CA1045967A - Adsorption-distillation system for separation of radioactive krypton and xenon - Google Patents
Adsorption-distillation system for separation of radioactive krypton and xenonInfo
- Publication number
- CA1045967A CA1045967A CA274,159A CA274159A CA1045967A CA 1045967 A CA1045967 A CA 1045967A CA 274159 A CA274159 A CA 274159A CA 1045967 A CA1045967 A CA 1045967A
- Authority
- CA
- Canada
- Prior art keywords
- xenon
- adsorption
- krypton
- purge
- process according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B23/00—Noble gases; Compounds thereof
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/028—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of noble gases
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/02—Treating gases
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/40—Processes or apparatus using other separation and/or other processing means using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/60—Processes or apparatus using other separation and/or other processing means using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/34—Krypton
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/36—Xenon
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/40—Capture or disposal of greenhouse gases of CO2
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- Inorganic Chemistry (AREA)
- High Energy & Nuclear Physics (AREA)
- Separation Of Gases By Adsorption (AREA)
- Separation By Low-Temperature Treatments (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a process for separating radioactive krypton ans xenon from waste gases such as those during the reprocessing of nuclear fuels or from nuclear reactors, wherein the waste gas is freed of krypton by a low-temperature rectification system, the improvement of separating the xenon from the waste gas by adsorption prior to the low temperature rectification step, and preferably conducted the adsorption in interchangeable adsorbers cyclically operated, the regeneration of the adsorbers being conducted by purging in at least two phases, wherein primarily adsorbed krypton is desorbed in the first purge phase and resultant krypton-containing purge gas is recycled;
and in the second purge phase, the xenon is desorbed and the xenon-containing purge gas is discharged from the process.
In a process for separating radioactive krypton ans xenon from waste gases such as those during the reprocessing of nuclear fuels or from nuclear reactors, wherein the waste gas is freed of krypton by a low-temperature rectification system, the improvement of separating the xenon from the waste gas by adsorption prior to the low temperature rectification step, and preferably conducted the adsorption in interchangeable adsorbers cyclically operated, the regeneration of the adsorbers being conducted by purging in at least two phases, wherein primarily adsorbed krypton is desorbed in the first purge phase and resultant krypton-containing purge gas is recycled;
and in the second purge phase, the xenon is desorbed and the xenon-containing purge gas is discharged from the process.
Description
~459~7 This invention relates to an improved system for the separation from waste gas of radioactive krypton and xenon. Such waste gases are derived, for example, from the reprocessing of nuclear fuels or from nuclear reactors, wherein there are produced the radioactive isotopes of Kr and Xe. It is common for such waste gases to contain, in addition to other components, nitrogen and argon as the carrier gases, and for the ~... ..
waste gas, after the other components have been separated, to be cooled and thereafter freed o krypton by distillation.
An example of a conventional process is described in "A Cryogenic Approach to Fuel Reprocessing Gaseous Radwaste Treatment" (J.S. Davis, J.R. Martin, Paper for Presentation at The Noble Gas Symposium, Las Vegas, 1973). This process comprises first subjecting ;
a waste gas from nuclear fuel reprocessing plant consisting essentially of nitrogen, oxygen, oxides of nitrogen, carbon dioxide, and water, as well as argon, krypton, and xenon, to a pretreatment in order to remove the oxygen, nitrogen oxides, carbon dioxide and water.
In this process, the oxygen and the nitrogen oxides are -~
catalytically reduced to nitrogen and water by the introduction o hydrogen. The resultant water and the carbon dioxide are removed by adsorption. The carrier gas of N2 + Ar thus freed of all other components except for the kryp-ton and xenon impurities, is thereafter fed to a ~ . .
low-temperature separation plant wherein in a first -: . . : . - : ~ :
~0~9~7 rectification column a fr~ction containing krypton and xenon is recovered. Then, in a second rectification column, krypton and xenon ~re separated from each other.
It is thus seen that in the conventional process, wherein a highly concentrated radioactive krypton fraction is treated, two rectification column are required, ~ogether with the associated conduits and switching members.
It is also to be noted, however, that the radioactivity of the xenon may be substantially diminished before the aforedescribed treatment of the waste gas because its half-life is only 5.3 days (xenon-133), and there is the possibility of conducting the waste gases through "holdup" zones prior to treatment. In contrast thereto, the radioactivity of krypton-85 (half life: 10.
years) remains prac-tically constant during the time generally available for the waste gas treatment.
