METHOD AND SYSTEM FOR LOW-TEMPERATURE AIR SEPARATION

Abstract

A method for low-temperature air separation, in which an air-separation system having a column system is used that has a first column, a second column, a third column, and a fourth column, wherein fluid from the first column is fed at least into the second column, fluid from the second column is fed at least into the third column, fluid from the third column is fed at least into the fourth column, and fluid from the fourth column is fed at least into the third column, and wherein the fluid fed from the third column into the fourth column includes at least a portion of a side flow, which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid. The present invention also relates to a corresponding system.

Claims

1-15 (canceled)

16. A method for low-temperature air separation, in which an air-separation system having a column system is used that has a first column, a second column, a third column, and a fourth column, wherein a) a first sump liquid is formed in the first column, a second sump liquid is formed in the second column, a third sump liquid is formed in the third column, and a fourth sump liquid is formed in the fourth column, b) the first column is operated in a first pressure range, the second column is operated in a second pressure range below the first pressure range, and the third column is operated in a third pressure range below the second pressure range, c) the second sump liquid is formed with a higher oxygen content and a higher argon content than the first sump liquid, and the third sump liquid is formed with a higher oxygen content and a lower argon content than the second sump liquid, d) fluid from the first column is fed at least into the second column, fluid from the second column is fed at least into the third column, fluid from the third column is fed into the fourth column, and fluid from the fourth column is fed at least into the third column, and e) the fluid fed from the third column into the fourth column comprises at least a portion of a side flow which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid, wherein f) a reflux liquid is formed by condensing overhead gas of the first column, and the reflux liquid is fed back to the first column in liquid form, g) in order to condense the overhead gas of the first column, a liquid cooling flow is evaporated or partially evaporated in indirect heat exchange with the overhead gas, and h) gas formed during the evaporation or partial evaporation of the cooling flow is expanded, so as to perform work, to a pressure in the second pressure range and fed into the second column.

17. The method according to claim 16, in which the cooling flow is formed using at least a fraction of the first sump liquid.

18. The method according to claim 17, in which a further liquid cooling flow is evaporated or partially evaporated in indirect heat exchange with the overhead gas in order to condense the overhead gas of the first column, wherein the further cooling flow is withdrawn above the sump from the first column and at least partially compressed after evaporation or partial evaporation and fed back to the first column.

19. The method according to claim 16, in which a forced-flow condenser evaporator is used for condensing the overhead gas of the first column and for evaporating the cooling flow.

20. The method according to claim 16, in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded and fed into the second column, is heated before the expansion.

21. The method according to claim 16, in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded to perform work and fed into the second column, is supplied to the expansion at a temperature at which it is present after evaporation or partial evaporation.

22. The method according to claim 16, in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded to perform work and fed into the second column, is fed into the second column at a temperature at which it is withdrawn from an expansion machine used for expansion.

23. The method according to claim 16, in which overhead gas of the fourth column is at least partially condensed in a condensation chamber of a condenser evaporator, from the evaporation chamber of which a gas mixture is withdrawn, wherein at least a portion of the gas mixture withdrawn from the evaporation chamber of the condenser evaporator is used to form a reflux flow, which is heated, compressed, cooled, and fed into the second column and/or is used as regeneration gas for an adsorber in which feed air is prepared which is fed to the column system is prepared.

24. The method according to claim 16, in which at least a portion of a gas mixture which is withdrawn from an upper region of the third column is used to form a reflux flow which is heated, compressed, cooled, and fed into the second column.

25. The method according to claim 23, in which the adsorber, in which the feed air which is fed to the column system is prepared, is operated without the use of regeneration gas, which is withdrawn from the third column and fed to the adsorber in a materially-unchanged composition.

26. The method according to claim 23, in which at least a portion of the gas mixture withdrawn from the evaporation chamber of the condenser evaporator is used as a first regeneration gas fraction, and in which at least a portion of the gas withdrawn from the third column is used as a second regeneration gas fraction, wherein the second regeneration gas fraction is provided at a lower pressure than the first one, compressed, and combined with the first regeneration gas fraction before it is fed to the adsorber.

27. The method according to claim 16, in which power released during work-performing expansion of the evaporated or partially evaporated cooling flow, or at least its fraction which is expanded to perform work and fed into the second column, is used for operating an electric generator.

28. The method according to claim 16, in which the second pressure range is 4 to 6.5 bar.

29. The method according to claim 16, in which the side flow formed with a lower oxygen content and a higher argon content than the third sump liquid and withdrawn from the third column is subjected to preparation in a further column to obtain an oxygen-depleted gas mixture and a sump liquid, wherein the oxygen-depleted gas mixture is fed from the further column at least in part into the fourth column.

