CN105823303A

CN105823303A - Improved separation of heavy hydrocarbons and NGLs from natural gas, and in integration with liquefaction of natural gas

Info

Publication number: CN105823303A
Application number: CN201610042600.3A
Authority: CN
Inventors: T.特隆; G.克里什纳墨菲; M.J.罗伯茨
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 2015-01-23
Filing date: 2016-01-22
Publication date: 2016-08-03
Also published as: AU2016200259B2; EP3048400A3; US20160216030A1; CN205619689U; EP3048400A2; JP6272921B2; AU2016200259A1; RU2016101593A; CA2918562A1; PE20160944A1; KR20160091268A; KR101724228B1; JP2016136083A

Abstract

Described herein is a method of and system for fractionating and liquefying a natural gas feed stream. The natural gas is first fractionated in a scrub column. The overhead vapor from the scrub column is cooled, condensed and divided to form a first, a second and at least one further stream of liquefied first overhead. The first stream of liquefied first overhead is returned to the scrub column as a reflux stream. The second stream of liquefied first overhead forms an LNG product. The further stream of liquefied first overhead is used to provide or generate reflux for a de-methanizer column used to fractionate the bottoms liquid from the scrub column.

Description

Heavy hydrocarbon separates from the improvement of natural gas with NGL, integrates with natural gas liquefaction

Background

The present invention relates to the method and system for fractional distillation and liquefied natural gas feed stream.

Heavy hydrocarbon (HHC) is removed from natural gas, such as C6+ hydrocarbon (have 6 or more carbon atom), the most usual, the liquefaction of natural gas is substantially in order to be reduced to certain level by these compositions concentration in natural gas, and wherein these compositions will not occur condensation in main heat exchanger.C2-C5+ hydrocarbon (having 2-5 or the hydrocarbon of more carbon atom) is also known as liquefied natural gas (NGL) in the art, generally also separates from natural gas, because they have high market value, and can therefore sell separately.Additionally, due to NGL has more higher calorific value than methane, it may be necessary to reduce NGL composition level in natural gas to make LNG product meet the product specification of regulation.When comprising one or more hydrocarbon cryogens for the cold-producing medium of gas deliquescence process, such as, especially when using ethane and/or the cascade of propane or cool dose of mixing cause is cycled to used in liquefaction process, also can expect to use the NGL composition (such as ethane or propane) separated to supplement as cryogen.Traditionally, distillation column has been used for this purpose.

Fig. 1 schematically depict the conventional configuration for fractional distillation and liquefied natural gas feed stream.Natural gas feed stream 101, pretreatment is to remove sour gas, water and hydrargyrum, and the most optionally precool in one or more heat exchangers, it is introduced to scrubbing tower 10, is separated into the overhead vapours of methane rich wherein and rich in the bottom liquid of the hydrocarbon heavier than methane.Take out vapor stream of top of the tower 202 from the top of scrubbing tower, and take out bottom liquid stream 103 from the bottom of scrubbing tower.

Vapor stream of top of the tower 202 sends to the warm bundle 22 around tubular type main heat exchanger 20, wherein said stream partial condensation.Then take out the stream 203 of partial condensation from warm bundle and phase separator 28, be separated into its liquid and vapor phase to produce liquid stream 120 and steam stream 207.Steam stream 207 sends the middle bundle 24 to main heat exchanger, and wherein said stream cools down further and liquefies, and described fluidized flow 204 is then supercool in the cold bundle 26 of main heat exchanger, produces LNG product stream 205.LNG product stream 205 can flash distillation being sent in LNG storage tank 30, steam gas (BOG) or flash gas 401 to be sent to fuel header (header) by described groove, through burning or recirculation (not shown) to vapor stream of top of the tower 202, charging is to main heat exchanger.Liquid stream 120 is back to the top of scrubbing tower 10 as backflow stream from phase separator 28, in order to provide the backflow that scrubbing tower operation is required.If the amount of the backflow produced is more than needed for scrubbing tower, a part of liquid stream 120 can be with the middle bundle 24 flowing 207 hybrid concurrencies and delivering to main heat exchanger.

From the bottom liquid stream 103 of scrubbing tower 10 rich in NGL and HHC, expanded being subsequently sent to the domethanizing column of fractionation unit so that described stream part evaporation, described stream stands further fractional distillation/separation wherein.In the layout that Fig. 1 illustrates, fractionation unit comprises domethanizing column (herein also referred to as DeC1 tower), dethanizer (herein also referred to as DeC2 tower), depropanizing tower (herein also referred to as DeC3 tower), and debutanizing tower (herein also referred to as DeC4 tower).Generally, these towers comprise multistage with improve HHC and NGL separate with the lighter component of methane and natural gas.

Bottom liquid 103 from scrubbing tower is separated into the overhead vapours of methane rich and rich in the bottom liquid of the hydrocarbon heavier than methane by domethanizing column 12.Overhead vapours partly condenses to produce the liquid reflux stream being back to domethanizing column 12 in overhead condenser, and the most remaining vapor portion takes out as vapor stream of top of the tower 104 from domethanizing column.A part for bottom liquid heats to provide the upflowing vapor (boil-up) of domethanizing column 12 in reboiler, and the remainder of bottom liquid takes out as stream 105, expands partly to vaporize described stream, and is sent to dethanizer 14.

The dethanizer 14 and then bottom liquid 105 from domethanizing column is separated into the overhead vapours of rich ethane and rich in the bottom liquid of the hydrocarbon heavier than ethane.Overhead vapours condenses in overhead condenser, and a part for the overhead materials of condensation is back to dethanizer 14 as backflow stream, and remainder takes out the liquefaction overhead stream 106 as rich ethane.A part for bottom liquid heats to provide the upflowing vapor of dethanizer 14 in reboiler, and the remainder of bottom liquid takes out as stream 107, expands and is sent to depropanizing tower 16.

Depropanizing tower 16, is operated by the mode similar with dethanizer, and then the bottom liquid 107 from dethanizer separates the overhead stream 108 of liquefaction to provide rich propane and the bottom liquid stream 109 rich in the hydrocarbon than propane more weight.Similarly, debutanizing tower 18, operate by the mode similar with dethanizer, then the bottom liquid 109 from depropanizing tower is separated the overhead stream 108 of liquefaction to provide rich butane and the bottom liquid stream 111 rich in the hydrocarbon than butane more weight.

Overhead stream 106,108 and 110 from the liquefaction of tower DeC2, DeC3 and DeC4 each mainly comprises ethane, propane and butane, and from the stream that bottom liquid 111 is rich C5+ (pentane and heavier hydrocarbon) of tower DeC4, these NGL streams can be sold as mentioned above or be used as cryogen in due course and supplement.In some cases, one or more these stream fractions also can reinject to LNG product stream with by the adjustment heat value of LNG product stream to optimal value.

As it has been described above, tower DeC1, DeC2, DeC3 and DeC4 are each equipped with overhead condenser, it is by condensing at least some of of overhead vapours, thus provides the liquid reflux stream being back to top of tower, produces the backflow of tower.There are these overhead condensers and add installation and the capital cost of the system of maintenance.But, remove overhead condenser and unwanted composition will be caused to carry to vapor stream of top of the tower.Condenser improves separation efficiency, and it is especially advantageous to have this condenser in DeC1 and DeC2 tower.The temperature of required cold reflux stream depends on the composition of natural gas flow.NGL content is the lowest, needs backflow stream the coldest, effectively to be isolated to liquid condensate stream by required NGL and HHC composition.Removing overhead condenser from DeC1 and DeC2 tower will cause ethane and propane to carry to from the vapor stream of top of the tower of DeC1 and DeC2 respectively.This is present in causing ethane to lose with DeC1 overhead materials and similarly result in extra propane in DeC2 overhead materials, and therefore the purity to the ethane in DeC2 overhead materials adversely affects (similarly adversely affecting its purposes as supplementary cryogen and/or the value as commodity).

Generally, propane is used as cryogen for providing the refrigeration duty of the overhead condenser used by DeC1 tower.Especially, such layout considers for using propane pre-cooling mixed cooling medium (C3MR) circulation but, and in fractional distillation that therefore propane refrigeration is the most easily applied and liquefaction system.

US2012/0090350A1 describes thermal value control system and the method for LNG product in middle natural gas liquefaction device.Natural gas feed stream, after initial pretreatment, is incorporated into scrubbing tower so that natural gas feed to be separated into overhead vapours and the bottom liquid of rich C3+ of lean C5+.The refluxing portion ground of scrubbing tower provides by using the overhead condenser of low-pressure propane refrigeration.Vapor stream of top of the tower from scrubbing tower sends and is used for liquefying to liquefaction device, and bottom liquid stream liquid stream of fractional distillation liquid stream with rich C4+ to provide rich C3 in NGL fractionation unit.

US6,662,589 and US2006/0260355A1 describe procedure below, and wherein natural gas feed stream is incorporated into scrubbing tower so that natural gas feed to be separated into overhead vapours and bottom liquid after initial pretreatment.The vapor stream of top of the tower taken out from scrubbing tower cools down in the warm district of main heat exchanger and partly condenses, then in phase separator, it is separated into liquid phase, it is back to the top of scrubbing tower as liquid reflux stream, and remaining vapor phase cools down further in the cold-zone of main heat exchanger and condenses to provide LNG product.The bottom liquid stream taken out from scrubbing tower NGL fractionation unit (comprising dethanizer, depropanizing tower and debutanizing tower) fractional distillation to provide the liquid stream of rich C3, C4 and C5+, and the steam stream of rich C1 and C2.The steam stream of rich C1 and C2 condenses to provide other LNG product in main heat exchanger.

US2008/0115532A1 described before natural gas liquefaction for removing the operation of the scrubbing tower of heavier hydrocarbon composition from natural gas flow.Backflow for scrubbing tower can be provided by the condensate of overhead condenser and/or LNG stream.

