EP3290843A2 - Method and device for extracting pressurised nitrogen and pressurised nitrogen by cryogenic decomposition of air - Google Patents

Abstract

The method and apparatus are for producing pressurized nitrogen and liquid nitrogen by cryogenic separation of air in a distillation column system comprising a high pressure column (9) and a low pressure column (10) and a main condenser (11) and a low pressure column top condenser (12), both are formed as a condenser-evaporator. Air (AIR) is compressed in a main air compressor (2), cleaned (6), cooled in a main heat exchanger (8) and introduced into the high-pressure column (9) (8). A first portion (44) of the gaseous overhead nitrogen of the low pressure column (10) is withdrawn as the first pressurized nitrogen product (18, 19, PGAN). A second part (45) of the gaseous top nitrogen of the low-pressure column (10) is at least partially liquefied in the liquefaction space of the low-pressure column top condenser (12). The vapor generated in the evaporation chamber of the low-pressure column top condenser (12) is withdrawn as residual gas stream (26) and expanded in a first expansion machine (28) to perform work. A second pressure nitrogen stream (17) from the head of the high-pressure column (9) is expanded in a second expansion machine (41) to perform work and then withdrawn as a second pressure nitrogen product (43, 19, PGAN). A portion (47) of the nitrogen (46) liquefied in the low-pressure column top condenser (12) is withdrawn as liquid nitrogen product (PLIN).

Description

The invention relates to a process for the production of pressurized nitrogen and liquid nitrogen by cryogenic separation of air according to the preamble of patent claim 1.

The production of air products in the liquid or gaseous state by cryogenic separation of air in air separation plants is known. Such air separation plants have distillation column systems which can be designed, for example, as two-column systems, in particular as classic Linde double-column systems, but also as three-column or multi-column systems. Furthermore, devices for obtaining further air components, in particular the noble gases krypton, xenon and / or argon, may be provided (cf., for example FG Kerry, Industrial Gas Handbook: Gas Separation and Purification, Boca Raton: CRC Press, 2006; Chapter 3: Air Separation Technology ). The distillation column system of the invention may be designed as a classical double column system, but also as a three or more column system. In addition to the nitrogen-oxygen separation columns, there may be other means for obtaining other air components, for example, to obtain impure, pure or high purity oxygen or noble gases.

A "main heat exchanger" serves to cool feed air in indirect heat exchange with recycle streams from the distillation column system. It may be formed from a single or a plurality of parallel and / or serially connected and functionally connected heat exchanger sections, for example one or more plate heat exchanger blocks.

The term "condenser-evaporator" refers to a heat exchanger in which a first condensing fluid stream undergoes indirect heat exchange with a second evaporating fluid stream. Each condenser-evaporator has a liquefaction space and an evaporation space, which consist of liquefaction passages or evaporation passages. By doing Liquefaction space, the condensation (liquefaction) of the first fluid flow is performed, in the evaporation space, the evaporation of the second fluid stream. Evaporation and liquefaction space are formed by groups of passages that are in heat exchange relationship with each other. The evaporation space of a condenser-evaporator can be designed as a bath evaporator, falling-film evaporator or forced-flow evaporator.

A "relaxation machine" can have any design. Turbines (turboexpanders) are preferably used here.

Conventional double column methods have only a single condenser-evaporator, the main condenser, and are operated at relatively low pressure, namely just above atmospheric pressure at the top of the low-pressure column. When large quantities of pressurized nitrogen are to be recovered, a modified double column process is used which operates under higher pressure. This makes it possible to use a low-pressure column overhead condenser and to cool it with an oxygen-rich residual fraction from the distillation column system. Such a procedure is over US 4453957 known.

So far, such processes have not been considered for significant liquid production of more than 5 mol% of the nitrogen product amount.

The invention has for its object to provide a method of the type mentioned above and a corresponding device for a relatively high liquid production of 6 to 10 mol% of the nitrogen product amount or more with a relatively high nitrogen product yield in the process of approx. 60% are suitable and moreover efficient to operate. (The nitrogen yield depends on other parameters, for example product purity.)

