EP3164654B1 - Method and device for the low-temperature separation of air at variable energy consumption - Google Patents

Description

The invention relates to a method and a device for the variable extraction of a compressed gas product by means of low-temperature separation of air.

Methods and devices for the low-temperature separation of air are, for example, out Hausen / Linde, low-temperature technology, 2nd edition 1985, chapter 4 (pages 281 to 337 ) known.

The distillation column system of such a system can be designed as a two-column system (for example as a classic Linde double-column system), or as a three- or more-column system. In addition to the columns for nitrogen-oxygen separation, it can have further devices for obtaining highly pure products and / or other air components, in particular noble gases, for example argon extraction and / or krypton-xenon extraction.

In the course of an "internal compression", a liquid product stream which is brought under pressure is vaporized against a heat transfer medium and finally obtained as an internally compressed compressed gas product. This method is also known as internal compression. It is used to obtain gaseous printed products. In the case of a supercritical pressure, there is no phase transition in the actual sense, the product stream is then "pseudo-evaporated". The product stream can be, for example, an oxygen product from the low-pressure column of a two-column system or a nitrogen product from the high-pressure column of a two-column system or from the liquefaction chamber of a main condenser, via which the high-pressure column and low-pressure column are in heat-exchanging connection

A heat carrier under high pressure is liquefied against the (pseudo) evaporating product stream (or pseudo-liquefied if it is under supercritical pressure). The heat transfer medium is often by part of the Air formed, in the present case from the "second partial flow" of the compressed feed air.

Internal compression methods are known for example from DE 830805 , DE 901542 (= US 2712738 / US 2784572 ), DE 952908 , DE 1103363 (= US 3083544 ), DE 1112997 (= US 3214925 ), DE 1124529 , DE 1117616 (= US 3280574 ), DE 1226616 (= US 3216206 ), DE 1229561 (= US 3222878 ), DE 1199293 , DE 1187248 (= US 3371496 ), DE 1235347 , DE 1258882 (= US 3426543 ), DE 1263037 (= US 3401531 ), DE 1501722 (= US 3416323 ), DE 1501723 (= US 3500651 ), DE 253132 (= US 4279631 ), DE 2646690 , EP 93448 B1 (= US 4555256 ), EP 384483 B1 (= US 5036672 ), EP 505812 B1 (= US 5263328 ), EP 716280 B1 (= US 5644934 ), EP 842385 B1 (= US 5953937 ), EP 758733 B1 (= US 5845517 ), EP 895045 B1 (= US 6038885 ), DE 19803437 A1 , EP 949471 B1 (= US 6185960 B1 ), EP 955509 A1 (= US 6196022 B1 ), EP 1031804 A1 (= US 6314755 ), DE 19909744 A1 , EP 1067345 A1 (= US 6336345 ), EP 1074805 A1 (= US 6332337 ), DE 19954593 A1 , EP 1134525 A1 (= US 6477860 ), DE 10013073 A1 , EP 1139046 A1 , EP 1146301 A1 , EP 1150082 A1 , EP 1213552 A1 , DE 10115258 A1 , EP 1284404 A1 (= US 2003051504 A1 ), EP 1308680 A1 (= US 6612129 B2 ), DE 10213212 A1 , DE 10213211 A1 , EP 1357342 A1 or DE 10238282 A1 DE 10302389 A1 , DE 10334559 A1 , DE 10334560 A1 , DE 10332863 A1 , EP 1544559 A1 , EP 1585926 A1 , DE 102005029274 A1 , EP 1666824 A1 , EP 1672301 A1 , DE 102005028012 A1 , WO 2007033838 A1 , WO 2007104449 A1 , EP 1845324 A1 , DE 102006032731 A1 , EP 1892490 A1 , DE 102007014643 A1 , EP 2015012 A2 , EP 2015013 A2 , EP 2026024 A1 , WO 2009095188 A2 or DE 102008016355 A1 .

DE 102010052545 A1 shows a stationary internal compression process, in which an air flow in the main heat exchanger is warmed up and returned to the main air compressor.

The invention relates in particular to systems in which the total feed air is at a pressure which is clearly above the highest distillation pressure which prevails inside the columns of the distillation column system (this is normally the high-pressure column pressure. Such systems are also called HAP processes (HAP - high air pressure), where the "first pressure", ie the outlet pressure of the main air compressor (MAC = main air compressor), in which the Total air is compressed, for example more than 4 bar, in particular 6 to 16 bar above the highest distillation pressure. In absolute terms, the "first pressure" is between 17 and 25 bar, for example. In HAP processes, the main air compressor is regularly the only machine powered by external energy to compress air. A "single machine" is understood here to mean a single-stage or multi-stage compressor, the stages of which are all connected to the same drive, all stages in are housed in the same housing or connected to the same gearbox.