An object of one aspect of this invention is to provide an improved system yenerally of the above-mentioned`type, and especially wherein there is a significant savings in the expenditure required for the low-temperature section.
According to the broad aspect of this invention, the improved system is obtained by separating the xenon hy adsorption even before the rectification step. ~ctivated carbon, - ;
for example, can serve as the adsorbent. General information concerning adsorption processes and techniques is contained in :
.
'.,~ ' . . . . . - . ~ .
J.W. carter "~dsor~tion Processes" (Chemical and Process Engineering, Sept. 1966, pp. 70-77) and ~.A. Johns-ton "Designing Fixed-Bed Adsorption Columnsl' (Chemical Engineering, Nov. 1972, ~p. 87-92).
By virtue of this pre-adsorption step, only a single rectification column is required, and thus the protective measures to be taken against the radioactive radiation emanating from the highly concentrated krypton fraction in the sump of thi~ column can be restricted to only the necessary and unavoidable minimum.
Since, during the adsorption of the xenon, ~-traces of krypton are concomitantly adsorbed, it is advantageous, according to another aspect of the invention, to provide that the regeneration of the adsorbers is conducted in at least two purging phases, wherein in the first phase primarily krypton is desorbed and the krypton-containing purge gas is recylced into the process, while in the second phase the xenon is desorbed and the xenon-containing purge gas is removed from the process.
.
In accordance with another aspect of this invention, ' a carrier gas mixture freed at least partially of the krypton is utilized as the purge gas. The purge gas withdrawn ~rom the low-temperature plant and comprised almost exclusively of nitrogen and argon is divided into two portions, one portion absorbing the adsorbed krypton and the other portion absorbing the xenon. Since the krypton, despite its low quantity, has a high radioactivity as compared to the xenon, the krypton-containing purge gas is not discharged from the process, but rather recycled to the process at a suitable location, e.g., the low pressure side of the compressor. ~n contrast thereto, ~'.
.
~14~i~67 the xenon-containing purge gas can eikher be discharged to the outside atmosphere or it can be further processed to obtain its components. If desired, the radioactivity of the xenon can be reduced further in holdup zones located either upstream or downstream of the adsorption zone.
According to another aspect of the process according to this invention, the xenon, optionally together with one of the other components contained in the waste gas, e.g., carbon dioxide, is separated in a mixed-bed adsorber or in divided adsorber beds. In ;
this connection the combined xenon-carbon dioxide adsorption can be conducted in two series-connected adsorber beds; in the second purge phase, xenon and carbon dioxide are distributed separately over the beds; and in a third purge phase with parallel-connected purge streams, xenon and carbon dioxide are purged out separately. The adsorption phase is terminated as soon as the xenon adsorption front has traveled through the second adsorber bed to an extent of about 75%. The relative dimensions of the two adsorber beds are designed so that at this instant the carbon dioxide front is still in the interior of the first adsorber bed. During the first purge phase, the xenon front advances to the end of the second adsorber bed. During the second purge phase, owing to the ready `
desorbability oE the xenon as compared to the carbon dioxide, the xenon is almost completely desorbed from the first adsorber bed and is deposited in the second bed, the carbon dioxide front advancing during this step to `
the end of the first bed. During the subsequent third ','~', purge ph~se, both beds are connected in parallel and freed separately of xenon arld carbon dioxide. The adsorber beds can contain zeolite and activated carbon, for example.
As mentioned above, the waste gases from nuclear fuel reprocessing plants or nuclear reactors generally contain, as additional components, oxygen and nitrogen oxides;-these are usually catalytically reduced -to nitrogen and water with the use of hydrogen. Most of the thus-formed water is removed in a separator. In such a case, it is advantageous, according to another aspect of this invention, to separate the residual water in reversible adsorbers even prior to the adsorptive xenon removal from the waste gases. Such adsorbers are then purged in the regenerating phase with hydrogen, and the H2O-~I2 resultant mixture is fed to the catalytic reduction stage. By the introduction of the H2O-containing hydrogen into the reduction stage, there is the advantage that even the residual water absorbed in the adsorbers is finally removed in the separator.
Suitable exemplary adsorbents for the water include, but are not limited to, silica gel and zeolite.
