PROCESS FOR CRYOGENIC FRACTIONATION OF AIR, AIR FRACTIONATION PLANT AND INTEGRATED SYSTEM COMPOSED OF AT LEAST TWO AIR FRACTIONATION PLANTS

Abstract

The invention relates to a process for cryogenic fractionation of air using an air fractionation plant comprising a rectification column system comprising a high-pressure column operated at a pressure level of 9 to 14.5 bar, a low-pressure column operated at a pressure level of 2 to 5 bar, and an argon column. It is envisaged that a recirculating stream is formed using the second tops gas or a portion thereof, which is heated, compressed, cooled again, and after partial or complete liquefaction or in the unliquefied state is introduced partially or completely, or in fractions, into the first rectification column and/or into the second rectification column. The present invention also relates to a corresponding system.

Claims

1. A process for cryogenic fractionation of air using an air fractionation plant with a rectification column system having a first rectification column, a second rectification column and a third rectification column, in which the first rectification column is operated at a first pressure level, a first feed stream is fed into the first rectification column, which is formed using cooled compressed air, and a first sump liquid enriched in relation to the first feed stream of oxygen and argon and a nitrogen-rich first top gas are formed in the first rectification column, the second rectification column is operated at a second pressure level, a second feed stream which is formed using at least a portion of the first sump liquid is fed into the second rectification column, and an oxygen-rich second sump liquid and a nitrogen-rich second top gas are formed in the second rectification column, and a third feed stream is fed into the third rectification column, which is formed using fluid which has a higher argon content than the second sump liquid and the second top gas and is removed from the second rectification column, and a third top gas enriched in relation to the third feed stream of argon is formed in the third rectification column, wherein the first pressure level ranges from 9 to 14.5 bar at the top of the first rectification column and the second pressure level ranges from 2 to 5 bar at the top of the second rectification column, and to form a recirculating stream, the second top gas or a part thereof is used, which is heated, compressed, cooled again, and after partial or complete liquefaction or in an unliquefied state, is fed partly or completely or in fractions into the first rectification column and/or into the second rectification column.

2. The process according to claim 1, wherein the second top gas used to form the recirculating stream or a part thereof is successively heated, compressed, cooled again and then fed into the first rectification column as a circulating gas.

3. The process according to claim 1, wherein a portion of the first top gas is discharged from the air fractionation plant at the first pressure level as a compressed nitrogen product.

4. The process according to claim 1, wherein a first portion of the second top gas is used to form the recirculating stream, and in which a second portion of the second top gas is only heated, compressed and used to provide a compressed nitrogen product that is discharged from the air fractionation plant.

5. The process according to claim 1, wherein the recirculating stream is fed into the first rectification column partially or completely in an unliquefied state in an intermediate region, above and below which separation plates are located.

6. The process according to claim 1, wherein the recirculating stream or a part thereof is condensed in a condenser evaporator, which connects the first rectification column and the second rectification column in a heat-exchanging manner, and is fed into the first rectification column.

7. The process according to claim 1, wherein the recirculating stream is condensed partly or completely using the condenser evaporator arranged in the sump area of the further rectification column and fed into the second rectification column.

8. The process according to claim 1, wherein a further air fractionation plant is used, wherein nitrogen-rich gas having an oxygen content of 0.1 to 100 ppm is provided by means of the further air fractionation plant at a pressure level of ambient pressure up to 1.5 bar and is partially or completely combined with the recirculating stream.

9. The process according to claim 6, wherein the nitrogen-rich gas provided by means of the further air fractionation plant is initially compressed partly or completely separated from the recirculating stream to the second pressure level and then combined with the recirculating stream.

10. The process according to claim 1, wherein the fluid having a higher argon content than the second sump liquid and the second top gas and being removed from the second rectification column is fed into a further rectification column, and in which the third feed stream is formed using fluid removed from the further rectification column.

11. The process according to claim 10, wherein the further rectification column has a first part and a second part, wherein the fluid which is removed from the second rectification column and which is used to form the third feed stream, is fed into a lower region of the first part, gas from an upper region of the first part is removed and used in the formation of the third feed stream, sump liquid is formed in the third column and is at least partially transferred into the upper region of the first part, liquid from an intermediate region of the first part is removed and fed into an upper region of the second part, gas from the upper region of the second part is removed and fed into the intermediate region of the first part, and pure oxygen is formed in a lower region of the second part and discharged from the air fractionation plant.

12. The process according to claim 10, wherein the lower region of the second part is heated using a condenser evaporator in which a part of the first top gas and/or of the recirculating gas is used as heating fluid.

13. The process according to claim 11, wherein the part of the first top gas and/or the recirculating gas used as heating fluid is thereafter fed into the first rectification column or into the second rectification column.

14. The process according to claim 1, wherein gas is removed from the second rectification column, heated, turbine expanded and discharged from the air fractionation plant.

15. The process according to claim 1, wherein the first sump liquid or at least its part which is used to form the second feed stream is fed to the condensation of top gas at least of the third rectification column.

