FR2945111A1 - Method for performing cryogenic distillation of air to produce gaseous oxygen, involves compressing part of air in cold compressor and sending air to exchange line and to column of double column - Google Patents

Method for performing cryogenic distillation of air to produce gaseous oxygen, involves compressing part of air in cold compressor and sending air to exchange line and to column of double column Download PDF

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Publication number
FR2945111A1
FR2945111A1 FR0952942A FR0952942A FR2945111A1 FR 2945111 A1 FR2945111 A1 FR 2945111A1 FR 0952942 A FR0952942 A FR 0952942A FR 0952942 A FR0952942 A FR 0952942A FR 2945111 A1 FR2945111 A1 FR 2945111A1
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France
Prior art keywords
column
air
oxygen
exchange line
flow
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.)
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Application number
FR0952942A
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French (fr)
Inventor
Golo Zick
Benoit Davidan
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.)
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Application filed by Air Liquide SA, LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical Air Liquide SA
Priority to FR0952942A priority Critical patent/FR2945111A1/en
Publication of FR2945111A1 publication Critical patent/FR2945111A1/en
Withdrawn legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04163—Hot end purification of the feed air
    • F25J3/04169—Hot end purification of the feed air by adsorption of the impurities
    • F25J3/04175—Hot end purification of the feed air by adsorption of the impurities at a pressure of substantially more than the highest 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
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
    • F25J3/04054—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of air
    • 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
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    • 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
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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
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    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04193—Division of the main heat exchange line in consecutive sections having different functions
    • F25J3/04206—Division of the main heat exchange line in consecutive sections having different functions including a so-called "auxiliary vaporiser" for vaporising and producing a gaseous product
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    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
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    • 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
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    • 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
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    • 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
    • F25J3/04309—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 nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
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    • 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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    • 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
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    • 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
    • F25J3/0446—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 the heat generated by mixing two different phases
    • F25J3/04466—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 the heat generated by mixing two different phases for producing oxygen as a mixing column overhead gas by mixing gaseous air feed and liquid oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
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    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration

Abstract

The method involves cooling a part of air in a main exchange line (7) to an intermediate temperature of the exchange line for a double column (21). The part of air is compressed in a cold compressor (17) and is sent to the exchange line and to a column of the double column. Flow of nitrogen from a medium pressure column (19) is released in nitrogen turbines (31, 33). Flow of liquid oxygen is sent from a low pressure column (23) to a head of the mixing column. Flow of oxygen-enriched gas is removed from the head of the mixing column and is heated in the exchange line. An independent claim is also included for a cryogenic distillation apparatus.

Description

La présente invention est relative à un procédé et à un appareil de séparation d'air par distillation cryogénique. Dans l'objectif d'éviter l'émission de CO2 dans l'atmosphère, les cycles d'oxycombustion trouvent un intérêt croissant. La taille des appareils de séparation d'air liée à la centrale pour la combustion avec l'oxygène au lieu d'air doit être beaucoup plus grande que les plus gros des appareils de séparation d'air existants. Pour ne pas trop dégrader l'efficacité globale de l'ensemble centrale électrique/appareil de séparation d'air, de l'oxygène avec un coût spécifique très bas est demandé, tout en gardant des coûts d'investissement le plus bas possible. Il n'existe pratiquement pas de besoin d'une production d'azote. Aujourd'hui, on recherche des procédés toujours plus performants pour satisfaire les demandes en oxygène de l'oxycombustion; regardant la taille possible et probable de ce marché, l'invention de nouveaux schémas spécialisés pour l'oxycombustion est nécessaire. On entend par le terme oxycombustion une combustion au cours de laquelle le charbon est brûlé dans un fluide pauvre en azote pouvant aller de l'oxygène pur (> 95 % mol.) à un fluide contenant entre 75 et 95 0/0 mol. d'oxygène. The present invention relates to a method and apparatus for air separation by cryogenic distillation. In order to avoid the emission of CO2 into the atmosphere, oxy-fuel combustion cycles are of increasing interest. The size of the plant-related air separation units for combustion with oxygen instead of air must be much larger than the larger existing air separation units. In order not to degrade the overall efficiency of the entire power plant / air separation unit, oxygen with a very low specific cost is required, while keeping investment costs as low as possible. There is virtually no need for nitrogen production. Today, more and more efficient processes are being sought to satisfy the oxygen demands of oxycombustion; considering the possible and probable size of this market, the invention of new specialized schemes for oxycombustion is necessary. The term "oxycombustion" is understood to mean combustion during which the coal is burned in a fluid that is low in nitrogen and can range from pure oxygen (> 95% mol) to a fluid containing between 75 and 95% by weight. oxygen.