The drawing is a schematic view of the preferred embodiment of the invention.
~ .
~LV~5967 A radioactive gaseous waste stream ls introduced via conduit 1, comprising 9000 mol/h of 67 mol-~ nitrogen, 16 mol-~ oxygen, 5 mol-~ water, 8 mol-% nitrogen dioxide, 3 mol-% nitrogen monoxide, and 1 mol-% argon, as well as 800 mol-p.p.m. xenon and 160 mol-p.p.m. krypton and containing traces of N2O, CO2 and CO. The radioactivity caused by the radioactive krypton isotope krypton-85 is 0.62 Ci/s. In a compressor 2, this waste gas is compressed from 1 bar to about 6 bars and introduced into a catalytic reduction stage 3 together with a hydrogen-enriched gas fed via conduit 24, as well as a recycling gas fed via conduit 25 tthis recycling gas will be defined in greater detail below). In this ca-talytic reduction stage, the nitrogen oxides along with the oxygen are reduced to nitrogen and water by reaction with the hydrogen. Platinum can be utilized as the catalyst, for example. In the subsequent phase separator 4, the largest portion of the water is separated in the liquid phase. To avoid the development of flames in the reduction stage, the gaseous mixture to be conducted over the catalyst must be diluted to such an extent that the total content of oxygen plus nitrogen oxides is only at most 3 mol-%. For this purpose, a corresponding portion of the gas discharged from the separator is recycled by means of a blower 5 to the inlet of the reduction stage.
The remaining portion of the gas withdrawn from the separator wherein the proportions of oxygen and nitrogen oxides are below 1 mol-p.p.m. and below 5 mol-p.p.m., .
S~67 respectively, is fed to one oE the two silica gel adsorbers 6 and 7, respectively, in order to remove the residual water. These adsorbers can be periodically switched over between the adsorption phase and the regenerating phase. The purge of the adsorbers during the regenerating phase is effected with hydrogen introduced at 8 into the process. The H2O-containing hydrogen is conducted to the reduction stage 3 via conduit 24.
The thus-pretreated waste gas, at this point - consisting essentially merely of the carrier gases nitrogen and argon, as well as carbon dioxide, krypton ans xenon, is now introduced into one of the three periodically reversible adsorbers 9, lO or 11. In this embodiment, the adsorbers are equipped with zeolite and activated-carbon mixed beds wherein the xenon as well as the carbon dioxide is adsorbed. In this step, activated carbon is used for the xenon adsorption, and zeolite having a pore size of 9 Angstrom ;
is used for the carbon dioxide adsorption. In addition to xenon and carbon dioxide, krypton is concomitantly adsorbed in minor quantities. The adsorption eront of the krypton travels the most rapidly through the adsorber, while the carbon dioxide front is the slowest.
As soon as the xenon front has migrated to about three quarters through the adsorber, the switchover to the regeneration phases is effected.
;:
.. ~
::.
109~596~
In the ~irst regenerating phase, krypton is desorbed at ambient temperature, and in the second re~enerating phase carbon dioxide and xenon are desorbed at about 420 K. The puriEied carrier gas mixture withdrawn in conduit 18 from the low-temperature plant 13 is utilized as the purge gas. Since krypton is more readily desorbable as compared to xenon or carbon dioxide, the purge gas is divided into two unequal parts upstream oE the adsorbers, and the smaller, e.g. about 10 to 30 ~
of the two partial quantities is conducted into the appropriate ~;
adsorber for krypton desorption. During the krypton desorption, the adsorption front of the xenon is advanced to the end oE the adsorber, since the purge gas flows through the adsorber in the same direction as the waste gas did`
previously~ The krypton-containing purge gas is recycled to the compressor 2 via conduit 19. The purge gas proportion coming from the second regeneration phase and containing xenon and carbon dioxide leaves the plant via conduit 20 `~
at 21. `
The krypton-containing carrier gas mixture, almost completely freed of xenon and all other components, is cooled to about 95 K in heat exchanger 12 and introduced into the rectification column 13 under a pressure oE about 5 bars. The amounts thus introduced are, in detail:
7,760 mol/h nitrogen; 144 mol/h hydrogen; 108 mol!h argon, and 1.44 ~ol/h krypton. The reflux liquid required for the rectification in the rectification column 13 is produced in condenser 17 by the indirect supply of cold with liquid nitrogen from the storage tank 16. A liquid fraction enriched in krypton to about 80% is withdrawn from the sump of the separating column, entirely vaporized in evaporator 14 and ~)4~67 heated to ambient temperature, withdrawn from the plant at 15, and thereafter stored in metered quantities. The withdrawal of the krypton fraction is preferably not executed continuously, but rather once a day in a quantity of respectively about 1.5 liters.
