporation mode - for the output of purified xenon isotopes from the freezer to the storage cylinder through a pipe installed between its two valves.

To ensure the continuity of the processes of isotope separation and purification from gas impurities, the device is equipped with at least two freezers connected in parallel with the cascade of centrifuges, with each freezer connected in series with the storage cylinder.

The main technical effect of the proposed method and device is expressed in expanding the range of removed gas impurities of xenon isotopes with an increase in the depth of their purification and the continuity of the process of obtaining the finished product.

The drawings illustrate the invention.

Figure 1 - known freezer (capacity).

Figure 2 - freezer according to patent 2134387.

Figure 3 - the claimed design of the freezer.

Figure 4 is a block diagram of a device that implements the inventive process for obtaining, purification from gas impurities and packaging of xenon isotopes.

Figure 5 is a graph of the temperature dependence of saturated steam pressure for the main components of the gas mixture. The logarithmic scale of divisions is used.

The device (figure 4) for cleaning xenon isotopes from gas impurities and isotope packing contains a freezer 2 or 3, which is connected to the selection route for the heavy or light fractions of the centrifuge cascade 1, an accumulation tank 4 or 5 of commercial products and a vacuum system 6.

The freezer 2 or 3 (Fig. 4) is made in the form of a hollow vertical cylindrical vessel, in the upper end part 17 or 18 of which there is a pipe 19 or 20 with valves 7, 8 or 9, 10 for entering the gas mixture and output (valve 8 or 10 ) cleaned xenon isotopes, pipe 21 or 22 with valve 11 or 12 for connecting to the vacuum system 6. Between valves 7, 8 or 9, 10 of pipe 19 or 20, pipe 24 or 25 with valve 26 or 27 is installed for connecting the accumulation tank 4 or 5, located in the Dewar vessel 16. The freezer 2 or 3 is installed in a removable Dewar vessel 15 or 23.

The device for cleaning xenon isotopes of gaseous impurities is as follows

- Freezing mode

A gas mixture containing xenon isotopes with gas impurities is supplied from the centrifuge cascade 1 through a pipe 19 or 20 and valves 7, 8 or 9, 10 to a freezer 2 or 3, previously cooled with liquid nitrogen in a Dewar vessel 15 or 23 and evacuated to pressure ( 3 ... 10) × 10 ^-3 mmHg vacuum system 6 through the pipe 21 or 22 through the valve 11 or 12.

On the inner walls of the freezer 2 or 3, xenon isotopes and part of gas impurities are deposited (Fig. 5), in which the saturated vapor pressure is lower than the saturated vapor pressure of xenon, and gas impurities in which the saturated vapor pressure is higher than xenon, periodically removed by vacuum system 6.

- The mode of heating and selection of xenon isotopes

After completion of the process of filling the product of the freezer 2 or 3, the supply of the gas mixture to it is stopped by closing the valves 7, 8 on the pipe 19 or 9, 10 on the pipe 20 while transferring it to the freezer 3 or 2 by opening the valves 9, 10 of the pipe 20 or valves 7, 8 of the pipe 19 on the freezer 3 or 2, prepared for work as a freezer 2 or 3.

At a temperature of minus 196 ° C using a vacuum system 6 through the pipe 21 and valve 11 or pipe 22 and valve 12, the working volume of the freezer 2 or 3 is evacuated to a residual pressure (3 ... 10) × 10 ^-3 mm Hg Then the vacuum system 6 is turned off by closing the valve 11 on the pipe 21 or the valve 12 on the pipe 22 and the evacuation scheme of the cleaned xenon isotopes from the freezer 2 or 3 through the pipe 19 or 20 and the pipe 24 or 25, is going to open the valves 8, 26, 13 or 10, 27, 14 into the cylinder of the accumulator 4 or 5, previously frozen to a temperature of minus 196 ° C in a Dewar vessel 16 and evacuated to a residual pressure of (3 ... 10) × 10 ^-3 mm Hg vacuum system 6 through valves 28 or 29. The evacuation of purified xenon isotopes is carried out by gradually heating the freezer 2 or 3 by removing from it a Dewar vessel 15 or 23 with liquid nitrogen, followed by placing the freezer 2 or 3 into a Dewar vessel 15 or 23 with “dry ice”. The process of removal of the purified xenon isotopes (Fig. 5) from the freezer 2 or 3 to the storage tank 4 or 5 is carried out at a negative temperature minus 70 ... 78 ° C of the freezer 2 or 3 to a residual pressure of 0.2 ... 1.0 mm Hg

Under conditions of continuity of the process of separation of xenon isotopes on a cascade of centrifuges 1, pairwise alternation of the operation of a freezer 2 or 3 with an accumulation cylinder 4 or 5 in the condensation-evaporation mode is provided.

