EP2963367A1 - Method and device for cryogenic air separation with variable power consumption - Google Patents

Abstract

The method and apparatus are for variable recovery of a compressed gas product (72; 73) by cryogenic separation of air in a distillation column system having a high pressure column (21) and a low pressure column (22). The total feed air is compressed in a main air compressor (2) to a first pressure which is at least 4 bar 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 expanded in a first air turbine (15) to perform work in the distillation column system ( 40, 18, 19, 20). A second partial flow (12, 27, 29, 30) of the feed air compressed in the main air compressor (2) is recompressed in a first after-compressor (9), cooled in the main heat exchanger (13) and then expanded (31) and introduced into the distillation column system , A first product stream (69; 75) is withdrawn liquid from the distillation column system, subjected to a pressure increase (71; 76) to a first product pressure, evaporated in the main heat exchanger (13) or pseudo-vaporized and warmed and used as the first compressed gas product (GOX IC; GAN IC) won. A first process stream is compressed in a multi-stage compressor (2; 57/59) from an inlet pressure to a final pressure. At least temporarily, a second process stream (65; 180) downstream of the first stage of the multi-stage compressor (2; 57/59) is mixed with the first process stream. In a first mode of operation, a first quantity of first compressed gas product is obtained and in a second mode of operation a second, smaller quantity. In the first mode of operation, a first amount of the second process stream (65; 180), which may also be zero, is compressed in the multi-stage compressor (2; 57/59), in the second mode of operation a second, larger amount.

Description

The invention relates to a method and apparatus for variable recovery of a compressed gas product by cryogenic separation of air.

Methods and devices for the cryogenic separation of air are, for example, Hausen / Linde, Cryogenics, 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. It may in addition to the columns for nitrogen-oxygen separation, further devices for obtaining highly pure products and / or other air components, in particular of noble gases have, for example, an argon production and / or a krypton-xenon recovery.

In the process, as part of an "internal compression", a product stream brought to liquid pressure is vaporized against a heat carrier and finally recovered as an internally compressed compressed gas product. This method is also called internal compression. It serves to obtain gaseous printed product. In the case of a supercritical pressure, no phase transition takes place in the true sense, the product stream is then "pseudo-evaporated". The product stream may 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 space of a main condenser via which the high-pressure column and low-pressure column are in heat-exchanging connection

Against the (pseudo) evaporating product stream, a high-pressure heat carrier is liquefied (or pseudo-liquefied when it is under supercritical pressure). The heat transfer medium is frequently replaced by a part of Air formed, in the present case of the "second partial flow" of the compressed feed air.

Internal compression methods are known, for example DE 830805 . DE 901542 (= US 2712738 / US 2784572 ) DE 952908 . DE 1103363 (= US 3,083,544 ) 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 3,416,323 ) DE 1501723 (= US 3,500,651 ) 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 6,189,960 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 , A1, EP 2015012 A2 . EP 2015013 A2 . EP 2026024 A1 . WO 2009095188 A2 or DE 102008016355 A1 ,

More particularly, the invention relates to systems in which all of the feed air is at a pressure well above the highest distillation pressure prevailing inside the columns of the distillation column system (normally, this compresses the high pressure column pressure.) Such systems are also referred to as HAP processes In this case, the "first pressure", ie the outlet pressure of the main air compressor (MAC), in which the total air is compressed, is for example more than 4 bar, in particular 6 to 16 bar above that Absolutely, the "first pressure" is, for example, between 17 and 25 bar. In HAP processes, the main air compressor is regularly the only external-energy-driven machine for compressing air. A "single machine" is understood here to mean a single-stage or multistage compressor whose stages are all connected to the same drive, all stages being accommodated in the same housing or connected to the same gear.

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 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 an external energy driven air booster (BAC). This higher pressure air component (often called the choke flow) provides the majority of the heat required for (pseudo) evaporation of the internally compressed product in the main heat exchanger. It is depressurised downstream of the main air compressor in a throttle valve or in a liquid turbine (DLE) to the pressure required in the distillation column system.