Un des points faibles des processus existants est le vaporiseur/condenseur : • Déjà pour les appareils de séparation d'air de grande capacité d'aujourd'hui (4000 t/j), il y a des problèmes pour les installer dans la virole ; ce problème va s'aggraver encore plus avec les capacités envisagées. • Même avec une meilleure épuration de l'air et/ou d'autres technologies, il y aura toujours le danger d'une vaporisation à sec et l'accumulation des hydrocarbures dans le vaporiseur, ce qui peut mener à des accidents graves. • Le vaporiseur demeurera un des éléments très coûteux, dû à sa construction et au matériel utilisé, généralement l'aluminium. Un but de l'invention est de montrer un procédé de séparation de l'air pour la production d'oxygène très basse pression (allant de 1.2 à 5barabs, ou inférieur à 4 bars, les exemple détaillés concernant une pression de 1.7 barabs) et à basse pureté (entre 75 et 95 % mol.) avec une énergie de séparation très basse, tout en respectant les contraintes des débits très élevées. En sus, aucun vaporiseur n'est nécessaire dans le schéma proposé. Par contre, il est possible d'opérer le procédé selon l'invention en dehors de ces gammes de pureté et de pression. Le principe d'un déflegmateur entre les colonnes de moyenne et de basse pression d'un appareil de séparation d'air est connu de US-A-3756035 et US-A-3535886. Toutes les pressions sont des pressions absolues. One of the weak points of the existing processes is the vaporizer / condenser: • Already for today's large-capacity air separation devices (4000 t / d), there are problems installing them in the shell; this problem will worsen even more with the capacities envisaged. • Even with better air cleaning and / or other technologies, there will always be the danger of dry spraying and the accumulation of hydrocarbons in the vaporizer, which can lead to serious accidents. • The vaporizer will remain a very expensive item, due to its construction and the material used, usually aluminum. An object of the invention is to show an air separation process for the production of oxygen at very low pressure (ranging from 1.2 to 5barabs, or less than 4 bars, the detailed examples relating to a pressure of 1.7 bars) and low purity (between 75 and 95 mol%) with a very low energy separation, while respecting the constraints of very high flows. In addition, no vaporizer is needed in the proposed scheme. On the other hand, it is possible to operate the process according to the invention outside these ranges of purity and pressure. The principle of a dephlegmator between the medium and low pressure columns of an air separation apparatus is known from US-A-3756035 and US-A-3535886. All pressures are absolute pressures.

