EP0413631A1 - Nitrogen production process - Google Patents

Nitrogen production process Download PDF

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Publication number
EP0413631A1
EP0413631A1 EP90402289A EP90402289A EP0413631A1 EP 0413631 A1 EP0413631 A1 EP 0413631A1 EP 90402289 A EP90402289 A EP 90402289A EP 90402289 A EP90402289 A EP 90402289A EP 0413631 A1 EP0413631 A1 EP 0413631A1
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EP
European Patent Office
Prior art keywords
nitrogen
fraction
pressure
column
expanded
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP90402289A
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German (de)
French (fr)
Other versions
EP0413631B1 (en
Inventor
Sophie Gastinne
Francois Venet
Bao Ha
Naohiko Yamashita
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Liquid Air Engineering Corp Canada
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Teisan KK
Original Assignee
Liquid Air Engineering Corp Canada
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Teisan KK
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Application filed by Liquid Air Engineering Corp Canada, Air Liquide SA, LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude, Teisan KK filed Critical Liquid Air Engineering Corp Canada
Priority to EP94106964A priority Critical patent/EP0610972B1/en
Publication of EP0413631A1 publication Critical patent/EP0413631A1/en
Application granted granted Critical
Publication of EP0413631B1 publication Critical patent/EP0413631B1/en
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    • 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
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    • 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
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    • 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
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    • F25J3/044—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 single pressure main column system only
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    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/42—Nitrogen or special cases, e.g. multiple or low purity N2
    • F25J2215/44—Ultra high purity nitrogen, i.e. generally less than 1 ppb impurities
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    • 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
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    • Y10S62/939—Partial feed stream expansion, air

Definitions

  • the present invention relates to a process for producing nitrogen gas under low or medium pressure, from a mixture to be separated, such as air, containing mainly nitrogen and oxygen.
  • the mixture to be treated is compressed at a pressure at least equal to the pressure (low or medium) of the column (of the order of 4 to 12 bars).
  • the cooled mixture is subjected to a fractional distillation (under low or medium pressure) to obtain at the bottom a fraction enriched in oxygen, and at the top a fraction rich in gaseous nitrogen under pressure.
  • an oxygen-enriched fraction is drawn off in liquid form and, for at least a fraction of said fraction, it is expanded to a pressure below the column pressure, and it is vaporized in exchange for heat with the nitrogen-enriched fraction of condensation.
  • This solution may be advantageous in the case where it is sought to produce a high percentage of liquid nitrogen, or in the case where it is sought to obtain flexibility between gas production and a mixed gas-liquid operation.
  • the expanded gas is mixed with the low pressure gas, or expanded in the vicinity of atmospheric pressure, which makes it possible to maximize the rate of expansion , and therefore minimize the relaxed and then recompressed flow.
  • This arrangement makes it possible to temporarily vary the production of nitrogen, by varying the operation of the turbine and the liquid stocks, between 40 to 50% and 140 to 160% of the nominal production.
  • the mixture to be treated is compressed to a pressure at least equal to the low pressure (of the order of 3 to 5 bars)
  • the compressed mixture is cooled, -
  • the cooled mixture is subjected to fractional distillation, under low pressure, to obtain at the bottom a fraction enriched in oxygen, and at the top a fraction enriched in nitrogen.
  • the fractional distillation is carried out in two stages, the first at a relatively low temperature, and the second at a relatively high temperature to separate a relatively heavy fraction, characterized in that at least part of the gas rich in nitrogen is compressed, cooled and condensed in exchange for heat with the tank fraction of the second distillation stage, then expanded and introduced at the top of said stage, a relatively heavy production flow being withdrawn from the stage, then reheated.
  • the present invention relates to a method as defined above, allowing both a good nitrogen extraction yield and a resistance to cold of the device by expansion in a turbine of a gas poor in oxygen.
  • the production of cold necessary for the process is ensured: - Either by expansion of at least one refrigerant gas flow, which may be the mixture to be treated, which is expanded at the low pressure of the column, and injected into the column. - Either by expansion of at least one refrigerant gas flow, which may be the mixture to be treated, which is expanded to the lower pressure of the waste, possibly mixed with the waste. - Either by expansion of a fraction of the recycled nitrogen, to a pressure less than or equal to the low pressure, then reheated and recompressed.
  • the refrigerant gas flow is at least part of the mixture to be treated, expanded before its introduction into the column and according to a variant, the refrigerant gas flow is a part of the mixture to be treated expanded at pressure below the low pressure then warmed up.
  • the refrigerant gas flow is combined with the gas flow enriched in oxygen before heating.
  • a condensed part of the cycle gas is diverted to a buffer capacity, with sampling and reintroduction into the column in the event of an increase in the nitrogen production flow rate, while part of the stream of liquid rich in oxygen is sent to a buffer capacity to be reinjected into the column head condenser, in the event of a reduction in the production of nitrogen gas, which makes it possible to replenish the stock of liquid nitrogen under pressure.
  • the actions of the refrigerant flow of gas origin to be treated are associated with the refrigeration flow of recycling gas.
  • a stream of gas for example air previously purified from, is compressed (not shown) at a pressure higher than the low pressure of the distillation column (4), defined below. traditional way.
  • this current is cooled to an intermediate temperature represented by the level (2a).
  • this gas stream is expanded at low pressure of the order of 3 to 5 bar abs. in the turbine (3), then introduced into the distillation column (4), at an intermediate level between two distillation stages, one upper (4a) and the other lower (4b).
  • a liquid fraction enriched with oxygen (7) is collected, which is extracted from the column, if necessary sub-cooled in the exchanger (10), expanded in the valve (8 ) and finally introduced into the condenser of the column (4), essentially consisting of an exchanger (5) for the condensation of all or part of the gaseous fraction available at the top of the column (4).
  • This oxygen-enriched fraction is extracted from the above-mentioned condenser, in the form of a current (9), which is, if necessary, heated in the exchanger (10), then the exchanger (2), and finally used or evacuated at the outlet of the exchanger (2).
  • a part condensed in the exchanger (5) ensures part of the reflux of the distillation.
  • a part can be extracted in liquid form through the conduit (12).
  • another part is extracted, in gaseous form through the conduit (11).
  • the corresponding current is heated if necessary, in the exchanger (10), then in the exchanger (2), to obtain at the outlet of the latter a stream of relatively pure nitrogen gas, under low pressure, one of which part (X and / or Y) constitutes the production of the separation unit.
  • This stream (14) is firstly cooled in the exchanger (2), at least partly condensed at the bottom of the column (4), in the exchanger (6), in exchange for heat with the fraction rich in oxygen, during vaporization. Then the stream (20) of condensed nitrogen is, if necessary, sub-cooled in the exchanger (10), expanded in the valve (17), and introduced at the head of the column (4). Beforehand, a part (15) can be derived from the current (20) to constitute another fraction of production liquid nitrogen, available at a pressure different from that which is extracted by the conduit (12).
  • the distillation column (4) works under a relatively low pressure, between 3 and 5 bar abs. for example.
  • the mode of execution according to FIG. 2 differs from that described above by the following essential characteristics:
  • the stream of compressed air (1) is divided into two parts, the first (2a) treated as above, that is to say expanded in the turbine (3) and introduced into the column (4), and a second and last part continuing its cooling in the exchanger (2) until total or partial liquefaction (111), expanded in the valve (112) and introduced into the column (4) at an intermediate level, above the point of introduction of the expanded gas stream.
  • the distillation column (4) can therefore be divided into 3 zones, respectively from top to bottom (4a), (4b), (4c).
  • FIG. 3 The mode of execution of FIG. 3 differs from that shown in FIG. 2 by the following essential characteristics:
  • a part (1b) of the compressed air (1) is diverted before passing through the exchanger (2) to be admitted into the compressor part (50) of a turbine assembly (3) booster (50), cooled to temperature ambient in the exchanger (51). This fraction is then introduced into the exchanger (2) to be extracted at an intermediate temperature, expanded in the turbine (3) and introduced into the column (4).
  • the other part (111) undergoes as before its cooling in the exchanger (2), where it is possibly partially condensed (111) before being expanded (112) and injected into the column (4).
  • the mode of execution according to FIG. 4 differs from that represented in FIG. 1, by the following essential characteristics, the reference numerals common with FIG. 1 designating identical currents or components or having the same function.
  • fractional distillation is carried out in two stages, namely: a first stage at a relatively low temperature, equivalent to the distillation column (4) of FIG. 1, - And a second stage (155) at relatively high temperature, operating under a relatively high pressure, between 6 and 12 bars.
  • this current (14) is condensed at least in part at the foot of the column (155), in the exchanger (166), by heat exchange with the fraction rich in relatively heavy nitrogen being vaporized, always at the foot of the same column. Then the current (14) optionally passes through an impurity trap such as CO of the cold adsorption type (167) shown in dotted lines, expanded in a valve (168), and introduced into the column (155) at an intermediate level.
  • an impurity trap such as CO of the cold adsorption type (167) shown in dotted lines, expanded in a valve (168), and introduced into the column (155) at an intermediate level.
  • the relatively light fraction available at the head of this same column (155) is almost entirely condensed in the exchanger (6) existing at the bottom of the column (4), in exchange for heat with the oxygen-rich fraction during vaporization. , available at the bottom of the column (4).
  • the non-condensed fraction available at the outlet of the exchanger (6) is mixed with the waste gas (9) after expansion.
  • the relatively heavy fraction at the bottom of the column (155) is discharged through the conduit (18) in gaseous form, heated in the exchanger (2), and discharged in the heated state of the installation.
  • a relatively heavy fraction available in liquid form at the bottom of the second stage (155) is drawn off into a stream (177) which is expanded in the valve (169) and introduced at the head of the first distillation stage (4).
  • the compressed air stream (1) is divided into two parts, the first (2a) treated as above, that is to say expanded in the turbine (3) and introduced into the column (4) , and a second and last part continuing to cool in the exchanger (2) until liquefaction (111), expanded in the valve (112) and introduced into the column (4), above the point of introduction of the current gaseous (1) relaxed.
  • the distillation column (4) can therefore be divided into three zones, respectively from top to bottom (4a), (4b), and (4c).
  • the mode of execution of FIG. 5 differs from that shown in FIG. 2 by the following essential characteristics: - First of all, as in FIG. 2, the stream of compressed air (1) is divided into two parts, on the one hand a part (2a) subjected to expansion in the turbine (3), and on the other hand a residual part (121), introduced into the column (4). But the relaxed air stream (112) is extracted from the installation, without passing through the distillation column (4), by joining with the fraction (9) rich in oxygen and vaporized, the whole (9-112) then being reheated in the exchanger (2) and used or removed. - For the rest, it is possible to store the liquid fractions available in the installation, during periods of relatively low production, and to return these liquid fractions to the installation, during periods of significant production.
  • the stream of recycled nitrogen can be extracted by a pipe (20a) to a buffer tank (20c), and returned by the pipe (20b) to the column (4), downstream of the valve (17 ).
  • the oxygen-rich fraction (7) can be extracted from the installation by a bypass duct (7a), to the buffer tank (7c), and returned by the duct (7b), to the column (4), downstream of the valve (8).
  • the mode of execution of figure 6 differs from that represented in figure 5 by the following characteristics: - A first part (1a) of the compressed air (1) is cooled in the exchanger (2), then introduced (121) into the column (4). - The other part (1b) of the compressed air (1) is diverted before it passes through the exchanger (2) to be admitted into the compressor part (50) of a turbine assembly (3) booster (50) , cooled to room temperature in the exchanger (51) and then introduced into the exchanger (2) to be extracted at an intermediate temperature, expanded (112) in the turbine (3) and combined with the fraction (9) rich in oxygen and vaporized in the condenser (5).
  • the two rocker-type versions described in FIGS. 5 and 6 have the advantage of being able to have a production of nitrogen gas which can range from 50 to 150% of the nominal production.
  • a portion (141) of the nitrogen-rich recycling gas (14) is drawn off at intermediate temperature (2b) from the exchanger (2) to be expanded to low pressure in a turbine (142), then, without passing in the column (4), is combined with the stream rich in nitrogen (11) extracted from the column (4), to form a stream (41) which is heated in the exchanger (2).
  • the air turbine (144) is used for the production of nitrogen gas (X / Y) without production of liquid.
  • Part of the recycled nitrogen (14) is sent to the turbine (142) to produce liquid nitrogen thanks to the additional frigories provided by the polytropic expansion of this turbinated nitrogen, to the detriment of the production of nitrogen gas.
  • This arrangement makes it possible to have gas / liquid flexibility on the production of nitrogen.
  • Part (152) of the nitrogen-rich recycling gas is diverted before passing through the exchanger (2) to be admitted into the compressor part (52) of a turbine (53) -brake or booster compressor assembly (52 ), and then introduced into the exchanger (2) to be extracted at an intermediate temperature (2c) and sent to the turbine (53).
  • the gas (66) from the turbine (53) is here expanded to a pressure lower than that of the stream rich in nitrogen (11). It is therefore reheated in the exchanger (2) in its own passages (67), the reheated current then being recompressed at (62) to be admitted to the suction of the compressor (13).
  • FIG. 9 differs from that shown in FIG. 8 in that the expanded gas at (56) is combined with the stream rich in nitrogen (11).

