PROCESS FOR PRODUCING ONE OR MORE AIR PRODUCTS, AND AIR SEPARATION PLANT

Abstract

A process and air separation plant for producing one or more air products by cryogenic separation of air in an air separation plant wherein a first fraction and a second fraction of feed air quantity are post-compressed in a post-compressor from a first pressure level to a second pressure level at least 3 bar above the first pressure level, and are extracted from a post-compressor jointly at the second pressure level, impure nitrogen, the nitrogen content of which lies below an overhead product of a high-pressure column, is extracted from the high-pressure column at the first pressure level and is expanded using a second turboexpander which is mechanically coupled to a first booster, and a fluid enriched with argon is extracted from a low-pressure column, is depleted of argon and is recycled into the low-pressure column.

Claims

1. A process for producing one or more air products by cryogenic separation of air in an air separation plant having a distillation column system which comprises a high-pressure column, which is operated at a first pressure level, and a low-pressure column, wherein a feed air quantity is compressed in a main air compressor to the first pressure level, from which a first fraction and a second fraction are post-compressed in a post-compressor and a third fraction is compressed only to the first pressure level and is fed at the first pressure level into the high-pressure column, the post-compressed first fraction of the feed air quantity is successively compressed further using a first booster and a second booster is subsequently cooled, expanded to the first pressure level and fed in at least partially liquefied form into the high-pressure column, and the post-compressed second fraction of the feed air quantity is cooled and is subsequently expanded, using a first turboexpander which is mechanically coupled to the first or to the second booster, to the first pressure level and fed into the high-pressure column, characterized in that the first fraction and the second fraction of the feed air quantity are post-compressed in the post-compressor from the first pressure level to a second pressure level at least 3 bar above the first pressure level, and are extracted from the post-compressor jointly at the second pressure level, impure nitrogen, the nitrogen content of which lies below the overhead product of the high-pressure column, is extracted from the high-pressure column at the first pressure level and is expanded using a second turboexpander, wherein the second turboexpander is mechanically coupled to the booster taken from the group of the first and second boosters, which is not coupled to the first turboexpander, and a fluid enriched with argon is extracted from the low-pressure column, is depleted of argon and is recycled into the low-pressure column.

2. The process according to claim 1, in which the impure nitrogen has an oxygen content of 0.5 to 2 mol percent.

3. The process according to claim 1, in which the post-compressed second fraction of the feed air quantity is supplied without a further pressure increase to the first turboexpander.

4. The process according to claim 1, in which the cooling of the first fraction of the feed air quantity after the compression thereof using the first booster and the second booster is performed in the main heat exchanger of the air separation plant, wherein the first fraction of the feed air quantity is extracted from the main heat exchanger at a temperature level of 95 to 110 K.

5. The process according to claim 1, in which the cooling of the second fraction of the feed air quantity before the expansion thereof using the first turboexpander is performed in the main heat exchanger of the air separation plant, wherein the second fraction of the feed air quantity is extracted from the main heat exchanger at a temperature level of 150 to 180 K.

6. The process according to claim 1, in which the impure nitrogen, before being expanded in the second turboexpander, is heated in the main heat exchanger of the air separation plant to a temperature level of 120 to 150 K.

7. The process according to claim 1, in which the impure nitrogen, before being expanded in the second turboexpander, is heated in a secondary heat exchanger, which is provided in addition to the main heat exchanger of the air separation plant, to a temperature level of 120 to 150 K.

8. The process according to claim 1, in which the argon depletion of the argon-enriched fluid is performed by means of a distillation column with fewer than 40 theoretical plates.

9. The process according to claim 1, in which the further compression of the post-compressed first fraction of the feed air quantity using the first booster and the second booster is performed to a third pressure level of 60 to 90 bar.

10. The process according to claim 1, in which the third fraction of the feed air quantity is cooled to the first pressure level and supplied to the high-pressure column.

11. The process according to claim 10, in which the first fraction of the feed air quantity comprises 20 to 30 percent of the feed air quantity, the second fraction of the feed air quantity comprises 10 to 20 percent of the feed air quantity, and the third fraction of the feed air quantity comprises 45 to 60 percent of the feed air quantity.

12. The process according to claim 1, in which impure nitrogen is extracted from the low-pressure column and is heated together with the impure nitrogen extracted from the high-pressure column and expanded using the second turboexpander.