Selon un objet de l'invention, il est prévu un procédé de distillation cryogénique de l'air pour la production d'oxygène gazeux à une pureté d'entre 75 et 95 mol. %, notamment d'entre 85 et 95 mol% et une pression inférieure à 5 bar abs, notamment inférieur à 2 bars abs avec une double colonne comprenant une colonne moyenne pression qui est intégralement ou partiellement thermiquement couplée avec une colonne basse pression, de préférence au moyen d'un déflegmateur,caractérisé en ce qu'une première partie de l'air destiné à la double colonne est refroidie dans une ligne d'échange jusqu'à une température intermédiaire de la ligne d'échange, comprimée dans un surpresseur froid, envoyée de nouveau à la ligne d'échange et ensuite envoyée à une colonne de la double colonne. Selon un autre objet de l'invention : - on détend un débit d'azote provenant de la colonne moyenne pression dans une turbine d'azote ; - une deuxième partie de l'air se refroidit dans la ligne d'échange et est envoyée en cuve d'une colonne de mélange et un débit d'oxygène liquide est envoyé de la colonne basse pression à la tête de la colonne de mélange, un débit de gaz riche en oxygène est soutiré de la tête de la colonne de mélange et réchauffé dans la ligne d'échange ; - on réchauffe l'oxygène liquide en amont de la colonne de mélange par échange de chaleur avec un débit d'azote gazeux soutiré de la colonne moyenne pression, de préférence après avoir détendu dans la turbine d'azote ; - la première partie de l'air est envoyée en aval du surpresseur froid à un vaporiseur d'oxygène, distinct de la ligne d'échange, alimenté par un débit d'oxygène liquide provenant de la colonne basse pression, éventuellement pressurisé, la première partie de l'air est au moins partiellement liquéfiée et envoyée à la double colonne et l'oxygène liquide est au moins partiellement vaporisé et l'oxygène gazeux produit se réchauffe dans la ligne d'échange ; - la colonne moyenne pression opère à entre 3,5 bars et 4,3 bars. Selon un autre objet de l'invention, il est prévu un appareil de distillation cryogénique de l'air capable de produire de l'oxygène gazeux à une pureté d'entre 75 et 95 mol. %%, notamment d'entre 85 et 95 mol% et une pression inférieure à 5 bar abs notamment inférieur à 2 bars abs comprenant une ligne d'échange et une double colonne comprenant une colonne moyenne pression qui est totalement ou partiellement thermiquement couplée avec une colonne basse pression, de préférence au moyen d'un déflegmateur, caractérisé en ce qu'il comprend un surpresseur froid et une conduite pour envoyer une première partie de l'air destiné à la double colonne dans une ligne d'échange pour la refroidir jusqu'à une température intermédiaire de la ligne d'échange, une conduite pour envoyer la première partie de l'air ainsi refroidie au surpresseur froid, une conduite pour envoyer la première partie de l'air du surpresseur froid de nouveau à la ligne d'échange et une conduite pour envoyer la première partie de l'air surpressée dans le surpresseur froid et refroidie à une colonne de la double colonne. According to one object of the invention, there is provided a process for the cryogenic distillation of air for the production of gaseous oxygen at a purity of between 75 and 95 mol. %, in particular between 85 and 95 mol% and a pressure of less than 5 bar abs, especially less than 2 bar abs, with a double column comprising a medium pressure column which is wholly or partially thermally coupled with a low pressure column, preferably by means of a dephlegmator, characterized in that a first part of the air intended for the double column is cooled in an exchange line to an intermediate temperature of the exchange line, compressed in a cold booster , sent back to the exchange line and then sent to a column in the double column. According to another object of the invention: a flow of nitrogen from the medium pressure column is expanded in a nitrogen turbine; a second part of the air cools in the exchange line and is sent to the bottom of a mixing column and a flow of liquid oxygen is sent from the low pressure column to the head of the mixing column; a flow of oxygen-rich gas is withdrawn from the head of the mixing column and reheated in the exchange line; the liquid oxygen is heated upstream of the mixing column by heat exchange with a nitrogen gas flow rate withdrawn from the medium pressure column, preferably after having been expanded in the nitrogen turbine; the first part of the air is sent downstream of the cold booster to an oxygen vaporizer, distinct from the exchange line, fed by a flow of liquid oxygen coming from the low pressure column, possibly pressurized, the first part of the air is at least partially liquefied and sent to the double column and the liquid oxygen is at least partially vaporized and the oxygen gas produced heats up in the exchange line; the medium pressure column operates at between 3.5 bars and 4.3 bars. According to another object of the invention, there is provided a cryogenic air distillation apparatus capable of producing oxygen gas at a purity of between 75 and 95 mol. %, in particular of between 85 and 95 mol% and a pressure of less than 5 bar, in particular less than 2 bar abs, comprising an exchange line and a double column comprising a medium pressure column which is totally or partially thermally coupled with a low pressure column, preferably by means of a dephlegmator, characterized in that it comprises a cold booster and a pipe for sending a first part of the air intended for the double column in a heat exchange line to cool it down at an intermediate temperature of the exchange line, a pipe to send the first part of the air thus cooled to the cold booster, a pipe to send the first part of the air of the cold booster again to the line of exchange and a pipe to send the first part of the supercharged air into the cold and cooled booster to a column of the double column.

L'appareil comprend éventuellement : - une turbine d'azote et une conduite pour envoyer un débit d'azote provenant de la colonne moyenne pression dans la turbine d'azote ; - une colonne de mélange, une conduite pour envoyer une deuxième partie de l'air se refroidir dans la ligne d'échange et ensuite en cuve de la colonne de mélange, une conduite pour envoyer un débit d'oxygène liquide de la colonne basse pression à la tête de la colonne de mélange et une conduite pour soutirer un débit de gaz riche en oxygène de la tête de la colonne de mélange et l'envoyer à la ligne d'échange ; - un échangeur de chaleur, une conduite pour envoyer l'oxygène liquide en amont de la colonne de mélange à l'échangeur pour échange de chaleur avec un débit d'azote gazeux soutiré de la colonne moyenne pression, de préférence en aval de la turbine d'azote ; - un vaporiseur d'oxygène, une conduite pour envoyer la première partie de l'air en aval du surpresseur froid au vaporiseur d'oxygène, une conduite pour envoyer au vaporiseur d'oxygène par un débit d'oxygène liquide provenant de la colonne basse pression, éventuellement en aval d'un moyen de pressurisation, une conduite pour envoyer la première partie de l'air au moins partiellement liquéfiée à la double colonne et une conduite pour envoyer l'oxygène liquide au moins partiellement vaporisé dans la ligne d'échange. L'invention sera décrite en plus de détails en se référant aux figures qui illustrent des procédés selon l'invention. The apparatus optionally comprises: - a nitrogen turbine and a pipe for sending a flow of nitrogen from the medium pressure column into the nitrogen turbine; a mixing column, a pipe for sending a second part of the air to cool in the exchange line and then in the tank of the mixing column, a pipe for sending a flow of liquid oxygen of the low pressure column; at the top of the mixing column and a line for withdrawing a flow of oxygen-rich gas from the head of the mixing column and sending it to the exchange line; a heat exchanger, a pipe for sending the liquid oxygen upstream of the mixing column to the exchanger for heat exchange with a nitrogen gas flow drawn off from the medium pressure column, preferably downstream of the turbine; nitrogen; an oxygen vaporizer, a pipe for sending the first part of the air downstream of the cold booster to the oxygen vaporizer, a pipe for sending to the oxygen vaporizer by a flow of liquid oxygen coming from the lower column; pressure, possibly downstream of a pressurizing means, a pipe for sending the first part of the air at least partially liquefied to the double column and a pipe for sending the liquid oxygen at least partially vaporized in the exchange line . The invention will be described in more detail with reference to the figures which illustrate methods according to the invention.

