JPS6367638B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method for producing krypton-xenon concentrates from liquid feedstocks, and in particular, in which such concentrates are produced with high efficiency and the rare earth gas-free liquid is recovered as a product. Regarding such improvement methods. BACKGROUND OF THE INVENTION Krypton and xenon are in increasing demand for many applications. Krypton is widely used in high-quality lighting equipment, including long-life lamps and automotive lamps. Xenon is used in medical applications, including in specialized x-ray equipment. Both of these gases are commonly used in many experimental and research applications. The main source of krypton and xenon is the atmosphere. Atmospheric air contains about 1.1 ppm krypton and about 0.08 ppm xenon. In general,
Krypton and xenon are recovered from air in connection with an integrated air separation process that separates air into oxygen and nitrogen. Due to the low vapor pressure of krypton and xenon, these gases concentrate in oxygen rather than nitrogen during air separation. Concentration of atmospheric krypton and xenon in oxygen increases their concentration by a factor of five, since oxygen makes up only about 1/5 of the air in the atmosphere. The air separation process can produce gaseous or liquid oxygen or both, and krypton and xenon are concentrated in either oxygen product. It is desirable that krypton and xenon be further concentrated so that their separation from oxygen can be carried out efficiently. When krypton and xenon are recovered in gaseous oxygen, the krypton-xenon enrichment process
Must be carried out simultaneously with the air separation process. This is because it is impractical to store the amount of gaseous oxygen produced by an air separation plant. Thus, it is desirable to recover krypton-xenon in liquid oxygen from an air separation plant. This is because this liquid can be stored and combined with other such liquids from other separate air separation plants to form the feedstock for the krypton-xenon enrichment process. It is from. However, removing liquid oxygen from air separation plants is expensive. This is because refrigeration energy is removed along with liquid oxygen from the air separation plant. Thus,
It would be desirable to have a krypton-xenon concentration process that uses a liquid feedstock but also produces a liquid product free of rare earth gases. As is well known, oxygen can be dangerous if not handled properly. Therefore, conventional krypton-xenon enrichment methods using liquid feedstocks have heretofore been extremely complicated to achieve the desired krypton-xenon enrichment with the required safety. It would therefore be desirable to provide a method for efficiently concentrating krypton and xenon using liquid feedstocks without the undue complications previously introduced by oxygen handling. It is therefore an object of the present invention to provide an improved method for producing krypton-xenon concentrates. Another object of the invention is to provide an improved method for producing krypton-xenon concentrate using liquid feedstock. Yet another object of the present invention is to provide an improved method for producing krypton-xenon concentrates that also produces a liquid product free of rare earth gases. Yet another object of the present invention is to provide a process for the production of krypton-xenon concentrates in which the desired concentration can be carried out without all the hitherto necessary complications of known methods. SUMMARY OF THE INVENTION The above objects, and other objects that will be apparent to those skilled in the art upon reading this disclosure, are to produce a krypton-xenon concentrate from a feedstock liquid while also recovering a liquid product substantially free of rare earth gases. A method comprising: (1) supplying a feedstock liquid containing oxygen, krypton, and xenon to a reboiling zone to form a reboil liquid; and (2) partially vaporizing the reboil liquid to form vapor and liquid krypton. producing a xenon concentrate; (3) recovering a krypton-xenon concentrate; (4) passing said vapor across a downstream reflux liquid in a column; and (5) converting krypton and xenon from said vapor to said reflux liquid. (6) passing said richer liquid to a reboiling zone to form a portion of the reboiling liquid; (7) withdrawing lean vapor from said column; , (8) heating the extracted lean steam, (9) compressing the heated lean steam, (10) cooling the compressed lean steam by indirect heat exchange with the heated lean steam, (11) ) condensing the cooled lean vapor by indirect heat exchange with a partially vaporized reboiling liquid in a reboiling zone to produce a lean liquid; (12) sending a portion of the lean liquid to the column; forming a reflux liquid; and (13) recovering a portion of the lean liquid as a liquid product substantially free of rare earth gas. The term "rare earth gas" used herein
means krypton and xenon. As used herein, the terms "lean", "leaner", "rich" and "richer" mean
Represents the concentration of rare earth gas unless otherwise specified. As used herein, the term "integrated heat pump circuit" refers to an arrangement in which the heat pump circuit is combined with a separation column to utilize process fluid obtained from the separation column. As used herein, the term "reboil zone" means
means a heat exchange zone in which the incoming liquid is indirectly heated and thereby partially vaporized to produce gas and residual liquid. As a result, the residual liquid becomes
It is enriched in the less volatile components present in the incoming liquid. The term "indirect heat exchange" used herein
means to bring two fluid streams into a heat exchange relationship without physically contacting or mixing with each other. As used herein, the term "equilibrium stage" refers to
refers to a gas-liquid contacting stage in which the vapor and liquid exiting the gas-liquid contacting stage are in mass transfer equilibrium.