13. The process according to claim 1, in which the first turboexpander is mechanically coupled to the second booster.

14. An air separation plant having a distillation column system which comprises a high-pressure column, which is designed for operation at a first pressure level, and a low-pressure column, wherein the air separation plant has: a main air compressor which is designed for compressing a feed air quantity to the first pressure level, a post-compressor which is designed for post-compressing a first fraction and a second fraction of the feed air quantity, and means which are designed for compressing a third fraction of the feed air quantity only to the first pressure level and feeding said third fraction into the high-pressure column at the first pressure level, a first booster and a second booster which are designed for successively further compressing the post-compressed first fraction of the feed air quantity, wherein means are provided which are designed for subsequently cooling the first fraction, expanding said first fraction to the first pressure level and feeding said first fraction in at least partially liquefied form into the high-pressure column, and means which are designed for cooling the post-compressed second fraction of the feed air quantity, and a first turboexpander which is mechanically coupled to the first or to the second booster and which is designed for subsequently expanding the second fraction of the feed air quantity to the first pressure level and feeding said second fraction into the high-pressure column, characterized by means which are designed for post-compressing the first fraction and the second fraction of the feed air quantity in the post-compressor from the first pressure level to a second pressure level at least 3 bar above the first pressure level, and extracting said first fraction and second fraction from the post-compressor jointly at the second pressure level, extracting impure nitrogen, the nitrogen content of which lies below the overhead product of the high-pressure column, from the high-pressure column at the first pressure level and expanding said impure nitrogen using a second turboexpander, wherein the second turboexpander is mechanically coupled to the booster taken from the group of the first and second boosters, which is not coupled to the first turboexpander, and extracting a fluid enriched with argon from the low-pressure column, depleting said fluid of argon and recycling said fluid into the low-pressure column.

15. The air separation plant according to claim 14, which is used for producing one or more air products by cryogenic separation of air in an air separation plant having a distillation column system which comprises a high-pressure column, which is operated at a first pressure level, and a low-pressure column, wherein a feed air quantity is compressed in a main air compressor to the first pressure level, from which a first fraction and a second fraction are post-compressed in a post-compressor and a third fraction is compressed only to the first pressure level and is fed at the first pressure level into the high-pressure column, the post-compressed first fraction of the feed air quantity is successively compressed further using a first booster and a second booster is subsequently cooled, expanded to the first pressure level and fed in at least partially liquefied form into the high-pressure column, and the post-compressed second fraction of the feed air quantity is cooled and is subsequently expanded, using a first turboexpander which is mechanically coupled to the first or to the second booster, to the first pressure level and fed into the high-pressure column, characterized in that the first fraction and the second fraction of the feed air quantity are post-compressed in the post-compressor from the first pressure level to a second pressure level at least 3 bar above the first pressure level, and are extracted from the post-compressor jointly at the second pressure level, impure nitrogen, the nitrogen content of which lies below the overhead product of the high-pressure column, is extracted from the high-pressure column at the first pressure level and is expanded using a second turboexpander, wherein the second turboexpander is mechanically coupled to the booster taken from the group of the first and second boosters, which is not coupled to the first turboexpander, and a fluid enriched with argon is extracted from the low-pressure column, is depleted of argon and is recycled into the low-pressure column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] FIG. 1 illustrates an air separation plant according to an embodiment of the present invention.

[0070] FIG. 2 illustrates an air separation plant according to an embodiment of the present invention.

[0071] FIG. 3 illustrates an air separation plant according to an embodiment of the present invention.

[0072] FIG. 4 illustrates an air separation plant according to an embodiment of the present invention.

[0073] FIG. 5 illustrates an air separation plant according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0074] In the figures below, elements which correspond to one another are denoted by identical reference designations. For the sake of clarity, said elements will not be discussed repeatedly. With regard to further details regarding the function of air separation plants and of the respective components thereof, reference is made to the cited technical literature (see for example Haring, FIG. 2.3A and associated explanations).

[0075] FIG. 1 shows an air separation plant which is configured for operation in accordance with an embodiment of the present invention. The air separation plant is denoted as a whole by 100.

