JP2008545819A - Integrated NGL recovery and liquefied natural gas production - Google Patents

Abstract

  Separation of methane from a mixture (110) of ethane and higher hydrocarbons, in particular natural gas, using a scrub column (114), the mixture being partially condensed (122) Is separated into a methane-rich top (116) that provides reflux to column 114 and a liquid methane-poor bottom liquid (126) that is rich in ethane from the bottom liquid fraction (128). Improved by providing additional reflux (136) from stream (130). Preferably, the absorbent liquid (140) from fraction (128) is also introduced into the scrub column. The vapor fraction (120) remaining after partial condensation can be liquefied (122) to obtain an LNG product (124).

Description

  The present invention relates to the separation of methane from mixtures with ethane and heavier hydrocarbons, in particular, but not exclusively, recovers natural gas liquid (NGL) and liquefies from natural gas (NG). Has application to an integrated process for producing natural gas (LNG).

  Natural gas contains mainly secondary components including methane and heavier hydrocarbons. Most of liquefied natural gas is methane. Hydrocarbons heavier than methane are usually condensed and recovered as natural gas liquids and fractionated to produce high value hydrocarbon products.

  A typical NG liquefaction apparatus includes a scrub column that is fed with feed gas or pipeline gas and produces methane-rich top vapor and NGL as the bottom liquid. A portion of the methane-rich top vapor is partially condensed to provide reflux to the tower and the remainder is liquefied to give an LNG product. The bottom liquid is fractionated, and individual hydrocarbons and / or hydrocarbon fractions (fractions) are obtained as high value products.

The efficiency of liquefaction improves with increasing pressure, so the NG liquefaction pressure should be significantly greater than the critical pressure of methane in order to minimize the power consumption of the LNG process. However, recovering heavy hydrocarbons with a scrub column becomes more difficult with increasing pressure, and it is impossible to separate the mixture at higher than its critical pressure. Thus, to achieve satisfactory separation, the scrub column must be operated at a pressure significantly below the critical pressure of methane. A common solution is to expand the scrub column feed and then compress the top vapor. The results obtained from the isentropic expansion of the feed can be used to operate at least partially the overhead compressor or compressors. Such a solution is shown in US-A-4065278 (published December 27, 1977). Expansion of the scrub column feed followed by overhead vapor compression can be avoided by recirculating heavy components from the NGL fraction to or near the top of the scrub column as an absorbent liquid. . For example, Chen-Hwa Chiu (Oil and Gas Journal, Nov. 24, 1997, 56-63) uses heavy alkane recycles, such as all or part of the C ₄ NGL fraction, in the scrub column of the LNG process. By doing so, it is reported that the critical pressure of the separated mixture and thereby the operating pressure on the scrub column can be increased. In an exemplary process, there is a recycle of some or all of the C ₄ NGL fraction recovered from the debutanizer.

  WO01101307 / US-A-2003005722 / US-B-6,742,358 (December 2, 2002 / January 9, 2003 / June 1, 2004) An LNG process is disclosed which is provided by condensing vapor drawn from the middle position of the column. The document also describes that the vapor and liquid fractions of the partially condensed feed gas are fractionated separately, and the bottom liquid from the vapor fraction fraction is intermediate or relative to the liquid fraction fraction. A process for providing overhead reflux is disclosed. In all of these processes, the top vapor from the scrub column is compressed before liquefaction.

DE-A-10205366 (published 21 August 2003) cools the ethane-rich steam from the scrub column and becomes the second column for removal of the remaining higher hydrocarbons. An LNG process to pass is disclosed. The second column bottoms provide reflux to the scrub column. Preferably, the C ₄ / C ₅ NGL fraction provides reflux to the second column. The adjustment and adsorption functions of the two towers can be combined into a single tower.

  US-A-6662589 / EP-A-1469266 (published on December 16, 2003 / October 20, 2004) discloses that an NGL fraction containing a plurality of components heavier than ethane is contained in a natural gas supply unit and methane. An LNG process is disclosed which is fed as an absorbent liquid to the scrub column at a location between the rich reflux feed. In an exemplary embodiment, the reflux is obtained by partial condensation of overhead vapor from a scrub column. The top of the scrub column is not compressed prior to liquefaction to give LNG product.

WO 2004/010064 (published January 29, 2004) discloses an LNG process in which the C ₄ / C ₅ NGL fraction is fed directly or indirectly to the scrub column to provide additional reflux. The fraction is fed to the column at or above the reflux feed provided by partial condensation of the top vapor.

The critical pressure of the mixture in the scrub column can also be increased by refluxing the column with a stream rich in ethane. This also allows a high recovery of good C ₂ -C ₃ propane from separation and NGL (C _3).