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Abstract

The cooling requirements of the plant are provided, from a fractional distillation (4) at a relatively low pressure, by decompressing (3) one or more fluids including the mixture to be treated, or by decompressing a part of the cycle gas. <IMAGE>

Description

La présente invention concerne un procédé de production d'azote gazeux sous basse ou moyenne pression, à partir d'un mélange à séparer, tel que de l'air, contenant principalement de l'azote et de l'oxygène.The present invention relates to a process for producing nitrogen gas under low or medium pressure, from a mixture to be separated, such as air, containing mainly nitrogen and oxygen.

Pour produire de l'azote à partir d'air atmosphérique par exemple, on connait déjà un procédé selon lequel :
. on comprime à une pression au moins égale à la pression (basse ou moyenne) de la colonne, le mélange à traiter (de l'ordre de 4 à 12 bars).
. on soumet le mélange refroidi à une distillation fractionnée (sous la basse ou moyenne pression) pour obtenir en pied une fraction enrichie en oxygène, et en tête une fraction riche en azote gazeux sous pression.
. on soutire une fraction enrichie en oxygène, sous forme liquide et, pour au moins une fraction de ladite fraction, on la détend à une pression inférieure à la pression de la colonne, et on la vaporise en échange de chaleur avec la fraction enrichie en azote de condensation.To produce nitrogen from atmospheric air, for example, we already know a process according to which:
. the mixture to be treated is compressed at a pressure at least equal to the pressure (low or medium) of the column (of the order of 4 to 12 bars).
. the cooled mixture is subjected to a fractional distillation (under low or medium pressure) to obtain at the bottom a fraction enriched in oxygen, and at the top a fraction rich in gaseous nitrogen under pressure.
. an oxygen-enriched fraction is drawn off in liquid form and, for at least a fraction of said fraction, it is expanded to a pressure below the column pressure, and it is vaporized in exchange for heat with the nitrogen-enriched fraction of condensation.

L'inconvénient majeur de ce procédé est la limitation du taux d'extraction (35 à 55 %). Cette limitation est essentiellement dûe à la concommittance de phases en cuve de la colonne.The major drawback of this process is the limitation of the extraction rate (35 to 55%). This limitation is essentially due to the concomitant phase in the bottom of the column.

Deux idées de base sont connues pour améliorer les performances de ce schéma, tout en gardant un système avec une seule colonne pour éliminer les lourds.