US2008/0016910A1 and US2013/0061632A1 describes procedure below, and wherein the natural gas feed stream of pretreatment is incorporated in scrubbing tower natural gas feed is separated into overhead vapours and bottom liquid.The vapor stream of top of the tower taken out from scrubbing tower cools down in the warm district of main heat exchanger and condenses.Then, condensate flow is divided into two streams, and a stream is back to the top of scrubbing tower as liquid reflux stream, and another is supercool to provide LNG product stream in the cold-zone of main heat exchanger.From scrubbing tower take out bottom liquid stream NGL fractionating system fractional distillation to provide C2, C3 and C4 product stream.

US4,065,278, CA1059425 and US5,659,109 describe the process producing LNG, wherein it is similar to US6, process described in 662,589 and US2006/0260355A1, the fractional distillation in scrubbing tower of the natural gas feed stream of pretreatment, with by partial condensation scrubbing tower overhead materials in main heat exchanger and as liquid reflux stream, the liquid phase of separation is back to scrubbing tower provides the backflow to scrubbing tower, at least some of cooling further of remaining vapor phase and condensation are to provide LNG product.

US4,445,917 describe the process producing LNG, wherein it is similar to the process described in 2008/0016910A1 and US2013/0061632A1, the fractional distillation in scrubbing tower of the natural gas feed stream of pretreatment, scrubbing tower overhead materials total condensation, then separately to provide LNG stream and to be back to the liquid reflux stream at scrubbing tower top.

US5,956,971 teach the process producing LNG, and wherein first natural gas feed processes in the fractionating column with controlled condensing zone.

US2007012071 describes process and the system producing LNG, and wherein the natural gas feed of pretreatment is separated into overhead materials and the bottom liquid of rich C2+ of methane rich in fractionating column.Overhead stream is condensed, cools down further, and then flash distillation is to produce LNG stream and flash gas.Flash gas is used as cryogen in main heat exchanger.Then a part for the flash gas of temperature recompresses, cooling, condenses and be incorporated into as backflow stream the top of fractionating column.

US5,588,308 describe the process removing NGL from natural gas flow, and wherein natural gas feed partly condenses and be separated into liquid and vapor phase, and vapor phase provides product of natural gas, and liquid phase is incorporated in stripper and fractional distillation is flowed with offer NGL in stripper.

US2004/0200353A1 describes the process using scrubbing tower to remove NGL from natural gas feed, providing back up through overhead condenser of described scrubbing tower.

Expect that the method and system with improvement is for fractional distillation and liquefied natural gas feed stream.

Summary

According to the first aspect of the invention, it is provided that fractional distillation and liquefied natural gas feed stream method, described method comprises:

A described natural gas feed stream is introduced to scrubbing tower by (), described natural gas feed stream is separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane wherein, described vapor fraction is collected as the first bottom liquid in described wash tower bottoms as the first overhead vapours, described liquid distillate at described scrubbing tower collected overhead；

B () takes out the first vapor stream of top of the tower from the top of described scrubbing tower, and cool down, condense and by described stream separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction；

C the described first-class of first overhead materials of liquefaction is back to described scrubbing tower by (), be incorporated into the top of described scrubbing tower as backflow stream, thus provide the backflow of described scrubbing tower；

D () is formed liquefied natural gas (LNG) product stream by the described second of the first overhead materials liquefied；

E () is taken out the first bottom liquid stream by the bottom of described scrubbing tower, and described stream is introduced to domethanizing column, described first bottom liquid stream is separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane wherein, described vapor fraction is collected as the second overhead vapours at described demethanizer overhead, and described liquid distillate is collected as the second bottom liquid at described demethanizer bottom；With

F () is refluxed to the offer of described domethanizing column by following:

(1) one of other stream described in the first overhead materials of liquefaction is introduced to as backflow stream the top of described domethanizing column；And/or

(2) by with one of other stream indirect heat exchange described in the first overhead materials of liquefaction, condense a part for described second overhead vapours to form the second overhead stream of the liquefaction as the top that backflow stream is re-introduced into described domethanizing column.

According to the second aspect of the invention, it is provided that for fractional distillation and the system of liquefied natural gas feed stream, described system comprises:

Scrubbing tower, described scrubbing tower is arranged and operation is used for receiving described natural gas feed stream, and be methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane by described flow separation, described vapor fraction is collected as the first bottom liquid in described wash tower bottoms as the first overhead vapours, described liquid distillate at described scrubbing tower collected overhead；

Pipeline group, one or more heat exchangers, the most one or more separators, it is arranged and operation is flowed for the first vapor stream of top of the tower being taken out from the top of described scrubbing tower and cooled down, condenses and separate at least one of first-class, the second of the first overhead materials that liquefies of the first overhead materials to form liquefaction and the first overhead materials of liquefaction；

Pipeline, it is arranged and operation is for being back to described scrubbing tower by the described first-class of the first overhead materials of liquefaction, is incorporated into the top of described scrubbing tower as backflow stream, thus provides the backflow for described scrubbing tower；

Pipeline, it is arranged and operation is for taking out liquefied natural gas (LNG) product stream formed by the second of the first overhead materials liquefied from described system；

Domethanizing column, it is arranged and operation is for from bottom reception first bottom liquid stream of described scrubbing tower, and be methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane by described flow separation, described methane rich vapor fraction is collected as the second overhead vapours at described demethanizer overhead, and the described liquid distillate rich in the hydrocarbon than methane more weight is collected as the second bottom liquid at described demethanizer bottom；

Pipeline, it is arranged and operation for taking out the first bottom liquid stream from the bottom of described scrubbing tower, and described stream is introduced to domethanizing column；With

One below or both:

(1) pipeline, it is arranged and operation for being introduced to the top of described domethanizing column using one of other stream described in the first overhead materials of liquefaction as backflow stream, thus provides the backflow of described domethanizing column；

(2) heat exchanger, its arrange and operation for by with one of other stream indirect heat exchange described in the first overhead materials of liquefaction, part condensation by described second overhead vapours forms the second overhead stream of liquefaction, it is re-introduced into the top to described domethanizing column as backflow stream, thus the backflow of described domethanizing column is provided, and arrange and operation will be for being introduced to the pipeline of described heat exchanger by other stream described in the first overhead materials of liquefaction.

Accompanying drawing is sketched

Fig. 1 is natural gas fractional distillation and liquefaction system and the schematic flow diagram of method describing contrast, not according to the present invention.

Fig. 2 is to describe according to the natural gas fractional distillation of embodiment of the present invention and liquefaction system and the schematic flow diagram of method.

Fig. 3 is to describe natural gas fractional distillation according to another embodiment of the invention and liquefaction system and the schematic flow diagram of method.

Fig. 4 is to describe natural gas fractional distillation according to another embodiment of the invention and liquefaction system and the schematic flow diagram of method.

Fig. 5 is to describe natural gas fractional distillation according to another embodiment of the invention and liquefaction system and the schematic flow diagram of method.

Fig. 6 is to describe natural gas fractional distillation according to another embodiment of the invention and liquefaction system and the schematic flow diagram of method.

Fig. 7 is to describe natural gas fractional distillation according to another embodiment of the invention and liquefaction system and the schematic flow diagram of method.

Describe in detail

The invention provides new option for providing backflow/condensation load to integrating in the domethanizing column having natural gas liquefaction.

More specifically, as mentioned above, according to the first aspect of the invention, the method providing fractional distillation and liquefied natural gas feed stream, wherein the overhead vapours from scrubbing tower top cools down, condenses and separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction.The first-class of first overhead materials of liquefaction is re-introduced into scrubbing tower to provide the backflow of scrubbing tower, the LNG product needed for the second offer of the first overhead materials of liquefaction, and other stream of the first overhead materials of liquefaction is for providing or produce the backflow of domethanizing column.

Especially, in preferred embodiments, other stream (other stream of the scrubbing tower overhead materials i.e. liquefied) of the first overhead materials of liquefaction is introduced to the top of domethanizing column as backflow stream, thus provides the backflow of described tower.

Describe with Fig. 1 and compared with above-mentioned conventional configuration, this advantageously allows to remove the overhead condenser for domethanizing column, thus substantially reduces the fund cost of described method and system.

Additionally, first overhead materials (the scrubbing tower tower top i.e. liquefied) of liquefaction is generally colder than condensed overhead materials, the overhead materials of described condensation can be raw by condensing demethanizer column overhead produce in the overhead condenser of propane-cooled.Such as, can be by the minimum temperature backflow stream typically about-31 DEG C using the condensation of propane still to obtain from the overhead materials of domethanizing column, even and if-40 DEG C or following backflow stream generally obtain for the cryogen of main heat exchanger when the scrubbing tower overhead materials being only partially condensate in main heat exchanger or use.Thus, use the first overhead stream of liquefaction as backflow stream in domethanizing column, rather than use the overhead condenser of propane-cooled to make described demethanizer reflux, generally improve methane in domethanizing column to separate with ethane and more heavy constituent, itself and then raising response rate of ethane in the bottom liquid of domethanizing column.

In another embodiment, the backflow of domethanizing column is as provided below: by the first overhead materials with liquefaction (i.e., liquefaction scrubbing tower overhead materials other stream) other stream indirect heat exchange, make a part for the second overhead vapours (i.e., overhead vapours from domethanizing column) condensation, to form the second overhead stream being re-introduced into the liquefaction to demethanizer overhead as backflow stream.

In the present embodiment, it is still desirable to special overhead condenser is used for domethanizing column, the capital cost saving obtained by previous embodiment can not therefore be obtained.But, the present embodiment remains and generally uses colder stream to produce the benefit of the backflow of demethaniser, because domethanizing column still uses the scrubbing tower overhead stream of liquefaction to provide for making the cooling load of demethanizer reflux rather than using propane refrigerant to provide described cooling load in the present embodiment.When propane is not precooling cryogen and possibility is unavailable, the present embodiment is also useful.Thus, the present embodiment still separates with ethane and more heavy constituent and to provide benefit improving methane in domethanizing column.

