EP0642649B1 - Method of separating higher-boiling hydrocarbons out of a mixture of gases - Google Patents

Method of separating higher-boiling hydrocarbons out of a mixture of gases Download PDF

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Publication number
EP0642649B1
EP0642649B1 EP92917822A EP92917822A EP0642649B1 EP 0642649 B1 EP0642649 B1 EP 0642649B1 EP 92917822 A EP92917822 A EP 92917822A EP 92917822 A EP92917822 A EP 92917822A EP 0642649 B1 EP0642649 B1 EP 0642649B1
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EP
European Patent Office
Prior art keywords
refrigerant
fraction
heat exchanger
heat exchange
gas mixture
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EP92917822A
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German (de)
French (fr)
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EP0642649A1 (en
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Heinz Bauer
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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
    • F25J3/0252—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
    • F25J3/0204—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
    • F25J3/0242—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 3 carbon atoms or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • 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
    • F25J3/0247—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 4 carbon atoms or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/72—Refluxing the column with at least a part of the totally 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/12—Refinery or petrochemical off-gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External 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
    • F25J2270/18—External refrigeration with incorporated cascade 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
    • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
    • 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
    • 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
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements

Definitions

  • the invention relates to a method for separating higher hydrocarbons from a gas mixture containing these and lower-boiling components by rectification, in which the gas mixture is partially condensed and fed to a separation column. a fraction rich in higher hydrocarbons is withdrawn from the bottom thereof and a fraction rich in lower-boiling components is withdrawn from the top. the top fraction partially condensing and the condensate being fed as reflux to the top of the separation column.
  • the invention is based on the object of specifying a method of the type mentioned at the outset which works more economically and can be used more flexibly with respect to boundary conditions and is also particularly suitable for relatively strongly fluctuating parameters of the gas mixture to be separated.
  • Such a procedure enables the refrigerant temperature to be adapted to the requirements specified by the composition of feed gas and products. Compared to a refrigerant cascade, for example, it enables both less equipment expenditure and less exergy losses. Peak cold can also be generated with reasonable effort. so that the method according to the invention can dispense with expansion turbines. The disadvantages associated with turbines in terms of flexibility are avoided.
  • the separation column used in the process is usually operated only as a reinforcement column. That is, the partially condensed gas mixture is fed in at the bottom of the column.
  • the refrigerant is preferably not only completely condensed, but additionally supercooled in order to have as high a proportion as possible in the liquid state after its relaxation.
  • the refrigerant that remains liquid after compression is also supercooled as much as possible.
  • the entire refrigerant flow can be combined again.
  • the refrigerant is exchanged with the top fraction after the heat exchange. usually supplemented by the refrigerant fraction that remained liquid after compression, brought into heat exchange with the gas mixture to be separated, and previously, if provided, brought into heat exchange with the intermediate fraction.
  • the refrigerant remaining in gaseous form after compression is thus used in a particularly advantageous manner to transfer peak cold to the top fraction of the separation column. This further improves the energy balance of the process,
  • an intermediate fraction is removed from the separation column at a central point, this is at least partially condensed in indirect heat exchange with the refrigerant and is returned to the separation column.
  • This heat exchange takes place at a temperature which lies between the temperature levels of the condensation of the feed gas mixture and that of the condensation of the top fraction.
  • the corresponding heat exchangers are preferably connected in series on the refrigerant side, so that optimum use is made of the sliding evaporation temperature profile of the multicomponent refrigerant.
  • the process is particularly economical to operate.
  • it is also possible and in many cases also advantageous to remove several such intermediate fractions in an analogous manner and to supply them with an indirect heat exchange with the refrigerant.
  • the method is carried out with a throughput and / or a composition of the gas mixture to be separated which is varied over time.
  • each process is subject to fluctuations in time, for example when starting and stopping a system.
  • changes are meant with a much shorter period, generally less than an hour, preferably in the minute range, which, for example, have temperature fluctuations of approximately 3 K / min and / or 10% load change per minute.
  • Such deviations from static behavior can also be predetermined by preceding process steps, for example if the gas mixture to be separated in the present process comes from a periodically operated apparatus, for example switchable reactors.
  • a process with the generation of peak cooling by turbines e.g. according to EP-B-O 318 504
  • the method according to the invention can cope with such fluctuations because the multi-component refrigerant run used is not subject to such wear fluctuations and can nevertheless provide cold at different temperature levels, similar to the previously known methods.
  • the necessary adjustments to the refrigeration budget are therefore not made by a regulation, but by a controller.
  • Certain parameters must be included in the calculation of the manipulated variables, which can only be partially determined in advance by theoretical considerations.
  • empirical values are necessary, which must be determined by the operating personnel when a system is started up for the first time. Since the fluctuations in throughput and / or composition of the gas mixture to be separated are generally periodic, such values can be determined by tests and then predefined. Self-learning systems are also conceivable that optimize such parameters automatically and also during ongoing operation.
  • heat exchangers are therefore preferably used for the indirect heat exchange between the top fraction and the refrigerant, which are made of a material with high long-term stability against mechanical stresses. Stainless steel is preferred. It is expedient to design the heat exchanger in a wound construction, that is to say with tubes arranged in a helical manner on concentric cylinder surfaces.
  • a plate heat exchanger in particular an aluminum plate heat exchanger, can be used for the indirect heat exchange (7 ') between the gas mixture (6) to be separated and the refrigerant.
  • the dehydrator product gas is introduced via line 1 and is initially subjected to a pretreatment.
  • the gaseous Antell is freed of traces of chlorine in an HCl reactor 4 and dried (5).
  • the pre-cleaned gas in position 6 now represents the gas mixture to be separated for the process according to the invention and is also referred to here as feed gas.
  • feed gas contains 30 to 70% more volatile constituents that are to be separated off. (The percentages here and in the following basically refer to the molar proportions.)
  • the feed gas in line 6 is cooled in heat exchanger 7 and partially (5 to 40%, preferably 10 to 30%) condensed and fed via line 8 into a separation column 9 above the sump.
  • the desired higher hydrocarbons are obtained as bottom product, are drawn off via line 27 and heated in heat exchanger 23.
  • they are fed via line 32 for further treatment, for example a depropanizer.
  • Line 10 leads the top fraction of the separation column to a heat exchanger 11 in which the fraction is partially condensed.
  • the two-phase mixture is fed via line 12 into a separator 13 which is integrated in the separation column.
  • a phase separation device designed as a separate component could also be used.
  • the liquid from the isolator flows back into the separation column; the remaining gaseous portion of the top fraction is discharged via a residual gas line 14 and warmed to approximately ambient temperature in heat exchanger 15.
  • This gas can be supplied partially or entirely via line 17 to a compressor unit and then to further processing, for example in a pressure swing adsorption.
  • residual gas is either removed via line 16 and used, for example, as fuel gas or to regenerate the dryer 5.
  • the refrigeration required for the condensation of feed gas (heat exchanger 7) and top fraction (heat exchanger 11) is generated by a multi-component refrigerant circuit 18 in which a refrigerant is compressed and partially liquefied in a known manner.
  • the refrigerant contains, for example, C2H4, C2H6, Iso-C4H10 and some CH4.
  • the exact composition is determined depending on the course of the respective evaporation curves.
  • an exact adaptation to the evaporation properties of feed and intermediate product streams with their respective special composition is possible.
  • Compressed refrigerant is introduced as a two-phase mixture into a refrigerant separator 19.
  • the gaseous portion (line 20) is condensed to recover peak cold in indirect heat exchange 15 with the gaseous portion 14 of the top fraction and supercooled.
  • the temperature of the refrigerant flow should be as low as possible so that all refrigerant remains liquid even in the subsequent expansion in throttle valve 25. As a result, a maximum amount of latent heat can be converted during the subsequent heat exchange 11 with the top fraction 10.
  • the liquid portion 21 of refrigerant from the refrigerant separator 19 is also supercooled, namely in heat exchanger 22 against low-pressure refrigerant and in heat exchanger 23 against the C3+- / C4+ product stream 27 from the bottom of the separation column 9 and again against Low pressure refrigerant.
  • a first part of the supercooled liquid is expanded in the throttle valve 26a, combined with the refrigerant portion remaining in gaseous form in the separator 19, warmed in the heat exchangers 24, 7 and 22 and compressed again.
  • a second part is expanded in FIG. 26 b, heated in the lower part of the heat exchanger 23 and then combined upstream of the heat exchanger 7 with the remaining leather pressure refrigerant.
  • an intermediate fraction 28 is led out of the separation column 9 in the exemplary embodiment, partially condensed in a heat exchange 24 with refrigerant and fed back into the separation column 9 via line 29.
  • several such intermediate fractions can be removed at different points for partial condensation. In individual cases, this must be decided on the basis of the trade-off between higher expenditure on equipment on the one hand and reduced exergy losses on the other.
  • the heat exchangers required in the exemplary embodiment are preferably implemented as wound apparatuses with stainless steel tubes.
  • the method works with a control device instead of an otherwise conventional regulating device.
  • the flow of gas mixture to be broken down is measured in line 6 (30).
  • setpoints for the cooling requirement are determined in a control unit 31 with the aid of additional parameters, which were partly calculated theoretically, partly based on experience, and then the flow rate in the refrigerant lines is set. This manipulation takes place by activating the expansion valves 25, 26a, 26b.
  • the following numerical example relates to the separation of C4 hydrocarbons from the product gas of a C4 dehydrogenation. Due to the discontinuous operation of the dehydrogenation reactors, the throughput and composition of the product gas fluctuate with an approximately four-minute period. Two values are given for each size: left for the phase of maximum throughput of gas mixture to be separated (612 mol / s through line 6) and the associated lower relative but higher absolute hydrogen content (approx. 55%, corresponds to 334 mol / s); right for minimum throughput (423 mol / s) and higher relative but lower absolute hydrogen content (about 64%, corresponds to 275 mol / s).
  • the refrigerant has the following molar composition: CH4 2% C2H4 20% C2H6 25% Iso-C4H10 53%
  • the diagram of Figure 2 shows a further embodiment of the method according to the invention, which is also preferably used for working up a product gas from a C3 or C4 dehydrogenation.
  • Corresponding method steps and devices have the same reference symbols in both drawings.
  • Dehydrogenation product gas is introduced via Leltung 1 and subjected to a pretreatment similar to that of Flgur 1 (cooling by means of external cooling in heat exchanger 2, phase separation in isolator 3, chlorine removal in HCl reactor 4, drying 5).
  • the feed gas in line 6 is cooled in heat exchanger 7 'and partially condensed.
  • the two-phase mixture is fed via line 8 above the bottom of the separation column 9.
  • the desired higher hydrocarbons are obtained as the bottom product, are withdrawn via line 27 and heated in the heat exchanger 7 '. They are discharged from separator 3 separately from the high-boiling components that have already condensed out during the pretreatment.
  • Line 10 leads the top fraction of the separation column to a heat exchanger 11, in which the Fractlon is partially condensed.
  • the two-phase mixture is fed via line 12 into a separator 13 arranged in the upper region of the separation column.
  • the gaseous fraction of the top fraction is discharged via a residual gas line 14 and heated to approximately ambient temperature in heat exchanger 15. This gas can be drawn off via line 16 (for example to regenerate the dryer 5) and / or via line 17.
  • the cold required for the condensation of feed gas (heat exchanger 7 ') and top fraction (heat exchanger 11) is generated by a multi-component refrigerant circuit 18 similar to the method in FIG.
  • the gaseous portion of the compressed refrigerant (Leltung 20) introduced into the refrigerant separator 19 is condensed and recovered in indirect heat exchange 15 with the portion 14 of the top fraction remaining in gaseous form in order to recover peak cold, and then expanded in throttle valve 25. and brought into indirect heat exchange 11 with the top fraction 10 from the separation column 9.
  • the liquefied portion 21 of refrigerant from the refrigerant separator 19 is subcooled in the heat exchanger 7 '.
  • the supercooled liquid is expanded in the throttle valve 26, combined with the refrigerant portion remaining in gaseous form in the separator 19, warmed in the heat exchanger 7 'and completely evaporated and then compressed again.
  • the intermediate cooling steps shown in FIG. 1 were dispensed with in the process of Flgur 2.
  • the heat exchanger 7 ' is designed as a plate heat exchanger. It combines the functions of the heat exchangers 7, 22 and 23 of FIG. 1.
  • the control in the method in FIG. 2 is similar to that described in FIG. 1.
  • measuring devices are provided for the flow of gas mixture (30) to be broken down in line 6 and for the pressure of the refrigerant (33) in line 20.
  • the measured values are converted in a control unit 31 into target values for the cooling requirement.
  • the flow in the refrigerant lines (expansion valves 25, 26) is set.