  • a) soit on recomprime tout ou partie du résiduaire (en limitant le débit détendu dans la turbine) pour le retraiter dans l'appareil. Cette façon de faire nécessite soit l'utilisation d'un éjecteur de mauvais rendement, soit la compression d'un fluide enrichi en oxygène, éventuellement en utilisant les derniers étages du compresseur d'air.
    Ce type de solution est déjà connu :
    Brevet Européen 0 241 817
    Brevet Américain 4 872 893
    Brevet Américain 4 867 773
  • b) soit on ajoute un système de "bouillage" en cuve de colonne, et là se présentent trois possibilités :
    - soit on utilise un fluide riche en oxygène, mais celà représente un surcoût de compression de l'oxygène.
    - soit on utilise de l'air. Cette solution est bien connue :
    Brevet Européen 0 183 446
    Brevet Américain 4 617 037
    Cette solution, comparée à la solution "azote" retenue dans la présente invention n'offre pas l'avantage d'augmenter simultanément le taux de reflux en tête de colonne, ce qui est particulièrement important, dans la mesure où l'on cherche à produire de l'azote pur.
    - soit on utilise de l'azote. L'arrangement proposé dans la présente invention offre les avantages suivants :
    * combiner le compresseur de recyclage avec le compresseur de produit,
    * la colonne de distillation travaille à une pression basse, pour minimiser le débit de recyclage et optimiser la distillation.
Two basic ideas are known to improve the performance of this scheme, while keeping a system with a single column for eliminating the heavy ones.
  • a) either all or part of the waste is recompressed (by limiting the expanded flow in the turbine) to reprocess it in the device. This procedure requires either the use of a poor efficiency ejector, or the compression of an oxygen-enriched fluid, possibly using the last stages of the air compressor.
    This type of solution is already known:
    European patent 0 241 817
    U.S. Patent 4,872,893
    U.S. Patent 4,867,773
  • b) either a "boiling" system is added to the column tank, and there are three possibilities:
    - either a fluid rich in oxygen is used , but this represents an additional cost of compression of the oxygen.
    - either we use air . This solution is well known:
    European patent 0 183 446
    U.S. Patent 4,617,037
    This solution, compared to the "nitrogen" solution used in the present invention, does not offer the advantage of simultaneously increasing the reflux rate at the head of the column, which is particularly important, insofar as it is sought to produce pure nitrogen.
    - either we use nitrogen . The arrangement proposed in the present invention offers the following advantages:
    * combine the recycling compressor with the product compressor,
    * the distillation column works at a low pressure, to minimize the recycling rate and optimize the distillation.

La deuxième fonction à assurer est la tenue en froid de l'appareil. A cet effet, on peut procéder de différentes façons :
. on injecte de l'azote liquide, en tête de colonne, (ce qui offre l'intérêt d'accroître encore le taux de reflux en tête de colonne).
Cette solution est connue :
Brevet Japonais 61-50951
. on détend dans une turbine ou un détendeur à clapets l'un des fluides suivants :
* soit le résiduaire (fluide riche en 02)
Cette solution est déjà connue:
Brevet Japonais 61-50951,
Brevet Américain 4 400 188The second function to ensure is the cold behavior of the device. There are several ways to do this:
. liquid nitrogen is injected at the top of the column (which has the advantage of further increasing the reflux rate at the top of the column).
This solution is known:
Japanese patent 61-50951
. one of the following fluids is expanded in a turbine or a valve regulator :
* or the waste (fluid rich in 02)
This solution is already known:
Japanese patent 61-50951,
U.S. Patent 4,400,188

Cette solution présente les inconvénients de devoir détendre un fluide riche en oxygène, et d'opérer la distillation à pression relativement élevée.
* soit l'azote :
Une solution avec détente d'azote est déjà connue.
(Brevet Américain 4 662 918)
Cette solution présente les inconvénients de la détente d'azote :
- Nécessité de recomprimer l'azote , puisque l'on cherche à le produire sous pression,
- Pertes de produit du fait des fuites aux paliers ou consommation d'azote comme gaz de barrage.This solution has the drawbacks of having to relax an oxygen-rich fluid, and of operating the distillation at relatively high pressure.
* or nitrogen:
A solution with nitrogen expansion is already known.
(U.S. Patent 4,662,918)
This solution has the drawbacks of nitrogen expansion:
- Need to recompress nitrogen, since we are trying to produce it under pressure,
- Product losses due to leaks at bearings or consumption of nitrogen as a barrier gas.

Cette solution peut être intéressante dans le cas où l'on cherche à produire un fort pourcentage d'azote liquide, ou dans le cas où l'on cherche à obtenir une flexibilité entre la production gazeuse et une marche mixte gaz - liquide.This solution may be advantageous in the case where it is sought to produce a high percentage of liquid nitrogen, or in the case where it is sought to obtain flexibility between gas production and a mixed gas-liquid operation.

D'autre part, dans les modes de mise en oeuvre de la présente invention faisant intervenir une détente azote, le gaz détendu est mélangé au gaz basse pression, ou détendu au voisinage de la pression atmosphérique, ce qui permet de maximiser le taux de détente, et donc de minimiser le débit détendu puis recomprimé.
* Soit le mélange à traiterOn the other hand, in the embodiments of the present invention involving nitrogen expansion, the expanded gas is mixed with the low pressure gas, or expanded in the vicinity of atmospheric pressure, which makes it possible to maximize the rate of expansion , and therefore minimize the relaxed and then recompressed flow.
* Either the mixture to be treated

Il est particulièrement intéressant de détendre le mélange à traiter de la pression d'entrée dans l'appareil à la pression de la colonne.It is particularly advantageous to relax the mixture to be treated from the pressure entering the apparatus to the pressure of the column.

En variante, il peut être intéressant de détendre le mélange à traiter à la pression du résiduaire et de le mélanger à celui-ci (Brevet Japonais 61-50951) mais en insérant des capacités Tampon liquide (liquide riche en oxygène, azote liquide).As a variant, it may be advantageous to relax the mixture to be treated at the pressure of the waste and to mix it with the latter (Japanese Patent 61-50951) but by inserting liquid buffer capacities (liquid rich in oxygen, liquid nitrogen).

Cet arrangement permet de faire varier temporairement la production d'azote, en jouant sur le fonctionnement de la turbine et les stocks de liquide, entre 40 à 50 % et 140 à 160 % de la production nominale.This arrangement makes it possible to temporarily vary the production of nitrogen, by varying the operation of the turbine and the liquid stocks, between 40 to 50% and 140 to 160% of the nominal production.

Enfin, il peut être intéressant de détendre une fraction du mélange à traiter jusqu'à une pression proche de la pression atmosphérique, ce qui permet de maximiser le taux de détente, et donc de minimiser le débit de cette fraction.Finally, it may be advantageous to expand a fraction of the mixture to be treated to a pressure close to atmospheric pressure, which makes it possible to maximize the rate of expansion, and therefore to minimize the flow rate of this fraction.

