EP0316768B1 - Air separation process by low temperature rectification - Google Patents

Air separation process by low temperature rectification Download PDF

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Publication number
EP0316768B1
EP0316768B1 EP88118753A EP88118753A EP0316768B1 EP 0316768 B1 EP0316768 B1 EP 0316768B1 EP 88118753 A EP88118753 A EP 88118753A EP 88118753 A EP88118753 A EP 88118753A EP 0316768 B1 EP0316768 B1 EP 0316768B1
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Prior art keywords
stream
sub
expansion
stage
streams
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German (de)
French (fr)
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EP0316768A2 (en
EP0316768A3 (en
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Werner Dipl.-Ing. Skolaude
Gunnar Dr. Eggendorfer
Horst Corduan
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Linde GmbH
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Linde GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04193—Division of the main heat exchange line in consecutive sections having different functions
    • F25J3/042—Division of the main heat exchange line in consecutive sections having different functions having an intermediate feed connection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04218—Parallel arrangement of the main heat exchange line in cores having different functions, e.g. in low pressure and high pressure cores
    • F25J3/04224—Cores associated with a liquefaction or refrigeration cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04278—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using external refrigeration units, e.g. closed mechanical or regenerative refrigeration units
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/0429—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
    • F25J3/04296—Claude expansion, i.e. expanded into the main or high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04333—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/04339—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of air
    • F25J3/04345—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of air and comprising a gas work expansion loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04333—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/04351—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of nitrogen
    • F25J3/04357—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of nitrogen and comprising a gas work expansion loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04375—Details relating to the work expansion, e.g. process parameter etc.
    • F25J3/04393—Details relating to the work expansion, e.g. process parameter etc. using multiple or multistage gas work expansion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S62/00—Refrigeration
    • Y10S62/939—Partial feed stream expansion, air
    • Y10S62/94—High pressure column

