METHOD FOR RECYCLING ARGON

Abstract

A method for recycling argon from an industrial process; in which the gaseous argon is compressed after the use thereof in the industrial process, is fed to a main heat exchanger and is cooled there in contact with a first cooling medium. The compressed and cooled argon is fed to a rectification column or another cryogenic separating device and is liquefied there by direct heat exchange with a second cooling medium and is freed of low-boiling substances by rectification. The liquefied argon is drawn from the bottom of the rectification column and, after use as the first cooling medium in the main heat exchanger, is fed back into the industrial process, the raw argon being brought into thermal contact with cryogenically liquefied pure argon in the main heat exchanger and/or the rectification column. The product argon that results is highly pure and can be fed back to the industrial process.

Claims

1. A method for reutilizing argon in an industrial process, in which argon kept in stock in the liquid state in a tank (pure argon) is taken from the tank, vaporized and fed in gaseous form to an industrial process, wherein: a. the gaseous argon which has been used in the industrial process (crude argon) is compressed in a compressor; b. the compressed crude argon is fed to a main heat exchanger and cooled there by indirect heat exchange with at least one first cooling medium; c. the compressed and cooled crude argon is fed to a separation device and cooled there by heat exchange with a second cooling medium to a temperature below the boiling point of argon at the pressure prevailing in the separation device, resulting in a gas phase composed of argon contaminated with low boilers and a liquid phase composed of argon which has been at least largely freed of low boilers (product argon) being formed; d. the gas phase is at least partly taken off from a head space of the separation device; e. the product argon is taken off in the liquid state from a bottom region of the separation device, depressurized and used in the main heat exchanger as cooling medium for cooling the crude argon, resulting in it vaporizing; f. the vaporized product argon is at least partly recirculated to the industrial process; g. where liquid pure argon is taken from the tank and brought into direct or indirect thermal contact with the crude argon in order to cool the crude argon in the separation device and/or during feeding of the crude argon to the separation device.

2. The method as claimed in claim 1, wherein the separation device is a rectification column or a condenser.

3. The method as claimed in claim 1, wherein the pure argon taken from the tank is fed into the head space of the separation device.

4. The method as claimed in claim 1, wherein argon enriched with low boilers is at least partly taken off from the head space of the separation device, fed to an overhead condenser, cooled there by indirect heat exchange with a third cooling medium and subsequently fed back into the separation device, with pure argon taken off from the tank and/or depressurized product argon being used as third cooling medium in the overhead condenser.

5. The method as claimed in claim 1, wherein pure argon taken off from the tank is used as cooling medium in the main heat exchanger.

6. The method as claimed in claim 3, wherein the pure argon which has been used as cooling medium in the overhead condenser and/or the main heat exchanger is fed to the industrial process.

7. The method as claimed in claim 1, wherein the product argon is fed to a device for separating off relatively high-boiling constituents before it is recirculated to the industrial process.

8. The method as claimed in claim 4, wherein the pure argon which has been used as cooling medium in the overhead condenser and/or the main heat exchanger is fed to the industrial process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Working examples of the invention will now be explained in more detail with the aid of the drawings. FIGS. 1-3 schematically show flow diagrams of three working examples of the method of the invention.

DETAILED DESCRIPTION

[0027] In the working example 1 shown in FIG. 1, crude argon 2 is obtained in an industrial process 3 in which the crude argon 2 has previously been contaminated with low boilers and high boilers. The industrial process 3 is, for example, a heat treatment of metallic workpieces, in which the crude argon has been used as inert gas or blowing gas. The crude argon 2 is compressed in a compressor 4 to a pressure of, for example, from 5 bar to 20 bar, goes through a main heat exchanger 5 in countercurrent to a number of cooling media, resulting in it being brought to a temperature which is, for example, just above the boiling point of argon at the pressure prevailing on the crude argon side in the main heat exchanger 5. Finally, the crude argon 2 is introduced into the bottom region of a cryogenic separation device, which is a rectification column 6 in the working examples shown here. In the rectification column 6, the crude argon 2 is cooled further by thermal contact with a cooling medium and separated into its constituents, resulting in liquid argon which has been largely freed of low boilers (product argon) collecting in the bottom region 7 of the rectification column 6 while part of the argon and low boilers ascend in gaseous form to the head space 8 of the rectification column 6.

[0028] Pure argon 9, which is kept in stock in the liquefied state in a tank 10, is used for cooling the process in the rectification column 6. The pure argon is taken from the tank 10 and fed in working example 1 as liquefied gas into the head space 8 of the rectification column 6.