WO-A-0188447 / US-A-6,401,486 (published on November 22, 2001 and June 11, 2002) shows that the top reflux for the scrub column is mostly methane, and very little Disclosed is an LNG process provided by condensation of steam containing ethane with propane. The scrub tower top vapor is totally liquefied to give the LNG product, and the scrub tower bottom is fractionated in the NGL purification tower. The vapor condensed to give the top reflux is
(I) overhead steam from NGL fraction, and any steam that has flowed vigorously obtained by vigorously flowing the liquefied and preferably subcooled scrub tower top to near atmospheric pressure,
(Ii) the wake of the feed gas part,
(Iii) Vigorously flowing steam obtained by vigorously flowing a liquefied and preferably subcooled scrub column top to near atmospheric pressure, or (iv) a liquefied and preferably subcooled scrub column top. part,
Can be derived from.

  Options (i), (iii), and (iv) can provide additional reflux to the scrub column by condensing the wake of the feed gas portion, but NGL fraction and partially condensed scrub There is no suggestion of providing reflux from both tower tops. In these processes, it is not necessary to compress the top of the scrub column before liquefaction.

  EP-A-0178207 / US-A-4,690,702 (released on April 15, 1986 / September 1, 1987), DE-A-3802553 / US-A-4,952,305 (1989) August 3 / August 28, 1990), and EP-A-03575752 / US-A-5,291,736 (April 7, 1993 / March 8, 1994) Both LNG processes are disclosed wherein reflux to is provided by a mixture of methane and ethane obtained by condensation of overhead vapor from the NGL fraction. None of these patents show the reflux obtained by partial condensation of the overhead product.

  The recovery of NGL and natural gas products can be improved by combining the benefits of reflux obtained by partial condensation at the top of the scrub column with the benefits of an ethane-rich reflux and an efficient mode of absorbent liquid. However, it was found from the viewpoint of calorific efficiency, facility simplicity, and recovery of high-value components such as propane and butane.

The invention, in its broadest aspect, provides a method for recovering components heavier than methane from a feed of methane mixed with ethane and heavier one or more hydrocarbons; The method
Introducing the feed into the scrub column at a first location;
Removing from the scrub column a first overhead vapor stream that is poor in a plurality of components heavier than methane and a bottom stream that is rich in a plurality of components heavier than methane;
Cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separating the bottom stream into a stream rich in ethane and one or more streams rich in a plurality of components heavier than ethane, and selected from a second position and a third position above the first position And introducing a second ethane-rich reflux derived from the ethane-rich stream into the scrub column at a location.

  In a preferred embodiment of the present invention, preferably the ethane-rich stream obtained from the NGL fraction is condensed and pumped, and the reflux obtained by partially condensing the scrub tower overhead vapor. Combine and recycle to a scrub column, preferably a scrub column reflux drum. This allows the scrub column to operate at higher pressures by increasing the critical pressure of the mixture and also improves ethane-propane separation. The ethane-rich stream can be fully condensed using mixed refrigerant (MR) cooling possible in the main heat exchanger of the LNG process to maximize the benefits.

  It is also advantageous to use heavy recycle streams, in particular pentane and isopentane. Such a stream can be introduced either to the reflux drum or directly to the scrub column. Heavy and light recycles can be combined and cooled separately or preferably mixed with the reflux obtained by condensation of the scrub column overhead vapor. The reflux obtained by condensation of the top vapor typically exceeds about 80% of the total liquid reflux (including any heavy recycle stream) to the scrub column. In the preferred implementation, the cooling is performed in the warm bundle of the main LNG process heat exchanger.

As noted above, the present invention, in its broadest process aspect, recovers multiple components heavier than methane from a feed of methane mixed with ethane and heavier one or more hydrocarbons. Provide a way for
Introducing the feed into the scrub column at a first location;
Removing from the scrub column a first overhead vapor stream that is heavier than a plurality of components heavier than methane and a bottom stream rich in a plurality of components heavier than methane;
Cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separating the bottom stream into a stream rich in ethane and one or more streams rich in a plurality of components heavier than ethane, and selected from a second position and a third position above the first position And introducing a second ethane-rich reflux derived from the ethane-rich stream into the scrub column at a location.

In a corresponding apparatus aspect, the present invention provides a method according to the preceding aspect, wherein a plurality of components heavier than methane are obtained from a feed of methane mixed with ethane and heavier one or more hydrocarbons. Providing an apparatus for retrieval, the apparatus comprising:
Scrub tower,
Conduit means for introducing a feed into the scrub column at a first location;
Conduit means for removing from the scrub column a first overhead vapor stream that is heavier than methane and less of a plurality of components;
Heat exchanger means for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separation means for separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Conduit means for introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separation means for separating the bottom stream into a stream rich in ethane and one or more streams rich in a plurality of components heavier than ethane, and from a second position and a third position above the first position It includes conduit means for introducing into the scrub column a second ethane-rich reflux derived from the ethane-rich stream at a selected location.

In a preferred process aspect, the present invention provides a process for obtaining liquefied methane from a feed of methane that is mixed with ethane and heavier hydrocarbon (s).
Introducing the feed into the scrub column at a first location;
Removing from the scrub column a first overhead vapor stream that is heavier than a plurality of components heavier than methane and a bottom stream rich in a plurality of components heavier than methane;
Cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Liquefying the second overhead vapor stream,
Introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separating the bottom stream into a stream rich in ethane and one or more streams rich in multiple components heavier than ethane, and a second reflux rich in ethane derived from the stream rich in ethane, Introducing into the scrub column at a position selected from a second position and a third position above the position.

