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EP0681153A1 - Process and apparatus for the low temperature separation of air - Google Patents

Process and apparatus for the low temperature separation of air Download PDF

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Publication number
EP0681153A1
EP0681153A1 EP95106750A EP95106750A EP0681153A1 EP 0681153 A1 EP0681153 A1 EP 0681153A1 EP 95106750 A EP95106750 A EP 95106750A EP 95106750 A EP95106750 A EP 95106750A EP 0681153 A1 EP0681153 A1 EP 0681153A1
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EP
European Patent Office
Prior art keywords
low
liquid
pressure stage
stage
pressure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP95106750A
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German (de)
French (fr)
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EP0681153B1 (en
Inventor
Wilhelm Dipl.-Ing. Rohde
Dietrich Dipl.-Ing. Rottmann
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Linde GmbH
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Linde GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04854—Safety aspects of operation
    • F25J3/0486—Safety aspects of operation of vaporisers for oxygen enriched liquids, e.g. purging of liquids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04472—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 cold from cryogenic liquids produced within the air fractionation unit and stored in internal or intermediate storages
    • F25J3/04478—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 cold from cryogenic liquids produced within the air fractionation unit and stored in internal or intermediate storages for controlling purposes, e.g. start-up or back-up procedures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04866—Construction and layout of air fractionation equipments, e.g. valves, machines
    • F25J3/04872—Vertical layout of cold equipments within in the cold box, e.g. columns, heat exchangers etc.
    • F25J3/04884—Arrangement of reboiler-condensers
    • 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/50—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/50—Processes or apparatus involving steps for recycling of process streams the recycled stream being oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/04—Down-flowing type boiler-condenser, i.e. with evaporation of a falling liquid film
    • 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
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/10—Control for or during start-up and cooling down of the installation
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/62—Details of storing a fluid in a tank

Definitions

  • the invention relates to a method and a device for the low-temperature separation of air, wherein in the process air is compressed, cleaned, cooled and at least partially fed to the pressure stage of a two-stage rectification and at least one fraction from the pressure stage is further broken down in the low-pressure stage, the low-pressure stage being a Oxygen fraction and a nitrogenous fraction can be taken as products and the lower area of the low pressure stage is in heat-exchanging connection with the upper area of the pressure stage.
  • the basics of air separation by rectification can be found in relevant manuals (e.g. Hausen / Linde, Low Temperature Technology, 2nd Edition 1985, Chapter 4.5 or Winnacker / Küchler, Chemical Technology, Volume 2, 3rd Edition, Chapter 4) and in Latimer, Distillation of Air , Chem. Eng. Progr., 63 , pages 35 to 59.
  • the two-stage rectification usually takes place in a double column, the low pressure stage of which is arranged above the pressure stage. (In principle, it is also possible to arrange the low-pressure and pressure stages of a double column separately.)
  • the return for the pressure stage is generated by the evaporation of liquid from the low-pressure stage, with steam rising at the same time in the low-pressure stage.
  • This indirect heat exchange is carried out in a condenser-evaporator, which is arranged in the low pressure column, usually in the sump.
  • This arrangement is fundamentally advantageous since there are no separate lines for connecting the evaporation passages of the condenser-evaporator to the low-pressure column.
  • the condenser-vaporizer contributes significantly to the total height of the double column and thus causes relatively high system costs.
  • the entire return liquid from the low-pressure stage runs into the sump and contaminates it with nitrogen. As a result, when the system is restarted, it takes a long time before pure oxygen product can be released again.
  • the invention is therefore based on the object of specifying a method and a device of the type mentioned at the outset which are economically more favorable, in particular due to reduced capital costs or greater flexibility in operation.
  • This object is achieved in that, in stationary operation, essentially all of the return liquid flowing down in the low pressure stage from the lower one
  • the area of the low-pressure stage is withdrawn and passed into a buffer tank, liquid is removed from the buffer tank and partially condensed in indirect heat exchange with condensing gas from the upper area of the pressure stage, and that at least some of the resulting steam is fed to the lower area of the low-pressure stage and the liquid remaining portion is at least partially returned to the buffer tank.
  • the term "stationary operation” means the usual operating state of an air separation plant after the start-up phase, in which the input and product flows over a longer period (at least 10 minutes in the case of a removable storage system up to many days or weeks in systems with constant product requirements) in remain essentially constant.
  • a buffer container for example a liquid tank.
  • a buffer container for example a liquid tank.
  • smaller parts of the return liquid can be guided in another way, for example as a liquid product or through a withdrawal through a safety drain.
  • that part of the reflux liquid which is required to generate steam rising in the column is fed into the buffer tank.
  • the buffer container is preferably designed as an insulated liquid tank.
  • liquid is taken from it, which is evaporated from the pressure column in indirect heat exchange with nitrogen-rich steam.
  • At least a part, preferably the largest part, of the gas formed is introduced into the low-pressure column and forms the vapor rising there in counterflow to the return liquid; another part can be withdrawn as a gaseous oxygen product if necessary. This is usually warmed up to air to be broken down to about ambient temperature.
  • the portion of the liquid withdrawn from the tank that has not evaporated during the indirect heat exchange is fed back into the buffer tank, for example together with the return liquid from the column.
  • the liquid can be pumped inexpensively by a pump.
  • This can be located downstream of the buffer tank, for example; alternatively or additionally, a pump can be arranged in the line from the low-pressure stage to the buffer tank, the tank itself either above the heat exchanger is arranged to evaporate the liquid from the tank or is under positive pressure.
  • the external evaporation of the return liquid in connection with the storage in a tank eliminates the need to maintain a sump liquid level in the low pressure column.
  • a very low liquid level is maintained (for example 10 to a maximum of 50 mm water column compared to a bottom liquid level of approximately 300 to 2000 mm water in previously known methods), or there is no liquid storage in the bottom of the low-pressure stage.
  • the integrated buffer tank also offers the possibility of obtaining an oxygen product of essentially constant purity by evaporation of the tank contents, even when the columns are not operating completely constantly (for example in the event of a fault or due to a change in the air throughput).
  • the process can be used very flexibly.
  • the integration of the buffer tank also simplifies the control of the process.
  • the control variable is the liquid level in the tank. This is easy to read and highly uncritical: it only has to be ensured that the tank is not completely empty or filled; in between, its content can basically fluctuate arbitrarily. (In practice, however, a medium liquid level is maintained in order to be able to actually use the buffer effect.) It is sufficient to read the liquid level in the tank from time to time and then to increase the external cooling supply and / or the internal cooling generation when the liquid level falls or rises increase or decrease. In principle, this can happen automatically. Because the adjustment of the cooling capacity in the usual If operation is only necessary at relatively large intervals (depending on the tank size, approximately every ten hours to five days), the control can also be carried out in manual mode. If, for example, cold is obtained in the process by relieving the pressure of air or nitrogen in a turbine, the throughput through this turbine can be adjusted accordingly, for example by hand, to regulate the cooling capacity.
  • Air separators are often operated discontinuously due to changing energy costs during the day. If the system is restarted after such interruptions in operation (or even after an interruption in operation), it takes a long time (even with the apparatus still cold) (up to two hours) until the rectification has returned to its steady state and products with the provided purity.
  • the method of the invention makes significant progress if, at the beginning of an interruption in operation, the return liquid is led from the low-pressure stage into the lower region of the pressure stage.
  • the invention further relates to a device for the low-temperature separation of air according to claims 4 to 6.
  • Compressed and cleaned air is fed via line 1 into pressure stage 3, a double column 2. (Part of the air to be separated can also be introduced directly into the low-pressure stage 4, for example after relaxation during work.)
  • Top gas of the pressure stage is fed via line 5 to a condenser-evaporator 6, where it is completely condensed.
  • the liquid formed flows back via line 7 to the top of the pressure column 3. It acts partly as a return in the pressure column 3, and partly it is applied to the low pressure column 4 (8th).
  • the line 8 to the low-pressure column can also be connected directly to the condensate line 7 from the condenser-evaporator 6 instead of the connection to the pressure column 3.
  • bottom liquid 9 from the pressure column is throttled at an intermediate point into the low-pressure column 4, from the top of which a nitrogen-rich one Product 10 is withdrawn.
  • the reflux liquid of the low pressure column 4 is taken off at the lower end of the column via a line 11. In stationary operation it consists of oxygen with residual impurities of 100 ppm to 20%, preferably 0.3 to 10%.
  • the line 11 is relatively close to the bottom of the container, which forms the low pressure column 4, so that very little or practically no liquid is present in the column bottom.
  • the liquid oxygen flows on (12) to an oxygen tank 13 used as a buffer tank. If required, a part can be removed as a liquid product via a product line 14.
  • the tank 13 is kept under pressure by a pump 15, so that liquid from the tank is pressed via line 16 to the condenser-evaporator 6, which works as a falling film evaporator. (In the case of an unpressurized storage, the pump would have to be arranged in line 16.)
  • a two-phase mixture emerges via line 17 from the evaporator passages of the condenser-evaporator 6, the vaporous portion of which partly flows back into the low-pressure column 4 (18), while another part is drawn off as a gaseous oxygen product 19.
  • the remaining liquid portion is returned to the buffer tank 13 via line 12.
  • Another liquid line 20 is connected to the lower region of the low-pressure stage 4, preferably below the outlet of the line 11. It is closed during normal operation of the system. (At most, for safety's sake, small amounts of liquid are occasionally drawn off and discarded via a safety drain, not shown.)
  • valve 21 in line 11 is closed after the air compressor has returned, so that the connection to tank 13 is interrupted.
  • the shut-off valve 22 is opened so that the return liquid arriving in the sump of the low pressure column flows into the pressure column and is stored in the sump thereof.
  • valve 21 in line 11 can be omitted.
  • the return liquid (11) flowing out of the low-pressure column also has the usual composition immediately after starting up and can be piped into the tank 13 flow.
  • connections 18 and 11 between the low pressure stage 4 on one side and the line 17/12 between the evaporation passages of the condenser-evaporator 6 and the buffer tank 13 on the other side can also be realized by a single tube with a large cross section, in the liquid and vapor flow against each other.