An alternative to such HAP processes are so-called MAC-BAC processes, in which the air in the main air compressor is compressed to a relatively low total air pressure, for example to the operating pressure of the high pressure column (plus line losses). Part of the air from the main air compressor is compressed to a higher pressure in a booster air compressor driven by external energy (BAC). This air section under higher pressure (often called a throttle flow) supplies the majority of the heat required for the (pseudo) evaporation of the internally compressed product in the main heat exchanger. It is expanded downstream of the main air compressor in a throttle valve or in a liquid turbine (DLE = dense liquid expander) to the pressure required in the distillation column system.

In many cases, a fluctuating demand for internally compressed products forces an air separation plant to be designed for variable operation with variable compressed gas production. Conversely, it can make sense to operate an air separation plant variably despite constant or essentially constant production by providing different operating modes which have different levels of energy consumption.

• Innenverdichtetes Stickstoffprodukt (GANIV)
• Anderes gasförmiges Druckprodukt wie zum Beispiel gasförmig aus der Hochdrucksäule entnommener Druckstickstoff (HPGAN), der gegebenenfalls in einem Stickstoffverdichter weiter verdichtet wird.
• Flüssigprodukt(e) wie flüssiger Sauerstoff, flüssiger Stickstoff und/oder flüssiges Argon.

A concrete example of such a boundary condition is the delivery of internally compressed oxygen (GOXIV) and possibly other gaseous and / or liquid products at an ethylene oxide production plant. It is often the case here that the oxygen requirement is adapted to the catalyst state during EO production; it can therefore be varied between 100% and approx. 70% during the catalyst life (usually around 3 years). It is essential that during this time the air separation plant has approximately the same times is operated with different GOXIV product quantities (between 100% and approx. 70%). It is therefore important that the system is operated efficiently not only in the design case with 100% GOXIV, but also in underload cases. This requirement is made even more difficult by the fact that the production of other air separation products is independent of the GOXIV product; for example, the need for one, more, or all other air separation products may remain unchanged while GOX production drops from 100% to about 70%. Such "other air separation products" can be, for example, one, several or all of the following products:

• Internally compressed nitrogen product (GANIV)
• Other gaseous pressure product, such as gaseous pressure nitrogen (HPGAN) taken from the high pressure column, which may be further compressed in a nitrogen compressor.
• Liquid product (s) such as liquid oxygen, liquid nitrogen and / or liquid argon.

This task can be accomplished relatively well with a conventional MAC-BAC method, since both compressors (MAC and BAC) are responsible for functionally separate tasks. In principle, the main air compressor only supplies the feed air for disassembly; the air post-compressor supplies energy for internal compression (GOXIV, GANIV) and for liquid production. Both machines can usually be controlled relatively easily between 70% and 100%.

1. a) das Maschinen-Kennfeld begrenzt ist und
2. b) der Auslegungsdruck für den "warmen" Anlagenteil (Vorkühlung, Adsorber etc.) darf nicht überschritten werden .

In a HAP process, these two tasks (supply of separation air and energy for internal compression / liquid production) are solved with a single compressor. This can lead to situations in which certain operating cases lie outside the compressor map and cannot be driven. The total energy requirement of an air separation plant is determined not only by the GOXIV product, but to a large extent by liquid production or by other internally compressed products. However, the GOXIV product is often decisive for the amount of separation air. If the amount of GOXIV is significantly reduced, significantly less separation air is fed into the system. However, this means that significantly less energy is introduced into the system, which may not be necessary for the desired production of other products (liquids, GANIV etc.) can suffice. In order to supply enough energy despite the significantly lower air volume, the compressor pressure must be increased significantly. However, this is only feasible to a limited extent with a HAP process because

1. a) the engine map is limited and
2. b) The design pressure for the "warm" part of the system (pre-cooling, adsorber, etc.) must not be exceeded.

The invention is based on the object of specifying a method and a corresponding device which combine the advantages of HAP methods with flexibility such as is known in a similar way to MAC-BAC methods. “Flexibility” is understood here in particular to mean that the system can be operated not only with low energy in a certain production quantity of internally compressed product, but also in a relatively wide load range with approximately constant low specific energy consumption. In particular, the production of other air separation products should remain the same, or at least change less than the product quantity of the internal compression product.