In a preferred apparatus aspect, the present invention provides for obtaining liquefied methane from a feed of methane mixed with ethane and heavier hydrocarbon (s) by a process according to the preferred process aspect described above. A device comprising:
Scrub tower,
Conduit means for introducing a feed into the scrub column at a first location;
Conduit means for removing from the scrub column a first overhead vapor stream that is heavier than methane and less of a plurality of components;
Heat exchanger means for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separation means for separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Heat exchange means for liquefying the second overhead vapor stream;
Conduit means for introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separation means for separating the bottom stream into a stream rich in ethane and one or more streams rich in a plurality of components heavier than ethane, and from a second position and a third position above the first position It includes conduit means for introducing into the scrub column a second ethane-rich reflux derived from the ethane-rich stream at a selected location.

  As indicated above, it is preferred that the feed is a cooled natural gas feed and the second overhead vapor is liquefied to provide a liquefied natural gas product.

  The second ethane-rich reflux can be fed to the scrub column separately from the methane-rich first reflux, but is preferably mixed with the methane-rich first reflux before introduction into the scrub column.

  The ethane rich stream can be partially or fully condensed before mixing with the first reflux rich in methane. The mixing is preferably effected by feeding a first two-phase stream upstream or inside the reflux drum or to the bottom of an absorber tower where a second reflux rich in ethane is fed as reflux.

  The ethane rich stream is introduced into the scrub column, preferably alone or after mixing with one or more other process streams, as feed temperature to the scrub column and a second ethane rich reflux. It is condensed at a temperature lower than the temperature of the condensate stream being pumped. The temperature is usually less than -32 ° F (-35.5 ° C).

  Usually, the ethane-rich stream (130) is the top vapor of the deethanizer. Methane can be removed from the ethane-rich stream so that the second reflux consists essentially of ethane. Preferably, the second reflux contains less than about 0.05% propane.

  Typically, the first reflux rich in methane can account for about 80% or more of the total reflux (ie, the liquid feed to the scrub column above the first location), and the second reflux is about It can be less than 20%.

  Preferably more than 90%, in particular more than 96% of the propane and / or butane contained in the feed is recovered as product from the bottoms stream.

  As shown in FIG. 6, the first overhead stream can be partially condensed in two stages and the liquid fraction from each condensate can be fed to the scrub column as reflux.

In a preferred embodiment, the method of the invention comprises:
Introducing the feed into the scrub column at a first location;
Removing from the scrub column a first overhead vapor stream that is poor in a plurality of components heavier than methane and a bottom stream that is rich in a plurality of components heavier than methane;
Cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separating the bottom stream into a stream rich in ethane and two or more streams rich in multiple components heavier than ethane, including an absorbent liquid stream rich in multiple components heavier than ethane;
Introducing a second ethane-rich reflux derived from the ethane-rich stream into the scrub column at a position selected from the second position and the third position above the first position; and an absorbent liquid In a scrub tower at a position selected from a second position, a third position and a fourth position above the first position.

In a related preferred device aspect, the device of the present invention comprises:
Scrub tower,
Conduit means for introducing a feed into the scrub column at a first location;
Conduit means for removing from the scrub column a first overhead vapor stream that is heavier than methane and less of a plurality of components;
Heat exchanger means for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separation means for separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Conduit means for introducing a first reflux rich in methane at a second location in the scrub column above the first location;
Separation to separate the bottom stream into two or more streams comprising an ethane rich stream and an absorbent liquid stream rich in one or more components heavier than ethane, rich in multiple components heavier than ethane means,
Conduit means for introducing an ethane-rich second reflux derived from the ethane-rich stream into the scrub column at a position selected from the second position and the third position above the first position; and Conduit means for introducing the absorbent liquid into the scrub column at a position selected from a second position, a third position and a fourth position above the first position.

  All of the above features for the broadest aspect apply to this preferred embodiment.

The absorbent liquid can contain one or more C ₄ hydrocarbons, but preferably contains one or more C ₅₊ hydrocarbons.

  The absorbent liquid can be fed to the scrub column separately from either the second reflux rich in ethane or the first reflux rich in methane. However, it is preferred to combine at least one of the first reflux rich in methane and the second reflux rich in ethane (136) prior to introduction into the scrub column. For example, it can be combined with a first two-phase flow upstream or inside the reflux drum and / or a second reflux rich in ethane, or an absorbent solution and optionally a second reflux rich in ethane as reflux. The first two-phase flow can be supplied to the bottom of the absorption tower to be supplied. The absorbent liquid can be combined with the first overhead vapor stream prior to partial condensation of the stream to form a first two-phase flow and / or a gaseous ethane rich stream and It can be combined prior to condensation of the stream to provide a second reflux.

