EP0081849B1 - Separation process and device for synthesis off-gas - Google Patents

Separation process and device for synthesis off-gas Download PDF

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Publication number
EP0081849B1
EP0081849B1 EP82111608A EP82111608A EP0081849B1 EP 0081849 B1 EP0081849 B1 EP 0081849B1 EP 82111608 A EP82111608 A EP 82111608A EP 82111608 A EP82111608 A EP 82111608A EP 0081849 B1 EP0081849 B1 EP 0081849B1
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Prior art keywords
nitrogen
compressor
pressure
separating
stage
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EP82111608A
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German (de)
French (fr)
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EP0081849A2 (en
EP0081849A3 (en
Inventor
Rainer Dipl.-Ing. Fabian
Wolfgang Dipl.-Ing. Schmid
Herwig Dipl.-Ing. Landes
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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
    • F25J3/0228—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
    • F25J3/028—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 noble gases
    • F25J3/0285—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 noble gases of argon
    • 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
    • F25J3/0252—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 hydrogen
    • 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
    • F25J3/0257—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 nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • 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
    • F25J2200/30—Processes or apparatus using separation by rectification using a side column in a single pressure 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
    • F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/76—Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
    • 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
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
    • 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
    • F25J2210/20—H2/N2 mixture, i.e. synthesis gas for or purge gas from ammonia synthesis
    • 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
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/04—Recovery of liquid products
    • 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
    • F25J2270/02—Internal refrigeration with liquid vaporising loop
    • 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
    • F25J2270/04—Internal refrigeration with work-producing gas expansion loop
    • 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
    • F25J2270/42—Quasi-closed internal or closed external nitrogen refrigeration cycle
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S62/00—Refrigeration
    • Y10S62/931—Recovery of hydrogen
    • Y10S62/934—From nitrogen

