Classifications

• • 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
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
  • F25J3/0209—Natural gas or substitute natural gas
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—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
  • F25J3/0238—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 2 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
  • F25J3/028—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
  • F25J3/029—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 helium
• • 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
  • F25J2200/04—Processes or apparatus using separation by rectification in a dual 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
  • F25J2200/76—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
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/78—Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • 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
• • 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
  • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
  • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• • 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
  • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
  • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• • 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
  • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
  • F25J2290/40—Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.

Definitions

• the present invention relates to a method for separating the components of a gaseous mixture containing methane, nitrogen and hydrocarbons heavier than methane.
• the present invention therefore applies to denitrogenation processes of natural gas with or without helium recovery.
• Natural gas is desirable for use as a fuel for use in heating buildings, to provide heat for industrial processes for the generation of electricity, for use as a feedstock for various synthesis processes for produce olefins, polymers and the like.
• Natural gas is found in many areas that are remote from natural gas users. Natural gas typically consists of methane (C1), ethane (C2) and heavier compounds such as hydrocarbons having at least three carbon atoms, such as propane, butane ... (C3 +). Often it may be advantageous to separate C2 and C3 + from natural gas for commercialization as separate co-products.
• nitrogen Another component often found in natural gas is nitrogen.
• the presence of nitrogen in natural gas can lead to difficulties in meeting the specifications for natural gas (typically the minimum heating value to be met). This is all the more true when hydrocarbons heavier than methane (C2 and C3 +) are removed because they have a lower heating value than methane, so removing them reduces the lower calorific value than the methane. it may then be necessary to increase by means of nitrogen separation. As a result, considerable effort has been devoted to developing ways to remove nitrogen from natural gas.
• the exploited natural gas fields contain more and more nitrogen. This is particularly due to the depletion and scarcity of fields rich enough that no enrichment treatment is necessary before the marketing of gas.
• Unconventional resources such as shale gas also have the same problem: to make them marketable, it may be necessary to increase their calorific value by means of a treatment that consists in de-gasing the gas.
• cryogenic separation The most widely used method for separating nitrogen and hydrocarbons heavier than methane is "cryogenic separation".
• a cryogenic nitrogen separation process more specifically a method employing a double column, is described in patent application US-A-4778498.
• Natural gas denitrogen units generally treat gases that come directly from wells at high pressure. After denaturing, the treated gas must be returned to the network, often at a pressure close to its inlet pressure.
• NTL natural gas-associated liquids
• a first unit operates the separation of NGL (later called NGL unit) while a second unit separates nitrogen from natural gas (later called NRU unit).
• NGL unit operates the separation of NGL
• NRU unit separates nitrogen from natural gas
• the NRU has a refrigeration cycle
• the associated machines have limited reliability, and failure of a cycle compressor will cause the NRU to shut down, but without stopping the NGL.
• this scheme is limited in terms of efficiency since all the gas is during a treatment in an NGL separation unit, a large fraction (typically more than 10%) of the feed gas is condensed. During this condensation, methane is condensed with heavier hydrocarbons (C2 + and / or C3 +).