This object is achieved by the features of patent claim 1.

In the invention, in the second operating mode, part of the quantity of feed air is bypassed the entire distillation column system. This quantity then does not take part in the generation of the first product stream, but can nevertheless be directed through the first turbine in order to produce enough cold or to supply the system with enough energy to be able to maintain or at least reduce the liquid production relatively less than the amount of the first print production.

• der mehrstufige Verdichter durch den Hauptluftverdichter,
• der erste Prozessstrom durch die gesamte Einsatzluft und
• der zweite Prozessstrom durch einen Teil des arbeitsleistend entspannten ersten Teilstroms der Einsatzluft

gebildet werden.According to the invention, part of the feed air is not introduced into the distillation column system, but is returned to the main air compressor by

• the multi-stage compressor through the main air compressor,
• the first process stream through the entire feed air and
• the second process stream through a part of the work-relieved, relaxed first part stream of the feed air

be formed.

The excess air is not fed into the distillation column system, but is fed back into the heat exchanger immediately after expansion in the turbine and then fed to a suitable point (for example after the second or third stage) of the main air compressor without throttling. As a result, the necessary amount of "excess" air is compressed not from atmospheric pressure, but, for example, from about 5 bar, and a lot of energy is saved.

Another possibility (if a low-pressure GAN compressor is not available) is to guide and separate the excess air into the distillation column system. This other possibility is not part of the invention claimed here. The argon present in this amount of air can be obtained. The excess amount of oxygen can be taken as low-pressure oxygen from the low-pressure column and fed to the UN2 stream. In principle, you only lose the separation work to obtain additional oxygen molecules, but at the same time significantly more argon is produced.

• ein dritter Prozessstrom in einem Stickstoffproduktverdichter von einem Eintrittsdruck auf einen Enddruck verdichtet wird und
• mindestens zeitweise ein vierter Prozessstrom stromabwärts der ersten Stufe des Stickstoffproduktverdichters mit dem dritten Prozessstrom vermischt wird, wobei
• der dritte Prozessstrom durch einen ersten gasförmigen Stickstoffstrom aus der Niederdrucksäule und
• der vierte Prozessstrom durch ersten gasförmigen Stickstoffstrom aus der Hochdrucksäule

gebildet werden.The variable air recirculation can also be combined with an intermediate nitrogen feed into a corresponding compressor by

• a third process stream is compressed in a nitrogen product compressor from an inlet pressure to a final pressure and
• at least at times a fourth process stream downstream of the first stage of the nitrogen product compressor is mixed with the third process stream, wherein
• the third process stream through a first gaseous nitrogen stream from the low pressure column and
• the fourth process stream through first gaseous nitrogen stream from the high pressure column

be formed.

It is advantageous if the mixing of the second and the first process stream is carried out at an intermediate stage of the multi-stage compressor.

In addition, in the second operating mode, an oxygen gas stream can be taken from the lower region of the low-pressure column, mixed with a nitrogen-enriched stream from the upper region of the low-pressure column, and the mixture can be warmed in the main heat exchanger.

Electricity from the upper area of the low pressure column is mixed and the mixture is warmed up in the main heat exchanger.

In addition, in a special embodiment of the invention, a second air turbine can be used, a third partial stream of the feed air compressed in the main air compressor being cooled to an intermediate temperature in a main heat exchanger and relaxed in the second air turbine in a work-performing manner, and at least a first part of the third partial stream being relaxed in the work Distillation column system is initiated.

In addition, the second partial flow of the feed air compressed in the main air compressor can be cooled to an intermediate temperature in the main heat exchanger, can be post-compressed in a second post-compressor, which is operated as a cold compressor and driven by the second turbine, to a third pressure which is higher than the first pressure. cooled in the main heat exchanger, (pseudo) liquefied and then expanded and introduced into the distillation column system. In this way, the pressure of the second partial stream can be increased further without using external energy. A correspondingly higher internal compression pressure can be achieved.

In addition, a fourth partial flow of the air compressed in the main air compressor can be cooled under the first pressure in the main heat exchanger and then expanded and introduced into the distillation column system. The heat exchange process in the main heat exchanger is further optimized by such a second throttle flow.

• in dem ersten Betriebsmodus eine erste Menge an Einsatzluft in dem Hauptluftverdichter verdichtet wird und
• in dem zweiten Betriebsmodus eine zweite Menge an Einsatzluft in dem Hauptluftverdichter verdichtet wird, wobei
• das Verhältnis von zweiter Menge an Einsatzluft zu erster Menge an Einsatzluft größer, insbesondere um mindestens 3 %, insbesondere um mehr als 5 %größer ist als das Verhältnis zwischen zweiter Menge an erstem Druckgasprodukt und erster Menge an erstem Druckgasprodukt.