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

Abstract

Compressed air is cleaned, cooled, and then fractionated in the pressure section (3). Streams (8,9) are further fractionated (2) by the two-stage LP section (4) into N2 and O2 products, at the head (10) and base (11) respectively. Heat is exchanged between the bottom of the LP stage (4), and the top of the pressure stage (3). Under steady state standby operation, virtually all fluid returning to the bottom of the LP section (4) is piped (11,12) to the buffer (13). This (13) supplies fluid (16) to the indirect heat exchanger (6), which is partially evaporated by heat from condensing gas (5) from the top of the pressure section (3). The vapour (17,18) is returned low in the LP column; residual fluid is returned (17,12) to the buffer (13). Plant to carry out the procedure described above, is also claimed. <IMAGE>

Description

Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Tieftemperaturzerlegung von Luft, wobei bei dem Verfahren Luft verdichtet, gereinigt, abgekühlt und mindestens teilweise der Druckstufe einer zweistufigen Rektifikation zugeleitet und mindestens eine Fraktion aus der Druckstufe in der Niederdruckstufe weiter zerlegt wird, wobei der Niederdruckstufe eine Sauerstofffraktion und eine stickstoffhaltige Fraktion als Produkte entnommen werden und der untere Bereich der Niederdruckstufe mit dem oberen Bereich der Druckstufe in wärmetauschender Verbindung stehen.The invention relates to a method and a device for the low-temperature separation of air, wherein in the process air is compressed, cleaned, cooled and at least partially fed to the pressure stage of a two-stage rectification and at least one fraction from the pressure stage is further broken down in the low-pressure stage, the low-pressure stage being a Oxygen fraction and a nitrogenous fraction can be taken as products and the lower area of the low pressure stage is in heat-exchanging connection with the upper area of the pressure stage.