16. The process according to claim 1, wherein the third top gas is purified in a pure argon column to give pure argon.

17. An air fractionation plant having a rectification column system which has a first rectification column, a second rectification column and a third rectification column, and which is configured to operate the first rectification column at a first pressure level, to feed a first feed stream which is formed using cooled compressed air into the first rectification column, and to form a first sump liquid enriched in relation to the first feed stream of oxygen and argon and a nitrogen-rich first top gas in the first rectification column, operate the second rectification column at a second pressure level, to feed a second feed stream formed using at least a portion of the first sump liquid into the second rectification column, and to form an oxygen-rich second sump liquid and a nitrogen-rich second top gas in the second rectification column, and feed into the third rectification column a third feed stream which is formed using fluid which has a higher argon content than the second sump liquid and the second top gas and is removed from the second rectification column, and to form a third top gas enriched with argon with respect to the third feed stream in the third rectification column, wherein the air fractionation plant is configured to be operated such that the first pressure level ranges from 9 to 14.5 bar at the top of the first rectification column and the second pressure level ranges from 2 to 5 bar at the top of the second rectification column, and it uses the second top gas or a part thereof to form a recirculating stream, and heats, compresses and cools it again, and, after partial or complete liquefaction or in an unliquefied state, feeds it partly or completely or in fractions into the first rectification column and/or into the second rectification column.

Description

DESCRIPTION OF FIGURES

[0047] FIGS. 1 to 5 illustrate air fractionation plants according to different embodiments of the present invention.

[0048] In the figures, elements corresponding functionally or structurally to one another are indicated by identical reference signs and for the sake of clarity are not explained repeatedly. Explanations relating to plants and plant components apply in the same way for corresponding processes and process steps.

[0049] In FIG. 1, an air fractionation plant according to an embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 100.

[0050] In the air fractionation plant 100, air is sucked by means of a main air compressor 1 via a Filter 2 and compressed to a pressure level of, for example, about 12.5 bar. After cooling and separation of water, the correspondingly compressed air is freed of residual water and carbon dioxide in an adsorber station 3, which can be designed in a manner known per se. For the design of the mentioned components, reference is made to the technical literature cited at the outset.

[0051] A correspondingly formed compressed air stream a is conducted from the warm to the cold end through a main heat exchanger 4 and fed as feed stream (referred to above and hereinafter also as “first feed stream”) into a pressure column 11 (“first rectification column”) of a rectification column system 10. In the example shown, the rectification column system 10 has, in addition to the pressure column 11, a low-pressure column 12 (“second rectification column”), a crude argon column 13 (“third rectification column”) and a pure oxygen column 14 (“fourth rectification column”) with an upper part 14a (“first part”) and a lower part 14b (“second part”) and a pure argon column 15 (“fifth rectification column”). The pressure column 11 is connected in a heat-exchanging manner to the low-pressure column 12 via a main condenser 16, which can in particular be designed as a multi-level bath evaporator, and a sump evaporator 17 is arranged in the bottom of the lower part 14b of the pure oxygen column 14. In the example shown, a subcooling heat exchanger 18 is also associated with the rectification column system 10.

[0052] At the top of the pressure column 11, a top gas (“first top gas”) is formed. In the example shown, part of this is fed in the form of a material stream b through the main condenser 16 and led to a further part in the form of a material stream c through the sump evaporator 17. Some of the condensate formed in this way is returned to the pressure column 11 as reflux. Further condensate can be fed in the form of a liquid nitrogen stream m through the subcooling heat exchanger 18 and, for example, can be provided as a corresponding product. In a deviation from the illustrated embodiment, the material stream c can also be fed separately to the material stream b into the pressure column 11 or can be subcooled separately in the subcooling heat exchanger 18 and fed into the low-pressure column 12. A further part of the top gas of the pressure column 11 is used to form a material stream d which is heated in the main heat exchanger 4 and is discharged from the air fractionation plant 100 as product at a content of, for example, about 10 ppb of oxygen and at a pressure of, for example, about 11.8 bar.

[0053] In the sump of the pressure column 11, a sump liquid (“first sump liquid”) is formed and is removed therefrom in the form of a material stream e. The material stream e is initially fed through the subcooling heat exchanger 18 and then used in a manner known per se to cool the top condensers of the crude argon column 13 and the pure argon column 15, which are not designated separately. Evaporated and unevaporated fractions are fed into the low-pressure column 12 in the form of material streams f (comprising a “second feed stream”). From an intermediate region of the pressure column 11, fluid with a lower nitrogen content than the top gas is removed from the pressure column 11, conducted through the subcooling heat exchanger 18 and then fed into the low-pressure column 12.

[0054] In the low-pressure column 12, sump liquid (“second sump liquid”) is formed, which is removed therefrom in the form of a material stream h, is pressurized in a pump 5, heated in the main heat exchanger 4 and discharged as an internally compressed oxygen product. Above the sump, gas is removed from the low-pressure column 12 in the form of a material stream i, combined with a material stream k explained below to form a collection stream I with a content of, for example, about 90% oxygen, partially heated in the main heat exchanger 4, expanded in a generator turbine 6, heated again in the main heat exchanger 4, and used, for example, as regeneration gas in the adsorber station 3.