Definitions

  • the invention relates to a process for the decomposition of synthesis exhaust gas in two successive separation stages with a nitrogen refrigeration cycle, in which nitrogen is compressed to an end pressure, cooled, further cooled by heating the two separation stages, expanded and partially liquefied, gaseous and re-evaporated liquid nitrogen again is compressed, and a device for performing the method.
  • Nitrogen from the top of the second separation stage and from a storage tank is compressed to 150 to 200 bar, cooled and partly relieved of work and used for the bottom heating of the second separation stage, and partly further cooled by heat exchange with the non-compressed nitrogen and for the bottom heating of the first Separation stage used.
  • the two partial flows are then expanded into the storage container in partially liquefied form.
  • Liquid nitrogen is removed from the storage container as washing liquid for the second separation stage and for head cooling of the first separation stage.
  • a part of the gaseous nitrogen is heated together with nitrogen from the head of the second separation stage in heat exchange with synthesis exhaust gas, while another part of the gaseous nitrogen is warmed up again in heat exchange with nitrogen for the heating of the first separation stage.
  • a part of the liquefied nitrogen, after it has been re-evaporated, is compressed again together with a part of the gaseous nitrogen.
  • Excess nitrogen is withdrawn from the system after heat exchange with the synthesis exhaust gas to be separated.
  • the present invention is therefore based on the object of providing a method of the type mentioned at the outset in which the high-pressure cooling circuit can be replaced by a medium-pressure cooling circuit without any energy losses.
  • This object is achieved in that a part of the nitrogen is already removed at a medium pressure below the final pressure and cooled in parallel with the nitrogen at the final pressure, further cooled by heating the two separation stages, partially liquefied and after with the nitrogen at the final pressure whose relaxation is combined.
  • part of the nitrogen is removed from an intermediate stage of the compressor.
  • Both nitrogen flows - both those at medium pressure and those at final pressure - are cooled together and used to heat the bottom of the first and second separation stages.
  • the two nitrogen streams are then depressurized and combined together in a partially liquefied state, the liquid nitrogen, as in the previously known process, partly being fed as washing liquid to the second separation stage and being used in part to cool the head of the first separation stage.
  • a nitrogen stream according to the invention is applied to a large extent lower pressure has been compressed, used for the bottom heating of both separation stages and at the same time another nitrogen stream, which is at an even lower pressure level, is used in parallel with the first nitrogen stream for bottom heating of the two separation stages.
  • the subject of the invention surprisingly makes it possible to drastically lower the final pressure of the nitrogen and still provide the cooling capacity required for the process.
  • the mean pressure is between 6 and 20 bar.
  • the mean pressure is preferably between 10 and 16 bar, in particular about 13.5 bar.
  • the final pressure is between 30 and 50 bar, preferably between 35 and 45 bar and in particular about 40.5 bar.
  • the specified pressure ranges for the medium pressure and the final pressure a sufficient cooling capacity for the process is achieved.
  • the respective pressure values depend on external ones Process conditions such as gas composition and gas pressure.
  • the pressures in the method according to the invention are in a pressure range which is significantly below the high pressures previously required for the refrigeration cycle.
  • plate heat exchangers can now be used with advantage instead of the previously used wound heat exchangers, which can be manufactured much more economically.
  • the nitrogen at the final pressure is still above the critical point and is therefore not liquefied when it cools down in the first separation stage, it is still cooled down over the steep part of the enthalpy curve when the first separation stage is heated. In this area, relatively small amounts of nitrogen are sufficient for the required heating output.
  • part of the compressed, cooled nitrogen is expanded while performing work and is fed to the gaseous fraction of the partially liquefied nitrogen.
  • the outlet pressure is advantageously chosen to be equal to the pressure of the re-evaporated nitrogen. If final pressure nitrogen is expanded while performing work, a higher outlet pressure is expediently set so that an optimal pressure drop is achieved on the expansion machine.
  • the nitrogen which has been relieved of work, is expanded to a pressure above the inlet pressure of the compressor and fed to the compressor at an intermediate point.
  • the pressure at the intermediate point is advantageously below the mean pressure of the nitrogen partial stream withdrawn from the compressor.
  • part of the nitrogen remaining in gaseous form after the expansion is heated together with nitrogen from the head of the second separation stage in heat exchange with synthesis exhaust gas and then admixed with the nitrogen stream to be compressed.
  • Part of the recompressed nitrogen is fed, for example, to the synthesis in this process.
  • part of the nitrogen liquefied during the expansion evaporate by cooling the first separation stage and be admixed with the nitrogen stream to be heated in the heat exchange with synthesis exhaust gas.
  • the nitrogen used to heat the first separation stage provides an intermediate pressure of between 5 and 20% of the total heating power required in the first separation stage.
  • the medium pressure nitrogen flow provides about 10% heating power.
  • the nitrogen used to heat the second separation stage provides an intermediate pressure of between 60 and 90% of the total heating power required in the second separation stage.
  • this medium pressure nitrogen flow provides about 75% of the heating power required.
  • the remaining heating power is supplied by the nitrogen at the final pressure.
  • a device for performing the method according to the invention comprises two series-connected separation columns and a nitrogen cooling circuit, which contains a compressor, a heat exchanger, reboiler in the sump of the two separation columns and a nitrogen storage container, the output of the compressor having the heat exchanger and its cold end is connected to the two reboilers, and the reboilers open on the outlet side into the storage container, and is characterized in that the compressor is designed at least in two stages, the outputs of the two compressor stages being separated from one another by the heat exchanger and the two reboilers and together in the Storage container open, and that the flow path for the nitrogen äus the first or second compressor stage is connected to an expansion machine.
  • the expansion machine is connected on the output side via a heat exchanger to a return line for gaseous nitrogen leading to the compressor.
  • a cooler in the head of the first separation column is connected on the inlet side to the nitrogen reservoir and on the outlet side to a further return line for gaseous nitrogen leading to the compressor.
  • a synthesis exhaust gas (purge gas) from ammonia synthesis has, for example, a composition of 31 mol% H 2 , 10 mol% N 2 , 19 mol% Ar and 40 mol% CH 4 . This gas mixture is to be broken down in order to To obtain synthesis gas and liquid argon.
  • the synthesis exhaust gas which is supplied at 1, has been freed of water and ammonia in a process step, not shown.
  • the synthesis exhaust gas is cooled to approximately 85 K in heat exchange with hydrogen product from the decomposition and a nitrogen refrigeration cycle, and is partially liquefied in the process.
  • the gaseous fraction which contains hydrogen with product purity (about 94.7 mol%), is withdrawn via the head of a downstream separator 3 and removed after heating in the heat exchanger 2.
  • the liquid fraction which contains almost all of the argon and methane and a large part of the nitrogen, is introduced via a line 4 into a first separation column 5 (methane column), from which a methane-free nitrogen-argon fraction (top side) and methane (bottom side) be removed.
  • the first separation column 5 is operated at a pressure of approximately 2.2 bar.
  • the methane (approx. 97 mol%) is removed via line 6 at a temperature of approximately 122 K.
  • the nitrogen-argon fraction is introduced via line 7 at about 89 K into a separation column 8 (argon column) operated at a pressure of about 2 bar, in which separation into nitrogen (top side) and argon product (bottom side) takes place.
  • the liquid argon runs through the second separation column 8 with approximately 94 K, the nitrogen with approximately 83.5 K.
  • the argon has a product purity of almost 100%, the nitrogen purity is approximately 94%.
  • a nitrogen refrigeration cycle is provided for performing the rectification in the separation columns 5, 8 and for generating refrigeration.
  • the nitrogen from the top of the second separation column 8 is partly passed (line 9) through the heat exchanger 2, in which it heats up with cooling of the synthesis exhaust gas, and is fed to the suction side of the first stage of a three-stage compressor 10.
  • the pressure at the compressor inlet is approximately 1.5 bar.
  • Another part of the nitrogen (line 11) is heated in heat exchangers 12, 13 in heat exchange with two nitrogen partial streams of the nitrogen cycle, which are still to be described, and then likewise fed to the first compressor stage.
  • a portion of the bottom liquid from the second separation column 8 is removed via a line 21, evaporated in the heat exchanger 12 and returned to the second separation column 8.
  • the nitrogen is compressed by a factor of 3 in each stage, i.e. to 4.5; 13.5 and finally to 40.5 bar.
  • the nitrogen compressed to the final pressure (line 15) is cooled in the heat exchanger 13 in heat exchange with the nitrogen stream 11 and with a further low-pressure nitrogen stream 19 to be described.
  • a refrigerant 14 provides additional cold.
  • Part of the nitrogen at the final pressure is cooled in a reboiler 16 in the bottom of the first separation column 5.
  • the nitrogen which is in the supercritical state, is guided over the steep part of the enthalpy curve (quasi-condensation). It then passes into the heat exchanger 12, in which it is subcooled, and is finally expanded into a nitrogen storage container 17, which is at a pressure of approximately 4.8 bar.
  • the remaining part of the nitrogen which is at the final pressure, is branched off from the heat exchanger 13 before the end of the heat exchange and expanded in a work-performing manner in a relaxation machine 18, its pressure rising from approx. 40 bar to approx. 5 bar and its temperature from approx. 132 K to approx 84 K lower. If required, part of the nitrogen at the final pressure is branched off via line 26 and used further, for example, as sealing gas for the compressor 10 or as synthesis gas.
  • the expanded in the expansion machine 18 nitrogen 19 is passed through part of the heat exchanger 12, in which it absorbs heat, further heated in the heat exchanger 13 and fed to the compressor 10 at an intermediate point, namely on the suction side of the second compressor stage.
  • a nitrogen stream is drawn from the compressor 10 at an intermediate point, which is at a mean pressure below the final pressure.
  • This medium-pressure nitrogen stream is withdrawn via line 20 at a pressure of 13.5 bar at the outlet of the second compressor stage and cooled in parallel with the nitrogen stream 15 under final pressure in the heat exchanger 13, further cooled in the reboiler 16, liquefied and supercooled in the heat exchanger 12 and finally also relaxed into the nitrogen reservoir 17.
  • the nitrogen streams 15 and 20 located at different pressure levels thus cover the heat requirement of the two separation columns 5, 8.
  • the majority of the heating power (approx. 90%) in the first separation column 5 is supplied by the nitrogen 15 at final pressure, while the larger one Share of the heating power in the second separation column 8 (approx. 75%) is supplied by the medium-pressure nitrogen 20.
  • Gaseous nitrogen 22 is removed from the storage container 17 and mixed with the work-relieved nitrogen 19 in front of the heat exchanger 12.
  • the liquid nitrogen 23 from the reservoir 17 is partially evaporated in a heat exchanger 27, for example in heat exchange with argon product (not shown), and fed to the gaseous nitrogen 9 in front of the heat exchanger 2.
  • the liquid nitrogen is fed on the one hand as a washing liquid to the second separation column 8 (line 24) and on the other hand through a cooler 25 in the head of the passed first separation column 5, in which it evaporates, and then also supplied in vapor form to the nitrogen stream 9.