Article " one " and " a kind of ", as used herein and unless otherwise described, refer to one or more when applying any feature in embodiment of the present invention that specification and claims describe.The use of " one " and " a kind of " is not restricted to refer to single features, unless shown this restriction especially.Article before odd number or plural noun or noun phrase " is somebody's turn to do " represent specially appointed feature and can have the connotation of odd number or plural number, depends on the context using this word.

As used herein, term " natural gas feed stream " also includes comprising synthesis and/or substituting the stream of natural gas.Natural gas be mainly composed of methane (it generally comprises at least about 85 moles % of feed stream, the most at least about 90 moles %, and the most about 95 moles of %).Natural gas feed stream is possibly together with other heavier hydrocarbon less amount of, such as ethane, propane, butane, pentane etc..Other typical composition of raw gas includes one or more compositions, such as nitrogen, helium, hydrogen, carbon dioxide and/or other sour gas, and hydrargyrum.But, the most preprocessed according to the natural gas feed stream that the present invention processes, if as required to reduce the level of any (relatively) high-solidification point composition, such as moisture, sour gas and hydrargyrum, reduce level necessary to the solidification to the scrubbing tower making to avoid natural gas feed stream to introduce or other operational issue.

As used herein, term " methane rich " refers to stream, fraction or the part comprising methane as its main component.Described stream, fraction or part can have especially and be similar to or more higher methane concentration than natural gas feed stream.Therefore, generally, described stream, fraction or part comprise at least about 85 moles %, the most at least about 90 moles % and the most about 95 moles of % or the methane of greater than about 95 moles of %.

As used herein, term " hydrocarbon heavier than methane " refers to the hydrocarbon with (i.e. higher boiling point) lower than methane volatility.Similarly, term " hydrocarbon heavier than ethane " refers to the hydrocarbon with (i.e. higher boiling point) lower than ethane volatility, and term " hydrocarbon heavier than propane " refers to the hydrocarbon with (i.e. higher boiling point) lower than propane volatility, etc..

As used herein, term " hydrocarbon rich in heavier than methane " refers to relative to natural gas feed stream, rich in stream, fraction or the part of the hydrocarbon heavier than methane, the hydrocarbon heavier with the ratio methane therefore compared with natural gas feed stream with higher mole of %.Similarly, term " rich ethane " refers to relative to natural gas feed stream, rich in stream, fraction or the part of ethane, etc..

As used herein, term " indirect heat exchange " refers to the heat exchange between two fluids, and wherein said two fluids keep by some form of physical barrier separating each other.

In one embodiment, step (b) according to first aspect comprises is taken out the first vapor stream of top of the tower by the top of described scrubbing tower, cool down and partly condense described stream, the liquid of isolated and vapor phase, separately the liquid phase of described separation is to form at least one other stream of the first overhead materials of the first-class of the first overhead materials of liquefaction and liquefaction, cool down and condense vapor phase at least some of of described separation further, to form the second of the first overhead materials of liquefaction.Preferably, the second of the first overhead materials of liquefaction is the most supercool, then forms LNG product stream.

In another embodiment, the step (b) of the method according to first aspect comprises is taken out the first vapor stream of top of the tower by the top of described scrubbing tower, flow described in cooling and partial condensation, the liquid of isolated and vapor phase, the first-class of the first overhead materials of liquefying is formed by the liquid phase separated at least some of, cool down and condense vapor phase at least some of of described separation further, and the stream of the cooling further that is made available separately and condensation is with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of liquefaction.Preferably, the second of the first overhead materials of liquefaction is the most supercool, then forms LNG product stream, or cooling and condensation flow through cold, then separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of liquefaction.

In another embodiment, according to first aspect, the step (b) of this method comprises the combination of first the first two embodiment.

In the above-described embodiment, preferably wound tube heat exchanger is for cooling down and condense the vapor phase of described separation further.Therefore, in one embodiment, the first vapor stream of top of the tower from scrubbing tower top can cool down and partial condensation in the warm bundle of tubular type main heat exchanger, and at least some of of the vapor phase separated is cooling down further in the middle bundle and/or cold bundle of tubular type main heat exchanger and condensing.In another embodiment, the first vapor stream of top of the tower from described scrubbing tower top can cool down in overhead condenser heat exchanger and partly condense, and at least some of of the vapor phase of described separation is cooling down and condensation in tubular type main heat exchanger further.

In another embodiment, the step (b) of the described method according to first aspect comprises takes out the first vapor stream of top of the tower from the top of described scrubbing tower, cooling and condense described stream, and by the stream of described cooling and condensation separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction.

In the present embodiment, the stream cooling down and condensing is supercooled, then separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction.Alternatively, the stream of described cooling and condensation can separate first-class and another liquid stream of the first overhead materials to form liquefaction, described liquid stream is the most supercool, other stream of at least one of the second of the first overhead materials then separately liquefied with formation and the first overhead materials of liquefaction.Alternatively, then the second of the first overhead materials of liquefaction is supercooled forms LNG product stream.

In the present embodiment, preferably wound tube heat exchanger for cooling and condenses the first vapor stream of top of the tower from described scrubbing tower top.

According to the method for first aspect, other stream being preferably used as liquefaction the first overhead materials first-class of backflow stream and liquefaction the first overhead materials for step (f) in step (c) has the flow-rate ratio of at least about 9:1.

Therefore, the first flow velocity of liquefaction the first overhead materials being preferably used as backflow in step (c) is about 9 times of the flow velocity of other stream of liquefaction the first overhead materials for step (f) or more than 9 times, identical benchmark contrasts (such as mass velocity specific mass flow velocity, or molar flow rate ratio mole flow velocity etc.).The most described method uses other stream other stream as the first overhead materials of backflow and liquefaction of the first overhead materials of liquefaction in step (f), by indirectly heating in those embodiments of the part condensing the second overhead vapours, 9 times of the combination flow velocity that the first flow velocity of liquefaction the first overhead materials being preferably used as backflow stream in step (c) is other stream described in two for liquefaction first overhead materials of step (f) or be more than 9 times.

According in the method for first aspect, other stream being preferably used as liquefaction the first overhead materials first-class of backflow stream and liquefaction the first overhead materials for step (f) in step (c) each has about-40 DEG C or following temperature.

In preferred embodiments, the first overhead vapours and the methane of each self-contained at least about 95 moles of % of the second overhead vapours.

In preferred embodiments, the second bottom liquid comprises the methane of less than about 5 moles of %.

In one embodiment, described method also comprises: taken out the second vapor stream of top of the tower by the top of domethanizing column；Cooling and condense all or part of of described stream to form other LNG product；And/or all or part of of described stream is used as fuel stream；And/or all or part of of described stream exports as gaseous natural gas product stream.

In one embodiment, described method also comprises is taken out the second bottom liquid stream by the bottom of described domethanizing column, and by the second bottom liquid stream fractional distillation to provide one or more natural gas liquids (NGL) stream.

In one embodiment, the step of fractional distillation the second bottom liquid stream comprises: described stream is introduced to dethanizer, wherein the second bottom liquid stream is separated into rich ethane fraction and the fraction rich in the hydrocarbon heavier than ethane, described rich ethane fraction at the collected overhead of dethanizer as the 3rd overhead vapours, the described fraction rich in the hydrocarbon than ethane more weight at the bottom collection of dethanizer as the 3rd bottom liquid.Described method can further include: takes out the 3rd vapor stream of top of the tower from the top of described dethanizer, and cools down and condense described stream to form NGL stream；And/or take out the 3rd bottom liquid stream from the bottom of dethanizer, and formed one or more NGL stream by it.Described method also can comprise the dethanizer that is back to as provided below: by the part with other stream indirect heat exchange condensation the 3rd overhead vapours of the first overhead materials of liquefaction, form the 3rd overhead stream of liquefaction, be re-introduced into the top to described dethanizer as backflow stream.Preferably, the 3rd overhead vapours comprises the ethane of at least about 95%.Preferably, the 3rd bottom liquid comprises the ethane of less than about 5 moles of %.If it is required, the 3rd bottom liquid can such as further fractional distillation in depropanizing tower and/or in debutanizing tower, further described 3rd bottom liquid to be separated into rich propane fraction, rich butane fraction and/or rich in pentane and the fraction of heavier hydrocarbon.

As known in the art, term " scrubbing tower ", " domethanizing column " and " dethanizer ", " depropanizing tower " and " debutanizing tower " refer to the type of distillation column.Term " distillation column " refers to the tower containing one or more separation levels, is made up of the device of such as filler or column plate, and it strengthens contact and therefore improves inside tower the mass transfer between rising steam and the liquid stream flowed downward upwards.In this way, in top of tower is collected as the rising steam of overhead vapours, the concentration of lighter component (the highest volatility and relatively low boiling point) increases, and the concentration of heavier composition (the most relatively low volatility and higher boiling point) increases in tower bottom collection is as the dropping liq of bottom liquid." top " of distillation column refers at the separation level pushed up most or the part of tower thereon." bottom " of tower refers to the part of the tower at the separation level at the end or under it." centre position " of tower refers to the position between the top and bottom of tower, separates between level at two.

In the case of scrubbing tower, natural gas feed stream is introduced to (as gaseous flow or as the two phase flow of partial condensation) scrubbing tower, in the centre position of tower, or more generally, in the bottom of tower.From feed stream upwards rise steam when it is by the one or more separation level within scrubbing tower, then contact with the liquid reflux stream flowed downward, thus " washing " is from the heavier composition of the ratio methane of described steam (that is, removing from volatile composition less described at least some of described steam).As mentioned above, this causes natural gas feed stream to be separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane, described vapor fraction at the collected overhead of scrubbing tower as overhead vapours (herein referring to " the first overhead vapours "), described liquid distillate at the bottom collection of scrubbing tower as bottom liquid (herein referring to " the first bottom liquid ").