[0076] In the air separation plant 100, feed air in the form of a substance stream a (AIR) is, by means of a main air compressor 101, drawn in in a feed air quantity via a filter 102 and compressed to a first pressure level. The feed air of the substance stream c compressed to the first pressure level is partially branched off in the form of a substance stream b (Air1) and is otherwise subjected, in the form of a substance stream c, to further treatment in a manner known per se in a post-cooling unit 103 and an adsorber station 104.

[0077] The feed air of the substance stream c compressed to the first pressure level and subjected to the treatment is, at the first pressure level, supplied, in one part, in the form of a substance stream d for post-compression in a post-compressor 105 and, in a further part, in the form of a substance stream e directly for cooling in a secondary heat exchanger 106 and a main heat exchanger 107.

[0078] In the illustrated example, the post-compressor 105 comprises two compressor sections and corresponding post-coolers (not separately designated). In the illustrated example, a partial stream of the substance stream d is extracted from the post-compressor 105 in the form of a substance stream f at an intermediate pressure level (Air2), and the rest is compressed in the post-compressor 105 to a second pressure level and exits the post-compressor in the form of a substance stream g.

[0079] The substance stream g is divided into a substance stream h and a substance stream i, wherein the substance stream h is supplied at the second pressure level to the main heat exchanger 107, and the substance stream i is subjected to a further pressure increase to a third pressure level in a first booster 108 and a second booster 109, and is supplied at the third pressure level to the main heat exchanger 107.

[0080] The substance stream h is extracted from the main heat exchanger 107 at an intermediate temperature level, is expanded to the first pressure level again in a first turboexpander 110, which is mechanically coupled to the second booster 109 in this embodiment, and (see also link A) is fed into a high-pressure column 111 of a distillation column system 10, which furthermore has a low-pressure column 112 and an argon discharge column 113.

[0081] The substance stream i is extracted from the main heat exchanger 107 at the cold side, is expanded using a generator turbine 114 or in a throttle valve (without designation) or in both, is thereby at least partially liquefied, and is likewise fed into the high-pressure column 111. The expansion of the substance stream i before the infeed into the high-pressure column 111 is likewise performed to the first pressure level.

[0082] Impure nitrogen in the form of a substance stream k with the above-stated exemplary specifications is extracted from the high-pressure column 111 at the first pressure level, is supplied to the main heat exchanger 107 at the cold side (see link B), is extracted from the latter at an intermediate temperature, and is expanded in a second turboexpander 115, which is in turn mechanically coupled to the first booster 108 in this embodiment. The second turboexpander 115 is the impure pressurized nitrogen turbine that has been mentioned multiple times.

[0083] In the context of this application, the air of the substance stream i will also be referred to as first fraction of the feed air quality (of the substance stream a), the air of the substance stream h will also be referred to as second fraction of the feed air quantity, and the air of the substance stream e will also be referred to as third fraction of the feed air quantity. As illustrated here, the feed air quantity is compressed in the main air compressor 101 to the first pressure level. The first fraction and the second fraction of the feed air quantity are post-compressed in the post-compressor 105 to the second pressure level and are extracted from the post-compressor 105 jointly at the second pressure level.

[0084] The first fraction of the feed air quantity is compressed further using the first booster 108 and the second booster 109 to a third pressure level, is cooled in the main heat exchanger 107, is subsequently expanded to the first pressure level, and is fed into the high-pressure column 111.

[0085] The second fraction of the feed air quantity, after cooling in the main heat exchanger 107, is expanded, in the first turboexpander 110 which is mechanically coupled to the second booster 109, to the first pressure level and fed into the high-pressure column 111. Impure nitrogen is extracted at the first pressure level from the high-pressure column and is expanded in the second turboexpander 115, which is mechanically coupled to the first booster 108.

[0086] The third fraction of the feed air quantity, that is to say the air of the substance stream e, is supplied to the secondary heat exchanger 106 in the form of two partial streams l and m, wherein the partial stream l is extracted from the secondary heat exchanger 106 at the cold side and the partial stream m is extracted from the secondary heat exchanger 106 at an intermediate temperature. The partial stream m is cooled further in, and extracted at the cold side from, the main heat exchanger 107. Optionally, as illustrated in the form of a substance stream z shown by dashed lines, a partial quantity of the third fraction of the feed air quantity may however also be cooled only in the main heat exchanger 107. The third fraction of the feed air quantity is ultimately likewise fed into the high-pressure column 111.