In another embodiment with a second turbine, it is expedient if the third partial flow in the second air turbine is expanded to a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column, and the work-relieved relaxed third partial flow in the main heat exchanger is cooled further and is then relaxed and introduced into the distillation column system. The heat exchange process in the main heat exchanger is further optimized by such a third throttle flow.

• in the first operating mode, a first amount of feed air is compressed in the main air compressor and
• in the second operating mode, a second amount of feed air is compressed in the main air compressor, wherein
• the ratio of the second quantity of feed air to the first quantity of feed air is larger, in particular by at least 3%, in particular by more than 5%, greater than the ratio between the second quantity of first compressed gas product and the first quantity of first compressed gas product.

In operating cases with lower GOXIV production, the amount of air used in the cold box is "artificially" increased, which means that more air is driven into the low-temperature part of the system than is necessary to obtain the pressurized oxygen products specified for this operating case. If the feed air is run in "excess", the pressure at the compressor outlet can be reduced, since the energy supply for the (pseudo) evaporation of the GOXIV product is then not with the air pressure, but with the amount of air. It is important that the air is not simply run in excess (compressed in the main air compressor, cooled in the heat exchanger, expanded in the turbine to the high pressure column pressure, warmed up again in the heat exchanger and finally throttled to atmospheric pressure), but it is further advantages are also achieved with the features described above.

As a result of this measure, sufficient air is still available for the extraction of other products. For example, sufficient cold can be generated to deliver a constant amount of liquid products.

In the invention, the first partial flow of the feed air compressed in the main air compressor is recompressed upstream of its introduction into the main heat exchanger in a first post-compressor which is operated in the warm state and is driven by the first turbine. As a result, the inlet pressure of the first turbine is significantly higher than the first pressure to which the total air is compressed. In contrast, the air for the second turbine, for example, is not post-compressed, i.e. its inlet pressure is at the lower level of the first pressure.

the second turbine, on the other hand, is not recompressed, for example, which means that its inlet pressure is at the lower level of the first pressure.

The invention also relates to a device according to claim 8. The device according to the invention can be supplemented by device features which correspond to the features of the dependent method claims.

The "means for switching between a first and a second operating mode" are complex regulating and control devices which, in cooperation, enable an at least partially automatic switching between the two operating modes, for example by means of an appropriately programmed operating control system.

Figur 1

ein Ausführungsbeispiel der Erfindung mit Rückführung von Turbinenluft zum Hauptluftverdichter in dem zweiten Betriebsmodus,

Figur 2

eine Verfahrensvariante, die nicht Teil der hier beanspruchten Erfindung ist, aber zur weiteren Erläuterung der Erfindung dient, mit Einführung von gasförmigem Stickstoff aus der Hochdrucksäule in einen Stickstoffproduktverdichter und

Figuren 3 und 4

Abwandlungen der Figur 1 mit einem dritten Drosselstrom.

The invention and further details of the invention are explained in more detail below on the basis of exemplary embodiments schematically illustrated in the drawings. Here show:

Figure 1

an embodiment of the invention with return of turbine air to the main air compressor in the second operating mode,

Figure 2

a process variant, which is not part of the invention claimed here, but serves to further explain the invention, with the introduction of gaseous nitrogen from the high pressure column in a nitrogen product compressor and

Figures 3 and 4

Variations of the Figure 1 with a third inductor current.

Based on Figure 1 The first operating mode of a first embodiment of the method according to the invention is first described. Atmospheric air (AIR) is drawn in by a main air compressor 2 via a filter 1. In the example, the main air compressor has five stages and compresses the total air flow to a "first pressure" of, for example, 22 bar. The total air flow 3 downstream of the main air compressor 2 is cooled under the first pressure in a pre-cooling 4. The pre-cooled total air flow 5 is cleaned in a cleaning device 6, which is formed in particular by a pair of switchable molecular sieve adsorbers. The cleaned total air flow 7 becomes a first part 8 in a hot air post-compressor 9 with after-cooler 10 to a second pressure of 28 bar, for example, and then divided into a "first partial flow" 11 (first turbine air flow) and a "second partial flow" 12 (first throttle flow).