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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)

Description

Die Erfindung betrifft ein Verfahren zur Zerlegung von Syntheseabgas in zwei aufeinanderfolgenden Trennstufen mit einem Stickstoff-Kältekreislauf, bei dem Stickstoff auf einen Enddruck verdichtet, abgekühlt, durch Beheizung der beiden Trennstufen weiter abgekühlt, entspannt und teilweise verflüssigt wird, wobei gasförmiger und zurückverdampfter flüssiger Stickstoff erneut verdichtet wird, sowie eine Vorrichtung zur Durchführung des Verfahrens.The invention relates to a process for the decomposition of synthesis exhaust gas in two successive separation stages with a nitrogen refrigeration cycle, in which nitrogen is compressed to an end pressure, cooled, further cooled by heating the two separation stages, expanded and partially liquefied, gaseous and re-evaporated liquid nitrogen again is compressed, and a device for performing the method.

Bei der Erzeugung von Ammoniak-Synthesegas nach dem Steam-Reforming-Verfahren entsteht ein Abgas, das neben Wasserstoff und Stickstoff reich an Argon und Methan ist. Gemäß einem bekannten Verfahren (Winnacker-Küchler, Chem. Technologie, Band 2 (1969), Seite 494) wird das Syntheseabgas in einem Tieftemperaturprozeß zerlegt, wobei einerseits der Wasserstoff zurückgewonnen und andererseits reines Argon erzeugt wird. Die Zerlegung erfolgt in zwei aufeinanderfolgenden Trennstufen. Zur Erzeugung der für die Zerlegung benötigten tiefen Temperaturen ist ein Stickstoff-Kältekreislauf vorgesehen. Stickstoff vom Kopf der zweiten Zerlegungsstufe sowie aus einem Speicherbehälter wird auf 150 bis 200 bar verdichtet, abgekühlt und zum einen Teil arbeitsleistend entspannt und zur Sumpfbeheizung der zweiten Trennstufe verwendet, und zum anderen Teil durch Wärmetausch mit dem unverdichteten Stickstoff weiter abgekühlt und zur Sumpfbeheizung der ersten Trennstufe verwendet. Die beiden Teilströme werden anschließend in teilweise verflüssigter Form in den Vorratsbehälter entspannt. Aus dem Vorratsbehälter wird flüssiger Stickstoff als Waschflüssigkeit für die zweite Trennstufe und zur Kopfkühlung der ersten Trennstufe entnommen. Ein Teil des gasförmig verbliebenen Stickstoffes wird zusammen mit Stickstoff vom Kopf der zweiten Trennstufe in Wärmetausch mit Syntheseabgas angewärmt, während ein anderer Teil des gasförmig verbliebenen Stickstoffes in Wärmetausch mit Stickstoff für die Beheizung der ersten Trennstufe angewärmt erneut verdichtet wird. Ein Teil des verflüssigten Stickstoffes wird, nachdem er rückverdampft worden ist, zusammen mit einem Teil des gasförmigen stickstoffes erneut verdichtet. Überschüssiger Stickstoff wird nach Wärmetausch mit dem zu zerlegenden Syntheseabgas aus der Anlage abgezogen.When ammonia synthesis gas is generated using the steam reforming process, an exhaust gas is produced which is rich in argon and methane in addition to hydrogen and nitrogen. According to a known method (Winnacker-Küchler, Chem. Technologie, Volume 2 (1969), page 494), the synthesis exhaust gas is broken down in a low-temperature process, whereby on the one hand the hydrogen is recovered and on the other hand pure argon is generated. The separation takes place in two successive separation stages. A nitrogen cooling circuit is provided to generate the low temperatures required for the decomposition. Nitrogen from the top of the second separation stage and from a storage tank is compressed to 150 to 200 bar, cooled and partly relieved of work and used for the bottom heating of the second separation stage, and partly further cooled by heat exchange with the non-compressed nitrogen and for the bottom heating of the first Separation stage used. The two partial flows are then expanded into the storage container in partially liquefied form. Liquid nitrogen is removed from the storage container as washing liquid for the second separation stage and for head cooling of the first separation stage. A part of the gaseous nitrogen is heated together with nitrogen from the head of the second separation stage in heat exchange with synthesis exhaust gas, while another part of the gaseous nitrogen is warmed up again in heat exchange with nitrogen for the heating of the first separation stage. A part of the liquefied nitrogen, after it has been re-evaporated, is compressed again together with a part of the gaseous nitrogen. Excess nitrogen is withdrawn from the system after heat exchange with the synthesis exhaust gas to be separated.

Dieses Verfahren hat zwar den großen Vorteil, daß es die Rückgewinnung des Wasserstoffes und die Erzeugung von Argon ermöglicht, aufgrund der hohen Drücke, die in dem Stickstoff-Kältekreislauf benötigt werden, ist es jedoch apparativ sehr aufwendig. Drücke in der Größenordnung von 150 bis 200 bar erfordern Verdichter und Wärmetauscher, die teuer, störanfällig und aufwendig zu warten sind.Although this method has the great advantage that it enables the recovery of hydrogen and the generation of argon, due to the high pressures that are required in the nitrogen refrigeration cycle, it is very expensive in terms of equipment. Pressures in the order of 150 to 200 bar require compressors and heat exchangers, which are expensive, prone to failure and expensive to maintain.

Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren der eingangs genannten Art zu schaffen, bei dem ohne energetische Einbußen der Hochdruck-Kältekreislauf durch einen Mitteldruck-Kältekreislauf ersetzt werden kann.The present invention is therefore based on the object of providing a method of the type mentioned at the outset in which the high-pressure cooling circuit can be replaced by a medium-pressure cooling circuit without any energy losses.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß ein Teil des Stickstoffes bereits bei einem unterhalb des Enddruckes liegenden Mitteldruck entnommen und in Parallelführung mit dem auf Enddruck befindlichen Stickstoff abgekühlt, durch Beheizung der beiden Trennstufen weiter abgekühlt, teilweise verflüssigt und mit dem auf Enddruck befindlichen Stickstoff nach dessen Entspannung vereinigt wird.This object is achieved in that a part of the nitrogen is already removed at a medium pressure below the final pressure and cooled in parallel with the nitrogen at the final pressure, further cooled by heating the two separation stages, partially liquefied and after with the nitrogen at the final pressure whose relaxation is combined.

