US2793511A - Method for obtaining krypton and xenon - Google Patents

Description

May 28, 1957 H. BONNAUD 2,793,511

METHOD FOR OBTAINING KRYPTON AND xenon Fild April 27, 1954 Illlllllllll Illlllllllll United States Patent METHOD FOR OBTAINING KRYPTON AND XENON Henri Bonnaud, Viroflay, France, assignor to LAir Inqmde, Societe Anonyme pour lEtude et IExploitatron des Procedes Georges Claude, Paris, France Application April 27, 1954, Serial No. 425,959 Claims priority, application France April 29, 1953 8 Claims. (Cl. 62-175.5)

This invention relates to a method for obtaining krypton and xenon from a gaseous mixture such as air, by washing said gaseous mixture with a washing liquid comprising one or more liquefied gases which are more volatile than krypton and xenon and concentrating the liquid resulting from the washing.

In fact, it has been already proposed particularly in the U. S. Patent No. 2,095,809 of October 12, 1937, for a Process for Obtaining Krypton and Xenon From Air, to wash a gaseous mixture such as air with a comparatively small amount of a mixture of oxygen and nitrogen for instance by means of an amount of washing liquid smaller than one tenth of the amount of air in process. The washing in liquid takes almost all the krypton and xenon contained in the air in process, then the liquid resulting from the washing is rectified and finally a small amount of liquid or gases containing a high proportion of oxygen is collected, said amount containing practically all the krypton and xenon contained in the air submitted to the washing action.

Owing to the extremely small proportions of krypton and xenon in the atmosphere (respectively l/ 1,000,000 and 1/ 11,000,000) it is very difiicult to obtain a nearly complete extraction. Nevertheless the particular uses which are made commercially of said gases and which are limited only by the quantities available are such that these gases are very valuable.

The main object of the invention is to provide a method which increases very substantially the yield of both of these extracted gases, by using the liquid resulting from the washing in the washing step itself.

Another object of the invention is to provide a method wherein the liquid resulting from the washing is used in the washing step after having been submitted to various operations.

In the accompanying drawing forming a part of this specification, the figure shows diagrammatically and as an example one embodiment relative to an apparatus for obtaining from atmospheric air a liquid in which krypton is comparatively concentrated. This gas will be extracted in the pure state in a further step, not shown. The apparatus thus shown has all the main features of the invention.

For the sake of clarity, in the present specification and claims, krypton will designate the whole of krypton and xenon contained in air.

The air from which krypton must be extracated, pre viously submitted to a pressure a little above the atmospheric pressure, for instance 1.7 absolute atmosphere, and brought to room temperature arrives through a pipe 1 and is refrigerated down near its condensation point in a group of two regenerators 2A and,2 B which run alternately. The heat of the air is thus exchanged accord ing to a known process and passed to the gases purified from krypton. The air which is cooled in the regenerators causes the vapor of water and carbonic anydride, both contained in the air, to be deposited. The corresponding deposits are then wept out by the gases freed of krypton and passing the reverse direction.

The air which is then cooled passes through an expansion turbine 45 and arrives through a pipe 3 at the bottom of a counter-current column 4 in which it is washed by liquids the origin of which will be explained further.

This washing column is preferably of a conventional type with superposed horizontal plates and ascending gas bubbling on each plate in the washing liquid descending from the top of the column. It could also be of the type with contact elements, such as Raschig rings or similar members.

The total amount of the washing liquids is comparatively small with respect to the amount of the air treated and is for instance about 10% of the latter. The air freed from krypton leaves the column 4 at the top through a pipe 5 while the liquid loaded with krypton flows out at the bottom of the column 4, passes through a filter 6 and gathers in the container 7 from which it is extracted by a pump 8. According to the invention, a part of the liquid returns to the column 4 through a pipe 9 provided with a valve 10 while another part is by-passed through a pipe 39 provided with an adjusting valve 40 and is injected through a nozzle into the tube 3 through which the air to be treated arrives to the washing column 4. The object of injecting this liquid in the gaseous air to be treated is twofold. First, the air to be treated is cooled and brought down to its dew point before entering the washing column; second, the particles of carbonic anhydride in suspension, which the air to be treated would still contain, and which could choke the first plates of the column 4, are made heavier and are cooled. These particles are carried away by the washing liquid and removed by the filter 6.