The first partial flow 11 is cooled in a main heat exchanger 13 to a first intermediate temperature. The cooled first partial flow 14 is expanded in a first air turbine 15 from the second pressure to about 5.5 bar in a work-performing manner. The first air turbine 15 drives the warm air post-compressor 9. The first partial stream 16, which is relaxed in terms of work, is introduced into a separator (phase separator) 17. The liquid portion 18 is introduced via lines 19 and 20 into the low pressure column 22 of the distillation column system.

The distillation column system comprises a high-pressure column 21, the low-pressure column 22 and a main condenser 23 and a conventional argon recovery 24 with crude argon column 25 and pure argon column 26. The main condenser 23 is designed as a condenser-evaporator, in the specific example as a cascade evaporator. The operating pressure at the top of the high pressure column is 5.3 bar in the example, that at the top of the low pressure column is 1.35 bar.

The second partial flow 12 of the feed air is cooled in the main heat exchanger 13 to a second intermediate temperature, which is higher than the first intermediate temperature, is fed via line 27 to a cold compressor 28 and there is further compressed to a "third pressure" of approximately 40 bar. The post-compressed second partial flow 29 is introduced again into the main heat exchanger 13 at a third intermediate temperature, which is higher than the second intermediate temperature, and is cooled there to the cold end. The cold second partial stream 30 is expanded in a throttle valve 31 to approximately the operating pressure of the high-pressure column and fed to the high-pressure column 21 via line 32. A part 33 is removed again, cooled in a subcooling countercurrent 34 and fed via lines 35 and 20 into the low-pressure column 22.

A "third partial flow" 36 of the feed air is introduced under the first pressure into the main heat exchanger 13 and is cooled there to a fourth intermediate temperature, which in the example is somewhat lower than the first intermediate temperature. The cooled third partial flow 37 is expanded in a second air turbine 38 from the first pressure to approximately high-pressure column pressure while performing work. The second Air turbine 38 drives cold compressor 28. The third partial stream 39, which is relaxed in terms of work, is fed via line 40 to the high-pressure column 21 at the bottom.

A "fourth partial flow" 41 (second throttle flow) flows through the main heat exchanger 13 from the warm to the cold end under the first pressure. The cold fourth partial flow 42 is expanded in a throttle valve 43 to approximately the operating pressure of the high-pressure column and fed to the high-pressure column 21 via line 32.

The oxygen-enriched bottom liquid of the high-pressure column 21 is cooled in the subcooling countercurrent 34 and introduced into the optional argon recovery 24 via line 45. Vapor 46 generated therefrom and remaining liquid 47 are fed into the low-pressure column 22.

A first part 49 of the top nitrogen 48 of the high-pressure column 21 is completely or substantially completely liquefied in the liquefaction chamber of the main condenser 23 against liquid oxygen evaporating in the evaporation chamber from the sump of the low-pressure column. A first part 51 of the liquid nitrogen 50 produced in the process is fed as a return to the high-pressure column 21. A second part 52 is cooled in the subcooling countercurrent 34 and fed into the low-pressure column 22 via line 53. At least a part of the liquid low-pressure nitrogen 53 serves as a return in the low-pressure column 21; another part 54 can be obtained as a liquid nitrogen product (LIN).

Gaseous low-pressure nitrogen 55 is drawn off from the top of the low-pressure column 22 and heated in the supercooling countercurrent 34 and in the main heat exchanger 13. The warm low-pressure nitrogen 56 is compressed in a two-section nitrogen product compressor (57, 59) with intermediate and after-cooling (58, 60) to the desired product pressure, which in the example is 12 bar. The first section 57 of the nitrogen product compressor consists, for example, of two or three stages with associated aftercoolers; the second section 59 has at least one stage and is preferably also intercooled and postcooled.

Gaseous impure nitrogen 61 is drawn off from an intermediate point of the low-pressure column 22 and in the supercooling counterflow 34 and in the main heat exchanger 13 warmed up. The warm impure nitrogen 62 can be blown off (63) into the atmosphere (ATM) and / or used as regeneration gas 64 for the cleaning device 6.

The lines 67 and 68 (so-called argon transition) connect the low-pressure column 22 to the crude argon column 25 of the argon extraction 24.

A first portion 70 of the liquid oxygen 69 from the bottom of the low pressure column 22 is withdrawn as a "first product stream", brought to a "first product pressure" of, for example, 37 bar in an oxygen pump 71 and evaporated under the first product pressure in the main heat exchanger 13 and finally via line 72 as the "first pressurized gas product" (GOX IC - internally compressed gaseous oxygen).