In many cases, a fluctuating demand for internally compressed product forces an air separation plant to be designed for variable operation with variable compressed gas production. Conversely, it may be useful to operate an air separation plant variable despite constant or substantially constant production by different modes of operation are provided, 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 constraint is the delivery of internally compressed oxygen (GOXIV) and optionally other gaseous and / or liquid products to an ethylene oxide production plant. Here it is often the case that the oxygen demand is adapted to the catalyst state in EO production; it can therefore be varied between 100% and about 70% during the catalyst life (usually around 3 years). It is essential that during this time the air separation plant is operated for about the same times with different GOXIV product quantities (between 100% and about 70%). Therefore, it is important that the system is operated efficiently not only in the design case with 100% GOXIV, but also in under load cases. This requirement is made even more difficult by the fact that the production of other air separation products regardless of the GOXIV product; for example, the demand for one, several or all other air separation products may remain unchanged while GOX production decreases from 100% to about 70%. Such "other air separation products" may be, for example, one, several or all of the following products:

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

With a conventional MAC-BAC method, this task is relatively easy to accomplish since both compressors (MAC and BAC) are responsible for functionally separate tasks. The main air compressor provides in principle only the feed air for the decomposition; the air compressor delivers energy for internal compression (GOXIV, GANIV) and for liquid production. Both machines can 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 darf.

In a HAP process, these two tasks (delivery of decomposition air and energy for internal compression / liquid production) are accomplished with a single compressor. This can lead to situations that certain operating cases are outside the compressor map and are not mobile. The total energy demand of an air separation plant is determined not only by the GOXIV product, but to a large extent by liquid production or other internally compressed products. However, the GOXIV product is often decisive for the amount of decomposition air. If the amount of GOXIV is significantly reduced, significantly less decomposition air is also fed into the system. However, significantly less energy is entered into the system, which under certain circumstances may no longer be sufficient for the desired production of other products (liquids, GANIV, etc.). In order to provide enough energy despite the significantly lower air volume, the compressor pressure must be increased significantly. However, this is only partially feasible with a HAP method because

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

The invention has for its object to provide a method and a corresponding device, which combine the advantages of HAP method with a flexibility, as is similar in MAC-BAC method known. "Flexibility" is understood here in particular that the system can be operated not only energetically favorable at a certain production amount of internally compressed product, but in a relatively wide load range at 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 compaction product.

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

In the invention, in the second mode of operation, a portion of the feed air amount or a nitrogen-enriched process stream ("second process stream") bypasses the low pressure column or the entire distillation column system, respectively. This amount then does not participate in the production of the first product stream, but can still be passed through the first turbine, so as to produce enough cold or to supply enough energy into the system to maintain liquid production, or at least relatively less as 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.In a first variant of the invention, a portion of the feed air is not introduced into the distillation column system, but returned to the main air compressor by

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

be formed.

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

• der mehrstufige Verdichter durch einen Stickstoffproduktverdichter,
• der erste Prozessstrom durch einen ersten gasförmigen Stickstoffstrom aus der Niederdrucksäule und
• der zweite Prozessstrom durch ersten gasförmigen Stickstoffstrom aus der Hochdrucksäule

gebildet werden.In a second variant of the invention, a portion of the nitrogen obtained in the high-pressure column is not introduced into the low-pressure column, but fed to a nitrogen product compressor by

• the multi-stage compressor through a nitrogen product compressor,
• the first process stream through a first gaseous nitrogen stream from the low pressure column and
• the second process stream through first gaseous nitrogen stream from the high pressure column

be formed.

If a low-pressure GAN compressor is provided as a nitrogen product compressor in the process, for example because of large amounts of nitrogen product, this can be relieved by interim feeding of pressure GAN from the high-pressure column. Unlike in the design case, in the case of lower GOXIV production significantly more air is driven into the rectification system and taken as pressure GAN from the pressure column, as for the oxygen production is necessary. After warming in the heat exchanger, this pressure GAN is fed into the nitrogen product compressor at an appropriate point (for example after the second or third compressor stage). As a result, the proportion of low-pressure GAN (the amount of gas to be compressed from approximately atmospheric pressure to approximately 5 bar) can be correspondingly reduced. Thus, for example (other than in the design case with 100% GOXIV) in operation with about 75% GOXIV, full liquid production and 100% HPGAN product quantity - about 70-75% low pressure GAN and about 25-30% Pressure GAN compressed from the pressure column (see Figure 2 ) . This partially recovers the energy absorbed by the excess air volume at the main air compressor.
Another possibility (with no low-pressure GAN compressor) is to direct and separate the excess air into the distillation column system. In this case, the argon present in this amount of air can be obtained. The Excess oxygen amount can be taken as low pressure oxygen from the low pressure column and fed to the UN2 stream. Here, in principle, only the separation work for the extraction of additional oxygen molecules is lost, but at the same time significantly more argon is produced.