[0029] The low-boiling gas constituents which collect in the head space 8 are discharged together with a relatively small amount of argon as residual gas 12. A substream 13 of the residual gas 12 is fed to an overhead condenser 14 in which it is liquefied and introduced back into the head space 8 of the rectification column 6. The remaining residual gas 12 is used as cooling medium for precooling the crude argon 2 in the main heat exchanger 5 and subsequently released into the surrounding atmosphere or optionally passed to a further use.

[0030] The argon which collects in the bottom region 7 of the rectification column 6 is discharged as pure, liquefied product argon 15. It goes through a depressurization valve 16, is cooled in the process and is subsequently used in the overhead condenser 14 for cooling the substream 13. Finally, it goes into the main heat exchanger 5 in which it serves, in addition to the residual gas 12, as cooling medium for precooling the crude argon 2. The now warmed product argon 15 is subsequently fed to a device 18 for removing high boilers from the product argon 15. If no high boilers are present in the crude gas stream 2 or these do not interfere in the subsequent process, passing the product argon 15 through the device 18 becomes superfluous. The device 18 can, furthermore, also be arranged fluidically upstream of the main heat exchanger 5.

[0031] The device 18 can encompass various gas purification methods (depending on type and concentration of the impurity), for example a condenser or a plurality of condensers in which the product argon 15 is cooled by thermal contact with a cooling medium to a temperature at which the high boilers present therein condense out. The product argon 15 itself remains in the gaseous state in this operation. The cooling medium used in the device 18 is, for example, likewise liquid pure argon from the tank 10 which is taken off there at a connection port 19 or is another cooling medium, for example liquid nitrogen.

[0032] The product argon 15 which has now been substantially freed of low boilers and high boilers is now fed as pure argon back to the industrial process 3 and used there.

[0033] In the working examples 20, 22 shown in FIG. 2 and FIG. 3, in which constituents having the same effect are denoted by the same reference numerals as in working example 1, crude argon 2 from an industrial process 3 is also freed of contaminating substances and fed back to the industrial process 3.

[0034] In the working example 20 shown in FIG. 2, the pure argon 9 from the tank 10 is, in contrast to working example 1, not introduced into the head space 8 of the rectification column 6 but instead the pure argon 9 travels as cooling medium for indirect heat exchange with the substream 13 through the overhead condenser 14 and at least partly vaporizes there. It is subsequently fed to the main heat exchanger 5 as cooling medium for indirect heat exchange with the crude argon 2. Otherwise, the process engineering structures and operations in working example 20 are essentially the same as in working example 1.

[0035] The cold content of the pure argon 9 is thus utilized only for indirect heat transfer in the heat exchangers 5 and 14 in the embodiment 20. The pure argon 9 from the tank 10 does not come into direct contact with the crude argon 2. This makes it possible to stock the pure argon 9 in the tank 10 at a pressure which is lower than the pressure of the crude argon 2 after compression thereof, for example at a pressure which corresponds approximately to the pressure in the industrial process 3. When the pure argon 9 is kept in stock in the tank 10 at a higher pressure, for example at a customary tank pressure of from 5 bar to 20 bar, it is advisable to depressurize the pure argon 9 at a depressurization valve 21 and thus bring it to a lower temperature before it passes through at least one of the heat exchangers 14, 5. For example, as shown in FIG. 2, the pure argon 9 which has been warmed in the heat exchangers 5, 14 is fed to the industrial process 3 or mixed with the product argon 15 downstream of the device 18, or it can be utilized in another way.

[0036] In the working example 22 shown in FIG. 3, too, only indirect heat exchange between the pure argon 9 from tank 10 and the crude argon 2 occurs. This occurs exclusively in the main condenser 5 in which the pure argon 9 functions, together with the residual gas 12 and product argon 15, as cooling medium. Here too, the process engineering structures and operations are essentially the same as in working example 1 or working example 20.

LIST OF REFERENCE NUMERALS

[0037] 1. Working example [0038] 2. Crude argon stream [0039] 3. Industrial process [0040] 4. Compressor [0041] 5. Main heat exchanger [0042] 6. Rectification column [0043] 7. Bottom region [0044] 8. Head space [0045] 9. Pure argon [0046] 10. Tank [0047] 11. - [0048] 12. Residual gas [0049] 13. Substream [0050] 14. Overhead condenser [0051] 15. Product argon [0052] 16. Depressurization valve [0053] 17. - [0054] 18. Device for removing high boilers [0055] 19. Connection port [0056] 20. Working example [0057] 21. Depressurization valve [0058] 22. Working example.