Bei dem erfindungsgemäßen Verfahren wird ein Teil des Stickstoffes an einer Zwischenstufe des Verdichters entnommen. Beide Stickstoffströme - sowohl der auf Mitteldruck, als auch der auf Enddruck befindliche - werden gemeinsam abgekühlt und zur Sumpfbeheizung der ersten und der zweiten Trennstufe verwendet. Anschließend werden die beiden Stickstoffströme entspannt und gemeinsam in teilweise verflüssigtem Zustand zusammengeführt, wobei der Flüssigstickstoff wie beim vorbekannten Verfahren zum Teil als Waschflüssigkeit auf die zweite Trennstufe aufgegeben und zum Teil zur Kopfkühlung der ersten Trennstufe verwendet wird. Während bisher der Stickstoff auf sehr hohen Druck verdichtet wurde und ein Teil des Stickstoffes unter dem hohen Druck zur Sumpfbeheizung der ersten Trennstufe verwendet wurde und der restliche Stickstoff arbeitsleistend entspannt und zur Sumpfbeheizung der zweiten Trennstufe verwendet wurde, wird erfindungsgemäß ein Stickstoffstrom, der auf einen weitaus niedrigeren Druck verdichtet worden ist, zur Sumpfbeheizung beider Trennstufen herangezogen und gleichzeitig ein weiterer Stickstoffstrom, der sich auf einem noch niedrigeren Druckniveau befindet, parallel zu dem ersten Stickstoffstrom zur Sumpfbeheizung der beiden Trennstufen verwendet.In the process according to the invention, part of the nitrogen is removed from an intermediate stage of the compressor. Both nitrogen flows - both those at medium pressure and those at final pressure - are cooled together and used to heat the bottom of the first and second separation stages. The two nitrogen streams are then depressurized and combined together in a partially liquefied state, the liquid nitrogen, as in the previously known process, partly being fed as washing liquid to the second separation stage and being used in part to cool the head of the first separation stage. While up to now the nitrogen has been compressed to very high pressure and part of the nitrogen under the high pressure has been used to heat the bottom of the first separation stage and the remaining nitrogen has been expanded to provide work and used to heat the bottom of the second separation stage, a nitrogen stream according to the invention is applied to a large extent lower pressure has been compressed, used for the bottom heating of both separation stages and at the same time another nitrogen stream, which is at an even lower pressure level, is used in parallel with the first nitrogen stream for bottom heating of the two separation stages.

Durch den Erfindungsgegenstand ist es überraschenderweise möglich, den Enddruck des Stickstoffes drastisch zu senken, und dabei dennoch die für den Prozeß erforderliche Kälteleistung bereitzustellen.The subject of the invention surprisingly makes it possible to drastically lower the final pressure of the nitrogen and still provide the cooling capacity required for the process.

Gemäß einer bevorzugten Ausgestaltung des erfindungsgemäßen Verfahrens beträgt der Mitteldruck zwischen 6 und 20 bar. Vorzugsweise beträgt der Mitteldruck zwischen 10 und 16 bar, insbesondere etwa 13,5 bar.According to a preferred embodiment of the method according to the invention, the mean pressure is between 6 and 20 bar. The mean pressure is preferably between 10 and 16 bar, in particular about 13.5 bar.

Gemäß einer weiteren bevorzugten Ausgestaltung des erfindungsgemäßen Verfahrens beträgt der Enddruck zwischen 30 und 50 bar, vorzugsweise zwischen 35 und 45 bar und insbesondere etwa 40,5 bar.According to a further preferred embodiment of the method according to the invention, the final pressure is between 30 and 50 bar, preferably between 35 and 45 bar and in particular about 40.5 bar.

Mit den angegebenen Druckbereichen für den Mitteldruck und den Enddruck wird eine ausreichende Kälteleistung für den Prozeß erzielt. Die jeweiligen Druckwerte hängen von äußeren Verfahrensbedingungen, wie Gaszusammensetzung und Gasdruck ab. In jedem Fall aber liegen die Drücke bei dem erfindungsgemäßen Verfahren in einem Druckbereich, der deutlich unter den bisher für den Kältekreislauf erforderlichen hohen Drücken liegt. Dadurch können mit Vorteil anstelle der bisher benötigten gewickelten Wärmetauscher nunmehr Plattenwärmetauscher verwendet werden, die wesentlich preisgünstiger hergestellt werden können. Selbst wenn sich der auf Enddruck befindliche Stickstoff noch oberhalb des kritischen Punktes befindet und daher beim Abkühlen in der ersten Trennstufe nicht verflüssigt wird, so wird er beim Beheizen der ersten Trennstufe doch über den steilen Teil der Enthalpiekurve abgekühlt. In diesem Bereich sind bereits relativ kleine Stickstoffmengen für die erforderliche Heizleistung ausreichend.With the specified pressure ranges for the medium pressure and the final pressure, a sufficient cooling capacity for the process is achieved. The respective pressure values depend on external ones Process conditions such as gas composition and gas pressure. In any case, however, the pressures in the method according to the invention are in a pressure range which is significantly below the high pressures previously required for the refrigeration cycle. As a result, plate heat exchangers can now be used with advantage instead of the previously used wound heat exchangers, which can be manufactured much more economically. Even if the nitrogen at the final pressure is still above the critical point and is therefore not liquefied when it cools down in the first separation stage, it is still cooled down over the steep part of the enthalpy curve when the first separation stage is heated. In this area, relatively small amounts of nitrogen are sufficient for the required heating output.

Es ist von Vorteil, wenn gemäß einer Weiterbildung des erfindungsgemäßen Verfahrens ein Teil des verdichteten, abgekühlten Stickstoffes arbeitsleistend entspannt und dem gasförmigen Anteil des teilweise verflüssigten Stickstoffes zugeführt wird.It is advantageous if, according to a further development of the method according to the invention, part of the compressed, cooled nitrogen is expanded while performing work and is fed to the gaseous fraction of the partially liquefied nitrogen.

Zur Kälteerzeugung wird entweder auf Mitteldruck oder auf Enddruck befindlicher Stickstoff arbeitsleistend entspannt. Wird ein Teil des Mitteldruck-Stickstoffes arbeitsleistend entspannt, so wird mit Vorteil der Austrittsdruck gleich dem Druck des rückverdampften Stickstoffs gewählt. Wird Enddruck-Stickstoff arbeitsleistend entspannt, wird zweckmäßigerweise ein höherer Austrittsdruck eingestellt, damit ein optimales Druckgefälle an der Entspannungsmaschine erreicht wird.For the generation of cold, work is relieved of pressure either at medium pressure or at the final pressure. If part of the medium-pressure nitrogen is expanded while performing work, the outlet pressure is advantageously chosen to be equal to the pressure of the re-evaporated nitrogen. If final pressure nitrogen is expanded while performing work, a higher outlet pressure is expediently set so that an optimal pressure drop is achieved on the expansion machine.

Gemäß einer bevorzugten Ausgestaltung des Erfindungsgegenstandes wird der arbeitsleistend entspannte Stickstoff auf einen Druck oberhalb des Eingangsdruckes des Verdichters entspannt und dem Verdichter an einer Zwischenstelle zugeführt. Dabei liegt der Druck an der Zwischenstelle vorteilhafterweise unterhalb des Mitteldruckes des aus dem Verdichter abgezogenen Stickstoff-Teilstroms.According to a preferred embodiment of the subject matter of the invention, the nitrogen, which has been relieved of work, is expanded to a pressure above the inlet pressure of the compressor and fed to the compressor at an intermediate point. The pressure at the intermediate point is advantageously below the mean pressure of the nitrogen partial stream withdrawn from the compressor.