  The combined absorbent liquid and gaseous ethane-rich stream can be phase separated, and the liquid fraction can be fed to the scrub column above the first location. The liquid fraction and the first overhead stream can be combined prior to partial condensation of the overhead stream to provide a first two-phase flow. The vapor fraction is condensed and the condensed stream is fed to the scrub column above the first location and added to the second overhead vapor before liquefaction, or the first overhead stream and the overhead stream It can be combined prior to partial condensation to give a first two-phase flow. Both the condensed vapor and liquid fractions can be combined to give a first two-phase flow prior to partial condensation of the first overhead stream and the overhead stream.

  Typically, the absorbent liquid comprises less than about 10% of the total reflux (ie, the liquid feed to the scrub column above the first location).

The following is a description of the presently preferred embodiments of the invention, by way of example only and with reference to the accompanying drawings. In the drawing
FIG. 1 illustrates one embodiment of the present invention,
FIG. 2 shows a variation of the embodiment of FIG. 1, wherein the reflux drum (118) is replaced by an absorption tower (218).
FIG. 3 shows another variation of the embodiment of FIG. 1, wherein the ethane rich stream (130) and the “absorbent liquid” stream (140) are combined to form a single stream (330).
FIG. 4 shows a variation of the embodiment of FIG. 3, wherein the combined second reflux and absorbent liquid stream (330) is phase separated (430).
FIG. 5 shows a variation of the embodiment of FIG. 4, wherein the separated vapor portion (436) is compressed, cooled and condensed, and the resulting stream (536) is combined with the liquid portion (438). Yes,
FIG. 6 shows another variation of the embodiment of FIG. 4, wherein the top vapor (116) from the scrub column (114) is condensed in two stages (612, 122) and separated to the scrub column (619). , 626).

Referring to FIG. 1, mainly contains methane with heavier hydrocarbons in the C _2-6 range, with very small amounts of water, acid gases such as CO ₂ and H ₂ S, and other contaminants such as mercury. The pretreated pressurized natural gas feed 110 is cooled in the heat exchanger 112 between about −20 ° F. (−29 ° C.) to about −40 ° F. (−40 ° C.) and scrubbed. It is supplied to the tower 114. Typically, the feed 110 is at a pressure between about 600 to about 900 psia (4 to 6.25 MPa) and around ambient temperature. The heat exchanger 112 represents multi-stage cooling by propane depressurization at various pressures. Any other cooling means such as vaporization of the mixed refrigerant in a single exchanger can be used. Stream 110, or the vapor portion of stream 110 downstream of heat exchanger 112, can be throttled or isentropically expanded into column 114. The energy resulting from the expansion can be used to at least partially compress other vapor streams, such as process streams 116, 120, 150, or 156.

The scrub column 114 separates the feed into bottom liquids 126 and 127 rich in heavier hydrocarbons and a “first” overhead vapor stream 116 rich in methane. One portion 127 of the bottom liquid is vaporized in the reboiler 128 to boil the column 114. The reboiler 128 may provide heat using a portion of the feed stream 110 or any other suitable process stream. The column may also have an intermediate reboiler and the feed stream portion can also provide heat to the intermediate reboiler. The remaining column bottom liquid 126 is generally referred to as a natural gas liquid (NGL) and is supplied to the NGL fractionator 128. Here, NGL is usually depressurized and separated using a known separation device such as a deethanizer, a depropanizer, and / or a debutanizer to give two or more hydrocarbon fractions. The bottom liquid 126 is composed of a stream containing methane and ethane together with very small amounts of propane (ethane rich stream) and a fraction containing mainly C ₃ , C ₄ and C ₅₊ hydrocarbons (ie n-pentane). , Isopentane and heavier). Typically, the ethane-rich stream 130 contains less than about 0.05% propane at the top of the deethanizer.

  The use of a second reflux 136 rich in ethane allows high recovery of propane (96-99%) and butane (almost 100%) in the fractionator.

A portion of the C ₅₊ hydrocarbons is removed as “absorbent” liquid 140, and the scrub column pressure (ie, sufficient pressure to introduce it into the scrub column 114 to reduce the equipment pressure drop and static pressure). Pumped by pump 142, cooled opposite to propane vaporization in heat exchanger 144, further cooled in main heat exchanger 122, and combined with a second reflux obtained by NGL fractionation Or directly into the reflux drum 118, either as indicated by the shaded lines. The heat exchanger 144 can be placed before or after the pump 142.

  Mixing the absorbent liquid 140 and the second reflux 136 prior to introduction into the reflux drum 118 is preferably performed because equilibrium and some absorption can occur in the conduit.

  As indicated by the shaded lines, the absorbent liquid 140 can be fed directly to or near the top of the scrub column 114 or, in a preferred implementation, combined with the first overhead vapor stream 116 upstream of the main heat exchanger 122. Can do.

  The ethane-rich stream 130 is cooled and partially condensed in the heat exchanger 132 as opposed to propane vaporization, cooled and fully condensed in the main heat exchanger 122, and pumped to the scrub column pressure. Pumped, preferably combined with the absorbent liquid 140 and introduced as a stream 136 into the reflux drum. Any uncondensed steam upstream of the pump 134 can be separated and condensed in the central bundle of the main heat exchanger 122 and combined with the liquefied natural gas product 124.