Le procédé de la Figure 1 utilise un déflegmateur entre les colonnes de moyenne et de basse pression d'un appareil de séparation d'air, soutire l'oxygène liquide en cuve de la colonne basse pression pour y éviter la vaporisation à sec et transforme ce liquide dans une colonne de mélange. Les colonnes moyenne et basse pression sont couplées entre elles au moyen d'un déflegmateur. Un débit d'air 1 est comprimé dans un compresseur principal 3 et divisé en deux. Une première partie 5 de l'air est envoyée directement à une ligne d'échange principale 7. Cette première partie 5 est soutirée de la ligne d'échange à un niveau intermédiaire de celle-ci, détendue dans une turbine 9 et envoyée en cuve d'une colonne de mélange 11 opérant à entre 1,8 et 2,1 bars, voire plus selon la pression de production de l'oxygène. La deuxième partie 13 de l'air est surpressée dans un surpresseur 15, envoyée à la ligne d'échange 7, soutirée à un niveau intermédiaire, comprimé dans un compresseur froid 17, renvoyée au bout chaud de la ligne d'échange 7 et ensuite refroidie dans la ligne d'échange avant d'être envoyée à la colonne moyenne pression 19 d'une double colonne 21 sous forme gazeuse. Cette colonne moyenne pression 19 opérant à entre 3,5 et 4 bars est posée côte à côte contre la colonne basse pression 23, opérant à environ 1,4 bar en cuve et 1,35 bar en tête, de sorte qu'il y a un échange de chaleur entre la paroi de la colonne moyenne pression et la paroi de colonne basse pression, de sorte qu'il constitue un ensemble à déflegmateur. L'air se sépare dans la colonne moyenne pression pour former un liquide enrichi en oxygène en cuve de colonne et un gaz enrichi en azote en tête de colonne. Le liquide enrichi en oxygène 25 est détendu et envoyé à un niveau intermédiaire de la colonne basse pression 23. Le gaz enrichi en azote 27 est divisé en deux. Une première partie enrichie en azote 29 est détendue dans une turbine 31 sans avoir été refroidie. La deuxième partie 32 est envoyée à la ligne d'échange 7 où elle se réchauffe partiellement, est détendue dans une turbine 33 et renvoyée à la ligne d'échange pour poursuivre son réchauffement jusqu'au bout chaud. Un liquide enrichi en azote 37 est soutiré d'un niveau intermédiaire de la colonne moyenne pression 19, détendue puis envoyée en tête de la colonne basse pression 23. Un gaz enrichi en azote 39 est soutiré en tête de la colonne basse pression 23 et se réchauffe dans la ligne d'échange principale 7. Un liquide riche en oxygène 41 est soutiré en cuve de la colonne basse pression 23, pressurisé par une pompe 52 et se refroidit contre la première partie d'azote détendu provenant de la turbine 31 dans un échangeur 39. L'azote détendu ainsi liquéfié est envoyé en tête de la colonne basse pression 23. Le liquide riche en oxygène est partiellement vaporisé dans l'échangeur 39 pour former un fluide diphasique. Le fluide diphasique riche en oxygène 41 est envoyé de l'échangeur 38 à la tête de la colonne de mélange 11. En tête de la colonne de mélange, de l'oxygène gazeux 43 est soutiré, envoyé à la ligne d'échange 7 et réchauffé pour former le produit principal de l'appareil contenant entre 75 et 95 mol. % d'oxygène à une pression inférieure à 5 bars, voire inférieur à 4 bars ou inférieur à 2 bars. The process of Figure 1 uses a dephlegmator between the medium and low pressure columns of an air separation apparatus, withdraws the liquid oxygen in the tank of the low pressure column to avoid dry vaporization and transforms liquid in a mixing column. The medium and low pressure columns are coupled together by means of a dephlegmator. An air flow 1 is compressed in a main compressor 3 and divided into two. A first part 5 of the air is sent directly to a main exchange line 7. This first part 5 is withdrawn from the exchange line at an intermediate level thereof, expanded in a turbine 9 and sent to the tank a mixing column 11 operating at between 1.8 and 2.1 bars or more depending on the oxygen production pressure. The second part 13 of the air is supercharged in a booster 15, sent to the exchange line 7, withdrawn at an intermediate level, compressed in a cold compressor 17, returned to the hot end of the exchange line 7 and then cooled in the exchange line before being sent to the medium pressure column 19 of a double column 21 in gaseous form. This medium pressure column 19 operating at between 3.5 and 4 bar is placed side by side against the low pressure column 23, operating at about 1.4 bar in the tank and 1.35 bar at the head, so that there is a heat exchange between the wall of the medium pressure column and the low pressure column wall, so that it constitutes a dephlegmator assembly. The air separates in the medium pressure column to form a column-enriched oxygen enriched liquid and a nitrogen-enriched gas at the top of the column. The oxygen enriched liquid is expanded and sent to an intermediate level of the low pressure column 23. The nitrogen enriched gas 27 is divided in two. A first portion enriched in nitrogen 29 is expanded in a turbine 31 without having been cooled. The second part 32 is sent to the exchange line 7 where it is partially heated, is expanded in a turbine 33 and returned to the exchange line to continue its warming to the hot end. A nitrogen-enriched liquid 37 is withdrawn from an intermediate level of the medium-pressure column 19, then expanded and sent to the top of the low-pressure column 23. A nitrogen-enriched gas 39 is withdrawn at the top of the low-pressure column 23 and is heated in the main exchange line 7. An oxygen-rich liquid 41 is withdrawn in the bottom of the low pressure column 23, pressurized by a pump 52 and is cooled against the first portion of expanded nitrogen from the turbine 31 in a Exchanger 39. The expanded nitrogen thus liquefied is sent to the top of the low pressure column 23. The oxygen-rich liquid is partially vaporized in the exchanger 39 to form a two-phase fluid. The oxygen-rich two-phase fluid 41 is sent from the exchanger 38 to the head of the mixing column 11. At the top of the mixing column, oxygen gas 43 is drawn off, sent to the exchange line 7 and heated to form the main product of the apparatus containing between 75 and 95 mol. % oxygen at a pressure of less than 5 bar, or even less than 4 bar or less than 2 bar.