For separation columns that use trays or plates, ie separate contact stages, for the liquid and gas phases, the equilibrium stage corresponds to the theoretical tray or plate. For separation columns that use packing or continuous contact of liquid and gas phases, the equilibrium stage corresponds to that height of the column packing that is equal to one theoretical plate. The actual contacting step, i.e. tray, plate or packing, corresponds to the equilibrium step depending on its mass transfer efficiency. As used herein, the term "column" refers to a distillation or fractionation column, i.e., on a series of vertically spaced trays or plates disposed within the column, or alternatively on packing members packed into the column. means a contacting column or zone in which separation of a fluid mixture is effected by contacting the liquid and gas phases countercurrently, such as by contacting the gas and liquid phases at a temperature. For a detailed description of fractionation towers, see The Chemical
Engineer's Handbook (the Chemical
Engineer’s Handbook, 5th Edition” (McGraw-Hill Book Company, New York, USA), “Distillation”,
See B.D. Smith et al., pp. 13-3, The Continuous Distillation Process. The term "double column" as used herein means a high pressure column having an upper end in heat exchange relationship with the lower end of the lower pressure column. For a detailed description of the double tower, see Mr. Luchman, “The Separation of Gases” (Oxford University Press, 1949), Chap.
“Industrial Air Separation” and Mr. Baron’s “Cryogenic Systems” (McGraw-Hill Incorporated, 1966);
Found on page 230, “Air Separation Systems”. DETAILED DESCRIPTION The method of the invention will now be described in detail with reference to the accompanying drawings. Referring now to FIG. 1, a fluid stream 32 containing oxygen, krypton and xenon is transferred to the reboiling zone 3 as stream 34, for example by pump means 33.
Sent to 6. In the embodiment of FIG. 1, feed stream 34 is combined with liquid from column 35 and the resulting combined stream 42 is sent to reboiling zone 36.
The concentrations of krypton and xenon in feed stream 34 may be any effective concentration, but generally the concentration of krypton in feed stream 34 will be at least 10 ppm and the concentration of xenon will be at least 1 ppm. The source of feedstock liquid for the process of the invention may be any source of rare earth gas-containing liquid oxygen. FIG. 1 shows one such source as liquid from the lower pressure column sump of a double column air separation process 10 capable of producing both liquid and gaseous oxygen products. As shown in FIG. 1, this liquid 26 can be sent to a storage receiver 31 prior to use in the method of the invention. The storage receiver 31 may be supplied with a suitable feed liquid from a source separately or in addition to the feed from the double column air separation plant shown. Figure 1 shows
One of the advantages of the method of the present invention is that it does not need to be coupled to an integrated air separation process.