In the case of domethanizing column, the first bottom liquid stream from scrubbing tower is further separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane as previously discussed, described vapor fraction at the collected overhead of domethanizing column as overhead vapours (" the second overhead vapours "), described liquid distillate at the bottom collection of domethanizing column as bottom liquid (" the second bottom liquid ").First bottom liquid stream normally partially evaporates (via heating and/or the expansion of stream), is then incorporated into domethanizing column as two phase flow.Generally, described stream is incorporated into domethanizing column in the centre position of tower, the steam that rises upwards from described stream is contacted with the liquid reflux stream flowed downward when it is by one or more separation level, thus " washing " is from the heavier composition of the ratio methane of described steam, with the liquid flowed downward made from described stream when it is by one or more separation level with rising steam upwards (generally, there is provided by making the part boiling of the bottom liquid of the bottom collection at tower) contact, thus " strip " methane and the composition (i.e. from described liquid remove at least some described in more volatile composition) lighter than methane from described liquid.

In the case of dethanizer, the second bottom liquid stream from domethanizing column is further separated into rich ethane fraction and the fraction rich in the hydrocarbon heavier than ethane as mentioned above, described rich ethane fraction at dethanizer collected overhead as overhead vapours (" the 3rd overhead vapours "), the described fraction rich in the hydrocarbon heavier than ethane at the bottom collection of dethanizer as bottom liquid (" the 3rd bottom liquid ").The operation of dethanizer is generally similar to the operation of domethanizing column, except the generally part evaporation of the second bottom liquid stream, then the centre position at tower is incorporated into dethanizer, make the withdrawing fluid flowed downward from the rising steam upwards of described stream wash out the composition heavier than ethane, and make the liquid flowed downward from described stream be stripped off ethane and the composition heavier than ethane by the steam that rises upwards.

As used herein, term " separator " or " phase separator " refer to such as to rouse or the device of container of other form, and wherein two phase flow can introduce so that described flow separation is its composition steam and liquid phase.

The system of a second aspect of the present invention is adapted for carrying out the method for first aspect, and the above-mentioned benefit of method the most according to the first aspect of the invention is equally applicable to the system of a second aspect of the present invention.

An embodiment according to second aspect, pipeline group, one or more heat exchanger and one or more separator are arranged and operation is to take out, to cool down, to condense and separately the first vapor stream of top of the tower, and it comprises: arrange and operate to take out the pipeline of the first vapor stream of top of the tower from described scrubbing tower top；Arrange and operation is with the heat exchanger flowed described in cooling and partial condensation or heat exchanger section；Arrange and operate the liquid with isolated and the separator of vapor phase；Arrange and operate the liquid phase with the most described separation to form other pipeline group flowed of the first overhead materials of the first-class of the first overhead materials of liquefaction and liquefaction；Heat exchanger or heat exchanger section with at least some of second to form the first overhead materials liquefied arranged and operate to receive, to cool down further and condense described separation vapor phase.

Described system can further include arranged and operates with reception and the heat exchanger of the second of the first overhead materials of supercool liquefaction or heat exchanger section.Arranged and operation can comprise the warm bundle around tubular type main heat exchanger with cooling and the heat exchanger section of partial condensation the first vapor stream of top of the tower, and arranged and operation can comprise the middle bundle around tubular type main heat exchanger and/or cold bundle cooling down and to condense at least one of heat exchanger section of described separation vapor phase further.Alternatively, arrange and operation can comprise overhead condenser heat exchanger with the heat exchanger of cooling and partial condensation the first vapor stream of top of the tower, and layout and operation can comprise around tubular type main heat exchanger with at least one of heat exchanger of the vapor phase of cooling and condensation separation further.

Another embodiment according to second aspect, pipeline group and one or more heat exchanger are arranged and operation is to take out, to cool down, to condense and separately the first vapor stream of top of the tower, and it comprises: arrange and operate the pipeline taking out the first vapor stream of top of the tower with the top from described scrubbing tower；Arrange and operation is to cool down and to condense heat exchanger or the heat exchanger section of described stream；With arrange and operation with by the stream of cooled and condensation separately with pipeline group of at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction.

Described system can further include heat exchanger or heat exchanger section, its arranged and operation is with supercool described cooled and the stream of condensation, and the most described stream is by separately with at least one other stream of the first overhead materials of first-class, the second of the first overhead materials of liquefaction and liquefaction that form the first overhead materials of liquefaction.Described system can further include heat exchanger or the heat exchanger section arranging and operating the second with supercool liquefaction the first overhead materials.

In the embodiment of second aspect, described system also comprises: dethanizer, it arranges and operates the second bottom liquid stream with reception from described demethanizer bottom and by described flow separation for rich ethane fraction and the fraction rich in the hydrocarbon heavier than ethane, described rich ethane fraction at the collected overhead of dethanizer as the 3rd overhead vapours, the described fraction rich in the hydrocarbon than ethane more weight at the bottom collection of dethanizer as the 3rd bottom liquid；With arrange and operation to take out the second bottom liquid stream from the bottom of domethanizing column and described stream be introduced to the pipeline of dethanizer.Described system can also comprise: arranges and operate to take out the pipeline of the 3rd vapor stream of top of the tower from the top of dethanizer, and arranges and operate to receive, cool down and condense described stream to form one or more heat exchangers of NGL stream；And/or arrange and operate to take out the pipeline of the 3rd bottom liquid stream from the bottom of dethanizer, its form one or more NGL stream.Described system can also comprise heat exchanger, described heat exchanger is arranged and operation is with by other stream indirect heat exchange with the first overhead materials of liquefaction, part condensation by described 3rd overhead vapours forms the 3rd overhead stream of liquefaction, 3rd overhead stream of described liquefaction is re-introduced into the top to described dethanizer as backflow stream, thus provides the backflow of described dethanizer；And arrange and operate other stream described in the first overhead materials of liquefaction is introduced to the pipeline of described heat exchanger.Heat exchanger is operable to flow to form NGL with cooling and condensation the 3rd vapor stream of top of the tower, threeth overhead stream that with the part of condensation threeth overhead vapours with formation liquefy operable with heat exchanger, 3rd overhead stream of described liquefaction is re-introduced into the top to dethanizer as backflow stream, and described heat exchanger can be a heat exchanger and identical heat exchanger.

Other embodiment of system according to second aspect by the embodiment of the method for first aspect discussed above obviously.

The preferred aspect of the present invention includes following aspect, numbering #1-#27:

#1. fractional distillation and the method for liquefied natural gas feed stream, described method comprises:

C the described first-class of first overhead materials of liquefaction is back to described scrubbing tower by (), be incorporated into the top of described scrubbing tower as backflow, thus provide the backflow of described scrubbing tower；

F () is refluxed to the offer of described domethanizing column by following:

(2) by with one of other stream indirect heat exchange described in the first overhead materials of liquefaction, condensing the part second overhead stream with formation liquefaction of described second overhead vapours, described second overhead stream is re-introduced into the top to described domethanizing column as backflow stream.

The method of #2. aspect #1, wherein step (b) comprises:

The first vapor stream of top of the tower is taken out by the top of described scrubbing tower, cool down and partly condense described stream, the liquid of isolated and vapor phase, by the liquid phase of described separation separately to form at least one other stream of the first overhead materials of the first-class of the first overhead materials of liquefaction and liquefaction, and cool down and condense the second of at least some of first overhead materials to form liquefaction of the vapor phase of described separation further；And/or

The first vapor stream of top of the tower is taken out by the top of described scrubbing tower, cool down and partly condense described stream, the liquid of isolated and vapor phase, is formed the first-class of the first overhead materials of liquefying by the liquid phase of described separation at least some of, cool down and condense vapor phase at least some of of described separation further, and by the stream of the cooling further obtained and condensation separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of liquefaction.

The method of #3. aspect #2, wherein:

The second making the first overhead materials of liquefaction is supercool, then forms described LNG product stream；Or

Make flowing through of cooling and condensation cold, then at least one other stream of separately second and liquefaction the first overhead materials to form liquefaction the first overhead materials.

#4. aspect #2 or the method for #3, wherein the first vapor stream of top of the tower from described scrubbing tower top is cooling down and partial condensation in the warm bundle of tubular type main heat exchanger, and at least some of of the vapor phase of described separation is cooling down and condensation in the fasciculus intermedius and/or cold bundle of tubular type main heat exchanger further.

#5. aspect #2 or the method for #3, wherein the first vapor stream of top of the tower from described scrubbing tower top cools down and partial condensation in overhead condenser heat exchanger, and at least some of of the vapor phase of described separation is cooling down and condensation in tubular type main heat exchanger further.

The method of #6. aspect #1, wherein step (b) comprises:

The first vapor stream of top of the tower is taken out from the top of described scrubbing tower, cooling and condense described stream, and by described cooling and condensate flow separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction.

The method of #7. aspect #6, wherein:

Make described cooling and condensate flow supercool, then separately with at least one other stream of the first overhead materials of the second and liquefaction that form the first overhead materials of first-class, the liquefaction of the first overhead materials of liquefaction；Or

Described cooling and condensate flow separate first-class and another liquid stream of the first overhead materials to form liquefaction, make described liquid stream the most supercool, other stream of at least one of the second of the first overhead materials then separately liquefied with formation and the first overhead materials of liquefaction；Or

The second making the first overhead materials of liquefaction is supercool, then forms described LNG product stream.

The method of #8. aspect any one of #1 to #7, other stream being wherein used as liquefaction the first overhead materials first-class of backflow stream and liquefaction the first overhead materials for step (f) in step (c) has the flow-rate ratio of at least about 9:1.

The method of #9. aspect any one of #1 to #8, other stream being wherein used as liquefaction the first overhead materials first-class of backflow stream and liquefaction the first overhead materials for step (f) in step (c) each has about-40 DEG C or following temperature.