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

Here, a second pressure nitrogen stream is withdrawn from the top of the high pressure column and expanded in a second expansion machine to a pressure that still allows the withdrawal of this stream as a printed product, preferably at about the pressure of the first pressure nitrogen stream from the head of the low pressure column. In addition, a part of the liquefied in the low-pressure column overhead condenser nitrogen withdrawn as liquid nitrogen product.

In this way, the cold required for higher liquid production can be efficiently produced with minimal additional effort. The second turbine with a different inlet temperature from the first turbine also improves the temperature profile in the main heat exchanger (lower thermodynamic losses due to lower temperature differences).

In the invention, preferably more than 90 mol% of the gaseous nitrogen product is recovered under the same pressure, namely that of the low pressure column.

There are known applications in which in addition to large amounts of pressurized nitrogen below about 8 bar and relatively much liquid product (LIN) is needed. These applications include, for example, petrochemical complexes or onsite gas supply gas sites for semiconductor industry customers. The liquid product is used either to cover demand peaks (especially in the case of petrochemical plants they are very large) and / or to operate the external liquid market. (The above print information is - as all the following, unless otherwise stated - to be understood as absolute pressure.)

These tasks have hitherto been accomplished, for example, by the use of "Spectra" methods (see e.g. US 4966002 or US 5582034 ) in combination with an external and intermittently operated condenser. Alternatively, only Spectra systems are used, whereby the liquid production is done temporarily at the expense of greatly reduced gas supply. In the first case, practically two systems are required, which entails particularly high investment costs. In the second case, although only one plant is used, it has very limited ability to produce liquid; especially in 8 bar versions, liquid production is not only limited, but also inefficient due to a relatively small pressure drop across the turbine; it usually can not cover the desired fluid requirement. In addition, the Spectra process has a relatively low efficiency over the two-pill method used in the invention.

The process according to the invention can be operated particularly favorably if the first pressure nitrogen stream is withdrawn from the top of the low-pressure column under a pressure of 8.0 to 9.0 bar, in particular 8.4 to 9.0 bar.

Preferably, the second pressure nitrogen stream is expanded in the expansion machine to about the pressure of the first pressure nitrogen stream; Subsequently, the two pressure nitrogen streams are combined and withdrawn as a common pressure nitrogen product stream. The merge is most easily done within the main heat exchanger; In principle, however, it can also be carried out in the warm, ie downstream of the main heat exchanger.

The two inlet temperatures of the expansion machines are preferably different, in particular the second intermediate temperature is at least 10 K higher than the first intermediate temperature. For example, the temperature difference is 90 to 30 K, preferably 70 to 50 K.

In a first variant of the invention, both expansion machines are coupled to a generator or a dissipative brake. Preferably, generator turbines are used. Although no energy is returned directly to the process here. This variant is particularly flexible with regard to different load cases.

Less flexible, but cheaper is a second variant of the method according to the invention. The two expansion machines each drive a compressor stage, and a process stream is compressed successively in the two compressor stages. Alternatively, only one of the two turbines, for example the pressurized nitrogen turbine ("second expansion machine"), may be coupled to a compressor stage and the other one (eg the residual gas turbine ("first expansion machine") to a generator.

• Mindestens einen Teil der gereinigten Einsatzluft, der dann stromabwärts der beiden Verdichterstufen in den Hauptwärmetauscher eingeleitet wird.
• Mindestens einen Teil des ersten und/oder zweiten Druckstickstoffproduktstroms, der dann stromabwärts der beiden Verdichterstufen als Druckstickstoffprodukt abgezogen wird.

This process stream can be formed, for example, by one of the following streams:

• At least a portion of the purified feed air, which is then introduced downstream of the two compressor stages in the main heat exchanger.
• At least a portion of the first and / or second pressurized nitrogen product stream, which is then withdrawn downstream of the two compressor stages as a pressurized nitrogen product.

In principle, the two condenser-evaporator can be designed as a classic bath evaporator.