The purified carrier gas discharged from the head ~
of the separating column via conduit 18 contains at this ~-point merely 0.1 mol-p.p.m. of krypton. This corresponds to a decontamination factor of 1 : 1,800. The thus-10 purified carrier gas is utilized, as described above, ~;
for purging the xenon carbon dioxide adsorbers 9, 10 and 11 .
Vaporized nitrogen is passed from column 13 via conduit 22 through heat exchanger 12 where it is warmed, and then withdrawn from the plant via condui~ 23.
' ~
'; ', "
g _ ., ' :
: :::: - .:: :
waste gas, after the other components have been separated, to be cooled and thereafter freed o krypton by distillation.
An example of a conventional process is described in "A Cryogenic Approach to Fuel Reprocessing Gaseous Radwaste Treatment" (J.S. Davis, J.R. Martin, Paper for Presentation at The Noble Gas Symposium, Las Vegas, 1973). This process comprises first subjecting ;
a waste gas from nuclear fuel reprocessing plant consisting essentially of nitrogen, oxygen, oxides of nitrogen, carbon dioxide, and water, as well as argon, krypton, and xenon, to a pretreatment in order to remove the oxygen, nitrogen oxides, carbon dioxide and water.
In this process, the oxygen and the nitrogen oxides are -~
catalytically reduced to nitrogen and water by the introduction o hydrogen. The resultant water and the carbon dioxide are removed by adsorption. The carrier gas of N2 + Ar thus freed of all other components except for the kryp-ton and xenon impurities, is thereafter fed to a ~ . .
low-temperature separation plant wherein in a first -: . . : . - : ~ :
~0~9~7 rectification column a fr~ction containing krypton and xenon is recovered. Then, in a second rectification column, krypton and xenon ~re separated from each other.
It is thus seen that in the conventional process, wherein a highly concentrated radioactive krypton fraction is treated, two rectification column are required, ~ogether with the associated conduits and switching members.
It is also to be noted, however, that the radioactivity of the xenon may be substantially diminished before the aforedescribed treatment of the waste gas because its half-life is only 5.3 days (xenon-133), and there is the possibility of conducting the waste gases through "holdup" zones prior to treatment. In contrast thereto, the radioactivity of krypton-85 (half life: 10.
years) remains prac-tically constant during the time generally available for the waste gas treatment.
An object of one aspect of this invention is to provide an improved system yenerally of the above-mentioned`type, and especially wherein there is a significant savings in the expenditure required for the low-temperature section.
According to the broad aspect of this invention, the improved system is obtained by separating the xenon hy adsorption even before the rectification step. ~ctivated carbon, - ;
for example, can serve as the adsorbent. General information concerning adsorption processes and techniques is contained in :
.
'.,~ ' . . . . . - . ~ .
J.W. carter "~dsor~tion Processes" (Chemical and Process Engineering, Sept. 1966, pp. 70-77) and ~.A. Johns-ton "Designing Fixed-Bed Adsorption Columnsl' (Chemical Engineering, Nov. 1972, ~p. 87-92).
By virtue of this pre-adsorption step, only a single rectification column is required, and thus the protective measures to be taken against the radioactive radiation emanating from the highly concentrated krypton fraction in the sump of thi~ column can be restricted to only the necessary and unavoidable minimum.
Since, during the adsorption of the xenon, ~-traces of krypton are concomitantly adsorbed, it is advantageous, according to another aspect of the invention, to provide that the regeneration of the adsorbers is conducted in at least two purging phases, wherein in the first phase primarily krypton is desorbed and the krypton-containing purge gas is recylced into the process, while in the second phase the xenon is desorbed and the xenon-containing purge gas is removed from the process.
.
In accordance with another aspect of this invention, ' a carrier gas mixture freed at least partially of the krypton is utilized as the purge gas. The purge gas withdrawn ~rom the low-temperature plant and comprised almost exclusively of nitrogen and argon is divided into two portions, one portion absorbing the adsorbed krypton and the other portion absorbing the xenon. Since the krypton, despite its low quantity, has a high radioactivity as compared to the xenon, the krypton-containing purge gas is not discharged from the process, but rather recycled to the process at a suitable location, e.g., the low pressure side of the compressor. ~n contrast thereto, ~'.