• demethanizer it is then typically necessary to use a column called demethanizer to reboil methane and not lose methane in C2 + and / or C3 + products. If nitrogen is present, it will however very little condensed and will be found mainly in the gas phase introduced into the demethanizer column.
• the inventors of the present invention have then bridged a solution to solve the problem raised above while optimizing energy costs such as those related to the power consumption during the implementation of such methods.
• the present invention relates to a process for separating the components of a gaseous mixture to be treated comprising methane, nitrogen and at least one hydrocarbon having at least two carbon atoms, or a mixture of these hydrocarbons, comprising the steps following:
• step b) introducing said first hydrocarbon-enriched liquid stream having at least two carbon atoms from step a) into a second distillation column to create, at the head of this column, a second gaseous stream rich in methane and in the tank; of this column, a second liquid stream comprising at least 85 mol% of the hydrocarbons having at least two carbon atoms initially present in the mixture to be treated;
• a portion of the second gas stream rich in methane from step b) at the outlet of the head of the second distillation column is compressed at a pressure greater than 1 bar at the pressure of the second distillation column then condensed to be introduced for a portion in the upper portion of the first distillation column and for the other portion in the upper portion of the second distillation column to reflux said distillation columns.
• an object of the present invention relates to:
• a process as defined above characterized in that a portion of the second gas stream is expanded in a turbine at a pressure at least 1 bar lower than the pressure of the distillation column.
• a process as defined above characterized in that the nitrogen content of said second gas stream is at least 1.5 times lower than the nitrogen content of the first gas stream.
• a process as defined above additionally containing step c): introducing said first methane-enriched gaseous stream from step a) into a denitrogenation unit to separate the nitrogen from the other components of this gaseous stream.
• a process as defined above characterized in that the second gaseous stream from step b) is not treated by the denitrogenation unit.
• a process as defined above characterized in that from 5 mol% to 30 mol% of the methane initially present in the gaseous mixture to be treated is included in the first hydrocarbon-enriched liquid stream having at least two carbon atoms resulting from the step at)
• a process as defined above characterized in that from 10 mol% to 20 mol% of the methane initially present in the gaseous mixture to be treated is included in the first hydrocarbon-enriched liquid stream having at least two carbon atoms resulting from the step at).
• step a) A method as defined above characterized in that prior to step a) it comprises the following steps:
• a process as defined above characterized in that said gaseous mixture to be treated comprises 70 mol% of methane, at least 4 mol% of nitrogen and 2 mol% of hydrocarbons having at least two carbon atoms.
• step b) the hydrocarbon-enriched liquid stream having at least two carbon atoms from step a) is introduced into said second distillation column at a theoretical stage below the head of said second column.
• the process of the invention makes it possible to separate a crude gas rich in C2 + and in nitrogen (typically at least 1% C2 + and at least 2% nitrogen).
• the method according to the invention typically comprises the following steps:
• Pre-treatment of the raw gas to be treated separation of water, CO2, methanol, heavy hydrocarbons for example.
• a stream 1 of pretreated natural gas (having typically undergone a separation of a part of at least one of the following constituents: water, CO 2 , methanol, sulfur compounds, very hydrocarbons heavy, that is to say having more than six or seven carbon atoms (such as C8 + for example)) comprising at least 30 mol% of methane, at least 0.1 mol% of hydrocarbons heavier than methane (i.e. comprising at least two carbon atoms) and between at least two 4 mol% and 50 mol%, or even 80 mol% of nitrogen is introduced into a system 2 allowing at least partial condensation of said stream 1.
• the pressure of this stream 1 is between 20 bara (absolute bar) and 100 bara (typically between 30 and 70 bara) and the temperature is close to room temperature, for example between 0 ° C and 60 ° C.
• the system 2 is for example a heat exchanger.
• the mixture 3 leaving this system 2 is in a two-phase state (gas and liquid). This mixture 3 is introduced into a phase separator pot 4.
• the operating pressure is between 20 and 100 bara, typically between 30 and 70 bara.