Pour produire de l'azote, à partir d'air atmosphérique par exemple :
- on comprime à une pression au moins égale à la basse pression le mélange à traiter (de l'ordre de 3 à 5 bars)
- on refroidit le mélange comprimé,
- on soumet le mélange refroidi à une distillation fractionnée, sous la basse pression, pour obtenir en pied une fraction enrichie en oxygène, et en tête une fraction enrichie en azote.
- on soutire au moins une partie de la fraction enrichie en azote sous forme gazeuse, constituant l'azote gazeux sous basse pression,
- on soutire une fraction enrichie en oxygène, sous forme liquide et, pour au moins une partie de ladite fraction, on la détend à une pression inférieure à la basse pression, et on la vaporise en échange de chaleur avec la fraction enrichie en azote de condension, caractérisé en ce que :
- on recycle une partie de l'azote réchauffé que l'on comprime et refroidit pour l'introduire dans un échangeur de pied de colonne, où il se condense; on en prélève éventuellement une faible part pour
production d'azote liquide sous forte pression, puis après détente, on l'introduit en tête de colonne.To produce nitrogen, for example from atmospheric air:
- the mixture to be treated is compressed to a pressure at least equal to the low pressure (of the order of 3 to 5 bars)
- the compressed mixture is cooled,
- The cooled mixture is subjected to fractional distillation, under low pressure, to obtain at the bottom a fraction enriched in oxygen, and at the top a fraction enriched in nitrogen.
- at least part of the fraction enriched in nitrogen in gaseous form, constituting nitrogen gas under low pressure, is withdrawn,
- an oxygen-enriched fraction is withdrawn in liquid form and, for at least part of said fraction, it is expanded to a pressure below the low pressure, and it is vaporized in exchange for heat with the nitrogen-enriched fraction condense, characterized in that:
- One recycles part of the heated nitrogen which is compressed and cooled to introduce it into a column bottom exchanger, where it condenses; we possibly take a small part of it for
production of liquid nitrogen under high pressure, then after expansion, it is introduced at the top of the column.

Selon une autre mise en oeuvre, la distillation fractionnée est effectuée en deux étages, le premier à température relativement basse, et le second à température relativement haute pour séparer une fraction relativement lourde, caractérisé en ce qu'au moins une partie du gaz riche en azote est comprimé, refroidi et condensé en échange de chaleur avec la fraction en cuve du deuxième étage de distillation, puis détendu et introduit en tête dudit étage, un flux de production relativement lourd étant soutiré de l'étage, puis réchauffé.According to another embodiment, the fractional distillation is carried out in two stages, the first at a relatively low temperature, and the second at a relatively high temperature to separate a relatively heavy fraction, characterized in that at least part of the gas rich in nitrogen is compressed, cooled and condensed in exchange for heat with the tank fraction of the second distillation stage, then expanded and introduced at the top of said stage, a relatively heavy production flow being withdrawn from the stage, then reheated.

La présente invention a pour objet un procédé tel que défini précédemment, permettant tout à la fois un bon rendement d'extraction en azote et une tenue au froid de l'appareil par détente dans une turbine d'un gaz pauvre en oxygène.The present invention relates to a method as defined above, allowing both a good nitrogen extraction yield and a resistance to cold of the device by expansion in a turbine of a gas poor in oxygen.

Selon la présente invention, la production de froid nécessaire au procédé est assurée :
- soit par détente d'au moins un flux gazeux frigorigène, pouvant être le mélange à traiter, qui est détendu à la basse pression de la colonne, et injecté dans la colonne.
- soit par détente d'au moins un flux gazeux frigorigène, pouvant être le mélange à traiter, qui est détendu à la pression inférieure du résiduaire, éventuellement mélangé au résiduaire.
- soit par détente d'une fraction de l'azote recyclé, à une pression inférieure ou égale à la basse pression, puis réchauffé et recomprimé.According to the present invention, the production of cold necessary for the process is ensured:
- Either by expansion of at least one refrigerant gas flow, which may be the mixture to be treated, which is expanded at the low pressure of the column, and injected into the column.
- Either by expansion of at least one refrigerant gas flow, which may be the mixture to be treated, which is expanded to the lower pressure of the waste, possibly mixed with the waste.
- Either by expansion of a fraction of the recycled nitrogen, to a pressure less than or equal to the low pressure, then reheated and recompressed.

Selon une forme de mise en oeuvre, le flux gazeux frigorigène est au moins une partie du mélange à traiter, détendu avant son introduction dans la colonne et selon une variante, le flux gazeux frigorifique est une partie du mélange à traiter détendu à pression inférieure à la basse pression puis réchauffé. Dans une forme particulière de mise en oeuvre, le flux gazeux frigorifique est réuni au flux gazeux enrichi en oxygène avant réchauffement. Dans ce cas, une partie condensée du gaz de cycle est dérivée vers une capacité tampon, avec prélèvement et réintroduction dans la colonne en cas d'accroissement du débit de production d'azote, tandis qu'une partie du courant de liquide riche en oxygène est envoyée vers une capacité tampon pour être réinjectée dans le condenseur de tête de colonne, en cas de réduction de la production d'azote gazeux, ce qui permet de reconstituer le stock d'azote liquide sous pression.According to one embodiment, the refrigerant gas flow is at least part of the mixture to be treated, expanded before its introduction into the column and according to a variant, the refrigerant gas flow is a part of the mixture to be treated expanded at pressure below the low pressure then warmed up. In a particular form of implementation, the refrigerant gas flow is combined with the gas flow enriched in oxygen before heating. In this case, a condensed part of the cycle gas is diverted to a buffer capacity, with sampling and reintroduction into the column in the event of an increase in the nitrogen production flow rate, while part of the stream of liquid rich in oxygen is sent to a buffer capacity to be reinjected into the column head condenser, in the event of a reduction in the production of nitrogen gas, which makes it possible to replenish the stock of liquid nitrogen under pressure.

Dans une réalisation particulière, on associe les actions du flux frigorigène d'origine gaz à traiter avec le flux frigorifique de gaz de recyclage.In a particular embodiment, the actions of the refrigerant flow of gas origin to be treated are associated with the refrigeration flow of recycling gas.

La présente invention est maintenant décrite par référence aux dessins annexés, dont les figures 1 à 9 représentent les différents modes d'éxécution du procédé selon l'invention.The present invention is now described with reference to the accompanying drawings, in which Figures 1 to 9 show the different modes of carrying out the method according to the invention.

Conformément à la figure 1, on comprime (de manière non représentée), à une pression supérieure à la basse pression de la colonne de distillation (4), définie ci-après, un courant de gaz, par exemple d'air préalablement épuré de manière traditionnelle. Dans l'échangeur de chaleur (2), ce courant est refroidi jusqu'à une température intermédiaire représentée par le niveau (2a). Puis ce courant gazeux est détendu à la basse pression de l'ordre de 3 à 5 bars abs. dans la turbine (3), puis introduit dans la colonne de distillation (4), à un niveau intermédiaire entre deux étages de distillation, l'un supérieur (4a) et l'autre inférieur (4b).In accordance with FIG. 1 , a stream of gas, for example air previously purified from, is compressed (not shown) at a pressure higher than the low pressure of the distillation column (4), defined below. traditional way. In the heat exchanger (2), this current is cooled to an intermediate temperature represented by the level (2a). Then this gas stream is expanded at low pressure of the order of 3 to 5 bar abs. in the turbine (3), then introduced into the distillation column (4), at an intermediate level between two distillation stages, one upper (4a) and the other lower (4b).

A la partie inférieure de la colonne (4), on recueille une fraction liquide enrichie en oxygène (7), laquelle est extraite de la colonne, le cas échéant sous-refroidie dans l'échangeur (10), détendue dans la vanne (8) et finalement introduite dans le condenseur de la colonne (4), constitué pour l'essentiel par un échangeur (5) pour la condensation de tout ou partie de la fraction gazeuse disponible en tête de la colonne (4). Cette fraction enrichie en oxygène est extraite du condenseur précité, sous la forme d'un courant (9), lequel est, le cas échéant, réchauffé dans l'échangeur (10), puis l'échangeur (2), et finalement utilisé ou évacué à la sortie de l'échangeur (2).At the bottom of the column (4), a liquid fraction enriched with oxygen (7) is collected, which is extracted from the column, if necessary sub-cooled in the exchanger (10), expanded in the valve (8 ) and finally introduced into the condenser of the column (4), essentially consisting of an exchanger (5) for the condensation of all or part of the gaseous fraction available at the top of the column (4). This oxygen-enriched fraction is extracted from the above-mentioned condenser, in the form of a current (9), which is, if necessary, heated in the exchanger (10), then the exchanger (2), and finally used or evacuated at the outlet of the exchanger (2).

