FR2607718A1 - Process for fractionating a liquid mixture employing a plate heat exchanger as fractionation column and its application to the production of liquefied petroleum gas - Google Patents

Process for fractionating a liquid mixture employing a plate heat exchanger as fractionation column and its application to the production of liquefied petroleum gas Download PDF

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Publication number
FR2607718A1
FR2607718A1 FR8617048A FR8617048A FR2607718A1 FR 2607718 A1 FR2607718 A1 FR 2607718A1 FR 8617048 A FR8617048 A FR 8617048A FR 8617048 A FR8617048 A FR 8617048A FR 2607718 A1 FR2607718 A1 FR 2607718A1
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Prior art keywords
column
vapors
exchanger
mixture
dehumidification
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FR8617048A
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French (fr)
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FR2607718B1 (en
Inventor
Jean-Charles Marcel Ja Viltard
Jean-Claude Amande
Guy Chiche Portiche
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Societe dEtude et dApplication des Techniques Nouvelles NeoTec
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Societe dEtude et dApplication des Techniques Nouvelles NeoTec
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14—Fractional distillation or use of a fractionation or rectification 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
    • F25J3/0204—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 characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • 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
    • F25J3/0204—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 characterised by the feed stream
    • F25J3/0219—Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
    • 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
    • F25J3/0228—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 characterised by the separated product stream
    • F25J3/0233—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 characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • 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
    • F25J3/0228—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 characterised by the separated product stream
    • F25J3/0242—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 characterised by the separated product stream separation of CnHm with 3 carbon atoms or more
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/80—Processes or apparatus using separation by rectification using integrated mass and heat exchange, i.e. non-adiabatic rectification in a reflux exchanger or dephlegmator
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/50—Processes or apparatus using other separation and/or other processing means using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
    • 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/12—Refinery or petrochemical off-gas
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/68—Separating water or hydrates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

Chemical engineering. The invention relates to a process for fractionating a mixture of at least three constituents with different boiling points, which is characterised by the use of a plate exchanger 11 as fractionating column. Application to the extraction of liquefied petroleum gas.

Description

L'invention concerne un procédé de fractionnement d'un mélange liquide utilisant un échangeur de chaleur à plaques comme colonne de fractionnement et son application à la production de gaz de pétrole liquéfié. The invention relates to a method for fractionating a liquid mixture using a plate heat exchanger as a fractionation column and its application to the production of liquefied petroleum gas.

On connaît bien les échangeurs à plaques. Plate exchangers are well known.

Ces échangeurs sont typiquement constitués d'un empilement alterné de tôles planes et de tôles ondulées avec disposition de barrettes entre les tôles planes adjacentes sur le pourtour de ces tôles, sauf aux emplacements des entrées et sorties de fluide, les tôles et barrettes étant soudées ensemble de façon à délimiter une pluralité de canaux ou niveaux de circulation de fluides. Ces échangeurs comprennent aussi des boites de raccordement soudées sur les bords de l'empilage de tôles, en regard de ces entrées et sorties de fluides. En variante, au lieu d'être constitués par empilement alterné de tôles planes et ondulées, les échangeurs peuvent être réalisés par un empilement de tôles présentant des ondulations ou reliefs convenablement décalés d'une tôle à la suivante.Il est connu aussi de prévoir des perforations ou des chicanes sur les ondulations des tôles pour créer des turbulences dans les canaux de l'échangeur. Ces échangeurs peuvent être parcourus par deux ou trois fluides différents, circulant à co-courants, à contre-courant, en courants croisés, certain(s) courant(s) pouvant n'intéresser qu'une partie de l'échangeur, par exemple sa partie supérieure, grâce à des cloisonnements appropriés.These exchangers typically consist of an alternating stack of flat sheets and corrugated sheets with the provision of bars between the adjacent flat sheets around the periphery of these sheets, except at the locations of the fluid inlets and outlets, the sheets and strips being welded together. so as to delimit a plurality of channels or levels of circulation of fluids. These exchangers also include connection boxes welded to the edges of the sheet stack, facing these fluid inlets and outlets. Alternatively, instead of being formed by alternating stacking of flat and corrugated sheets, the exchangers can be made by a stack of sheets having corrugations or reliefs suitably offset from one sheet to the next. It is also known to provide perforations or baffles on the corrugations of the sheets to create turbulence in the channels of the exchanger. These exchangers can be traversed by two or three different fluids, circulating in co-currents, against the current, in cross currents, certain current (s) which may only interest a part of the exchanger, for example its upper part, thanks to appropriate partitions.