Die Grundlagen der Luftzerlegung durch Rektifikation sind in einschlägigen Handbüchern (z.B. Hausen/Linde, Tieftemperaturtechnik, 2. Auflage 1985, Kapitel 4.5 oder Winnacker/Küchler, Chemische Technologie, Band 2, 3. Auflage, Kapitel 4) sowie in Latimer, Distillation of Air, Chem. Eng. Progr., 63, Seiten 35 bis 59 beschrieben. Die zweistufige Rektifikation findet üblicherweise in einer Doppelsäule statt, deren Niederdruckstufe über der Druckstufe angeordnet ist. (Grundsätzlich ist es auch möglich Niederdruck- und Druckstufe einer Doppelsäule getrennt anzuordnen.) Rücklauf für die Druckstufe wird durch Verdampfung von Flüssigkeit aus der Niederdruckstufe erzeugt, wobei gleichzeitig in der Niederdruckstufe aufsteigender Dampf entsteht. Dieser indirekte Wärmeaustausch wird in einem Kondensator-Verdampfer durchgeführt, der in der Niederdrucksäule angeordnet ist, üblicherweise in deren Sumpf. Diese Anordnung ist grundsätzlich vorteilhaft, da eigene Leitungen zur Verbindung der Verdampfungspassagen des Kondensator-Verdampfers mit der Niederdrucksäule entfallen. Allerdings gibt es auch Nachteile. So trägt der Kondensator-Verdampfer nicht unwesentlich zur Gesamthöhe der Doppelsäule bei und verursacht damit relativ hohe Anlagekosten. Außerdem läuft beim Abschalten der Anlage die gesamte Rücklaufflüssigkeit der Niederdruckstufe in den Sumpf ab und verunreinigt diesen mit Stickstoff. In der Folge dauert es beim Wiederanfahren der Anlage lange Zeit, bis wieder reines Sauerstoffprodukt abgegeben werden kann.The basics of air separation by rectification can be found in relevant manuals (e.g. Hausen / Linde, Low Temperature Technology, 2nd Edition 1985, Chapter 4.5 or Winnacker / Küchler, Chemical Technology, Volume 2, 3rd Edition, Chapter 4) and in Latimer, Distillation of Air , Chem. Eng. Progr., 63 , pages 35 to 59. The two-stage rectification usually takes place in a double column, the low pressure stage of which is arranged above the pressure stage. (In principle, it is also possible to arrange the low-pressure and pressure stages of a double column separately.) The return for the pressure stage is generated by the evaporation of liquid from the low-pressure stage, with steam rising at the same time in the low-pressure stage. This indirect heat exchange is carried out in a condenser-evaporator, which is arranged in the low pressure column, usually in the sump. This arrangement is fundamentally advantageous since there are no separate lines for connecting the evaporation passages of the condenser-evaporator to the low-pressure column. However, there are disadvantages. The condenser-vaporizer contributes significantly to the total height of the double column and thus causes relatively high system costs. In addition, when the system is switched off, the entire return liquid from the low-pressure stage runs into the sump and contaminates it with nitrogen. As a result, when the system is restarted, it takes a long time before pure oxygen product can be released again.

Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren und eine Vorrichtung der eingangs genannten Art anzugeben, die wirtschaftlich günstiger sind, insbesondere durch verringerte Kapitalkosten beziehungsweise durch höhere Flexibilität im Betrieb.The invention is therefore based on the object of specifying a method and a device of the type mentioned at the outset which are economically more favorable, in particular due to reduced capital costs or greater flexibility in operation.

Diese Aufgabe wird dadurch gelöst, daß im stationären Betrieb im wesentlichen die gesamte in der Niederdruckstufe herabfließende Rücklaufflüssigkeit aus dem unteren Bereich der Niederdruckstufe abgezogen und in einen Pufferbehälter geleitet wird, dem Pufferbehälter Flüssigkeit entnommen und in indirektem Wärmeaustausch mit kondensierendem Gas aus dem oberen Bereich der Druckstufe teilweise kondensiert wird und daß dabei der dabei entstandene Dampf mindestens zum Teil dem unteren Bereich der Niederdruckstufe zugeführt und der flüssig verbliebene Anteil mindestens teilweise in den Pufferbehälter zurückgeleitet wird.This object is achieved in that, in stationary operation, essentially all of the return liquid flowing down in the low pressure stage from the lower one The area of the low-pressure stage is withdrawn and passed into a buffer tank, liquid is removed from the buffer tank and partially condensed in indirect heat exchange with condensing gas from the upper area of the pressure stage, and that at least some of the resulting steam is fed to the lower area of the low-pressure stage and the liquid remaining portion is at least partially returned to the buffer tank.

Die Bezeichnung "stationärer Betrieb" bedeutet hier den üblichen Betriebszustand einer Luftzerlegungsanlage nach Abschluß der Anfahrphase, bei dem die Einsatz- und Produktströme über einen längeren Zeitraum (mindestens 10 Minuten im Falle einer Wechselspeicheranlage bis zu vielen Tagen oder Wochen bei Anlagen mit gleichbleibendem Produktbedarf) im wesentlichen konstant bleiben.The term "stationary operation" means the usual operating state of an air separation plant after the start-up phase, in which the input and product flows over a longer period (at least 10 minutes in the case of a removable storage system up to many days or weeks in systems with constant product requirements) in remain essentially constant.

In diesem stationären Betrieb wird gemäß der Erfindung im wesentlichen die gesamte Rücklaufflüssigkeit zu einem Pufferbehälter, beispielsweise einem Flüssigtank, geleitet. Dies bedeutet, daß kleinere Teile der Rücklaufflüssigkeit auf einem anderen Weg geführt werden können, zum Beispiel als Flüssigprodukt oder über eine Entnahme durch einen Sicherheitsablaß. In den Pufferbehälter wird jedenfalls derjenige Teil der Rücklaufflüssigkeit geführt, der zur Erzeugung von in der Kolonne aufsteigendem Dampf benötigt wird.In this stationary operation, essentially all of the return liquid is conducted to a buffer container, for example a liquid tank. This means that smaller parts of the return liquid can be guided in another way, for example as a liquid product or through a withdrawal through a safety drain. In any case, that part of the reflux liquid which is required to generate steam rising in the column is fed into the buffer tank.

Der Pufferbehälter ist vorzugsweise als isolierter Flüssigtank ausgebildet. Ihm wird wiederum Flüssigkeit entnommen, die in indirektem Wärmetausch mit stickstoffreichem Dampf aus der Drucksäule verdampft wird. Mindestens ein Teil, vorzugsweise der größte Teil, des dabei entstandenen Gases wird in die Niederdrucksäule eingeleitet und bildet dort den im Gegenstrom zur Rücklaufflüssigkeit aufsteigenden Dampf; ein anderer Teil kann bei Bedarf als gasförmiges Sauerstoffprodukt abgezogen werden. Dieses wird in der Regel gegen zu zerlegende Luft auf etwa Umgebungstemperatur angewärmt. Der bei dem indirekten Wärmeaustausch nicht verdampfte Anteil der aus dem Tank abgezogenen Flüssigkeit wird - beispielsweise gemeinsam mit der Rücklaufflüssigkeit aus der Säule - in den Pufferbehälter zurückgespeist.The buffer container is preferably designed as an insulated liquid tank. In turn, liquid is taken from it, which is evaporated from the pressure column in indirect heat exchange with nitrogen-rich steam. At least a part, preferably the largest part, of the gas formed is introduced into the low-pressure column and forms the vapor rising there in counterflow to the return liquid; another part can be withdrawn as a gaseous oxygen product if necessary. This is usually warmed up to air to be broken down to about ambient temperature. The portion of the liquid withdrawn from the tank that has not evaporated during the indirect heat exchange is fed back into the buffer tank, for example together with the return liquid from the column.