.
~14~i~67 the xenon-containing purge gas can eikher be discharged to the outside atmosphere or it can be further processed to obtain its components. If desired, the radioactivity of the xenon can be reduced further in holdup zones located either upstream or downstream of the adsorption zone.
According to another aspect of the process according to this invention, the xenon, optionally together with one of the other components contained in the waste gas, e.g., carbon dioxide, is separated in a mixed-bed adsorber or in divided adsorber beds. In ;
this connection the combined xenon-carbon dioxide adsorption can be conducted in two series-connected adsorber beds; in the second purge phase, xenon and carbon dioxide are distributed separately over the beds; and in a third purge phase with parallel-connected purge streams, xenon and carbon dioxide are purged out separately. The adsorption phase is terminated as soon as the xenon adsorption front has traveled through the second adsorber bed to an extent of about 75%. The relative dimensions of the two adsorber beds are designed so that at this instant the carbon dioxide front is still in the interior of the first adsorber bed. During the first purge phase, the xenon front advances to the end of the second adsorber bed. During the second purge phase, owing to the ready `
desorbability oE the xenon as compared to the carbon dioxide, the xenon is almost completely desorbed from the first adsorber bed and is deposited in the second bed, the carbon dioxide front advancing during this step to `
the end of the first bed. During the subsequent third ','~', purge ph~se, both beds are connected in parallel and freed separately of xenon arld carbon dioxide. The adsorber beds can contain zeolite and activated carbon, for example.
As mentioned above, the waste gases from nuclear fuel reprocessing plants or nuclear reactors generally contain, as additional components, oxygen and nitrogen oxides;-these are usually catalytically reduced -to nitrogen and water with the use of hydrogen. Most of the thus-formed water is removed in a separator. In such a case, it is advantageous, according to another aspect of this invention, to separate the residual water in reversible adsorbers even prior to the adsorptive xenon removal from the waste gases. Such adsorbers are then purged in the regenerating phase with hydrogen, and the H2O-~I2 resultant mixture is fed to the catalytic reduction stage. By the introduction of the H2O-containing hydrogen into the reduction stage, there is the advantage that even the residual water absorbed in the adsorbers is finally removed in the separator.
Suitable exemplary adsorbents for the water include, but are not limited to, silica gel and zeolite.
The drawing is a schematic view of the preferred embodiment of the invention.
~ .
~LV~5967 A radioactive gaseous waste stream ls introduced via conduit 1, comprising 9000 mol/h of 67 mol-~ nitrogen, 16 mol-~ oxygen, 5 mol-~ water, 8 mol-% nitrogen dioxide, 3 mol-% nitrogen monoxide, and 1 mol-% argon, as well as 800 mol-p.p.m. xenon and 160 mol-p.p.m. krypton and containing traces of N2O, CO2 and CO. The radioactivity caused by the radioactive krypton isotope krypton-85 is 0.62 Ci/s. In a compressor 2, this waste gas is compressed from 1 bar to about 6 bars and introduced into a catalytic reduction stage 3 together with a hydrogen-enriched gas fed via conduit 24, as well as a recycling gas fed via conduit 25 tthis recycling gas will be defined in greater detail below). In this ca-talytic reduction stage, the nitrogen oxides along with the oxygen are reduced to nitrogen and water by reaction with the hydrogen. Platinum can be utilized as the catalyst, for example. In the subsequent phase separator 4, the largest portion of the water is separated in the liquid phase. To avoid the development of flames in the reduction stage, the gaseous mixture to be conducted over the catalyst must be diluted to such an extent that the total content of oxygen plus nitrogen oxides is only at most 3 mol-%. For this purpose, a corresponding portion of the gas discharged from the separator is recycled by means of a blower 5 to the inlet of the reduction stage.
The remaining portion of the gas withdrawn from the separator wherein the proportions of oxygen and nitrogen oxides are below 1 mol-p.p.m. and below 5 mol-p.p.m., .