Les échangeurs à plaques sont habituellement réalisés en aluminium, spécialement en vue d'applications impliquant des basses températures, mais peuvent aussi être réalisés en acier inoxydable.  Plate heat exchangers are usually made of aluminum, especially for applications involving low temperatures, but can also be made of stainless steel.

La demanderesse a trouvé que de tels échangeurs à plaques pouvaient être employés comme colonnes de fractionnement très efficaces et très souples d'emploi, pour fractionner des mélanges liquides comprenant au moins trois constituants de volatilités différentes. The Applicant has found that such plate exchangers could be used as highly efficient and very flexible fractionation columns, for fractionating liquid mixtures comprising at least three constituents of different volatilities.

Plus précisément, l'invention concerne un procédé de fractionnement d'un mélange comprenant au moins trois constituants, à savoir un constituant A relativement peu volatil, un constituant C relativement très volatil et un constituant B de volatilité intermédiaire, selon lequel on introduit en continu ledit mélange dans une colonne de fractionnement où règnent des conditions telles qu'une partie au moins dudit mélange s'élève sous forme de vapeurs vers la partie supérieure de la colonne; on condense partiellement lesdites vapeurs dans la partie supérieure de la colonne et on laisse le condensat résultant refluer vers la partie inférieure de la colonne; on évacue en continu une fraction liquide enrichie en constituants de moindre volatilité A et B du fond de la colonne; et on évacue en continu de la tête de la colonne une fraction de vapeurs enrichie en le constituant le plus volatil C, caractérisé en ce qu'on utilise comme colonne de fractionnement certains des canaux ou niveaux de circulation de fluides d'un échangeur à plaques comprenant une pluralité de canaux ou niveaux de circulation de fluides séparés les uns des autres par une tôle d'échange de chaleur, et en ce qu'on fait passer dans au moins certains des autres canaux ou niveaux de circulation de fluides de l'échangeur un ou plusieurs fluide(s) apportant les calories et/ou des frigories pouvant être requises pour la mise en ébullition du mélange à fractionner dans la partie inférieure de l'échangeur et pour la condensation partielle des vapeurs dans sa partie intermédiaire et/ou supérieure. More specifically, the invention relates to a process for fractionating a mixture comprising at least three constituents, namely a relatively low volatile component A, a relatively very volatile component C and a component B of intermediate volatility, according to which one continuously introduces said mixture in a fractionation column where conditions prevail such that at least part of said mixture rises in the form of vapors towards the upper part of the column; partially condensing said vapors in the upper part of the column and allowing the resulting condensate to flow back to the lower part of the column; a liquid fraction enriched in constituents of lower volatility A and B is continuously discharged from the bottom of the column; and a fraction of vapors enriched by the most volatile constituent C is continuously discharged from the head of the column, characterized in that some of the channels or levels of circulation of fluids of a plate exchanger are used as fractionation column comprising a plurality of fluid circulation channels or levels separated from each other by a heat exchange sheet, and in that one passes through at least some of the other channels or fluid circulation levels of the exchanger one or more fluid (s) providing the calories and / or frigories which may be required for boiling the mixture to be fractionated in the lower part of the exchanger and for the partial condensation of the vapors in its intermediate and / or upper part .