Bei einer zweckmäßigen Weiterbildung des Erfindungsgegenstandes wird ein Teil des nach der Entspannung gasförmig verbliebenen Stickstoffes zusammen mit Stickstoff vom Kopf der zweiten Trennstufe in Wärmetausch mit Syntheseabgas angewärmt und anschließend dem zu verdichteten Stickstoffstrom beigemischt. Ein Teil des erneut verdichteten Stickstoffes wird bei dieser Verfahrensführung beispielsweise der Synthese zugeführt.In an expedient development of the subject matter of the invention, part of the nitrogen remaining in gaseous form after the expansion is heated together with nitrogen from the head of the second separation stage in heat exchange with synthesis exhaust gas and then admixed with the nitrogen stream to be compressed. Part of the recompressed nitrogen is fed, for example, to the synthesis in this process.

In Weiterbildung des Erfindungsgegenstandes wird vorgeschlagen, daß ein Teil des bei der Entspannung verflüssigten Stickstoffes durch Kühlen der ersten Trennstufe verdampft und dem im Wärmetausch mit Syntheseabgas anzuwärmenden Stickstoffstrom beigemischt wird.In a further development of the subject matter of the invention, it is proposed that part of the nitrogen liquefied during the expansion evaporate by cooling the first separation stage and be admixed with the nitrogen stream to be heated in the heat exchange with synthesis exhaust gas.

Bei einer bevorzugten Ausgestaltung des Erfindungsgegenstandes liefert der zur Beheizung der ersten Trennstufe verwendete Stickstoff mit Mitteldruck zwischen 5 und 20 % der benötigten Gesamtheizleistung in der ersten Trennstufe. Vorzugsweise liefert der Mitteldruck-Stickstoffstrom etwa 10 % Heizleistung.In a preferred embodiment of the subject matter of the invention, the nitrogen used to heat the first separation stage provides an intermediate pressure of between 5 and 20% of the total heating power required in the first separation stage. Preferably, the medium pressure nitrogen flow provides about 10% heating power.

Bei einer weiteren bevorzugten Ausgestaltung des Erfindungsgegenstandes liefert der zur Beheizung der zweiten Trennstufe verwendete Stickstoff mit Mitteldruck zwischen 60 und 90 % der benötigten Gesamtheizleistung in der zweiten Trennstufe. Insbesondere liefert dieser Mitteldruck-Stickstoffstrom etwa 75 % der benötigten Heizleistung.In a further preferred embodiment of the subject matter of the invention, the nitrogen used to heat the second separation stage provides an intermediate pressure of between 60 and 90% of the total heating power required in the second separation stage. In particular, this medium pressure nitrogen flow provides about 75% of the heating power required.

In beiden Trennstufen wird die restliche Heizleistung durch den auf Enddruck befindlichen Stickstoff geliefert.In both separation stages, the remaining heating power is supplied by the nitrogen at the final pressure.

Eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens umfaßt zwei hintereinandergeschaltete Trennsäulen sowie einen Stickstoff-Kältekreislauf, der einen Verdichter, einen Wärmetauscher, Aufkocher im Sumpf der beiden Trennsäulen und einen Stickstoff-Vorratsbehälter enthält, wobei der Ausgang des Verdichters mit dem Wärmetauscher und dessen kaltes Ende mit den beiden Aufkochern in Verbindung steht, und die Aufkocher ausgangsseitig in den Vorratsbehälter münden, und ist dadurch gekennzeichnet, daß der Verdichter mindestens zweistufig ausgebildet ist, wobei die Ausgänge der beiden Verdichterstufen getrennt voneinander durch den Wärmetauscher und die beiden Aufkocher geführt sind und gemeinsam in den Vorratsbehälter münden, und daß der Strömungsweg für den Stickstoff äus der ersten oder zweiten Verdichterstufe mit einer Entspannungsmaschine verbunden ist.A device for performing the method according to the invention comprises two series-connected separation columns and a nitrogen cooling circuit, which contains a compressor, a heat exchanger, reboiler in the sump of the two separation columns and a nitrogen storage container, the output of the compressor having the heat exchanger and its cold end is connected to the two reboilers, and the reboilers open on the outlet side into the storage container, and is characterized in that the compressor is designed at least in two stages, the outputs of the two compressor stages being separated from one another by the heat exchanger and the two reboilers and together in the Storage container open, and that the flow path for the nitrogen äus the first or second compressor stage is connected to an expansion machine.

Bei einer vorteilhaften Ausgestaltung der erfindungsgemäßen Vorrichtung ist die Entspannungsmaschine ausgangsseitig über einen Wärmetauscher mit einer zum Verdichter führenden Rückführungsleitung für gasförmigen Stickstoff verbunden.In an advantageous embodiment of the device according to the invention, the expansion machine is connected on the output side via a heat exchanger to a return line for gaseous nitrogen leading to the compressor.

Bei einer weiteren vorteilhaften Ausgestaltung der erfindungsgemäßen Vorrichtung ist ein Kühler im Kopf der ersten Trennsäule eingangsseitig mit dem Stickstoff-Vorratsbehälter und ausgangsseitig mit einer weiteren zum Verdichter führenden Rückführungsleitung für gasförmigen Stickstoff verbunden.In a further advantageous embodiment of the device according to the invention, a cooler in the head of the first separation column is connected on the inlet side to the nitrogen reservoir and on the outlet side to a further return line for gaseous nitrogen leading to the compressor.

Die Erfindung sowie weitere Einzelheiten der Erfindung werden anhand von schematisch dargestellten Ausführungsbeispielen näher erläutert.The invention and further details of the invention are explained in more detail with reference to schematically illustrated exemplary embodiments.

Hierbei zeigen:

  • Figur 1 eine Ausführungsform des erfindungsgemäßen Verfahrens,
  • Figur 2 eine modifizierte Ausführungsform des erfindungsgemäßen Verfahrens.
Here show:
  • FIG. 1 shows an embodiment of the method according to the invention,
  • Figure 2 shows a modified embodiment of the method according to the invention.

Ein Syntheseabgas (Purge-Gas) aus der Ammoniaksynthese weist beispielsweise eine Zusammensetzung von 31 Mol % H2, 10 Mol % N2, 19 Mol % Ar und 40 Mol % CH4 auf. Dieses Gasgemisch soll zerlegt werden, um Ammoniak-Synthesegas und flüssiges Argon zu gewinnen.A synthesis exhaust gas (purge gas) from ammonia synthesis has, for example, a composition of 31 mol% H 2 , 10 mol% N 2 , 19 mol% Ar and 40 mol% CH 4 . This gas mixture is to be broken down in order to To obtain synthesis gas and liquid argon.