S~67 respectively, is fed to one oE the two silica gel adsorbers 6 and 7, respectively, in order to remove the residual water. These adsorbers can be periodically switched over between the adsorption phase and the regenerating phase. The purge of the adsorbers during the regenerating phase is effected with hydrogen introduced at 8 into the process. The H2O-containing hydrogen is conducted to the reduction stage 3 via conduit 24.
The thus-pretreated waste gas, at this point - consisting essentially merely of the carrier gases nitrogen and argon, as well as carbon dioxide, krypton ans xenon, is now introduced into one of the three periodically reversible adsorbers 9, lO or 11. In this embodiment, the adsorbers are equipped with zeolite and activated-carbon mixed beds wherein the xenon as well as the carbon dioxide is adsorbed. In this step, activated carbon is used for the xenon adsorption, and zeolite having a pore size of 9 Angstrom ;
is used for the carbon dioxide adsorption. In addition to xenon and carbon dioxide, krypton is concomitantly adsorbed in minor quantities. The adsorption eront of the krypton travels the most rapidly through the adsorber, while the carbon dioxide front is the slowest.
As soon as the xenon front has migrated to about three quarters through the adsorber, the switchover to the regeneration phases is effected.
;:
.. ~
::.
109~596~
In the ~irst regenerating phase, krypton is desorbed at ambient temperature, and in the second re~enerating phase carbon dioxide and xenon are desorbed at about 420 K. The puriEied carrier gas mixture withdrawn in conduit 18 from the low-temperature plant 13 is utilized as the purge gas. Since krypton is more readily desorbable as compared to xenon or carbon dioxide, the purge gas is divided into two unequal parts upstream oE the adsorbers, and the smaller, e.g. about 10 to 30 ~
of the two partial quantities is conducted into the appropriate ~;
adsorber for krypton desorption. During the krypton desorption, the adsorption front of the xenon is advanced to the end oE the adsorber, since the purge gas flows through the adsorber in the same direction as the waste gas did`
previously~ The krypton-containing purge gas is recycled to the compressor 2 via conduit 19. The purge gas proportion coming from the second regeneration phase and containing xenon and carbon dioxide leaves the plant via conduit 20 `~
at 21. `
The krypton-containing carrier gas mixture, almost completely freed of xenon and all other components, is cooled to about 95 K in heat exchanger 12 and introduced into the rectification column 13 under a pressure oE about 5 bars. The amounts thus introduced are, in detail:
7,760 mol/h nitrogen; 144 mol/h hydrogen; 108 mol!h argon, and 1.44 ~ol/h krypton. The reflux liquid required for the rectification in the rectification column 13 is produced in condenser 17 by the indirect supply of cold with liquid nitrogen from the storage tank 16. A liquid fraction enriched in krypton to about 80% is withdrawn from the sump of the separating column, entirely vaporized in evaporator 14 and ~)4~67 heated to ambient temperature, withdrawn from the plant at 15, and thereafter stored in metered quantities. The withdrawal of the krypton fraction is preferably not executed continuously, but rather once a day in a quantity of respectively about 1.5 liters.
The purified carrier gas discharged from the head ~
of the separating column via conduit 18 contains at this ~-point merely 0.1 mol-p.p.m. of krypton. This corresponds to a decontamination factor of 1 : 1,800. The thus-10 purified carrier gas is utilized, as described above, ~;
for purging the xenon carbon dioxide adsorbers 9, 10 and 11 .
Vaporized nitrogen is passed from column 13 via conduit 22 through heat exchanger 12 where it is warmed, and then withdrawn from the plant via condui~ 23.
' ~
'; ', "
g _ ., ' :
: :::: - .:: :
Claims (10)
1. In a process for separating radioactive krypton and xenon from waste gases such as those during the reprocessing of nuclear fuels or from nuclear reactors, wherein the waste gas is freed of krypton by a low-temperature rectification step, the improvement which comprises separating the xenon from the waste gas by adsorption prior to the low-temperature rectification step and conducting said low-temperature rectification setp in a single rectification column to recover an overhead waste gas at least partially freed of krypton.
2. A process according to claim 1, wherein the adsorption is conducted in interchangeable adsorbers cyclically operated and including a regenerating period and an adsorption period, the regeneration of the adsorbers being conducted by purging in at least two phases, wherein primarily co-adsorbed krypton is desorbed in the first purge phase and resultant krypton-containing purge gas is recycled; and in the second purge phase, the xenon is desorbed and the xenon-containing purge gas is discharged from the process, and the desorption steps are conducted by purging with separate portions of said waste gas at least partially freed of krypton.