Abstract

Described is a method of separating higher-boiling hydrocarbons from a gas mixture containing these hydrocarbons plus lower-boiling compounds by fractional distillation. The gas mixture (6) is partially condensed (7) and passed into a separation column (9). A fraction (27) rich in higher-boiling hydrocarbons is drawn off at the bottom of the column (9) and a fraction (10) rich in lower-boiling compounds is drawn off at the head of the column. The head fraction (10) is partially condensed (11). The condensate thus formed is returned to the separation column (9). Both the partial condensation of the gas mixture and that of the head fraction are produced by indirect heat exchange (7, 11) with a refrigerant which is made up of several components and is circulated in an external circuit (18).

Description

Die Erfindung betrifft ein Verfahren zum Abtrennen höherer Kohlenwasserstoffe aus einem diese und leichter siedende Komponenten enthaltenden Gasgemisch durch rektifikatorische Zerlegung, bei dem das Gasgemisch partiell kondensiert und einer Trennsäule zugeleitet wird. an deren Sumpf eine an höheren Kohlenwasserstoffen reiche Fraktion und an deren Kopf eine an leichter siedenden Komponenten reiche Fraktion abgezogen werden. wobei die Kopffraktion teilweise kondensiert und das Kondensat als Rücklauf auf den Kopf der Trennsäule gegeben wird.The invention relates to a method for separating higher hydrocarbons from a gas mixture containing these and lower-boiling components by rectification, in which the gas mixture is partially condensed and fed to a separation column. a fraction rich in higher hydrocarbons is withdrawn from the bottom thereof and a fraction rich in lower-boiling components is withdrawn from the top. the top fraction partially condensing and the condensate being fed as reflux to the top of the separation column.