Preferably, however, low-pressure column top condenser is designed on its evaporation side as a forced-flow evaporator. This results in no hydrostatic pressure loss on the evaporation side and also a comparatively low pressure on the liquefaction side.

Alternatively or additionally, the main condenser is formed on its evaporation side as a forced-flow evaporator. This results in comparison with a bath evaporator, a lower hydrostatic pressure loss on the evaporation side and also a comparatively low pressure on the liquefaction side.

In another embodiment of the invention, in the first mode of operation, at least a portion of the liquefied nitrogen is vaporized under pressure and subsequently recovered as a pressurized nitrogen product. The corresponding evaporation device is operated with external heat, that is, the heat source is in particular no process stream of the cryogenic separation. In the second mode of operation, no liquefied nitrogen or only a lesser amount than in the first mode of operation (eg, less than 50%) is vaporized in the evaporator. The evaporation device has, in particular, an air-heated evaporator, a water bath evaporator and / or a solid-state cold storage.

The invention also relates to a device for generating pressurized nitrogen and liquid nitrogen by cryogenic separation of air according to claim 14. The device according to the invention can be supplemented by device features which correspond to the characteristics of individual, several or all dependent method claims.

• Betriebsdrücke (jeweils am Kopf der Säulen):
  • Hochdrucksäule: beispielsweise 12 bis 17 bar, vorzugsweise 13 bis 15 bar Niederdrucksäule: beispielsweise 6 bis 10 bar, vorzugsweise 7 bis 9 bar
• Niederdrucksäulen-Kopfkondensator:
  • Verdampfungsraum: beispielsweise 2 bis 5 bar, vorzugsweise 3 bis 4 bar
• Luftdrücke:
  • Eintrittstemperaturen der beiden Turbinen (Entspannungsmaschinen):
    • "Erste Zwischentemperatur" (Restgasturbine): beispielsweise 160 bis 120 K, vorzugsweise 150 bis 130 K
    • "Zweite Zwischentemperatur" (Stickstoffturbine): beispielsweise 220 bis 180 K, vorzugsweise 210 bis 190 K

In the method according to the invention, for example, the following pressures and temperatures are used:

• Operating pressures (at the top of each column):
  • High-pressure column: for example, 12 to 17 bar, preferably 13 to 15 bar low pressure column: for example, 6 to 10 bar, preferably 7 to 9 bar
• Low-pressure column top condenser:
  • Evaporation space: for example, 2 to 5 bar, preferably 3 to 4 bar
• Air pressures:
  • Inlet temperatures of the two turbines (expansion machines):
    • "First intermediate temperature" (residual gas turbine): for example 160 to 120 K, preferably 150 to 130 K.
    • "Second intermediate temperature" (nitrogen turbine): for example 220 to 180 K, preferably 210 to 190 K.

Figur 1

ein erstes Ausführungsbeispiel mit Generatorturbinen,

Figur 2

ein zweites Ausführungsbeispiel mit Turbinen-Boostern, die seriell geschaltet sind und Luft verdichten,

Figur 3

ein drittes Ausführungsbeispiel mit Turbinen-Boostern, die seriell geschaltet sind und Stickstoff verdichten,

Figur 4

eine erste Variante von Figur 1 mit Unterkühlung des Flüssigstickstoffprodukts,

Figur 5

eine zweite Variante von Figur 1 mit Reinsauerstoffgewinnung,

Figur 6

eine dritte Variante von Figur 1 mit einer Zusatzsäule für Spülflüssigkeit aus der Hochdrucksäule,

Figur 7

eine Abwandlung des Systems von Figur 6 und

Figur 8

ein System mit zeitweiser externer Verdampfung von Flüssigstickstoff.

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

FIG. 1

a first embodiment with generator turbines,

FIG. 2

A second embodiment with turbine boosters, which are connected in series and compress air,

FIG. 3

A third embodiment with turbine boosters, which are connected in series and compress nitrogen,

FIG. 4

a first variant of FIG. 1 with subcooling of the liquid nitrogen product,

FIG. 5

a second variant of FIG. 1 with pure oxygen production,

FIG. 6

a third variant of FIG. 1 with an additional column for rinsing liquid from the high-pressure column,

FIG. 7

a modification of the system of FIG. 6 and

FIG. 8

a system with temporary external evaporation of liquid nitrogen.