Le liquide de cuve 45 et un liquide intermédiaire 47 de la colonne de mélange sont détendus et envoyés à la colonne basse pression 23 au même niveau que le liquide enrichi en oxygène. En ajoutant un groupe frigorifique dans la ligne d'échange principale, l'écart au bout chaud est de 3 K et monte jusqu'au bout froid à environ 7 K avec une différence logarithmique moyenne de température d'environ 2.5K. Ce schéma possède une énergie de séparation d'environ 0.283 kWh/Nm3, pour de l'oxygène à 1,7 bars, inférieure à celle que l'on trouve pour les schémas de l'art antérieur, en particulier, ceux de US-A-5592832, US-A-6079223, EP-A-1050729 et US-A-6318119. Ce chiffre de 0.283 kWh/Nm3 est obtenu avec une vaporisation partielle de l'oxygène d'environ 10% dans la ligne d'échange avant la colonne de mélange. L'échangeur 38 permettant la vaporisation partielle et la turbine froide 31 pour l'azote moyen pression peuvent être supprimés avec une petite dégradation de l'énergie de séparation. La pureté de l'oxygène liquide soutiré en cuve de la colonne basse pression est de 97.8% mol. pour ce cas particulier. La pression en tête de la colonne moyenne pression est d'environ 4.3 barabs. La différence de température minimale peut même être diminuée jusqu'à 0 K en baissant la pression de la colonne moyenne pression . Si le processus d'oxycombustion permet une pureté de l'oxygène de 90 % mol., l'énergie de séparation diminue à environ 0.261 kWh/Nm3, pour 85 % mol., même à environ 0.246 kWh/Nm3, tout en gardant le rendement à 99 %. Ceci s'explique par la chute de la pression de la colonne moyenne pression de 4.3 barabs pour 95 % mol. de pureté jusqu'à 3.55 barabs pour 85 % mol. de pureté. Le processus de la Figure 2 utilise un déflegmateur entre les colonnes de moyenne et de basse pression d'un appareil de séparation d'air, soutire d'oxygène liquide en cuve de la colonne basse pression pour y éviter la vaporisation à sec et transforme ce liquide en vapeur dans un vaporiseur. Un débit d'air 1 est comprimé dans un compresseur principal 3 et divisé en deux. Une première partie 5 de l'air est envoyée directement à une ligne d'échange principale 7 où elle se refroidit avant être envoyée à la colonne moyenne pression 19 sous forme gazeuse La deuxième partie 13 de l'air est surpressée dans un surpresseur 15, envoyée à la ligne d'échange 7, soutirée à un niveau intermédiaire, comprimée dans un compresseur froid 17, renvoyée au bout chaud de la ligne d'échange 7 et ensuite refroidie dans la ligne d'échange avant d'être envoyée au vaporiseur d'oxygène 51 où elle se condense au moins partiellement. L'air au moins partiellement condensé est divisé en deux débits 16,18 envoyés respectivement à la colonne moyenne pression 19 et à la colonne basse pression 23. Cette colonne moyenne pression 19 opérant à entre 3,5 bar et 4,3 bar est posée côte à côte contre la colonne basse pression 23 opérant à environ 1,4 bar en cuve et 1,35 bar en tête, de sorte qu'il y a un échange de chaleur entre la paroi de la colonne moyenne pression et la paroi de colonne basse pression à travers un déflegmateur. The tank liquid 45 and an intermediate liquid 47 of the mixing column are expanded and sent to the low pressure column 23 at the same level as the oxygen-enriched liquid. By adding a refrigeration unit in the main exchange line, the hot end differential is 3 K and rises to the cold end at around 7 K with a mean logarithmic difference in temperature of about 2.5K. This scheme has a separation energy of about 0.283 kWh / Nm3, for oxygen at 1.7 bar, lower than that found for the prior art schemes, in particular those of US Pat. A-5592832, US-A-6079223, EP-A-1050729 and US-A-6318119. This figure of 0.283 kWh / Nm3 is obtained with a partial vaporization of oxygen of about 10% in the exchange line before the mixing column. The exchanger 38 allowing the partial vaporization and the cold turbine 31 for the medium pressure nitrogen can be removed with a small degradation of the separation energy. The purity of the liquid oxygen withdrawn in the bottom of the low pressure column is 97.8 mol%. for this particular case. The pressure at the top of the medium pressure column is approximately 4.3 barabs. The minimum temperature difference can even be reduced to 0 K by lowering the pressure of the medium pressure column. If the oxycombustion process allows a purity of oxygen of 90 mol%, the separation energy decreases to about 0.261 kWh / Nm3, for 85 mol%, even at about 0.246 kWh / Nm3, while keeping the 99% yield. This is explained by the drop in pressure of the medium pressure column of 4.3 barabs for 95 mol%. purity up to 3.55 barabs for 85 mol%. of purity. The process of Figure 2 uses a dephlegmator between the medium and low pressure columns of an air separation apparatus, withdrawing liquid oxygen in the bottom of the low pressure column to avoid dry spraying and transforms liquid vapor in a vaporizer. An air flow 1 is compressed in a main compressor 3 and divided into two. A first portion 5 of the air is sent directly to a main exchange line 7 where it cools before being sent to the medium pressure column 19 in gaseous form The second part 13 of the air is supercharged in a booster 15, sent to the exchange line 7, withdrawn at an intermediate level, compressed in a cold compressor 17, returned to the hot end of the exchange line 7 and then cooled in the exchange line before being sent to the vaporizer d oxygen 51 where it condenses at least partially. The at least partially condensed air is divided into two flow rates 16, 18 sent respectively to the medium pressure column 19 and to the low pressure column 23. This medium pressure column 19 operating at between 3.5 bar and 4.3 bar is placed side by side against the low pressure column 23 operating at about 1.4 bar in the tank and 1.35 bar at the head, so that there is a heat exchange between the wall of the medium pressure column and the column wall low pressure through a dephlegmator.