30. An air-separation system which has a column system having a first column, a second column, a third column, and a fourth column and is configured a) to form a first sump liquid in the first column, to form a second sump liquid in the second column, to form a third sump liquid in the third column, and to form a fourth sump liquid in the fourth column, b) to operate the first column in a first pressure range, to operate the second column in a second pressure range below the first pressure range, and to operate the third column in a third pressure range below the second pressure range, c) to form the second sump liquid with a higher oxygen content and a higher argon content than the first sump liquid, and to form the third sump liquid with a higher oxygen content and a lower argon content than the second sump liquid, d) to feed fluid from the first column at least into the second column, to feed fluid from the second column at least into the third column, to feed fluid from the third column at least into the fourth column, and to feed fluid from the fourth column at least into the third column, and e) to use at least a portion of a side flow which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid as the fluid fed from the third column into the fourth column, wherein means are configured f) to form a reflux liquid by condensing overhead gas of the first column, and to feed back the reflux liquid to the first column in liquid form, g) to evaporate or partially evaporate a liquid cooling flow in indirect heat exchange with the overhead gas in order to condense the overhead gas of the first column, and, h) to expand gas formed during the evaporation or partial evaporation of the cooling flow, so as to perform work, to a pressure in the second pressure range and to feed it into the second column.

Description

DESCRIPTION OF THE FIGURES

[0070] FIGS. 1 through 4 show air-separation systems, which correspond to embodiments of the present invention where they fall within the scope of protection of the patent claims, and otherwise relate to the technical background and/or embodiments not according to the invention. The air-separation systems according to FIGS. 1 through 4 are respectively designated as a whole by reference signs 100 through 400. Although the following explanations relate to corresponding air-separation systems 100 through 400, they relate to corresponding methods in the same way. The air-separation system 500 illustrated in FIG. 5 is shown as a variant of the air-separation system 100 illustrated in FIG. 1. The aspects illustrated here can nevertheless also be implemented by other systems—in particular, by systems 200 through 400. The following explanations—in particular, regarding the system 100 according to FIG. 1—relate to the system 500 in the same way, even if this reference is not specifically made.

[0071] All the air-separation systems 100 through 400 shown in FIGS. 1 through 4 are equipped with a column system which, irrespective of the different design and, optionally, different number of columns, is in each case designated overall by 10. The column systems 10 each have a first column 11, a second column 12, a third column 13, and a fourth column 14.

[0072] The second column 12 and the third column 13 are each designed as parts of a double column of a type known in principle. Reference is expressly made in this context to the technical literature cited at the outset regarding air-separation systems—in particular, to the explanations relating to FIG. 23A in Häring (see above), in which a corresponding double column is shown.

[0073] The first column 11 is formed separately from the second column 12 and from the third column 13. The first column 11 is equipped with a condenser evaporator 111, which is used for condensing overhead gas of the first column 11 and is designed as a traditional overhead condenser in the embodiments according to FIGS. 1 through 3. In each case, sump liquid, which is conveyed without the use of a pump, is fed from the first column 11 into the condenser evaporator 111, which is in each case designed as a forced-flow condenser evaporator in the examples shown.

[0074] An essential aspect of the embodiments of the invention illustrated here is in each case that a reflux liquid is formed by condensing overhead gas of the first column 11 and that the reflux liquid is fed back to the first column 11. In order to condense the overhead gas of the first column 11, a liquid cooling flow, which is formed using the mentioned sump liquid from the first column 11, is evaporated or partially evaporated with the overhead gas of the first column 11. Gas formed during the evaporation or partial evaporation of the cooling flow is expanded, so as to perform work, by means of an expansion machine 5 to a pressure in the second pressure range and fed into the second column 12.

[0075] The second column 12 and the third column 13 are connected to each other, so as to exchange heat, via an internal condenser evaporator 121—the so-called main condenser. The main condenser 121 is used, on the one hand, for condensing an overhead gas of the second column 12 and, on the other, for evaporating a sump liquid of the third column 13. As an alternative to the embodiment illustrated here, the second column 12 and the third column 13 can also be separate. The main condenser 121 can, alternatively, also be designed to be on the outside. Different types of condenser evaporators can be used as main condensers 121.

[0076] The fourth column 14 is used for argon production in all the air-separation systems 100 through 400 according to FIGS. 1 through 4. In the examples shown, no crude-argon column is present, but, rather, the systems 100 through 400 are each designed for withdrawal of an argon product from the fourth column 14. For crude- and pure-argon columns and corresponding modifications, reference is likewise made to the above citations from the technical literature.