Das Syntheseabgas, das bei 1 zugeführt wird, ist in einer nicht dargestellten Verfahrensstufe von Wasser und Ammoniak befreit worden. In einem Wärmetauscher 2 wird das Syntheseabgas in Wärmetausch mit Wasserstoff-Produkt aus der Zerlegung und einem Stickstoff-Kältekreislauf auf etwa 85 K abgekühlt und dabei teilweise verflüssigt. Der gasförmige Anteil, der Wasserstoff mit Produktreinheit (etwa 94,7 Mol %) enthält, wird über den Kopt eines nachfolgenden Abscheiders 3 abgezogen und nach Anwärmung im Wärmetauscher 2 entnommen. Die flüssige Fraktion, die nahezu das gesamte Argon und Methan sowie einen Großteil des Stickstoffres enthält, wird über eine Leitung 4 in eine erste Trennsäule 5 (Methansäule) eingeführt, aus der eine methanfreie Stickstoff-Argon-Fraktion (kopfseitig) und Methan (sumpfseitig) entnommen werden. Die erste Trennsäule 5 wird mit einem Druck von ca. 2,2 bar betrieben. Das Methan (ca. 97 Mol %) wird bei einer Temperatur von etwa 122 K über Leitung 6 entnommen.The synthesis exhaust gas, which is supplied at 1, has been freed of water and ammonia in a process step, not shown. In a heat exchanger 2, the synthesis exhaust gas is cooled to approximately 85 K in heat exchange with hydrogen product from the decomposition and a nitrogen refrigeration cycle, and is partially liquefied in the process. The gaseous fraction, which contains hydrogen with product purity (about 94.7 mol%), is withdrawn via the head of a downstream separator 3 and removed after heating in the heat exchanger 2. The liquid fraction, which contains almost all of the argon and methane and a large part of the nitrogen, is introduced via a line 4 into a first separation column 5 (methane column), from which a methane-free nitrogen-argon fraction (top side) and methane (bottom side) be removed. The first separation column 5 is operated at a pressure of approximately 2.2 bar. The methane (approx. 97 mol%) is removed via line 6 at a temperature of approximately 122 K.

Die Stickstoff-Argon-Fraktion wird über Leitung 7 mit etwa 89 K in eine bei einem Druck von etwa 2 bar betriebene Trennsäule 8 (Argonsäule) eingeführt, in der eine Zerlegung in Stickstoff (kopfseitig) und Argon-Produkt (sumpfseitig) erfolgt. Das flüssige Argon verläuft die zweite Trennsäule 8 mit etwa 94 K, der Stickstoff mit etwa 83,5 K. Das Argon hat eine Produktreinheit von nahezu 100 %, die Stickstoffreinheit beträgt ca. 94 %.The nitrogen-argon fraction is introduced via line 7 at about 89 K into a separation column 8 (argon column) operated at a pressure of about 2 bar, in which separation into nitrogen (top side) and argon product (bottom side) takes place. The liquid argon runs through the second separation column 8 with approximately 94 K, the nitrogen with approximately 83.5 K. The argon has a product purity of almost 100%, the nitrogen purity is approximately 94%.

Zur Durchführung der Rektifikation in den Trennsäulen 5, 8 und zur Kälteerzeugung ist ein Stickstoff-Kältekreislauf vorgesehen. Der Stickstoff vom Kopf der zweiten Trennsäule 8 wird zum Teil (Leitung 9) durch den Wärmetauscher 2 geleitet, in dem er sich unter Abkühlung des Syntheseabgases erwärmt, und der Saugseite der ersten Stufe eines dreistufigen Verdichters 10 zugeführt. Der Druck am Verdichtereingang beträgt ca.1,5 bar. Ein anderer Teil des Stickstoffes (Leitung 11) wird in Wärmetauschern 12, 13 in Wärmetausch mit zwei noch zu beschreibenden Stickstoff-Teilströmen des Stickstoff-Kreislaufs angewärmt und anschließend ebenfalls der ersten Verdichterstufe zugeführt.A nitrogen refrigeration cycle is provided for performing the rectification in the separation columns 5, 8 and for generating refrigeration. The nitrogen from the top of the second separation column 8 is partly passed (line 9) through the heat exchanger 2, in which it heats up with cooling of the synthesis exhaust gas, and is fed to the suction side of the first stage of a three-stage compressor 10. The pressure at the compressor inlet is approximately 1.5 bar. Another part of the nitrogen (line 11) is heated in heat exchangers 12, 13 in heat exchange with two nitrogen partial streams of the nitrogen cycle, which are still to be described, and then likewise fed to the first compressor stage.

Ein Teil der Sumpfflüssigkeit aus der zweiten Trennsäule 8 wird über eine Leitung 21 entnommen, im Wärmetauscher 12 verdampft und wieder in die zweite Trennsäule 8 zurückgeleitet.A portion of the bottom liquid from the second separation column 8 is removed via a line 21, evaporated in the heat exchanger 12 and returned to the second separation column 8.

Um jede Verdichterstufe optimal auszunutzen wird der Stickstoff in jeder Stufe etwa um einen Faktor 3 verdichtet, d.h. auf 4,5; 13,5 und schließlich auf 40,5 bar. Der auf den Enddruck verdichtete Stickstoff (Leitung 15) wird im Wärmetauscher 13 in Wärmetausch mit dem Stickstoffstrom 11 sowie mit einem weiteren noch zu beschreibenden NiederdruckStickstoffstrom 19 abgekühlt. Zusätzliche Kälte liefert ein Kältemittel 14.In order to make optimal use of each compressor stage, the nitrogen is compressed by a factor of 3 in each stage, i.e. to 4.5; 13.5 and finally to 40.5 bar. The nitrogen compressed to the final pressure (line 15) is cooled in the heat exchanger 13 in heat exchange with the nitrogen stream 11 and with a further low-pressure nitrogen stream 19 to be described. A refrigerant 14 provides additional cold.

Ein Teil des auf Enddruck befindlichen Stickstoffes wird in einem Aufkocher 16 im Sumpf der ersten Trennsäule 5 abgekühlt. Der Stickstoff, der sich im überkritischen Zustand befindet, wird dabei über den steilen Teil der Enthalpiekurve geführt (Quasi-Kondensation). Er gelangt anschließend in den Wärmetauscher 12, in dem er unterkühlt wird, und wird schließlich in einen Stickstoff-Vorratsbehälter 17, der sich auf einem Druck von ca. 4,8 bar befindet, entspannt.Part of the nitrogen at the final pressure is cooled in a reboiler 16 in the bottom of the first separation column 5. The nitrogen, which is in the supercritical state, is guided over the steep part of the enthalpy curve (quasi-condensation). It then passes into the heat exchanger 12, in which it is subcooled, and is finally expanded into a nitrogen storage container 17, which is at a pressure of approximately 4.8 bar.