Die Flüssigkeit kann kostengünstig durch eine Pumpe gefördert werden. Diese kann sich beispielsweise stromabwärts des Puffertanks befinden; alternativ oder zusätzlich kann eine Pumpe in der Leitung von der Niederdruckstufe zum Pufferbehälter angeordnet sein, wobei der Behälter selbst entweder oberhalb des Wärmetauschers zur Verdampfung der Flüssigkeit aus dem Tank angeordnet ist oder unter Überdruck steht.The liquid can be pumped inexpensively by a pump. This can be located downstream of the buffer tank, for example; alternatively or additionally, a pump can be arranged in the line from the low-pressure stage to the buffer tank, the tank itself either above the heat exchanger is arranged to evaporate the liquid from the tank or is under positive pressure.

Durch die Außenverdampfung der Rücklaufflüssigkeit in Verbindung mit der Speicherung in einem Tank entfällt die Notwendigkeit, einen Sumpfflüssigkeitsstand in der Niederdrucksäule aufrechtzuerhalten. Beim erfindungsgemäßen Verfahren wird entweder nur ein sehr geringer Flüssigkeitsstand aufrechterhalten (beispielsweise 10 bis maximal 50 mm Wassersäule im Vergleich zu einem Sumpfflüssigkeitsstand von etwa 300 bis 2000 mm WS bei bisher bekannten Verfahren), oder es wird vollkommen auf eine Flüssigkeitsspeicherung im Sumpf der Niederdruckstufe verzichtet.The external evaporation of the return liquid in connection with the storage in a tank eliminates the need to maintain a sump liquid level in the low pressure column. In the method according to the invention, either only a very low liquid level is maintained (for example 10 to a maximum of 50 mm water column compared to a bottom liquid level of approximately 300 to 2000 mm water in previously known methods), or there is no liquid storage in the bottom of the low-pressure stage.

Durch die Auslagerung des Kondensator-Verdampfers, unterstützt durch den weitgehenden Verzicht auf die Speicherung von Sumpfflüssigkeit innerhalb der Säule, wird eine entsprechend geringe Bauhöhe der Rektifziersäule erzielt. Dies ist insbesondere bei Großanlagen von Vorteil, bei denen die Doppelsäule eine Höhe von bis zu 40 Metern erreichen kann. Daneben werden auch hinsichtlich der Betriebssicherheit Vorteile erzielt, da die Niederdruckstufen-Sumpfflüssigkeit, in der sich tendenziell Kohlenwasserstoffe anreichern können, nicht in der Säule, sondern außerhalb in einem Behälter mit sehr großem Puffervolumen gespeichert wird.By outsourcing the condenser-evaporator, supported by largely dispensing with the storage of sump liquid within the column, a correspondingly low overall height of the rectification column is achieved. This is particularly advantageous in large systems where the double column can reach a height of up to 40 meters. In addition, advantages are also achieved in terms of operational safety, since the low-pressure stage sump liquid, in which hydrocarbons tend to accumulate, is not stored in the column, but outside in a container with a very large buffer volume.

Der integrierte Pufferbehälter bietet außerdem die Möglichkeit, auch bei nicht vollständig konstantem Betrieb der Säulen (etwa im Falle einer Störung oder aufgrund einer Veränderung des Luftdurchsatzes) ein Sauerstoffprodukt von im wesentlichen gleichbleibender Reinheit durch Verdampfung des Tankinhalts zu gewinnen. Durch diese Pufferung von Schwankungen von Qualität und Menge des Sauerstoffprodukts aus der Niederdrucksäule kann das Verfahren sehr flexibel eingesetzt werden.The integrated buffer tank also offers the possibility of obtaining an oxygen product of essentially constant purity by evaporation of the tank contents, even when the columns are not operating completely constantly (for example in the event of a fault or due to a change in the air throughput). By buffering fluctuations in the quality and quantity of the oxygen product from the low pressure column, the process can be used very flexibly.

Die Integration des Pufferbehälters vereinfacht außerdem die Steuerung des Verfahrens. Regelgröße ist dabei der Flüssigkeitsstand im Tank. Diese ist einfach abzulesen und in höchstem Maße unkritisch: Es muß lediglich sichergestellt werden, daß der Tank nicht vollständig leer oder gefüllt ist; dazwischen kann sein Inhalt grundsätzlich beliebig schwanken. (In der Praxis wird jedoch ein mittlerer Flüssigkeitsstand aufrechterhalten, um die Pufferwirkung tatsächlich nutzen zu können.) Es genügt dabei, von Zeit zu Zeit den Flüssigkeitsstand im Tank abzulesen und dann die externe Kältezufuhr und/oder die interne Kälteerzeugung bei sinkendem beziehungsweise steigendem Flüssigkeitsstand zu erhöhen beziehungsweise zu verringern. Dies kann grundsätzlich automatisch geschehen. Da die Anpassung der Kälteleistung im üblichen Betrieb nur in relativ großen Zeitabständen (je nach Tankgröße etwa alle zehn Stunden bis fünf Tage) notwendig ist, kann die Regelung auch im Handbetrieb vorgenommen werden. Wird beispielsweise Kälte im Verfahren durch arbeitsleistende Entspannung von Luft oder Stickstoff in einer Turbine gewonnen, so kann zur Regulierung der Kälteleistung der Durchsatz durch diese Turbine - beispielsweise von Hand - entsprechend angepaßt werden.The integration of the buffer tank also simplifies the control of the process. The control variable is the liquid level in the tank. This is easy to read and highly uncritical: it only has to be ensured that the tank is not completely empty or filled; in between, its content can basically fluctuate arbitrarily. (In practice, however, a medium liquid level is maintained in order to be able to actually use the buffer effect.) It is sufficient to read the liquid level in the tank from time to time and then to increase the external cooling supply and / or the internal cooling generation when the liquid level falls or rises increase or decrease. In principle, this can happen automatically. Because the adjustment of the cooling capacity in the usual If operation is only necessary at relatively large intervals (depending on the tank size, approximately every ten hours to five days), the control can also be carried out in manual mode. If, for example, cold is obtained in the process by relieving the pressure of air or nitrogen in a turbine, the throughput through this turbine can be adjusted accordingly, for example by hand, to regulate the cooling capacity.

Dabei ist es besonders günstig, wenn der indirekte Wärmeaustausch zur teilweisen Verdampfung der dem Pufferbehälter entnommenen Flüssigkeit als Fallfilmverdampfung durchgeführt wird. Einzelheiten zum Betrieb eines Wärmetauschers als Fallfilmverdampfer sind in Billet, Verdampfung und ihre technischen Anwendungen, 1981, Kapitel 3.5.5 beschrieben. In dem Fallfilmverdampfer werden etwa 25 bis 75 Gew.-% vorzugsweise 40 bis 60 Gew.-% der vom Pufferbehälter herangeführten Flüssigkeit verdampft. Der Rest wird in der Regel in den Tank zurückgeleitet.It is particularly advantageous if the indirect heat exchange for partial evaporation of the liquid removed from the buffer tank is carried out as falling film evaporation. Details on the operation of a heat exchanger as a falling film evaporator are described in Billet, Evaporation and its Technical Applications, 1981, Chapter 3.5.5. In the falling film evaporator, about 25 to 75% by weight, preferably 40 to 60% by weight, of the liquid brought in from the buffer container is evaporated. The rest is usually returned to the tank.

