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EP2895811B1 - Method and apparatus for separating air by cryogenic distillation - Google Patents

Method and apparatus for separating air by cryogenic distillation Download PDF

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Publication number
EP2895811B1
EP2895811B1 EP13767026.1A EP13767026A EP2895811B1 EP 2895811 B1 EP2895811 B1 EP 2895811B1 EP 13767026 A EP13767026 A EP 13767026A EP 2895811 B1 EP2895811 B1 EP 2895811B1
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EP
European Patent Office
Prior art keywords
exchanger
column
pressure
nitrogen
air
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EP13767026.1A
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German (de)
French (fr)
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EP2895811A1 (en
Inventor
Marie Cognard
Richard Dubettier-Grenier
Sylvain Gerard
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Classifications

    • 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
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04812—Different modes, i.e. "runs" of operation
    • 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
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/04084—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of nitrogen
    • 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
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/0409—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of oxygen
    • 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
    • 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
    • F25J3/04303—Lachmann expansion, i.e. expanded into oxygen producing or low 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
    • F25J3/04406—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
    • 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
    • F25J3/0443—A main column system not otherwise provided, e.g. a modified double column flowsheet

Definitions

  • the present invention relates to a method and apparatus for air separation by cryogenic distillation.
  • the invention proposes in particular a method and describes an apparatus for the transient production of a gas from an apparatus producing, in normal operation, oxygen and nitrogen gas and liquid oxygen and nitrogen.
  • the apparatus comprises a double column having a first column operating at a first so-called medium pressure (MP) and a second column operating at a second so-called low pressure (BP), lower than the first pressure.
  • MP medium pressure
  • BP low pressure
  • This gas, produced in transient mode may for example be pure nitrogen and under pressure and used during inerting phases of petrochemical processes requiring continuous large amounts of nitrogen over several days before requiring the gas requirements of normal walking.
  • the present invention proposes an arrangement of dedicated body heat exchangers making it possible to specifically produce the gaseous requirement during the transient phase, and also produce the need for the other gas (s) (eg oxygen); the production of liquid nitrogen and oxygen can be reduced or even zero during the transient phase.
  • the arrangement of the exchange bodies then makes it possible to produce in normal operation the gas and liquid requirements.
  • the flexibility required of the main exchanger of the separating apparatus is all the greater as the productions required (in terms of pressure and flow) between different operating modes are remote.
  • the dimensioning of the heat exchanger resulting from the different operating steps thus departs from a technico-economic optimum for a given step.
  • an air separation apparatus producing industrial gases for a petrochemical complex will be required to produce very different amounts, at different pressures, depending on the specific operations of the consuming units.
  • the storage of liquids nitrogen, oxygen, argon
  • the use of liquid storage is however limited by the storage capacity.
  • unusual steps of the consuming units require large volumes over several days, it may be preferable to produce directly from the air separation apparatus rather than sizing the storage for this transient step.
  • the production flexibility of the air separation apparatus required by this step can then be provided by the present invention, without degrading the efficiency of normal steps.
  • An alternative solution is the production of medium pressure nitrogen gas from a medium pressure (MP) column and compressor compression. If the gas withdrawal from the MP column is insufficient, vaporization of stored liquid nitrogen will then be necessary.
  • MP medium pressure
  • the nitrogen can be produced by the upper stages of a low pressure column and then compressed by a compressor.
  • the present invention provides an arrangement of dedicated body heat exchangers comprising a dedicated transient exchange line for specifically producing the gaseous requirement during the transient phase.
  • the transient gas considered in this example is nitrogen but the invention is also applicable to other gases produced by the air separation apparatus.
  • the transient nitrogen is pumped from the first column (MP column) and vaporized through a dedicated line of exchanger (called here exchange line transient) against high pressure air (HP) coming from the discharge of a booster possibly driven by a turbine; simultaneously, the pumped oxygen is vaporized through another dedicated line of exchangers against HP air from the discharge of the same booster or a second booster.
  • the production of nitrogen gas which is normally produced from the MP column and heated against MP air from the air purification unit in a dedicated third exchange line, is stopped.
  • the transient nitrogen production is stopped while the normal production of nitrogen gas from the MP column is established.
  • the production of gaseous oxygen is maintained, and the liquid productions are adjusted to their normal instructions.
  • the exchange line dedicated to the production of transient nitrogen gas only involves fluids that will change state as it passes: liquid nitrogen (LIN) vaporises into high pressure nitrogen (HP GAN) against HP air that liquefies.
  • LIN liquid nitrogen
  • HP GAN high pressure nitrogen
  • the expected gain in compactness is substantial because, for the same 'charge' exchanged, the exchange volume can be less than half the volume usually required in the presence of a third fluid without change of state. That is, (Volume / Charge) transient exchanger ⁇ 0.5 x (Volume / Charge) conventional exchanger .
  • a cryogenic distillation air separation installation comprising a double column comprising a first column and a second column, the second column operating at a lower pressure than the first column, a first column heat exchanger, a second heat exchanger.
  • a third heat exchanger capable of, and connected to, supply lines for, allowing indirect heat exchange between only two fluids, a third heat exchanger, means for sending a flow of air to a first pressure substantially equal to the operating pressure of the first column at the first exchanger and the first exchanger at the first column, means for dividing air at a second pressure greater than the first pressure into a first and a second fractions, means for sending the first fraction to the second pressure at the second exchanger through a first era of the supply lines, a valve to prevent the sending of the first fraction to the second exchanger, means to send the second fraction to the second pressure to the third exchanger, possibly other means to send an air flow at a pressure greater than the first pressure at the third exchanger, means for sending a pressurized liquid from the double column to vaporize in the third exchanger, means for sending a liquid required punctually from the double column to vaporize in the second exchanger through a second of the supply lines, a valve to prevent the liquid from being sent occasionally from the double column to the second
  • At least the first and third heat exchangers are brazed aluminum plate and fin exchangers.
  • the apparatus used comprises three heat exchangers 1, 2, 3 which can be brazed aluminum plate and fin heat exchangers. It also comprises a system of distillation columns 25, comprising at least one double distillation column.
  • the double column comprises a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure.
  • the apparatus comprises three air compressors, a main compressor, a first booster for supercharging a portion 13 of the air from the main compressor, a portion of the air of the first booster supplying a turbine and a second booster to boost a compressor. part 7 of the air from the first booster, this second booster being driven by the turbine. An air flow 5 at the first pressure is sent from the main compressor to the first column without being overpressed. Part 7 of the air is at least partially condensed before being sent to the column system.
  • the apparatus has at least two operating steps. According to a first of these steps, which is the normal operation of the process, the air flow 5 at the first pressure is cooled in the exchanger 1 and sent to the first column where it is separated. A flow of nitrogen gas 23 from the first column and a flow of residual nitrogen 21 from the second column are heated in this first exchanger 1: the heat exchanger 1 allows the exchange between three fluids.
  • the second heat exchanger 2 receives no fluid to cool or to heat.
  • the third exchanger 3 cools air 7, 11 from the second booster driven by the turbine.
  • the air partially condensed 11 is sent to the system of columns 25.
  • the air 13 of the first booster is cooled and is sent to an intermediate temperature thereof to the turbine and then to the first or second column.
  • the third exchanger heats residual nitrogen 17 from the second column and liquid oxygen from the second column after a pressurization step.
  • the liquid oxygen can be replaced by gaseous oxygen from the second column.
  • cryogenic liquid as final product 27 which may be liquid nitrogen and / or liquid oxygen.
  • a second step called a transient step
  • the air flow 5 at the first pressure is cooled in the exchanger 1 and sent to the first column where it is separated.
  • a flow of residual nitrogen 21 from the second column is heated in this first exchanger 1: the heat exchanger 1 exchanges between two fluids only, the flow 23 is no longer sent to the exchanger 1, the valve V1 being closed.
  • the second exchanger 2 receives air 9 through a valve V2 from the second booster and pump-pressurized liquid nitrogen 19 from the first column through the valve V3.
  • the third exchanger 3 cools air 7, 11 from the second booster driven by the turbine.
  • the partially condensed air 11 is sent to the column system 25.
  • the air 13 of the first booster is cooled and is sent to an intermediate temperature thereof to the turbine, thus driving the second booster, and then to the first or second column.
  • the third exchanger heats residual nitrogen 17 from the second column and liquid oxygen from the second column after a pressurization step.
  • the liquid oxygen can be replaced by gaseous oxygen from the second column.
  • cryogenic liquid 27 as final product which may be liquid nitrogen and / or liquid oxygen, the total amount of liquid produced as final product being lower than that produced during normal operation.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Emergency Medicine (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Description