The methane of each self-contained at least about 95 moles of % of the method for #10. aspect any one of #1 to #9, wherein said first overhead vapours and the second overhead vapours, and the second bottom liquid comprises the methane of less than about 5 moles of %.

The method of #11. aspect any one of #1 to #10, wherein said method also comprises: taken out the second vapor stream of top of the tower by the top of domethanizing column；Cooling and condense all or part of of described stream to form other LNG product；And/or all or part of of described stream is used as fuel stream；And/or using described stream all or part of as gaseous natural gas product stream export.

The method of #12. aspect any one of #1 to #11, wherein said method also comprises is taken out the second bottom liquid stream by the bottom of described domethanizing column, and by the second bottom liquid stream fractional distillation to provide one or more natural gas liquids (NGL) stream.

The method of #13. aspect #12, wherein the fractionating step of the second bottom liquid stream comprises: be introduced in dethanizer by described stream, second bottom liquid stream is separated into the fraction of rich ethane and wherein rich in the fraction of the hydrocarbon heavier than ethane, the fraction of described rich ethane at the collected overhead of dethanizer as the 3rd overhead vapours, the described fraction rich in the hydrocarbon than ethane more weight at the bottom collection of dethanizer as the 3rd bottom liquid.

The method of #14. aspect #13, wherein said method also comprises:

Taken out the 3rd vapor stream of top of the tower by the top of described dethanizer, and cool down and condense described stream to form NGL stream；And/or

Taken out the 3rd bottom liquid stream by the bottom of described dethanizer, and formed one or more NGL stream by it.

#15. aspect #13 or the method for #14, wherein said method also comprises as provided below being back in dethanizer: by other stream indirect heat exchange with the first overhead materials of liquefaction, make the part condensation of the 3rd overhead vapours, forming the 3rd overhead stream of liquefaction, described 3rd overhead stream is re-introduced into the top to described dethanizer as backflow stream.

The method of #16. aspect any one of 13 to #15, wherein said 3rd overhead vapours comprises the ethane of at least about 95%, and described 3rd bottom liquid comprises the ethane of less than about 5 moles of %.

#17. is used for fractional distillation and the system of liquefied natural gas feed stream, and described system comprises:

One below or both:

The system of #18. aspect #17, wherein said pipeline group, one or more heat exchangers, and one or more separator are arranged and operation is to take out described first vapor stream of top of the tower, cool down, condense and to separate, and it comprises:

Arrange and operation for taking out the pipeline of the first vapor stream of top of the tower from the top of described scrubbing tower；

Arrange and operation is for cooling and the heat exchanger or the heat exchanger section that partly condense described stream；

Arrange and operate the liquid for isolated and the separator of vapor phase；

Pipeline group, arranges and operates the liquid phase for the most described separation with other stream of the first overhead materials of the first overhead materials first-class and liquefaction that form liquefaction；With

Heat exchanger or heat exchanger section, arrange and operate for receiving, cool down further and condense the second of at least some of first overhead materials to form liquefaction of the vapor phase of described separation.

The system of #19. aspect #18, wherein said system also comprises arranges and operation is for receiving and making the supercool heat exchanger of the second of the first overhead materials of described liquefaction or heat exchanger section.

#20. aspect #18 or the system of #19, wherein arrange and operate and comprise the warm bundle around tubular type main heat exchanger for the described heat exchanger section of the first vapor stream of top of the tower described in cooling and partial condensation, and arrange and operation comprises the middle bundle around tubular type main heat exchanger and/or cold bundle cooling down and to condense at least one of described heat exchanger section of described separation vapor phase further.

#21. aspect #18 or the system of #19, wherein arrange and operate and comprise overhead condenser heat exchanger for the described heat exchanger of the first vapor stream of top of the tower described in cooling and partial condensation, and at least one of described heat exchanger arranging and operating the vapor phase for cooling down further and condensing described separation comprises around tubular type main heat exchanger.

The system of #22. aspect #17, wherein arranges and operates for taking out, cool down, condense and the described pipeline group of the most described first vapor stream of top of the tower and one or more heat exchanger comprising:

Arrange and operation is for cooling down and condense heat exchanger or the heat exchanger section of described stream；With

Pipeline group, its arrange and operation for the stream of the most described cooled and condensation with at least one other stream of the first overhead materials of first-class, the second of the first overhead materials of liquefaction and liquefaction that form the first overhead materials of liquefaction.

The system of #23. aspect #22, wherein said system also comprises heat exchanger or heat exchanger section, it is arranged and operation is for making flowing through of described cooled and condensation cold, and the most described stream is by separately with at least one other stream of the first overhead materials of first-class, the second of the first overhead materials of liquefaction and liquefaction that form the first overhead materials of liquefaction.

The system of #24. aspect #22, wherein said system also comprises arranges and heat exchanger that the second of the operation the first overhead materials for making described liquefaction is supercool or heat exchanger section.

The system of #25. aspect #17 to #24, wherein said system also comprises:

Dethanizer, it is arranged and operation is for from bottom reception second bottom liquid stream of described domethanizing column, and be rich ethane fraction and the fraction rich in the hydrocarbon heavier than ethane by described flow separation, described rich ethane fraction is collected as the 3rd bottom liquid at described Deethanizer bottom as the 3rd overhead vapours, the described fraction rich in the hydrocarbon than ethane more weight at described dethanizer collected overhead；With

Pipeline, it is arranged and operation for taking out the second bottom liquid stream from the bottom of described domethanizing column, and described stream is introduced to dethanizer.

The system of #26. aspect #25, wherein said system also comprises:

Arrange and operation for taking out the pipeline of the 3rd vapor stream of top of the tower from the top of described dethanizer, and layout and operation are for receiving, cool down and condense described stream to form one or more heat exchangers of NGL stream；And/or

Arrange and operation for taking out the pipeline of the 3rd bottom liquid stream from the bottom of described dethanizer, it form one or more NGL stream.

#27. aspect #25 or the system of #26, wherein said system also comprises heat exchanger, it is arranged and operation is for by other stream indirect heat exchange with the first overhead materials of liquefaction, make the part condensation of described 3rd overhead vapours, form the 3rd overhead stream of liquefaction, it is re-introduced into the top to described dethanizer as backflow stream, thus provides the backflow of described dethanizer, and arranges and operation is for being introduced to the pipeline of described heat exchanger by other stream described in the first overhead materials of liquefaction.

It is only used as example, describes the certain preferred embodiments of the present invention with reference now to accompanying drawing 2-7.In above-mentioned Fig. 1 and following Fig. 2-7, when a feature has for multiple figures, for clarity and conciseness for the sake of, this feature specifies identical reference in each figure.

In the embodiment that Fig. 2-7 describes, the main heat exchanger for liquefied natural gas is shown as wound tube heat exchanger.But, although this heat exchanger is preferably used, but main heat exchanger can be equally plate-fin heat exchanger or the heat exchanger of other kind any known in the art.Similarly, although in the embodiment described, the coil pipe bundle of main heat exchanger is shown received within single cover or shell, form individual unit, but main heat exchanger can equally comprise two or more unit a series of, each bundle has the cover/shell of oneself, or one or more bundle is contained in a cover/shell, and other bundle one or more is contained in one or more different cover/shell.Refrigerant cycle for the cryogen cold to main heat exchanger supply can be similarly for being applicable to implement any type of natural gas liquefaction.Exemplary cycle that is known in the art and use and that can be used for the present invention includes that propane pre-cooling but hybrid refrigeration cycle (C3MR), single mixing cause cool dose of circulation (SMR), nitrogen expander cycle, methane expander cycle, double mixing and cause cool dose of circulation (DMR) and cascade cycle.

With reference now to Fig. 2, in one embodiment of the invention, natural gas feed stream 101 is the most preprocessed to remove sour gas, water and hydrargyrum, and it precools the most in one or more heat exchangers, is incorporated into the bottom of scrubbing tower 10 containing multiple separation levels.Natural gas feed is separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane by scrubbing tower 10, described vapor fraction is collected as overhead vapours (also referred to herein as " the first overhead vapours " or " scrubbing tower overhead vapours ") at top of tower, described liquid distillate at the bottom collection of tower as bottom liquid (also referred to herein as " the first bottom liquid " or " wash tower bottoms liquid ").Take out vapor stream of top of the tower 202 from the top of scrubbing tower, and take out bottom liquid stream 103 from the bottom of scrubbing tower.

First vapor stream of top of the tower 202 sends to main heat exchanger 20 for cooling down and liquefying.In the embodiment described in which, main heat exchanger 20 is containing warm bundle 22, middle bundle 24 and the wound tube heat exchanger of cold bundle 26 accommodated in single clamshell.Main heat exchanger can provide any applicable cryogen (not shown) by any applicable refrigerant cycle being effective to implement natural gas liquefaction.Vapor stream of top of the tower 202 is incorporated into the warm end of main heat exchanger 20, and cooled and be partially condensed to form partial condensation (biphase) stream 203 in warm bundle 22.Then described partial condensation stream 203 take out from warm bundle and be separated into liquid phase and vapor phase in phase separator 28 to produce liquid stream 120 and steam stream 207.

Steam stream 207 is back to main heat exchanger 20, and first it cool down in middle bundle 24 further and total condensation is to form the first overhead stream 204 of liquefaction wherein.First overhead stream of this liquefaction is then supercool in cold bundle 26, thus produces LNG product stream 205.LNG product stream 205 can be as shown through flash distillation (such as by by stream by J-T valve) and be sent in LNG storage tank 30 for storing.From groove steam gas (BOG) or flash gas 401 can be sent to fuel header, through burning or be recycled to be fed in the vapor stream of top of the tower of main heat exchanger (not shown).