3. A process according to claim 1, wherein nitrogen oxides and oxygen, contained as additional components in the waste gas, are in preceding steps catalytically reduced with hydrogen to nitrogen and water and water in the liquid phase is removed in part in a phase separator, and wherein residual gaseous H2O is separated from the waste gas before the adsorptive xenon removal, in reversible adsorbers; and wherein adsorbers are purged with hydrogen in a regenerating period; and the H2O-containing hydrogen is used in the catalytic reduction stage.
4. A process according to claim 1, wherein xenon deposited during adsorption is desorbed in a subsequent purging step utilizing as the purge gas the waste gas freed from krypton in the low-temperature rectification step.
5. A process according to claim 1, wherein xenon and carbon dioxide contained in the waste gas are separated in a mixed-bed adsorber or in divided adsorber beds.
6. A process according to claim 5, wherein xenon and carbon dioxide are subjected to adsorption conducted in two series-connected adsorber beds cyclically operated and including a regenerating period and an adsorption period, the regeneration of the adsorber being conducted by purging in three phases, the carbon dioxide and xenon adsorption fronts being still within the interior of the first and second adsorption beds respectively upon termination of the adsorption period;
during the first purge phase, the xenon adsorption front is advanced to the end of the second adsorption bed; during the second purge phase, the xenon still remaining in the first adsorption bed is deposited in the second adsorption bed and the carbon dioxide adsorption front is advanced to the end of the first adsorption hed; and in the third purge period, xenon and carbon dioxide are purged out separately with parallel connected purge streams.
during the first purge phase, the xenon adsorption front is advanced to the end of the second adsorption bed; during the second purge phase, the xenon still remaining in the first adsorption bed is deposited in the second adsorption bed and the carbon dioxide adsorption front is advanced to the end of the first adsorption hed; and in the third purge period, xenon and carbon dioxide are purged out separately with parallel connected purge streams.
7. A process according to claim 6, wherein the adsorption phase is terminated when the xenon adsorption front has traveled through the second adsorber bed to an extent of about 75%.
8. A process according to claim 1, wherein the waste gases to be purified contain krypton-85 having a half-life of 10.8 years.
9. A process according to claim 1, wherein the waste gases contain nitrogen and argon as carrier gases.
10. A process according to claim 9, wherein the carrier gases are recovered from the top of the rectification column and split into two portions; one of said portions used to desorb the adsorbed krypton and the other portion used to desorb the adsorbed xenon.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2611833A DE2611833C2 (en) | 1976-03-19 | 1976-03-19 | Process for the separation of radioactive krypton and xenon from exhaust gases from nuclear fuel reprocessing plants or nuclear reactors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1045967A true CA1045967A (en) | 1979-01-09 |
Family
ID=5972981
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,159A Expired CA1045967A (en) | 1976-03-19 | 1977-03-17 | Adsorption-distillation system for separation of radioactive krypton and xenon |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS531800A (en) |
| BR (1) | BR7701641A (en) |
| CA (1) | CA1045967A (en) |
| DE (1) | DE2611833C2 (en) |
| FR (1) | FR2344933A1 (en) |
| GB (1) | GB1525686A (en) |
| ZA (1) | ZA771486B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4270938A (en) * | 1978-12-04 | 1981-06-02 | Airco, Inc. | Processes for decontaminating nuclear process off-gas streams |
| WO1981000413A1 (en) * | 1979-08-06 | 1981-02-19 | Science Applic Inc | Method for treating a nuclear process off-gas stream |
| DE3304690A1 (en) * | 1983-02-11 | 1984-08-16 | Kernforschungszentrum Karlsruhe Gmbh, 7500 Karlsruhe | Method for environmentally friendly removal of the noble fission gas krypton 85 |