Quant à la fraction enrichie en azote disponible en tête de la colonne (4), une partie condensée dans l'échangeur (5) assure une partie du reflux de la distillation. Une partie peut être extraite sous forme liquide par le conduit (12). Et une autre partie est extraite, sous forme gazeuse par le conduit (11). Le courant correspondant est réchauffé le cas échéant, dans l'échangeur (10), puis dans l'échangeur (2), pour obtenir à la sortie de ce dernier un courant d'azote gazeux relativement pur, sous la basse pression, dont une partie (X et/ou Y) constitue la production de l'unité de séparation.As for the fraction enriched in nitrogen available at the top of the column (4), a part condensed in the exchanger (5) ensures part of the reflux of the distillation. A part can be extracted in liquid form through the conduit (12). And another part is extracted, in gaseous form through the conduit (11). The corresponding current is heated if necessary, in the exchanger (10), then in the exchanger (2), to obtain at the outlet of the latter a stream of relatively pure nitrogen gas, under low pressure, one of which part (X and / or Y) constitutes the production of the separation unit.

Une autre partie comprimée en (13) de ce courant (11), sous la forme du flux (14), est recyclée dans l'unité de séparation. Ce courant (14) est tout d'abord refroidi dans l'échangeur (2), au moins en partie condensé au pied de la colonne (4), dans l'échangeur (6), en échange de chaleur avec la fraction riche en oxygène, en cours de vaporisation. Puis le courant (20) d'azote condensé est, le cas échéant, sous-refroidi dans l'échangeur (10), détendu dans la vanne (17), et introduit en tête de la colonne (4). Préalablement, une partie (15) peut être dérivée du courant (20) pour constituer une autre fraction d'azote liquide de production, disponible à une pression différente de celle qui est extraite par le conduit (12).Another part compressed at (13) of this stream (11), in the form of the stream (14), is recycled in the separation unit. This stream (14) is firstly cooled in the exchanger (2), at least partly condensed at the bottom of the column (4), in the exchanger (6), in exchange for heat with the fraction rich in oxygen, during vaporization. Then the stream (20) of condensed nitrogen is, if necessary, sub-cooled in the exchanger (10), expanded in the valve (17), and introduced at the head of the column (4). Beforehand, a part (15) can be derived from the current (20) to constitute another fraction of production liquid nitrogen, available at a pressure different from that which is extracted by the conduit (12).

Selon ce premier mode d'éxécution, la colonne de distillation (4) travaille sous une pression relativement basse, comprise entre 3 et 5 bars abs. par exemple.According to this first embodiment, the distillation column (4) works under a relatively low pressure, between 3 and 5 bar abs. for example.

Le mode d'éxécution selon la figure 2, diffère de celui décrit précédement, par les caractéristiques essentielles suivantes :The mode of execution according to FIG. 2 differs from that described above by the following essential characteristics:

Le courant d'air comprimé (1) est divisé en deux parties, la première (2a) traitée comme précédemment, c'est-à-dire détendue dans la turbine (3) et introduite dans la colone (4), et une seconde et dernière partie poursuivant son refroidissement dans l'échangeur (2) jusqu'à liquéfaction totale ou partielle (111), détendue dans la vanne (112) et introduite dans la colonne (4) à un niveau intermédiaire, au dessus du point d'introduction du courant gazeux détendu. La colonne de distillation (4) peut donc être divisée en 3 zones, respectivement de haut en bas (4a), (4b), (4c).The stream of compressed air (1) is divided into two parts, the first (2a) treated as above, that is to say expanded in the turbine (3) and introduced into the column (4), and a second and last part continuing its cooling in the exchanger (2) until total or partial liquefaction (111), expanded in the valve (112) and introduced into the column (4) at an intermediate level, above the point of introduction of the expanded gas stream. The distillation column (4) can therefore be divided into 3 zones, respectively from top to bottom (4a), (4b), (4c).

Le mode d'éxécution de la figure 3 diffère de celui représenté à la figure 2 par les caractéristiques essentielles suivantes :The mode of execution of FIG. 3 differs from that shown in FIG. 2 by the following essential characteristics:

Une partie (1b) de l'air comprimé (1) est dérivée avant passage dans l'échangeur (2) pour être admise dans la partie compresseur (50) d'un ensemble turbine (3) booster (50), refroidie à température ambiante dans l'échangeur (51). Cette fraction est ensuite introduite dans l'échangeur (2) pour être extraite à une température intermédiaire, détendue dans la turbine (3) et introduite dans la colonne (4).A part (1b) of the compressed air (1) is diverted before passing through the exchanger (2) to be admitted into the compressor part (50) of a turbine assembly (3) booster (50), cooled to temperature ambient in the exchanger (51). This fraction is then introduced into the exchanger (2) to be extracted at an intermediate temperature, expanded in the turbine (3) and introduced into the column (4).

L'autre partie (111) subit comme précédemment son refroidissement dans l'échangeur (2), où elle est éventuellement partiellement condensée (111) avant d'être détendue (112) et injectée dans la colonne (4).The other part (111) undergoes as before its cooling in the exchanger (2), where it is possibly partially condensed (111) before being expanded (112) and injected into the column (4).

Le mode d'éxécution selon la figure 4 diffère de celui représenté à la figure 1, par les caractéristiques essentielles suivantes, les références numériques communes avec la figure 1 désignant des courants ou composants identiques ou ayant la même fonction.The mode of execution according to FIG. 4 differs from that represented in FIG. 1, by the following essential characteristics, the reference numerals common with FIG. 1 designating identical currents or components or having the same function.

Tout d'abord, la distillation fractionnée est effectuée en deux étages, à savoir :
- un premier étage à température relativement basse, équivalent à la colonne de distillation (4) de la figure 1,
- et un second étage (155) à température relativement haute, fonctionnant sous une pression relativement haute, comprise entre 6 et 12 bars.First of all, fractional distillation is carried out in two stages, namely:
a first stage at a relatively low temperature, equivalent to the distillation column (4) of FIG. 1,
- And a second stage (155) at relatively high temperature, operating under a relatively high pressure, between 6 and 12 bars.

En correspondance avec ce deuxième étage (155), le courant d'azote recyclé (14) est introduit dans ce dernier, au lieu d'être introduit comme précédement dans le premier étage (4). Plus précisément, ce courant (14) est condensé au moins en partie au pied de la colonne (155), dans l'échangeur (166), par échange de chaleur avec la fraction riche en azote relativement lourde en cours de vaporisation, toujours au pied de la même colonne. Puis le courant (14) passe éventuellement dans un piège à impuretés -telle CO- du type à adsorption froide (167) représenté en pointillé, détendu dans une vanne (168), et introduit dans la colonne (155) à un niveau intermédiaire. La fraction relativement légère disponible en tête de cette même colonne (155) est en quasi totalité condensée dans l'échangeur (6) éxistant au pied de la colonne (4), en échange de chaleur avec la fraction riche en oxygène en cours de vaporisation, disponible au pied de la colonne (4). La fraction non condensée disponible en sortie de l'échangeur (6) est mélangée au gaz résiduaire (9) après détente.In correspondence with this second stage (155), the stream of recycled nitrogen (14) is introduced into the latter, instead of being introduced as previously into the first stage (4). More precisely, this current (14) is condensed at least in part at the foot of the column (155), in the exchanger (166), by heat exchange with the fraction rich in relatively heavy nitrogen being vaporized, always at the foot of the same column. Then the current (14) optionally passes through an impurity trap such as CO of the cold adsorption type (167) shown in dotted lines, expanded in a valve (168), and introduced into the column (155) at an intermediate level. The relatively light fraction available at the head of this same column (155) is almost entirely condensed in the exchanger (6) existing at the bottom of the column (4), in exchange for heat with the oxygen-rich fraction during vaporization. , available at the bottom of the column (4). The non-condensed fraction available at the outlet of the exchanger (6) is mixed with the waste gas (9) after expansion.