Liquid stream 120 from phase separator 28 is typically about the temperature of-40 DEG C to about-70 DEG C, is separated thus forms two streams 125 and 121 of the first overhead materials of liquefaction.Stream 125 generally comprise stream 120 most of flows, stream 125 with stream 121 flow-rate ratio be typically about 9:1 (stream 125 the most generally account for stream 120 at least 90%, and stream 121 generally account for stream 120 less than 10%).Stream 125 is back to scrubbing tower 10 (generally by pumping or gravity), is incorporated into the top of scrubbing tower as backflow stream, in order to provide the backflow that scrubbing tower operation is required.Flowing 121 and send the top to (generally after by J-T valve) domethanizing column 12, as backflow stream to provide domethanizing column to operate required backflow, further describing in will be described in more detail below.

The first bottom liquid stream 103 expanded (such as, as indicated, pass through J-T valve) taken out from scrubbing tower 10, partly to evaporate described stream, is then incorporated into the centre position of the domethanizing column 12 also containing multiple separation level.First bottom liquid 103 is separated into methane rich vapor fraction and the liquid distillate rich in the hydrocarbon heavier than methane by domethanizing column 12, described vapor fraction is collected as overhead vapours (herein also referred to as " the second overhead vapours " or " demethanizer column overhead vapor ") at top of tower, and described liquid distillate is collected as bottom liquid (herein also referred to as " the second bottom liquid " or " demethanizer bottom liquid ") at tower bottom.In the present embodiment, and as previously discussed, by the first overhead stream 121 of liquefaction is introduced to demethanizer overhead provides the backflow of domethanizing column as backflow stream.A part for demethanizer bottom liquid heats as shown to provide the upflowing vapor of domethanizing column 12 in reboiler (it can use any applicable thermal source).The remainder of bottom liquid takes out as the second bottom liquid stream 105.

Temperature and pressure in scrubbing tower and domethanizing column generally makes the first overhead vapours and the methane of each self-contained at least about 95 moles of % of the second overhead vapours (i.e. scrubbing tower overhead vapours and demethanizer column overhead vapor) through control, and makes the second bottom liquid (i.e. demethanizer bottom liquid) comprise the methane less than 5 moles of %.This is done so that the response rate of NLG and HHC (i.e. C2+ hydrocarbon) taken out from domethanizing column and the concentration the second bottom liquid stream maximize.Temperature at scrubbing tower and demethanizer overhead is controlled by the temperature of backflow stream 125, and 125 are formed by the first overhead materials liquefied, and this backflow stream is generally of about-40 DEG C or following temperature as above.The temperature of demethanizer bottom is controlled by demethanizer reboiler.Pressure in tower is limited by the pressure of natural gas feed stream 101, and when the first bottom liquid stream 103 (i.e. wash tower bottoms liquid stream) expands, surging declines.

From the demethanizer column overhead vapor of demethanizer overhead taking-up as the second vapor stream of top of the tower 104, can be used for any applicable or purpose of needs.Such as, it can be used as fuel stream, and/or be sent to pipeline or sell as gaseous natural gas product stream and output.In addition or alternatively, it (not shown) can cool down and condense (separate with the first overhead vapours and/or combine) to form and to provide other LNG product in main heat exchanger.

The the second bottom liquid stream 105 further fractional distillation NGL fractionating system taken out from the bottom of domethanizing column 12, the most described NGL fractionating system comprises dethanizer 14, depropanizing tower 16 and debutanizing tower 18, so that the NGL needed for Ti Gonging flows (such as with as discussed above, it can be used as supplementing cryogen, as independent merchandise sales, and/or optionally with LNG product in conjunction with to regulate the calorific value of LNG product).

More specifically, second bottom liquid stream (demethanizer bottom liquid) is the most cooled (such as, as shown, by using empty gas and water or the heat exchanger of another kind of ambient temperature cooling medium), the most expanded with cooling stream 105 (such as, as indicated, pass through heat exchanger and J-T valve) flows with forming part evaporation (biphase), it is incorporated into the centre position of dethanizer 14, and described dethanizer 14 is possibly together with multiple separation levels.Second bottom liquid 105 is separated into rich ethane vapor fraction and the liquid distillate rich in the hydrocarbon heavier than ethane by dethanizer 14, described vapor fraction is collected as overhead vapours (being also known as " the 3rd overhead vapours " or " deethanizer overhead vapor " herein) at top of tower, and described liquid distillate is collected as bottom liquid (being also known as " the 3rd bottom liquid " or " Deethanizer bottom liquid " herein) at tower bottom.As provided below for the backflow of dethanizer: condensation deethanizer overhead vapor in overhead condenser heat exchanger (it can be provided with any applicable cryogen), a part for the overhead materials of condensation is back to dethanizer 14 as backflow stream, and remainder takes out the 3rd overhead stream 106 as liquefaction.A part for Deethanizer bottom liquid, as indicated, heating in reboiler (it can use any applicable thermal source), in order to the upflowing vapor of dethanizer 14 is provided.The remainder of bottom liquid takes out as the 3rd bottom liquid stream 107.

Owing to generally the most very small amount of methane is present in the fact that feed to the second bottom liquid stream 105 (demethanizer bottom liquid) of dethanizer (as discussed above), with due to the usual extraordinary fact of the response rate/productivity of ethane (with other NGL) in the second bottom liquid, dethanizer can produce the vapor stream of top of the tower of rich ethane in the present embodiment, its existing high-purity is again with relatively high volume production, so that can be used for supplementing cryogen and/or the amount maximization of the high-purity ethane as the sale of NGL product stream.Generally, the 3rd overhead vapours (deethanizer overhead vapor) comprises the ethane of at least about 95 moles of %, and the 3rd bottom liquid (Deethanizer bottom liquid) comprises the ethane of less than about 5 moles of %.

3rd bottom liquid stream (Deethanizer bottom liquid) 107 expanded (such as by J-T valve) flows with (biphase) of forming part evaporation, is introduced into the centre position of the depropanizing tower 16 also containing multiple separation level.3rd bottom liquid 107 is separated into rich propane vapor fraction and the liquid distillate rich in the hydrocarbon heavier than propane by depropanizing tower 16, described vapor fraction is collected as overhead vapours (being also known as " the 4th overhead vapours " or " depropanizing tower overhead vapours " herein) at top of tower, and described liquid distillate is collected as bottom liquid (being also known as " the 4th bottom liquid " or " depropanizing tower bottom liquid " herein) at tower bottom.Depropanizing tower back up through in overhead condenser heat exchanger, (be provided with any applicable cryogen) condensation depropanizing tower overhead vapours provide, the part of overhead materials for condensation is back to depropanizing tower 16 as backflow, and remainder takes out as the 4th overhead stream 108 liquefied.A part for depropanizing tower bottom liquid heats as shown to provide the upflowing vapor of depropanizing tower 16 in reboiler (it can use any applicable thermal source).The remainder of bottom liquid takes out as the 4th bottom liquid stream 109.

4th bottom liquid stream (depropanizing tower bottom liquid) 109 expanded (such as by J-T valve) flows with (biphase) of forming part evaporation, is introduced into the centre position of the debutanizing tower 18 also containing multiple separation level.4th bottom liquid 109 is separated into rich butane vapor fraction and the liquid distillate rich in the hydrocarbon heavier than butane by debutanizing tower 18, described vapor fraction is collected as overhead vapours (being also known as " the 5th overhead vapours " or " debutanizing tower overhead vapours " herein) at top of tower, and described liquid distillate is collected as bottom liquid (being also known as " the 5th bottom liquid " or " debutanizing tower bottom liquid " herein) at tower bottom.Debutanizing tower back up through in overhead condenser, (be provided with any applicable cryogen) condensation debutanizing tower overhead vapours provide, the part of overhead materials for condensation is back to debutanizing tower 18 as backflow, and remainder takes out as the 5th overhead stream 110 liquefied.A part for debutanizing tower bottom liquid heats as shown to provide the upflowing vapor of debutanizing tower 18 in reboiler (it can use any applicable thermal source).The remainder of bottom liquid takes out as the 5th bottom liquid stream 111.

Compared with the conventional layout that Fig. 1 shows, therefore the method and system of the embodiment of the present invention described in Fig. 2 is back in the mode of domethanizing column difference in offer.Especially, although in layout in FIG, the overhead stream that the vapor stream of top of the tower taken out from scrubbing tower is cooled, condenses and separately liquefies with offer exactly two, one of them (steam 205) is used as the backflow stream of scrubbing tower as LNG product taking-up and another (stream 120), but the vapor stream of top of the tower (the i.e. first vapor stream of top of the tower) in the arrangement of fig. 2, taken out from scrubbing tower is cooled, condense and separate at least three stream of the first overhead materials liquefied with offer.First-class (stream 125) of the first overhead materials of liquefaction is back to scrubbing tower as backflow stream, the second (stream 204) of the first overhead materials of liquefaction takes out as LNG product (stream 205), and other stream of at least one of the first overhead materials of liquefaction (stream 121) is introduced to the top of domethanizing column as backflow stream.As it has been described above, this provides the advantage that eliminates the needs of special overhead condenser for domethanizing column, and (generally) provides colder and is back to domethanizing column (thus ethane recovery that enhancing is in demethanizer bottom liquid).

And the liquid that non-usage separates in phase separator 28 from the first overhead materials partial condensation stream 203 makes scrubbing tower and demethanizer reflux, but in alternative arrangement, scrubbing tower and/or the backflow of domethanizing column can be obtained by the one or more colder position of main heat exchanger.