Derartige Verfahren sind aus der EP-8-0 318 504 und aus der EP-A-0 153 984 bekannt. Die zur Kondensation von Einsatzgas und Kopffraktion benötigte Kälte wird bei den bekannten Verfahren zum einen Teil von einem oder mehreren Kältekreisläufen, zum anderen Teil durch arbeitsleistende Entspannung von Einsatz- oder Restgas zur Verfügung gestellt. Die Kältekreisläufe arbeiten bei konstanter Verdampfungstemperatur und verursachen beim Wärmeaustausch mit kondensierendem Einsatz- oder Kopfgasgemisch relativ hohe Temperaturdifferenzen und damit Exergieverluste. Die für die Erzeugung von Spitzenkälte verwendeten Turbinen sind nicht für alle Verfahren geeignet. Insbesondere bei Temperaturschwankungen beispielsweise infolge nicht-stationärer Prozeßbedingungen weisen sie einen hohen Verschleiß auf. Das vorbekannte Verfahren arbeitet daher wirtschaftlich nicht vollständig zufriedenstellend und ist nur unter Beachtung bestimmter Randbedingungen zuverlässig im Betrieb.Such methods are known from EP-8-0 318 504 and from EP-A-0 153 984. The cold required for the condensation of feed gas and top fraction is made available in the known processes on the one hand by one or more cooling circuits and on the other hand by work-related expansion of feed or residual gas. The refrigeration circuits work at constant evaporation temperature and cause relatively high temperature differences and thus exergy losses when exchanging heat with a condensing feed or top gas mixture. The turbines used to generate peak cold are not suitable for all processes. In particular in the case of temperature fluctuations, for example as a result of non-stationary process conditions, they exhibit high wear. The previously known method therefore does not work completely economically satisfactorily and is only reliable in operation if certain boundary conditions are observed.

Darüber hinaus ist aus der EP-A-0 132 984 und aus dem Artikel "Die Verflüssigung von Erdgas" von W. Förg und V. Etzbach in den Linde-Berichten aus Technik und Wissenschaft. Nr. 28. Juni 1970. Seiten 27 bis 39 der Einsatz von Mehrkomponenten-Kältemitteln zur Kondensation kohlenwässerstoffhältiger Prozeßströme bekannt.Furthermore, from EP-A-0 132 984 and from the article "The liquefaction of natural gas" by W. Förg and V. Etzbach in the Linde reports from technology and science. No. 28 June 1970. Pages 27 to 39 the use of multi-component refrigerants for the condensation of hydrocarbon-containing process streams is known.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren der eingangs genannten Art anzugeben, das wirtschaftlich günstiger arbeitet und gegenüber Randbedingungen flexibler einzusetzen ist und sich insbesondere auch für relativ stark schwankende Parameter des zu trennenden Gasgemisches eignet.The invention is based on the object of specifying a method of the type mentioned at the outset which works more economically and can be used more flexibly with respect to boundary conditions and is also particularly suitable for relatively strongly fluctuating parameters of the gas mixture to be separated.

Diese Aufgabe wird dadurch gelöst. daß die Kondensation des Gasgemisches und die Kondensation der Kopffraktion durch indirekten Wärmeaustausch mit einem Kältemittel bewirkt werden. das aus mehreren Komponenten besteht und in einem externen Kreislauf geführt wird und daß verdichtetes Kältemittel innerhalb des externen Kältekreislaufs in eine gasförmige und in eine flüssige Fraktion separiert wird und die gasförmige Fraktion in indirektem Wärmeaustausch mit dem bei der Kondensation der Kopffraktion gasförmig verbliebenen Anteil abgekühlt und dabei kondensiert wird und anschließend zum indirekten Wärmeaustausch mit der Kopffraktion geleitet wird.This will solve this task. that the condensation of the gas mixture and the condensation of the top fraction by indirect heat exchange with a refrigerant be effected. which consists of several components and is conducted in an external circuit and that compressed refrigerant is separated into a gaseous and a liquid fraction within the external refrigeration circuit and the gaseous fraction is cooled in indirect heat exchange with the portion remaining in gaseous form during the condensation of the top fraction and thereby is condensed and then passed for indirect heat exchange with the top fraction.

Eine solche Verfahrensführung ermöglicht eine gleitende Anpassung der Kältemittel temperatur an die durch die Zusammensetzung von Einsatzgas und Produkten vorgegebenen Anforderungen. Es ermöglicht beispielsweise gegenüber einer Kältemittel-Kaskade sowohl geringeren apparativen Aufwand als auch geringere Exergieverluste. Auch Spitzenkälte kann mit vertretbarem Aufwand erzeugt werden. so daß das erfindungsgemäße Verfahren auf Entspannungsturbinen verzichten kann. Die mit Turbinen verbundenen Nachteile hinsichtlich der Flexibilität werden vermieden.Such a procedure enables the refrigerant temperature to be adapted to the requirements specified by the composition of feed gas and products. Compared to a refrigerant cascade, for example, it enables both less equipment expenditure and less exergy losses. Peak cold can also be generated with reasonable effort. so that the method according to the invention can dispense with expansion turbines. The disadvantages associated with turbines in terms of flexibility are avoided.

Die energetischen Vorteile des erfindungsgemäßen Verfahrens sind überraschenderweise so groß, daß sie die durch den Mehrkomponenten-Kältemittel-Kreislauf verursachten Mehrkosten nicht nur aufwiegen. sondern sich insgesamt eine deutliche Erhöhung der Wirtschaftlichkeit des Verfahrens ergibt. Zusätzlich sind Anwendungsmöglichkeiten des Verfahrens außerordentlich flexibel.The energetic advantages of the method according to the invention are surprisingly so great that they do not only outweigh the additional costs caused by the multi-component refrigerant circuit. but overall there is a significant increase in the economics of the process. In addition, possible uses of the method are extremely flexible.

Die in dem Verfahren eingesetzte Trennsäule wird in der Regel nur als Verstärkungssäule betrieben. das heißt das partiell kondensierte Gasgemisch wird im unteren Bereich der Kolonne eingespeist.The separation column used in the process is usually operated only as a reinforcement column. that is, the partially condensed gas mixture is fed in at the bottom of the column.

Bei dem Wärmeaustausch mit der gasförmig verbliebenen Kopffraktion wird das Kältemittel vorzugweise nicht nur vollständig kondensiert, sondern zusätzlich unterkühlt, um nach seiner Entspannung einen möglichst hohen Anteil in flüssigem Zustand zur Verfügung zu haben. Das nach dem Verdichten flüssig verblieben Kältemittel wird ebenfalls so weit wie möglich unterkühlt.When the heat is exchanged with the gaseous top fraction, the refrigerant is preferably not only completely condensed, but additionally supercooled in order to have as high a proportion as possible in the liquid state after its relaxation. The refrigerant that remains liquid after compression is also supercooled as much as possible.

Stromabwärts des Wärmetauschers zur Rücklauferzeugung kann der gesamte Kältemittelstrom wieder vereinigt werden. Das Kältemittel wird nach dem Wärmeaustausch mit der Kopffraktion. in der Regel ergänzt durch die nach dem Verdichten flüssig verbliebene Kältemittelfraktion, in Wärmeaustausch mit dem zu zerlegenden Gasgemisch und vorher, falls vorgesehen, in Wärmeaustausch mit der Zwischen fraktion gebracht.Downstream of the heat exchanger for generating the return flow, the entire refrigerant flow can be combined again. The refrigerant is exchanged with the top fraction after the heat exchange. usually supplemented by the refrigerant fraction that remained liquid after compression, brought into heat exchange with the gas mixture to be separated, and previously, if provided, brought into heat exchange with the intermediate fraction.

Das nach dem Verdichten gasförmig verbliebene Kältemittel wird damit auf besonders günstige Weise zur Übertragung von Spitzenkälte auf die Kopffraktion der Trennsäule ausgenutzt. Die Energiebilanz des Verfahrens wird dadurch weiter verbessert,The refrigerant remaining in gaseous form after compression is thus used in a particularly advantageous manner to transfer peak cold to the top fraction of the separation column. This further improves the energy balance of the process,

Zur weiteren Verbesserung der Rektifizierwirkung der Trennsäule ist es günstig, wenn der Trennsäule an einer mittleren Stelle eine Zwischenfraktion entnommen, diese in indirektem Wärmeaustausch mit dem Kältemittel mindestens teilweise kondensiert und in die Trennsäule zurückgeleitet wird.To further improve the rectifying effect of the separation column, it is advantageous if an intermediate fraction is removed from the separation column at a central point, this is at least partially condensed in indirect heat exchange with the refrigerant and is returned to the separation column.