Here are two examples. The only input to the process of the invention is feedstock stream 34, which may be from any suitable source. The entire krypton-xenon condensation process 30, including mass transfer in the column, heat transfer in the integrated heat pump circuit, and condensation phase change in the reboiling zone, is performed without inputting any other streams to the process. This makes the process of the invention unique and allows krypton-xenon enrichment in a much simpler manner than previously available methods. Returning to FIG. 1, the reboiling liquid 61 in the reboiling zone is partially vaporized by heat exchange with the condensate in the condenser 37, thereby generating vapor 43 and krypton-xenon concentrate 40 (this can be recovered for further use). Typically, the krypton concentration in concentrate 40 is at least 200 ppm, preferably at least
400 ppm and the xenon concentration in concentrate 40 is at least 15 ppm preferably at least
It is 30ppm. Steam 43, which is leaner in krypton and xenon than the feed liquid to the reboiling zone, is passed upwardly through column 35 against the downstream reflux liquid. In Figure 1, the reboiling zone 36 is
Although shown separate from column 5, a reboiling zone may be located within column 35 and at its bottom. When the reboiling zone is separate from column 35, as in the embodiment of FIG. 1, steam 43 is introduced into column 35 at its bottom. In column 35, the krypton and xenon in vapor 43 are stripped into the reflux liquid downstream from the vapor. The resulting krypton-xenon enriched liquid 41 is sent to the reboil zone to form a portion of the reboil liquid 61. Column 35 is operated ^at a pressure within the range of 10-75 ^psia , preferably 15-30 psia, and a significant portion of the krypton and xenon in vapor 43 is Preferably it serves to strip substantially all of it into the downstream reflux liquid. This produces a steam stream 44, which
This vapor stream 44 is preferably transferred from column 35 to column 3.
5 in a lean state and preferably substantially free of rare earth gases. Lean vapor stream 44, consisting essentially of oxygen, is heated by indirect heat exchange in heat exchanger 39, and heated stream 45 is compressed in compressor 38 to form compressed stream 46. flow 45
need only be subjected to a negligible degree of compression, preferably stream 46 is no more than 2.1 kg/kg less than stream 45.
cm ² (30 psi) higher and most preferably at most 1.1 Kg/cm ² (15 psi) higher pressure. Although not shown, the compressed stream can be cooled by cooling water. Compressed stream 45 is then cooled by indirect heat exchange by passing heat exchanger 39 against heated vapor stream 44, and the resulting cooled compressed lean vapor stream 47 is reboiled. It is sent to condenser 37 in zone 36. The cooled and compressed lean vapor is then condensed to produce lean liquid 48 through indirect heat exchange with the partially vaporized reboiling liquid. A portion 49 of this lean liquid 48 (10 to 40 of the lean liquid 48)
% (preferably corresponding to 15-25%) is expanded by valve 51 and sent as stream 52 to column 35, preferably to the top of the column, to form the downstream reflux liquid mentioned above. The other portion 50, preferably the remaining portion, of the lean liquid 48 is recovered as a liquid product consisting essentially of oxygen and substantially free of rare earth gases. In general, the flow 50 is at most
It has a krypton concentration of 5 ppm preferably at most 1 ppm and a negligible xenon concentration. As previously explained, the krypton-xenon concentration process of the present invention does not require any input streams other than the feedstock. Thus, the liquid feedstock is transferred to column 3
krypton-xenon mass transfer in 5, heat transfer in an integrated heat pump circuit associated with heat exchanger 39;
It can be seen that the condensation phase change in the reboiling zone 36 is possible. Since the heat exchange in the reboiling zone 36 takes place between very similar fluids, i.e. the reboiling liquid 61
Since both the compressed lean vapor 47 and the condensing compressed lean vapor 47 typically consist of more than 99% oxygen, heat exchange within the reboiling zone 36 can be carried out with only a negligible degree of compression in the compressor 38. . This is beneficial both in terms of energy utilization and integrity. This is because compression of oxygen can become dangerous as the amount of compression increases.
The integrated heat pump circuit also serves to reduce the complexity of the concentration process. This is because other fluids such as nitrogen or argon are not required as heat exchange media. This also helps the method of the present invention to be more unique regardless of other low temperature methods. As previously noted, FIG. 1 shows a double column air separation plant that produces both gaseous and liquid oxygen products and which eliminates substantially all of the krypton and xenon in the atmosphere from the gaseous products. Illustrated is a particularly preferred arrangement where the feed liquid to the krypton-xenon concentration process is taken from a double column air separation plant modified from the usual two product double column arrangement to be placed in a rather liquid product. do.