Le mélange introduit dans l'échangeur à plaque peut être à l'état gazeux (vapeurs), liquide ou mixtes (mélange de phases liquides et gazeuses). Si une phase liquide est présente, on ajuste les conditions de température régnant dans la partie inférieure de l'échangeur à plaques de façon qu'il se produise une certaine ébullition de cette phase. The mixture introduced into the plate heat exchanger can be in the gaseous (vapor), liquid or mixed state (mixture of liquid and gaseous phases). If a liquid phase is present, the temperature conditions prevailing in the lower part of the plate heat exchanger are adjusted so that a certain boiling of this phase occurs.

La circulation des fluides caloporteur et/ou frigoporteur peut se faire dans le même sens que la circulation du mélange à fractionner, à contre-courant ou selon des courants croisés, selon le cas. On peut également prévoir des configurations mixtes, par exemple des circulations parallèles dans la partie inférieure de l'échangeur et des circulations croisées dans la partie supérieure, en utilisant des cloisonnements appropriés. The circulation of coolant and / or coolant fluids can be done in the same direction as the circulation of the mixture to be fractionated, against the current or according to crossed currents, as the case may be. Mixed configurations can also be provided, for example parallel circulations in the lower part of the exchanger and crossed circulations in the upper part, using appropriate partitions.

Il est important d'assurer un bon contact physique entre le reflux descendant de condensat liquide et les vapeurs montantes. A cette fin, on utilisera, de préférence, un échangeur dont les tôles ondulées sont pourvues de perforations, de chicanes ou d'autres moyens générateurs de turbulences dans les écoulements. It is important to ensure good physical contact between the falling backward flow of liquid condensate and the rising vapors. To this end, use will preferably be made of an exchanger, the corrugated sheets of which are provided with perforations, baffles or other means generating turbulence in the flows.

Le procédé de fractionnement de l'invention peut être mis en oeuvre dans une gamme de pressions de O à 100 bars et dans une gamme de températures de -1500C à +4000C. On peut s'en servir tant pour la rectification que l'épuisement. The fractionation process of the invention can be implemented in a pressure range from 0 to 100 bar and in a temperature range from -1500C to + 4000C. It can be used for both rectification and exhaustion.

L'invention concerne aussi un procédé d'extraction de gaz de pétrole liquéfié (GPL) à partir de divers gaz (gaz de raffinerie, de distillation, de réformage, etc..) mettant en oeuvre le procédé de fractionnement sus-décrit, remarquable par le fait qu'il met en oeuvre des températures moins basses que les procédés classiques actuellement utilisés et permet, donc, d'importantes économies d'énergie tout en assurant un taux de récupération élevé des butanes. The invention also relates to a process for extracting liquefied petroleum gas (LPG) from various gases (refinery gas, distillation gas, reforming, etc.) implementing the above-mentioned fractionation process, remarkable by the fact that it uses lower temperatures than the conventional methods currently used and therefore allows significant energy savings while ensuring a high recovery rate of butanes.

La description qui va suivre, en regard du dessin annexé donné à titre d'exemple non limitatif, fera bien comprendre comment l'invention peut être réalisée, les particularités qui ressortent tant du texte que du dessin faisant, bien entendu, partie de ladite invention. The description which follows, with reference to the appended drawing given by way of nonlimiting example, will make it clear how the invention can be implemented, the features which emerge both from the text and from the drawing forming, of course, part of said invention .

La figure unique est une représentation schématique d'une installation d'extraction de gaz de pétrole liquéfié (GPL) (hydrocarbures en C3-C4) à partir de gaz naturel ou de raffinerie, mettant en oeuvre le procédé de fractionnement de l'invention. The single figure is a schematic representation of an installation for extracting liquefied petroleum gas (LPG) (C3-C4 hydrocarbons) from natural gas or refinery, implementing the fractionation process of the invention.