The liquid which remains arrives through a pipe 11 at the higher part of a rectifying column 13 and fills up a container 15 from which it overflows through a pipe 17 in order to descend towards the bottom of the column while being more concentrated in krypton. The liquid thus concentrated is gathered at the base of the column 13 and is extracted by a tube 18 for going to a further step of concentration and purification.

A gaseous fraction constituted mainly of oxygen, but still containing small quantities of krypton, is extracted from the column 13 through a pipe 19 the inlet of which is located a few plates above the base. It is sent to a tube nest 16 sunk in container 15 arranged at the upper part of the column 13. As this gaseous fraction is mainly constituted of oxygen it may be liquefied. in the tubular nest 16 owing to the indirect contact with the liquid of container 15 which contains a high proportion of nitrogen. The liquid that is thus formed in the tube nest 16 is used according to the invention as a washing liquid in the column 4. As it contains a small quantity of krypton it is sent to this column through a tube 20 delivering a few plates below the top. From the top of the column 13 a gaseous fraction containing a small quantity of krypton gets out through a pipe 21. This fraction is first used in an exchanger 22 to cool a liquid the origin of which will be explained further, then it enters through a pipe 23 the base of the washing column.

The washing liquid freed of krypton which is discharged into the top of the washing column 4 is obtained in the following way:

An amount of air offor instance 7% of the quantity of air to bewashed is compressed up to about 20 atmospheres in a compressor, not shown, and arrives through a pipe 123 to an exchanger 24 in which it is cooled by means of the portion of the washed air leaving the washing column by pipe 34. It is then expanded down to 4 atmospheres with production of external work in an expansion machine 25 and enters the base of the rectifying column 14 which works at the same pressure. The air whichis then introduced into the column 14 is rectified and gives on the one hand a fraction composed of comparatively pure nitrogen and at any rate freed from krypton and on the other hand a fraction containing about 40% of oxygen and all the krypton of the air treated in the column 14. The latter is connected at its upper part through a condenser vaporizer 26 with the rectifying column 13. According to a known device the condensed vapors which ascend in the column 14 produce the calories necessary for heating the base of the column 13. A part of the liquid resulting from the condensation of these vapors falls in the column 14. The remainder of the liquid is gathered in the annular gutter 27, leaves the column 14 through the pipe 28, is further cooled in the exchanger 22 by the gaseous fraction leaving the top of the column 13, then is expanded by the valve 29 down to the pressure of the column 4, is finally discharged at the top of this column and constitutes a part of the washing liquid freed from krypton. The gas eous fraction leaves the top of the column 14 through the pipe 30, goes to an exchanger 31 where it is cooled by the washed air leaving the top of the column by the pipes and 32. This fraction which is at a pressure of about 4 atmospheres is liquefied in the pipes of the exchanger 31. It is then expanded by means of the valve 33 down to the pressure of the column 4 and constitutes the other part of the washing liquid freed from krypton.

The fraction having 40% of oxygen and containing all the krypton of the air treated in the column 14 leaves the latter in the liquid state by the pipe 38 provided with an expansion valve 41. It is used as an auxiliary washing liquid in the column 4 which it enters at an intermediary height.

The air freed from krypton leaves the top of the column 4 by the pipe 5 and is divided into two unequal parts. The smaller goes through the pipe 34 and cools, in the exchanger 24, the air providing the washing liquids of the column 4 and then leaves the exchanger through the pipe 35. The other part of the air washed goes to the exchanger 31 where it cools and condenses one of the washing liquids of the column 4, then goes through the pipe 36 and cools the regenerator 2A and 2B, and finally leaves the latter by the pipe 37.

The liquid loaded with krypton and passing through the pipe 18 is directed to a further step of concentration and purification by known means.