Dieser Wärmeaustausch findet bei einer Temperatur statt, die zwischen den Temperaturniveaus der Kondensation des Einsatzgasgemisches und demjenigen der Kondensation der Kopffraktion liegt. Vorzugsweise werden die entsprechenden Wärmetauscher kältemittelseitig seriell geschaltet, so daß sich eine optimale Ausnutzung des gleitenden Verdampfungstemperaturverlaufs des Mehrkomponenten-Kältemittels ergibt. Dadurch ist das Verfahren energetisch besonders günstig zu betreiben. Selbstverständlich ist es auch möglich und in vielen Fällen auch vorteilhaft, mehrere solcher Zwischenfraktionen in analoger Weise zu entnehmen und einem indirekten Wärmeaustausch mit dem Kältemittel zuzuführen.This heat exchange takes place at a temperature which lies between the temperature levels of the condensation of the feed gas mixture and that of the condensation of the top fraction. The corresponding heat exchangers are preferably connected in series on the refrigerant side, so that optimum use is made of the sliding evaporation temperature profile of the multicomponent refrigerant. As a result, the process is particularly economical to operate. Of course, it is also possible and in many cases also advantageous to remove several such intermediate fractions in an analogous manner and to supply them with an indirect heat exchange with the refrigerant.

Gemäß einer Weiterbildung des Erfindungsgedankens wird das Verfahren mit zeitlich veränderlichem Durchsatz und/oder zeitlich veränderlicher Zusammensetzung des zu trennenden Gasgemisches durchgeführt.According to a development of the concept of the invention, the method is carried out with a throughput and / or a composition of the gas mixture to be separated which is varied over time.

Selbstverständlich unterliegt jedes Verfahren zeitlichen Schwankungen, beispielsweise beim An- und Abfahren einer Anlage. Hler sind jedoch Veränderungen mit wesentlich kürzerer Periode, im allgemeinen kleiner als eine Stunde, vorzugsweise im Minutenbereich, gemeint, die beispielsweise Temperaturschwankungen von etwa 3 K/min und/oder 10% Laständerung pro Minute aufweisen. Derartige Abweichungen von statlonärem Verhalten können auch durch vorausgehende Verfahrensschritte vorgegeben sein, beispielsweise wenn das in dem vorliegenden Verfahren zu trennende Gasgemisch aus einer periodisch betriebenen Apparatur, etwa umschaltbaren Reaktoren, stammt. Insbesondere bei derartigen Voraussetzungen würde ein Verfahren mit Erzeugung von Spitzenkälte durch Turbinen (z.B. gemäß EP-B-O 318 504) zu sehr hohem Verschleiß der Turbinen führen und damit häufigen Stillstand und hohe Kosten für die Anlage, insbesondere durch Produktionsausfall bedeuten. Das erfindungsgemäße Verfahren kann dagegen solche Schwankungen verkraften, weil der verwendete Mehrkomponenten-Kältemittel-Krelslauf keinen derartigen Verschleißerschelnungen unterliegt und trotzdem ähnlich den vorbekannten Verfahren Kälte auf verschiedenen Temperaturniveaus zur Verfügung stellen kann.Of course, each process is subject to fluctuations in time, for example when starting and stopping a system. However, changes are meant with a much shorter period, generally less than an hour, preferably in the minute range, which, for example, have temperature fluctuations of approximately 3 K / min and / or 10% load change per minute. Such deviations from static behavior can also be predetermined by preceding process steps, for example if the gas mixture to be separated in the present process comes from a periodically operated apparatus, for example switchable reactors. In particular under such conditions, a process with the generation of peak cooling by turbines (e.g. according to EP-B-O 318 504) would lead to very high wear of the turbines and would therefore mean frequent downtimes and high costs for the plant, in particular due to production downtime. The method according to the invention, on the other hand, can cope with such fluctuations because the multi-component refrigerant run used is not subject to such wear fluctuations and can nevertheless provide cold at different temperature levels, similar to the previously known methods.

Im Falle einer derartig nicht-stationären Durchführung des Verfahrens mit relativ kurzen Perloden stoßen herkömmliche Regelverfahren häufig an ihre Grenzen, da sie zu träge reagieren. Gemäß einer Weiterbildung des erfindungsgemäßen Verfahrens ist daher vorgesehen, daß der Durchsatz und/oder die Zusammensetzung des zu trennenden Gasgemisches gemessen und der Durchsatz an Kältemittel in den verschiedenen Kondensationsstufen in Abhängigkeit von diesem Meßwert eingestellt wird.In the case of such a non-stationary implementation of the method with relatively short periods, conventional control methods often reach their limits because they react too sluggishly. According to a development of the method according to the invention, it is therefore provided that the throughput and / or the composition of the gas mixture to be separated is measured and the throughput of refrigerant in the various condensation stages is set as a function of this measured value.

Die notwendigen Anpassungen am Kältehaushalt werden also nicht durch eine Regelung, sondern durch eine Steuerung vorgenommen. Dabei müssen bestimmte Parameter in die Berechnung der Stellgrößen eingehen, die nur teilweise durch theoretische Betrachtungen im voraus bestimmt werden können. Darüber hinaus sind Erfahrungswerte notwendig, die bei der ersten Inbetriebnahme einer Anlage vom Bedienungspersonal ermittelt werden müssen. Da die Schwankungen in Durchsatz und/oder Zusammensetzung des zu trennenden Gasgemisches in der Regel periodisch sind, können derartige Werte durch Versuche ermittelt und anschließend fest vorgegeben werden. Denkbar sind auch selbstlernende Systeme, die solche Parameter automatisch und auch während des laufenden Betriebs optimieren.The necessary adjustments to the refrigeration budget are therefore not made by a regulation, but by a controller. Certain parameters must be included in the calculation of the manipulated variables, which can only be partially determined in advance by theoretical considerations. In addition, empirical values are necessary, which must be determined by the operating personnel when a system is started up for the first time. Since the fluctuations in throughput and / or composition of the gas mixture to be separated are generally periodic, such values can be determined by tests and then predefined. Self-learning systems are also conceivable that optimize such parameters automatically and also during ongoing operation.

Bei relativ kurzzeitigen Schwankungen der Zusammensetzungen der Einsatz-, Zwischenprodukt- und Produktströme, die entweder indirekt über unterschiedlich hohe Durchsätze oder direkt über entsprechend anfallendes Einsatzgas entstehen, ergibt sich bei den bisher bekannten gattungsgemäßen Verfahren ein weiteres Problem. Die üblicherweise verwendeten Aluminium-Plattenwärmetauscher halten nämlich den resultierenden häufigen und kurzzeitigen Temperaturschwankungen und dadurch induzierten mechanischen Spannungen in der Regel nur sehr kurze Zeit stand. Auch gewickelte Wärmeaustauscher mit Aluminiumrohren, deren Aufbau für die Kompensatlon von thermischen Längenänderungen besser geeignet ist, können mit der Zeit undicht werden.In the case of relatively short-term fluctuations in the compositions of the feed, intermediate and product streams, which arise either indirectly through differently high throughputs or directly via corresponding feed gas, a further problem arises in the previously known generic processes. The commonly used aluminum plate heat exchangers usually only withstand the resulting frequent and short-term temperature fluctuations and the mechanical stresses induced thereby for only a very short time. Even wound heat exchangers with aluminum tubes, the structure of which is more suitable for compensating for thermal changes in length, can leak over time.