Sur cette figure, la charge gazeuse à traiter qui se compose d'un mélange de composés lourds (en C3,
C4 et plus) et légers (en C1 et C2) parvient à l'installation par une conduite 1 après avoir subi une phase de compression qui n'est pas représentée. Par exemple, pour une charge gazeuse contenant, en poids, 16 de composés en C3 et 8 de composés en C4, on pourra faire arriver la charge gazeuse sous une pression de 31,3 bars à une température de 520C environ. La conduite 1 arrive à un premier échangeur de chaleur 2 où la charge gazeuse subit un premier refroidissement par échange de chaleur avec les vapeurs froides (10C environ) provenant de la tête de l'échangeur à plaques, comme décrit ciaprès.In this figure, the gas charge to be treated which consists of a mixture of heavy compounds (in C3,
C4 and more) and light (in C1 and C2) reaches the installation via a pipe 1 after having undergone a compression phase which is not shown. For example, for a gas charge containing, by weight, 16 of C3 compounds and 8 of C4 compounds, it is possible to cause the gas charge to arrive at a pressure of 31.3 bars at a temperature of approximately 520C. Line 1 arrives at a first heat exchanger 2 where the gas charge undergoes a first cooling by heat exchange with the cold vapors (approximately 10C) coming from the head of the plate exchanger, as described below.

A la sortie de l'échangeur 2, la charge gazeuse emprunte la conduite 3 et passe dans un deuxième échangeur 4 dont le fluide réfrigérant est produit par une unité de réfrigération 4', à la sortie duquel elle a une température de 220C environ. La charge refroidie est alors amenée, via la conduite 5, dans une colonne de séparationdéshumidification 6 comprenant deux portions superposées
Sa et 6b, séparées par un dispositif 7 laissant passer les vapeurs montant de la portion inférieure 6a vers la portion supérieure 6b, mais retenant toute phase liquide descendante condensée dans la portion supérieure 6b, la conduite 5 débouchant dans la colonne 6 à un niveau situé juste en-dessous du dispositif 7. Dans la portion inférieure Ga, la charge se sépare en une fraction liquide contenant une partie des composés lourds (C3-C4) qui tombe dans le fond de la colonne et en des vapeurs contenant les composés légers (C1-C2; et entraî nant le restant des composés lourds. Ces vapeurs traversent le dispositif 7, s'élèvent dans la portion supérieure 6b où elles sont débarrassées de l'eau qu'elles contiennent. Ce résultat peut être obtenu par lavage à contrecourant par un courant de glycol arrivant en tête de la portion 6b par la conduite 8, qui absorbe l'humidité présente dans les vapeurs. Le mélange de glycol et d'eau est retenu par le dispositif 7 et évacué par la conduite 9 vers une unité de régénération du glycol (non représentée).Cette déshumidification préalable est nécessaire pour éviter la formation d'hydrates dans l'échangeur à plaques 11. L'emploi d'inhibiteurs de formation d'hydrates dans l'échangeur 11 lui-même n'est pas envisagé car cela entraîne des phénomènes de moussage avec le mélange d'hydrocarbures gazeux et liquide.At the outlet of the exchanger 2, the gaseous charge borrows the line 3 and passes into a second exchanger 4, the refrigerant of which is produced by a refrigeration unit 4 ', at the outlet of which it has a temperature of approximately 220C. The cooled load is then brought, via line 5, to a dehumidification separation column 6 comprising two superposed portions
Sa and 6b, separated by a device 7 allowing the rising vapors to pass from the lower portion 6a to the upper portion 6b, but retaining any descending liquid phase condensed in the upper portion 6b, the pipe 5 opening into the column 6 at a level located just below the device 7. In the lower portion Ga, the charge separates into a liquid fraction containing part of the heavy compounds (C3-C4) which falls into the bottom of the column and into vapors containing the light compounds ( C1-C2; and entraining the rest of the heavy compounds. These vapors pass through the device 7, rise in the upper portion 6b where they are freed of the water which they contain. This result can be obtained by backwashing by a stream of glycol arriving at the head of the portion 6b via line 8, which absorbs the moisture present in the vapors. The mixture of glycol and water is retained by device 7 and evacuated via line 9 to a glycol regeneration unit (not shown). This prior dehumidification is necessary to avoid the formation of hydrates in the plate exchanger 11. The use of hydrate formation inhibitors in the exchanger 11 itself n 'is not envisaged because this leads to foaming phenomena with the mixture of gaseous and liquid hydrocarbons.