La présente invention est relative à un procédé et à un appareil de séparation d'air par distillation cryogénique.The present invention relates to a method and apparatus for air separation by cryogenic distillation.

L'invention propose en particulier une méthode et décrit un appareil de production transitoire d'un gaz à partir d'un appareil produisant en marche normale de l'oxygène et azote gazeux et de l'oxygène et azote liquides. L'appareil comprend une double colonne ayant une première colonne opérant à une première pression dite moyenne pression (MP) et une deuxième colonne opérant à une deuxième pression dite basse pression (BP), plus basse que la première pression.The invention proposes in particular a method and describes an apparatus for the transient production of a gas from an apparatus producing, in normal operation, oxygen and nitrogen gas and liquid oxygen and nitrogen. The apparatus comprises a double column having a first column operating at a first so-called medium pressure (MP) and a second column operating at a second so-called low pressure (BP), lower than the first pressure.

Ce gaz, produit en mode transitoire, peut par exemple être de l'azote pur et sous pression et utilisé lors de phases d'inertage de procédés pétrochimiques nécessitant en continu de grandes quantités d'azote sur plusieurs jours avant de nécessiter les besoins gazeux de la marche normale.This gas, produced in transient mode, may for example be pure nitrogen and under pressure and used during inerting phases of petrochemical processes requiring continuous large amounts of nitrogen over several days before requiring the gas requirements of normal walking.