A second part 73 of the liquid oxygen 69 from the bottom of the low-pressure column 22 is optionally cooled in the supercooling countercurrent 34 and obtained as a liquid oxygen product (LOX) via line 74.

In the example, a third part 75 of the liquid nitrogen 50 from the high-pressure column 21 or the main condenser 23 is also subjected to an internal compression by bringing it to a second product pressure of, for example, 37 bar in a nitrogen pump 76, under the second product pressure in the main heat exchanger 13 pseudo evaporated and finally obtained via line 77 as an internally compressed gaseous nitrogen pressure product (GAN IC).

A second part 78 of the gaseous top nitrogen 48 of the high-pressure column 21 is heated in the main heat exchanger and either obtained via line 79 as a gaseous medium-pressure product or - as shown - used as a sealing gas (seal gas) for one or more of the process pumps shown.

If one calls the "first operating mode" the operation with the maximum oxygen production (100% according to the design), the lines 65/66 shown in bold will remain inoperative in this operating mode.

A lower oxygen production (for example 75%) can then be regarded as a "second operating mode". Here, part of the gaseous portion 17 of the first partial stream 16 relaxed as a "second process stream" via the lines 65, 66 through the main heat exchanger to an intermediate stage of the main air compressor 2. In the example, the recycle stream is admixed to the feed air between the second and third stages or between the third and fourth stages of the main air compressor. (This feed air represents the "first process stream".) As a result, the amount of air through the turbine 15 can be kept relatively high and an unchanged - or at least a less reduced - amount of nitrogen and liquid products can be obtained.

A 95% mode of operation could just as well be regarded as the "first mode of operation". A "second operating mode" is then achieved, for example, with an oxygen production of 90% of the design value.

The following table shows exemplary numerical values of two different operating modes of the system Figure 1 on: GOX IC lot 72 Air flow through filter 1 Return quantity 65/66 * 100% 100% 0% 76% 83% 4.2%

The return quantity in the table relates to the current air quantity through filter 1. All percentages here and in the rest of the text refer to molar quantities, unless otherwise stated.

The flexibility of the process can be further increased by the optional measure described below. In the second operating mode, gaseous oxygen 181 is withdrawn from the low-pressure column and mixed with the gaseous impure nitrogen 61 from the low-pressure column. The mixing takes place downstream of the supercooling counterflow 34 in the example. In the first operating mode, line 181 is closed, or less gas is conducted via line 181.

In Figure 2 An embodiment of a second method variant is shown, which is not part of the invention claimed here. It differs from Figure 1 by the following features.

The return line 65, 66 for air is missing here. Instead, in the second operating mode, in addition to the amount of sealing gas 79, an additional part 180 of the gaseous top nitrogen 48 is led from the top of the high-pressure column as a "second process stream" 180 via lines 178, 179 and finally between the two sections 57, 59 of the nitrogen product compressor with the nitrogen 56 mixed from the low pressure column, which forms the "first process stream" in the variant.

The corresponding amount of nitrogen 180 from the high pressure column is not condensed in the main condenser 23 and is not introduced into the low pressure column. As a result, it does not take part in the rectification in the low-pressure column (neither indirectly via the evaporation of the bottoms oxygen, nor directly through use as a return liquid) and thereby enables the reduction in oxygen production. At the same time, the same amount of air (or only slightly less) is available for cold production and nitrogen generation.

In the first operating mode, a smaller amount of second process stream 180 is moved to the intermediate point of the nitrogen product compressor or line 180 is completely closed.

The flexibility of the process can be further increased by the optional measure described below. In the second operating mode, gaseous oxygen 181 is withdrawn from the low-pressure column and mixed with the gaseous impure nitrogen 61 from the low-pressure column. The mixing takes place downstream of the supercooling counterflow 34 in the example. In the first operating mode, line 181 is closed, or less gas is conducted via line 181.

The following table shows exemplary numerical values of two different operating modes of the system Figure 2 on: GOX IC lot 72 Air volume through main air compressor 2 Amount of nitrogen through line 180 Amount of oxygen through line 181 100% 100% 0% 0% 76% 83% 5% 0%

The amount of nitrogen through line 180 relates to the amount of air through filter 1 in the design case.