However, the two variants of the invention can also be combined, as described in claim 4.

In principle, the second process stream can also be mixed with the first process stream at the inlet of a nitrogen product compressor. In many cases, however, it is favorable if the mixing of the second with the first process stream or the fourth with the second process stream is carried out at an intermediate stage of the multistage compressor or the nitrogen product compressor.

Additionally, in the second mode of operation, an oxygen gas stream may be withdrawn from the lower region of the low pressure column, mixed with a nitrogen-enriched stream from the top of the low pressure column, and the mixture heated in the main heat exchanger.

In addition, in a specific embodiment of the invention, a second air turbine can be used, wherein a third part of the stream compressed in the main air compressor feed air is cooled to an intermediate temperature in a main heat exchanger and expanded work in the second air turbine and at least a first part of the working expanded third partial flow in the Distillation column system is initiated.

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

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

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

• 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 the method according to the invention, in particular during the transition from the first to the second operating mode, the total air quantity compressed in the main air compressor is not reduced at all or is reduced less than the pressure oxygen product quantity by

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

In operating cases with lower GOXIV production, the amount of feed air in the cold box is "artificially" raised, that is, more air is driven into the cryogenic part of the system than is necessary to obtain the specified for this operating case pressure oxygen products. If one moves the feed air in the "excess", the pressure at the compressor outlet can be reduced, since the energy supply for the (Pseudo-) evaporation of the GOXIV product is then done not with the air pressure, but with the amount of air. It is of importance that the air is not simply driven in excess (compressed in the main air compressor, cooled in the heat exchanger, expanded in the turbine to the high-pressure column pressure, reheated in the heat exchanger and finally throttled to atmospheric pressure), but instead Other 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 may be generated to provide a consistent amount of liquid products.

Preferably, 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 after-compressor which is operated warm and in particular 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. For example, the air for the second turbine is not recompressed, that is, its inlet pressure is at the lower level of the first pressure.

The invention also relates to a device according to claim 13. 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 mode of operation" are complex control devices which, in conjunction, enable at least partial automatic switching between the two modes of operation, for example by means of a suitably programmed operational control system.

Figur 1

ein Ausführungsbeispiel für die erste Variante der Erfindung mit Rückführung von Turbinenluft zum Hauptluftverdichter in dem zweiten Betriebsmodus,

Figur 2

ein Ausführungsbeispiel für die zweite Variante der Erfindung mit Einführung von gasförmigem Stickstoff aus der Hochdrucksäule in einen Stickstoffproduktverdichter und

Figuren 3 und 4

Abwandlungen der Figur 1 und 2 mit einem dritten Drosselstrom.

The invention and further details of the invention are explained below with reference to embodiments schematically illustrated in the drawings. Hereby show:

FIG. 1

An embodiment of the first variant of the invention with feedback of turbine air to the main air compressor in the second operating mode,

FIG. 2

an embodiment of the second variant of the invention with introduction of gaseous nitrogen from the high pressure column in a nitrogen product compressor and

FIGS. 3 and 4

Modifications of the FIG. 1 and 2 with a third inductor current.

Based on FIG. 1 First, the first operating mode of an embodiment of the method according to the first variant of the invention will be described. Atmospheric air (AIR) is drawn in via a filter 1 from a main air compressor 2. The main air compressor has five stages in the example 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 purified in a cleaning device 6, which is formed in particular by a pair of switchable molecular sieve adsorber. The purified total air flow 7 is recompressed to a first part 8 in a hot air compressor 9 with aftercooler 10 to a second pressure of, for example, 28 bar and then into a "first partial flow" 11 (first turbine air flow) and a "second partial flow" 12 (FIG. first inductor current) divided.

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 to perform work. The first air turbine 15 drives the warm air compressor 9. The work-performing relaxed first partial flow 16 is introduced in 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 production 24 with crude argon column 25 and pure argon column 26. The main condenser 23 is designed as a condenser-evaporator, in the concrete Example as a cascade evaporator. The operating pressure at the top of the high pressure column is in the example 5.3 bar, the one at the top of the low pressure column 1.35 bar.