Definitions

  • the invention relates to a method for air separation by low-temperature rectification, in which the stream of gases involved in the air separation is passed through a cooling stage in which process cooling is produced by compression and expansion of at least part of this gas stream, the gas stream being compressed in the cooling stage and in two Partial streams is divided, which are at least partially cooled and relieved of work, the relaxation of the first partial stream being carried out at a higher temperature and that of the second partial stream being carried out at a lower temperature, in which at least one partial stream is further compressed before the expansion using the work obtained in the expansion is, and in which at least one of the two substreams is at least partially fed to the rectification.
  • This method has the disadvantage that the proportion of the mechanical energy recovered during the expansion processes is unsatisfactory when using the expansion turbines which are usually used.
  • the object of the present invention is to develop a method with a cooling stage mentioned at the outset which works particularly economically in terms of energy.
  • This object is achieved in that the post-compression of the second partial stream is carried out in two stages and that the work obtained in the expansion of the two partial streams is used in the two stages for post-compression of the second partial stream.
  • the procedure according to the invention causes a high pressure difference between the point of branching in the two partial flows and the entry of the second partial flow into the expansion process.
  • the pressure and thus also the enthalpy difference is high on the expansion device operating at a lower temperature, and a high proportion of the mechanical energy of the highly compressed partial flow can be obtained as work during the expansion and fed back into the process.
  • the pressure at the branching point can be chosen to be low and energy saved from outside for compression can thus be saved.
  • the work which is obtained in the expansion of the first partial flow is used in the second stage of the post-compression of the second partial flow.
  • the first partial stream is expanded to perform the work without post-compression.
  • the pressure difference between the inlet and outlet of the expansion device operating at a higher temperature is therefore relatively small, which is why the expansion process can be carried out with high efficiency. This means that a high proportion of the energy released during relaxation can be obtained as work and returned to the process.
  • both partial flows are fed completely to the rectification.
  • the outlay on equipment can thus be kept lower than in the version with a circuit.
  • At least some of the partial flows are cooled by heat exchange with an external coolant.
  • cold can additionally be introduced into the process from the outside in a particularly economical manner.
  • the heat exchange with the external coolant is carried out to a temperature which is greater than or equal to the temperature at which the expansion of the first partial stream begins.
  • This cold can be supplied particularly cheaply if the temperature difference between the inlet and outlet is particularly high during heat exchange with the external coolant.
  • the maximum of this difference is essentially that Difference between ambient temperature and inlet temperature in the relaxation device operating at a higher temperature. This temperature is particularly low if, according to an inventive feature mentioned above, the pressure difference when the expansion of the first partial flow is chosen to be low.
  • pre-compressed and pre-cleaned air is used as the working gas for the cooling stage.
  • This version proves to be particularly favorable if a small part of the products, based on the broken down air volume, is to be obtained in the liquid state.
  • nitrogen-rich gas which is removed from the rectification is used as the working gas for the cooling stage. If a larger proportion of the products is removed in the liquid state, this version of the method is particularly useful.
  • air to be broken down is fed via a line 1 to a compressor 2, in which it is compressed to a pressure of 6 to 7 bar, preferably 6.4 bar.
  • the compressed air is passed via an aftercooler 3 to a molecular sieve adsorber 4 in order to separate water vapor and carbon dioxide therefrom.
  • the air stream is then passed into the cooling stage, where it is compressed to a pressure of 28 to 32 bar in a compressor 5 and cooled in an aftercooler 6.
  • the air flow then separates into a first partial flow 7 and a second partial flow 8.
  • the second partial flow is compressed in two post-compression stages 9, 11 to 45 to 60 bar.
  • the heat of compression is dissipated in the associated aftercoolers 10, 12.
  • the first partial flow is fed directly to a heat exchanger 13 and there cooled in countercurrent to decomposition products to 230 to 280 K and expanded to 5.4 to 6.5 bar in an expansion device 14.
  • the work obtained in this way is delivered to the post-compression stage 11.
  • the first partial flow has a temperature of 150 to 170 K and is returned to the compressor 5 via the heat exchanger 13.
  • a side stream 16 is branched off from the second partial stream behind the aftercooler 12 and is cooled to the temperature of the first partial stream upstream of the expansion device 14 by means of heat exchange with an external coolant, preferably halogenated hydrocarbons, and in the heat exchanger 13 is combined again with the remaining second partial stream.
  • the heat exchange with the external coolant is carried out here specifically in two stages 17. This cooling could just as well be carried out in one stage.
  • a side stream of the partial stream 7 or a side stream of each of the two partial streams 7, 8 could be cooled by means of heat exchange with the external coolant.
  • a further partial flow 18 is branched off from the second partial flow and expanded in the expansion device 19 to 5.6 to 6.6 bar.
  • the work obtained in this way is handed over to post-compression stage 9.
  • the relaxed side stream 18 is then partly fed to the first stage 21 of a two-stage rectification column 20, and partly returned to the compressor 5 via the heat exchangers 15 and 13.
  • the remaining second partial flow is throttled after further cooling in the heat exchanger 15 and fed to the first stage 21 of the rectification column.
  • the first stage 21 of the rectification is operated at a pressure of 5.6 to 6.6 bar. It is connected to a second stage 22, which operates at a pressure of 1.5 to 1.7 bar, via a condenser-evaporator 23 in a heat-exchanging manner.
  • Oxygen-rich liquid 24 is removed from the bottom of the first stage, and nitrogen-rich liquid 25 is removed from the top of the first stage.
  • the two streams 24, 25 are subcooled in heat exchange with gaseous nitrogen 27 from the top of the second stage and with residual gas 33 in a heat exchanger 26, then relaxed throttle and introduced into the second stage 22 according to their composition.
  • the nitrogen stream 27 and the residual gas stream 33 are heated in the heat exchanger 26.
  • oxygen in the gaseous state is removed via a line 28.
  • the two product streams 27 and 28 are then passed together with the residual gas stream 33 through the heat exchangers 15 and 13 and warmed to almost ambient temperature.
  • FIG. 2 A further example is shown in FIG. 2 in which the cooling stage is operated with nitrogen-rich gas from the rectification column as the working gas. This method is very similar to that shown in Figure 1. The different process parts are mainly described below.
  • the pre-compressed and pre-cleaned air is not fed to the cooling stage, but is cooled to about saturation temperature in the heat exchange 29 with gaseous decomposition products and a compensating stream 34 and is fed to the first stage 21 of the rectification column 20.
  • nitrogen is withdrawn via line 30 and fed as working gas to the cooling stage, which is constructed essentially like the cooling stage in FIG. 1.
  • the working gas Before entering the compressor 5, the working gas is heated. One part is passed through the heat exchangers 15, 13, another part through the equalizing flow 34 through the heat exchanger 29. A part of the equalizing flow 34 is branched off in the heat exchanger 29 and led to the heat exchanger 13 via the line 35. After heating, all branch flows of the working gas are combined again and fed to the compression in compressor 5.
  • the entire second partial flow 8 is introduced into the heat exchanger 13 after the compression, without using an external coolant for the additional supply of cold. All versions with or without external coolant can optionally be used for both working gases.
  • the side stream 18 of the second partial stream is largely returned to the compressor 5 after the expansion.
  • Liquid oxygen 31 and liquid nitrogen 32 are taken as products from the first and second stages of the rectification column.