Therefore, at present with reference to Fig. 3, the alternative embodiment of the present invention is described as follows: wherein main heat exchanger has only two bundles, i.e. warm bundle 22 and cold bundle 26.The first vapor stream of top of the tower 202 taken out from scrubbing tower 10 top is re-introduced into warm bundle 22, but in this case, warm bundle is for cooling down with total condensation vapor stream of top of the tower to form the first overhead stream of liquefaction, then the second 204 of the first overhead materials of first-class 125, the liquefaction of the first overhead materials to form liquefaction, and other stream 121 of the first overhead materials of liquefaction are separated.In embodiment as shown in Fig. 2, first-class the 125 of first overhead materials of liquefaction are then return to the top of scrubbing tower 10 as backflow stream, the second 204 of the first overhead materials of liquefaction is supercool to provide LNG product stream 205 in cold bundle 26, and other stream 121 of the first overhead materials of liquefaction is introduced to the top of domethanizing column as backflow stream.

Equally, at present with reference to Fig. 4, in still another embodiment, main heat exchanger also only has two bundles, i.e. warm bundle 22 and cold bundle 26, but in the present embodiment, from stream 202 all cooled first overhead streams 204 liquefied with formation with total condensation warm bundle 22 of the first overhead materials that scrubbing tower 10 takes out, and this stream the most then mistake cold flow of supercool the first overhead materials to form liquefaction in cold bundle 26, then separated to form first-class the 125 of the first overhead materials liquefied, other stream 121 of the second 205 of the first overhead materials of liquefaction and the first overhead materials of liquefaction.In the present embodiment, the second 205 of the first overhead materials of liquefaction this as LNG product stream take out, it is not necessary to other cooling or process.Embodiment as shown in Fig. 2, first-class the 125 of the first overhead materials of liquefaction are back to the top of scrubbing tower 10 as backflow stream, and other stream 121 of the first overhead materials of liquefaction is introduced to the top of domethanizing column as backflow stream.

In the embodiment that Fig. 3 and 4 describes, first-class the 125 of first overhead materials of liquefaction and other stream 121 generally than in the embodiment that Fig. 2 describes first-class the 125 of the first overhead materials of the liquefaction of generation, to flow 121 much cooler, owing to described stream is derived from the colder position of main heat exchanger in Fig. 3 and 4 with other.In the embodiment depicted in fig. 3, stream 125 and 121 is generally the temperature of about-100 DEG C to about-135 DEG C.In the embodiment shown in the diagram, stream 125 and 121 is generally the temperature of about-130 DEG C to about-160 DEG C.Because these streams are in colder temperature, need the flow velocity that these streams are the lowest, and it can be used for providing scrubbing tower 10 and the necessary backflow of domethanizing column 12, and (flow velocity of stream 125 and 121 required in the diagram is less than those in Fig. 3；Flow velocity needed for stream 125 and 121 is less than those in Fig. 2 the most in figure 3).The layout described in Fig. 3 and 4 also eliminates the needs to phase separator 28 and reduces the quantity of bundle required in main heat exchanger, thus reduces these capital costs arranged further.

In further embodiment (not shown), two or more combinations arranged described in Fig. 2,3 and 4 can be used for providing scrubbing tower and the backflow stream of domethanizing column.Such as, in arranging at one, for making first-class the 125 of liquefaction the first overhead materials that scrubbing tower refluxes can produce as follows: the first vapor stream of top of the tower 202 taken out from scrubbing tower is partly condensed, liquid phase is separated in phase separator 28, and the similar fashion shown with Fig. 2 uses liquid phase to form first-class the 125 of the first overhead materials of liquefaction, for making other stream 121 of the first overhead materials of the liquefaction of demethanizer reflux produce the most as follows: other cooling of the middle bundle of main heat exchanger or cold bundle and fluidized flow or supercool stream will be left separately with other stream 121 of the first overhead materials of the second 204/205 and liquefaction that form the first overhead materials of liquefaction, with the similar fashion described in Fig. 3 or 4.

Equally, in another is arranged, the backflow of scrubbing tower and/or domethanizing column can be obtained by other position any in main heat exchanger cold end downstream, such as by LNG groove.They also can be obtained by the LNG stream produced in equipment another part, such as end-flash distillation exchanger (not shown), a part 101 for its liquefied natural gas stream, heat BOG or flash gas stream 401 simultaneously.

In still another embodiment, the backflow provided to scrubbing tower and/or domethanizing column by first and other stream of the first overhead materials of liquefaction can be supplemented by the backflow that overhead condenser provides to tower, or add to overhead condenser and provide to the backflow of tower, described overhead condenser is supplied with cryogen and operates with condensation from overhead materials at least some of of described tower.

At present with reference to Fig. 5 and 6, yet another embodiment of the present invention shows different from the embodiment of display in Fig. 2, it is that initial cooling and the partial condensation of the first vapor stream of top of the tower 202 do not occur the warm bundle at main heat exchanger, and be to occur in single overhead condenser heat exchanger, by supplying cryogen with the identical kind of refrigeration cycle of cooling load to described overhead condenser heat exchanger to main heat exchanger supply cryogen.In figs. 5 and 6, depict two bundle formula wound tube heat exchangers, cause cool dose of circulation (C3MR) by propane pre-cooling mixing and supply cryogen to it.As previously noted, main heat exchanger can be another type of heat exchanger, and different types of kind of refrigeration cycle can use equally, but the most only shows wound tube heat exchanger and C3MR circulation.

In the embodiment that Fig. 5 and 6 describes, natural gas and propane refrigerant precool in precooler heat exchanger 34, are then introduced to scrubbing tower as natural gas feed stream 101.Then the first vapor stream of top of the tower 202 taken out from the top of scrubbing tower 10 partly cools down and condenses (biphase) stream 203 with forming part condensation overhead condenser heat exchanger 32.The stream 203 of partial condensation is separated into its liquid and vapor phase to produce liquid stream 120 and steam stream 207 in phase separator 28.Then, by liquid stream 120 separately to form other stream 121 of first-class the 125 of the first overhead materials of liquefaction and the first overhead materials of liquefaction, then it is introduced to scrubbing tower 10 and domethanizing column 12 as backflow stream, as previously mentioned with respect to described in the embodiment of display in Fig. 2.Steam stream 207 is incorporated into main heat exchanger 20, wherein its cooling further, condensation and the second of supercool the first overhead materials to form liquefaction, and it takes out as LNG product stream 205.Overhead condenser heat exchanger 32 can be plate-fin heat exchanger, printed circuit heat exchanger or other heat exchanger being suitable for any.

In the embodiment shown by Fig. 5, the warm mixed cooling medium stream 309 taken out from the bottom of main heat exchanger 20 sends to compressibility and (comprises motor 36, with relevant compressor and intercooler and aftercooler), this its compressed to form high-pressure refrigerant stream 312.Then, this stream in separator 38 be separated with produce mixed cooling medium steam (MRV) flow 302 and mixed cooling medium liquid (MRL) flow 301.Two streams 301 and 302 send to main heat exchanger to cool down in single loop.Cooled and at least partly condensation MRV stream takes out from the cold end of the cold bundle of main heat exchanger, expand (such as, by J-T valve, as shown), and it is re-introduced into the shell-side to main heat exchanger, as evaporation (vaporized)/vapo(u)rability (vaporizing) the cryogen stream 308 of cold low-pressure to provide cooling load to the cold bundle of main heat exchanger and warm bundle.Cooled MRL stream takes out from the cold end of the warm bundle of main heat exchanger, then separates to form two streams.One flows through to expand and cold evaporates/low-pressure cryogen the stream 307 of vapo(u)rability to be formed, and the shell-side being re-introduced into main heat exchanger to provide other cooling load to the warm bundle of main heat exchanger.Another flow 320 expanded (such as, by J-T valve, as shown) cold evaporate/low-pressure cryogen the stream of vapo(u)rability to be formed, generally the temperature of about-60 DEG C to about-120 DEG C, it is by overhead condenser heat exchanger 32 to provide cooling load for partial condensation the first vapor stream of top of the tower 202, and described first vapor stream of top of the tower 202 is from the taking-up of the top of scrubbing tower 10.Then the warm cryogen stream 350 leaving overhead condenser heat exchanger 32 can warm up the cryogen the warmed up combination of end as stream 309 with leaving main heat exchanger.Alternatively, if stream 350 remains biphase, its shell-side that can expand further and send to the main heat exchanger in centre position is with the other cooling load of the warm bundle offer to main heat exchanger.

In single tower top heat exchanger rather than in the warm bundle of main heat exchanger self, it is that it eliminates the multiple loops in main heat exchanger and bundle from the benefit of the first vapor stream of top of the tower of scrubbing tower via carrying out partial condensation with the cryogen heat exchange from main heat exchanger.This also results in the system of the relatively low-complexity being physically easier to perform.Diverter tower top temperature based on tower between stream refrigerant vapor 307 and 320 regulates, and tower top temperature required purity based on the overhead stream from described tower again determines.

In the embodiment that Fig. 6 shows, the operation of kind of refrigeration cycle is similar to as Fig. 5 and described above.The only difference is that, in the embodiment that Fig. 6 describes, the cryogen stream 320 provided to overhead condenser heat exchanger 32 obtains not by being come by the MRL flow point of cooling that the cold end warming up bundle from main heat exchanger takes out, but is separated by the MRV stream of the cooling will taken out from the cold end of the cold bundle of main heat exchanger and at least partly condensation and obtain.In this case, stream 320 temperature after inflation are about-140 DEG C to-160 DEG C, therefore much cooler than the cryogen stream 320 of equivalent in the embodiment shown at Fig. 5.

In addition to MRL and the MRV stream of Fig. 5-6 display, exist and can obtain other position thus sending the cryogen stream to overhead condenser heat exchanger 32.These change with the kind of refrigeration cycle used.Such as, in using the SMR circulation of mixed cooling medium stream of most four different compositions, can be obtained by these streams any for producing the cryogen of backflow.