Der restliche Teil des auf Enddruck befindlichen Stickstoffes wird vor Beendigung des Wärmetausches aus dem Wärmetauscher 13 abgezweigt und in einer Entspannungsmaschine 18 arbeitsleistend entspannt, wobei sich sein Druck von ca. 40 bar auf ca. 5 bar und seine Temperatur von ca. 132 K auf ca. 84 K senken. Bei Bedarf wird ein Teil des auf Enddruck befindlichen Stickstoffes über Leitung 26 abgezweigt und beispielsweise als Sperrgas für den Verdichter 10 oder als Synthesegas weiter verwendet.The remaining part of the nitrogen, which is at the final pressure, is branched off from the heat exchanger 13 before the end of the heat exchange and expanded in a work-performing manner in a relaxation machine 18, its pressure rising from approx. 40 bar to approx. 5 bar and its temperature from approx. 132 K to approx 84 K lower. If required, part of the nitrogen at the final pressure is branched off via line 26 and used further, for example, as sealing gas for the compressor 10 or as synthesis gas.

Der in der Entspannungsmaschine 18 entspannte Stickstoff 19 wird durch einen Teil des Wärmetauschers 12 geführt, in dem er Wärme aufnimmt, im Wärmetauscher 13 weiter erwärmt und dem Verdichter 10 an einer Zwischenstelle, nämlich auf der Saugseite der zweiten Verdichterstufe, zugeführt.The expanded in the expansion machine 18 nitrogen 19 is passed through part of the heat exchanger 12, in which it absorbs heat, further heated in the heat exchanger 13 and fed to the compressor 10 at an intermediate point, namely on the suction side of the second compressor stage.

Erfindungsgemäß wird aus dem Verdichter 10 an einer Zwischenstelle ein Stickstoffstrom entnommen, der sich auf einem unterhalb des Enddruckes liegenden mittleren Druck befindet. Dieser Mitteldruck-Stickstoffstrom wird über Leitung 20 mit einem Druck von 13,5 bar am Ausgang der zweiten Verdichterstufe entnommen und in Parallelführung zu dem unter Enddruck befindlichen Stickstoffstrom 15 im Wärmetauscher 13 abgekühlt, im Aufkocher 16 weiter abgekühlt, im Wärmetauscher 12 verflüssigt und unterkühtt und zuletzt ebenfalls in den Stickstoff-Vorratsbehälter 17 entspannt.According to the invention, a nitrogen stream is drawn from the compressor 10 at an intermediate point, which is at a mean pressure below the final pressure. This medium-pressure nitrogen stream is withdrawn via line 20 at a pressure of 13.5 bar at the outlet of the second compressor stage and cooled in parallel with the nitrogen stream 15 under final pressure in the heat exchanger 13, further cooled in the reboiler 16, liquefied and supercooled in the heat exchanger 12 and finally also relaxed into the nitrogen reservoir 17.

Erfindungsgemäß decken somit die auf unterschiedlichen Druckniveaus befindlichen Stickstoffströme 15 und 20 den Wärmebedarf der beiden Trennsäule 5, 8. Der überwiegende Teil der Heizleistung (ca. 90 Ofo) in der ersten Trennsäule 5 wird von dem auf Enddruck befindlichen Stickstoff 15 geliefert, während der größere Anteil der Heizleistung in der zweiten Trennsäule 8 (ca. 75 %) von dem Mitteldruck-Stickstoff 20 geliefert wird.According to the invention, the nitrogen streams 15 and 20 located at different pressure levels thus cover the heat requirement of the two separation columns 5, 8. The majority of the heating power (approx. 90%) in the first separation column 5 is supplied by the nitrogen 15 at final pressure, while the larger one Share of the heating power in the second separation column 8 (approx. 75%) is supplied by the medium-pressure nitrogen 20.

Aus dem Vorratsbehälter 17 wird gasförmiger Stickstoff 22 entnommen und dem arbeitsleistend entspannten Stickstoff 19 vor dem Wärmetauscher 12 zugemischt. Der flüssige Stickstoff 23 aus dom Vorratsbehälter 17 wird zum Teil in einem Wärmetauscher 27 verdampft, beispielsweise in Wärmetausch mit Argon-Produkt (nicht dargestellt), und dem gasförmigen Stickstoff 9 vor dem Wärmetauscher 2 zugeführt. Zum anderen Teil wird der flüssige Stickstoff einerseits als Waschflüssigkeit auf die zweite Trennsäule 8 aufgegeben (Leitung 24) und andererseits durch einen Kühler 25 im Kopf der ersten Trennsäule 5 geleitet, in welchem er verdampft, und anschließend dampfförmig ebenfalls dem Stickstoffstrom 9 zugeführt.Gaseous nitrogen 22 is removed from the storage container 17 and mixed with the work-relieved nitrogen 19 in front of the heat exchanger 12. The liquid nitrogen 23 from the reservoir 17 is partially evaporated in a heat exchanger 27, for example in heat exchange with argon product (not shown), and fed to the gaseous nitrogen 9 in front of the heat exchanger 2. On the other hand, the liquid nitrogen is fed on the one hand as a washing liquid to the second separation column 8 (line 24) and on the other hand through a cooler 25 in the head of the passed first separation column 5, in which it evaporates, and then also supplied in vapor form to the nitrogen stream 9.