Figure 3 differs from Figure 1 through a third inductor current. For this purpose, the second turbine 38 is operated with a relatively high outlet pressure and a relatively high outlet temperature. Turbine flow 339, which has been relieved of work, then has a pressure which is at least 1 bar, in particular 4 to 11 bar, above the operating pressure of the high-pressure column, and a temperature which is at least 10 K, in particular 20 to 60 K, above the inlet temperature of low-pressure nitrogen flows 55 , 61 is at the cold end of the main heat exchanger. This stream is then further cooled in the cold part of the main heat exchanger. The further cooled third partial flow 340 is expanded as a third throttle flow in a throttle valve 341 to approximately high-pressure column pressure and introduced into the high-pressure column via line 32. This allows the heat exchange process in the main heat exchanger to be further optimized.

In Figure 4 is in deviation from Figure 3 the third partial flow 436 is introduced into the second turbine 38 not under the first pressure but under the higher second pressure.

The additional measures of Figures 3 and 4th can not only be used in the invention, but also in the variant according to Figure 2 .

Claims (8)

1. Method for the variable production of a compressed gas product (72; 77) by means of the low-temperature separation of air in a distillation column system having a high-pressure column (21) and a low-pressure column (22) and in which

   - the entire feed air is compressed in a main air compressor (2) to a first pressure, which is at least 4 bars higher than the operating pressure of the high-pressure column (21),

   - a first partial flow (8, 11, 14) of the feed air (7) compressed in the main air compressor (2) is cooled to an intermediate temperature in a main heat exchanger (13) and is expanded in a first air turbine (15) to perform work,

   - at least a first part of the first partial flow (16) expanded to perform work is introduced (40; 18, 19, 20) into the distillation column system,

   - a second partial flow (12, 27, 29, 30) of the feed air compressed in the main air compressor (2) is post-compressed in a first post-compressor (9), which is operated in warm mode and driven by the first turbine (15), to a second pressure that is higher than the first pressure, is cooled in the main heat exchanger (13) and then expanded (31), and is introduced into the distillation column system,

   - a first product flow (69; 75) is withdrawn in liquid form from the distillation column system and is subjected to a pressure increase (71; 76) to a first product pressure,

   - the first product flow is evaporated or pseudo-evaporated and heated under the first product pressure in the main heat exchanger (13),

   - the heated first product flow (72; 77) is produced as the first compressed gas product (GOX IC; GAN IC),

   - a first process flow containing at least 78 mol% nitrogen is compressed in a multi-stage compressor (2) from an inlet pressure to a final pressure, wherein

   - the multi-stage compressor is formed by the main air compressor (2), and

   - the first process flow is formed by the entire feed air,

   - at least temporarily, a second process flow (65) containing at least 78 mol% nitrogen is mixed, downstream of the first stage of the multi-stage compressor (2), with the first process flow, wherein the second process flow is formed by a part (65) of the first partial flow (16), expanded to perform work, of the feed air,

   - in a first operating mode, a first quantity of the first compressed gas product is produced,

   - in a second operating mode, a second quantity of the first compressed gas product, which is less than the first quantity, is produced,

   - in the first operating mode, a first quantity of the second process flow (65), which may also be zero, is compressed in the multi-stage compressor (2),

   - in the second operating mode, a second quantity of the second process flow (65), which is greater than the first quantity of the second process flow, is compressed in the multi-stage compressor (2),

   characterized in that

   - in the first operating mode, a first quantity of feed air is compressed in the main air compressor (2), and

   - in the second operating mode, a second quantity of feed air, which is less than the first quantity of feed air, is compressed in the main air compressor (2), wherein

   - the ratio of the second quantity of feed air to the first quantity of feed air is greater - in particular, more than 3% greater - than the ratio between the second quantity of the first compressed gas product and the first quantity of the first compressed gas product.
2. Method according to claim 1, characterized in that

   - a third process flow is compressed in a nitrogen product compressor from an inlet pressure to a final pressure, and

   - at least temporarily, a fourth process flow is mixed, downstream of the first stage of the nitrogen product compressor, with the third process flow, wherein

   - the third process flow is formed by a first gaseous nitrogen flow from the low-pressure column, and

   - the fourth process flow is formed by a first gaseous nitrogen flow from the high-pressure column.
3. Method according to one of claims 1 through 2, characterized in that, in the second operating mode, an oxygen gas flow (181) is withdrawn from the lower area of the low-pressure column (22) and is mixed with a nitrogen-enriched flow (61) from the upper area of the low-pressure column (22), and the mixture is heated in the main heat exchanger (13).
4. Method according to one of claims 1 through 3, characterized in that

   - a third partial flow (36, 37) of the feed air (7) compressed in the main air compressor (2) is cooled to an intermediate temperature in the main heat exchanger (13) and is expanded in a second air turbine (38) to perform work, and