Here, the double column air separation process illustrated in FIG. 1 will be briefly explained. To explain FIG. 1, the feed air 14 is 1.2
It is introduced into ^a high pressure column 13 operated at a pressure of 17 to 150 psia where it is separated into a nitrogen richer vapor 16 and an oxygen richer liquid 15. Vapor 16 is concentrated in condenser 12 by indirect thermal conversion with low pressure column bottoms 62 and the resulting nitrogen is converted into richer liquid 1
7 is sent to the high pressure column as stream 19 and to the low pressure column as stream 18 and stream 23 through valve 22 to serve as the reflux liquid for the column. Fluid 15 is connected to valve 2
0 and sent as stream 21 (as a partially flushed feedstock) to the lower pressure column. Also introduced into the column 11 is an air stream 51 as a feedstock, which can be used for cold end heat exchanger temperature control and/or to develop refrigeration of the plant. Column 11 is at a lower pressure than column 13 and 1.1-2.1 Kg/cm ² (15-30 psia)
Operated at pressures within the range of Within column 11, each input stream is separated into a nitrogen-rich component, which is withdrawn as stream 24, and an oxygen-rich component. This oxygen-rich component is withdrawn from the column as a gaseous stream 25 and a liquid stream 26. In conventional dual product, liquid and gaseous oxygen production, the gaseous oxygen product is withdrawn above the retentate in such a manner that the two withdrawn streams are in equilibrium. Therefore, krypton and xenon are in equilibrium in both withdrawn product streams. Although the equilibrium krypton and xenon content of the liquid product is higher than that of the gaseous product, sometimes the amount of the liquid product is less than that of the gaseous product, thereby reducing the amount of krypton and xenon by the gaseous product. The loss is significant. To overcome this situation, the double column arrangement illustrated in FIG. ) in tower 1
Gaseous oxygen product 25 is withdrawn from 1.
Instead, in such an arrangement, a significant amount of krypton-xenon, which under normal practice would be removed with the gaseous products, remains in the liquid and is thus sent to the krypton-xenon enrichment process. was discovered. If desired, the gaseous oxygen product may be placed in trays 28 or 2, for example, rather than in the reservoir.
It can be extracted from above even more than 9. The optimum withdrawal point depends on the lowest krypton-xenon value obtained for the extra trays in the low pressure column. Generally, liquid oxygen product 26 is
The total oxygen product from column 11 is about 2 to about 75%, preferably about 5 to 30%, and most preferably about 20%. The double column process illustrated in FIG. 1 is particularly beneficial when used in conjunction with the krypton-xenon enrichment process of the present invention. In the double column process, substantially all of the atmospheric krypton and xenon is concentrated into a liquid oxygen product, which is then used as a feedstock for the process of the present invention. The krypton-xenon enrichment process of the present invention results in a liquid oxygen product stream containing negligible or negligible amounts of rare earth gases. Thus, the two processes taken together as shown in Figure 1 produce a gaseous oxygen product 25, a liquid oxygen product 50, and substantially all of the krypton and xenon in the feedstock which is atmospheric air. 40 krypton-xenon concentrates can be recovered. This highly desirable result is achieved with high efficiency and in an uncomplicated and complete manner. The example in Figure 1 shows that the feedstock to the krypton-xenon enrichment process comes from a double column air separation plant that produces both gaseous and liquid oxygen products, and that the feedstock in air is It is particularly preferred in that it represents a variation of the double column process in which substantially all of the krypton and xenon can be fixed in liquid oxygen rather than in gaseous oxygen. First, the results of a computer simulation of the method of the invention carried out according to the specific examples in the table are described. This data is provided for the purpose of illustrating the invention and is not intended to limit the invention. The abbreviations “CFH” and “PSIA” respectively refer to the ambient temperature (21℃; 70〓)
and "ft ³ /hr" and "lb/in ² absolute" measured at atmospheric pressure (1.0 Kg/cm ² ; 14.7 psia). The flow numbers correspond to those in FIG. Stream concentrations are expressed in either mole % or ppm volume.
In addition to the stated oxygen, krypton and xenon contents, each stream contains some argon and small amounts of hydrocarbons.