• the temperature of this pot is between -100 ° C and 0 ° C, typically between -80 ° C and -20 ° C.
• At least a portion 8 'of the gas phase 8 from the separator pot 4 is expanded by means of a turbine 9.
• the flow from the turbine 9 is introduced into a first distillation column 7 at a stage 10 located in the part lower of said column 7.
• the liquid phase 5 coming from the separator pot 4 is expanded through a valve 6 and then injected at a pressure of between 10 bara and 40 bara and a temperature for example between -1 10 ° C. and -30 ° C. a demethanizer column 7 ', hereinafter also called second distillation column.
• This liquid phase 5 is introduced at a theoretical stage 10 'below the head of said column T.
• a liquid stream 12 of hydrocarbons heavier than methane is recovered in the lowest part 16 (in the tank) of column T.
• a reboiler 1 1 is placed at a level to reboil the bottom liquid of the column 7 'in order to heat a portion of the liquid of said column in order to adjust the maximum threshold of methane contained in the stream 12 of hydrocarbons heavy.
• At least 50% (typically at least 85%) molar heavy hydrocarbons present in the gaseous mixture 1 to be treated are recovered in this stream 12. Preferably at least 90% is recovered.
• the hydrocarbon liquid stream 12 does not contain more than 1 mol% of methane.
• a gas stream 15 enriched in methane typically containing less than 0.5 mol% of hydrocarbons having more than two carbon atoms ( containing not more than half the amount of heavy hydrocarbons - having more than 2 carbon atoms - present in the feed gas) is extracted.
• the temperature of the gas stream is less than -80 ° C.
• a liquid stream 39 is extracted to be introduced into said second distillation column 7 'at a stage 10 "substantially at the same level as that 10' where the liquid phase 5 coming from the phase separator pot 4.
• This liquid stream 39 from the first distillation column 7 is depleted in nitrogen (typically containing less than 10%, preferably less than 5%), as is the liquid phase 5 from the separator pot 4.
• nitrogen-depleted gas means a gas stream having a nitrogen content less than half the nitrogen content of the initial gas stream 1 to be treated and preferably less than a quarter of this content. As a result, very little nitrogen is introduced into the second distillation column 7 '.
• demethanizer column is meant a distillation column for producing at least two streams of different composition from a feed stream to be treated according to the method of the present invention.
• the at least two streams are the following: one at the top of the gaseous column, depleted in hydrocarbons having at least two carbon atoms, that is to say comprising less than half of the so-called heavy hydrocarbons contained in the feed gas (ethane, propane, butane, etc.) and the other, in the bottom of the column, in liquid form, depleted of methane present in the feed stream to be treated.
• the stream 39 is a liquid comprising mainly methane and a minority of ethane and propane and contains virtually no nitrogen.
• demethanization unit any system comprising at least one distillation column to enrich the methane in the overhead gas and to lower the methane tank liquid.
• the gaseous stream 15 ' is extracted at the top 14' of the second distillation column 7 'at a temperature between -80 ° C and -120 ° C and at a pressure greater than 10 bara (typically between 15 bara and 30 bara ).
• Part of this gaseous stream 15 ' is introduced into a heat exchanger 17 so as to be heated to a temperature of between -50 ° C and -110 ° C and is then introduced into a turbine 43 before joining a current It is enriched in methane at the outlet of denitrogenation unit A and is produced at the end of the process as a natural gas.
• the pressure of this natural gas produced is for example between 15 bara and 30 bara (before re-compression) and the temperature is higher than 0 ° C. after reheating in the exchanger 2.
• This condensation is achieved by means of a heat exchanger 17 fed by a portion 8 "of the gas stream 8 from the phase separator pot 4 and by a portion 44 of the gas stream 15 'extracted from the head 14' of the second distillation column 7 '.
• this gas stream 44 is compressed using a compressor 46, ideally a cold compressor, that is to say whose temperature is below 0 ° C. . It is this compressed current 45 which supplies the heat exchanger 17.
• the power of the compressor 46 can advantageously come from the turbine 43, which makes it possible to optimize the compression.
• the pressure of the stream 44 is increased by a few bara only so that the stream 45 can be recondensed against the current.