Gemäß einer Ausführungsform der Erfindung werden deshalb vorzugsweise für den indirekten Wärmeaustausch zwischen der Kopffraktion und dem Kältemittel Wärmetauscher verwendet, die aus einem Material mit hoher Langzeitstabilität gegen mechanische Spannungen hergestellt sind. Dabei wird bevorzugt Edelstahl eingesetzt. Günstig ist eine Ausführung des Wärmetauschers in gewickelter Bauweise, also mit schraubenförmig auf konzentrischen Zylinderflächen angeordneten Rohren.According to one embodiment of the invention, heat exchangers are therefore preferably used for the indirect heat exchange between the top fraction and the refrigerant, which are made of a material with high long-term stability against mechanical stresses. Stainless steel is preferred. It is expedient to design the heat exchanger in a wound construction, that is to say with tubes arranged in a helical manner on concentric cylinder surfaces.

In ähnlicher Weise ist es vorteilhaft, für den indirekten Wärmeaustausch zwischen dem bei der Kondensatlon der Kopffraktlon gasförmig verbliebenen Antell und der gasförmigen Fraktion des Kältemittels und/oder für den indirekten Wärmeaustausch (7) zwischen zu zerlegendem Gasgemisch (6) und Kältemittel und/oder für den indirekten Wärmeaustausch (24) zwischen der Zwischenfraktion (28) und dem Kältemittel jeweils einen Wärmetauscher zu verwenden, der aus einem Material mit hoher Langzeitstabilität gegen mechanische Spannungen hergestellt ist.Similarly, it is advantageous for the indirect heat exchange between the Antell remaining in gaseous form in the condensate fraction and the gaseous fraction of the refrigerant and / or for the indirect heat exchange (7) between the gas mixture (6) and refrigerant to be separated and / or for to use the indirect heat exchange (24) between the intermediate fraction (28) and the refrigerant in each case a heat exchanger which is made of a material with high long-term stability against mechanical stresses.

Gemäß einer weiteren Ausführungsform der Erfindung kann für den indirekten Wärmeaustausch (7') zwischen zu zerlegendem Gasgemisch (6) und Kältemittel ein Plattenwärmetauscher, insbesondere ein Aluminium-Plattenwärmetauscher verwendet werden.According to a further embodiment of the invention, a plate heat exchanger, in particular an aluminum plate heat exchanger, can be used for the indirect heat exchange (7 ') between the gas mixture (6) to be separated and the refrigerant.

Die Erfindung sowie weitere Einzelheiten der Erfindung werden nun anhand zweier Ausführungsbeispiele näher erläutert, die in den Zeichnungen als Verfahrensschemata dargestellt sind. Sie betreffen eine Anwendung des erfindungsgemäßen Verfahrens, in der dessen Vorzüge besonders stark zur Geltung kommen, nämlich die Aufarbeltung eines Produktgases aus einer C₃- oder C₄-Dehydrierung. Ein derartiges Gas enthält außer den höheren Kohlenwasserstoffen leichter flüchtige Anteile, vor allem Wasserstoff, aber auch geringere Antelle an Wasser, Kohlenmonoxid, Kohlendioxid, Stickstoff, C₂ -Kohlenwasserstoffen usw. Die Verfahrensschritte der Erfindung dienen zur Abtrennung der unerwünschten leichteren Komponenten, die Voraussetzung ist für die weitere Verarbeitung der C₃- beziehungsweise C₄-Bestandteile.The invention and further details of the invention will now be explained in more detail with reference to two exemplary embodiments, which are shown in the drawings as process diagrams. They relate to an application of the method according to the invention in which its advantages are particularly effective, namely the reprocessing of a product gas from a C₃ or C₄ dehydrogenation. Such a gas contains, in addition to the higher hydrocarbons, more volatile components, especially hydrogen, but also lower amounts of water, carbon monoxide, carbon dioxide, nitrogen, C₂-hydrocarbons, etc. The process steps of the invention serve to separate the undesired lighter components, which is a prerequisite for the further processing of the C₃ or C₄ components.

Das Dehydrler-Produktgas wird beim Verfahren von Figur 1 über Leitung 1 herangeführt und zunächst einer Vorbehandlung unterzogen. Nach einer Abkühlung mit Hilfe einer externen Kälteanlage in einem Wärmetauscher 2 und einer nachfolgenden Phasentrennung in einem Abscheider 3 wird der gasförmig verbliebene Antell in einem HCl-Reaktor 4 von Chlorspuren befreit und getrocknet (5). Das vorgereinigte Gas in Leltung 6 stellt nun das zu trennende Gasgemisch für das Verfahren gemäß der Erfindung dar und wird hier auch als Einsatzgas bezeichnet. Es enthält beispielsweise 30 bis 70% leichter flüchtige Bestandteile, die abgetrennt werden sollen. (Die Prozentangaben beziehen sich hier und im folgenden grundsätzlich auf die molaren Anteile.)In the process of FIG. 1, the dehydrator product gas is introduced via line 1 and is initially subjected to a pretreatment. After cooling with the help of an external refrigeration system in a heat exchanger 2 and a subsequent phase separation in a separator 3, the gaseous Antell is freed of traces of chlorine in an HCl reactor 4 and dried (5). The pre-cleaned gas in position 6 now represents the gas mixture to be separated for the process according to the invention and is also referred to here as feed gas. For example, it contains 30 to 70% more volatile constituents that are to be separated off. (The percentages here and in the following basically refer to the molar proportions.)

Das Einsatzgas in Leltung 6 wird in Wärmetauscher 7 abgekühlt und partiell (zu 5 bis 40%, vorzugsweise 10 bis 30%) kondensiert und über Leitung 8 oberhalb des Sumpfes in eine Trennsäule 9 eingespeist. Am Boden der Trennsäule fallen die gewünschten höheren Kohlenwasserstoffe als Sumpfprodukt an, werden Über Leltung 27 abgezogen und in Wärmetauscher 23 angewärmt. Zusammen mit den bereits bei der Vorbehandlung auskondensierten schwerersiedenden Komponenten aus Abscheider 3 werden sie Über Leitung 32 der weiteren Behandlung, beispielsweise einem Depropanizer, zugeführt.The feed gas in line 6 is cooled in heat exchanger 7 and partially (5 to 40%, preferably 10 to 30%) condensed and fed via line 8 into a separation column 9 above the sump. At the bottom of the separation column, the desired higher hydrocarbons are obtained as bottom product, are drawn off via line 27 and heated in heat exchanger 23. Together with the high-boiling components from separator 3 which have already been condensed out during the pretreatment, they are fed via line 32 for further treatment, for example a depropanizer.

Leitung 10 führt die Kopffraktlon der Trennsäule zu einem Wärmetauscher 11, in dem die Fraktion partiell kondensiert wird. Das Zwei-Phasen-Gemisch wird über Leltung 12 in einen Abscheider 13 geführt, der in die Trennsäule integriert ist. Es könnte jedoch ebenso eine als separates Bautell ausgeführte Phasentrenneinrichtung verwendet werden. Die Flüssigkeit aus dem Abschelder fließt als Rücklauf in die Trennsäule; der gasförmig verbliebene Antell der Kopffraktion wird über eine Restgasleitung 14 abgeführt und in Wärmetauscher 15 auf etwa Umgebungstemperatur angewärmt. Dieses Gas kann teilweise oder ganz über Leltung 17 einer Verdichtereinheit und anschließend einer weiteren Aufarbeitung, etwa in einer Druckwechsel-Adsorption, zugeführt werden. Alternativ oder parallel dazu wird Restgas entweder über Leitung 16 entfernt und beispielsweise als Brenngas oder zu Regenerlerung des Trockners 5 eingesetzt.Line 10 leads the top fraction of the separation column to a heat exchanger 11 in which the fraction is partially condensed. The two-phase mixture is fed via line 12 into a separator 13 which is integrated in the separation column. However, a phase separation device designed as a separate component could also be used. The liquid from the isolator flows back into the separation column; the remaining gaseous portion of the top fraction is discharged via a residual gas line 14 and warmed to approximately ambient temperature in heat exchanger 15. This gas can be supplied partially or entirely via line 17 to a compressor unit and then to further processing, for example in a pressure swing adsorption. Alternatively or in parallel, residual gas is either removed via line 16 and used, for example, as fuel gas or to regenerate the dryer 5.