The absorbent liquid 140 can be obtained either purely or blended together from lighter products of NGL fractions such as C ₃ and C ₄ hydrocarbons. This can include most C ₅ hydrocarbons without a additional may not accept a distillation column C ₆ and heavier components. Stream 130 can be nearly pure ethane, methane, which is not accepted by additional distillation columns. Part of the ethane or ethane-methane mixture can be recovered as a product.

  The first overhead vapor stream 116 is cooled and partially condensed in the warm temperature bundle of the main heat exchanger 122 and introduced into the reflux drum 118. This can be condensed before cooling in the main heat exchanger 122 (not shown). The liquid portion returns to the scrub column as the “first” liquid reflux 119. The “second” vapor portion 120 enriched in methane is liquefied and preferably subcooled in the middle low temperature bundle of the main heat exchanger to obtain the LNG product 124.

  In a preferred implementation, the partially condensed first overhead vapor stream 116 is combined within or upstream of the second reflux 136 and / or sorbent liquid 140 and the reflux drum 118, thereby providing some equilibrium. Happens. Thus, the first liquid reflux (the liquid portion of the first overhead vapor partially condensed) is mixed with the second liquid reflux 136 and / or the absorbent liquid 140.

  Typically, depending on the natural gas feed composition, the second reflux 136 is less than about 20% of the total reflux (including any absorbent liquid) and the absorbent liquid 140 is about the total reflux. Less than 10%. If the natural gas feed 110 does not contain suitable components in the absorbent liquid 140 or does not contain them in sufficient quantities, they can be introduced as additional feeds.

  The second vapor stream 120 can be condensed (not shown) prior to introduction into the main heat exchanger 122 and / or depressurized prior to subcooling. If the LNG product 124 is stored at high pressure (PNGL), there is no need to subcool in the low temperature bundle.

  The main heat exchanger 122 is cooled by vaporizing a recirculated mixed refrigerant (MR) stream 150 that is compressed, cooled, and liquid in multiple stages to vaporize propane. 152 and lighter steam 156 (compression, cooling and phase separation not shown). Steam 156 condenses, cools and expands through throttle valve 158. Liquid 152 is cooled, expanded, and combined with vaporized condensed vapor 156 via a throttle valve 154. The combined MR stream is fully vaporized and exits main heat exchanger 122 as stream 150. Throttle valves 154 and / or 156 can be replaced with isentropic rich fluid expanders such as hydraulic turbines. The main heat exchanger 122 can be cooled using any other cooling device or combination of devices such as a pure fluid cascade and isentropic vapor expansion as described in US-A-6308531.

  FIG. 2 shows a variation of the embodiment of FIG. 1 with the reflux drum 118 replaced with an absorption tower 218. Absorbent liquid 140 and / or second reflux 136, preferably a combination of both in stream 136, are fed to the top of absorption tower 218. They can also enter the tower with at least one of the two streams fed to the top of the absorption tower 218 independently at the same or different positions. For example, the absorbent liquid 140 can be supplied to several stages below the top of the tower or at the bottom of the tower. The second top vapor stream 120 is withdrawn from the top of tower 218 and the first reflux 119 is withdrawn from the bottom. Multiple stages within column 218 improve the absorption of heavy components from the rising steam.

  FIG. 3 shows another variation of the embodiment of FIG. 1, wherein the ethane rich stream 130 and the absorbent liquid 140 are combined to form a single stream 330. Stream 330 is cooled and partially condensed in heat exchanger 332 as opposed to propane vaporization, further cooled and fully condensed in main heat exchanger 122, pumped to pump 334 to scrub column pressure, and refluxed. Introduced into the drum. Mixing streams 130 and 140 at a warmer temperature and condensing them together is more thermodynamically more effective than the arrangement shown in FIGS. This advantage is similar to that of the absorption tower 218 as absorption occurring in the heat exchangers 332 and 122. This arrangement also eliminates the passage in the main heat exchanger 122. With the arrangement of FIG. 1, streams 116 and 330 can be combined downstream of main heat exchanger 122 and in front of reflux drum 118.

  FIG. 4 shows a variation of the embodiment of FIG. 3 wherein a combined ethane rich stream and absorbent liquid stream 330 is fed to the phase separator 430. The liquid portion 438 is pumped with a pump 432 to the pressure of the scrub column 114 and combined with the first overhead vapor 116 upstream of the main heat exchanger 122. The combined stream 416 exiting the main heat exchanger 122 is then fed to the reflux drum 118. The smaller vapor portion 436 is condensed in the main heat exchanger 122, pumped by the pump 434 and introduced into the reflux drum 118, optionally combined with the stream 416, or the liquid may be depressurized before subcooling. Combined with liquefied natural gas upstream of the subcooled portion (low temperature bundle) of the main heat exchanger 122. Combining both streams 130 and 116 and the absorbent liquid 140 upstream of the main heat exchanger 122 further increases the thermodynamic effectiveness of the method.