In accordance with the claimed method for purification of xenon isotopes and a device for its implementation, Table 1-4 presents the comparative results of the analysis of the chemical composition of the impurities of purified xenon enriched in xenon-136 isotope, as well as customer requirements for the chemical purity of enriched xenon and GOST 10219-77.

Table 1
Mass spectrometric analysis of impurities Analysis stage Molar fraction of impurities, ppm N ₂ O ₂ Ar Kr CH ₄ CF ₄ Other before use of invention 2,8 0.3 0.04 0.04 1,2 0.04 644 after 0.46 0.2 <0.02 <0.02 0.08 <0.02 2,3 GOST 10219-77 10 2 - 10 one - - Customer requirements <5 <5 <0.5 <0.1 <1 <5 <7.4

table 2
Mass - spectrometric analysis of the isotopic composition of commodity xenon Analysis stage Atomic fraction of isotopes,% 124 126 128 129 130 131 132 134 136 Commodity Content - - - - - 0,03 0.26 18.95 80.76 isotopic content of natural xenon 0,096 0,090 1,919 26.44 4.08 21.18 26.89 10.44 8.87 Table 3
Chromatographic analysis of impurities Analysis stage Molar fraction of impurities, ppm ethanol acetone propanol Butyl alcohol toluene Butyl acetate xylene before use of invention 158 366 34 44 22 2 eighteen after <0.2 <0.2 <0.2 <0.4 <0.4 <0.4 <0.5 Table 4
Impurity analysis by IR spectrometry Analysis stage Molar fraction of impurities, ppm CO ₂ H ₂ O before use of invention 2.7 6.7 after 0.3 <1.0 GOST 10219-77 one 5 Customer requirements one 5

From the results of the analysis it follows that the purification depth of xenon isotopes obtained on a cascade of centrifuges and cleaned in the inventive installation using the inventive method increased from 657.82 ppm to <4.4 ppm, i.e. ~ 150 times. This indicates that the inventive method has high efficiency, and the device for its implementation - high performance in terms of continuity of the process.

In the world practice of centrifugal separation of stable isotopes of chemical elements, there are no known cases of obtaining highly enriched isotopes of such a high degree of chemical purity.

The study of the claimed invention provides the following technical and useful advantages:

- continuous process of separation of xenon isotopes in a cascade of centrifuges and at the same time the process of their deep cleaning from a wide range of gaseous chemical impurities,

- increasing the depth of purification of xenon isotopes by at least two orders of magnitude,

- no need to create complex special installations for the purification of xenon isotopes from gas impurities,

- reducing the cost of obtaining marketable products by combining two processes into one continuous process with ease of maintenance.

Claims (5)

1. A method for the deep cleaning of xenon isotopes from gaseous impurities, including the supply and condensation of a gas mixture in a freezer, followed by removal of non-condensed gas impurities from it by evacuation at a temperature of minus 196 ° C and the selection of purified xenon isotopes in an accumulation cylinder after termination of evacuation by gradually heating the worker freezer volume, characterized in that the gas mixture is fed directly to the freezer directly from the cascade of centrifuges, and when selecting purified xenon isotopes, p Work feedrate volume minus vymorazhivatelya heated to 70 ÷ 78 ° C at a residual pressure of 0.2 ÷ 1.0 mm Hg 2. The method according to claim 1, characterized in that during the condensation of the gas mixture in the freezer, air impurities are periodically removed from it by evacuation to a residual pressure of (3 ÷ 10) · 10 ^-3 mm Hg 3. A device for the deep cleaning of xenon isotopes from gaseous impurities, containing a freezer, a vacuum system and an accumulation tank of purified isotopes, characterized in that the freezer is made in the form of a hollow vertical cylindrical vessel, in the openings of the upper end part of which there are two nozzles, the first of which is equipped two valves for introducing the gas mixture from the cascade of centrifuges, one of these valves being used to select purified isotopes in the storage cylinder by fitting ceiling elements disposed on the first pipe between the two valves, and the second branch pipe disposed at an end portion of said vessel, a valve is provided for connection to a vacuum system vymorazhivatelya. 4. The device according to claim 3, characterized in that it is equipped with at least two freezers, each of which is connected to the cascade of centrifuges by means of the first nozzle, and through an additional nozzle connected to the accumulation cylinder. 5. The device according to claim 4, characterized in that the freezers are connected in parallel with the cascade of centrifuges, and in series with accumulation cylinders.

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