[0087] An oxygen-enriched liquid is drawn off, in the form of a substance stream n, from the bottom of the high-pressure column 111, is conducted through a subcooler 116 and, after use as cooling medium in a top condenser of the argon discharge column 113, is fed into the low-pressure column 112.

[0088] Gaseous nitrogen is extracted, in the form of a substance stream o, from the top of the high-pressure column 111, is heated in the main heat exchanger 107, and is made available in the form of one or more pressure products (seal gas, PGAN). Further gaseous nitrogen is drawn off, in the form of a substance stream p, from the top of the high-pressure column 111 and is at least partially liquefied in a main condenser 117 which connects the high-pressure column 111 and the low-pressure column 112 in heat-exchanging fashion. A partial stream q is recycled into the high-pressure column 111, a partial stream r is conducted through the subcooler 116 and is made available as liquid nitrogen product (LIN). In addition to the mentioned substance stream k, impure nitrogen is also drawn off in liquid form, in the form of a substance stream s, from the high-pressure column 111, conducted through the subcooler 116 and fed into the low-pressure column 112.

[0089] Oxygen is drawn off, in the form of a substance stream t, from the bottom of the low-pressure column 112, is increased in pressure in the liquid state in a pump 118 (internal compression), is at least partially heated in the main heat exchanger 107 in the form of substance streams u and v and changed into the gaseous or supercritical state, and is output as corresponding pressure products (IC GOX1, IC GOX2). Further oxygen is drawn off, in the form of a substance stream w, from the low-pressure column 112, is partially conducted through the subcooler 116, and is output as liquid product (LOX). The stream w may possibly also be branched off from the substance stream at the pump outlet or from the substance stream v, throttled to a lower pressure, supplied to the subcooler 116 and subsequently output as product.

[0090] Impure nitrogen drawn off from the top of the low-pressure column 112 is conducted in the form of a substance stream x through the subcooler 116, is subsequently heated in parts in the secondary heat exchanger 106 and in the main heat exchanger 107, and is finally utilized as desired and in accordance with demand in the post-cooling unit 103 and/or in the adsorber station 104 (in this regard, see also link C).

[0091] Fluid drawn off from the top of the argon discharge column 113 (in this regard, see also link D) can be heated in the secondary heat exchanger 106 and released to the atmosphere (ATM). Thus, no argon product is obtained, it rather being the case that argon is merely discharged. As already mentioned above, a corresponding plant may however also be equipped with a conventional argon system, which may comprise in particular a crude argon column and a pure argon column.

[0092] Whereas FIG. 1 illustrates an air separation plant 100 in which the substance stream k, that is to say the impure nitrogen from the high-pressure column 111, is fed, after being expanded in the turboexpander 115, to that fraction of the substance stream x which is conducted through the main heat exchanger 107, FIG. 2 illustrates an air separation plant in which the feed to the fraction conducted through the secondary heat exchanger 106 is illustrated.

[0093] In the air separation plant illustrated in FIG. 3, the substance stream m is conducted not through the secondary heat exchanger 106 but through the main heat exchanger 107 (correspondingly to the substance stream z in FIGS. 1 and 2). In the secondary heat exchanger 106, it is instead the case that the substance stream k (see links B and E) is heated.

[0094] In the air separation plant illustrated in FIG. 4, the secondary heat exchanger 106 is not provided, and the substance stream e is therefore conducted entirely through the main heat exchanger 107. Correspondingly, the substance stream x is heated entirely in the main heat exchanger 107. The substance stream y is also heated in the main heat exchanger 107.

[0095] In the air separation plant illustrated in FIG. 4, the low-pressure column 112 has been expanded to include a section 112a for obtaining low-pressure nitrogen. A low-pressure nitrogen stream j can therefore be drawn off from the top of the low-pressure column 112. The low-pressure nitrogen stream j is conducted through the subcooler 116 and is heated in a separate passage of the main heat exchanger 107. A partial stream of the substance stream r can be applied in liquid form to the top of the low-pressure column 112. The embodiment illustrated in FIG. 4 may basically be realized with all of the heat exchanger configurations shown in the preceding figures, that is to say the secondary heat exchanger 106 may be present or absent.