Description

Die Erfindung betrifft ein Verfahren zur Luftzerlegung durch Tieftemperaturrektifikation, bei dem Strom von an der Luftzerlegung beteiligten Gasen durch eine Kühlstufe geführt wird, in der durch Verdichtung und Entspannung zumindest eines Teils dieses Gasstroms Verfahrenskälte erzeugt wird, wobei in der Kühlstufe der Gasstrom verdichtet und in zwei Teilströme aufgeteilt wird, die mindestens teilweise abgekühlt und arbeitsleistend entspannt werden, wobei die Entspannung des ersten Teilstroms bei höherer, die des zweiten Teilstroms bei niedrigerer Temperatur durchgeführt wird, bei dem ferner mindestens ein Teilstrom vor der Entspannung unter Verwendung der bei der Entspannung gewonnenen Arbeit nachverdichtet wird, und bei dem mindestens einer der beiden Teilströme mindestens teilweise der Rektifikation zugeführt wird.The invention relates to a method for air separation by low-temperature rectification, in which the stream of gases involved in the air separation is passed through a cooling stage in which process cooling is produced by compression and expansion of at least part of this gas stream, the gas stream being compressed in the cooling stage and in two Partial streams is divided, which are at least partially cooled and relieved of work, the relaxation of the first partial stream being carried out at a higher temperature and that of the second partial stream being carried out at a lower temperature, in which at least one partial stream is further compressed before the expansion using the work obtained in the expansion is, and in which at least one of the two substreams is at least partially fed to the rectification.

Ein solches Verfahren ist in der US-Patentschrift 4,152,130 beschrieben. Dort wird die zu zerlegende Luft nach Vorverdichtung und Vorreinigung, bei der im wesentlichen Wasserdampf und Kohlendioxid abgetrennt werden, in die Kühlstufe eingeführt und dort als Arbeitsgas verwendet. In der Kühlstufe wird durch Verdichtung und Entspannung dieses Arbeitsgases Kälte erzeugt und dem Verfahren zugeführt. Innerhalb der Kühlstufe werden der zweite Teilstrom und ein Seitenstrom des ersten Teilstroms arbeitsleistend entspannt. Die beiden Entspannungsvorgänge und die damit verbundene Abkühlung werden parallel zum Wärmetausch mit Zerlegungsprodukten in zwei verschiedenen Temperaturbereichen durchgeführt. Die Temperatur am Ausgang der bei höherer Temperatur arbeitenden Entspannungseinrichtung ist etwa gleich der Temperatur am Eingang der bei niedrigerer Temperatur arbeitenden Entspannungseinrichtung. Mit der in den beiden Entspannungseinrichtungen gewonnenen Energie werden beide Teilströme parallel durch je eine Nachverdichtungsstufe komprimiert.One such method is described in U.S. Patent 4,152,130. There, the air to be separated is pre-compressed and pre-cleaned, in which essentially water vapor and carbon dioxide are separated, into the cooling stage introduced and used there as a working gas. In the cooling stage, compression and expansion of this working gas generate cold and add it to the process. Within the cooling stage, the second partial stream and a side stream of the first partial stream are expanded to perform work. The two expansion processes and the associated cooling are carried out in parallel with the heat exchange with decomposition products in two different temperature ranges. The temperature at the outlet of the relaxation device operating at a higher temperature is approximately equal to the temperature at the inlet of the relaxation device operating at a lower temperature. With the energy obtained in the two expansion devices, both partial streams are compressed in parallel by a post-compression stage.

Dieses Verfahren weist den Nachteil auf, daß der Anteil der während der Entspannungsvorgänge zurückgewonnenen mechanischen Energie bei Verwendung der üblicherweise eingesetzten Entspannungsturbinen nicht zufriedenstellend ist.This method has the disadvantage that the proportion of the mechanical energy recovered during the expansion processes is unsatisfactory when using the expansion turbines which are usually used.

Aufgabe der vorliegenden Erfindung ist es, ein Verfahren mit einer eingangs genannten Kühlstufe zu entwickeln, das energetisch besonders günstig arbeitet.The object of the present invention is to develop a method with a cooling stage mentioned at the outset which works particularly economically in terms of energy.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß die Nachverdichtung des zweiten Teilstroms in zwei Stufen durchgeführt wird und daß die bei der Entspannung der beiden Teilströme gewonnene Arbeit in den beiden Stufen zur Nachverdichtung des zweiten Teilstroms verwendet wird.This object is achieved in that the post-compression of the second partial stream is carried out in two stages and that the work obtained in the expansion of the two partial streams is used in the two stages for post-compression of the second partial stream.