La fraction relativement lourde au pied de la colonne (155), est évacuée par le conduit (18), sous forme gazeuse, réchauffée dans l'échangeur (2), et évacuée à l'état réchauffé de l'installation. Une fraction relativement lourde disponible sous forme liquide au pied du deuxième étage (155) est soutirée en un courant (177) qui est détendu dans la vanne (169) et introduit en tête du premier étage (4) de distillation.The relatively heavy fraction at the bottom of the column (155) is discharged through the conduit (18) in gaseous form, heated in the exchanger (2), and discharged in the heated state of the installation. A relatively heavy fraction available in liquid form at the bottom of the second stage (155) is drawn off into a stream (177) which is expanded in the valve (169) and introduced at the head of the first distillation stage (4).

Par ailleurs, le courant d'air comprimé (1), est divisé en deux parties, la première (2a) traitée comme précédement, c'est-à-dire détendue dans la turbine (3) et introduite dans la colonne (4), et une seconde et dernière partie poursuivant son refroidissement dans l'échangeur (2) jusqu'à liquéfaction (111), détendue dans la vanne (112) et introduite dans la colonne (4), au dessus du point d'introduction du courant gazeux (1) détendu. La colonne de distillation (4) peut donc être divisée en trois zones, respectivement de haut en bas (4a), (4b), et (4c).Furthermore, the compressed air stream (1) is divided into two parts, the first (2a) treated as above, that is to say expanded in the turbine (3) and introduced into the column (4) , and a second and last part continuing to cool in the exchanger (2) until liquefaction (111), expanded in the valve (112) and introduced into the column (4), above the point of introduction of the current gaseous (1) relaxed. The distillation column (4) can therefore be divided into three zones, respectively from top to bottom (4a), (4b), and (4c).

Le mode d'éxécution de la figure 5 diffère de celui représenté à la figure 2 par les caractéristiques essentielles suivantes :
- Tout d'abord, comme à la figure 2, le courant d'air comprimé (1) est divisé en deux parties, d'une part une partie (2a) soumise à la détente dans la turbine (3), et d'autre part une partie résiduelle (121), introduite dans la colonne (4). Mais le courant d'air détendu (112) est extrait de l'installation, sans passage dans la colonne de distillation (4), par réunion avec la fraction (9) riche en oxygène et vaporisée, l'ensemble (9-112) étant ensuite réchauffé dans l'échangeur (2) et utilisé ou évacué.
- Pour le reste, il est possible de stocker les fractions liquides disponibles dans l'installation, pendant des périodes de production relativement faible, et de restituer ces fractions liquides à l'installation, pendant les périodes de production importante.The mode of execution of FIG. 5 differs from that shown in FIG. 2 by the following essential characteristics:
- First of all, as in FIG. 2, the stream of compressed air (1) is divided into two parts, on the one hand a part (2a) subjected to expansion in the turbine (3), and on the other hand a residual part (121), introduced into the column (4). But the relaxed air stream (112) is extracted from the installation, without passing through the distillation column (4), by joining with the fraction (9) rich in oxygen and vaporized, the whole (9-112) then being reheated in the exchanger (2) and used or removed.
- For the rest, it is possible to store the liquid fractions available in the installation, during periods of relatively low production, and to return these liquid fractions to the installation, during periods of significant production.

A cette fin, le courant d'azote recyclé peut être extrait par un conduit (20a) vers une capacité-tampon (20c), et restituée par le conduit (20b) à la colonne (4), en aval de la vanne (17). De la même manière, la fraction riche en oxygène (7) peut être extraite de l'installation par un conduit de dérivation (7a), vers la capacité-tampon (7c), et restituée par le conduit (7b), à la colonne (4), en aval de la vanne (8).To this end, the stream of recycled nitrogen can be extracted by a pipe (20a) to a buffer tank (20c), and returned by the pipe (20b) to the column (4), downstream of the valve (17 ). In the same way, the oxygen-rich fraction (7) can be extracted from the installation by a bypass duct (7a), to the buffer tank (7c), and returned by the duct (7b), to the column (4), downstream of the valve (8).

Le mode d'éxécution de la figure 6 diffère de celui représenté à la figure 5 par les caractéristiques suivantes :
- Une première partie (1a) de l'air comprimé (1) est refroidi dans l'échangeur (2), puis introduite (121) dans la colonne (4).
- L'autre partie (1b) de l'air comprimé (1) est dérivée avant son passage dans l'échangeur (2) pour être admise dans la partie compresseur (50) d'un ensemble turbine (3) booster (50), refroidie à température ambiante dans l'échangeur (51) et ensuite introduite dans l'échangeur (2) pour être extraite à une température intermédiaire, détendue (112) dans la turbine (3) et réunie avec la fraction (9) riche en oxygène et vaporisée dans le condenseur (5).The mode of execution of figure 6 differs from that represented in figure 5 by the following characteristics:
- A first part (1a) of the compressed air (1) is cooled in the exchanger (2), then introduced (121) into the column (4).
- The other part (1b) of the compressed air (1) is diverted before it passes through the exchanger (2) to be admitted into the compressor part (50) of a turbine assembly (3) booster (50) , cooled to room temperature in the exchanger (51) and then introduced into the exchanger (2) to be extracted at an intermediate temperature, expanded (112) in the turbine (3) and combined with the fraction (9) rich in oxygen and vaporized in the condenser (5).

Les deux versions type bascule décrites dans les figures 5 et 6 présentent l'avantage de pouvoir disposer d'une production en azote gazeux pouvant aller de 50 à 150 % de la production nominale.The two rocker-type versions described in FIGS. 5 and 6 have the advantage of being able to have a production of nitrogen gas which can range from 50 to 150% of the nominal production.

Le mode d'éxécution conforme à la figure 7 diffère de celui représenté à la figure 2 par les caractéristiques essentielles suivantesThe embodiment in accordance with FIG. 7 differs from that shown in FIG. 2 by the following essential characteristics

Une partie (141) du gaz de recyclage riche en azote (14) est soutirée à température intermédiaire (2b) de l'échangeur (2) pour être détendue jusqu'à la basse pression dans une turbine (142), puis, sans passer dans la colonne (4), est réunie au courant riche en azote (11) extrait de la colonne (4), pour former un courant (41) qui est réchauffé dans l'échangeur (2).A portion (141) of the nitrogen-rich recycling gas (14) is drawn off at intermediate temperature (2b) from the exchanger (2) to be expanded to low pressure in a turbine (142), then, without passing in the column (4), is combined with the stream rich in nitrogen (11) extracted from the column (4), to form a stream (41) which is heated in the exchanger (2).

Dans ce mode de réalisation, la turbine air (144) est utilisée pour la production d'azote gazeux (X/Y) sans production de liquide. On envoie une partie de l'azote (14) recyclé dans la turbine (142) pour produire de l'azote liquide grâce aux frigories supplémentaires apportées par la détente polytropique de cet azote turbiné, au détriment de la production en azote gazeux.In this embodiment, the air turbine (144) is used for the production of nitrogen gas (X / Y) without production of liquid. Part of the recycled nitrogen (14) is sent to the turbine (142) to produce liquid nitrogen thanks to the additional frigories provided by the polytropic expansion of this turbinated nitrogen, to the detriment of the production of nitrogen gas.

Cette disposition permet d'avoir une flexibilité gaz/liquide sur la production d'azote.This arrangement makes it possible to have gas / liquid flexibility on the production of nitrogen.

Le mode d'éxécution de la figure 8 diffère de celui représenté à la figure 7 par les caractéristiques essentielles suivantes :
Une partie (152) du gaz de recyclage riche en azote est dérivée avant passage dans l'échangeur (2) pour être admis dans la partie compresseur (52) d'un ensemble turbine (53) -compresseur frein ou "booster" (52), et ensuite introduit dans l'échangeur (2) pour être extrait à une température intermédiaire (2c) et envoyé dans la turbine (53).The mode of execution of FIG. 8 differs from that represented in FIG. 7 by the following essential characteristics:
Part (152) of the nitrogen-rich recycling gas is diverted before passing through the exchanger (2) to be admitted into the compressor part (52) of a turbine (53) -brake or booster compressor assembly (52 ), and then introduced into the exchanger (2) to be extracted at an intermediate temperature (2c) and sent to the turbine (53).