In FIG. 1 is the total feed air (AIR) via a filter 1 of a main air compressor 2 with aftercooling 3 (and unillustrated intermediate cooling) on compressed a pressure of about 14.6 bar. The subsequent pre-cooling system has a direct contact cooler 4. The pre-cooled feed air 5 is fed to a cleaning device 6, preferably a switchable molecular sieve adsorber.

Via line 7, the entire purified feed air (except for smaller branches, for example for instrument air) flows to the main heat exchanger 8. It is cooled down to the cold end. The cold, completely or almost completely gaseous air 8 is introduced into the high-pressure column 9. The high-pressure column 9 is part of a distillation column system, which also has a low-pressure column 10, a main condenser 11 and a low-pressure column top condenser 12. The two condenser-evaporators 11, 12 are formed on the evaporation side as a forced-flow evaporator.

Liquid raw oxygen 13 from the bottom of the high pressure column 9 is cooled in a subcooling countercurrent 14 and fed via line 15 of the low pressure column 10 at an intermediate point. The gaseous nitrogen head 16 of the high pressure column 9 is withdrawn to a first part 17 as the first pressure nitrogen stream and fed to the main heat exchanger 8. A second part 20 of the gaseous top nitrogen 16 is at least partially liquefied in the liquefaction space of the main condenser 11. The liquid nitrogen 21 produced in the process is used to a first part as reflux in the high-pressure column 9. The remainder 22/23 is cooled in the subcooling countercurrent 14 and fed to the top of the low pressure column 10.

A liquid oxygen-rich fraction 24 from the bottom of the low-pressure column or from the evaporation space of the main condenser 11 is cooled in the subcooling countercurrent 14 and introduced via line 25 as a coolant flow in the evaporation chamber of the low-pressure column top condenser 12 and there at least partially evaporated. The vapor generated in the evaporation chamber of the low-pressure column top condenser 12 is withdrawn as residual gas stream 26 and heated in the main heat exchanger 8 to a first intermediate temperature of, for example, 142 K. The residual gas stream 27 is introduced at the first intermediate temperature in a first expansion machine 28, which is designed here as a generator turbine, where it works to just above Atmospheric pressure relaxes. The work-performing relaxed residual gas stream 29 is in the main heat exchanger 8 completely, that is heated to approximately ambient temperature.

The warm residual gas 30 can be discharged via line 31 directly into the atmosphere (ATM). Alternatively or in part, it can be used as regeneration gas in the purification device 6 via line 32, optionally after heating in a regeneration gas heater 33. Used regeneration gas is discharged via line 34 into the atmosphere.

A first portion 44 of the gaseous overhead nitrogen of the low-pressure column 10 is taken as the first pressure nitrogen stream, warmed in the main heat exchanger 8 and withdrawn as the first pressure nitrogen product (PGAN) 18, 19. A second part 45 of the gaseous nitrogen head of the low-pressure column 10 is in the liquefaction space low-pressure column top condenser 12th at least partially liquefied. A portion 47 of the nitrogen 46 liquefied in the low-pressure column top condenser 12 is withdrawn as liquid nitrogen product (PLIN).

The second pressure nitrogen stream 17 from the high-pressure column 9 is heated in the main heat exchanger 8 to a second intermediate temperature of 207 K. The second pressure nitrogen stream 40 is introduced under the second intermediate temperature in a second expansion machine 41 and there relaxes work to about the operating pressure at the top of the low-pressure column 10. The second expansion machine 41 is also designed here as a generator turbine. The working expanded second pressure nitrogen stream 42 is completely warmed in the main heat exchanger. The warm second pressurized nitrogen stream 43 is combined with the warm first pressurized nitrogen stream 18 and withdrawn via line 19 together with the first pressurized nitrogen product as the second pressurized nitrogen product (PGAN).