Die erfindungsgemäße Verfahrensführung bewirkt eine hohe Druckdifferenz zwischen der Stelle der Verzweigung in die beiden Teilströme und dem Eintritt des zweiten Teilstroms in den Entspannungsvorgang. Dadurch ist einerseits an der bei niedrigerer Temperatur arbeitenden Entspannungseinrichtung die Druck- und damit auch die Enthalpiedifferenz hoch, und es kann bei der Entspannung ein hoher Anteil der mechanischen Energie des hochverdichteten Teilstroms als Arbeit gewonnen und dem Verfahren wieder zugeführt werden. Andererseits kann der Druck am Verzweigungspunkt niedrig gewählt und damit von außen zur Verdichtung eingesetzte Energie eingespart werden. Beim Nachverdichten des zweiten Teilstroms wird die gewonnene Arbeit dem Verfahren in Form von mechanischer Energie wieder zugeführt.The procedure according to the invention causes a high pressure difference between the point of branching in the two partial flows and the entry of the second partial flow into the expansion process. As a result, on the one hand, the pressure and thus also the enthalpy difference is high on the expansion device operating at a lower temperature, and a high proportion of the mechanical energy of the highly compressed partial flow can be obtained as work during the expansion and fed back into the process. On the other hand, the pressure at the branching point can be chosen to be low and energy saved from outside for compression can thus be saved. When the second partial stream is recompressed, the work obtained is returned to the process in the form of mechanical energy.

Es erweist sich als besonders vorteilhaft, gemäß einer bevorzugten Weiterbildung der vorliegenden Erfindung die Arbeit, die bei der Entspannung des zweiten Teilstroms gewonnen wird, in der ersten Teilstufe der Nachverdichtung des zweiten Teilstroms zu verwenden.It has proven to be particularly advantageous to use the work obtained in the expansion of the second partial stream in the first partial stage of the post-compression of the second partial stream, in accordance with a preferred development of the present invention.

Weiterhin erweist es sich als vorteilhaft, wenn gemäß einer bevorzugten Weiterbildung des erfindungsgemäßen Verfahrens die Arbeit, die bei der Entspannung des ersten Teilstroms gewonnen wird, in der zweiten Stufe der Nachverdichtung des zweiten Teilstroms verwendet wird.Furthermore, it proves to be advantageous if, according to a preferred development of the method according to the invention, the work which is obtained in the expansion of the first partial flow is used in the second stage of the post-compression of the second partial flow.

Bei einer besonders bevorzugten Weiterbildung des erfindungsgemäßen Verfahrens wird der erste Teilstrom ohne Nachverdichtung arbeitsleistend entspannt. Die Druckdifferenz zwischen Ein- und Ausgang der bei höherer Temperatur arbeitenden Entspannungseinrichtung ist damit relativ gering, weshalb der Entspannungsvorgang mit hohem Wirkungsgrad durchgeführt werden kann. Somit kann ein hoher Anteil der Energie, die bei der Entspannung frei wird, als Arbeit gewonnen und dem Verfahren wieder zugeführt werden.In a particularly preferred development of the method according to the invention, the first partial stream is expanded to perform the work without post-compression. The pressure difference between the inlet and outlet of the expansion device operating at a higher temperature is therefore relatively small, which is why the expansion process can be carried out with high efficiency. This means that a high proportion of the energy released during relaxation can be obtained as work and returned to the process.

Es erweist sich als zweckmäßig, wenn gemäß einer Weiterbildung des erfindungsgemäßen Verfahrens ein Teil der Teilströme nach der Entspannung in den zu verdichtenden Gasstrom zurückgeführt wird. Die Menge des zurückgeführten Gases relativ zur Menge der zugeführten Luft bestimmt die Kälteleistung der Kühlstufe. Damit kann bei ansonsten gleichbleibendem Verfahren über den Fluß im zurückgeführten Strom reguliert werden, welcher Anteil der Endprodukte in flüssigem und welcher in gasförmigem Zustand erzeugt wird.It proves to be expedient if, according to a development of the method according to the invention, a part of the partial streams is returned to the gas stream to be compressed after the expansion. The amount of gas returned relative to the amount of air supplied determines the cooling capacity of the cooling stage. With an otherwise constant process, it is thus possible to regulate via the flow in the returned stream which portion of the end products is produced in the liquid and which in the gaseous state.

Bei einer anderen Weiterbildung des erfindungsgemäßen Verfahrens werden beide Teilströme vollständig der Rektifikation zugeführt. Der apparative Aufwand kann damit geringer gehalten werden als bei der Ausführung mit Kreislauf.In another development of the method according to the invention, both partial flows are fed completely to the rectification. The outlay on equipment can thus be kept lower than in the version with a circuit.

Bei einer besonders bevorzugten Weiterbildung des erfindungsgemäßen Verfahrens wird mindestens ein Teil der Teilströme durch Wärmetausch mit einem externen Kühlmittel abgekühlt. Dadurch kann auf besonders wirtschaftliche Weise zusätzlich von außen Kälte in das Verfahren eingebracht werden.In a particularly preferred development of the method according to the invention, at least some of the partial flows are cooled by heat exchange with an external coolant. As a result, cold can additionally be introduced into the process from the outside in a particularly economical manner.