It is to be noted that the different liquids used in the column 3 are introduced at levels corresponding to their respective concentrations in krypton. Only the liquids freed from krypton are discharged at the top of the washing column.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various changes, particularly in arrangement of parts, may be resorted to without departing from the spirit of the invention, or the scope of the subjoined claims.

I claim:

1. A method of obtaining krypton and xenon from a gaseous mixture comprising washing a gaseous mixture with at least one liquefied gas more volatile than krypton and xenon, withdrawing the liquid resulting from said washing, forcing a part of the liquid resulting from the washing to the gaseous mixture prior to its washing, and expanding said part into said gaseous mixture before washing.

2. The method of claim 1 which comprises concentrating another part of the liquid resulting from the washing,

extracting from said part during concentration a gaseous fraction containing a small amount of krypton, condensing said gaseous fraction, and introducing said condensed fraction as a washing liquid into the upper portion of the washing column at a stage of the washing operation corresponding approximately to the concentration in krypton and xenon of said condensed fraction.

3. A method of obtaining krypton and xenon from a gaseous mixture comprising washing a gaseous mixture in a column with a washing liquid constituted of at least one liquefied gas more volatile than krypton and xenon, withdrawing the liquid resulting from said washing, forcing a part of said liquid resulting from the washing back to the washing column and using it as a second washing liquid, said part being introduced into said column at a height where the concentration in krypton and xenon corresponds approximately to the concentration of said liquid in said column.

4, The method of claim 3 which comprises concentrating another part of the liquid resulting from the washing, extracting from said part during concentration a gaseous fraction containing a small amount of krypton, condensing said gaseous fraction, and introducing said condensed fraction as a washing liquid into the upper portion of the washing column at a stage of the washing operation corresponding approximately to the concentration in krypton and xenon of said condensed fraction.

5. A method of obtaining krypton and xenon from a gaseous mixture comprising washing a gaseous mixture in a column with at least one liquefied gas more volatile than krypton and xenon, withdrawing the liquid resulting from said washing, forcing the liquid resulting from said washing into at least two paths, expending the liquid in one of said paths into said gaseous mixture before washing, and introducing the liquid in another of said paths into said column at a height where the concentration in krypton and xenon corresponds approximately to the concentration of said liquid in said column.

6. A method as in claim 3 wherein the gaseous mixture is air.

7. A method of obtaining krypton and xenon from air, comprising washing air with a liquefied gas rich in nitrogen, withdrawing the liquid resulting from said washing, concentrating at least a part of said liquid, extracting from said part during concentration a gaseous fraction rich in oxygen and containing only a small amount of krypton and xenon, condensing said gaseous fraction only by heat exchange with the liquid resulting from the washing, and introducing said condensed fraction into the upper portion of the washing column at a stage of the washing operation corresponding approximately to the concentration in krypton and xenon of said condensed fraction.

8. A method of obtaining krypton and xenon comprising washing air with a liquefied gas rich in nitrogen, collecting the liquid resulting from said washing, concentrating at least. a part of said liquid, extracting from said part during the concentrating step a gaseous fraction rich in oxygen and containing only a small amount of krypton and xenon, condensing said gaseous fraction substantially at the same pressure as and by heat exchange with the liquid resulting from the washing, and using said condensed fraction in the washing operation at a stage corresponding approximately to the concentration in krypton and xenon of said condensed fraction.

References Cited in the tile of this patent UNITED STATES PATENTS

Claims (1)

1. A METHOD OF OBTAINING KRYPTON AND XENON FROM A GASEOUS MIXTURE COMPRISING WASHING A GASEOUS MIXTURE WITH AT LEAST ONE LIQUEFIED GAS MORE VOLATILE THAN KRYPTON AND XENON, WITHDRAWING THE LIQUID RESULTING FROM SAID WASHING, FORCING A PART OF THE LIQUID RESULTING FROM THE WASHING TO THE GASEOUS MIXTURE PRIOR TO ITS WASHING, AND EXPANDING SAID PART INTO SAID GASEOUS MIXTURE BEFORE WASHING.

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