Die für die Kondensation von Einsatzgas (Wärmetauscher 7) und Kopffraktlon (Wärmetauscher 11) benötigte Kälte wird durch einen Mehrkomponenten-Kältemittel-Kreislauf 18 erzeugt, in dem in bekannter Weise ein Kältemittel verdichtet und teilweise verflüssigt wird. Das Kältemittel enthält beispielsweise C₂H₄, C₂H₆, Iso-C₄H₁₀ und etwas CH₄. Die genaue Zusammensetzung wird in Abhängigkeit von dem Verlauf der jeweiligen Verdampfungskurven festgelegt. Hier ist eine genaue Anpassung an die Verdampfungseigenschaften von Einsatz- und Zwischenproduktströmen bei deren jeweiliger speziellen Zusammensetzung möglich.The refrigeration required for the condensation of feed gas (heat exchanger 7) and top fraction (heat exchanger 11) is generated by a multi-component refrigerant circuit 18 in which a refrigerant is compressed and partially liquefied in a known manner. The refrigerant contains, for example, C₂H₄, C₂H₆, Iso-C₄H₁₀ and some CH₄. The exact composition is determined depending on the course of the respective evaporation curves. Here, an exact adaptation to the evaporation properties of feed and intermediate product streams with their respective special composition is possible.

Verdichtetes Kältemittel wird als Zwei-Phasen-Gemisch in einen Kältemittelabschelder 19 eingeleitet. Der gasförmige Anteil (Leitung 20) wird zur Rückgewinnung von Spitzenkälte in indirektem Wärmeaustausch 15 mit dem gasförmig verbliebenen Anteil 14 der Kopffraktion kondensiert und unterkühlt. Die Temperatur des Kältemittelstroms sollte möglichst so niedrig sein, daß auch beim nachfolgenden Entspannen in Drosselventil 25 sämtliches Kältemittel flüssig bleibt. Dadurch kann beim anschließenden Wärmeaustausch 11 mit der Kopffraktion 10 ein maximaler Betrag an latenter Wärme umgesetzt werden.Compressed refrigerant is introduced as a two-phase mixture into a refrigerant separator 19. The gaseous portion (line 20) is condensed to recover peak cold in indirect heat exchange 15 with the gaseous portion 14 of the top fraction and supercooled. The temperature of the refrigerant flow should be as low as possible so that all refrigerant remains liquid even in the subsequent expansion in throttle valve 25. As a result, a maximum amount of latent heat can be converted during the subsequent heat exchange 11 with the top fraction 10.

Der flüssig verbliebene Anteil 21 an Kältemittel aus dem Kältemittelabscheider 19 wird ebenfalls unterkühlt, und zwar in Wärmetauscher 22 gegen unter niedrigem Druck stehendes Kältemittel und in Wärmetauscher 23 gegen den C₃₊-/C₄₊-Produktstrom 27 aus dem Sumpf der Trennsäule 9 und nochmals gegen Niederdruck-Kältemittel. Ein erster Teil der unterkühlten Flüssigkeit wird im Drosselventil 26a entspannt, mit dem im Abscheider 19 gasförmig verbliebenen Kältemittelanteil vereinigt, in den Wärmetauschern 24, 7 und 22 angewärmt und erneut verdichtet. Ein zweiter Teil wird in 26b entspannt, im unteren Teil des Wärmetauschers 23 angewärmt und anschlleßend stromaufwärts des Wärmetauschers 7 mit dem übrigen Nlederdruck-Kältemittel vereinigt.The liquid portion 21 of refrigerant from the refrigerant separator 19 is also supercooled, namely in heat exchanger 22 against low-pressure refrigerant and in heat exchanger 23 against the C₃₊- / C₄₊ product stream 27 from the bottom of the separation column 9 and again against Low pressure refrigerant. A first part of the supercooled liquid is expanded in the throttle valve 26a, combined with the refrigerant portion remaining in gaseous form in the separator 19, warmed in the heat exchangers 24, 7 and 22 and compressed again. A second part is expanded in FIG. 26 b, heated in the lower part of the heat exchanger 23 and then combined upstream of the heat exchanger 7 with the remaining leather pressure refrigerant.

Zur weiteren Verbesserung der Energiebilanz des Verfahrens wird bei dem Ausführungsbeispiel eine Zwischenfraktion 28 aus der Trennsäule 9 herausgeführt, in Wärmetausch 24 mit Kältemittel partiell kondensiert und über Leitung 29 in die Trennsäule 9 zurückgespeist. Analog können auch mehrere solcher Zwischenfraktionen an verschiedenen Stellen zur partiellen Kondensation entnommen werden. Dies muß im Einzelfall anhand der Abwägung zwischen höherem apparativem Aufwand einerseits und verringerten Exergieverlusten andererseits entschieden werden.To further improve the energy balance of the method, an intermediate fraction 28 is led out of the separation column 9 in the exemplary embodiment, partially condensed in a heat exchange 24 with refrigerant and fed back into the separation column 9 via line 29. Similarly, several such intermediate fractions can be removed at different points for partial condensation. In individual cases, this must be decided on the basis of the trade-off between higher expenditure on equipment on the one hand and reduced exergy losses on the other.

Die in dem Ausführungsbeispiel benötigten Wärmetauscher werden bevorzugt als gewickelte Apparate mit Rohren aus Edelstahl realisiert.The heat exchangers required in the exemplary embodiment are preferably implemented as wound apparatuses with stainless steel tubes.

Das Verfahren arbeitet mit einer Steuervorrichtung anstelle einer ansonsten üblichen Regeleinrichtung. Dazu wird der Durchfluß an zu zerlegendem Gasgemlsch in Leitung 6 gemessen (30). Aus diesem Meßwert werden in einer Steuereinheit 31 mit Hllfe von zusätzlichen Parametern, die teils theoretisch errechnet wurden, teils auf Erfahrungen beruhen, Sollwerte für den Kältebedarf ermittelt und danach der Durchfluß in den Kältemittelleitungen eingestellt. Diese Manipulation findet durch Ansteuerung der Entspannungsventile 25, 26a, 26b statt.The method works with a control device instead of an otherwise conventional regulating device. For this purpose, the flow of gas mixture to be broken down is measured in line 6 (30). From this measured value, setpoints for the cooling requirement are determined in a control unit 31 with the aid of additional parameters, which were partly calculated theoretically, partly based on experience, and then the flow rate in the refrigerant lines is set. This manipulation takes place by activating the expansion valves 25, 26a, 26b.