Bei bestimmten Anwendungen, beispielsweise in der Stahlindustrie, schwankt der Bedarf an Produkten eines Luftzerlegers, insbesondere von Sauerstoff, stark. Falls keine andere Verwendungsmöglichkeit für die Produkte gegeben ist, müssen diese Luftzerlegungsanlagen zeitweise abgeschaltet werden. Oft werden Luftzerleger auch aufgrund tageszeitlich veränderlicher Energiekosten diskontinuierlich betrieben. Wird nach derartigen Betriebsunterbrechungen (oder auch nach störungsbedingter Unterbrechung des Betriebs) die Anlage wieder angefahren, so dauert es - selbst bei noch kalter Apparatur - lange Zeit (bis zu zwei Stunden), bis die Rektifikation wieder ihren stationären Zustand erreicht hat und Produkte mit der vorgesehenen Reinheit liefert.In certain applications, for example in the steel industry, the demand for air separation products, in particular oxygen, fluctuates greatly. If there is no other possible use for the products, these air separation plants must be switched off temporarily. Air separators are often operated discontinuously due to changing energy costs during the day. If the system is restarted after such interruptions in operation (or even after an interruption in operation), it takes a long time (even with the apparatus still cold) (up to two hours) until the rectification has returned to its steady state and products with the provided purity.

Hier bringt das Verfahren der Erfindung einen wesentlichen Fortschritt, wenn zu Beginn einer Betriebsunterbrechung die Rücklaufflüssigkeit aus der Niederdruckstufe in den unteren Bereich der Druckstufe geleitet wird.Here, the method of the invention makes significant progress if, at the beginning of an interruption in operation, the return liquid is led from the low-pressure stage into the lower region of the pressure stage.

Die Speicherung von Rücklaufflüssigkeit ist an sich bekannt aus der DE-A-3732363. Bei dem dort geschilderten Verfahren sind jedoch eigene Einrichtungen zum Auffangen der Rücklaufflüssigkeit notwendig. Im Rahmen des erfindungsgemäßen Verfahrens sind fast keine zusätzlichen Apparaturen erforderlich: Zur Ableitung der Rücklaufflüssigkeit kann die - ohnehin regelmäßig vorhandene - Leitung für den Sicherheitsablaß verwendet werden; lediglich eine Verbindung zur Druckstufe ist notwendig, beispielsweise über die Eintrittsleitung für Zerlegungsluft.The storage of return liquid is known per se from DE-A-3732363. In the process described there, however, separate devices for collecting the return liquid are necessary. Within the scope of the method according to the invention, almost no additional apparatus is required: the line, which is present regularly anyway, can be used to discharge the return liquid for the safety drain; only a connection to the pressure stage is necessary, for example via the inlet line for separation air.

Beim Abfahren der Anlage wird nach dem Abstellen des Luftverdichters die Verbindung zur Einführung der Rücklaufflüssigkeit in den Pufferbehälter unterbrochen und die Leitung zur Drucksäule geöffnet. (Falls die Leitung zum Tank oberhalb der Leitung zur Drucksäule angeordnet ist, entfällt die Notwendigkeit des Absperrens der Leitung zum Tank.) Die in der Niederdrucksäule noch vorhandene Rücklaufflüssigkeit fließt dann aufgrund ihrer Schwerkraft in den Sumpf der Drucksäule ab. Somit wird eine Verunreinigung des im Tank gespeicherten Sumpfprodukts durch die stickstoffhaltige Rücklaufflüssigkeit vermieden.When the system is shut down, after the air compressor has been switched off, the connection to the introduction of the return liquid into the buffer tank is interrupted and the line to the pressure column is opened. (If the line to the tank is arranged above the line to the pressure column, there is no need to shut off the line to the tank.) The return liquid still present in the low pressure column then flows out into the sump of the pressure column due to its gravity. Contamination of the sump product stored in the tank by the nitrogen-containing return liquid is thus avoided.

Beim Wiederanfahren wird innerhalb von kürzester Zeit wieder reines Sauerstoffprodukt geliefert. Wenige Minuten nach dem Start des Luftverdichters haben die Molsiebanlage zur Luftreinigung und die Drucksäule wieder ihren Betriebsdruck erreicht. Sofort fließt unter Druck stehendes Gas vom Kopf der Druckstufe durch den Wärmetauscher, und die Verdampfung von Sauerstoff aus dem Tank springt an. Die dabei verdampfte Fraktion - Sauerstoff aus dem Tank - kann unmittelbar als Produkt mit üblicher Reinheit abgegeben werden. Die Zeit bis zum Erreichen des stationären Betriebszustands der Rektifikation (etwa eine bis fünf Minuten) kann durch Verdampfen von im Puffertank gespeicherter Flüssigkeit überbrückt werden, ohne daß Einbußen an Produktreinheit oder -menge entstünden.When restarting, pure oxygen product is delivered again within a very short time. A few minutes after the start of the air compressor, the molecular sieve system for air purification and the pressure column have returned to their operating pressure. Gas under pressure immediately flows from the top of the pressure stage through the heat exchanger, and the evaporation of oxygen from the tank starts. The vaporized fraction - oxygen from the tank - can be released immediately as a product with the usual purity. The time to reach the steady-state operating state of the rectification (about one to five minutes) can be bridged by evaporating liquid stored in the buffer tank without any loss of product purity or quantity.

Des weiteren betrifft die Erfindung eine Vorrichtung zur Tieftemperaturzerlegung von Luft gemäß den Ansprüchen 4 bis 6.The invention further relates to a device for the low-temperature separation of air according to claims 4 to 6.

Die Erfindung sowie weitere Einzelheiten der Erfindung werden im folgenden anhand eines in der Zeichnung dargestellten Ausführungsbeispiels näher erläutert. Details wie Turbinen zur kälteleistenden Entspannung von Prozeßströmen oder die Direktenspeisung von Luft in die Niederdrucksäule sind in dem stark vereinfachten Schema nicht dargestellt.The invention and further details of the invention are explained below with reference to an embodiment shown in the drawing. Details such as turbines for the cooling relief of process streams or the direct feeding of air into the low pressure column are not shown in the greatly simplified diagram.