Les vapeurs débarrassées de liteau sortent en tête de la portion 6b de la colonne à une température de 230C environ, et sont envoyées via la conduite 10, à la partie inférieure de certains des canaux de circulation de fluides d'un échangeur à plaques 11. Ces vapeurs s'élèvent dans l'échangeur et une partie d'entre elles est condensée à la partie supérieure de l'échangeur grâce au refroidissement exercé par un fluide réfrigérant produit par l'unité de réfrigération îîa et circulant à une température de -6aC dans la partie des autres canaux de circulation de fluides de l'échangeur situé à la partie supérieure de l'échangeur.Le condensat liquide, riche en hydrocarbures en C3 et C4, reflue vers le fond de l'échangeur, lavant les vapeurs qui montent et absorbant les composants lourds entraînés par lesdites vapeurs.The stripped vapors exit at the head of the portion 6b of the column at a temperature of about 230C, and are sent via the pipe 10, to the lower part of some of the fluid circulation channels of a plate exchanger 11. These vapors rise in the exchanger and part of them is condensed at the top of the exchanger thanks to the cooling exerted by a refrigerant fluid produced by the refrigeration unit îîa and circulating at a temperature of -6aC in the part of the other fluid circulation channels of the exchanger located at the top of the exchanger. The liquid condensate, rich in C3 and C4 hydrocarbons, flows back to the bottom of the exchanger, washing the rising vapors and absorbing the heavy components entrained by said vapors.

Il s'établit ainsi une espèce d'équilibre liquide-vapeurs dans l'échangeur qui joue donc en même temps le rôle d'une colonne de fractionnement. Du condensat liquide est évacué en continu du fond de l'échangeur, riche en hydrocarbures en C3 et C4, et est recyclé par la conduite 12, a la partie supérieure de la portion inférieure 6a de la colonne de séparation-déshumidification 6. Un liquide, formé principalement d'hydrocarbures en C3 et C4 est soutiré en continu du fond de la colonne de séparation-déshumidifica tion 6, par la conduite 13, une partie de ce soutirage étant recyclée par le rebouilleur 14 dans la colonne 6 afin d'entretenir l'ébullition du liquide occupant le fond de cette colonne. La partie restante du soutirage est envoyée à un débutaniseur (non représenté) de conception classique.Par ailleurs, les vapeurs, riches en méthane et éthane, s 'échap- pant par la tête de l'échangeur - colonne 11, qui sortent à une température d'environ 10C, sont envoyées par la conduite 15 à l'échangeur 2 de pré-refroidissement de la charge gazeuse avant d'être évacuées par la conduite 16 à une température d'environ 470C. Ces vapeurs, formées principalement d'hydrocarbures en C1 et C2, peuvent servir de source d'énergie.A kind of liquid-vapor equilibrium is thus established in the exchanger which therefore plays the role of a fractionation column at the same time. Liquid condensate is continuously discharged from the bottom of the exchanger, rich in C3 and C4 hydrocarbons, and is recycled through line 12, to the upper part of the lower portion 6a of the separation-dehumidification column 6. A liquid , formed mainly of C3 and C4 hydrocarbons is continuously drawn off from the bottom of the separation-dehumidification column 6, via line 13, part of this withdrawal being recycled by reboiler 14 into column 6 in order to maintain the boiling of the liquid occupying the bottom of this column. The remaining part of the withdrawal is sent to a debananizer (not shown) of conventional design. Furthermore, the vapors, rich in methane and ethane, escaping through the head of the exchanger - column 11, which exit at a temperature of approximately 10C, are sent via line 15 to the exchanger 2 for pre-cooling the gas charge before being discharged through line 16 at a temperature of approximately 470C. These vapors, formed mainly of C1 and C2 hydrocarbons, can be used as a source of energy.