The procedures of the two Figures 2 and 3 differ from it by FIG. 1 in that they use the work done on the turbines to compress a process stream. This is accomplished by two compressor stages (booster) 70, 72, which are coupled to the turbines 28 and 41 and connected to one another in series, and each having an aftercooler 71, 73. It can compressors and Instead of the illustrated configuration, turbines can also be connected in reverse, that is to say the first expansion machine 41 with the first compressor stage 70 and the second expansion machine 41 with the second compressor stage 72.

Optionally, a portion 50 of the second pressurized nitrogen stream 17 may be passed from the high pressure column 9 to the warm end of the main heat exchanger 8 and discharged as a high pressure product HPGAN at a pressure of 13 to 14 bar (not shown).

In FIG. 2 In this case, part of the compression of the total air 7A, 7B is taken over by these turbine-driven compressor stages 70, 72. The main air compressor, for example, only has to compress this to 12.5 bar. Accordingly, a stage can be saved on the main air compressor.

In contrast, in FIG. 3 the entire pressurized nitrogen product 19A, 19B sent through the compressor stages 70, 72. As a result, the product pressure can be raised from about 8 bar to about 11 bar without having to supply energy. In comparison to the use of an externally driven nitrogen compressor thus also results in a cost savings.

FIG. 4 is identical to FIG. 1 with the exception of an additional subcooling countercurrent 414, in which the liquid nitrogen 47 withdrawn from the low pressure column 10 is subcooled against an evaporating nitrogen stream 415/416. For this purpose, a small portion of the supercooled liquid nitrogen is branched off via a valve 417. The vaporized nitrogen 416 is added to the exhaust 29 of the residual gas turbine 28 and heated together with this in the main heat exchanger 8.

FIG. 5 contains in addition to FIG. 1 a pure oxygen column 550, in whose sump highly pure liquid oxygen is produced, which is withdrawn via line 551 and recovered as a high-purity liquid oxygen product HLOX. Via line 552, an oxygen fraction is withdrawn from the low-pressure column 10, which is free of less volatile constituents. It is undercooled in the bottom evaporator 553 of the pure oxygen column 550 and fed via line 554 and throttle valve 555 to the top of the pure oxygen column 550. There, the more volatile components are separated. The sump evaporator 553 is also from a part 556 of heated gaseous nitrogen head 16 of the high pressure column 9; Resulting liquid nitrogen 557 is applied to the low-pressure column 10. The impure gaseous oxygen 558 from the top of the pure oxygen column 550 is mixed with the residual gas 26 upstream of the residual gas turbine 28.

In the case of relatively low pressures (for example, below 3 bar) in the evaporation space of the low-pressure column top condenser 12, it is beneficial to take additional measures, for example, the accumulation of propane at a safe location in the plant and the disposal of this enriched liquid from the Rectification system (for example, to the ejector, into the open or into the impure nitrogen stream before being blown off into the atmosphere). The enrichment can be carried out in a known manner directly in the high pressure column by means of the use of the barrier floors.

Because of the relatively high liquid production, the air at the entrance to the high pressure column is already pre-liquefied (for example to about 1% or more). The existing because of this Vorverflüssigung liquid is deposited in the sump and can be discarded together with the rinsing liquid. As a result, the efficiency of the process is significantly reduced, as it is lost a lot of cold and nitrogen molecules.

One solution to this problem is provided by the method of FIG. 6 Which otherwise also on the process of FIG. 1 touches down. By using an additional column 660 for a high-pressure column flushing liquid 661 from the high-pressure column 9, the flushing amount, which is then withdrawn via line 662, can be drastically reduced.