L'air se sépare dans la colonne moyenne pression 19 pour former un liquide enrichi en oxygène en cuve de colonne et un gaz enrichi en azote en tête de colonne. Le liquide enrichi en oxygène 25 est détendu et envoyé à un niveau intermédiaire de la colonne basse pression 23. Le gaz enrichi en azote 27 est détendu dans une turbine 33 et renvoyé à la ligne d'échange pour poursuivre son réchauffement jusqu'au bout chaud. Un liquide enrichi en azote 37 est soutiré d'un niveau intermédiaire de la colonne moyenne pression 19, détendu puis envoyé en tête de la colonne basse pression 23. Un gaz enrichi en azote 39 est soutiré en tête de la colonne basse pression 23 et se réchauffe dans la ligne d'échange principale 7. Un liquide riche en oxygène est soutiré en cuve de la colonne basse pression 23, pressurisé par la pompe 52 puis envoyé au vaporiseur d'oxygène où il se vaporise. Ensuite, l'oxygène se réchauffe pour former le produit principal 53 de l'appareil, de l'oxygène gazeux ayant une pureté entre 75 et 95 mol. % d'oxygène qui se réchauffe dans l'échangeur 7. Le compresseur froid de ces schémas est entraîné uniquement par la turbine d'air 9 de la Figure 1 ou par la turbine d'azote 33 des deux figures. Des schémas simplifiés avec moins des compresseurs/turbines sont facilement envisageables.30 The air is separated in the medium-pressure column 19 to form an oxygen enriched liquid in the bottom of the column and a nitrogen-enriched gas at the top of the column. The oxygen enriched liquid 25 is expanded and sent to an intermediate level of the low pressure column 23. The nitrogen enriched gas 27 is expanded in a turbine 33 and returned to the exchange line to continue its warming to the hot end . A nitrogen-enriched liquid 37 is withdrawn from an intermediate level of the medium-pressure column 19, expanded and then sent to the top of the low-pressure column 23. A nitrogen-enriched gas 39 is withdrawn at the top of the low-pressure column 23 and is heated in the main exchange line 7. An oxygen-rich liquid is withdrawn in the bottom of the low pressure column 23, pressurized by the pump 52 and sent to the oxygen vaporizer where it vaporizes. Then, the oxygen is heated to form the main product 53 of the apparatus, oxygen gas having a purity between 75 and 95 mol. % oxygen which is heated in the exchanger 7. The cold compressor of these diagrams is driven only by the air turbine 9 of Figure 1 or by the nitrogen turbine 33 of the two figures. Simplified schematics with less compressors / turbines are easily feasible.30