Il est à noter que la tête de l'échangeurcolonne 11 constitue le point le plus froid de l'installation et détermine le point de rosée du mélange gazeux, formé principalement de méthane et d'éthane qui sort en tête de l'échangeur. Il est à noter aussi que la totalité du méthane et de l'éthane sont en un même point, à savoir la tête de 1 'échangeur-colonne 11. It should be noted that the head of the column exchanger 11 constitutes the coldest point of the installation and determines the dew point of the gas mixture, formed mainly of methane and ethane which leaves at the head of the exchanger. It should also be noted that all of the methane and ethane are at the same point, namely the head of the column exchanger 11.

Avec une installation telle que décrite, on
produit arrive à récupérer, dans le CPL/, jusqu'à 98% des butanes contenus dans la charge gazeuse initiale, avec une puis sance frigorifique absorbée moitié moindre que celle né cessitéepar des installations classiques.With an installation as described, we
product manages to recover, in the CPL /, up to 98% of the butanes contained in the initial gaseous charge, with a refrigerant capacity absorbed half that of that required by conventional installations.

Bien entendu, les conditions de température et de pression indiquées ne sont que des exemples qu'il conviendra d'adapter à la composition particulière du mélange gazeux à fractionner. Of course, the temperature and pressure conditions indicated are only examples which should be adapted to the particular composition of the gas mixture to be fractionated.

Il va de soi que des modifications peuvent être apportées au procédé qui vient d'être décrit, notamment par substitution d'équivalents techniques, sans sortir pour cela du cadre de la présente invention.  It goes without saying that modifications can be made to the process which has just been described, in particular by substitution of technical equivalents, without thereby departing from the scope of the present invention.

Claims (5)