The high pressure column has one to five practical trays as barrier bottoms 663. The crude liquid oxygen 13 is withdrawn above the barrier bottoms, the high pressure column flushing liquid 661 below, namely directly from the sump; it contains both the return liquid from the high-pressure column or from the barrier floors, as well as the introduced via line 8 pre-liquefied air. The stream 661 is fed to the top of the additional column 660 (possibly after subcooling), accumulates in the mass transfer within the column to gravitational and finally - withdrawn in much lesser amount from the bottom of the additional column 660 via line 662. The deducted amount is for example, about 40 to 50 Nm ³ / h; Relatively, at 100,000 Nm ³ / h of total air quantity, the ratio of amounts of electricity 662 to 661 is for example between 1 and 10%. The sump evaporator 664 of the additional column 660 is heated with gaseous air 665 from the high-pressure column 9. The condensed in the bottom evaporator 664 666 air is supplied to the low pressure column 10. The head gas 667 formed in the additional column 660 is likewise supplied to the low-pressure column 10 at a suitable point.

The C ₃ H ₈ from the partial air flow 665 to the condenser of the additional column 660 is retained in the system. However, this amount of air is relatively small compared to the amount of feed air (about 1%), so that the reliability is not affected. As a result of the flushing 662 being removed from the additional column 660, the return flow rate to the blocking section 663 in the high-pressure column can be increased. Thus, more xenon is washed out and the actual purging 662 from the additional column can also be used and processed as a xenon concentrate; The xenon yield can in a method according to FIG. 6 over 50%.

Deviating from the illustration in FIG. 6 For example, the high pressure column purge fluid 661 in the subcooler countercurrent 14 may be subcooled. Also, the liquid stream 666 from the sump evaporator 664 may be subcooled in the subcooling countercurrent 14 before being introduced into the low pressure column 10.

FIG. 7 is different from this FIG. 6 in that the purge stream 662 is not discarded in the liquid state. Rather, it is introduced via line 762 into the hot residual gas line 763, evaporates there abruptly and is then blown very dilute into the atmosphere.

The method described so far has only limited flexibility in operating cases with relatively low liquid production (ie deviating from the design case). In such cases, the pressure in the evaporation space of the upper condenser and thus also the inlet pressure of the residual gas turbine and the suction pressure in a downstream downstream compressor fall; for example, this refers to the use of blending natural gas to adjust the calorific value. However, a significantly reduced intake pressure in the supercharger is heavily involved in the dimensioning of the machine and also means a limitation of the usual underload behavior.

A relatively inexpensive and yet relatively efficient way out of this situation is with the in FIG. 8 shown interconnection possible. In a first mode of operation with reduced liquid delivery, the liquid production in the plant is not significantly reduced, but a part of the applied separation or liquefaction energy is recovered from the liquid. This can be realized either by the use of an air- or steam-heated emergency supply evaporator or by incorporating one or more cold storage. In the latter case, the cold of the liquefaction process is also partially stored - for example, to increase the liquid production in other operating cases. In the first mode of operation (exit phase), an air partial flow can also be liquefied.

In the exit phase, either the performance of the main air compressor or the performance of the nitrogen product compressor (s) is reduced or, alternatively, more gaseous product is recovered with unchanged performance. Of course, two or three of these measures can be used in combination.

Especially with relatively high Produktabgabe- or intermediate pressures, it may be useful to apply this solution, since the savings in compressor performance on the product compressor with increasing pressure is always higher.

In a second mode, less or no liquid product is vaporized. For example, the additional process steps that are used in the first mode of operation are shut down.

In contrast to FIG. 1 is in FIG. 8 a portion 830 of the relaxed stream in the residual gas turbine 28 is warmed separately before being vented to the atmosphere (ATM). The nitrogen product 44, 18 from the low pressure column 10 is further densified by two two-stage (820, 821) nitrogen product compressors before being discharged via line 819 as a pressurized product. The product compressor 820, 821 as a whole thus has four stages. (Alternatively, one or three nitrogen product compressors with one, three, or more stages may be used.) The compressed stream may be either fully pressurized to final pressure; alternatively, a part between the two nitrogen product compressors 820 and 821 are taken on an intermediate pressure (not shown).