Cet azote transitoire ne pouvant pas être fourni intégralement par le(s) stockage(s) d'azote liquide, la présente invention propose une disposition d'échangeurs de chaleur en corps dédiés permettant de produire spécifiquement le besoin gazeux pendant la phase transitoire, et produire également le besoin du ou des autres gaz (e.g. l'oxygène) ; les productions d'azote et d'oxygène liquides peuvent être réduites voire nulles pendant la phase transitoire. La disposition des corps d'échange permet ensuite de produire en marche normale les besoins de gaz et de liquides.Since this transient nitrogen can not be supplied in its entirety by the storage (s) of liquid nitrogen, the present invention proposes an arrangement of dedicated body heat exchangers making it possible to specifically produce the gaseous requirement during the transient phase, and also produce the need for the other gas (s) (eg oxygen); the production of liquid nitrogen and oxygen can be reduced or even zero during the transient phase. The arrangement of the exchange bodies then makes it possible to produce in normal operation the gas and liquid requirements.

La flexibilité demandée à l'échangeur principal de l'appareil de séparation est d'autant plus grande que les productions demandées (en termes de pression et débit) entre différents modes de marche sont éloignées. Le dimensionnement de l'échangeur résultant des différentes marches opératoires s'éloigne ainsi d'un optimum technico-économique pour une marche donnée.The flexibility required of the main exchanger of the separating apparatus is all the greater as the productions required (in terms of pressure and flow) between different operating modes are remote. The dimensioning of the heat exchanger resulting from the different operating steps thus departs from a technico-economic optimum for a given step.

Le recours à une ou plusieurs lignes d'échange dédiée(s) à un ou plusieurs cas de marche transitoire(s) permet d'atteindre la flexibilité requise par ces cas de marche, tout en assurant l'optimum technico-économique des marches concernées.The use of one or more exchange lines dedicated to one or more cases of transient market (s) makes it possible to achieve the flexibility required by these market cases, while ensuring the technical and economic optimum of the markets concerned. .

Par exemple, un appareil de séparation d'air produisant des gaz industriels pour un complexe pétro-chimique sera amené à produire des quantités très différentes, à des pressions différentes, selon les opérations spécifiques des unités consommatrices. Habituellement, les stockages de liquides (azote, oxygène, argon) permettent d'améliorer la flexibilité du schéma de production de l'appareil de séparation d'air. Le recours aux stockages de liquides est cependant limité par la capacité du stockage. Lorsque des marches inhabituelles des unités consommatrices nécessitent de grands volumes sur plusieurs jours, il peut être préférable de produire directement à partir de l'appareil de séparation d'air plutôt que de dimensionner le stockage pour cette marche transitoire. La flexibilité de production de l'appareil de séparation d'air requise par cette marche peut alors être apportée par la présente invention, sans toutefois dégrader l'efficacité des marches normales.For example, an air separation apparatus producing industrial gases for a petrochemical complex will be required to produce very different amounts, at different pressures, depending on the specific operations of the consuming units. Usually, the storage of liquids (nitrogen, oxygen, argon) makes it possible to improve the flexibility of the production scheme of the air separation apparatus. The use of liquid storage is however limited by the storage capacity. When unusual steps of the consuming units require large volumes over several days, it may be preferable to produce directly from the air separation apparatus rather than sizing the storage for this transient step. The production flexibility of the air separation apparatus required by this step can then be provided by the present invention, without degrading the efficiency of normal steps.

Une solution alternative est la production d'azote gazeux moyenne pression à partir d'une colonne moyenne pression (MP) et compression par compresseur. Si le soutirage gazeux à partir de la colonne MP est insuffisant, la vaporisation d'azote liquide stocké sera alors nécessaire.An alternative solution is the production of medium pressure nitrogen gas from a medium pressure (MP) column and compressor compression. If the gas withdrawal from the MP column is insufficient, vaporization of stored liquid nitrogen will then be necessary.

Pour produire plus d'azote gazeux que ce qui peut être soutiré à la colonne MP, sans recours à la vaporisation du liquide stocké, l'azote peut être produit par les étages supérieurs d'une colonne basse pression puis également comprimé par un compresseur.To produce more nitrogen gas than can be withdrawn at the MP column, without resorting to the vaporization of the stored liquid, the nitrogen can be produced by the upper stages of a low pressure column and then compressed by a compressor.

Dans les deux cas, un compresseur d'azote est nécessaire, voire également une section à diamètre réduit en tête de la colonne basse pression.In both cases, a nitrogen compressor is necessary, or even a reduced diameter section at the top of the low pressure column.

La présente invention propose une disposition d'échangeurs en corps dédiés comportant une ligne d'échange transitoire dédiée permettant de produire spécifiquement le besoin gazeux pendant la phase transitoire.The present invention provides an arrangement of dedicated body heat exchangers comprising a dedicated transient exchange line for specifically producing the gaseous requirement during the transient phase.