REVENDICATIONS 1. Un procédé de fractionnement d'un mélange comprenant au moins trois constituants, à savoir un constituant A relativement peu volatil, un constituant 1. A process for fractionating a mixture comprising at least three constituents, namely a relatively low volatile constituent A, a constituent C relativement très volatil et un constituant B de volatilité intermédiaire, selon lequel on introduit en continu ledit mélange dans une colonne de fractionnement où règnent des conditions telles qu'une partie au moins dudit mélange s'élève sous forme de vapeurs vers la partie supérieure de la colonne; on condense partiellement lesdites vapeurs dans la partie supérieure de la colonne et on laisse le condensat résultant refluer vers la partie inférieure de la colonne; on évacue en continu une fraction liquide enrichie en constituants de moindre volatilité A et B du fond de la colonne; et on évacue en continu de la tête de la colonne une fraction de vapeurs enrichie en le constituant le plus volatil C, caractérisé en ce qu'on utilise comme colonne de fractionnement certains des canaux ou niveaux de circulation de fluides d'un échangeur à plaques comprenant une pluralité de canaux ou niveaux de circulation de fluides séparés les uns des autres par une tôle d'échange de chaleur, et en ce qu'on fait passer dans au moins certains des autres canaux ou niveaux de circulation de fluides de l'échangeur un ou plusieurs fluide(s) apportant les calories et/ou les frigories pouvant être requises pour la mise en ébullition du mélange à fractionner dans la partie inférieure de l'échangeur et pour la condensation partielle des vapeurs dans sa partie intermédiaire et/ou supérieure.C relatively very volatile and a component B of intermediate volatility, according to which said mixture is continuously introduced into a fractionation column where conditions prevail such that at least part of said mixture rises in the form of vapors towards the upper part of the column; partially condensing said vapors in the upper part of the column and allowing the resulting condensate to flow back to the lower part of the column; a liquid fraction enriched in constituents of lower volatility A and B is continuously discharged from the bottom of the column; and a fraction of vapors enriched by the most volatile constituent C is continuously discharged from the head of the column, characterized in that some of the channels or levels of circulation of fluids of a plate exchanger are used as fractionation column comprising a plurality of fluid circulation channels or levels separated from each other by a heat exchange sheet, and in that one passes through at least some of the other channels or fluid circulation levels of the exchanger one or more fluid (s) providing the calories and / or frigories which may be required for boiling the mixture to be fractionated in the lower part of the exchanger and for the partial condensation of the vapors in its intermediate and / or upper part . 2.Un procédé d'extraction de gaz de pétrole liquéfié (GPL) à partir d'un gaz d'alimentation, caractérisé en ce qu'on y met en oeuvre le procédé défini à la revendication 1. 2. A process for extracting liquefied petroleum gas (LPG) from a feed gas, characterized in that the process defined in claim 1 is implemented there. 3. Un procédé d'extraction de gaz de pétrole liquéfié selon la revendication 2, caractérisé en ce qu il comprend les étapes suivantes  3. A method of extracting liquefied petroleum gas according to claim 2, characterized in that it comprises the following steps a) amenée d'un mélange de gaz à une colonne de séparation-déshumidification (6) à une pression et une température telles que ledit mélange se fractionne en une fraction liquide demeurant dans la partie inférieure (6a) de la colonne (6) et une fraction vapeur montant dans la partie supérieure (6b) de la colonne, a) bringing a mixture of gases to a separation-dehumidification column (6) at a pressure and a temperature such that the said mixture breaks up into a liquid fraction remaining in the lower part (6a) of the column (6) and a vapor fraction rising in the upper part (6b) of the column, b) soumettre les vapeurs à un lavage déshumidificateur dans la partie supérieure (6b) de la colonne (6), b) subjecting the vapors to a dehumidifying wash in the upper part (6b) of the column (6), c) envoyer les vapeurs déshumidifiées à la partie inférieure d'un échangeur à plaques (11) dans la partie supérieure duquel le ou les constituant(s) les moins volatil(s) sont condensés et reflués vers la partie inférieure de l'échangeur, c) send the dehumidified vapors to the lower part of a plate exchanger (11) in the upper part of which the least volatile component (s) are condensed and flowed back to the lower part of the exchanger, d) renvoyer le condensat liquide de l'étape (c) dans la partie inférieure de la colonne de séparationdéshumidification, d) return the liquid condensate from step (c) to the lower part of the dehumidification separation column, e) évacuer du produit liquide du fond de la colonne de séparation-déshumidification en en recyclant une partie dans la partie inférieure de la colonne de séparation-déshumidification après réchauffage de celleci afin d'entretenir l'ébullition du produit liquide demeurant dans la partie inférieure de ladite colonne de séparation-déshumidification, la partie restante dudit produit liquide étant envoyée à un débutaniseur et, e) evacuate liquid product from the bottom of the separation-dehumidification column by recycling a portion of it in the lower part of the separation-dehumidification column after heating it in order to maintain the boiling of the liquid product remaining in the lower part of said separation-dehumidification column, the remaining part of said liquid product being sent to a debananizer and, f) évacuer du sommet de l'échangeur à plaques de la tête de l'échangeur à plaques des vapeurs des constituants les plus volatils. f) evacuating the vapors of the most volatile constituents from the top of the plate exchanger of the head of the plate exchanger. 4. Un procédé selon la revendication 3, carac 4. A method according to claim 3, charac térisé en ce que la tête de l'échangeur à plaques (11  characterized in that the head of the plate heat exchanger (11 constitue le point le plus froid du processus. is the coldest point in the process. 5. Un procédé selon la revendication 3 ou 4, 5. A method according to claim 3 or 4, caractérisé en ce que la totalité des vapeurs des consti tuants les plus volatils est est é v a e u é e e n LI n m êm e p o i n t  characterized in that all of the vapors of the most volatile constituents are ev e e u e e n LI n even p o i n t du procédé.  of the process.
FR8617048A 1986-12-05 1986-12-05 METHOD FOR FRACTIONATING A LIQUID MIXTURE USING A PLATE HEAT EXCHANGER AS A FRACTIONATION COLUMN AND ITS APPLICATION TO THE PRODUCTION OF LIQUEFIED OIL GAS Expired FR2607718B1 (en)

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