At present with reference to Fig. 7, display yet another embodiment of the present invention, it is different from the embodiment that Fig. 2 shows, it is that other stream 121 of the first overhead materials of liquefaction is incorporated into the top of domethanizing column 12 not as backflow stream, but in overhead condenser heat exchanger, it is used as cryogen stream, wherein part the second overhead vapours (i.e. part demethanizer column overhead vapor) is condensed by other stream indirect heat exchange with the first overhead materials of liquefaction, to form the second overhead stream of liquefaction, it is re-introduced into the top to domethanizing column as backflow stream.Therefore, although other stream of the first overhead materials of liquefaction is not to itself function as the backflow stream in domethanizing column, but in the present embodiment, other stream of the first overhead materials of liquefaction supply cooling load really, for producing the backflow in domethanizing column, produces the backflow of domethanizing column the most indirectly.

More specifically, with as it is shown in fig. 7, in the present embodiment, first liquefaction the overhead stream 202 the most cooled and partial condensation the warm bundle 22 of main heat exchanger 20 taken out from scrubbing tower 10 top, to form two phase flow 203, in separator 28, then it is separated into its liquid phase and vapor phase.Liquid phase 120 is spaced further apart first-class 125 of the first overhead materials to form liquefaction, and in this case, two of the first overhead materials of liquefaction other streams 121 and 122 again.The top that first-class the 125 of first overhead materials of liquefaction are re-introduced into as previously mentioned to scrubbing tower 10 is to provide the backflow of this tower.But, two of the first overhead materials of liquefaction other streams 121 and 125 are used as cryogen stream in this case to supply cooling load to demethanizer column overhead condenser heat exchanger 40 and deethanizer overhead condenser heat exchanger 42 respectively.

In this case, the backflow of domethanizing column 12 is therefore by following generation: taken out demethanizer column overhead vapor stream (" the second overhead vapours ") by the top of domethanizing column；Described stream by one of other stream of the first overhead materials 121 indirect heat exchanges with liquefaction at demethanizer column overhead condenser 40 partial condensation；Separate liquid phase and vapor phase；As the second overhead stream liquefied, liquid phase is back to domethanizing column, and it is re-introduced into the top to tower as backflow stream；With take out remaining vapor phase as the second vapor stream of top of the tower 104 (such as with as discussed above, this stream can be used as fuel, exports as gaseous natural gas product, and/or liquefaction is to provide other LNG product).

Similarly, in the present embodiment, the backflow of dethanizer 14 is therefore by following generation: take out deethanizer overhead vapor stream (" the 3rd overhead vapours ") from the top of described dethanizer；Described stream by with the first overhead materials of liquefaction another other flow 122 indirect heat exchanges and condense in deethanizer overhead condenser 42；As the 3rd overhead stream liquefied, a part for liquefaction overhead materials is back to dethanizer, and it is re-introduced into top of tower as backflow stream；With take out the remainder of overhead materials of liquefaction as the 3rd overhead stream 106 (such as with as discussed above, this stream can be sold as NGL product, is used as to supplement cryogen, and/or with LNG product combination to regulate the calorific value of the latter) of liquefaction.

The warm current 126 and 127 of the first overhead materials leaves demethanizer column overhead condenser 40 and deethanizer overhead condenser 42, can be used for any applicable or required purposes.Such as, they can reinject to natural gas feed, and/or it is supplementary to be used as cryogen.

Additionally, the many changes arranged shown in Fig. 7 are also possible.Such as, some or all of stream 125,121 and 122 are obtained the most as shown in Figure 7 by phase separator 28, but stream 125,121 and/or 122 can be obtained by the colder position of main heat exchanger, by the first-class of the first overhead materials of the liquefaction produced in the embodiment that Fig. 3 and 4 describes and the similar fashion of other stream.

Embodiment

In order to the operation of the present invention is described, the method removing cryogen such as Fig. 2 and 3 in the natural gas liquefaction system described and describe use the simulation of ASPENPlus software.

Table 1 below lists condition and the composition of each stream of the simulation of the method described for Fig. 2, and the condition of simulation and the composition of each stream of the method described for Fig. 3 listed by table 2.Data explanation in these forms, utilize a part (the first overhead vapours taken out from scrubbing tower is cooled down, liquefies and separated and produces) for other stream of the first overhead materials of liquefaction, to make demethanizer reflux, cause efficiently separating of heavy hydrocarbon and NGL composition and natural gas.Additionally, compared with conventional layout the most depicted in figure 1, these arrange the minimizing causing equipment cost, by eliminating demethanizer column overhead condenser and reflux drum, thus cause cost savings and simpler operation.

Table 1

Table 2

It should be understood that the present invention is not limited to the details described above with reference to preferred embodiment, but many improvement and change can be carried out under the spirit of the invention limited without departing from following claims or scope.

Claims

1. fractional distillation and the method for liquefied natural gas feed stream, described method comprises:

F () is refluxed to the offer of described domethanizing column by following:

2. the process of claim 1 wherein that step (b) comprises:

3. the method for claim 2, wherein:

4. the method for claim 2, wherein the first vapor stream of top of the tower from described scrubbing tower top is cooling down and partial condensation in the warm bundle of tubular type main heat exchanger, and at least some of of the vapor phase of described separation is cooling down and condensation in the fasciculus intermedius and/or cold bundle of tubular type main heat exchanger further.

5. the method for claim 2, wherein the first vapor stream of top of the tower from described scrubbing tower top cools down and partial condensation in overhead condenser heat exchanger, and at least some of of the vapor phase of described separation is cooling down and condensation in tubular type main heat exchanger further.

6. the process of claim 1 wherein that step (b) comprises:

7. the method for claim 6, wherein:

8. the process of claim 1 wherein that other stream of liquefaction the first overhead materials first-class and liquefaction the first overhead materials for step (f) that being used as backflow stream in step (c) has the flow-rate ratio of at least about 9:1.

9. the process of claim 1 wherein that other stream of liquefaction the first overhead materials first-class and liquefaction the first overhead materials for step (f) that being used as backflow stream in step (c) each has about-40 DEG C or following temperature.

10. the process of claim 1 wherein described first overhead vapours and the methane of each self-contained at least about 95 moles of % of the second overhead vapours, and the second bottom liquid comprises the methane of less than about 5 moles of %.

11. the process of claim 1 wherein that described method also comprises: taken out the second vapor stream of top of the tower by the top of domethanizing column；Cooling and condense all or part of of described stream to form other LNG product；And/or all or part of of described stream is used as fuel stream；And/or using described stream all or part of as gaseous natural gas product stream export.

12. the process of claim 1 wherein that described method also comprises is taken out the second bottom liquid stream by the bottom of described domethanizing column, and by the second bottom liquid stream fractional distillation to provide one or more natural gas liquids (NGL) stream.

The method of 13. claim 12, wherein the fractionating step of the second bottom liquid stream comprises: be introduced in dethanizer by described stream, second bottom liquid stream is separated into the fraction of rich ethane and wherein rich in the fraction of the hydrocarbon heavier than ethane, the fraction of described rich ethane at the collected overhead of dethanizer as the 3rd overhead vapours, the described fraction rich in the hydrocarbon than ethane more weight at the bottom collection of dethanizer as the 3rd bottom liquid.

The method of 14. claim 13, wherein said method also comprises:

The method of 15. claim 13, wherein said method also comprises as provided below being back in dethanizer: by other stream indirect heat exchange with the first overhead materials of liquefaction, make the part condensation of the 3rd overhead vapours, forming the 3rd overhead stream of liquefaction, described 3rd overhead stream is re-introduced into the top to described dethanizer as backflow stream.

The method of 16. claim 13, wherein said 3rd overhead vapours comprises the ethane of at least about 95%, and described 3rd bottom liquid comprises the ethane of less than about 5 moles of %.

17. for fractional distillation and the system of liquefied natural gas feed stream, described system comprises:

One below or both:

The system of 18. claim 17, wherein said pipeline group, one or more heat exchangers, and one or more separator are arranged and operation is to take out described first vapor stream of top of the tower, cool down, condense and to separate, and it comprises:

Arrange and operate the liquid for isolated and the separator of vapor phase；

The system of 19. claim 18, wherein said system also comprises arranges and operation is for receiving and making the supercool heat exchanger of the second of the first overhead materials of described liquefaction or heat exchanger section.

The system of 20. claim 18, wherein arrange and operate and comprise the warm bundle around tubular type main heat exchanger for the described heat exchanger section of the first vapor stream of top of the tower described in cooling and partial condensation, and arrange and operation comprises the middle bundle around tubular type main heat exchanger and/or cold bundle cooling down and to condense at least one of described heat exchanger section of described separation vapor phase further.

The system of 21. claim 18, wherein arrange and operate and comprise overhead condenser heat exchanger for the described heat exchanger of the first vapor stream of top of the tower described in cooling and partial condensation, and at least one of described heat exchanger arranging and operating the vapor phase for cooling down further and condensing described separation comprises around tubular type main heat exchanger.

The system of 22. claim 17, wherein arranges and operates for taking out, cool down, condense and the described pipeline group of the most described first vapor stream of top of the tower and one or more heat exchanger comprising:

The system of 23. claim 22, wherein said system also comprises heat exchanger or heat exchanger section, it is arranged and operation is for making flowing through of described cooled and condensation cold, and the most described stream is by separately with at least one other stream of the first overhead materials of first-class, the second of the first overhead materials of liquefaction and liquefaction that form the first overhead materials of liquefaction.

The system of 24. claim 22, wherein said system also comprises arranges and heat exchanger that the second of the operation the first overhead materials for making described liquefaction is supercool or heat exchanger section.

The system of 25. claim 17, wherein said system also comprises:

The system of 26. claim 25, wherein said system also comprises:

The system of 27. claim 25, wherein said system also comprises heat exchanger, it is arranged and operation is for by other stream indirect heat exchange with the first overhead materials of liquefaction, make the part condensation of described 3rd overhead vapours, form the 3rd overhead stream of liquefaction, it is re-introduced into the top to described dethanizer as backflow stream, thus provides the backflow of described dethanizer, and arranges and operation is for being introduced to the pipeline of described heat exchanger by other stream described in the first overhead materials of liquefaction.