Das folgende Zahlenbeispiel bezieht sich auf die Abtrennung von C₄-Kohlenwasserstoffen aus dem Produktgas einer C₄-Dehydrierung. Wegen des diskontinuierlichen Betriebs der Dehydrier-Reaktoren schwanken Durchsatz und Zusammensetzung des Produktgases mit einer etwa vierminütigen Perlode. Für jede Größe sind zwei Werte angegeben: links für die Phase maximalen Durchsatzes an zu zerlegendem Gasgesmisch (612 mol/s durch Leitung 6) und damit verbundenen geringeren relativen, aber höheren absoluten Wasserstoffanteils (etwa 55%, entspricht 334 mol/s); rechts für minimalen Durchsatz (423 mol/s) und höheren relativen, aber niedrigeren absoluten Wasserstoffgehalt (etwa 64%, entspricht 275 mol/s).The following numerical example relates to the separation of C₄ hydrocarbons from the product gas of a C₄ dehydrogenation. Due to the discontinuous operation of the dehydrogenation reactors, the throughput and composition of the product gas fluctuate with an approximately four-minute period. Two values are given for each size: left for the phase of maximum throughput of gas mixture to be separated (612 mol / s through line 6) and the associated lower relative but higher absolute hydrogen content (approx. 55%, corresponds to 334 mol / s); right for minimum throughput (423 mol / s) and higher relative but lower absolute hydrogen content (about 64%, corresponds to 275 mol / s).

Die verschiedenen Ströme, für die in der Tabelle Daten angegeben sind, werden durch Großbuchstaben A bis G gekennzeichnet. Sie bedeuten im einzelnen:

  • A Einsatzgas vor der partiellen Kondensation (Leitung 6)
  • B Einsatzgas nach der partiellen Kondensation (Leitung 8)
  • C Sumpfprodukt (Leitung 27)
  • D Kopffraktion vor der partiellen Kondensation (Leitung 10)
  • E Kopffraktion nach der partiellen Kondensatlon (Leitung 12)
  • F Zwischenfraktion vor der partiellen Kondensation (Leltung 28)
  • G Zwischenfraktion nach der partiellen Kondensation (Leitung 29)
The different streams for which data are given in the table are identified by capital letters A to G. They mean in particular:
  • A feed gas before partial condensation (line 6)
  • B feed gas after partial condensation (line 8)
  • C bottom product (line 27)
  • D head fraction before partial condensation (line 10)
  • E head fraction after the partial condensation (line 12)
  • F intermediate fraction before partial condensation (Leltung 28)
  • G intermediate fraction after partial condensation (line 29)

Das Kältemittel weist in dieser speziellen Anwendung folgende molare Zusammensetzung auf:
CH₄  2%
C₂H₄  20%
C₂H₆  25%
Iso-C₄H₁₀  53%

Figure imgb0001
Figure imgb0002
 Das Schema von Figur 2 zeigt ein weiteres Ausführungsbeispiel des erfindungsgemäßen Verfahrens, das ebenfalls vorzugsweise zur Aufarbeitung eines Produktgases aus einer C₃- oder C₄-Dehydrierung eingesetzt wird. Einander entsprechende Verfahrensschritte und Vorrichtungen tragen in beiden Zeichnungen die gleichen Bezugszeichen.In this special application, the refrigerant has the following molar composition:
CH₄ 2%
C₂H₄ 20%
C₂H₆ 25%
Iso-C₄H₁₀ 53%
Figure imgb0001
Figure imgb0002
 The diagram of Figure 2 shows a further embodiment of the method according to the invention, which is also preferably used for working up a product gas from a C₃ or C₄ dehydrogenation. Corresponding method steps and devices have the same reference symbols in both drawings.

Dehydrier-Produktgas wird über Leltung 1 herangeführt und einer ähnlichen Vorbehandlung wie beim Verfahren von Flgur 1 unterzogen (Abkühlung mittels externer Kälte in Wärmetauscher 2, Phasentrennung in Abschelder 3, Chlorentfernung in HCl-Reaktor 4, Trocknung 5). Das Einsatzgas in Leitung 6 wird in Wärmetauscher 7' abgekühlt und partiell kondensiert. Das Zwei-Phasengemisch wird über Leitung 8 oberhalb des Sumpfes der Trennsäule 9 zugespeist. Am Boden der Trennsäule fallen die gewünschten höheren Kohlenwasserstoffe als Sumpfprodukt an, werden über Leltung 27 abgezogen und im Wärmetauscher 7' angewärmt. Sie werden hier getrennt von den bereits bei der Vorbehandlung auskondensierten schwerersiedenden Komponenten aus Abscheider 3 abgeführt.Dehydrogenation product gas is introduced via Leltung 1 and subjected to a pretreatment similar to that of Flgur 1 (cooling by means of external cooling in heat exchanger 2, phase separation in isolator 3, chlorine removal in HCl reactor 4, drying 5). The feed gas in line 6 is cooled in heat exchanger 7 'and partially condensed. The two-phase mixture is fed via line 8 above the bottom of the separation column 9. At the bottom of the separation column, the desired higher hydrocarbons are obtained as the bottom product, are withdrawn via line 27 and heated in the heat exchanger 7 '. They are discharged from separator 3 separately from the high-boiling components that have already condensed out during the pretreatment.

Leitung 10 führt die Kopffraktion der Trennsäule zu einem Wärmetauscher 11, in dem die Fraktlon partiell kondensiert wird. Das Zwei-Phasen-Gemisch wird über Leitung 12 in einen im oberen Berelch der Trennsäule angeordneten Abscheider 13 geführt. Der gasförmig verbliebene Anteil der Kopffraktion wird über eine Restgasleitung 14 abgeführt und in Wärmetauscher 15 auf etwa Umgebungstemperatur angewärmt. Dleses Gas kann über Leltung 16 (beispielsweise zur Regenerierung des Trockners 5) und/oder über Leitung 17 abgezogen werden.Line 10 leads the top fraction of the separation column to a heat exchanger 11, in which the Fractlon is partially condensed. The two-phase mixture is fed via line 12 into a separator 13 arranged in the upper region of the separation column. The gaseous fraction of the top fraction is discharged via a residual gas line 14 and heated to approximately ambient temperature in heat exchanger 15. This gas can be drawn off via line 16 (for example to regenerate the dryer 5) and / or via line 17.

Die für die Kondensation von Einsatzgas (Wärmetauscher 7') und Kopffraktion (Wärmetauscher 11) benötigte Kälte wird ähnlich wie im Verfahren von Figur 1 durch einen Mehrkomponenten-Kältemittel-Kreislauf 18 erzeugt.The cold required for the condensation of feed gas (heat exchanger 7 ') and top fraction (heat exchanger 11) is generated by a multi-component refrigerant circuit 18 similar to the method in FIG.

Der gasförmige Anteil des in Kältemittelabscheider 19 eingeleiteten verdichteten Kältemittels (Leltung 20) wird zur Rückgewinnung von Spitzenkälte in indirektem Wärmeaustausch 15 mit dem gasförmig verbliebenen Anteil 14 der Kopffraktion kondensiert und unterkühlt, anschließend in Drosselventil 25 entspannt. und in indirekten Wärmeaustausch 11 mit der Kopffraktion 10 aus der Trennsäule 9 gebracht.The gaseous portion of the compressed refrigerant (Leltung 20) introduced into the refrigerant separator 19 is condensed and recovered in indirect heat exchange 15 with the portion 14 of the top fraction remaining in gaseous form in order to recover peak cold, and then expanded in throttle valve 25. and brought into indirect heat exchange 11 with the top fraction 10 from the separation column 9.

Der verflüssigte Anteil 21 an Kältemittel aus dem Kältemittelabscheider 19 wird in Wärmetauscher 7' unterkühlt. Die unterkühlte Flüssigkeit wird im Drosselventil 26 entspannt, mit dem im Abscheider 19 gasförmig verbliebenen Kältemittelanteil vereinigt, im Wärmetauscher 7' angewärmt und vollständig verdampft und anschließend erneut verdichtet.The liquefied portion 21 of refrigerant from the refrigerant separator 19 is subcooled in the heat exchanger 7 '. The supercooled liquid is expanded in the throttle valve 26, combined with the refrigerant portion remaining in gaseous form in the separator 19, warmed in the heat exchanger 7 'and completely evaporated and then compressed again.