Claims (10)

REVENDICATIONS1. Procédé de distillation cryogénique de l'air pour la production d'oxygène gazeux à une pureté d'entre 75 et 95 mol. %, notamment d'entre 85 et 95 mol% et une pression inférieure à 5 bar abs, notamment inférieur à 2 bars abs avec une double colonne (21) comprenant une colonne moyenne pression (19) qui est intégralement ou partiellement thermiquement couplée avec une colonne basse pression (23),de préférence au moyen d'un déflegmateur, caractérisé en ce qu'une première partie de l'air destiné à la double colonne est refroidie dans une ligne d'échange (7) jusqu'à une température intermédiaire de la ligne d'échange, comprimée dans un surpresseur froid (17), envoyée de nouveau à la ligne d'échange et ensuite envoyée à une colonne de la double colonne. REVENDICATIONS1. Process for the cryogenic distillation of air for the production of gaseous oxygen at a purity of between 75 and 95 mol. %, especially between 85 and 95 mol% and a pressure of less than 5 bar abs, especially less than 2 bar abs with a double column (21) comprising a medium pressure column (19) which is wholly or partially thermally coupled with a low pressure column (23), preferably by means of a dephlegmator, characterized in that a first part of the air intended for the double column is cooled in an exchange line (7) to an intermediate temperature of the exchange line, compressed in a cold booster (17), sent back to the exchange line and then sent to a column of the double column. 2. Procédé selon la revendication 1 dans lequel on détend un débit d'azote provenant de la colonne moyenne pression dans une turbine d'azote (31,33). 2. Method according to claim 1 wherein a flow of nitrogen from the medium pressure column is expanded in a nitrogen turbine (31,33). 3. Procédé selon la revendication 1 ou 2 dans lequel une deuxième partie de l'air se refroidit dans la ligne d'échange et est envoyé en cuve d'une colonne de mélange (11) et un débit d'oxygène liquide est envoyé de la colonne basse pression à la tête de la colonne de mélange, un débit de gaz riche en oxygène est soutiré de la tête de la colonne de mélange et réchauffé dans la ligne d'échange. 3. Method according to claim 1 or 2 wherein a second part of the air cools in the exchange line and is sent to the bottom of a mixing column (11) and a flow of liquid oxygen is sent from the low pressure column at the head of the mixing column, a flow of oxygen-rich gas is withdrawn from the head of the mixing column and reheated in the exchange line. 4. Procédé selon la revendication 3 dans lequel on réchauffe l'oxygène liquide en amont de la colonne de mélange (11) par échange de chaleur avec un débit d'azote gazeux soutiré de la colonne moyenne pression, de préférence après l'avoir détendu dans la turbine d'azote (31). 4. Method according to claim 3 wherein the liquid oxygen is heated upstream of the mixing column (11) by heat exchange with a nitrogen gas flow withdrawn from the medium pressure column, preferably after having relaxed in the nitrogen turbine (31). 5. Procédé selon l'une des revendications précédentes dans lequel la première partie de l'air est envoyée en aval du surpresseur froid (17) à un vaporiseur d'oxygène (51), distinct de la ligne d'échange, alimenté par un débit d'oxygène liquide provenant de la colonne basse pression (23), éventuellement pressurisé, la première partie de l'air est au moins partiellement liquéfiée et envoyée à la double colonne et l'oxygène liquide est au moins partiellement vaporisé et l'oxygène gazeux produit se réchauffe dans la ligne d'échange. 5. Method according to one of the preceding claims wherein the first part of the air is sent downstream of the cold booster (17) to an oxygen vaporizer (51), distinct from the exchange line, fed by a flow of liquid oxygen from the low pressure column (23), possibly pressurized, the first part of the air is at least partially liquefied and sent to the double column and the liquid oxygen is at least partially vaporized and the oxygen gaseous product is heated in the exchange line. 6. Appareil de distillation cryogénique de l'air capable de produire de l'oxygène gazeux à une pureté d'entre 75 et 95 mol. %%, notamment d'entre 85 et 95 mol% et une pression inférieure à 5 bar abs notamment inférieur à 2 bars abs comprenant une ligne d'échange (7) et une double colonne (21) comprenant une colonne moyenne pression (19) qui est totalement ou partiellement thermiquement couplée avec une colonne basse pression (23), de préférence au moyen d'un déflegmateur, caractérisé en ce qu'il comprend un surpresseur froid (17) et une conduite pour envoyer une première partie de l'air destiné à la double colonne dans la ligne d'échange pour la refroidir jusqu'à une température intermédiaire de la ligne d'échange, une conduite pour envoyer la première partie de l'air ainsi refroidie au surpresseur froid, une conduite pour envoyer la première partie de l'air du surpresseur froid de nouveau à la ligne d'échange et une conduite pour envoyer la première partie de l'air surpressée dans le surpresseur froid et refroidie à une colonne de la double colonne. 