The second partial stream 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, fed via line 27 to a cold compressor 28 and there recompressed to a "third pressure" of about 40 bar. The recompressed second partial stream 29 is at a third intermediate temperature, which is higher than the second intermediate temperature, again introduced into the main heat exchanger 13 and 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 via line 32 to the high-pressure column 21. A part 33 is removed again, cooled in a supercooling countercurrent 34 and fed via the lines 35 and 20 in the low-pressure column 22.

A "third substream" 36 of the feed air is introduced under the first pressure in the main heat exchanger 13 and cooled there to a fourth intermediate temperature, which is slightly lower than the first intermediate temperature in the example. The cooled third partial flow 37 is expanded in a second air turbine 37 from the first pressure to about high-pressure column pressure to perform work. The second air turbine 38 drives the cold compressor 28. The working expanded third partial stream 39 is supplied via line 40 of 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 hot to the cold end under the first pressure. The cold fourth partial stream 42 is expanded in a throttle valve 43 to approximately the operating pressure of the high-pressure column and fed via line 32 to the high-pressure column 21.

The oxygen-enriched bottom liquid of the high pressure column 21 is cooled in the subcooling countercurrent 34 and introduced via line 45 into the optional argon recovery 24. Resulting vapor 46 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 in the liquefaction space of the main condenser 23 against evaporating in the evaporation space liquid oxygen from the bottom of the low pressure column completely or substantially completely liquefied. A first part 51 of the liquid nitrogen 51 produced in this process is introduced as reflux to the high-pressure column 21. A second part 52 is cooled in the subcooling countercurrent 34, fed via line 53 into the low pressure column 22. At least a portion of the liquid low pressure nitrogen 53 serves as reflux in the low pressure column 21; another part 54 can be obtained as liquid nitrogen product (LIN).

From the top of the low-pressure column 22 gaseous low-pressure nitrogen 55 is withdrawn, warmed 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 step and is preferably also intermediate and post-cooled.

From an intermediate point low pressure column 22 gaseous impurity nitrogen 55 is withdrawn, warmed in the subcooling countercurrent 34 and the main heat exchanger 13. The warm impure nitrogen 62 may be vented (63) into the atmosphere (ATM) and / or used as the regeneration gas 64 for the purifier 6.

The lines 67 and 68 (so-called argon transition) connect the low-pressure column 21 with the crude argon column 25 of argon recovery 24th

A first portion 70 of the liquid oxygen 69 from the bottom of the low-pressure column 21 is withdrawn as the "first product stream", brought to a "first product pressure" of, for example, 37 bar in an oxygen pump 71 and vaporized under the first product pressure in the main heat exchanger 13 and finally via line 72 as "first compressed gas product" (GOX IC - compressed gas internal oxygen) won.

A second portion 73 of the liquid oxygen 69 from the bottom of the low-pressure column 21 is optionally cooled in the subcooling countercurrent 34 and recovered via line 74 as a liquid oxygen product (LOX).

In the example, a third part 75 of the liquid nitrogen 50 from the high-pressure column 21 and the main condenser 23 is also subjected to internal compression by being brought in a nitrogen pump 76 to a second product pressure of 37 bar, for example, under the second product pressure in the main heat exchanger 13 pseudo and finally recovered via line 77 as 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 warmed in the main heat exchanger and recovered via line 79 either as a gaseous medium pressure product or - as shown - used as a sealing gas (seal gas) for one or more of the illustrated process pumps.

In this mode of operation, if the operation with the maximum oxygen production (100% according to the design) is designated as the "first operating mode", the lines 65/66 shown in bold remain out of operation.

A lower oxygen production (for example 75%) may then be considered a "second mode of operation". Here, part of the gaseous portion 17 of the work-performing expanded first partial flow 16 is returned as "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 recirculation flow between the second and the third stage and between the third and fourth stage of the main air compressor is added to the feed air. (This feed air is in the first variant of the invention, the "first process stream".) This allows the amount of air to be kept relatively high by the turbine 15 and an unchanged - or at least a less greatly reduced - amount of nitrogen and liquid products can be obtained.

Equally well, a 95% operation could be considered a "first mode of operation". A "second mode of operation" is then achieved, for example, with an oxygen production of 90% of the design value.

The following table shows example numerical values of two different operating modes of the system FIG. 1 at: GOX IC amount 72 Air volume through filter 1 Return quantity 65/66 * 100% 100% 0% 76% 83% 4.2%

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

In FIG. 2 an embodiment of the second variant of the invention is shown. It is different from FIG. 1 by the following features.