Es erweist sich als zweckmäßig, wenn in Weiterbildung des erfindungsgemäßen Verfahrens der Wärmetausch mit dem externen Kühlmittel bis auf eine Temperatur durchgeführt wird, die größer oder gleich der Temperatur ist, bei der die Entspannung des ersten Teilstroms beginnt. Dadurch werden Mischuungseffekte beim Wärmetausch weitgehend vermieden. Besonders günstig kann diese Kälte zugeführt werden, wenn beim Wärmetausch mit dem externen Kühlmittel die Temperaturdifferenz zwischen Ein- und Austritt besonders hoch ist. Das Maximum dieser Differenz ist im wesentlichen die Differenz zwischen Umgebungstemperatur und Eintrittstemperatur in die bei höherer Temperatur arbeitende Entspannungseinrichtung. Diese Temperatur ist besonders niedrig, wenn gemäß eines obengenannten Erfindungsmerkmals die Druckdifferenz bei der Entspannung des ersten Teilstroms niedrig gewählt wird.It has proven expedient if, in a development of the method according to the invention, the heat exchange with the external coolant is carried out to a temperature which is greater than or equal to the temperature at which the expansion of the first partial stream begins. This largely avoids mixing effects during heat exchange. This cold can be supplied particularly cheaply if the temperature difference between the inlet and outlet is particularly high during heat exchange with the external coolant. The maximum of this difference is essentially that Difference between ambient temperature and inlet temperature in the relaxation device operating at a higher temperature. This temperature is particularly low if, according to an inventive feature mentioned above, the pressure difference when the expansion of the first partial flow is chosen to be low.

In einer vorteilhaften speziellen Weiterbildung des erfindungsgemäßen Verfahrens wird vorverdichtete und vorgereinigte Luft als Arbeitsgas für die Kühlstufe verwendet. Diese Ausführung erweist sich als besonders günstig, wenn ein kleiner Teil der Produkte, bezogen auf die zerlegte Luftmenge, in flüssigem Zustand gewonnen werden soll.In an advantageous special development of the method according to the invention, pre-compressed and pre-cleaned air is used as the working gas for the cooling stage. This version proves to be particularly favorable if a small part of the products, based on the broken down air volume, is to be obtained in the liquid state.

In einer anderen vorteilhaften Weiterbildung des erfindungsgemäßen Verfahrens wird stickstoffreiches Gas, das der Rektifikation entnommen wird, als Arbeitsgas für die Kühlstufe verwendet. Wird ein größerer Anteil der Produkte in flüssigem Zustand entnommen, ist diese Version des Verfahrens besonders zweckmäßig.In another advantageous development of the method according to the invention, nitrogen-rich gas which is removed from the rectification is used as the working gas for the cooling stage. If a larger proportion of the products is removed in the liquid state, this version of the method is particularly useful.

Die Erfindung sowie weitere Einzelheiten der Erfindung werden anhand von schematisch dargestellten Ausführungsbeispielen näher erläutert.The invention and further details of the invention are explained in more detail with reference to schematically illustrated exemplary embodiments.

Hierbei zeigen:

  • Figur 1 eine Ausführungsform des erfindungsgemäßen Verfahrens mit Luft als Arbeitsgas für die Kühlstufe,
  • Figur 2 eine weitere Ausführung des erfindungsgemäßen Verfahrens mit stickstoffreichem Gas aus der Rektifikation als Arbeitsgas für die Kühlstufe.
Here show:
  • FIG. 1 shows an embodiment of the method according to the invention with air as the working gas for the cooling stage,
  • Figure 2 shows a further embodiment of the method according to the invention with nitrogen-rich gas from the rectification as working gas for the cooling stage.

In beiden Figuren sind für analoge Bauteile dieselben Bezugszeichen verwendet.The same reference numerals are used in both figures for analog components.

Im Verfahren von Figur 1 wird zu zerlegende Luft über eine Leitung 1 einem Verdichter 2 zugeführt, in dem sie auf einen Druck von 6 bis 7 bar, vorzugsweise 6,4 bar verdichtet wird. Die komprimierte Luft wird über einen Nachkühler 3 zu einem Molsiebadsorber 4 geleitet, um Wasserdampf und Kohlendioxid daraus abzutrennen.In the process of FIG. 1, air to be broken down is fed via a line 1 to a compressor 2, in which it is compressed to a pressure of 6 to 7 bar, preferably 6.4 bar. The compressed air is passed via an aftercooler 3 to a molecular sieve adsorber 4 in order to separate water vapor and carbon dioxide therefrom.

Anschließend wird der Luftstrom in die Kühlstufe geleitet und dort in einem Verdichter 5 auf einen Druck von 28 bis 32 bar komprimiert und in einem Nachkühler 6 abgekühlt. Danach trennt sich der Luftstrom in einen ersten Teilstrom 7 und einem zweiten Teilstrom 8 auf.The air stream is then passed into the cooling stage, where it is compressed to a pressure of 28 to 32 bar in a compressor 5 and cooled in an aftercooler 6. The air flow then separates into a first partial flow 7 and a second partial flow 8.