[Table] N, ppm
As illustrated by the data in the table, the process of the present invention efficiently yields a krypton-xenon concentrate with negligible loss of krypton and xenon in streams other than the concentrate product stream. The process of the present invention accomplishes this using a liquid feedstock, yet also produces a liquid product that is substantially free of rare earth gases. As can be seen in the table, the majority of liquid feedstocks (generally at least 75
%, and in this case 92%) is recovered as liquid oxygen product, and only a small amount of liquid feed is required to produce the krypton-xenon concentrate. Furthermore, the process of the present invention can achieve these desirable results without inputting other streams such as nitrogen or argon heat pump circulation and without the need to return process streams to the air separation plant;
This allows the method to be unique without the need for an associated cryogenic cooling plant. Still further, the method of the present invention achieves all of these desirable results using a limited combination of process steps and a liquid feedstock as the only process stream, while still allowing the separation to operate. Does not require large energy input.

[Brief explanation of drawings]

FIG. 1 is a schematic flowchart of one preferred embodiment of the method of the present invention, and the reference numerals representing the main parts are as follows. 11: low pressure column, 13: high pressure column, 35: stripping column, 36: reboiling zone, 39: heat exchanger.

Claims (1)

[Scope of Claims] 1. A method for producing a krypton-xenon concentrate from a liquid feedstock and also recovering a liquid product substantially free of rare earth gases, comprising: (1) a feedstock containing oxygen, krypton, and xenon; supplying the liquid to a reboiling zone to form a reboiling liquid; (2) partially vaporizing the reboiling liquid to produce a vapor and liquid krypton-xenon concentrate; and (3) recovering the krypton-xenon concentrate. (4) passing said vapor against a downstream reflux liquid in a column; (5) stripping krypton and xenon from said vapor to said reflux liquid to produce a lean vapor and richer liquid; ) passing said richer liquid to a reboiling zone to form a portion of the reboiling liquid; (7) withdrawing lean vapor from said column; (8) heating the withdrawn lean vapor; and (9) heating. (10) the compressed lean steam is cooled by indirect heat exchange with the heated lean steam; (11) the cooled lean steam is partially vaporized in a reboiling zone. (12) sending a portion of the lean liquid to the column to form a reflux liquid; and (13) condensing the portion of the lean liquid by indirect heat exchange with a liquid to produce a lean liquid; A method comprising: recovering a liquid product substantially free of rare earth gases. 2 The krypton concentration in the feedstock is at least
The method according to claim 1, wherein the amount is 10 ppm. 3 The xenon concentration in the feedstock is at least
The method according to claim 1, wherein the amount is 1 ppm. 4. The method according to claim 1, wherein the reboiling zone is within the column. 5. The method of claim 1, wherein the reboiling zone is separate from the column. 6. The method of claim 1, wherein the feed liquid and the richer liquid are combined prior to introduction into the reboiling zone. 7. The method of claim ¹ , wherein the column is operated at a pressure in the range of 10 to 75 psia. 8. The method of claim 1, wherein ^the heated lean steam is compressed to increase its pressure to at most 30 psi. 9. The method of claim ¹ , wherein the heated lean steam is compressed to increase its pressure to at most 15 psi. 10. The method of claim 1, wherein the portion of lean liquid sent to the column as reflux liquid corresponds to 10 to 40% of the lean liquid. 11. The method of claim 1, wherein the concentration of krypton in the krypton-xenon concentrate is at least 200 ppm. 12. The method of claim 1, wherein the concentration of xenon in the krypton-xenon concentrate is at least 15 ppm. 13. A liquid product substantially free of rare earth gases is present at least 75% of the feed liquid on a volumetric flow rate basis.
%. 14. The method of claim 1, wherein the feedstock liquid is obtained from a double column cryogenic air separation plant. 15. The method of claim 14, wherein the air separation plant produces a gaseous oxygen product in addition to the liquid that constitutes the feed liquid. 16. The method of claim 15, wherein the gaseous oxygen product is withdrawn from the air separation plant at a point above the at least one equilibration stage at which the liquid constituting the feedstock liquid is withdrawn.