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

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

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

The flexibility of the method can be further increased by the optional measure described below (which basically also applies to the first variant) FIG. 1 can be used). In this case, in the second operating mode gaseous oxygen 181 is withdrawn from the low pressure column and with the gaseous impurity nitrogen 61 mixed from the low pressure column. The mixing takes place in the example downstream of the subcooling countercurrent 34. In the first operating mode, the conduit 181 is closed or less gas is supplied via conduit 181.

The following table shows example numerical values of two different operating modes of the system FIG. 2 at: GOX IC amount 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 refers to the amount of air through filter 1 in the design case.

FIG. 3 differs from FIG. 1 through a third inductor current. For this purpose, the second turbine 38 is operated with a relatively large outlet pressure and a relatively high outlet temperature. The work-expanded turbine stream 339 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 the low-pressure nitrogen streams 55 , 61 is located 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 about high-pressure column pressure and introduced via line 32 into the high-pressure column. As a result, the heat exchange process in the main heat exchanger can be further optimized.

In FIG. 4 will deviate from FIG. 3 the third partial flow 436 is not introduced into the second turbine 38 under the first pressure but under the higher second pressure.

The additional measures of Figures 3 and 4 can be used not only in the first variant of the invention, but also in the second variant.

Claims (13)

A method of variably recovering a compressed gas product (72; 73) by cryogenic separation of air in a distillation column system having a high pressure column (21) and a low pressure column (22), wherein - the total feed air in a main air compressor (2) is compressed to a first pressure which is at least 4 bar 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 expanded in a first air turbine (15) to perform work, at least a first part of the work-performing expanded first partial flow (16) is introduced into the distillation column system (40, 18, 19, 20), - A second partial stream (12, 27, 29, 30) of the main air compressor (2) compressed feed air in a first booster (9), which is in particular from the first turbine (15) is driven to a second pressure is recompressed, the higher is cooled as the first pressure, cooled in the main heat exchanger (13) and then expanded (31) and introduced into the distillation column system, a first product stream (69; 75) is removed from the distillation column system in liquid form and subjected to a pressure increase (71; 76) to a first product pressure, the first product stream is vaporized or pseudo-evaporated and heated under the first product pressure in the main heat exchanger (13), the warmed first product stream (72; 77) is obtained as the first compressed gas product (GOX IC; GAN IC), a first process stream containing at least 78 mol% nitrogen is compressed in a multistage compressor (2; 57/59) from an inlet pressure to a final pressure, at least temporarily mixing a second process stream (65; 180) containing at least 78 mol% of nitrogen downstream of the first stage of the multistage compressor (2; 57/59) with the first process stream, - In a first mode of operation, a first amount of first compressed gas product is obtained and in a second operating mode, a second quantity of first compressed gas product is obtained which is less than the first quantity,
characterized in that - In the first mode of operation of a first amount of the second process stream (65; 180), which may also be zero, is compressed in the multi-stage compressor (2; 57/59) and in the second mode of operation, compressing a second amount of the second process stream (65; 180) in the multi-stage compressor (2; 57/59) that is greater than the first amount of the second process stream. Method according to claim 1, characterized in that the multi-stage compressor through the main air compressor (2), - the first process flow through the entire feed air and - The second process flow through a part (65) of the working expanded first partial flow (16) of the feed air
be formed. Method according to claim 1, characterized in that the multi-stage compressor through a nitrogen product compressor (57/59), - The first process flow through a first gaseous nitrogen stream (55, 56) from the low pressure column and - the second process stream (180) by first gaseous nitrogen stream (178, 179) from the high-pressure column (21)
be formed. A method according to claim 2, characterized in that a third process stream in a nitrogen product compressor is compressed from an inlet pressure to a final pressure, - At least temporarily, 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 the first gaseous nitrogen stream from the high pressure column