Der zweite Teilstrom wird in zwei Nachverdichtungsstufen 9, 11 auf 45 bis 60 bar komprimiert. In den dazugehörigen Nachkühlern 10, 12 wird jeweils die Verdichtungswärme abgeführt.The second partial flow is compressed in two post-compression stages 9, 11 to 45 to 60 bar. The heat of compression is dissipated in the associated aftercoolers 10, 12.

Der erste Teilstrom wird direkt zu einem Wärmetauscher 13 geführt und dort im Gegenstrom mit Zerlegungsprodukten auf 230 bis 280 K abgekühlt und in einer Entspannungseinrichtung 14 auf 5,4 bis 6,5 bar entspannt. Die dabei gewonnene Arbeit wird an die Nachverdichtungsstufe 11 abgegeben. Nach der Entspannung besitzt der erste Teilstrom eine Temperatur von 150 bis 170 K und wird über den Wärmetauscher 13 wieder zum Verdichter 5 zurückgeführt.The first partial flow is fed directly to a heat exchanger 13 and there cooled in countercurrent to decomposition products to 230 to 280 K and expanded to 5.4 to 6.5 bar in an expansion device 14. The work obtained in this way is delivered to the post-compression stage 11. After the expansion, the first partial flow has a temperature of 150 to 170 K and is returned to the compressor 5 via the heat exchanger 13.

Vom zweiten Teilstrom wird hinter dem Nachkühler 12 ein Seitenstrom 16 abgezweigt, der mittels Wärmetausch mit einem externen Kühlmittel, vorzugsweise Halogenkohlenwasserstoffen, auf die Temperatur des ersten Teilstroms vor der Entspannungseinrichtung 14 abgekühlt und im Wärmetauscher 13 wieder mit dem übrigen zweiten Teilstrom vereinigt wird. Der Wärmetausch mit dem externen Kühlmittel wird hier speziell in zwei Stufen 17 durchgeführt. Genausogut könnte diese Abkühlung in einer Stufe durchgeführt werden. Ebenso könnte ein Seitenstrom des Teilstroms 7 oder je ein Seitenstrom jedes der beiden Teilströme 7, 8 mittels Wärmetausch mit dem externen Kühlmittel abgekühlt werden.A side stream 16 is branched off from the second partial stream behind the aftercooler 12 and is cooled to the temperature of the first partial stream upstream of the expansion device 14 by means of heat exchange with an external coolant, preferably halogenated hydrocarbons, and in the heat exchanger 13 is combined again with the remaining second partial stream. The heat exchange with the external coolant is carried out here specifically in two stages 17. This cooling could just as well be carried out in one stage. Likewise, a side stream of the partial stream 7 or a side stream of each of the two partial streams 7, 8 could be cooled by means of heat exchange with the external coolant.

Nach weiterer Abkühlung des gesamten zweiten Teilstroms im Wärmetauscher 13 auf 150 bis 170 K wird vom zweiten Teilstrom ein weiterer Teilstrom 18 abgezweigt und in der Entspannungseinrichtung 19 auf 5,6 bis 6,6 bar entspannt. Die dabei gewonnene Arbeit wird an die Nachverdichtungsstufe 9 abgegeben. Anschließend wird der entspannte Seitenstrom 18 teilweise der ersten Stufe 21 einer zweistufigen Rektifizierkolonne 20 zugeführt, teilweise über die Wärmetauscher 15 und 13 zum Verdichter 5 zurückgeführt. Der restliche zweite Teilstrom wird nach weiterer Abkühlung im Wärmetauscher 15 abgedrosselt und der ersten Stufe 21 der Rektifizierkolonne zugeführt.After further cooling of the entire second partial flow in the heat exchanger 13 to 150 to 170 K, a further partial flow 18 is branched off from the second partial flow and expanded in the expansion device 19 to 5.6 to 6.6 bar. The work obtained in this way is handed over to post-compression stage 9. The relaxed side stream 18 is then partly fed to the first stage 21 of a two-stage rectification column 20, and partly returned to the compressor 5 via the heat exchangers 15 and 13. The remaining second partial flow is throttled after further cooling in the heat exchanger 15 and fed to the first stage 21 of the rectification column.

Die erste Stufe 21 der Rektifikation wird bei beim Druck von 5,6 bis 6,6 bar betrieben. Sie steht mit einer zweiten Stufe 22, die bei einem Druck von 1,5 bis 1,7 bar arbeitet, über einen Kondensator-Verdampfer 23 in wärmetauschender Verbindung.The first stage 21 of the rectification is operated at a pressure of 5.6 to 6.6 bar. It is connected to a second stage 22, which operates at a pressure of 1.5 to 1.7 bar, via a condenser-evaporator 23 in a heat-exchanging manner.