  As an option, stream 438 can be cooled in a separation circuit within main heat exchanger 122 prior to introduction to reflux drum 118. If stream 130 contains little methane that may not be accepted in the scrub column 114 or additional demethanizer in the fractionator, stream 330 can be fully condensed and no phase separator 430 is required, There can be no flow 436 and no pump 434. Further, stream 438 can be fed directly to scrub column 114, eg, a second stage below the top of the column.

  FIG. 5 is a variation of the embodiment of FIG. 4 in which the separated vapor portion 436 is compressed by the compressor 530 to the pressure of the scrub column 114 and cooled and condensed in the heat exchanger 532 resulting in the resulting stream 536. Are combined with the liquid portion 438 to form a flow 538. The heat exchanger 532 can be a series of heat exchangers, the first using cooling water and the other one or more using propane vaporization. Stream 438 is warmed to near ambient temperature prior to compression in the additional heat exchanger and is also followed by additional heat efficiency in the post-cooler and the same additional heat exchanger following the compression. Can be cooled. Stream 536 may be a rich supercritical fluid.

  FIG. 6 is another variation of the embodiment of FIG. 4 in which the first overhead vapor 116 is replaced in the heat exchanger 612 with, for example, one or both of reflux 136 and absorbent liquid 140, but preferably propane. What is partially condensed by being cooled by vaporization is shown. The resulting first two-phase stream is separated in a phase separator 618 into a “second” overhead vapor stream 616 and a liquid stream 619 rich in methane. Liquid stream 619 is returned to scrub column 114 as reflux. At this time, stream 616, which is at a temperature consistent with the temperature at the bottom of main heat exchanger 122, is mixed with stream 438, cooled in main heat exchanger 122, and fed to reflux drum 628 as two-phase stream 626. Is done. The overhead vapor stream 620 from the reflux drum 628 is liquefied in the main heat exchanger 122 and recovered as a liquefied natural gas product 124. Liquid stream 629 from reflux drum 628, optionally reheated in main heat exchanger 122, is returned to scrub column 114 at the same or different position as reflux 619.

  The phase separator 618 and / or reflux drum 628 can be replaced with an absorption tower having a two-phase feed at the bottom of the tower and reflux provided by the cooled streams 136 and / or 140 at the top of the tower.

  Individual features or combinations of these features described in connection with any aspect shown may be incorporated into any other aspect shown as appropriate. For example, the additional reheating of the reflux 629 in the main heat exchanger 122 described in connection with FIG. 6 can be applied to any of FIGS. Additionally or alternatively, the supply of reflux to the scrub column 114 by the liquid fraction 619 derived from the first overhead vapor 116 of the embodiment of FIG. 6 is also applicable to any of the embodiments of FIGS.

EXAMPLE Using the embodiment of FIG. 3, a 97,904 lbmol / h (44,408.5 kgmol / h) pre-purified natural gas stream 110 at 950 psia (6.5 MPa) is passed through a heat exchanger 112 in three stages. Cool to -32.3 ° F. (−35.7 ° C.) with propane cooling and feed to scrub column 114. This feed stream 110 consists of 0.6% nitrogen, 84.8% methane, 7.3% ethane, 4.4% propane, 0.7% isobutane, 1.5% butane,. Contains 3% isopentane, 0.2% pentane, and 0.2% hexane. The column 114 operates at 840 psia (5.8 MPa) and is an intermediate reboiler heated by propane cooling and 40% of the stream 110 that does not pass through the first two stages of the bottom reboiler 128 at about 130 ° F. (55 ° C.). Have The top 116 is cooled from −62.3 ° F. (−52.4 ° C.) to −77.5 ° F. (−60.8 ° C.) in the warm temperature bundle of the main heat exchanger 122 and is about 15% Is introduced into the reflux drum 118 as a two-phase flow containing a liquid. The scrub column bottom stream 126 is sent to a fractionator 128 comprising a series of distillation towers including a deethanizer, a depropanizer, and a debutanizer. 96% of the propane present in the feed stream 110 is recovered as depropanizer overhead. Almost all of butane and isobutane is recovered as the debutanizer overhead. Deethanizer overhead with about 39% methane, 61% ethane, and only 0.05% propane at a flow rate of 6,105 lbmol / h (2,769 kgmol / h) and pressure 420 psia (2.9 MPa) Constitutes 39% of the debutanizer bottoms and is mixed with stream 140 where the remainder is recovered as C ₅₊ product Low propane concentration is important for high propane recovery. Stream 140 is liquid at 17 psia (117 kPa) and a flow rate of 406 lbmol / h (184 kgmol / h) and contains about 51% isopentane, 36% pentane, 12% hexane and less than 1% lighter components. This is pumped to 420 psia (2.9 MPa) before mixing with ethane rich stream 130 with a pump not shown in FIG. Combined stream 330 is cooled to -32.3 ° F. (−35.7 ° C.) by propane in heat exchanger 332 and -77.5 ° F. (in the warm temperature bundle of main heat exchanger 122) By further cooling to −60.8 ° C., it is completely condensed. The condensed stream is pumped to the scrub column pressure with pump 334 and introduced into reflux drum 118. Liquid reflux 119 is returned to the top of scrub column 114 at −74.2 ° F. (−59.0 ° C.) and has the thermal effect of pumping and mixing in the phase separator. Stream 120 contains 91.3% methane, 7.8% ethane, 0.7% nitrogen, 0.2% propane, and only traces of heavier hydrocarbons, −74.2 ° F (−59.0 ° C.) and a flow rate of 83,571 lbmol / h (37,907 kgmol / h). This is cooled to −161.6 ° F. (−107.6 ° C.) in a low temperature bundle in the middle of the main heat exchanger 122 and then lowered to a storage pressure of 15.3 psia (105.5 kPa) as a liquid stream 124. . The main heat exchanger 122 is cooled by a mixed refrigerant containing nitrogen, methane, ethane and propane, as described with reference to FIG.