be formed. Method according to one of claims 1 to 4, characterized in that the second process stream or the fourth process stream is mixed at an intermediate stage of the multi-stage compressor or the nitrogen product compressor with the first process stream or with the second process stream. Method according to one of claims 1 to 5, characterized in that in the second operating mode, an oxygen gas stream (181) taken from the lower region of the low pressure column (22), mixed with a nitrogen-enriched stream (61) from the upper region of the low pressure column (22) and the mixture in the main heat exchanger (13) is warmed. Method according to one of claims 1 to 6, characterized in that - A third partial stream (36, 37) of the compressed air in the main compressor (2) compressed air (7) in the main heat exchanger (13) to an intermediate temperature and in a second air turbine (38) is designed to perform work and at least a first part of the work-performing expanded third substream (39) is introduced into the distillation column system (40), - The turbine inlet pressure of the second air turbine is in particular equal to the first pressure. Method according to one of the claims 7, characterized in that the second partial flow (12, 27, 29, 30) of the feed air (7) compressed in the main air compressor (2) downstream of the first after-compressor (9) in the main heat exchanger (13) is cooled to an intermediate temperature, in a second after-compressor (28), operated as a cold compressor and driven by the second turbine (38) is recompressed to a third pressure which is higher than the first pressure, cooled in the main heat exchanger (13) and then expanded (31) and introduced into the distillation column system (32) becomes. Method according to one of claims 1 to 8, characterized in that a fourth partial flow (41, 42) of the compressed air in the main air compressor (2) compressed air (7) under the first pressure in the main heat exchanger (13) and then relaxed (43) and is introduced into the distillation column system. Method according to Claim 7 or 8 or according to Claim 9 relating to one of Claims 7 or 8, characterized in that - The third partial flow (37, 339) is relaxed in the second air turbine (38) to a pressure which is at least 1 bar higher than the operating pressure of the high-pressure column (21), and - The work-performing relaxed third part stream (339) in the main heat exchanger (13) further cooled and then relaxed (341) and introduced into the distillation column system. Method according to one of claims 1 to 9, characterized in that - In the first mode of operation, a first amount of feed air in the main air compressor (2) is compressed and - In the second mode of operation, a second amount of feed air in the main air compressor (2) is compressed, wherein - The ratio of the second amount of feed air to the first amount of feed air greater, in particular by more than 3% greater than the ratio between the second amount of first compressed gas product and the first amount of first compressed gas product. Method according to one of claims 1 to 11, characterized in that the first part stream (8, 11) of the main air compressor (2) compressed feed air (7) upstream of its introduction into the main heat exchanger (13) is recompressed in a first after-compressor (9) , which is operated in the warm and in particular driven by the first turbine. Apparatus for variable recovery of a compressed gas product (72, 73) by means of cryogenic separation of air with a distillation column system comprising a high pressure column (21) and a low pressure column (22), - A main air compressor (2) for compressing the total feed air to a first pressure which is at least 4 bar higher than the operating pressure of the high-pressure column (21), Means for cooling a first partial flow (8, 11, 14) of the feed air (7) compressed in the main air compressor (2) in a main heat exchanger (13) to an intermediate temperature, - A first air turbine (15) for work-relaxing of the cooled first partial flow, - means for introducing (40; 18, 19, 20) the work-performing expanded first partial flow (16) into the distillation column system, - A first secondary compressor (9) for recompressing a second partial flow (12, 27, 29, 30) of the compressed air in the main compressor (2) compressed feed air to a second pressure, which is higher than the first pressure, wherein the after-compressor (9) in particular is driven by the first turbine (15) is recompressed, Cooling means for cooling the post-compressed second substream in the main heat exchanger (13), - means for expansion (31) and introduction into the distillation column system of the cooled second substream, - means for liquid removal of a first product stream (69; 75) taken from the distillation column system and for pressure increase (71; 76) of the liquid first product stream to a first product pressure, Means for vaporizing or pseudo-evaporating and heating the first product stream below the first product pressure in the main heat exchanger (13), Means for obtaining the warmed first product stream (72, 77) as the first compressed gas product (GOX IC, GAN IC), a multi-stage compressor (2; 57/59) for compressing a first process stream containing at least 78 mol% of nitrogen from an inlet pressure to a final pressure, - means for mixing a second process stream (65; 180) containing at least 78 mol% nitrogen with the first process stream downstream of the first stage of the multi-stage compressor (2; 57/59), - And with means for switching between a first and a second operating mode, wherein - In the first mode of operation, a first amount of first compressed gas product is obtained and in a second operating mode, a second quantity of first compressed gas product is obtained which is less than the first quantity,
characterized in that the means for switching between the first and second modes of operation are arranged such that in the first mode of operation, a first amount of the second process stream (65; 180), which may also be zero, is compressed in the multi-stage compressor (2; 57/59) from an inlet pressure to a final pressure in the second mode of operation, compressing a second amount of the second process stream (65; 180) in the multi-stage compressor (2; 57/59) that is greater than the first amount of the second process stream.

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