Le gaz (66) issu de la turbine (53) est ici détendu à une pression plus basse que celle du courant riche en azote (11). Il est donc réchauffé dans l'échangeur (2) dans les passages qui lui sont propres (67), le courant réchauffé étant ensuite recomprimé en (62) pour être admis à l'aspiration du compresseur (13).The gas (66) from the turbine (53) is here expanded to a pressure lower than that of the stream rich in nitrogen (11). It is therefore reheated in the exchanger (2) in its own passages (67), the reheated current then being recompressed at (62) to be admitted to the suction of the compressor (13).

Le mode d'éxécution de la figure 9 diffère de celui représenté à la figure 8 en ce que le gaz détendu en (56) est réuni au courant riche en azote (11).The embodiment of FIG. 9 differs from that shown in FIG. 8 in that the expanded gas at (56) is combined with the stream rich in nitrogen (11).

Claims (11)

1. Procédé de production d'azote gazeux (X/Y) à partir d'un mélange (1) à traiter contenant principalement de l'azote et de l'oxygène, par exemple de l'air, selon lequel :
- on comprime à une pression au moins égale à la basse pression le mélange (1) à traiter, de l'ordre de 3 à 5 bars.
- on refroidit (2) le mélange comprimé,
- on soumet le mélange refroidi à une distillation fractionnée (4), sous la basse pression, pour obtenir en pied une fraction enrichie en oxygène et en tête une fraction enrichie en azote,
- on soutire au moins une partie (11), de la fraction enrichie en azote, sous forme gazeuse, constituant l'azote gazeux sous basse pression,
- on soutire une fraction (7) enrichie en oxygène, sous forme liquide, et, pour au moins une partie de ladite fraction (7), on la détend (8) à une pression inférieure à la basse pression, et on la vaporise (5) en échange de chaleur avec la fraction enrichie en azote en condensation, caractérisé en ce que :
- on recycle une partie (14) de l'azote réchauffé, que l'on comprime (13) et refroidit (2) pour l'introduire dans un échangeur (6) (166) de pied de colonne, pour condensation, puis après détente (17) on l'introduit à un niveau supérieur de la colonne ou en tête de colonne.1. Process for the production of nitrogen gas (X / Y) from a mixture (1) to be treated containing mainly nitrogen and oxygen, for example air, according to which:
- The mixture (1) to be treated is compressed to a pressure at least equal to the low pressure, of the order of 3 to 5 bars.
- the compressed mixture is cooled (2),
the cooled mixture is subjected to fractional distillation (4), under low pressure, to obtain a fraction enriched in oxygen at the bottom and a fraction enriched in nitrogen at the top,
- at least part (11) of the nitrogen-enriched fraction is withdrawn in gaseous form, constituting nitrogen gas under low pressure,
- a fraction (7) enriched in oxygen, in liquid form, is withdrawn and, for at least part of said fraction (7), it is relaxed (8) to a pressure below the low pressure, and it is vaporized ( 5) in exchange for heat with the fraction enriched in condensing nitrogen, characterized in that:
- One recycles part (14) of the heated nitrogen, which is compressed (13) and cooled (2) to introduce it into a heat exchanger (6) (166) at the bottom of the column, for condensation, then after trigger (17) is introduced at a higher level of the column or at the top of the column. 2. Procédé selon la revendication 1, caractérisé en ce que la distillation fractionnée est effectuée en deux étages, le premier (4) à température relativement basse, et le second (155) à température relativement haute, pour séparer une fraction (177) relativement exempte de légers, et caractérisé en ce qu'au moins une partie du gaz riche en azote (14) est comprimée (13), refroidie (2) et condensée (166) en échange de chaleur avec la fraction en cuve du deuxième étage de distillation (155), puis détendue (168) et introduite à un niveau intermédiaire du dit étage (155), un flux de production (18), relativement exempt de légers étant soutiré de l'étage (155), puis réchauffé en (2).2. Method according to claim 1, characterized in that the fractional distillation is carried out in two stages, the first (4) at relatively low temperature, and the second (155) at relatively high temperature, to separate a fraction (177) relatively free of light, and characterized in that at least part of the nitrogen-rich gas (14) is compressed (13), cooled (2) and condensed (166) in exchange for heat with the tank fraction of the second stage of distillation (155), then expanded (168) and introduced at an intermediate level of said stage (155), a production stream (18), relatively free of light being withdrawn from stage (155), then reheated in (2 ). 3. Procédé selon les revendication 1 ou 2, caractérisé en ce que la tenue en froid de l'appareil est assurée par détente adiabatique (polytropique) d'un ou plusieurs flux gazeux frigorigènes, dont l'un au moins est le mélange à traiter.3. Method according to claim 1 or 2, characterized in that the resistance to cold of the device is ensured by adiabatic expansion (polytropic) of one or more refrigerant gas flows, at least one of which is the mixture to be treated . 4. Procédé selon la revendication 3, caractérisé en ce que le flux gazeux frigorigène est au moins 1 partie du mélange à traiter (1), détendu (3) avant son introduction dans la colonne (4).4. Method according to claim 3, characterized in that the refrigerant gas flow is at least 1 part of the mixture to be treated (1), expanded (3) before its introduction into the column (4). 5. Procédé selon la revendication 3, caractérisé en ce que le flux gazeux frigorigène est au moins une partie du mélange (1) à traiter, détendu (3) à pression proche de la pression atmosphérique.5. Method according to claim 3, characterized in that the refrigerant gas flow is at least part of the mixture (1) to be treated, expanded (3) at pressure close to atmospheric pressure. 6. Procédé selon la revendication 5, caractérisé en ce que le flux gazeux frigorigène est au moins une partie du gaz à traiter (1), détendu (3) à pression inférieure à la basse pression, et réuni au flux gazeux (9) enrichi en oxygène avant réchauffement, et caractérisé en ce que une partie condensée (20a) du gaz de cycle 14 est dérivée vers une capacité-tampon (20c), alors qu'une partie du liquide riche en 02 stocké dans la capacité (7c) est injectée dans l'appareil, lorsque la production d'azote gazeux est réduite, et qu'une partie d'azote liquide, stockée dans la capacité-tampon (20c) est injectée dans la colonne, alors qu'une fraction (7) du liquide riche en 02 (7) est dérivée et stockée dans la capacité-tampon (7c) lorsque la production d'azote gazeux est maximum. La turbine (3) fonctionne en marche nominale ou réduite, et est arrêtée en marche maximale.6. Method according to claim 5, characterized in that the refrigerant gas flow is at least part of the gas to be treated (1), expanded (3) at pressure lower than the low pressure, and combined with the enriched gas flow (9) in oxygen before heating, and characterized in that a condensed part (20a) of the cycle gas 14 is diverted to a buffer capacity (20c), while part of the liquid rich in 02 stored in the capacity (7c) is injected into the apparatus, when the production of nitrogen gas is reduced, and a portion of liquid nitrogen, stored in the buffer capacity (20c) is injected into the column, while a fraction (7) of the liquid rich in 02 (7) is derived and stored in the buffer capacity (7c) when the production of nitrogen gas is maximum. The turbine (3) operates in nominal or reduced mode, and is stopped in maximum mode. 7. Procédé selon la revendication 5, caractérisé en ce que le flux gazeux frigorigène est au moins une partie du gaz à traiter (1), détendu (3) à une pression proche de la pression atmosophérique, puis réchauffé dans un passage particulier de l'échangeur (2).7. Method according to claim 5, characterized in that the refrigerant gas flow is at least part of the gas to be treated (1), expanded (3) to a pressure close to atmospheric pressure, then reheated in a particular passage of l 'exchanger (2). 8. Procédé selon les revendications 1 ou 2, caractérisé en ce que le flux gazeux frigorigène est une partie de l'azote recyclé (14), qui est détendu (142) jusqu'à une pression au plus égale à la basse pression, avant d'être réchauffé dans l'échangeur (2), puis recomprimée (13).8. Method according to claims 1 or 2, characterized in that the refrigerant gas flow is part of the recycled nitrogen (14), which is expanded (142) to a pressure at most equal to the low pressure, before to be reheated in the exchanger (2), then recompressed (13). 9. Procédé selon la revendication 8, caractérisé en ce que le flux gazeux frigorifique (141) est, après détente (142) réuni au flux riche en azote (11) extrait de la colonne.9. Method according to claim 8, characterized in that the refrigerant gas flow (141) is, after expansion (142) joined to the nitrogen-rich flow (11) extracted from the column. 10. Procédé selon la revendication 8, caractérisé en ce que le flux gazeux frigorifique (141) est détendu à une pression proche de la pression atmosphérique, puis réchauffé dans un passage particulier de l'échangeur (2) recomprimé dans un compresseur (62) puis mélangé au flux (11) riche en azote réchauffé à la basse pression.10. Method according to claim 8, characterized in that the refrigerant gas flow (141) is expanded to a pressure close to atmospheric pressure, then reheated in a particular passage of the exchanger (2) recompressed in a compressor (62) then mixed with the stream (11) rich in nitrogen heated at low pressure. 11. Procédé selon les revendications prédédentes, caractérisé en ce que la turbine est accouplée à un des compresseurs, ou liée à un booster, permettant de récupérer de l'énergie pour la compression du gaz à traiter, ou de l'azote, de comprimer à une pression supérieure uniquement la fraction de gaz utilisée comme flux gazeux frigorigène, moyennant adjonction d'un passage supplémentaire dans l'échangeur (2).11. Method according to the preceding claims, characterized in that the turbine is coupled to one of the compressors, or linked to a booster, making it possible to recover energy for the compression of the gas to be treated, or nitrogen, to compress at a higher pressure only the fraction of gas used as refrigerant gas flow, by adding an additional passage in the exchanger (2).
EP90402289A 1989-08-18 1990-08-13 Nitrogen production process Expired - Lifetime EP0413631B1 (en)