Um die Investlonskosten der Anlage zu verringern wurde beim Verfahren von Flgur 2 auf die in Figur 1 dargestellten Zwischenkühlungsschritte verzichtet. Der Wärmetauscher 7' ist bei dieser Variante als Plattenwärmeaustauscher ausgeführt. Er vereinigt die Funktionen der Wärmeaustauscher 7, 22 und 23 der Figur 1.In order to reduce the investment costs of the plant, the intermediate cooling steps shown in FIG. 1 were dispensed with in the process of Flgur 2. In this variant, the heat exchanger 7 'is designed as a plate heat exchanger. It combines the functions of the heat exchangers 7, 22 and 23 of FIG. 1.

Die Steuerung bei dem Verfahren von Figur 2 läuft ähnlich wie oben bei Figur 1 beschrieben ab. Dazu sind Meßvorrichtungen für den Durchfluß an zu zerlegendem Gasgemisch (30) in Leitung 6 und für den Druck des Kältemlttels (33) in Leitung 20 vorgesehen. Die Meßwerte werden in einer Steuereinheit 31 in Sollwerte für den Kältebedarf umgewandelt. Danach wird der Durchfluß in den Kältemittelleitungen (Entspannungsventile 25, 26) eingestellt.The control in the method in FIG. 2 is similar to that described in FIG. 1. For this purpose, measuring devices are provided for the flow of gas mixture (30) to be broken down in line 6 and for the pressure of the refrigerant (33) in line 20. The measured values are converted in a control unit 31 into target values for the cooling requirement. Then the flow in the refrigerant lines (expansion valves 25, 26) is set.

Die Zahlenbeispiele aus der obigen Tabelle sind auch für die Variante nach Flgur 2 gültig. Der Verzicht auf die Zwischenkühlung (Wärmetauscher 24 von Figur 1) bewirkt in den Parametern der übrigen Ströme nur geringfügige Änderungen.The numerical examples from the table above are also valid for the variant according to Flgur 2. Dispensing with intermediate cooling (heat exchanger 24 from FIG. 1) causes only minor changes in the parameters of the other flows.

Claims (10)

  1. Process for separating off higher hydrocarbons from a gas mixture containing these and lower-boiling components by rectifying fractionation, in which the gas mixture (6) is partially condensed (7; 7') and passed to a separation column (9), at the bottom of which a fraction (27) rich in higher hydrocarbons is taken off and at the top of which a fraction (10) rich in lower-boiling components is taken off, the overhead fraction (10) being partially condensed (11) and the condensate being added as reflux to the top of the separation column (9), characterized in that the condensation (7; 7') of the gas mixture (6) and the condensation (11) of the overhead fraction (10) is effected by indirect heat exchange with a refrigerant which comprises a plurality of components and is externally circulated (18) and in that the compressed refrigerant is separated within the external refrigeration circuit (18) into a gaseous (20) and a liquid (21) fraction and in that the gaseous fraction (20) is cooled and thus condensed in indirect heat exchange with the portion (14) which has remained in the gaseous state in the condensation of the overhead fraction and is then passed for the indirect heat exchange (11) with the overhead fraction (10).
  2. Process according to Claim 1, characterized in that an intermediate fraction is withdrawn from the separation column (9) at a central point, this intermediate fraction is at least partially condensed in indirect heat exchange with the refrigerant and is passed back (29) to the separation column (9).
  3. Process according to Claim 1 or 2, characterized in that the process is carried out with time-variable throughput and/or time-variable composition of the gas mixture (6) to be separated.
  4. Process according to Claim 3, characterized in that the throughput and/or the composition of the gas mixture (6) to be separated is measured (30) and the throughput of refrigerant in the various condensation stages (7; 7', 11, 15, 24) is set (25, 26,; 26a, 26b) as a function of this measured value.
  5. Process according to one of Claims 1 to 4, characterized in that a heat exchanger is used for the indirect heat exchange (11) between overhead fraction (10) and refrigerant, which heat exchanger is produced from a material having high long-term stability against mechanical stresses.
  6. Process according to one of Claims 1 to 5, characterized in that a heat exchanger is used for the indirect heat exchange (15) between the portion (14) which has remained in the gaseous state in the condensation of the overhead fraction and the gaseous fraction (20) of the refrigerant, which heat exchanger is produced from a material having high long-term stability to mechanical stresses.
  7. Process according to one of Claims 1 to 6, characterized in that a heat exchanger is used for the indirect heat exchange (7) between the gas mixture (6) to be fractionated and refrigerant, which heat exchanger is produced from a material having high-long term stability to mechanical stresses.
  8. Process according to one of Claims 1 to 7, characterized in that a plate heat exchanger is used for the indirect heat exchange (7') between the gas mixture (6) to be fractionated and refrigerant.
  9. Process according to Claim 8, characterized in that an aluminium plate heat exchanger is used for the indirect heat exchange (7') between the gas mixture (6) to be fractionated and refrigerant.
  10. Process according to one of Claims 2 to 9, characterized in that a heat exchanger is used for the indirect heat exchange (24) between the intermediate fraction (28) and the refrigerant, which heat exchanger is produced from a material having high-long term stability to mechanical stresses.
EP92917822A 1991-08-19 1992-08-13 Method of separating higher-boiling hydrocarbons out of a mixture of gases Expired - Lifetime EP0642649B1 (en)

Applications Claiming Priority (3)

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DE4127406A DE4127406A1 (en) 1991-08-19 1991-08-19 METHOD FOR REMOVING HIGHER CARBON HYDROCARBONS FROM A GAS MIXTURE
DE4127406 1991-08-19
PCT/EP1992/001857 WO1993004327A1 (en) 1991-08-19 1992-08-13 Method of separating higher-boiling hydrocarbons out of a mixture of gases

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EP0642649B1 true EP0642649B1 (en) 1996-01-10

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DE4235006A1 (en) * 1992-10-16 1994-04-21 Linde Ag Process for separating a feed stream consisting essentially of hydrogen, methane and C¶3¶ / C¶4¶ hydrocarbons
DE19526225C1 (en) * 1995-07-18 1997-01-02 Linde Ag Refrigerant circuit for cooling fluids
US7082787B2 (en) * 2004-03-09 2006-08-01 Bp Corporation North America Inc. Refrigeration system
US7833339B2 (en) 2006-04-18 2010-11-16 Franklin Industrial Minerals Mineral filler composition
US7651559B2 (en) 2005-11-04 2010-01-26 Franklin Industrial Minerals Mineral composition
WO2007144306A1 (en) * 2006-06-15 2007-12-21 Elcold Frysere Hobro Aps A refrigerant and a refrigeration system
RU2576934C1 (en) * 2015-02-24 2016-03-10 Андрей Владиславович Курочкин Fractioning refrigerator-condenser

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US4455158A (en) * 1983-03-21 1984-06-19 Air Products And Chemicals, Inc. Nitrogen rejection process incorporating a serpentine heat exchanger
US4501600A (en) * 1983-07-15 1985-02-26 Union Carbide Corporation Process to separate nitrogen from natural gas
DE3408760A1 (en) * 1984-03-09 1985-09-12 Linde Ag, 6200 Wiesbaden METHOD FOR DETERMINING C (DOWN ARROW) 3 (DOWN ARROW) (DOWN ARROW) + (DOWN ARROW) HYDROCARBONS
US4714487A (en) * 1986-05-23 1987-12-22 Air Products And Chemicals, Inc. Process for recovery and purification of C3 -C4+ hydrocarbons using segregated phase separation and dephlegmation

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