Le gaz transitoire considéré dans cet exemple est l'azote mais l'invention s'applique aussi aux autres gaz produits par l'appareil de séparation d'air.The transient gas considered in this example is nitrogen but the invention is also applicable to other gases produced by the air separation apparatus.

Pendant cette phase transitoire, la production d'oxygène gazeux est maintenue mais les productions d'azote et d'oxygène liquides peuvent être réduites voire nulles.During this transitional phase, the production of oxygen gas is maintained but the production of nitrogen and liquid oxygen can be reduced or even zero.

L'azote transitoire est pompé de la première colonne (colonne MP) et vaporisé à travers une ligne dédiée d'échangeur (appelée ici ligne d'échange transitoire) contre de l'air à haute pression (HP) venant du refoulement d'un surpresseur éventuellement entraîné par une turbine ; simultanément, l'oxygène pompé est vaporisé à travers une autre ligne dédiée d'échangeurs contre de l'air HP venant du refoulement du même surpresseur ou d'un deuxième surpresseur. La production d'azote gazeux, qui est normalement produit à partir de la colonne MP et réchauffé contre de l'air MP venant de l'unité d'épuration d'air dans une troisième ligne d'échange dédiée, est arrêtée.The transient nitrogen is pumped from the first column (MP column) and vaporized through a dedicated line of exchanger (called here exchange line transient) against high pressure air (HP) coming from the discharge of a booster possibly driven by a turbine; simultaneously, the pumped oxygen is vaporized through another dedicated line of exchangers against HP air from the discharge of the same booster or a second booster. The production of nitrogen gas, which is normally produced from the MP column and heated against MP air from the air purification unit in a dedicated third exchange line, is stopped.

Lors de la phase normale, la production d'azote transitoire est arrêtée tandis que la production normale d'azote gazeux à partir de la colonne MP est établie. La production d'oxygène gazeux est maintenue, et les productions liquides sont ajustées à leurs consignes normales.In the normal phase, the transient nitrogen production is stopped while the normal production of nitrogen gas from the MP column is established. The production of gaseous oxygen is maintained, and the liquid productions are adjusted to their normal instructions.

La ligne d'échange dédiée à la production d'azote gazeux transitoire ne fait ici intervenir que des fluides qui vont changer d'état à son passage: l'azote liquide (LIN) se vaporise en azote haute pression (HP GAN) contre de l'air HP qui se liquéfie. L'absence de troisième fluide, habituellement de l'azote résiduaire permettant de réduire l'écart au bout chaud afin de gagner en efficacité énergétique de l'appareil de séparation d'air, permet ici d'améliorer fortement la compacité de l'échangeur transitoire pour une même quantité de chaleur échangée (ou 'charge') ; cela permet aussi d'utiliser des ondes plus denses. Dans le cas de la présente invention, le gain attendu en compacité est conséquent car, pour une même 'charge' échangée, le volume d'échange peut être inférieur de moitié au volume habituellement nécessaire en présence d'un troisième fluide sans changement d'état. Soit, (Volume/Charge)échangeur transitoire < 0,5 x (Volume/Charge)échangeur classique.The exchange line dedicated to the production of transient nitrogen gas only involves fluids that will change state as it passes: liquid nitrogen (LIN) vaporises into high pressure nitrogen (HP GAN) against HP air that liquefies. The absence of a third fluid, usually residual nitrogen, which makes it possible to reduce the gap at the hot end so as to improve the energy efficiency of the air separation apparatus, makes it possible here to greatly improve the compactness of the exchanger. transient for the same amount of heat exchanged (or 'charge'); it also allows to use more dense waves. In the case of the present invention, the expected gain in compactness is substantial because, for the same 'charge' exchanged, the exchange volume can be less than half the volume usually required in the presence of a third fluid without change of state. That is, (Volume / Charge) transient exchanger <0.5 x (Volume / Charge) conventional exchanger .

Cette solution permet également de produire spécifiquement l'azote nécessaire selon la marche demandée par le client par une redistribution des flux sur les corps d'échanges concernés par la production. Lors de la phase transitoire, seul l'azote transitoire est produit et le passage du corps d'échange utilisé pour l'azote normal est à l'arrêt. Pendant la phase normale, seul l'azote normal est produit et le corps d'échange transitoire est à l'arrêt. Le document US5355682A divulgue la préambule de la revendication 1.This solution also makes it possible to specifically produce the necessary nitrogen according to the step required by the customer by a redistribution of the flows on the bodies of exchange concerned by the production. During the transient phase, only the transient nitrogen is produced and the passage of the exchange body used for the normal nitrogen is stopped. During the normal phase, only normal nitrogen is produced and the transient exchange body is stopped. The document US5355682A discloses the preamble of claim 1.