At least a portion of the liquid nitrogen 47 is stored in a liquid nitrogen tank 870. From this liquid nitrogen tank 870 preferably also the liquid product delivery (in FIG. 8 not shown). In the first mode of operation, liquid nitrogen 871 is pressurized by a pump 872 (eg, approximately the pressure between the two nitrogen product compressors 820, 821); alternatively, the pump delivers to the pressure before the first nitrogen product compressor 820 or to the pressure behind the second nitrogen product compressor 821 (not shown). The high pressure nitrogen is vaporized in an atmospheric evaporator 873; Alternatively, a steam-heated water bath evaporator can be used. The gaseous high pressure nitrogen is mixed via one of the lines 875a, 875b, 875c with the hot gaseous nitrogen 18 from the low pressure column 10.

In a second mode of operation, the atmospheric evaporator 873 is shut down and all liquid production PLIN is delivered as an end product or stored in the liquid nitrogen tank 870.

Claims (14)

A process for producing pressurized nitrogen and liquid nitrogen by cryogenic separation of air in a distillation column system comprising a high pressure column (9) and a low pressure column (10) and a main condenser (11) and a low pressure column top condenser (12), both as a condenser Evaporator are formed, wherein a feed air stream (AIR) is compressed in a main air compressor (2), purified (6), cooled in a main heat exchanger (8) and introduced into the high-pressure column (9) (8), a first part (44) of the gaseous top nitrogen of the low-pressure column (10) is withdrawn as the first pressurized nitrogen stream, heated in the main heat exchanger (8) and withdrawn as the first pressurized nitrogen product (18, 19, PGAN), - A second part (45) of the gaseous nitrogen head of the low-pressure column (10) in the liquefaction space of the low-pressure column top condenser (12) is at least partially liquefied, a liquid coolant stream (25) is at least partially evaporated in the evaporation space of the low-pressure column top condenser (12), - the steam generated in the evaporation chamber of the low-pressure column top condenser (12) is withdrawn as residual gas stream (26) and heated in the main heat exchanger (8) to a first intermediate temperature, - The residual gas stream (27) is introduced under the first intermediate temperature in a first expansion machine (28) and there relaxes work, - The work performing relaxed residual gas stream (29) in the main heat exchanger (8) is completely warmed up and - a second pressure nitrogen stream (17) is withdrawn from the top of the high-pressure column (9) and heated in the main heat exchanger (8), characterized in that the second pressure nitrogen stream (17) in the main heat exchanger (8) is heated to a second intermediate temperature, - The second pressure nitrogen stream (40) is introduced under the second intermediate temperature in a second expansion machine (41) and there relaxes work, - The work expanded relaxed second pressure nitrogen stream (42) in the main heat exchanger (8) completely warmed and withdrawn as a second pressure nitrogen product (43, 19, PGAN) and - A portion (47) of the low-pressure column top condenser (12) liquefied nitrogen (46) is withdrawn as liquid nitrogen product (PLIN). A method according to claim 1, characterized in that the first pressure nitrogen stream (44) under a pressure of 8.0 to 9.0 bar in particular 8.4 to 9.0 bar from the top of the low-pressure column (10) is withdrawn. The method of claim 1 or 2, characterized in that the work-expanded second pressure nitrogen stream (42, 43) is combined with the first pressure nitrogen stream (44, 18) and the first pressure nitrogen product and the second pressure nitrogen product withdrawn as a common pressure nitrogen product stream (19, PGAN) become. Method according to one of claims 1 to 3, characterized in that the second intermediate temperature is at least 10 K higher than the first intermediate temperature. Method according to one of claims 1 to 4, characterized in that the first and the second expansion machine (28, 41) are coupled to a generator or a dissipative brake. Method according to one of claims 1 to 4, characterized in that each of the two expansion machines (28, 41) each one compressor stage (70, 72) drives, wherein a process stream (7A, 19A) is compressed successively in the two compressor stages. A method according to claim 6, characterized in that the process stream is formed by at least a portion of the purified feed air (7A) which is introduced downstream of the two compressor stages (70, 72) in the main heat exchanger (8). A method according to claim 6, characterized in that the process