[0077] The fourth column is equipped with a condenser evaporator (overhead condenser) 141 which condenses overhead gas. In the embodiments according to FIGS. 1 through 3, this is cooled with a portion of sump liquid from the first column 11, whereas sump liquid from the second column 12 is used for this purpose in the embodiment according to FIG. 4. The sump liquid used in each case is previously supercooled by a supercooling, counterflow heat exchanger 18. A fraction unevaporated in the overhead condenser 141 is at least partially fed into the third column 13 in the examples illustrated here. On the other hand, in the examples illustrated here, an evaporated fraction is used to regenerate an adsorber and, in the case of the air-separation system 300 according to FIG. 3, to form a reflux flow, as explained below.

[0078] In all the air-separation systems 100 through 400 according to FIGS. 1 through 4, a further column 15 is provided, in which a material exchange is carried out between a fraction of a sump flow from the fourth column 14 and a side flow from the third column 13, and a fraction of the sump flow from the fourth column 14 is depleted of highly-volatile components. The further column 15 has an upper and a lower region, which are, functionally, completely separated from one another. Further details are explained in each case below. The further column 15 is designed with a condenser evaporator 152 which is heated with overhead gas from the second column 12.

[0079] As a component directly associated with the column system 10, a pump 19 is present in all the air-separation systems 100 through 300 according to FIGS. 1 through 3 and conveys the sump liquid back from the fourth column 14 into the further column 15.

[0080] In all the air-separation systems 100 through 400 according to FIGS. 1 through 4, a sump liquid is formed in the first column 11 and is referred to here as first sump liquid. Accordingly, a second sump liquid is formed in the second column 12, a third sump liquid is formed in the third column 13, and a fourth sump liquid is formed in the fourth column 14. The first column 11 is operated in a first pressure range, the second column 12 is operated in a second pressure range below the first pressure range, and the third column 13 is operated in a third pressure range below the second pressure range. The second sump liquid is formed with a higher oxygen content and a higher argon content than the first sump liquid, and the third sump liquid is formed with a higher oxygen content and a lower argon content than the second sump liquid. Reference is made to the above explanations regarding the pressure ranges and oxygen or argon content.

[0081] In the manner explained below, in all the air-separation systems 100 through 400 according to FIGS. 1 through 4, fluid is fed from the first column 11 into the second column 12 (and also into the third column 13 in the air-separation systems 100 through 300 according to FIGS. 1 through 3). Furthermore, fluid is fed from the second column 12 into the third column 13, and fluid is fed from the fourth column 14 into the third column 13. In all the air-separation systems 100 through 400 according to FIGS. 1 through 4, the fluid fed into the fourth column 14 from the third column 13 comprises at least a portion of a side flow which is withdrawn from the third column 13 and has a lower oxygen content and a higher argon content than the second sump liquid. At least in the embodiments illustrated here, the other fluids mentioned each comprise at least portions of the respective sump liquids. In all cases, direct feeding or feeding via an intermediate overhead condenser or the like and corresponding partial feeding can take place.

[0082] In particular, the air-separation system 100 according to FIG. 1 is first explained in more detail below. For the sake of clarity, the explanations relating to the air-separation systems 200, 300, and 400 according to FIGS. 2 through 4 each relate only to the features deviating therefrom. In FIGS. 2, 3, and 4, identical features are also provided with corresponding reference symbols only in some cases.

[0083] In the air-separation system 100 according to FIG. 1, a feed air flow a from the atmosphere, which is generally designated A here, is introduced by means of a main air compressor 1 via a filter, which is indicated by crosshatching and without a separate designation, cooled in an aftercooler, which likewise has no separate designation, and supplied to a direct-contact cooler 2, which is operated with cooling water W.

[0084] After the pre-cooling takes place in the direct-contact cooler 2, the feed air flow still designated a is freed of water and carbon dioxide in an adsorption device 3 in a manner described multiple times in the literature. The adsorption device 3, also generally referred to as an “adsorber” above, can be regenerated by means of a regeneration gas flow z. The formation of the regeneration gas flow z is explained below.

[0085] The feed air flow, which is still denoted by a, correspondingly treated, and thus purified, is fed to the warm side of a main heat exchanger 4. The feed air flow a is withdrawn from the main heat exchanger 4 on the cold side or near its cold end and fed into the first column 11.