Selon un objet de l'invention, il est prévu un procédé de production d'un premier gaz sous pression ainsi qu'un deuxième gaz de manière ponctuelle par distillation cryogénique de l'air dans une double colonne comprenant une première colonne et une deuxième colonne, la deuxième colonne fonctionnant à plus basse pression que la première colonne dans lequel :

  1. i) selon une première marche, de l'air se refroidit à une première pression qui est substantiellement la pression d'opération de la première colonne, dans un premier échangeur de chaleur et est envoyé à la première colonne, deux débits gazeux riches en azote provenant de la première et la deuxième colonne se réchauffent dans le premier échangeur, aucun fluide ne se réchauffe ni se refroidit dans un deuxième échangeur de chaleur, au moins un débit d'air à une deuxième pression supérieure à la première pression se refroidit dans un troisième échangeur de chaleur, un liquide pressurisé se vaporise dans le troisième échangeur et un débit gazeux riche en azote provenant de la deuxième colonne se réchauffe dans le troisième échangeur, et
  2. ii) selon une deuxième marche, de l'air se refroidit à la première pression dans le premier échangeur et est envoyé à la première colonne, un débit gazeux riche en azote provenant de la deuxième colonne se réchauffe dans le premier échangeur, un débit liquide pressurisé provenant de la double colonne se réchauffe et se vaporise dans le deuxième échangeur pour former un gaz requis ponctuellement, un débit d'air à la deuxième pression se refroidit et éventuellement se condense dans le deuxième échangeur, ce débit d'air et le débit liquide pressurisé étant les seuls fluides échangeant de la chaleur dans le deuxième échangeur, un débit d'air à la deuxième pression se refroidit dans le troisième échangeur, éventuellement un autre débit d'air à une pression supérieure à la première, voire à la deuxième, pression se refroidit dans le troisième échangeur, un liquide pressurisé se vaporise dans le troisième échangeur et un débit gazeux riche en azote provenant de la deuxième colonne se réchauffe dans le troisième échangeur.
According to one object of the invention, there is provided a method for producing a first pressurized gas and a second gas in a pointwise manner by cryogenic distillation of the air in a double column comprising a first column and a second column, the second column operating at a lower pressure than the first column in which:
  1. i) in a first step, air is cooled to a first pressure which is substantially the operating pressure of the first column, in a first heat exchanger and is sent to the first column, two gas flows rich in nitrogen from the first and second columns are heated in the first heat exchanger, no fluid is heated or cooled in a second heat exchanger, at least one air flow at a second pressure greater than the first pressure cools in a third heat exchanger, a pressurized liquid vaporizes in the third exchanger and a nitrogen-rich gas flow from the second column is heated in the third exchanger, and
  2. ii) according to a second step, air is cooled at the first pressure in the first exchanger and is sent to the first column, a nitrogen-rich gas flow from the second column is heated in the first exchanger, a liquid flow pressurized from the double column heats up and vaporizes in the second exchanger to form a gas required punctually, a flow of air at the second pressure cools and eventually condenses in the second exchanger, this air flow and flow pressurized liquid being the only fluids exchanging heat in the second heat exchanger, an air flow at the second pressure cools in the third heat exchanger, possibly another air flow at a pressure greater than the first, or even the second , pressure cools in the third exchanger, a pressurized liquid vaporizes in the third exchanger and a gas flow rich in az ote from the second column warms up in the third exchanger.

Selon d'autres caractéristiques facultatives :

  • pendant la deuxième marche un seul débit gazeux riche en azote provenant de la deuxième colonne se réchauffe dans le premier échangeur.
  • un des débits d'air à la pression supérieure à la pression d'opération de la première colonne se refroidit partiellement dans le troisième échangeur dans les première et deuxième marches, est détendu dans une turbine et envoyé à la première ou la deuxième colonne.
  • le débit envoyé à la turbine provient d'un premier surpresseur l'autre des débits d'air à la pression supérieure à la pression d'opération de la première colonne provient d'un deuxième surpresseur entraîné par la turbine.
  • l'on produit une quantité de liquide comme produit final selon la première marche et l'on ne produit aucun liquide comme produit final selon la deuxième marche.
  • l'on produit une quantité de liquide comme produit final selon la première marche et l'on produit une quantité de liquide inférieure à celle produit dans la première marche comme produit final selon la deuxième marche.
  • le débit liquide pressurisé est riche en azote.
According to other optional features:
  • during the second step a single gas flow rich in nitrogen from the second column is heated in the first exchanger.
  • one of the air flows at the pressure greater than the operating pressure of the first column cools partially in the third heat exchanger in the first and second steps, is expanded in a turbine and sent to the first or second column.
  • the flow rate sent to the turbine comes from a first booster the other of the air flows at the pressure greater than the operating pressure of the first column comes from a second booster driven by the turbine.
  • a quantity of liquid is produced as the final product according to the first step and no liquid is produced as final product according to the second step.
  • a quantity of liquid is produced as the final product according to the first step and a lower quantity of liquid is produced than that produced in the first step as the final product according to the second step.
  • the pressurized liquid flow is rich in nitrogen.