Über Leitung 1 wird verdichtete und gereinigte Luft in die Druckstufe 3, einer Doppelsäule 2 eingespeist. (Ein Teil der zu zerlegenden Luft kann auch direkt in die Niederdruckstufe 4 eingeleitet werden, beispielsweise nach arbeitsleistender Entspannung.) Kopfgas der Druckstufe wird über Leitung 5 zu einem Kondensator-Verdampfer 6 geführt und dort vollständig kondensiert. Dabei gebildete Flüssigkeit fließt über Leitung 7 zurück zum Kopf der Drucksäule 3. Sie wirkt zum einen Teil als Rücklauf in der Drucksäule 3, zum anderen Teil wird sie auf die Niederdrucksäule 4 aufgegeben (8). (Die Leitung 8 zur Niederdrucksäule kann anstelle der Verbindung mit der Drucksäule 3 auch direkt an die Kondensatleitung 7 vom Kondensator-Verdampfer 6 angeschlossen sein.) Außerdem wird Sumpfflüssigkeit 9 aus der Drucksäule an einer Zwischenstelle in die Niederdrucksäule 4 eingedrosselt, von deren Kopf ein stickstoffreiches Produkt 10 abgezogen wird. Die Rücklaufflüssigkeit der Niederdrucksäule 4 wird am unteren Ende der Kolonne über eine Leitung 11 abgenommen. Sie besteht im stationären Betrieb aus Sauerstoff mit Restverunreinigungen von 100 ppm bis 20 %, vorzugsweise 0,3 bis 10 %. Die Leitung 11 ist relativ nahe am Boden des Behälters angebracht, der die Niederdrucksäule 4 bildet, so daß im Kolonnensumpf sehr wenig oder praktisch gar keine Flüssigkeit ansteht.Compressed and cleaned air is fed via line 1 into pressure stage 3, a double column 2. (Part of the air to be separated can also be introduced directly into the low-pressure stage 4, for example after relaxation during work.) Top gas of the pressure stage is fed via line 5 to a condenser-evaporator 6, where it is completely condensed. The liquid formed flows back via line 7 to the top of the pressure column 3. It acts partly as a return in the pressure column 3, and partly it is applied to the low pressure column 4 (8th). (The line 8 to the low-pressure column can also be connected directly to the condensate line 7 from the condenser-evaporator 6 instead of the connection to the pressure column 3.) In addition, bottom liquid 9 from the pressure column is throttled at an intermediate point into the low-pressure column 4, from the top of which a nitrogen-rich one Product 10 is withdrawn. The reflux liquid of the low pressure column 4 is taken off at the lower end of the column via a line 11. In stationary operation it consists of oxygen with residual impurities of 100 ppm to 20%, preferably 0.3 to 10%. The line 11 is relatively close to the bottom of the container, which forms the low pressure column 4, so that very little or practically no liquid is present in the column bottom.

Der flüssige Sauerstoff fließt weiter (12) zu einem als Pufferbehälter eingesetzten Sauerstofftank 13. Bei Bedarf kann über eine Produktleitung 14 ein Teil als Flüssigprodukt entnommen werden. Im Beispiel der Zeichnung wird der Tank 13 durch eine Pumpe 15 auf Druck gehalten, so daß Flüssigkeit aus dem Tank über Leitung 16 zu dem als Fallfilmverdampfer arbeitenden Kondensator-Verdampfer 6 gedrückt wird. (Im Falle einer drucklosen Speicherung müßte die Pumpe in der Leitung 16 angeordnet sein.)The liquid oxygen flows on (12) to an oxygen tank 13 used as a buffer tank. If required, a part can be removed as a liquid product via a product line 14. In the example of the drawing, the tank 13 is kept under pressure by a pump 15, so that liquid from the tank is pressed via line 16 to the condenser-evaporator 6, which works as a falling film evaporator. (In the case of an unpressurized storage, the pump would have to be arranged in line 16.)

Über Leitung 17 tritt ein Zwei-Phasengemisch aus den Verdampferpassagen des Kondensator-Verdampfers 6 aus, dessen dampfförmiger Anteil zum einen Teil in die Niederdrucksäule 4 zurückströmt (18), während ein anderer Teil als gasförmiges Sauerstoffprodukt 19 abgezogen wird. Der flüssig verbliebene Anteil wird über Leitung 12 wieder in den Pufferbehälter 13 zurückgeleitet.A two-phase mixture emerges via line 17 from the evaporator passages of the condenser-evaporator 6, the vaporous portion of which partly flows back into the low-pressure column 4 (18), while another part is drawn off as a gaseous oxygen product 19. The remaining liquid portion is returned to the buffer tank 13 via line 12.

Eine weitere Flüssigkeitsleitung 20 ist mit dem unteren Bereich der Niederdruckstufe 4 verbunden, vorzugsweise unterhalb des Austritts der Leitung 11. Sie ist während des Normalbetriebs der Anlage geschlossen. (Allenfalls werden über diesen Anstich sicherheitshalber gelegentlich kleine Mengen Flüssigkeit über einen nicht dargestellten Sicherheitsablaß abgezogen und verworfen.) Bei einer Betriebsunterbrechung wird nach Zurückfahren des Luftverdichters Ventil 21 in Leitung 11 geschlossen, so daß die Verbindung zum Tank 13 unterbrochen ist. Gleichzeitig wird die Absperrarmatur 22 geöffnet, so daß die im Sumpf der Niederdrucksäule ankommende Rücklaufflüssigkeit in die Drucksäule abfließt und in deren Sumpf gespeichert wird. (Je nach Anordnung der Verbindungsstellen der Leitungen 11 und 20 mit der Niederdruckstufe 4 ist es möglich, daß die Rücklaufflüssigkeit selbsttätig über die Leitung 20 abfließt. In diesem Fall kann das Ventil 21 in Leitung 11 entfallen.)Another liquid line 20 is connected to the lower region of the low-pressure stage 4, preferably below the outlet of the line 11. It is closed during normal operation of the system. (At most, for safety's sake, small amounts of liquid are occasionally drawn off and discarded via a safety drain, not shown.) In the event of an interruption in operation, valve 21 in line 11 is closed after the air compressor has returned, so that the connection to tank 13 is interrupted. At the same time the shut-off valve 22 is opened so that the return liquid arriving in the sump of the low pressure column flows into the pressure column and is stored in the sump thereof. (Depending on the arrangement of the connection points of lines 11 and 20 with low-pressure stage 4, it is possible for the return liquid to flow off automatically via line 20. In this case, valve 21 in line 11 can be omitted.)