Priority Applications (1)

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EP94106964A EP0610972B1 (en) 1989-08-18 1990-08-13 Process for preparing nitrogen

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FR8911009A FR2651035A1 (en) 1989-08-18 1989-08-18 PROCESS FOR THE PRODUCTION OF NITROGEN BY DISTILLATION
FR8911009 1989-08-18

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CA (1) CA2023503C (en)
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FR (1) FR2651035A1 (en)

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FR2697325A1 (en) * 1992-10-27 1994-04-29 Air Liquide Process and installation for the production of nitrogen and oxygen.
FR2700205A1 (en) * 1993-01-05 1994-07-08 Air Liquide Method and installation for producing at least one gaseous product under pressure and at least one liquid by air distillation.
WO1997014008A1 (en) * 1995-10-11 1997-04-17 Linde Aktiengesellschaft Double-column process and device for the low-temperature separation of air
EP1732978A2 (en) * 2003-12-24 2006-12-20 Praxair Technology, Inc. Cryogenic system for producing elevated pressure nitrogen

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US5251450A (en) * 1992-08-28 1993-10-12 Air Products And Chemicals, Inc. Efficient single column air separation cycle and its integration with gas turbines
US5511380A (en) 1994-09-12 1996-04-30 Liquid Air Engineering Corporation High purity nitrogen production and installation
JP3447437B2 (en) * 1995-07-26 2003-09-16 日本エア・リキード株式会社 High-purity nitrogen gas production equipment
US5832748A (en) * 1996-03-19 1998-11-10 Praxair Technology, Inc. Single column cryogenic rectification system for lower purity oxygen production
US5682762A (en) * 1996-10-01 1997-11-04 Air Products And Chemicals, Inc. Process to produce high pressure nitrogen using a high pressure column and one or more lower pressure columns
US5794458A (en) * 1997-01-30 1998-08-18 The Boc Group, Inc. Method and apparatus for producing gaseous oxygen
US5868006A (en) * 1997-10-31 1999-02-09 The Boc Group, Inc. Air separation method and apparatus for producing nitrogen
US5934106A (en) * 1998-01-27 1999-08-10 The Boc Group, Inc. Apparatus and method for producing nitrogen
DE19843629A1 (en) 1998-09-23 2000-03-30 Linde Ag Process and liquefier for the production of liquid air
US6279345B1 (en) 2000-05-18 2001-08-28 Praxair Technology, Inc. Cryogenic air separation system with split kettle recycle
GB0119500D0 (en) * 2001-08-09 2001-10-03 Boc Group Inc Nitrogen generation
US20050247005A1 (en) * 2004-04-01 2005-11-10 Chris Mroz Rigid ribbon having overall sinusoidal-like waveform shape
US8753440B2 (en) * 2011-03-11 2014-06-17 General Electric Company System and method for cooling a solvent for gas treatment
JP6900230B2 (en) 2017-04-19 2021-07-07 レール・リキード−ソシエテ・アノニム・プール・レテュード・エ・レクスプロワタシオン・デ・プロセデ・ジョルジュ・クロード Nitrogen production system for producing nitrogen with different purity and its nitrogen production method
US11686528B2 (en) 2019-04-23 2023-06-27 Chart Energy & Chemicals, Inc. Single column nitrogen rejection unit with side draw heat pump reflux system and method
WO2021242308A1 (en) * 2020-05-26 2021-12-02 Praxair Technology, Inc. Enhancements to a dual column nitrogen producing cryogenic air separation unit

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FR2697325A1 (en) * 1992-10-27 1994-04-29 Air Liquide Process and installation for the production of nitrogen and oxygen.
EP0595673A1 (en) * 1992-10-27 1994-05-04 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and installation for the production of nitrogen and oxygen
US5404725A (en) * 1992-10-27 1995-04-11 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and installation for producing nitrogen and oxygen
FR2700205A1 (en) * 1993-01-05 1994-07-08 Air Liquide Method and installation for producing at least one gaseous product under pressure and at least one liquid by air distillation.
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US5428962A (en) * 1993-01-05 1995-07-04 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and installation for the production of at least one gaseous product under pressure and at least one liquid by distillation of air
US5303556A (en) * 1993-01-21 1994-04-19 Praxair Technology, Inc. Single column cryogenic rectification system for producing nitrogen gas at elevated pressure and high purity
WO1997014008A1 (en) * 1995-10-11 1997-04-17 Linde Aktiengesellschaft Double-column process and device for the low-temperature separation of air
EP1732978A2 (en) * 2003-12-24 2006-12-20 Praxair Technology, Inc. Cryogenic system for producing elevated pressure nitrogen
EP1732978A4 (en) * 2003-12-24 2012-08-15 Praxair Technology Inc Cryogenic system for producing elevated pressure nitrogen

Also Published As

Publication number Publication date
JPH03186183A (en) 1991-08-14
EP0610972B1 (en) 1997-03-26
FR2651035A1 (en) 1991-02-22
EP0610972A3 (en) 1994-09-28
EP0610972A2 (en) 1994-08-17
CA2023503A1 (en) 1991-02-19
DE69030327D1 (en) 1997-04-30
DE69015504T2 (en) 1995-06-01
US5325674A (en) 1994-07-05
US5373699A (en) 1994-12-20
EP0413631B1 (en) 1994-12-28
DE69030327T2 (en) 1997-10-30
CA2023503C (en) 2000-06-27
JP3162361B2 (en) 2001-04-25
DE69015504D1 (en) 1995-02-09
FR2651035B1 (en) 1994-12-23

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