Selon un autre objet de l'invention, il est prévu une installation de séparation d'air par distillation cryogénique comprenant une double colonne comprenant une première colonne et une deuxième colonne, la deuxième colonne fonctionnant à plus basse pression que la première colonne, un premier échangeur de chaleur, un deuxième échangeur de chaleur.capable de, et relié à des conduites d'alimentation pour, permettre un échange de chaleur indirect entre seulement deux fluides, un troisième échangeur de chaleur, des moyens pour envoyer un débit d'air à une première pression substantiellement égale à la pression d'opération de la première colonne au premier échangeur et du premier échangeur à la première colonne, des moyens pour diviser de l'air à une deuxième pression supérieure à la première pression en une première et une deuxième fractions, des moyens pour envoyer la première fraction à la deuxième pression au deuxième échangeur à travers une première des conduites d'alimentation, une vanne pour empêcher l'envoi de la première fraction vers le deuxième échangeur, des moyens pour envoyer la deuxième fraction à la deuxième pression au troisième échangeur, éventuellement d'autres moyens pour envoyer un débit d'air à une pression supérieure à la première pression au troisième échangeur, des moyens pour envoyer un liquide pressurisé de la double colonne se vaporiser dans le troisième échangeur, des moyens pour envoyer un liquide requis ponctuellement de la double colonne se vaporiser dans le deuxième échangeur à travers une deuxième des conduites d'alimentation, une vanne pour empêcher l'envoi de liquide requis ponctuellement de la double colonne vers le deuxième échangeur, des moyens pour envoyer un gaz riche en azote de la première colonne se réchauffer dans le premier échangeur, une vanne pour empêcher l'envoi de gaz riche en azote de la première colonne vers le premier échangeur, des moyens pour envoyer un gaz enrichi en azote de la double colonne vers le premier échangeur et des moyens pour envoyer un gaz enrichi en azote de la double colonne vers le troisième échangeur.According to another object of the invention, there is provided a cryogenic distillation air separation installation comprising a double column comprising a first column and a second column, the second column operating at a lower pressure than the first column, a first column heat exchanger, a second heat exchanger. capable of, and connected to, supply lines for, allowing indirect heat exchange between only two fluids, a third heat exchanger, means for sending a flow of air to a first pressure substantially equal to the operating pressure of the first column at the first exchanger and the first exchanger at the first column, means for dividing air at a second pressure greater than the first pressure into a first and a second fractions, means for sending the first fraction to the second pressure at the second exchanger through a first era of the supply lines, a valve to prevent the sending of the first fraction to the second exchanger, means to send the second fraction to the second pressure to the third exchanger, possibly other means to send an air flow at a pressure greater than the first pressure at the third exchanger, means for sending a pressurized liquid from the double column to vaporize in the third exchanger, means for sending a liquid required punctually from the double column to vaporize in the second exchanger through a second of the supply lines, a valve to prevent the liquid from being sent occasionally from the double column to the second exchanger, means for sending a nitrogen-rich gas from the first column to heat up in the second column; the first exchanger, a valve for preventing the delivery of nitrogen-rich gas from the first column to the first exchanger, means for sending a nitrogen enriched gas from the double column to the first exchanger and means for sending an enriched gas in nitrogen from the double column to the third exchanger.

Eventuellement au moins le premier et le troisième échangeur de chaleur sont des échangeurs à plaques et à ailettes en aluminium brasés.Optionally at least the first and third heat exchangers are brazed aluminum plate and fin exchangers.

L'invention sera décrite plus en détail en se référant à la figure qui illustre un procédé selon l'invention. L'appareil utilisé comprend trois échangeurs de chaleur 1, 2, 3 pouvant être des échangeurs à plaques et à ailettes en aluminium brasé. Il comprend également un système de colonnes de distillation 25, comprenant au moins une double colonne de distillation. La double colonne comprend une première colonne opérant à une première pression et une deuxième colonne opérant à une deuxième pression, plus basse que la première pression.The invention will be described in more detail with reference to the figure which illustrates a method according to the invention. The apparatus used comprises three heat exchangers 1, 2, 3 which can be brazed aluminum plate and fin heat exchangers. It also comprises a system of distillation columns 25, comprising at least one double distillation column. The double column comprises a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure.

L'appareil comprend trois compresseurs d'air, un compresseur principal, un premier surpresseur pour surpresser une partie 13 de l'air provenant du compresseur principal, une partie de l'air du premier surpresseur alimentant une turbine et un deuxième surpresseur pour surpresser une partie 7 de l'air provenant du premier surpresseur, ce deuxième surpresseur étant entraîné par la turbine. Un débit d'air 5 à la première pression est envoyé du compresseur principal à la première colonne sans avoir été surpressé. La partie 7 de l'air est au moins partiellement condensée avant d'être envoyé au système de colonnes.The apparatus comprises three air compressors, a main compressor, a first booster for supercharging a portion 13 of the air from the main compressor, a portion of the air of the first booster supplying a turbine and a second booster to boost a compressor. part 7 of the air from the first booster, this second booster being driven by the turbine. An air flow 5 at the first pressure is sent from the main compressor to the first column without being overpressed. Part 7 of the air is at least partially condensed before being sent to the column system.