Beim Wiederanfahren der Anlage wird in extrem kurzer Zeit erneut reines Sauerstoffprodukt über Leitung 19 abgegeben: Sobald nämlich der Druck in der Druckstufe 3 aufgebaut ist, fließt Kopfgas 5 zum Kondensator-Verdampfer 6 und setzt dort die Verdampfung in Gang. Da die Verdampfungsseite mit reinem Sauerstoff 16 aus dem Pufferbehälter 13 gespeist wird, steht unmittelbar danach in Leitung 19 das gasförmige Produkt wieder zur Verfügung. Die Anlaufzeit, die vergeht, bis sich die stationären Produktkonzentrationen in der Niederdrucksäule wieder eingestellt haben, wird also durch Verdampfung eines Teils des Tankinhalts überbrückt. Da in der Niederdruckstufe sofort nach dem Anspringen der Verdampfung im Kondensator-Verdampfer 6 Sauerstoffgas mit entsprechender Reinheit zur Verfügung steht, hat auch die aus der Niederdrucksäule abfließende Rücklaufflüssigkeit (11) sofort nach dem Anfahren die übliche Zusammensetzung und kann über Leitung 12 in den Tank 13 fließen.When the system is restarted, pure oxygen product is again released in an extremely short time via line 19: as soon as the pressure in pressure stage 3 has built up, top gas 5 flows to the condenser-evaporator 6 and starts the evaporation there. Since the evaporation side is fed with pure oxygen 16 from the buffer container 13, the gaseous product is immediately available again in line 19. The start-up time that elapses until the steady-state product concentrations in the low-pressure column have returned is bridged by the evaporation of part of the tank content. Since oxygen gas of the appropriate purity is available in the low-pressure stage 6 immediately after the evaporation has started in the condenser-evaporator, the return liquid (11) flowing out of the low-pressure column also has the usual composition immediately after starting up and can be piped into the tank 13 flow.

Die Verbindungen 18 und 11 zwischen der Niderdruckstufe 4 auf der einen Seite und der Leitung 17/12 zwischen Verdampfungspassagen des Kondensator-Verdampfers 6 und Pufferbehälter 13 auf der anderen Seite können auch durch ein einziges Rohr mit großem Querschnitt realisiert sein, in der Flüssigkeit und Dampf gegeneinander strömen.The connections 18 and 11 between the low pressure stage 4 on one side and the line 17/12 between the evaporation passages of the condenser-evaporator 6 and the buffer tank 13 on the other side can also be realized by a single tube with a large cross section, in the liquid and vapor flow against each other.

Claims (6)

Verfahren zur Tieftemperaturzerlegung von Luft, bei dem Luft verdichtet, gereinigt, abgekühlt und mindestens teilweise der Druckstufe (3) einer zweistufigen Rektifikation (2) zugeleitet wird und bei dem mindestens eine Fraktion (8,9) aus der Druckstufe (3) in der Niederdruckstufe (4) weiter zerlegt wird, wobei der Niederdruckstufe (4) eine Sauerstofffraktion (11) und eine stickstoffhaltige Fraktion (10) als Produkte entnommen werden und der untere Bereich der Niederdruckstufe (4) mit dem oberen Bereich der Druckstufe in wärmetauschender Verbindung steht, dadurch gekennzeichnet, daß im stationären Betrieb im wesentlichen die gesamte in der Niederdruckstufe (4) herabfließende Rücklaufflüssigkeit aus dem unteren Bereich der Niederdruckstufe abgezogen (11) und in einen Pufferbehälter (13) geleitet (12) wird, dem Pufferbehälter (13) Flüssigkeit entnommen (16) und in indirektem Wärmeaustausch (6) mit kondensierendem Gas (5) aus dem oberen Bereich der Druckstufe (3) teilweise verdampft wird und daß der dabei entstandene Dampf (17,18) mindestens zum Teil dem unteren Bereich der Niederdruckstufe (4) zugeführt und der bei dem indirekten Wärmeaustausch (6) flüssig verbliebene Anteil mindestens teilweise dem Pufferbehälter (13) zurückgeleitet (17,12) wird.Process for the low-temperature decomposition of air, in which air is compressed, cleaned, cooled and at least partially fed to the pressure stage (3) of a two-stage rectification (2) and in which at least one fraction (8,9) from the pressure stage (3) in the low-pressure stage is further decomposed (4), wherein the low pressure stage (4) be an oxygen fraction (11) and a nitrogen-containing fraction (10) taken out as a product and the lower portion of the low pressure stage (4) is in heat exchanging connection with the upper region of the pressure stage, characterized characterized in that in stationary operation essentially all of the return liquid flowing down in the low pressure stage (4) is drawn off (11) from the lower region of the low pressure stage and passed (12) into a buffer tank (13), liquid is taken from the buffer tank (13) (16 ) and partially in indirect heat exchange (6) with condensing gas (5) from the upper area of the pressure stage (3) is steamed and that the resulting steam (17, 18) is at least partially fed to the lower area of the low-pressure stage (4) and the portion that remains liquid in the indirect heat exchange (6) is at least partially returned to the buffer tank (13) (17, 12) becomes. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der indirekte Wärmeaustausch (6) zur teilweisen Verdampfung der dem Pufferbehälter (13) entnommenen Flüssigkeit (16) als Fallfilmverdampfung durchgeführt wird.Method according to Claim 1, characterized in that the indirect heat exchange (6) for the partial evaporation of the liquid (16) removed from the buffer container (13) is carried out as falling film evaporation. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß zu Beginn einer Betriebsunterbrechung die Rücklaufflüssigkeit aus der Niederdruckstufe (4) in den unteren Bereich der Druckstufe (3) geleitet (20) wird.Method according to claim 1 or 2, characterized in that at the beginning of an interruption in operation the return liquid from the low-pressure stage (4) is passed (20) into the lower region of the pressure stage (3). Vorrichtung zur Tieftemperaturzerlegung von Luft mit einem Luftverdichter, einer Reinigungseinrichtung, einem Wärmetauscher und einer zweistufigen Rektifiziereinrichtung (2), die eine Drucksäule (3) und eine Niederdrucksäule (4) aufweist, und mit einem Kondensator-Verdampfer (6), der über eine Dampfzuleitung (5) und eine Kondensatrückleitung (7) mit dem oberen Bereich der Drucksäule (3) verbunden ist und der Verdampfungspassagen zur Verdampfung von Flüssigkeit aus dem unteren Bereich der Niederdrucksäule (4) aufweist, gekennzeichnet durch eine Rücklaufflüssigkeitsleitung (11,12), die mit dem unteren Bereich der Niederdruckstufe und mit einem Pufferbehälter (13) verbunden ist, durch eine Flüssigkeitsleitung (16), die vom Pufferbehälter (13) zum Eingang der Verdampfungspassagen des Kondensator-Verdampfers (6) führt, durch eine Dampfleitung (17,18), die den Ausgang der Verdampfungspassagen mit dem unteren Bereich der Niederdrucksäule (4) verbindet und durch eine Rückführungsleitung (17,12) für Flüssigkeit zwischen Ausgang der Verdampfungspassagen und Pufferbehälter (13).Device for the low-temperature separation of air with an air compressor, a cleaning device, a heat exchanger and a two-stage rectification device (2), which has a pressure column (3) and a low-pressure column (4), and with a condenser-evaporator (6), which has a steam feed line (5) and a condensate return line (7) is connected to the upper region of the pressure column (3) and has evaporation passages for the evaporation of liquid from the lower region of the low pressure column (4), characterized by a return liquid line (11, 12), which with the lower area of the low pressure stage and connected to a buffer tank (13) by a liquid line (16), which leads from the buffer tank (13) to the entrance of the evaporation passages of the condenser-evaporator (6), through a steam line (17, 18) which connects the exit of the evaporation passages to the lower region of the low-pressure column (4) and through a Return line (17, 12) for liquid between the outlet of the evaporation passages and the buffer tank (13). Vorrichtung nach Anspruch 4, dadurch gekennzeichnet, daß der Kondensator-Verdampfer (6) als Fallfilmverdampfer ausgebildet ist.Apparatus according to claim 4, characterized in that the condenser-evaporator (6) is designed as a falling film evaporator. Vorrichtung nach Anspruch 4 oder 5, gekennzeichnet durch eine Flüssigkeitsleitung (20), die aus dem unteren Bereich der Niederdrucksäule (4) in die Drucksäule (3) führt und in der eine Absperrarmatur (22) angeordnet ist.Apparatus according to claim 4 or 5, characterized by a liquid line (20) which leads from the lower region of the low pressure column (4) into the pressure column (3) and in which a shut-off valve (22) is arranged.
EP95106750A 1994-05-04 1995-05-04 Process and apparatus for the low temperature separation of air Expired - Lifetime EP0681153B1 (en)