In Figur 2, die eine modifizierte Ausführungsform des erfindungsgemäßen Verfahrens gemäß Figur 1 zeigt, sind für analoge Anlagenteile dieselben Bezugszeichen verwendet. Es soll hier nur auf die unterschiedlichen Merkmale zu dem Verfahren gemäß Figur 1 hingewiesen werden. Bei dem Verfahren gemäß Figur 2 wird nicht der auf Enddruck befindliche Stickstoff, sondern der auf Mitteldruck befindliche Stickstoff 20 nach Passieren des Wärmetauschers 13 arbeitsleistend entspannt. Um einen optimalen Wirkungsgrad an der Entspannungsmaschine 18 zu erreichen, wird der Stickstoff von etwa 13 bar auf 2 bar entspannt, wobei er sich von etwa 132 K auf ca. 84 K abkühlt. Der Auspuff 19 der Entspannungsmaschine 18 wird dem Stickstoff 22 aus dem Vorratsbehälter 17 zugeführt und strömt nach Anwärmung in den Wärmetauschern 12 und 13 zum Verdichter 10 zurück. Allerdings wird der Stickstoff hier im Gegensatz zu dem Verfahren gemäß Figur 1 bereits auf der Saugseite der ersten Verdichterstufe zugeführt. In dem Vorratsbehälter 17 herrscht im Gegensatz zu dem oben beschriebenen Verfahren ein Druck von etwa 2 bar.In Figure 2, which shows a modified embodiment of the method according to the invention according to Figure 1, the same reference numerals are used for analog system parts. Only the different features of the method according to FIG. 1 should be pointed out here. In the method according to FIG. 2, it is not the nitrogen which is at the final pressure but the nitrogen 20 which is at the medium pressure that is relaxed during the work after passing through the heat exchanger 13. In order to achieve optimal efficiency on the expansion machine 18, the nitrogen is expanded from about 13 bar to 2 bar, cooling down from about 132 K to about 84 K. The exhaust 19 of the expansion machine 18 is fed to the nitrogen 22 from the storage container 17 and flows back to the compressor 10 after heating in the heat exchangers 12 and 13. However, in contrast to the method according to FIG. 1, the nitrogen is already supplied to the first compressor stage on the suction side. In contrast to the method described above, there is a pressure of approximately 2 bar in the storage container 17.

Claims (12)

1. A process for separating synthesis waste gas in two consecutive separating stages, having a nitrogen cooling cycle in which nitrogen is compressed to a final pressure, cooled, further cooled by heating the two separating stages, expanded and partially liquified, gaseous and re- vaporised, liquid nitrogen are re-compressed, characterised in that a part of the nitrogen (20) is withdrawn at an intermediate pressure below the final pressure and is cooled in parallel with the nitrogen (15) which is at the final pressure, further cooled by heating the two separating stages (5, 8), expanded, at least partially liquified, and combined with the nitrogen (15) which is at the final pressure after the expansion thereof.
2. A process as claimed in Claim 1, characterised in that the intermediate pressure is between 6 and 20 bar.
3. A process as claimed in Claim 1 or Claim 2, characterised in that the final pressure is between 30 and 50 bar.
4. A process as claimed in one of Claims 1 to 3, characterised in that a part of the compressed, cooled nitrogen is expanded with the performance of external work and is fed to the gaseous component (22) of the partially liquified nitrogen.
5. A process as claimed in Claim 4, characterised in that the nitrogen which is expanded with the performance of external work is expanded to a pressure above the input pressure of the compressor (10) and is fed to the compressor (10) at an intermediate point.
6. A process as claimed in one of Claims 1 to 4, characterised in that a part of the nitrogen (22) which remains in gaseous form after expension is heated, together with nitrogen from the head of the second separating stage (8), in heat exchange with synthesis waste gas (1) and is then added to the nitrogen stream (9) to be compressed.
7. A process as claimed in one of Claims 1 to 6, characterised in that a part of the nitrogen (23) which liquifies during the expansion step is vaporised by cooling the first separating stage and is added to the nitrogen stream (9) which is to be heated in heat exchange with synthesis waste gas (1).
8. A process as claimed in one of Claims 1 to 7, characterised in that the nitrogen at intermediate pressure (2), which is used to heat the first separating stage (5), supplies between 5 and 20 % of the total heating required in the first separating stage.
9. A process as claimed in one of Claims 1 to 8, characterised in that the nitrogen at intermediate pressure (20), which is used to heat the second separating stage (8), supplies between 60 and 90 % of the total heating required in the second separating stage (8).
10. Apparatus for carrying out the process claimed in Claim 1, comprising two separating columns connected in series and a nitrogen cooling cycle which contains a compressor, a heat exchanger, boilers in the sump of the two separating columns, and a nitrogen storage container, the output of the compressor being connected to the heat exchanger and the cold end thereof being connected to the two boilers, and the boilers at the output end opening into the storage container, characterised in that the compressor (10) consists of at least two stages, the outputs of the two compressor stages leading separately through the heat exchanger (13) and the two boilers and leading commonly into the feed container (17); and that the flow path for the nitrogen from the first or second compressor stage is connected to an expansion machine (18).
11. Apparatus as claimed in Claim 10, characterised in that the expansion machine (18) is connected at its output end through a heat exchanger (12) to a return line (11, 19) for gaseous nitrogen which leads to the compressor (10).
12. Apparatus as claimed in Claim 10 or Claim 11, characterised in that a cooler (25) in the head of the first separating column (5) is connected at its input end to the nitrogen storage container (17) and at its output end to another return line (9) for gaseous nitrogen which leads to the compressor (10).
EP82111608A 1981-12-16 1982-12-14 Separation process and device for synthesis off-gas Expired EP0081849B1 (en)

Applications Claiming Priority (2)

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DE3149846 1981-12-16
DE19813149846 DE3149846A1 (en) 1981-12-16 1981-12-16 "METHOD AND DEVICE FOR DISASSEMBLING SYNTHESIS EXHAUST GAS"

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EP0081849A2 EP0081849A2 (en) 1983-06-22
EP0081849A3 EP0081849A3 (en) 1986-03-12
EP0081849B1 true EP0081849B1 (en) 1987-07-01

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US4689062A (en) * 1986-02-24 1987-08-25 The Boc Group, Inc. Argon recovery from ammonia plant purge gas utilizing a combination of cryogenic and non-cryogenic separating means
US4805414A (en) * 1987-12-15 1989-02-21 Union Carbide Corporation Process to recover hydrogen-free higher boiling synthesis gas component
US5289688A (en) * 1991-11-15 1994-03-01 Air Products And Chemicals, Inc. Inter-column heat integration for multi-column distillation system
US5685170A (en) * 1995-11-03 1997-11-11 Mcdermott Engineers & Constructors (Canada) Ltd. Propane recovery process
US5775128A (en) * 1997-05-02 1998-07-07 Praxair Technology, Inc. Process for producing ammonia and recovering argon using low purity oxygen

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DE1467202A1 (en) * 1963-03-21 1969-03-13 Linde Eismasch Ag Method and device for regulating the cold balance when producing NH3 synthesis gas
GB1351598A (en) * 1970-03-26 1974-05-01 Air Prod & Chem Separation of gas mixtures
DE2814660A1 (en) * 1978-04-05 1979-10-11 Linde Ag Carbon mon:oxide and hydrogen recovery from gas mixt. - by partial liquefaction, rectification and scrubbing with liquid nitrogen

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IN158298B (en) 1986-10-11
EP0081849A2 (en) 1983-06-22
DE3149846A1 (en) 1983-07-21
EP0081849A3 (en) 1986-03-12
DE3276671D1 (en) 1987-08-06
US4473385A (en) 1984-09-25

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