[0086] The sump liquid of the first column 11 is withdrawn therefrom and divided into two partial flows d and e in the air-separation systems 100 through 300 according to FIGS. 1 through 3. The partial flow d is here fed into the condenser evaporator 111 and evaporated. The evaporated partial flow d is then partially heated in the main heat exchanger 4 and then expanded to the operating pressure of the second column 12 in an expansion machine 5, which is coupled to a generator G, and fed into this second column 12 in a lower region. The treatment of the sump liquid in the air-separation system 400 according to FIG. 4 differs therefrom. Reference is made to the specific explanations below.

[0087] In contrast, in the air-separation systems 100 through 300 according to FIGS. 1 through 3, the partial flow e is conducted through the supercooling, counterflow heat exchanger 18 and then through the condenser evaporator 141. As illustrated in the form of a linkage f, a portion can also be fed into the second column 12. Gas formed in the overhead condenser 141 can be used as the aforementioned regeneration gas flow z. For this purpose, it is first heated in the supercooling, counterflow heat exchanger 18 and then in the main heat exchanger 4. As illustrated here in the form of a material flow g, a fraction which remains liquid is fed into the third column 13. In the air-separation system 400 according to FIG. 4, no corresponding partial flow e or f is formed. Reference is also expressly made here to the specific explanations below.

[0088] The overhead gas of the first column 11 is partially conducted through the condensation chamber of the overhead condenser 111 in the form of a material flow h and fed back to the first column 11 as a liquid reflux. A further fraction is heated in the form of a material flow i in the main heat exchanger 4 and, as a gaseous, compressed nitrogen product, discharged from the air-separation system 100 or used otherwise.

[0089] The sump liquid of the second column 12 is withdrawn therefrom in the form of a material flow j, conducted through the supercooling, counterflow heat exchanger 18, and fed into the third column 13. In the air-separation system 400 according to FIG. 4, the material flow j is conducted through the condenser evaporator 141 for cooling, as an alternative to the material flow e (see above). Gas formed in the overhead condenser 141 of the air-separation system 400 can also be used here as a regeneration gas flow, which is likewise designated z for the sake of simplicity. In the air-separation system 400 according to FIG. 4, gas is, furthermore, fed from the overhead condenser 141 or its evaporation chamber into the third column 13. As also illustrated in FIG. 4 in the form of a material flow g, a fraction which remains liquid is fed into the third column 13.

[0090] The overhead gas of the second column 12 is partially conducted in the form of a material flow k through the condensation chamber of the main condenser 121, liquefied there, and again fed back in part to the second column 12 as a liquid reflux. A further fraction is liquefied in the form of a material flow I in the condensation chamber of the condenser evaporator 152. In the air-separation systems 100 through 300 according to FIGS. 1 through 3, this further fraction is combined with the fraction liquefied in the condensation chamber of the main condenser 121, as illustrated in the form of the linkage I. Corresponding liquid can also be delivered by means of a pump 6 as reflux to the first column 11. In the embodiments according to FIGS. 1 through 3, the pump 6 conveys a liquid, nitrogen-rich flow b, which is withdrawn from the second column 12 in an upper region. In the examples according to FIGS. 1 through 3, a further fraction of overhead gas from the second column 12 is discharged from the system in the form of a material flow c.

[0091] In the embodiment of the air-separation system 400 according to FIG. 3, the liquefied fraction of the material flow k and of the material flow I are not combined. Rather, in this case, fractions of the material flow k are delivered separately from one another to the second column 12 and the third column 13 after liquefaction. The material flow I is fed separately into the third column 13.

[0092] The sump liquid of the third column 13 is withdrawn from it in the form of a material flow o, pressurized in liquid form by means of an internal compression pump 7, converted into the gaseous or critical state in the main heat exchanger 4 by heating, and discharged from the air-separation system 100 as a gaseous, compressed oxygen product or used otherwise. In contrast, gas withdrawn above the sump from the third column 13 in the form of a material flow p is combined with residual gas from the third column 13 (see below) to form a collective flow q, which is subsequently heated in the main heat exchanger 4 and discharged from the air-separation system 100 or used otherwise.

[0093] The overhead gas of the third column 13 is conducted through the supercooling, counterflow heat exchanger 18 in the form of a material flow r and, in the air-separation systems 100 through 300 according to FIGS. 1 through 3, combined with the material flow o to form the collective flow q, as mentioned. In the air-separation system 400 according to FIG. 4, a separate discharge takes place.

[0094] Furthermore, a side flow t is withdrawn in gaseous form from the third column 13 and first fed into an upper part of the further column 15. In contrast, a material flow u is fed back in liquid form from the upper part of the further column 15 into the third column 13. In the upper part of the further column 15, a mass transfer with sump liquid from the fourth column 14 is carried out, which, in the air-separation systems 100 through 300 according to FIGS. 1 through 3, is delivered in liquid form in the form of a material flow v into the upper and lower parts of the further column 15. In the air-separation system 400 according to FIG. 4, the material flow v is fed only into the upper part of the further column 15.