  Of course, the present invention is not limited to the above-described details regarding the preferred embodiments, and numerous modifications and variations can be made without departing from the scope of the invention as defined in the appended claims.

FIG. 1 illustrates one embodiment of the present invention. FIG. 2 shows a variation of the embodiment of FIG. 1, wherein the reflux drum (118) is replaced with an absorption tower (218). FIG. 3 shows another variation of the embodiment of FIG. 1, wherein the ethane rich stream (130) and the “absorbent liquid” stream (140) are combined to form a single stream (330). FIG. 4 shows a variation of the embodiment of FIG. 3, wherein the combined second reflux and absorbent liquid stream (330) is phase separated (430). FIG. 5 shows a variation of the embodiment of FIG. 4, wherein the separated vapor portion (436) is compressed, cooled and condensed, and the resulting stream (536) is combined with the liquid portion (438). Yes. FIG. 6 shows another variation of the embodiment of FIG. 4, wherein the top vapor (116) from the scrub column (114) is condensed in two stages (612, 122) and separated to the scrub column (619). , 626).

Claims (41)

Recovering a heavier component than methane from a supply of methane mixed with ethane and one or more heavier hydrocarbons,
Introducing the feed into the scrub column at a first location;
Removing from the scrub column a first overhead vapor stream that is less heavier than methane and a bottom stream that is heavier than methane;
Cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separating the first two-phase stream to provide a second overhead vapor stream and a first reflux rich in methane;
Introducing a first methane-rich reflux at a second location in the scrub column above the first location, and enriching the bottom stream with an ethane-rich stream and a plurality of components heavier than ethane. Separating into one or more streams,
And a second reflux rich in ethane is introduced into the scrub column at a position derived from the ethane-rich stream and selected from the second position and the third position above the first position. A method characterized by that.   The method of claim 1, wherein the feed is a cooled natural gas feed.   The method of claim 1 or 2, wherein the first reflux rich in methane comprises about 80% or more of the total reflux (i.e., liquid feed to the scrub column above the first location).   The method of any preceding claim, wherein the second reflux is less than about 20% of the total reflux (ie, the liquid feed to the scrub column above the first location).   The ethane rich stream is condensed below the temperature of the feed to the scrub column and the temperature of the condensed stream pumped before being introduced as a second ethane rich reflux into the scrub column, supra. A method according to any of the claims.   The process according to any of the preceding claims, wherein the second ethane-rich reflux is fed to the scrub column separately from the first methane-rich reflux.   6. A process according to any preceding claim, wherein the second reflux rich in ethane is mixed with the first reflux enriched in methane prior to introduction into the scrub column.   The method of claim 7, wherein the second ethane-rich reflux is combined with the first two-phase flow at a location selected from upstream and inside the reflux drum.   8. The process of claim 7, wherein the first two-phase stream is fed to the bottom of an absorption tower where a second reflux rich in ethane is fed as reflux.   10. A process according to any of claims 7 to 9, wherein the ethane rich stream is fully condensed before being mixed with the first methane rich reflux.   A process according to any of the preceding claims, wherein the ethane-rich stream is the vapor at the top of the deethanizer.   The absorbent liquid derived from one or more streams rich in components heavier than the ethane is scrubbed at a position selected from the second position, the third position and the fourth position above the first position. A method according to any of the preceding claims, which is introduced into the tower.   The method of claim 12, wherein the absorbent liquid comprises pentane and isopentane. The absorbent solution comprises a C ₄ hydrocarbons of one or more, The method of claim 12 or 13. _15. A method according to any of claims 12 to 14, wherein the absorbent liquid comprises one or more C5 ₊ hydrocarbons.   17. A process according to any of claims 12 to 16, wherein the absorbent liquid is fed to the scrub column separately from either the second reflux rich in ethane or the first reflux rich in methane.   16. A process according to any of claims 12 to 15 wherein the absorbent liquid is combined with at least one of a first reflux rich in methane and a second reflux rich in ethane prior to introduction into the scrub column.   The method of claim 17, wherein the absorbent liquid is combined with at least one of a first two-phase flow and an ethane rich second reflux at a location selected from upstream and inside the reflux drum.   18. The method of claim 17, wherein the first two-phase stream is fed to the bottom of an absorption tower in which at least one of an absorbent liquid and an ethane rich second reflux is fed as reflux.   21. The method of claim 19, wherein the absorbent liquid is combined with a first overhead vapor stream prior to forming a first two-phase stream with partial condensation of the stream.   