   - at least a first part of the third partial flow (39) expanded to perform work is introduced (40) into the distillation column system,

   - wherein the turbine inlet pressure of the second air turbine is, in particular, equal to the first pressure.
5. Method according to claim 4, characterized in that

   - the second partial flow (12, 27, 29, 30) of the feed air (7) compressed in the main air compressor (2) is cooled downstream of the first post-compressor (9) to an intermediate temperature in the main heat exchanger (13), is post-compressed in a second post-compressor (28), which is operated as a cold compressor and is driven by the second turbine (38), to a third pressure that is higher than the first pressure, is cooled in the main heat exchanger (13), and then expanded (31) and introduced (32) into the distillation column system.
6. Method according to one of claims 1 through 5, characterized in that a fourth partial flow (41, 42) of the air (7) compressed in the main air compressor (2) is cooled under the first pressure in the main heat exchanger (13) and then expanded (43) and introduced into the distillation column system.
7. Method according to claim 4 or 5 or according to claim 6 relating back to one of claims 4 or 5, characterized in that

   - the third partial flow (37, 339) is expanded in the second air turbine (38) to a pressure that is at least 1 bar higher than the operating pressure of the high-pressure column (21), and

   - the third partial flow (339), which is expanded to perform work, is further cooled in the main heat exchanger (13) and then expanded (341) and introduced into the distillation column system.
8. Device for the variable production of a compressed gas product (72; 73) by means of the low-temperature separation of air, with

   - a distillation column system having a high-pressure column (21) and a low-pressure column (22),

   - a main air compressor (2) for compressing the entire feed air to a first pressure that is at least 4 bar higher than the operating pressure of the high-pressure column (21),

   - means for cooling in a main heat exchanger (13) a first partial flow (8, 11, 14) of the feed air (7), compressed in the main air compressor (2), to an intermediate temperature,

   - a first air turbine (15) for the expansion of the cooled first partial flow to perform work,

   - means for introducing (40; 18, 19, 20) the first partial flow (16) expanded to perform work into the distillation column system,

   - a first post-compressor (9) for post-compressing a second partial flow (12, 27, 29, 30) of the feed air, compressed in the main air compressor (2), to a second pressure that is higher than the first pressure, wherein the post-compressor (9) is operable in warm mode and is driven by the first turbine (15), - means for cooling the post-compressed, second partial flow in the main heat exchanger (13),

   - means for expanding (31) and introducing the cooled, second partial flow into the distillation column system,

   - means for the liquid withdrawal of a first product flow (69; 75) from the distillation column system and for increasing the pressure (71; 76) of the liquid first product flow to a first product pressure,

   - means for evaporating or pseudo-evaporating and heating the first product flow under the first product pressure in the main heat exchanger (13),

   - means for producing the heated first product flow (72; 77) as the first compressed gas product (GOX IC; GAN IC),

   - a multi-stage compressor (2) for compressing a first process flow containing at least 78 mol% nitrogen from an inlet pressure to a final pressure, wherein

   - the multi-stage compressor is formed by the main air compressor (2), and

   - the first process flow is formed by the entire feed air,

   - means for mixing, downstream of the first stage of the multi-stage compressor (2; 57/59), a second process flow (65), which contains at least 78 mol% nitrogen, with the first process flow, wherein the second process flow (180) is formed by a part (65) of the first partial flow (16), expanded to perform work, of the feed air,

   - means for switching between a first and a second operating mode, wherein

   - in the first operating mode, a first quantity of the first compressed gas product is produced,

   - in a second operating mode, a second quantity of the first compressed gas product, which is less than the first quantity, is produced, and

   - the means for switching between the first and the second operating modes are designed such that

   - in the first operating mode, a first quantity of the second process flow (65), which may also be zero, is compressed in the multi-stage compressor (2) from an inlet pressure to a final pressure,

   - in the second operating mode, a second quantity of the second process flow (65; 180), which is larger than the first quantity of the second process flow, is compressed in the multi-stage compressor (2; 57/59),

   characterized in that the means for switching between the first and the second operating modes are designed such that

   - in the first operating mode, a first quantity of feed air is compressed in the main air compressor (2), and

   - in the second operating mode, a second quantity of feed air, which is less than the first quantity of feed air, is compressed in the main air compressor (2), wherein

   - the ratio of the second quantity of feed air to the first quantity of feed air is greater - in particular, more than 3% greater - than the ratio between the second quantity of the first compressed gas product and the first quantity of the first compressed gas product.

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