L'appareil a au moins deux marches d'opération. Selon une première de ces marches, qui est la marche normale du procédé, le débit d'air 5 à la première pression est refroidi dans l'échangeur 1 et envoyé à la première colonne où il est séparé. Un débit d'azote gazeux 23 de la première colonne et d'un débit d'azote résiduaire 21 de la deuxième colonne se réchauffent dans ce premier échangeur 1 : l'échangeur de chaleur 1 permet l'échange entre trois fluides.The apparatus has at least two operating steps. According to a first of these steps, which is the normal operation of the process, the air flow 5 at the first pressure is cooled in the exchanger 1 and sent to the first column where it is separated. A flow of nitrogen gas 23 from the first column and a flow of residual nitrogen 21 from the second column are heated in this first exchanger 1: the heat exchanger 1 allows the exchange between three fluids.

Selon cette marche, le deuxième échangeur 2 ne reçoit aucun fluide à refroidir ou à réchauffer. Par contre le troisième échangeur 3 refroidit de l'air 7, 11 provenant du deuxième surpresseur entraîné par la turbine. L'air partiellement condensé 11 est envoyé au système de colonnes 25. Egalement dans cet échangeur 3, l'air 13 du premier surpresseur se refroidit et est envoyé à une température intermédiaire de celui-ci à la turbine et ensuite à la première ou la deuxième colonne.According to this step, the second heat exchanger 2 receives no fluid to cool or to heat. On the other hand, the third exchanger 3 cools air 7, 11 from the second booster driven by the turbine. The air partially condensed 11 is sent to the system of columns 25. Also in this exchanger 3, the air 13 of the first booster is cooled and is sent to an intermediate temperature thereof to the turbine and then to the first or second column.

Le troisième échangeur réchauffe de l'azote résiduaire 17 provenant de la deuxième colonne et de l'oxygène liquide 15 provenant de la deuxième colonne, après une étape de pressurisation. L'oxygène liquide 15 peut être remplacé par de l'oxygène gazeux provenant de la deuxième colonne.The third exchanger heats residual nitrogen 17 from the second column and liquid oxygen from the second column after a pressurization step. The liquid oxygen can be replaced by gaseous oxygen from the second column.

Pendant cette marche, il y a également une production de liquide cryogénique comme produit final 27 pouvant être de l'azote liquide et/ou de l'oxygène liquide.During this step, there is also a production of cryogenic liquid as final product 27 which may be liquid nitrogen and / or liquid oxygen.

Pendant une deuxième marche, dite marche transitoire, le débit d'air 5 à la première pression est refroidi dans l'échangeur 1 et envoyé à la première colonne où il est séparé. Un débit d'azote résiduaire 21 de la deuxième colonne se réchauffe dans ce premier échangeur 1 : l'échangeur de chaleur 1 effectue l'échange entre deux fluides seulement, le débit 23 n'étant plus envoyé à l'échangeur 1, la vanne V1 étant fermée.During a second step, called a transient step, the air flow 5 at the first pressure is cooled in the exchanger 1 and sent to the first column where it is separated. A flow of residual nitrogen 21 from the second column is heated in this first exchanger 1: the heat exchanger 1 exchanges between two fluids only, the flow 23 is no longer sent to the exchanger 1, the valve V1 being closed.

Selon cette marche, le deuxième échangeur 2 reçoit de l'air 9 à travers une vanne V2 provenant du deuxième surpresseur et de l'azote liquide 19 pressurisé par pompe provenant de la première colonne à travers la vanne V3.According to this step, the second exchanger 2 receives air 9 through a valve V2 from the second booster and pump-pressurized liquid nitrogen 19 from the first column through the valve V3.

Par contre le troisième échangeur 3 refroidit de l'air 7, 11 provenant du deuxième surpresseur entraîné par la turbine. L'air partiellement condensé 11 est envoyé au système de colonnes 25. Egalement dans cet échangeur 3, l'air 13 du premier surpresseur se refroidit et est envoyé à une température intermédiaire de celui-ci à la turbine, ainsi entraînant le deuxième surpresseur, et ensuite à la première ou la deuxième colonne.On the other hand, the third exchanger 3 cools air 7, 11 from the second booster driven by the turbine. The partially condensed air 11 is sent to the column system 25. Also in this exchanger 3, the air 13 of the first booster is cooled and is sent to an intermediate temperature thereof to the turbine, thus driving the second booster, and then to the first or second column.

Le troisième échangeur réchauffe de l'azote résiduaire 17 provenant de la deuxième colonne et de l'oxygène liquide 15 provenant de la deuxième colonne, après une étape de pressurisation. L'oxygène liquide 15 peut être remplacé par de l'oxygène gazeux provenant de la deuxième colonne.The third exchanger heats residual nitrogen 17 from the second column and liquid oxygen from the second column after a pressurization step. The liquid oxygen can be replaced by gaseous oxygen from the second column.