| DE3334629A1 (en) * | 1983-09-24 | 1985-04-04 | Kraftwerk Union AG, 4330 Mülheim | METHOD FOR OPERATING A CORE REACTOR |
| JPS6090589A (en) * | 1983-10-25 | 1985-05-21 | 蛇の目ミシン工業株式会社 | Sewing condition display device in electronic sewing machine |
| JPH0226519A (en) * | 1988-07-15 | 1990-01-29 | Sanyo Electric Co Ltd | Vacuum cleaner |
| CA3098869A1 (en) * | 2018-05-08 | 2019-11-28 | Curium Us Llc | Systems and methods for production of xenon-133 |
| CN116573611A (en) * | 2023-07-13 | 2023-08-11 | 杭氧集团股份有限公司 | Device for coupling power generation, carbon capture and inert component recovery and use method |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3944646A (en) * | 1972-05-11 | 1976-03-16 | Union Carbide Corporation | Radioactive krypton gas separation |
| US4012490A (en) * | 1972-07-25 | 1977-03-15 | Airco, Inc. | Removing radioactive noble gases from nuclear process off-gases |
| JPS5241840B2 (en) * | 1973-05-30 | 1977-10-20 | ||
| GB1509581A (en) * | 1974-07-31 | 1978-05-04 | Commissariat Energie Atomique | Method of eliminating radioactivity from air containing radioactive rare gases |
| JPS5852200B2 (en) * | 1974-10-07 | 1983-11-21 | エアコ インコ−ポレ−テツド | Kakukoutei Higaskarahoshiya Seikigas Obunrisurukei |
-
1976
- 1976-03-19 DE DE2611833A patent/DE2611833C2/en not_active Expired
-
1977
- 1977-03-11 ZA ZA00771486A patent/ZA771486B/en unknown
- 1977-03-15 FR FR7707638A patent/FR2344933A1/en active Granted
- 1977-03-16 GB GB11046/77A patent/GB1525686A/en not_active Expired
- 1977-03-17 BR BR7701641A patent/BR7701641A/en unknown
- 1977-03-17 CA CA274,159A patent/CA1045967A/en not_active Expired
- 1977-03-17 JP JP2871777A patent/JPS531800A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB1525686A (en) | 1978-09-20 |
| BR7701641A (en) | 1978-01-03 |
| JPS531800A (en) | 1978-01-10 |
| FR2344933A1 (en) | 1977-10-14 |
| DE2611833C2 (en) | 1985-12-05 |
| FR2344933B1 (en) | 1982-04-23 |
| ZA771486B (en) | 1978-01-25 |
| JPS5617040B2 (en) | 1981-04-20 |
| DE2611833A1 (en) | 1977-09-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5125934A (en) | Argon recovery from argon-oxygen-decarburization process waste gases | |
| US3944646A (en) | Radioactive krypton gas separation | |
| US5220797A (en) | Argon recovery from argon-oxygen-decarburization process waste gases | |
| US5486227A (en) | Integrated process for purifying and liquefying a feed gas mixture with respect to its less strongly adsorbed component of lower volatility | |
| US3762133A (en) | Process for the separation of components from gas mixtures | |
| US5100447A (en) | Argon recovery from partial oxidation based ammonia plant purge gases | |
| CA2055520A1 (en) | Hydrogen and carbon monoxide production by hydrocarbon steam reforming and pressure swing adsorption purification | |
| US6658894B2 (en) | Process and adsorbent for the recovery of krypton and xenon from a gas or liquid stream | |
| EP0114911B1 (en) | Novel repressurization for pressure swing adsorption system | |
| US3691779A (en) | Hydrogen purification | |
| US5425240A (en) | Purification of oxygen by cryogenic adsorption | |
| EP0684066A2 (en) | Method of recovering a light element from a dilute feed | |
| EP1316357B1 (en) | Process and adsorbent for the recovery of krypton and xenon from a gas or liquid stream | |
| US4043770A (en) | Absorption-adsorption system for purifying cryogenic gases | |
| CA1045967A (en) | Adsorption-distillation system for separation of radioactive krypton and xenon | |
| EP0367618B1 (en) | Process for producing carbon monoxide gas | |
| JPH10113502A (en) | Method and apparatus for producing low temperature fluid in high purity liquid | |
| US4874592A (en) | Production process of xenon | |
| JP3824838B2 (en) | Noble gas recovery method | |
| US4045191A (en) | Radioactive krypton gas separation | |
| JPS58190799A (en) | Method and device for seperating krypton from radioactive gaseous waste | |
| EP0395221A1 (en) | Method of reducing the oxygen concentration in a gas stream | |
| NZ248804A (en) | Argon purification by cryogenic adsorption | |
| JP3294067B2 (en) | Krypton manufacturing method | |
| US4834956A (en) | Process for the production of high purity argon |