• the reflux of the second distillation column 7 ' is ensured, in the same way as for the reflux of the first distillation column 7, by the introduction into its upper part 41 of at least one stream 18c which has been cooled in exchanger 17 and expanded by means of, for example, at least one valve 19c.
• the use of a part 44 of the gas stream 15 'enriched in methane and not containing nitrogen makes it possible not to have to recycle flows in order to increase the yield of C2 + products.
• the gas stream enriched in methane 15 from the head 14 of the distillation column 7 is partially condensed by means of, for example, a heat exchanger 21. At the outlet of this exchanger 21, a two-phase (gas-liquid) stream 22 (comprising from 20% to 80 mol% of gas) emerges.
• the temperature of the stream 15 is kept below -80 ° C (or even below -100 ° C) and said stream 15 is directly in the heat exchanger 21 to obtain the stream 22.
• the diphasic current 22 is, after a possible expansion in a valve or a turbine 23, introduced into a phase separator pot 25.
• the liquid phase 29 from the phase separator pot 25 is, after a possible expansion, heated through the heat exchangers 27 and 21 and finally 2 to join the output stream 30 of methane-rich gas produced at the output of the process.
• the outlet stream contains less than 5 mol% of nitrogen.
• the gaseous phase 26 coming from the separator pot 25 is partially condensed in a heat exchanger 27 and then expanded at the outlet of said exchanger 27 by means of a turbine or a valve 28 before being introduced into a distillation column 31.
• the distillation column 31 is a so-called "stripping" column of nitrogen for the purpose of separating the nitrogen from the liquid enriched in output methane, also called denitrogenation column.
• the methane-enriched liquid comprises less than 5 mol% of nitrogen. This is a distillation column joined to a reboiler 32 but does not have an associated condenser system.
• a stream 33 very rich in methane in liquid form is extracted.
• This stream 33 contains less than 5 mol% of nitrogen, preferably less than 4%.
• the liquid stream 33 is then mixed with the liquid phase 29 from the phase separator pot 25 and follows the same path to the output streams 30, 30 '.
• a nitrogen-rich gas stream 36 at a temperature below -1 10 ° C is produced.
• Said stream 36 rich in nitrogen comprises at least 20 mol% of nitrogen.
• the nitrogen-rich stream 36 is heated through the successive exchangers 27, 21 and then 2. It can also be a single exchanger according to a particular embodiment of the invention. And according to another particular embodiment of the invention, more than three exchangers can be implemented.
• the denitrogenation system B aims to produce a gaseous flow even richer in nitrogen than the stream 37.
• This system B may for example include at least one separator pot and a denitrogenation column.
• the nitrogen specification at the outlet of system B is strict ( ⁇ 100ppm typically), it may be necessary to add a cycle compressor, for example a nitrogen or methane compressor, to the system B. provide the necessary reflux to obtain nitrogen purity at the top of the B system denazotation column.
• a cycle compressor for example a nitrogen or methane compressor
• NRU unit has been described in this figure, but the method of the present invention applies to any type of NRU unit downstream of a unit called NGL.
• the method which is the subject of the present invention makes it possible to achieve savings in terms of electrical consumption for example. Indeed, only a part of the methane included in the gas to be treated is sent to a NRU unit, because the other part which is in the tank of the first distillation column in liquid form does not contain nitrogen so that the NRU unit downstream of the NGL unit is much less loaded.
• the method that is the subject of the present invention enables the device that will implement it to process a lower flow rate because the recycling from the outside necessary in the usual methods of the state of the art is eliminated: only the flow rate of the gaseous mixture to treat 1 is used. This may represent a saving of gas usually used for the reflux of the distillation columns of the order of 10%.

Landscapes

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

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=55022582

Family Applications (1)

Country Status (4)

Families Citing this family (4)

Citations (6)

Family Cites Families (6)

• 2015
  • 2015-11-03 FR FR1560528A patent/FR3042983B1/fr active Active
• 2016
  • 2016-09-29 EA EA201891032A patent/EA035004B1/ru not_active IP Right Cessation
  • 2016-09-29 WO PCT/FR2016/052489 patent/WO2017077203A1/fr active Application Filing
  • 2016-09-29 US US15/773,431 patent/US20180320960A1/en not_active Abandoned

Patent Citations (6)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events