Pendant cette marche, soit il n'y aucune production de liquide comme produit final ou il y a également une production de liquide cryogénique 27 comme produit final pouvant être de l'azote liquide et/ou de l'oxygène liquide, la quantité totale de liquide produit comme produit final étant inférieure à celle produite pendant la marche normale.During this step, either there is no liquid production as final product or there is also a production of cryogenic liquid 27 as final product which may be liquid nitrogen and / or liquid oxygen, the the total amount of liquid produced as final product being lower than that produced during normal operation.

Claims (10)

  1. Method for producing a first pressurised gas and a second gas on a one-off basis by cryogenic distillation of air in a dual column including a first column and a second column, the second column operating at a lower pressure than the first column, wherein:
    i) according to a first step, the air (5) cools down at a first pressure, which is substantially the operating pressure of the first column, in a first heat exchanger (1) and is sent to the first column, two nitrogen-rich gas flows (21, 23) originating from the first and second columns heat up in the first exchanger, at least one air flow (11, 13) at a second pressure that is greater than the first pressure cools down in a third heat exchanger (3), a pressurised liquid (15) vaporises in the third exchanger and a nitrogen-rich gas flow (17) originating from the second column heats up in the third exchanger, and
    ii) according to a second step, air (5) cools down at the first pressure in the first exchanger and is sent to the first column, a nitrogen-rich gas flow (21) originating from the second column heats up in the first exchanger, a pressurised liquid flow (19) originating from the dual column heats up and vaporises in a second exchanger to form a gas required on a one-off basis, an air flow (9) at the second pressure cools down and potentially condenses in the second exchanger, whereby this air flow and the pressurised liquid flow are the only fluids exchanging heat in the second exchanger, an air flow (11, 13) at the second pressure cools down in the third exchanger, another air flow at a pressure that is greater than the first pressure, or even the second pressure, potentially cools down in the third exchanger, a pressurised liquid (15) vaporises in the third exchanger and a nitrogen-rich gas flow (17) originating from the second column heats up in the third exchanger,
    characterised in that according to the first step, no fluid heats up or cools down in the second heat exchanger (2).
  2. Method according to claim 1 wherein, during the second step, a single nitrogenrich gas flow (21) originating from the second column heats up in the first exchanger.
  3. Method according to one of the previous claims, wherein one of the air flows (13) at the pressure that is greater than the operating pressure of the first column partially cools down in the third exchanger (3) in the first and second steps, is expanded in a turbine and sent to the first or second column.
  4. Method according to claim 3, wherein the flow sent to the turbine originates from a first supercharger.
  5. Method according to claim 3 or 4, wherein the other (7, 11) of the air flows at the pressure that is greater than the operating pressure of the first column originates from a second supercharger driven by the turbine.
  6. Method according to one of the previous claims, wherein a quantity of liquid (27) is produced as an end product according to the first step and no liquid is produced as an end product according to the second step.
  7. Method according to one of claims 1 to 5, wherein a quantity of liquid (27) is produced as an end product according to the first step and a lesser quantity of liquid to that produced in the first step is produced as an end product according to the second step.
  8. Method according to one of claims 1 to 7, wherein the pressurised liquid flow (19) is rich in nitrogen.
  9. Installation for air separation by cryogenic distillation suitable for performing the method of claim 1, comprising a dual column including a first column and a second column, the second column operating at a lower pressure than the first column, a first heat exchanger (1), a second heat exchanger (2) capable of allowing for, and connected to feed lines in order to allow for indirect heat exchange to take place solely between two fluids, a third heat exchanger (3), means (5) for sending an air flow at a first pressure that is substantially equal to the operating pressure of the first column to the first exchanger and from the first exchanger to the first column, means for dividing the air (7) at a second pressure that is greater than the first pressure into a first (9) and a second fraction (11), means for sending the first fraction (9) at the second pressure to the second exchanger through a first of the feed lines, a valve (V2) for preventing the first fraction from being sent to the second exchanger, means for sending the second fraction (11) at the second pressure to the third exchanger, other potential means for sending an air flow at a pressure that is greater than the first pressure to the third exchanger, means for sending a pressurised liquid (15) from the dual column to vaporise in the third exchanger, means for sending a liquid required on a one-off basis from the dual column to vaporise in the second exchanger through a second (19) of the feed lines by exchanging heat with the first fraction, a valve (V3) for preventing liquid required on a one-off basis from being sent from the dual column to the second exchanger, means for sending a nitrogen-rich gas from the first column to heat up in the first exchanger, a valve (V1) for preventing the nitrogen-rich gas from being sent from the first column to the first exchanger, means for sending a nitrogen-rich gas from the dual column to the first exchanger, and means for sending a nitrogen-rich gas from the dual column to the third exchanger.
  10. Installation according to claim 9, wherein at least the first and third heat exchangers (1, 3) are brazed aluminium plate-fin heat exchangers.
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FR2995393B1 (en) 2014-10-03
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FR2995393A1 (en) 2014-03-14
CN104620067B (en) 2017-03-08

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