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DE4415747A DE4415747C2 (en) 1994-05-04 1994-05-04 Method and device for the low-temperature separation of air
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EP0895045A2 (en) * 1997-07-30 1999-02-03 Linde Aktiengesellschaft Air separation process
EP1110588A1 (en) * 1999-12-23 2001-06-27 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Apparatus for separating by distillation and process for cleaning vaporizer-condensor of the apparatus
US6272884B1 (en) 1998-04-08 2001-08-14 Praxair Technology, Inc. Rapid restart system for cryogenic air separation plant
FR2855598A1 (en) * 2003-05-28 2004-12-03 Air Liquide METHOD AND INSTALLATION FOR BACKUP SUPPLY OF A GAS UNDER PRESSURE BY VAPORIZATION OF CRYOGENIC LIQUID
EP2503270A1 (en) * 2011-03-22 2012-09-26 Linde Aktiengesellschaft Method and device for creating an oxygen product by cryogenic decomposition of air
CN103537107A (en) * 2012-07-11 2014-01-29 蓝星(北京)化工机械有限公司 Evaporation system and application thereof
CN108072234A (en) * 2016-11-15 2018-05-25 北大方正集团有限公司 The control method of air-separating plant

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FR2797942B1 (en) * 1999-08-24 2001-11-09 Air Liquide VAPORIZER-CONDENSER AND CORRESPONDING AIR DISTILLATION SYSTEM
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DE102016013091A1 (en) * 2016-11-04 2018-05-09 Linde Aktiengesellschaft Method and system for purifying a gas
KR102354278B1 (en) 2017-10-12 2022-01-21 주식회사 엘지에너지솔루션 The Battery Charger/Discharger
CN112629160A (en) * 2020-12-21 2021-04-09 华能（天津）煤气化发电有限公司 Air separation natural reheat overhauling method

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Publication number Priority date Publication date Assignee Title
EP0895045A2 (en) * 1997-07-30 1999-02-03 Linde Aktiengesellschaft Air separation process
EP0895045A3 (en) * 1997-07-30 1999-06-16 Linde Aktiengesellschaft Air separation process
US6038885A (en) * 1997-07-30 2000-03-21 Linde Aktiengesellschaft Air separation process
US6272884B1 (en) 1998-04-08 2001-08-14 Praxair Technology, Inc. Rapid restart system for cryogenic air separation plant
EP1110588A1 (en) * 1999-12-23 2001-06-27 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Apparatus for separating by distillation and process for cleaning vaporizer-condensor of the apparatus
FR2802825A1 (en) * 1999-12-23 2001-06-29 Air Liquide DISTILLATION SEPARATION APPARATUS AND METHOD FOR CLEANING A CONDENSER VAPORIZER OF THE APPARATUS
FR2855598A1 (en) * 2003-05-28 2004-12-03 Air Liquide METHOD AND INSTALLATION FOR BACKUP SUPPLY OF A GAS UNDER PRESSURE BY VAPORIZATION OF CRYOGENIC LIQUID
WO2004109207A1 (en) * 2003-05-28 2004-12-16 L'air Liquide Societe Anonyme A Directoire Et Conseil De Surveillance Pour L'etude Et L' Exploitation Des Procedes Georges Claude Process and arrangement for the backup supply of a pressurized gas through cryogenic liquid spraying
US7870759B2 (en) 2003-05-28 2011-01-18 L'air Liquide, Societe Anonyme A Directoire Et Conseil De Surveillance Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and arrangement for the backup supply of a pressurized gas through cryogenic liquid vaporization
EP2503270A1 (en) * 2011-03-22 2012-09-26 Linde Aktiengesellschaft Method and device for creating an oxygen product by cryogenic decomposition of air
CN103537107A (en) * 2012-07-11 2014-01-29 蓝星(北京)化工机械有限公司 Evaporation system and application thereof
CN103537107B (en) * 2012-07-11 2015-04-22 蓝星(北京)化工机械有限公司 Evaporation system and application thereof
CN108072234A (en) * 2016-11-15 2018-05-25 北大方正集团有限公司 The control method of air-separating plant

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CN1124345A (en) 1996-06-12
EP0681153B1 (en) 1997-09-10
DE4415747C2 (en) 1996-04-25
JPH0842962A (en) 1996-02-16
DE59500625D1 (en) 1997-10-16
PL308454A1 (en) 1995-11-13
DE4415747A1 (en) 1995-11-16
TW288984B (en) 1996-10-21
ES2106594T3 (en) 1997-11-01
KR950033380A (en) 1995-12-22
GR3025534T3 (en) 1998-02-27

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