16. A method according to any of claims 12 to 15, wherein the absorbent liquid is combined with a gaseous ethane rich stream to provide a second reflux prior to condensing the stream.   The method of claim 21, wherein the combined absorbent liquid and gaseous ethane-rich stream are phase separated and the liquid fraction is fed to a scrub column above the first location.   23. The method of claim 22, wherein the vapor fraction is condensed and fed to a scrub column above the first location.   24. A method according to claim 22 or 23, wherein the liquid fraction and the first overhead stream are combined prior to partial condensation of the overhead stream to provide a first two-phase flow.   24. The method of claim 22 or 23, wherein the condensed vapor fraction and the first overhead stream are combined prior to partial condensation of the overhead stream to provide a first two-phase flow.   26. A method according to any of claims 12 to 25, wherein the absorbent liquid is less than about 10% of the total reflux (i.e., liquid feed to the scrub column above the first location).   The process of any preceding claim, wherein the second reflux comprises less than about 0.05% propane.   The method according to any of the preceding claims, wherein the second reflux consists essentially of ethane by removing methane from the ethane-rich stream. An apparatus for recovering components heavier than methane from a feed of methane mixed with ethane and heavier one or more hydrocarbons by the method of claim 1, comprising:
Scrub tower (114),
Conduit means (110) for introducing the feed into the scrub column at a first location;
Conduit means (116) for removing from the scrub column a first overhead vapor stream rich in components heavier than methane and a bottoms stream (126) rich in components heavier than methane;
Heat exchange means (122) for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;
Separation means (118, 218) for separating the first two-phase stream to provide a second overhead vapor stream and a methane-rich first reflux;
Conduit means (119) for introducing the first reflux rich in methane at a second location in the scrub column above the first location;
Separation means (128) for separating the bottom stream into an ethane-rich stream and one or more streams rich in a plurality of components heavier than ethane; and a second position above the first position and Conduit means (130, 136 and 119) for introducing into the scrub column a second ethane-rich reflux derived from an ethane-rich stream at a position selected from the third position;
Including the device.   Before introducing the ethane rich stream as a second ethane rich reflux into the scrub column (114), heat exchange means for condensing the ethane rich stream below the temperature of the feed to the scrub column, and 30. Apparatus according to claim 29, comprising pump means (134) for pumping the condensed stream.   31. Apparatus according to claim 29 or 30, comprising a reflux drum (118) from which a mixture of a second reflux rich in ethane and a first reflux rich in methane is fed to a scrub column (114). .   An absorption tower (218) that accepts the first two-phase stream as bottom feed and the second reflux rich in ethane as reflux, from which the bottom liquid is fed to the scrub tower (114) Apparatus according to claim 29 or 30.   An absorbent liquid enriched with one or more components heavier than ethane and supplied by a separating means (128) for separating the bottom stream of the scrub column, a second position above the first position; 33. Apparatus according to any of claims 29 to 32, comprising conduit means (140, 136 and 119) for introduction into the scrub tower (114) at a position selected from the third position and the fourth position. .   Comprising a reflux drum (118) from which a mixture of absorbent liquid and at least one of a first reflux rich in methane and a second reflux rich in ethane is fed to a scrub column (114). Item 34. The apparatus according to Item 33.   An absorption tower (218) for receiving a first two-phase stream as a bottom feed and receiving at least one of an absorbent liquid and a second reflux rich in ethane as a reflux, 34. Apparatus according to claim 33, fed to a scrub tower (114).   36. Means for combining (438) the absorbent liquid and the first overhead vapor stream prior to partial condensation of the stream to form a first two-phase stream. The apparatus in any one of.   37. A means according to any of claims 33 to 36 comprising means (140 and 330) for combining the absorbent liquid and the gaseous ethane-rich stream prior to condensation of the stream to provide a second reflux. The device described.   Separator means (430) for phase separating the combined absorbent liquid and gaseous ethane rich stream, and for feeding the liquid fraction to a scrub column (114) above the first location. 38. Apparatus according to claim 37 comprising conduit means (438 and 416).   Heat exchange means (122, 532) for condensing the vapor fraction and conduit means (436, 536, 538 and 516) for supplying condensed steam to the scrub column (114) above the first location 40. The apparatus of claim 38, comprising:   40. Means for combining (438) the liquid fraction and the first overhead stream prior to partial condensation of the overhead stream to provide a first two-phase flow. The device described in 1.   Means (532 and 538) for combining the condensed vapor fraction and the first overhead stream prior to partial condensation of the overhead stream to provide a first two-phase flow; 41. Apparatus according to claim 39 or 40.

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