Vom Boden der ersten Stufe wird sauerstoffreiche Flüssigkeit 24, vom Kopf der ersten Stufe stickstoffreiche Flüssigkeit 25 entnommen. Die beiden Ströme 24, 25 werden in Wärmetausch mit gasförmigem Stickstoff 27 vom Kopf der zweiten Stufe und mit Restgas 33 in einem Wärmetauscher 26 unterkühlt, anschließend drosselentspannt und entsprechend ihrer Zusammensetzung in die zweite Stufe 22 eingeführt. Der Stickstoffstrom 27 und der Restgasstrom 33 werden im Wärmetauscher 26 erwärmt. Oberhalb des Sumpfes der zweiten Stufe 22 wird Sauerstoff in gasförmigen Zustand über eine Leitung 28 entnommen. Die beiden Produktströme 27 und 28 werden anschließend zusammen mit dem Restgasstrom 33 durch die Wärmetauscher 15 und 13 geleitet und auf nahezu Umgebungstemperatur angewärmt.Oxygen-rich liquid 24 is removed from the bottom of the first stage, and nitrogen-rich liquid 25 is removed from the top of the first stage. The two streams 24, 25 are subcooled in heat exchange with gaseous nitrogen 27 from the top of the second stage and with residual gas 33 in a heat exchanger 26, then relaxed throttle and introduced into the second stage 22 according to their composition. The nitrogen stream 27 and the residual gas stream 33 are heated in the heat exchanger 26. Above the bottom of the second stage 22, oxygen in the gaseous state is removed via a line 28. The two product streams 27 and 28 are then passed together with the residual gas stream 33 through the heat exchangers 15 and 13 and warmed to almost ambient temperature.

Das in Figur 1 dargestellte Verfahren bietet im Vergleich zu bekannten Verfahren, z.B. dem in der US-Patentschrift 4,152,130 beschriebenen, einen energetischen Vorteil von etwa 2%, insbesondere bei kleineren Mengen von im Verdichter 5 komprimiertem Gas.The method shown in Figure 1 offers compared to known methods, e.g. that described in US Pat. No. 4,152,130 has an energetic advantage of about 2%, especially with smaller amounts of gas compressed in the compressor 5.

In Figur 2 ist als weiteres Beispiel ein Verfahren dargestellt, bei dem die Kühlstufe mit stickstoffreichem Gas aus der Rektifizierkolonne als Arbeitsgas betrieben wird. Dieses Verfahren ist dem in Figur 1 abgebildeten sehr ähnlich. Im folgenden werden hauptsächlich die unterschiedlichen Verfahrensteile beschrieben.A further example is shown in FIG. 2 in which the cooling stage is operated with nitrogen-rich gas from the rectification column as the working gas. This method is very similar to that shown in Figure 1. The different process parts are mainly described below.

Nach dem Molsiebadsorber 4 wird die vorverdichtete und vorgereinigte Luft nicht der Kühlstufe zugeführt, sondern im Wärmetausch 29 mit gasförmigen Zerlegungsprodukten und einem Ausgleichsstrom 34 auf etwa Sättigungstemperatur abgekühlt und der ersten Stufe 21 der Rektifizierkolonne 20 zugeführt. Am Kopf der ersten Stufe wird über die Leitung 30 Stickstoff entnommen und als Arbeitsgas der Kühlstufe zugeleitet, die im wesentlichen wie die Kühlstufe in Figur 1 aufgebaut ist.After the molecular sieve adsorber 4, the pre-compressed and pre-cleaned air is not fed to the cooling stage, but is cooled to about saturation temperature in the heat exchange 29 with gaseous decomposition products and a compensating stream 34 and is fed to the first stage 21 of the rectification column 20. At the top of the first stage, nitrogen is withdrawn via line 30 and fed as working gas to the cooling stage, which is constructed essentially like the cooling stage in FIG. 1.

Vor dem Eintritt in den Verdichter 5 wird das Arbeitsgas erwärmt. Ein Teil wird durch die Wärmetauscher 15, 13, ein anderer Teil über den Ausgleichsstrom 34 durch den Wärmetauscher 29 geführt. Ein Teil des Ausgleichsstroms 34 wird im Wärmetauscher 29 abgezweigt und über die Leitung 35 zum Wärmetauscher 13 geführt. Nach der Erwärmung werden alle Zweigströme des Arbeitsgases wieder vereinigt und der Kompression in Verdichter 5 zugeführt.Before entering the compressor 5, the working gas is heated. One part is passed through the heat exchangers 15, 13, another part through the equalizing flow 34 through the heat exchanger 29. A part of the equalizing flow 34 is branched off in the heat exchanger 29 and led to the heat exchanger 13 via the line 35. After heating, all branch flows of the working gas are combined again and fed to the compression in compressor 5.