[0095] In the lower part of the further column 15, more volatile components are expelled through heating by means of the condenser evaporator 152. Gas is withdrawn from the upper and lower parts of the further column 15 and, in the air-separation systems 100 through 300 according to FIGS. 1 through 3, fed into the fourth column 14 in the form of a material flow w. In contrast, in the air-separation system 400 according to FIG. 4, the fourth column 14 is fed only with a gas flow w′ from the upper part of the further column 15. Gas and liquid exchange between the upper and lower parts of the further column 15 takes place here in the form of the material flows w″ and w′″. A portion of the side flow t is thus ultimately fed into the fourth column 14, and a portion of the sump liquid is ultimately fed back from it into the third column 13. In all the examples illustrated here, the further column 15 can, for example, also be arranged above the overhead condenser 111 of the first column 11.

[0096] Sump liquid from the lower part of the further column 15 is withdrawn in the form of a material flow x and, in the example shown, fed into a tank system T. If necessary, a material flow, also designated x for the sake of clarity, is withdrawn from the tank system T, evaporated in the main heat exchanger 4, and discharged as a high-purity, gaseous oxygen product.

[0097] Argon-rich liquid is withdrawn from the fourth column 14 in the form of a material flow y by means of a further internal compression pump 8, pressurized in liquid form, converted to the gaseous or critical state in the main heat exchanger 4 by heating, and discharged from the air-separation system 100 as a gaseous, compressed argon product or used otherwise. In the air-separation system 400 according to FIG. 4, a corresponding tank system T′ is also illustrated in this context.

[0098] Liquid nitrogen, liquid oxygen (optionally, also having different purities), and liquid argon can be provided as further products of the system 100, as is known in principle and shown, for example, in the form of a partial flow of the liquefied overhead gas h of the first column 11. In the embodiment of the air-separation system 400 according to FIG. 4, a liquid nitrogen feed into the condenser evaporator 111 is also shown using a material flow h′.

[0099] The air-separation system 200 illustrated in FIG. 2 and designed according to an embodiment of the invention differs from the air-separation system shown in FIG. 1 essentially in that the material flow d is not heated in the expansion machine 8 prior to its expansion.

[0100] The air-separation system 300 illustrated in FIG. 3 differs from the air-separation system 200 shown in FIG. 2 essentially in that a division of the material flow z is carried out on the warm side of the main heat exchanger 4, wherein a partial flow z′ of the material flow z is compressed by means of a compressor 9, cooled in the main heat exchanger 4, and fed into the second column 12. The air-separation system 300 can otherwise also be the same as the air-separation system 100 illustrated in FIG. 1.

[0101] The air-separation system 400 shown in FIG. 4 illustrates the measures proposed according to the invention in connection with a SPECTRA process known per se. In this case, in addition to the sump flow d, which has already been explained above, a further material flow d′ is withdrawn above the sump from the first column 11 and, like the material flow d, cooled again in the main heat exchanger 4. Evaporation then takes place in the condenser evaporator 111.

[0102] The material flow d is, in the expansion machine 5, which is coupled to a generator G, expanded in part and, as mentioned, fed into the second column 12 (see linkage D). The remainder of the material flow d is partially heated in the main heat exchanger 4 and then expanded in a further expansion machine 401, which is coupled to a compressor 402 and a brake 403. Discharge from the air-separation system 400 then takes place. A portion of the liquefied material flow h is discharged in liquid form and, optionally, supercooled against a portion of the same material flow in a supercooler 404. The fraction used for supercooling can be combined with the expanded remainder of the material flow d.

[0103] In contrast, after its evaporation in the condenser evaporator 111, the material flow d′ is at least partially subjected to compression in the compressor 402, cooled again in the main heat exchanger 4, and fed back to the first column 11.

[0104] As mentioned, the air-separation system 500 shown in FIG. 5 is illustrated as a variant of the air-separation system 100 according to FIG. 4. It is characterized in particular by the use of a blower 501, by means of which a portion of the material flow q, here denoted by q′, is brought to the pressure of the material flow z and fed to the latter.

[0105] As mentioned, such an embodiment is particularly advantageous when no refrigeration machine is used in the precooling of the feed air, and the regeneration gas requirement is therefore comparatively high. Advantages result even if the requirements for the hydrogen content in the nitrogen product are comparatively high. Reference is made to the corresponding explanations above.