stream is formed by at least a portion of the first and / or second pressurized nitrogen product stream (19A) withdrawn downstream of the two compressor stages as pressurized nitrogen product (19B, PGAN). Method according to one of claims 1 to 8, characterized in that the low-pressure column top condenser (12) is formed on its evaporation side as a forced-flow evaporator. Method according to one of claims 1 to 9, characterized in that the main condenser (11) is formed on its evaporation side as a forced-flow evaporator. Process according to one of claims 1 to 10, characterized in that an oxygen fraction (552) is withdrawn from the low-pressure column (10) and fed to a pure oxygen column (550), wherein a highly pure liquid oxygen product is withdrawn from the bottom of the pure oxygen column (550) and the pure oxygen column in particular has a bottom evaporator which is heated with at least part of the oxygen fraction (552) and / or with gaseous nitrogen (556) from the top of the high-pressure column (9). Method according to one of claims 1 to 11, characterized in that a high-pressure column rinsing liquid (661) is withdrawn from the high-pressure column and introduced into an additional column (660) having a sump evaporator (664), in particular with an air partial flow ( 665) is heated, wherein taken from the sump of the additional column (664), a purge stream and discarded or fed to a xenon recovery. Method according to one of claims 1 to 12, characterized in that in a first operating mode at least a part of the (871) liquefied nitrogen (47) - brought to an elevated pressure in the liquid state (872), - Evaporated in an operated with external heat evaporation device (873) and - subsequently obtained as pressurized nitrogen product (874, 819), and in a second mode of operation, no liquefied nitrogen (47) or less than in the first mode of operation is vaporized in the external heat driven evaporator (873),
wherein the external heat driven evaporation device (873) in particular an air-heated evaporator, a water bath evaporator and / or - A solid refrigerant storage having. Apparatus for generating pressurized nitrogen and liquid nitrogen by cryogenic separation of air with a distillation column system comprising a high pressure column (9) and a low pressure column (10) and a main condenser (11) and a low pressure column top condenser (12), both of which are condenser evaporators, a main air compressor (2) for compressing a feed air stream (AIR), - A cleaning device (6) for cleaning the compressed feed air (5) a main heat exchanger (8) for cooling purified feed air (7), - means for introducing (8) the cooled feed air into the high-pressure column (9), - Means for removing a first part (44) of the gaseous nitrogen head of the low pressure column (10) as a first pressure nitrogen stream Means for heating the first pressurized nitrogen stream in the main heat exchanger (8), Means for withdrawing the heated first pressurized nitrogen stream as the first pressurized nitrogen product (18, 19, PGAN), - Means for introducing a second part (45) of the gaseous nitrogen head of the low-pressure column (10) in the liquefaction space of the low-pressure column top condenser (12), Means for introducing a liquid coolant stream (25) into the evaporation space of the low-pressure column overhead condenser (12), Means for drawing off the vapor generated in the evaporation space of the low-pressure column top condenser (12) as residual gas stream (26), Means for introducing the residual gas stream (26) into the main heat exchanger, - Means for removal from the main heat exchanger (8) of the residual gas stream (27) at a first intermediate temperature, - a first expansion machine (28) for work-performing expansion of the warmed to the first intermediate temperature residual gas flow (27), - means for complete heating of the work-performing expanded residual gas flow (29) in the main heat exchanger (8), - means for removing a second pressure nitrogen stream (17) from the head of the high pressure column (9) and with Means for heating the second pressurized nitrogen stream (17) in the main heat exchanger (8), marked by Means for drawing off the second pressurized nitrogen stream (17) from the main heat exchanger (8) at a second intermediate temperature, Means for completely heating the work-performing expanded second pressurized nitrogen stream (42) in the main heat exchanger (8), - means for removing the heated second pressurized nitrogen stream as second pressurized nitrogen product (43, 19, PGAN) and - means for withdrawing a portion (47) of the low-pressure column overhead condenser (12) liquefied nitrogen (46) as a liquid nitrogen product (PLIN).

Images