[0055] A gaseous compressed nitrogen stream (“second top gas”) is removed from the top of the low-pressure column 12 in the form of a material stream n. This is present, for example, at a pressure level of approximately 3.7 bar and has a content of, for example, about 100 ppb of oxygen. It is used, minus the above-mentioned material stream k, to form a recirculating stream, which is initially fed through the subcooling heat exchanger 18, then heated in the main heat exchanger 4, compressed in a compressor 7, cooled again in the main heat exchanger 4, and is fed into the pressure column 11 in the intermediate region already mentioned.

[0056] From the low-pressure column 11, gas enriched in argon is removed in the form of a material stream o and fed into the upper part 14a of the pure oxygen column 14. As already mentioned, this upper part 14a in the example shown is functionally a part of the crude argon column 13. Therefore, reference is made to the explanations above. In another embodiment with a correspondingly modified crude argon column, the material stream o can also be fed directly into the crude argon column. From the lower region of upper part 14a, sump liquid in the form of a material stream p is recycled into the low-pressure column 11. Top gas from the upper part 14a of the pure oxygen column 14 is used to feed the crude argon column 13, sump liquid of the crude argon column is pumped back by means of a pump 8 onto the upper part 14a of the pure oxygen column 14. The upper part 14a and the lower part 14b of the pure oxygen column 14 are connected to one another via material stream s and t. The material stream s is removed in liquid form from an intermediate region of the upper part 14a and fed onto the lower part 14b. The material stream t is removed in gaseous form at the top of the lower part 14b and fed into the intermediate region of the upper part 14a. From the sump of the lower part 14b of the pure oxygen column, a high-purity oxygen stream u having a residual content of, for example, about 10 ppb of argon is removed. In this case, for example, a use of a pressure buildup evaporation and a corresponding provision of an internal compression product are also possible.

[0057] The operation of the crude argon column 13 and the pure argon column 15 essentially corresponds to the prior art and is not explained separately. From the pure argon column 15, a pure argon stream v is removed, which is partly stored or temporarily stored in a Tank T and partially compressed using a pump 8 and can be provided as an internal compression product with a content of, for example, about 1 ppm of oxygen.

[0058] In FIG. 2, an air fractionation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 200.

[0059] In contrast to the air fractionation plant 100 according to FIG. 1, the material stream d is not formed here and a nitrogen product is provided instead using the top gas of the low-pressure column 12. In this case, a material stream denoted by w is removed from the low-pressure column 12. After channeling off the material stream k as above, heating in the main heat exchanger 4 and compression in the compressor 7, a portion in the form of a material stream x is provided as a product, whereas another portion in the form of a material stream also designated here as n is cooled again and combined with the top gas removed from the pressure column 11 and treated in the same way as the latter. Reference is made to the explanations of FIG. 1 with respect to the “first top gas”.

[0060] In other words, it is provided here that parts of the material stream n, such as the top gas removed from the first rectification column, are fed into the pressure column 11 and into the low-pressure column 12. In the embodiment of the invention illustrated here, the material stream n is fed to the top gas of the pressure column 11 before its condensation, so that here the material streams b and c are formed using the material stream n. Instead of being formed from the intermediate region, as is the case in the air fractionation plant 100 shown in FIG. 1, a material stream g, also denoted g here for simplicity, is formed from corresponding condensate.

[0061] In FIG. 3, an air fractionation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 300.

[0062] The air fractionation plant 300 according to FIG. 3 represents a variant of the air fractionation plant 200 according to FIG. 2, in which the material stream n, comparable to the air fractionation plant 100 according to FIG. 1, is fed into an intermediate region into the pressure column 11. However, the formation of material stream g takes place in this embodiment as in the air fractionation plant 200 according to FIG. 2.

[0063] In FIG. 4, an air fractionation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 400.

[0064] In the example illustrated here, the air fractionation plant 400 according to FIG. 4 represents a variant of the air fractionation plant 100 according to FIG. 1; the measures explained below and illustrated in FIG. 4 can however also be used in all other embodiments of the invention.

[0065] The air fractionation plant 400 according to FIG. 4 is associated with a further air fractionation plant 1000, by means of which a material stream z is supplied, which is present, for example, at a pressure level of about 1.1 bar and has a content of about 1 ppm of oxygen and otherwise nitrogen. The material stream z can in particular be removed from a low-pressure column (not illustrated) of the further air fractionation plant 1000. It can be brought to the pressure level of the material stream n in a corresponding compressor 1001. The feed of the material stream z to the material stream n makes it possible to dispense with purification of the material stream z, for example to a content of about 1 ppb of oxygen, because the material stream z is used to provide the material stream d with a correspondingly low oxygen content.

[0066] In FIG. 5, an air fractionation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 500.

[0067] The air fractionation plant 500 illustrated in FIG. 5 represents a modification of the previously illustrated air fractionation plants in that here the material stream n, after cooling in the main heat exchanger 4, is combined with the material stream c to form a material stream designated here as y, which is first fed through the condenser evaporator 17 and then through the subcooling heat exchanger 18 and fed in a liquefied state at the head of the second rectification column 12.