6. Apparatus for the cryogenic distillation of air capable of producing oxygen gas at a purity of between 75 and 95 mol. %, in particular of between 85 and 95 mol% and a pressure of less than 5 bar abs in particular of less than 2 bar abs comprising an exchange line (7) and a double column (21) comprising a medium pressure column (19) which is totally or partially thermally coupled with a low pressure column (23), preferably by means of a dephlegmator, characterized in that it comprises a cold booster (17) and a pipe for sending a first part of the air intended for the double column in the exchange line to cool it to an intermediate temperature of the exchange line, a pipe to send the first part of the air thus cooled to the cold booster, a pipe to send the first part of the air from the cold booster again to the exchange line and a pipe to send the first part of the air supercharged into the cold booster and cooled to a column of the double column. 7. Appareil selon la revendication 6 comprenant une turbine 25 d'azote (31,33) et une conduite pour envoyer un débit d'azote provenant de la colonne moyenne pression dans la turbine d'azote. An apparatus according to claim 6 comprising a nitrogen turbine (31,33) and a conduit for delivering a nitrogen flow from the medium pressure column into the nitrogen turbine. 8. Appareil selon la revendication 6 ou 7 comprenant une colonne de mélange, une conduite pour envoyer une deuxième partie de l'air se 30 refroidir dans la ligne d'échange et ensuite en cuve de la colonne de mélange, une conduite pour envoyer un débit d'oxygène liquide de la colonne basse pression à la tête de la colonne de mélange (11) et une conduite pour soutirer un débit de gaz riche en oxygène de la tête de la colonne de mélange et l'envoyer à la ligne d'échange. Apparatus according to claim 6 or 7 comprising a mixing column, a conduit for sending a second part of the air to cool in the exchange line and then in the tank of the mixing column, a conduit for sending a flow of liquid oxygen from the low pressure column to the top of the mixing column (11) and a line for withdrawing a flow of oxygen-rich gas from the head of the mixing column and sending it to the line of exchange. 9. Appareil selon la revendication 8 comprenant un échangeur de chaleur (38), une conduite pour envoyer l'oxygène liquide en amont de la colonne de mélange à l'échangeur pour échange de chaleur avec un débit d'azote gazeux soutiré de la colonne moyenne pression, de préférence en aval de la turbine d'azote (31). 9. Apparatus according to claim 8 comprising a heat exchanger (38), a pipe for sending the liquid oxygen upstream of the mixing column to the exchanger for heat exchange with a nitrogen gas flow withdrawn from the column medium pressure, preferably downstream of the nitrogen turbine (31). 10. Appareil selon l'une des revendications 6 à 9 comprenant un vaporiseur d'oxygène (51), une conduite pour envoyer la première partie de l'air en aval du surpresseur froid au vaporiseur d'oxygène, une conduite pour envoyer au vaporiseur d'oxygène par un débit d'oxygène liquide provenant de la colonne basse pression (23), éventuellement en aval d'un moyen de pressurisation (52), une conduite pour envoyer la première partie de l'air au moins partiellement liquéfiée à la double colonne et une conduite pour envoyer l'oxygène liquide au moins partiellement vaporisé dans la ligne d'échange (7). 10. Apparatus according to one of claims 6 to 9 comprising an oxygen vaporizer (51), a pipe for sending the first part of the air downstream of the cold booster to the oxygen vaporizer, a pipe to send to the vaporizer oxygen by a flow of liquid oxygen from the low pressure column (23), possibly downstream of a pressurizing means (52), a pipe for sending the first part of the air at least partially liquefied to the double column and a pipe for sending the liquid oxygen at least partially vaporized in the exchange line (7).
FR0952942A 2009-05-04 2009-05-04 Method for performing cryogenic distillation of air to produce gaseous oxygen, involves compressing part of air in cold compressor and sending air to exchange line and to column of double column Withdrawn FR2945111A1 (en)

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