In einer von Figur 1 abweichenden Variante wird hier der gesamte zweite Teilstrom 8 nach der Nachverdichtung in den Wärmetauscher 13 eingeleitet, ohne daß ein externes Kühlmittel zur zusätzlichen Kältezufuhr benutzt wird. Sämtliche Versionen mit oder ohne externes Kühlmittel können wahlweise für beide Arbeitsgase verwendet werden.In a variant deviating from FIG. 1, the entire second partial flow 8 is introduced into the heat exchanger 13 after the compression, without using an external coolant for the additional supply of cold. All versions with or without external coolant can optionally be used for both working gases.

Weiterhin wird im Unterschied zum Verfahren der Figur 1 der Seitenstrom 18 des zweiten Teilstroms nach der Entspannung größtenteils zum Verdichter 5 zurückgeführt.Furthermore, in contrast to the method in FIG. 1, the side stream 18 of the second partial stream is largely returned to the compressor 5 after the expansion.

Als Produkt werden flüssiger Sauerstoff 31 und flüssiger Stickstoff 32 aus der ersten bzw. zweiten Stufe der Rektifizierkolonne entnommen.Liquid oxygen 31 and liquid nitrogen 32 are taken as products from the first and second stages of the rectification column.

Claims (10)

1. A process for separating air by low-temperature rectification wherein a stream of gases which participate in the air separation is conducted through a cooling stage in which process cold is produced by the compression and expansion of at least a part of this gas stream, wherein in the cooling stage the gas stream is compressed and then divided into two sub-streams which are at least partially cooled and expanded with the production of work, where the expansion of the first sub-stream takes place at a higher temperature and the expansion of the second sub-stream takes place at a lower temperature, wherein moreover at least one sub-stream is subjected to secondary compression prior to the expansion using the work obtained by the expansion and wherein at least one of the two sub-streams is fed at least in part to the rectification column, characterised in that the secondary compression of the second sub-stream (8) is carrier out in two stages (9, 11) and that the work obtained by the expansion (14, 19) of the two sub-streams (7, 8) is used in the two stages (9, 11) for the secondary compression of the second sub-stream (8).
2. A process as claimed in claim 1, characterised in that the work obtained by the expansion (19) of the second sub-stream is used in the first stage (9) of the secondary compression of the second sub-stream.
3. A process as claimed in one of claims 1 or 2, characterised in that the work obtained by the expansion (14) of the first sub-stream is used in the second stage (11) of the secondary compression of the second sub-stream.
4. A process as claimed in one of claims 1 to 3, characterised in that the first sub-stream (7) is expanded with the production of work without secondary compression.
5. A process as claimed in one of claims 1 to 4, characterised in that a part of the sub-streams is returned, following the expansion, to the gas stream which is to be compressed.
6. A process as claimed in one of claims 1 to 4, characterised in that the two sub-streams are fed entirely to the rectification column.
7. A process as claimed in one of claims 1 to 6, characterised in that at least a part of the sub-streams is cooled by heat exchange with in external coolant (17).
8. A process as claimed in claim 7, characterised in that the heat exchange with the external coolant (17) is carried out to a temperature which is greater than or equal to the temperature at which the expansion (14) of the first sub-stream commences.
9. A process as claimed in one of claims 1 to 8, characterised in that pre-compressed and pre-purified air is used as working gas for the cooling stage.
10. A process as claimed in one of claims 1 to 8, characterised in that nitrogen-rich gas obtained from the rectification column is used as working gas for the cooling stage.
EP88118753A 1987-11-13 1988-11-10 Air separation process by low temperature rectification Revoked EP0316768B1 (en)

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DE3738559 1987-11-13
DE19873738559 DE3738559A1 (en) 1987-11-13 1987-11-13 METHOD FOR AIR DISASSEMBLY BY DEEP TEMPERATURE RECTIFICATION

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EP0316768A3 EP0316768A3 (en) 1989-08-09
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US4555256A (en) * 1982-05-03 1985-11-26 Linde Aktiengesellschaft Process and device for the production of gaseous oxygen at elevated pressure
US4595405A (en) * 1984-12-21 1986-06-17 Air Products And Chemicals, Inc. Process for the generation of gaseous and/or liquid nitrogen
US4705548A (en) * 1986-04-25 1987-11-10 Air Products And Chemicals, Inc. Liquid products using an air and a nitrogen recycle liquefier

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DE3738559A1 (en) 1989-05-24
EP0316768A2 (en) 1989-05-24
DE3863345D1 (en) 1991-07-25
US4883518A (en) 1989-11-28
EP0316768A3 (en) 1989-08-09
JPH01239376A (en) 1989-09-25

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